21218997 Rate Based MEOH Model

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.

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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.

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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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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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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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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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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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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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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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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).

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21218997 Rate Based MEOH Model