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Aspen Plus
10
7
STE ADY STATE SIMUL ATION
Unit Operation Models
REFERENCE MANUAL
AspenTech7
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Contents
About the Unit Operation Models Reference Manual
For More Information..............................................................................................................x
Technical Support ..................................................................................................................xi
1 Mixers and Splitters
Mixer .....................................................................................................................................1-2
Flowsheet Connectivity for Mixer....................................................................................1-2
Specifying Mixer...............................................................................................................1-3
FSplit.....................................................................................................................................1-5
Flowsheet Connectivity for FSplit...................................................................................1-5
Specifying FSplit ...............................................................................................................1-6
SSplit.....................................................................................................................................1-8
Flowsheet Connectivity for SSplit ....................................................................................1-8
Specifying SSplit ...............................................................................................................1-8
2 Separators
Flash2....................................................................................................................................2-2
Flowsheet Connectivity for Flash2..................................................................................2-2
Specifying Flash2 .............................................................................................................2-3
Flash3....................................................................................................................................2-5
Flowsheet Connectivity for Flash3..................................................................................2-5
Specifying Flash3 .............................................................................................................2-6
Decanter................................................................................................................................2-8
Flowsheet Connectivity for Decanter ..............................................................................2-8
Specifying Decanter .........................................................................................................2-9
Sep.......................................................................................................................................2-12
Flowsheet Connectivity for Sep ......................................................................................2-12
Specifying Sep .................................................................................................................2-13
Sep2 .....................................................................................................................................2-14
Flowsheet Connectivity for Sep2 ....................................................................................2-14
Specifying Sep2...............................................................................................................2-15
3 Heat Exchangers
Heater ...................................................................................................................................3-2
Flowsheet Connectivity for Heater..................................................................................3-2
Specifying Heater .............................................................................................................3-3
HeatX ....................................................................................................................................3-5
Flowsheet Connectivity for HeatX...................................................................................3-5
Specifying HeatX ..............................................................................................................3-6
References...........................................................................................................................3-18
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MHeatX .............................................................................................................................. 3-19
Flowsheet Connectivity for MHeatX ............................................................................ 3-19
Specifying MHeatX........................................................................................................ 3-20
Hetran ................................................................................................................................ 3-23
Flowsheet Connectivity for Hetran .............................................................................. 3-23
Specifying Hetran.......................................................................................................... 3-24
Aerotran ............................................................................................................................. 3-26
Flowsheet Connectivity for Aerotran ........................................................................... 3-26
Specifying Aerotran....................................................................................................... 3-27
4 Columns
DSTWU ................................................................................................................................ 4-3
Flowsheet Connectivity for DSTWU ................................................................................ 4-3
Specifying DSTWU........................................................................................................... 4-4
Distl ...................................................................................................................................... 4-6
Flowsheet Connectivity for Distl...................................................................................... 4-6
Specifying Distl ................................................................................................................ 4-7
SCFrac.................................................................................................................................. 4-8
Flowsheet Connectivity for SCFrac ................................................................................. 4-8
Specifying SCFrac ............................................................................................................ 4-9
RadFrac.............................................................................................................................. 4-11
Flowsheet Connectivity for RadFrac ............................................................................ 4-12
Specifying RadFrac........................................................................................................ 4-13
Free-Water and Rigorous Three-Phase Calculations .................................................. 4-20
Efficiencies ..................................................................................................................... 4-20
Algorithms...................................................................................................................... 4-22
Rating Mode................................................................................................................... 4-23
Design Mode................................................................................................................... 4-24
Reactive Distillation ...................................................................................................... 4-25
Solution Strategies ........................................................................................................ 4-25
Physical Properties........................................................................................................ 4-28
Solids Handling ............................................................................................................. 4-28
MultiFrac ........................................................................................................................... 4-30
Flowsheet Connectivity for MultiFrac .......................................................................... 4-31
Specifying MultiFrac ..................................................................................................... 4-33
Efficiencies ..................................................................................................................... 4-41
Algorithms...................................................................................................................... 4-42
Rating Mode................................................................................................................... 4-42
Design Mode................................................................................................................... 4-42
Column Convergence..................................................................................................... 4-43
Physical Properties........................................................................................................ 4-46
Free Water Handling..................................................................................................... 4-46
Solids Handling ............................................................................................................. 4-46
Sizing and Rating of Trays and Packings .................................................................... 4-47
PetroFrac............................................................................................................................ 4-48
Flowsheet Connectivity for PetroFrac.......................................................................... 4-49
Specifying PetroFrac...................................................................................................... 4-51
Efficiencies ..................................................................................................................... 4-57
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Unit Operation Models
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Convergence....................................................................................................................4-58
Rating Mode....................................................................................................................4-59
Design Mode ...................................................................................................................4-59
Physical Properties.........................................................................................................4-60
Free Water Handling .....................................................................................................4-60
Solids Handling ..............................................................................................................4-61
Sizing and Rating of Trays and Packings .....................................................................4-61
RateFrac..............................................................................................................................4-62
Flowsheet Connectivity for RateFrac............................................................................4-63
The Rate-Based Modeling Concept................................................................................4-65
Specifying RateFrac .......................................................................................................4-66
Mass and Heat Transfer Correlations...........................................................................4-77
References...........................................................................................................................4-85
Extract ................................................................................................................................4-87
Flowsheet Connectivity for Extract...............................................................................4-87
Specifying Extract ..........................................................................................................4-88
5 Reactors
RStoic ....................................................................................................................................5-2
Flowsheet Connectivity for RStoic ..................................................................................5-2
Specifying RStoic..............................................................................................................5-3
RYield....................................................................................................................................5-6
Flowsheet Connectivity for RYield..................................................................................5-6
Specifying RYield .............................................................................................................5-7
REquil ...................................................................................................................................5-8
Flowsheet Connectivity for REquil..................................................................................5-8
Specifying REquil .............................................................................................................5-9
RGibbs.................................................................................................................................5-10
Flowsheet Connectivity for RGibbs ...............................................................................5-10
Specifying RGibbs ..........................................................................................................5-11
References...........................................................................................................................5-15
RCSTR ................................................................................................................................5-16
Flowsheet Connectivity for RCSTR...............................................................................5-16
Specifying RCSTR ..........................................................................................................5-17
RPlug...................................................................................................................................5-21
Flowsheet Connectivity for RPlug.................................................................................5-21
Specifying RPlug ............................................................................................................5-22
RBatch ................................................................................................................................5-25
Flowsheet Connectivity for RBatch...............................................................................5-25
Specifying RBatch ..........................................................................................................5-26
6 Pressure Changers
Pump .....................................................................................................................................6-2
Flowsheet Connectivity for Pump ...................................................................................6-2
Specifying Pump ...............................................................................................................6-3
Compr....................................................................................................................................6-9
Flowsheet Connectivity for Compr..................................................................................6-9
Specifying Compr ............................................................................................................6-10
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MCompr.............................................................................................................................. 6-13
Flowsheet Connectivity for MCompr ............................................................................. 6-13
Specifying MCompr........................................................................................................ 6-15
References .......................................................................................................................... 6-19
Valve................................................................................................................................... 6-20
Flowsheet Connectivity for Valve................................................................................. 6-20
Specifying Valve ............................................................................................................ 6-20
References .......................................................................................................................... 6-29
Pipe..................................................................................................................................... 6-30
Flowsheet Connectivity for Pipe ................................................................................... 6-30
Specifying Pipe .............................................................................................................. 6-31
Two-Phase Correlations ................................................................................................ 6-35
Closed-Form Methods.................................................................................................... 6-39
References .......................................................................................................................... 6-40
Pipeline .............................................................................................................................. 6-42
Flowsheet Connectivity for Pipeline............................................................................. 6-42
Specifying Pipeline ......................................................................................................... 6-43
Two-Phase Correlations ................................................................................................ 6-47
Closed-Form Methods.................................................................................................... 6-50
References .......................................................................................................................... 6-52
7 Manipulators
Mult ...................................................................................................................................... 7-2
Flowsheet Connectivity for Mult...................................................................................... 7-2
Specifying Mult................................................................................................................ 7-3
Dupl ...................................................................................................................................... 7-4
Flowsheet Connectivity for Dupl...................................................................................... 7-4
Specifying Dupl................................................................................................................ 7-5
ClChng ................................................................................................................................. 7-6
Flowsheet Connectivity for ClChng................................................................................ 7-6
Specifying ClChng............................................................................................................ 7-6
8 Solids
Crystallizer .......................................................................................................................... 8-3
Flowsheet Connectivity for Crystallizer .......................................................................... 8-3
Specifying Crystallizer ..................................................................................................... 8-4
References .......................................................................................................................... 8-11
Crusher............................................................................................................................... 8-13
Flowsheet Connectivity for Crusher............................................................................. 8-13
Specifying Crusher ........................................................................................................ 8-14
References .......................................................................................................................... 8-18
Screen ................................................................................................................................. 8-19
Flowsheet Connectivity for Screen ............................................................................... 8-19
Specifying Screen........................................................................................................... 8-19
References .......................................................................................................................... 8-22
FabFl .................................................................................................................................. 8-23
Flowsheet Connectivity for FabFl................................................................................. 8-23
Specifying FabFl............................................................................................................. 8-23
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Unit Operation Models
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References...........................................................................................................................8-26
Cyclone ................................................................................................................................8-27
Flowsheet Connectivity for Cyclone................................................................................8-27
Specifying Cyclone ..........................................................................................................8-28
References...........................................................................................................................8-35
VScrub.................................................................................................................................8-36
Flowsheet Connectivity for VScrub ................................................................................8-36
Specifying VScrub ...........................................................................................................8-37
References...........................................................................................................................8-39
ESP......................................................................................................................................8-40
Flowsheet Connectivity for ESP .....................................................................................8-40
Specifying ESP ................................................................................................................8-41
References...........................................................................................................................8-44
HyCyc ..................................................................................................................................8-45
Flowsheet Connectivity for HyCyc..................................................................................8-45
Specifying HyCyc ............................................................................................................8-46
References...........................................................................................................................8-51
CFuge ..................................................................................................................................8-52
Flowsheet Connectivity for CFuge ................................................................................8-52
Specifying CFuge............................................................................................................8-53
References...........................................................................................................................8-55
Filter ...................................................................................................................................8-56
Flowsheet Configuration for Filter................................................................................8-56
Specifying Filter .............................................................................................................8-56
References...........................................................................................................................8-59
SWash .................................................................................................................................8-61
Flowsheet Connectivity for SWash................................................................................8-61
Specifying SWash ...........................................................................................................8-62
CCD .....................................................................................................................................8-64
Flowsheet Connectivity for CCD ...................................................................................8-64
Specifying CCD...............................................................................................................8-65
9 User Models
User .......................................................................................................................................9-2
Flowsheet Connectivity for User .....................................................................................9-2
Specifying User.................................................................................................................9-3
User2 .....................................................................................................................................9-4
Flowsheet Connectivity for User2 ...................................................................................9-4
Specifying User2...............................................................................................................9-5
10 Pressure Relief
Pres-Relief...........................................................................................................................10-2
Specifying Pres-Relief ....................................................................................................10-2
Scenarios .........................................................................................................................10-3
Compliance with Codes ..................................................................................................10-6
Stream and Vessel Compositions and Conditions........................................................10-6
Rules to Size the Relief Valve Piping ............................................................................10-7
Reactions.........................................................................................................................10-9
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Relief System ............................................................................................................... 10-10
Data Tables for Pipes and Relief Devices................................................................... 10-12
Valve Cycling ............................................................................................................... 10-16
Vessel Types................................................................................................................. 10-16
Disengagement Models ............................................................................................... 10-18
Stop Criteria ................................................................................................................ 10-18
Solution Procedure for Dynamic Scenarios................................................................ 10-19
Flow Equations ............................................................................................................ 10-20
Calculation and Convergence Methods ...................................................................... 10-23
Vessel Insulation Credit Factor.................................................................................. 10-24
References ........................................................................................................................ 10-25
A Sizing and Rating for Trays and Packings
Single-Pass and Multi-Pass Trays..................................................................................A-2
Modes of Operation for Trays .........................................................................................A-8
Flooding Calculations for Trays......................................................................................A-8
Bubble Cap Tray Layout .................................................................................................A-9
Pressure Drop Calculations for Trays ..........................................................................A-10
Foaming Calculations for Trays ...................................................................................A-11
Packed Columns ............................................................................................................A-12
Packing Types and Packing Factors.............................................................................A-12
Modes of Operation for Packing....................................................................................A-12
Maximum Capacity Calculations for Packing .............................................................A-13
Pressure Drop Calculations for Packing ......................................................................A-15
Liquid Holdup Calculations for Packing ......................................................................A-16
Pressure Profile Update ................................................................................................A-17
Physical Property Data Requirements.........................................................................A-17
References ..........................................................................................................................A-18
Index
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Unit Operation Models
Version 10
About the Unit Operation
Models Reference Manual
Volume 1 of the ASPEN PLUS Reference Manuals, Unit Operation Models,
includes detailed technical reference information for all ASPEN PLUS unit
operation models and the Pres-Relief model. The information in this manual is
also available in online help and prompts.
Models are grouped in chapters according to unit operation type. The reference
information for each model includes a description of the model and its typical
usage, a diagram of its flowsheet connectivity, a discussion of the specifications
you must provide for the model, important equations and correlations, and other
relevant information.
An overview of all ASPEN PLUS unit operation models, and general information
about the steps and procedures in using them is in the ASPEN PLUS User Guide
as well as in the online help and prompts in ASPEN PLUS.
Unit Operation Models
Version 10
ix
For More Information
Online Help ASPEN PLUS has a complete system of online help and
context-sensitive prompts. The help system contains both context-sensitive help
and reference information. For more information about using ASPEN PLUS help,
see the ASPEN PLUS User Guide, Chapter 3.
ASPEN PLUS Getting Started Building and Running a Process Model
This tutorial includes several hands-on sessions to familiarize you with
ASPEN PLUS. The guide takes you step-by-step to learn the full power and scope
of ASPEN PLUS.
ASPEN PLUS User Guide The three-volume ASPEN PLUS User Guide
provides step-by-step procedures for developing and using an ASPEN PLUS
process simulation model. The guide is task-oriented to help you accomplish the
engineering work you need to do, using the powerful capabilities of
ASPEN PLUS.
ASPEN PLUS reference manual series ASPEN PLUS reference manuals
provide detailed technical reference information. These manuals include
background information about the unit operation models and the physical
properties methods and models available in ASPEN PLUS, tables of
ASPEN PLUS databank parameters, group contribution method functional
groups, and a wide range of other reference information. The set comprises:
• Unit Operation Models
• Physical Property Methods and Models
• Physical Property Data
• User Models
• System Management
• Summary File Toolkit
ASPEN PLUS application examples A suite of sample online ASPEN PLUS
simulations illustrating specific processes is delivered with ASPEN PLUS.
ASPEN PLUS Installation Guides These guides provide instructions on
platform and network installation of ASPEN PLUS. The set comprises:
•
•
•
ASPEN PLUS Installation Guide for Windows
ASPEN PLUS Installation Guide for OpenVMS
ASPEN PLUS Installation Guide for UNIX
The ASPEN PLUS manuals are delivered in Adobe portable document format
(PDF) on the ASPEN PLUS Documentation CD. You can also order printed
manuals from AspenTech.
x
Unit Operation Models
Version 10
Technical Support
World Wide Web For additional information about AspenTech products and
services, check the AspenTech World Wide Web home page on the Internet at:
http://www.aspentech.com/
Technical resources To obtain in-depth technical support information on the
Internet, visit the Technical Support homepage. Register at:
http://www.aspentech.com/ts/
Approximately three days after registering, you will receive a confirmation e-mail
and you will then be able to access this information.
The most current Hotline contact information is listed. Other information
includes:
•
•
•
Frequently asked questions
Product training courses
Technical tips
AspenTech Hotline If you need help from an AspenTech Customer Support
engineer, contact our Hotline for any of the following locations:
If you are located in:
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Unit Operation Models
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Unit Operation Models
Version 10
Chapter 1
1
Mixers and Splitters
This chapter describes the unit operation models for mixing and splitting
streams. The models are:
Unit Operation Models
Version 10
Model
Description
Purpose
Use For
Mixer
Stream mixer
Combines multiple streams
into one stream
Mixing tees. Stream mixing operations.
Adding heat streams. Adding work streams
FSplit
Stream splitter
Divides feed based on splits
specified for outlet streams
Stream splitters. Bleed valves
SSplit
Substream splitter
Divides feed based on splits
specified for each
substream
Stream splitters. Perfect fluid-solid
separators
1-1
Mixers and
Splitters
Mixer
Stream Mixer
Use Mixer to combine streams into one stream. Mixer models mixing tees or other
types of mixing operations.
Mixer combines material streams (or heat streams or work streams) into one
stream. Select the Heat (Q) and Work (W) Mixer icons from the Model Library for
heat and work streams respectively. A single Mixer block cannot mix streams of
different types (material, heat, work).
Flowsheet Connectivity for Mixer
Material
(2 or more)
Material
Water (optional)
Flowsheet for Mixing Material Streams
Material Streams
Inlet
At least two material streams
Outlet One material stream
One water decant stream (optional)
1-2
Unit Operation Models
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Chapter 1
Heat
(2 or more)
Heat
Flowsheet for Adding Heat Streams
Heat Streams
Inlet
At least two heat streams
Outlet One heat stream
Work
(2 or more)
Work
Flowsheet for Adding Work Streams
Work Streams
Inlet
At least two work streams
Outlet One work stream
Specifying Mixer
Use the Mixer Input Flash Options sheet to specify operating conditions.
When mixing heat or work streams, Mixer does not require any specifications.
Unit Operation Models
Version 10
1-3
Mixers and
Splitters
When mixing material streams, you can specify either the outlet pressure or
pressure drop. If you specify pressure drop, Mixer determines the minimum of
the inlet stream pressures, and applies the pressure drop to the minimum inlet
stream pressure to compute the outlet pressure. If you do not specify the outlet
pressure or pressure drop, Mixer uses the minimum pressure from the inlet
streams for the outlet pressure.
You can select the following valid phases:
Valid Phase
Solids?
Number of phases?
Free Water?
Phase?
Vapor-Only
Yes or no
1
No
V
Liquid-Only
Yes or no
1
No
L
Vapor-Liquid
Yes or no
2
No

