Aspen Plus DEPG Model

8/13/2019 Aspen Plus DEPG Model

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Aspen Plus

Aspen Plus Model of theCO2Capture Process byDEPG


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Copyright (c) 2009 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., Burlington, 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) 221-6400

Toll Free: (1) (888) 996-7100URL: http://www.aspentech.com


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Revision History 1

Revision HistoryVersion Description

V7.0 First version

V7.1 Re-verified simulation results using Aspen Plus V7.1

V8.0 Add formic acid and its PC-SAFT parameters


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2 Contents

ContentsIntroduction............................................................................................................31 Components .........................................................................................................42 Process Description..............................................................................................53 Physical Properties...............................................................................................64 Simulation Approaches.......................................................................................155 Simulation Results .............................................................................................186 Conclusions........................................................................................................20References ............................................................................................................21


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Introduction 3

Introduction

This document describes an Aspen Plus model of the CO2capture process by

the physical solvent DEPG from a gas mixture of CO, CO2, H2, H2O, N2, Ar,CH4, NH3, and H2S from gasification of Illinois No. 6 bituminous coal

[1]. The

operation data from an engineering evaluation design case by EnergySystems Division, Argonne National Laboratory (1994)[1]are used to specify

the feed conditions and unit operation block specifications in the processmodel. Since only the equilibrium stage results are available in the literature,

the process model developed here is based on the equilibrium stage

distillation model instead of the more rigorous rate-based model.

DEPG[2]is a mixture of the dimethyl ethers of polyethylene glycol with

formula CH3O(C2H4O)nCH3where nranges from 2 to 9. However, DEPG in this

model is represented by an Aspen Plus databank component, also called DEPG(dimethyl ether of polyethylene glycol), with the average molecular weight of

280 - corresponding to n = 5.3. DEPG data from Coastal Chemical[3]for vaporpressure, liquid density, heat capacity, viscosity, and thermal conductivity are

used to determine parameters in thermophysical property and transportproperty models used in this work. For all other components, thermophysical

property models have been validated against DIPPR correlations[4], which areavailable in Aspen Plus, for component vapor pressure and liquid density.

Vapor-liquid equilibrium data from Xu et al. (1992)[5]between DEPG and

selected components are used to adjust binary parameters in thermophysicalproperty models. The designed packing information from the literature[1]is

also included in the process model, which allows rigorous rate-basedsimulation to be performed.

The model includes the following key features:

PC-SAFT equation of state model for vapor pressure, liquid density, heatcapacity, and phase equilibrium

Transport property models Equilibrium distillation model for absorber with designed packing

information from the literature[1]


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4 1 Components

1 Components

The following components represent the chemical species present in the

process. As already stated, DEPG in real processes is a mixture of thedimethyl ethers of polyethylene glycol with formula CH3O(C2H4O)nCH3where n

ranges from 2 to 9[2]and in this model an average molecular weight of 280corresponding to n = 5.3 is used to represent the DEPG solvent by an Aspen

Plus databank component DEPG.

Table 1. Components Used in the Model

ID Type Name Formula

DEPG CONV DIMETHYL-ETHER-POLYETHYLENE-GLYCOL DEPG

CO CONV CARBON-MONOXIDE CO

CO2 CONV CARBON-DIOXIDE CO2

H2 CONV HYDROGEN H2

H2O CONV WATER H2O

N2 CONV NITROGEN N2

AR CONV ARGON AR

CH4 CONV METHANE CH4

NH3 CONV AMMONIA H3N

H2S CONV HYDROGEN-SULFIDE H2S

HCN CONV HYDROGEN-CYANIDE CHN

COS CONV CARBONYL-SULFIDE COS

CH2O2 CONV FORMIC-ACID CH2O2


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2 Process Description 5

2 Process Description

The flowsheet for CO2capture by DEPG in the report by Energy Systems

Division, Argonne National Laboratory (ANL) [1]includes an absorber for CO2absorption by DEPG at elevated pressure, flash tanks to release CO2and

regenerate solvent at several different pressure levels, and compressors andturbines to change pressures of streams. However, the process model

presented in this work focuses only on the absorber and the other unitoperations are not included.

The sour gas enters the bottom of the absorber, contacts with lean DEPG

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 solventwith absorbed CO2and some other gas components.

