Steady-State and Dynamic Modeling of a

Moving Bed Reactor for Solid-Sorbent CO2

Capture

Srinivasarao Modekurti, Debangsu Bhattacharyya

West Virginia University, Morgantown, WV

Stephen E. Zitney

National Energy Technology Laboratory, Morgantown, WV

David C. Miller

National Energy Technology Laboratory, Pittsburgh, WV

1

AIChE 2013 Annual Meeting

San Francisco, CA, USA, November 3-8, 2013

OUTLINE

Motivation

Dynamic Model Development

Results and Discussions

Conclusions

2

MOTIVATION

Under the auspices of US DOE’s Carbon Capture

Simulation Initiative (CCSI), we are developing

computational models of various post-combustion CO2

capture technologies

As part of this project, our current focus is on the

development of dynamic models and control systems for

solid-sorbent CO2 capture processes.

3

4

Optimized Process Developed using CCSI Toolset

GHX-001

CPR-001

ADS-001

RGN-001

BLR-001

Flue Gas from Plant

Clean Gas to Stack

CO2 to Sequestration SHX-01

SHX-02

CPR-002

LP/IP Steam from Power Plant

CPP-002

ELE-002

ELE-001

Flue Gas

Clean Gas

Rich Sorbent

LP Steam

HX Fluid

Legend

Rich CO2 Gas

Lean Sorbent

Parallel ADS Units

Parallel RGN Units

Parallel ADS Units

GHX-002

CPP-000

Cooling Water

Injected Steam

Cooling Water

Saturated Steam Return to Power Plant

Mild SteamDirectly Injected into Reactor

Compression Train

Co

nd

en

sed

W

ate

r

Co

nd

en

sed

W

ate

r

Solid Sorbent MEA27

(D10°C HX) MEA27

(D5°C HX) Q_Rxn (GJ/tonne CO2) 1.82 1.48 1.48

Q_Vap (GJ/tonne CO2) 0 0.61 0.74

Q_Sen (GJ/tonne CO2) 0.97 1.35 0.68

Total Q 2.79 3.44 2.90

ADS-001A ADS-001B

Diameter (m) 9.748

Bed Depth (m) 7.232 4.854

Total HX Area (m2) 1733.7 941.3

RGN-001

Diameter (m) 7.147

Height (m) 4.592

Total HX Area (m2) 1573.1

Solid Sorbent:

NETL 32D,

a mesoporous

amine-impregnated

silica substrate

MOVING BED DYNAMIC MODEL DEVELOPMENT

1-D two-phase pressure-driven non-isothermal dynamic

model of a moving bed reactor as part of a solid-

sorbent CO2 capture process

Model Assumptions Vertical shell & tube type reactor

Gas and solids flows are modeled by plug flow

model with axial dispersion.

Particles are uniformly dispersed through the

reactor with constant voidage

Particle attrition ignored

Temperature is uniform within the particles

Solid In

Solid Out

Gas In

Gas Out

Utility In

Utility Out

• Gaseous species : CO2, N2, H2O

• Solid phase components: bicarbonate,

carbamate, and physisorbed water.

5

MODEL DEVELOPMENT

• Radial variation neglected

• Perforated trays are used to distribute the solids

uniformly

• Stripping steam is used

• The solids enter the bed from a preheater at about 95oC

6

CONSERVATION EQUATIONS

Effective Axial Dispersion Coefficient*

Solid Phase

Gas Phase

7

*Ruthven, D. M. Principles of adsorption and adsorption processes; Wiley-Interscience, 1984

CONSERVATION EQUATIONS CONTD.

Energy Balance

Gas Phase

Solid Phase

Tube wall

8

Immersed Heat Exchanger Model

Heat Transfer Coefficient calculated by modified Packet Renewal theory1

0.140.225

22

,

0.44p p

i

xmf n i h

d g d

dv f a

0.14

22

,

, 0.33mf n i h

b i

p

v f af

d g

1Baskakov, et al., Heat Transfer to Objects Immersed in Fluidized Beds. Powder Technology, 1973. 8, pg. 273-282. 2Mickley and Fairbanks., Heat Transfer to Objects Immersed in Fluidized Beds. Powder Technology, 1973. 8, pg. 273-282.