Vapor-Liquid-Liquid
Yes or no
3
No

Yes or no
1
Yes

Yes or no
2
Yes

Yes
1
No
S
Liquid Free-Water
†
Vapor-Liquid Free-Water
Solid-Only
†
†
Check Use Free Water Calculations checkbox on the Setup Specifications Global sheet.
An optional water decant stream can be used when free-water calculations are
performed.
Mixer performs an adiabatic calculation on the product to determine the outlet
temperature, unless Mass Balance Only Calculations is specified on the Mixer
BlockOptions SimulationOptions sheet or the Setup SimulationOptions
Calculations sheet.
Use the following forms to enter specifications and view results for Mixer:
1-4
Use this form
To do this
Input
Enter operating conditions and flash convergence parameters
BlockOptions
Override global values for physical properties, simulation options, diagnostic message levels,
and report options for this block
Results
View Mixer simulation results
Dynamic
Specify parameters for dynamic simulations
Unit Operation Models
Version 10
Chapter 1
FSplit
Stream Splitter
FSplit combines streams of the same type (material, heat, or work streams) and
divides the resulting stream into two or more streams of the same type. All outlet
streams have the same composition and conditions as the mixed inlet. Select the
Heat (Q) and Work (W) FSplit icons from the Model Library for heat and work
streams respectively. Use FSplit to model flow splitters, such as bleed valves.
FSplit cannot split a stream into different types. For example, FSplit cannot split
a material stream into a heat stream and a material stream.
To model a splitter where the amount of each substream sent to each outlet can
differ, use an SSplit block. To model a splitter where the composition and
properties of the output streams can differ, use a Sep block or a Sep2 block.
Flowsheet Connectivity for FSplit
Material
(any number)
Material
(2 or more)
Flowsheet for Splitting Material Streams
Material Streams
Inlet
At least one material stream
Outlet At least two material streams
Unit Operation Models
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1-5
Mixers and
Splitters
Heat
(any number)
Heat
(2 or more)
Flowsheet for Splitting Heat Streams
Heat Streams
Inlet
At least one heat stream
Outlet At least two heat streams
Work
(any number)
Work
(2 or more)
Flowsheet for Splitting Work Streams
Work Streams
Inlet
At least one work stream
Outlet At least two work streams
Specifying FSplit
To split material streams Give one of the following specifications for each
outlet stream except one:
• Fraction of the combined inlet flow
• Mole flow rate
• Mass flow rate
• Standard liquid volume flow rate
• Actual volume flow rate
• Fraction of the residue remaining after all other specifications are satisfied
FSplit puts any remaining flow in the unspecified outlet stream to satisfy material
balance. You can specify mole, mass, or standard liquid volume flow rate for one of
the following:
•
•
1-6
The entire stream
A subset of key components in the stream
Unit Operation Models
Version 10
Chapter 1
To specify the flow rate of a component or group of components in an outlet stream,
specify a group of key components and the total flow rate for the group (the sum of
the component flow rates) on the Input Specifications sheet, and define the key
components in the group on the Input KeyComponents sheet.
Outlet streams have the same composition as the mixed inlet stream. For this
reason, when you specify the flow rate of a key component, the total flow rate of
the outlet stream is greater than the flow rate you specify.
When FSplit has more than one inlet, you can do one of the following:
•
•
Enter the outlet pressure on the FSplit Input FlashOptions sheet
Let the outlet pressure default to the minimum pressure of the inlet streams
To split heat streams or work streams Specify the fraction of the combined
inlet heat or work for each outlet stream except one. FSplit puts any remaining
heat or work in the unspecified outlet stream to satisfy energy balance.
Use the following forms to enter specifications and view results for FSplit:
Unit Operation Models
Version 10
Use this form
To do this
Input
Enter split specifications, flash conditions and calculation options, and key
components associated with split specifications
BlockOptions
Override global values for physical properties, simulation options,
diagnostic message levels, and report options for this block
Results
View split fractions for outlet streams, and material and energy balance
results
1-7
Mixers and
Splitters
SSplit
Substream Splitter
SSplit combines material streams and divides the resulting stream into two or
more streams. Use SSplit to model a splitter where the split of each substream
among the outlet streams can differ.
Substreams in the outlet streams have the same composition, temperature, and
pressure as the corresponding substreams in the mixed inlet stream. Only the
substream flow rates differ. To model a splitter in which the composition and
properties of the substreams in the output streams can differ, use a Sep block or
a Sep2 block.
Flowsheet Connectivity for SSplit
Material
(any number)
Material
(2 or more)
Material Streams
Inlet
At least one material stream
Outlet At least two material streams
Specifying SSplit
For each substream, specify one of the following for all but one outlet stream:
•
•
•
•
Fraction of the inlet substream
Mole flow rate
Mass flow rate
Standard liquid volume flow rate
SSplit puts any remaining flow for each substream in the unspecified stream.
You cannot specify standard liquid volume flow rate when the substream is of
type CISOLID, and mole and standard liquid volume flow rates when the
substream is of type NC.
1-8
Unit Operation Models
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Chapter 1
You can specify mole or mass flow rate for one of the following:
• The entire substream
• A subset of components in the substream
You can specify the flow rate of a component in a substream of an outlet stream. To
do this, define a key component and specify the flow rate for the key component.
Similarly, you can specify the flow rate for a group of components in a substream of
an outlet stream. To do this, define a key group of components and specify the total
flow rate for the group (the sum of the component flow rates).
Substreams in outlet streams have the same composition as the corresponding
substream in the mixed inlet stream. For this reason, when you specify the flow
rate of a key, the total flow rate of the substream in the outlet stream is greater
than the flow rate you specify.
When SSplit has more than one inlet, you can do one of the following:
• Enter the outlet pressure on the Input FlashOptions sheet.
• Let the outlet pressure default to the minimum pressure of the inlet streams.
The composition, temperature, pressure, and other substream variables for all
outlet streams have the same values as the mixed inlet. Only the substream flow
rates differ.
Use the following forms to enter specifications and view results for SSplit:
Use this form
To do this
Input
Enter split specifications, flash conditions, calculation options, and key components
associated with split specifications
BlockOptions
Override global values for physical properties, simulation options, diagnostic message
levels, and report options for this block
Results
View split fractions of each substream in each outlet stream, and material and energy
balance results
❖
Unit Operation Models
Version 10
❖
❖
❖
1-9
Mixers and
Splitters
1-10
Unit Operation Models
Version 10
Chapter 2
2
Separators
This chapter describes the unit operation models for component separators, flash
drums, and liquid-liquid separators. The models are:
Model
Description
Purpose
Use For
Flash2
Two-outlet flash
Separates feed into two outlet
streams, using rigorous vaporliquid or vapor-liquid-liquid
equilibrium
Flash drums, evaporators, knock-out
drums, single stage separators
Flash3
Three-outlet flash
Separates feed into three
outlet streams, using rigorous
vapor-liquid-liquid equilibrium
Decanters, single-stage separators with
two liquid phases
Decanter
Liquid-liquid decanter
Separates feed into two liquid
outlet streams
Decanters, single-stage separators with
two liquid phases and no vapor phase
Sep
Component separator
Separates inlet stream
components into multiple outlet
streams, based on specified
flows or split frractions
Component separation operations, such
as distillation and absorption, when the
details of the separation are unknown or
unimportant
Sep2
Two-outlet component
separator
Separates inlet stream
components into two outlet
streams, based on specified
flows, split fractions, or purities
Component separation operations, such
as distillation and absorption, when the
details of the separation are unknown or
unimportant
You can generate heating or cooling curve tables for Flash2, Flash3, and
Decanter models.
Unit Operation Models
Version 10
2-1
Separators
Flash2
Two-Outlet Flash
Use Flash2 to model flashes, evaporators, knock-out drums, and other singlestage separators. Flash2 performs vapor-liquid or vapor-liquid-liquid equilibrium
calculations. When you specify the outlet conditions, Flash2 determines the
thermal and phase conditions of a mixture of one or more inlet streams.
Flowsheet Connectivity for Flash2
Vapor
Heat (optional)
Material
(any number)
Water (optional)
Heat
(optional)
Liquid
Material Streams
Inlet
At least one material stream
Outlet One material stream for the vapor phase
One material stream for the liquid phase. (If three phases exist, the liquid
outlet contains both liquid phases.)
One water decant stream (optional)
You can specify liquid and/or solid entrainment in the vapor stream.
2-2
Unit Operation Models
Version 10
Chapter 2
Heat Streams
Inlet
Any number of heat streams (optional)
Outlet One heat stream (optional)
If you give only one specification (temperature or pressure) on the Input
Specifications Sheet, Flash2 uses the sum of the inlet heat streams as a duty
specification. Otherwise, Flash2 uses the inlet heat stream only to calculate the
net heat duty. The net heat duty is the sum of the inlet heat streams minus the
actual (calculated) heat duty.
You can use an optional outlet heat stream for the net heat duty.
Specifying Flash2
Use the Input Specifications sheet for all required specifications and valid
phases. For valid phases you can choose the following options:
You can choose the following
options
Solids?
Number of phases?
Free Water?
Vapor-Liquid
Yes or no
2
No
Vapor-Liquid-Liquid
Yes or no
3
No
Vapor-Liquid-FreeWater
Yes or no
2
Yes
Use the Input FlashOptions sheet to specify temperature and pressure estimates
and flash convergence parameters.
Use the Input Entrainment sheet to specify liquid and solid entrainment in the
vapor phase.
Use the Hcurves form to specify optional heating or cooling curves.
Use the following forms to enter specifications and view results for Flash2:
Unit Operation Models
Version 10
Use this form
To do this
Input
Enter flash specifications, flash convergence parameters, and entrainment specifications
Hcurves
Specify heating or cooling curve tables and view tabular results
Block Options
Override global values for physical properties, simulation options, diagnostic message
levels, and report options for this block
Results
View Flash2 simulation results
Dynamic
Specify parameters for dynamic simulations
2-3
Separators
Solids
All phases are in thermal equilibrium. Solids leave at the same temperature as
the fluid phases.
Flash2 can simulate fluid phases with solids when the stream contains solid
substreams or when you request electrolytes chemistry calculations.
Solid Substreams Materials in solid substreams do not participate in phase
equilibrium calculations.
Electrolyte Chemistry Calculations You can request these on the Properties
Specifications Global sheet or the BlockOptions Properties sheet. Solid salts
participate in liquid-solid phase equilibrium and thermal equilibrium
calculations. The salts are in the MIXED substream.
2-4
Unit Operation Models
Version 10
Chapter 2
Flash3
Three-Outlet Flash
Use Flash3 to model flashes, evaporators, knock-out drums, decanters, and other
single-stage separators in which two liquid outlet streams are produced. Flash3
performs vapor-liquid-liquid equilibrium calculations. When you specify outlet
conditions, Flash3 determines the thermal and phase conditions of a mixture of
one or more inlet streams.
Flowsheet Connectivity for Flash3
Vapor
Heat (optional)
Material
(any number)
1st Liquid
Heat
(optional)
2nd Liquid
Material Streams
Inlet
At least one material stream
Outlet One material stream for the vapor phase
One material stream for the first liquid phase
One material stream for the second liquid phase
You can specify liquid entrainment of each liquid phase in the vapor stream. You
can also specify entrainment for each solid substream in the vapor and first
liquid phase.
Unit Operation Models
Version 10
2-5
Separators
Heat Streams
Inlet
Any number of heat streams (optional)
Outlet One heat stream (optional)
If you give only one specification on the Input Specifications Sheet (temperature
or pressure), Flash3 uses the sum of the inlet heat streams as a duty
specification. Otherwise, Flash3 uses the inlet heat stream only to calculate the
net heat duty. The net heat duty is the sum of the inlet heat streams minus the
actual (calculated) heat duty.
You can use an optional outlet heat stream for the net heat duty.
Specifying Flash3
Use the Input Specifications sheet for all required specifications.
Use the Input Entrainment sheet to specify solid entrainment.
To specify optional heating or cooling curves, use the Hcurves form.
Use the following forms to enter specifications and view results for Flash3:
Use this form
To do this
Input
Enter flash specifications, key components, flash convergence parameters, and
entrainment specifications
Hcurves
Specify heating or cooling curve tables and view tabular results
Block Options
Override global values for physical properties, simulation options, diagnostic
message levels, and report options for this block
Results
View Flash3 simulation results
Dynamic
Specify parameters for dynamic simulations
Solids
All phases are in thermal equilibrium. Solids leave at the same temperature as
the fluid phases.
Flash3 can simulate fluid phases with solids when the stream contains solid
substreams, or when you request electrolyte chemistry calculations.
Solid Substreams Materials in solid substreams do not participate in phase
equilibrium calculations.
2-6
Unit Operation Models
Version 10
Chapter 2
Electrolyte Chemistry Calculations You can request these on the Properties
Specifications Global sheet or on the Input BlockOptions Properties sheet. Solid
salts do participate in liquid-solid phase equilibrium and thermal equilibrium
calculations. You can only specify apparent component calculations (Select
Simulation Approach=Apparent Components on the BlockOptions Properties
sheet). The salts will not appear in the MIXED substream.
Unit Operation Models
Version 10
2-7
Separators
Decanter
Liquid-Liquid Decanter
Decanter simulates decanters and other single stage separators without a vapor
phase. Decanter can perform:
• Liquid-liquid equilibrium calculations
• Liquid-free-water calculations
Use Decanter to model knock-out drums, decanters, and other single-stage
separators without a vapor phase. When you specify outlet conditions, Decanter
determines the thermal and phase conditions of a mixture of one or more inlet
streams.
Decanter can calculate liquid-liquid distribution coefficients using:
• An activity coefficient model
• An equation of state capable of representing two liquid phases
• A user-specified Fortran subroutine
• A built-in correlation with user-specified coefficients
You can enter component separation efficiencies, assuming equilibrium stage is
present.
Use Flash3 if you suspect any vapor phase formation.
Flowsheet Connectivity for Decanter
Material
(any number)
Heat
(optional)
1st Liquid
2nd Liquid
Heat
(optional)
Material Streams
Inlet
At least one material stream
Outlet One material stream for the first liquid phase
One material stream for the second liquid phase
You can specify entrainment for each solid substream in the first liquid phase.
2-8
Unit Operation Models
Version 10
Chapter 2
Heat Streams
Inlet
Any number of heat streams (optional)
Outlet One heat stream (optional)
If you specify only pressure on the Input Specifications sheet, Decanter uses the
sum of the inlet heat streams as a duty specification. Otherwise, Decanter uses
the inlet heat stream only to calculate the net heat duty. The net heat duty is the
sum of the inlet heat streams minus the actual (calculated) heat duty.
You can use an optional outlet heat stream for the net heat duty.
Specifying Decanter
You can operate Decanter in one of the following ways:
• Adiabatically
• With specified duty
• At a specified temperature
Use the Input Specifications sheet to enter:
• Pressure
• Temperature or duty
Use the following forms to enter specifications and view results for Decanter:
Unit Operation Models
Version 10
Use this form
To do this
Input
Specify operating conditions, key components, calculation options, valid phases,
efficiency, and entrainment
Properties
Specify and/or override property methods, KLL equation parameters, and/or user
subroutine for phase split calculations
Hcurves
Specify heating or cooling curve tables and view tabular results
Block Options
Override global values for physical properties, simulation options, diagnostic
message levels, and report options for this block
Results
Display simulation results
Dynamic
Specify parameters for dynamic simulations
2-9
Separators
Defining the Second Liquid Phase
If two liquid phases are present at the decanter operating condition, Decanter
treats the phase with higher density as the second phase, by default.
When only one liquid phase exists and you want to avoid ambiguities, you can
override the default by:
•
•
Specifying key components for identifying the second liquid phase on the
Input Specifications sheet
Optionally specifying the threshold key component mole fraction on the Input
Specifications sheet
When
Decanter treats the
Two liquid phases are present
Phase with the higher mole fraction of key components as the second liquid phase
One liquid phase is present
Liquid phase as the first liquid phase, unless the mole fraction of key components exceeds
the threshold value
Methods for Calculating the Liquid-Liquid Distribution
Coefficients (KLL)
When calculating liquid-liquid distribution coefficients (KLL), by default
Decanter uses the physical property method specified for the block on the
Properties PhaseProperty sheet or BlockOptions Properties sheet.
On the Input CalculationOptions sheet, you can override the default by doing one
of the following:
• Specify separate property methods for the two liquid phases using the
Properties PhaseProperty sheet
• Use a built-in KLL correlation. Enter correlation coefficients on the
Properties KLLCorrelation sheet.
• Use a Fortran subroutine that you specify on the Properties KLLSubroutine
sheet
See ASPEN PLUS User Models for more information about writing Fortran
subroutines.
Phase Splitting
Decanter has two methods for solving liquid-liquid phase split calculations:
• Equating fugacities of two liquid phases
• Minimizing Gibbs free energy of the system
You can select a method on the Input CalculationOptions sheet.
2-10
Unit Operation Models
Version 10
Chapter 2
If you select Minimizing Gibbs free energy of the system, the following must be
thermodynamically consistent:
• Physical property models
• Block property method
You cannot use the Minimizing Gibbs free energy of the system method when:
You specify
On this sheet
Separate property methods for the two liquid
phases
Properties PhaseProperty
The built-in correlation for liquid-liquid
distribution coefficient ( KLL) calculations
Input CalculationOptions
A user subroutine for liquid-liquid distribution
coefficient (KLL) calculations
Input Calculation Options
Equating fugacities of two liquid phases is not restricted by physical property
specifications. However, Decanter can calculate solutions that do not minimize
Gibbs free energy.
Efficiency
Decanter outlet streams are normally at equilibrium. However, you can specify
separation efficiencies on the Input Efficiency sheet to account for departure from
equilibrium. If you select Liquid-FreeWater for Valid Phases on the Input
CalculationOptions sheet, you cannot specify separation efficiencies.
Solids Entrainment
If solids substreams are present, they do not participate in phase equilibrium
calculations, but they do participate in enthalpy balance. You can use the Input
Entrainment sheet to specify solids entrainment in the first liquid outlet stream.
Decanter places any remaining solids in the second liquid outlet stream.
Unit Operation Models
Version 10
2-11
Separators
Sep
Component Separator
Sep combines streams and separates the result into two or more streams
according to splits specified for each component. When the details of the
separation are unknown or unimportant, but the splits for each component are
known, you can use Sep in place of a rigorous separation model to save
computation time .
If the composition and conditions of all outlet streams of the block you are
modeling are identical, you can use an FSplit block instead of Sep.
Flowsheet Connectivity for Sep
Material
(any number)
Material
(2 or more)
Heat
(optional)
Material Streams
Inlet
At least one material stream
Outlet At least two material streams
Heat Streams
Inlet
No inlet heat streams
Outlet One stream for the enthalpy difference between inlet and outlet material
streams (optional)
2-12
Unit Operation Models
Version 10
Chapter 2
Specifying Sep
For each substream of each outlet stream except one, use the Sep Input
Specifications sheet to specify one of the following for each component present:
• Fraction of the component in the corresponding inlet substream
• Mole flow rate of the component
• Mass flow rate of the component
• Standard liquid volume flow rate of the component
Sep puts any remaining flow in the corresponding substream of the unspecified
outlet stream.
Use the following forms to enter specifications and view results for Sep:
Use this form
To do this
Input
Enter split specifications, flash specifications, and convergence parameters for the mixed inlet
and each outlet stream
BlockOptions
Override global values for physical properties, simulation options, diagnostic message levels,
and report options for this block
Results
View Sep simulation results
Inlet Pressure
Use the Sep Input Feed Flash sheet to specify either the pressure drop or the
pressure at the inlet. This is useful when Sep has more than one inlet stream. The
inlet pressure defaults to the minimum inlet stream pressure.
Outlet Stream Conditions
Use the Sep Input Outlet Flash sheet to specify the conditions of the outlet
streams. If you do not specify the conditions for a stream, Sep uses the inlet
temperature and pressure.
Unit Operation Models
Version 10
2-13
Separators
Sep2
Two-Outlet Component Separator
Sep2 separates inlet stream components into two outlet streams. Sep2 is similar to
Sep, but offers a wider variety of specifications. Sep2 allows purity (mole-fraction)
specifications for components.
You can use Sep2 in place of a rigorous separation model, such as distillation or
absorption. Sep2 saves computation time when details of the separation are
unknown or unimportant.
If the composition and conditions of all outlet streams of the block you are
modeling are identical, you can use FSplit instead of Sep2.
Flowsheet Connectivity for Sep2
Material
Material
(any number)
Material
Heat
(optional)
Material Streams
Inlet
At least one material stream
Outlet Two material streams
Heat Streams
Inlet
No inlet heat streams
Outlet One stream for the enthalpy difference between inlet and outlet material
streams (optional)
2-14
Unit Operation Models
Version 10
Chapter 2
Specifying Sep2
Use the Input Specifications sheet to specify stream and/or component fractions
and flows. The number of specifications for each substream must equal the
number of components in that substream.
You can enter these stream specifications:
•
•
•
•
Fraction of the total inlet stream going to either outlet stream
Total mass flow rate of an outlet stream
Total molar flow rate of an outlet stream (for substreams of type MIXED or
CISOLID)
Total standard liquid volume flow rate of an outlet stream (for substreams of
type MIXED)
You can enter these component specifications:
• Fraction of a component in the feed going to either outlet stream
• Mass flow rate of a component in an outlet stream
• Molar flow rate of a component in an outlet stream (for substreams of type
MIXED or CISOLID)
• Standard liquid volume flow rate of a component in an outlet stream (for
substreams of type MIXED)
• Mass fraction of a component in an outlet stream
• Mole fraction of a component in an outlet stream (for substreams of type
MIXED or CISOLID)
Sep2 treats each substream separately. Do not:
• Specify the total flow of both outlet streams
• Enter more than one flow or frac specification for each component
• Enter both a mole-frac and a mass-frac specification for a component in a
stream
Use the following forms to enter specifications and view results for Sep2:
Unit Operation Models
Version 10
Use this form
To do this
Input
Enter split specifications, flash specifications, and convergence parameters for the mixed inlet
and each outlet stream
Block Options
Override global values for physical properties, simulation options, diagnostic message levels,
and report options for this block
Results
View Sep2 simulation results
2-15
Separators
Inlet Pressure
Use the Input Feed Flash sheet to specify either the pressure drop or pressure at
the inlet. This information is useful when Sep2 has more than one inlet stream.
The inlet pressure defaults to the minimum of the inlet stream pressures.
Outlet Stream Conditions
Use the Input Outlet Flash sheet to specify the conditions of the outlet streams.
If you do not specify the conditions for a stream, Sep2 uses the inlet temperature
and pressure.
❖
2-16
❖
❖
❖
Unit Operation Models
Version 10
Chapter 3
3
Heat Exchangers
This chapter describes the unit operation models for heat exchangers and heaters
(and coolers), and for interfacing to the B-JAC heat exchanger programs. The
models are:
Unit Operation Models
Version 10
Model
Description
Purpose
Use For
Heater
Heater or cooler
Determines thermal and phase
conditions of outlet stream
Heaters, coolers, condensers, and so on
HeatX
Two-stream heat exchanger
Exchanges heat between two
streams
Two-stream heat exchangers. Rating
shell and tube heat exchangers when
geometry is known.
MHeatX
Multistream heat exchanger
Exchanges heat between any
number of streams
Multiple hot and cold stream heat
exchangers. Two-stream heat
exchangers. LNG exchangers.
Hetran
Shell and tube heat
exchanger
Provides interface to the
B-JAC Hetran shell and tube
heat exchanger program
Shell and tube heat exchangers,
including kettle reboilers
Aerotran
Air-cooled heat exchanger
Provides interface to the
B-JAC Aerotran air-cooled heat
exchanger program
Crossflow heat exchangers, including air
coolers
3-1
Heat
Exchangers
Heater
Heater/Cooler
You can use Heater to represent:
• Heaters
• Coolers
• Valves
• Pumps (whenever work-related results are not needed)
• Compressors (whenever work-related results are not needed)
You also can use Heater to set the thermodynamic condition of a stream.
When you specify the outlet conditions, Heater determines the thermal and
phase conditions of a mixture with one or more inlet streams.
Flowsheet Connectivity for Heater
Heat (optional)
Material
(any number)
Heat
(optional)
Material
Water (optional)
Material Streams
Inlet
At least one material stream
Outlet One material stream
One water decant stream (optional)
Heat Streams
Inlet
Any number of heat streams (optional)
Outlet One heat stream (optional)
3-2
Unit Operation Models
Version 10
Chapter 3
If you give only one specification (temperature or pressure) on the Specifications
sheet, Heater uses the sum of the inlet heat streams as a duty specification.
Otherwise, Heater uses the inlet heat stream only to calculate the net heat duty.
The net heat duty is the sum of the inlet heat streams minus the actual
(calculated) heat duty.
You can use an optional outlet heat stream for the net heat duty.
Specifying Heater
Use the Heater Input Specifications sheet for all required specifications and valid
phases.
Dew point calculations are two- or three-phase flashes with a vapor fraction of
unity.
Bubble point calculations are two- or three-phase flashes with a vapor fraction of
zero.
Use the Heater Input FlashOptions sheet to specify temperature and pressure
estimates and flash convergence parameters.
Use the Hcurves form to specify optional heating or cooling curves.
This model has no dynamic features. The pressure drop is fixed at the steady
state value. The outlet flow is determined by the mass balance.
Use the following forms to enter specifications and view results for Heater.
Unit Operation Models
Version 10
Use this form
To do this
Input
Enter operating conditions and flash convergence parameters
Hcurves
Specify heating or cooling curve tables and view tabular results
Block Options
Override global values for physical properties, simulation options, diagnostic
message levels, and report options for this block
Results
View Heater results
3-3
Heat
Exchangers
Solids
Heater can simulate fluid phases with solids when the stream contains solid
substreams or when you request electrolyte chemistry calculations.
All phases are in thermal equilibrium. Solids leave at the same temperature as
fluid phases.
Solid Substreams Materials in solid substreams do not participate in phase
equilibrium calculations.
Electrolyte Chemistry Calculations You can request these on the Properties
Specifications Global sheet or the Heater BlockOptions Properties sheet. Solid
salts participate in liquid-solid phase equilibrium and thermal equilibrium
calculations. The salts are in the MIXED substream.
3-4
Unit Operation Models
Version 10
Chapter 3
HeatX
Two-Stream Heat Exchanger
HeatX can model a wide variety of shell and tube heat exchanger types including:
• Countercurrent and cocurrent
• Segmental baffle TEMA E, F, G, H, J, and X shells
• Rod baffle TEMA E and F shells
• Bare and low-finned tubes
HeatX can perform a full zone analysis with heat transfer coefficient and
pressure drop estimation for single- and two-phase streams. For rigorous heat
transfer and pressure drop calculations, you must supply the exchanger
geometry.
If exchanger geometry is unknown or unimportant, HeatX can perform simplified
shortcut rating calculations. For example, you may want to perform only heat
and material balance calculations.
HeatX has correlations to estimate sensible heat, nucleate boiling, and
condensation film coefficients.
HeatX cannot:
•
•
•
Perform design calculations
Perform mechanical vibration analysis
Estimate fouling factors
Flowsheet Connectivity for HeatX
Cold Outlet
Water (optional)
Hot
Inlet
Hot Outlet
Water
(optional)
Cold Inlet
Unit Operation Models
Version 10
3-5
Heat
Exchangers
Material Streams
Inlet
One hot inlet
One cold inlet
Outlet One hot outlet
One cold outlet
One water decant stream on the hot side (optional)
One water decant stream on the cold side (optional)
Specifying HeatX
Consider these questions when specifying HeatX:
• Should rating calculations be simple (shortcut) or rigorous?
• What specification should the block have?
• How should the log-mean temperature difference correction factor be
calculated?
• How should the heat transfer coefficient be calculated?
• How should the pressure drops be calculated?
• What equipment specifications and geometry information are available?
The answers to these questions determine the amount of information required to
complete the block input. You must provide one of the following specifications:
•
•
•
•
•
•
•
Heat exchanger area or geometry
Exchanger heat duty
Outlet temperature of the hot or cold stream
Temperature approach at either end of the exchanger
Degrees of superheating/subcooling for the hot or cold stream
Vapor fraction of the hot or cold stream
Temperature change of the hot or cold stream
Use the following forms to enter specifications and view results for HeatX:
Use this form
To do this
Setup
Specify shortcut or detailed calculations, flow direction, exchanger pressure drops, heat transfer
coefficient calculation methods, and film coefficients
Options
Specify different flash convergence parameters and valid phases for the hot and cold sides, HeatX
convergence parameters, and block-specific report option
Geometry
Specify the shell and tube configuration and indicate any tube fins, baffles, or nozzles
UserSubroutines
Specify parameters for user-defined Fortran subroutines to calculate overall heat transfer coefficient,
LMTD correction factor, tube-side liquid holdup, or tube-side pressure drop
Hot-Hcurves
Specify hot stream heating or cooling curve tables and view tabular results
continued
3-6
Unit Operation Models
Version 10
Chapter 3
Use this form
To do this
Cold-Hcurves
Specify cold stream heating or cooling curve tables and view tabular results
BlockOptions
Override global values for physical properties, simulation options, diagnostic message
levels, and report options for this block
Results
View a summary of results, mass and energy balances, pressure drops, velocities, and
zone analysis
Detailed Results
View detailed shell and tube results, and information about tube fins, baffles, and
nozzles
Dynamic
Specify parameters for dynamic simulations
Shortcut Versus Rigorous Rating Calculations
HeatX has two rating modes: shortcut and rigorous. Use the Calculation Type
field on the Setup Specifications sheet to specify shortcut or rigorous rating
calculations.
In shortcut rating mode you can simulate a heat exchanger block with the
minimum amount of required input. The shortcut calculation does not require
exchanger configuration or geometry data.
For rigorous rating mode, you can use exchanger geometry to estimate:
• Film coefficients
• Pressure drops
• Log-mean temperature difference correction factor
Rigorous rating mode provides more specification options for HeatX, but it also
requires more input.
Rigorous rating mode provides defaults for many options. You can change the
defaults to gain complete control over the calculations. The following table lists
these options with valid values. The values are described in the following
sections.
Unit Operation Models
Version 10
3-7
Heat
Exchangers
Variable
Calculation Method
Available in
Shortcut Mode
Available in
Rigorous Mode
LMTD Correction
Factor
Constant
Geometry
User subroutine
Default
No
No
Yes
Default
Yes
Heat Transfer
Coefficient
Constant value
Phase-specific values
Power law expression
Film coefficients
Exchanger geometry
User subroutine
Yes
Default
Yes
No
No
No
Yes
Yes
Yes
Yes
Default
Yes
Film Coefficient
Constant value
Phase-specific values
Power law expression
Calculate from geometry
No
No
No
No
Yes
Yes
Yes
Default
Pressure Drop
Outlet pressure
Calculate from geometry
Default
No
Yes
Default
Calculating the Log-Mean Temperature Difference
Correction Factor
The standard equation for a heat exchanger is:
Q = U ⋅ A ⋅ LMTD
where LMTD is the log-mean temperature difference. This equation applies for
exchangers with pure countercurrent flow.
The more general equation is:
Q = U ⋅ A ⋅ F ⋅ LMTD
where the LMTD correction factor, F, accounts for deviation from countercurrent
flow.
Use the LMTD Correction Factor field on the Setup Specifications sheet to enter
the LMTD correction factor.
3-8
Unit Operation Models
Version 10
Chapter 3
In shortcut rating mode, the LMTD correction factor is constant. In rigorous
rating mode, use the LMTD Correction Method field on the Setup Specifications
sheet to specify how HeatX calculates the LMTD correction factor. You can
choose from the following calculation options:
If LMTD Correction Method is Then
Constant
The LMTD correction factor you enter is constant.
Geometry
HeatX calculates the LMTD correction factor using the exchanger specification
and stream properties
User subroutine
You supply a user subroutine to calculate the LMTD correction factor.
Calculating the Heat Transfer Coefficient
To determine how the heat transfer coefficient is calculated, set the Calculation
Method on the Setup U Methods sheet. You can use these options in shortcut or
rigorous rating mode:
If Calculation Method is
HeatX uses
And you specify
Constant value
A constant value for the heat transfer coefficient
The constant value
Phase-specific values
A different heat transfer coefficient for each heat transfer
zone of the exchanger, indexed by the phase for the hot
and cold streams
A constant value for
each zone
Power law expression
A power law expression for the heat transfer coefficient as
a function of one of the stream flow rates
Constants for the power
law expression
In rigorous rating mode, three additional values are allowed:
Unit Operation Models
Version 10
If Calculation Method is
Then
Exchanger geometry
HeatX calculates the heat transfer coefficient using exchanger geometry and stream
properties to estimate film coefficients.
Film coefficients
HeatX calculates the heat transfer coefficients using the film coefficients. You can use
any option on the Setup Film Coefficients sheet to calculate the film coefficients.
User subroutine
You supply a user subroutine to calculate the heat transfer coefficient.
3-9
Heat
Exchangers
Film Coefficients
HeatX does not calculate film coefficients in shortcut rating mode. In rigorous
rating mode, if you use film coefficients or exchanger geometry for the heat
transfer coefficient calculation method, HeatX calculates the heat transfer
coefficient using:
1
1
1
=
+
U hc hh
Where:
hc
=
Cold stream film coefficient
hh
=
Hot stream film coefficient
To choose an option for calculating film coefficients, set the Calculation Method
on the Setup Film Coefficients sheet. The following are available:
If Calculation Method is
HeatX uses
And you specify
Constant value
A constant value for the film coefficient
A constant value to be
used throughout the
exchanger
Phase-specific values
A different film coefficient for each heat
transfer zone (phase) of the exchanger,
indexed by the phase of the stream
A constant value for
each phase
Power law expression
A power law expression for the film coefficient
as a function of the stream flow rate
Constants for the power
law expression
Calculate from geometry
The exchanger geometry and stream
properties to calculate the film coefficient
The hot stream and cold stream film coefficient calculation methods are
independent of each other. You can use any combination that is appropriate for
your exchanger.
Pressure Drop Calculations
To enter exchanger pressure or pressure drop for the hot and cold sides, use the
Outlet Pressure fields on the Setup Pressure Drop sheet. In shortcut rating mode
the pressure drop is constant.
3-10
Unit Operation Models
Version 10
Chapter 3
In rigorous rating mode, you can choose how pressure drops are calculated by
setting the pressure options on the Setup PressureDrop sheet. The following
pressure drop options are available:
If Pressure Option is
Then
Outlet Pressure
You must enter the outlet pressure or pressure drop for the stream.
Calculate from geometry
HeatX calculates the pressure drop using the exchanger geometry and stream
properties
HeatX calls the Pipeline model to calculate tube-side pressure drop. You can set
the correlations for pressure drop and liquid holdup that the Pipeline model uses
on the Setup PressureDrop sheet.
Exchanger Configuration
Exchanger configuration refers to the overall patterns of flow in the heat
exchanger. If you choose Calculate From Geometry for any of the heat transfer
coefficients, film coefficients, or pressure drop calculation methods, you may be
required to enter some information about the exchanger configuration on the
Geometry Shell sheet. This sheet includes fields for:
• TEMA shell type (see the next figure, TEMA Shell Types)
• Number of tube passes
• Exchanger orientation
• Tubes in baffle window
• Number of sealing strips
• Tube flow for vertical exchangers
Unit Operation Models
Version 10
3-11
Heat
Exchangers
E Shell
One Pass Shell
F Shell
Two Pass Shell
with Longitudinal Baffle
G Shell
Split Flow
H Shell
Double Split Flow
J Shell
Divided Flow
X Shell
Cross Flow
TEMA Shell Types
3-12
Unit Operation Models
Version 10
Chapter 3
The Geometry Shell sheet also contains two important dimensions for the shell:
• Inside shell diameter
• Shell to bundle clearance
The next figure shows the shell dimensions.
Outer Tube
Limit
Shell Diameter
Shell to Bundle
Clearance
Shell Dimensions
Baffle Geometry
Calculation of shell-side film coefficient and pressure drop require information
about the baffle geometry within the shell. Enter baffle geometry on the
Geometry Baffles sheet.
HeatX can calculate shell-side values for both segmental baffle shells and rod
baffle shells. Other required information depends on the baffle type. For
segmental baffles, required information includes:
• Baffle cut
• Baffle spacing
• Baffle clearances
For rod baffles, required information includes:
• Ring dimensions
• Support rod geometry
Unit Operation Models
Version 10
3-13
Heat
Exchangers
The next two figures show the baffle dimensions. The Baffle Cut in the
Dimensions for Segmental Baffles figure is a fraction of the shell diameter. All
clearances are diametric.
Baffle Cut
Tube Hole
Shell to Baffle
Clearance
Dimensions for Segmental Baffles
Rod Diameter
Ring Outside
Diameter
Ring Inside
Diameter
Dimensions for Rod Baffles
Tube Geometry
Calculation of the tube-side film coefficient and pressure drop require
information about the geometry of the tubebank. HeatX also uses this
information to calculate the heat transfer coefficient from the film coefficients.
Enter tube geometry on the Geometry Tubes sheet.
3-14
Unit Operation Models
Version 10
Chapter 3
You can select a heat exchanger with either bare or low-finned tubes. The sheet
also includes fields for:
• Total number of tubes
• Tube length
• Tube diameters
• Tube layout
• Tube material of construction
The next two figures show tube layout patterns and fin dimensions.
o
o
30
o
45
Tube
Pitch
Tube
Pitch
Triangle
o
90
60
Rotated
Square
Tube
Pitch
Rotated
Triangle
Tube
Pitch
Square
Direction of Flow
Tube Layout Patterns
Fin Thickness
Outside
Diameter
Root Mean
Diameter
Fin Height
Fin Dimensions
Nozzle Geometry
Calculations for pressure drop include the calculation of pressure drop in the
exchanger nozzles. Enter nozzle geometry on the Geometry Nozzles sheet.
Model Correlations
HeatX uses open literature correlations for calculating film coefficients and
pressure drops. The next four tables list the model correlations.
Unit Operation Models
Version 10
3-15
Heat
Exchangers
Tube-side Heat Transfer Coefficient Correlations
Mechanism
Flow Regime
Correlation
References
Single-phase
Laminar
Turbulent
Schlunder
Gnielinski
[1]
[1]
Boiling - vertical tubes
Steiner/Taborek
[2]
Boiling - horizontal tubes
Shah
[3, 4]
Condensation - vertical tubes
Laminar
Laminar wavy
Turbulent
Shear-dominated
Nusselt
Kutateladze
Labuntsov
Rohsenow
[5]
[6]
[7]
[8]
Condensation - horizontal tubes
Annular
Stratifying
Rohsenow
Jaster/Kosky method
[8]
[9]
Shell-side Heat Transfer Coefficient Correlations
Mechanism
Correlation
References
Single-phase segmental
Bell-Delaware
[10, 11]
Single-phase ROD
Gentry
[12]
Boiling
Jensen
[13]
Nusselt
Kutateladze
Labuntsov
Rohsenow
[5]
[6]
[7]
[8]
Kern
[9]
Condensation - vertical
Flow Regime
Laminar
Laminar wavy
Turbulent
Shear-dominated
Condensation - horizontal
Tube-side Pressure Drop Correlations
Mechanism
Correlation
Single-phase
Darcy’s Law
Two-phase
See Chapter 6
†
†
See Pipeline, Two-Phase Correlations, for the correlations available for two-phase pressure drop in a
pipe.
Shell-side Pressure Drop Correlations
3-16
Mechanism
Correlation
References
Single-phase segmental
Bell-Delaware
[10, 11]
Single-phase ROD
Gentry
[12]
Two-phase segmental
Bell-Delaware method with Grant’s correction for twophase flow
[10, 11], [14]
Two-phase ROD
Gentry
[12]
Unit Operation Models
Version 10
Chapter 3
Flash Specifications
Use the Options Flash Options sheet to enter flash specifications.
If you want to perform
these calculations
Solids?
Set Valid Phases to
Vapor phase
Yes or no
Vapor-only
Liquid phase
Yes or no
Liquid-only
2-fluid flash phase
Yes or no
Vapor-Liquid
3-fluid flash phase
Yes or no
Vapor-Liquid-Liquid
3-fluid phase free-water flash
Yes or no
Vapor-Liquid-FreeWater
Solids only
Yes
Solid-only
Physical Properties
To override global or flowsheet section property specifications, use the
BlockOptions Properties sheet. You can use different physical property options
for the hot side and cold side of the heat exchanger. If you supply only one set of
property specifications, HeatX uses that set for both hot and cold side
calculations.
Solids
All phases are in thermal equilibrium. Solids leave at the same temperature as
the fluid phases.
HeatX can simulate fluid phases with solids when the stream contains solid
substreams, or when you request electrolyte chemistry calculations.
Solid Substreams Materials in solid substreams do not participate in phase
equilibrium calculations.
Electrolyte Chemistry Calculations You can request these on the Properties
Specifications Global sheet or HeatX BlockOptions Properties sheet. Solid salts
participate in liquid-solid phase equilibrium and thermal equilibrium
calculations. The salts are in the MIXED substream.
Unit Operation Models
Version 10
3-17
Heat
Exchangers
References
1. Gnielinski, V., "Forced Convection in Ducts." In: Heat Exchanger Design
Handbook. New York: Hemisphere Publishing Corporation, 1983.
2. Steiner, D. and Taborek, J., "Flow Boiling Heat Transfer in Vertical Tubes
Correlated by an Asymptotic Model." In: Heat Transfer Engineering, 13(2):4369, 1992.
3. Shah, M.M., "A New Correlation for Heat Transfer During Boiling Flow
Through Pipes." In: ASHRAE Transactions, 82(2):66-86, 1976.
4. Shah, M.M., "Chart Correlation for Saturated Boiling Heat Transfer:
Equations and Further Study." In: ASHRAE Transactions, 87(1):185-196,
1981.
5. Nusselt, W., "Surface Condensation of Water Vapor." Z. Ver. Dtsch, Ing.,
60(27):541-546, 1916.
6. Kutateladze, S.S., Fundamentals of Heat Transfer. New York: Academic
Press, 1963.
7. Labuntsov, D.A., "Heat Transfer in Film Condensation of Pure Steam on
Vertical Surfaces and Horizontal Tubes." In: Teploenergetika, 4(7):72-80,
1957.
8. Rohsenow, W.M., Webber, J.H., and Ling, A.T., "Effect of Vapor Velocity on
Laminar and Turbulent Film Condensation." In: Transactions of the ASME,
78:1637-1643, 1956.
9. Jaster, H. and Kosky, P.G., "Condensation Heat Transfer in a Mixed Flow
Regime." In: International Journal of Heat and Mass Transfer, 19:95-99,
1976.
10. Taborek, J., "Shell-and-Tube Heat Exchangers: Single Phase Flow." In: Heat
Exchanger Design Handbook. New York: Hemisphere Publishing
Corporation, 1983.
11. Bell, K.J., "Delaware Method for Shell Side Design." In: Kakac, S., Bergles,
A.E., and Mayinger, F., editors, Heat Exchangers: Thermal-Hydraulic
Fundamentals and Design. New York: Hemisphere Publishing Corp., 1981.
12. Gentry, C.C., "RODBaffle Heat Exchanger Technology." In: Chemical
Engineering Progress 86(7):48-57, July 1990.
13. Jensen, M.K. and Hsu, J.T., "A Parametric Study of Boiling Heat Transfer in
a Tube Bundle." In: 1987 ASME-JSME Thermal Engineering Joint
Conference, pages 133-140, Honolulu, Hawaii, 1987.
14. Grant, I.D.R. and Chisholm, D., "Two-Phase Flow on the Shell Side of a
Segmentally Baffled Shell-and-Tube Heat Exchanger." In: Journal of Heat
Transfer, 101(1):38-42, 1979.
3-18
Unit Operation Models
Version 10
Chapter 3
MHeatX
Multistream Heat Exchanger
Use MHeatX to represent heat transfer between multiple hot and cold streams,
such as in an LNG exchanger. You can also use MHeatX for two-stream heat
exchangers. Free water can be decanted from any outlet stream. MHeatX ensures
an overall energy balance but does not account for the exchanger geometry.
MHeatX can perform a detailed, rigorous internal zone analysis to determine the
internal pinch points and heating and cooling curves for all streams in the heat
exchanger. MHeatX can also calculate the overall UA for the exchanger and
model heat leak to or from an exchanger.
MHeatX uses multiple Heater blocks and heat streams to enhance flowsheet
convergence. ASPEN PLUS automatically sequences block and stream
convergence unless you specify a sequence or tear stream.
Flowsheet Connectivity for MHeatX
Cold Inlets
(any number)
Hot Outlets
Hot Inlets
(any number)
Water (optional)
Hot Outlets
Water (optional)
Cold
Outlets
Water
(optional)
Material Streams
Inlet
At least one material stream on the hot side. At least one material stream
on the cold side
Outlet One outlet stream for each inlet stream
One water decant stream for each outlet stream (optional)
The inlet stream sides are non-contacting.
Unit Operation Models
Version 10
3-19
Heat
Exchangers
Specifying MHeatX
You must give outlet specifications for each stream on one side of the heat
exchanger. On the other side you can specify any of the outlet streams, but you
must leave at least one unspecified stream.
Different streams can have different types of specifications. MHeatX assumes
that all unspecified streams have the same outlet temperature. An overall energy
balance determines the temperature of any unspecified stream(s).
You can use a different property method for each stream in MHeatX. Specify the
property methods on the BlockOptions Properties sheet.
Use the following forms to enter specifications and view results for MHeatX:
Use this form
To do this
Input
Specify operating conditions, flash convergence parameters, parameters for
zone analysis, flash table, MHeatX convergence parameters, and block-specific
report options
Hcurves
Specify heating or cooling curve tables and view tabular results
BlockOptions
Override global values for physical properties, simulation options, diagnostic
message levels and report options for this block
Results
View stream results, exchanger results, zone profiles, stream profiles, flash
profiles, and material and energy balance results
Zone Analysis
MHeatX can perform a detailed, rigorous internal zone analysis to determine:
• Internal pinch points
• UA and LMTD of each zone
• Total UA of the exchanger
• Overall average LMTD
To obtain a zone analysis, specify Number of zones greater than 0 on the MHeatX
Input Zone Analysis sheet. During zone analysis MHeatX can add:
•
•
•
Stream entry points (if all feed streams are not at the same temperature)
Stream exit points (if all product streams are not at the same temperature)
Phase change points (if a phase change occurs internally)
MHeatX can also account for the nonlinearities of zone profiles by adding zones
adaptively. MHeatX can perform zone analysis for both countercurrent and cocurrent heat exchangers.
3-20
Unit Operation Models
Version 10
Chapter 3
Using Flash Tables in Zone Analysis
Use Flash Tables to estimate zone profiles and pinch points quickly. These tables
are most useful for heat exchangers that have many streams, for which zone
analysis calculations can take a long time.
To use a Flash Table for a stream, specify the number of flash points for the
stream on the MHeatX Input Flash Table sheet. When you specify a flash table
for a stream, MHeatX generates a temperature-enthalpy profile of that stream
before zone analysis, and interpolates that profile during zone analysis, rather
than flashing the stream.
You can also specify the fraction of total pressure drop in each phase region of a
stream on the MHeatX Input Flash Table sheet. ASPEN PLUS uses these
fractions to determine the pressure profile during Flash Table generation.
Computational Structure for MHeatX
The computational structure of MHeatX may affect your specifications.
Unlike other unit operation blocks, MHeatX is not simulated by a single
computation module. Instead, ASPEN PLUS generates heaters and heat streams
to represent the multistream heat exchanger. A Heater block represents streams
with outlet specifications. A multistream heater block represents streams with
no outlet specifications. The next figure shows the computational structure
generated for a sample exchanger.
$LNGH02
S3
$LNGH03
S4
S5
HEATER
$LNGH04
S6
S7
S8
HEATER
HEATER
$LNGQ03
$LNGQ04
$LNGQ02
$LNGHTR
S1
LNGIN
S2
MHEATER LNGOUT
Example of MHeatX Computational Structure
This computational sequence converges much more rapidly than simulation of
MHeatX as a single block. Block results are given for the entire MHeatX
sequence. In most cases, you do not need to know about the individual blocks
generated in the sequence. The following paragraphs describe the exceptions.
Unit Operation Models
Version 10
3-21
Heat
Exchangers
Simulation history and control panel messages are given for the generated
Heater blocks and heat streams.
You can provide an estimate for duty of the internally generated heat stream. If
the heat stream is a tear stream in the flowsheet, ASPEN PLUS uses this
estimate as an initial value.
You can give convergence specifications for the flowsheet resulting when MHeatX
blocks are replaced by their generated networks. The generated Heater block and
heat stream IDs must be used on the Convergence SequenceSpecifications and
Convergence TearSpecifications sheets.
Automatic flowsheet analysis is based on the flowsheet resulting when MHeatX
blocks are replaced by generated Heater blocks. The generated Heater blocks,
instead of the MHeatX block, appear in the calculation sequence. You can select
generated heat streams as tear streams.
Solids
MHeatX can simulate fluid phases with solids when the stream contains solid
substreams, or when you request electrolyte chemistry calculations.
All phases are in thermal equilibrium. Solids leave at the same temperature as
the fluid phases.
Solid Substreams Materials in solid substreams do not participate in phase
equilibrium calculations.
Electrolyte Chemistry Calculations You can request these on the Properties
Specifications Global sheet or the MHeatX BlockOptions Properties sheet. Solid
salts participate in liquid-solid phase equilibrium and thermal equilibrium
calculations. The salts are in the MIXED substream.
3-22
Unit Operation Models
Version 10
Chapter 3
Hetran
Interface to the B-JAC Hetran Program for Shell and Tube Heat
Exchangers
Hetran is the interface to the B-JAC Hetran program for designing and
simulating shell and tube heat exchangers. Hetran can be used to simulate shell
and tube heat exchangers with a wide variety of configurations. To use Hetran,
place the block in the flowsheet, connect inlet and outlet streams, and specify a
small number of block inputs, including the name of the B-JAC input file for that
exchanger.
You enter information related to the heat exchanger configuration and geometry
through the Hetran standalone program interface. The exchanger specification is
saved as a B-JAC input file. You do not have to enter information about the
exchanger’s physical characteristics through the ASPEN PLUS user interface or
through input language.
Flowsheet Connectivity for Hetran
Cold Inlet
Hot Inlet
Hot Water (optional)
Hot Outlet
Cold Outlet
Cold Water (optional)
Material Streams
Inlet
One hot inlet
One cold inlet
Outlet One hot outlet
One cold outlet
One water decant stream on the hot side (optional)
One water decant stream on the cold side (optional)
Unit Operation Models
Version 10
3-23
Heat
Exchangers
Specifying Hetran
Enter the input for the shell and tube heat exchanger through the Hetran
program’s graphical user interface. The input for Hetran in ASPEN PLUS is
limited to:
• The B-JAC input file name that contains the heat exchanger specification
• A set of parameters to control how property curves are generated
• A set of Hetran program inputs that you can change from within
ASPEN PLUS (for example, fouling factors and film coefficients)
Use the following forms to enter specifications and view results for Hetran:
Use this form
To do this
Input
Specify the name of the B-JAC input file, parameters for calculating the property curves,
optional Hetran program inputs, flash convergence parameters, and valid phases
BlockOption
s
Override global values for physical properties, simulation options, diagnostic message
levels, and report options for this block
Results
View inlet and outlet stream conditions and material and energy balance results
Detailed
Results
View overall results and detailed results for the shell side and tube side
Flash Specifications
Use the FlashOptions sheet to enter flash specifications.
3-24
If you want to perform these calculations
Solids?
Set Valid Phases to
Vapor phase
Yes or no
Vapor-only
Liquid phase
Yes or no
Liquid-only
2-fluid flash phase
Yes or no
Vapor-Liquid
3-fluid flash phase
Yes or no
Vapor-Liquid-Liquid
3-fluid phase free-water flash
Yes or no
Vapor-Liquid-FreeWater
Solids only
Yes
Solid-only
Unit Operation Models
Version 10
Chapter 3
Physical Properties
To override global or flowsheet section property specifications, use the
FlashOptions sheet. You can use different physical property methods for the hot
side and cold side of the heat exchanger. If you supply only one set of property
specifications, Hetran uses that set for both hot- and cold-side calculations.
Solids
Hetran cannot currently handle streams with solids substreams.
Unit Operation Models
Version 10
3-25
Heat
Exchangers
Aerotran
Interface to the B-JAC Aerotran Program for Air-cooled Heat Exchangers
Aerotran is the interface to the B-JAC Aerotran program for designing and
simulating air-cooled heat exchangers. Aerotran can be used to simulate aircooled heat exchangers with a wide variety of configurations. It can also be used
to model economizers and the convection section of fired heaters. To use
Aerotran, place the block in the flowsheet, connect inlet and outlet streams, and
specify a small number of block inputs, including the name of the B-JAC input
file for that exchanger.
You enter information related to the air cooler configuration and geometry
through the Aerotran standalone program interface. The air cooler specification
is saved as a B-JAC input file. You do not have to enter information about the air
cooler’s physical characteristics through the ASPEN PLUS user interface or
through input language.
Flowsheet Connectivity for Aerotran
Cold Water (optional)
Hot Inlet
Cold (Air) Outlet
Hot Water (optional)
Hot Outlet
Cold (Air) Inlet
Material Streams
Inlet
One hot inlet
One cold (air) inlet
Outlet One hot outlet
One cold (air) outlet
One water decant stream on the hot side (optional)
One water decant stream on the cold side (optional)
3-26
Unit Operation Models
Version 10
Chapter 3
Specifying Aerotran
Enter the input for the air-cooled heat exchanger through the Aerotran program’s
graphical user interface. The input for Aerotran in ASPEN PLUS is limited to:
• The B-JAC input file name that contains the heat exchanger specification
• A set of parameters to control how property curves are generated
• A set of Aerotran program inputs that you can change from within ASPEN
PLUS (for example, fouling factors and film coefficients)
Use the following forms to enter specifications and view results for Aerotran:
Use this form
To do this
Input
Specify the name of the B-JAC input file, parameters for calculating the property
curves, optional Aerotran program inputs, flash convergence parameters, and valid
phases
BlockOptions
Override global values for physical properties, simulation options, diagnostic
message levels, and report options for this block
Results
View inlet and outlet stream conditions and material and energy balance results
Detailed Results
View overall results, detailed results for the outside and tube side, and fan results
Flash Specifications
Use the FlashOptions sheet to enter flash specifications.
Unit Operation Models
Version 10
If you want to perform these calculations
Solids?
Set Valid Phases to
Vapor phase
Yes or no
Vapor-only
Liquid phase
Yes or no
Liquid-only
2-fluid flash phase
Yes or no
Vapor-Liquid
3-fluid flash phase
Yes or no
Vapor-Liquid-Liquid
3-fluid phase free-water flash
Yes or no
Vapor-Liquid-FreeWater
Solids only
Yes
Solid-only
3-27
Heat
Exchangers
Physical Properties
To override global or flowsheet section property specifications, use the
FlashOptions sheet. You can use different physical property methods for the hot
side and cold side of the air cooler. If you supply only one set of property
specifications, Aerotran uses that set for both hot- and cold-side calculations.
Solids
Aerotran blocks cannot currently handle streams with solids substreams.
❖
3-28
❖
❖
❖
Unit Operation Models
Version 10
Chapter 4
4
Columns
This chapter describes the unit operation models for distillation columns using
shortcut and rigorous calculations, and for liquid-liquid extraction. The models
are:
Model
Description
Purpose
Use For
DSTWU
Shortcut distillation design
using the WinnUnderwood-Gilliland
method
Determines minimum reflux ratio,
minimum number of stages, and either
actual reflux ratio or actual number of
stages
Columns with one feed
and two product streams
Distl
Shortcut distillation rating
using the Edmister method
Determines separation based on reflux
ratio, number of stages, and distillate-tofeed ratio
Columns with one feed
and two product streams
SCFrac
Shortcut distillation for
complex petroleum
fractionation units
Determines product composition and flow,
number of stages per section, and heat
duty using fractionation indices
Complex columns, such as
crude units and vacuum
towers
RadFrac
Rigorous fractionation
Performs rigorous rating and design
calculations for single columns
Ordinary distillation,
absorbers, strippers,
extractive and azeotropic
distillation, three-phase
distillation, reactive
distillation
MultiFrac
Rigorous fractionation for
complex columns
Performs rigorous rating and design
calculations for multiple columns of any
complexity
Heat integrated columns,
air separation columns,
absorber/stripper
combinations ethylene
plant primary fractionator
quench tower
combinations, petroleum
refining applications
continued
Unit Operation Models
Version 10
4-1
Columns
Model
Description
Purpose
Use For
PetroFrac
Petroleum refining
fractionation
Performs rigorous rating and design
calculations for complex columns in
petroleum refining applications
Preflash tower,
atmospheric crude unit,
vacuum unit, catalytic
cracker main fractionator,
delayed coker main
fractionator, vacuum lube
fractionator, ethylene plant
primary fractionator and
quench tower
combinations
Rate-based distillation
Performs rigorous rating and design for
single and multiple columns. Based on
nonequilibrium calculations. Does not
require efficiencies and HETPs.
Distillation columns,
absorbers, strippers,
reactive systems, heat
integrated units, petroleum
applications, such as
crude and vacuum units,
absorber-stripper
combination
Rigorous liquid-liquid
extraction
Models countercurrent extraction of a
liquid stream using a solvent
Liquid-liquid extractors
RateFrac
Extract
†
†
RateFrac requires a separate license and can be used only by customers who have purchased it through
a specific license agreement with Aspen Technology, Inc.
This chapter is organized into the following sections:
4-2
Section
Models
Shortcut Distillation
DSTWU, Distl, SCFrac
Rigorous Distillation
RadFrac, MultiFrac, PetroFrac, RateFrac
Liquid-Liquid Extraction
Extract
Unit Operation Models
Version 10
Chapter 4
DSTWU
Shortcut Distillation Design
DSTWU performs shortcut design calculations for single-feed, two-product
distillation columns with a partial or total condenser.
DSTWU assumes constant molal overflow and constant relative volatilities.
DSTWU uses this method/correlation
To estimate
Winn
Minimum number of stages
Underwood
Minimum reflux ratio
Gilliland
Required reflux ratio for a specified number of stages or the required
number of stages for a specified reflux ratio
For the specified recovery of light and heavy key components, DSTWU estimates:
• Minimum reflux ratio
• Minimum number of theoretical stages
DSTWU then estimates one of the following:
• Required reflux ratio for the specified number of theoretical stages
• Required number of theoretical stages for the specified reflux ratio
DSTWU also estimates the optimum feed stage location and the condenser and
reboiler duties. DSTWU can produce tables and plots of reflux ratio versus
number of stages.
Flowsheet Connectivity for DSTWU
Heat
(optional)
Heat
(optional)
Distillate
Water
(optional)
1
2
Feed
N-1
N
Heat
(optional)
Unit Operation Models
Version 10
Bottoms
Heat
(optional)
4-3
Columns
Material Streams
Inlet
One material feed stream
Outlet One distillate stream
One bottoms stream
One water decant stream from condenser (optional)
Heat Streams
Inlet
One stream for condenser cooling (optional)
One stream for reboiler heating (optional)
Outlet One stream for condenser cooling (optional)
One stream for reboiler heating (optional)
Each outlet heat stream contains the net heat duty for either the condenser or the
reboiler. The net heat duty is the inlet heat stream minus the actual (calculated)
heat duty.
If you use heat streams for the reboiler, you must also use them for the
condenser.
Specifying DSTWU
Use the Input Specifications sheet to enter column specifications. The following
table shows the specifications and what is calculated based on them:
Specification
Result
Recovery of light and heavy key components
Minimum reflux ratio and minimum number of theoretical stages
Number of theoretical stages
Required reflux ratio
Reflux ratio
Required number of theoretical stages
DSTWU also estimates the optimum feed stage location, and the condenser and
reboiler duties.
DSTWU can generate an optional table of reflux ratio versus number of stages.
Use the Input CalculationOptions sheet to enter specifications for the table.
4-4
Unit Operation Models
Version 10
Chapter 4
Use the following forms to enter specifications and view results for DSTWU:
Unit Operation Models
Version 10
Use this form
To do this
Input
Specify configuration and calculation options, block-specific report options, flash
convergence parameters, valid phases, and DSTWU convergence parameters
BlockOptions
Override global values for physical properties, simulation options, diagnostic message
levels, and report options for this block
Results
View summary results, material and energy balance results, and reflux ratio profile
4-5
Columns
Distl
Shortcut Distillation Rating
Distl simulates multistage multicomponent columns with a feed stream and two
product streams.
Distl performs shortcut distillation rating calculations for a single-feed, twoproduct distillation column. The column can have either a partial or total
condenser. Distl calculates product composition using the Edmister approach. Distl
assumes constant mole overflow and constant relative volatilities.
Flowsheet Connectivity for Distl
Heat
(optional)
Heat
(optional)
Distillate
Water
(optional)
1
2
Feed
N-1
N
Heat
(optional)
Bottoms
Heat
(optional)
Material Streams
Inlet
One material feed stream
Outlet One distillate stream
One bottoms stream
One water decant stream from condenser (optional)
Heat Streams
Inlet
One stream for condenser cooling (optional)
One stream for reboiler heating (optional)
Outlet One stream for condenser cooling (optional)
One stream for reboiler heating (optional)
4-6
Unit Operation Models
Version 10
Chapter 4
Each outlet heat stream contains the net heat duty for either the condenser or the
reboiler. The net heat duty is the inlet heat stream minus the actual (calculated)
heat duty.
If you use heat streams for the reboiler, you must also use them for the
condenser.
Specifying Distl
Use the Input Specifications sheet to enter the number of stages, reflux ratio,
distillate to feed ratio, and other column specifications.
Use the Input Convergence sheet to override default valid phases for condenser,
convergence parameters for flash calculations, and model convergence parameters.
Use the following forms to enter specifications and view results for Distl:
Unit Operation Models
Version 10
Use this form
To do this
Input
Specify basic column configuration, operating conditions, Distl convergence parameters, and flash
convergence parameters
BlockOptions
Override global values for physical properties, simulation options, diagnostic message levels, and
report options for this block
Results
View summary of column results and material and energy balance results
Dynamic
Specify parameters for dynamic simulation
4-7
Columns
SCFrac
Shortcut Distillation for Complex Columns
Use SCFrac to simulate complex distillation columns with a single feed, optional
stripping steam, and any number of products. SCFrac also estimates the number
of theoretical stages and the heating/cooling duty for each section.
SCFrac can model complex columns, such as crude units and vacuum towers.
SCFrac performs shortcut distillation calculations for columns with a single feed,
one optional stripping steam stream, and any number of products. SCFrac
divides a column with n products into n – 1 sections. These sections are
numbered from the top down. SCFrac assumes:
• Relative volatilities are constant for each section
• The flow of liquid from section to section is negligible
SCFrac does not handle solids. SCFrac can perform free-water calculations in the
condenser.
Flowsheet Connectivity for SCFrac
Distillate
Side Products
(any number)
Steam
(optional)
Feed
Bottoms
Material Streams
Inlet
One material feed stream
One optional stripping steam stream (used for all sections)
Outlet One distillate stream
One bottoms stream
At least one side product stream
4-8
Unit Operation Models
Version 10
Chapter 4
Specifying SCFrac
SCFrac divides an n–product column into n – 1 sections (see the next figure,
SCFrac Multidraw Column). SCFrac numbers the column sections from the top
down. For each section, you must specify:
• Product pressure
• Estimate of product flow or flow fraction based on feed flow
You must specify the ratio of steam to product flow rate for all product streams
except the distillate. You must also enter 2(n – 1) specifications from the following:
•
•
•
•
•
Fractionation index (number of theoretical stages at total reflux) of a section
Total flow, flow rate, or recovery of any group of components for a product
stream
Value of a property set property for a product stream (see ASPEN PLUS User
Guide, Chapter 28)
Difference of any pair of property set properties for one or a pair of product
stream(s)
Ratio of any pair of property set properties for one or a pair of product
stream(s)
Because SCFrac performs steam calculations, water must always be present. All
water flow leaves with the top product stream.
A Multidraw
Column
P1
P1
P2
Stream-1
P3
Stream-2
P4
Feed
Feed
Stream-3
P5
Stream-1
P2
Stream-2
P3
Stream-3
P4
Stream-4
P5
Stream-4
SCFrac Multidraw Column
Unit Operation Models
Version 10
4-9
Columns
Use the following forms to enter specifications and view results for SCFrac:
4-10
Use this form
To do this
Input
Specify operating parameters, valid phases, SCFrac convergence parameters, and
flash convergence parameters
BlockOptions
Override global values for physical properties, simulation options, diagnostic
message levels, and report options for this block
Results
View condenser results, material and energy balance results, design specification
results, section profiles, and product summary
Unit Operation Models
Version 10
Chapter 4
RadFrac
Rigorous Fractionation
RadFrac is a rigorous model for simulating all types of multistage vapor-liquid
fractionation operations. These operations include:
• Ordinary distillation
• Absorption
• Reboiled absorption
• Stripping
• Reboiled stripping
• Extractive and azeotropic distillation
RadFrac is suitable for:
• Two-phase systems
• Three-phase systems
• Narrow and wide-boiling systems
• Systems exhibiting strong liquid phase nonideality
RadFrac can detect and handle a free-water phase or other second liquid phase
anywhere in the column. RadFrac can handle solids on every stage.
RadFrac can handle pumparounds leaving any stage and returning to the same
stage or to a different stage.
RadFrac can model columns in which chemical reactions are occurring. Reactions
can have fixed conversions, or they can be:
• Equilibrium
• Rate-controlled
• Electrolytic
RadFrac can also model columns in which two liquid phases and chemical
reactions occur simultaneously, using different reaction kinetics for the two
liquid phases. In addition, RadFrac can model salt precipitation.
Although RadFrac assumes equilibrium stages, you can specify either Murphree
or vaporization efficiencies. You can manipulate Murphree efficiencies to match
plant performance.
You can use RadFrac to size and rate columns consisting of trays and/or
packings. RadFrac can model both random and structured packings.
Unit Operation Models
Version 10
4-11
Columns
Flowsheet Connectivity for RadFrac
Top Stage
or Condenser
Heat Duty
Feeds
Vapor Distillate
1
Heat (optional)
Liquid Distillate
Water Distillate
(optional)
Reflux
Heat
(optional)
Heat
(optional)
Heat (optional)
Bottom Stage
or Reboiler
Heat Duty
Products (optional)
Decanters
Return
Product
Boil-Up
Nstage
Heat (optional)
Bottoms
RadFrac can have any number of:
• Stages
• Interstage heaters/coolers
• Decanters
• Pumparounds
Material Streams
Inlet
At least one inlet material stream
Outlet One vapor or liquid distillate product stream, or both
One water distillate product stream (optional)
One bottoms liquid product stream
Up to three side product streams per stage (optional)
Any number of pseudo-product streams (optional)
Each stage can have:
• Any number of inlet streams
• Up to three outlet streams (one vapor and two liquid)
Outlet streams can be partial or total drawoffs of the stage flows.
Decanter outlet streams can return to the stage immediately below. Or they can
be split into any number of streams, each returning to a different user-specified
stage. Pumparounds can go between any two stages, or to the same stage.
Any number of pseudoproduct streams can represent column internal flows,
pumparound flows, and thermosyphon reboiler flows. A pseudoproduct stream
does not affect column results.
4-12
Unit Operation Models
Version 10
Chapter 4
Heat Streams
Inlet
One inlet heat stream per stage (optional)
One heat stream per pumparound (optional)
Outlet One outlet heat stream per stage (optional)
One heat stream per pumparound (optional)
RadFrac uses an inlet heat stream as a duty specification for all stages except the
condenser, reboiler, and pumparounds. If you do not give two column operating
specifications on the Setup Configuration sheet, RadFrac uses a heat stream as a
specification for the condenser and reboiler. If you do not give two specifications on
the Pumparounds Specifications sheet, RadFrac uses a heat stream as a
specification for pumparounds.
If you give two specifications on the Setup Configuration sheet or Pumparounds
Specifications sheet, RadFrac does not use the inlet heat stream as a
specification. The inlet heat stream supplies the required heating or cooling.
Use optional outlet streams for the net heat duty of the condenser, reboiler, and
pumparounds. The value of the outlet heat stream equals the value of the inlet
heat stream (if any) minus the actual (calculated) heat duty.
Specifying RadFrac
This section describes the following topics on RadFrac column configuration:
• Stage Numbering
• Feed Stream Conventions
• Columns Without Condensers or Reboilers
• Reboiler Handling
• Heater and Cooler Specifications
• Decanters
• Pumparounds
Use the following forms to enter specifications and view results for RadFrac:
Use this form
To do this
Setup
Specify basic column configuration and operating conditions
DesignSpecs
Specify design specifications and view convergence results
Vary
Specify manipulated variables to satisfy design specifications and view final values
HeatersCoolers
Specify stage heating or cooling
Pumparounds
Specify pumparounds and view pumparound results
continued
Unit Operation Models
Version 10
4-13
Columns
Use this form
To do this
Pumparounds Hcurves
Specify pumparound heating or cooling curve tables and view tabular
results
Decanters
Specify decanters and view decanter results
Efficiencies
Specify stage, component or sectional efficiencies
Reactions
Specify equilibrium, kinetic, and conversion reaction parameters
CondenserHcurves
Specify condenser heating or cooling curve tables and view tabular
results
ReboilerHcurves
Specify reboiler heating or cooling curve tables and view tabular results
TraySizing
Specify sizing parameters for tray column sections and view results
TrayRating
Specify rating parameters for tray column sections and view results
PackSizing
Specify sizing parameters for packed column sections and view results
PackRating
Specify rating parameters for packed column sections and view results
Properties
Specify physical property parameters for column sections
Estimates
Specify initial estimates for stage temperatures, vapor and liquid flows,
and compositions
Convergence
Specify convergence parameters for the column and feed flash
calculations, and block-specific diagnostic message levels
Report
Specify block-specific report options and pseudostreams
BlockOptions
Override global values for physical properties, simulation options,
diagnostic message levels, and report options for this block
UserSubroutines
Specify user subroutines for reaction kinetics, KLL calculations, tray
sizing and rating, and packing sizing and rating
ResultsSummary
View key column results for the overall RadFrac column
Profiles
View and specify column profiles
Dynamic
Specify parameters for dynamic simulations
Stage Numbering
RadFrac numbers stages from the top down, starting with the condenser (or
starting with the top stage if there is no condenser).
Feed Stream Conventions
Use the Setup Streams sheet to specify the feed and product stages.
RadFrac provides three conventions for handling feed streams:
• Above-Stage
• On-Stage
• Decanter (for three phase calculations only)
4-14
Unit Operation Models
Version 10
Chapter 4
(See the following figures, RadFrac Feed Convention Above-Stage and RadFrac
Feed Convention On-Stage.)
When the feed convention is Above-Stage, RadFrac introduces a material stream
between adjacent stages. The liquid portion flows to the stage you specify. The
vapor portion flows to the stage above. You can introduce a liquid feed to the top
stage (or condenser) by specifying Stage=1. You can introduce a vapor feed to the
bottom stage (or reboiler) by specifying Stage= the number of equilibrium stages
+ 1. Feed convention Decanter is used only in three-phase calculations (Valid
Phases=Vapor-Liquid-Liquid on the Setup Configuration sheet) involving
decanters. You can introduce a feed directly to a decanter attached to a stage
using this convention.
n-1
Vapor
Mixed feed
to stage n
Liquid
n
RadFrac Feed Convention Above-Stage
n-1
Mixed feed to
stage n
n
n+1
RadFrac Feed Convention On-Stage
When the Feed Convention is On-Stage, both the liquid and vapor portions of a
feed flow to the stage you specify.
Unit Operation Models
Version 10
4-15
Columns
Columns Without Condensers or Reboilers
You can specify the column configuration on the Setup Configuration sheet.
If the column has no
Then specify
On sheet
Condenser
None for
Condenser
Setup Configuration
Reboiler
None for Reboiler
Setup Configuration
Reboiler Handling
RadFrac can model two reboiler types:
• Kettle
• Thermosyphon
A kettle reboiler is modeled as the last stage in the column on the Setup
Configuration sheet. Select Kettle for reboiler. By default, RadFrac uses a kettle
reboiler. To specify the reboiler duty, enter Reboiler Duty as one of the operating
specifications on the Setup Configuration sheet or leave it as a calculated value.
A thermosyphon reboiler is modeled as a pumparound with a heater, from and to
the bottom stage. Select Thermosyphon for Reboiler on the Setup Configuration
sheet. Enter all other thermosyphon reboiler specifications on the Setup Reboiler
sheet.
The next figure shows the thermosyphon reboiler configuration. By default,
RadFrac returns the reboiler outlet to the last stage using the On-Stage feed
convention. You can also use the Reboiler Return Feed Convention on the
Reboiler sheet to specify Above-Stage. This directs the vapor portion of the
reboiler outlet to Stage= the number of equilibrium stages - 1.
Nstage - 1
Nstage
Reboiler
Bottoms (B)
Thermosyphon Reboiler
4-16
Unit Operation Models
Version 10
Chapter 4
The thermosyphon reboiler model has five related variables:
• Pressure
• Flow rate
• Temperature
• Temperature change
• Vapor fraction
You must specify one of the following:
•
•
•
•
•
•
•
Temperature
Temperature change
Vapor fraction
Flow rate
Flow rate and temperature
Flow rate and temperature change
Flow rate and vapor fraction
If you choose an option consisting of two variables, you must specify the reboiler
heat duty on the Setup Configuration sheet. RadFrac treats the value you enter
for the reboiler heat duty as an initial estimate.
The reboiler pressure is optional. If you do not enter a value, RadFrac uses the
bottom stage pressure.
Heater and Cooler Specifications
You can specify interstage heaters and coolers in one of two ways:
• Specifying the duty directly on the HeatersCoolers SideDuties sheet
• Requesting UA calculations on the HeatersCoolers UtilityExchangers sheet
If you specify the duty directly on the HeatersCoolers SideDuties sheet, enter a
positive duty for heating and a negative duty for cooling.
If you request UA calculations on the HeatersCoolers UtilityExchangers sheet,
RadFrac calculates the duty and outlet temperature of the heating/cooling fluid
simultaneously with the column. The UA calculations:
• Assume the stage temperature is constant
• Use an arithmetic average temperature difference
• Assume the heating or cooling fluid does not experience any phase change
To request UA calculations, specify the:
•
•
•
Unit Operation Models
Version 10
UA
Heating or cooling fluid component
Flow and inlet temperature of the fluid
4-17
Columns
You can specify the heat capacity of the fluid directly on the HeatersCoolers
UtilityExchangers sheet or RadFrac can compute it from a property method. If
RadFrac computes the heat capacity, you must also enter the pressure and phase
of the heating or cooling fluid. By default, RadFrac calculates the heat capacity
using the block property method. But you can also use a different property
method.
You can also specify the heat loss for sections of the column on the
HeatersCoolers HeatLoss sheet.
Decanters
For three-phase calculations (Valid Phases=Vapor-Liquid-Liquid on the Setup
Configuration sheet), you can define any number of decanters. Enter decanter
specifications on the Decanters form.
For the decanter on the top stage, you must enter the return fraction of at least
one of the two liquid phases (Fraction of 1st Liquid Returned, Fraction of 2nd
Liquid Returned on the Decanters Specifications sheet). For decanters on other
stages, you must always specify both Fraction of 1st Liquid Returned and
Fraction of 2nd Liquid Returned.
You can enter Temperature and Degrees Subcooling on the Decanters Options
sheet to model subcooled decanters. If you do not specify Temperature and
Degrees Subcooling, the decanter is operated at the temperature of the stage to
which the decanter is attached. If side product streams are decanter products,
you cannot specify their flow rates. RadFrac calculates their flow rates from the
Fraction of 1st Liquid Returned and Fraction of 2nd Liquid Returned.
By default RadFrac returns decanter streams to the stage immediately below.
You can return the decanter streams to any other stage by entering a different
Return Stage number on the Decanters Specifications sheet. You can split a
return stream into any number of streams by giving a split fraction (Split
Fraction of Total Return for the 1st Liquid and 2nd Liquid). Each resulting
stream may go to a different return stage.
When return streams do not go to the next stage, a feed or pumparound must go
to the next stage. This prevents dry stages.
Pumparounds
RadFrac can handle pumparounds from any stage to the same or any other stage.
Use the Pumparounds form to enter all pumparound specifications.
You must enter the source and destination stage locations for pumparounds. A
pumparound can be either a partial or total drawoff of the:
• Stage liquid
• First liquid phase
4-18
Unit Operation Models
Version 10
Chapter 4
•
•
Second liquid phase
Vapor phase
You can associate a heater or cooler with a pumparound. If the pumparound is a
partial drawoff of the stage flow, you must enter two of the following
specifications:
• Flow rate
• Temperature
• Temperature change
• Vapor fraction
• Heat Duty
If the pumparound is a total drawoff, you must enter one of the following
specifications:
• Temperature
• Temperature change
• Vapor fraction
• Heat Duty
Vapor fraction is allowed only when Valid Phases=Vapor-Liquid or
Vapor-Liquid-Liquid.
Use the Pumparounds Specifications sheet to enter these operating
specifications.
Pressure specification is optional. The default pumparound pressure is the same
as the source stage pressure. RadFrac assumes that the pumparound at the
heater/cooler outlet has the same phase condition as the pumparound at the
inlet. You can override the phase condition using the Valid phases field on
Pumparound Specifications sheet.
RadFrac can return the pumparound to a stage using either the:
• On-stage option
• Above-stage option (returns the pumparound to the column between two
stages)
In three-phase columns, RadFrac can also return the pumparound to a decanter
associated with a stage. You can select above-stage using the Return option field.
RadFrac assumes the pumparound at the heater/cooler outlet has the same
phase condition as the inlet.
You can use Return-Phase on the Pumparounds Specifications sheet to assign a
different phase at the heater/cooler outlet. Or you can specify Valid
Phases=VaporLiquid or Vapor-Liquid-Liquid and let RadFrac determine the
return phase condition from the heater/cooler specifications.
Unit Operation Models
Version 10
4-19
Columns
Free-Water and Rigorous Three-Phase Calculations
RadFrac can perform both free-water and rigorous three-phase calculations. (See
ASPEN PLUS Physical Property Methods and Models, Chapter 6.) These
calculations are controlled by options you specify on the Setup Configuration sheet.
You can select from three types of calculations:
•
•
•
Free water in the condenser only
Free water on any or all stages
Rigorous three-phase calculations
When you choose free-water calculations in the condenser, only free water can be
decanted from the condenser. You cannot use nonideal for the Overall Loop
convergence method.
Specify one of the following on the Setup Configuration sheet:
Valid Phases=
On Sheet
For
Vapor-Liquid-FreeWaterCondenser
Setup
Configuration
Free water in the condenser only
Vapor-Liquid-FreeWaterAnyStage
Setup
Configuration
Free water on all stages
Vapor-Liquid-Liquid
Setup
Configuration
Rigorous three-phase calculations
For RadFrac calculations, you must also specify which stages to test for two
liquid phases on the Setup 3-Phase sheet.
When you choose completely rigorous three-phase calculations on all stages
selected, RadFrac makes no assumptions about the nature of the two liquid
phases. You can associate a decanter with any stage. You cannot use Sum-Rates
for the Overall Loop convergence method.
Efficiencies
You can specify one of two types of efficiencies:
• Vaporization
• Murphree
Vaporization efficiency is defined as:
Effi v =
4-20
yi , j
K i, j x i , j
Unit Operation Models
Version 10
Chapter 4
Murphree efficiency is defined as:
Eff i ,Mj =
y i , j − yi , j + 1
K k , j x i , j − y i , j +1
Where:
K
=
Equilibrium K value
x
=
Liquid mole fraction
y
=
Vapor mole fraction
Eff
v
=
Vaporization efficiency
Eff
M
=
Murphree efficiency
i
=
Component index
j
=
Stage index
To specify vaporization or Murphree efficiencies, enter the number of actual
stages on the Setup Configuration sheet. Then use the Efficiencies form to enter
the efficiencies.
For three-phase calculations, the vaporization and Murphree efficiencies you
enter apply equally to the following equilibrium by default:
• Vapor-liquid1 (VL1E)
• Vapor-liquid2 (VL2E)
You can use the Efficiencies form to enter separate efficiencies for VL1E and
VL2E. You cannot enter separate efficiencies for VL1E and VL2E when you
specify equilibrium reactions or when using Murphree efficiencies.
You can use any of these efficiencies to account for departure from equilibrium.
But you cannot convert from one efficiency to the other. Magnitudes of the
efficiencies can be quite different. You should manipulate the Murphree
efficiency to match the operating data when:
• Efficiency is unknown
• Actual column operating data are available
When manipulating the Murphree efficiency, use design specifications on the
DesignSpecs and Vary forms. Details on using and estimating efficiencies are
described by Holland, Fundamentals of Multi-Component Distillation, McGrawHill Book Company, 1981.
Unit Operation Models
Version 10
4-21
Columns
Algorithms
You can select an algorithm and/or initialization option for column simulation on
the Convergence Basic sheet. The default standard algorithm and standard
initialization option are appropriate for most applications. You can improve
convergence behavior for the following applications using the guidelines described
in this section:
• Petroleum and Petrochemical Applications
• Highly Nonideal Systems
• Azeotropic Distillation
• Absorbers and Strippers
• Cryogenic Applications
To change the algorithm and initialization option on the Convergence Basic
sheet, you must first choose Custom as the option in the Convergence field on the
Setup Configuration sheet.
Petroleum and Petrochemical Applications
In petroleum and petrochemical applications involving extremely wide-boiling
mixtures and/or many components and design specifications, you can improve the
convergence efficiency and reliability by choosing Sum-Rates in the Algorithm field
on the Convergence Basic sheet.
Highly Nonideal Systems
When liquid phase nonidealities are exceptionally strong, choose Nonideal in the
Algorithm field on the Convergence Basic sheet to improve the convergence
behavior. Use this algorithm only when the number of outside loop iterations
(using the standard algorithm) exceeds 25.
You can also use the Newton algorithm for highly nonideal systems. Newton is
better for columns with highly sensitive specifications. But it is usually slower,
especially for columns with many stages and components.
Azeotropic Distillation
For azeotropic distillation applications where an entraining agent separates an
azeotropic mixture, specify the following on the Convergence Basic sheet:
•
•
Algorithm, Newton
Initialization method, Azeotropic
A classic example of azeotropic distillation is ethanol dehydration using benzene.
4-22
Unit Operation Models
Version 10
Chapter 4
Absorbers and Strippers
To model absorbers and strippers, specify Condenser=None and Reboiler=None on
the Setup Configuration sheet. The heat duty is zero for adiabatic operation. For
extremely wide-boiling mixtures, specify one of the following:
• Algorithm=Sum-Rates on the Convergence Basic sheet
• Convergence=Standard on the Setup Configuration sheet and choose
Absorber=Yes on the Convergence Basic sheet
Cryogenic Applications
For cryogenic applications such as air separation, the standard algorithm is
recommended. To invoke a special initialization procedure designed for cryogenic
systems, specify Cryogenic for Initialization on the Convergence Basic sheet.
Rating Mode
RadFrac allows the column to be operated in a rating mode or a design mode.
Rating mode requires different column specifications for two- and three-phase
calculations.
For two-phase calculations, you must enter the following on the Setup Form:
• Valid Phases=Vapor-Liquid or Vapor-Liquid-FreeWaterCondenser for
handling free water in condenser
• A Total, Subcooled, or Partial-Vapor condenser
• Two additional column operating variables
If the condenser or reflux is subcooled, you can also specify the degrees
subcooling or the subcooled temperature.
For three-phase calculations, you must specify Valid Phases= Vapor-LiquidLiquid or Vapor-Liquid-FreeWaterAnyStage (for free water calculations) on the
Setup Configuration sheet. The required specifications depend on what you
specify for the return fractions of the two liquid phases (Fraction of 1st Liquid
Returned and Fraction of 2nd Liquid Returned) in the top stage decanter. The
following table lists the three specification options:
Unit Operation Models
Version 10
If you specified this on
Decanters Specifications
Enter on Setup Configuration
Fraction of 1st Liquid Returned or Fraction
of 2nd Liquid Returned, or no top decanter
A Total, Subcooled, or Partial-Vapor condenser and two operating
specifications
Fraction of 1st Liquid Returned and
Fraction of 2nd Liquid Returned
A Total, Subcooled, or Partial-Vapor condenser and one operating
specification
Fraction of 1st Liquid Returned and
Fraction of 2nd Liquid Returned
Two operating specifications, and an estimate for the amount of vapor in the
distillate on the Estimates Vapor Composition sheet. RadFrac assumes a
partial condenser with both vapor and liquid distillates.
4-23
Columns
Design Mode
RadFrac allows the column to be operated in rating mode or design mode. In design
mode, use the DesignSpecs form to specify column performance parameters (such
as purity or recovery). You must indicate which variables to manipulate to achieve
these specifications. You can manipulate any variables that are allowed in rating
mode, except:
• Number of stages
• Pressure profile
• Vaporization efficiency
• Subcooled reflux temperature
• Degrees of subcooling
• Decanter temperature and pressure
• Locations of feeds, products, heaters, pumparounds, and decanters
• Pressures of thermosyphon reboiler and pumparounds
• UA specifications for heaters
The flow rates of inlet material streams and the duties of inlet heat streams can
also be manipulated variables.
These are the design specifications:
You can specify
For any
Purity
Stream including internal streams
Recovery of any components groups
Set of product streams, including sidestreams
Flow rate of any components groups
Internal stream or set of product streams
Temperature
Stage
Value of any Prop-Set property
Internal or product stream
Ratio or difference of any pair of
Prop-Set properties
Single or paired internal or product streams
Flow ratio of any components groups to any
other component groups
Internal streams to any other internal streams, or to any set of feed or product
streams
†
††
†††
4-24
†
††
†††
Express the purity as the sum of mole, mass, or standard liquid volume fractions of any group of
components relative to any other group of components .
Express recovery as a fraction of the same components in any set of feed streams.
See ASPEN PLUS User Guide.
Unit Operation Models
Version 10
Chapter 4
Reactive Distillation
RadFrac can handle chemical reactions. These reactions can occur in the liquid
and/or vapor phase. The details about the reactions are entered on a generic
Reactions form outside RadFrac. RadFrac allows two different reaction model
types: REAC-DIST or USER. RadFrac can model the following types of reactions:
• Equilibrium-controlled
• Rate-controlled
• Conversion
• Electrolytic
RadFrac can also model salt precipitation, especially in the case of electrolytic
systems. You can request reaction calculations for the entire column, or you can
restrict reactions to a certain column segment (for example, to model the
presence of catalyst). For three-phase calculations, you can restrict reactions to
one of the two liquid phases, or use separate reaction kinetics for the two liquid
phases.
To include reactions in RadFrac you must enter the following information on the
Reactions Specifications sheet:
• Reaction type and Reaction/Chemistry ID
• Column section in which the reactions occur
Depending on the reaction type, you must enter equilibrium constant, kinetic, or
conversion parameters on the generic Reactions form outside RadFrac. For
electrolytic reactions, you can also enter the reaction data on the Reactions
Chemistry form outside RadFrac. To consider salt precipitation, enter the salt
precipitation parameters on the Reactions Salt sheet or the Reactions Chemistry
form outside RadFrac.
To associate reactions and salt precipitation with a column segment, enter the
corresponding Reactions ID (or Chemistry ID) on the Reactions Specifications
sheet.
For rate-controlled reactions, you must enter holdup or residence time data in
the phase where the reactions occur. Use the Reactions Holdups or Residence
Times sheets. For conversion reactions, use the Reactions Conversion sheet to
override the conversion parameters specified on the Reactions Conversion form.
RadFrac also supports User Reaction Subroutine. The name and other details of
the reaction subroutine are entered on the UserSubroutines form.
Solution Strategies
RadFrac uses two general approaches for column convergence:
•
•
Unit Operation Models
Version 10
Inside-out
Napthali-Sandholm
4-25
Columns
The standard, sum-rates, and nonideal algorithms are variants of the inside-out
approach. The MultiFrac, PetroFrac, and Extract models also use this approach.
The Newton algorithm uses the classical Napthali-Sandholm approach. Use the
Convergence form to select the algorithm and specify the associated parameters.
Inside-Out Algorithms
The inside-out algorithms consist of two nested iteration loops.
The K-value and enthalpy models you specify are evaluated only in the outside
loop to determine parameters of simplified local models. When using nonideal,
algorithm RadFrac introduces a composition dependence into the local models.
The local model parameters are the outside loop iteration variables. The outside
loop is converged when the changes of the outside loop iteration variables are
sufficiently small from one iteration to the next. Convergence uses a combination
of the bounded Wegstein method and the Broyden quasi-Newton method for
selected variables.
In the inside loop, the basic describing equations (component mass balances,
total mass balance, enthalpy balance, and phase equilibrium) are expressed in
terms of the local physical property models. RadFrac solves these equations to
obtain updated temperature and composition profiles. Convergence uses one of
the following methods:
• Bounded Wegstein
• Broyden quasi-Newton
• Schubert quasi-Newton
• Newton
RadFrac adjusts the inside loop convergence tolerance with each outside loop
iteration. The tolerance becomes tighter as the outside loop converges.
Newton Algorithm
The Newton algorithm solves column-describing equations simultaneously, using
Newton’s method. The convergence is stabilized using the dogleg strategy of
Powell. Design specifications may be solved either simultaneously with the columndescribing equations or in an outer loop.
Design Mode Convergence
RadFrac provides two methods for handling design specification convergence:
• Nested convergence
• Simultaneous convergence
4-26
Unit Operation Models
Version 10
Chapter 4
Nested Design Spec Convergence (for all algorithms
except SUM-RATES)
The Nested Middle Loop convergence method attempts to satisfy the design
specifications by determining the values of the manipulated variables (within
their bounds) that minimize the weighted sum of squares function:
Φ=
∑
m

∧
 G m − GM 
Wm

Gm*




2
Where:
m
=
Design specification number
G
=
Calculated value
G
=
Desired value
G*
=
Scaling factor
w
=
Weighting factor
∧
The algorithm that manipulates the variables to minimize Φ does not depend on
matching particular variables with corresponding design specifications. You
should carefully select the manipulated variables and design specifications. Make
sure that each manipulated variable has a significant effect on at least one
design specification.
The number of design specifications must be equal to or greater than the number
of manipulated variables. If there are more design specifications than
manipulated variables, assign weighting factors to reflect the relative importance
of the specifications. The larger the weighting factor, the more nearly a
specification will be satisfied. Scale factors normalize the errors, so that different
specification types are compared on a consistent basis.
When a value of a manipulated variable reaches a bound, that bound is active. If
a problem has no active bounds and the same number of manipulated variables
as design specifications, then Φ will approach zero (within some tolerance) when
all specifications are satisfied.
If there are active bounds or more design specifications than manipulated
variables, RadFrac minimizes Φ . The weighting factors determine the relative
degree to which the design specifications are satisfied.
Unit Operation Models
Version 10
4-27
Columns
Simultaneous Design Spec Convergence (for
Algorithm=SUM-RATES, NEWTON)
The Simultaneous Middle Loop convergence method algorithm solves the design
specification functions simultaneously with the column-describing equations:
∧

