RMIT University
DETAILED DESIGN REPORT
PROC 1025 Project Design – AMINE
REGENERATOR
Brennan Raymakers
Monday 5th October 2015
1
Executive Summary
The amine regenerator column is an important application in the process of natural gas extraction and
purifying. The acid gases are dissolved into the solution by an absorption tower, in which the product
is therefore sent to the regenerator column that regenerats the amine solvent by steam and heat, ideally
breaking the molecular bonds of the dissolved gases and separates the two states.
The gas extracted in this unit comprises of carbon dioxide (CO2) and hydrogen sulphide (H2S).
Through this report the methodology, ideology and implementation of certain processes of regenerator
column applications will be investigated and once delegated, the mechanical design will be
engineered according to the maximal beneficiary plausible to both external and internal stakeholders.
Within the Amine regeneration column, certain considerations should be met in order to ensure
appropriate choice of process selection. The main design considerations that are prevalent throughout
industry including distillation, absorber and regenerator columns which consist of vertical columns or
towers that use trays, in which the different arrangements and their applications will be investigated.
Due the large flow rates, the construction will require two carbon steel regenerator columns that are
inherently designed with twenty sieve trays made from stainless steel. The total cost for both columns
in the current year 2015 is US $1,435,584.8. The regenerator column will treat 981.6 tonnes of gas
dissolved in a solvent flow rate of 2571.64 tonnes MEA (monoethalamine) each day.
The reboiler analysis will also be conducted and designed mechanically within the report to best suit
the strippers operation, in which the total power input required is 49MW using steam as the heating
medium. Other major components involved in the extractors operation are omitted within this report
as the sole operation surrounding the stripper (including reboiler) is discussed and designed.
The total life of the column is taken as 20 years along with entirety of the plant which will require
specific attention in maintenance and quality grading inspections to ensure high operability.
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Contents
1
Executive Summary ......................................................................................................................... 2
Contents .................................................................................................................................................. 3
2
Table of Figures .............................................................................................................................. 6
3
Table of Tables ................................................................................................................................ 9
4
Nomenclature ................................................................................................................................ 10
5
Introduction ................................................................................................................................... 12
6
Literature Review and Assessment of Alternatives ....................................................................... 13
6.1
Packed Column ..................................................................................................................... 13
6.1.1
Cost of Packing ............................................................................................................. 14
6.1.2
Operation of Packing .................................................................................................... 14
6.1.3
Conclusion .................................................................................................................... 14
6.2
Tray Column Bubble Cap Application .................................................................................. 15
6.2.1
Operation of Bubble cap ............................................................................................... 15
6.2.2
Comparison & Summary .............................................................................................. 16
6.3
Tray Column Valve Application............................................................................................ 16
6.3.1
6.4
Operation of Valve ........................................................................................................ 17
Tray Column Sieve (With Weir) Application ........................................................................ 18
6.4.1
Operation of Sieve ........................................................................................................ 18
6.4.2
Comparison & summary ............................................................................................... 19
6.4.3
Cost Analysis of Tray Variations ................................................................................... 19
6.5
Tray Column Size Calculation & Comparison ..................................................................... 20
6.5.1
Sieve Tray Example ...................................................................................................... 21
6.5.2
Valve Tray Example ...................................................................................................... 22
6.5.3
Bubble Cap Calculation ................................................................................................ 23
Table 2: Bubble Cap Calculation Data, (Perry 1997) ........................................................................... 23
6.5.4
6.6
Results ........................................................................................................................... 23
Conclusion & Justification of Tray Arrangement ................................................................. 23
6.6.1
Tray Efficiency Comparison ......................................................................................... 24
6.6.2
GEMI Stakeholder Relevance ....................................................................................... 25
6.6.3
Conclusion .................................................................................................................... 25
6.7
Reboiler Arrangement Selection ........................................................................................... 26
6.7.1
Natural Recirculation Reboiler ..................................................................................... 26
6.7.2
Forced Circulation Reboiler .......................................................................................... 27
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7
6.7.3
Thermosyphon Reboiler ................................................................................................ 28
6.7.4
Kettle Reboiler .............................................................................................................. 29
6.7.5
Reboiler Summary ........................................................................................................ 30
Equipment Design Regenerator Column ...................................................................................... 31
7.1
Mass & Energy Balance ........................................................................................................ 31
Table 5: Energy Balance of Regenerator ............................................................................................... 31
Table 6: Mass Balance of Regenerator.................................................................................................. 32
7.1.1
Tray Specifications........................................................................................................ 32
7.1.2
Number of theoretical trays........................................................................................... 33
7.1.3
Actual trays ................................................................................................................... 33
7.2
Tray Hydraulics..................................................................................................................... 34
7.2.1
Design Procedure .......................................................................................................... 34
7.3
Relevant Data & Assumptions .............................................................................................. 35
7.4
Summary of Design Results .................................................................................................. 36
Table 10: Summary of Design Results .................................................................................................. 36
7.5
Detailed Design ..................................................................................................................... 37
7.5.1
Top and bottom diameter calculation and comparison.................................................. 37
7.5.2
Liquid flow arrangement ............................................................................................... 40
7.5.3
Provisional Tray Design ................................................................................................ 41
7.5.4
Entrainment ................................................................................................................... 46
7.6
Weeping ................................................................................................................................ 48
Expressed in kilopascals, the pressure difference is ............................................................................. 51
Lmd = liquid flow rate downcomer kg/s ............................................................................................... 53
7.7
8
Safety and Environmental Considerations ............................................................................ 55
7.7.1
Safety Considerations ................................................................................................... 55
7.7.2
Environmental Considerations ...................................................................................... 55
Equipment Design Kettle Reboiler ............................................................................................... 56
8.1
Area calculation .................................................................................................................... 57
Table 14: Data obtained from energy balance....................................................................................... 58
9
10
Mechanical Design of Reboiler..................................................................................................... 63
9.1
Internal Velocity .................................................................................................................... 63
9.2
Tube Layout & Bundle Diameter .......................................................................................... 63
9.3
Dimensions of Kettle Reboiler .............................................................................................. 65
Mechanical Design of Regenerator ........................................................................................... 66
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10.1
Materials of Construction...................................................................................................... 66
10.2
Overall Vessel ....................................................................................................................... 69
10.2.1
Height of vessel............................................................................................................. 69
10.2.2
Dead weight of column ................................................................................................. 69
10.2.3
Vessel Support- skirt design .......................................................................................... 71
10.2.4
Vessel Heads and Closures ............................................................................................ 75
10.2.5
Head and vessel thickness ............................................................................................. 76
10.2.6
Vessel Erection and Transportation ............................................................................... 77
10.3
Maintenance .......................................................................................................................... 79
10.3.1
Fouling .......................................................................................................................... 79
10.3.2
Cleaning ........................................................................................................................ 79
10.3.3
Alarms and trips ............................................................................................................ 80
10.4
Mechanical Illustrations ........................................................................................................ 81
10.4.1
10.5
Manway......................................................................................................................... 84
Flanges & Nozzles ................................................................................................................ 85
10.5.1
Flange types .................................................................................................................. 85
10.5.2
Lap-joint flange ............................................................................................................. 87
10.5.3
Flange Face ................................................................................................................... 88
10.5.4
Gaskets .......................................................................................................................... 90
10.5.5
Nozzles .......................................................................................................................... 91
10.6
Functionality of Column ....................................................................................................... 92
10.6.1
Start Up Procedure ........................................................................................................ 92
10.6.2
Steady state operation ................................................................................................... 93
10.6.3
Shut down procedure .................................................................................................... 94
11
Data Sheet ................................................................................................................................. 95
12
Process Instrumentation & Control Diagram ............................................................................ 96
Table 28: PID Controls ......................................................................................................................... 97
12.1
Process Variables................................................................................................................... 97
12.2
Process Control ..................................................................................................................... 98
12.3
Level Sensors & Control ....................................................................................................... 99
12.4
Flow Sensors & Control...................................................................................................... 101
12.5
Temperature Sensors ........................................................................................................... 103
12.6
Pressure Sensors & Control ................................................................................................ 104
12.7
Equipment cost.................................................................................................................... 106
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13
2
References ............................................................................................................................... 108
Table of Figures
Figure 1: Structured Packing ................................................................................................................. 13
Figure 2: Random Packing ..................................................................................................................... 13
Figure 3: Cost of Packing Materials ....................................................................................................... 14
Figure 4: Random Packing, [Engineering Data Book. 2004] .................................................................. 14
Figure 5: Tray vs Packed MEA System Comparison, Hall, Stephen. (2012) ........................................... 14
Figure 6: Bubble Cap [Engineering Data Book. 2004] ........................................................................... 15
Figure 7: Bubble Cap Gas Flow [Engineering Data Book. 2004]............................................................ 16
Figure 8: Valve. [ Walas, S.M.. (1990)] .................................................................................................. 17
Figure 9: Sieve Tray, [Coker, A. Kayode. (2010)] .................................................................................... 18
Figure 10: Tray Cost Analysis, [Coker, A. Kayode. (2010).] .................................................................... 19
Figure 11: Tray Cost Analysis, [Perry, Robert H. Green, Don W. 1997].................................................. 19
Figure 12: Cost of Materials, [Perry, Robert H. Green Don W. 1997] .................................................... 20
Figure 13: Sieve tray Design, [Perry, Robert H. Green, Don W. 1997] ................................................... 21
Figure 14: Tray Design Pass, [Perry, Robert H. Green, Don W. 1997] .................................................... 22
Figure 15: Tray Efficiency Comparison, [Walas, S.M.. (1990)] ............................................................... 24
Figure 16: Application Comparison of Trays, [Hall, Stephen. (2012)] ................................................... 24
Figure 17: Natural Circulation Reboiler, [Hall, Stephen. (2012)] ........................................................... 26
Figure 18: Forced-Circulation Reboiler, [Hall, Stephen. (2012)]............................................................ 27
Figure 19: Thermosyphon Reboiler (horizontal), [Hall, Stephen. (2012)] ............................................. 28
Figure 20: Thermosyphon Reboiler (vertical), [Hall, Stephen. (2012)] ................................................. 28
Figure 21: Kettle reboiler, [Hall, Stephen. (2012)] ................................................................................ 29
Figure 22: Overall Regenerator ............................................................................................................. 31
Figure 23: Regenerator Column ............................................................................................................ 31
Figure 24: Tray Efficiencies, (Sinnott 2009) ........................................................................................... 33
Figure 25: Single Pass Column & Tray, [Moss, Dennis R. Basic, Michael M.. (2013)] ............................ 36
Figure 26: Picket Weir, Sinnott, Ray K. Towler, Gavin. (2009)................................................................ 36
Figure 27: Flv Vs K1, , Sinnott, Ray K. Towler, Gavin. (2009) ................................................................. 38
Figure 28: Dc Vs Volumetric Liq Flowrate, (Sinnott 2009) ..................................................................... 40
Figure 29: Flow Arrangement, (Coker 2010) ......................................................................................... 41
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Figure 30: Angle Relation ...................................................................................................................... 42
Figure 31: Ad/Ac Vs lw/Dc, (Sinnott 2009) ............................................................................................ 43
Figure 32: Ah/Ap Vs Lp/dh, (Sinnott 2009) ........................................................................................... 45
Figure 33: FLV Vs Ψ, (Sinnott 2009)....................................................................................................... 47
Figure 34: liquid height vs K2 ................................................................................................................ 48
Figure 35: Ah/Ap Vs Co.......................................................................................................................... 50
Figure 36: Downcomer Backup ............................................................................................................. 52
Figure 37: Kettle Reboiler Arrangement ............................................................................................... 56
Figure 38: Reboiler ................................................................................................................................ 56
Figure 39: Pitch Arrangements, (Sinnott 2009) ..................................................................................... 63
Figure 40: Mechanical Design of Kettle Reboiler, (Sinnott 2009).......................................................... 65
Figure 42: Material Selection Summary ............................................................................................... 68
Figure 41: Stainless Steel Metallurgy, (Moss 2013) .............................................................................. 68
Figure 43: Skirt Arrangement, (Moss 2013) .......................................................................................... 71
Figure 44: Supporting Skirt Dimensions, (Sinnott 2009) ....................................................................... 72
Figure 45: Vessel Domed Heads, (Sinnott 2009) ................................................................................... 75
Figure 46: Torispherical Head................................................................................................................ 76
Figure 47: Typical Trucking Compliance Audit, (Moss 2013)................................................................. 77
Figure 48: lifting lug dimensions ........................................................................................................... 78
Figure 49: Lifting lug, (Moss 2013) ........................................................................................................ 78
Figure 50: Low level trip, (Lieberman 2009) ......................................................................................... 80
Figure 51: Typical Sieve Tray Arrangement, (Moss 2013) ................................................................... 81
Figure 52: Column outer dimensions .................................................................................................... 82
Figure 53: Sieve tray dimensions .......................................................................................................... 83
Figure 54: Column internal & external applications ............................................................................. 83
Figure 55: Manway Illustration, (Arnold 2008) ..................................................................................... 84
Figure 56: Welding rock flange.............................................................................................................. 85
Figure 57: slip on flange ........................................................................................................................ 85
Figure 58: Lap-point flange ................................................................................................................... 85
Figure 59: screwed flange ..................................................................................................................... 85
Figure 60: Blind flange .......................................................................................................................... 85
Figure 61: Lap-joint flange measurements ........................................................................................... 87
Figure 62: Lap-joint flange dimensions ................................................................................................. 87
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Figure 63: Spigot and Socket ................................................................................................................. 88
Figure 64: Narrow faced flange ............................................................................................................. 88
Figure 65: Full face flange ..................................................................................................................... 88
Figure 66: Stripper Operating Actions .................................................................................................. 93
Figure 67: Process Instrumentation Diagram (PID) ............................................................................... 96
Figure 68: Float Level Control,[Battikha, N.E.. (2007).] ......................................................................... 99
Figure 69: Level Measurement Comparisons, [Battikha, N.E.. (2007).] .............................................. 100
Figure 70: Orifice Plate Pressure Sensor, [Battikha, N.E.. (2007)] ....................................................... 101
Figure 71: Flow Measurement Comparison, [Battikha, N.E.. (2007).] ................................................ 102
Figure 72: Temperature Sensor Comparison, [Battikha, N.E.. (2007).] ............................................... 103
Figure 73: Temperature Sensor Thermocouple, [Battikha, N.E.. (2007).] ........................................... 104
Figure 74: Pressure Piezoeletric Sensor, [Battikha, N.E.. (2007).] ....................................................... 104
