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7/31/2019 21218997 Rate Based MEOH Model
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Aspen Plus
Rate-Based Model of theCO2 Capture Process byMethanol using AspenPlus
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Copyright (c) 2008 by Aspen Technology, Inc. All rights reserved.
Aspen Plus, the aspen leaf logo and Plantelligence and Enterprise Optimization are trademarks or registeredtrademarks of Aspen Technology, Inc., Cambridge, MA.
All other brand and product names are trademarks or registered trademarks of their respective companies.
This document is intended as a guide to using AspenTech's software. This documentation contains AspenTechproprietary and confidential information and may not be disclosed, used, or copied without the prior consent ofAspenTech or as set forth in the applicable license agreement. Users are solely responsible for the proper use ofthe software and the application of the results obtained.
Although AspenTech has tested the software and reviewed the documentation, the sole warranty for the softwaremay be found in the applicable license agreement between AspenTech and the user. ASPENTECH MAKES NOWARRANTY OR REPRESENTATION, EITHER EXPRESSED OR IMPLIED, WITH RESPECT TO THIS DOCUMENTATION,ITS QUALITY, PERFORMANCE, MERCHANTABILITY, OR FITNESS FOR A PARTICULAR PURPOSE.
Aspen Technology, Inc.200 Wheeler RoadBurlington, MA 01803-5501USAPhone: (1) (781) 221-4300
Toll Free: (1) (888) 996-7100URL: http://www.aspentech.com
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Contents 1
ContentsIntroduction............................................................................................................21 Components .........................................................................................................32 Process Description..............................................................................................43 Physical Properties...............................................................................................64 Simulation Approaches.......................................................................................155 Simulation Results .............................................................................................176 Conclusions........................................................................................................18References ............................................................................................................19
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2 Introduction
Introduction
This document describes an Aspen Plus rate-based model of the CO2 capture
process by methanol (MEOH) from a gas mixture of H2, CO2, CO, N2, CH4, H2Sand COS from gasification of Western Kentucky coal char[1]. The operation
data from a pilot scale absorber[1] are used to specify the feed conditions andunit operation block specifications in the model. Thermophysical property
models have been validated against DIPPR correlations[2] for componentvapor pressure and liquid density, and literature data for vapor-liquid
equilibrium from Semenova (1979)[3] and Leo(1992)[4]. Transport property
models have been validated against literature data for viscosity[5-9], thermalconductivity[10-13] , surface tension[7, 14-18], and diffusivity[19].
The model includes the following key features:
PC-SAFT equation of state model for vapor pressure, liquid density andphase equilibrium
Transport property models Rate-based model for absorber with ceramic Intalox saddles packing
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1 Components 3
1 Components
The following components represent the chemical species present in the
process:
Table 1. Components Used in the Model
ID Type Name Formula
MEOH CONV METHANOL CH4O
CO2 CONV CARBON-DIOXIDE CO2
H2S CONV HYDROGEN-SULFIDE H2S
CO CONV CARBON-MONOXIDE CO
N2 CONV NITROGEN N2
COS CONV CARBONYL-SULFIDE COS
H2 CONV HYDROGEN H2
CH4 CONV METHANE CH4
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4 2 Process Description
2 Process Description
The flowsheet for the pilot plant[1] for CO2 capture by MEOH includes an
absorber, a flash tank, a stripper and so on. However, only the absorber dataare reported.
The sour gas enters the bottom of the absorber, contacts with lean MEOH
solvent from the top counter-currently and leaves at the top as sweet gas,while the solvent flows out of the absorber at the bottom as the rich solvent
with absorbed CO2 and some other gas components.
Table 2 presents the absorbers typical operation data.
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2 Process Description 5
Table 2. Data of the Absorber from the Pilot Plant [1]
Absorber
Diameter 0.127 m
Nominal Packing Height* 2.2 m
Packing Type ceramic Intalox saddles
Packing Size 6.25 mm(0.25 in)
Sour Gas
Flow rate 2.17 lbmol/hr
CO2 in Sour Gas 0.2801(mole fraction)
H2S in Sour Gas 0.00807(mole fraction)
Sweet Gas
CO2 in Sweet Gas 0.0095 (mole fraction)
H2S in Sweet Gas 0.00037 (mole fraction)
Lean MEOH
Flow rate 8.29lbmol/hr
Temperature -34.7F
Pressure 400psia**
* The column was found to be too high for the experiments and no absorptionwas detected above certain height of the packing [1]. Liquid and gas samples
were taken at the height of 1.5m from the bottom as liquid feed and gas
product. Therefore, effective packing height (1.5m), is used instead of thereal height (2.2m) in this simulation model. This effective height was also
used in the literature model [1].