 G m − GM 
Fm = 
 =0
Gm*




Because the Simultaneous Middle Loop convergence method uses an equationsolving approach, there must be an equal number of design specifications and
manipulated variables. In the nested method, no coupling is assumed between
design specifications and manipulated variables. However, each design
specification must be significantly affected by at least one manipulated variable.
Bounds and weighting factors are not used. In general, the Simultaneous method
gives better performance if all the specifications are feasible.
Physical Properties
To override the global physical property method, use the Properties
PropertySections sheet. You can specify different physical properties for different
parts of the column.
For three-phase calculations, you can specify separate calculation methods for
Vapor-Liquid1 Equilibrium (VL1E) and Liquid1-Liquid2 Equilibrium (LLE). Use
one of the following methods:
• Associate separate property methods with VL1E and LLE using the Phase
Equilibrium list box
• Calculate VL1E using a property method. Specify LLE using liquid-liquid
distribution (KLL) coefficients
You can use the Properties KLLSections sheet to enter the KLL coefficients using
a built-in temperature polynomial, and associate the coefficients with one or
more column segments. Or you can use the Properties KLLCorrelations sheet to
associate a user-KLL subroutine with one or more column segments.
Solids Handling
RadFrac has two methods for handling inert solids:
• Overall-balance
• Stage-by-stage
4-28
Unit Operation Models
Version 10
Chapter 4
Use the Solids handling option on the Convergence Basic sheet to select either an
overall balance or stage-by-stage. The two methods differ in how they treat solids
in the mass and energy balances. Neither method considers inert solids in the
phase equilibrium calculations. However, salts formed by salt precipitation
reactions (see Reactive Distillation) are considered in phase equilibrium
calculations.
The overall-balance method:
• Temporarily removes all solids from inlet streams
• Performs column calculations without solids
• Adiabatically mixes solids removed from inlet streams with liquid product
from the bottom stage
The overall-balance method maintains an overall mass and energy balance
around the column. But it does not satisfy individual stage balances. This is the
default method.
The stage-by-stage method treats solids rigorously in all stage mass and energy
balances. The ratio of liquids to solids on a stage is maintained in the product
streams withdrawn from that stage. The specified product flow is the total flow
rate of the stream, including the solids. If a nonconventional (NC) solids
substream is present in the column feeds, you must give all column flow and flow
ratio specifications on a mass basis.
When you specify a decanter, RadFrac can decant the solids partially or totally.
By default, RadFrac decants the solids partially along with the second liquid
phase. RadFrac uses the return fraction you specify for the second liquid phase
(Fraction of 2nd Liquid Returned on the Decanters Specifications sheet) to decant
the solids. If there is no second liquid phase in the decanter, RadFrac decants the
solids partially along with the first liquid phase. RadFrac uses the return
fraction you specify for the first liquid phase (Fraction of 2nd Liquid Returned on
the Decanters Specifications sheet) in this case. You can request complete
decanting of the solids by selecting Decant Solids Totally on the Decanters
Options sheet.
Unit Operation Models
Version 10
4-29
Columns
MultiFrac
Rigorous Fractionation
MultiFrac is a rigorous model for simulating general systems of interlinked
multistage fractionation units. MultiFrac models can handle a complex
configuration consisting of:
• Any number of columns, each with any number of stages
• Any number of connections between columns or within each column
• Arbitrary flow splitting and mixing of connecting streams
MultiFrac can handle operations with:
• Side strippers
• Pumparounds
• External heat exchangers
• Single-stage flashes
• Feed furnace
Typical MultiFrac applications include:
• Heat-interstaged columns, such as Petlyuk towers
• Air separation column systems
• Absorber/stripper combinations
• Ethylene plant primary fractionator/quench tower combinations
You can also use MultiFrac for petroleum refining fractionation units such as
atmospheric crude units and vacuum units. But for these applications, PetroFrac
is more convenient to use. Use MultiFrac only when the configuration is beyond
the capabilities of PetroFrac.
MultiFrac can detect a free-water phase in the condenser or anywhere in the
column. It can decant the free-water phase on any stage.
Although MultiFrac assumes equilibrium stage calculations, you can specify
either Murphree or vaporization efficiencies.
You can use MultiFrac for both sizing and rating trays and packings. MultiFrac
can model both random and structured packings.
4-30
Unit Operation Models
Version 10
Chapter 4
Flowsheet Connectivity for MultiFrac
Top Stage
or Condenser
Heat Duty
(optional)
Vapor Distillate
1
Reflux
Heat
Liquid Distillate (optional)
Water Distillate (optional)
Feeds
Side Products (optional)
Heat
Interconnecting Streams
(Heater Optional)
Pumparounds
and Bypasses
(Heater Optional)
Interconnecting Streams
(Heater Optional)
Heat (optional)
Bottom Stage or
Reboiler Heat Duty
(optional)
Top Stage
or Condenser
Heat Duty
(optional)
Nstage
Nstage
Heat (optional)
Bottoms
(or Interconnecting
Stream)
Vapor Distilate
1
Heat
Liquid Distillate (optional)
Water Distillate (optional)
Feeds
Side Products (optional)
Heat
Interconnecting Streams
(Heater Optional)
Pumparounds
and Bypasses
(Heater Optional)
Interconnecting Streams
(Heater Optional)
Heat (optional)
Bottom Stage or
Reboiler Heat Duty
(optional)
Unit Operation Models
Version 10
Nstage
Heat (optional)
Bottoms
(or Interconnecting
Stream)
4-31
Columns
Material Streams
Inlet
At least one inlet material stream
Outlet Any number of optional pseudo-product streams
Up to three optional outlet material streams per stage (one vapor, one
liquid, and one free water)
You can connect any number of columns by any number of connecting streams. For
each column, any number of connecting streams can represent pumparounds and
bypasses. These streams can flow between any two stages, or to the same stage.
Each connecting stream can have an associated heater.
Each column must have one liquid product or connecting stream leaving the
bottom stage. The top stage of the main column (column 1) must have a product
stream, which cannot be a connecting stream. The top stage of the other columns
(column 2, 3, ...) must have a vapor product or a vapor connecting stream.
The pseudoproduct streams represent column internal flows and connecting
stream flows.
Heat Streams
Inlet
One inlet heat stream per stage (optional)
One inlet heat stream per connecting stream (optional)
Outlet One outlet heat stream per connecting stream (optional)
MultiFrac uses an inlet heat stream as a duty specification for all stages except the
condenser, reboiler, and connecting streams. If you do not provide two column
operating specifications on the Columns Setup Configuration sheet, MultiFrac uses
a heat stream as a specification for the condenser and reboiler.
If you do not provide two specifications on the ConnectStreams form, MultiFrac
uses a heat stream as a specification for connecting streams.
If you provide two specifications on the Columns Setup Configuration sheet or
ConnectStreams form, MultiFrac does not use the inlet heat stream as a
specification. The inlet heat stream supplies the required heating or cooling.
You can use optional outlet heat streams for the net heat duty of the condenser,
reboiler, and connecting streams. The value of the outlet heat stream equals the
value of the inlet heat stream (if any), minus the actual (calculated) heat duty.
4-32
Unit Operation Models
Version 10
Chapter 4
Specifying MultiFrac
Individual columns are identified by column numbers. The numbering order does
not affect algorithm performance. Column 1 has different specifications from the
other columns. Within each column, the stages are numbered from the top down,
starting with the condenser.
Use the following forms to enter specifications and view results for MultiFrac:
Unit Operation Models
Version 10
Use this form
To do this
Columns Setup
Specify basic column configuration and operating conditions
Columns HeatersCoolers
Specify interstage heaters/coolers
Columns FlowSpecs
Specify liquid and vapor flow specifications
Columns Efficiencies
Specify stage or component efficiencies
Columns Properties
Specify physical property parameters for column sections
Columns Estimates
Specify initial estimates for stage temperatures, and vapor and liquid flows and
compositions
Columns Results
View column summary
Columns Profiles
View column profiles
InletsOutlets
Specify inlet and outlet material and heat stream locations
ConnectStreams
Specify sources and destinations of connecting material and heat streams, view connecting
stream results
FlowRatios
Specify stream flow ratios
DesignSpecs
Specify design specifications, and view convergence results
Vary
Specify manipulated variables to satisfy design specifications and view final values
CondenserHcurves
Specify condenser heating or cooling curve tables and view tabular results
ReboilerHCurves
Specify reboiler heating or cooling curve tables and view tabular results
ConnectStreamHCurves
Specify connecting stream heating or cooling curve tables and view tabular results
TraySizing
Specify sizing parameters for tray column sections, and view results
TrayRating
Specify rating parameters for tray column sections, and view results
PackSizing
Specify sizing parameters for packed column sections, and view results
PackRating
Specify rating parameters for packed column sections, and view results
Convergence
Specify convergence parameters for column calculations, and block-specific diagnostic
message levels
Report
Specify block-specific report options and pseudostream information
BlockOptions
Override global values for physical properties, simulation options, diagnostic message
levels, and report options for this block
UserSubroutines
Specify user subroutine parameters for tray sizing and rating, and packing sizing and rating
ResultsSummary
View results of balances and splits
4-33
Columns
Stream Definitions
MultiFrac uses four types of streams:
• External streams
• Connecting streams
• Internal streams
• Pseudostreams
External streams are standard MultiFrac inlet and outlet streams. They are
identified by stream IDs.
Connecting streams are within MultiFrac but external to individual columns.
They can connect two columns, or stages of the same column (bypasses and
pumparounds). You can associate a heater with any connecting stream.
Connecting stream heaters are identified by connecting stream numbers.
Internal streams are liquid or vapor flows between adjacent stages of the same
column. An internal stream is identified by a source stage number and a column
number.
Pseudostreams store the results of internal and connecting streams. They are a
subset of external outlet streams. Unlike normal outlet streams, pseudostreams
do not participate in block mass balance calculations.
Required Specifications
Follow these guidelines when entering specifications for column 1:
• The number of stages must be greater than 1
• Two additional operating specifications are required
• The distillate flow may not be a connecting stream
You must specify:
• Bottoms rate or distillate rate. The distillate rate includes both the vapor and
liquid distillate flows
• Either condenser duty, reboiler duty, reflux ratio or reflux rate
• Distillate vapor fraction or condenser temperature
If you specify the condenser stage temperature:
• Both liquid and vapor distillate products must be present (distillate vapor
fraction is greater than 0 or less than 1)
• You must also specify an estimate for the distillate vapor fraction
4-34
Unit Operation Models
Version 10
Chapter 4
Follow these guidelines when entering specifications for other columns:
• The number of stages can be 1 (for example, to model a single-stage flash or
feed furnace)
• The distillate can be a connecting stream
• MultiFrac calculates the distillate vapor fraction
• The distillate rate includes only the vapor distillate flow and must be greater
than zero. If a liquid distillate is present, specify flow on the InletsOutlets
form.
For columns with more than one stage, you may specify condenser duty, reboiler
duty, bottoms rate, distillate rate, and reflux rate.
For columns with one stage, you must specify either:
• Bottoms rate
• Distillate rate (includes only the vapor distillate)
• Condenser duty
Feed Stream Conventions
MultiFrac provides two conventions for handling feed streams (see MultiFrac Feed
Convention Above-Stage and MultiFrac Feed Convention On-Stage in the following
figures):
• Above-Stage
• On-Stage
When Feed-Convention is Above-Stage, MultiFrac introduces a material stream
between adjacent stages. The liquid portion flows to the stage (n) you specify. The
vapor portion flows to the stage above (n – 1). You can introduce a liquid feed to
the top stage (or condenser) by specifying Stage=1. You can introduce a vapor
feed to the bottom stage (or reboiler) by specifying Stage=Number of stages + 1.
n-1
Vapor
Mixed feed
to stage n
Liquid
MultiFrac Feed Convention Above-Stage
Unit Operation Models
Version 10
4-35
Columns
n-1
Mixed feed
to stage n
n
n+1
MultiFrac Feed Convention On-Stage
When Feed-Convention is On-Stage, both the liquid and vapor portions of a feed
flow to the stage (n) you specify.
Connecting Streams
MultiFrac allows any number of connecting streams. Any number of these streams
can have the same:
• Source column, stage, and phase
• Destination column and stage
MultiFrac introduces connecting streams on the destination stage regardless of
their phase (that is, Feed Convention=On-Stage). All connecting streams can
have a heater with heat duty, temperature, or temperature change specified. Use
the ConnectStreams form to enter all specifications for connecting streams.
Each terminal stream can be the source of a product stream and any number of
connecting streams. If there is no product stream, at least one connecting stream
must have an unspecified flow.
For a connecting stream, required specifications depend on whether the stream:
•
•
•
4-36
Has a flow rate that is fixed indirectly on the FlowRatios or Columns
FlowSpecs form
Is a terminal stream
Is a pumparound to the top stage of column 1
Unit Operation Models
Version 10
Chapter 4
For this type of connecting
stream
You must specify
†
One that does not satisfy the
above conditions
Two of the following: flow, temperature (or temperature change), and duty
One whose flow is fixed
indirectly on the FlowRatios or
Columns FlowSpecs form
Either temperature (or temperature change), or duty
A terminal stream (vapor
distillate or liquid bottoms)
Either temperature (or temperature change) or duty
†
†
†
Duty can default to 0 if necessary.
You can enter a second specification. If this specification is missing, MultiFrac
uses the net flow from the stage excluding any other connecting stream with flow
specifications.
For a connecting stream that is the liquid pumparound to the top stage of column
1, enter two of the following:
• Flow
• Temperature (or temperature change)
• Duty (specify 0 if there is no associated heater or cooler)
If you enter only one of flow, temperature, or temperature change, MultiFrac
uses the top stage duty for the missing requirement.
When a stage is the destination of a connecting stream, MultiFrac uses the heat
duty associated with the stage to determine the temperature of the connecting
stream. When you enter the duty, temperature, or temperature change of the
connecting stream, the stage duty does not affect the connecting stream
temperature. Stage duty is properly accounted for in the stage enthalpy
calculations.
When a pumparound, bypass, or other connecting stream has a specified
temperature change or outlet temperature, MultiFrac assumes that the specific
value does not result in a phase change of any fraction of the stream. When you
specify heat duty, a phase change may occur.
Connecting streams can be either a total or partial drawoff of the stage flow.
MultiFrac determines the drawoff type based on the number of specifications you
give.
If the drawoff type is
You enter
Partial
Two of the following: flow, temperature, temperature change, and heat duty
Total
One of the following: temperature, temperature change, and heat duty
†
††
Unit Operation Models
Version 10
†
††
Enter zero for heat duty if heater is absent.
Flow rate is taken as the net flow of the stage, excluding any product flow and any other connecting
stream flow.
4-37
Columns
MultiFrac allows total drawoff only for the top vapor stream and bottom liquid
stream. For partial drawoffs you can specify the flow rate. Or MultiFrac can
determine the flow rate based on one of the following:
• Another flow specification (Columns FlowSpecs form)
• A flow ratio specification (FlowRatios form)
If you enter only one specification for pumparounds to the top stage of the main
column, MultiFrac uses the top stage heat duty as the second specification.
When a connecting stream has a specified temperature or temperature change,
MultiFrac assumes the specified value does not result in a phase change of any
fraction of the stream. When you specify the heat duty, a phase change can occur.
Heaters
Use the Columns HeatersCoolers form to enter heater stage locations and duties.
You can specify heaters indirectly by choosing a heater duty as the adjusted
variable in one of the following forms:
Form
Used to specify
Columns FlowSpecs
Stage liquid or vapor flow rate
FlowRatios
Vapor-to-liquid flow ratio
Flow Rate Specifications
You can use the Columns FlowSpecs form to specify any stage liquid and vapor
flow rates. The value you specify refers to the net flow of the stage liquid or vapor
flow. This value excludes any portions withdrawn by side products and other
connecting streams with flow specifications. This feature is typically used for
specifying:
• Internal reflux rate or total internal drawoff
• Overflash in refining applications
• Boilup rate
For a terminal stream, flow specifications refer to the net flow of the stream
excluding any portion withdrawn by connecting streams with flow specifications.
Flow specifications include:
•
•
•
Specifications provided on the ConnectStreams form
Specifications fixed by the associated heater specifications
Another FlowSpecs or FlowRatios specification
For an internal stream, flow specifications refer to the net flow of the stream
excluding any portions withdrawn as products or connecting streams.
4-38
Unit Operation Models
Version 10
Chapter 4
When you enter a flow specification, MultiFrac adjusts the flow rate of a
connecting stream or the duty of a heater.
If the adjusted variable is
You enter the
A connecting stream flow
Connecting stream number in the IC-Stream field
A heater duty
Heater column and stage numbers
You can place the calculated heat duty in an outlet heat stream using the
InletsOutlets form. Initial estimates for adjusted variables are not required.
If a product or connecting stream of the same phase is leaving the stage, a
specified value may be zero to model a total drawoff .
MultiFrac will vary the heat duty associated with the heater of the same stage or
another stage or the flow rate of an associated connecting stream to satisfy
enthalpy and mass balances.
If this will be varied
You must specify
Heat duty
Q-Column and Stage
Flow rate of a connecting
stream
Stream number (IC-Stream)
Be cautious when selecting the:
• Associated stage with varied heat duty
• Connecting stream with varied flow rate
An initial guess for the associated heat duty is not required.
Unit Operation Models
Version 10
4-39
Columns
Flow Ratio Specifications
Use the FlowRatios form to specify the ratio of two flow rates. The flows can be of
different phases, and come from any stage of any column. This feature is typically
used for specifying the:
• Internal reflux ratio
• Overflash in refining applications
• Boilup ratio
For a terminal stream, the flows refer to the net flow of a stream, excluding any
portion withdrawn by connecting streams with flow specifications. Flow
specifications include those:
• Specified on the ConnectStreams form
• Fixed by either the associated heater specification, another Columns
FlowSpecs sheet, or a FlowRatios Specifications sheet)
For an internal stream, the flows refer to the net flow of the stream, excluding
any portion withdrawn as products or connecting streams. When you specify a
flow ratio, these will be varied to satisfy enthalpy and mass balances:
• Heat duty of the same stage or another stage
• Flow rate of an associated connecting stream
When you enter a flow ratio specification, MultiFrac adjusts the flow rate of a
connecting stream or the duty of a heater.
If the adjusted variable is
You enter the
A connecting stream flow
Connecting stream number in the IC-Stream field
A heater duty
Heater column and stage numbers
You can place the calculated heat duty in an outlet heat stream using the
InletsOutlets form. Initial estimates for these adjusted variables are not
required.
Be cautious when selecting the:
•
•
4-40
Associated stage with varied heat duty
Connecting stream with varied flow rate
Unit Operation Models
Version 10
Chapter 4
Efficiencies
You can specify one of two types of efficiencies:
• Vaporization
• Murphree
Vaporization efficiency is defined as:
Effi v =
yi , j
Ki, j xi, j
Murphree efficiency is defined as:
Effi ,Mj =
yi, j − yi , j +1
K i, j x i , j − yi , j +1
Where:
K
=
Equilibrium K value
x
=
Liquid mole fraction
y
=
Vapor mole fraction
Eff v
=
Vaporization efficiency
Eff M
=
Murphree efficiency
i
=
Component index
j
=
Stage index
To specify vaporization or Murphree efficiencies, enter the number of actual
stages on the Columns Setup Configuration sheet. Then use the Columns
Efficiencies form to enter the efficiencies.
You can use any of these efficiencies to account for departure from equilibrium.
But you cannot convert from one efficiency to the other. Magnitudes of the
efficiencies can be quite different. Details on using and estimating these
efficiencies are described by Holland, Fundamentals of Multi-Component
Distillation, McGraw-Hill Book Company, 1981.
Unit Operation Models
Version 10
4-41
Columns
Algorithms
MultiFrac has three convergence algorithms. Use the Overall field on the
Convergence Methods sheet to select the algorithm. The default standard
algorithm is appropriate for most applications. Your choice of algorithm depends
on the types of systems you are modeling:
Application
Algorithm
Air separation
Standard
Close-boiling, e.g., C3 splitter
Standard
Wide-boiling, e.g., absorbers
Sum-Rates
Petroleum refining, e.g., crude unit
Sum-Rates
Ethylene plant primary fractionator
Sum-Rates
Highly-nonideal, e.g., azeotropic
Newton
Highly-coupled design specifications
Sum-rates or Newton
Rating Mode
In rating mode, MultiFrac calculates column profiles and product compositions
based on specified values of column parameters. Examples of column parameters
are reflux ratio, reboiler duties, and feed flow rates.
Design Mode
In design mode, use the DesignSpecs form to specify column performance
parameters (such as purity or recovery). You must indicate which variables to
manipulate to achieve these specifications using the Vary form. You can specify
any variables that are allowed in rating mode, except:
• Number of stages
• Pressure profile
• Efficiencies
• Subcooled reflux temperature
• Degrees of subcooling
• Locations of feeds, products, heaters, and connecting streams
4-42
Unit Operation Models
Version 10
Chapter 4
The flow rates of inlet material streams and the duties of inlet heat streams can
also be manipulated variables.
You can specify
For any
Purity
Stream, including an internal stream
Recovery of any component groups
Set of product streams
Flow rate of any component groups
Internal stream or set of product streams
Temperature
Stage
Heat duty
Stage or connecting stream
Heat duty ratio
Stage or connecting stream to any other stage or connecting stream
Value of any Prop-Set property
Internal or product stream
Ratio or difference of any pair of properties in
a Prop-Set
Single or paired internal or product stream
Flow ratio of any component groups to any
other component groups
First group can be in any internal streams
†
††
†††
††††
†
††
†††
††††
Express the purity as the sum of mole, mass, or standard liquid volume fractions of any group of
components, relative to any other group of components.
You can express recovery as a fraction of the same components in a subset of the feed stream.
See ASPEN PLUS User Guide.
The second group can be in any other internal streams, or set of feed or product streams.
Column Convergence
MultiFrac uses the inside-out approach for column convergence. You can choose
from two algorithm variants of this approach:
• Standard
• Sum-rates
To select an algorithm, use the Overall field on the Convergence Methods sheet.
The standard algorithm uses the standard inside-out formulation for the inside
loop. It uses either the nested or simultaneous approach (specified as the Middle
loop method on the Convergence Methods sheet) to converge the design
specifications. This algorithm is appropriate for most systems.
The sum-rates algorithm uses:
• A sum-rates variant formulation for the inside loop
• The simultaneous approach to converge the design specifications
Unit Operation Models
Version 10
4-43
Columns
Sum-rates is well suited for:
• Wide-boiling systems
• Columns with steep flow gradients
MultiFrac also has the Newton algorithm, which uses a Napthali-Sandholm
formulation. It solves the column-describing equations and design specifications
simultaneously, using Newton’s method. This method can enhance convergence
for highly-nonideal systems, such as azeotropic distillation. The Newton
algorithm is generally slower than the other algorithms.
Design Specification Convergence
MultiFrac provides two methods for handling design specification convergence:
• Nested middle loop
• Simult middle loop
When you use the nested middle loop method, the algorithm attempts to satisfy
the design specifications by determining the values of the manipulated variables
(within their bounds) that minimize the weighted sum of squares function:
 G^ − G 

Φ = ∑wm 


G
**
m


2
Where:
m
=
Design specification number
G$
=
Calculated value
G
=
Desired value
G **
=
Scaling factor
w
=
Weighting factor
For purity and recovery, G$ and G are transformed by taking the logarithm, and
G ** is taken as unity.
When you use the simult middle loop method, the following algorithm solves the
design specification functions simultaneously with the column describing
equations:
(
)
Fm = G$ m − Gm / Gm** = 0
4-44
Unit Operation Models
Version 10
Chapter 4
The weighting factor is not available for this method.
You can handle design specification convergence by using either scaling factors or
weighting factors. The following algorithm attempts to satisfy design
specifications by determining the values of the manipulated variables (within
their bounds) that minimize the weighted sum of squares function:
 G$ − G 
Φ = ∑wm  ** 
 G 
m
2
Where:
m
=
Design specification number
G$
=
Calculated value
G
=
Desired value
G **
=
Scaling factor
w
=
Weighting factor
Initialization
Use Initialization Method on the Convergence Methods sheet to choose the
initialization method.
MultiFrac has two initialization procedures:
• Standard
• Crude
Standard is appropriate for most systems. You must enter at least the top and
bottom temperature estimates for each column.
Crude invokes a special initialization procedure designed for petroleum refining
and ethylene plant primary fractionator/quench tower applications. This
procedure is designed for systems consisting of a main column connected to any
number of sidestrippers. If you specify the following information on the Columns
Setup and/or Columns FlowSpecs forms, you do not need to provide estimates:
•
•
All stripper bottoms flow rates
Either the distillate or bottoms flow rate of the main column
Otherwise, you must enter at least the top and bottom temperature estimates for
each column. You may enter profile estimates on the Columns Estimates form to
enhance convergence. Temperature estimates are usually adequate. Highly
nonideal systems may require composition estimates.
Unit Operation Models
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Columns
Physical Properties
Use the BlockOptions form to override the global physical property method. You
can specify a single property method on the BlockOptions form. MultiFrac uses this
property method for all stages in all columns.
Use the Columns Properties form to specify physical property methods when you
use a separate property method for an individual column. You can also split a
column into any number of segments, each using a different property methods.
Free Water Handling
MultiFrac can perform free-water calculations. By default, MultiFrac performs
free-water calculations for the main column condenser. The free-water phase, if
present, is decanted.
Use the Columns Properties form to request free-water calculations for
additional stages in any column. You can define additional water decant product
streams on the InletsOutlets form. You can use this capability to simulate the
primary fractionator/quench tower combination of an ethylene plant.
Solids Handling
MultiFrac handles solids by:
• Temporarily removing all solids from inlet streams
• Performing calculations without solids
• Adiabatically mixing solids removed from inlet streams with main column
liquid bottoms
This calculation approach maintains an overall mass and energy balance around
the MultiFrac block. But the bottom stage liquid product will not be in exact
thermal or phase equilibrium with other bottom stage flows (for example, the
bottom stage vapor flow).
4-46
Unit Operation Models
Version 10
Chapter 4
Sizing and Rating of Trays and Packings
MultiFrac has extensive capability to size, rate, and perform pressure drop
calculations for trayed and packed columns. Use the following forms to enter
specifications:
• TraySizing
• TrayRating
• PackSizing
• PackRating
See Appendix A for details on tray and packing types and correlations.
Unit Operation Models
Version 10
4-47
Columns
PetroFrac
Rigorous Fractionation
PetroFrac is a rigorous model designed for simulating all types of complex vaporliquid fractionation operations in the petroleum refining industry. Typical
operations include:
• Preflash tower
• Atmospheric crude unit
• Vacuum unit
• Catalytic cracker main fractionator
• Delayed coker main fractionator
• Vacuum lube fractionator
You also can use PetroFrac to model the primary fractionator/quench tower
combination in the quench section of an ethylene plant. PetroFrac can detect a
free-water phase in the condenser or anywhere in the column. It can decant the
free-water phase on any stage. Although PetroFrac assumes equilibrium stage
calculations, you can specify either Murphree or vaporization efficiencies. You
can use PetroFrac to size and rate columns consisting of trays and/or packings.
PetroFrac can model both random and structured packings.
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Chapter 4
Flowsheet Connectivity for PetroFrac
PetroFrac models column configurations consisting of a main column with any
number of pumparounds and side strippers. You can specify a feed furnace. For
single columns without pumparounds and side strippers, use RadFrac. For other
multicolumn systems such as air separation systems, Petlyuk towers, and
complex primary fractionators, use MultiFrac.
Material Streams
Inlet
At least one inlet material stream
One steam feed per stripper (optional)
Outlet One vapor or liquid distillate, or both
One free water distillate stream (optional)
One bottoms product from the main column
Any number of side products from main column (optional)
Any number of water decant products from main column (optional)
One bottoms product per side stripper
Any number of pseudoproduct streams (optional)
Unit Operation Models
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4-49
Columns
You can use any number of pseudoproduct streams to represent:
• Column internal streams
• Pumparound streams
• Column connecting streams
A pseudoproduct stream does not affect column results.
Heat Streams
Inlet
One heat stream per stage for the main column (optional)
One heat stream per pumparound heater/cooler (optional)
One heat stream per stripper reboiler (optional)
One heat stream per stripper bottom liquid return (optional)
Outlet One heat stream per stage for the main column (optional)
One heat stream per pumparound heaters/cooler (optional)
One heat stream per stripper reboiler (optional)
One heat stream per stripper bottom liquid return (optional)
PetroFrac uses an inlet heat stream as a duty specification for all stages except
the condenser, reboiler, pumparounds, and stripper bottom liquid return.
If you do not give sufficient operating column specifications on the Setup
Configuration sheet, PetroFrac uses a heat stream as a specification for the
condenser and reboiler.
If you do not give two specifications on the Pumparounds Specifications sheet,
PetroFrac uses a heat stream as a specification for pumparounds.
If you do not give two specifications for the bottom liquid return on the Strippers
Setup LiquidReturn sheet, PetroFrac uses a heat stream as a specification.
If you give two specifications on the Setup Configuration sheet or Pumparounds
Specifications sheet, PetroFrac does not use the inlet heat stream as a
specification. The heat stream supplies the required heating or cooling.
Use optional outlet streams for the net heat duty of the condenser, reboiler, and
pumparounds. The value of the outlet heat stream equals the value of the inlet
heat stream (if any) minus the actual (calculated) heat duty.
Main Column
The main column can have any number of inlet streams. It can also have up to
three product streams per stage (one vapor, one hydrocarbon liquid, and one free
water).
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Chapter 4
Side Strippers
The side strippers can have a steam feed. They must have a liquid bottoms
product. You can use a heat stream as the heat source for the reboiler. If you do not
specify the reboiler duty, bottoms flow rate, and steam feed, PetroFrac uses the
heat stream as a duty specification.
Optionally, the stripper liquid bottoms may be partially returned to the main
column. To specify a bottom liquid return, you must enter two specifications on
the Strippers Setup LiquidReturn sheet.
Feed Furnace
You can specify a feed furnace. A feed furnace can have any number of feeds. The
vapor and liquid streams from the furnace are fed to the stage where the furnace is
attached.
Specifying PetroFrac
Within each column or stripper, stages are numbered from the top down. If
present, the main column condenser is stage 1.
Use the following forms to enter specifications and view results of PetroFrac:
Use this form
To do this
Setup
Specify basic column configuration and operating conditions
Pumparounds
Specify pumparound specifications and view results
Pumparounds Hcurves
Specify pumparound heating or cooling curve tables and view tabular results
Strippers Setup
Specify stripper operating specifications
Strippers Efficiencies
Specify stripper column or stage efficiencies
Strippers ReboilerHcurves
Specify stripper reboiler heating or cooling curve tables and view tabular results
Strippers TraySizing
Specify sizing calculation parameters for tray stripper sections, and view results
Strippers TrayRating
Specify rating calculation parameters for tray stripper sections, and view results
Strippers PackSizing
Specify sizing calculation parameters for packed stripper sections, and view results
Strippers PackRating
Specify rating calculation parameters for packed stripper sections, and view results
Strippers Properties
Specify physical property parameters for stripper sections
continued
Unit Operation Models
Version 10
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Columns
4-52
Use this form
To do this
Strippers Estimates
Specify estimates for stripper temperatures and flows
Strippers Results
View stripper product stream and connecting stream results
Strippers Profiles
View stripper profiles
HeatersCoolers
Specify stage heating or cooling specifications
RunbackSpecs
Specify runback specification parameters
Efficiencies
Specify stage or component efficiencies
DesignSpecs
Specify design specifications, manipulated variables, and view results
CondenserHcurves
Specify condenser heating or cooling curve tables and view tabular results
ReboilerHcurves
Specify reboiler heating or cooling curve tables and view tabular results
TraySizing
Specify sizing calculation parameters for tray column sections, and view results
TrayRating
Specify rating calculation parameters for tray column sections, and view results
PackSizing
Specify sizing calculation parameters for packed column sections, and view results
PackRating
Specify rating calculation parameters for packed column sections, and view results
Properties
Specify physical property parameters for column sections
Estimates
Specify estimates for column temperatures and flows
Convergence
Specify convergence parameters
Report
Specify block-specific report options and pseudostreams
BlockOptions
Override global values for physical properties, simulation options, diagnostic message levels,
and report options for this block
UserSubroutines
Specify user subroutines for tray and packing rating and sizing
Connectivity
View stream connectivity for the PetroFrac block
ResultsSummary
View key column results for the overall PetroFrac column
Profiles
View column profiles
Unit Operation Models
Version 10
Chapter 4
Main Column
You define the main column configuration using Condenser and Reboiler on the
Setup Configuration sheet. PetroFrac allows six condenser types:
• Subcooled
• Total
• Partial with vapor distillate product only
• Partial with both vapor and liquid distillate products
• No condenser, with pumparound to top stage
• No condenser, with external feed to top stage
You can specify one of three reboiler types:
• Kettle reboiler
• No reboiler, with pumparound to bottom stage
• No reboiler, with external feed to bottom stage
The types and number of required operating specifications depend on the column
configuration. Normally, you must enter two column operating specifications. If
either a condenser or a reboiler is absent, you must enter one specification. If
both the condenser and reboiler are absent, do not enter any specification.
Feed Stream Handling
Use the Setup Streams sheet to specify the feed and product stage locations. You
may also identify a feed as the stripping steam, and override its flow by specifying
a steam-to-product ratio.
PetroFrac provides three conventions for handling feed streams (see PetroFrac
Feed Convention Above-Stage and PetroFrac Feed Convention On-Stage in the
following figures):
• Above-Stage
• On-Stage
• Furnace
When Feed-Convention is Above-Stage, PetroFrac introduces a material stream
between adjacent stages. The liquid portion flows to the stage (n) you specify. The
vapor portion flows to the stage above (n – 1). You can introduce a liquid feed to
the top stage (or condenser) by specifying Stage=1. You can introduce a vapor
feed to the bottom stage (or reboiler) by specifying Stage=Number of stages+1.
When Feed-Convention is On-Stage, both the liquid and vapor portions of a feed
flow to the stage (n) you specify.
Unit Operation Models
Version 10
4-53
Columns
n-1
Vapor
Mixed feed
to stage n
Liquid
PetroFrac Feed Convention Above-Stage
n-1
Mixed feed
to stage n
n
n+1
PetroFrac Feed Convention On-Stage
When Feed-Convention is Furnace, a furnace is attached to the stage (n) you
specify. The feed enters the furnace before being introduced to the specified
stage.
Feed Furnace
PetroFrac can simulate a feed furnace simultaneously with the column/strippers.
You can simulate the feed furnace as a simple heater or as a single stage flash with
or without feed overflash bypass to the furnace. You can specify one of the
following:
•
•
•
4-54
Heat Duty
Temperature
Fractional overflash
Unit Operation Models
Version 10
Chapter 4
To do this
Use this sheet
Define a feed to the feed furnace
Setup Streams (Feed Convention)
Enter a furnace model type and associated specifications
Setup Furnace
You can select from three furnace model types, as shown in the next three
figures.
Main Column
Heat
Feed
Furnace Modeled as a Stage Heat Duty
Main Column
Feed
Furnace
Furnace Modeled as a Single Stage Flash
Unit Operation Models
Version 10
4-55
Columns
Main Column
Feed
Furnace
Furnace Modeled as a Single Stage Flash with Overflash Bypass
If Model=
PetroFrac models the furnace as
And calculates
Heater
Stage heat duty on the feed stage
—
Flash
Single-stage flash
Furnace temperature, degree of vaporization,
vapor/liquid compositions
Flash-Bypass
Single-stage flash with the overflash bypassed
back to the furnace
Furnace temperature, degree of vaporization,
vapor/liquid compositions
Liquid Runbacks
Use the RunbackSpecs form to specify the flow rate of liquid runback from any
stage. When you enter a liquid runback specification, you must allow PetroFrac to
adjust one of the following:
• Flow rate of a pumparound
• Duty of an interstage heater/cooler
Pumparounds
Use the following sheets to enter specifications for pumparounds.
4-56
Use this sheet
To enter
Pumparounds
Specifications
Pumparound connectivity and cooler/heater specifications
Report PseudoStreams
Pseudostream assignment for the pumparound
Hcurves Specifications
Heating/cooling curve specifications
Unit Operation Models
Version 10
Chapter 4
Pumparounds are associated with the maincolumn. They can be total or partial
drawoffs of the stage liquid flow. You must specify the draw and return stage
locations for each pumparound. For partial drawoffs, you must specify two of the
following:
• Flow rate
• Temperature
• Temperature change
• Heat Duty
For total drawoffs, you must specify one of the following:
•
•
•
Temperature
Temperature change
Heat Duty
Side Strippers
Use the Stripper forms and sheets to enter specifications for side strippers.
Side strippers may be either steam-stripped or reboiled. For steam strippers, you
must enter a steam stream. You can override its flow rate by specifying a steamto-product ratio. For reboiled strippers, you must specify a reboiler duty.
PetroFrac assumes:
• A liquid draw goes from the main column to the top of the stripper.
• The stripper overhead is returned to the main column.
You must specify the draw and return stage locations. You can also:
• Return a fraction of the stripper bottoms to the main column
• Specify additional liquid draws from other stages of the main column as feeds
to the strippers
Efficiencies
You can specify one of two types of efficiencies:
• Vaporization
• Murphree
Vaporization efficiency is defined as:
Effi v =
yi , j
K i, j x i , j
Murphree efficiency is defined as:
Effi ,Mj =
Unit Operation Models
Version 10
yi, j − yi , j +1
ki , j x i , j − yi , j +1
4-57
Columns
Where:
K
=
Equilibrium K value
x
=
Liquid mole fraction
y
=
Vapor mole fraction
Eff v
=
Vaporization efficiency
Eff M
=
Murphree efficiency
i
=
Component index
j
=
Stage index
To specify vaporization or Murphree efficiencies, enter the number of actual
stages on the Setup Configuration sheet and Strippers Setup Configuration sheet
as Number of stages. Then use the Efficiencies and Strippers Efficiencies forms
to enter the efficiencies.
You can use any of these efficiencies to account for departure from equilibrium.
But you cannot convert from one efficiency to the other. Magnitudes of the
efficiencies can be quite different. Details on using and estimating these
efficiencies are described by Holland, Fundamentals of Multi-Component
Distillation, McGraw-Hill Book Company, 1981.
Convergence
For convergence PetroFrac uses:
• The sum-rates variant of the inside-out algorithm
• A special initialization procedure designed for petroleum refining applications
PetroFrac generally does not need initial estimates. For ethylene plant primary
fractionator/quench tower combinations, you should provide temperature
estimates.
To enhance convergence, you may enter profile estimates on the following
PetroFrac forms:
• Estimates
• Strippers Estimates
Temperature estimates are usually adequate. You can increase convergence
stability by selecting varying degrees of damping on the Convergence Basic sheet.
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Unit Operation Models
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Chapter 4
Rating Mode
In rating mode, PetroFrac calculates the column profiles and product compositions
based on specified values of column parameters. Examples of column parameters
are:
• Reflux ratio
• Reboiler duties
• Feed flow rates
• Furnace temperature
• Pumparound loads
Design Mode
In design mode you can manipulate subsets of the column parameters to achieve
certain specifications on column performance.
You can specify
For any
Purity
Stream, including internal streams
Recovery of any components group
Set of product streams
Flow rate of any components group
Internal stream or set of product streams
Flow rates of any components groups to any
other component groups
Internal streams to any other internal streams, or set of feed or product
streams
Temperature
Stage
Heat duty
Stage
Fractional overflash
Stage
TBP and D86 temperature gaps
Pair of product streams
TBP temperature
Product stream
D86 temperature
Product stream
D1160 temperature
Product stream
Vacuum distillation temperature
Product stream
API gravity
Product stream
Standard liquid density
Product stream
Specific gravity
Product stream
Flash point
Product stream
Pour point
Product stream
Refractive index
Product stream
†
††
continued
Unit Operation Models
Version 10
4-59
Columns
You can specify
For any
Reid vapor pressure
Product stream
Value of any Prop-Set property
Internal or product stream
Difference of any pair of Prop-Set properties
Pair of product streams
Watson UOP K factor
Product stream
†
††
†††
†††
Express the purity as the sum of mole, mass, or standard liquid volume fraction of any group of
components relative to any other group of components.
Express recovery as a fraction of the same components in a subset of feed streams.
See ASPEN PLUS User Guide, Chapter 28.
You can also specify overflash for a furnace feed stream.
Physical Properties
Use the BlockOptions form to override the global physical property method. You
can specify one method on this form, which PetroFrac uses for all stages in the
main column and strippers.
You can also split the main column or a stripper into any number of segments,
each using a different property method.
Use this sheet
When you use different properties for
Properties Property Sections
The main column
Strippers Properties Property Sections
A stripper
Free Water Handling
PetroFrac can perform free-water calculations in the main column and side
strippers. By default, PetroFrac performs free-water calculations for the main
column condenser. The free-water phase, if present, is decanted.
4-60
To do this
Use these sheets
Request free-water calculations for additional stages in the
main columns and strippers
Properties Freewater Stages
Strippers Properties Freewater Stages
Define additional water decant product streams for the main
column
Setup Streams
Unit Operation Models
Version 10
Chapter 4
Solids Handling
PetroFrac handles solids by:
• Temporarily removing all solids from inlet streams
• Performing calculations without solids
• Adiabatically mixing solids removed from inlet streams with main column
liquid bottoms
This calculation approach maintains an overall mass and energy balance around
the PetroFrac block. But the bottom stage liquid product will not be in exact
thermal or phase equilibrium with other bottom stage flows (for example, the
bottom stage vapor flow).
Sizing and Rating of Trays and Packings
PetroFrac has extensive capabilities to size, rate, and perform pressure drop
calculations for trayed and packed columns. Use the following PetroFrac forms to
enter specifications:
• TraySizing, TrayRating, PackSizing, PackRating
• Strippers TraySizing, Strippers TrayRating, Strippers PackSizing, Strippers
PackRating
See Appendix A for details on tray and packing types and correlations.
Unit Operation Models
Version 10
4-61
Columns
RateFrac
Rate-Based Distillation
RateFrac is a rate-based nonequilibrium model for simulating all types of
multistage vapor-liquid fractionation operations. RateFrac simulates actual tray
and packed columns, rather than the idealized representation of equilibrium
stages. RateFrac explicitly accounts for the underlying interphase mass and heat
transfer processes to determine the degree of separation. RateFrac does not use
empirical factors such as efficiencies and the Height Equivalent to a Theoretical
Plate (HETP).
RateFrac is applicable for:
• Ordinary distillation
• Absorption
• Reboiled absorption
• Stripping
• Reboiled stripping
• Extractive and azeotropic distillation
RateFrac is suitable for:
•
•
•
Two-phase systems
Narrow and wide-boiling systems
Systems exhibiting strong liquid phase nonideality
RateFrac can also detect and handle a free water phase in the condenser.
RateFrac can model columns with chemical reactions. Reactions include:
• Equilibrium
• Rate-controlled
• Electrolytic
RateFrac models a complex configuration consisting of a single column or
interlinked columns. The configuration may have:
•
•
•
Any number of columns, each with any number of RateFrac Segments
Any number of connections between columns or within each column
Arbitrary flow splitting and mixing of connecting streams
RateFrac can handle operations with:
• Side strippers
• Pumparounds
• Bypasses
• External heat exchangers
RateFrac can be used to
• Rate existing columns
• Design new columns
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Unit Operation Models
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Chapter 4
You can define pseudoproduct streams to represent column internal flows or
connecting streams in RateFrac.
You can use Fortran Blocks, Sensitivity Analysis, and Case Study blocks to vary
configuration parameters, such as feed location or number of segments.
RateFrac can produce segmentwise column profile plots.
RateFrac can be used with other ASPEN PLUS features and capabilities much in
the same way as the equilibrium-based models, RadFrac, PetroFrac, and
MultiFrac.
Flowsheet Connectivity for RateFrac
Top Segment or
Condenser Heat
Duty (optional)
Feeds
Vapor Distillate or
Interconnecting Stream
1
Reflux
Heat (optional)
Heat (optional)
Liquid Distillate (optional)
Water Distillate (optional)
Side Products
Interconnecting Streams
(Heater optional)
Pumparounds
and Bypasses
(Heater optional)
Interconnecting Streams
(Heater optional)
Heat (optional)
Bottom Segment
or Reboiler Heat
Duty (optional)
N
Heat (optional)
Bottoms or
Interconnecting Streams
RateFrac models single and interlinked columns. Any number of columns can be
connected by any number of connecting streams. Each connecting stream can
have an associated heater.
Each column may have:
• Any combination of packed and tray segments
• Any number of connecting streams
• Any number of side product streams
Unit Operation Models
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4-63
Columns
Material Streams
Inlet
At least one material stream
Outlet Up to two product streams (one vapor, one liquid) per segment
One water distillate product stream (optional)
Any number of pseudoproduct streams (optional)
Each column must have:
• At least one vapor or liquid stream leaving the top segment
• One liquid stream leaving the bottom segment
When you model interlinked columns, the top and bottom streams can be
connecting streams. However, the free-water stream from the condenser cannot
be a connecting stream.
Heat Streams
Inlet
One heat stream per segment (optional)
One heat stream per connecting stream (optional)
Outlet One heat stream per connecting stream (optional)
RateFrac uses an inlet heat stream as a duty specification for all segments except
the condenser, reboiler, and connecting streams. If you do not provide two column
operating specifications on the Columns Setup Configuration sheet, RateFrac uses
a heat stream as a specification for the condenser and reboiler.
If you do not provide two specifications on the ConnectStreams Input sheet,
RateFrac uses a heat stream as a specification for connecting streams.
If you provide two specifications on the Columns Setup Configuration sheet or
ConnectStreams Input sheet, RateFrac does not use the inlet heat stream as a
specification. The inlet heat stream supplies the required heating or cooling.
You can use optional outlet heat streams for the net heat duty of the condenser,
reboiler, and connecting streams. The value of the outlet heat stream equals the
value of the inlet heat stream (if any), minus the actual (calculated) heat duty.
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Unit Operation Models
Version 10
Chapter 4
The Rate-Based Modeling Concept
Most models available for simulating and designing multicomponent, multistage
separation processes are based on the idealized concept of equilibrium or
theoretical stages. This approach assumes that the liquid and vapor phases
leaving any stage are in thermodynamic equilibrium with each other. The phase
compositions, temperature, and vapor and liquid flow profiles are calculated by
solving the governing material balances, energy balances, and equilibrium
relations for each stage.
In practice, columns rarely operate under thermodynamic equilibrium conditions.
Vapor-liquid equilibrium prevails only at the interface separating vapor and
liquid phases. The separation achieved in a multistage column depends on the
interphase mass and heat transfer rate processes. Multicomponent mass transfer
interactions can also have pronounced effects on the separation.
When the equilibrium approach is used to model a tray column, a correction
factor (referred to as an efficiency) attempts to account for the departure from
equilibrium. Many definitions for efficiency exist, with wide variations in
complexity and accuracy. In general, efficiencies depend on:
• Physical characteristics of the equipment, such as column configuration
• Hydrodynamics of the column
• Fluid properties of the system
Murphree vapor efficiencies are the most widely used. These efficiencies
generally vary from stage to stage within a column, and from component to
component. For multicomponent systems, there are no theoretical limitations on
Murphree efficiencies. Experimental evidence shows that component efficiencies:
• May vary strongly from component to component
• Can take any value including negative values
Methods used to calculate component efficiencies generally do not include the
effect of the departure from thermal equilibrium.
Packed columns are also designed using the equilibrium stage concept. However,
HETP is commonly used in place of efficiencies. HETP varies with:
• Type and size of the packing
• Hydrodynamics of the column
• Fluid properties of the system
Like efficiencies, HETPs may vary strongly from point to point within a column
and from system to system.
Unit Operation Models
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Columns
RateFrac is based on a fundamental and rigorous approach. This approach avoids
uncertainties that result when the equilibrium approach is used with estimated
efficiencies or HETP. RateFrac directly includes mass and heat transfer rate
processes in the system of equations representing the operation of separation
process units. RateFrac:
• Describes the simultaneous mass and heat transfer rate phenomena
• Accounts for the multicomponent interactions between simultaneously
diffusing species
For nonreactive systems, RateFrac comprises:
•
•
•
•
Mass and heat balances around vapor and liquid phases
Mass and heat transfer rate models to determine interphase transfer rates
Vapor-liquid equilibrium relations applied at interfacial conditions
Correlations to estimate mass and heat transfer coefficients and interfacial
areas
For chemically reactive systems, RateFrac includes equations to account for the
influence of chemical reactions on heat and mass transfer rate processes. For
systems involving equilibrium reactions, RateFrac includes equations to
represent the chemical equilibrium conditions.
RateFrac completely avoids the need for efficiencies in tray columns or HETPs in
packed columns. RateFrac has far greater predictive capabilities than the
conventional equilibrium model.
Specifying RateFrac
RateFrac numbers segments from the top down, starting with the condenser (or
starting with the top segment if there is no condenser).
Use the following forms to enter specifications and view results for RateFrac:
Use this form
To do this
BlockParameters
Specify overall block parameters, convergence and initialization parameters, blockspecific diagnostic message levels, and feed flash convergence parameters
Columns Setup
Specify basic column configuration and operating conditions
Columns TraySpecs
Specify tray column section parameters
Columns PackSpecs
Specify packed column section parameters
Columns Reactions
Assign reactions to column sections, and specify vapor and liquid holdup data
continued
4-66
Unit Operation Models
Version 10
Chapter 4
Use this form
To do this
Columns Estimates
Specify initial estimates for segment temperatures, and vapor and liquid flows and
compositions
Columns
EquilibriumSegments
Specify optional equilibrium segments and column efficiencies
Columns HeatersCoolers
Specify segment heating or cooling and utility exchangers
Columns FlowTempSpecs
Specify liquid, vapor, and temperature specifications
Columns Results
View column performance summary
Columns Profiles
View column profiles
Columns InterfaceProfiles
View column interface profiles
Columns EfficienciesFlooding
View tray and component efficiencies, packing HETPs, and flooding summary
Columns TransferCoefficients
View binary diffusion, binary mass, and heat transfer coefficients
InletsOutlets
Specify feed and product stream locations and conventions, inlet and outlet heat
streams
ConnectStreams
Specify connecting stream sources and destinations and view results
DesignSpecs
Specify design specifications and view convergence results
Vary
Specify manipulated variables to satisfy design specifications and view final values
FlowRatios
Specify the flow ratio and view results
CondenserHcurves
Specify condenser heating or cooling curve tables and view tabular results
ReboilerHcurves
Specify reboiler heating or cooling curve tables and view tabular results
ConnectStreamHcurves
Specify connecting stream heating or cooling curve tables and view tabular results
Reports
Specify block-specific report options, and pseudostream information
BlockOptions
Override global values for physical properties, simulation options, diagnostic message
levels, and report options for this block
UserSubroutines
Specify user subroutine parameters for mass and heat transfer coefficients, interfacial
area, pressure drop, and kinetics
ResultsSummary
View material and energy balance results and overall split fractions
Column Numbering
Individual columns are identified by a column number. The numbering order does
not affect algorithm performance. Within each column, segments are numbered
from top to bottom, starting with the condenser (when present).
Unit Operation Models
Version 10
4-67
Columns
Stream Definition
RateFrac uses four types of streams:
• External streams
• Connecting streams
• Internal streams
• Pseudostreams
External streams are the standard RateFrac inlet and outlet streams. They are
identified by stream IDs.
Connecting streams are streams within RateFrac but external to individual
columns. These streams are identified by connecting stream numbers.
Connecting streams may connect two columns or segments of the same column
(such as bypasses and pumparounds). You can associate a heater with any
connecting stream. Heaters are identified by the connecting stream number.
Internal streams are the liquid or vapor flows between adjacent segments of the
same column. These streams are identified by a segment number and a column
number.
Pseudostreams store the results of internal and connecting streams. They are a
subset of external outlet streams. Unlike normal outlet streams, pseudostreams
do not participate in the block material balance calculations.
Material Feed Streams
RateFrac uses two conventions for handling material feed streams (see RateFrac
Feed Conventions in the following figures):
• Above segment
• On segment
Segment n-1
Mixed Feed to
Vapor
Liquid
Segment n
Segment n
RateFrac Feed Convention Above Segment
4-68
Unit Operation Models
Version 10
Chapter 4
Segment n-1
Liquid
Mixed Feed to
Segment n
Segment n
Vapor
Segment n + 1
RateFrac Feed Convention On Segment
When the feed convention is defined as Above segment, RateFrac introduces a
material stream between adjacent segments. The liquid portion flows to segment
n, specified as the feed segment. The vapor portion flows to the segment above
(segment n-1 in the figure RateFrac Feed Convention Above segment). You can
introduce a liquid to the top segment (or condenser) by specifying Segment=1.
You can introduce a vapor feed to the bottom segment (or reboiler), by specifying
the segment equal to the last segment in the column +1. When a two-phase feed
stream is fed to segment 1, the vapor phase is combined directly with the vapor
distillate. Similarly, when a two-phase feed stream is fed to the last segment of
that column + 1, the liquid phase is combined directly with the liquid bottoms
product.
When the feed convention is defined as On segment, both the liquid and vapor
portions of the feed flow to segment specified (segment n in the previous figure
RateFrac Feed Convention On segment).
RateFrac assumes that a vapor feed (or the vapor portion of a mixed feed)
combines with the vapor phase in the segment it enters. RateFrac also assumes
that a liquid feed (or the liquid portion of a mixed feed) combines with the liquid
phase in the segment it enters.
Unit Operation Models
Version 10
4-69
Columns
Column Configuration
Specify the column configuration by indicating the following on the Columns
Configuration sheet:
• Number of segments
• Presence or absence of condensers and reboilers
• Equilibrium and nonequilibrium segments
Connecting Streams
RateFrac allows any number of connecting streams. Any number of these streams
can have the same:
• Source column, segment, and phase
• Destination column and segment
RateFrac introduces connecting streams on the destination segment regardless of
their phase (Convention = On Segment). All connecting streams can have a
heater. Enter all specifications for connecting streams on the ConnectStreams
Input sheet. RateFrac does not allow phase change for connecting streams.
Connecting streams can be either a total or a partial drawoff of the segment flow.
Enter the required specifications as follows:
If the drawoff type is
You enter
Partial
Two of the following: flow, temperature or temperature change and heat duty
Total
One of the following: temperature or temperature change and heat duty
†
††
†
††
Enter zero for heat duty if heater is absent.
Flow is taken as the net flow of the segment, excluding any product flow and any other connecting
stream flow.
Required Specifications
You must specify the total number of columns and connecting streams.
4-70
Use this form
To enter
Such as
Columns TraySpecs
Tray specifications
Number of trays or
Number of trays per segment
Tray type
Tray characteristics
Columns PackSpecs
Packing specifications
Total height of packing or
Height of packing per segment
Packing type
Packing characteristics
Unit Operation Models
Version 10
Chapter 4
You must also specify:
• Inlet stream locations
• Heat stream locations, heat duty, and phase
• Pressure profile for each column
• Condenser type
• Two operating specifications for multisegment columns and one for singlesegment columns
• Source and destination of any connecting stream and associated heater
specifications
• Outlet stream locations and phases. If the outlet stream is a side drawoff
stream from a segment, you must specify its flow.
A segment refers to one of the following:
• A slice (or portion) of packing in a packed column (see the preceding figure,
Nonequilibrium Segment in a Packed Column)
• One (or more) tray(s) in a tray column (see the preceding figure,
Nonequilibrium Segment in a Tray Column)
A column consists of segments. To evaluate mass and heat transfer rates
between contacting phases, RateFrac uses one of the following:
•
•
Height of packing in a packed segment
Number of trays in a tray segment
Nonequilibrium Segment in a Packed Column
Unit Operation Models
Version 10
4-71
Columns
Nonequilibrium Segment in a Tray Column
Equilibrium Stages
RateFrac can model both equilibrium stages and nonequilibrium segments in the
same column. Use the Columns EquilibriumSegments form to specify the location
of equilibrium stages. When all stages are equilibrium, you can obtain the same
results using RateFrac as you can using RadFrac, MultiFrac, or PetroFrac with
ideal stages.
Reactive Systems
RateFrac can handle kinetically controlled reactions and equilibrium reactions in
both liquid and vapor phases. Chemical reactions can be of any type, including:
• Simultaneous
• Consecutive
• Parallel
• Forward
• Reverse
For kinetically controlled reactions, the kinetics can be defined by one of the
following:
• Built-in power law expressions
• User-supplied Fortran subroutines
4-72
Unit Operation Models
Version 10
Chapter 4
For equilibrium reactions, the chemical reaction equilibrium constant can be
defined either in terms of user-supplied coefficients for a temperature-dependent
polynomial, or can be computed from the reference state free energies of
participating components.
RateFrac can model electrolyte systems using both the apparent and the true
component approaches.
Enter the following information on the Reactions form:
•
•
•
Reaction stoichiometry
Reaction type
Phase in which reactions occur
Depending on the reaction type, you must enter either the equilibrium constant
or kinetic parameters. For electrolytic reactions, you can also enter the reaction
data on the Chemistry form.
To associate reactions with a column segment, enter the corresponding Reactions
ID (or Chemistry ID or User Reactions ID) on the Columns Reactions
Specifications sheet.
For rate-controlled reactions, you must enter holdup data for the phase where
reactions occur.
For these segments
Use this form to enter holdup information
Equilibrium
Columns Reactions
Tray
Columns TraySpecs
Packed
Columns PackSpecs
Heaters and Coolers
Use the Columns HeatersCoolers Side Duties sheet to specify:
• Heat duty for a segment
• Heater segment location (column and segment)
• Phase
Use the Columns HeatersCoolers Utility Exchangers sheet to specify cooling (or
heating) of any segment using a coolant (or heating fluid).
You can use a heat stream to provide heat integration. Heat integration occurs
when the duty recovered from another block is used as the heat source of heaters
and coolers. Enter heat stream data on the InletsOutlets Heat Streams sheet.
Unit Operation Models
Version 10
4-73
Columns
Physical Property Specifications
Use the RateFrac BlockOptions form to override the global physical property
property method. You can specify only one property method on the BlockOptions
form. RateFrac uses this property method for the whole column. RateFrac does not
allow multiple physical property methods.
Handling Free Water
RateFrac can perform free-water calculations only in condensers.
Rating Mode
In rating mode, RateFrac calculates temperatures, flows, and mole fraction profiles
based on specified values of column parameters such as:
• Reflux ratio
• Product flows
• Heat duties
Design Mode
In design mode, use the DesignSpecs form to specify column performance
parameters (such as purity or recovery). You must indicate which variables to
manipulate to achieve these specifications using the Vary form. You can specify
any variables that are allowed in rating mode, except:
• Number of columns, segments, and connecting streams
• Pressure profile
• Locations of feeds, products, heaters, and connecting streams
• Column configurations, including the number of trays, tray characteristics,
height of packing, packing specifications
4-74
Unit Operation Models
Version 10
Chapter 4
The flows of inlet material streams and the duties of inlet heat streams can also
be manipulated variables.
You can specify
For any
Purity
Stream, including an internal stream
Recovery of any component groups
Set of product streams
Flow of any component groups
Internal stream or set of product streams
Component ratio
Internal stream and a second internal stream or feed streams and product streams
Temperature of vapor stream
Segment
Temperature of liquid stream
Segment
Heat duty
Condenser, reboiler, or a connecting stream
Value of any Prop-Set property
Internal or product stream
Ratio or difference of any pair of
properties in a Prop-Set
Single or paired internal or product stream
†
††
†††
†
††
†††
Express the purity as the sum of mole, mass, or standard liquid volume fractions of any group of
components, relative to any other group of components.
You can express recovery as a fraction of the same components in a subset of the feed stream.
See ASPEN PLUS User Guide, Chapter 28.
Calculating Efficiency and HETP
From converged vapor and liquid composition profiles, RateFrac back-calculates
the component Murphree vapor efficiencies. These efficiencies are defined for each
component as the fractional approach to equilibrium of the vapor stream leaving
any segment, with the liquid stream leaving the same segment.
Eff ij =
y ij − y ij +1
K ij x ij − Yij +1
Where:
Eff
K
x
y
i
j
Unit Operation Models
Version 10
=
=
=
=
=
=
Murphree vapor efficiency
Vapor-liquid equilibrium K value
Liquid mole fraction
Vapor mole fraction
Component index
Segment index
4-75
Columns
For each segment of packed columns, RateFrac calculates the fractional approach
to equilibrium using the same definition as used for Murphree vapor efficiency.
RateFrac reports the height of packing required to achieve equilibrium as the
HETP for that segment.
Convergence and Computing Time
RateFrac must solve many more equations for a given column than an equilibrium
model. Computing times for RateFrac are greater than they are for equilibrium
models, particularly for problems containing many components. The solution
algorithm RateFrac uses is an efficient, Newton-based simultaneous correction
approach. RateFrac solution times increase with the square of the number of
components. Solution times can be an order of magnitude greater than RadFrac,
MultiFrac, or PetroFrac solution times for the same problems.
References for Built-In Correlations
RateFrac uses well-known and accepted correlations to calculate:
• Binary mass transfer coefficients for the vapor and liquid phase
• Interfacial areas
In general, these quantities depend on column diameter and operating
parameters such as:
• Vapor and liquid flow
• Densities
• Viscosities
• Surface tension of liquid
• Vapor and liquid phase binary diffusion coefficients
Mass transfer coefficients and interfacial areas depend on:
Packing characteristics
Tray characteristics
Type (random or structured)
Type (sieve, valve, or bubble-cap)
Size
Weir and flow path length
Specific surface area
Downcomer area
Material of construction
Weir height
The correlations involve well-defined dimensionless groups, such as the
Reynolds, Froude, Weber, Schmidt, and Sherwood numbers. The correlations
have been fitted to experimental measurements from laboratory and pilot plant
absorption and distillation columns.
4-76
Unit Operation Models
Version 10
Chapter 4
The correlations RateFrac uses for mass transfer coefficients and interfacial
areas are:
Column type
Correlation used
Packed Columns (random packing)
Onda et al. (1968)
Packed Columns (structured)
Bravo et al. (1985, 1992)
†
Chan and Fair (1984)
Sieve Trays
Valve Trays
Scheffe and Weiland (1987)
†
Bubble-Cap Trays
†
Grester et al. (1958)
These correlations do not provide the mass transfer coefficients and interfacial areas separately.
RateFrac allows you to write Fortran subroutines to calculate:
• Binary mass transfer coefficients
• Heat transfer coefficients
• Interfacial areas
The subroutines are described in the ASPEN PLUS User Models reference
manual.
By applying a rigorous multicomponent mass transfer theory (Krishna and
Standart, 1976), RateFrac uses binary mass transfer coefficients to evaluate:
•
•
Multicomponent binary mass transfer coefficients
Component mass transfer rates between vapor and liquid phases
RateFrac calculates the vapor phase and liquid phase heat transfer coefficients
using the Chilton-Colburn analogy (King, 1980). This analogy relates:
• Mass transfer coefficients
• Heat transfer coefficients
• Schmidt number
• Prandtl number
Mass and Heat Transfer Correlations
RateFrac uses several mass and heat transfer correlations for:
• Packed columns.
• Valve Tray columns
• Bubble-Cap Tray columns
• Sieve Tray columns
Packed Column
RateFrac calculates the mass transfer coefficients and the interfacial area
available for mass transfer using the correlations developed by Onda et al., 1968.
Unit Operation Models
Version 10
4-77
Columns
The correlation for the liquid phase binary mass transfer coefficients is:
2/3
 L  ρ  1/ 3 
 L 
−1/ 2
L
k in 
 ( ScinL )
a pd p
  = 0.0051
 aω µ L 
  gµ L  
(
)
0 .4
The correlation for the gas phase binary mass transfer coefficient is:
 g  RT g  
 G 
  = 5.23