, , , , , ,

,

12

p a i s p s e i d i

d i

i

k ch

0.5 0.33

,

,

,

,

0.009 Prh i i i

l i p

h i

g i

Nu Ar

h dNu

k

, , , , ,1t i b i d i b i l ih f h f h

Between Solids and Heat Exchanger Tube2

Between Gas and Heat Exchanger Tube1 Overall Heat Transfer Coefficient

9

10.632 1.1Pr Re

gs p

p

g

h dNu

k

Pressure drop

Modified Ergun Equation is used by using the slip velocity between the interstitial

fluid velocity and particle velocity instead of the superficial velocity

10

HYDRODYNAMIC MODEL

Maximum Gas Velocity for Maintaining the Bed in the Moving Bed Regime*

External mass transfer resistance is considered by using Frössling correlation

Constraint

3

, ,

2

,

p g i s g i

i

g i

d gAr

11

* Chehbouni, et al., The Canadian Journal of Chemical Engineering 1995, 73, 41–50.

g cv U

REACTION KINETICS

𝐻2𝑂 𝑔 ↔ 𝐻2𝑂 𝑝ℎ𝑦𝑠

2𝑅2𝑁𝐻 + 𝐶𝑂2,(𝑔) ↔ 𝑅2𝑁𝐻2+ + 2𝑅2𝑁𝐶𝑂2

−

𝑅2𝑁𝐻 + 𝐶𝑂2,(𝑔) + 𝐻2𝑂 𝑝ℎ𝑦𝑠 ↔ 𝑅2𝑁𝐻2+ + 𝐻𝐶𝑂3

−

12

*Lee et al. A model for the Adsorption Kinetics of CO2 on Amine-Impregnated Mesoporous Sorbents in the Presence of Water, 28th

International Pittsburgh Coal Conference 2011, Pittsburgh, PA, USA.

12

REACTION KINETICS

*Lee et al. A model for the Adsorption Kinetics of CO2 on Amine-Impregnated Mesoporous Sorbents in the Presence of Water, 28th

International Pittsburgh Coal Conference 2011, Pittsburgh, PA, USA.

-52,100 -78.5

-36,300 -88.1

-64,700 -174.6

28,200 0.0559

58,200 2.6167

57,700 0.0989

1.17

13

H2O

Bic

Bic

Car

Car

m

H2O

Modeling of Balance of the Unit

Pressure flow-network developed along with the control valves

14

Variable Base Value Units

Reactor Diameter 9 m

Reactor Height 7 m

Average voidage 0.6

Steam inlet flow rate 1000 kmol/hr

HX steam flow rate 2983.09 kmol/hr

Diameter of HX tube 0.015 m

Solids inlet flow rate 550000 Kg/hr

Solids inlet temperature 52.32 oC

Initial loading of bicarbonate 0.263 mol/kg sorbent

Initial loading of carbamate 1.797 mol/kg sorbent

Initial loading of water 0.651 mol/kg sorbent

Regenerator Parameters and Operating Conditions

15

SOLUTION METHODOLOGY

All the equations are written and solved in

Aspen Custom Modeler

The dynamic model is solved using the

Method of Lines

16

Moving Bed Regenerator: Results

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Z/L

Mo

le F

racti

on

CO2

H2O

Gas OutletGas Inlet

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.4

0.6

0.8

1

1.2

1.4

1.6

1.8

Z/L

Mo

lar

Lo

adin

g (

mo

l/kg

so

lids)

Bic

Car

H2O

Solids InletSolids Outlet

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9110

112

114

116

118

120

122

124

126

128

130

Z/L

So

lids

Tem

per

atu

re (C

)

Solids Outlet Solids Inlet 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9900

1000

1100

1200

1300

1400

1500

1600

1700

1800

1900

Z/L

Gas

Flo

w R

ate

(km

ol/h

r)

Gas Inlet Gas Outlet

17

Transient Response of Key Regenerator Variables Due to 10% Step

Increase in Sorbent Flowrate (open- loop)

W

Time Seconds

Str

ipper_

TC

.PV

C

B1.S

olid

OU

T.w

("H

2O

") m

ol/kg s

olid

B1.S

olid

OU

T.w

("C

ar"

) m

ol/kg s

olid

B1.S

olid

OU

T.w

("B

ic")

mol/kg s

olid

0.0 100.0 200.0 300.0 400.0 500.0

115.0

120.0

125.0

130.0

135.0

140.0

0.7

50.7

75

0.8

0.8

25

0.8

50.8

75

0.9

0.9

25

0.8

0.8

25

0.8

50.8

75

0.9

0.9

25

0.9

50.9

75

0.2

80.2

90.3

0.3

10.3

20.3

30.3

4

18

Sorbent flowrate increased by 10%, only outlet temperature controlled W

Time Seconds

Str

ipper_

TC

.PV

C

B1.S

olid

OU

T.w

("H

2O

") m

ol/kg s

olid

B1.S

olid

OU

T.w

("C

ar"