Figure 75: Pressure Measurement Comparisons, [Battikha, N.E.. (2007)] ......................................... 105
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3
Table of Tables
Table 1:Example Data ............................................................................................................................ 20
Table 2: Bubble Cap Calculation Data, (Perry 1997) ........................................................................... 23
Table 3: Overall Summary Tray Type [Trambouze, Pierre. (2000) ...................................................... 23
Table 4: Reboiler Comparison, [Hall, Stephen. (2012)] ......................................................................... 30
Table 5: Energy Balance of Regenerator ............................................................................................... 31
Table 6: Mass Balance of Regenerator.................................................................................................. 32
Table 7: Tray Parameters ....................................................................................................................... 32
Table 8: : Relevant Data (obtained from energy & mass balance) ........................................................ 35
Table 9: Assumed Values for Design .................................................................................................... 35
Table 10: Summary of Design Results .................................................................................................. 36
Table 11: Liquid Flow Arrangment ........................................................................................................ 40
Table 12: Energy & Mass Balance of Reboiler ..................................................................................... 56
Table 13: Relevant Data......................................................................................................................... 57
Table 14: Data obtained from energy balance....................................................................................... 58
Table 15: Relevant Data Assumed According to Operability ............................................................... 59
Table 16: Relevant Data Obtained ........................................................................................................ 60
Table 17: Pitch of Tube Parameters, Reboiler, (Sinnott 2009) .............................................................. 63
Table 18: Kettle Reboiler Summary...................................................................................................... 65
Table 19: Metallurgical recommendations for MEA (Ropital 2009) .................................................... 67
Table 20: Insulation Properties ............................................................................................................. 67
Table 21: lifting lug dimensions............................................................................................................ 78
Table 22: Column manway sizing .......................................................................................................... 84
Table 23: Tray manway sizing ................................................................................................................ 84
Table 24: Flange location and dimension ............................................................................................. 89
Table 25: Gasket sizing .......................................................................................................................... 90
Table 26: Nozzle Properties .................................................................................................................. 91
Table 27: Data Sheet ............................................................................................................................. 95
Table 28: PID Controls ......................................................................................................................... 97
Table 29: CAPCOST data ...................................................................................................................... 106
Table 30: Exchange rates ..................................................................................................................... 107
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4
Nomenclature
A
Ad
Am
Ao
Avg.MWt
C
CS
Ct
Cw
D
Db
Dm
do
Ds
E
Ey
Fouling
Fp
g
h
h2
hb
Hc
hd
hd
Hh
Hi
Hnb
hnb
Ho
how
how
hr
Ht
ht
ht
Hv
hw
hw
k1
Kl
l
Lm
Lmd
LMTD
Lt
Lw
lw
Lw
M
Ms
Ms
Area
downcomer area,
clearance of plate spacing
area of pipe
average molecule weight of vapour
seismic coefficient
Carbon steel
corrosion allowance
correlation factor to account for nozzles, manways, internal supports
diameter
bundle diameter
mean diameter of vessel
outer diameter of tubes
inside diameter of skirt
joint efficiency
youngs modulus
heat transfer to compromise fouling
Correlation of Prandtl constant
gravity
height of from base to knuckle radius
height of head
downcomer backup
heat transfer of condensation
dry plate drop
downcomer pressure drop
height of head
enthalpy of feed
heat transfer of pool boiling
Pool boiling heat capacity
enthalpy at exit
weir crest
crest height
residual head
height of trays
pressure drop
total pressure drop
height of vessel
height of weir
height of the weir
data constant
Thermal conductivity of liquid condensate
length of tubes
liquid flow rate
liquid flow rate downcomer
log mean temperature difference
tray spacing, m
Liquid flow rate minimum,
weir length
liquid weight
gasket factor
maximum bending moment
wind stress
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n
n1
ni
no
Nt
Nt
P
Pc
Pi
Pr
Ps
Pv
Pw
Pw
Qc
r1
r2
Rc
Rok
S
SS
Ss
Ƭ
T
t
t
ti
Ts
Tsk
Tsk
Tsk
U
V
Vi
VL
Vm
Vs
W
Wc
Wi
Wl
Ws
Wv
WvT
ρL
ρV
σbs
𝝆�i
𝝆�L
𝝆�m
𝝆�v
𝝈�sc
𝝈�st
𝝈�ws
standard mol quantity
data constant
molar flow rate of feed
molar flow rate at exit
number of trays
number of tubes,
Operating pressure
Critical pressure
safety pressure (10% above operating pressure)
Prandtl Number: ratio of critical pressure to operating pressure
thickness of plate
volume of plate
dynamic wind pressure, 1280 N/m2 (Sinnott 2009)
plate weight
Critical heat flux
radius
knuckle radius
knuckle radius
radius outside the skirt
stress at knuckle point
Stainless steel
maximum allowable design stress
horizontal tube loading
operating temperature
thickness of vessel
thickness
insulation thickness
standard temperature conditions
thickness of skirt
thickness of the skirt
thickness of skirt
overall heat transfer coefficient
velocity
volume of insulation
volume of liquid in vessel
vapour flowrate
standard volume conditions
dead weight of the vessel
calming zone
insulation weight
wind loading
unperforated strip
dead weight of vessel
total weight of vessel
liquid density
vapour density
bending stress
density of insulation
density of liquid
density of vessel material
density of vapour
compressive stress
tensile stress
deadweight stress on skirt
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5
Introduction
The stripper column will be inherently designed around the mass and energy balance required to
power an entire natural gas processing plant. The design basis therefore will reference data and
conditions specified for the mass and heat necessities which are part of the preliminary stage of the
project (see report one for feasibility study)
The column has twenty stages and twenty stainless steel sieve trays that operate at a pressure of
130kpa and an overall temperature of 110C⁰ in order to vaporise the water to steam and strip the gas
from the amine solvent. The amine solvent concentration is 30wt% as feed to the column.
The variation in applicable trays are discussed, as well as a comparison of packed vs tray columns in
which the conclusion will be based on all valid parameters of engineering, environmental and
economical that are classified according to all stakeholders internal and external.
All matters of mechanical infrastructure, mechanical design and mechanical transportation and
operation are specified in depth and great detail, enabling the report to not only assist, but found the
basis for the construction of the unit.
The process variables and instrumentation of the stripper unit along with the necessary controls
required for the overhead condenser, reboiler and pipelines are illustrated and outlined enabling
operation of controls. The capital cost estimation was estimated using CAPCOST and applying the
relevant conversions to represent the plant location in Cartagena, Colombia.
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6
Literature Review and Assessment of Alternatives
6.1 Packed Column
Traditionally, columns used in industry are designed with a tray assembly due to their wide range of
applications and selectivity; however the alternative to tray columns presents other advantages found
in packed columns.
There are generally three types of volume used in packed columns called random packing, structured
packing and grids. Random packing is a design that utilises delegated pieces of material that are filled
throughout the column forming no apparent unison or order. The packing types differ depending on
the desired surface area, pressure drop and operational conditions. Structured packing is an assembly
of material that is desired from calculations predicting and specifying particular geometry and
necessary orientation of packing structure. These specific types of packing come in two arrangements
called knitted-type (mesh) or sectioned beds made of corrugated sheets. There are various types of
readily available packing’s that have specific attributes of crimps, surface personality and the
utilisation of perforations.
Figure 1: Random Packing
Figure 2: Structured Packing
An alternative to both structured and random column packing is called grids. These grids are
conventionally used for applications involving vacuum operation and minimal pressure type systems.
The packing operation seen in the industry is well manifested amongst low liquid loading applications
such as glycol dehydration. Packing has the advantage over tray columns in that the surface area is
substantially higher than packing and intimate contact can be established between materials.
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6.1.1
Cost of Packing
Figure 3: Cost of Packing Materials
Comparing the cost of packing to tray columns and considering the operating conditions (see figure 5)
the packing as an alternative to tray column costs up to 3 times the amount, and has relatively similar
operating conditions analysis for the use of MEA in an amine regenerator column.
6.1.2
Operation of Packing
6.1.3 Packing,
Conclusion
Figure 4: Random
[Engineering Data Book. 2004]
Figure 5: Tray vs Packed MEA System Comparison, Hall, Stephen. (2012)
In conclusion, as an alternative packing column in use of on amine regeneration column stripping
hydrogen sulfide and carbon dioxide, this selection is not sufficient when in comparison to economic
comparison to a tray column, and according to the GEMI analysis of external and internal stakeholder
investigation, economic performance is of high significance. Since the particular conditions require no
special consideration for a substantial increase in surface area, the use of tray remains justified and is
further discussed in detail in the following selections.
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6.2
Tray Column Bubble Cap Application
The tray column is a design that is very common in industry and is an alternative to the packed
column depending on the utilisation of the unit, these columns can contain variational types of trays
that can be engineered to provide better operational conditions depending on properties such as
substance characteristics, viscosities, flow rates, densities, contact surface area, retention time,
corrosivity and more. Shown in Figure 6 is a visual representation of a bubble cap tray [Engineering
Data Book. 2004].
6.2.1
Operation of Bubble cap
The bubble caps in compilation with the weirs and downcomer
sections sustain a specific liquid level on the trays. The liquid
flows down through the volume of the columns by pressure and
gravity alternating direction with each tray. The gas flows up
through the trays via the bubble caps and orifices which create a
contact mix between the solvent and gas [Engineering Data
Book. 2004]. Because of the design of a bubble cap, it is the
alternative to sieve and valve trays as the bubble cap design is
the only method that is able to prevent liquid from weeping
through orifices that are designed for gas flow, and is only
intended for vapour allowance. For the design of a valve of sieve
tray, the gas velocity parameters must be specifically engineered
and controlled to prevent the phenomena of weeping from
occurring [Engineering Data Book. 2004]. The bubble cap design
Figure 6: Bubble Cap [Engineering Data Book. 2004]
also contains the highest reliability for turn-down ratio averaging at 9:1, while sieve ratio is 3:1 and
valve tray is 5:1. [Engineering Data Book. 2004] The valve and sieve trays are commonly chosen due
to their cheap cost benefits and high capacity and capability in which is greater than bubble cap over
the same design parameters.
The working site of the bubble cap is called the “slot” at which the point of location of bubbling
occurs. The initiation of the bubbling action is caused by either of two possible shapes being
rectangular or trapezoidal. The trapezoidal capacity is demonstrated to give a high capacity limit
while rectangular gives better performance at lower gas rates (Coker 2010).
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6.2.2
Comparison & Summary
The capacity of bubble tray is relatively high,however, iss less than
sieve or perforated and efficiency is the same as any other tray (as
efficiency is due to optimal operating conditionswithin
theedesignn). The entrainment of bubble tray compared to sieve
and perforated is about three times as much (Coker 2010). The
flexibility status is the highest of all tray selections over both high
and low vapour and liquid rates and also is permissible for positive
drainage of solution from trays. (Coker 2010). The bubble cap
applications remain practical excluding extreme coking conditions,
polymer forming or high fouling system production. Its best
attribute is that it can maintain operation through extremely low
gas flow rate operations and weeping is prohibited due to the
geometry of bubble cap (Coker 2010).
Figure 7: Bubble Cap Gas Flow [Engineering Data
Book. 2004]
The major disadvantage of bubble cap is that the cost is significantly higher, so when good operability
conditions are present within the process, the use of a bubble cap design would be unsuitable as the
use of its application would not be necessary, and would perform at an economic and engineering loss
(Couper 2010).
6.3 Tray Column Valve Application
The valve column trays contain valves that have a retractable or lift-able cap that moves in height
proportional to the gas velocity and flow rate entering the orifice (shown in figure 7). The caps are
generally located about 0.25 cm from the base of the tray and rise to a maximum of 0.81cm .(Walas
1990). The design of a valve tray is more complex to design than an alternative sieve tray, however,
they tend to remain at a cheaper purchase cost due to their trait of pertaining larger holes and thicker
plates which require less support from the column and lower their expense of construction.(Walas
1990).
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6.3.1
Operation of Valve
Valve trays are often regarded as the intermediate choice between bubble caps and sieve plates as they
contain some of the benefits over both solutions by incorporating a mix of advantages and
disadvantages that deliver special characteristics. For example, they allow for better control and
flexibility like a bubble cap when gas flow rates and velocities may be diverse, it can have inherit
design to counteract the loss of efficiency by having variable valve configuration closing and opening
at certain strengths (bubble cap also has properties to allow for flexibility) however sieve trays are
limited (Richardson 2002). The major disadvantage with valve and bubble cap alike is that they
operate poorly with highly fouling conditions as they raised distance from the plate allows for capture
of material and trap materials which greatly decreases efficiency.
The valves on the plate are either designed from metal discs or
metal strips. The cap is connected by what is called the legs, which
control the vertical displacement of the valve, and in some special
cases it is possible to design a cap that is plausible in fully sealing
the valve from liquid by designing the valve to remain closed
when gas limits are insufficient limited (Richardson 2002).
During operation when the gas velocity is greatly decreased for
any reason, the efficiency also greatly declines as the liquid
passing over the bubble caps or perforations has minimal contact
Figure 8: Valve. [ Walas, S.M.. (1990)]
with the flow of gas (Stewart 2014). It may even be possible that at these
conditions the solution can travel over the whole column area without contacting any vapour at all. In
this circumstance there are no compensations to alter this phenomena except change the operating
conditions (Stewart 2014). During operation for any reason if this does occur, valve trays can
incorporate a specific design that consists of differing types of valve rates called “heavy” and “light”.
As the vapour rate declines during the process due to any reason, the specific valves will orientate
themselves accordingly and begin to close (Stewart 2014). As the tray pertains both heavy and light
sites, the heavy valves will close primarily before the light valves, allowing for re-direction of gas
flow in which will increase its quantity over the light valve orifice allowing for liquid-gas contact
which sustains the process (Stewart 2014). With the inherit design, the operating conditions if
temperamental may benefit from this design in weeping considerations are considered and altered to
mitigate where possible (Stewart 2014).
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6.4 Tray Column Sieve (With Weir) Application
6.4.1
Operation of Sieve
The performance of sievetrays iss likened to that of a bubble cap and even more the valve tray as the
basic mechanical characteristics are the same (Coker 2010). Instead of having either bubble caps or
valves, they’re replaced with sieves of perforations throughout the distribution in the plate that can be
orientated accordingly. The gas rises vertically through the orifices in the plate into the liquid causing
contact and mixing (Richardson 2002). The sieve tray is said to one of the cheapest designs when on
its own (Coker 2010). The major disadvantage that is seen with sieve trays is that they have very poor
flexibility as they have little selectively (Coker 2010). It cannot be engineered to account for weeping
or flooding conditions in its mechanical inherit design, instead, operating parameters hold the
responsibility for system production (unlike bubble tray and valve which give high selectivity and
contribution). Any low vapour rate that occurs will cause weeping and reduce overall efficiency
(Coker 2010)
Figure 9: Sieve Tray, [Coker, A. Kayode. (2010)]
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6.4.2
Comparison & summary
The uses of sieve trays are stated to be utilised only when very specific conditions that do not
fluctuate. However, because of the design of the sieve tray, it’s operability is good for conditions of
fouling as they’re cleaner than the alternative (Richardson 2002). The action through the perforations
known as bubbling causes any solids or contaminants to travel down from each tray till the exit as
there are no raised hindrances from the plate unlike both bubble cap and valve (Richardson 2002).
When the design range is appropriate for operation, sieve trays are the preferable choice of tray as
they have better performance and capacity ranging from 1.5 to 3 times as much as either valve or
bubble.
Sieve trays produce lessened rates of jetting action causing frothing and the entrainment levels
measured from the surface of the plate are averaged to be a third less than bubble cap (relatively
similar to valve) for the same dimensions.
6.4.3
Cost Analysis of Tray Variations
As seen in figure 10 and figure 11, the most expensive tray type is the bubble variation being
considerably high, followed by the valve orientation, and the cheapest method of regeneration column
shown to be sieve tray. Since amine is a toxic substance in the particular environment; stainless steel
will be required to ensure long term insurability of duration of the regeneration unit were specified.
(Richardson 2002)
Figure 11: Tray Cost Analysis, [Perry, Robert H. Green, Don W. 1997]
Figure 10: Tray Cost Analysis, [Coker, A. Kayode. (2010).]
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Figure 12: Cost of Materials, [Perry, Robert H. Green Don W. 1997]
6.5 Tray Column Size Calculation & Comparison
A comparison of column size for sieve, valve and bubble-cap are calculated in the following example
in order to calculate the size differential. The parameters will remain constant; the following
conditions are used… (Following example and equations, (Perry 1997))
C3 Splitter containing 24 inch tray displacement with 80% flooding operation.
Table 1:Example Data
Parameter
Value
Vapour flow rate
271,500 lbs/HR
Vapour volumetric flow rate
27.52 CFs
Liquid flow rate
259,000 lbs/HR
Liquid volumetric flow rate
1100 gpm
Vapour density
2.748 lb/Cu ft
Liquid density
29.29 lb/Cu ft
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6.5.1
Sieve Tray Example
(𝐷𝑐) =
𝐿 𝜌𝐺
259100 2.75
√
√
=�
= 0.2924
𝐺 𝜌𝐿
271500 29.3
(𝜌𝐿 − 𝜌𝐺)
29.3
𝐺𝑎𝑠�𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦 = 𝐷𝑐 × √
= 0.24 × √
= 0.746𝑓𝑝𝑠
𝜌𝐿
2.75 − 1
𝐺𝑎𝑠�𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 = 0.8 × 0.746 = 0.597𝑓𝑝𝑠
𝑄𝑣
27.52
𝐷𝑖𝑎𝑚𝑒𝑡𝑒𝑟�𝑜𝑓�𝑐𝑜𝑙𝑢𝑚𝑛 = � √𝜋
= √𝜋
� = 7.67𝑓𝑡
×
𝑈𝑔
×
0.597
4
4
Figure 13: Sieve tray Design, [Perry, Robert H. Green, Don W. 1997]
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6.5.2
Valve Tray Example
𝑈𝑠𝑖𝑛𝑔�𝐹𝑖𝑔𝑢𝑟𝑒�11, 𝐷𝑖𝑎𝑚𝑒𝑡𝑒𝑟 = 9.4𝑓𝑡�(𝑜𝑛𝑒�𝑝𝑎𝑠𝑠), 7.6𝑓𝑡(𝑡𝑤𝑜�𝑝𝑎𝑠𝑠)
𝜌𝑉
2.75
𝐺𝑎𝑠�𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦�(𝑈𝑔) = 𝑄𝑣 × √
= 27.52 × √
= 8.86𝑓𝑡 3 /𝑠
𝜌𝐿 − 𝜌𝑉
29.3 − 2.75
Figure 14: Tray Design Pass, [Perry, Robert H. Green, Don W. 1997]
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Bubble Cap Calculation
6.5.3
𝐶𝑜𝑙𝑢𝑚𝑛�𝐷𝑖𝑎𝑚𝑒𝑡𝑒𝑟 = 0.0956 (
0.5
𝑊𝑣
𝐾 × √𝜌𝐿𝜌𝑉
)
271500
0.5
= 0.0956 (
)
4.2 × √29.3 × 2.75
= 8.11𝑓𝑡
Table 2: Bubble Cap Calculation Data, (Perry 1997)
T RAY SPACING
(IN.)
K
18
24
30
<30
3.4
4.2
4.7
5.0
Wv = vapour rate (lb/hr)
ρV= vapour density (lb/cuft)
ρL= liquid density (lb/cuft)
Results
6.5.4
Sieve tray = 7.67 ft
Bubble cap tray =8.11 ft
Valve tray = 9.4ft (one pass), 7.6ft (two pass)
6.6
Conclusion & Justification of Tray Arrangement
Type
Bubble Cap
Valve
Sieve with Weir
Sieve without Weir
capacity
Average
High
High
Very High
Flexibility
Excellent
Good
Average
Poor
Entrainment
High
Moderate
Moderate
Moderate
Pressure Drop
High
Average
Average
Average
Cost
High = 2 to 3
Moderate = 1 to 2
Low = 1
Low
Maintenance
Fairly High
Moderate
Low
Low
Plugging Tendency
High
Moderate
Low
Low
Design
Well known
Well know by
suppliers
Well known
Less well known
Recommended
Applications
Low liquid flow
rate
Very wide range
If flexibility
unnecessary
If plugging expected
Market Share
5%
70%
25%
Specific applications
Table 3: Overall Summary Tray Type [Trambouze, Pierre. (2000)
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6.6.1
Tray Efficiency Comparison
Figure 15: Tray Efficiency Comparison, [Walas, S.M.. (1990)]
From the following illustration, sieve and valve perform better than bubble cap over several
comparisons concerning different solvent utilisation. Sieve valves also perform slightly better than
valve, as it can handle larger capacities and are cheaper to purchase and operate.
Figure 16: Application Comparison of Trays, [Hall, Stephen. (2012)]
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6.6.2
GEMI Stakeholder Relevance
From the GEMI analysis (see feasibility study) of intern and external stakeholder validity and
relevance investigation, economic performance of the financial status, ease of maintenance and repair
and waste generation and management as the proclaimed key indicators were rated of significance. In
reference to worksheet 2a and 2b, it is appropriate to incorporate the stakeholder validity into the
contribution of the process selection as outlawed in the following report.
Sieve tray regeneration columns are the cheapest to produce and operate. Because they have high
fouling tolerance and simplistic design they’re easy to incorporate man holes and therefore the easiest
and readily available access for both maintenance and repair.
6.6.3
Conclusion
The sieve tray design is also the most known design and the easiest to operate in production, Since the
specific design is relatively constant conditions requiring little flexibility without extreme low or high
vapour rates and no specific requirements outside normal operability of regenerator column design,
sieve trays with weir is the ideal methodology to be used proving most suitable and beneficial
economically, mechanically and operationally optimal.
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6.7 Reboiler Arrangement Selection
There are many types of reboiler designs that can be implemented according to certain parameters that
may require special consideration or attention in the regeneration column [Engineering Data Book.
2004]. The main types investigated and considered are Natural circulation, forced circulation,
thermosyphon and kettle reboiler. The delegation of each type of reboiler is classified to certain
criteria in which are then evaluated depending on the priority and significance of each key attribute.
The general selection criteria for reboilers are [Engineering Data Book. 2004]