k in 
 a p ug 
  a p Din  
0 .7
(Sc ) (a
g 1/ 3
in
p
dp
)
−2
The interfacial area available for mass transfer is given by the correlation:
{
[
aω = a p 1 − exp − 145
. Re L
0.1
FrL −0.05We L
0 .2
(σ σ )
−0.75
c
]}
Where:
2
aρ L2
L
L
Re L =
, FrL =
2 , We L =
a p σρ L
a pµ L
gρ L
and:
L
=
Binary mass transfer coefficient for the binary pair i and n
in the liquid phase (m/sec)
ρL
=
Density of liquid (kg/m 3 )
g
=
Acceleration due to gravity (m/sec 2 )
µL
=
Viscosity of liquid (Newton-sec/m 2 )
L
=
Liquid superficial mass velocity (kg/m 2 /sec)
aw
=
Wetted interfacial area (m 2 interfacial area/m 3 packing
volume)
=
Schmidt number for the binary pair i and n in the liquid
phase =
k in
L
Sc in
L
D in
ap
µ L (ρ L DinL )
=
Binary Maxwell-Stefan diffusion coefficient for the binary
pair i and n
(m 2 /sec)
=
Specific surface area of the packing
continued
4-78
Unit Operation Models
Version 10
Chapter 4
dp
=
Nominal diameter of packing or packing size (m)
g
=
Binary mass transfer coefficient for the binary pair i and n
in the vapor phase (kg mole/atm/m 2 /sec)
=
Universal gas constant (m 3 atm/kg mole/K)
=
Gas phase temperature (K)
G
=
Gas superficial mass velocity (kg/m 2 /sec)
µg
=
Viscosity of gas mixture (Newton-sec/m 2 )
=
Gas phase Schmidt number for the binary pair i and n =
k in
R
T
g
g
Sc in
ρg
(ρ D )
µg
g
in
g
=
Density of gas mixture (kg/m 3 )
=
Gas-phase binary Maxwell-Stefan diffusion coefficient for
the binary pair i and n (m 2 /sec)
σ
=
Surface tension (Newton/m)
σc
=
Critical surface tension of the packing material (Newton/m)
g
D in
Valve Tray Column
RateFrac calculates the mass transfer coefficients and the interfacial area
available for mass transfer using the correlations developed by Scheffe and
Weiland, 1987.
The correlation for the liquid phase binary mass transfer coefficient is:
( ) ( Re )
0.68
ShinL = 125.4 Re g
0.09
L
(v )0.05 (ScinL )
0.5
The correlation for the gas phase binary mass transfer coefficients is:
( ) (Re )
Shing = 9.93 Re g
0.87
0.13
L
(ϖ) 0.39 (Scing )
0.5
The interfacial area available for mass transfer is given by the correlation:
( ) ( Re )
a = 0.27 Re g
Unit Operation Models
Version 10
0.37
L
0.25
( ϖ) 0.52
4-79
Columns
Where:
L
Sh =
L
in
Re L =
k in ad
ρ L D in
L
g
, Sh =
g
in
k in ad
ρ g D in
g
, ScinL =
µL
ρ L D in
L
, Scing =
µg
ρ g D in
g
,
Gd
Ld
W
, Re g =
, ϖ=
µg
d
µL
and:
L
=
Liquid mass velocity (kg/m 2 /sec) (Velocity is based on tower
active area.)
d
=
Geometric parameter of unit length (m)
µL
=
Viscosity of liquid mixture (Newton-sec/m 2 )
G
=
Gas mass velocity (kg/m 2 /sec) (Velocity is based on tower
active area.)
µg
=
Viscosity of gas mixture (Newton-sec/m 2 )
L
=
Binary mass transfer coefficient for the binary pair i and n
in the liquid phase (kg mole/m 2 /sec)
a
=
Interfacial area (m 2 interfacial area/m 2 tower active area)
ρL
=
Molar density of liquid (kg mole/m 3 )
=
Binary Maxwell-Stefan diffusion coefficient for the binary
pair i and n
(m 2 /sec)
=
Binary mass transfer coefficient for the binary pair i and n
in the vapor phase (kg mole/m 2 /sec)
=
Molar density of gas mixture (kg mole/m 3 )
=
Gas-phase binary Maxwell-Stefan diffusion coefficient for
the binary pair i and n (m 2 /sec)
ρL
=
Density of liquid mixture (kg/m 3 )
ρg
=
Density of gas mixture (kg/m 3 )
W
=
Weir height (m)
k in
L
D in
g
k in
ρg
g
D in
4-80
Unit Operation Models
Version 10
Chapter 4
Bubble-Cap Tray Column
RateFrac calculates the product of the binary mass transfer coefficients and
interfacial areas using the correlations developed by Grester et al., 1958.
The product of liquid phase binary mass transfer coefficients and interfacial area
is given by the correlation:
k in a = (4.127 × 108 DinL ) (0.21313F + 015
. ) Lt L
0.5
L
The product of gas phase binary mass transfer coefficient and interfacial area is
given by the correlation:
k in a =
g
(0.776 + 4.567h
w
− 0.2377 F + 104.85Q L )
(Sc )
g 0.5
in
G
Where:
L
k in
a
L
D in
F
=
Binary mass transfer coefficient for the binary pair i and n
in the liquid phase (kg mole/m 2 /sec)
=
Interfacial area (m 2 interfacial area/m 2 tower active area)
=
Binary Maxwell-Stefan diffusion coefficient for the binary
pair i and n
(m 2 /sec)
=
F-Factor =
µ g ρ1g/ 2  kg 1/2 / sec / m1/2 
µg
=
Gas volumetric flow per unit active area (m 3 /sec/m 2 )
ρg
=
Density of gas mixture (kg/m 3 )
L
=
Liquid molar velocity (kg mole/m 2 /sec) (Velocity is based on
active area.)
tL
=
Liquid residence time =
0.9998hL Z L / QL (sec)
hL
=
Liquid holdup =
0.04191 + 0.19hw + 2.4545QL − 0.0135 F ( m )
ZL
=
Liquid flow path length (m)
continued
Unit Operation Models
Version 10
4-81
Columns
QL
=
Liquid flow per average path width (m 3 /sec/m)
hw
=
Outlet weir height (m)
g
=
Binary mass transfer coefficient for the binary pair i and n
in the vapor phase (kg mole/m 2 /sec)
=
Gas molar velocity (kg mole/m 2 /sec) (Velocity is based on
active area.)
=
Gas-phase Schmidt number for the binary pair i and n =
k in
G
g
Sc in
µg
g
D in
µg
(ρ D )
g
g
in
=
Viscosity of gas mixture (Newton-sec/m 2 )
=
Gas-phase binary Maxwell-Stefan diffusion coefficient for
the binary pair i and n (m 2 /sec)
Sieve Tray Column
RateFrac calculates the product of mass transfer coefficients and interfacial
areas using the correlations developed by Chan and Fair, 1984.
The product of liquid phase binary mass transfer coefficient and interfacial area
is given by the correlation:
L
k in a = (4.127 x108 DinL ) (0.21313F + 0.15) Lt L
0.5
The product of the gas phase binary mass transfer coefficient and interfacial area
is given by the correlation:
k a=
g
in
( D ) (1030 F − 867 F )
g 0.5
in
2
h L 0.5
Where:
L
k in
a
L
D in
=
Binary mass transfer coefficient for the binary pair i and n
in the liquid phase (kg mole/m 2 /sec)
=
Interfacial area (m 2 interfacial area/m 2 tower active area)
=
Binary Maxwell-Stefan diffusion coefficient for the binary
pair i and n
(m 2 /sec)
continued
4-82
Unit Operation Models
Version 10
Chapter 4
=
F
F-Factor =
µ gρg
( kg
1/ 2
/ sec / m1/ 2 )
µg
=
Gas volumetric flow per unit active area (m 3 /sec/m 2 )
ρg
=
Density of gas mixture (kg/m 3 )
L
=
Liquid molar velocity (kg mole/m 2 /sec) (Velocity is based on
active area.)
tL
=
Liquid residence time =
0.9998hL Z L / QL (sec)
hL
=
Liquid holdup =
0.04191 + 0.19hw + 2.4545QL − 0.0135 F ( m )
ZL
=
Liquid flow path length (m)
QL
=
Liquid flow per average path width (m 3 /sec/m)
hw
=
Outlet weir height (m)
g
=
Binary mass transfer coefficient for the binary pair i and n
in the vapor phase (m/sec)
=
Binary Maxwell-Stefan diffusion coefficient for the binary
pair i and n
(m 2 /sec)
F
=
Fractional approach to flooding gas velocity =
µgF
=
Gas velocity through active area at flooding (m/sec)
hL
=
Liquid height =
Γe
=
exp(− 12.55K s 0.91 )
B
=
0.0327 + 0.0286 exp(− 137.8hω )
Ks
=
µ g ρ g (ρ L − ρ g )
ρL
=
Density of liquid mixture (kg/m 3 )
k in
g
D in
Unit Operation Models
Version 10
1/ 2
µg / µgF
Γe hw + 1533Γe B(Q L / Γe ) ( m)
2/ 3
(
)
0.5
(m / sec)
4-83
Columns
Heat Transfer Coefficients
RateFrac calculates the heat transfer coefficients, using the Chilton-Colburn
analogy (King, 1980).
The heat transfer coefficient is given by:
k av ( Sc)
2/3
=
htc
Cpmix
Where:
4-84
k av
=
Average binary mass transfer coefficients (kg
mole/sec)
Sc
=
Schmidt number
htc
=
Heat transfer coefficient (Watts/K)
Cpmix
=
Molar heat capacity (Joules/kg mole/K)
Pr
=
Prandtl number
Unit Operation Models
Version 10
Chapter 4
References
Bravo, J.L., Rocha, J.A., and Fair, J.R., "Mass Transfer in Gauze Packings,"
Hydrocarbon Processing, January, 91 (1985).
Bravo, J.L., Rocha, J.A., and Fair, J.R., "A Comprehensive Model for the
Performance of Columns Containing Structured Packings," ICHEME Symposium
Series, 128, A439 (1992).
Chan, H. and Fair, J.R., "Prediction of Point Efficiencies in Sieve Trays: 1. Binary
Systems, 2. Multicomponent Systems," Ind. Eng. Chem. Process Des. Dev., 23,
(1984) p. 814.
Grester, J.A., Hill, A.B., Hochgraf, N.N., and Robinson, D.G., "Tray Efficiencies
in Distillation Columns," AIChE Report, (1958).
King, C.J., Separation Processes, Second Edition, McGraw-Hill Company, (1980).
Krishna, R. and Standart, G.L., "A Multicomponent Film Model Incorporating a
General Matrix Method of Solution to the Maxwell-Stefan Equations," AIChE J.,
22, (1976) p. 383.
Onda, K., Takeuchi, H., and Okumoto, Y., "Mass Transfer Coefficients between
Gas and Liquid Phases in Packed Columns," J. Chem. Eng., Japan, 1, (1968) p.
56.
Perry, R.H. and Chilton, C.H., "Chemical Engineers’ Handbook," Fifth Edition,
McGraw-Hill Book Company, Section 18 (1973).
Scheffe, R.D. and Weiland, R.H., "Mass Transfer Characteristics of Valve Trays,"
Ind. Eng. Chem. Res., 26, (1987) p. 228.
Unit Operation Models
Version 10
4-85
Columns
4-86
Unit Operation Models
Version 10
Chapter 4
Extract
Rigorous Extraction
Extract is a rigorous model for simulating liquid-liquid extractors. It can have
multiple feeds, heater/coolers, and side streams. Extract can calculate
distribution coefficients using:
• An activity coefficient model or equation of state capable of representing two
liquid phases
• A built-in temperature-dependent correlation (KLL Correlation sheet)
• A Fortran subroutine (KLL Subroutine sheet)
Although equilibrium stages are assumed, you can specify component or stage
separation efficiencies. Extract can be used only for rating calculations.
You can define pseudoproduct streams (Report PseudoStreams sheet) to
represent extractor internal flows. You can use Fortran and sensitivity blocks to
vary configuration parameters, such as feed location or number of stages.
Flowsheet Connectivity for Extract
L2 Phase
L1 Phase
Side feeds
(any number)
1
Side products
(any number)
Nstage
L1 Phase
L2 Phase
Material Streams
Inlet
One material stream to the first (top) stage, rich in the first liquid phase
(L1)
One material stream to the last (bottom) stage, rich in the second liquid
phase (L2)
One material stream per intermediate stage (optional)
Outlet One material stream for L1 from the last stage
One material stream for L2 from the first stage
Up to two side product streams per stage, one for L1 and one for L2
(optional)
Unit Operation Models
Version 10
4-87
Columns
Specifying Extract
Extract can operate in one of the following ways:
• Adiabatically (default)
• At a specified temperature
• With specified stage heater or cooler duties
You must specify:
• Number of stages
• Feed and product stream stage locations
• Side product stream phase and mole flow rate
• Pressure profile
The first liquid phase (L1) flows from the first stage to the last stage. The second
(L2) flows in the opposite direction. You must identify the key components in each
phase using L1-Comps and L2-Comps on the Setup form. Extract can treat phase
L1 as the solvent/extract phase or the feed/raffinate phase.
Liquid-liquid distribution coefficients are required to represent the liquid-liquid
equilibrium. Extract calculates these coefficients using one of the following
methods:
You can use
You enter
On sheet
Any physical property method that can
represent two liquid phases
A global property method or an Opset
name to override the global physical
property method
BlockOptions Properties
A built-in temperature-dependent
polynomial
Polynomial coefficients
Properties KLL Correlation
A Fortran subroutine
Subroutine name
Properties KLL Subroutine
Use the following forms to enter specifications and view results for Extract:
Use this form
To do this
Setup
Specify basic column configuration and operating conditions
Efficiencies
Specify stage or component efficiencies
Properties
Specify parameters for KLL correlations and KLL subroutines
Estimates
Specify initial estimates for stage temperatures and compositions
Convergence
Specify convergence parameters and block-specific diagnostic message levels
Report
Specify block-specific report options and pseudostream information
continued
4-88
Unit Operation Models
Version 10
Chapter 4
Use this form
To do this
Block Options
Override global values for physical properties, simulation options, diagnostic message
levels, and report options for this block
Results
View column performance summary, material and energy balance results, and split
fractions
Profiles
View extractor profiles
Dynamic
Specify parameters for dynamic simulations
See ASPEN PLUS User Models for more information about Fortran subroutines.
❖
Unit Operation Models
Version 10
❖
❖
❖
4-89
Columns
4-90
Unit Operation Models
Version 10
Chapter 5
5
Reactors
This chapter describes the unit operation models for reactors. The models are:
Model
Description
Purpose
Use For
RStoic
Stoichiometric reactor
Models stoichiometric
reactor with specified
reaction extent or
conversion
Reactors where reaction kinetics are unknown
or unimportant but stoichiometry and extent of
reaction are known
RYield
Yield reactor
Models reactor with
specified yield
Reactors where stoichiometry and kinetics are
unknown or unimportant but a yield distribution
is known
REquil
Equilibrium reactor
Performs chemical and
phase equilibrium by
stoichiometric calculations
Reactors with simultaneous chemical
equilibrium and phase equilibrium
RGibbs
Equilibrium reactor with
Gibbs energy minimization
Performs chemical and
phase equilibrium by Gibbs
energy minimization
Reactors with phase equilibrium or
simultaneous phase and chemical equilibrium.
Calculating phase equilibrium for solid
solutions and vapor-liquid-solid systems.
RCSTR
Continuous stirred tank
reactor
Models continuous stirred
tank reactor
One-, two, or three-phase stirred tank reactors
with rate-controlled and equilibrium reactions in
any phase based on known stoichiometry and
kinetics
RPlug
Plug flow reactor
Models plug flow reactor
One-, two-, or three-phase plug flow reactors
with rate-controlled reactions in any phase
based on known stoichiometry and kinetics
RBatch
Batch reactor
Models batch or semi-batch
reactor
One-, two-, or three-phase batch and semibatch reactors with rate-controlled reactions in
any phase based on known stoichiometry and
kinetics
RCSTR, RPlug, and RBatch are kinetic reactor models. Use the Reactions
Reactions form to define the reaction stoichiometry and data for these models.
Unit Operation Models
Version 10
5-1
Reactors
You do not need to specify heats of reaction, because ASPEN PLUS uses the
elemental enthalpy reference state for the definition of the component heat of
formation. Therefore, heats of reaction are accounted for in the mixture enthalpy
calculations for the reactants versus the products.
RStoic
Stoichiometric Reactor
Use RStoic to model a reactor when:
• Reaction kinetics are unknown or unimportant and
• Stoichiometry and the molar extent or conversion is known for each reaction
RStoic can model reactions occurring simultaneously or sequentially. In addition,
RStoic can perform product selectivity and heat of reaction calculations.
Flowsheet Connectivity for RStoic
Material
(any number)
Heat
(optional)
Heat (optional)
Water (optional)
Material
Material Streams
Inlet
At least one material stream
Outlet One product stream
One water decant stream (optional)
5-2
Unit Operation Models
Version 10
Chapter 5
Heat Stream
Inlet
Any number of heat streams (optional)
RStoic uses the sum of the inlet heat streams as the heat duty specification, if
you do not specify an outlet heat stream.
Outlet One heat stream (optional)
The value of the outlet heat stream is the net heat duty (sum of the inlet heat
streams minus the calculated heat duty) for the reactor.
Specifying RStoic
Use the Setup Specifications sheet to specify the reactor operating conditions and
to select the phases to consider in flash calculations in the reactor.
Use the Setup Reactions sheet to define the reactions occurring in the reactor.
You must specify the stoichiometry for each reaction. In addition, you must
specify either the molar extent or the fractional conversion for all reactions.
When solids are created or changed by the reactions, you may specify the
component attributes and the particle size distribution in the outlet stream using
the Setup Component Attr. sheet and the Setup PSD sheet respectively.
If you wish to calculate the heats of reaction, use the Setup Heat of Reaction
sheet to specify the reference component for each reaction defined in the Setup
Reactions sheet. You may also choose to specify the heats of reaction, and RStoic
adjusts the calculated reactor duty, if needed.
If you wish to calculate product selectivities use the Setup Selectivity sheet to
specify the selected product component and the reference reactant component.
Use the following forms to enter specifications and view results for RStoic:
Unit Operation Models
Version 10
Use this form
To do this
Setup
Specify operating conditions, reactions, reference conditions for heat of reaction
calculations, product and reactant components for selectivity calculations, particle size
distribution, and component attributes
Convergence
Specify estimates and convergence parameters for flash calculations
BlockOptions
Override global values for physical properties, simulation options, diagnostic message
levels, and report options for this block
Results
View summary of operating results, mass and energy balances, heats of reaction,
product selectivities, reaction extents, and phase equilibrium results for the outlet
stream
Dynamic
Specify parameters for dynamic simulations
5-3
Reactors
Heat of Reaction
RStoic calculates the heat of reaction from the heats of formation in the
databanks when you select the Calculate Heat of Reaction option on the Setup
Heat of Reaction sheet. The heats of reaction are calculated at the specified
reference conditions based on consumption of a unit mole or mass of the reference
reactant selected for each reaction. The following reference conditions are used
by default:
Specification
Default
Reference temperature
25 °C
Reference pressure
1 atm
Reference fluid phase
Vapor phase
You can also use the Setup Heat of Reaction sheet to specify the heats of
reaction. The specified heat of reaction may differ from the heat of reaction that
ASPEN PLUS computes from the heats of formation at reference conditions. If
this occurs, RStoic adjusts the calculated reactor heat duty to reflect the
differences. Under these circumstances, the calculated reactor heat duty will not
be consistent with the inlet and outlet stream enthalpies.
Selectivity
The selectivity of the selected component P to the reference component A is
defined as:
S P, A =
 ∆P 
 ∆A 
Real
 ∆P 
 ∆A 
Ideal
Where:
∆P
=
Change in number of moles of component P due to reaction
∆A
=
Change in number of moles of component A due to reaction
In the numerator, real represents changes that actually occur in the reactor.
ASPEN PLUS obtains this value from the mass balance between the inlet and
outlet.
5-4
Unit Operation Models
Version 10
Chapter 5
In the denominator, ideal represents changes according to an idealized reaction
scheme. This scheme assumes that no reactions are present, except for the
reaction that produces the selected component from the reference component.
Therefore, the denominator indicates how many moles of P are produced per
mole of A consumed in an ideal stoichiometric equation, or:
υ
 ∆P 
= P
 ∆A 
υ
Ideal
A
where υ A and υ P are stoichiometric coefficients.
This example shows how RStoic calculates selectivity:
a1 A + b1 B → c1 C + d1 D
c2 C + e2 E → p2 P
a3 A + f3 F → q3 Q
The selectivity of P to A is:
 Moles of P produced   c1∗ p2 
S P, A = 
/

 Moles of A consumed   a1∗ c2 
In most cases, selectivity ranges between 0 and 1. However, if the selected
component is also produced from components other than the reference
component, selectivity may be greater than 1. If the selected component is
consumed in other reactions, selectivity may be less than 0.
Unit Operation Models
Version 10
5-5
Reactors
RYield
Yield Reactor
Use RYield to model a reactor when:
• Reaction stoichiometry is unknown or unimportant
• Reaction kinetics are unknown or unimportant
• Yield distribution is known
You must specify the yields (per mass of total feed, excluding any inert
components) for the products or calculate them in a user-supplied Fortran
subroutine. RYield normalizes the yields to maintain a mass balance. RYield can
model one-, two-, and three-phase reactors.
Flowsheet Connectivity for RYield
Material
(any number)
Heat
(optional)
Heat (optional)
Water (optional)
Material
Material Streams
Inlet
At least one material stream
Outlet One product stream
One water decant stream (optional)
Heat Streams
Inlet
Any number of heat streams (optional)
Outlet One heat stream (optional)
5-6
Unit Operation Models
Version 10
Chapter 5
If you give only one specification on the Setup Specifications sheet (temperature
or pressure), RYield uses the sum of the inlet heat streams as a duty
specification. Otherwise, RYield uses the inlet heat stream(s) only to calculate
the net heat duty. The net heat duty is the sum of the inlet heat streams minus
the actual (calculated) heat duty.
You can use an outlet heat stream for the net heat duty.
Specifying RYield
Use the Setup Specifications and Setup Yield sheets to specify the reactor
conditions and the component yields. For each reaction product, specify the yield
as either moles or mass of a component per unit mass of feed. If you specify inert
components on the Setup Yield sheet, the yields will be based on unit mass of
non-inert feed.
Calculated yields are normalized to maintain an overall material balance. For
this reason, yield specifications establish a yield distribution, rather than
absolute yields. RYield does not maintain atom balances because you enter the
fixed yield distribution.
You can request one-, two-, or three-phase calculation.
When solids are created or changed by the reactions, you can specify their
component attributes and/or particle size distribution in the outlet stream using
the Setup Component Attr. and Setup PSD sheets, respectively.
Use the following forms to enter specifications and view results for RYield:
Unit Operation Models
Version 10
Use this form
To do this
Setup
Specify reactor operating conditions, component yields, inert components, flash
convergence parameters, and PSD and component attributes for the outlet stream
UserSubroutine
Specify subroutine name and parameters for the user-supplied yield subroutine
BlockOptions
Override global values for physical properties, simulation options, diagnostic message
levels, and report options for this block
Results
View summary of operating results, mass and energy balances for the reactor and
phase equilibrium results for the outlet stream
Dynamic
Specify parameters for dynamic simulations
5-7
Reactors
REquil
Equilibrium Reactor
Use REquil to model a reactor when:
• Reaction stoichiometry is known and
• Some or all reactions reach chemical equilibrium
REquil calculates simultaneous phase and chemical equilibrium. REquil allows
restricted chemical equilibrium specifications for reactions that do not reach
equilibrium. REquil can model one- and two-phase reactors.
Flowsheet Connectivity for REquil
Material
(any number)
Material (vapor phase)
Material (liquid phase)
Heat
(optional)
Heat (optional)
Material Streams
Inlet
At least one material stream
Outlet One material stream for the vapor phase
One material stream for the liquid phase
Heat Streams
Inlet
Any number of heat streams (optional)
Outlet One heat stream (optional)
If you give only one specification on the REquil Input Specifications sheet
(temperature or pressure), REquil uses the sum of the inlet heat streams as a
duty specification. Otherwise, REquil uses the inlet heat stream(s) only to
calculate the net heat duty. The net heat duty is the sum of the inlet heat
streams minus the actual (calculated) heat duty.
You can use an outlet heat stream for the net heat duty.
5-8
Unit Operation Models
Version 10
Chapter 5
Specifying REquil
You must specify the reaction stoichiometry and the reactor conditions. If no
additional specifications are given, REquil assumes that the reactions will reach
equilibrium.
REquil calculates equilibrium constants from the Gibbs energy. You can restrict
the equilibrium by specifying one of the following:
•
•
The molar extent for any reaction
A temperature approach to chemical equilibrium (for any reaction)
If you specify temperature approach, ∆T, REquil evaluates the chemical
equilibrium constant at T + ∆T, where T is the reactor temperature (specified or
calculated).
REquil performs single-phase property calculations or two-phase flash
calculations nested inside a chemical equilibrium loop. REquil cannot perform
three-phase calculations.
Use the following forms to enter specifications and view results for REquil:
Use this form
To do this
Input
Specify reactor operating conditions, valid phases, reactions, convergence
parameters, and solid and liquid entrainment in the vapor stream
Block Options
Override global values for physical properties, simulation options, diagnostic
message levels, and report options for this block
Results
View summary of operating results, mass and energy balances, and calculated
chemical equilibrium constants
Solids
Reactions can include conventional solids. REquil treats each participating solid
component as a separate pure solid phase, not as a component in a solid solution.
Any participating solids must have a free energy formation (DGSFRM) and
enthalpy of formation (DHSFRM), or heat capacity parameters (CPSXP1).
Solids not participating in reactions, including any nonconventional components,
are treated as inert. These solids have no effect on the equilibrium calculations
except on the energy balance.
Unit Operation Models
Version 10
5-9
Reactors
RGibbs
Equilibrium Reactor (Gibbs Free Energy Minimization)
RGibbs uses Gibbs free energy minimization with phase splitting to calculate
equilibrium. RGibbs does not require that you specify the reaction stoichiometry.
Use RGibbs to model reactors with:
• Single phase (vapor or liquid) chemical equilibrium
• Phase equilibrium (an optional vapor and any number of liquid phases) with
no chemical reactions
• Phase and/or chemical equilibrium with solid solution phases
• Simultaneous phase and chemical equilibrium
RGibbs can also calculate the chemical equilibria between any number of
conventional solid components and the fluid phases. RGibbs also allows
restricted equilibrium specifications for systems that do not reach complete
equilibrium.
Flowsheet Connectivity for RGibbs
Material
(any number)
Heat
(optional)
Material
(any number)
Heat
(optional)
Material Streams
Inlet
At least one material stream
Outlet At least one material stream
If you specify as many outlet streams as the number of phases that RGibbs
calculates, RGibbs assigns each phase to an outlet stream. If you specify fewer
outlet streams, RGibbs assigns the additional phases to the last outlet stream.
5-10
Unit Operation Models
Version 10
Chapter 5
Heat Streams
Inlet
Any number of heat streams (optional)
Outlet One heat stream (optional)
If you specify only pressure on the Setup Specifications sheet, RGibbs uses the
sum of the inlet heat streams as a duty specification. Otherwise, RGibbs uses the
inlet heat stream(s) only to calculate the net heat duty. The net heat duty is the
sum of the inlet heat streams minus the actual (calculated) heat duty.
You can use an outlet heat stream for the net heat duty.
Specifying RGibbs
This section describes how to specify:
• Phase equilibrium only
• Phase and chemical equilibrium
• Restricted chemical equilibrium
• Reactions
• Solids
Use the following forms to enter specifications and view results for RGibbs:
Unit Operation Models
Version 10
Use this form
To do this
Setup
Specify reactor operating conditions and phases to consider in equilibrium
calculations, identify possible products, assign phases to outlet streams, specify
inert components and specify equilibrium restrictions.
Advanced
Specify atomic formula of components, estimates for temperature and component
flows, and convergence parameters.
Block Options
Override global values for physical properties, simulation options, diagnostic
message levels and report options for this block.
Results
View summary of operating results, mass and energy balances, molar
compositions of fluid and solid phases present, the atomic formula of
components, and calculated reaction equilibrium constants.
Dynamic
Specify parameters for dynamic simulations
5-11
Reactors
Phase Equilibrium Only
To specify
Use this option
On
Phase equilibrium
calculations only
Phase Equilibrium Only
Setup Specifications sheet
Maximum number of fluid
phases that RGibbs should
consider
Maximum Number of Fluid
Phases
Setup Specifications sheet
Maximum number of solid
solution phases
Maximum Number of Solid
Solution Phases
Solid Phases dialog box from the Setup
Specifications sheet
RGibbs distributes all species among all solution phases by default. You can use
the Setup Products sheet to assign different sets of species to each solution
phase. You can also assign different thermodynamic property methods to each
phase.
If there is a possibility that a solid solution phase may exist, use the Setup
Products sheet to identify the species that will exist in that phase.
Phase Equilibrium and Chemical Equilibrium
To specify
Use this option
On
Chemical equilibrium
calculations (with or without
phase equilibrium)
Phase Equilibrium and
Chemical Equilibrium
Setup Specifications sheet
Maximum number of fluid
phases that RGibbs should
consider
Maximum Number of Fluid
Phases
Setup Specifications sheet
Maximum number of solid
solution phases
Maximum Number of Solid
Solution Phases
Solid Phases dialog box from the Setup
Specifications sheet
By default, RGibbs considers all components entered on the Components
Specifications Selection sheet as possible fluid phase or solid products. You can
specify an alternate list of products on the Setup Products sheet.
RGibbs distributes all solution species among all solution phases by default. You
can use the Setup Products sheet to assign different sets of species to each
solution phase. You can also assign different thermodynamic property methods to
each phase.
5-12
Unit Operation Models
Version 10
Chapter 5
RGibbs needs the molecular formula for each component that is present in a feed
or product stream. RGibbs retrieves this information from the component
databanks. For non-databank components, use the Properties Molec-Struct
Formula sheet to enter:
• Atom (the atom type)
• Number of occurrences (the number of atoms of each type)
Alternatively, you can enter the atom matrix on the Advanced Atom Matrix
sheet. The atom matrix defines the number of each atom in each component. If
you enter the atom matrix, you must enter it for all components and atoms,
including databank components.
If there is a possibility that a solid solution phase may exist, use the Setup
Products sheet to identify the species which will exist in that phase.
Restricted Chemical Equilibrium
To restrict chemical equilibrium:
Specify
On
The molar extent of the reaction
Edit Reactions dialog box (from the Setup
RestrictedEquilibrium sheet)
A temperature approach to equilibrium for individual reactions
Edit Reactions dialog box (from the Setup
RestrictedEquilibrium sheet)
A temperature approach to chemical equilibrium for the entire system
Edit Reactions dialog box (from the Setup
RestrictedEquilibrium sheet)
The outlet amount of any component as total mole flow or as a fraction of
the feed of that component
Setup Inerts sheet
†
†
You can specify inert components by setting the fraction to 1.
For temperature approach specifications, RGibbs evaluates the chemical
equilibrium constant at T + ∆T , where T is the actual reactor temperature
(specified or calculated) and ∆T is the desired temperature approach.
You can enter one of the following restricted equilibrium specifications for
individual reactions:
• The molar extent of a reaction
• The temperature approach for an individual reaction
Use the Setup RestrictedEquilibrium sheet to supply the reaction stoichiometry.
If you enter one of the preceding specifications, you must also supply the
stoichiometry for a set of linearly independent reactions involving all components
in the system.
Unit Operation Models
Version 10
5-13
Reactors
Reactions
You can have RGibbs consider only a specific set of reactions. You can restrict the
chemical equilibrium by specifying temperature approach or molar extent for the
reactions. You must specify the stoichiometric coefficients for a complete set of
linearly independent chemical reactions, even if only one reaction is restricted.
The number of linearly independent reactions required equals the total number
of products in the product list, including solids (see the Setup Products sheet),
minus the number of atoms present in the system. The reactions must involve all
participating components. A component is participating if it satisfies these
criteria:
• It is in the product list.
• It is not inert. A component is inert if it consists entirely of atoms not present
in any other product components.
• It has not been dropped. A component listed on the Setup Products sheet is
dropped if it contains an atom not present in the feed.
Solids
RGibbs can calculate the chemical equilibria between any number of
conventional solid components and the fluid phases. RGibbs detects whether the
solid is present at equilibrium, and if so, calculates the amount. RGibbs treats
each solid component as a pure solid phase, unless it is specified as a component
in a solid solution. Any solid that RGibbs considers a product must have both:
• Free energy of formation (DGSFRM or CPSXP1)
• Heat of formation (DHSFRM or CPSXP1)
Nonconventional solids are treated as inert and have no effect on equilibrium
calculations. If chemical equilibrium is not considered, RGibbs treats all solids as
inert. RGibbs cannot perform solids-phase-only calculations.
RGibbs places all pure solids in the last outlet stream unless you specify
otherwise on the Setup AssignStreams sheet. RGibbs can handle only a single
CISOLID substream, which contains all conventional solids products defined as
pure solid phases. RGibbs places the solid solution phases in the MIXED
substream of the outlet stream(s).
RGibbs cannot directly handle phase equilibrium between solids and fluid phases
(for example, water-ice equilibrium). To work around this, you can list the same
component twice on the Components Specifications Selection sheet, with
different component IDs. If you want RGibbs to calculate the chemical
equilibrium between these components:
• Specify both component IDs on the Setup Products sheet.
• Designate one ID as a solids phase component, the other as a fluid phase
component.
5-14
Unit Operation Models
Version 10
Chapter 5
References
Gautam, R. and Seider, W.D., "Computation of Phase and Chemical
Equilibrium," Parts I, II, and III, AIChE J. 25, 6, November, 1979, pp. 991-1015.
White, C.W. and Seider, W.D., "Computation of Phase and Chemical
Equilibrium: Approach to Chemical Equilibrium," AIChE J., 27, 3, May, 1981,
pp. 446-471.
Schott, G. L., "Computation of Restricted Equilibria by General Methods," J.
Chem. Phys., 40, 1964.
Unit Operation Models
Version 10
5-15
Reactors
RCSTR
Continuous Stirred Tank Reactor
RCSTR rigorously models continuous stirred tank reactors. RCSTR can model
one-, two-, or three-phase reactors. RCSTR assumes perfect mixing in the
reactor, that is, the reactor contents have the same properties and composition as
the outlet stream.
RCSTR handles kinetic and equilibrium reactions as well as reactions involving
solids. You can provide the reaction kinetics through the built-in Reactions
models or through a user-defined Fortran subroutine.
Flowsheet Connectivity for RCSTR
Heat (optional)
Material
(any number)
Material
Heat
(optional)
Material Streams
Inlet
At least one material stream
Outlet One material stream
Heat Streams
Inlet
Any number of heat streams (optional)
Outlet One heat stream (optional)
If you specify only pressure on the Setup Specifications sheet, RCSTR uses the
sum of the inlet heat streams as a duty specification. Otherwise, RCSTR uses the
inlet heat stream only to calculate the net heat duty. The net heat duty is the
sum of the inlet heat streams minus the actual (calculated) heat duty.
You can use an outlet heat stream for the net heat duty.
5-16
Unit Operation Models
Version 10
Chapter 5
Specifying RCSTR
You must specify the reactor operating conditions, which are pressure and either
temperature or heat duty. You must also enter the reactor volume or residence
time (overall or phase).
Use the following forms to enter specifications and view results for RCSTR:
Use this form
To do this
Setup
Specify reactor operating conditions and holdup, select the reaction sets to be included,
and specify PSD and component attributes in the outlet stream
Convergence
Provide estimates for component flow rates, reactor temperature and volume, and specify
flash convergence parameters, RCSTR convergence methods and parameters, and
initialization options
UserSubroutine
Specify parameters for the user-supplied kinetics subroutine and block-specific report
option for the kinetics subroutine
BlockOptions
Override global values for physical properties, simulation options, diagnostic message
levels, and report options for this block
Results
View summary of operating results and mass and energy balances for the block
Dynamic
Specify parameters for dynamic simulations
Reactions
You must specify reaction kinetics on the Reactions Reactions forms and select
the Reaction Set ID on the Setup Reactions sheet.
You can specify one-, two-, or three-phase calculations. You can specify the phase
for each reaction on the Reactions Reactions forms. RCSTR can handle kinetic
and equilibrium type reactions.
Phase Volume
In a multi-phase reactor, by default, ASPEN PLUS calculates the volume of each
phase, using phase equilibrium results, as:
V Pi = VR
Vi f i
ΣV j f j
Where:
Unit Operation Models
Version 10
VPi
=
Volume of phase i
VR
=
Reactor volume
Vi
=
Molar volume of phase i
fi
=
Molar fraction of phase i
5-17
Reactors
You can override the default calculation by specifying the volume of a phase
directly (Phase Volume) or as a fraction of the reactor volume (Phase Volume
Frac) on the Setup Specifications sheet.
Alternatively, when you specify the residence time of a phase in the reactor,
ASPEN PLUS calculates the phase volume iteratively.
Residence Time
ASPEN PLUS calculates the residence time (overall and phase) in the CSTR as:
RT =
VR
F * Σfi Vi
RTi =
V Pi
F * f iVi
Where:
RT
=
Overall residence time
RTi
=
Residence time of phase i
VR
=
Reactor volume
F
=
Total molar flow rate (outlet)
Vi
=
Molar volume of phase i
fi
=
Molar fraction of phase i
VPi
=
Volume of phase i
When the default calculation for phase volume, based on phase equilibrium
results, is used, the phase residence time is equal for all phases. If you specify
Phase Volume or Phase Volume Frac on the Setup Specifications sheet, the
residence time for the phase specified in the Holdup Phase is calculated with the
specified phase volume rather than the default phase volume.
Solids
RCSTR can handle reactions involving solids. RCSTR assumes that solids are at
the same temperature as the fluid phase. RCSTR cannot perform solids-phaseonly calculations.
5-18
Unit Operation Models
Version 10
Chapter 5
Scaling of Variables
Four types of variables are predicted by RCSTR: component flow rates, stream
enthalpy, component attributes and PSD (if present). RCSTR normalizes these
variables, for faster convergence, by dividing each one by a scale factor.
Two types of scaling are available in RCSTR: component-based scaling and
substream-based scaling. Component-based scaling weighs each variable against
its previous or estimated value. Substream-based scaling weighs each variable in
a substream against the substream flow rate. For component-based scaling,
minimum scale values are set by the Trace Scaling Factor in the Advanced
Parameters dialog box (from the Convergence Parameters sheet). You may
reduce the trace scaling threshold to increase the prediction accuracy of trace
components.
Component-based scaling generally provides more accuracy than substreambased scaling, especially for trace components. Use component-based scaling
when:
• The reaction network involves trace intermediates
• The reaction rates are very sensitive to trace reactants (such as catalysts and
initiators which participate in degradation reactions)
The following tables summarize the scale factors used by each method.
Substream-based Scaling Method
Variable Type
Variable
Initial Scale Factor
Component Flows
Component mole flow in
outlet stream
Estimated outlet substream mole flow rate
Stream Enthalpy
Net enthalpy flow of outlet
stream
Net enthalpy flow of inlet stream
Component Attributes
(attr/kg)
Product of component mass
flow (with attributes) and
attribute value in outlet
stream
Default attribute scale factor
PSD
Product of substream mass
flow rate (with PSD) and
PSD value in outlet stream
Default attribute scale factor
Note
Unit Operation Models
Version 10
If any substream-based scaling factor is equal to zero, the default
scaling factor is used instead (the default factor is 1.0 for
component flow rates and 1.0E5 for stream enthalpy).
5-19
Reactors
Component-based Scaling Method
Variable Type
Variable
Initial Scale Factor
Component Flows
Component mole flow in
outlet stream
Larger of:
- Estimated component mole flow in outlet stream
- Product of Trace threshold and estimated outlet
substream mole flow
Stream Enthalpy
Net enthalpy flow of outlet
stream
Net enthalpy flow of inlet stream
Component Attributes
(attr/kg)
Product of component mass
flow with attributes and
attribute value in outlet
stream
Larger of:
- Product of estimated attributed component mass flow
and estimated attribute value in outlet stream
- Product of Trace threshold and estimated outlet
substream mole flow
PSD
Product of substream mass
flow rate and PSD value in
outlet stream
Larger of:
- Product of estimated substream mass flow with PSDs
and estimated PSD value in outlet stream
- Product of Trace threshold and default attribute scale
factor
5-20
Unit Operation Models
Version 10
Chapter 5
RPlug
Plug Flow Reactor
RPlug is a rigorous model for plug flow reactors. RPlug assumes that perfect
mixing occurs in the radial direction and that no mixing occurs in the axial
direction. RPlug can model one-, two-, or three-phase reactors. You can also use
RPlug to model reactors with coolant streams (co-current or counter-current).
RPlug handles kinetic reactions, including reactions involving solids. You must
know the reaction kinetics when you use RPlug to model a reactor. You can
provide the reaction kinetics through the built-in Reactions models or through a
user-defined Fortran subroutine.
Flowsheet Connectivity for RPlug
Heat (optional)
Material
Material
Flowsheet Reactor without Coolant Stream
Material Coolant
(optional)
Material
Material
Material Coolant
(optional)
Flowsheet Reactor with Coolant Stream
Unit Operation Models
Version 10
5-21
Reactors
Material Streams
Inlet
One material feed stream
One coolant stream (optional)
Outlet One material product stream
One coolant stream (optional)
Heat Streams
Inlet
No inlet heat streams
Outlet One heat stream (optional) for the reactor heat duty. Use the heat outlet
stream only for reactors without a coolant stream.
Specifying RPlug
Use the Setup Configuration sheet to specify reactor tube length and diameter. If
the reactor consists of multiple tubes, you can also specify the number of tubes.
You can specify the pressure drop across the reactor on the Setup Pressure sheet.
Additional required input for RPlug depends on the reactor type.
When you use this
Reactor Type
And solid phase is
And fluid and solid phase
temperatures are
Reactor with specified
temperature
—
—
Reactor temperature, or
temperature profile
Adiabatic reactor
Not present
—
No required specifications
Present
Same
No required specifications
Present
Different
U (fluid phase - solids phase)
Not present
—
Coolant temperature, and
U (coolant - process stream)
Present
Same
Coolant temperature, and
U (coolant - process stream)
Present
Different
Coolant temperature,
U (coolant - fluid phase),
U (coolant - solids phase),
and
U (fluid phase - solids phase)
Not present
—
U (coolant - process stream)
Present
Same
U (coolant - process stream)
Reactor with constant coolant
temperature
Reactor with co-current
coolant
Specify
continued
5-22
Unit Operation Models
Version 10
Chapter 5
When you use this
Reactor Type
Reactor with co-current
coolant
Reactor with counter-current
coolant
And solid phase is
And fluid and solid phase
temperatures are
Specify
Not present
—
U (coolant - process stream)
Present
Same
U (coolant - process stream)
Present
Different
U (coolant - fluid phase),
U (coolant - solids phase),
and
U (fluid phase - solids phase)
Not present
—
Coolant outlet temperature or
molar vapor fraction, and
U (coolant - process stream)
Present
Same
Coolant outlet temperature or
molar vapor fraction, and
U (coolant - process stream)
Present
Different
Coolant outlet temperature or
molar vapor fraction,
U (coolant - fluid phase),
U (coolant - solids phase),
and
U (fluid phase - solids phase)
For reactors with countercurrent external coolant, RPlug calculates the coolant
inlet temperature. The result overrides your specified inlet coolant temperature.
You can use a design specification that manipulates the coolant exit temperature
or vapor fraction to achieve a specified coolant inlet temperature.
For reactors with an external coolant stream, you can use different physical
property methods and options (BlockOptions Properties sheet) for the process
stream and the coolant stream.
Use the following forms to enter specifications and view results for RPlug:
Use this form
To do this
Setup
Specify operating conditions and reactor configuration, select reaction sets to be included,
and specify pressure drops
Convergence
Specify flash convergence parameters, calculation options and parameters for the
integrator
Report
Specify block-specific report options
UserSubroutine
Specify user subroutine parameters for kinetics, heat transfer, pressure drop, and list user
variables to be included in the profile report
BlockOptions
Override global values for property methods, simulation options, diagnostic levels, and
report options for this block
continued
Unit Operation Models
Version 10
5-23
Reactors
Use this form
To do this
Results
View summary of operating results and mass and energy balances for the block
Profiles
View profiles versus reactor length for process stream conditions, coolant stream
conditions, properties, component and substream attributes, and user variables
Dynamic
Specify parameters for dynamic simulations
Reactions
You must specify reaction kinetics on the Setup Reactions sheet, by referring to
Reaction IDs that you select. You can specify one-, two-, or three-phase
calculations. Specify the reaction phases on the Reactions Reactions forms. RPlug
can handle only kinetic type reactions.
Solids
Reactions can involve solids. Solids can be:
• At the same temperature as the fluid phases
• At a different temperature from the fluid phases (only for Reactor Types other
than the reactor with specified temperature)
In the latter case, you must specify the heat transfer coefficients on the Setup
Specifications sheet.
5-24
Unit Operation Models
Version 10
Chapter 5
RBatch
Batch Reactor
RBatch is a rigorous model for batch or semi-batch reactors. Use RBatch when
you know the kinetics of the reactions taking place. You can specify any number
of continuous feed streams. A continuous vent is optional. The reaction runs until
it reaches a stop criterion that you specify.
Batch operations are unsteady-state processes. RBatch uses holding tanks and
your specified cycle times to provide an interface between the discrete operations
of the batch reactor and the continuous streams used by other models.
RBatch can model one-, two-, or three-phase reactors.
Flowsheet Connectivity for RBatch
Batch charge
Heat (optional)
Vent
(optional)
Continuous feed
(any number)
Product
Material Streams
Inlet
One batch charge stream (required)
One or more continuous feed streams for semi-batch reactors (optional)
Outlet One product stream (required)
One vent stream for semi-batch reactors (optional)
Heat Streams
Inlet
No inlet heat streams
Outlet One heat stream (optional)
Unit Operation Models
Version 10
5-25
Reactors
Specifying RBatch
Use the Setup Specifications sheet to specify the reactor conditions.
Use the Setup Operations sheet to specify:
• One or more stop criteria
• Either a feed time or a batch cycle time
Other required input for RBatch depends on reactor type.
To establish the pressure of the vessel, enter one of the following specifications
on the Setup Specifications sheet:
• Constant pressure
• Pressure profile
• Reactor volume
Use the Setup ContinuousFeeds sheet to enter mass flow rates for the continuous
feeds at any number of points in time. You can thus simulate delayed feeds and
step changes in feeds.
For specified duty reactors, you can specify either a constant heat duty or a heat
duty profile. For a reactor with constant duty, RBatch assumes adiabatic
operation if you do not specify a heat duty.
For reactors with specified coolant temperature, you must specify:
• Coolant temperature
• An over-all heat transfer coefficient
• Total heat transfer area
For constant temperature and specified temperature reactors, RBatch handles
the temperature specification in one of the following ways:
• By assuming perfect control
• By interpreting the specified temperature(s) as the setpoint(s) of a PID
controller
Use the following forms to enter specifications and view results for RBatch:
Use this form
To do this
Setup
Specify operating conditions, select reaction sets to be included, specify operation stop
criteria, operation times, continuous feeds, and controller parameters
Convergence
Specify convergence parameters for flash calculations, integration, and pressure
calculations
Report
Specify block-specific report options for profiles and reactor, vent, and vent accumulator
property profiles
UserSubroutine
Specify parameters for the user kinetics subroutine, name and parameters for the user heat
transfer subroutine, and user variables for the profile report.
continued
5-26
Unit Operation Models
Version 10
Chapter 5
Use this form
To do this
Block Options
Override global values for physical properties, simulation options, diagnostic message
levels, and report options for this block
Results
View summary of block operating results and mass and energy balances
Profiles
View time profiles of reactor conditions, compositions, continuous feed stream flows,
properties, component attributes, and user variables
Controller
RBatch assumes perfect control when one of these conditions exists:
• Pressure in the reactor is converged upon (that is, reactor volume is specified)
• A single-phase batch reactor is used with no continuous feed streams
If RBatch cannot assume perfect control, it interprets the specified
temperature(s) as the setpoint(s) of a PID controller. This interpretation occurs
when:
• A two-phase reactor is used
• RBatch performs pressure convergence calculations (that is, reactor volume is
specified)
• Continuous feeds are present during semi-batch operation
Use the Setup Controllers sheet to specify the controller tuning parameters.
The controller equation is:
t

d (T − T s ) 
s
s
Q = M c  K (T − T ) + ( K / I ) ∫ (T − T )dt + KD

dt
0


Where:
Q
=
Reactor heat duty (J/sec)
Mc
=
Reactor charge (kg)
K
=
Proportional gain (J/kg/K)
T
=
Reactor temperature (K)
Ts
=
Temperature set point (K)
I
=
Integral time (sec)
D
=
Derivative time (sec)
t
=
Time (sec)
The gain factor is a specific gain per unit mass.
Unit Operation Models
Version 10
5-27
Reactors
Reactions
Reactions may or may not be present in RBatch. If they are, you must include the
Reaction Set IDs on the Setup Reactions sheet. You can specify one-, two-, or
three-phase calculations. You specify the reaction phases on the Reactions
Reactions forms. RBatch can only handle kinetic type reactions.
Specifying Stop Criteria
A reaction runs until one of your specified stop criteria reached. A stop criterion
can be one of the following:
• Reaction time
• Reactor composition
• Vent accumulator or continuous vent composition
• Conversion of a component
• Amount of material in the reactor or vent accumulator
• Vent flow rate
• Temperature in the reactor
• Vapor fraction in the reactor
• Any property specified on the Properties Prop-Sets Properties sheet
As the stop criterion variable approaches its cut-off from above or below, you can
specify whether or not RBatch should halt the reaction. If you specify more than
one stop criterion, RBatch halts the reaction as soon as one of the criteria is
reached. In addition, you must specify a halt time for the reaction. If the reaction
does not reach the specified stop criteria by this time, RBatch halts the reaction.
Cycle Time
You can specify a reactor cycle time. Or, you can let RBatch calculate it from your
specified reaction and down times for draining, cleaning, and charging the
reactor. If you do not specify reactor cycle time, then specify a feed cycle time.
RBatch uses this time to determine the batch charge, because the reaction time
is not known at the beginning of block execution.
Note
If the reactor batch charge stream is in a recycle loop, you must
specify the reactor cycle time.
Mass Balances
Because RBatch uses different cycle times to calculate time-averaged flows,
RBatch may not maintain a mass balance around the block. For example,
suppose you specify a feed time of 30 minutes, but the down time plus the
calculated value reaction time equals 45 minutes. The resulting net mass flow
from the reactor is less than the charge flow by a factor of 45/30=1.5.
5-28
Unit Operation Models
Version 10
Chapter 5
Remember that the mass balance pertains to the time-averaged inlet and outlet
continuous streams. RBatch always satisfies a mass balance for its own internal
batch computations. If there is no continuous feed stream, the mass balance
around RBatch closes only if the cycle time is specified. This ensures that the
same time is used for averaging the batch change and product streams. If there is
a continuous feed stream, and it is not time-varying, the mass balance closes only
if the cycle time is specified, and the specified value is equal to the calculated
reaction time. In all other cases, the mass balance around RBatch does not close,
although the compositions, temperature, and so on are correct.
Batch Operation
RBatch can operate in a batch or in semi-batch mode. The reactor mode is
determined by the streams you enter on the flowsheet. A semi-batch reactor can
have a vent product stream, one or more continuous feed streams, or both. The
vent product stream exits a vent accumulator. It does not exit the reactor itself.
The vent accumulator is for the continuous (but time-varying) vapor vent leaving
the reactor. The composition and temperature of each continuous feed stream
remain constant throughout the reaction. The flow rate also remains constant,
unless you specify a time profile for the flow rate of a continuous stream.
Batch operations are unsteady-state processes. Variables like temperature,
composition, and flow rate change with time, in contrast to steady-state
processes. To interface RBatch with a steady-state flowsheet, it is necessary to
use time-averaged streams.
Four types of streams are associated with RBatch, as follows:
Batch Charge The material transferred to the reactor at the start of the
reactor cycle. The mass of the batch charge equals the flow rate of the batch
charge stream, multiplied by the feed cycle time. The mass of the batch charge is
equivalent to accumulating the batch charge stream in a holding tank during a
reactor cycle. The contents of the holding tank are transferred to the reactor at
the beginning of the next cycle . (See figure RBatch Reactor Configuration - No
Vent Case.)
To compute the amount of the batch charge, RBatch multiplies the flowsheet
stream representing the batch charge by a cycle time you enter (either Cycle
Time or Batch Feed Time). Batch Feed Time is not the time required to charge
the reactor; it is a total cycle time used only to compute the amount of the charge.
Batch Feed Time is required when Cycle Time is unknown.
If Batch Feed Time differs from the actual computed cycle time, the RBatch
flowsheet inlet and outlet streams are not in mass balance. However, all internal
RBatch calculations and reports will be correct for the computed batch charge.
Unit Operation Models
Version 10
5-29
Reactors
Continuous Feed A steady-state flowsheet stream fed continuously to the
reactor during reaction. Its composition and temperature remain constant
throughout the reaction. Its flow rate either remains constant or follows a
specified time profile.
Reactor Product The material left in the reactor at the end of the reactor
cycle. The flow rate of the reactor product stream equals the total mass in the
reactor, divided by the reactor cycle time. You can think of this process as
analogous to transferring the reactor product to a product holding tank. This
tank is drawn down during the next reactor cycle to feed the continuous blocks
downstream (see figure RBatch Reactor Configuration - No Vent Case ).
Vent Product The contents of the vent accumulator at the end of the reactor
cycle. During the reactor cycle, the time-varying vent stream accumulates in the
vent accumulator (see figure RBatch Reactor Configuration - Vent Case). The
flow rate of the vent product stream is the total mass in the vent accumulator,
divided by the reactor cycle time.
Feed
Holding
Tank
Flowsheet
Stream for
Batch
Charge
Batch charge
transferred
once each
Reactor
cycle
Product
Holding
Tank
Reactor
product
transferred
once each
cycle
Flowsheet
Stream for
Reactor
Product
RBatch Reactor Configuration—No Vent Case
5-30
Unit Operation Models
Version 10
Chapter 5
Feed
Holding
Tank
Vent
Accumulator
Flowsheet
Stream for
Batch
Charge
Batch charge
transferred
once each
Reactor
cycle
Vent
Holding
Tank
Vent
Flowsheet
Product
Stream for
transferred
Vent
once per
Product
cycle
Product
Holding
Tank
Reactor
product
transferred
once each
cycle
Optional Flowsheet
Stream for
Continuous Feed
Flowsheet
Stream for
Reactor
Product
RBatch Reactor Configuration—Vent Case
❖
Unit Operation Models
Version 10
❖
❖
❖
5-31
Reactors
5-32
Unit Operation Models
Version 10
Chapter 6
6
Pressure Changers
This chapter describes the unit operation models for pumps and compressors,
and models for calculating pressure change through pipes and valves. The models
are:
Model
Description
Purpose
Use For
Pump
Pump or hydraulic turbine
Changes stream pressure
when the power requirement
is needed or known
Pumps and hydraulic turbines
Compr
Compressor or turbine
Changes stream pressure
when power requirement is
needed or known
Polytropic compressors, polytropic positive
displacement compressors, isentropic
compressors, isentropic turbines
MCompr
Multistage compressor or
turbine
Changes stream pressure
across multiple stages with
intercoolers. Allows for liquid
knockout streams from
intercoolers
Multistage polytropic compressors, polytropic
positive displacement compressors, isentropic
compressors, isentropic turbines
Valve
Valve pressure drop
Models pressure drop
through a valve
Control valves and pressure changers
Pipe
Single segment pipe
Models pressure drop
through a single segment of
pipe
Pipe with constant diameter (may include
fittings)
Pipeline
Multiple segment pipeline
Models pressure drop
through a pipe or annular
space
Pipeline with multiple lengths of different
diameter or elevation
Use Pump, Compr, and MCompr models when energy-related information such as
power requirement is needed or known.
Unit Operation Models
Version 10
6-1
Pressure
Changers
Pump
Pump/Hydraulic Turbine
Use Pump to model a pump or a hydraulic turbine.
Pump is designed to handle a single liquid phase. For special cases, you can
specify two- or three-phase calculations to determine the outlet stream conditions
and to compute the fluid density used in the pump equations. The accuracy of the
results depends on a number of factors, such as the relative amounts of the
phases present, the compressibility of the fluid, and the efficiency specified.
Use Pump to change pressure when the power requirement is needed or known.
For pressure change only, you can use other models such as Heater.
Pump can model pumps and hydraulic turbines.
Use the Pump block to rate a pump or a turbine by specifying scalar parameters
or by specifying the related performance curves. To use the performance curves,
you can specify either:
•
•
Dimensional curves such as head versus flow or power versus flow
Dimensionless curves such as head coefficient versus flow coefficient
Flowsheet Connectivity for Pump
Work (optional)
Material
Material
(any number)
Water (optional)
Work
(optional)
Material Streams
Inlet
At least one material stream
Outlet One material stream
One water decant stream (optional)
6-2
Unit Operation Models
Version 10
Chapter 6
Work Streams
Inlet
Any number of work streams (optional)
Outlet One work stream for the net work load (optional)
If you do not specify either power or pressure on the Setup Specifications sheet,
Pump uses the sum of the inlet work streams as a power specification.
Otherwise, Pump uses the inlet work stream(s) only to calculate the net work
load. The net work load is the sum of the inlet work streams minus the actual
(calculated) work load.
You can use an optional outlet work stream for the net work load.
Specifying Pump
Use the Setup Specifications sheet for Pump specifications.
If you specify
Pump calculates
Discharge pressure
Power required or produced
Pressure increase (for a pump) or decrease (for a turbine)
Power required or produced
Pressure ratio (outlet pressure to inlet pressure)
Power required or produced
Power required (for a pump) or produced (for a turbine)
Discharge pressure
Curves of head, discharge pressure, pressure ratio,
pressure change, or head coefficient
Power required or produced
Power curve
Discharge pressure
You can supply a Fortran subroutine to calculate performance curves in Pump.
See ASPEN PLUS User Models for more information.
Use the following forms to enter specifications and view results for Pump:
Unit Operation Models
Version 10
Use this form
To do this
Setup
Specify operating conditions, efficiencies, net positive suction head parameters,
specific speed parameters, valid phases, and flash convergence parameters
PerformanceCurves
Specify parameters and enter data for the performance curves
UserSubroutines
Specify name and parameters for the user performance curve subroutine
BlockOptions
Override global values for physical properties, simulation options, diagnostic
message levels, and report options for this block
Results
View summary of Pump results, material and energy balance results, and
performance curve summary
6-3
Pressure
Changers
NPSH Available
The Net Positive Suction Head (NPSH) available for a pump is defined as:
NPSHA = Pin − Pvapor + H v + H s
Where:
NPSHA
=
Net Positive Suction Head Available
Pin
=
Inlet pressure
Pvapor
=
Vapor pressure of the liquid at inlet conditions
Hv
=
Velocity head
(= u 2 / 2 g , u is the velocity and g is gravitation constant)
Hs
=
Hydraulic static head corrected to the pump centerline
The NPSH available has to be greater than the NPSH required (NPSHR) to avoid
cavitation. NPSH required is a function of pump design.
NPSH Required
The Net Positive Suction Head (NPSH) required can be considered the suction
pressure required by the pump for safe, reliable operation. The NPSHR can be
specified using the performance curves on the PerformanceCurves NPSHR sheet,
or calculated from the following empirical equation by specifying suction specific
speed ( N ss ) on the Setup CalculationOptions sheet.
 N Q 0.5 
NPSHR = 

