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Modelling and Initialisation of a Distillation Modelling and Initialisation of a Distillation Column for the Separation of Binary Systems Column for the Separation of Binary Systems Simone Christa , Orestis Almpanis-Lekkas, Walter Wukovits Institute of Chemical Engineering, Vienna University of Technology, Vienna, Austria Contact: [email protected] Introduction Institute of Chemical Engineering, Vienna University of Technology, Vienna, Austria Contact: [email protected] Model Assumptions Introduction Distillation is an important separation process used in different industrial fields. Increasing requirements on Model Assumptions • steady state: no material or energy accumulation on the trays • no reaction terms D & different industrial fields. Increasing requirements on yields, product purity and economical feasibility require efficient models to analyse and predict system performances without time consuming and • consideration of ideal trays: perfect mixing of the vapour and liquid phase thermal equilibrium for every component on each tray F & R & system performances without time consuming and complex investigations on real processes. The target of this work is to develop a mathematical model of a distillation column for binary systems. Due to the thermal equilibrium for every component on each tray • no heat loss x L ⋅ & y G ⋅ & F & Equation Description p x p y ⋅ ⋅ = ⋅ ⋅ γ ϕ distillation column for binary systems. Due to the flexibility in the programming structure and the flowsheeting capability the implementation of this F i, x F ⋅ & 1 - n i, 1 - n x L ⋅ & n i, n y G ⋅ & S & Equilibrium Component mass balance n i, n n i, n 1 - n i, 1 - n 1 n i, 1 F i, x L y G x L y G x F n ⋅ + ⋅ = ⋅ + ⋅ + ⋅ + + & & & & & i i i i p x p y , 0 i ⋅ ⋅ = ⋅ ⋅ γ ϕ model took place within the environment of the gPROMS ModelBuilder. 1 n i, 1 + + ⋅ y G n & n i, n x L ⋅ & B & Summation condition Heat balance 1 , 1 1 , 1 , = = ∑ ∑ = = nc i n i nc i n i y x l v l v h L h G h L h G h F ⋅ + ⋅ = ⋅ + ⋅ + ⋅ & & & & & Model Description The steady state column model for the separation of Process Initialisation Procedure Heat balance n n 1 1 - n 1 1 F l n v n l n v n n h L h G h L h G h F ⋅ + ⋅ = ⋅ + ⋅ + ⋅ - + + & & & & & The steady state column model for the separation of binary mixtures is based on mass and energy balances. It is designed as an n-equilibrium stage model including a total condenser, a splitter and a reboiler . Process Initialisation Procedure The mass/energy balances and equilibrium conditions form a complex system of non-linear coupled equations. For the handling of this numerical challenge, an initialisation procedure is developed in regard to both, model robustness and including a total condenser, a splitter and a reboiler . For the calculation of the equilibrium state in each stage, the thermodynamic properties (e. g. enthalpies, flexibility in user defined specification. The following sequence of initialisation steps proved to be effective: Initial state Condenser Condenser Reboiler Stage equilibrium activities) of Multiflash are used. For the consideration of the deviation from ideal equilibrium state, the murphree efficiency and pressure drop can be Initial state equilibrium enthalpy balance equilibrium Stage equilibrium murphree efficiency and pressure drop can be defined. Murphree efficiency Pressure drop Reflux ratio Reboiler enthalpy balance Stage enthalpy balance Simulation Results To validate the model, simulation results of two different binary systems are cross-referenced with Aspen Plus. The reboiler