** Because pressure unit is not reported explicitly [1], it is assumed to be
psia based on the pressure data in Table II and Figure 12 of [1]
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6 3 Physical Properties
3 Physical Properties
The PC-SAFT equation of state model is used to calculate vapor pressure,
liquid density and phase equilibrium. The PC-SAFT pure componentparameters for CO2, H2S, CO and COS have been regressed against vapor
pressure and liquid density data generated from DIPPR correlations[2] for eachcomponent. For all other components, the PC-SAFT pure component
parameters are taken from the work by Gross and Sadowski (2001,2002)[20,21]. The binary parameters between CO2 and MEOH and H2S and
MEOH have been regressed against vapor-liquid equilibrium data from
Semenova (1979)[3] and Leu (1992)[4].
DIPPR correlation models[2] are used to calculate MEOH viscosity, thermal
conductivity and surface tension, respectively; the predictions are in excellentagreement with literature data[5-18] as showed in Figures 13-15.
Wilke-Chang model[22] is used for calculating the gas diffusivity in MEOH. The
model quality has been justified by CO2 diffusivity data from Littel(1991)[19]
as showed in Figure 16.
Figures 1-16 show property predictions together with literature data.
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3 Physical Properties 7
MEOH vapor pressure
0.00001
0.0001
0.001
0.01
0.1
1
10
100
150 250 350 450 550
Temperature, K
Vaporpressure,ba
r
Data
PC-SAFT
Figure 1. MEOH vapor pressure. PC-SAFT is used to fit data generated fromDIPPR correlation[2] for methanol.
MEOH liquid density
300
400
500
600
700
800
900
1000
150 250 350 450 550
Temperature, K
Liqu
iddens
ity,
kg/m
3
Data
PC-SAFT
Figure 2. MEOH liquid density. PC-SAFT is used to fit data generated fromDIPPR correlation[2] for methanol.
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8 3 Physical Properties
CO2 vapor pressure
0
10
20
30
40
50
60
70
200 220 240 260 280 300 320
Temperature, K
Vaporpressure,ba
r Data
PC-SAFT
Figure 3. CO2 vapor pressure. PC-SAFT is used to fit data generated fromDIPPR correlation[2] for CO2.
CO2 liquid density
500
600
700
800
900
1000
1100
1200
1300
200 220 240 260 280 300 320
Temperature, K
Liqu
iddens
ity,
kg/m
3
Data
PC-SAFT
Figure 4. CO2 liquid density. PC-SAFT is used to fit data generated fromDIPPR correlation[2] for CO2
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3 Physical Properties 9
H2S vapor pressure
0
10
20
30
40
50
60
70
80
180 230 280 330 380
Temperature, K
Vaporpressure,ba
rData
PC-SAFT
Figure 5. H2S vapor pressure. PC-SAFT is used to fit data generated fromDIPPR correlation[2] for H2S.
H2S liquid density
300
400
500
600
700
800
900
1000
1100
180 230 280 330 380
Temperature, K
Liqu
iddens
ity,
kg/m
3
Data
PC-SAFT
Figure 6. H2S liquid density. PC-SAFT is used to fit data generated fromDIPPR correlation[2] for H2S.
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10 3 Physical Properties
CO vapor pressure
0
5
10
15
20
25
30
35
40
70 90 110 130
Temperature, K
Vaporpressure,ba
r
Data
PC-SAFT
Figure 7. CO vapor pressure. PC-SAFT is used to fit data generated fromDIPPR correlation[2] for CO
CO liquid density
400
450
500
550
600
650
700750
800
850
70 90 110 130
Temperature, K
Liqu
iddens
ity,
kg/m
3
Data
PC-SAFT
Figure 8. CO liquid density. PC-SAFT is used to fit data generated fromDIPPR correlation[2] for CO.
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3 Physical Properties 11
COS vapor pressure
0
10
20
30
40
50
60
130 180 230 280 330 380
Temperature, K
Vaporpressure,ba
r
Data
PC-SAFT
Figure 9. COS vapor pressure. PC-SAFT is used to fit data generated fromDIPPR correlation[2] for COS.
COS liquid density
600
700
800
900
1000
1100
1200
1300
1400
130 180 230 280 330 380
Temperature, K
Liqu
iddens
ity,
kg/m
3
Data
PC-SAFT
Figure 10. COS liquid density. PC-SAFT is used to fit data generated fromDIPPR correlation[2] for COS.
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12 3 Physical Properties
Figure 11. Vapor-liquid equilibria of CO2-MEOH at three temperatures.Comparison of experimental data[3] to calculation results of PC-SAFT withadjustable binary parameter.
Figure 12. Vapor-liquid equilibria of H2S-MEOH at three temperatures.Comparison of experimental data[4] to calculation results of PC-SAFT withadjustable binary parameter.