Heat transfer surface prerequisite

Area and piping required

Ability of ease and cost of maintenance

Fouling occurrence

Stability of operation controls

Cost of operation and capital

Column and skirt elevation requirements.
6.7.1
Natural Recirculation Reboiler
Figure 17: Natural Circulation Reboiler, [Hall, Stephen. (2012)]
Natural circulation reboilers are the most prevalent of all reboilers found in industry. This type of
system is designed in two differential systems, one through reboiler and recirculating reboiler shown
in figure 17.
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All the liquid at the base of the regeneration column is directed into the reboiler where the system
partially vaporisers the solution. The fraction of unvapourised solution is withdrawn from the reboiler
with the exiting bottom product, the remaining vapour is returned into the column. The recirculating
boiler operates slightly different in that the liquid and vapour are permitted to circulate according to
the pressure difference show in figure 17 (b) as the liquid static head pressure . [Engineering Data
Book. 2004]
6.7.2
Forced Circulation Reboiler
Figure 18: Forced-Circulation Reboiler, [Hall, Stephen. (2012)]
In a forced circulation reboiler, also known as a “pump through” reboiler, all the liquid from the
bottom tray of the regeneration column is pumped into the reboiler which may occur as many times as
economically plausible in order to regular vaporisation rates within the stripper [Engineering Data
Book. 2004]. This particularly type of setup is utilised when high pressures exceed the use of
conventional designs such as natural recirculation.
The main advantage consistent with forced recirculation is that it possess the ability to stringently
control circulation rate of components and can handle viscous and solid pertaining substances ,
however its operational cost is high than natural circulation, which if applicable is more suitable
[Engineering Data Book. 2004].
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6.7.3
Thermosyphon Reboiler
Figure 19: Thermosyphon Reboiler (horizontal), [Hall, Stephen. (2012)]
Figure 20: Thermosyphon Reboiler (vertical), [Hall, Stephen. (2012)]
Thermosyphon heat exchangers as shown in Figure 19 and 20 can be either horizontal of vertical. The
Thermosyphon reboiler has a construction arrangement that generally contains a relatively simple
design consisting of simply a one tube pass shell heat exchanger [Engineering Data Book. 2004]. The
main attribute of this design is that it is capable of relatively large surface area heat transfer rates due
to its design and requires simple construction and piping.
The Thermosyphon due to its primitive application has high tolerance for potential fouling and has a
good level of controllability of circulation rate and vaporisation [Engineering Data Book. 2004]. The
vertical arrangement sits close to the stripper and usually is built with additional column skirts which
make maintenance difficult. The horizontal type is similar in nature to the vertical however it has less
skirt height (as it doesn’t require as much circulation head, i.e pressure). The horizontal type
thermosyphon can be either natural or forced in its circulatory system design [Engineering Data Book.
2004].
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6.7.4
Kettle Reboiler
Figure 21: Kettle reboiler, [Hall, Stephen. (2012)]
The kettle reboiler is designed with relatively different configuration and applications of its boiling
approach. Liquid from the bottom of the column is directed driven by gravity into the boiler. A weir is
established within the kettle design that maintains the desired liquid height. The tube bundle is fully
submersed within the aqueous phase. As the fluid is vaporised it is fed back into the column for
further stripping of material [Engineering Data Book. 2004].
The un-vaporised solution is fed from the bottom as product. The approach of the kettle reboiler
makes it easy to control and no multiphase flow or circulation rate needs to be integrated or
considered. The kettle reboiler simply acts as an extra tray in the column in which control of
vaporisation can be employed. Because of vapour disengagement phenomena that occur as subset, the
kettle shape is formed which has larger construction costs than alternative designs, however because
the external skirt requirement is reduced the overall cost is balanced [Engineering Data Book. 2004].
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6.7.5
Reboiler Summary
Table 4: Reboiler Comparison, [Hall, Stephen. (2012)]
Reboiler type
Kettle
Advantages




Extra piping and space
High cost
Fouls with dirty fluids






One theoretical tray
Ease of maintenance
vapour disengaging
Low skirt height
Handles viscosity greater
than 0.5cP
Ease of control
No limit on vapour lead
One theoretical tray
Simple piping and compact
Not easily fouled
Less cost than kettle




Difficult maintenance
High skirt height
No control of circulation
Moderate controllability



Good controllability
Simple piping and compact
Less cost than kettle





No theoretical tray
Accumulation of high boiling point components
in feed line, temperature may be higher than
column
Too high liquid level could cause loss of
efficiency
Fouls easier
Difficult to maintain
High skirt height
One theoretical tray
Simple piping and compact
Not easily fouled
Lower skirt height than
vertical
Less pressure drop than
vertical
Longer tubes possible



No control of circulation
Moderate controllability
High skirt height
Ease of maintenance
Lower skirt height than
vertical
Less pressure drop than
vertical
Less cost than kettle
One theoretical tray
Handles high viscous
solids-containing liquids
Circulation controlled
High transfer coefficient




No theoretical tray
Extra space and piping compared to vertical
Fouls easier
Accumulation of higher boiling point (may be
higher than stripper temperature)


Vertical onethrough
Vertical natural
circulation
Disadvantages

Horizontal once
through






Horizontal natural
circulation



Forced circulation





Because of the operating conditions and the nature of process, the delegated mode of heating is a
kettle reboiler as it can handle high flow rates, orientation is suitable, is tolerable with the type of
solvent and is the conventionally most preferred.
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7
Equipment Design Regenerator Column
S-10
7.1 Mass & Energy Balance
S-11
H-103
S-12
S-9
S-9
S-12
S-15
MEA Regenerator
Column DC-102
S-10
S-14
Figure 22: Overall Regenerator
S-15
DC-102
H-102
S-16
S-14
Figure 23: Regenerator Column
Table 5: Energy Balance of Regenerator
DC-102
99%
Efficiency
Temperature (⁰C)
110.00
45.00
110.00
110.00
90.00
Pressure (kPa)
245.00
150.00
130.00
130.00
130.00
Mass Flow (Tonnes/hr)
144.70
67.52
73.99
108.35
114.69
Density (kg/m3)
908.43
943.20
0.95
0.795
950
Components / Streams (Mmol/hr)
S-9
S-12
S-15
S-10
S-14
Methane
0.18
(g)
0.18
-
(g)
0.18
(g)
-
(g)
Ethane
0.01
(g)
0.01
-
(g)
0.01
(g)
-
(g)
Propane
0.00
(g)
0.00
-
(g)
0.00
(g)
-
(g)
i-Butane
0.00
(g)
0.00
-
(g)
0.00
(g)
-
(g)
n-Butane
0.00
(g)
0.00
-
(g)
0.00
(g)
-
(g)
Pentanes
0.00
(g)
0.00
-
(g)
0.00
(g)
-
(g)
Nitrogen
0.01
(g)
0.01
-
(g)
0.01
(g)
-
(g)
Carbon dioxide
0.20
(g)
0.00
0.00
(g)
0.19
(g)
0.00
(g)
Oxygen
0.00
(g)
0.00
-
(g)
0.00
(g)
-
(g)
Hydrogen Sulphide
0.84
(g)
0.01
0.00
(g)
0.84
(g)
0.25
(g)
Water
4.17
(g)
3.71
4.09
(g)
3.75
(g)
4.13
(l)
MEA
1.04
(l)
0.01
0.01
(l)
0.01
(l)
1.03
(l)
Triethylene Glycol
-
(l)
-
-
(l)
-
(l)
-
(l)
Air
-
(g)
-
-
(g)
-
(g)
-
(g)
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Table 6: Mass Balance of Regenerator
Mass Balance (Ton/hr)
Temperature (⁰C)
110.00
110.00
45.00
90.00
110.00
Pressure (kPa)
150.00
130.00
150.00
130.00
130.00
S-9
S-10
Components / Streams
S-14
S-15
Methane
2.87
2.87
2.84
-
-
Ethane
0.33
0.33
0.33
-
-
Propane
0.08
0.08
0.08
-
-
i-Butane
0.03
0.03
0.03
-
-
n-Butane
0.03
0.03
0.03
-
-
Pentanes
0.00
0.00
0.00
-
-
Nitrogen
0.18
0.18
0.18
-
-
Carbon dioxide
8.61
8.52
0.09
0.09
0.00
Oxygen
0.00
0.00
0.00
-
-
Hydrogen Sulphide
28.76
28.47
0.28
8.45
0.08
Water
75.01
67.51
66.83
74.33
73.59
MEA
32.15
0.32
0.32
31.82
0.32
Triethylene Glycol
-
-
-
-
-
Air
-
-
-
-
-
148.05
108.35
71.01
114.69
73.99
SUM
7.1.1
S-12
Tray Specifications
The following tray calculations use Perry’s methodology using a stripping factor to determine
theoretical stages for a regenerator (Perry 1997).
Table 7: Tray Parameters
Parameter
Value
Stripping factor (Perry 1997)
1.4
X2 Liquid mole fraction feed
0.23
X1 Liquid mole fraction exit
0.0025
X2° Liquid mole fraction of equilibrium feed (pure steam)
0
X1° Liquid mole fraction of equilibrium exit) (pure steam)
0
A = S −1 ��(Perry 1997)
0.714
Tray efficiency
50%
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7.1.2
Number of theoretical trays
When the stripping is being done by steam and the liquid feed is diluted with substance, the stripping
factor can be used to determine the number of stages in and equilibrium line considering that the
efficiency is high. This method is used namely for theoretical tray estimation, and combined with tray
efficiency provides an alternative solution than conventional methodologies. Note: this technique is
only applicable to stripping operations (Perry 1997).
ln [
𝑁=
(1 − 𝐴)(X2 − X1°)
(1 − 0.714)(0.23 − 0)
+ 𝐴] ln [
+ 0.714]
X1 − X1°
0.23 − 0
=
= 9.8 ≈ 10�
ln(𝑆)
ln(1.4)
Because the stripping steam is pure, both X2° and X1° has a data value of 0 as there are no
contaminants or other components in equilibrium.
7.1.3
Actual trays
Since the theoretical tray quantity is 10, with the design parameter of the 50% efficiency the actual
tray amount is calculated in the following.
Figure 24: Tray Efficiencies, (Sinnott 2009)
According to the above figure, using the viscosity of 0.36 Cp, the design for lowest efficiency is
calculated.
Actual�Trays�(Nt) =
10
= 20�trays�(includind�reboler�and�condenser�stages)
50%
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7.2 Tray Hydraulics
7.2.1
Design Procedure
The methodology consistent with the approach to designing the regenerator column follows a
systematic procedure that act as steps ensuring key parameters, requirements and foundations are
correlated and synchronized.
The steps to the approach are outlined as the following marginal guidelines
1. Calculate maximum/minimum vapour and liquid flow rates and top and bottom of column
(from mass balance)
2. Estimate and gather system properties
3. Select plate spacing
4. Calculate the column diameter at top and bottom and design for the largest section (For this
design we will use a uniform diameter as the largest as it greatly reduces capital cost of
column)
5. Classify the liquid flow arrangement across plate tray
6. Provide tray layout specifications such as: downcomer area, active area, hole area, hole size
and weight height
7. Check satisfactory operation conditions with the weeping rate
8. Check satisfactory pressure drop of column
9. Check downcomer backup
10. Assure correct operability according to estimated dimensions
11. Check entrainment values are satisfactory
12. Finalise design
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7.3 Relevant Data & Assumptions
Table 8: : Relevant Data (obtained from energy & mass balance)
Data
Value
Liquid flow rate (bottom) Lm
5.5
𝑘𝑔
𝑠
Liquid flow rate (top) Lm
9.3
𝑘𝑔
𝑠
Vapour flow rate (top) Vm
13.3
Vapour flow rate (bottom) Vm
1
Density liquid ρL
950 𝑚3
Density Vapour ρV
0.89 𝑚3
Surface Tension 𝝈�
0.036
𝑘𝑔
𝑠
𝑘𝑔
𝑠
𝑘𝑔
𝑘𝑔
𝑁
𝑚
The amine regenerator column will be based on the top diameter conditions as this is the delegated
uniform diameter of the entire tower (assumption justified by calculations below).
Table 9: Assumed Values for Design
Parameter
Value
Plate Spacing
0.9 m
Percentage flooding
70%
Turn down ratio
80%
Hole diameter dh
10mm
Ad (downcomer area)
12% of Ac
Plate thickness
10mm
Weir height hw
40mm
Ah/Ap
0.01
Unperforated strip Ws
50mm
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7.4 Summary of Design Results
Table 10: Summary of Design Results
Parameter
Value
Column Diameter, Dc
Top = 2.8m
Bottom = 0.79m
Chosen uniform diameter Dc
2.8m, as top diameter is the largest
Pressure drop of plate Ht
118.54mm
Pressure drop of column ∆𝑃𝑡
1.00kPa
Actual vapour velocity Uv
21m/s
Fractional entrainment ψ
0.07
Downcomer backup hb
190.23mm
Downcomer residence time tr
22 seconds
Perforated area Ap
0.19m2
Number of holes per tray
6165
Number of trays Nt
20
Height of stripper column H
19.1 metres
Figure 25: Single Pass Column & Tray, [Moss,
Dennis R. Basic, Michael M.. (2013)]
Liquid arrangement across tray Cross flow single path
Tray spacing Lt
0.9 metres
Weir type
Picket-weir
Number of strippers
2
Flooding regime
Froth mechanism
Figure 26: Picket Weir, Sinnott, Ray K. Towler, Gavin. (2009)
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7.5 Detailed Design
The following calculation is to only to provide primary justification in choosing the uniform diameter
of the column by comparing the top and bottom parameters and measurements. The actual design
methodology follows after this comparison, and is in full detail, considering all plausible conditions
and reporting all calculations and ideology to the design of the column.
Top and bottom diameter calculation and comparison
7.5.1
7.5.1.1
Top diameter calculation
𝜌𝑣 =
𝑃 𝑛 𝑇𝑠
𝑘𝑔
� � × �𝐴𝑣𝑔. 𝑀𝑊𝑡��������������������������𝜌𝐿�𝐻2 𝑂 = 950 3
𝑃𝑠 𝑉𝑠 𝑇
𝑚
𝝆�v= density of vapour =, kg/m3
𝝆�l= density of liquid, kg/m3
P= pressure of system, kpa
Ps= standard pressure conditions, kpa
n= standard mol quantity, mol
Vs=standard volume conditions, m3
Ts=standard temperature conditions, K
T= operating temperature
Avg.MWt = average molecule weight of vapour
𝜌𝑣 =
101.325�𝑘𝑝𝑎
1�𝑚𝑜𝑙
1�𝑘𝑚𝑜𝑙
273𝑘
𝑘𝑔
𝑘𝑔
�
�
×
× 36.36
= �0.89� 3
3
130�𝑘𝑝𝑎
0.022415�𝑚
1000�𝑚𝑜𝑙 383𝑘
𝑘𝑚𝑜𝑙
𝑚
The density of vapour at the top of the column primarily consists of water vapour (highest fraction at
62% of the mass, while hydrogen sulphide and carbon dioxide balance). The density calculation is
applicable for our conditions modelling with an assumption of ideal gas behaviour.
By using a correlation that describes the conditions of a plate, taking into account both the liquid and
vapour limits, we can use the FLV (liquid-vapour flow factor) in order to calculate a constant K1 that
we can use to determine necessary velocities in of the particular conditions (Sinnott 2009).
𝐹𝐿𝑉 =
𝐿𝑚 𝜌𝑣
9.3 0.89
√
�√ =
= 0.022
𝑉𝑚 𝜌𝑙 13.34 950
Where,
Lm= liquid flowrate, kg/s
Vm= vapour flowrate, kg/s
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Figure 27: Flv Vs K1, , Sinnott, Ray K. Towler, Gavin. (2009)
With an assumed plate spacing of 0.9m (see assumptions) 𝐾1 =0.13 using the Flv values as an
indicator
𝜌𝑙 − 𝜌𝑣
𝜎 0.2
950 − 0.89 0.036 0.2
√
𝑢𝑓 = 𝐾1 √
��(
) = 0.13
�(
) = 4.77�𝑚/𝑠
𝜌𝑣
0.02
0.89
0.02
The upper limit velocity denoted in this case in the above equation as uf is the velocity of vapour
rising through the sieve plates contacting the fluid (the reflux of water condensate in stream 12)
Recommended by Sinnott it is advised to calculate the flooding vapour velocity design as 70% of the
upper limit vapour velocity uf in order to provide good operability of flooding conditions that will
prevent phenomena such as weeping to occur as
𝑈𝑣�𝐷𝑒𝑠𝑖𝑔𝑛�𝑣𝑎𝑝𝑜𝑢𝑟�𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 = 0.70 × 𝑢𝑓 = 3.34�𝑚/𝑠
qv =
Vm 13.34�kg/s
m3
𝑞𝑣 15�m3 /s�
=
=
15�
,����������������𝐴
=
=
= 5.6�m2 ������������������
𝑛
ρv 0.89�kg/m3
s
𝑢𝑣 3.34�𝑚/𝑠
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Assumed value of downcomer area was assumed as 12% of column cross sectional-area denoted as
Ac. This is a standard design specification for tray columns as stated and recommended by Sinnott.
𝐴𝑑 = 0.12𝐴𝑐 ,
𝐴𝑛 = 𝐴𝑐 − 0.12,���𝑡ℎ𝑢𝑠�𝐴𝑐 = 𝐴𝑛 /0.88
𝐴𝑐 =
5.6
= 6.37�m2
0.88
,
4 × 𝐴𝑐�
4 × 6.37�m2
𝐶𝑜𝑙𝑢𝑚𝑛�𝐷𝑖𝑎𝑚𝑒𝑡𝑒𝑟�𝐷𝑐 = √
=√
= 2.8𝑚
𝜋
𝜋
7.5.1.2
Bottom diameter calculation
(This is the same methodology as used above, just different conditions at base of column)
𝐹𝐿𝑉 =
𝐿𝑚
𝜌𝑣
�√
𝑉𝑚
𝜌𝑙
=
5.46 0.89
√
1
950
= 0.11�� �𝐹𝑟𝑜𝑚�𝑎𝑏𝑜𝑣𝑒�𝑓𝑖𝑔𝑢𝑟𝑒�𝐾1=0.13
𝜌𝑙 − 𝜌𝑣
𝜎 0.2
950 − 0.89 0.036 0.2
𝑢𝑓 = 𝐾1 √
��(
) = 0.13√
�(
) = 4.77�𝑚/𝑠
𝜌𝑣
0.02
0.89
0.02
𝑎𝑠�𝑈𝑣�𝐷𝑒𝑠𝑖𝑔𝑛 = 0.70 × 𝑢𝑓 = 3.34�𝑚/𝑠
��qv =
Vm
1�kg/s
m3
𝑞𝑣 1.16�m3 /s�
=
=
1.16�
,����������������𝐴
=
=
= 0.433�m2 ������������������
𝑛
ρv 0.89�kg/m3
s
𝑢𝑣
3.34�𝑚/𝑠
Assumed value of downcomer area was assumed as 12% of activated area
�𝐴𝑑 = 0.12𝐴𝑐 ,
𝐴𝑛 = 𝐴𝑐 − 0.12,���𝑡ℎ𝑢𝑠�𝐴𝑐 = 𝐴𝑛 /0.88
𝐴𝑐 =
0.433
= 0.5�m2
0.88
4 × 𝐴𝑐�
4 × 0.5�m2
𝐶𝑜𝑙𝑢𝑚𝑛�𝐷𝑖𝑎𝑚𝑒𝑡𝑒𝑟�𝐷𝑐 = √
=√
= 0.79𝑚
𝜋
𝜋
Top diameter 2.8m < Bottom diameter 0.79m
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39
Because the top diameter is larger, this will be chosen to design the regenerator column as a uniform
diameter which saves with complications and large capital cost as two diameters at such a larger
difference is extremely expensive and very difficult to mechanically design for support (not logical),
Therefore fixed column design is the top diameter of 2.8m.
All formulas and relationships reference: (Sinnott 2009)
7.5.2
Liquid flow arrangement
Based on the liquid flow rate from the mass balance of 9.28 kg/s, the liquid volumetric flow rate in
order to calculate the type of flow
9.28𝑘𝑔
𝑚3
𝑚3
𝑠
𝐿𝑚
=
= 0.00977
950𝑘𝑔
𝑠
𝑠
𝑚3
Table 11: Liquid Flow Arrangement
Volumetric FLowrate
𝑚3
0.00977
𝑠
Diameter
2.8 metres
Pass
Single
Flow
Cross
Figure 28: Dc Vs Volumetric Liquid Flow rate, (Sinnott 2009)
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Figure 29: Flow Arrangement, (Coker 2010)
7.5.3
Provisional Tray Design
Based on the column calculation, the diameter per stripper as 𝐷𝑐 = 2.84 m, the following tray
parameters are designed accordingly to accommodate operability such as flow rates, weeping,
entrainment and other specifications.
Since the perforated area Ap will be subsidised by mechanical instruments such as support beams and
rings, as well as the calming zone of the tray, the perforated area must be calculated with all
considering design parameters. For a column diameter of 2.84 meters, it is recommended by (Sinnott
2009) to have an unperforated strip Ws equal to 50mm surrounding the edge of the plate, this is to
account for as the calming zones as
𝑊𝑐 = 𝑊𝑠 = 50𝑚𝑚
Wc= calming zone
Ws= unperforated strip
To calculate the mean length of the calming zone, or unperforated strip, the relation can be used as
𝑙𝑠 = � (𝐷𝑐 − 𝑤𝑠 )
𝜋𝜃𝑠
360
Where θs is relation between the angle subtended by the chord, chord height and chord length, it can
𝑙𝑤
be found by the using the following figure, and the ratio between 𝐷𝑐
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Figure 30: Angle Relation
Since
𝑙𝑤
2.20
=�
= 0.77
𝐷𝑐
2.48
θs therefore equates to 99 using figure 30. The mean length of the calming zone is therefore
𝑙𝑠 = � (𝐷𝑐 − 𝑤𝑠 )
𝜋𝜃𝑠
𝜋 × 99
= (2.48 − 0.05)
= 1.98𝑚
360
360
The area of the unperforated strip can then be calculated as
𝐴𝑠 = � 𝑙𝑠 ∗ 𝑤𝑠 = 1.98 ∗ 0.05 = �0.099�𝑚2
The calming zone length is
𝑙𝑐 = � 𝑤𝑠 + � 𝑙𝑤 = 0.05 + 2.20 = 2.24��𝑚2
Where lw is calculated from the following figure using the assumed recommended weir height ℎ𝑤 =
50 mm
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Figure 31: Ad/Ac Vs lw/Dc, (Sinnott 2009)
From
𝐴𝑑
𝐴𝑐
× 100�𝑉𝑠�
𝑆𝑖𝑛𝑐𝑒
𝐿𝑊
𝐷𝑐
graph
𝐴𝑑
= 0.12
𝐴𝑐
The weir length therefore can be calculated from the correlation shown in the figure and described by
(Sinnott 2009),
𝑙𝑤 = �0.77� × 𝐷𝑐 = 0.77 × 2.84𝑚�,
𝑙𝑤 = �2.20�m��
The calming zone area is then calculated by:
𝐴𝑐𝑧 = � 𝑙𝑐 ∗ � 𝑤𝑐 = 2.24 ∗ 0.05 = 0.11�𝑚2 ��
The total unperforated area therefore is calculated by
𝐴𝑢𝑝 = 2 ∗ � (𝐴𝑠 + � 𝐴𝑐𝑧 ) = 2 ∗ (0.099 + 0.11) = 0.422�𝑚2
Since the perforated area is simply the area that is not unperforated, we can find this as
𝐴𝑝 = � 𝐴𝑎 − � 𝐴𝑢𝑝 ��
Aa as the active area is found by
𝐴𝑎 = � 𝐴𝑐 − 2�𝐴𝑑
Where,
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43
𝐴𝑑 = 0.12𝐴𝑐 ,
𝐴𝑛 = 𝐴𝑐 − 0.12,���𝑇ℎ𝑒𝑟𝑒𝑓𝑜𝑟𝑒�𝐴𝑐 =
𝐴𝑛
0.88
Because An Can be found by
m3
15
𝑞𝑣
s = 5.6�m2
𝐴𝑛 =
=
𝑢𝑣 3.34 𝑚
𝑠
Where
��qv =
Vm 13.34�kg/s
m3
=
=
15�
������
ρv 0.89�kg/m3
s
The cross sectional area of the column can be found,
𝐴𝑐 =
5.6
= 6.37�𝑚2 , 𝑎𝑛𝑑��𝐴𝑑� = 0.12 × 6.37 = 0.76𝑚2
0.88
Therefore the Active area can now be found to be
𝐴𝑎 = � 𝐴𝑐 − 2�𝐴𝑑 = 0.76 − 2 × 0.76 = 4.84m2
𝐴𝑝 = � 𝐴𝑎 − � 𝐴𝑢𝑝 = 4.85 − 0.422 = 4.42𝑚2 ��
In order to calculate the number of perforations per plate, we can use the area of holes vs the area of a
single hole in order to determine their count,
𝑁 =�
𝐴ℎ
𝐴𝑜
Since
𝐴ℎ = 0.1𝐴𝑎 = 0.1 ∗ 4.84 = 0.484�𝑚2
And the area of a single hole calculated from the assumed hole diameter as 10mm,
𝐴𝑜 =
𝜋𝑑ℎ2
𝜋0.00102
=�
= 7.85� × 10−5 𝑚2
4
4
The number of perforations per plate is therefore equal to
𝑁 =�
0.484
= 6165�ℎ𝑜𝑙𝑒𝑠�
7.85� × 10−5
To conform this value, we can check the hole pitch with the following figure
𝐴ℎ
0.484
=�
= 0.11�
𝐴𝑝
04.42
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Figure 32: Ah/Ap Vs Lp/dh, (Sinnott 2009)
𝑙𝑝
As we can see from the figure, 𝑑 = 2.7 which is acceptable as it is between 2 and 4. We can further
ℎ
𝑙
justify by showing that 𝑙𝑝 > 2.5 × 𝑑ℎ. Using the correlation 𝑑𝑝 = 2.7 dervied from the figure, we can
ℎ
show that
𝑙𝑝 = 2.7 × 10 = 27
𝑙𝑝�𝑑𝑒𝑠𝑖𝑔𝑛�𝑚𝑖𝑛𝑖𝑚𝑢𝑚 = 2.5 × 10 = 25
Since 27 > 25, this pitch and these conditions are correct and suitable.
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7.5.4
Entrainment
Entrainment is an important design parameter to include as it greatly impacts the way the tower
performs and how the stripping occurs between the liquid and the vapour. There are two main types of
entrainment that occur, one is at high liquid velocity and is known as froth entrainment, the other is
low liquid velocity and is known as spray entrainment.