and condenser data are added as stages in the graphics. To validate the model, simulation results of two different binary systems are cross-referenced with Aspen Plus. The reboiler and condenser data are added as stages in the graphics. a) C H OH / H O mixture a) C 2 H 5 OH / H 2 O mixture Specifications Feedflow [kg/h] 89000 Beer-Column profile (temperature and ethanol fractions) Rectification-Column profile (temperature and ethanol fractions) Feed Feedflow [kg/h] 89000 Concentration ethanol in feed [wt %] 0.08 Temperature feed [K] 308 0,8 0,9 1,0 373 378 fractions) 0,8 0,9 1,0 415 420 ethanol fractions) Pressure feed [mbar] 1000 Feed preheater Temperature [K] 368 Pressure [mbar] 2000 0,5 0,6 0,7 0,8 368 373 mole fraction [-] erature [K] 0,5 0,6 0,7 0,8 405 410 mole fraction [-] erature [K] Mixer Pressure [mbar] 2000 Recycle heater Temperature [K] 308 Pressure [mbar] 1000 0,2 0,3 0,4 358 363 ethanol m tempe 0,2 0,3 0,4 390 395 400 ethanol m tempe 0,0 0,1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 353 number of stages 0,0 0,1 1 2 3 4 5 6 7 8 9 10 11 12 385 390 number of stages Column specifications Number of trays [-] Feed tray location [-] Reflux ratio (mole based) [-] Distillate rate [kg/h] Condenser pressure [mbar] Pressure drop [mbar] Murphree efficiency [-] Activity coefficient model ASPEN temperature gPROMS temperature gPROMS vapour fr. ASPEN vapour fr. ASPEN liquid fr. gPROMS liquid fr. ASPEN temperature gPROMS temperature gPROMS vapour fr. ASPEN vapour fr. ASPEN liquid fr. gPROMS liquid fr. Beer-Column 13 3 1 19822 1000 200 1 NRTL Rectification-Column 10 7 9 9360 3500 500 1 NRTL b) CH 3 OH / H 2 O mixture Conclusion & Outlook Good accordance between the simulation results of gPROMS and Specifications Feed Feedflow [kg/h] 10000 Concentration methanol in feed [wt %] 0.05 Good accordance between the simulation results of gPROMS and ASPENplus The initialisation procedure is robust for different user defined specifications Temperature feed [K] 293 Pressure feed [mbar] 1013 Feed preheater Temperature [K] 313 Pressure [mbar] 1013 specifications Further validation of different binary systems 1,0 375 Column profile (temperature and methanol fractions) Pressure [mbar] 1013 References 0,7 0,8 0,9 1,0 365 370 375 -] Column specifications Number of trays [-] 10 A. Friedl, lecture notes for “Thermische Verfahrenstechnik 1“: course 159.731, version 3, Vienna University of Technology, 2000. R.H. Perry, D . W . Green & J. O. Maloney , Perry‘s Chemical Engineers‘ Handbook: 7th ed., 0,3 0,4 0,5 0,6 350 355 360 ol mole fraction [- mperature [K] Number of trays [-] 10 Feed tray location [-] 6 Reflux ratio (mole based) [-] 4.36 New York: VCH, 1997. K. Sattler, Thermische Trennverfahren: Grundlagen, Auslegung, Apparate, Cambridge: VCH Verlagsgesellschaft mbH, 1988. A. Schönbucher, Thermische Verfahrenstechnik: Grundlagen und 0,0 0,1 0,2 0,3 335 340 345 methano tem Reflux ratio (mole based) [-] 4.36 Distillate rate [kg/h] 473 Pressure drop [mbar] 0 A. Schönbucher, Thermische Verfahrenstechnik: Grundlagen und Berechnungsmethoden für Ausrüstungen und Prozesse. Berlin: Springer, 2002. 1 2 3 4 5 6 7 8 9 10 11 12 number of stages ASPEN temperature gPROMS temperature gPROMS vapour fr. ASPEN vapour fr. ASPEN liquid fr. gPROMS liquid fr. Pressure drop [mbar] 0 Activity coefficient model NRTL Advanced Process Modelling Forum 2014 – London, United Kingdom, 2 – 3 April 2014 Advanced Process Modelling Forum 2014 – London, United Kingdom, 2 – 3 April 2014
Transcript of Modelling and Initialisation of a Distillation Column for ... · PDF fileIt is designed as an...