Two pressure levels for absorption were evaluated in the ANL report: 250psiaand 1000psia. For each pressure case study, the gas feeds into the absorber

is the same, but solvent flow rates and number of equilibrium stages used are

different. Typically, to achieve a certain CO2recovery, the high pressure caseused less solvent and fewer stages. Table 2 represents some operation data:

Table 2. Data of the Absorber

Low Pressure Case High Pressure Case

Absorber

Number of Stages 12 10

Diameter, ft 17 11

Packing Height, ft 3 3

Packing Type Pall ring Pall ring

Packing Size, mm 50 50

Sour Gas

Flow rate, lbmol/hr 17614.58 17614.58

CO2in Sour Gas, mole fraction 0.2461 0.2461

Lean DEPG

Flow rate, lbmol/hr 23000 6900

Temperature, F 30 30

Pressure, psia 250 1000


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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 CO, CO2, NH3, H2S have been regressed against vapor

pressure and liquid density generated from DIPPR correlations[4]for eachcomponent. The PC-SAFT pure parameters for DEPG have been regressed to

fit vapor pressure and liquid density data from Coastal Chemical[3]. For allother components, the PC-SAFT pure parameters are taken from the work by

Gross and Sadowski (2001, 2002)[6,7]. The binary parameters between CO2and DEPG and H2S and DEPG have been regressed against vapor-liquidequilibrium data form Xu et al. (1992)[5]. Based on solubility ratio of H2to H2S

in DEPG at 25C[8,9]and experimental vapor-liquid equilibrium data for H2S inDEPG, we also estimated vapor-liquid equilibrium data for H2in DEPG and

used these estimated data for regression of binary parameters between H2and DEPG. In the same way, we got binary parameters between the other gas

components and DEPG[8,9], except for Ar because of missing solubility ratio of

Ar.

DIPPR model parameters for DEPG are regressed to fit data from Coastal

Chemical[3]for viscosity and thermal conductivity. ASPEN ideal gas heatcapacity model parameters for DEPG are also regressed to fit liquid heat

capacity data from Coastal Chemical[3]. Finally, the dipole moment from

DIPPR database[4]for PENTAETHYLENE GLYCOL DIMETHYL ETHER is used forDEPG.

Figures 1-15 show property predictions together with literature data.


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3 Physical Properties 7

DEPG vapor pressure

0.0000001

0.000001

0.00001

0.0001

0.001

0.01

0.1

250 300 350 400 450

Temperature, K

Vaporpressure,ba

r Data

PC-SAFT

Figure 1. DEPG vapor pressure. PC-SAFT is used to fit data from CoastalChemical[3].

DEPG liquid density

800

850

900

950

1000

1050

1100

1150

1200

250 300 350 400 450

Temperature, K

Liquiddensity,

kg/m3 Data

PC-SAFT

Figure 2. DEPG liquid density. PC-SAFT is used to fit data from CoastalChemical[3].


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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. CO2vapor pressure. PC-SAFT is used to fit data generated fromDIPPR correlation[4]for CO2.

CO2 liquid density

500

600

700

800

900

1000

1100

1200

1300

200 220 240 260 280 300 320

Temperature, K

Liquiddensity,

kg/m3

Data

PC-SAFT

Figure 4. CO2liquid density. PC-SAFT is used to fit data generated fromDIPPR correlation[4]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[4]for H2S.

H2S liquid density

300

400

500

600

700

800

900

1000

1100

180 230 280 330 380

Temperature, K

Liquiddensity,

kg/m3

Data

PC-SAFT

Figure 6. H2S liquid density. PC-SAFT is used to fit data generated fromDIPPR correlation[4]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[4]for CO.

CO liquid density

400

450

500

550

600

650

700

750

800

850

70 90 110 130

Temperature, K

Liquiddensity,

kg/m3

Data

PC-SAFT

Figure 8. CO liquid density. PC-SAFT is used to fit data generated from DIPPRcorrelation[4]for CO.


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NH3 vapor pressure

0

10

20

30

40

50

60

70

80

90

200 250 300 350 400

Temperature, K

Vaporpressure,ba

r

Data

PC-SAFT

Figure 9. NH3vapor pressure. PC-SAFT is used to fit data generated fromDIPPR correlation[4]for NH3.

NH3 liquid density

400

450

500

550

600

650

700

750

200 250 300 350 400

Temperature, K

Liquiddensity,

kg/m3

Data

PC-SAFT

Figure 10. NH3liquid density. PC-SAFT is used to fit data generated fromDIPPR correlation[4]for NH3.


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VLE for CO2-DEPG

0.5

0.6

0.7

0.8

0.9

1

50 70 90 110 130 150

Temperature, F

Pressure,psia

Data

PC-SAFT

Figure 11. Vapor-liquid equilibria of CO2-DEPG. Comparison of experimentaldata[5]to calculation results of PC-SAFT with adjustable binary parameter.