Froth entrainment
Forth entrainment flooding occurs when the liquid velocity and flow rate becomes excessive
to the point where the plate holds a high amount of liquid at each time, possibly causing high
flooding and backup levels. As the vapour velocity is then pressurised through the orifices in
the sieve plate, the high amount of liquid begins to bubble and froth as the vapour is entrained
within the liquid state and is not able to successfully travel throughout the tower accordingly

Spray entrainment
Spray entrainment is the opposite of froth entrainment as it occurs when the liquid velocity
and flow rate is diminished causing the liquid present at any given time on the plate to form
collective puddles preventing the flow to essentially cross the sieve plate. As these thin layers
of puddles settle on the sieve plate, the upcoming vapour propelled through the orifices
contact the collective pools and sprays them throughout the area of the tray spacing.
In order to prevent either of the two types of entrainment, we can calculate the conditions of
the tower in regard to flooding upon each plate which allows for mitigating the effect, or
changing the conditions to reduce the possibility of it occurring at high calibre.
The correlation between flooding and flow rate is calculated by measuring the actual velocity based
on the neat area of the sieve plate in ratio to the maximum vapour flooding limit. Since the vapour
flooding is assumed to be 70%, which essentially is the ratio of vapour velocity at flooding shown in
the equation below. (See assumptions)
Percentage flooding chosen
𝑚
3.34
𝑢𝑣�
𝑠
=�
× 100 =
𝑚 = 70%
𝑢𝑓
4.78 𝑠
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Figure 33: FLV Vs Ψ, (Sinnott 2009)
The liquid vapour factor at these conditions calculated from figure 33 = 0.021. FLv=0.021. The
correlation between entrainment and FLV displayed in the following figure at a flood percentage of
70% gives an entrainment indications factor of 0.07.
From figure 33, Ψ = 0.07 < Ψupper�limit Since the upper limit is referred to as
Ψupper�limit = 0.1
[Sinnot, 2009]
Therefore the entrainment level is satisfactory.
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7.6 Weeping
The weeping point is known as the limit at which liquid begins to seep through the orifices of the
plate and the leakage becomes excessive due to the vapour velocity being insufficient in providing
enough driving force to divert liquid from the holes. In order to calculating weeping conditions, it is
therefore necessary to measure the vapour velocity to make sure it’s operating parameter is above the
limit at which weeping is caused.
From Sinnott, weeping vapour velocity limit is calculated as,
�𝑢𝑣(𝑤𝑒𝑒𝑝𝑖𝑛𝑔) =
𝐾2 − �0.9�(25.4 − 𝑑ℎ )
𝜌𝑣0.5
The constant K2 which is a measurement dependent upon the liquid depth equal to the height of the
weir hw is used to calculated from both the height of the weir and the crest height how combined. K2=
hw+ how (mm)
Height of the weir crest is calculated,
ℎ𝑜𝑤 = 750� (
2/3
�𝐿𝑤�𝑚𝑖𝑛 2/3
7.147
)
= �750� (
) = 17�𝑚𝑚
𝜌𝑙 �𝑥�𝑙𝑤
940 × �2.19
lw = weir length, m
how = weir crest, mm liquid
Lw = Liquid flow rate minimum, kg/s
From the recommended turndown ratio (Sinnott 2009), the minimum liquid flow rate 𝐿𝑚(min�) =
0.70*9.28= 7.147 kg/s
The weir length is calculated in the provisional tray design section (above) to be lw = 2.20m, and the
height of each weir is assumed to be 40mm, k2 can be derived from the following figure, since
ℎ𝑤 + ℎ𝑜𝑤 = 40𝑚𝑚 + 17𝑚𝑚 = 57𝑚𝑚, 𝑡ℎ𝑒𝑟𝑒𝑓𝑜𝑟𝑒�𝑘2 = 30.2
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With the following data, we can calculate the minimum limit of vapour velocity that causes weeping,
so that we can measure the operational velocity in order to check for weeping conditions in the
column
𝑢𝑣(𝑤𝑒𝑒𝑝𝑖𝑛𝑔) =
𝐾2 − �0.9�(25.4 − 𝑑ℎ )
30.2 − 0.9(25.4 − 5 ∗ 10^ − 10)
=�
= 17.3�𝑚/𝑠
0.5
𝜌𝑣
√0.89
The actual operating vapour velocity is calculated by comparing the distribution of volumetric flow
over the area of the plate with holes Ah (as this is the section subjected to weeping)
12𝑚3
𝑞𝑣
21𝑚
𝑠
𝑈𝑣�𝑎𝑐𝑡𝑢𝑎𝑙�𝑚𝑖𝑛𝑖𝑢𝑚 =
=
=
2
𝐴ℎ 0.58𝑚
𝑠
Since the vapour velocity at process conditions is greater than the conditions required to produce
weeping 21m/s < 17.m/s, our design is sustainable, and can ensure good efficiency.
7.6.1.1
Liquid throw
Liquid throw is known as the liquid displacement that travels horizontally over the downcomer weir.
With a column that is cross flow single pass, this occurrence proposes no threat to operation as the
measure of liquid moving horizontally is namely persistent double and quadruple pass type flows.
7.6.1.2
Hydraulic Gradient
Hydraulic gradient is known as the driving force in order to move the liquid across the tray propelled
by the difference in the liquid level. For the current design of sieve plate trays, hydraulic gradient is
not of any concern is the process as resistance to the flow is justifiable to negligence with such a tray
type (Sinnott 2009)
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7.6.1.3
Pressure Drop across the plate and in the Column.
Pressure drop is a significant design parameter that holds high levels of validity when it comes to
operational efficiency. There are two main variables that contribute to the variation of pressure
changes: vapour flow rate through the plates (i.e. orifices) and the static head of liquid displayed on
the plate/tray.
In order to alter the pressure drop of the column, it must be defined using key parameters. In order to
calculate the pressure drop ht, the correlation of the following additional values are equated
ℎ𝑡 = � ℎ𝑑 + � ℎ𝑤 + � ℎ𝑜𝑤 + � ℎ𝑟
ht= pressure drop, mm
hd = dry plate drop, mm
hw = height of weir, mm
how = weir crest, mm
hr= residual head, mm
The dry plate drop is calculated by the vapour velocity through the orifice, and the ratio of density of
liquid to vapour contact,
𝑢
2 𝜌
ℎ𝑑 = 51 ( 𝑐 0 ) ( 𝜌𝑣 )
0
𝑙
The orifice constant that is the measure of the plate thickness and ratio between the area that is
perforated along the tray and the size of the perforations is determined as a constant in the following
figure, (Sinnott 2009)
Figure 35: Ah/Ap Vs Co
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Assuming
𝐴ℎ
𝐴𝑝
= 0.01�and the
𝑃𝑙𝑎𝑡𝑒�𝑡ℎ𝑖𝑐𝑘𝑛𝑒𝑠𝑠
𝐻𝑜𝑙𝑒�𝐷𝑖𝑎𝑚𝑒𝑡𝑒𝑟
= 1.0, where the area consisting of holes in the plate is
10% that of the cross sectional area of the column, (Sinnott 2009) Ah=0.1*Ac.
Co according to figure 35 is 0.84. The dry plate pressure drop can therefore be calculated as
𝑢0 2 𝜌𝑣
25.8 2 0.89
ℎ𝑑 = 51 ( ) ( ) = 51 (
) (
) = 45.10�𝑚𝑚
𝑐0
𝜌𝑙
0.84
950
Where uo is
𝑢0 = �
𝑞𝑣
11.5
𝑚
=�
= 25.8
𝐴ℎ
0.58
𝑠
The residual loss is the measurement described as the pressure difference between the pressure drop
and the dry plate drop with consideration to the liquid height on the tray.
Because of this correlation the effects of bubbling caused by vapour, and the froth personality of the
liquid.
The equation is calculated therefore as
ℎ𝑟 = �
12.5�𝑥�103 12.5�𝑥�103
=
= 13.16�𝑚𝑚
𝜌𝑙
950
Calculated from the weeping section, ℎ𝑤 + ℎ𝑜𝑤 = 40𝑚𝑚 + 17𝑚𝑚 = 57𝑚𝑚, the total pressure
drop is therefore
ℎ𝑡 = � ℎ𝑑 + � ℎ𝑤 + � ℎ𝑜𝑤 + � ℎ𝑟 = 45.10 + 40 + 17 + 13.16 = 118.54𝑚𝑚
Expressed in kilopascals, the pressure difference is
∆𝑃𝑡 = 9.81 × 10−3 ℎ𝑡 × 𝜌𝑙 = 9.81 × 10−3 × 118.54 × 950 = ��1𝑘𝑃𝑎
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7.6.1.4
Downcomer design (back-up)
The downcomer back design is a marginal parameter that certifies the allowance between every plate
proceeding it’s former. This is down by ensuring that the tray spacing limit is calibrated to account for
the amount of liquid in the downcomer and the frothing height that it is below the level of the plate
above. There are two main key occurrences that cause liquid to excessively backup the downcomer
passage, downcomer chocking and backup

Downcomer chocking is the occurrence when the entrained liquid caused by vapour velocity
exceeds a point in which the liquid trying to pass down the column due to gravity is halted,
causing chocking and blocking of stream ways.