 N ss 
4
3
Where:
6-4
NPSHR
=
Net Positive Suction Head Required
N
=
Pump shaft speed (rpm)
Q
=
Volumetric flow rate at the suction conditions
N ss
=
Suction specific speed
Unit Operation Models
Version 10
Chapter 6
The units for Q and NPSHR are:
US:
Q in gal/min and NPSHR in feet
Metric:
Q in cum/hr and NPSHR in meters
Specific Speed
Specific speed and suction specific speed are two important parameters that
define the suitability of a pump design for its intended conditions. The pump
specific speed is defined as:
Ns =
N Q 0.5
Head 0.75
Where:
Head
= Head developed across the pump
Ns
= Specific speed
N
= Pump shaft speed (rpm)
Q
= Volumetric flow rate at the suction conditions
The units for Q and Head are:
Unit Operation Models
Version 10
US:
Head in feet
Metric:
Head in meters
6-5
Pressure
Changers
In general, pumps with a low specific speed are termed low capacity and those
with a high specific speed are termed high capacity. For a turbine, the specific
speed is defined as follows:
Ns =
N BHP 0.5
Head 1.25
Where:
Ns
=
Specific speed
BHP
=
Developed horsepower
Head
=
Total dynamic head across turbine
Suction Specific Speed
Suction specific speed ( N ss ) is an index number for a centrifugal pump and is
used to define its suction characteristic. It is defined as follows:
N ss =
N Q 0.5
NPSHR 0.75
Where:
NPSHR
=
Net positive suction head required for a pump or net
positive discharge head required for a turbine
N ss
=
Suction specific speed
N
=
Pump shaft speed (rpm)
Q
=
Volumetric flow rate at the suction conditions
The units for Q and NPSHR are:
6-6
US:
Q in gal/min and NPSHR in feet
Metric:
Q in cum/hr and NPSHR in meters
Unit Operation Models
Version 10
Chapter 6
Suction specific speed is a criterion of a pump’s performance with regard to
cavitation. For a pump of normal design, values of N ss vary from 6,000 to 12,000
in US units. A typical value is 8,500.
Head Coefficient
Head coefficient is defined as follows:
Headc =
Head g
u2
Where:
Headc
=
Head coefficient
Head
=
Head developed across the pump
g
=
Gravitational constant
u
=
Impeller tip speed
Flow Coefficient
Flow coefficient is the ratio of discharge throat velocity to impeller tip speed. It is
defined as:
Flowc =
Q
A1 u
A1 = π × d 12 / 4
Where:
Unit Operation Models
Version 10
Flowc
=
Flow coefficient
Q
=
Volumetric flow rate
A1
=
Cross-sectional area of discharge throat
d1
=
Diameter of discharge throat
u
=
Impeller tip speed
6-7
Pressure
Changers
The diameter of throat and diameter of impeller are related by the following
empirical equation:
N s = 5500
d1
Diam
Where:
Ns
=
Specific speed at the best efficiency point
Diam
=
Diameter of impeller
You can specify Specific Speed ( N s ) on the Setup CalculationOptions sheet.
6-8
Unit Operation Models
Version 10
Chapter 6
Compr
Compressor/Turbine
Use Compr to model:
• A polytropic centrifugal compressor
• A polytropic positive displacement compressor
• An isentropic compressor
• An isentropic turbine
Use Compr to change stream pressure when energy-related information, such as
power requirement, is needed or known.
Compr can handle single-phase as well as two- and three-phase calculations.
You can use Compr to rate a single stage of a compressor or a single wheel of a
compressor, by specifying the related performance curves. Compr allows you to
specify either:
• Dimensional curves, such as head versus flow or power versus flow
• Dimensionless curves, such as head coefficient versus flow coefficient
Compr can also calculate compressor shaft speed.
Compr cannot handle performance curves for a turbine.
Flowsheet Connectivity for Compr
Material
(any number)
Work
(optional)
Work (optional)
Water (optional)
Material
Material Streams
Inlet
At least one material stream
Outlet One material stream
One water decant stream (optional)
Unit Operation Models
Version 10
6-9
Pressure
Changers
Work Streams
Inlet
Any number of work streams (optional)
Outlet One work stream for net work load (optional)
If you do not specify either power or pressure on the Compr Setup Specifications
sheet, Compr uses the sum of the inlet work streams as a power specification.
Otherwise, Compr uses the inlet work stream(s) only to calculate the net work
load. The net work load is the sum of the inlet work streams minus the actual
(calculated) work load.
You can use an optional outlet work stream for the net work load.
Specifying Compr
If you specify
Compr calculates
Discharge pressure
Power required or produced
Power required (for a compressor) or produced (for a turbine)
Discharge pressure
Curves of head, power, discharge pressure, pressure ratio, pressure
change, or head coefficient
Power required and discharge pressure
Discharge pressure and curves of head or power or head coefficient
Power required, discharge pressure, and shaft
speed
Power required and curves of discharge pressure, pressure ratio, or
pressure change
Discharge pressure, and shaft speed
When you use performance curves, you can specify either a scalar value of
efficiency or efficiency curves.
You can supply a Fortran subroutine to calculate performance curves in Compr.
See ASPEN PLUS User Models for more information.
Some required specifications depend on the compressor type. Specify the
compressor type on the Setup Specifications sheet.
You can model a polytropic compressor using either the GPSA or ASME method.
You can model an isentropic compressor/turbine using either the GPSA, ASME,
or Mollier-based methods.
The GPSA method can be based on either:
• Suction conditions
• Average of suction and discharge conditions
6-10
Unit Operation Models
Version 10
Chapter 6
The ASME method is more rigorous than the GPSA method for polytropic or
isentropic compressor calculations. The Mollier method is the most rigorous for
isentropic calculations.
Use the following forms to enter specifications and view results for Compr:
Use this form
To do this
Setup
Identify compressor specifications, calculation options, convergence parameters,
and valid phases
Performance Curves
Specify parameters and enter data for the performance curves
User Subroutine
Enter performance curve subroutine parameters and name
BlockOptions
Override global values for physical properties, simulation options, diagnostic
message levels, and report options for this block
Results
View summary of Compr results, material and energy balance results, and
performance curve summary
Dynamic
Specify parameters for dynamic simulations
Polytropic Efficiency
The polytropic efficiency η p is used in the equation for the polytropic
compression ratio:
n − 1  k − 1
=
 η
 k  p
n
The basic compressor relation is:
n −1


Pin Vin  Pout  n
∆h =

 − 1

n − 1  Pin 

ηp 


 n  
Where:
n
k
Unit Operation Models
Version 10
ηp
=
=
=
Polytropic coefficient
Heat capacity ratio Cp/Cv
Polytropic efficiency
∆h
=
Enthalpy change per mole
P
V
=
=
Pressure
Molar volume
6-11
Pressure
Changers
Isentropic Efficiency
There are two equations for the isentropic efficiency ηs
For compression:
ηs =
s
hout
− hin
hout − hin
For expansion:
ηs =
hout − hin
s
hout
− hin
Where :
h
s
hout
=
=
Molar enthalpy
Outlet molar enthalpy assuming isentropic compression or
expansion to the specified outlet pressure
Mechanical Efficiency
Mechanical efficiency ηm is used to calculate the brake horsepower:
IHP = F∆h
BHP = IHP / ηm
Where:
IHP
F
∆h
BHP
ηm
6-12
=
=
=
Indicated horsepower
Mole flow rate
Enthalpy change per mole
=
=
Brake horsepower
Mechanical efficiency
Unit Operation Models
Version 10
Chapter 6
MCompr
Multistage Compressor/Turbine
Use MCompr to model:
• A multi-stage polytropic compressor
• A multi-stage polytropic positive displacement compressor
• A multi-stage isentropic compressor
• A multi-stage isentropic turbine
For polytropic compressors, MCompr can handle a single, compressible phase.
For special cases you can specify two- or three-phase calculations. These
calculations determine the outlet stream conditions and the properties used in
the compressor equations. The accuracy of results depends primarily on the
relative amounts of the phases present and the efficiency specified. The rigorous
polytropic compressor uses real fluid properties calculated from the property
method you specify. It does not assume ideal gas behavior.
MCompr handles single-phase isentropic compressors and turbines. MCompr can
also handle two- and three-phase mixtures.
You can use MCompr to rate a multi-stage compressor, by using either:
• Stage-by-stage dimensional performance curves, such as head versus flow or
power versus flow
• Wheel-by-wheel dimensionless performance curves, such as head coefficient
versus flow coefficient
MCompr can also calculate shaft speed.
MCompr cannot handle performance curves for a turbine.
Flowsheet Connectivity for MCompr
Work
(any number)
From
Stage
K-1
Feed to
Heat
(any number) Stage
K+1
(any number)
Cooler
Compressor
Stage K
To
Stage
K+1
Heat
(optional)
Stage K
Work
(optional)
Stage K
Unit Operation Models
Version 10
Knockout
Water
(optional)
6-13
Pressure
Changers
Material Streams
Inlet
At least one material stream for the first compressor stage
One or more material streams for stages after the first (optional). These
streams enter the intercooler before the stages you specify.
Outlet One material stream leaving the last compressor stage
Either one optional knockout material stream for each intercooler for the
liquid formed, or one optional global knockout for the liquid formed in all
intercoolers
Either one optional water decant stream for each intercooler, or one
optional global water decant stream
If you use liquid knockout outlet streams from one stage, you must use them for
all stages. The last stage cannot have a liquid knockout material stream or a
water decant stream.
Heat Streams
Inlet
Any number of heat streams to each intercooler (optional)
Outlet Either one optional heat stream for the net heat load of each intercooler,
or one global heat outlet stream for the net heat duty for all intercoolers
If you do not specify cooler conditions on the Setup Cooler sheet, MCompr adds
the heat streams together and uses the total as a duty specification for the cooler.
The net heat load equals the heat in the inlet heat streams minus the actual
(calculated) heat duty.
If you use a heat outlet from one stage, you must use one for all stages.
Work Streams
Inlet
Any number of work streams to each compressor stage (optional)
Outlet Either one optional work stream for net work load, or one global work
stream for the net power for all compressor stages
MCompr adds all work inlet streams together to provide the power requirement.
If you do not specify power or pressure on the Setup Specs sheet, MCompr uses
the total power as a power specification for the stage.
The power in the outlet work stream equals the power in the inlet work streams
minus the actual (calculated) power required.
If you use a work outlet from one stage, you must use one for all stages.
6-14
Unit Operation Models
Version 10
Chapter 6
Specifying MCompr
If you specify
MCompr calculates
Discharge pressure
Power required or produced
Power required (for a compressor) or produced (for a turbine)
Discharge pressure
Curves of head, power, discharge pressure, pressure ratio,
pressure change, or head coefficient
Power required and discharge pressure
Discharge pressure and curves of head or power or head
coefficient
Power required and shaft speed
When you use performance curves, you can specify either a scalar value for
efficiency or efficiency curves.
You can supply a Fortran subroutine to calculate performance curves in
MCompr. See ASPEN PLUS User Models for more information.
MCompr can have an intercooler between each compression (or expansion) stage,
and an aftercooler after the last stage. You can perform one-, two-, or three-phase
flash calculations in the intercoolers. Each cooler can have a liquid knockout
stream, except the cooler after the last stage.
You can model a polytropic compressor using either the GPSA1 or ASME2
method. You can model an isentropic compressor/turbine using either the GPSA,
ASME, or Mollier-based methods.
The GPSA method can be based on either:
• Suction conditions
• Average of suction and discharge conditions
The ASME method is more rigorous than the GPSA method for polytropic or
isentropic compressor calculations. The Mollier method is the most rigorous for
isentropic calculations.
Use the following forms to enter specifications and view results for MCompr:
Use this form
To do this
Setup
Identify multi-stage compressor specifications, stage specifications, cooler specifications,
convergence parameters, and valid phases
Performance Curves
Specify parameters and enter data for the performance curves
User Subroutine
Specify performance curve user subroutine parameters and name
Hcurves
Specify heating or cooling curve tables and view tabular results
continued
Unit Operation Models
Version 10
6-15
Pressure
Changers
Use this form
To do this
BlockOptions
Override global values for physical properties, simulation options, diagnostic message levels, and report
options for this block
Results
View summary of operating results, material and energy balance results, compressor and cooler profiles,
and performance profiles
Dynamic
Specify parameters for dynamic simulations
Polytropic Efficiency
The polytropic efficiency η p is used in the equation for the polytropic compression
ratio:
n − 1  k − 1
=
 η
 k  p
n
The basic compressor relation is:
Pin Vin
∆h =
n − 1
η p 

 n 
n −1


n


P
 out  − 1
 Pin 



Where:
n
=
Polytropic coefficient
k
=
Heat capacity ratio Cp/Cv
ηp
=
Polytropic efficiency
∆h
=
Enthalpy change per mole
P
=
Pressure
V
=
Molar volume
Isentropic Efficiency
There are two equations for the isentropic efficiency η s
For compression:
ηs =
6-16
s
hout
− hin
hout − hin
Unit Operation Models
Version 10
Chapter 6
For expansion:
ηs =
hout − hin
s
hout
− hin
Where :
h
=
Molar enthalpy
s
hout
=
Outlet molar enthalpy assuming isentropic compression or
expansion to the specified outlet pressure
Mechanical Efficiency
Mechanical efficiency ηm is used to calculate the brake horsepower:
IHP = F∆h
BHP = IHP / ηm
Where:
IHP
=
Indicated horsepower
F
=
Mole flow rate
∆h
=
Enthalpy change per mole
BHP
=
Brake horsepower
ηm
=
Mechanical efficiency
Parasitic Pressure Loss
The parasitic pressure loss at the suction of a stage is calculated using the
equation:
V2
∆P = Kρ
2
Where:
Unit Operation Models
Version 10
∆P
=
Parasitic pressure loss
K
=
Velocity head multiplier
ρ
=
Density
V
=
Linear velocity of process gas at suction conditions
6-17
Pressure
Changers
Specific Speed
The specific speed is defined as:
ShSpd (VflIn) 0.5
SpSpd =
(Head) 0.75
Where:
ShSpd
=
Shaft speed
VflIn
=
Suction volumetric flow rate
Head
=
Head developed
Specific Diameter
The specific diameter is defined as:
ImpDiam (Head) 0.25
SpDiam =
(VflIn) 0.5
Where:
ImpDiam
=
Impeller diameter of compressor wheel
Head
=
Head developed
VflIn
=
Volumetric flow rate at suction conditions
Head Coefficient
The head coefficient is defined as:
Hc =
Head g
( π ShSpd ImpDiam) 2
Where:
6-18
Head
=
Head developed
g
=
Gravitational constant
π
=
3.1416
ShSpd
=
Shaft speed
ImpDiam
=
Impeller diameter of compressor wheel
Unit Operation Models
Version 10
Chapter 6
Flow Coefficient
The flow coefficient is defined as:
Fc =
VflIn
ShSpd (ImpDiam) 3
Where:
VflIn
=
Volumetric flow rate at suction conditions
ShSpd
=
Shaft speed
ImpDiam
=
Impeller diameter of compressor wheel
References
1. GPSA Engineering Data Book, 1979, Chapter 4, pp. 5-6 to 5-10.
2. ASME Power Test Code 10, 1965, pp. 31-32.
Unit Operation Models
Version 10
6-19
Pressure
Changers
Valve
Valve Pressure Drop
Valve models control valves and pressure changers. Valve relates the pressure
drop across a valve to the valve flow coefficient. Valve assumes the flow is
adiabatic, and determines the thermal and phase condition of the stream at the
valve outlet. Valve can perform one-, two-, or three-phase calculations.
Flowsheet Connectivity for Valve
Material
Material
Material Streams
Inlet
One material stream
Outlet One material stream
Specifying Valve
Use the Input Operation sheet to select the calculation type.
If you select the Pressure changer option or the Design option for the calculation
type, you must specify, on the same sheet, one of the following:
• Outlet pressure
• Pressure drop
If you select the Pressure changer option, the specification is complete and Valve
performs an adiabatic flash to calculate the thermal and phase condition of the
outlet stream.
If you select the Rating option for the calculation type, you must specify, on the
same sheet, one of the following:
•
•
6-20
Flow coefficient at operating valve position
Valve operating position (% Opening)
Unit Operation Models
Version 10
Chapter 6
If you specify the valve operating position, you must also specify one of the
following on the Input ValveParameters sheet:
• Characteristic equation type and flow coefficient at maximum valve opening
• Data for flow coefficient (Cv) versus valve opening in the Valve Parameters
Table
• A valve from the built-in library based on valve type, manufacturer,
series/style, and size
On the Input CalculationOptions sheet, you can specify that Valve:
• Check for choked flow
• Calculate cavitation index
For vapor-containing streams, you must specify the pressure drop ratio factor
(Xt) for the valve. For liquid-containing streams, if you specify that Valve check
for choked flow, you must also specify the pressure recovery factor (Fl) for the
valve. You can specify the pressure drop ratio factor and the pressure recovery
factor for the valve in one of the following ways on the Input ValveParameters
sheet:
Specify
Value at the operating valve position (Pres Drop Ratio Factor, Pres Recovery Factor)
Data for pressure drop ratio factor (Xt) and for pressure recovery factor (Fl) versus valve opening (% Opening) in the Valve
Parameters Table
A valve from the built-in library based on Valve Type, Manufacturer, Series/Style, and Size
If you want to include the effect of head loss from pipe fittings on the valve flow
capacity, you must specify the diameters of the valve and pipe fittings on the
Input PipeFittings sheet. Valve uses the valve and pipe diameters, and estimates
the piping geometry factor to account for the reduction in flow capacity.
Use the following forms to enter specifications and view results for Valve:
Unit Operation Models
Version 10
Use this form
To do this
Input
Specify valve operating conditions, flash convergence parameters, valid phases, valve
parameters, sizes for pipe fittings, calculation options, and Valve convergence parameters
Block Options
Override global values for physical properties, simulation options, diagnostic message levels,
and report options for this block
Results
View summary of operating results and mass and energy balances
6-21
Pressure
Changers
Pressure Drop Ratio Factor
The pressure drop ratio factor ( X t ) accounts for the effect of the internal
geometry of the valve on the change in fluid density as it passes through the
valve.
The pressure drop ratio factor is the limiting value (under choked conditions) of
the pressure drop ratio and is given by:
Xt =
1  dPch 


Fk  Pin 
(1)
Where:
dPch
=
Pressure drop for choked vapor flow
Fk
=
Ratio of specific heats factor
Pin
=
Inlet pressure
You can specify the pressure drop ratio factor on the Input ValveParameters
sheet in one of the following ways:
• Choose a Library Valve
• Enter data for Xt and % Opening in the Valve Parameters Table
• Specify the value at the operating valve position in Valve Factors
If you know the ratio of the gas sizing coefficient (C g ) to the liquid sizing
coefficient (Cv ) , as defined in Fisher Controls Company Control Valve Handbook,
you can calculate the pressure drop ratio factor (with the assumption Fk = 1) by
either:
Cg
 dPch 
 versus
in equation (1)
Cv
 Pin 
•
Using valve manufacturer’s data for 
•
Using the expression
6.31 × 10 − 4  C g 
 
Xt =
Fk
 Cv 
2
This relationship is based on equating the choked flow calculated (in US units of
measure) with:
6-22
Universal Gas Sizing Equation
Wch = 106
. C g rPin
ISA Standard Valve Sizing Equation
Wch = N 6 Cv Y Fk X t rPin
Unit Operation Models
Version 10
Chapter 6
Where:
Wch
=
Mass flow rate (choked flow)
r
=
Mass density of inlet stream
Y
=
Expansion factor (= 0.667 for choked flow)
N6
=
Numerical constant (= 63.3 for US units of measure)
If you specify the pressure drop ratio factor by choosing a valve from the built-in
library or by entering data in the Valve Parameters Table on the Input
ValveParameters sheet, Valve uses cubic splines to interpolate the value of the
pressure drop ratio factor at the operating valve position.
Valve uses the pressure drop ratio factor only when both of the following are
true:
• Vapor is present in the inlet stream
• The Design or Rating option is selected for Calculation Type on the Input
Operation sheet
Pressure Recovery Factor
( )
The pressure recovery factor Fl accounts for the effect of the internal geometry
of the valve on its liquid flow capacity under choked conditions.
The pressure recovery factor is defined as:
 dPch 
Fl = 

 Pin − Pvc 
1/ 2
Where:
dPch
=
Pressure drop for choked liquid flow
Pin
=
Inlet pressure
Pvc
=
Pressure at the vena contracta in the valve
=
F f Pv
Pv
=
Vapor pressure of inlet liquid stream
Ff
=
Liquid critical pressure ratio factor
and
Pvc
with
Unit Operation Models
Version 10
6-23
Pressure
Changers
You can specify the pressure recovery factor on the Input ValveParameters sheet
in one of the following ways:
• Choose a Library Valve
• Enter data for Fl and % Opening in the Valve Parameters Table
• Specify the value at the operating valve position in Valve Factors
The pressure recovery factor is equivalent to the valve recovery coefficient K m , as
defined in Fisher Controls Company Control Valve Handbook.
You can use the valve recovery coefficient to calculate the pressure recovery
factor as:
Fl =
Km
If you specify the pressure recovery factor by choosing a valve from the built-in
library or by entering tabular data in the Valve Parameters Table on the Input
ValveParameters sheet, Valve uses cubic splines to interpolate the value of the
pressure recovery factor at the operating valve position.
The pressure recovery factor is used in the Valve model calculations only when
all of the following are true:
• Liquid is present in the inlet stream
• The Check for Choked Flow box is checked or the Set Equal to Choked Outlet
Pressure option is selected on the Input CalculationOptions sheet
• The Design or Rating option is selected for Calculation Type on the Input
Operation sheet.
Valve Flow Coefficient
The valve flow coefficient (Cv ) measures the flow capacity of the valve. The flow
coefficient is defined as the number of US gallons per minute of water (at 60 °F)
that will pass through the valve with a pressure drop of 1 psi.
The valve flow coefficient relates the pressure drop across the valve to the flow
rate as (Instrument Society of America, 1985) 1:
6-24
Liquid
W = N 6 Fp Cv r ( Pin − Pout )
Gas/Vapor
W = N 6 Fp Y r ( Pin − Pout )
with
Y = 1−
Pin − Pout
3 Fk X t Pin
Unit Operation Models
Version 10
Chapter 6
Where:
W
=
Mass flow rate
N6
=
Numerical constant (based on the units of measure)
Fp
=
Piping geometry factor
Cv
=
Valve flow coefficient
Y
=
Expansion factor
Pin
=
Inlet pressure
Pout
=
Outlet pressure
r
=
Mass density of inlet stream
Fk
=
Ratio of specific heats factor
Xt
=
Pressure drop ratio factor
You can specify the flow coefficient in one of the following ways:
• Use Flow Coef on the Input Operation sheet to specify the value at the
operating valve position
• Choose a Library Valve on the Input ValveParameters sheet
• Enter data for Cv and % Opening in the Valve Parameters Table on the Input
ValveParameters sheet
• Specify Valve Characteristics in the Input ValveParameters sheet
If you specify the flow coefficient by choosing a valve from the built-in library or
by entering data in the Valve Parameters Table, Valve uses cubic splines to
interpolate the value of the flow coefficient at the operating valve position.
Unit Operation Models
Version 10
6-25
Pressure
Changers
Characteristic Equation Type
The characteristic equation for the valve relates the flow coefficient to the valve
opening. Use the Input ValveParameters sheet to specify the characteristic
equation type. The six built-in characteristic equations are:
†
Type
Equation
Linear
V=P
Parabolic
V = 0.01P 2
Square Root
V = 10.0 P
Quick Opening
V =
Equal Percentage
V =
Hyperbolic
†
V =
10.0 P
(10. + 9.9 × 10 −3 P 2 )
0.01P 2
2.0 − 10
. × 10 −8 P 4
01
. P
(10. − 9.9 × 10 −5 P 2 )
Where:
P = Valve opening as a percentage of maximum opening
V = Flow coefficient as a percentage of flow coefficient at maximum opening
Piping Geometry Factor
The piping geometry factor is defined as:
Fp =
Cυp
Cυ
Where:
Cυp
=
Flow coefficient of the valve with attached fittings
Cυ
=
Flow coefficient of the valve installed in a straight pipe of the
same size
The piping geometry factor accounts for the reduction in the flow capacity of a
valve due to the head loss from the pipe fittings. The piping geometry factor has
a default value of 1.0 if the valve and pipe fittings have the same diameter.
6-26
Unit Operation Models
Version 10
Chapter 6
ASPEN PLUS calculates the piping geometry factor as (Instrument Society of
America, 1985)1:
 ΣKC 2 


υ
Fp = 
4 + 1

 N 2d


−0.5
with ΣK = K1 + K2 + K B1 − K B2
Where:
2
2
4


 d 
 d 
d2 
d2 
K1 = 0.5 1 − 2  , K 2 = 10
.  1 − 2  , K B1 = 1 −   , K B2 = 1 −  
D1 
D2 
 D1 
 D2 


4
and:
Fp
=
Piping geometry factor
Cυ
=
Valve flow coefficient
N2
=
Numerical constant (based on the units of measure)
d
=
Valve diameter
K1, K 2
=
Resistance coefficients of the inlet and outlet fittings
K B1 , K B2
=
Bernoulli coefficients for the inlet and outlet fittings
D1
=
Inlet pipe diameter
D2
=
Outlet pipe diameter
If the valve and pipe fittings diameters are different and you wish to include the
effect of the additional head loss on the valve flow capacity, you must specify the
valve and pipe diameters on the Input PipeFittings sheet.
Unit Operation Models
Version 10
6-27
Pressure
Changers
Choked Flow
ASPEN PLUS calculates the limiting pressure drop for choked flow conditions
using (Instrument Society of America, 1985)1:
(
Liquid
dPlc = F L Pin − F f Pυ
Vapor
dPυc = Fk X T Pin
with
 Pv 
F f = 0.96 − 0.28 
 Pc 
2
)
0.5
Where:
FL
=
Pressure recovery factor
Ff
=
Liquid critical pressure ratio factor
Fk
=
Ratio of specific heats factor
XT
=
Pressure drop ratio factor
Pin
=
Inlet pressure
Pυ
=
Vapor pressure at inlet
Pc
=
Critical pressure at inlet
dPlc
=
Limiting pressure drop, liquid phase
dPvc
=
Limiting pressure drop, vapor phase
For multi-phase streams, Valve takes the limiting pressure drop for choked flow
to be the smaller of dPlc and dPvc . Flow in the valve is choked when the pressure
drop exceeds this limiting pressure drop. Valve displays the choking status of the
valve if you check the Check for Choking box on the Input CalculationOptions
sheet.
6-28
Unit Operation Models
Version 10
Chapter 6
Cavitation Index
The likelihood of cavitation in a valve is measured by the cavitation index.
ASPEN PLUS calculates the cavitation index as (Instrument Society of America,
1985)1:
 P − Pout 