VLE for H2S-DEPG

0.05

0.07

0.09

0.11

0.13

0.15

50 70 90 110 130 150

Temperature, F

Pressure,psia

Data

PC-SAFT

Figure 12. Vapor-liquid equilibria of H2S-DEPG. Comparison of experimentaldata[5]to calculation results of PC-SAFT with adjustable binary parameter.


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DEPG liquid heat capacity

550000

650000

750000

250 300 350 400 450

Temperature, K

Heatcapacity,

J/kmol-K

Data

DIPPR

Figure 13. DEPG liquid heat capacity. Aspen ideal gas heat capacity modelisused to fit data from Coastal Chemical[3].

DEPG liquid viscosity

0.0001

0.001

0.01

0.1

200 250 300 350 400 450

Temperature, K

Viscosity,

Pa.s

Data

DIPPR

Figure 14. DEPG liquid viscosity. DIPPR correlation model[4] is used to fit datafrom Coastal Chemical[3].


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DEPG liquid thermal conductivity

0.13

0.15

0.17

0.19

0.21

200 250 300 350 400 450

Temperature, K

Thermalconductivity,

W/m

-K Data

DIPPR

Figure 15. DEPG liquid thermal conductivity. DIPPR correlation model[4] isused to fit data from Coastal Chemical[3].


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4 Simulation Approaches 15

4 Simulation Approaches

The high pressure case and the low pressure case are included in the process

model as two separate absorber columns. The absorbers are modeled withthe Equilibrium calculation type instead of the more rigorous rate-based

calculation type because the design cases from [1] were based on equilibriumstage calculations. This allows us to make meaningful comparison between

our model and the literature. However, we included designed packing

information from the literature in the model so that the rate-based calculationtype can be used. In addition, as shown above, transport properties, which

are crucial for rate-based calculations, have also been validated. Therefore,this model is ready for rate-based calculations, in which correlations and scale

factors of interfacial area, mass transfer coefficient, heat transfer coefficient,

liquid holdup and so on can be selected and adjusted. You can also select thefilm resistance types and flow models to be used.

Simulation Flowsheet The absorbers for the two cases have been

modeled with the following simulation flowsheet in Aspen Plus, shown inFigure 16, in which ABSORB-H is the absorber for the high pressure case and

ABSORB-L is the absorber for the low pressure case.

LEAN-L

GASIN-L

GASOUT-L

RICH-L

ABSORB-L

LEAN-H

GASIN-H

GASOUT-H

RICH-H

ABSORB-H

Figure 16. DEPG Process Flowsheet in Aspen Plus


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16 4 Simulation Approaches

Unit Operations Major unit operations in this model have beenrepresented by Aspen Plus Blocks as outlined in Table 3.

Table 3. Aspen Plus Unit Operation Blocks Used in theDEPG Model

Unit Operation Aspen Plus Block Comments / Specifications

ABSORB-H RadFrac The absorber for the high pressure case with the followingsettings:

1. Calculation type: Equilibrium stage

2. Number of stages: 10

3. Top Pressure: 1000psia

4. Column diameter: 11ft

5. Packing Type: Pall ring

6. Packing Size: 50mm(2in)

7. Packing Height per stage: 3ft

ABSORB-L RadFrac The absorber for the low pressure case with the followingsettings:

1. Calculation type: Equilibrium stage

2. Number of stages: 12

3. Top Pressure: 250psia

4. Column diameter: 17ft

5. Packing Type: Pall ring

6. Packing Size: 50mm(2in)

7. Packing Height per stage: 3ft


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4 Simulation Approaches 17

Streams The gas feeds of the DEPG model are GASIN-H for the highpressure absorber ABSOR-H and GASIN-L for the low pressure absorber

ABSORB-L, both containing CO, CO2, H2, H2O, N2, Ar, CH4, NH3, and H2S.

The solvent liquid feeds are LEAN-H for the high pressure absorber ABSORB-Hand LEAN-L for the low pressure absorber ABSORB-L, both containing DEPG

and a small amount of CO2and H2O.

Feed conditions are summarized in Table 4.