Downcomer backup is the same phenomena as chocking; however it is caused by a slightly
different design flaw. Backup is due primarily to the liquid flow rate, unlike chocking, vapour
flow rate is irrelevant. When the rate of liquid increases to the point at which the rate of flow in
the downcomer is significantly less than the liquid flow rate specified, building up on the
penultimate plate occurs and stacking up of liquid in the plate spacing causes liquid to flood and
rise up the down passages.
Downcomer backup is the measure by the addition of the following
ℎ𝑏 = � ℎ𝑡 + � ℎ𝑤 + � ℎ𝑜𝑤 + � ℎ𝑑𝑐
Where,
ht= total pressure drop
hw= height of the weir
how= crest height
hdc= downcomer pressure drop
hb= downcomer backup
Figure 36: Downcomer Backup, (Sinnott 2009)
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All the valid variables have been previously solved in the former sections except the downcomer
pressure backup hdc. At the downcomer site, the restrictions occur due to the resistance to flow
previously mentioned in any of the two possibilities, for this reason, hdc is calculated as a measure of
clearance area, density of flow and the flow rate.
2
𝐿𝑚𝑑 2
9.28
ℎ𝑑𝑐 = �166(
) =(
) = 1.63𝑚𝑚
𝜌𝑙 � × �𝐴𝑚
950 × 0.01
Lmd = liquid flow rate downcomer kg/s
Am = clearance of plate spacing m2
Where Am is equal to the downcomer apron area specified as 𝐴𝑎𝑝 = ℎ𝑎𝑝 × 𝑙𝑤 where hap is the height
of the bottom edge of the apron above the plate, and is recommended by (Sinnott 2009) to be 5-10mm
below the outlet weir height. Therefore,
ℎ𝑎𝑝� = ℎ𝑤 − 5𝑚𝑚 = 45𝑚𝑚
Where,
𝐴𝑎𝑝 = ℎ𝑎𝑝 × 𝑙𝑤 = 0.045 × 2.20 = 0.10𝑚2
Since Am = Aap for this particular design, the downcomer backup hb can therefore be calculated as
ℎ𝑏 = ℎ𝑡 + � ℎ𝑤 + � ℎ𝑜𝑤 + � ℎ𝑑𝑐 = �118.54 + 40 + 17 + 1.63 = 177.22𝑚𝑚��
To check whether these limits are acceptable, we can compare the downcomer backup to the upper
limit of frothing noted by (Sinnott 2009) as
ℎ𝑏� ≤
Since
1
2
1
× (𝑙𝑡 + ℎ𝑤)
2
× (𝑙𝑡 + ℎ𝑤) = 0.5 × (0.9 × 0.04) = 470𝑚𝑚
The downcomer backup is well within the frothing limit as 177mm < 470mm
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7.6.1.5
Downcomer residence time
Stated by (Sinnott 2009), sufficient residence time must be permissible for the vapour entrained in the
liquid to become stripped in the downcomer. To prevent loss of stripping efficiency caused by heavily
aerated liquid, the recommended residence time should be greater than 3 seconds.
Since stripping efficiency is due to a pressure constraining the gas from evolving from the liquid, the
downcomer residence time may be calculated using a correlation the describes the allowance of
vapour through the liquid by measuring the pressure in downcomer, density flow rate and the
downcomer area, where tr is
𝑡𝑟 = �
𝜌𝑙 𝐴𝑑 ℎ𝑏𝑐
950 × 1.11 × 177.22�
=�
= 20.20�𝑠𝑒𝑐𝑜𝑛𝑑𝑠
𝐿𝑤𝑑
9.28
Since 20 seconds > 3 seconds the vapour entrained in liquid has a suitable duration period that allows
the hydrogen sulphide and carbon dioxide to be stripped from the MEA solution.
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7.7 Safety and Environmental Considerations
7.7.1 Safety Considerations
The key safety implementation of controls to be integrated into the operation of an amine stripper
column are categorised by three main key aspects considered to be of most valid and significant
severity.

The breakthrough of gas from the column at the expense of loss of liquid. In order to prevent
this from occurring it should be inherently compensated by ensuring that the rating of the
piping and control valving systems to adjust back pressuring of vapour (GPS 2010).

The return flow of gas due to loss of operational pressure. This can be easily avoided by
installing upstream of the feed line one flow valves or shut off valves that do not allow back
flow. At locations suspected of this occurrence there should be available personal protective
clothing for any personnel in the vicinity (GPS 2010)..

When discharge of gas or vapour is released at a sudden time due to any operational issues, it
can cause other design parameters to been thrown off calibration. For this reason, relief valves
should be installed at necessary locations for emergency discharge or pressurised vapours in
closed vessels (GPS 2010).
7.7.2 Environmental Considerations
The most significant issue of the amine sweetening process in regards to environmental harm is the
treatment of acid as that is an unwanted product of natural gas processing. The acid gas as a byproduct can only be treated by two plausible means, incineration of flaring. However, it is possible to
use the acid gas as a commodity for sulphuric acid production plants as hydrogen sulphide is a
product used as feed stock (EPA 2000).
Because the cost of hydrogen sulphide is low for purchasing, it justified as an economic loss to
process the hydrogen sulphide by isolating, purifying and then transporting to a sulphuric plant If
there are none locally.
In order to reduce the levels of H2S discharged through flaring and incineration, an elevated flare
stack should be implemented so that dispersion of the gas can be a result, reducing high
concentrations and therefore harmful effects (EPA 2000).
A significant aspect worth monitoring is that catastrophe of unprecedented occurrences such as spills
of substances, fires and other environmentally threatening misfortunes. In order to mitigate such
areas, it should be taken as strict caution to safely operate equipment within reasonable process
conditions such that when a threat is confronted, there is time and ability to diminish the potential
effects before they occur (EPA 2000).
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8
Equipment Design Kettle Reboiler
The following design is based on a kettle reboiler that is selected from the literature review in analysis
of alternative schemes.
S-14
Kettle Reboiler
(H-102)
S-15
S-16
Figure 38: Reboiler
Figure 37: Kettle Reboiler Arrangement
Table 12: Energy & Mass Balance of Reboiler
H-102
99%
Efficiency
Temperature (⁰C)
NO
90.00
110.00
110.00
Pressure (kPa)
130.00
130.00
130.00
Mass Flow (Tonnes/hr)
114.69
73.99
40.70
1,029.02
949.95
1,221.70
Density (kg/m3)
0.00
Power (kW)
Components / Streams (Mmol/hr)
S-14
S-15
S-16
Methane
-
(g)
-
(g)
-
(g)
Ethane
-
(g)
-
(g)
-
(g)
Propane
-
(g)
-
(g)
-
(g)
i-Butane
-
(g)
-
(g)
-
(g)
n-Butane
-
(g)
-
(g)
-
(g)
Pentanes
-
(g)
-
(g)
-
(g)
Nitrogen
-
(g)
-
(g)
-
(g)
0.00
(g)
0.00
(g)
0.00
(g)
-
(g)
-
(g)
-
(g)
Hydrogen Sulphide
0.25
(g)
0.00
(g)
0.25
(g)
Water
4.13
(l)
4.09
(g)
0.04
(g)
MEA
1.03
(l)
0.01
(l)
1.02
(l)
Triethylene Glycol
-
(l)
-
(l)
-
(l)
Air
-
(g)
-
(g)
-
(g)
Carbon dioxide
Oxygen
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Table 13: Relevant Data
Data
Value
ρ Solvent Density (Water + MEA)
1000 kg/m3
Steam Density ρ
2.227 kg/m3
Steam Flow rate
5 kg/s
Thermal Conductivity kl
0.75 j/s.m.K
Viscosity Steam µ
0.001 kg/m.s
Heat Capacity Steam cp
2.347 kJ/kg.K
Saturation temperature at steam conditions
153 𝑐 °
Fouling Factor
10000 w/m2.k
Reference
Sinnott, Ray K. Towler, Gavin. (2009)
8.1 Area calculation
temperature�of�feed�s14 = 90𝑐 ° ,
inlet�steam�temperature = 300𝑐 ° ,
Condensed�steam�outlet = � 40𝑐 °
�
outlet�vapour + liquid�temperature�S(15 + 16) = 120𝑐 °
In order to accurately depict the temperature different between the exchanging heat streams, we can
use the log mean temperature difference (LMTD) as a value for constant flow rate and thermal
properties.
LMTD�� =
�∆𝑇𝑏𝑖𝑔− ∆𝑇𝑠𝑚𝑎𝑙𝑙
�(300 − 40) − (120 − 100)
�=
= 104.88�𝑐 °
∆𝑇𝑏𝑖𝑔
ln (∆𝑇
)
300 − 40
𝑠𝑚𝑎𝑙𝑙
ln ( 120 )
100
In designing any type of heat exchanger, since we are calculating the overall heat transfer coefficient
as a value in order to size the reboiler, we must first assume an appropriate value so that we may be
able to continue with the calculations and provide the necessary data variables. This process may take
numerous iterations until the initial assumed value is similar to the outcome given by the calculations.
In this case we have assumed a value of
Assuming U= 3500 w/m2.k
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Where Q is calculated from energy balance as a means of flow rate (molar) with its energy capacities
(enthalpies)
𝑄 = 𝛴𝑛𝑖𝐻𝑖 − 𝛴𝑛𝑜𝐻𝑜
ni= molar flow rate of feed, mol/hr
no= molar flow rate at exit, mol/hr
Hi= enthalpy of feed, kj/mol
Ho= enthalpy at exit, kj/mol
Table 14: Data obtained from energy balance
Component Enthalpy in (s-13)
(Hi) at 90 °C
Water
6.8
MEA
49
kj
mol
Enthalpy out (s-15+16)
Mol flow In
Molar flow out
(Ho) at 110 °C
(s-13) (ni)
(s15+15) (no)
48.5
kj
mol
kj
mol
53.503
kj
mol
4129497
mol
hr
4129497
mol
hr
1029105
mol
hr
1029105
mol
hr
Using the data obtained from the energy balance, we can calculate the amount of energy required
heating the incoming stream from the bottom of the column s-14 and the amount of heat required for
s-15.
𝑄 = 𝛴𝑛𝑖𝐻𝑖 − 𝛴𝑛𝑜𝐻𝑜
𝑄 = (4129497 × 6.8 + 1029105 × 49) − (4129497 × 48.5 + 1029105 × 53.5)
𝑄 = 49089
𝑘𝑗
= 49.09�𝑀𝑊
𝑠
Therefore the total area at these parameters is calculated by using this value of power in the following
correlation where,
𝑄 = 𝑈 × 𝐴 × 𝐿𝑀𝑇𝐷,��
𝐴=
𝑄
49.09
=𝐴=
= 133.5𝑚2
𝑈 × 𝐿𝑀𝑇𝐷
3500 × 104.86
U= Assumed heat transfer coefficient, w/m2.k
A= area required for specified heat transfer, m2
LMTD= log mean temperature difference, C°
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Since this is the total area of the required power to operate two regenerator columns, the size of one
reboiler is therefore,
𝐴=
8.1.1.1
𝑇𝑜𝑡𝑎𝑙�𝐴𝑟𝑒𝑎 133.5
=
= 67𝑚2
2
2
Number of tubes
Table 15: Relevant Data Assumed According to Operability
Parameter
Value
Thickness of piping
5mm
Length of pipe
8m
Inner diameter of pipe
25mm
Outer diameter of pipe
30mm
The number of tubes can be calculated by finding first the area of one tube, which is calculated from
assumed values that are recommended for certain design standards (Sinnott 2009). Using therefore the
area of one tube, we can calculate the necessary total number of tubes by dividing the required area
based on our assumed energy values.
Area of one pipe
Ao = (𝜋 × (
𝑑𝑜
) × 𝑙) = (𝜋 × (30 × 10−3 𝑚) × 8𝑚) = 0.75�𝑚2
1000
Ao= area of pipe, m2
do= outer diameter of tubes, m
l= length of tubes, m
Nt= number of tubes
𝐴
66.7
𝑁𝑡 = (
)=
= 177�𝑡𝑢𝑏𝑒𝑠
𝐴𝑡𝑢𝑏𝑒𝑠
0.75
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8.1.1.2
Overall Heat Transfer Coefficient Calculation
Table 16: Relevant Data Obtained
Data
Value
Water Density ρ
1000 kg/m3
Steam Density ρ
2.227 kg/m3
Steam Flowrate
12.8 kg/s
Thermal Conductivity kl
0.75 j/s.m.K
Viscosity Steam µ
0.001 kg/m.s
Heat Capacity Steam cp
2.347 kJ/kg.K
Saturation temperature at steam conditions
153 𝑐 °
Fouling Factor
10000 w/m2.k
Change in temperature (Δt): Saturation temperature - Inlet temperature = 153𝑐 ° –145𝑐 ° = 8𝑐 °
In order to calculate the overall heat transfer coefficient of the kettle reboiler, we use a correlation that
combines the necessary parameters that are involved in collaborating with the overall energy output.
The overall energy output is found by the sum as,
1
1
1
1
=
+ +
𝑈 ℎ𝑛𝑏 ℎ𝑐 𝑓𝑜𝑢𝑙𝑖𝑛𝑔
Where,
U= overall heat transfer coefficient, w/m2.k
Hnb = heat transfer of pool boiling, w/m2.k
Hc = heat transfer of condensation, w/m2.k
Fouling= heat transfer to compromise fouling, w/m2.k
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Heat transfer coefficient involved in the condensation around the internal piping is calculated by
1
1
𝜌𝑙 2 × 𝑔 3
−
(ℎ𝑐)ℎ𝑏 = 0.95 × 𝑘𝑙 × (
) × 𝑁𝑡 9
µ𝑙 × Ƭ
Kl= Thermal conductivity of liquid condensate, W/m.C°
Ƭ= horizontal tube loading,
g= gravity, m/s2
Nt= number of tubes,
𝑘𝑔
𝑇𝑜𝑡𝑎𝑙�𝑐𝑜𝑛𝑑𝑒𝑛𝑠𝑎𝑡𝑒�𝑓𝑙𝑜𝑤� ( 𝑠 )
𝑊𝑐
5
Ƭ=
=
=�
= 0.00353
𝑇𝑢𝑏𝑒�𝑙𝑒𝑛𝑔𝑡ℎ�(𝑚) × 𝑇𝑢𝑏𝑒𝑠�𝑝𝑒𝑟�𝑏𝑢𝑛𝑑𝑙𝑒 𝐿 × 𝑁𝑡
8 × 177
Therefore, the overall heat transfer in respect to condensation of hot steam cooled, settling in and
around the piping of the kettle reboiler can be found as,
1
1
10002 × 9.8 3
𝑤
(ℎ𝑐)ℎ𝑏 = 0.95 × 0.75 × (
) × 497−9 = 5635.74 2
0.001 × 0.016
𝑚 .𝑘
During the process of heating up liquid within the reboiler, the nature of the process is termed as
“pool boiling”, which is essentially the behaviour of having the heat source (pipe work) submerged in
a stagnant pool of liquid. This data value is correlated by several values where,
ℎ𝑛𝑏 = 1.167 × 10−8 × 𝑃𝑐 2.3 × ΔT 2.333 × 𝐹𝑝3.333
𝐹𝑝 = 1.8 × 𝑃𝑟 0.17 + 4 × 𝑃𝑟1.2 = 1.8 × 0.0060.17 + 4 × 0.0061.2 = 0.76
𝑃𝑟 =
𝑃
𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒
130�𝑘𝑃𝑎
=�
=
= 0.006
𝑃𝑐
𝐶𝑟𝑖𝑡𝑖𝑐𝑎𝑙�𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒 22064�𝑘𝑃𝑎
ℎ𝑛𝑏 = 1.167 × 10−8 × 220642.3 × 82.333 × 0.763.333 = 128013
𝑤
𝑚2 . 𝑘
Fp= Correlation of Prandtl constant
Pc= Critical pressure, kpa
Pr= Prandtl Number: ratio of critical pressure to operating pressure
P= Operating pressure, kpa
hnb= Pool boiling heat capacity, w/m2.k
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To check the operability in regards to capability of the current parameters, we must ensure that the
plausible energy required to be produced by the kettle reboiler is within the limits of the design. This
can be found by calculating the critical heat flux which must not be exceeded, to compare our energy
output. The critical heat flux is found by,
𝑄𝑐�
𝑤
= 367 × 𝑃𝑐 × 𝑃𝑟 0.35 × (1 − 𝑃𝑟)0.9
𝑚2
Qc= Critical heat flux, w/m2
𝑄𝑐 = 367 × 22064 × 0.0060.35 × (1 − 0.006)0.9 = 1201204.91
𝑤
𝑚2
𝑤
𝑤
Since Pool Boiling < Critical Heat flux, system is satisfactory. 128013 𝑚2 .𝑘 < �1201204.91 𝑚2,
The overall heat transfer coefficient can now be calculated as all parameters have been checked to be
satisfactory. By adding each heating coefficient, we can find the overall and compare to our assumed
initial value for similarity in which will determine whether we are required to iterate again, or the
parameters are suitable which will justify the kettle reboiler efficient for regeneration heating.
𝑤
Since the fouling factor = 10000 𝑚2 .𝑘
1
1
1
1
=
+ +
𝑈 ℎ𝑛𝑏 ℎ𝑐 𝑓𝑜𝑢𝑙𝑖𝑛𝑔
1
1
1
1
=
+
+
𝑤
𝑤
𝑤
𝑈 128013
5635.74 2
10000 2
𝑚2 . 𝑘
𝑚 .𝑘
𝑚 .𝑘
𝑈 = 3505.69�
𝑤
𝑚2 . 𝑘
The estimated heat transfer coefficient was 3500w/m^2.K which after the design procedure produced
through iteration a final value concluding the overall transfer coefficient to be 3506 w/m^2.K. This
value is proved satisfactory based on the foundations of the parameters utilised and assumptions
stated.
Formulas - (Sinnott 2009)
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9
9.1
Mechanical Design of Reboiler
Internal Velocity
To avoid excessive entrainment the maximum allowable velocity which is calculated through the
characteristics of the steam heating the liquid which Is MEA solution, the velocity should be found to
be no greater than
𝜌𝐿 − 𝜌𝑣 0.5
1000 − 2.227 0.5
𝑚
𝑈𝑣 < 0.2 (
) = 0.2 (
) = 4.32
𝜌𝑉
2.227
𝑠
Since the operating velocity through tubes at operational conditions is
𝑘𝑔
)
5
𝑚
𝑠
× 𝐴𝑟𝑒𝑎�𝑜𝑓�𝑝𝑖𝑝𝑒�𝑚2 =
× 0.75 = 1.7
𝑘𝑔
2.227
𝑠
𝐷𝑒𝑛𝑠𝑖𝑡𝑦 3
𝑚
𝐹𝑙𝑜𝑤𝑟𝑎𝑡𝑒� (
The velocity comparison of between maximum and operational area 1.7m/s < 4.32m/s we can
specify that the tube dimensions are satisfactory, and the velocity of the vapour passing through them.
9.2
Tube Layout & Bundle Diameter
Table 17: Pitch of Tube Parameters, Reboiler, (Sinnott 2009)
Using square pitch with a two pass kettle reboiler (U tube)
Figure 39: Pitch Arrangements, (Sinnott 2009)
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By using the constants recommended by Sinnott, it is possible to find a recommended bundle
diameter for the amount of tubes submerged in the liquid. This is an important feature of the design as
if the pipes are not correctly submerged, the pool boiling effect will greatly be reduced and the heat
transfer load compromised at the exposed piping, which could lead to damage of the reboiler.
From table 17
K1 = 0.156
n1 = 2.291,
The bundle diameter is therefore,
1
1
𝑁𝑡 𝑛1
177 2.291
𝐷𝑏 = 𝑑𝑜 ( ) = 30 (
)
= 647𝑚𝑚
𝐾1
0.156
Db= bundle diameter, mm
do= outer pipe diameter, mm
k1= data constant
n1= data constant
Nt= number of tubes
Therefore the overall shell diameter required for the reboiler recommended by (Sinnott 2009) to be an
additional 75mm clearance illustrated as follows is found to be,
𝑆ℎ𝑒𝑙𝑙�𝐷𝑖𝑎𝑚𝑒𝑡𝑒𝑟� = �𝐷𝑏 + 75𝑚𝑚� = �722𝑚𝑚
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9.3 Dimensions of Kettle Reboiler
722mm
647mm
8m
Figure 40: Mechanical Design of Kettle Reboiler, (Sinnott 2009)
Table 18: Kettle Reboiler Summary
Specification
Value
Overall heat transfer coefficient
3505.70 w/m2.k
Type of Heat Exchanger
U tube Kettle Re-boiler
Number of tubes
177 tubes
Shell Bundle diameter
722mm
Design velocity through tubes
1.7m/s
Passes in reboiler
2 (one U tube)
Area of each Kettle Re-boiler
67 m2
Number of Kettle re-boiler
2
Tube Pitch
Square pitch
Flow rate of steam
5kg/s
Maximum Velocity
4.32m/s
Pressure Drop
Negligible
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10 Mechanical Design of Regenerator
10.1 Materials of Construction
The solvent used in the amine process is MEA (monoethanolamine) which was delegated through the
previous report (see feasibility study) through analysis and comparison to be optimal for the specific
operation and conditions. Throughout the process of the regenerator column, solvent (MEA) entering
at the top is relatively rich and at high temperature. The corrosive severity therefore is high which
poses risk or corrosion to equipment and machinery, however it should be noted that amine itself is
not overly corrosive, but instead the corrosivity severity is catalysed but the conditions and presence
of acid gas, high temperatures (particularly heat transfer surface corrosion) and high velocity and flow
rate (Hartson 2007).
Throughout the regeneration step of sweetening as the product uses amine as a solvent carrier, wet
gas erosion is a frequent occurrence that is observed in industry and a notable risk, namely at the exit
product points of the acid gas (Ropital 2009). For this reason it may be observed that the condenser,
reboiler and regenerator column top can experience high erosion rates due to presence of high
concentrated acid gas, in order to control this, observations conclude that maintaining that gas flow
rate between 7-9m/s can significantly reduce corrosion occurrence by mitigating the possibility of
accumulation (Ropital 2009).
The following conditions are advised in order to reduce the corrosivity effects of amine solutions in
carbon steel plants (Hartson 2007).

