Operational Aspects
Process, Energy and System
Typical:
Processes are designed & optimized based on given
(fixed) data (flowrates, temperatures, pressures, etc.)
But:
Processes (and Heat Exchanger Networks) are:
− often operated “off” design (above/below)
− subject to disturbances
− to be started up and shut down
The Result:
The Process Engineer will over-design before the
Control Engineer adds new Units for Manipulation
Various Topics for Heat Exchanger Networks
T. Gundersen
OPER 01
•
Various Operational Aspects
Controllability

Process, Energy and System
•
•
•
•
•
•
•

Property of the Process, not the Control System
Ability to handle operational Variations
Flexibility

Ability to cope with different Operating Conditions
Start-Up and Shut-Down

Starting up from “Cold” Conditions is challenging
“Switchability”

Change Operation from one Condition to another
Environmental Aspects
Safety
Maintenance
“RAMS”

Reliability, Availability, Maintainability, Safety
Various Topics for Heat Exchanger Networks
T. Gundersen
OPER 02
Two important Aspects of Operability
• Controllability of Processes
Process, Energy and System


“Ability to handle Short Term Variations”
Withstand (unwanted) Disturbances
 Stability Issues

•
Follow (wanted) Set-Point Changes
 On-line Optimization
Flexibility of Processes


“Ability to handle Long Term Variations”
Undesirable Variations
 Fouling (or Scaling) in Heat Exchangers
 Deactivation of Catalysts