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3 Physical Properties 13
MEOH liquid viscosity
0.0001
0.001
0.01
0.1
150 200 250 300 350
Temperature, K
Viscosity,
Pa.s
Data
DIPPR
Figure 13. MEOH liquid viscosity. Comparison of literature data[5-9] tocalculation results of DIPPR correlation model[2].
MEOH liquid thermal conductivity
0.15
0.2
0.25
200 250 300 350 400
Temperature, K
Thermalconductivity,W
/m-K
Data
DIPPR
Figure 14. MEOH liquid thermal conductivity. Comparison of literaturedata[10-13] to calculation results of DIPPR correlation model[2].
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14 3 Physical Properties
MEOH surface tension
0.0001
0.001
0.01
0.1
250 300 350 400 450 500 550
Temperature, K
Surface
tens
ion,
N/M
Data
DIPPR
Figure 15. MEOH liquid surface tension. Comparison of literaturedata[7,14-18] to calculation results of DIPPR correlation model[2].
Diffusivity of CO2 in MEOH
0
2
4
6
8
250 275 300 325 350
Temperature, K
Diffus
ivity
(m2/s)*E
Data
Wilke-Chang
Figure 16. CO2 diffusivity in MEOH. Comparison of experimental data[19] to
calculation results of Wilke-Chang model[22].
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4 Simulation Approaches 15
4 Simulation Approaches
Run 35I of the pilot absorber [1] is used in this work.
Simulation Flowsheet The pilot absorber has been modeled with thefollowing simulation flowsheet in Aspen Plus as shown in Figure 17.
LEANIN
GASIN
GASOUT
RICHOUT
ABSORBER
Figure 17. Rate-Based MEOH Flowsheet in Aspen Plus
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16 4 Simulation Approaches
Unit Operations - The unit operation in this model has been represented byan Aspen Plus Block as outlined in Table 3.
Table 3. Aspen Plus Unit Operation Blocks Used in theRate-Based MEOH Model
Unit Operation Aspen Plus Block Comments / Specifications
Absorber RadFrac 1. Calculation type: Rate-Based
2. Number of Stages: 10
3. Top Pressure: 400psia
4. Packing: 6.25mm(0.25in) ceramic Intalox saddles
5. Packing Height: 1.5m*
6. Mass transfer coefficient method: Onda (1968)
7. Interfacial area method: Onda (1968)
8. Interfacial area factor: 1
9. Film resistance option: Film for liquid and vapor
10. Flow model: Mixed
* The column was found to be too high for the experiments and no absorptionwas detected above certain height of the packing[1]. Liquid and gas samples
were taken at the height of 1.5m from the bottom as liquid feed and gasproduct. Therefore, effective packing height(1.5m), is used instead of the
real height(2.2m) in this simulation model. This effective height was alsoused in the literature model [1].
Streams - Feeds to the Rate-Based MEOH model are gas stream GASIN
containing H2, CO2, CO, N2, CH4, H2S and COS and liquid solvent streamLEANIN containing pure MEOH solvent. Feed conditions are summarized in
Table 4.
Table 4. Feed specification
Stream ID GASIN LEANIN
Substream: MIXED
Temperature: F 53.9 -34.7
Pressure:psia 400 400
Mole-flow: lbmol/hr
MEOH 0 8.29
CO2 0.608109 0.0
H2S 0.01752 0.0
CO 0.438551 0.0N2 0.340854 0.0
COS 0.000977 0.0
H2 0.720569 0.0
CH4 0.043421 0.0
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5 Simulation Results 17
5 Simulation Results
The simulation was performed using Aspen Plus version 2006.5. Key
simulation results are presented in Table 5 and Figure 18. To illustrate theeffectiveness of the rate-based approach, simulation results for the absorber
using the equilibrium stage calculation type are also shown in Figure 18.
Table 5. Key Simulation Results
Measurement Rate-Based MEOH model
CO2 mole fraction in GASOUT 0.95% 1.235%
H2S mole fraction in GASOUT 0.037% 0.0008%
Temperature of RICHOUT, F 0.7 2.65
0
0.15
0.3
0.45
0.6
0.75
0.9
1.051.2
1.35
1.5
-45 -40 -35 -30 -25 -20 -15 -10 -5 0 5 10 15
Temperature, F
Pac
king
He
ight,m
Literature Data
ASPEN RateSep
ASPEN Equilibrium Stages
Figure 18. Absorber Liquid Temperature Profile
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18 6 Conclusions
6 Conclusions
The Rate-Based MEOH model provides a rate-based rigorous simulation of the
process. Key features of this rigorous simulation include the PC-SAFTequation of state model for vapor pressure, liquid density and phase
equilibrium, rigorous transport property modeling, rate-based multi-stagesimulation with Aspen Rate-Based Distillation which incorporates heat and
mass transfer correlations accounting for columns specifics and hydraulics.