Amine concentration – MEA: ≈17.5% by weight or lean< 0.09/rich<0.44

Temperature of the reboiler < 131°C

Flow rate within the piping constituting MEA, <2m/s

Heat stable amine salts
Due to these issues of corrosivity, the material selection is recommended through the selection of the
following table which a hybrid use of stainless and carbon steel is considered.
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Table 19: Metallurgical recommendations for MEA (Ropital 2009)
Sweet Feed
Sour Feed
Corrosion resistant alloy (304)
Corrosion resistant alloy (304/306)
Heat exchanger
Shell
Tubes
Carbon Steel
Corrosion resistant alloy (304)
Carbon Steel
Either option
Regenerator column
Shell
Internal structure
Carbon Steel/Resistant In spots
Corrosion resistant alloy (304/316)
Carbon Steel
Corrosion resistant allow (304)
Condenser
Shell
Tubes
Carbon Steel
Corrosion resistant alloy (304/316)
Carbon Steel
Corrosion resistant allow (304)
Reboiler
Shell
Tubes
Carbon Steel
Corrosion resistant alloy (304/316)
Carbon Steel
Corrosion resistant allow (304)
Mechanical Unit
Amine rich piping
The reason to delegate the following compositions of carbon steel and stainless steel in different areas
of constructions of each unit is to reduce where possible the economic margins of capital cost. It is of
course most recommended to build, with considerations in mind, all equipment with stainless steel
including the shell but dramatically increases the capital cost. However, it is plausible to combine the
regions as mentioned in the above table for the following process. Since external casings and shells
have no direct contact with the operational substance, namely at operating conditions, the severity of
corrosion is greatly reduced allowing for plausible use of materials that do not require corrosivity
mitigation.
In order to reduce corrosion, fouling and scaling occurrences in the pipes, industrial lagging will be
utilised namely in the regenerator feed and exit pipelines (TIAC). The recommended lagging
insulation for high temperatures is

Calcium Silicate

Mineral Fibre – High temperature
Since calcium silicate is widely available and is a slightly denser material (200kg/m3) as opposed to
mineral fibre (130kg/m3), the insulation will have the following properties (Sinnott 2009).
Table 20: Insulation Properties
Material
Density
Thickness
Thermal capacity (373 k)
Calcium Silicate
200 kg/m3
75mm
0.063 w/m.K
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Typical stainless steel properties are shown in the following figure as a comparison. Due to the
corrosion occurrence, stainless steel 304 will be used as construction material, however carbon steel is
applicable as casing but as high recommendation, frequent inspection and quality grading should be
conducted to monitor the conditions of the carbon steel in case of leaking or spills occur (Moss 2013).
Figure 41: Stainless Steel Metallurgy, (Moss 2013)
The equipment material selection delegated is identified in the following table as a calibration of both
carbon steel and stainless steel. The justification of this is to reduce cost where possible by integrating
the carbon steel selection in locations that are not prone to corrosive behaviour or threat. However, if
there is large concern, special alloys can be arranged to support corrosion occurrence that can also be
malleable and easily constructive into the necessary equipment, as stainless steel has poor high
temperature behaviour as it has high levels of expansion.
Therefore the following material selection is advised.
Equipment
Material Selection
Corrosion Allowance
stripper column
CS
6mm
Trays
304 SS
Nozzle’s
304 SS
Stripper flash drum
CS
Demister
SS
Kettle reboiler
Channel
Tubes
6mm
6mm
CS
SS
Condenser
6mm
Tubes
304L SS
Shell
CS
Figure 42: Material Selection Summary
Where,
CS= Carbon steel
SS = Stainless steel
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10.2 Overall Vessel
10.2.1 Height of vessel
The height of the stripper column is found by calculating the number of trays and the tray spacing
area. The closures consisting of two torispherical heads and the top and bottom make the additional to
the column length (see design summary for tray and plate spacing specifications). Since the height of
the column trays is as follows
𝐻𝑡 = 𝑁𝑡 × 𝑙𝑡 = 20 × 0.9 = 18𝑚
Ht= height of trays, m
Lt= tray spacing, m
Nt= number of trays
Therefore the total height of the column is
𝐻𝑡 + 2 × 𝐻ℎ = 18 + 2 × 0.54 = 19.1𝑚
Hh= height of head, m
10.2.2 Dead weight of column
The weight of the column as a stainless steel vessel considering internal insulation and tray weight,
the dead weight of the entire structure can be estimated by the following correlation (Sinnott 2009)
Total weight of vessel is equal to
𝑊𝑣𝑇 = 𝑊𝑖 + 𝑊𝑣 + 𝑃𝑤 + 𝐿𝑤 = 75.70 + 199 + 4.13 + 120 = 394.10�𝑘𝑁�
Where,
𝑊𝑣 = 𝐶𝑤 × 𝜋 × 𝜌𝑚 × 𝐷𝑚 × 𝑔(𝐻𝑣 + 0.8 × 𝐷𝑚) × 𝑡 × 1 × 10−3
𝑊𝑣 = 1.15 × 𝜋 × 7999.5 × 2.84 × 9.81(19.8 + 0.8 × 2.84) × 12 × 1 × 10−3 = 199𝑘𝑁
Assuming a liquid volume of 10% and the density of MEA, we can calculate the weight of liquid in
the vessel at any given time to be,
𝐷𝑐 2
2.84 2
950
×
0.1
×
(
)
×
𝐻𝑣
×
𝜋
950
×
0.1
×
(
𝜌𝐿 × 𝑉𝐿
2
2 ) × 19.8 × 𝜋 = 120𝑘𝑁
𝐿𝑤 =
=
=
1000
1000
1000
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The weight of each tray in this case constructed of stainless steel, is the volume of the tray vs the
density of material, therefore the weight of the accumulated value of every tray is pressure applied
inside the vessel accumulating to the overall weight,
10
𝑃𝑣 = (𝐴𝑐 − 𝐴𝑑) × 𝑃𝑡 = (6.37 − 1.11) × (
) = 0.05𝑚3
1000
Weight of all plates therefore,
𝑃𝑤 = 𝑃𝑣 × �𝜌𝐿 × 𝑁𝑡 = 0.05 × 950 × 20 = 413𝑘𝑔�𝑜𝑟�4.13�𝑘𝑁
Considering also the weight of insulation required, by measuring the volume of thickness and the
density of selected material we can calculate the contribution of insulting effects to the total weight of
the vessel. The weight of the insulation can be found by taking the overall volume of the insulation by
its density, such as
𝑊𝑖 = 𝑉𝑖 × 𝜌𝑖 = 37.84 × 200 = 7569.20�𝑘𝑔�𝑜𝑟�75.70�𝑘𝑁
Where,
𝑉𝑖� = �𝜋 × (
𝐷𝑐 2
2.84 2
75
) × 𝐻𝑣 × 𝑡𝑖 = 𝜋 × (
) × 19.8 ×
= 37.84𝑚3
2
2
1000
Nt= number of trays or plates
WvT= total weight of vessel, kN
Wv= weight of vessel, kN
Cw= correlation factor to account for nozzles, manways, internal supports, 1.15 (Sinnott 2009)
𝝆�m= density of vessel material, stainless steel 7999.5, kg/m3
Dm=mean diameter of vessel, m
g= gravity, m/s2
Hv= height of vessel, m
t= thickness of vessel, mm
Pw= plate weight
Wi= insulation weight, kN
Lw= liquid weight, kN
VL= volume of liquid in vessel, m3
𝝆�L= density of liquid, kg/m3
Pv= volume of plate, m3
Pt= thickness of plate, m
Ac= cross-sectional area of column, m2
Ad= downcomer area, m2
Vi= volume of insulation, m3
𝝆�i= density of insulation, kg/m3
ti= insulation thickness, mm
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10.2.3 Vessel Support- skirt design
There are various methods of vessel support that differ according to the required number of beams,
support load and stress. The most common types of support are

Skirt supports

Leg supports

Saddle supports

Lug supports
The most common use of support for vertical vessels is a conical or cylindrical outing shell known as
a skirt. The skirt connection to the vessel can be attached through three main connections: lap, fillet or
butt welding directly onto the vessel body (Moss 2009).
The supporting is designed to uniformly distribute the weight of the vessel over the load to minimise
stress. Conical skirts are generally more expensive then cylindrical support in terms of fabrication,
and is frequently noted to be an overdesigned necessity for most vessel circumstances, however if the
vessel is tall they provide better support and higher strength capability (Moss 2009).
Figure 43: Skirt Arrangement, (Moss 2013)
The skirt supporting infrastructure consists of the shell being supported by the skirt at the base of the
column. The flange at the bottom transmits the necessary load to the functions illustrated in the above
figure. Openings are provided in the skirt body to allow for piping, maintenance and access. The
typical dimensions of the skirt are shown in the following figure.
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Figure 44: Supporting Skirt Dimensions, (Sinnott 2009)
Since the diameter of the column is 2.84m, the overall dimensions supporting the vessel are as
follows,
Measurement
Length
Vessel diameter
2.8m
Maximum weight
1350kN
V- skirt height
1.58m
Y - beam spacing
0.25m
C-skirt base width
2.50m
E-skirt radius
1.10m
J-inner skirt radius
0.625m
G-bolt spacing
0.150m
t2
16mm
t1
12mm
Bolt diameter
27mm
bolt holes
33mm
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10.2.3.1 Dead weight stress on skirt
In order the check the over skirt is satisfactory with the vessel, using the vessel weight being stainless
steel including internals such as trays and insulation; we can use this to calculate the actual stress
applied on the vessel support rig.
𝜎𝑤𝑠 =
𝑊𝑣 × 1000
394.10 × 1000
𝑁
=
= 3.70
= 1650𝑘𝑁�
𝜋(𝐷𝑠 × 1000 + 𝑡𝑠𝑘)𝑡𝑠𝑘 𝜋(2.64 × 1000 + 12)12
𝑚𝑚2
Where,
𝝈�ws= deadweight stress on skirt, N/mm2
Wv= weight of vessel, N/mm2
Ds= inside diameter of skirt, m
Tsk=thickness of skirt, mm
10.2.3.2 Bending stress in skirt
The bending stress in the skirt is
𝑀𝑠
5121.70 × 1000 × 1000
𝑁
𝜎𝑏𝑠 = 4 ×
=4×
= 12.98
𝜋(𝐷𝑠 + 𝑡𝑠𝑘)𝑡𝑠𝑘 × 𝐷𝑠
𝜋(2.72 + 12)12 × 2.72
𝑚𝑚2
Ms= maximum bending moment, kN.m
Tsk = thickness of skirt, mm
Ds = inside diameter of skirt, mm
Wv= total weight of vessel, N
σbs = bending stress, N/mm2
10.2.3.3 Wind loading applied on skirt
Wind loading stress can be calculated by assuming dynamic wind pressure and wind loading as
𝑀𝑠 = 𝑃𝑤 × 𝑊𝑙 = 3646 × 1280 = 5121.70�𝑘𝑁. 𝑚
Ms= wind stress, kN.m
Pw= dynamic wind pressure, 1280 N/m2 (Sinnott 2009)
Wl= wind loading, 3646 N/m (Sinnott 2009)
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10.2.3.4 Seismic load
The stresses due to seismic loads such as vibrations, shutters and earthquakes can be calculated using
a constant, weight and thickness of skirt material, this is found to be
2
𝐶×𝐻×𝑊
2
0.8 × 19.8 × 394000
0.0135�𝑁
𝑓𝑠𝑏 = � × �
= �
=
2
2
3 𝜋 × (𝑅𝑜𝑘 ) × � 𝑡𝑠𝑘 3 𝜋 × (2.84 × 1000 + 16) × �12
𝑚𝑚2
C= seismic coefficient, 0.8
W= dead weight of the vessel, N
Rok= radius outside the skirt, mm
Tsk= thickness of the skirt, mm
10.2.3.1 Strength of skirt
Analysis of skirt strength must then be tested to prove sustainable under such loads, in order to
determine the strength of the skirt we must calculate by two main measures, compressive and tensile.
It is very important to make sure that the stress of the skirt is well within the limit of the skirt strength,
the calculations are correlated by taking into account weld efficiency as 0.7 and base angle of the
conical skirt at 80°. The young’s modulus is a constant value recommended by (Sinnott 2009)
𝜎𝑠𝑡�𝑀𝑎𝑥 = 𝑆𝑠 × 𝐸 × 𝑆𝑖𝑛Ѳ = 89 × 0.7 × 0.98 = 61
𝑁
𝑚𝑚2
𝑡𝑠𝑘
12
𝑁
𝜎𝑠𝑐�𝑀𝑎𝑥 = 0.125 × 𝐸𝑦 × ( ) × 𝑠𝑖𝑛𝜃 = 0.125 × 200000 ×
× 0.9 = 108.10
𝐷𝑠
2.72 × 1000
𝑚𝑚2
𝝈�st= tensile stress, N/mm2
𝝈�sc=compressive stress, N/mm2
Ss=maximum allowable design stress, 89 (Sinnott 2009), N/mm2
E= joint efficiency
Wv= dead weight of vessel, N/mm2
Ey = young’s modulus, 200,000 N/mm2
𝜎𝑠𝑡�𝐴𝑐𝑡𝑢𝑎𝑙 = �𝜎𝑏𝑠 − 𝜎𝑤𝑠 = 12.98 − 3.7 = 9.33
𝑁
𝑚𝑚2
𝜎𝑠𝑐�𝑎𝑐𝑡𝑢𝑎𝑙 = 𝜎𝑏𝑠 + 𝜎𝑤𝑠 = 12.98 + 3.7 = 16.65
𝑁
𝑚𝑚2
Since the tensile and compressive stress exerted on the skirt is less than the maximum limit , the skirt
strength and thickness is well suitable for the load present.
𝑁
𝑁
< �61
2
𝑚𝑚
𝑚𝑚2
𝑁
𝑁
�𝜎𝑠𝑐�𝑎𝑐𝑡𝑢𝑎𝑙 < �𝜎𝑠𝑐�𝑚𝑎𝑥𝑖𝑚𝑢𝑚��16.65
� < �108.10
2
𝑚𝑚
𝑚𝑚2
𝜎𝑠𝑡�𝐴𝑐𝑡𝑢𝑎𝑙 < 𝜎𝑠𝑡�𝑚𝑎𝑥𝑖𝑚𝑢𝑚��9.33�
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10.2.4 Vessel Heads and Closures
Cylindrical vessels have various possibilities for end of
vessel closures and heads that are designed according to
operational requirements and cost. The four principle
types of heads include (Sinnott 2009)