Desirable Variations/Changes
 New Raw Materials and/or new Products
 Changes in Production Volume
Various Topics for Heat Exchanger Networks
T. Gundersen
OPER 03
Similarities/Analogies between Synthesis
of Processes and Control Systems
Process, Energy and System
Process
Control
Levels
• Production Site
• Process
• Equipment
• Optimizing
• Advisory
• Basic Control
Structure
• Choice of Units
• Matching
• Sequences
• Manipulators
• Pairing
• Controller Types
Parameters
• Pressures
• Temperatures
• Flowrates
• Gain
• Integral Time
• Derivative Time
Various Topics for Heat Exchanger Networks
T. Gundersen
OPER 04
WS-1: Heat Integration
Process, Energy and System
Stream
H1
H2
C1
Steam
ΔH
Ts
Tt
mCp
°C
°C
kW/°C kW
300 100
200 100
50 250
280 280
Cooling Water 15
20
1.5
5.0
4.0
300
500
800
(var)
(var)
Specification:
ΔTmin = 20°C
Find:
QH,min , QC,min
Tpinch , Umin
Umin,MER
and Network
Notice:
1) H1 and H2 provide as much heat as C1 needs (800 kW)
2) Ts (C1) < Tt (H1,H2) − 20° and Ts (H1) > Tt (C1) + 20°
Heat Integration − Introduction
T. Gundersen
OPER 05
WS-1: What about Controllability?
Process, Energy and System
III
I
300°C
mCp
(kW/°C)
200ºC
186.7ºC
H1
100°C
C
1.5
130
200°C
II
100°C
5.0
H2
50°C
250°C
H
130
217.5°C
180°C
150
55°C
500
C1
4.0
20
MER Design with QH = QH,min , QC = QC,min , U = Umin,MER
Consider: Disturbance for H1 inlet T, while controlling H2 outlet T
Heat Integration − Introduction
T. Gundersen
OPER 06
Flexibility in Heat Exchanger Networks
Process, Energy and System
mCp
310°
1.0
H1
1
450°
2.0
3.0
2.0
50°
290°
3
H2
2
280°
285°
C
10 kW
120°
290°
1
20 kW
280°
40°
2
C1
240 kW
115°
3
C2
330 kW
Various Topics for Heat Exchanger Networks
T. Gundersen
OPER 07
Flexibility in Heat Exchanger Networks
Process, Energy and System
mCp
310°
1.85
H1
1
450°
2.0
3.0
2.0
50°
179.7°
3
H2
2
280°
395.5°
C
231 kW
120°
290°
1
241 kW
169.5°
40°
2
C1
240 kW
115°
3
C2
109 kW
Various Topics for Heat Exchanger Networks
T. Gundersen
OPER 08
Flexibility in Heat Exchanger Networks
Process, Energy and System
mCp
310°
1.35
H1
1
50°
227.8°
2
450°
2.0
3.0
2.0
3
H2
280°
330.5°
C
101 kW
120°
290°
1
111 kW
234.5°
40°
2
C1
240 kW
115°
3
C2
239 kW
Various Topics for Heat Exchanger Networks
T. Gundersen
OPER 09
Flexibility in Heat Exchanger Networks
Process, Energy and System
In Summary:
The Network Structure was Flexible (Resilient) for
the Cases when mCp was 1.0 and 1.85 for Stream
H1, but did not work when mCp was 1.35 even
with infinite Heat Transfer Area.
The Reason:
The Problem is Non-Convex, which happens when:
− the Pinch point changes
− there is a change in Mass Flowrates
Various Topics for Heat Exchanger Networks
T. Gundersen
OPER 10
WS-5: Design for Flexibility
Q: How to handle Fouling ?
Process, Energy and System
U1 (W/m2K)
200°
1
1
170°
115°
2
155°
3
2
175°
1
175°
H
90°
120
4
20°
84°
138°
134°
Exchanger 1
has fouling
above 125°C
3
2
3
73°
81
20°
4
4
6
12 Time
(months)
Ref.: Kotjabasakis and Linnhoff, Oil & Gas Jl., Sept. 1987
Various Topics for Heat Exchanger Networks
T. Gundersen
OPER 11
WS-5: Fouling in Heat Exchangers
1: The Traditional Approach
Process, Energy and System
200°
1
170°
115°
2
1
155°
3
2
175°
1
175°
H
90°
4
New Area:
148 m2
20°
84°
138°
134°
3
2
73°
4
3
Energy Usage:
20°
Constant (the same)
4
Various Topics for Heat Exchanger Networks
T. Gundersen
OPER 12
WS-5: Fouling in Heat Exchangers
2: An alternative Solution
Process, Energy and System
200°
170°
115°
2
1
1
155°
3
2
175°
H
175°
H
1
138°
134°
90°
4
New Unit:
Heater on Stream 3
20°
84°
3
2
73°
4
3
Energy Usage:
20°
From 1850 to 2140 kW
4
Various Topics for Heat Exchanger Networks
T. Gundersen
OPER 13
WS-5: Fouling in Heat Exchangers
3: Use Network Interactions
Process, Energy and System
200°
1
170°
115°
2
1
155°
3
2
175°
1
175°
H
90°
4
New Area:
103 m2
20°
84°
138°
134°
3
2
73°
4
3
Energy Usage:
20°
15% Reduction !!
4
Various Topics for Heat Exchanger Networks
T. Gundersen
OPER 14
WS-5: Fouling in Heat Exchangers
Summary
Process, Energy and System
“Method/Approach”
ΔArea
ΔEnergy
Traditional Approach
148 m2
0
Alternative Solution
New Heater
+ 13%
Network Interactions
103 m2
- 15%
Best Result obtained by using a “Systems Approach”
Various Topics for Heat Exchanger Networks
T. Gundersen
OPER 15
Summary of Operability
Process, Energy and System
•
•
•
•
•
Plant Operation is often “Off-Design”
•
Process Integration has a Focus precisely
on the Structural Aspects of Process Plants
Controllability (Short Term Variations)
Flexibility (Long Term Variations)
A new Design Strategy for Fouling
The importance of Topology (Flowsheet or
Network Structure) has been proven
Various Topics for Heat Exchanger Networks
T. Gundersen
OPER 16

Objectives
Process, Energy and System




from Energy Cost
to Equipment Cost
to Total Annualized Cost
and also Operability, including
 Flexibility
 Controllability
 Switchability
Expansions
of PA & PI
 Start-up & Shut-down
 New Operating Conditions
 and finally Environment, including
 Emissions Reduction
 Waste Minimization
Expansions of Process Integration
T. Gundersen
EXP 01