Modelling and Initialisation of a Distillation Modelling and Initialisation of a Distillation
Column for the Separation of Binary SystemsColumn for the Separation of Binary Systems
Simone Christa, Orestis Almpanis-Lekkas, Walter Wukovits
Institute of Chemical Engineering, Vienna University of Technology, Vienna, Austria Contact: [email protected]
Introduction
Institute of Chemical Engineering, Vienna University of Technology, Vienna, Austria Contact: [email protected]
Model AssumptionsIntroductionDistillation is an important separation process used in
different industrial fields. Increasing requirements on
Model Assumptions• steady state: no material or energy accumulation on the trays
• no reaction termsD&different industrial fields. Increasing requirements on
yields, product purity and economical feasibility
require efficient models to analyse and predict
system performances without time consuming and
no reaction terms
• consideration of ideal trays:
� perfect mixing of the vapour and liquid phase
� thermal equilibrium for every component on each trayF&
R&
system performances without time consuming and
complex investigations on real processes. The target
of this work is to develop a mathematical model of a
distillation column for binary systems. Due to the
� thermal equilibrium for every component on each tray
• no heat loss
xL ⋅&yG ⋅&
F&
Equation Description
pxpy ⋅⋅=⋅⋅ γϕdistillation column for binary systems. Due to the
flexibility in the programming structure and the
flowsheeting capability the implementation of thisFi,
xF ⋅&
1-ni,1-nxL ⋅&
ni,nyG ⋅&
S&
Equilibrium
Component
mass balance
ni,nni,n1-ni,1-n1ni,1Fi,xLyGxLyGxF n ⋅+⋅=⋅+⋅+⋅
++&&&&&
iiii pxpy,0i
⋅⋅=⋅⋅ γϕ
flowsheeting capability the implementation of this
model took place within the environment of the
gPROMS ModelBuilder.1ni,1 ++
⋅ yGn&
ni,nxL ⋅&
B&
mass balance
Summation
condition
Heat balance
1,11
,
1
,== ∑∑
==
nc
i
ni
nc
i
ni yx
lvlv
hLhGhLhGhF ⋅+⋅=⋅+⋅+⋅ &&&&&
Model DescriptionThe steady state column model for the separation of Process Initialisation Procedure
Heat balance nn11-n11F
l
n
v
n
l
n
v
nn hLhGhLhGhF ⋅+⋅=⋅+⋅+⋅−++
&&&&&
The steady state column model for the separation of
binary mixtures is based on mass and energy balances.
It is designed as an n-equilibrium stage model
including a total condenser, a splitter and a reboiler.
Process Initialisation ProcedureThe mass/energy balances and equilibrium conditions form a complex system of non-linear coupled equations. For the
handling of this numerical challenge, an initialisation procedure is developed in regard to both, model robustness and
including a total condenser, a splitter and a reboiler.
For the calculation of the equilibrium state in each
stage, the thermodynamic properties (e.g. enthalpies,
flexibility in user defined specification. The following sequence of initialisation steps proved to be effective:
Initial stateCondenser Condenser Reboiler
Stage equilibriumstage, the thermodynamic properties (e.g. enthalpies,
activities) of Multiflash are used. For the consideration
of the deviation from ideal equilibrium state, the
murphree efficiency and pressure drop can be
Initial stateCondenserequilibrium
Condenserenthalpy balance
Reboilerequilibrium
Stage equilibrium
murphree efficiency and pressure drop can be
defined.Murphreeefficiency
Pressure drop Reflux ratioReboiler enthalpy
balanceStage enthalpy
balance
Simulation ResultsTo validate the model, simulation results of two different binary systems are cross-referenced with Aspen Plus. The reboiler and condenser data are added as stages in the graphics.To validate the model, simulation results of two different binary systems are cross-referenced with Aspen Plus. The reboiler and condenser data are added as stages in the graphics.