Flat Plate

Hemispherical heads

Ellipsoidal heads

Tori spherical heads.
The selection of plate to be used consists by classifying
the relevant conditions and minimal cost available.
Flat plate heads are the cheapest of all designs; however
they’re very limited as they are only permissible for small
Figure 45: Vessel Domed Heads, (Sinnott 2009)
and low pressure vessels.
Their main operation is to cover man ways (Sinnott 2009). Torispherical heads (also referred to as
dished ends) are said to be the most utilised design in industry as they can withstand pressures of up to
15bar however when systems exceed 10 bar they should be critically analysed as they became an
economic loss compared to ellipsoidal above such ranges (Sinnott 2009). Hemispherical heads are the
strongest designs due to its shape in which is capable of twice the pressure of a tori spherical head and
the same thickness (Sinnott 2009), however their cost is high.
The measure of strength is due to the welding necessary in design, as a chain is as strong as it’s
“weakest link” the vessel head is as strong as the welding joint. Since hemispherical contains no
welding it is the strongest, however unnecessary for this particular design as the pressure is not
excessive.
Because the pressure is maximum 150kpa, there is no need for hemispherical or ellipsoidal as
torispherical design is well capable for operation, and is the cheapest of domed vessel heads
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10.2.5 Head and vessel thickness
In order to find the height of the head, we must first find the thickness required under the relevant
conditions. According to (Sinnott 2009) the thickness can be found by adding the corrosion allowance
and calculating the torispherical correlation with recommended joint efficiency and knuckle radius as
0.7 and 0.135 to collaborate an inherit safe design specification. According to (White 2009) a good
corrosion allowance for the amine sweetening step in the regenerator column considering
temperatures averages 100 C°, 6mm is a good compensation figure as too large increases cost, and too
small will cause to damage of vessel. The thickness of the vessel will be uniform to the head.
𝑡=
0.885 × 𝑃𝑖 × 𝑅𝑐
0.885 × 0.265 × 1.5
+ 𝐶𝑡 =
+ 6𝑚𝑚 = 11𝑚𝑚
𝑆 × 𝐸 − 0.1 × 𝑃𝑖
103.421 × 0.7 − 0.1 × 0.265
Where,
S= stress at knuckle point, N/mm2
E= joint efficiency
Pi= safety pressure (10% above operating pressure), kpa
Rc= knuckle radius, mm
Ct= corrosion allowance, mm
10.2.5.1 Head Height
The height of the vessel head can be calculated according to (Couper 2010) by the following
correlation specified specifically for torispherical heads
ℎ2 = 0.1935 × 𝐷𝑜 − 0.455 × 𝑡 = 0.1935 × 2.84 − 0.455 × 0.0011 = 0.54𝑚
Figure 46: Torispherical Head
Where,
r1=radius, m
r2=knuckle radius, m
h= height of from base to knuckle radius, m
h2=height of head, m
Do=outer diameter, m
t= thickness, m
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10.2.6 Vessel Erection and Transportation
Vessel erection can be carried out in numerous ways, depending on the weight, height, angles,
characteristics and material of construction (Moss 2013). The methods used in industry to lift vessels
and columns consist of



Single cranes
Multiple cranes,
Gin poles
During the transportation of the unit, there will be different modes of erection established as certain
lifting is exhibited in the harbour for shipping and a different requirement for docking and unloading,
for this reason it is justified that the listing arrangement should not be designed to dictate the erection
variation of choice, but instead remain only as a consideration. (Moss 2013) There are specific
legislations that dictate clearances that must remain permissible for the mode of transport utilised.
These standards are consistent with railroads, shipping and trucking laws that govern the allowed
weight and height to safely move equipment where necessary. A typical trucking audit is shown in the
following illustration that clearly states required compliance.
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Figure 47: Typical Trucking Compliance Audit, (Moss 2013)
77
10.2.6.1 Lifting Lug design
Because of the type of vessel being relatively tall at around 20 metres in height and weighing 27
tonnes including insulation, the best method of erection is using a rigging crane. This method allows
the column to be lifted vertically by having two attached lifting lugs on either side of the column. A
typical lifting lug is illustrated in the following diagram,
Figure 48: lifting lug dimensions
Figure 49: Lifting lug, (Moss 2013)
For a vessel inner diameter of 144inch or 3.6 metres, the recommended top lug measurements
corresponding to 27 tons is illustrated as (Moss 2013)
Table 21: lifting lug dimensions
Weight
(ton)
Shackle
size (ton)
Lug
thickness
A
mm
B
mm
C
mm
E
mm
R3
mm
W1
mm
Gusset
thickness
mm
D3
tP
W2
m
mm
mm
254
152
457
76
13
13
N/A
N/A
N/A
mm
0-30
35
25
356
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D1
mm
60
10.3 Maintenance
10.3.1 Fouling
During the operation of the amine regenerator there shouldn’t be any solids in the solvent or solution,
and fouling quantity should be relatively low, however it is recommended to have what is known as a
candle filter placed within the regeneration amine cycle. Candle filters are simply pressure filters that
are used for polishing of solutions, generally used as low moisture cake filtering (Hartson 2007).
Due to maintenance and other phenomena, it is possible to get contamination of solvent by means of
solid infiltration. If the solids exceed to a limit of 20 mg for every 100ml, Vacco filters should be
installed upstream of the contaminated location, and then followed by an activated carbon filter to
mitigate hydrocarbons (Hartson 2009).
10.3.2 Cleaning
Cleaning for the amine regenerator should be a rare venture as it does not require frequent cleaning
because the nature of the internal components should be clean, with little suspended solids within the
solvent. However, if scaling or solids become a contaminant, it is recommended by (Lieberman 2009)
to clean the tower in the following manner,

Obtain a clear sample of the contaminant or fouling component to test whether it is
dissolvable in HCL

Fill the tower with a HCL solution strength between 5-10% in concentration with 1%
corrosion inhibitor and uniformly dilute a surfactant agent throughout the mixture

Circulate the mixture from the column top to bottom while monitoring the acid strength so
that damage to equipment of material grading is avoided

Rinse the tower with water for a prolonged duration and then completely drain of all fluids

Refill the stripper from the top with low concentrated KOH circulation and then circulate the
liquid before draining

Rinse the tower with water extensively and thoroughly before expecting the column
conditions
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10.3.3 Alarms and trips
The need for trips and alarms in this particular process it relatively low compared to other process
plant where they contain extreme conditions and high velocity machinery the pose great danger as
they’re both difficult to operate and possess hazardous chemicals. The alarms located within the
regenerator are at the base of the column where there is a low level and high level alarm to alert the
operator of the liquid conditions.
Because of the danger mainly to the equipment if there becomes a critical low level of liquid which
causes overheating of the process, the operator and onsite personnel will be warned with an alarm that
sounds before conditions escalate (Lieberman 2009). The same method is used for high levels of
settling liquid to prevent spillage.
Figure 50: Low level trip, (Lieberman 2009)
A trip would be advised to be installed at a specific parameter of liquid level both low and high that
would cut the feed or cut the drain accordingly, rectifying damage or disaster.
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10.4 Mechanical Illustrations
Since the chosen method of stripper was delegated to be plate a plate instead of packed column, the
internals consist of 18 stainless steel sieve trays (excluding reboiler and condenser stages). Each sieve
plate has the following internals and is constructed as illustrated in the figure below.
Figure 51: Typical Sieve Tray Arrangement, (Moss 2013)
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Column Diameter
706 mm
Head thickness
2.84 m
Vapour nozzle diameter
12 mm
Feed nozzle diameter
88.32 mm
64.5 mm
Top reflux nozzle
diameter
19.2 m
Column Height
12 mm
Tray Spacing
0.9 m
Wall Thickness
313 mm
Bottom reflux nozzle
diameter
Liquid nozzle diameter
313 mm
0.54 m
Head height
Figure 52: Column outer dimensions
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0.05 meres
6165 holes per tray
0.49 metres
10 mm
0.76 m2
5.57 m2
2.84 metres
Figure 53: Sieve tray dimensions
Figure 54: Column internal & external applications
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10.4.1 Manway
10.4.1.1 Column Manway
Manways are personnel access through into the column. They’re designed to allow a person to pass
through for inspections and maintenance. This is displayed in the above figure in a typical sieve plate.
It is recommended by (Arnold 2008) that any vessel with a diameter larger than 36inch or 0.9meteres
should have a minimum manway size of 18inch (0.45 metres). Since the designed stripper column is
2.84 metres in diameter, the manhole diameter will be designed to a 0.45 metre dimension (Arnold
2008). Within the manway it is also recommended to have two 100mm holes as flange inspection
openings. The material covering the manway is referred to as a devit which is a movable opening that
allows safe and easy opening, and should be 0.3 metres in diameter for convenient access (Arnold
2008) Recommended for the stripper column there should be a minimum of 6 manways for a 19
metres column, to allow access at various degrees of vertical length. A typical manway is shown in
the following figure (note that the column man way is different separate to the tray manway)
Table 22: Column manway sizing
Manway Orientation
Circular
Manway diameter
0.45 metres
Flange inspection openings
100 mm
Devit diameter
0.3 meters
Manway quantity
6 manways
10.4.1.2 Tray manway
Tray manways are an important design of
columns as they provide personnel access
up through the centre of the column.
The recommended width and length per
tray is 430mm by 430mm to allow for
manoeuvring.
Table 23: Tray manway sizing
Manway Orientation
Square
Length* Width
430mm * 430mm
Manway Quantity
18 (per tray)
Figure 55: Manway Illustration, (Arnold 2008)
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10.5 Flanges & Nozzles
There are several types of flanges that can be used to various applications. The primary types used
most frequent in industry are (Moss 2013)
10.5.1 Flange types

Welding rock flange: welding rock flanges have a long tapered hub
between both the flange and the welded joint. This feature helps reduce the
continuity of stresses applied and breaks the tension between the flange and
branch, also increasing the overall strength as it’s tolerance limit is increased
Figure 56: Welding rock flange

Slip-on flange: Slip on flanges are cheaper than welding rock and are easily
removed and aligned, there application is designed in a way so that they are
able to slip over the pipe of nozzle and can be attached externally by
welding. However, they have relatively poor performance when considering
shock and vibration loads, and are about 2/3 that of the strength of a welding
rock flange

Figure 57: slip on flange
Lap-joint flange: Lap point flanges are used for pipework
infrastructure. They are an economical when are used in combination
with expensive alloys as the flange itself can be made from inexpensive
carbon steels, also isolating corrosion points. Because lap joint flanges
are both easy to assemble and align they’re favoured for low pressure
vessels and also supplied without a hub which reduced their capital cost.

Figure 58: Lap-point flange
Screwed flange: Screwed flanges are used to connect screwed
fittings to the flange. They can be useful in the sense that in the
circumstance of having alloy piping which can be difficult to
weld they can act as a suitable and strong substitute.
Figure 59: screwed flange

Plate/blind flange: plate flanges are simply flat plates that used to
cover flange connections and manways of a vessel.
Figure 60: Blind flange
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In order to determine the type of flange to be used in the design of the vessel mechanics, it is advised
to use already preconceived designs as custom design flanges are very expensive to fabricate. In order
to classify the necessary properties of a flange, there are several flange standards that categorised each
variation according to their quality grade, which is primarily measured by temperature and pressure
response.
Due to the nature of the process containing corrosive conditions because of the temperature and
property of vapour and gas, it is strongly advised to use a corrosion resistant flange which
constitutions an alloy that can withstand the design specifications.
Since our particular stripping column is operating at very reasonable conditions as the pressure is very
low (150kpa maximum) and the temperature not rising above standard design procedure of 110C⁰, we
will not require any specialised flange fabrication. For this reason the considerations for the inherit
design of the flange will be based upon the seating force limitations rather than the flange limitations,
as low pressure conditions are easily withstood by the flange itself.
The following recommendations for low pressure flanges is the design of

Minimising where possible the overall gasket width to reduce the force required to seat the
gasket upon the flange foundation

Use smaller bolt sizes with more bolts in order to minimise the bolt circle diameter and
therefore reducing the moment arm which will decrease the necessary flange thickness

Make use of what is known as hub-less flanges to minimise to cost of forgings (considerations
can be either lap joint or plate flanges)
To meet these conditions, the chosen use of flange will classified as lap joint because it both is easy to
align and requires not hub. The specific dimensions are discussed on the following page. Classified by
the ability of each flanges to withstand pressure, lap joints are in the lowest class classified in imperial
units known as 150lb. Since our design as previously mention will not exceed 150kpa, the low
pressure lap joint is the most suitable and not higher strength is required.
In order to allow to give uniform compression of gasket impacted by the flange, it is important to
calculate the bolt spacing limit to consider even stress loads through all bolts. It is recommended by
(Sinnott 2009) that the bolt spacing to be no less than 2.5 times than of the bolt diameter itself, which
will allow manual tool clearance such as a spanner or wrench to readily manoeuvre.
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10.5.2 Lap-joint flange
Figure 61: Lap-joint flange measurements
Figure 62: Lap-joint flange dimensions
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10.5.3 Flange Face
When it comes to choosing a type of flange face, there are two main classifications that describe the
basic application. The two primary variations are (Moss 2013):

Full faced flange: This is simply a flange where the face contacting area covers the entire
outside including the bolts and the face of the flange itself. These designs are only suitable for
low pressure operating conditions and are inexpensive compared to other arrangements.
Because the area required for the gasket is large, there is a high bolt tension in order to
provide good sealing application