) m

ol/kg s

olid

B1.S

olid

OU

T.w

("B

ic")

mol/kg s

olid

0.0 250.0 500.0 750.0 1000.0 1250.0 1500.0 1750.0 2000.0

120.0

125.0

130.0

135.0

140.0

0.7

50.7

75

0.8

0.8

25

0.8

50.8

75

0.9

0.9

25

0.8

0.8

25

0.8

50.8

75

0.9

0.9

25

0.9

50.9

75

0.2

80.2

90.3

0.3

10.3

20.3

30.3

4Transient Response of Key Regenerator Variables Due to 10% Step

Increase in Sorbent Flowrate (Only Outlet Temperature Controlled)

19

W

Time Seconds

Str

ipper_

TC

.PV

C

B1.S

olid

OU

T.w

("H

2O

") m

ol/kg s

olid

B1.S

olid

OU

T.w

("C

ar"

) m

ol/kg s

olid

B1.S

olid

OU

T.w

("B

ic")

mol/kg s

olid

0.0 250.0 500.0 750.0 1000.0 1250.0 1500.0 1750.0

127.9

128.0

128.1

128.2

128.3

128.4

0.8

30.8

35

0.8

40.8

45

0.8

50.8

55

0.8

6

0.8

90.8

95

0.9

0.9

05

0.3

05

0.3

10.3

15

0.3

20.3

25

Transient Response of Key Regenerator Variables Due to 10% Step

Increase in Sorbent Flowrate (Both Outlet Temperature and Steam to

Sorbent Ratio Controlled)

20

Comparison of Initial Steady State Conditions to the Steady

State Conditions After 10% Step Increase in Sorbent Flowrate

21

Bicarbamate (mol/kg solid)

Carbamate (mol/kg solid)

Physiosorbed Water

(mol/kg solid)

Initial 0.311 0.891 0.837

Only Outlet Temperature

Control

0.322 0.923 0.836

Both Outlet Temperature

and Ratio Controlled

0.313 0.895 0.842

W

Time Seconds

Str

ipper_

TC

.PV

C

B1.S

olid

OU

T.w

("H

2O

") m

ol/kg s

olid

B1.S

olid

OU

T.w

("C

ar"

) m

ol/kg s

olid

B1.S

olid

OU

T.w

("B

ic")

mol/kg s

olid

0.0 250.0 500.0 750.0 1000.0 1250.0 1500.0 1750.0

120.0

125.0

130.0

135.0

140.0

0.7

50.7

75

0.8

0.8

25

0.8

50.8

75

0.9

0.9

25

0.8

0.8

25

0.8

50.8

75

0.9

0.9

25

0.9

50.9

75

0.2

80.2

90.3

0.3

10.3

20.3

30.3

4Transient Response of Key Regenerator Variables Due to 20% Step

Increase in Carbamate Loading (Both Outlet Temperature and Ratio Controlled)

22

CONCLUSIONS 1. A one-dimensional, non-isothermal, pressure-driven dynamic

model of a moving bed reactor mainly to be used as the

regenerator has been developed in ACM.

2. The model has been developed in analogy to fixed bed and

fluidized bed reactors.

3. When both the outlet temperature and the ratio of the

stripping steam flowrate to the solids flowrate are controlled,

the reactor is found to reject disturbances satisfactorily.

23

Acknowledgements: • As part of the National Energy Technology Laboratory’s

Regional University Alliance (NETL-RUA), a collaborative

initiative of the NETL, this technical effort was performed under

the RES contract DEFE0004000.

Disclaimer: This presentation was prepared as an account of work sponsored by an

agency of the United States Government. Neither the United States

Government nor any agency thereof, nor any of their employees, makes

any warranty, express or implied, or assumes any legal liability or

responsibility for the accuracy, completeness, or usefulness of any

information, apparatus, product, or process disclosed, or represents that

its use would not infringe privately owned rights. Reference herein to any

specific commercial product, process, or service by trade name,

trademark, manufacturer, or otherwise does not necessarily constitute or

imply its endorsement, recommendation, or favoring by the United States

Government or any agency thereof. The views and opinions of authors

expressed herein do not necessarily state or reflect those of the United

States Government or any agency thereof.

24

Thank you

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