Table 4. Feed specification

Stream ID GASIN-H LEAN-H GASIN-L LEAN-L

Substream: MIXED

Temperature: F 68.17 30 68.13 30

Pressure:psia 998 1000 248 250

Mole-flow: lbmol/hr

DEPG 0 6900 0 23000

CO 77.37 0.0 77.37 0.0CO2 4335.99 115.55 4335.99 395.00

H2 5611.86 0.0 5611.86 0.0

H2O 61.91 0.07 61.91 2.25

N2 7306.65 0.0 7306.65 0.0

AR 88.6 0.0 88.6 0.0

CH4 128.77 0.0 128.77 0.0

NH3 2.99 0.0 2.99 0.0

H2S 0.4 0.0 0.4 0.0

HCN 0.0 0.0 0.0 0.0

COS 0.0 0.0 0.0 0.0

CH2O2 0.0 0.0 0.0 0.0


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18 5 Simulation Results

5 Simulation Results

The simulation was performed using Aspen Plus V7.1 with the absorbers

calculation type set to Equilibrium. Key simulation results are presented inTable 5 and 6 and Figure 17 and 18, together with available design data from

the report of the Energy Systems Division, Argonne National Laboratory[1].

A problem was found in the literature that their calculation was based onimproper solubility ratios of the gas components in DEPG solvent, in which

N2:H2is 0, while UOP reported a ratio of 1.5[2]and this model reports a ratio

of about 3.8. As a result, this model gives less CO2absorption than that

reported in the literature. In addition, the temperature of the rich solventfrom the bottom of the absorbers is also lower in our simulation.

Table 5. Key Simulation Results for the High PressureCase

Literature This model

CO2mole fraction in GASOUT-H 0.01619 0.050

Temperature of RICH-H, F 83.82 60.4

Table 6. Key Simulation Results for the Low Pressure Case

Literature This model

CO2mole fraction in GASOUT-L 0.01629 0.036

Temperature of RICH-L, F 46.68 42.1


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5 Simulation Results 19

1

2

3

4

5

6

7

8

9

10

0 5 10 15 20 25 30 35 40 45 50 55 60 65

Temperature, F

StageNumb

er

ABSORB-H

Figure 17. Absorber Temperature Profile for the High Pressure Case

1

2

3

4

5

6

7

8

9

10

11

12

0 5 10 15 20 25 30 35 40 45 50 55 60 65

Temperature, F

StageNumber

ABSORB-L

Figure 18. Absorber Temperature Profile for the Low Pressure Case


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20 6 Conclusions

6 Conclusions

The DEPG model provides an equilibrium stage simulation of the process and

validated transport property models which allow rigorous rate-basedsimulation. Key features of this model include the PC-SAFT equation of state

model for vapor pressure, liquid density and phase equilibrium, rigoroustransport property modeling, equilibrium stage simulation with RadFrac and

packing information from the literature[1].

The model is meant to be used as a guide for modeling the CO2captureprocess with DEPG. 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

[1] R.D. Doctor, J.C. Molburg, P.R. Thimmapuram, G.F. Berry, C.D. Livengood,

Gasification Combined Cycle: Carbon Dioxide Recovery, Transport, andDisposal, Energy System Divison, Argonne National Laboratory (1994)

[2] D.J. Kubek, E. Polla, F.P. Wilcher, Purification and Recovery Options for

Gasification, Gasification Technologies Conference, San Francisco (1996)

[3] Coastal AGR Solvent Bulletin, Coastal Chemical Co., L.L. C

[4] DIPPR801 database, BYU-Thermophysical Properties Laboratory (2007).

[5] Y. Xu, R.P. Schutte, L.G. Helper, Solubilities of Carbon Dioxide, Hydrogen

Sulfide and Sulfur Dioxide in Physical Solvents, Can. J. Chem. Eng., 70, 569-573 (1992)

[6] J. Gross, G. Sadowski, Perturbed-Chain SAFT: An Equation of StateBased on a Perturbation Theory for Chain Molecules, Ind. Eng. Chem. Res.,

40, 1244-1260 (2001)

[7] J. Gross, G. Sadowski, Application of the Perturbed-Chain SAFT Equation

of State to Associating Systems, Ind. Eng. Chem. Res., 41, 5510-5515 (2002)

[8] G. Ranke, V. H. Mohr, The Rectisol Wash: New Developments in Acid Gas

Removal from Synthesis Gas, from Acid and Sour Gas Treating Processes,Stephen A. Newman, ed., Gulf Publishing Company, Houston, 80-111 (1985)

[9] R. Epps, Processing of Landfill Gas for Commercial Applications: theSELEXOL Solvent Process, Union Carbide Chemicals & Plastics Technology

Corporation, June, 1992. (Prepared for Presentation at ECO WORLD 92, June

15, 1992, Washington D. C.)

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