K c =  in
 Pin − Pv 
Where:
Kc
=
Cavitation index
Pin
=
Inlet pressure
Pout
=
Outlet pressure
Pv
=
Vapor pressure at inlet
The cavitation index definition is valid only for all-liquid streams. Valve
calculates the cavitation index if you check the Calculate Cavitation Index box on
the Input CalculationOptions sheet.
References
1. Flow Equations for Sizing Control Valves, ISA-S75.01-1985, Instrument
Society of America, 1985.
Unit Operation Models
Version 10
6-29
Pressure
Changers
Pipe
Pipe Pressure Drop
Pipe calculates the pressure drop and heat transfer in a single segment pipe. You
can also use Pipe to model the pressure drop due to fittings.
Pipe handles a single inlet and outlet material stream. Pipe assumes the flow is
one-dimensional, steady-state, and fully developed (that is, no entrance effects
are modeled). Pipe can perform one-, two-, or three-phase calculations. Flow
direction and elevation angle are arbitrary.
To model multiple pipe segments of different diameters or elevations, use
Pipeline instead of Pipe.
If the inlet pressure is known, Pipe calculates the outlet pressure. If the outlet
pressure is known, Pipe calculates the inlet pressure and updates the state
variables of the inlet stream.
Use Pipe to:
• Calculate inlet or discharge conditions
• Calculate pressure drops for one-, two-, or three-phase vapor and liquid flows
Flowsheet Connectivity for Pipe
Material
Material
Material Streams
Inlet
One material stream
Outlet One material stream
6-30
Unit Operation Models
Version 10
Chapter 6
Specifying Pipe
You must specify the following for Pipe:
• Pipe length, diameter, roughness, and angle on the Setup PipeParameters
sheet
• Thermal specification type on the Setup ThermalSpecification sheet to
determine whether Pipe operates with a temperature profile or temperature
is calculated
• Whether to integrate, assume constant dP/dL, or use a closed form equation
on the Advanced Methods sheet
• Frictional and holdup correlation when a closed form equation is not used on
the Advanced Methods sheet
• Pressure and temperature grid for fluid property calculations on the
Advanced PropertyGrid sheet, if you request a pressure-temperature grid on
the AdvancedCalculation Options sheet
• Integration direction in which calculations proceed with respect to flow on the
Advanced CalculationOptions sheet
If the option selected is
Pipe needs the
And the integration direction is
Calculate pipe outlet
pressure (default)
Inlet pressure
Downstream
Calculate pipe inlet pressure
Outlet pressure
Upstream
Pipe uses the inlet or outlet stream pressure to start the calculations. If the
stream is an external feed to your flowsheet, or the outlet of a block that will
execute after Pipe, use the Stream Specifications sheet to specify the stream
pressure. If the integration direction is upstream, you can also specify the initial
pressure for Pipe on the Advanced CalculationOptions sheet, by entering the
outlet pressure. This pressure value will override the stream pressure entered on
the Stream Specifications sheet.
Select the flow calculation option on the Advanced CalculationOptions sheet to
specify whether Pipe is to calculate the outlet or inlet stream flow and
composition.
Unit Operation Models
Version 10
If the option selected is
Pipe needs the
Reference inlet stream
(default)
Inlet flow and composition
Use outlet stream flow
Outlet flow and composition
6-31
Pressure
Changers
Use the following forms to enter specifications and view results for Pipe:
Use this form
To do this
Setup
Specify pipe parameters, thermal specifications, fittings, flash convergence
parameters and property profiles to be reported
Advanced
Specify calculation options, solution methods, property grid, integration
parameters and Beggs and Brill coefficients
UserSubroutine
Specify pressure drop and/or holdup user subroutine name and parameters
BlockOptions
Override global values for physical properties, simulation options, diagnostic
message levels, and report options for this block
Results
View summary of Pipe results, inlet and outlet stream results, material and
energy balance results, and profiles
Stream Specification
You must initialize the inlet stream to Pipe whenever the option to reference
inlet stream is selected, even if the inlet pressure is being calculated. Similarly,
you must initialize the outlet stream whenever the option to use the outlet
stream flow is selected. The initialized stream must be one of the following:
• Entered on a Stream Specifications sheet
• An outlet stream from part of the flowsheet executed (if option to use outlet
stream flow is selected)
• Transferred from another part of a flowsheet using a Transfer block
Physical Property Calculations
You can specify that a rigorous flash is to be performed each time properties are
calculated, by selecting the option to do Flash at Each Integration Step on the
Advanced CalculationOptions sheet. If you select the option to Interpolate from
Property Grid, Pipe will determine properties by interpolating in a table of
property values at various temperatures and pressures. Specify one of the
following if you use the Property Grid:
• A range of temperatures and pressures on the Advanced Property Grid sheet.
Pipe will calculate properties at these conditions and interpolate
• The block ID of a Pipe block for which the option to interpolate from property
grid was also selected, and which will be executed before the current block in
the flowsheet
6-32
Unit Operation Models
Version 10
Chapter 6
Pressure Drop Calculations
Pipe can calculate pressure drop for either one-, two-, or three-phase vapor and
liquid flows. If vapor-liquid flow exists, Pipe also calculates liquid holdup and
flow regime (pattern). You may specify a flowing fluid temperature profile, or
Pipe can determine it from heat transfer calculations. Pipe treats multiple liquid
phases (for example, oil and water) as a single homogeneous liquid phase for
pressure-drop and holdup calculations. Pipe automatically detects the special
case of a single component fluid (for example, steam) and treats it appropriately.
Downstream and Upstream Integration
For downstream and upstream integration, the combination of options selected
for pressure and flow calculation on the Advanced CalculationOptions sheet
determine which stream Pipe will update. The following table describes the
available combinations. The next figure, Downstream and Upstream Integration,
defines the inlet and outlet stream and pressure variables:
If the pressure calculation option is
And the flow calculation option is
Then Pipe updates the
Calculate pipe outlet pressure
Reference inlet stream
Outlet stream only
Calculate pipe outlet pressure
Use outlet stream flow
Outlet stream thermodynamic conditions
Inlet stream composition and flow
Calculate pipe inlet pressure
Use outlet stream flow
Inlet stream only
Calculate pipe inlet pressure
Reference inlet stream
Inlet stream thermodynamic conditions
Outlet stream composition and flow
Inlet Stream
Inlet Pressure
Outlet Stream
Outlet Pressure
Downstream and Upstream Integration
Unit Operation Models
Version 10
6-33
Pressure
Changers
Design-Spec Convergence Loop
Use caution when using Pipe inside a Design-Spec convergence loop. For
example, you can manipulate the flow rate to a pipe to achieve a desired pipe
outlet pressure. During the design specification convergence, the flow rate
variables may become unreasonable in an intermediate iteration, causing Pipe to
predict a negative pressure. Convergence difficulties occur as a result. You can
avoid this situation by doing one of the following:
•
•
Keep the upper limit of the flow rate sufficiently low in Design-Spec
Perform an upstream integration from the known outlet pressure. Select
option to calculate pipe inlet pressure on the Advanced CalculationOptions
sheet for this purpose. Define a Design-Spec to manipulate the flow rate to
achieve the specified inlet pressure.
Erosional Velocity
Erosional velocity is the velocity of the fluid in the pipe, above which the pipe
material will start to break off. The fluid is traveling so fast that it starts to strip
material from the walls of the pipe. In general use, the flow rate should be below
this value.
You can specify the erosional velocity coefficient on the Setup Pipe Parameters
sheet.
The erosional velocity is related to the erosional velocity coefficient by the
following equation:
υc =
c
ρ
Where:
υc = Erosional velocity in ft/second
c = Erosional velocity coefficient (default=100)
ρ = Density in lbs/cubic ft
Methane Gas Systems
Gas systems consisting mostly of methane occur frequently in the dense-phase
region of wellbores and flowlines. In the dense-phase region, definable vapor and
liquid phases do not exist. Equation-of-state methods classify the dense-phase
material as either all vapor or all liquid. Significant differences in the predicted
fluid transport properties may occur, depending on whether you choose the vapor
or liquid state.
6-34
Unit Operation Models
Version 10
Chapter 6
Experience has shown that gas system flow in the dense-phase region is best
modeled by using vapor-phase properties. For systems consisting of mostly
methane, where the pipe conditions lie above the cricondenbar of the phase
envelope, specify vapor-only valid phase on the Setup FlashOptions sheet.
Modeling Valves and Fittings
Pipe assumes that the pressure drop due to valves and fittings is distributed
evenly along the specified length of the pipe. The total length Pipe uses in
calculations corresponds to the specified pipe length, plus any equivalent pipe
length due to valves, fittings, and miscellaneous L/D.
If the pipe is not horizontal, Pipe adjusts the angle from the horizontal to achieve
the same vertical rise or fall for the total length used in the calculations. This
adjustment ensures the correct pressure drop due to elevation.
If the order and position of the valves and fittings are important, you need to
model each valve and fitting separately with a Pipe model, specifying zero length
of pipe.
Two-Phase Correlations
The following tables list the two-phase frictional pressure drop and holdup
correlations available.
Two-Phase Friction Factor Correlations
Pipe orientation
Inclination
Friction factor correlations
Horizontal
-2 deg to +2 deg
Beggs and Brill (BEGGS-BRILL)
Dukler (DUKLER)
Lockhart-Martinelli (LOCK-MART)
User subroutine (USER-SUBR)
Vertical
+45 deg to +90 deg
Beggs and Brill (BEGGS-BRILL)
Orkiszewski (ORK)
Angel-Welchon-Ros (AWR)
Hagedorn-Brown (H-BROWN)
†
User subroutine (USER-SUBR)
Downhill
-2 deg to -90 deg
Beggs and Brill (BEGGS-BRILL)
Slack (SLACK)
Darcy (DARCY)
†
User subroutine (USER-SUBR)
†
See ASPEN PLUS User Models.
continued
Unit Operation Models
Version 10
6-35
Pressure
Changers
Pipe orientation
Inclination
Friction factor correlations
Inclined
+2 deg to +45 deg
Beggs and Brill (BEGGS-BRILL)
Dukler (DUKLER)
Orkiszewski (ORKI)
Angel-Welchon-Ros (AWR)
Hagedorn-Brown (H-BROWN)
Darcy (DARCY)
†
User subroutine (USER-SUBR)
†
See ASPEN PLUS User Models.
Two-Phase Liquid Holdup Correlations
Pipe orientation
Inclination
Liquid holdup correlations
Horizontal
-2 deg to +2 deg
Beggs and Brill (BEGGS-BRILL)
Eaton (EATON)
Lockhart-Martinelli (LOCK-MART)
Hoogendorn (HOOG)
Hughmark (HUGH)
†
User subroutine (USER-SUBR)
Vertical
+45 deg to +90 deg
Beggs and Brill (BEGGS-BRILL)
Orkiszewski(ORKI)
Angel-Welchon-Ros (AWR)
Hagedorn-Brown (H-BROWN)
†
User subroutine (USER-SUBR)
Downhill
-2 deg to -90 deg
Beggs and Brill (BEGGS-BRILL)
Slack (SLACK)
†
User subroutine (USER-SUBR)
Inclined
+2 deg to +45 deg
Beggs and Brill (BEGGS-BRILL)
Flanigan (FLANIGAN)
Orkiszewski (ORKI)
Angel-Welchon-Ros (AWR)
Hagedorn-Brown (H-BROWN)
†
User subroutine (USER-SUBR)
†
See ASPEN PLUS User Models.
Note
6-36
Some of the related information for the two-phase friction factor
and liquid holdup correlations was taken from "Two-Phase Flow
in Pipes" by James P. Brill and H. Dale Beggs, Sixth Edition,
Third Printing, January, 1991.
Unit Operation Models
Version 10
Chapter 6
Beggs and Brill Correlation
The Beggs and Brill correlation1 considers slip and flow regimes are considered
with this method. Friction factor and holdup correlations depend on flow regime
and pipe inclination. It is suitable for all inclinations, including vertical flow
downward.
Dukler Correlation
The Hughmark holdup method should be used with this pressure drop method.
2
The Dukler method was developed from field data using air-water mixtures in
1-inch pipes. It tends to overpredict frictional pressure drop. It is recommended
in a design manual published jointly by the AGA and API.
Hagedorn-Brown Correlation
The Hagedorn-Brown correlation3 considers slip between phases, but flow regime
is not considered. It uses the same correlations for liquid holdup and friction
factor for all flow regimes. It is an old method which works well for conventional
oil wells. It is suitable for vertical upward flow, but not downward. It is generally
recommended for gas wells, and is based on data obtained from U.S. Gulf Coast
oil wells with 2-3/8 inch and 2-7/8 inch tubing.
Lockhart-Martinelli Correlation
The Lockhart-Martinelli correlation4 is one of the oldest pressure drop
correlations. It does not consider pressure drop due to acceleration. The method
treats the vapor and liquid phases separately and uses a correction factor to find
the 2-phase pressure gradient. Our implementation assumes turbulent gas and
liquid phase flow.
Orkiszewski Correlation
5
Slip and flow regimes are considered in the Orkiszewski correlation . The friction
factor and holdup correlation depend on the flow regime. It is suitable for vertical
flow upward, but not downward. It is generally reliable for oil wells. It may
exhibit problems for oil wells with high water cuts or high total gas to liquid
ratios. It can significantly underpredict pressure drop for higher rate and higher
3
pressure wells (Beggs and Brill/1984) .
Unit Operation Models
Version 10
6-37
Pressure
Changers
Angel-Welchon-Ros Correlation
The Angel-Welchon-Ros correlation method6, 7 was developed for low gas-to-liquid
ratio water wells. It assumes no slip between the vapor and liquid phases when
calculating liquid holdup.
Slack Correlation
The Slack correlation method assumes a stratified flow regime, and should be
used only for downhill flow.
Eaton Correlation
The Eaton correlation8 holdup method was developed from data on 2- and 4-inch
pipes with a gas-water-crude mixture, and a 17-inch pipe with a gas-oil mixture.
It is often used with the Dukler frictional pressure drop correlation.
Flanigan Correlation
The Flanigan correlation9 holdup methodwas developed from data taken in a
16-inch pipe. It calculates liquid holdup as a function of superficial gas velocity.
It is suitable for inclined flow.
Beggs and Brill Correlation Parameters
The following table lists the Beggs and Brill liquid holdup correlation
parameters.
Flow Regime
Name
Description
Segregated
BB1
BB2
BB3
Leading coefficient, A (default = 0.98)
Liquid volume fraction exponent, alpha (default = 0.4846)
Froude no. exp., beta (default = 0.0868)
Intermittent
BB4
BB5
BB6
Leading coefficient, A (default = 0.845)
Liquid volume fraction exponent, alpha (default = 0.5351)
Froude no. exp., beta (default = 0.0173)
Distributed
BB7
BB8
BB9
Leading coefficient, A (default = 1.065)
Liquid volume fraction exponent, alpha (default = 0.5824)
Froude no. exp., beta (default = 0.0609)
In addition, you can change the Beggs and Brill two-phase Friction Factor modifier,
BB10 (default = 1.0).
6-38
Unit Operation Models
Version 10
Chapter 6
Closed-Form Methods
The following are closed-form methods:
• Smith
• Weymouth
• AGA
• Oliphant
• Panhandle A
• Panhandle B
• Hazen-Williams
Smith
The Smith method10 may be used for vertical dry gas flow. It should be considered
for gas wells with condensate-gas ratios less than 50 bbls/mcf, water-gas ratios
less than 3.5 bbls/mcf, and flow rates above the Turner predicted critical rate.
Smith does not model gas well loadup, and will significantly under predict
wellbore pressure drop if loadup is actually occurring. Smith results must be
cross-checked against the Turner predicted critical rates to verify that the well is
unloaded. Smith also does not model condensation of water vapor in the wellbore.
Weymouth
11
The Weymouth horizontal gas flow equation was first published in 1912. It is
based on data taken on pipes with diameters from 0.8 inches to 11.8 inches. As a
result, it is most accurate for smaller pipes having a diameter less than 12
inches.
AGA
12
The AGA method may be used for horizontal gas applications.
Oliphant
The Oliphant method13 may be used for horizontal gas applications with
pressures between vacuum and 100 PSI.
Unit Operation Models
Version 10
6-39
Pressure
Changers
Panhandle A
The Panhandle A method14 was developed by Panhandle Eastern for horizontal
gas flow in large diameter cross country gas transmission lines. As a result, it is
best used on lines having diameters larger than 12 inches. However, it does not
account for gas compressibility (Z-factor), and assumes completely turbulent
flow.
Panhandle B
The Panhandle B method14 is a revised version of the Panhandle A method for
horizontal gas flow and was developed by Panhandle Eastern. It is also called the
"Panhandle Eastern Revised Equation". It accounts for the gas compressibility
factor, and has revised exponents. This equation is not quite so Reynolds-Number
dependent as the Panhandle A equation, although it, too, is best for pipe
diameters of 12 inches or more.
Hazen-Williams
The Hazen-Williams method14 was developed for the horizontal flow of water.
When this method is used, the Hazen-Williams Coefficient must be specified in
place of the Segment Efficiency on the Connectivity Edit dialog box.
References
1. Beggs, H.D. and Brill, J.P., "A Study of Two-Phase Flow in Inclined Pipes,"
Journal of Petroleum Technology, May 1973, pp. 607-617.
2. Dukler, A.E., Wicks, M., and Cleveland, R.G, "Frictional Pressure Drop in
Two-Phase Flow: An Approach Through Similarity Analysis," AIChE Journal,
Vol. 10, No. 1, January 1964, pp. 44-51.
3. Beggs, H.D. and Brill, J.P., "Two-Phase Flow in Pipes," University of Tulsa
Short Course Notes, Third Printing, February 1984.
4. Lockhart, R.W. and Martinelli, R.C., "Proposed Correlation of Data for
Isothermal Two-Phase, Two-Component Flow in Pipes," Chemical
Engineering Progress, Vol. 45, 1949, pp. 39-48.
5. Orkiszewski, J., "Predicting Two-Phase Pressure Drops in Vertical Pipe,"
Journal of Petroleum Technology, June 1967, pp. 829-838.
6-40
Unit Operation Models
Version 10
Chapter 6
6. Angel, R.R., and Welchon, J.K., "Low-Ratio Gas-Lift Correlation for CasingTubing Annuli and Large Diameter Tubing," API Drilling and Production
Practice, 1964, pp. 100-114.
7. Ros, N.C.J., "Simultaneous Flow of Gas and Liquid as Encountered in Well
Tubing," Journal of Petroleum Technology, October 1961, pp. 1037-1049.
8. Eaton, B.A. et al., "The Prediction of Flow Patterns, Liquid Holdup, and
Pressure Losses Occurring During Continuous Two-Phase Flow in Horizontal
Pipelines," Trans. AIME, June 1967, pp. 815-828.
9. Flanigan, Orin, "Effect of Uphill Flow on Pressure Drop in Design of TwoPhase Gathering Systems," Oil and Gas Journal, March 10, 1958, pp. 132141.
10. Smith, R. V., "Determining Friction Factors for Measuring Productivity of
Gas Wells," AIME Petroleum Transactions, Volume 189, 1950, pp. 73-82.
11. Weymouth, T.R., Transactions of the American Society of Mechanical
Engineers, Vol. 34, 1912.
12. "Steady Flow in Gas Pipes," American Gas Association, IGT Technical Report
10, Chicago, 1965.
13. Oliphant, F.N., "Production of Natural Gas," Report of USGS, 1902.
14. Engineering Data Book, Volume II, Gas Processors Suppliers Association,
Tulsa, Oklahoma, Revised Tenth Edition, 1994.
Unit Operation Models
Version 10
6-41
Pressure
Changers
Pipeline
Pipe Pressure Drop
Use Pipeline to calculate the pressure drop in a straight pipe or annular space.
Pipeline can:
• Simulate a piping network with successive blocks, including wellbores and
flowlines
• Contain any number of segments within each block to describe pipe geometry
• Calculate inlet or discharge conditions
• Calculate pressure drops for one-, two-, or three-phase vapor and liquid flows.
Pipeline treats multiple liquid phases (for example, oil and water) as a single
homogeneous liquid phase for pressure-drop and holdup calculations. If
vapor-liquid flow exists, Pipeline calculates liquid holdup and flow regime
(pattern).
You may specify a flowing fluid temperature profile, or Pipeline can calculate it
from heat transfer calculations. Flow is assumed to be one-dimensional, steadystate, and fully developed (no entrance effects are modeled). Flow direction and
elevation angle are arbitrary. To model a single pipe segment with constant
diameter and elevation, you can also use Pipe.
Flowsheet Connectivity for Pipeline
Material
Material
Pipeline Streams
Material Streams
Inlet
One material stream
Outlet One material stream
6-42
Unit Operation Models
Version 10
Chapter 6
Specifying Pipeline
Use the Calculation Direction option on the Setup Configuration sheet to specify
whether Pipeline is to calculate the outlet or inlet pressure.
If Calculation Direction =
Pipeline will need the
And the integration direction is
Calculate outlet pressure
(default)
Inlet pressure
Downstream
Calculate inlet pressure
Outlet pressure
Upstream
Pipeline uses the inlet or outlet stream pressure to start the calculations. If the
stream is an external feed to your flowsheet, or the outlet of a block that will
execute after Pipeline, use the Streams Specifications sheet to specify the stream
pressure. You can also specify the initial pressure for Pipeline on the Setup
Configuration sheet by entering the pressure value at the inlet or outlet. This
pressure value overrides the stream pressure.
Use the Pipeline flow basis option on the Setup Configuration sheet to specify
whether Pipeline is to calculate the outlet or inlet stream flow and composition.
If Pipeline flow basis=
Pipeline will need the
Use inlet stream flow
(default)
Inlet flow and composition
Reference outlet stream
flow
Outlet flow and composition
Use Thermal Options on the Setup Configuration sheet to specify whether or not
the node temperatures are to be calculated by Pipeline using an energy balance.
When you select the Specify Temperature Profile option, the temperature at each
node can be specified. When you choose the Constant Temperature option, the
temperature will be same at every node. You can define this temperature by
specifying the inlet temperature (for downstream integrations) or the outlet
temperature (for upstream integrations). If neither the inlet nor the outlet
temperatures are specified, the temperature of the referenced stream will be
used. When you choose the linear temperature profile option, you can specify the
temperature at one or more nodes. Pipeline will do a linear interpolation between
the temperatures specified to calculate the fluid temperature in each segment.
Unit Operation Models
Version 10
6-43
Pressure
Changers
Use the following forms to enter specifications and view results for Pipeline:
Use this form
To do this
Setup
Specify pipeline configuration, segment connectivity and characteristics, calculation methods,
property grid parameters, flash convergence parameters, valid phases, and block-specific
diagnostic message level
Convergence
Override default values for integration parameters, downhill flow options, correlation
parameters and Beggs and Brill coefficients (optional input)
BlockOptions
Override global values for physical properties, simulation options, diagnostic message levels,
and report options for this block
UserSubroutines
Specify name and parameters for pressure drop and liquid holdup user subroutines
Results
View summary of Pipeline results, inlet and outlet stream results, profiles, and material and
energy balance results
Stream Specification
You must initialize the inlet stream to Pipeline whenever the Use Inlet Flow option
is selected for Pipeline Flow Basis, even if the inlet pressure is being calculated.
Similarly, you must initialize the outlet stream whenever you select the Reference
Outlet Stream Flow option. The initialized stream must be one of the following:
• On a stream form
• An outlet stream from part of the flowsheet executed previously
• Transferred from another part of a flowsheet using a Transfer block
Nodes and Segments
Create at least one segment using the New button on the Pipeline Setup
Connectivity sheet.
Enter specifications for each segment on the Setup Connectivity Segment Data
dialog box . For each segment, enter the inlet and outlet node names (maximum 4
characters). The required data depends on the options selected on the Setup
Configuration sheet. If you select Do Energy Balance with Surroundings, you
must specify a heat transfer coefficient (U-Value) and the ambient temperature.
If you select the Linear Temperature Profile option, Pipeline uses the
temperatures specified for the nodes to override the stream values. If specifications
are not made for the nodes, then Pipeline uses the stream values.
If you select Enter Node Coordinate, you must enter node coordinates (X, Y, and
Elevation) for each segment node. You must enter Length and Angle for each
segment if you select Enter Segment Length and Angle.
6-44
Unit Operation Models
Version 10
Chapter 6
Physical Property Calculations
You can specify a rigorous flash each time properties are calculated by selecting Do
Flash at Each Step on the Setup Configuration sheet. If Interpolate from Property
Grid is selected, Pipeline will determine properties by interpolating in a table of
property values at various temperatures and pressures. Specify one of the following
if you use the Property Grid:
• A range of temperatures and pressures grid on the Setup PropertyGrid sheet.
Pipeline calculates properties under these conditions and interpolates them.
• The block ID of a Pipeline block for which you selected Interpolate from the
Property Grid, and which will be executed before the current block in the
flowsheet.
Pressure Drop Calculations
Pipeline can calculate pressure drop for either one-, two-, or three-phase vapor and
liquid flows. If vapor-liquid flow exists, Pipeline also calculates liquid holdup and
flow regime (pattern). You may specify a flowing fluid temperature profile, or
Pipeline can calculate it from heat transfer calculations. Pipeline treats multiple
liquid phases (for example, oil and water) as a single homogeneous liquid phase for
pressure-drop and holdup calculations. Pipeline automatically detects the special
case of a single component fluid (for example, steam) and treats it appropriately.
Downstream and Upstream Integration
For downstream and upstream integration, the combination of the selections
made for Calculation Direction and Pipeline Flow Basis on the Setup
Configuration sheet determine which stream Pipeline will update. The following
table describes the available combinations. The next figure, Downstream and
Upstream Integration, defines the inlet and outlet stream and pressure
variables.
If you specify Calculation
Direction=
And Pipeline Flow Basis=
Then Pipeline updates the
Calculate Outlet Pressure
Reference inlet stream flow
Outlet stream only
Calculate Outlet Pressure
Use outlet stream flow
Outlet stream thermodynamic conditions
Inlet stream composition and flow
Calculate Inlet Pressure
Reference Outlet Stream Flow
Inlet stream only
Calculate Inlet Pressure
Use Inlet Stream Flow
Inlet stream thermodynamic conditions
Outlet stream composition and flow
Unit Operation Models
Version 10
6-45
Pressure
Changers
Inlet Stream
Outlet Stream
Inlet Pressure
Outlet Pressure
Downstream and Upstream Integration
Design Spec Convergence Loop
Use caution when using Pipeline inside a Design-Spec convergence loop. For
example, suppose you achieve a desired pipeline outlet pressure by varying the
flow rate to the pipeline. In this case, the flow rate variable might cause Pipeline to
predict negative pressures, resulting in convergence problems. You can avoid this
situation by doing one of the following:
• Keep the upper limit of the flow rate sufficiently low in the Design-Spec
• Perform an upstream integration from the known outlet pressure. Use
Calculate Inlet Pressure on the Setup Configuration sheet for this purpose.
Your Design-Spec will then need to manipulate the flow rate to achieve the
specified inlet pressure.
Erosional Velocity
Erosional velocity is the velocity of the fluid in the pipe over which the pipe
material will start to break off. The fluid is traveling so fast that it starts to strip
material from the walls of the pipe. In general usage, the flow rate should be below
this value.
You can specify the erosional velocity coefficient in the C-Erosion field on the
Segment Data dialog box on the Setup Connectivity sheet.
The erosional velocity is related to the erosional velocity coefficient by the
following equation:
vc =
c
ρ
Where:
vc
=
Erosional velocity in ft/sec
c
=
=
Erosional velocity coefficient (default=100)
Density in lb/cubic ft
ρ
6-46
Unit Operation Models
Version 10
Chapter 6
Methane Gas Systems
Gas systems consisting mostly of methane occur frequently in the dense-phase
region of wellbores and flowlines. In the dense-phase region, definable vapor and
liquid phases do not exist. Equation-of-state methods classify the dense-phase
material as either all vapor or all liquid. Significant differences in the predicted
fluid transport properties may occur, depending on whether you choose the vapor
or liquid state.
Experience has shown that gas system flow in the dense-phase region is best
modeled by using vapor-phase properties. For systems consisting of mostly
methane, where the pipeline conditions lie above the cricondenbar of the phase
envelope, specify Valid Phases = Vapor only on the Setup FlashOptions sheet.
Two-Phase Correlations
The following tables list the two-phase frictional pressure drop and holdup
correlations available.
Two-Phase Friction Factor Correlations
Pipe orientation
Inclination
Friction factor correlations
Horizontal
-2 deg to +2 deg
Beggs and Brill (BEGGS-BRILL)
Dukler (DUKLER)
Lockhart-Martinelli (LOCK-MART)
Darcy (DARCY)
†
User subroutine (USER-SUBR)
Vertical
+45 deg to +90 deg
Beggs and Brill (BEGGS-BRILL)
Orkiszewski (ORKI)
Angel-Welchon-Ros (AWR)
Hagedorn-Brown (H-BROWN)
Darcy (DARCY)
†
User subroutine (USER-SUBR)
Downhill
-2 deg to -90 deg
Beggs and Brill (BEGGS-BRILL)
Slack (SLACK)
Darcy (DARCY)
†
User subroutine (USER-SUBR)
Inclined
+2 deg to +45 deg
Beggs and Brill (BEGGS-BRILL)
Dukler (DUKLER)
Orkiszewski (ORKI)
Angel-Welchon-Ros (AWR)
Hagedorn-Brown (H-BROWN)
Darcy (DARCY)
†
User subroutine (USER-SUBR)
†
Unit Operation Models
Version 10
See ASPEN PLUS User Models.
6-47
Pressure
Changers
Two-Phase Liquid Holdup Correlations
Pipe orientation
Inclination
Liquid holdup correlations
Horizontal
-2 deg to +2 deg
Beggs and Brill (BEGGS-BRILL)
Eaton (EATON)
Lockhart-Martinelli (LOCK-MART)
Hoogendorn (HOOG)
Hughmark (HUGH)
†
User subroutine (USER-SUBR)
Vertical
+45 deg to +90 deg
Beggs and Brill (BEGGS-BRILL)
Orkiszewski (ORKI)
Angel-Welchon-Ros (AWR)
Hagedorn-Brown (H-BROWN)
†
User subroutine (USER-SUBR)
Downhill
-2 deg to -90 deg
Beggs and Brill (BEGGS-BRILL)
Slack (SLACK)
†
User subroutine (USER-SUBR)
Inclined
+2 deg to +45 deg
Beggs and Brill (BEGGS-BRILL)
Flanigan (FLANIGAN)
Orkiszewski (ORKI)
Angel-Welchon-Ros (AWR)
Hagedorn-Brown (H-BROWN)
†
User subroutine (USER-SUBR)
†
See ASPEN PLUS User Models.
Note
Some of the related information for the two-phase friction factor
and liquid holdup correlations was taken from "Two-Phase Flow
in Pipes" by James P. Brill and H. Dale Beggs, Sixth Edition,
Third Printing, January, 1991.
Beggs and Brill Correlation
Slip and flow regimes are considered with this method. Friction factor and
holdup correlations depend upon flow regime and pipe inclination. It is suitable
1
for all inclinations, including vertical flow downward.
Dukler Correlation
The Hughmark holdup method should be used with this pressure drop method.
The Dukler method was developed from field data using air-water mixtures in
2
1-inch pipes. It tends to over-predict frictional pressure drop. It is recommended
in a design manual published jointly by the AGA and API.
6-48
Unit Operation Models
Version 10
Chapter 6
Hagedorn-Brown Correlation
The Hagedorn-Brown correlation3 considers slip between phases, but flow regime
is not considered. It uses the same correlations for liquid holdup and friction
factor for all flow regimes. It is an old method that works well for conventional oil
wells. It is suitable for vertical upward flow, but not downward. It is generally
recommended for gas wells, and is based on data obtained from U.S. Gulf Coast
oil wells with 2-3/8 inch and 2-7/8 inch tubing.
Lockhart-Martinelli Correlation
The Lockhart-Martinelli correlation4 is one of the oldest pressure drop
correlations. It does not consider pressure drop due to acceleration. The method
treats the vapor and liquid phases separately and uses a correction factor to find
the 2-phase pressure gradient. Our implementation assumes turbulent gas and
liquid phase flow.
Orkiszewski Correlation
The Orkiszewsi correlation considers slip and flow regimes 5. The friction factor
and holdup correlation depend on the flow regime. It is suitable for vertical flow
upward, but not downward. It is generally reliable for oil wells. It may exhibit
problems for oil wells with high water cuts or high total gas to liquid ratios. It
can significantly underpredict pressure drop for higher rate and higher pressure
3
wells (Beggs and Brill/1984) .
Angel-Welchon-Ros Correlation
This Angel-Welchon-Ros method6,7 was developed for low gas-to-liquid ratio water
wells. It assumes no slip between the vapor and liquid phases when calculating
liquid holdup.
Slack Correlation
This method assumes a stratified flow regime, and should be used only for
downhill flow.
Eaton Correlation
The Eaton correlation8 holdup method was developed from data on 2- and 4-inch
pipes with a gas-water-crude mixture, and a 17-inch pipe with a gas-oil mixture.
It is often used with the Dukler frictional pressure drop correlation.
Unit Operation Models
Version 10
6-49
Pressure
Changers
Flanigan Correlation
The Flanigan correlation9 holdup method was developed from data taken in a
16-inch pipe. It calculates liquid holdup as a function of superficial gas velocity.
It is suitable for inclined flow.
Beggs and Brill Correlation Parameters
The following table lists the Beggs and Brill liquid holdup correlation
parameters.
Flow Regime
Name
Description
Segregated
BB1
BB2
BB3
Leading coefficient, A (default = 0.98)
Liquid volume fraction exponent, alpha (default = 0.4846)
Froude no. exp., beta (default = 0.0868)
Intermittent
BB4
BB5
BB6
Leading coefficient, A (default = 0.845)
Liquid volume fraction exponent, alpha (default = 0.5351)
Froude no. exp., beta (default = 0.0173)
Distributed
BB7
BB8
BB9
Leading coefficient, A (default = 1.065)
Liquid volume fraction exponent, alpha (default = 0.5824)
Froude no. exp., beta (default = 0.0609)
In addition, you can change the Beggs and Brill two-phase Friction Factor modifier,
BB10 (default = 1.0).
Closed-Form Methods
The following are closed-form methods:
•
•
•
•
•
•
•
6-50
Smith
Weymouth
AGA
Oliphant
Panhandle A
Panhandle B
Hazen-Williams
Unit Operation Models
Version 10
Chapter 6
Smith
The Smith method10 may be used for vertical dry gas flow. It should be considered
for gas wells with condensate-gas ratios less than 50 bbls/mcf, water-gas ratios
less than 3.5 bbls/mcf, and flow rates above the Turner predicted critical rate.
Smith does not model gas well loadup, and will significantly underpredict
wellbore pressure drop if loadup is actually occurring. Smith results must be
cross-checked against the Turner predicted critical rates to verify that the well is
unloaded. Smith also does not model condensation of water vapor in the wellbore.
Weymouth
The Weymouth11 horizontal gas flow equation was first published in 1912. It is
based on data taken on pipes with diameters from 0.8 inches to 11.8 inches. As a
result, it is most accurate for smaller pipes having a diameter less than 12
inches.
AGA
The AGA method12 may be used for horizontal gas applications.
Oliphant
The Oliphant method13 may be used for horizontal gas applications with
pressures between vacuum and 100 PSI.
Panhandle A
The Panhandle A method14 was developed by Panhandle Eastern for horizontal
gas flow in large diameter cross country gas transmission lines. As a result, it is
best used on lines having diameters larger than 12 inches. However, it does not
account for gas compressibility (Z-factor), and assumes completely turbulent
flow.
Panhandle B
The Panhandle B method14 is a revised version of the Panhandle A method for
horizontal gas flow and was developed by Panhandle Eastern. It is also called the
"Panhandle Eastern Revised Equation". It accounts for the gas compressibility
factor, and has revised exponents. This equation is not quite so Reynolds-Number
dependent as the Panhandle A equation, although it, too, is best for pipe
diameters of 12 inches or more.
Unit Operation Models
Version 10
6-51
Pressure
Changers
Hazen-Williams
The Hazen-Williams method14 was developed for the horizontal flow of water
When this method is used, the Hazen-Williams Coefficient must be specified in
place of the Segment Efficiency on the Connectivity Edit Dialog Box.
References
1. Beggs, H.D. and Brill, J.P., "A Study of Two-Phase Flow in Inclined Pipes,"
Journal of Petroleum Technology, May 1973, pp. 607-617.
2. Dukler, A.E., Wicks, M., and Cleveland, R.G, "Frictional Pressure Drop in
Two-Phase Flow: An Approach Through Similarity Analysis," AIChE Journal,
Vol. 10, No. 1, January 1964, pp. 44-51.
3. Beggs, H.D. and Brill, J.P., "Two-Phase Flow in Pipes," University of Tulsa
Short Course Notes, Third Printing, February 1984.
4. Lockhart, R.W. and Martinelli, R.C., "Proposed Correlation of Data for
Isothermal Two-Phase, Two-Component Flow in Pipes," Chemical
Engineering Progress, Vol. 45, 1949, pp. 39-48.
5. Orkiszewski, J., "Predicting Two-Phase Pressure Drops in Vertical Pipe,"
Journal of Petroleum Technology, June 1967, pp. 829-838.
6. Angel, R.R. and Welchon, J.K., "Low-Ratio Gas-Lift Correlation for CasingTubing Annuli and Large Diameter Tubing," API Drilling and Production
Practice, 1964, pp. 100-114.
7. Ros, N.C.J., "Simultaneous Flow of Gas and Liquid as Encountered in Well
Tubing," Journal of Petroleum Technology, October 1961, pp. 1037-1049.
8. Eaton, B.A. et al., "The Prediction of Flow Patterns, Liquid Holdup, and
Pressure Losses Occurring During Continuous Two-Phase Flow in Horizontal
Pipelines," Trans. AIME, June 1967, pp. 815-828.
9. Flanigan, Orin, "Effect of Uphill Flow on Pressure Drop in Design of TwoPhase Gathering Systems," Oil and Gas Journal, March 10, 1958, pp. 132141.
10. Smith, R. V., "Determining Friction Factors for Measuring Productivity of
Gas Wells," AIME Petroleum Transactions, Volume 189, 1950, pp. 73-82.
11. Weymouth, T.R., Transactions of the American Society of Mechanical
Engineers, Vol. 34, 1912.
12. "Steady Flow in Gas Pipes," American Gas Association, IGT Technical Report
10, Chicago, 1965.
6-52
Unit Operation Models
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Chapter 6
13. Oliphant, F.N., "Production of Natural Gas," Report of USGS, 1902.
14. Engineering Data Book, Volume II, Gas Processors Suppliers Association,
Tulsa, Oklahoma, Revised Tenth Edition, 1994.
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Unit Operation Models
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6-53
Pressure
Changers
6-54
Unit Operation Models
Version 10
Chapter 7
7
Manipulators
This chapter describes the models for stream manipulators. The models are:
Model
Description
Purpose
Use For
Mult
Stream multiplier
Multiplies component and total flow rates by
a factor
Scaling streams by a factor
Dupl
Stream duplicator
Copies inlet stream into any number of
duplicate outlet streams
Duplicating feed or internal
streams
ClChng
Stream class changer
Changes stream class between blocks and
flowsheet sections
Adding or deleting empty
solid substreams between
flowsheet sections
Use stream manipulators to modify stream variables for your convenience. They do
not represent real unit operations.
Unit Operation Models
Version 10
7-1
Manipulators
Mult
Stream Multiplier
Mult multiplies the component flow rates and the total flow rate of a material
stream by a factor you supply on the Mult Input Specifications sheet. For heat or
work streams, Mult multiplies the heat or work flow. Select the Heat (Q) and Work
(W) Mult icons from the Model Library for heat and work streams respectively.
Mult is useful when other conditions during the simulation determine the flow rate
of the stream. Mult does not maintain heat or material balances. For material
streams, the outlet stream has the same composition and intensive properties as
the inlet stream.
Flowsheet Connectivity for Mult
Material
Material
or
or
Heat
Heat
or
or
Work
Work
Material Streams
Inlet
One material stream
Outlet One material stream
Heat Streams
Inlet
One heat stream
Outlet One heat stream
Work Streams
Inlet
One work stream
Outlet One work stream
7-2
Unit Operation Models
Version 10
Chapter 7
The outlet stream must be the same type (material, heat, or work) as the inlet
stream.
Specifying Mult
The stream multiplication factor, specified on the Input Specifications sheet, is
the only input required for Mult. This factor has to be positive for material
streams. You can specify either a positive or negative factor for heat or work
streams, thus allowing a change in direction for the heat or work flow.
Use the Input Diagnostics sheet to override global values for the stream and
simulation message levels specified on the Setup Specifications Diagnostics
sheet.
This model has no dynamic features. For material stream multipliers the
pressure of each outlet stream is equal to the pressure of the inlet stream. The
flow rate of each outlet stream is equal to the flow rate of the inlet stream
multiplied by the factor as specified in the steady-state simulation.
Unit Operation Models
Version 10
7-3
Manipulators
Dupl
Stream Duplicator
Dupl copies an inlet stream (material, heat, or work) to any number of duplicate
outlet streams. It is useful for simultaneously processing a stream in different
types of units. Select the Heat (Q) and Work (W) Dupl icons from the Model
Library for heat and work streams respectively. Dupl does not maintain heat or
material balances.
Flowsheet Connectivity for Dupl
Material
Material
(any number)
Flowsheet for Duplicating Material Streams
Material Streams
Inlet
One material stream
Outlet At least one material stream, which is a copy of the inlet stream
Heat
(any number)
Heat
Flowsheet for Duplicating Heat Streams
Heat Streams
Inlet
One heat stream
Outlet At least one heat stream, which is a copy of the inlet stream
7-4
Unit Operation Models
Version 10
Chapter 7
Work
(any number)
Work
Flowsheet for Duplicating Work Streams
Work Streams
Inlet
One work stream
Outlet At least one work stream, which is a copy of the inlet stream
Specifying Dupl
Dupl requires no input parameters. Use the Input Diagnostics sheet to override
global values for the stream and simulation message levels specified on the Setup
Specifications Diagnostics sheet.
This model has no dynamic features. For material stream duplicators the
pressure of each outlet stream is equal to the pressure of the inlet stream. The
flow rate of each outlet stream is equal to the flow rate of the inlet stream.
Unit Operation Models
Version 10
7-5
Manipulators
ClChng
Stream Class Changer
ClChng changes the stream class between blocks and flowsheet sections. You can
use ClChng to add or delete empty solid substreams between flowsheet sections.
ClChng does not represent a real unit operation.
Flowsheet Connectivity for ClChng
Feed
Product
Material Streams
Inlet
One material feed stream
Outlet One material product stream
Specifying ClChng
ClChng does not require input. It copies substreams from the inlet stream to the
corresponding substreams of the outlet stream.
If a substream is
Then ClChng
In the outlet but not in the inlet
Initializes the substream to zero flow
In the inlet but not in the outlet
Drops the substream
ClChng does not maintain mass and energy balances if any dropped substream
contains material flow or heat/work information.
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7-6
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Unit Operation Models
Version 10
Chapter 8
8
Solids
This chapter describes the unit operation models for solids processing such as
crystallizers, solid crushers and separators, gas-solid separators, liquid-solid
separators, and solids washers. The models are:
Unit Operation Models
Version 10
Model
Description
Purpose
Use For
Crystallizer
Crystallizer
Produces crystals from solution based on
solubility
Mixed suspension, mixed product removal
(MSMPR) crystallizer
Crusher
Solids crusher
Breaks solid particles to reduce particle
size
Wet and dry crushers, primary and
secondary crushers
Screen
Solids separator
Separates solid particles based on particle
size
Upper and lower
dry and wet screens
FabFl
Fabric filter
Separates solids from gas using fabric
filter baghouses
Rating and sizing baghouses
Cyclone
Cyclone
separator
Separates solids from gas using gas
vortex in a cyclone
Rating and sizing cyclones
VScrub
Venturi scrubber
Separates solids from gas by direct
contact with an atomized liquid
Rating and sizing
venturi scrubbers
ESP
Electrostatic
precipitator
Separates solids from gas using an
electric charge between two plates
Rating and sizing dry electrostatic
precipitators
HyCyc
Hydrocyclone
Separates solids from liquid using liquid
vortex in a hydrocyclone
Rating or sizing hydrocyclones
CFuge
Centrifuge filter
Separates solids from liquid using a
rotating basket
Rating or sizing centrifuges
Filter
Rotary vacuum
filter
Separates solids from liquid using a
continuous rotary vacuum filter
Rating or sizing rotary vacuum filters
SWash
Single-stage
solids washer
Models recovery of dissolved components
from an entrained liquid of a solids stream
using a washing liquid
Single -stage solids washer
CCD
Counter-current
decanter
Models multi-stage recovery of dissolved
components from an entrained liquid of a
solids stream using a washing liquid
Multi-stage solids washers
8-1
Solids
This chapter is organized into the following sections:
8-2
Section
Models
Crystallizer
Crystallizer
Crushers and Screens
Crusher, Screen
Gas-Solid Separators
FabFl, Cyclone, VScrub, ESP
Liquid-Solid Separators
HyCyc, CFuge, Filter
Solids Washers
SWash, CCD
Unit Operation Models
Version 10
Chapter 8
Crystallizer
Mixed Suspension Mixed Product Removal Crystallizer
Crystallizer models a mixed suspension, mixed product removal (MSMPR)
crystallizer. It performs mass and energy balance calculations and optionally
determines the crystal size distribution.
Crystallizer assumes that the product magma leaves the crystallizer in
equilibrium, so the mother liquor in the product magma is saturated.
The feed to Crystallizer mixes with recirculated magma and passes through a
heat exchanger before it enters the crystallizer.
The product stream from Crystallizer contains liquids and solids. You can pass
this stream through a hydrocyclone, filter, or other fluid-solid separator to
separate the phases. Crystallizer can have an outlet vapor stream.
Flowsheet Connectivity for Crystallizer
Vapor
(optional)
Material
(any number)
Liquid
and Solid
Heat
(optional)
Heat
(optional)
Material Streams
Inlet
At least one material stream
Outlet One material stream for liquid and solid
One optional vapor stream
The outlet material stream should normally have at least one solid substream for
the crystals formed. If you select Calculate PSD from Growth Kinetics or UserSpecified Values on the PSD PSD sheet, each substream must have a particle
size distribution (PSD) attribute.
Unit Operation Models
Version 10
8-3
Solids
If electrolyte salts are formed based on electrolyte chemistry calculations, a solid
substream is not required when you select Copy from Inlet Stream on the PSD
PSD sheet.
If you do not use the vapor outlet stream, vapor products will be placed in the
liquid/solid product stream.
Heat Streams
Inlet
Any number of optional inlet heat streams
Outlet One optional outlet heat stream
If you give only one specification on the Setup Specifications sheet (temperature
or pressure), Crystallizer uses the sum of the inlet heat streams as a duty
specification. Otherwise, Crystallizer uses the inlet heat streams only to
calculate the net heat duty. The net heat duty is the sum of the inlet heat
streams minus the actual (calculated) heat duty.
You can use an optional outlet heat stream for the net heat duty.
Specifying Crystallizer
Crystallizer calculates crystal product flow rate and/or vapor flow, based on
solubility data you supply. Or you can specify the chemistry for electrolyte systems
instead of specifying solubility data.
You must specify two of the following:
• Crystallizer temperature
• Pressure or pressure drop
• Heat duty for the heat exchanger
• Crystal product flow rate
• Vapor flow
8-4
If you specify
Crystallizer calculates
Temperature and Pressure
Heat duty, crystal product flow rate, vapor flow rate
Pressure and Heat Duty
Temperature, crystal product flow rate, vapor flow rate
Temperature and Heat Duty
Pressure, crystal product flow rate, vapor flow rate
Pressure and Crystal Product Flow Rate
Temperature, heat duty, vapor flow rate
Temperature and Crystal Product Flow Rate
Pressure, heat duty, vapor flow rate
Pressure and Vapor Flow Rate
Temperature, heat duty, crystal product flow rate
Temperature and Vapor Flow Rate
Pressure, heat duty, crystal product flow rate
Unit Operation Models
Version 10
Chapter 8
Use the following forms to enter specifications and view results for Crystallizer:
Use this form
To do this
Setup
Specify operating parameters, crystal product and solubility parameters,
recirculation options, and flash convergence parameters
PSD
Specify PSD and crystal growth calculation parameters
Advanced
Specify component attributes, convergence parameters, and name and parameters
for user solubility subroutine
BlockOptions
Override global values for physical properties, simulation options, diagnostic
message levels, and report options for this block
Results
View summary of Crystallizer results, material and energy balance results, and
crystal size distribution results
Recirculation Specifications
You can model crystallizer with or without magma recirculation. To activate
recirculation, specify one of the following on the Setup Recirculation sheet:
• Recirculation fraction
• Recirculation flow rate
• Temperature change across heat exchanger
If you want to model a different crystallization process flowsheet, you can use
Crystallizer without recirculation, and use other blocks in the flowsheet to model
the recirculation.
Solubility
Crystallizer calculates the amount of crystal produced at its saturation (class II
crystallization). You can provide solubility data in one of these ways:
• Enter solubility data on the Setup Solubility sheet
• Reference an electrolyte chemistry (defined in the Reactions Chemistry
forms) in which the crystallizing component has been declared as a "salt"
• Supply a subroutine to provide the saturation concentration or to calculate
crystal product flow rate directly
Unit Operation Models
Version 10
8-5
Solids
Saturation Calculation Method
Choose the saturation calculation method from these options:
• Solubility method: Identify the crystallizing component as solid product on
the Setup Crystallization sheet. Enter solubility data on the Setup Solubility
sheet. This data applies to the reactant species in the mixed substream.
• Chemistry method: Create a new Chemistry on the Reactions Chemistry
object manager. Enter the crystallization as a salt reaction on the Reactions
Stoichiometry sheet. On the BlockOptions Properties sheet of the crystallizer,
enter the Chemistry ID and select True Species for Simulation Approach. You
must specify the crystallizing component as a Salt Component ID on the
Setup Specifications sheet.
• User Subroutine method: Identify the crystallizing component on the Setup
Crystallization sheet and the solubility data basis and solvent ID on the
Setup Solubility sheet. Specify a user subroutine to calculate saturation
concentration or crystallizer yield on the Advanced UserSubroutine sheet.
In general, when using the Solubility method, you should blank out the
Chemistry ID field on the BlockOptions Properties sheet. If you specify chemistry
when using the Solubility method, the chemistry must not contain the
crystallizing component.
Supersaturation
The degree of supersaturation is the driving force for crystallization processes.
Supersaturation is defined as:
S = C − Cs
Where:
S
=
3
Supersaturation (kg of solute/m of solution)
C
=
Solute concentration
Cs
=
Solute saturation concentration
Because the crystallizer model assumes that the product magma is in phase
equilibrium, this equation is not used. It is provided only for reference.
8-6
Unit Operation Models
Version 10
Chapter 8
Crystal Growth Rate
The crystal growth rate can be expressed as a function of the degree of
supersaturation (S):
Go = kg S n
Where:
Go
=
Growth rate dependence on supersaturation (m/s)
kg
=
Growth rate expression coefficient
n
=
Exponent
This expression is provided as background information only.
In ASPEN PLUS, G o is calculated implicitly from the third moment of the
population density.
For a size-dependent growth rate, the growth rate is a function of crystal
length (L):
G = G o (1 + γL )α
For 0 ≤ α ≤ 1
Where:
γ
=
Constant
α
=
Exponent
If the growth rate is independent of crystal size, then the values for γ and α are
set to zero.
Unit Operation Models
Version 10
8-7
Solids
Crystal Nucleation Rate
The overall nucleation rate can be expressed as the sum of specific contributing
factors (Bennett, 1984)1:
B o = kb G i MTj R k
Where:
Bo
=
Overall nucleation rate
i, j, k
=
Exponents
kb
=
Overall nucleation rate expression coefficient
MT
=
Magma density = P/q (kg/m )
G
=
Crystal growth rate
R
=
Impeller rotation rate (revs/s)
P
=
Crystal mass flow rate (kg/s)
q
=
3
Volumetric flow rate of slurry in the discharge (m /s)
3
Population Balance
If the feed stream contains no crystals, the population balance for a well-mixed
continuous crystallizer can be written as (Randolph and Larson, 1988) 2:
d (nG ) qn
+
=0
dL
V
Where:
8-8
G
=
Crystal growth rate
n
=
3
Population density (no. /m /m)
L
=
Crystal length (m)
V
=
Crystallizer volume (m )
q
=
3
Volumetric flow rate of slurry in the discharge (m /s)
3
Unit Operation Models
Version 10
Chapter 8
The boundary condition is n = n o at L = 0, where n o = B o / G is the population
density of nuclei. For a constant crystal growth rate, the population density is:
−L
n( L) = n o exp  
 Gτ 
where τ = V / q is the crystal residence time.
PSD Statistics
ASPEN PLUS calculates the crystal size distribution statistics once you select
the Calculate PSD from Growth Kinetics option on the PSD PSD sheet.
Properties of the distribution may be evaluated from the moment equations. The
j-th moment of the particle size distribution is defined as:
∞
m j = ∫ Lj n( L) dL
0
The system reports several crystal size distribution statistics, measured on a
volume or mass basis, including:
• Mean size
• Standard deviation
• Skewness
• The coefficient of variation (expressed as a percentage)
The mean size is the mass-weighted average crystal size, as determined by the
ratio of the fourth moment to the third moment, as follows:
L=
m4
m3
The skewness of a symmetric size distribution about the mean is zero. Negative
values of skewness indicate the distribution is skewed toward the presence of
small crystals. Positive values of skewness indicate the crystal distribution
contains an excess of large crystals.
Skewness is defined as
Unit Operation Models
Version 10
∑ f ( x − mean) 3
(standard deviation) 3
8-9
Solids
The system uses the coefficient of variation to calculate variation related to the
cumulative volume (or mass) distribution.
Coeff − Var(%) = 100
pd @ (.84) − pd @ (.16)
2 pd @ (.50)
where pd@ (x) is the particle diameter corresponding to fraction x of the
cumulative volume (or mass) distribution. The fraction can be entered as the
Fractional Coefficient on the PSD CrystalGrowth sheet; otherwise, it defaults to
.16.
Calculating PSD
The magma density, defined as total mass of crystals per unit volume of slurry,
can be obtained from the third moment:
∞
M T = ρ c k v ∫ L3 n( L) dL
0
Where:
ρc
=
Density of crystal (kg/m )
kv
=
Volume shape factor of the crystal
3
Since:
−L
n( L) = n o exp   ,
 Gτ 
no =
Bo
,
Go
and B o = kb G i MTj R k
these equations can be substituted into the third moment of population density,
yielding:
M T = ρc k v ∫
∞
0
Gi
− L
L kb o M Tj R k exp 
dL
G
 Gτ 
3
where G = G o (1 + γL )α .
Because L is made discrete by the increments of the particle size distribution, the
equations can be solved for G o .
8-10
Unit Operation Models
Version 10
Chapter 8
References
1. Bennett, R.C. "Crystallization from Solution," Perry’s Chemical Engineers’
Handbook, 6th Ed., pp. 19.24-19.40, McGraw-Hill, 1984.
2. Randolph, A.D. and Larson, M.A., Theory of Particulate Processes, 2nd Ed.,
Academic Press, 1988.
Unit Operation Models
Version 10
8-11
Solids
8-12
Unit Operation Models
Version 10
Chapter 8
Crusher
Solids Crusher
Use Crusher to simulate the breaking of solid particles.
Crusher can model the wet or dry continuous operation of:
• Gyratory/jaw crushers
• Single-roll crushers
• Multiple-roll crushers
• Cage mill impact breakers
Crusher assumes the feed is homogeneous. The breaking process creates
fragments with the same composition as the feed. Crusher calculates the power
required for crushing, and the particle size distribution of the outlet solids
stream.
Crusher does not account for the heat produced by the breaking process.
Flowsheet Connectivity for Crusher
Feed
Crushed Solids
Work (optional)
Material Streams
Inlet
One material stream with at least one solids substream
Outlet One material stream
Each solids substream must have a particle size distribution (PSD) attribute.
Unit Operation Models
Version 10
8-13
Solids
Work Streams
Inlet
No inlet work streams
Outlet One work stream containing the calculated power requirement
(optional)
Specifying Crusher
Use the Input Specifications and Grindability sheets to specify operating
conditions. You must enter the type of crusher and maximum particle diameter on
the Input Specifications sheet. You must also specify the Bond work index or the
Hardgrove grindability index for each solids substream on the Grindability sheet.
The outlet flow rate of crushed product in the k-th size interval is:
Pk (β) = ∑
j
∑
i
Fij Si (β) Bik (β) + ∑ [1 − Sk (β)]Fkj
j
Where:
Bik
=
Breakage function. Fraction of particles originally in size
interval i that end up in size interval k
Fij
=
Flow rate of feed in the size interval i and particle size
distribution j
Pk
=
Flow rate of solid in size interval k
Si
=
Selection function. Fraction of feed particles in size interval i
to be crushed at the outlet diameter β
Sk
=
Selection function. Fraction of feed particles in size interval
k to be crushed at the outlet diameter β
β
=
Crusher outlet diameter (Maximum Particle Diameter field)
i
=
Size interval counter within a PSD
j
=
PSD counter for multiple size distribution
If the inlet stream contains no liquid, then Crusher assumes dry crushing, and
power requirements increase by 34%.
8-14
Unit Operation Models
Version 10
Chapter 8
You can enter tabular values for the breakage ( Bik ) function on the Input
BreakageFunction sheet and for the selection ( Si ) function on the Input
SelectionFunction sheet, or let Crusher use the built-in tables (U.S. Bureau of
Mines, 1977) (see the following two tables).
Breakage Function Correlations B ik (β)
Feed size/solids
outlet diameter <1.7
Feed size/solids outlet diameter >1.7
Ratio of product size to
feed size
Multiple roll
crusher
Gyratory/jaw
crusher
Single roll
crusher
Cage mill
crusher
All crushers
1.0
1.0
1.0
1.0
1.0
1.0
0.8308
0.95
0.95
0.96
0.84
0.8972
0.5882
0.85
0.85
0.79
0.50
0.7035
0.4176
0.65
0.70
0.45
0.32
0.54
0.2065
0.35
0.35
0.20
0.15
0.2952
0.1041
0.22
0.20
0.10
0.052
0.1564
0.0522
0.14
0.19
0.05
0.019
0.0805
0.0368
0.11
0.17
0.03
0.011
0.0572
0.026
0.09
0.12
0.02
0.0066
0.0406
0.0131
0.03
0.08
0.0
0.002
0.0206
0.0
0.0
0.0
0.0
0.0
0.0
Selection Function Correlations, Si (β)
Ratio of feed size to
outlet diameter
Primary crusher
Secondary crusher
0.95
0.5695
0.7693
0.9
0.3817
0.6962
0.8
0.1716
0.5695
0.7
0.0771
0.4667
0.6
0.0347
0.3817
0.5
0.0156
0.3128
0.4
0.007
0.256
0.3
0.00315
0.2096
0.2
0.00145
0.1716
continued
Unit Operation Models
Version 10
8-15
Solids
Ratio of feed size to
outlet diameter
Primary crusher
Secondary crusher
0.1
0.0006
0.1405
0.05
0.00043
0.1271
0.001
0.00026
0.1153
0.0001
0.00026
0.1148
If the ratio of feed size to outlet diameter is greater than 1.0, then Si (β) = 0.85 .
Use the following forms to enter specifications and view results for Crusher:
Use this form
To do this
Input
Enter crusher operating parameters, the Bond work index or the Hardgrove
grindability index, and user-specified selection and breakage functions
BlockOptions
Override global values for physical properties, simulation options, diagnostic
message levels, and report options for this block
Results
View summary of Crusher results and material and energy balances
Primary and Secondary Crushers
Crushing operations are usually performed in stages. The reduction ratio is the
ratio of the maximum diameter of feed particles to product particles. The
reduction ratio in crushers ranges from 3 to 6 per stage. Feed particles are fed to
the primary crushers. Outlet particles from the primary crushers are reduced
further by the secondary crushers.
Crusher uses different correlations for primary and secondary crushers. Use the
Operating Mode field on the Input Specifications sheet to enter the type of
crusher.
To improve the efficiency of multistage crushers, use screens between stages.
Power Requirement
The following equation determines the power requirement for Crusher:
POWER =
8-16
(
0.01
)
X F − X p × BWI × FLOWT
XF × Xp
Unit Operation Models
Version 10
Chapter 8
Where:
POWER
=
Required power (Watt)
XF
=
Diameter larger than 80% of feed particle mass (m)
XP
=
Diameter larger than 80% of product particle mass (m)
BWI
=
Bond work index
FLOWT
=
Total solids mass flow rate (kg/s)
For dry crushing, power requirement increases by 34%.
If X p is less than 70 micrometers, then the power required is further adjusted
by:
 10.6 × 10 −6 + X p 

POWER = POWER 
Xp
1145
.


Bond Work Index
The Bond equation defines the work consumed in size reduction:
XF −
E = Ei
XF
XP
100
XP
Where:
E
=
Work required to reduce a unit weight of feed with 80%
passing a diameter X F microns to a product with 80%
passing a diameter X p microns
Ei
=
Bond work index, that is, the work required to reduce a unit
weight from a theoretical infinite size to 80% passing a
diameter of 100 micrometers
The Bond work index is a semi-empirical parameter that depends on the properties
of the material processed. The Bond work indices have been measured
experimentally for a wide range of materials, and are available in Perry’s Chemical
Engineers’ Handbook. Use experimental values with caution. The Bond work index
is also a function of the:
•
•
Unit Operation Models
Version 10
Particle size for non-homogeneous materials
Efficiency of the size-reduction equipment
8-17
Solids
Hardgrove Grindability Index
The Hardgrove grindability index indicates the difficulty of grinding coal based on
physical properties such as hardness, fracture, and tensile strength. The
Hardgrove grindability index can be approximated by:
BWI =
435
HGI 0.91
Where:
BWI
=
Bond work index
HGI
=
Hardgrove grindability index
The HGI for some United States coals are available in Perry’s Chemical
Engineers’ Handbook.
References
1. Computer Simulation of Coal Preparation Plants, U.S. Bureau of Mines,
Grant No. GO-155030, Final Report August (1977).
th
2. Perry’s Chemical Engineers’ Handbook, 6 Ed., McGraw Hill, 1984.
8-18
Unit Operation Models
Version 10
Chapter 8
Screen
Solids Separator
Screen simulates the separation by screens of a mixture containing various sizes of
solid particles into particles that have more uniform sizes than the original
mixture. You can use Screen to model wet or dry operations and upper or lower
level screens.
Screen calculates the separation efficiency of the screen from the size of screen
openings you specify.
Flowsheet Connectivity for Screen
Overflow
Feed
Underflow
Material Streams
Inlet
One material stream with at least one solids substream
Outlet One material stream for particles that do not pass through the
screen (overflow)
One material stream for particles that pass through the screen
(underflow)
Each solids substream must have a particle size distribution attribute.
Specifying Screen
Use the Input Specifications sheet to enter:
•
•
•
•
Unit Operation Models
Version 10
Screen size opening
Operating level (Upper or Lower)
Operating mode (Wet or Dry)
Entrainments
8-19
Solids
You can also use the Input SelectionFunction sheet to enter the following
functions:
• Selection function ( Si ) (optional)
• Separation strength (optional)
Use the following forms to enter specifications and view results for Screen:
Use this form
To do this
Input
Specify screen parameters, operating conditions, and user-specified screen
separation strength and selection functions
BlockOptions
Override global values for physical properties, simulation options, diagnostic
message levels, and report options for this block
Results
View summary of Screen results and material and energy balances
Upper and Lower Level Screens
You can specify the operating level as Upper or Lower. The most efficient
configuration is a multiple-deck screen with a series of Screen blocks. The inlet
stream is fed over the upper level screen. The underflow from the upper level
screens is fed over the lower level screens. Screen uses different correlations for
upper and lower level screens.
Screen calculates the flow rate of the screen overflow stream as:
Fo = ∑ Si ∑ Fij
i
j
Where:
Si
=
Selection function. The fraction of feed particles in size range
i that passes over the screen into the overflow product
Fij
=
Flow rate of feed in size range i and particle size distribution
attribute j
Selection Function and Separation Strength
Screen calculates the selection function for a certain size interval as:
Si =
exp A 1 − d p S o
Si = 1
8-20
[(
1
)]
for d p < S o
for d p ≥ S o
Unit Operation Models
Version 10
Chapter 8
Where:
dp
=
Particle diameter
So
=
Size of screen opening
A
=
Separation strength
The default value of the screen separation strength, A, is a function of the size of
the screen opening. Screen has four built-in functions (U.S. Bureau of Mines,
1977)1 for all possible combinations of screen types (see the table, Screen Separation
Strength/Screen Size Correlation):
• Upper level dry
• Lower level dry
• Upper level wet
• Lower level wet
You can enter your own separation strength value, separation strength correlation
or selection function correlation on the Input SelectionFunction sheet. Screen then
uses these selection function values for its mass balance calculation.
Screen Separation Strength/Screen Size Correlation
Size of screen
opening (m)
Dry, upper level
Dry, lower level
Wet, upper level
Wet, lower level
0.457
60
60
60
60
0.152
20
20
20
20
0.038
8
8
9
9
0.0095
8
6
8.5
6.6
0.00635
5
4
5.5
4.5
0.00236
3
2
3.5
2.3
0.00059
0.7
0.7
0.8
0.8
0.00042
0.6
0.6
0.7
0.7
0.000295
0.5
0.5
0.55
0.55
Separation Efficiency
The separation efficiency of the screen is calculated as the ratio of the mass flow
rate of the underflow to the fraction of the feed flow rate containing particles
smaller than the screen openings.
Unit Operation Models
Version 10
8-21
Solids
References
Computer Simulation of Coal Preparation Plants, U.S. Bureau of Mines, Grant
No. GO-155030, Final Report August (1977).
8-22
Unit Operation Models
Version 10
Chapter 8
FabFl
Fabric Filter
FabFl is a gas-solids separator model used to separate an inlet gas stream
containing solids into a solids stream and a gas stream carrying the residual
solids. Use FabFl to simulate or design baghouse units in which solid particles
are separated from the inlet gas stream. A baghouse consists of a number of cells
in which vertically-mounted cylindrical fabric filter bags operate in parallel.
You can use FabFl to rate or size baghouses.
Flowsheet Connectivity for FabFl
Gas (overflow)
Feed
Solids (underflow)
Material Streams
Inlet
One material stream with at least one solids substream
Outlet One overflow stream for the cleaned gas
One underflow stream for the solids particles
Each solids substream must have a particle size distribution (PSD) attribute.
Solids may be entrained in the overflow, based on the separation efficiency.
Specifying FabFl
Use the Input Specifications sheet to specify operating conditions and baghouse
characteristics.
Unit Operation Models
Version 10
For these calculations
Set Mode=
And number of cells is
Rating
Simulation
Specified
Sizing
Design
Calculated
8-23
Solids
For sizing or rating calculations:
If you enter
FabFl calculates
Maximum allowable pressure drop
Filtration time
Filtration time
Pressure drop
Use the following forms to enter specifications and view results for FabFl:
Use this form
To do this
Input
Enter operating conditions, baghouse characteristics, and separation
efficiency
BlockOptions
Override global values for physical properties, simulation options,
diagnostic message levels, and report options for this block
Results
View summary of FabFl results and material and energy balances
Operating Ranges
FabFl uses empirical models because no theoretical models exist. Expect unreliable
results when operating conditions exceed the ranges of the experimental data on
which the models are based. Your data should fall within these ranges:
•
•
Diameter of solid particles between 10 −7 to 10 −4 m (0.1 to 100 micrometers)
Maximum gas velocity through the cloth between 0.1 and 0.2 m/s (20 to 40
ft/min)
Filtering Time
When rating fabric filters, FabFl calculates the filtering time t as:
t=
∆Pf − ∆Pi
CKVo2
Where:
8-24
∆Pf
=
Final pressure drop across collected dust and filter cloth
∆Pi
=
Pressure drop of the clean bag
C
=
Dust concentration
K
=
Dust resistance coefficient
Vo
=
Air to cloth ratio (gas velocity through the cloth)
Unit Operation Models
Version 10
Chapter 8
The air to cloth ratio Vo is:
Vo =
Q
( N cell − N shake ) Abag N bag
Where:
Q
=
Volumetric flow rate of the gas
N cell
=
Number of cells
N shake
=
Number of cells being cleaned
Abag
=
Total filter surface of all bags
N bag
=
Number of bags per cell
Resistance Coefficient
The resistance coefficient K depends on the particle size and nature of solid
particles. In an industrial-scale baghouse, the resistance coefficient also varies
with time and bag position. If specific resistance coefficients are not available,
the following values can be used as rough estimates 1:
Dust particle diameter
−6
m)
( 10
Resistance coefficients
2
[Pa/(kg/m ) (m/s)]
Less than 20
300,000
20 to 90
60,000
Greater than 90
15,000
These coefficients were determined from a small fabric filter. The filter has an air
flow of 2 ft 3 / min through 0.2 ft 2 of cloth area (a filtering gas velocity of 10
ft/min). The pressure drop across the bag and dust was 8 inches of H 2 O .
An approximation for the resistance coefficient 2 is:
K=
1000
d p2
Where:
dp
=
The average particle size in microns
The units for K are (inches of water)/(lbs dust/ft 2 of area)(ft/min velocity).
Unit Operation Models
Version 10
8-25
Solids
Separation Efficiency
The overall separation efficiency of the baghouse is:
∑∑Sη
ij
ηo =
j
ij
i
Total inlet flow rate of solids
=
flow rate of solids removed from the inlet
total inlet flow rate of solids
Where:
Sij
=
Flow rate of solid j in size increment i
In FabFl, the separation efficiency is a function of the particle diameter of the
solids. For large particles (greater than 10 micrometers in diameter), fractional
collection efficiency ( ηi ) is 1.0. For particles smaller than 10 micrometers,
efficiency decreases rapidly.
ηi
When
1.0
( d p ) av > 10 µm
0.0011 ( d p ) av + 0.989
1µm < (d p ) av < 10 µm
0.495 ( d p ) av + 0.495
( d p ) av < 1µm
You also can enter efficiency as a function of particle sizes on the Input Efficiency
sheet to override the built-in correlations.
References
1. Air Pollution Engineering Manual, Public Health Service Publication No. 999AP-40, pp. 106-135, Washington D.C., DHEW (1967).
2. Billings, C.E. and Wilder, J., Handbook of Fabric Filter Technology, Vol. I,
NIIS PB 200648.
8-26
Unit Operation Models
Version 10
Chapter 8
Cyclone
Cyclone Separator
Cyclone separates an inlet gas stream containing solids into a solids stream and a
gas stream carrying the residual solids.
Use Cyclone to simulate cyclone separators in which solid particles are removed by
the centrifugal force of a gas vortex. You can use Cyclone to size or rate cyclone
separators. In simulation mode, Cyclone calculates the separation efficiency and
pressure drop from a user-specified cyclone diameter.
In design mode, the cyclone geometry is calculated to meet the user-specified
separation efficiencies and maximum pressure drop. In both calculation modes,
the particle size distributions of the outlet solids streams are determined.
Flowsheet Connectivity for Cyclone
Gas
Feed
Solids
Material Streams
Inlet
One material stream with at least one solids substream
Outlet One stream for the cleaned gas
One stream for the solids
Each solids substream must have a particle size distribution (PSD) attribute.
Unit Operation Models
Version 10
8-27
Solids
Specifying Cyclone
Use the Input Specifications sheet to specify the type of cyclone and operating
conditions.
Use the Input Dimensions sheet to enter cyclone dimensions, or use the Input
Ratios sheet to enter ratios of cyclone dimensions.
To perform
these calculations
Specify
Cyclone calculates
Rating
Simulation mode
Cyclone Diameter
Number of Cyclones
Separation efficiency
Pressure drop
Sizing
Design mode
Separation Efficiency
Maximum Pressure
Drop (optional)
Maximum Number of
Cyclones (optional)
Cyclone diameter
Number of cyclones
For rating calculations, if you specify Type=User-Specified or User-Specified
Ratios, you can specify cyclone dimensions on the Input Dimensions or Input
Ratios sheets.
For design calculations, you must also enter the Maximum Number of Cyclones
in parallel. If either of the following occurs, Cyclone calculates the number of
cyclones in parallel:
• The efficiency of a single cyclone is less than the required separation efficiency.
• The calculated pressure drop exceeds the maximum pressure drop specified.
Use the following forms to enter specifications and view results for Cyclone:
8-28
Use this form
To do this
Input
Enter cyclone specifications, dimensions, dimension ratios, separation efficiencies,
and solids loading
BlockOptions
Override global values for physical properties, simulation options, diagnostic
message levels, and report options for this block
Results
View summary of Cyclone results and material and energy balances
Unit Operation Models
Version 10
Chapter 8
Separation Efficiency
The overall separation efficiency is:
ηm =
flow rate of solids removed from the inlet
total inlet flow rate of solids
ηm =
Co − Ci Qo Co − E
E
=
= 1−
Co
Qo Co
Qo Co
Where:
Co
=
Concentration of solids in inlet gas
Ci
=
Concentration of solids in outlet cleaned gas
Qo
=
Inlet gas flow rate
E
=
Outlet emission rate of solids in the cleaned gas
Cyclone attains higher separation efficiencies with particles that are 5 to 10
microns or greater in diameter. For particles smaller than 5 microns, Cyclone
efficiency decreases. Even with large particles, it is difficult to obtain a collection
efficiency greater than 95%.
If you enter a design efficiency higher than 95%, use either:
• Multi-stage cyclones
• Cyclone as a precleaner, followed by other collectors
You can specify the Efficiency Correlation field on the Input Specifications sheet. If
Efficiency Correlation=User-Specified, you can enter efficiency as a function of
particle sizes on the Input Efficiency sheet.
Operating Ranges
Cyclone uses correlations that are semi-empirical models. Do not expect
satisfactory accuracy when the specified conditions exceed the ranges of
experimental data from which the models were developed. In general, the pressure
drop should be less than 2500 N / m 2 (10 inches of H 2 O ). The operating pressure
should not exceed atmospheric pressure. The inlet gas velocity should be in the
range of 15 to 27 m/s (50 to 90 ft/s).
The Leith and Licht efficiency correlation is accurate for inlet velocities
approximately 25 m/s (80 ft/s). The correlation overestimates the separation
efficiency at high velocities.
Unit Operation Models
Version 10
8-29
Solids
The Shepherd and Lapple correlation is accurate for particle sizes of 5 to 200
microns. This correlation tends to overestimate the efficiency of large particles
(greater than 200 microns). The Shepherd and Lapple correlation also
underestimates the efficiency of fine particles (smaller than 5 microns).
Pressure Drop
Cyclone calculates the pressure drop (Shepherd and Lapple, 1939)1 as:
∆P = 0.0030 ρ f U t2 N h
Where:
ρf
=
Density of the fluid
Ut
=
Inlet gas velocity
Nh
=
Inlet velocity speeds
Use the Input SolidsLoading sheet to enter values to correct for solids loading.
The inlet velocity speed, N h , is:
Nk = K
ab
De2
Where:
K
=
Dimensionless ratio
a
=
Inlet height of the cyclone
b
=
Inlet width of the cyclone
De
=
Outlet diameter of the cyclone
The dimensionless ratio K is:
K=
8(Vs + Vnl / 2)
abDc
Where:
8-30
Vs
=
Annular shaped volume above the exit duct to midlevel of
the entrance duct
Vnl
=
Effective volume of the cyclone calculated by natural length l
Dc
=
Body diameter of the cyclone
Unit Operation Models
Version 10
Chapter 8
The annular shaped volume Vs above the exit duct to midlevel of the entrance duct is:
Vs =
π( s − a / 2 ) ( Dc2 − De2 )
4
Cyclone Diameter
Cyclone calculates the diameter of the body of the cyclone Dc as:
 Qρ2f

(1 − b / Dc )
Dc = 0.0502 
×
2.2 
 µ(ρ p − ρ f ) ( a / Dc ) (b / Dc ) 
0 . 454
Where:
Q
=
Overflow gas flow rate
ρf
=
Density of the fluid
µ
=
Viscosity of gas fluid
ρp
=
Density of the particles
In this empirical equation, units are:
Unit type
Unit
Length
Feet
Mass
Pounds
Time
Seconds
Dimension Ratios
Use the Input Dimensions sheet to enter the dimensions of a cyclone when
Mode=Simulation and Type=User-Specified. If you specify Type=User-Specified
Ratios, you can use the Input Ratios sheet to enter dimension ratios (dimension /
cyclone diameter) for a cyclone.
Unit Operation Models
Version 10
8-31
Solids
The dimension ratios and some default values of the two built-in configurations
are:
Dimension ratio (dimension/cyclone diameter)
Type = High efficiency
Type = Medium efficiency
Cyclone diameter
1.0
1.0
Inlet height
0.5
0.75
Inlet width
0.2
0.375
Length of overflow
0.5
0.875
Diameter of overflow
0.5
0.75
Length of cone section
1.5
1.50
Overall length
4.0
4.0
Diameter of underflow
0.375
0.375
Number of gas turn in cyclone
7.0
4.0
Maximum diameter (m)
1.5
5.0
Minimum diameter (m)
0.1
0.1
Cyclone calculates the dimensions of the built-in cyclones using these ratios and
the cyclone diameter you specify. The built-in configurations (Type=High or
Medium) may not be the best designs. It is recommended that you enter
dimensions or dimension ratios, if available.
Vane Constant
Use the Vane Constant field on the Input Specifications sheet to specify the vane
constant. The vane constant varies with the configuration of the inlet duct. In the
common configuration, the inlet duct terminates at the wall of the cyclone. The
vane constant is 16. To reduce friction loss, extend the duct into the interior of the
cyclone. When the duct is in the middle of the cyclone separator, the vane constant
is 7.5.
Cyclone Dimensions
The next figure shows the Cyclone geometry. The table following the figure shows
the Cyclone dimensions.
8-32
Unit Operation Models
Version 10
Chapter 8
Dc
b
De
s
a
h
H
B
Cyclone Geometry
The Cyclone design configurations are:
Unit Operation Models
Version 10
Term
Description
High efficiency
High throughput
Dc
Body diameter
1.0
1.0
a
Inlet height
0.5
0.75
b
Inlet width
0.2
0.375
s
Outlet length
0.5
0.875
De
Outlet diameter
0.5
0.75
h
Cylinder height
1.5
1.50
H
Overall height
4.0
4.0
B
Dust outlet diameter
0.375
0.375
8-33
Solids
Solids Loading Correction
The feed concentration of solids affects the separation efficiency. Concentration
higher than 1.0 gm m 3 usually leads to higher efficiency. Smolik (1975)2, 3
presented the following relationship between the efficiency and solids
concentration:
1 − ET*  c * 
= 
1 − ET  c 
a
Where:
c*
=
"Low loading" solids concentration, 1.0 gm / m 3
c
=
Solids concentration
E *T
=
Total efficiency
ET
=
"Low loading" total efficiency
α
=
Exponent
Smolik gives values of α = 0.182. This form can only serve as a guide, because the
effect of dust concentration depends on the nature of the solids, the humidity of the
gas, and many other factors that do not figure in the existing correlations.
The actual pressure drops with dust-laden gases are normally lower than those
obtained with clean gas. Smolik gives an empirical correlation for the effect of
feed concentration on pressure in the form:
∆p *
= 1 − βc γ
∆p
Where:
c
=
Solids concentration in the feed, g / m 3
∆p *
=
Pressure drop
∆p
=
Pressure drop with clean gas
β ,γ
=
Constants depending on the material
Smolik gives values of β = 0.02 and γ 0.6.
8-34
Unit Operation Models
Version 10
Chapter 8
References
1. Shepherd, G.B. and Lapple, C.E., "Flow Pattern and Pressure Drop in
Cyclone Dust Collectors," Industrial and Engineering Chemistry, 31, pp. 972984 (1939).
2. Smolik, J. et al., Air Pollution Abatement, Part I. Scriptum No. 401-2099 (in
Czech). Technical University of Prague (1975). Quoted by Svarovsky, L.,
"Solid-Gas Separation," Handbook of Powder Technology, Williams, J.C. and
Allen, T. (Eds.), Amsterdam: Elsevier, 1981.
3. Svarovsky, L., Solid-Gas Separation, Chapter 3, New York: Elsevier, 1981.
Unit Operation Models
Version 10
8-35
Solids
VScrub
Venturi Scrubber
Use VScrub to simulate venturi scrubbers.
Venturi scrubbers remove solid particles from a gas stream by direct contact with
an atomized liquid stream.
You can use VScrub to rate or size venturi scrubbers.
Flowsheet Connectivity for VScrub
Liquid
Gas
Feed Gas
with Solids
Liquid and
Solids
Material Streams
Inlet
One stream for solids with at least one solids substream
One stream for the atomized liquid
Outlet One stream for the cleaned gas
One stream for the liquid with solid particles
8-36
Unit Operation Models
Version 10
Chapter 8
Specifying VScrub
Use the VScrub Input Specifications sheet to specify operating conditions and
parameters for sizing or rating calculations.
To perform these
calculations
Set Mode =
Enter scrubber
VScrub calculates
Rating
Simulation
Throat Diameter
Throat Length
Separation efficiency
Pressure drop
Design
Separation efficiency
Liquid flow rate
Throat diameter
Throat length
Pressure drop
†
Sizing
†
Because the required liquid flow rate is varied to meet the efficiency, the material balance is
not satisfied if the calculated liquid flow rate is different from the rate you enter.
In both modes, VScrub also calculates the particle size distributions of the solids in
the outlet streams.
VScrub assumes that the liquid stream is introduced before or at the beginning of
the scrubber throat. It also assumes the separation of the solid particles from the
gas stream occurs only at the scrubber throat.
Use the following forms to enter specifications and view results for VScrub:
Unit Operation Models
Version 10
Use this form
To do this
Input
Specify operating parameters and throat operating conditions
Block Options
Override global values for physical properties, simulation options, diagnostic
message levels, and report options for this block
Results
View summary of VScrub results and material and energy balances
8-37
Solids
Pressure Drop
VScrub calculates the pressure drop (Yung, S. et al., 1977)1 ∆ p across the throat of
the scrubber as:
∆p =
2ρl Vt 2
gc
(
 Ql 
  1 − x 2 + x 4 − x 2
 Qg 
)
Where:
ρl
=
Density of the liquid
Vt
=
Relative velocity of gas to liquid at the throat
gc
=
Conversion factor in Newton’s law of motion
Ql
Qg
=
Liquid to gas volume flow rate
x
=
Dimensionless throat length defined by:
3lt C D ρ g
x=
+1
16 Dd ρl
lt
=
Throat length
CD
=
Drag coefficient, as a function of the Reynolds number
(Dickinson and Marshall, 1968)2 N Re .
Where:
C D = .22 +
24
0.6
(1 + 0.15 N Re
)
N Re
ρg
=
Density of the gas
ρl
=
Density of the liquid
Dd
=
Drop diameter (Sauter mean), defined by (Nukiyama, S.,
Tanasawa, Y. 1939)3:
585  σ l 
 