The model is meant to be used as a guide for modeling the CO2 capture
process with MEOH. Users may use it as a starting point for more
sophisticated models for process development, debottlenecking, plant andequipment design, among others.
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References 19
References
[1] Kelly, R.M.; Rousseau, R.W.; Ferrell, K.F., Design of Packed, Adiabatic
Absorber: Physical Absorption of Acid Gases in Methanol,Ind. Eng. Chem.Process. Des. Dev., 23, 102-109 (1984).
[2] DIPPR 801 database, BYU-Thermophysical Properties Laboratory (2007).
[3] Semenova, A.I.; Emelyanova, E.A.; Tsimmerman, S.S.; Tsiklis, D.S., ThePhase Equilibrium in the System Methanol - Carbon Dioxide,Zh. Fiz. Khim.,
53, 2502-2505 (1979).
[4] Leu, A.D.; Carroll, J.J.; Robinson, D.B., The Equilibrium Phase Propertiesof the Methanol Hydrogen Sulfide Binary System,Fluid Phase Equilib., 72,
163-172 (1992).
[5] Komarenko, V.G.; Manzhelii, V.G.; Radtsig, A.V., "Viscosity and Density ofNormal Monobasic Alcohols at Low Temperatures, " Ukr. Fiz. Zh., 12, 4, 681
(1967).
[6] Bretsznajder, S., "Prediction of Transport and Other Physical Properties of
Fluids, " International Series of Monographs in Chemical Engineering,
Pergamon Press, Oxford, 2 (1971).
[7] Selected Values of Properties of Chemical Compounds, Data Project,
Thermodynamics Research Center, Texas A&M University, College Station,
Texas (1980-extant); loose-leaf data sheets.
[8] Rauf, M.A.; Stewart, G.H.; Farhataziz, "Viscosities and Densities of BinaryMixtures of 1-Alkanols from 15 to 55 C, "J. Chem. Eng. Data, 28, 324
(1983).
[9] Stephan, K.; Lucas, K., "Viscosity of Dense Fluids, " New York: Plenum
Press (1979).
[10] Raal, J.D., Rijsdijk, R.L., "Measurement of Alcohol Thermal Conductivities
Using a Relative Strain-Compensated Hot-Wire Method, "J. Chem. Eng. Data,26, 351 (1981).
[11] Takizawa, S.; Murata, H.; Nagashima, A., "Measurement of the ThermalConductivity of Liquids by Transient Hot-Wire Method, " Bull. Jsme., 21, 152,
273 (1978).
[12] Rastorguev, Yu. L.; Ganiev, Yu. A., "Thermal Conductivity of AqueousSolutions of Organic Liquids, " Russ. J. Phys. Chem., 40, 7, 869 (1966).
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[13] Mukhamedzyanov, I.Kh.; Mukhamedzyanov, G.Kh.; Usmanov, A.G.,
"Thermal Conductivity of Liquid Saturated Monobasic Alcohols at Pressures
Below 2500 Bars, " Proc. of Kazan Chem. Tech. Inst. of S.W. Kirov, 44, 57(1971).
[14] Kaye, G.W.C.; Laby, T.H., "Tables of Physical and Chemical Constants,
14th ed., " Longman Group, Limited, London (1973).
[15] Vargaftik, N.B., "Tables on the Thermophysical Properties of Liquids and
Gases, 2nd ed., " Halsted Press, New York (1975).
[16] Jasper, J.J., "The Surface Tension of Pure Liquid Compounds, " J Phys
Chem Ref Data, 1, 4, 841-1009 (1972).
[17] Riddick, J.A.; Bunger, W.B., "Organic Solvents: Physical Properties andMethods of Purification, 3rd ed., " Wiley Interscience, New York (1970).
[18] Won, Y.S.; Chung, D.K.; Mills, A.F., "Density, Viscosity, Surface Tension,
and Carbon Dioxide Solubility and Diffusitivity of Methanol, Ethanol, Acqueous
Propanol, and Acqueous Ethylene Glycol at 25 C, "J. Chem. Eng., 26, 2, 140(1981).
[19] Littel, R.J.; Versteeg,G.F.; van Swaaij,W.P.M., Physical absorption intononaqueous solutions in a stirred cell reactor,Chem. Eng. Sci., 46, 3308-
3313 (1991).
[20] Gross, J.; Sadowski, G., Perturbed-Chain SAFT: An Equation of StateBased on a Perturbation Theory for Chain Molecules,Ind. Eng. Chem. Res.,
40, 1244-1260 (2001).
[21] Gross, J.; Sadowski, G., Application of the Perturbed-Chain SAFTEquation of State to Associating Systems, Ind. Eng. Chem. Res., 41, 5510-
5515 (2002).
[22] Reid, R.C.; Prausnitz, J.M.; Poling, B.E., The Properties of Gases andLiquids, 4th ed.; McGraw-Hill: New York (1987).