a) C H OH / H O mixturea) C2H5OH / H2O mixture
Specifications
Feedflow [kg/h] 89000
Beer-Column profile (temperature and ethanol
fractions)
Rectification-Column profile (temperature and
ethanol fractions)
Feed
Feedflow [kg/h] 89000
Concentration ethanol in
feed [wt %]0.08
Temperature feed [K] 3080,8
0,9
1,0
373
378
fractions)
0,8
0,9
1,0
415
420
ethanol fractions)
Pressure feed [mbar] 1000
Feed
preheater
Temperature [K] 368
Pressure [mbar] 2000 0,5
0,6
0,7
0,8
368
373
eth
an
ol m
ole
fra
ctio
n [
-]
tem
pe
ratu
re [
K]
0,5
0,6
0,7
0,8
405
410
eth
an
ol m
ole
fra
ctio
n [
-]
tem
pe
ratu
re [
K]
Mixer Pressure [mbar] 2000
Recycle
heater
Temperature [K] 308
Pressure [mbar] 1000 0,2
0,3
0,4
358
363
eth
an
ol m
ole
fra
ctio
n [
tem
pe
ratu
re [
K]
0,2
0,3
0,4
390
395
400
eth
an
ol m
ole
fra
ctio
n [
tem
pe
ratu
re [
K]
0,0
0,1
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
353
number of stages
0,0
0,1
1 2 3 4 5 6 7 8 9 10 11 12
385
390
number of stages
Column specificationsNumber of
trays [-]
Feed tray
location [-]
Reflux ratio
(mole based)
[-]
Distillate
rate [kg/h]
Condenser
pressure
[mbar]
Pressure
drop [mbar]
Murphree
efficiency
[-]
Activity
coefficient
model
ASPEN temperature gPROMS temperature gPROMS vapour fr.
ASPEN vapour fr. ASPEN liquid fr. gPROMS liquid fr.
ASPEN temperature gPROMS temperature gPROMS vapour fr.
ASPEN vapour fr. ASPEN liquid fr. gPROMS liquid fr.
Beer-Column 13 3 1 19822 1000 200 1 NRTL
Rectification-Column 10 7 9 9360 3500 500 1 NRTL
b) CH3OH / H2O mixture
Conclusion & Outlook� Good accordance between the simulation results of gPROMS and
Specifications
Feed
Feedflow [kg/h] 10000
Concentration methanol in feed [wt %] 0.05
� Good accordance between the simulation results of gPROMS and
ASPENplus
� The initialisation procedure is robust for different user defined
specifications
FeedTemperature feed [K] 293
Pressure feed [mbar] 1013
Feed preheaterTemperature [K] 313
Pressure [mbar] 1013 specifications
� Further validation of different binary systems
1,0 375
Column profile (temperature and methanol fractions)
Feed preheaterPressure [mbar] 1013
References0,7
0,8
0,9
1,0
365
370
375
-]
Column specifications
Number of trays [-] 10A. Friedl, lecture notes for “Thermische Verfahrenstechnik 1“: course 159.731, version
3, Vienna University of Technology, 2000.
R.H. Perry, D.W. Green & J.O. Maloney, Perry‘s Chemical Engineers‘ Handbook: 7th ed.,0,3
0,4
0,5
0,6
350
355
360
me
tha
no
lmo
lefr
act
ion
[-
tem
pe
ratu
re [
K]
Number of trays [-] 10
Feed tray location [-] 6
Reflux ratio (mole based) [-] 4.36
R.H. Perry, D.W. Green & J.O. Maloney, Perry‘s Chemical Engineers‘ Handbook: 7th ed.,
New York: VCH, 1997.
K. Sattler, Thermische Trennverfahren: Grundlagen, Auslegung, Apparate, Cambridge:
VCH Verlagsgesellschaft mbH, 1988.
A. Schönbucher, Thermische Verfahrenstechnik: Grundlagen und
0,0
0,1
0,2
0,3
335
340
345
me
tha
no
l
tem
pe
ratu
re [
K]
Reflux ratio (mole based) [-] 4.36
Distillate rate [kg/h] 473
Pressure drop [mbar] 0
VCH Verlagsgesellschaft mbH, 1988.
A. Schönbucher, Thermische Verfahrenstechnik: Grundlagen und
Berechnungsmethoden für Ausrüstungen und Prozesse. Berlin: Springer, 2002.
1 2 3 4 5 6 7 8 9 10 11 12
number of stages
ASPEN temperature gPROMS temperature gPROMS vapour fr.
ASPEN vapour fr. ASPEN liquid fr. gPROMS liquid fr.
Pressure drop [mbar] 0
Activity coefficient model NRTL
Advanced Process Modelling Forum 2014 – London, United Kingdom, 2 – 3 April 2014Advanced Process Modelling Forum 2014 – London, United Kingdom, 2 – 3 April 2014
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