Scope
Expansions
of PA & PI
Process, Energy and System
 from Heat Exchanger Networks
 to Separation Systems, especially
 Distillation and Evaporation (heat driven)
 to Reactor Systems
 to Heat & Power, including
 Steam & Gas Turbines and Heat Pumps
 to Utility Systems, including
 Steam Systems, Furnaces, Refrigeration Cycles
 to Entire Processes
 to Total Sites
 to Regions
Expansions of Process Integration
T. Gundersen
EXP 02

Expansions
Plants
Process, Energy and System
 from Continuous
 to Batch and Semi-Batch

of PA & PI
Projects
 from New Design
 to Retrofit
 to Debottlenecking

Thermodynamics
 from Simple 1st Law Considerations
 to Various 2nd Law Applications
 Exergy in Distillation and Refrigeration
Expansions of Process Integration
T. Gundersen
EXP 03
Expansions
Process, Energy and System

Methods
of PA & PI
 Pinch based Methodologies from Analogies
 from Heat Pinch for Heat Recovery and CHP in
Thermal Energy Systems
 to Mass Pinch for Mass Transfer / Mass
Exchange Systems
 to Water Pinch for Wastewater Minimization
and Distributed Effluent Treatment Systems
 to Hydrogen Pinch for Hydrogen Management
in Oil Refineries
 Other Schools of Methods
 was discussed on a previous slide
Expansions of Process Integration
T. Gundersen
EXP 04
Process, Energy and System
Expansions
in Process
Integration
Process Integration is much
more than Pinch Analysis for
Heat Exchanger Networks
Strategic
Planning
Heat
Integration
Conceptual
Design
Detailed
Engineering
Expansions of Process Integration
T. Gundersen
EXP 05
Stages and Analogies in Methods
T
Process, Energy and System
Heat Pinch
Heat
Pinch
Modeling
Q
Mass Pinch
Data Extraction
Graphical Diagrams
Analysis
Representations
and Concepts
Water Pinch
Design
Performance Targets
ahead of Design
Hydrogen Pinch
Optimization
Pinch Decomposition
Expansions of Process Integration
T. Gundersen
EXP 06
Wastewater Minimization
Process, Energy and System
Topic:
Efficient Use of Wastewater
Reuse, Regeneration and Recycling
- both Targets and Design
Methods:
Ref.:
Water Pinch (discussed here)
Mathematical Programming
Wang and Smith “Wastewater Minimization”,
Chem. Engng. Sci., vol. 49, pp 981-1006, 1994
Water Pinch Demonstration
T. Gundersen
EXP 07
Wastewater Minimization
Process, Energy and System
Graphical Representation
T
C
mass/heat
analogy
Cpr,in
Cout,max
Cpr,out
Cin,max
3
2
1
m
H
H = mCp ΔT
Δm = mH2O C
Water Pinch Demonstration
T. Gundersen
EXP 08
Main Results from Pinch Analysis
QH,min
Process, Energy and System
T
C
Heat
Pinch
QC,min
Water
Pinch
Watermin
H
m
• The Concept of Composite Curves


Applicable whenever an “Amount” has a “Quality”
Heat & Temperature, Mass & Concentration, etc.
• A Two Step Approach: Targets ahead of Design
• A fundamental Decomposition at the Pinch
Final Summary
T. Gundersen
SUM 01
Objectives for using Process Integration
Process, Energy and System
• Minimize Total Annual Cost by optimal Trade•
•
•
•
•
•
off between Energy, Equipment and Raw Material
Within this trade-off: minimize Energy, improve
Raw Material usage and minimize Capital Cost
Increase Production Volume by Debottlenecking
Reduce Operating Problems by correct rather
than maximum use of Process Integration
Increase Plant Controllability and Flexibility
Minimize undesirable Emissions
Add to the joint Efforts in the Process Industries
and Society for a Sustainable Development
Final Summary
T. Gundersen
SUM 02