Narrow faced flange: Where the face contacting perimeter is found within the circle of bolts.
This is the most common type of flange as it can withstand reasonable operating conditions
and is relatively simple in design. It however does cost more than a full face flange but
provides a larger variability due to their increased level of tolerance. The most common type
of narrow faced flange is the raised-face.
Other types of flanges do exist called plain face, such as spigot and socket. These arrangements are
the strongest design as they prevent blowouts due from excessive pressure. Their inherit nature is due
to their design holding the plain face in place by friction between the gasket and flange surface.
Figure 65: Full face flange
Figure 64: Narrow faced flange
Figure 63: Spigot and Socket
The narrow faced flange is the most suited to the design, since full face is tolerant for low pressure
vessels which is what we are operating, however, for insurability in case of over pressuring of the
system, it is inherently safer to incorporate narrow faced as it has a high tolerance and will be able to
withstand any extremities that are unprecedented (i.e. pressure relief valve failure).
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Flange sizes at each nozzle location corresponding to the figure illustrating each dimension. Each
flange is a stainless steel lap joint flange with a stainless steel gasket thickness of 10mm.
Table 24: Flange location and dimension
Flange
location
Nozzle
size
Diameter
mm
Piping
size
standard
(actual)
A
mm
B
mm
C
mm
D
mm
R
mm
F
mm
H
mm
I
mm
J
mm
Weight
kg, per
piece
Feed
88.32
88.90
190.50
91.40
23.90
30.20
9.70
108.0
4
19.10
152.40
3.81
Column
top
706
610
812.8
616.0
47.80
11.30
12.70
663.4
20
35.10
749.3
86.60
Top
reflux
64.5
60.30
152.40
62.50
19.10
25.40
7.90
77.70
4
19.10
120.70
2.03
Bottom
42
42.20
117.3
43.7
15.7
20.6
4.8
58.7
4
15.7
88.9
1
Bottom
reflux
313
323
482.60
328.20
31.80
55.60
12.70
365.30
12
25.40
431.80
26.10
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10.5.4 Gaskets
The gasket material used for the flanges of the stripper column are stainless steel corrugated metal in
order to prevent corrosion, and therefore leaks ensuring long time durability. The minimum gasket
thickness should be greater than 10mm for a stainless steel gasket. Because of the material being
relatively dense, there is a limit at which the gasket must be fastened into place so that it is properly
seated within the flange. This factor is called seating pressure. In order to determine the correct
internal pressure minimum to apply to the flange and gasket bols, we need to take into account the
gasket factor, and the minimum seating pressure yield strength. Recommended by (Sinnott 2009) the
gasket factor is 3.5 and the minimum seating pressure of 44.8 N/mm2. Therefore the necessary
applied pressure will be
𝐴𝑝𝑝𝑙𝑖𝑒𝑑�𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒 = 𝑚 × 𝑆𝑒𝑎𝑡𝑖𝑛𝑔�𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒 = 156.8
𝑁
𝑚𝑚2
Where,
M= gasket factor
With this type of necessary pressure it will require machine assisted torque in order to securely fasten
a gasket with such a seating pressure.
Table 25: Gasket sizing
Material
Stainless Steel
Seating pressure
44.8 N/mm2
Applied pressure
156.8 N/mm2
Gasket factor (M)
3.5
Minimum gasket thickness
10mm
Number of gaskets per column
5
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10.5.5 Nozzles
In order to specify the correct nozzle size, we need to consider the velocities at each nozzle location
whether it’s liquid or vapour. Once a feasible assumed value for vapour or liquid pipe velocity is
established, we can calculate the required area and therefore diameter of nozzle necessary in the
column wall. The following calculations have been made to determine the main 5 nozzle locations at
which are located at feed, top reflux, column top vapour exit, bottom column liquid exit, bottom
reflux.
The diameter of nozzle inlet,
4 0.5
𝐷 = (𝐴 × ) × 1000
𝜋
D= diameter, m
A= area, m2
Where the area at each nozzle location is,
𝐴=
𝐿𝑚 + 𝑉𝑚
(𝜌𝑣 + 𝜌𝐿) × 𝑉
Lm= liquid flow rate, kg/s
Vm= vapour flow rate, kg/s
V= velocity, m/s
ρV= vapour density, kg/m3
ρL= liquid density, kg/m3
Therefore the following calculations can be made at each nozzle,
Table 26: Nozzle Properties
Nozzle
Feed
Top outlet
Top reflux
Bottom outlet
Bottom reflux
Velocity
5 m/s
27 m/s
3 m/s
5 m/s
15 m/s
Flow rate
29.12 kg/s
22.63 kg/s
9.28 kg/s
6.49 kg/s
1 kg/s
Density
950.89 kg/m3
2.89 kg/m3
1000 kg/m3
950.89 kg/m3
0.89 kg/m3
State
Liquid
Vapour
Condensate
Liquid
Steam
Area
0.006 m2
0.29 m2
0.0033 m2
0.0014 m2
0.078 m2
Diameter
88.32 mm
607.76 mm
64.41 mm
41.71 mm
313.80 mm
(See energy and mass balance for operating details)
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10.6 Functionality of Column
10.6.1 Start Up Procedure
Proceeding the pre-commissioning have been satisfactory of all equipment and piping utilised in the
regenerator column and all valves are checked for operation start up, filing of the stripper can begin.
The reboiler should be primed prior to filling the column and temperature approaching operating level
as liquid is filling the tower simultaneously. The condenser overhead the column should also begin
running at the same time as reboiler which may present to be unusually cooler as the column
gradually heats up (this is okay as the overhead vapour will soon begin to increase in both velocity
and flow rate as the partial pressure gradually increases from the reboiler power input)
Careful monitoring of reboiler should be stringent as low liquid levels will cause a rapid increase in
temperature as there is no thermal resistance from the inner tubes heated by steam to the kettle
reboiler shell (this is the reason for reboiler priming as initial start-up is to check high liquid levels
within reboiler shell, properly submerging the inner tubes). As the liquid is filling the base of the
column and heating up, careful operation should be monitored, flow rates on constant check, pressure
and temperature balancing in order to reach a careful steady state operation where it will run
continually.
Pressure relief opening lines should operate from the controller room in case of any unprecedented
start up procedures prolapse and pressure or temperature reaches to high.
Check the overhead and bottom flow rate grading quality to ensure stripping process is established
and that the there is sufficient amount of vaporised steam passing through the column into the
condenser. All reflux loops should be open, and efficiency approaching maximal.
Once the expected steam rates are passing overhead and being looped back into column the reboiler
can enter a stead state condition as increasing in further temperature is unnecessary.
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10.6.2 Steady state operation
Process Parameter
Corrective Action
Inclination in operating pressure
1. Failure of pressure/valve controllers
2. Valve stuck shut and hinged
3. Damage to outlet gas lines at column
top. Inspect for unintentional closed
valve (freeze up if cold weather)
Declination in operating pressure
1. Failure of pressure/valve controllers
2. Check Valve control unhinged and stuck
open
3. Check Obstruction to gas lines entering
or exiting stripping column
Inclination in temperature (outside of
condenser)
1. Low cooling water flow rate
2. Damage to cooling water pipelines
3. Temperature transmitter or valve
damage, ineffective operation or dull
transmission signalling to control
Variability in reflux flow rates
1. Levelling transmitter is faulty
2. Valve false operation
3. Reboiler heating conditions incorrectly
operating
Reboiler energy input temperamental
1. Pressure fluctuation within inlet of
heating steam
2. Incorrect transmitting of flow
controllers
3. Heating steam supplied to reboiler is
compromised
Figure 66: Stripper Operating Actions
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10.6.3 Shut down procedure
Before beginning with shut down, inform all operators of concern the procedure will proceed.
Shut off feed pumps and gradually reduce valves but keep the bottom and overhead valves open
slightly longer as the primary objective is to remove all corrosive components first, and then water.
Once the feed valves begin to close the flow of MEA will reduce and the column will begin to
decrease as it drains out the bottom. Because of this, the reboiler will reduce its steam flow rate and
start cooling down, however because the draining rate is higher than cooling rate, the vaporised water
from the top reflux will continue to cycle.
As the gas is removed out of the MEA solvent and there is no longer any solvent incoming, the
bottom column will be drained of liquid and recycled back to the absorber to be treated upon start up
(as it will continue dissolve gases).
The reboiler by this stage will be fully closed by the condenser will be reducing to ensure all water is
returned to the column and down the plates enabling a pre-wash effect to clear materials of corrosive
substance. However, because MEA is not corrosive as low temperatures the cleaning process is
relatively simple as it is only necessary at low calibre compared to other sections of the plant.
Moreover, an external washing source will still be required.
Once the column levels are cleared to be empty, a fresh water source will be directed into the top
reflux nozzle and should allow for a prolonged duration for water to coherently pass down the
column, over plates and through holes removing where possible remaining substance that may cause
fouling or corrosion. Once the satisfactory washing time is completed, inspection is possible through
either manway concerning the column, and once conditions are satisfactory, the operation can be fully
closed.
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11 Data Sheet
Table 27: Data Sheet
Capacity
Operational mode
Solvent feed rate (30wt%)
Gas feed rate
Steam inlet rate
Operating Conditions
Pressure
Temperature
Heating mode
Residence time
Pressure drop (column)
Power
Materials of Construction
Vessel internals
Vessel shell
Vessel heads and closures
Insulation
Trays
Reboiler shell
Reboiler pipes
Gaskets
nozzles
Flanges
Vessel dimensions
Vessel dead weight
Vessel head
Vessel orientation
Inner diameter
Height
Vessel wall thickness
Vessel head thickness
Head height
Reboiler bundle diameter
Reboiler length
Reboiler inner pipe diameter
Reboiler pipe thickness
Vessel internals
Tray thickness
Tray spacing
Tray type
Holes per tray
Vessel support
Skirt support
Skirt thickness
Continuous
107.15 tonnes/hr
387.34 tonnes/hr
75 tonnes/hr
130 kPa
110 C⁰
Kettle reboiler
22 seconds
1 kPa
49 MW
304 Stainless steel
Carbon steel
Carbon steel
Calcium silicate
304 stainless steel
Carbon steel
304 stainless steel
304 stainless steel
304 stainless steel
Carbon steel
39 tonne
Torispherical
Vertical
2.84 m
19.2 m
12 mm
12 mm
0.54 m
722 mm
8m
25 mm
5 mm
10 mm
0.9 m
Sieve
6165
Conical
16mm
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12 Process Instrumentation & Control Diagram
S-11
Cooling water
PC
V-4
Gas
PT
S-13
V-5
TT
FC
FC
LT
S-13
S-10
V-6
S-12
TT
FC
S-9
Steam
V-2
TT
FC
S-15
Steam
LAL
HAL
V-3
FC
LT
S-14
feed
S-16
S-9
Bottom product
V-1
Figure 67: Process Instrumentation Diagram (PID)
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Condensate
Table 28: PID Controls
Equipment
Rig
Controls
Valve
Controller
Justification
Action
Regenerator
Reboiler
Flash Drum
LC (V-1)
Regenerator
AO
R
Prevents Column from
Bottom, Level
overflowing and mitigating
control
spills
TC
Steam feed,
(feed)
temperature
overheating, controls feed
(V-2)
control
temperature
TC (V-3)
Steam feed,
PT (V-5)
AO
AO
R
R
Prevents column and reboiler
temperature
temperature to overheat, also
control
controls rate of heating
Gas Product,
AC
R
pressure control
LC (V-6)
Prevents column from
Condensate
Prevents overpressure,
backflow and vessel damage
AC
R
Prevents overflow of liquid
AC
D
Prevents overheating and
Product, level
control
Condenser
TC (V-4)
Cooling Water,
temperature
boiling of flash drum liquid
control
and increases cooling rate
12.1 Process Variables
The Process variables related to the control scheme of the amine regeneration system including heat
exchangers (reboiler, condenser, feed heat exchanger) consist of 3 transmitter types being temperature
(stripper bottom, stripper temperature, feed temperature and distillate temperature) pressure (flash
drum pressure) and level (stripper liquid level, flash drum liquid level). The controls that are
translated through signal variation and operate accordingly include flow (temperature and pressure
transmission) and pressure (pressure transmission).
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12.2 Process Control
From the previous process the feed is fed into the column via a heat exchanger that controls the feed
temperature by means of hot steam contact controlled by a valve (V-2) that is AO in order to mitigate
possibility of overheating which increases corrosivity, toxicity and loss of efficiency as the MEA is
required to operate at a specific temperature to be stripped of acid gases. The control of the level
situated at the base of the column is through the feed injection into the column. The regenerator is
equipped with a high level alarm and a low level alarm in case of dire need, the operators and any on
site personnel can be warned of severe operating conditions. For this reason the feed valve is AO as
it’s better for the column to run hot than to cause leak of backflow down piping. The reboiler is
controlled by an AO valve in order to prevent over heating of the column, this is controlled via a
temperature transmitter that receives signal via measuring the operational conditions of the base of the
column.
The condenser situated at the top of the regeneration column is equipped to control temperature by
means of varying the flow rate of cooling water through the tubes. The condenser cooling water feed
is an AC valve as fail safe is better to have extra cold rather than vapour passing into the flash drum.
The flash drum is measured by two parameters, pressure and level. The pressure control is through an
AC valve to ensure low pressures rather than fail safe high pressure. The level of the flash drum is
controlled by the condensate that is exiting the flash drum and syphoned for either reflux or further
processing. This valve is also an AC to prevent flooding of the flash drum.
All valve signalling is operated through the use of a pneumatic signal denoted by the double slashed
signal, this is because the pneumatic signal opposed to electrical or digital as the signal diminishes
instead of shutting off which is necessary in high production utilisation and because the use of an
actuator must remain attached to the valve processing constantly (Carlos 2003). All control
identification is located in the control room and not on-site as plant capacity is too large for manual
labour control.
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12.3 Level Sensors & Control
The type of transmitter than signals the control of levelling from the stripper bottom and the flash
drum is specified to utilise the float application (see figure 68 for comparison of all sensors).The float
transmitter works by having a float that is generally a hallow ball that sits on the surface of the liquid
at the amounted location (Battikha 2007).
The position of the hallow ball acting as a float is a direct measurement of the present liquid. For
maximum accuracy and high sensitivity, the ball is designed so that it will sink in the greatest middle
section, illustrated in the following figure
Figure 68: Float Level Control,[Battikha, N.E.. (2007).]
The function of this application requires the liquid to have a specific known gravity (in this case,
MEA and water at operating conditions, see design section) location (Battikha 2007) The float
indicator is both simple, cheap and a reliable mode of measurement. Because it is a mechanical design
it has a large life span and can be used in harsh operating conditions, whereas electrical may cause
safety hazards and susceptible to breaking under high temperature and pressure conditions (Battikha
2007).
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Figure 69: Level Measurement Comparisons, [Battikha, N.E.. (2007).]
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12.4 Flow Sensors & Control
From careful analysis of different flow rate sensors used for the temperature and level controlling of
the flash drum, feed and feed temperature to the column, steam feed to the reboiler, and feed of
cooling water to condenser (see PID). Due to the conditions and nature of the pressure being relatively
and low flow rates not extreme and an easy application, the orifice plate design is most well suited
(Battikha 2007).
The orifice plate in comparison to conventional methods such as venturi pipes, magnetic sensors, flow
nozzles, pilot tubes and others, the design provides attractive advantages (see figure 70 for
comparison). Because the application of pressure measurement is simple in this case, the benefit of
having an easy install, transmitters apply to all sizes, stainless steel and any material can be used,
there are no moving parts and there availability and documentation is very widely known, as well as
being reputable (Battikha 2007).
Figure 70: Orifice Plate Pressure Sensor, [Battikha, N.E.. (2007)]
The accuracy of the orifice plate is solely dependent upon the properties of the substance being
viscosity, density, temperature and may require frequent calibration location (Battikha 2007).
However since the mode in which it is being utilised is constant operational condition and low
pressures, this design is well suitable to the circumstance. With the use of chemical seals the
mitigation of freezing and plugging can be achieved (Battikha 2007).
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Figure 71: Flow Measurement Comparison, [Battikha, N.E.. (2007).]
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12.5 Temperature Sensors
Used in the control scheme of the MEA regenerator of temperature transmitting, the temperature is monitored to control flow. In reference to the PID, stream
9 & 10 and steam feed to feed heat exchanger and reboiler.
The chosen method of measurement is thermo coupling for the particular design (Battikha 2007). Thermocouples have a wide range of application and can
handle large variations of temperatures and calibration specifications. They’re self-powered controllers that are advantageous as they are shock resistant,
resilient, simple and not expensive (Battikha 2007). Their accuracy tends to vary with temperature but is generally quite high in comparison to other modes of
measurement. Their applications can lead to quality depleting through the use and adverse conditions (Battikha 2007).
Figure 72: Temperature Sensor Comparison, [Battikha, N.E.. (2007).]
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Figure 73: Temperature Sensor Thermocouple, [Battikha, N.E.. (2007).]
12.6 Pressure Sensors & Control
In the process control scheme for the regenerator system, there is only one component that utilises a
pressure transmitter located in the flash drum separation of gases and the pressure is vital to its
operation and efficiency, and is controlled by the outlet flow rate of gas via a valve in stream 13 (see
PID). The chosen method of pressure sensor in an analysis seen in figure 74 delegated for the specific
gas control in the flash drum is classified as the piezoelectric transmitter. The methodology of this
design consists of a diaphragm in which the pressure is activated according to its severity which
translates as stress onto a crystal (generally quartz) (Battikha 2007). As the strain is applied to the
crystal and electrical signal is produced and is converted as output to an indicator (Battikha 2007).
These types of sensors are resilient and little in size. Their application gives high frequency results
with an output of good linearity that not require constant maintenance and calibration, however,
piezoelectric sensors can be sensitive to temperature variability and can react poorly when the system
pressure rises above specified calibration (overpressure of the system) (Battikha 2007)
Figure 74: Pressure Piezoeletric Sensor, [Battikha, N.E.. (2007).]
In figure 74, a comparison of pressure gauges are compared an analysed specifically to their
environment and application
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Figure 75: Pressure Measurement Comparisons, [Battikha, N.E.. (2007)]
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12.7 Equipment cost
In order to calculate the bare module cost of a regenerator column, the following assumptions based
on the data of this design report are considered

Diameter of column = 2.84m

Height of column = 19.2 m

Operating pressure = 130 kPa

Material of column = carbon steel

Material of sieve trays = stainless steel

Number of trays = 20

Insulation material = ceramic (for estimation)

Number of columns = 2
This bare module cost is simply a reference a real price may vary as certain parameters were omitted
in the calculation such as internal fittings and piping.
From these parameters, the estimated cost using the CAPCOST application is as follows,
Table 29: CAPCOST data
This estimation is found in US $ 619,000 in 2008, therefore to calculate a more accurate value we will
take into account the inflation rate for the year 2015, using CEPCI (Chemical Engineering Plant Cost
Index) the adjustment can be correlated as,
𝐶𝐵𝑀 2015 = 𝐶𝐵𝑀 (2008) × �
𝐶𝐸𝑃𝐶𝐼�2015
𝐶𝐸𝑃𝐶𝐼�2008
According the CEPCI the Chemical Engineering annual index for 2008 from CAPCOST was 500, and
for the end of 2014 which is the most recently reviewed period, the final index was 579.8. By using
these index figures we can calculate using the inflation percentage to find the actual bare module cost
for the most recent period.
𝐶𝐵𝑀 2015 = 619000 × �
579.8
= $717,792.4
500
Therefore the base module cost in 2015 for two amine regenerator column is US$ 1,435,584.8.
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Since the plant is located in Colombia, the exchange rates will be calculated using a location factor in
Brazil as it is the same continent and relatively close proximity for calculating purposes.
Recommended by (Sinnott 2009) the location factor is 1.14 which is based on 2003 data, therefore the
2015 exchange rate adjustment from U.S dollar to COP (Colombian pesos) is based as (x-rates)
Table 30: Exchange rates
Currency
Year
Value
US to COP
2003
US$ 0.000392
2015
US$ 0.000325
𝐿𝐹(𝑎𝑑𝑗) = �1.14 ×
𝑒𝑥𝑐ℎ𝑎𝑛𝑔𝑒�𝑟𝑎𝑡𝑒�2015
0.000325
= 1.14 ×
= 1.16
𝑒𝑥𝑐ℎ𝑎𝑛𝑔𝑒�𝑟𝑎𝑡𝑒�2003
0.000392
Therefore the overall cost in Colombia for the current year,
𝐶𝑜𝑠𝑡 = 1.16 ×
1,435,584.8
= 5,123,933,440�pesos
0.000325
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13 References
Arnold, Ken Stewart, Maurice. (2008). Surface Production Operations - Design of Oil Handling
Systems and Facilities, Volume 1 (3rd Edition). Elsevier
Battikha, N.E.. (2007). Condensed Handbook of Measurement and Control (3rd Edition). ISA.
Carlos A. Smith, 2003. Automated Continuous Process Control. John Wiley & Sons.
Coker, A. Kayode. (2010). Ludwig's Applied Process Design for Chemical and Petrochemical
Plants, Volume 2 (4th Edition). Elsevier
Couper, James R. Penney, W. Roy Fair, James R. Walas, Stanley M.. (2010). Chemical Process
Equipment - Selection and Design (Revised 2nd Edition). Elsevier.
Couper, James R. Penney, W. Roy Fair, James R. Walas, Stanley M.. (2010). Chemical Process
Equipment - Selection and Design (Revised 2nd Edition). Elsevier.
Engineering Data Book. 2004. Volumes I & II. Sections 1-26
EPA 2000. U.S Environmental Protection Agency. Associated Waste Report: Sweetening Wastes.
Office of Solid Waste
GPS 2010. Global Process Sysems. Guideline for the Design of Amine unit. Document NO. GPSP-PR-0027
Guo, Boyun Ghalambor, Ali. (2012). Natural Gas Engineering Handbook (2nd Edition). Gulf
Publishing Company
Hall, Stephen. (2012). Rules of Thumb for Chemical Engineers (5th Edition). Elsevier.
Harston, J.D. Ropital, F.. (2007). Amine Unit Corrosion in Refineries (EFC 46). Woodhead
Publishing
http://www.x-rates.com/
Kohl, Arthur L. Nielsen, Richard B.. (1997). Gas Purification (5th Edition)
Lieberman, Norman P.. (2009). Troubleshooting Process Operations (4th Edition). PennWell.
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Moss, Dennis R. Basic, Michael M.. (2013). Pressure Vessel Design Manual (4th Edition).
Elsevier
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