Vt  ρl 
0.5
 µl 
+ 597 

 σ l ρ l 
0 . 45
1000Ql 


 Qg 
1.5
Where:
8-38
σl
=
Surface tension
µl
=
Viscosity of liquid
Unit Operation Models
Version 10
Chapter 8
Separation Efficiency
The separation efficiency (Yung, S., et al., 1978) 4 ηo is defined as:
ηo =
=
Mass flow rate of particles in outlet liquid stream
Mass flow rate of particles in inlet gas stream
∑ Sη
i
i
Total inlet flow rate of solids
Where:
ηi
=
Efficiency for size increment i
Si
=
Mass flow rate of size increment i
References
1. Yung, S. et al., Journal of the Air Pollution Control Association, 27, 348
(1977).
2. Dickinson, D.R. and Marshall, W.R., AIChE Journal, 14, 541, (1968).
3. Nukiyama, S. and Tanasawa, Y., Transcripts of the Society of Mechanical
Engineers (Japan), 5, 63 (1939).
4. Yung, S. et al., Environmental Science and Technology, 12, 456 (1978).
Unit Operation Models
Version 10
8-39
Solids
ESP
Electrostatic Precipitator
Use ESP to simulate dry electrostatic precipitators.
Dry electrostatic precipitators separate solids from a gaseous stream.
Electrostatic precipitators have vertically mounted collecting plates with
discharge wires. The wires are parallel and positioned midway between the
plates.
The corona discharge of the high-voltage wire electrodes first charges the solid
particles in the inlet gas stream. Then the electrostatic field of the collecting
plate electrodes removes the solids from the gas stream.
You can use ESP to size or rate electrostatic precipitators.
Flowsheet Connectivity for ESP
Gas
Feed
Solids
Material Streams
Inlet
One material stream with at least one solids substream
Outlet One material stream for the cleaned gas
One material stream for the solids
Each solids substream must have a particle size distribution (PSD) attribute.
8-40
Unit Operation Models
Version 10
Chapter 8
Specifying ESP
Use the Input Specifications sheet to specify parameters for sizing or rating
calculations.
To perform these
calculations
Set Mode=
Enter
ESP calculates
Rating
Simulation
Number of plates
Plate height
Plate length
Separation efficiency
Power required
Corona voltage
Pressure drop
Precipitator width
Sizing
Design
Separation efficiency
Number of plates
Precipitator dimensions
Power required
Pressure drop
You can specify maximum dimensions for sizing calculations on the Input
Specifications sheet.
Use the following forms to enter specifications and view results for ESP:
Use this form
To do this
Input
Specify operating parameters and dielectric constants and precipitator
dimensions
BlockOptions
Override global values for physical properties, simulation options, diagnostic
message levels, and report options for this block
Results
View summary of ESP results and material and energy balances
Operating Ranges
The velocity of gas should be between 1 and 2.5 m/sec (for plate spacing 200 and
300 mm). If the gas velocity is larger than 3 m/s or less than 0.5 m/s, then the
models for efficiency and pressure drop are not valid. This is because the transport
of fine particles by turbulent diffusion may become more significant than transport
by electrostatic force.
ESP models wire-and-plate precipitators with relatively high dust concentration
(≥ 1011 particles / m 3 or 0.1 kg / m 3 ). If the particle concentration is too low, ESP
may overestimate the results. ESP is not suitable for a cylindrical electrostatic
precipitator.
Unit Operation Models
Version 10
8-41
Solids
Separation Efficiency
The separation efficiency is defined as (Crawford, M. 1976)1:
ηov =
Mass outlet flow rate of solids
Total mass flow rate of the inlet solids substream
ηov = 1 −
 ( X s − L)q ps E c C 
Cnvs
exp 

Cnvo
3πµdWV


Where:
Cnvs
=
Particle concentration at X s
Cnvo
=
Particle concentration at inlet
Xs
=
Point at which all particles have acquired a saturation charge
L
=
Plate length
q ps
=
Particle saturation charge
Ec
=
Collecting field strength ( = 0.25( Eo ))
C
=
Conningham correction factor
µ
=
Viscosity of the gas
d
=
Particle diameter
W
=
Distance between wires and plates
V
=
Actual gas velocity through the precipitator
The point at which all particles have acquired a saturation charge X s , is defined
as:
Xs =
µdW 2 swV (Cnvo − Cnvs )
0.332ε o E c C (0.8 E c Wsw − E 0 r0 )
Where:
8-42
sw
=
Distance between two wires
εo
=
Electric permissivity constant = 8.85 x 10 −12 c / vm
Eo
=
Corona field strength 2
ro
=
Corona radius
Unit Operation Models
Version 10
Chapter 8
The collecting field strength Ec , is defined as:

T P
To P  
 
E c = 0.25  − VB f  o + 0.03
TPo ro  
 TPo

Where:
VB
=
Breakdown voltage
f
=
Roughness factor of wire
To
=
Atmospheric temperature
Po
=
Atmospheric pressure
T
=
Temperature
P
=
Pressure
The particle concentration at the point where the particles first have saturation
charge, Cnvs is:
Cnvs =
0.212( k + 2)
kd 2
0.8 E c
Ws w − E o ro
0.427 Ws w E c + 2 E o ro (0.533 Ws w − ro )
Where:
k
= Dielectric constant ( = ε / ε o )
The particle saturation charge, q ps is:
q ps =
3kπε o d 2
k+2
2
2.5 Eo ro
 Ec +
Wsw
 3
 2 1.25 ro 
 −

Wsw 
3



Pressure Drop
ESP calculates the pressure drop across the precipitator as:
∆p = 45.5 ρ g Vg2
Where:
Unit Operation Models
Version 10
ρg
=
Gas density
Vg
=
Gas velocity
8-43
Solids
Required Power
The power required2 Pw to meet a specified separation efficiency is:
Pw = 52.75 ln(1 − ηov ) Q
Where:
Q
= Volumetric gas flow rate
Gas Velocity
The models used in ESP are valid for inlet gas velocities ranging from 0.5 to 3
m/s. Outside this range, transport by turbulent diffusion becomes more
significant than by electrostatic force and large errors should be expected.
Particle Diameter
You can use ESP to model the separation of fine particles with diameters ranging
from 0.01 to 10 microns. ESP is accurate when the inlet particle concentration is
high (≥ 1011 particles / m 3 or 0.1 kg / m 3 ). If the concentration is too low, the model
tends to overestimate the separation efficiency.
References
1. Crawford, M., Air Pollution Control Theory, Chapter 8: Electrostatic
Precipitation, pp. 298-358. New York: McGraw-Hill, 1976.
2. White, H.J., Industrial Electrostatic Precipitation, 204, pp. 91-92 (1963).
8-44
Unit Operation Models
Version 10
Chapter 8
HyCyc
Hydrocyclone Solids Separator
Use HyCyc to simulate hydrocyclones. Hydrocyclones separate solids from the inlet
liquid stream by the centrifugal force of a liquid vortex.
You can use HyCyc to rate or size hydrocyclones. In simulation mode (rating),
HyCyc calculates the particle diameter with 50% separation efficiency from the
user-specified hydrocyclone diameter. In design mode (sizing), HyCyc determines
the hydrocyclone diameter required to achieve the user-specified separation
efficiency of the solids with the desired particle size.
In both calculation modes, pressure drop and the particle size distribution of the
outlet solids streams are determined.
Flowsheet Connectivity for HyCyc
Liquid
Feed
Solids
Material Streams
Inlet
One liquid stream with at least one solids substream
Outlet One stream for the cleaned liquid with residual solids
One stream for solids
Each inlet solids substream must have a particle size distribution (PSD)
attribute.
Unit Operation Models
Version 10
8-45
Solids
Specifying HyCyc
Use the Input Specifications sheet to specify hydrocyclone operating conditions.
To perform these calculations
Enter
HyCyc calculates
Rating
Simulation Mode
Hydrocyclone Diameter
Separation efficiency
Particle diameter with 50% separation
efficiency
Pressure drop, particle size distribution of
outlet solids stream
Sizing
Design Mode
Separation Efficiency
Hydrocyclone diameter
Pressure drop, particle size
distribution of outlet solids stream
To obtain practical dimensions when sizing hydrocyclones, enter the:
• Maximum diameter of the hydrocyclone
• Maximum pressure drop allowed across the hydrocyclone
HyCyc designs multiple hydrocyclones in parallel if one of the following conditions
exists:
• The calculated diameter is greater than the maximum specified diameter.
• The calculated pressure drop is greater than the maximum specified pressure
drop.
Use the following forms to enter specifications and view results for HyCyc:
Use this form
To do this
Input
Specify simulation parameters, dimensions, tangential velocity correlation
parameters, and separation efficiency
BlockOptions
Override global values for physical properties, simulation options, diagnostic
message levels, and report options for this block
Results
View summary of HyCyc results and material and energy balances
Operating Ranges
HyCyc uses empirical and semi-empirical correlations. Expect unreliable results
when operating conditions (Bradley, D., 1965)1 are outside the ranges of
experimental data on which the models are based. In general, your data should fall
within these ranges:
•
•
•
•
8-46
Particle diameter between and (5 to 200 micrometers)
Hydrocyclone diameter between 0.01 and 0.6 m
Pressure drop between 35 and 345 kPa
Separation efficiency between 2% and 98%
Unit Operation Models
Version 10
Chapter 8
The solids concentration should be less than 11% of the volume fraction, or less
than 25% of the weight fraction.
Separation Efficiency
Separation efficiency E is defined as:
E=
mass underflow rate of solids
mass feedflow rate of solids
Reduced efficiency E ′ is defined as the fraction of feed solids that go to the
underflow minus the fraction of the feed liquid that also goes to the underflow.
E′ =
E − Rf
1 − Rf
Where R f is the volumetric ratio of underflow to feed flow (see Material Split ,
this chapter).
The reduced efficiency is obtained from the following equation 2:
3

  d
  


− 0.115  
E ′ = 100 1 − exp −
d

 

50



Where:
d
=
Diameter of the solid particles to be separated
d50
=
Particle diameter for which 50% of feed passes through underflow
In turn, d 50 is obtained from the following equation which includes operational
and geometric parameters (Bradley, D., 1965)1:
d 50 Dc 3(0.38) n
=
α
Di2
Unit Operation Models
Version 10
0.5
 µ Dc (1 − R f )
θ
tan 

2
 Q(σ − ρ )
8-47
Solids
Where:
Q
=
Volumetric flow rate at inlet
Dc
=
Chamber diameter
Di
=
Inlet diameter
n
=
Power of R in the tangential velocity distribution function
α
=
Inlet velocity loss coefficient
σ
=
Density of solid
Rf
=
Underflow rate/feed rate
θ
=
Cone angle
ρ
=
Density of liquid
µ
=
Viscosity of liquid
Material Split
HyCyc splits the feed according to the following empirical correlation (Moder, J.M.
and Dahlstrom, D.A., 1952)3:
S=β(
Du
)
Do
4. 4
Q −.44
Where:
8-48
S
=
Volume split = underflow rate/overflow rate
β
=
A constant, 6.13
Du
=
Diameter for underflow
Do
=
Diameter for overflow
Q
=
Inlet volumetric flow rate (gal/min)
Unit Operation Models
Version 10
Chapter 8
The flow ratio R f (underflow rate/feed rate) is then obtained by:
1 − Rf =
1
1+ S
Tangential Velocity
The following empirical correlation gives the tangential velocity V (Dahlstrom,
D.A., 1954)4 in a hydrocyclone at a radius R:
D 
VR n = constant = α Vi  c 
 2 
n
Where:
α
=
Inlet velocity loss coefficient
Vi
=
Inlet velocity
Dc
=
Diameter of the hydrocyclone
n
=
Exponent of radial dependence
R
=
Radius
For most cases, α and n are determined experimentally to be 0.45 and 0.8. These
two variables are then used to determine d 50 .
Dimension Ratios
Common hydrocyclones have the following ranges of dimension ratios
(dimension/chamber diameter):
Unit Operation Models
Version 10
Inlet diameter:
1/7
to
1/3
Length:
4
to
12
Overflow diameter:
1/8
to
1/2.3
Underflow diameter:
1/10
to
1/5
Cone angle:
9 deg.
to
20 deg.
8-49
Solids
Pressure Drop
For the pressure drop correlation to be valid (overflow diameter/underflow
diameter) should be 0.6 to 2.0. HyCyc uses the empirical pressure drop
correlation (Dahlstrom, D.A., 1954)4:
Q
= 6.38 ( Do × Di ) 0.9
H 0.5
Where:
Q
=
Volumetric flow rate (US gallons/minute) at the inlet
H
=
Height of fluid (feet) or length of vortex finder
Do
=
Overflow diameter
Di
=
Inlet diameter
Hydrocyclone Dimensions
The next figure shows the HyCyc geometry.
Inlet Di
Dc
Do
L
θ
Du
Hydrocyclone Dimensions
8-50
Unit Operation Models
Version 10
Chapter 8
The following table describes the HyCyc dimensions.
Term
Description
Dc
Chamber diameter
Di
Inlet diameter
Do
Overflow diameter
Du
Underflow diameter
L
Length of hydrocyclone
θ
Cone angle
References
st
1. Bradley, D., The Hydrocyclone, 1 edition., Pergamon Press, London (1965).
2. Yoshioka, H. and Hatta, Y., Kagaku Kagolar, Chemical Engineering, Japan,
19, 633 (1955).
3. Moder, J.M. and Dahlstrom, D.A., Chemical Engineering Progress, 48,75
(1952).
4. Dahlstrom, D.A., “Mineral Engineering Techniques,” Chemical Engineering
Progress Symposium Series 50, No. 15, 41 (1954).
Unit Operation Models
Version 10
8-51
Solids
CFuge
Centrifuge Filter
Use CFuge to simulate centrifuge filters. The centrifuge filters separate liquids
and solids by the centrifugal force of a rotating basket.
Use CFuge to rate or size centrifuge filters.
CFuge assumes that the separation efficiency of the solids equals 1, so that the
outlet filtrate stream contains no residual solids.
Flowsheet Connectivity for CFuge
Liquid
Feed
Solids
Material Streams
Inlet
One material stream with at least one solids substream
Outlet One material stream for the liquid
One material stream for the solids
If you specify the particle size distribution (PSD), CFuge calculates the average
particle size.
8-52
Unit Operation Models
Version 10
Chapter 8
Specifying CFuge
Use the Input Specifications sheet to specify operating conditions and the Input
FilterCake sheet to specify filter cake properties.
To perform these
calculations
Enter
CFuge calculates
Rating
Diameter
Rate of revolution
Filter cake properties
Filtrate flow rate
Filter cake moisture content
Height of centrifuge basket
Sizing
List of centrifuge diameters and rates
of revolution
Filter cake moisture content (CFuge
estimates if not entered)
Filtrate flow rate
Filter cake moisture content
Height of centrifuge basket
For sizing calculations, CFuge also calculates the liquid-handling capacities of all
of the centrifuges you specify. CFuge selects the centrifuge with a liquid-handling
capacity greater than or equal to the required filtrate flow rate. If more than one
centrifuge satisfies this criterion, CFuge selects the one with the smallest
capacity. If none of the centrifuges satisfies this criterion, CFuge selects the one
with the highest filtrate flow rate.
In both rating and sizing calculations, CFuge calculates the content and height of
the centrifuge basket.
Use the following forms to enter specifications and view results for CFuge:
Use this form
To do this
Input
Specify centrifuge and filter cake parameters and centrifuge dimensions
BlockOptions
Override global values for physical properties, simulation options, diagnostic message
levels, and report options for this block
Results
View summary of CFuge results and material and energy balances
Filter Cake Characteristics
Use the Input FilterCake sheet to specify:
•
•
•
•
•
•
Unit Operation Models
Version 10
Cake resistance
Moisture Content
Sphericity
Medium resistance
Porosity
The average diameter of the solid particles in the cake
8-53
Solids
The filter cake moisture content is the ratio of the mass flow rate of liquid to that
of the solid in the outlet solids stream. The filter cake moisture content is an
important design parameter. You should provide it if possible. If you do not enter
it, CFuge calculates an estimate from the average particle diameter and cake
parameters (Dombrowski, H.S., and Brownell, L.E., 1954) 1.
If you enter the particle size distribution (PSD) of the inlet solid stream, CFuge
calculates the average particle diameter, so you do not need to enter average
diameter on the Input FilterCake sheet.
Filtrate Flow Rate
CFuge calculates the filtrate volumetric flow rate from:
Q=
1
( F − WM )
ρl
Where:
F
=
Feed liquid volumetric flow rate
M
=
Moisture content, mass of liquid/mass of dried solid
(specified as Moisture Content on the FilterCake sheet or
calculated by the model)
W
=
Dry solids feed rate
ρl
=
Liquid density
Pressure Drop
CFuge calculates the pressure drop (Grace, H.P., 1953) 2 across the filter cake as:
∆p =
ρl ω 2 (r22 − r12 )
2
Where:
8-54
ω
=
Rotational speed
r1
=
Radius of liquid surface
r2
=
Radius of inner wall of bowl
ρl
=
Liquid density
Unit Operation Models
Version 10
Chapter 8
Separation Efficiency
Separation efficiency, E, is defined as:
E=
underflow rate of solids
feedflow rate of solids
CFuge assumes that the separation efficiency of the solids equals 1, so that the
outlet filtrate stream contains no residual solids.
References
1. Dombrowski, H.S., and Brownell, L.E., Industrial and Engineering
Chemistry, 46, 6, 1207 (1954).
2. Grace, H.P., Chemical Engineering Progress, 49, 8, 427 (1953).
Unit Operation Models
Version 10
8-55
Solids
Filter
Rotary Vacuum Filter
Use Filter to simulate continuous rotary vacuum filters. You can use Filter to
rate or size rotary vacuum filters.
Filter assumes the separation efficiency of the solids equals 1, so that the outlet
filtrate stream contains no residual solids.
Flowsheet Configuration for Filter
Filtrate
Feed
Solids
Material Streams
Inlet
One material stream with at least one solids substream
Outlet One material stream for the liquid filtrate
One material stream for the solids
Specifying Filter
Use the Input Specifications sheet to specify operating conditions and
parameters.
8-56
Unit Operation Models
Version 10
Chapter 8
To perform these
calculations
Enter
Filter calculates
Rating
Simulation
Diameter
Width
Rate of revolution
Filter cake characteristics (optional)
Pressure drop
across filter
Sizing
Design
Maximum allowable pressure drop across the filter cake and
medium
Rate of revolution
Filter cake characteristics (optional)
Width to diameter ratio (optional)
Diameter
Width
In both calculation modes, ASPEN PLUS determines the following:
• Filtrate volumetric flow rate
• Cake thickness
• Mass fraction of solids in the solids filter cake
Use the following forms to enter specifications and view results for Filter:
Use this form
To do this
Input
Specify filter and filter cake parameters
BlockOptions
Override global values for physical properties, simulation options, diagnostic
message levels, and report options for this block
Results
View summary of Filter results and material and energy balances
Filter Cake Characteristics
Filter assumes:
•
•
•
The cake thickness is greater than 0.00635 m.
The capillary number is greater than 1.
The filter cake is incompressible or compacted uniformly throughout its
thickness2
When the specific cake resistance α at the required pressure drop ∆P is not
available, Filter can estimate it using the following empirical correlation:
α = α O (∆P)
k
Where:
Unit Operation Models
Version 10
αO
=
Specific cake resistance at unit pressure drop
k
=
Cake compressibility
8-57
Solids
You can use this equation for interpolation and short-range extrapolation when
some experimental data of α O and ∆P are available. α O is the intercept of the
log-log plot of α versus ∆P. α and α O both have the units determined by the
specified units set, and ∆P is always in Pascals.
Use the Average Diameter field on the FilterCake sheet to specify the average
diameter of solid particles in the filter cake. If you enter the particle size
distribution (PSD) of the inlet solid stream, Filter calculates the average particle
size.
Pressure Drop
Filter calculates the pressure drop1 across the filter cake with:
 2 ∆ pωθ V 
Q = ω RHV = RH 

 µα W 
1/ 2
Where:
Q
=
Filtrate volume flow rate
ω
=
Angular velocity
R
=
Radius
H
=
Width
V
=
Filtrate volume per unit area
∆p
=
Pressure drop
θ
=
Wetting angle
µ
=
Viscosity
α
=
Filtration resistance
W
=
Solid mass per unit area
Separation Efficiency
Separation efficiency, E, is defined as:
E=
8-58
underflow rate of solids
feedflow rate of solids
Unit Operation Models
Version 10
Chapter 8
Filter assumes the separation efficiency of the solids equals 1, so that the outlet
filtrate stream contains no residual solids.
References
1. Brownell, L.E. and Katz, D. I., Chemical Engineering Progress, 43, 11, 601
(1947).
2. Dombrowski, H.S. and Brownell, L.E., Industrial and Engineering Chemistry,
46, 6, 1207 (1954).
Additional Reading:
Brownell, L.E. and Katz, D. I., Chemical Engineering Progress, 43, 10, 537
(1947).
Dahlstrom, D.A. and Silverblatt, C.E., Solid/Liquid Separation Equipment Scale
Up, Chapter 2, Purchas, D.B., Ed., Uplands Press Ltd. (1977).
Silverblatt, C.E., Risbud, H., and Tiller, F.M., Chemical Engineering, 127 (April
27, 1974).
Unit Operation Models
Version 10
8-59
Solids
8-60
Unit Operation Models
Version 10
Chapter 8
SWash
Single-Stage Solids Washer
Use SWash to simulate solids washers in which dissolved components in the
entrained liquid of a solids stream are recovered by a washing liquid. SWash
simulates a single-stage solids washer; it does not consider the presence of a
vapor phase.
SWash calculates the flow rates and compositions of the outlet solids and liquid
streams from a user-specified liquid-to-solid mass ratio of the outlet solids
stream and the mixing efficiency of the washer. For non-adiabatic operations,
SWash determines the outlet temperature when outlet pressure and heat duty
are given. Alternatively, SWash calculates the required heat duty when outlet
temperature and pressure are specified.
Flowsheet Connectivity for SWash
Liquid
Liquid
Solids
Solids
Heat (optional)
Heat (optional)
Material Streams
Inlet
One stream for the solids particles with an entrained liquid
One stream for the washing liquid
Outlet One stream for the washed solids particles
One stream for the washing liquid and entrained liquid from the inlet
solids stream
Heat Streams
Inlet
One stream for heat duty (optional)
Outlet One stream for net heat duty (optional)
Unit Operation Models
Version 10
8-61
Solids
If you specify only pressure on the Input OutletFlash sheet, SWash uses the inlet
heat stream as a duty specification. Otherwise, SWash only uses the inlet heat
stream to calculate the net heat duty. The net heat duty is the inlet heat stream
minus the actual (calculated) heat duty.
You can use an outlet heat stream for the net heat duty.
Specifying SWash
You must specify the mixing efficiency of the washer and the liquid-to-solid mass
ratio of the outlet solids stream. For non-adiabatic operations, you must specify
the pressure of the washer and one of the following:
• The temperature of the washer
• Heat duty (or an inlet heat stream without an outlet heat stream)
Alternatively, SWash calculates the required heat duty when outlet temperature
and pressure are specified.
SWash assumes adiabatic operations if neither temperature nor heat duty is
specified.
Use the following forms to enter specifications and view results for SWash:
Use this form
To do this
Input
Specify operating parameters, flash specifications, and convergence parameters
BlockOptions
Override global values for physical properties, simulation options, diagnostic message
levels, and report options for this block
Results
View summary of SWash results and material and energy balances
Mixing Efficiency
The mixing efficiency of the washer, E, is defined as:
S
S
x IN
− xOUT
E= S
L
x IN − xOUT
Where:
8-62
S
x IN
=
Mass fraction of dissolved components in the entrained
liquid of the inlet solids stream
S
xOUT
=
Mass fraction of dissolved components in the entrained
liquid of the outlet solids stream
L
x OUT
=
Mass fraction of dissolved components in the outlet liquid
stream
Unit Operation Models
Version 10
Chapter 8
Bypass Fraction
The bypass fraction is the fraction of liquid in the feed that bypasses the mixing,
when mixing efficiency is less than 1. It is calculated as:
Bypass fraction = (1 − mixing efficiency) ×
Unit Operation Models
Version 10
liquid − to − solid ratio specified for SWash
liquid − to − solid ratio in inlet solids stream
8-63
Solids
CCD
Counter-Current Decanter
CCD simulates a counter-current decanter or a multistage washer. CCD
calculates the outlet flow rates and compositions from:
• Mixing efficiency
• Liquid-to-solid mass ratio of each stage
CCD can calculate:
• The heat duty profile from a specified temperature profile
• The temperature profile from a specified heat duty profile
CCD does not consider a vapor phase.
Flowsheet Connectivity for CCD
Solids
(Top feed)
Overflow
1
Feed To
Underflow
(optional)
Product From
Underflow
(optional)
Product From
Overflow
(optional)
Feed To
Overflow
(optional)
Nstage
Underflow
Washing
Liquid
(Bottom feed)
Material Streams
Inlet
One solids inlet material stream (top feed)
One liquid inlet material stream (bottom feed)
Any number of optional inlet material side streams per stage
Outlet One top product stream (overflow)
One bottom product stream (underflow)
One optional stream per stage for the solids (underflow)
One optional stream per stage for the liquid (overflow)
Any number of pseudoproduct streams (optional)
8-64
Unit Operation Models
Version 10
Chapter 8
Any number of pseudoproduct streams can represent internal underflows or
overflows. A pseudoproduct stream does not affect the results of the simulation.
Specifying CCD
Use the CCD Input Specifications sheet to enter the number of stages, pressure,
mixing efficiency, and liquid-to-solid mass ratio.
Use the CCD Input Streams to enter feed, product, and optional heat stream
locations.
On the CCD Input Temp-DutyProfiles sheet, note the following:
If you enter
CCD calculates
Stage temperature
Stage heat duty
Stage heat duty
Stage temperature
Stage overall heat transfer
coefficient
Stage temperature
You cannot enter both temperature profiles and heat duties or overall heat
transfer coefficients. If you enter stage heat duty and/or an overall heat transfer
coefficient, and you do not enter values for all stages, the system assumes
unspecified values to be zero. Enter the medium temperature of each stage when
you enter overall heat transfer coefficients. Use the Estimated Temperature field
to enter estimated stage temperatures.
Note
CCD interpolates unspecified values and, by default, assumes
them to be the same as the ambient temperature.
Use the CCD Input PseudoStream sheet to transfer the internal overflow or
underflow of a stage to a pseudostream.
Use the following forms to enter specifications and view results for CCD:
Unit Operation Models
Version 10
Use this form
To do this
Input
Specify operating parameters, temperature profile parameters,
pseudostream information, and convergence parameters
BlockOptions
Override global values for physical properties, simulation options,
diagnostic message levels, and report options for this block
Results
View summary of CCD results, material and energy balances, and stage
profiles
8-65
Solids
Component Attributes
CCD does not consider the mixing of component attributes and PSDs. CCD
assumes all outlet solids streams have the same attributes and PSD as the solids
feed stream to stage one. CCD also assumes all outlet liquid streams have the
same attributes and PSD as the liquid feed stream throughout the final stages.
Multistage Washer Profiles
For any CCD profile, such as mixing efficiency, liquid-to-solid-ratio, temperature,
duty, enter a value for every stage, as information becomes available. If you enter
only some of the values for some stages, CCD generates the complete profile by
linear interpolation of the given values. If you enter only one value, CCD
assumes a constant profile of that value throughout the washer.
Mixing Efficiency
The mixing efficiency of stage n is defined as:
S
S
x IN
− xOUT
E= S
L
x IN − xOUT
Where:
8-66
S
x IN
=
Mass fraction of dissolved components in the entrained liquid of the
total inlet solids stream to stage n.
S
x OUT
=
Mass fraction of dissolved components in the entrained liquid of the
total outlet solids stream from stage n.
L
x OUT
=
Mass fraction of dissolved components in the outlet liquid stream
from stage n.
Unit Operation Models
Version 10
Chapter 8
Medium Temperature
The duty for each stage is calculated according to the following equations:
Qi = UAi (Tcalci − Tmed i )
Where:
Qi
=
Heat duty for stage i
UAi
=
Product of heat transfer coefficient and area for stage i
Tcalci
=
Calculated outlet temperature of stage i
Tmed i
=
Temperature of the heat transfer medium at stage i
❖
Unit Operation Models
Version 10
❖
❖
❖
8-67
Solids
8-68
Unit Operation Models
Version 10
Chapter 9
9
User Models
This chapter describes the models that allow you to write your own unit
operation models as Fortran subroutines. These subroutines must follow the
guidelines described in the ASPEN PLUS User Models reference manual. The
models are:
Unit Operation Models
Version 10
Model
Description
Purpose
Use For
User
User-defined unit operation
model
Model a unit operation using a user-supplied
Fortran subroutine
Unit operations with four (or
fewer) inlet and outlet
streams
User2
User-defined unit operation
model
Model a unit operation using a user-supplied
Fortran subroutine.
Unit operations with no limit
on number of streams
9-1
User Models
User
User-Supplied Unit Operation Model
User can model any unit operation model. You must write a Fortran subroutine
to calculate the values of the outlet streams based on the inlet streams and
parameters you specify.
User and User2 differ only in the number of inlet and outlet streams allowed and
the argument lists to the model subroutine. User is limited to a maximum of four
material and one heat or work inlet stream and a maximum of four material and
one heat or work outlet stream. User2 has no limits on the number of inlet and
outlet streams.
Flowsheet Connectivity for User
Material
Heat (optional)
Work (optional)
Heat (optional)
Work (optional)
Material Streams
Inlet
One to four inlet material streams
Outlet One to four outlet material streams
Heat Streams
Inlet
One heat stream (optional)
Outlet One heat stream (optional)
Work Streams
Inlet
One work stream (optional)
Outlet One work stream (optional)
9-2
Unit Operation Models
Version 10
Chapter 9
Specifying User
You must specify the name of the subroutine model on the Input Specifications
sheet. You have the option of specifying:
• A report subroutine name
• Size of the integer and real arrays (INT and REAL) passed to the user model
subroutine
• Values of the integer and real arrays passed to the user model subroutine
• Length of integer and real workspace vectors
• Thermodynamic conditions of each outlet stream
• Type of flash calculations (vapor, liquid, two-phase, three-phase)
For information on writing Fortran subroutines for user models, see the
ASPEN PLUS User Models reference manual.
Use the following forms to enter specifications and view results for User:
Unit Operation Models
Version 10
Use this form
To do this
Input
Specify name and parameters for user subroutine, calculation options, and
outlet stream conditions and flash convergence parameters
BlockOptions
Override global values for physical properties, simulation options, diagnostic
message levels, and report options for this block
Results
View summary of User results and material and energy balances
9-3
User Models
User2
User-Supplied Unit Operation Model
User2 can model any unit operation model. You must write a Fortran subroutine
to calculate the values of the outlet streams based on the inlet streams and
parameters you specify.
User and User2 differ only in the number of inlet and outlet streams allowed and
the argument lists to the model subroutine. User2 has no limits on the number of
inlet and outlet streams. User is limited to a maximum of four material and one
heat or work inlet stream, and a maximum of four material and one heat or work
outlet stream.
Flowsheet Connectivity for User2
Material
Heat (optional)
Work (optional)
Heat (optional)
Work (optional)
Material Streams
Inlet
At least one inlet material stream
Outlet At least one outlet material stream
Heat Streams
Inlet
Any number of heat streams (optional)
Outlet Any number of heat streams (optional)
Work Streams
Inlet
Any number of work streams (optional)
Outlet Any number of work streams (optional)
9-4
Unit Operation Models
Version 10
Chapter 9
Specifying User2
You must specify the name of the subroutine model on the User2 Input
Specifications sheet. You have the option of specifying:
• A report subroutine name
• Size of the integer and real arrays (INT and REAL) passed to the user model
subroutine
• Values of the integer and real arrays passed to the user model subroutine
• Length of integer and real workspace vectors
• Thermodynamic conditions of each outlet stream
• Type of flash calculations (vapor, liquid, two-phase, three-phase)
For information on writing Fortran subroutines for user models, see ASPEN
PLUS User Models reference manual.
Use the following forms to enter specifications and view results for User2:
Use this form
To do this
Input
Specify name and parameters for user subroutine, calculation options, and outlet
stream conditions and flash convergence parameters
BlockOptions
Override global values for physical properties, simulation options, diagnostic
message levels, and report options for this block
Results
View summary of User2 results and material and energy balances
❖
Unit Operation Models
Version 10
❖
❖
❖
9-5
User Models
9-6
Unit Operation Models
Version 10
Chapter 10
10
Pressure Relief
This chapter contains detailed reference information on the ASPEN PLUS
Pres-Relief model for pressure relief calculations. For information on using
Pres-Relief, see the ASPEN PLUS User Guide, Chapter 33.
This chapter describes the following topics:
• Specifying Pres-Relief
• Scenarios
• Rules to size the relief valve piping
• Compliance with codes
• Stream and vessel compositions and conditions
• Reactions
• Relief system
• Data tables for pipes and relief devices
• Valve cycling
• Vessel types
• Disengagement models
• Stop criteria
• Solution procedure for dynamic scenarios
• Flow equations
• Calculation and convergence methods
• Vessel insulation credit factor
Unit Operation Models
Version 10
10-1
Pressure
Relief
Pres-Relief
Pressure Relief Model
Use Pres-Relief to do either of the following:
• Determine the steady-state flow rating of pressure relief systems
• Dynamically model vessels undergoing pressure relief due to a fire or heat
input specified by the user. You may specify that reactions occur in the vessel.
Specifying Pres-Relief
Use Pres-Relief to do either of the following:
• Determine the steady-state flow rating of pressure relief systems
• Dynamically model vessels undergoing pressure relief due to a fire or heat
input specified by the user. You may specify that reactions occur in the vessel
Use the Setup form to specify the pressure relief scenario, general specifications
such as the discharge pressure and the estimated flow rate, inlet stream
conditions, initial vessel conditions, design rules, and any reactions (dynamic
scenarios only) that occur.
Use the Relief Device form to specify the relief system. You must select a relief
device and specify its characteristics. You must also specify the vessel neck and
the number of inlet and tail pipe sections to be used.
Use the Dynamic Input form to specify the required parameters for dynamic
scenarios. These include vessel specifications, disengagement models and details
specific to the chosen scenario. For the fire scenario, you must specify the fire
standard and the credits to be used. When the scenario is Dynamic run with
specified heat flux, you must specify the heat input parameters.
When the number of inlet and tail pipe sections exceeds 0, you must specify the
details for each section in the Inlet Pipes and Tail Pipes forms.
For dynamic scenarios, use the Operations form to specify one or more variables
to be used as stop criteria. The simulation will stop when the value of any of
these variables exceeds the user-specified limit.
10-2
Unit Operation Models
Version 10
Chapter 10
Use the following forms to enter specifications and view results for Pres-Relief:
Use this form
To do this
Setup
Specify pressure relief scenario, general specifications, initial stream conditions, design
rules, and any reactions that occur (required input)
Relief Device
Specify the type of relief device and the characteristics of the device (required input)
Inlet Pipes
Specify piping, fittings, and valves immediately upstream of the relief device (optional
input)
Tail Pipes
Specify piping, fittings, and valves immediately downstream of the relief device (optional
input)
Dynamic Input
Specify parameters describing the dynamic event (required for dynamic scenarios)
Operations
Specify criteria that will terminate the dynamic simulation (required for dynamic
scenarios)
Convergence
Override default methods and convergence parameters for the algorithms involved in the
pressure relief simulation (optional input)
Block Options
Override default methods and options for property calculation, simulation, diagnostics,
and reporting (optional input)
Results
Review calculated results and profiles for the steady-state scenarios
Dynamic Results
Review calculated results and profiles for the dynamic scenarios
Scenarios
Scenarios are situations that cause venting through the pressure relief system to
occur. Pres-Relief supports the following scenarios:
• Dynamic run with vessel engulfed by fire
• Dynamic run with specified heat flux into vessel
• Steady state flow rating of relief system
• Steady state flow rating of relief valve
Dynamic Run with Vessel Engulfed by Fire
Use this scenario to model a vessel engulfed by fire. You must specify the vessel
geometry and initial composition. ASPEN PLUS can compute the energy input
for this scenario according to the following standards:
•
•
•
Unit Operation Models
Version 10
NFPA-30
API-520
API-2000
10-3
Pressure
Relief
ASPEN PLUS assumes the calculated energy input is constant during the entire
venting transient. ASPEN PLUS uses credit factors for drainage, water-spray,
fire-fighting equipment, and insulation to reduce energy input, if appropriate for
the chosen standard. You may specify a total credit factor instead of individual
credit factors. You must specify the fire duration time. This is a dynamic
scenario. The vessel contents and relief rate change as a function of time.
The following tables describe how ASPEN PLUS calculates wetted area, energy
input, and credit factors for each of the three standards.
Calculation of Wetted Area
Vessel type
NFPA-30
API-2000
API-520
Horizontal
75% of total exposed
area
75% of total area or area to a height of
30 ft. above grade, whichever is greater
Wetted area up to 25 ft. above grade
(based on specified liquid level)
Vertical
Area up to 30 ft.
above grade. Bottom
plate is included if
exposed
Area up to 30 ft. above grade. If on
ground, bottom plate is not included.
Wetted area up to 25 ft above grade
(based on specified liquid level).
Bottom plate is included if exposed.
Sphere
55% of total exposed
area
55% of surface area, or surface area to
a height 30 ft. above grade, whichever
is greater
Up to a maximum horizontal diameter
or up to height of 25 ft. above grade,
whichever is greater
Calculation of Q (Btu/hr), Based on Area (sq-ft)
†
NFPA-30 and API-2000
Area range
Heat input
20 < area < 200
Q=20,000Area
200 < area < 1000
Q=199,300(Area
1000 < area < 2800
Q=963,400(Area
2800 < area
†
Q=21000(Area
0.566
0.82
)
0.338
)
)
For NFPA-30 , QMAX=14,090,000 at 2800 square feet if operating pressure < 1 PSIG
API-520
Heat input
Q=34,500(Area
10-4
0.82
)
Unit Operation Models
Version 10
Chapter 10
Calculation of Credit Factors
Type
NFPA-30
Insulation only
.3
API-2000
API-520
†
F=K(1660-TF)/21,000t
Same as API-2000
You must specify F
Drainage only
.5
1.
Not defined
(Area > 200 sq. ft.)
Water and drainage
.3
1.
Not defined
Water, insulation, and
drainage
.15
NSUL
Not defined
Insulation and drainage
.15
Not defined
Not defined
(Area > 200 sq. ft.)
(Area > 200 sq. ft.)
Drainage and prompt fire
fighting effort
No credit
Not defined
0.6*INSUL
Portable
No credit factors allowed
Not defined
Not defined
†
See Vessel Insulation Credit Factor, this chapter.
Dynamic Run with Specified Heat Flux into Vessel
This scenario is similar to the fire exposure scenario, except it can model any
energy input. ASPEN PLUS can compute the energy input for this scenario in
three ways depending on whether you specify:
• A constant duty
• A duty profile
• An area for heat transfer, a heat transfer coefficient, and a source fluid
temperature
This scenario is a dynamic scenario and is typically used for electrical heaters
and other energy sources.
Steady State Flow Rating of Relief System
Use this scenario to find the flow rate through a specified relief system at the
specified composition. For this scenario, you must enter your own:
• Relief rate
• Piping description
• Feed stream composition
• Feed stream condition
Unit Operation Models
Version 10
10-5
Pressure
Relief
Steady State Flow Rating of Relief Valve
Use this scenario to find the flow rate through a valve, given the composition and
condition at the entrance to the valve. This is the simplest scenario. It is similar
to the steady state flow rating of relief system scenario, except no piping is
allowed.
Compliance with Codes
Pres-Relief allows two types of runs:
• Code capacity
• Actual capacity
The primary purpose of the code capacity run is to ensure that the capacity of the
relief system, rated as required by code, exceeds the maximum capacity dictated
by the scenario. The maximum pressure reached during the relief event must be
less than the code allowable accumulation. The Code Capacity run includes the:
• ASME valve rating factor of .90
• Valve flow coefficient
• A combination coefficient
The combination coefficient is only included if a rupture disk/relief valve
combination is being designed. Typical combination coefficients for NBBI
certified combinations are close to 1.00. If the combination is not certified, the
ASME code requires a combination coefficient of .90. The primary purpose of the
actual capacity run is to provide the best estimate of the actual flow through the
system. Design of downstream equipment (other than the tail pipe) is one
example why you might need this information. The actual capacity run contains
the valve flow coefficient, but not the ASME valve rating factor of .90 or the
combination coefficient.
Stream and Vessel Compositions and Conditions
For the steady-state scenarios, you must specify the composition and conditions
(two of temperature, pressure, and vapor fraction) of the feed stream. You can do
this on the Setup Streams sheet in two ways:
• Reference an ASPEN PLUS stream
• Give the composition and conditions of the stream as input to Pres-Relief
10-6
Unit Operation Models
Version 10
Chapter 10
For the dynamic scenarios, you must specify the composition and the conditions
in the vessel at the beginning of the pressure relief calculations. Do this by
referencing an ASPEN PLUS stream, or by specifying the composition and two of
temperature, pressure, and vapor fraction on the Setup Vessel Contents sheet.
As with the steady-state scenarios, you may reference an ASPEN PLUS stream
or give the composition and conditions as input to Pres-Relief. When vapor
fraction is not specified, you may also specify:
•
•
Initial liquid fill fraction (fillage) of the vessel
Pad-gas pressure and Component ID
Only two of temperature, pressure, and vapor fraction can be specified or
referenced from a stream.
Rules to Size the Relief Valve Piping
ASPEN PLUS uses several rules (3% rule, X% rule, and 97% rule) to size the
inlet and outlet piping with PSVs. The rules use the following terminology:
DSP
CBP
Psta
Ptot
IDP
=
=
=
=
=
BBP
=
Differential set pressure
Constant back pressure
Static pressure
Static pressure + velocity pressure
Inlet pressure drop
Ptot (vessel) - Ptot (valve in)
Built-up back pressure
Psta (valve out) - CBP
These rules are applied for both actual and code capacity runs and are applied at
the converged solution for the steady-state scenarios.
For dynamic scenarios, the 3% Rule and X% Rule are applied once, at 10%
overpressure. If all pressures are above 10% overpressure, the test is not
performed and a warning is issued. If all pressures are below 10% overpressure,
the highest pressure value is scaled up to 10% overpressure, and the scaled
values are used in applying the rule. The 97% rule is applied when the pressure
at the valve inlet is at or above 10% overpressure.
None of the required standards mentions any of these rules except for the X%
rule with X=10. The X% rule is mentioned in the non-mandatory appendix of the
ASME code.
Unit Operation Models
Version 10
10-7
Pressure
Relief
3% Rule
According to the 3% rule, the total pressure loss in the inlet must be less than 3%
of the differential set pressure when the flow rate is equal to the code capacity of
the valve at 10% overpressure.
IDP ≤ 0.03DSP
For cases where the overpressure does not reach 10%, adjust the pressure drop
rule by multiplying by the ratio of the maximum flowing pressure to 10%
overpressure (psig).
IDP ≤ 0.03
RP
11
. SP
X% Rule
According to the X% rule, the built-up back pressure must be less than X% of the
differential set pressure when the flow rate is equal to the code capacity of the
valve at 10% overpressure.
BBP ≤
X
DSP
100
For cases where the overpressure does not reach 10% adjust the pressure drop
rule by multiplying by the square of the ratio of the maximum flowing pressure
to 10% overpressure (psig).
X  RP 
BBP ≤


100  11
. PS 
2
97% Rule
According to the 97% rule, 97% of the differential set pressure must be available
across the valve anytime the over pressure is equal to or above 10% with a flow
through the valve based on code capacity.
RP − CBP − IDP − BBP ≥ 0.97 DSP
For cases where the overpressure does not reach 10%, apply the rule at peak
overpressure.
10-8
Unit Operation Models
Version 10
Chapter 10
Recommendations for Specific Valve Types
For standard spring loaded valves or pop action pilot valves with
unbalanced pilots vented to the discharge:
The differential set pressure is the set pressure minus the constant back
pressure.
DSP = SP − CBP
Size the inlet piping using the 3% rule.
Size the outlet piping using the 97% rule.
-OrSize the outlet piping with the X% rule using X = 10.
For balanced bellows spring loaded valves:
The differential set pressure is the set pressure.
DSP = SP
Size the inlet piping using the 3% rule.
Size the outlet piping with the X% rule using X = 30.
For modulating pilot operated valves with balanced pilots or pilots
vented to atmosphere:
The differential set pressure is the set pressure.
DSP = SP
You can use the scenario required flow rather than the valve capacity for
pressure drop calculations as an option. This can easily be simulated by changing
the input orifice area until the overpressure reaches 10%.
There is no inlet pressure drop rule.
Size the outlet piping with the X% rule using X = 50.
Reactions
If the protected vessel is a vertical, horizontal, API, spherical , or user-specified
tank, you may model it with or without reactions. Specify the reactions by giving
the Reactions ID on the Setup Reactions sheet.
Unit Operation Models
Version 10
10-9
Pressure
Relief
Relief System
The venting system consists of:
• A vessel neck
• One or two sections of inlet pipe
• The relief device itself
• One or two sections of tail pipe
In a simulation, the system being modeled may consist of an inlet pipe without a
relief device, or a relief device connected to the vessel without an inlet pipe. The
tail pipe is optional.
Relief Devices
Pres-Relief can model the following types of relief devices:
• Safety relief valves (PSVs; both liquid and gas/2-phase)
• Rupture disks (PSDs)
• Emergency relief valves (ERVs)
• SRV/rupture disk combinations
• Open vent pipes
Internal tables (accessed from the ReliefDevice SafetyValve sheet) contain
several standard commercially available valves, along with all the mechanical
specifications and certified coefficients needed in the relief calculations. You may
choose one valve from the tables, or enter your own valve specifications and
coefficients.
For liquid service valves, you must also specify the full-lift overpressure. This
allows ASPEN PLUS to simulate some of the older style valves which do not
achieve full lift until 25% overpressure is reached.
For gas/2-phase service valves, you must also specify the average opening and
closing factors. The valve does not open until the pressure drop across the valve
reaches (opening factor * Dif-Setp). The valve closes when the pressure drop
across it reaches (closing factor * Dif-Setp).
In an actual capacity run, the rupture disk is modeled as a bit of resistance using
the pipe model. The default value of L/D is 8 for a rupture disk with a diameter
of 2 inches or less and 15 if the diameter is greater than 2 inches. You can
override the default by specifying a value on the Relief Device Rupture Disk
sheet.
In the code capacity run, the rupture disk is modeled as an ideal nozzle with a
certified discharge coefficient. If no certified discharge coefficient is available, a
value of 0.62 is suggested.
In a code capacity run in combination with a safety relief valve, the resistance of
the rupture disk is modeled by the combination coefficient in the valve model.
10-10
Unit Operation Models
Version 10
Chapter 10
The emergency relief vent is modeled as a nozzle. A de-rating factor of 0.9 is used
in a code capacity run.
Piping System
The inlet piping system can be made of one of the following:
• One pipe section
• Two sections of pipe plus a vessel neck, all with different diameters
The tail pipe can be made of one section of pipe or of two sections of pipe with
different diameters.
For each pipe section, specify:
•
•
•
•
Pipe diameter
Length
Elevation
Whether the pipes are screwed together or held together with flanges or
welds
If pipes of different diameters are used, reducer and expander resistance
coefficients ("K" factors) can be specified. ASPEN PLUS uses the equation
K=4*fr*(L/D) to convert from resistance coefficients to equivalent L/D, where the
term "fr" is the friction factor. Optional information for each section consists of
the number of 90 degree elbows, straight tees, branched tees, gate valves,
butterfly valves, transflo valves, and control valves. You can add other fittings
not listed by specifying the L/D value. ASPEN PLUS calculates a total equivalent
L/D before modeling the pipe section.
You may also specify:
• Ambient temperature at the inlet and outlet of the pipe
• A heat transfer coefficient to exchange heat with the pipe contents
While modeling the pipe section, ASPEN PLUS detects the choked condition in
the pipe by keeping track of the Mach Number as integration down the pipe
proceeds. If the Mach Number goes above 1.0, integration is stopped and a flag is
returned to indicate that the pipe choked.
Pipeline pressure drop modeling can work in two ways. You may specify one of
the following:
• Rigorous flashes are to be done at each step in the integration
• A flash table is used during pipe integration
Unit Operation Models
Version 10
10-11
Pressure
Relief
If you request a table, specify the number of temperature and pressure points in
the table. At each temperature-pressure pair, ASPEN PLUS performs a flash and
calculates all necessary properties (density, viscosity, surface tension, and so on).
As integration proceeds, ASPEN PLUS interpolates in this table to get the
necessary properties. If properties outside the table are needed, a rigorous flash
is performed at that point. In general, the pipe integration proceeds faster if the
flash table is used. Several correlations are available, depending on the pipe
inclination. The default method for all inclinations (holdup and frictional
pressure loss) is Beggs and Brill. Other available options are:
• Darcy
• Lockhart-Martinelli
• Dukler for frictional loss
• Lockhart-Martinelli, Slack, and Flanigan for holdup
Data Tables for Pipes and Relief Devices
Pres-Relief includes several customizable tables that list the available options for
pipes, general purpose valves, safety relief valves, emergency relief vents, and
rupture disks. You can modify the tables by changing data files. Then process the
files through ModelManager Table Building System (MMTBS).
Pipes
Pres-Relief includes a table of actual diameters for several steel pipe schedules.
Use this table when choosing the piping for the inlet and tail pipes. You can modify
this table by including more pipe materials and/or schedules. The following section
shows the table organization.
10-12
Unit Operation Models
Version 10
Chapter 10
first material of construction
# of types
first type
# of diameters
nominal diameter actual diameter
nominal diameter actual diameter
.
.
second type
# of diameters
nominal diameter actual diameter
nominal diameter actual diameter
.
.
second material of construction
# of types
first type
# of diameters
nominal diameter actual diameter
nominal diameter actual diameter
.
.
second type
nominal diameter actual diameter
nominal diameter actual diameter
.
.
General-Purpose Valves
For general-purpose valves in the inlet or tail pipes, Pres-Relief includes a table of
various manufacturers’ valves from 1 inch to 10 inches. The valves include:
•
•
•
•
•
Unit Operation Models
Version 10
Durco Plug
Tufline Plug
Jamesbury Ball
AGCO Selector
KTM Ball (L-Port and T-Port)
10-13
Pressure
Relief
For each manufacturer, the table contains:
• Valve type (for example., L-Port or T-Port)
• Nominal diameter
• Port area
• Flow coefficient
The table is organized as follows:
first manufacturer
# of types
first type
# of diameters
nominal diameter
nominal diameter
.
.
second type
# of diameters
nominal diameter
nominal diameter
.
.
port area
port area
flow coeff
flow coeff
port area
port area
flow coeff
flow coeff
Safety Relief Valves
Pres-Relief includes a table of manufacturers’ safety relief valves. It contains
valves for liquid and gas/2-phase service. For each valve, the table contains:
• Service
• Type
• Manufacturer
• Series, size (for example, 3L4)
• Throat diameter
• Inlet diameter
• Outlet diameter
• Discharge coefficient
• Overpressure factor (for liquid service valves)
10-14
Unit Operation Models
Version 10
Chapter 10
The table is organized as follows:
Service (Liquid, Gas, or 2-phase)
# of types
first type
# of manufacturers
first manufacturer
# of series
first series
# of sizes
first size
# of throat diameters
throat diam inlet diam outlet diam
throat diam inlet diam outlet diam
.
.
throat diam inlet diam outlet diam
throat diam inlet diam outlet diam
dischg coeff over pr factor
dischg coeff over pr factor
dischg coeff over pr factor
dischg coeff over pr factor
Emergency Relief Vents
This table contains:
• Nominal diameter
• Effective diameter
• Allowed setpoint for several Protectoseal and Groth emergency relief vents
You must specify an over-pressure factor. The table is organized as follows:
first manufacturer
# of types
first type
# of nominal diameters
nominal diameter effective diameter allowed setpoint
nominal diameter effective diameter allowed setpoint
.
.
Rupture Disks
This table contains manufacturers’ information on rupture disks. Each entry
contains:
• A manufacturer
• Type
• Nominal diameter
• Actual diameter
• Discharge coefficient
Unit Operation Models
Version 10
10-15
Pressure
Relief
The table is organized as follows:
first manufacturer
# of types
first type
# of nominal diameters
first nominal diam actual diam discharge coeff
second nominal diam actual diam discharge coeff
.
.
Valve Cycling
If a relief valve is too large for a given application, valve cycling may occur. In this
situation, the pressure in the vessel builds up to a point where the valve opens, but
then closes almost immediately because enough material is released to lower the
vessel pressure below the closing pressure. In some simulations, the valve may
open and close several times per second. The simulation may run for a long time,
just opening and closing the valve over and over.
To stop such a simulation, you can specify whether or not to stop cycling, and
how many openings and closings of the valve are allowed in a specified amount of
time.
Vessel Types
You must enter vessel geometry for the dynamic scenarios. You can choose one of
the following vessel types:
• Vertical Vessel
• Horizontal Vessel
• API Tank
• Sphere
• Heat exchanger shell
• Vessel jacket
• User-specified
If you choose user-specified, you must specify surface area and volume. Surface
area is also required for vessel jacket. Maximum Allowable Working Pressure
(MAWP) with corresponding temperature is required for all vessel types. Some
vessel types require diameter, length, and volume of internals.
10-16
Unit Operation Models
Version 10
Chapter 10
Vertical Vessel, Horizontal Vessel, and API Tank
If you choose vertical vessel, horizontal vessel, or API tank, choose one of these
head types:
• Flanged and dished
• Ellipsoidal
• User-specified
If you choose user-specified head type, you must specify the area and volume of a
head.
Sphere
If the protected vessel is a sphere, you must specify:
• Diameter
• MAWP with corresponding temperature
• Volume of internals
Heat Exchanger Shell
If the protected vessel is a heat exchanger shell, in addition to the items specified
for a vertical vessel you must also specify whether the vessel is mounted
vertically or horizontally.
Vessel Jacket
If the protected vessel is a vessel jacket, you must specify:
• MAWP with corresponding temperature
• Volume of internals
• Jacket volume
User-Specified
If the protected vessel is user-specified, you must specify:
•
•
•
•
Unit Operation Models
Version 10
Volume
Area
MAWP with corresponding temperature
Volume of internals
10-17
Pressure
Relief
Disengagement Models
The following disengagement options are available:
Option
Description
Homogeneous
Vapor fraction leaving vessel is the same as vapor fraction in vessel
All-vapor
All vapor leaving vessel
All-liquid
All liquid leaving vessel
Bubbly
DIERS bubbly model
Churn-turbulent
DIERS churn-turbulent model
User-specified
Homogeneous venting until vessel vapor fraction reaches the user-specified value,
then all vapor venting
For the bubbly and churn-turbulent methods, ASPEN PLUS uses the DIERS
“switch-point” calculations to compute the point at which total vapor-liquid
disengagement occurs. Use the bubbly and churn-turbulent models only for
vertical or API tanks.
Stop Criteria
For dynamic scenarios, stop criteria need to be specified which will terminate the
simulation. You must:
• Select a specification type
• Enter a value for the specification at which the simulation will stop
• Select a component and substream for component-related specification types
• Specify which approach direction (above or below) to use in stopping the
simulation
You may select from the following specification types:
• Simulation time
• Vapor fraction in the vessel
• Mole fraction of a specified component
• Mass fraction of a specified component
• Conversion of a specified component
• Total moles or moles of a specified component
• Total mass or mass of a specified component
• Vessel temperature
• Vessel pressure
• Vent mole flow rate or mole flow rate of a component
• Vent mass flow rate or mass flow rate of a component
10-18
Unit Operation Models
Version 10
Chapter 10
You must also select the location of the stop criteria specification. You may select
from the following locations:
• Vessel
• Relief vent system
• Accumulator
Certain restrictions apply depending on the location selected.
When location = vessel, mole and mass flow rate are not allowed.
When location = vent accumulator, only the following specifications are allowed:
•
•
•
•
Mass fraction of a specified component
Mole fraction of a specified component
Total moles of a specified component
Total mass of a specified component
When location = vent, only the flowing specifications are allowed:
• Mass fraction of a specified component
• Mole fraction of a specified component
• Vent molar flow rate
• Vent mass flow rate
Solution Procedure for Dynamic Scenarios
The problem to be solved is:
Given the initial conditions in the vessel, a description of the pressure relief
system, and the heat flow into the vessel, calculate the flow rate through the
pressure relief system and determine if the pressure relief system meets code
requirements.
The problem is solved as outlined below. This algorithm is for the Heat-Input and
Fire Scenarios.
1. Given the heat input to the vessel, solve the energy balance and flash
equations along with the reaction equations for the vessel at the present time
step. If any of the termination criteria are met, go to Step 6. The options for
specifying termination criteria include:
•
•
•
•
Time for scenario exceeded
Specified vapor fraction reached
Vessel contents have reached specified value
Pressure in the vessel is greater than the maximum allowed
2. If the pressure in the vessel is less than the device opening pressure,
increment time and go to Step 1.
Unit Operation Models
Version 10
10-19
Pressure
Relief
3. Calculate the maximum flow rate possible through the pressure relief system.
This value is calculated by finding the smallest diameter of any pipe or valve
in the system, and calculating the sonic velocity through that diameter.
4. Calculate the pressure at the end of the vessel neck, after each section of the
inlet pipe, after the pressure relief device, and after each section of the tail
pipe based on the current flow estimate. If the pressure at the end of any
section is less than the user-specified discharge pressure, it is not necessary
to do the calculations for the next section.
5. If the pressure at the end of the pressure relief system is within tolerance of
the user-specified discharge pressure, increment time and go to Step 1.
Otherwise, calculate a new guess for the flow through the relief system and
go to Step 4.
6. Given the flow at any time, check where the choke point is. If the choke point
is not at the pressure relief valve, the system is unacceptable. Check if any
applicable codes are violated. If so, the system is unacceptable.
Flow Equations
Pipe Flow
This is the general differential equation for flow through a constant diameter pipe:


υ2  
υ dp + G  υ dυ +  4 f
 dL  + g sin ΦdL = 0
2D 


2
(1)
Where:
υ
=
Specific volume of stream
p
G
f
D
L
g
=
=
=
=
=
=
=
Static (flowing) pressure of stream
Mass flow rate per unit area
Friction factor
Inside diameter of pipe
Equivalent pipe length
Acceleration due to gravity
Vertical rise/equivalent pipe length
sin Φ
10-20
Unit Operation Models
Version 10
Chapter 10
Φ represents the physical angle of the pipe with respect to the horizontal only if
the equivalent pipe length is the same as the physical flow path length (that is,
only pipe, no fittings or other resistances). The potential energy term in the
equation assumes that the vertical elevation is distributed evenly along the
entire equivalent length.
For example, you have only a single 20 meter length of pipe that rises a total of
six meters, then
sin Φ =
6
= 0.3
20
If the same system also includes a fitting resistance of 5 equivalent meters, then:
sin Φ =
6
= 0.24
20 + 5
Equation (1) applies to any flow system (all vapor, non-flashing liquid, flashing
two-phase, non-flashing two-phase, etc.). All that is needed to solve the equation
is the proper relationship between the pressure (p) and the stream specific
volume ( υ ). This relationship is determined by the type of constraint chosen.
For adiabatic flow, the defining equation is:
H + KE + PE = CONSTANT
Where:
H
KE
PE
=
=
=
Stream enthalpy
Kinetic energy of stream
Potential energy of stream
Between points 1 and 2:
H1 + KE1 + PE1 = H 2 + KE 2 + PE 2
Thus:
H 2 = H1 − ∆KE − ∆PE
ASPEN PLUS flash routines can be used to calculate enthalpy at point 2.
Unit Operation Models
Version 10
10-21
Pressure
Relief
Nozzle Flow
ASPEN PLUS calculates nozzle flow by treating the flow as adiabatic through a
perfect nozzle which has no friction losses and is short enough so that any potential
energy effects can be neglected. The actual flow is then calculated by applying a
correction factor (the flow coefficient, Cd) to the flow calculated as if the nozzle
behaved as perfect. Frictionless flow is described by:
udu + υ dp = 0
(2)
Where:
u
υ
=
=
Stream linear velocity
Specific volume of stream
For adiabatic flow:


u2
d  U + PV +
+ PE  = 0
2


Where:
U
PV
=
=
Internal energy
Pressure-volume product
Neglecting PE, and combining the definition of enthalpy (H = U + PV) into this
equation gives:
dH + udu = 0
(3)
Combining (2) and (3) gives:
dH = υ dp
(4)
By definition:
dH =υ dp
(5)
(4) and (5) yield:
Tds = 0
or
ds = 0
Thus, adiabatic frictionless flow is isentropic.
10-22
Unit Operation Models
Version 10
Chapter 10
The flow equation (2) can be integrated to describe the flow through a perfect
nozzle as follows:
Let p0 = The upstream stagnation pressure where the velocity is zero (u0 = 0).
Let p1 = The pressure in the nozzle throat at which the flow is accelerated to
velocity u.
Thus, the integrated form of (2) becomes:
p
1
1 2
u = − ∫ υ dp
2
p01
which can be re-written (noting that u = G υ ):
p1
G υ = −2 ∫ υ dp
2
2
1
(6)
p0
Equation (6) provides the means to calculate the flow rate through a perfect
nozzle given the upstream stagnation pressure and the proper p-v relationship
(which is isentropic). As one integrates (6) from p0 to p1, a maximum G indicates
that the flow has become choked at the current value of p. (6) also serves as a
method for converting between stagnation and static pressures at any point in
the flow system (pipe or nozzle).
Calculation and Convergence Methods
ASPEN PLUS uses the same equations used to model the safety relief valve as to
model the conversion from stagnation to flowing pressure and back again. To be
completely accurate, the valve should be modeled as in equation (6) in the Nozzle
Flow section, this chapter. This model requires that constant entropy flashes be
performed at each point in the integration of equation (6). This is a very time
consuming calculation, so several options are provided to speed up the calculations.
First, you can choose to do constant enthalpy flashes rather than constant entropy
flashes through the nozzle. This speeds up the calculations by an order of
magnitude, since the constant entropy flash is modeled by a series of constant
enthalpy flashes converging on entropy.
ASPEN PLUS also provides a shortcut method to calculate molar volume as a
function of pressure during the nozzle integration. This method was developed by
L. L. Simpson1 and gives very good results. Instead of doing a flash calculation to
calculate the molar volume at each point in the integration, two flashes are done
at the start and parameters are calculated which allow you to calculate the molar
volume at other pressures without doing flashes.
Unit Operation Models
Version 10
10-23
Pressure
Relief
Vessel Insulation Credit Factor
When Fire Standard API-520 or API-2000 is used, you may claim an insulation
credit factor calculated from the formula:
F=
k (1660 − Tf )
21000t
Where:
k
=
Thermal conductivity of insulation, in British thermal units per
hour per square foot per degree Fahrenheit per inch at mean
temperature.
Tf
=
Temperature of vessel contents at relieving conditions, in degrees
Fahrenheit.
t
=
Thickness of insulation, in inches.
Assuming a k value of 4.0, and Tf of 0.0, the following table, which was taken
from API-2000, gives values of F for various values of insulation thickness:
10-24
Insulation thickness (t)
F Factor
6 inches (152 millimeters)
0.05
8 inches (203 millimeters)
0.037
10 inches (254 millimeters)
0.03
12 inches (305 millimeters)
or more
0.025
Unit Operation Models
Version 10
Chapter 10
References
Simpson, L.L., "Estimate Two-Phase Flow in Safety Devices," Chemical
Engineering, August, 1991, pp. 98-102.
Additional Reading
"Sizing, Selection, and Installation of Pressure-Relieving Devices in Refineries"
Part I - Sizing and Selection, API Recommended Practice 520, American
Petroleum Institute, 1220 L Street Northwest, Washington, D.C. 20005.
"Venting Atmospheric and Low Pressure Storage Tanks," (Non-refrigerated and
Refrigerated), API Standard 2000, American Petroleum Institute, 1220 L Street
Northwest, Washington, D.C. 20005.
❖
Unit Operation Models
Version 10
❖
❖
❖
10-25
Pressure
Relief
10-26
Unit Operation Models
Version 10
Appendix A
A
Sizing and Rating for
Trays and Packings
ASPEN PLUS has extensive capabilities to size, rate, and perform pressure drop
calculations for trayed and packed columns. Use the following Tray/Packing forms
to enter specifications:
• TraySizing
• TrayRating
• PackSizing
• PackRating
These capabilities are available in the following column unit operation models:
•
•
•
RadFrac
MultiFrac
PetroFrac
You can choose from the following five commonly-used tray types:
• Bubble caps
• Sieve
• Glitsch Ballast®
• Koch Flexitray®
• Nutter Float Valve
ASPEN PLUS can model a variety of random packings. You can also use any of
the following types of structured packings:
•
•
•
•
•
Unit Operation Models
Version 10
®
Goodloe
Glitsch Grid®
Norton Intalox Structured Packing
Sulzer BX, CY, Mellapak, and Kerapak
Koch Flexipac, Flexeramic, Flexigrid
A-1
Sizing and
Rating for
Trays and
Packings
For sizing and rating calculations, ASPEN PLUS divides a column into sections.
Each section can have a different tray type, packing type, and diameter. The tray
details can vary from section to section. A column can have an unlimited number
of sections. In addition, you can size and rate the same section with different
types of trays and packings.
The calculations are based on vendor-recommended procedures whenever these
are available. When vendor procedures are not available, well-established
literature methods are used.
ASPEN PLUS calculates sizing and performance parameters such as:
•
•
•
•
Column diameter
Flooding approach or approach to maximum capacity
Downcomer backup
Pressure drop
These parameters are based on:
• Column loadings
• Transport properties
• Tray geometry
• Packing characteristics
You can use the computed pressure drop to update the column pressure profile.
Single-Pass and Multi-Pass Trays
You can use the column models in ASPEN PLUS to:
• Size one- and two-pass trays
• Rate trays with up to four passes
Schematics of one-, two-, three-, and four-pass trays are shown in the next four
figures. ASPEN PLUS performs and reports rating calculations for all panels.
When specifying Weir heights, cap positioning, and number of valves:
A-2
For
Specify
One-pass tray
A single value
Two-pass tray
Up to two values, one for each panels A and B
Three-pass tray
Up to three values, one for each panel (A, B and C)
Four-pass tray
Up to four values, one for each panel (A, B, C and D)
Unit Operation Models
Version 10
Appendix A
The values for the number of caps and number of valves applies for each panel.
For example, two-pass trays have two A panels for tray AA, and two B panels for
tray BB. Therefore, the number of caps per panel is the number of caps per tray
divided by two. Similar consideration is necessary for three- and four-pass trays.
If you specify only one value for multi-pass trays, that value applies to all panels.
When specifying downcomer clearance and width:
Unit Operation Models
Version 10
For
Specify
One-pass tray
A single value for the side downcomer
Two-pass tray
Up to two values, one for the side downcomer, one for the center downcomer
Three-pass tray
Up to two values, one for the side downcomer, one for the off-center downcomer
Four-pass tray
Up to three values: one for the side downcomer, one for the center downcomer, and one for
the off-center downcomer
A-3
Sizing and
Rating for
Trays and
Packings
Outlet Weir Length
Column Diameter
DC-WTOP
WEIR-HT
DCWBOT
DC-HT
DC-CLEAR
A One-Pass Tray
A-4
Unit Operation Models
Version 10
Appendix A
Outlet Weir Length
Column Diameter
CTR. DC
CTR. DC
DC-WTOP
Below
~
~
WEIR-HT
DCWBOT
Panel A
DC-HT
DC-CLEAR
DCWTOP
DCWBOT
Tray AA
Side
Downcomer
Panel B Tray BB
Center
DC-HT
Downcomer
DC-CLEAR
~ ~
~~
A Two-Pass Tray
Unit Operation Models
Version 10
A-5
Sizing and
Rating for
Trays and
Packings
Outlet Weir Length
Column Diameter
OFF-CTR.DC
OFF-CTR.DC
DC-WTOP
DC-WTOP
WEIR-HT
DC-HT
DCCLEAR
Panel A. B. C.
DCOF
DC-WBOT
DC-WTOP
B
A
B
A
C
Panel C. B. A.
Panel A. B. C.
A Three-Pass Tray
A-6
Unit Operation Models
Version 10
Appendix A
Outlet Weir Length
Column Diameter
OFF-CTR.DC
OFF-CTR.DC
SIDE DC
CTR.DC
DC-WTOP
DC-WTOP
WEIR-HT
DC-HT
Panel A. B.
DC-WBOT
DC-WBOT
DCCLEAR
D
D
Panel C. D.
C
DCOF
A
B
B
A
Panel A. B.
A Four-Pass Tray
Unit Operation Models
Version 10
A-7
Sizing and
Rating for
Trays and
Packings
Modes of Operation for Trays
ASPEN PLUS provides two modes of operation for trays:
• Sizing
• Rating
In either mode, you can divide a column into any number of sections. Each
section can have a different column diameter, tray type, and tray geometry. You
can re-rate or re-design the same section with different tray types and/or
packings.
ASPEN PLUS performs the calculations one section at a time. In sizing mode,
the column model determines tray diameter to satisfy the flooding approach you
specified for each stage. The largest diameter is selected.
In rating mode, you specify the column section diameter and other tray details.
For each stage, the column model calculates tray performance and hydraulic
information such as flooding approach, downcomer backup, and pressure drop.
Flooding Calculations for Trays
For bubble caps and sieve trays, ASPEN PLUS provides two procedures for
calculating the approach to flooding. The first procedure is based on the Fair 1
method. The second uses the Glitsch procedure 2 for ballast trays. This procedure
de-rates the calculated flooding approach by 15% for bubble caps and by 5% for
sieve trays. All other hydraulic calculations are based on the Fair and Bolles1,3
methods. For sizing calculations, you can also supply your own calculation
procedure:
= Specify
On form
Flooding calculation method = USER
TraySizing or PackSizing
Subroutine name
UserSubroutines
For valve trays (Glitsch Ballast, Koch Flexitray, and Nutter Float Valve trays),
ASPEN PLUS uses procedures from vendor design bulletins.2,4,5
A-8
Unit Operation Models
Version 10
Appendix A
Bubble Cap Tray Layout
RadFrac uses cap diameter only for tray type CAPS. Valid entries are:
Cap Diameter
Default Weir Height
Inches
Millimeters
Inches
Millimeters
3
76.2
2.75
69.85
4
101.6
3.00
76.20
6
152.4
3.25
82.55
Use the cap diameter to retrieve cap characteristics based on standard cap
designs.
For columns with diameter
The default is
Up to 48 in (1219.2 mm).
3 in (76.2 mm)
Greater than 48 in (1219.2
mm)
4 in (101.6 mm)
The following table lists standard cap designs:
Materials
Stainless Steel
Nominal Size, in
3
4
6
U.S. Standard gauge
16
16
16
OD, in
2.999
3.999
5.999
ID, in
2.875
3.875
5.875
Height overall, in
2.500
3.000
3.750
Number of slots
20
26
39
Type of slots
Trapezoidal
Trapezoidal
Trapezoidal
Bottom
0.333
0.333
0.333
Top
0.167
0.167
0.167
Slot height, in
1.000
1.250
1.500
Height shroud ring, in
0.250
0.250
0.250
Cap
Slot width, in
continued
Unit Operation Models
Version 10
A-9
Sizing and
Rating for
Trays and
Packings
Materials
Nominal size, in
Stainless Steel
3
4
6
U.S. Standard gauge
16
16
16
OD, in
1.999
2.624
3.999
ID, in
1.875
2.500
3.875
0.5-in skirt height
2.250
2.500
2.750
1.0-in skirt height
2.750
3.000
3.250
1.5-in skirt height
3.250
3.500
3.750
0.500
0.500
0.500
Riser
2.65
4.80
11.68
Reversal
4.18
7.55
17.80
Annular
3.35
6.38
14.55
Slot
5.00
8.12
14.64
Cap
7.07
12.60
28.30
Reversal/riser
1.58
1.57
1.52
Annular/riser
1.26
1.33
1.25
Slot/riser
1.89
1.69
1.25
Slot/cap
0.71
0.65
0.52
Riser
Standard heights, in
Riser-slot seal, in
Cap areas, in
Area ratios
Pressure Drop Calculations for Trays
Normally, RadFrac, MultiFrac, and PetroFrac treat the stages you enter as
equilibrium stages. You must enter overall efficiency to:
• Convert the calculated pressure drop per tray to pressure drop per
equilibrium stage
• Compute the column pressure drop
If you do not enter overall efficiency, these models assume 100% efficiency. If you
specify Murphree or vaporization efficiency, you should not enter overall
efficiency. RadFrac, MultiFrac, and PetroFrac will treat the stages as actual
trays.
A-10
Unit Operation Models
Version 10
Appendix A
Foaming Calculations for Trays
Suggested values for Ballast trays are:
Service
System Foaming Factor
Non-foaming systems
1.00
Fluorine systems
0.90
Moderate foamers, such as oil
absorbers, amine, and glycol
regenerators
0.85
Heavy foamers, such as
amine and glycol absorbers
0.73
Severe foamers, such as MEK
units
0.60
Foam stable systems, such as
caustic regenerators
0.30
Suggested values for Flexitrays are:
Service
System Foaming Factor
Depropanizers
0.85-0.95
Absorbers
0.85
Vacuum towers
0.85
Amine regenerators
0.85
Amine contactors
0.70-0.80
High pressure deethanizers
0.75-0.80
Glycol contactors
0.70-0.75
Suggested values for Float valve trays are:
Unit Operation Models
Version 10
Service
System Foaming Factor
Non foaming
1.00
Low foaming
0.90
Moderate foaming
0.75
High foaming
0.60
A-11
Sizing and
Rating for
Trays and
Packings
Packed Columns
The calculations for packings are based on the height equivalent of a theoretical
plate (HETP). HETP=packed height/number of stages. The HETP is required.
You can provide it using one of the following methods:
• Enter it directly on the PackSizing or PackRating forms
• Enter the packing height on the same form
Packing Types and Packing Factors
ASPEN PLUS can handle a wide variety of packing types, including different
sizes and materials from various vendors.
For random packings, the calculations require packing factors. ASPEN PLUS
stores packing factors for the various sizes, materials, and vendors allowed in a
databank. If you provide the following information, ASPEN PLUS retrieves these
packing factors automatically for calculations:
• Packing type
• Size
• Material
You may specify the vendor on the PackSizing or PackRating form.
Is the vendor
specified?
ASPEN PLUS uses
Yes
The packing factor published by the vendor
No
A value compiled from various literature sources
†
††
†,††
Fair, J.R., et al., "Liquid-Gas Systems," Perry’s Chemical Engineers’ Handbook, R.H. Perry and D.
Green, ed., 6th ed. (New York: McGraw Hill, 1984).
Tower Packings, Bulletin No. 15 (Tokyo: Tokyo Special Wire Netting Company).
You can enter the packing factor directly to override the built-in values. ASPEN
PLUS uses the packing type to select the proper calculation procedure.
Modes of Operation for Packing
The column models have two modes of operation for packing:
•
•
A-12
Sizing
Rating
Unit Operation Models
Version 10
Appendix A
In either mode, you can divide a column into any number of sections. Each
section can have different packings. You can re-rate or re-design the same section
with different packings and/or tray types. ASPEN PLUS performs the
calculations one section at a time.
In sizing mode, ASPEN PLUS determines the column section diameter from:
•
•
The approach to the maximum capacity
A design capacity factor you specify
You can impose a maximum pressure drop per unit height (of packing or per
section) as an additional constraint. Once ASPEN PLUS has determined the
column section diameter, it re-rates the stages in the section with the calculated
diameter.
In rating mode, you specify the column diameter. ASPEN PLUS calculates the
approach to maximum capacity and pressure drop.
Maximum Capacity Calculations for Packing
ASPEN PLUS provides several methods for maximum capacity calculations. For
random packings you can use:
Method
For this type of packings
†
Mass Transfer, Ltd. (MTL)
††
Norton
†††
MTL
Norton IMTP
Koch
Koch
Eckert
All other random packings
†
††
†††
Cascade Mini-Ring Design Manual (Tokyo: Dodwell & Company, Ltd., 1984).
Intalox High-Performance Separation Systems, Bulletin IHP-1 (Akron: Norton Company, 1987).
McNulty, K.J., "Hydraulic Model for Packed Tower Design." Paper presented at the American Institute
of Chemical Engineers Spring Meeting in Houston, 1993.
For structured packings, ASPEN PLUS provides vendor procedures for each type.
If you specify the maximum capacity factor, ASPEN PLUS bypasses the
maximum capacity calculations.
The definition of approach to maximum capacity depends on the type of packings.
Unit Operation Models
Version 10
A-13
Sizing and
Rating for
Trays and
Packings
For Norton IMTP and Intalox structured packings, approach to maximum
capacity refers to the fractional approach to the maximum efficient capacity.
Efficient capacity is the operating point at which efficiency of the packing
deteriorates due to liquid entrainment. The efficient capacity is approximately 10
to 20% below the flood point.
For Sulzer structured packings (BX, CY, Kerapak, and Mellapak), approach to
maximum capacity refers to the fractional approach to maximum capacity.
Maximum capacity is the operating point at which a pressure drop of 12 mbar/m
(1.47 in-water/ft) of packing is obtained. At this condition, stable operation is
possible, but the gas load is higher than that at which maximum separation
efficiency is achieved.
The gas load corresponding to the maximum capacity is 5 to 10% below the flood
point. Sulzer recommends a usual design range between 0.5 and 0.8 for approach
to flooding.
For all other packings, approach to maximum capacity refers to the fractional
approach to the flood point.
Because there are different definitions for approach to maximum capacity, sizing
results are not on the same basis for packings from different vendors, even when
you use the same value for approach to maximum capacity. Direct performance
comparison of packings from different vendors is not recommended.
The capacity factor is:
CS = VS
ρV
ρ L − ρV
Where:
A-14
CS
=
Capacity factor
VS
=
Superficial velocity of vapor to packing
ρV
=
Density of vapor to packing
ρL
=
Density of liquid from packing
Unit Operation Models
Version 10
Appendix A
Pressure Drop Calculations for Packing
For random packings, ASPEN PLUS provides several built-in methods to
compute the pressure drop.
Vendor
Pressure drop method
MTL
Vendor
Norton
Vendor procedure
Koch
Vendor procedure♦♦
Not specified
Eckert GPDC♦♦♦, Norton GPDC
†
††
†††
♦
♦♦
♦♦♦
§
§§
†
††, †††, ♦
††, †††, ♦
§
§§
, Prahl GPDC , Tsai GPDC
Cascade Mini-Ring Design Manual (Tokyo: Dodwell & Company, Ltd., 1984).
Dolan, M.J. and Strigle, R.F., "Advances in Distillation Column Design," CEP, Vol.76, No.11
(November 1980), pp. 78-83.
Intalox High-Performance Separation Systems, Bulletin IHP-1 (Akron: Norton Company, 1987).
Intalox Metal Tower Packing, Bulletin IM82 (Akron: Norton Company, 1979).
McNulty, K.J., "Hydraulic Model for Packed Tower Design." Paper presented at the American Institute
of Chemical Engineers Spring Meeting in Houston, 1993.
Fair, J.R., et al., "Liquid-Gas Systems," Perry’s Chemical Engineers’ Handbook, R.H. Perry and D.
Green, ed., 6th ed. (New York: McGraw Hill, 1984), pp. 18-22.
McNulty, K.J. and Hsieh, C.L., "Hydraulic Performance and Efficiency of Koch Flexipac Structured
Packings." Paper presented at American Institute of Chemical Engineers Annual Meeting in Los
Angeles, 1982.
Tsai, T.C. "Packed Tower Program Has Special Features," Oil and Gas Journal, Vol. 83 No. 35
(September, 1985), p. 77.
If you specify the vendor, ASPEN PLUS uses the vendor procedure. If you do not
specify the vendor, you can choose one of four different pressure drop methods. If
you do not specify a method, ASPEN PLUS uses the Eckert generalized pressure
drop correlation (GPDC).
Unit Operation Models
Version 10
A-15
Sizing and
Rating for
Trays and
Packings
For structured packings, vendor pressure drop correlations are available for all
packings:
Packing type
Pressure drop method
Goodloe
Vendor procedure
Glitsch Grid
Vendor procedure
Norton Intalox Structured Packings
Vendor procedure
Sulzer BX, CY, Mellapak, and Kerapak
Vendor procedure♦
Koch Flexipac, Flexeramic, and Flexigrid
Vendor procedure♦♦
†
††
†††
♦
♦♦
†
††
†††
Goodloe, Bulletin 520A (Dallas: Glitsch, Inc., 1981).
Glitsch Grid-Grid/Ring Combination Bed, Bulletin No. 7070 (Dallas: Glitsch, Inc., 1978).
Norton Company, private communication, 1992.
Spiegel, L. and Meier, W., "Correlations of the Performance Characteristics of the Various Mellapak
Types." Paper presented at the 4th International Symposium of Distillation and Absorption, Brighton,
England, 1987.
McNulty, K.J., "Hydraulic Model for Packed Tower Design." Paper presented at the American Institute
of Chemical Engineers Spring Meeting in Houston, 1993.
Liquid Holdup Calculations for Packing
ASPEN PLUS performs liquid holdup calculations for both random and
6
structured packings. The calculations use the Stichlmair correlation. The
Stichlmair correlation requires these parameters:
• Packing void fraction and surface area
• Three Stichlmair correlation constants
ASPEN PLUS provides these parameters for a variety of packings in the built-in
packing databank. If these parameters are missing for a particular packing,
ASPEN PLUS will not perform liquid holdup calculations for that packing.
You can also enter these parameters to provide missing values, or to override the
databank values.
A-16
Unit Operation Models
Version 10
Appendix A
Pressure Profile Update
You can update the pressure profile using:
• Computed pressure drops for the rating mode of both trays and packings
• The sizing mode of packings
If you choose to update the pressure profile, the column models solve the tray or
packing calculation procedures simultaneously with the column-describing
equations. For updating the pressure profile during calculations check Update
Section Pressure Profile on the following forms:
•
•
•
TrayRating
PackSizing
PackRating
Also, you can fix the pressure at the top or bottom of the column and you can
specify this option on the above forms. The stage pressures become additional
variables. ASPEN PLUS uses the pressure specifications given on the
Pres-Profile form to:
• Initialize the column pressure profile
• Fix the pressure drop of stages for which the pressure profile is not updated
Physical Property Data Requirements
Several physical properties that are not normally used for heat and material
balance calculations are required for column sizing and rating. These properties
are:
• Liquid and vapor densities
• Liquid surface tension
• Liquid and vapor viscosities
The physical property method that you specify for a unit operation model must be
able to provide the required properties. In addition, the physical property
parameters needed to calculate the required properties must be available for all
components in the column. See the descriptions of properties in the ASPEN
PLUS User Guide Volume 1, for details on specifying physical property methods
and determining property parameter requirements.
Unit Operation Models
Version 10
A-17
Sizing and
Rating for
Trays and
Packings
References
1. Fair, J.R., et al., “Liquid-Gas Systems,” Perry’s Chemical Engineers'
th
Handbook, R.H. Perry and D. Green, ed. 6 ed., New York: McGraw Hill,
1984.
rd
2. Ballast Tray Design Manual, Glitsch, Inc., Bulletin No. 4900, 3 ed.,
Dallas:1980.
3. Smith, B.D., “Tray Hydraulics: Bubble Cap Trays” and “Tray Hydraulics:
Perforated Trays,” Design of Equilibrium Stage Processes, New York:
McGraw Hill, 1963, pp. 474-569.
4. Koch Flexitray Design Manual, Koch Engineering Co., Inc. Bulletin No. 90,
Wichita.
5. Nutter Float Valve Design Manual, Tulsa: Nutter Engineering Co., 1976.
6. Stichlmair, J., et al., "General Model for Prediction of Pressure Drop and
Capacity of Countercurrent Gas/Liquid Packed Columns," Gas Separation
and Purification, Vol. 3 (1989), p. 22.
❖
A-18
❖
❖
❖
Unit Operation Models
Version 10
B
Index
A
Absorbers
MultiFrac 4-30
RadFrac 4-23
RateFrac 4-62
Aerotran
flash specifications 3-27
flowsheet connectivity 3-26
overview 3-26
physical properties 3-28
solids 3-28
specifying 3-27
AGA method
Pipe model 6-39
Pipeline 6-51
Air separation
MultiFrac 4-30
Air-cooled heat exchangers
Aerotran 3-26
Algorithms
convergence 4-22, 4-25, 4-27, 4-28, 4-42, 4-58
inside-out 4-26, 4-43
Newton 4-22, 4-26, 4-42, 4-44
nonideal 4-22, 4-26
standard 4-26, 4-42, 4-43
sum-rates 4-22, 4-26, 4-42, 4-43
Angel-Welchon-Ros correlation
Pipe model 6-38
Pipeline 6-49
ASME method
Compr 6-10
MCompr 6-15
Azeotropic distillation
RadFrac 4-22
Unit Operation Models
Version 10
Baffle geometry
HeatX 3-13
Baghouses
FabFl 8-23
resistance coefficients 8-25
separation efficiency 8-26
Ballast trays
values A-11
Batch reactors
RBatch 5-25
Beggs and Brill correlation
Pipe model 6-37
Pipeline 6-48
Beggs and Brill correlation parameters
Pipe model 6-38
Pipeline 6-50
B-JAC
Aerotran interface 3-26
Hetran interface 3-23
Bolles method
tray flooding calculations A-8
Bond work index (BWI)
Crusher 8-14, 8-17
Brake horsepower
Compr 6-12
MCompr 6-17
Bubble cap trays
cap diameter A-9
C
Cavitation index
Valve model 6-29
CCD
component attributes 8-66
flowsheet connectivity 8-64
medium temperature 8-67
mixing efficiency 8-66
overview 8-64
profiles 8-66
pseudostreams 8-65
specifying 8-65
Centrifuge filters
CFuge 8-52
CFuge
filter cake 8-53
filtrate flow rate 8-54
flowsheet connectivity 8-52
overview 8-52
Index-1
CFuge (continued)
pressure drop 8-54
rating 8-53
separation efficiency 8-55
sizing 8-53
specifying 8-53
Chilton-Colburn analogy
RateFrac 4-77, 4-84
ClChng
flowsheet connectivity 7-6
overview 7-6
specifying 7-6
stream class change 7-6
Coal
grinding 8-18
Column configuration
RateFrac 4-70
Columns
Distl 4-6
DSTWU 4-3
Extract 4-87
MultiFrac 4-30
packings A-12
PetroFrac 4-48
physical property requirements A-17
pressure drop calculations A-1
RadFrac 4-11, 4-16
RateFrac 4-62
rating A-1
SCFrac 4-8
sizing A-1
Component ratio
RateFrac 4-75
Component separators
Sep 2-12
Sep2 2-14
Compr
ASME method 6-10
flowsheet connectivity 6-9
GPSA method 6-10
isentropic efficiency 6-12
mechanical efficiency 6-12
Mollier method 6-10
net work load 6-10
overview 6-9
performance curves 6-10
polytropic efficiency 6-11
specifying 6-10
steam pressure 6-9
Compressors
Compr 6-9
Heater model 3-2
Index-2
Compressors (continued)
MCompr 6-13
Condensers
PetroFrac 4-51
RateFrac 4-71
Connecting streams
RateFrac 4-70
Continuous stirred tank reactor
RCSTR 5-16
Convergence
algorithms 4-42, 4-43
RateFrac 4-76
Convergence algorithms
PetroFrac 4-58
RadFrac 4-25
Coolers
Heater model 3-2
RadFrac 4-17
RateFrac 4-73
Crude units
SCFrac 4-8
Crusher
Bond work index (BWI) 8-14, 8-17
breakage functions 8-14
flowsheet connectivity 8-13
Hardgrove grindability index (HGI) 8-14, 8-18
overview 8-13
power requirement 8-16
primary crusher 8-16
reduction ratios 8-16
secondary crusher 8-16
selection functions 8-14
specifying 8-14
Cryogenic applications
RadFrac 4-23
Crystallizer
crystal growth rate 8-7
crystal nucleation rate 8-8
flowsheet connectivity 8-3
magma recirculation 8-5
overview 8-3
particle size distribution (PSD) 8-9, 8-10
population balance 8-8
recirculation 8-5
saturation calculation 8-6
solubility 8-5
specifying 8-4
supersaturation 8-6
Cyclone
design calculations 8-28
diameter calculation 8-31
dimension ratios 8-31
Unit Operation Models
Version 10
Cyclone (continued)
dimensions 8-28, 8-32
efficiency correlations 8-29
flowsheet connectivity 8-27
geometry 8-32
Leith and Licht correlation 8-29
operating ranges 8-29
overview 8-27
pressure drop 8-30
rating calculations 8-28
separation efficiency 8-29
Shepherd and Lapple correlation 8-29
solids loading correction 8-34
specifying 8-28
vane constant 8-32
D
Darcy correlation
Pres-Relief 10-12
Decanter model
flowsheet connectivity 2-8
Gibbs free energy 2-10
KLL coefficients 2-10
liquid phases 2-10
liquid-liquid distribution coefficients 2-10
overview 2-8
phase-splitting methods 2-10
separation efficiencies 2-11
solids entrainment 2-11
specifying 2-9
Decanters
CCD 8-64
Decanter model 2-8
Flash3 2-5
RadFrac 4-18, 4-29
Design mode
RateFrac 4-74
Design mode convergence
RadFrac 4-26
Design specification convergence
MultiFrac 4-44
DIERS calculations
Pres-Relief 10-18
Distillation
Distl 4-6
DSTWU 4-3
MultiFrac 4-30
RateFrac 4-62
SCFrac 4-8
Unit Operation Models
Version 10
Distl
Edmister approach 4-6
flowsheet connectivity 4-6
overview 4-6
specifying 4-7
DSTWU
flowsheet connectivity 4-4
Gilliland’s method 4-3
overview 4-3
reflux ratio 4-3
specifying 4-4
Underwood’s method 4-3
Winn’s method 4-3
Dukler correlation
Pipe model 6-37
Pipeline 6-48
Pres-Relief 10-12
Dupl
flowsheet connectivity 7-4
overview 7-4
specifying 7-5
Dynamic scenario algorithm
Pres-Relief 10-19
E
Eaton correlation
Pipe model 6-38
Pipeline 6-49
Edmister approach
Distl 4-6
Efficiencies
Compr 6-12
MCompr 6-16, 6-17
RadFrac 4-20
Electrostatic precipitators
ESP 8-40
Emergency relief vents (ERV)
Pres-Relief 10-15
Equilibrium constants
REquil 5-9
RGibbs 5-13
Equilibrium reactors
REquil 5-8
RGibbs 5-10
ESP
flowsheet connectivity 8-40
gas velocity 8-41, 8-44
operating range 8-41
overview 8-40
particle separation 8-42, 8-44
Index-3
ESP (continued)
power requirement 8-44
pressure drop 8-43
separation efficiency 8-42
specifying 8-41
Ethylene plant primary fractionators
MultiFrac 4-30
PetroFrac 4-48
Evaporators
Flash2 2-2
Flash3 2-5
Exchanger configuration
HeatX 3-11
Exchanger geometry
HeatX 3-5
Extract
flowsheet connectivity 4-87
overview 4-87
specifying 4-88
F
FabFl
calculation options 8-23
filtering time 8-24
flowsheet connectivity 8-23
operating ranges 8-24
overview 8-23
resistance coefficients 8-25
separation efficiency 8-26
specifying 8-23
Fabric filters
FabFl 8-23
Fair method
tray flooding calculations A-8
Feed furnaces
PetroFrac 4-54
Feed stream conventions
RateFrac 4-68
Feed streams
PetroFrac 4-53
Film coefficients
HeatX 3-10, 3-15
Filter model
filter cake characteristics 8-57
flowsheet connectivity 8-56
overview 8-56
pressure drop 8-58
separation efficiency 8-58
specifying 8-56
Index-4
Filters
CFuge 8-52
FabFl 8-23
Filter model 8-56
Flanigan correlation
Pipe model 6-38
Pipeline 6-50
Pres-Relief 10-12
Flash tables
zone analysis 3-21
Flash2
electrolytes 2-4
flowsheet connectivity 2-2
overview 2-2
solids 2-4
specifying 2-3
Flash3
electrolytes 2-6
flowsheet connectivity 2-5
overview 2-5
solids 2-6
specifying 2-6
streams 2-5
Flashes
Flash2 2-2
Flash3 2-5
Flexitrays
values A-11
Float valve trays
values A-11
Fractionators
PetroFrac 4-48
Free-water calculations
MultiFrac 4-46
PetroFrac 4-60
RadFrac 4-20
RateFrac 4-74
FSplit
flowsheet connectivity 1-5
overview 1-5
specifying 1-6
G
Gas-solid separators
Cyclone 8-27
ESP 8-40
FabFl 8-23
VScrub 8-36
General purpose valves
Pres-Relief 10-13
Unit Operation Models
Version 10
Gibbs free energy
Decanter model 2-10
REquil 5-9
RGibbs 5-10
Gilliland’s correlation
DSTWU 4-3
Glitsch Ballast method
tray flooding calculations A-8
GPSA method
Compr 6-10
MCompr 6-15
H
Hagedorn-Brown correlation
Pipe model 6-37
Pipeline 6-49
Hardgrove grindability index (HGI)
Crusher 8-14, 8-18
Hazen-Williams method
Pipe model 6-40
Pipeline 6-52
Heat exchangers
Aerotran 3-26
computational structure 3-21
equations 3-8
Heater model 3-2
HeatX 3-5
Hetran 3-23
MHeatX 3-19
multistream 3-19
zone analysis 3-21
Heat transfer coefficient
HeatX 3-9
Heater model
electrolytes 3-4
flowsheet connectivity 3-3
overview 3-2
solids 3-4
specifying 3-3
Heaters
Heater model 3-2
MultiFrac 4-38
RadFrac 4-17
RateFrac 4-73
Heat-interstaged columns
MultiFrac 4-30
HeatX
baffle geometry 3-13
electrolytes 3-17
exchanger configuration 3-11
Unit Operation Models
Version 10
HeatX (continued)
exchanger geometry 3-5
film coefficients 3-10, 3-15
flash specifications 3-17
flowsheet connectivity 3-6
heat transfer coefficient 3-9
log-mean temperature difference 3-8
model correlations 3-15
nozzle geometry 3-15
option sets 3-17
overview 3-5
physical properties 3-17
pressure drop 3-13, 3-14, 3-15
pressure drop calculations 3-10, 3-15
rating calculations 3-5, 3-6, 3-7, 3-8, 3-9
shell-side film coefficient 3-13
solids 3-17
specifying 3-6
streams 3-6
TEMA shells 3-11
tube geometry 3-14
tube-side film coefficient 3-14
zone analysis 3-5
HETP
packings calculations A-12
RateFrac 4-75
Hetran
flash specifications 3-24
flowsheet connectivity 3-23
overview 3-23
physical properties 3-25
solids 3-25
specifying 3-24
Hughmark method
Pipe model 6-37
Pipeline 6-48
HyCyc
dimension ratios 8-49
dimensions 8-50, 8-51
feed splitting 8-48
flowsheet connectivity 8-45
geometry 8-50
operating ranges 8-46
overview 8-45
particle velocity 8-49
pressure drop correlation 8-50
rating 8-46
separation efficiency 8-47
sizing 8-46
solids separation 8-45
specifying 8-46
velocity correlation 8-49
Index-5
Hydraulic turbines
Pump model 6-2
Hydrocyclones
HyCyc 8-45
I
Inside-out algorithms
MultiFrac 4-43
RadFrac 4-26
Isentropic compressors
Compr 6-9, 6-12
MCompr 6-13
Isentropic turbines
Compr 6-9
MCompr 6-13
K
Kettle reboilers
RadFrac 4-16
Knock-out drums
Decanter model 2-8
Flash2 2-2
Flash3 2-5
L
Leith and Licht correlation
Cyclone 8-29
Liquid-liquid extraction
Extract 4-87
Liquid-solid separators
CFuge 8-52
Filter model 8-56
HyCyc 8-45
LNG exchanger
MHeatX 3-19
Lockhart-Martinelli correlation
Pipe model 6-37
Pipeline 6-49
Pres-Relief 10-12
Log-mean temperature
HeatX 3-8
M
Manipulators
ClChng 7-6
Dupl 7-4
Index-6
Manipulators (continued)
Mult 7-2
MCompr
ASME method 6-15
brake horsepower 6-17
flow coefficient 6-19
flowsheet connectivity 6-14
GPSA method 6-15
head coefficient 6-18
isentropic efficiency 6-16
mechanical efficiency 6-17
Mollier method 6-15
overview 6-13
parasitic pressure loss 6-17
polytropic efficiency 6-16
specific diameter 6-18
specific speed 6-18
specifying 6-14, 6-15
MHeatX
computational structure 3-21
electrolytes 3-22
flash tables 3-21
flowsheet connectivity 3-19
LNG exchanger 3-19
overview 3-19
solids 3-22
specifying 3-20
zone analysis 3-19, 3-20, 3-21
Mixer model
flowsheet connectivity 1-2
overview 1-2
specifying 1-3
Mixers
Heater model 3-2
Mixer model 1-2
Model correlations
HeatX 3-15
Mollier method
Compr 6-10
MCompr 6-15
Mult
flowsheet connectivity 7-2
overview 7-2
specifying 7-3
MultiFrac
algorithms 4-43
connecting streams 4-36
convergence algorithms 4-42, 4-43
design mode 4-42
design specification convergence 4-44
efficiencies 4-41
ethylene plant primary fractionator 4-30
Unit Operation Models
Version 10
MultiFrac (continued)
feed stream conventions 4-35
flow rate 4-38, 4-42
flow ratio 4-40
flowsheet connectivity 4-32
free-water calculations 4-46
heaters 4-38
initialization methods 4-45
Murphree efficiency 4-41
Newton algorithm 4-44
overview 4-30
packings 4-47
physical properties 4-46
property methods 4-46
rating mode 4-42
solids 4-46
specifying 4-33, 4-34
stream definitions 4-34
streams 4-32, 4-33, 4-35, 4-36, 4-42
sum-rates algorithm 4-43
trays 4-47
vaporization efficiency 4-41
Multistage fractionation units
MultiFrac 4-30
Murphree efficiency
MultiFrac 4-41
PetroFrac 4-57
RadFrac 4-21
RateFrac 4-65, 4-75
N
Napthali-Sandholm algorithm
RadFrac 4-26
Nested convergence
RadFrac 4-27
Newton algorithm
MultiFrac 4-44
RadFrac 4-22, 4-26
RateFrac 4-76
Nonequilibrium fractionation
RateFrac 4-62
Nozzle geometry
HeatX 3-15
O
Oliphant method
Pipe model 6-39
Pipeline 6-51
Unit Operation Models
Version 10
Orkiszewski correlation
Pipe model 6-37
Pipeline 6-49
P
Packings
calculations A-12
capacity calculations A-13
liquid holdup calculations A-16
MultiFrac 4-47
PetroFrac 4-61
pressure drop calculations A-15
pressure profile A-17
RateFrac 4-70
rating A-12
sizing A-12
specifying A-1
Stichlmair correlation A-16
types A-1, A-12, A-13
Panhandle methods
Pipe model 6-40
Pipeline 6-51
Particle separation
ESP 8-42, 8-44
PetroFrac
condensers 4-51
convergence algorithms 4-58
design mode 4-59
efficiencies 4-57
ethylene plant primary fractionator 4-48
feed furnace 4-51, 4-54
feed streams 4-53
flowsheet connectivity 4-49
free-water calculations 4-60
liquid runback 4-56
main column 4-50, 4-51
Murphree efficiency 4-57
overview 4-48
packings 4-61
physical properties 4-60
property methods 4-60
pumparounds 4-56
rating mode 4-59
reboilers 4-51
side strippers 4-51, 4-57
solids 4-61
specifying 4-51
streams 4-49
trays 4-61
vaporization efficiency 4-57
Index-7
Petroleum refining fractionation
MultiFrac 4-30
PetroFrac 4-48
Petroleum/petrochemical applications
RadFrac 4-22
Physical properties
columns A-17
HeatX 3-17
Physical property methods
RateFrac 4-74
Pinch points
estimating 3-21
Pipe model
AGA method 6-39
Angel-Welchon-Ros correlation 6-38
Beggs and Brill correlation 6-37
Beggs and Brill correlation parameters 6-38
closed-form methods 6-39
Design-Spec convergence loop 6-34
downstream and upstream integration 6-33
Dukler correlation 6-37
Eaton correlation 6-38
erosional velocity 6-34
fittings modeling 6-35
Flanigan correlation 6-38
flash options 6-32
flowsheet connectivity 6-30
fraction factor correlations 6-35
Hagedorn-Brown correlation 6-37
Hazen-Williams method 6-40
holdup correlations 6-35
Hughmark method 6-37
integration direction 6-33
liquid holdup correlations 6-35
Lockhart-Martinelli correlation 6-37
methane gas systems 6-34
Oliphant method 6-39
Orkiszewski correlation 6-37
overview 6-30
Panhandle methods 6-40
physical property calculations 6-32
pressure drop calculations 6-33
pressure specification 6-31
Slack correlation 6-38
Smith method 6-39
specifying 6-31
stream specification 6-32
two-phase correlations 6-35
valve modeling 6-35
Weymouth method 6-39
Index-8
Pipeline
AGA method 6-51
Angel-Welchon-Ros correlation 6-49
Beggs and Brill correlation 6-48
Beggs and Brill correlation parameters 6-50
closed-form methods 6-50
Design-Spec convergence loop 6-46
downstream and upstream integration 6-45
Dukler correlation 6-48
Eaton correlation 6-49
erosional velocity 6-46
Flanigan correlation 6-50
flowsheet connectivity 6-42
fraction factor correlations 6-47
Hagedorn-Brown correlation 6-49
Hazen-Williams method 6-52
holdup correlations 6-47
Hughmark method 6-48
integration direction 6-45
liquid holdup correlations 6-47
Lockhart-Martinelli correlation 6-49
methane gas systems 6-47
nodes and segments 6-44
Oliphant method 6-51
Orkiszewski correlation 6-49
overview 6-42
Panhandle methods 6-51
physical property calculations 6-45
pressure drop calculations 6-45
Slack correlation 6-49
Smith method 6-51
specifying 6-43
stream specification 6-44
two-phase correlations 6-47
Weymouth method 6-51
Pipes
Pipe model 6-30
Pipeline 6-42
Piping system
Pres-Relief 10-11
Plug flow reactors
RPlug 5-21
Polytropic compressors
Compr 6-9, 6-11
MCompr 6-13
Pres-Relief
3% rule 10-8
97% rule 10-8
Beggs and Brill correlation 10-12
calculation methods 10-23
Unit Operation Models
Version 10
Pres-Relief (continued)
capacity runs 10-6
code compliance 10-6
convergence methods 10-23
credit factors 10-4
Darcy correlation 10-12
data tables 10-12–10-16
DIERS calculations 10-18
disengagement options 10-18
Dukler correlation 10-12
dynamic scenarios 10-2, 10-7, 10-16, 10-18, 10-19
energy input calculations 10-4
fire scenario 10-3
flow equations 10-20
heat exchanger shell 10-17
heat flux scenario 10-5
insulation credit factor 10-24
Lockhart-Martinelli correlation 10-12
manufacturers' tables 10-12–10-16
nozzle flow equation 10-22
overview 10-2
pipe diameters 10-12
pipe flow equation 10-20
pipe specifications 10-11
reactions 10-9
relief system 10-10
relief system flow rating scenario 10-5
relief valve flow rating scenario 10-6
rupture disks 10-15
safety relief valves 10-14
sample solution 10-19
scenarios 10-3
sizing rules 10-7, 10-9
Slack correlation 10-12
specifying 10-2, 10-10, 10-11
spheres 10-17
steady-state scenarios 10-6
stop criteria 10-18
streams 10-7
user-specified vessel 10-17
valve cycling 10-16
valve types 10-10, 10-13
vents 10-15
vessel geometry 10-16
vessel head types 10-17
vessel jacket 10-17
wetted area calculations 10-4
X% rule 10-8
Pressure changers
Compr 6-9
MCompr 6-13
Pipe model 6-30
Unit Operation Models
Version 10
Pressure changers (continued)
Pipeline 6-42
Pump model 6-2
Valve model 6-20
Pressure drop
HeatX 3-13, 3-14, 3-15
Pressure drop calculations
HeatX 3-10, 3-15
Pressure drop models
Pipe model 6-30
Pipeline 6-42
Pressure relief systems
Pres-Relief 10-2
Pump model
flow coefficient 6-7
flowsheet connectivity 6-2
head coefficient 6-7
net positive suction head (NPSH) 6-4
overview 6-2
specific speed 6-5
specifying 6-3
suction specific speed 6-6
Pumparounds
RadFrac 4-18
Pumps
Heater model 3-2
Pump model 6-2
R
RadFrac 4-23
absorbers 4-23
algorithms 4-22
azeotropic distillation 4-22
column configuration 4-13, 4-16
convergence algorithms 4-22, 4-25
convergence methods 4-26, 4-27, 4-28
coolers 4-17
decanters 4-18, 4-29
design mode 4-24
design mode convergence 4-26
design specifications 4-27
efficiencies 4-20
feed streams 4-14
flowsheet connectivity 4-12
free-water calculations 4-20
heaters 4-17
inside-out algorithms 4-26
kettle reboilers 4-16
Murphree efficiency 4-21
Napthali-Sandholm algorithm 4-26
Index-9
RadFrac (continued)
Newton algorithm 4-22, 4-26
nonideal systems 4-22
overview 4-11
petroleum/petrochemical applications 4-22
physical properties 4-28
property methods 4-28
pumparounds 4-18
rating mode 4-23
reactive distillation 4-25
reboilers 4-16
salt precipitation 4-25
simultaneous convergence 4-28
solids handling 4-28
specifying 4-12
stage numbering 4-14
streams 4-12
strippers 4-23
thermosyphon reboilers 4-16
three-phase calculations 4-20, 4-23
two-phase calculations 4-23
UA calculations 4-17
vaporizaton efficiency 4-20
Rate-based modeling
RateFrac 4-62, 4-65
RateFrac
bubble-cap tray column 4-81
Chilton-Colburn analogy 4-77, 4-84
column configuration 4-70
column numbering 4-67
component ratio 4-75
connecting streams 4-70
convergence 4-76
coolers 4-73
correlations 4-76, 4-77
design mode 4-74
efficiencies 4-65, 4-75
equilibrium stages 4-72
feed stream conventions 4-68
flowsheet connectivity 4-63
Fortran subroutines 4-77
free-water calculations 4-74
heat transfer coefficients 4-84
heaters 4-73
HETP 4-65, 4-75
interfacial areas 4-76, 4-77, 4-79, 4-81, 4-82
mass transfer coefficients 4-76, 4-77, 4-79, 4-81, 4-82
Murphree efficiency 4-65
Newton algorithm 4-76
overview 4-62
packing specifications 4-70
Index-10
RateFrac (continued)
physical property method 4-74
rate-based modeling 4-65
rating mode 4-74
reactions 4-72
reactive distillation 4-72
segments 4-71, 4-75
side duties 4-73
sieve tray column correlations 4-82
solution times 4-76
specifying 4-64, 4-66, 4-70
stream definitions 4-68
streams 4-63
tray column 4-79
tray column correlations 4-81, 4-82
tray specifications 4-70
utility exchangers 4-73
valve tray column 4-79
Rating mode
RateFrac 4-74
RBatch
batch operation 5-29
cycle time 5-28
flowsheet connectivity 5-25
mass balances 5-28
overview 5-25
reactions 5-28
specifying 5-26
stop criteria 5-28
temperature controller 5-27
RCSTR
flowsheet connectivity 5-16
overview 5-16
phase volume 5-17
reaction kinetics 5-17
residence time 5-18
scaling methods 5-19
solids reactions 5-18
specifying 5-17
variable scaling 5-19
Reactions
RateFrac 4-72
Reactive distillation
RadFrac 4-25
Reactors
RBatch 5-25
RCSTR 5-16
REquil 5-8
RGibbs 5-10
RPlug 5-21
RStoic 5-2
RYield 5-6
Unit Operation Models
Version 10
Reboilers
PetroFrac 4-51
RadFrac 4-16
Relief devices
Pres-Relief 10-10
REquil
equilibrium constants 5-9
flowsheet connectivity 5-8
Gibbs free energy 5-9
net heat duty 5-8
overview 5-8
solids 5-9
specifying 5-9
streams 5-8
RGibbs
chemical equilibrium 5-12
flowsheet connectivity 5-11
overview 5-10
phase equilibrium 5-12, 5-13
reactions 5-14
restricted chemical equilibrium 5-13
solids 5-14
specifying 5-11
Rigorous distillation
MultiFrac 4-30
PetroFrac 4-48
RadFrac 4-11
RateFrac 4-62
Rigorous extraction
Extract 4-87
RPlug
coolant 5-23
flowsheet connectivity 5-22
overview 5-21
reactions 5-24
solids 5-24
specifying 5-22
RStoic
flowsheet connectivity 5-3
heat of reaction 5-3, 5-4
overview 5-2
product selectivity 5-3, 5-4
specifying 5-3
stream specifications 5-3
RYield
calculation types 5-7
flowsheet connectivity 5-6
heat duty specification 5-7
overview 5-6
specifying 5-7
yield distribution 5-7
Unit Operation Models
Version 10
S
Salt precipitation
RadFrac 4-25
SCFrac
crude units 4-8
flowsheet connectivity 4-8
overview 4-8
specifying 4-9
vacuum towers 4-8
Screen
flowsheet connectivity 8-19
operating levels 8-20
overview 8-19
screen size correlation 8-21
selection function 8-20
separation efficiency 8-21
separation strength 8-20
specifying 8-19
Sep
flowsheet connectivity 2-12
inlet pressure 2-13
outlet stream conditions 2-13
overview 2-12
specifying 2-13
Sep2
flowsheet connectivity 2-14
inlet pressure 2-16
outlet stream conditions 2-16
overview 2-14
specifying 2-15
substreams 2-15
Separators
Decanter model 2-8
Flash2 2-2
Flash3 2-5
Sep 2-12
Sep2 2-14
Shell heat exchangers
Hetran 3-23
Shell-side film coefficient
HeatX 3-13
Shepherd and Lapple correlation
Cyclone 8-29
Shortcut distillation
Distl 4-6
DSTWU 4-3
SCFrac 4-8
Simultaneous convergence
RadFrac 4-28
Sizing recommendations
Pres-Relief 10-9
Index-11
Slack correlation
Pipe model 6-38
Pipeline 6-49
Pres-Relief 10-12
Smith method
Pipe model 6-39
Pipeline 6-51
Solids
Crystallizer 8-3
Flash2 2-4
Flash3 2-6
Heater model 3-4
MHeatX 3-22
RGibbs 5-14
Solids crushers
Crusher 8-13
Solids separators
CFuge 8-52
Crusher 8-13
Cyclone 8-27
ESP 8-40
FabFl 8-23
Filter model 8-56
HyCyc 8-45
Screen 8-19
VScrub 8-36
Solids washers
CCD 8-64
SWash 8-61
Splitters
FSplit 1-5
Sep 2-12
Sep2 2-14
SSplit 1-8
SSplit
flowsheet connectivity 1-8
overview 1-8
specifying 1-8
Stichlmair correlation
packings calculations A-16
Stoichiometric reactors
RStoic 5-2
Stream classes
changing 7-6
Stream definitions
RateFrac 4-68
Stream manipulators
ClChng 7-6
Dupl 7-4
Mult 7-2
Stream mixers
Mixer model 1-2
Index-12
Stream multiplication
Mult 7-2
Stream pressure changers
Pump model 6-2
Stream splitters
FSplit 1-5
SSplit 1-8
Streams
combining 1-8
Flash3 2-5
splitting 2-12, 2-14
Strippers
MultiFrac 4-30
RadFrac 4-23
RateFrac 4-62
Substream splitters
SSplit 1-8
Sum-rates algorithm
MultiFrac 4-43
SWash
bypass fraction 8-63
flowsheet connectivity 8-61
mixing efficiency 8-62
overview 8-61
specifying 8-62
T
TEMA shells
HeatX 3-11
Thermosyphon reboilers
RadFrac 4-16
Three-phase calculations
RadFrac 4-20
Trays
Bolles method A-8
bubble cap A-9
downcomer specifications A-3
Flexitrays A-11
float valve A-11
flooding calculations A-8
foaming calculations A-11
MultiFrac 4-47
PetroFrac 4-61
pressure drop calculations A-10
pressure profile A-17
RateFrac 4-70
rating A-2, A-8
sizing A-2, A-8
specifying A-1
types A-1
Unit Operation Models
Version 10
Tube geometry
HeatX 3-14
Tube heat exchangers
Hetran 3-23
Tube-side film coefficient
HeatX 3-14
Turbines
Compr 6-9
MCompr 6-13
Pump model 6-2
U
Underwood’s method
DSTWU 4-3
Unit operation models
user-supplied 9-2, 9-4
User model
flowsheet connectivity 9-2
Fortran subroutines 9-3
overview 9-2
specifying 9-3
User2
flowsheet connectivity 9-4
Fortran subroutines 9-5
overview 9-4
specifying 9-5
V
Vacuum filters
Filter model 8-56
Vacuum towers
SCFrac 4-8
Valve model
calculation types 6-20
cavitation index 6-29
characteristic equation 6-26
choked flow 6-28
flow coefficient 6-24
flowsheet connectivity 6-20
overview 6-20
piping geometry factor 6-26
pressure drop calculation 6-20, 6-28
pressure drop ratio factor 6-22
pressure recovery factor 6-23
specifying 6-20
Valves
cycling 10-16
Heater model 3-2
Pipe model 6-35
Unit Operation Models
Version 10
Valves (continued)
safety relief 10-14
types used in Pres-Relief 10-10, 10-13–10-16
Valve model 6-20
Vaporization efficiency
MultiFrac 4-41
PetroFrac 4-57
RadFrac 4-20
Vents
Pres-Relief 10-15
Venturi scrubbers
VScrub 8-36
VScrub
flowsheet connectivity 8-36
overview 8-36
pressure drop 8-38
rating 8-37
separation efficiency 8-39
sizing 8-37
specifying 8-37
W
Weymouth method
Pipe model 6-39
Pipeline 6-51
Winn's method
DSTWU 4-3
Y
Yield reactors
RYield 5-6
Z
Zone analysis
HeatX 3-5
MHeatX 3-19, 3-20, 3-21
Index-13
Index-14
Unit Operation Models
Version 10
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