Sorption-Enhanced Water-

Gas Shift (SEWGS): Reactor model development and validation

J. Boon

September 2012

ECN-L--12-060

www.ecn.nl

Sorption-Enhanced

Water-Gas Shift (SEWGS)

Reactor model development and validation

Jurriaan Boon

ISCRE22, Maastricht 3 September 2012

Sorption-Enhanced

Water-Gas Shift (SEWGS)

• What is SEWGS?

• SEWGS in pre-combustion CO2 capture

• SEWGS process cycle

• Alkasorb (K-promoted hydrotalcite)

– Sorbent characteristics: CO2 acceptor and water-gas shift catalyst

– Adsorption of CO2 and H2O

• SEWGS model

– Verification

– Validation (ongoing)

• Sorption-enhanced water-gas shift: novel reactor?

The SEWGS process

• Sorption-enhanced water-gas shift: novel reactor?

The SEWGS process

• Sorption-enhanced water-gas shift: novel reactor?

CO + H2O = CO2 + H2

The SEWGS process

300 350 400 450 5001

10

100

Ke

q (

-)

T (°C)

• Sorption-enhanced water-gas shift: novel reactor?

CO + H2O = CO2 + H2

CO2 + ● CO2●

CO + H2O + ● CO2● + H2

• Efficiently regenerable CO2 sorbent (400°C, high 𝑝H2O)

– Minerals forming carbonates, e.g. CaO + CO2 CaCO3 regeneration by heating [Gülker (1927) Production of hydrogen DE446488]

– Potassium carbonate promoted hydrotalcite chemisorption regeneration by lowering 𝑝CO2 [Hufton et al. (1999) AIChE Journal, 45, 248]

The SEWGS process

SEWGS for

pre-combustion CO2 capture

• SEWGS process for pre-combustion CO2 capture in power plants hydrogen production for tuning H2:CO in SNG production from biomass for CO2,H2S capture …

depressurise repressurise

SEWGS process steps

AD

SOR

PTI

ON

RIN

SE

PU

RG

E

Multicolumn SEWGS

• Cyclic process, repeating – Adsorption

– Rinse

– Depressurisation

– Purge

– Repressurisation

SEWGS cycle design

• Multiple columns, complex cycle design

• More columns: higher CAPEX, higher efficiency

• Rinse: H2O or CO2

• Need for cycle design tool and system optimisation

• Column modelling

• Cycle modelling

H2O rinse cycle 8 columns 2 concurrently on feed [Wright et al. (1999) Energy Proc, 1, 707]

CO2 rinse cycle 8 columns 2 concurrently on feed

Material

Hydrotalcite (HTC)

• Hydrotalcite, a layered double hydroxide mineral

• Stable under high temperatures, high 𝑝H2O

• Adsorbs CO2, H2O [Yong et al. (2001) Ind.Eng.Chem.Res., 40, 204]

Mg6Al2(OH)16CO3.4H2O

(varying Mg:Al ratio)

depressurise repressurise

SEWGS process steps

H2O – loading and regeneration

AD

SOR

PTI

ON

RIN

SE

PU

RG

E

Material

K2CO3-promoted HTC (K-HTC)

• Alkasorb – Hydrotalcite promoted with K2CO3

– Promotion strongly enhances CO2 adsorption capacity [Hufton et al. (1999) AIChE Journal, 45, 248; Reijers et al. (2006) Ind.Eng.Chem.Res., 45, 2522]

– Interaction of K+ with alumina centres creates basic sites for CO2 adsorption [Walspurger et al. (2008) ChemSusChem, 1, 643]

– K-MG30: no bulk formation of MgCO3 (slow kinetics, mechanical degradation)

[Van Selow et al. (2011) Energy Proc., 4, 1090]

• Alkasorb sorbent adsorbs CO2 and H2O on several sites

• Data available (K-HTC), for CO2 adsorption at low pressure (up to 3 bar)

Experimental

Measure adsorption isotherms

• Breakthrough measurements to measure capacity for CO2, H2O – Dry measurement of CO2 breakthrough

CO2 isotherm

– CO2-free measurement of H2O breakthrough H2O isotherm

– Breakthrough of CO2-H2O mixtures multicomponent effects

• Syngas measurements, including CO, H2, to test water-gas shift reaction kinetics

SEWGS Modelling

• Pellet – Adsorbs CO2 and H2O Adsorption isotherm, bi-Langmuir?

Adsorption kinetics, linear driving force (LDF)

– Heterogeneous catalysis WGS Reaction kinetics, power rate law

• Reactor – Convection, diffusion of species (×6) Transport of concentrated species

– Temperature Energy balance (pseudohomogeneous)

– Gas velocity Continuity equation

– Pressure Pressure drop equation, Ergun equation

– Density Equation of state, ideal gas law

• Cycle – Cycle design, process requirements Shell around reactor model

– Number, size of columns Simulate in series, store results

SEWGS Model verification

0 2 4 6 8 10 12 14 16 18 200

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

[-]C

[-]

<SE> = 3.93e-07

= 6.0

<SE> = 2.79e-07

= 12.0

NP = 800, err = 0.0001

NP = 800, err = 0.0001

analytic

• Analytic solution – breakthrough of trace adsorbate,

Heaviside step at inlet [Anzelius (1926) Z. f. angew. Math. u. Mech., 6, 291]

– linear isotherm, no axial dispersion

• Error versus grid refinement Δz

[mm] <SE> 10-6

ξ=6 <SE> 10-6

ξ=12

60 26.5 17.6

30 6.7 3.9

15 1.7 0.8

7.5 0.4 0.3

-5%

0%

5%

10%

15%

20%

25%

30%

35%

40%

0 500 1000 1500 2000

Spec

ies

mas

s fr

acti

on [

-]

Time [s]

ω CO2 [kg/kg]

ω H2O [kg/kg]

ω Ar [kg/kg]

ω5 end [kg/kg]

ω2 end [kg/kg]

ω1 end [kg/kg]

― Model

··· Experiment

SEWGS Model validation

• Model validation: breakthrough mass fractions

Ar (inert) breakthrough: convection and dispersion

H2O (adsorbed) breakthrough: adsorption, equilibrium and kinetics

CO2 (adsorbed) breakthrough: adsorption, equilibrium and kinetics

-5%

0%

5%

10%

15%

20%

25%

30%

35%

40%

0 500 1000 1500 2000

Spec

ies

mas

s fr

acti

on [

-]

Time [s]

ω CO2 [kg/kg]

ω H2O [kg/kg]

ω Ar [kg/kg]

ω5 end [kg/kg]

ω2 end [kg/kg]

ω1 end [kg/kg]

― Model

··· Experiment

SEWGS Model validation

• Model validation: breakthrough mass fractions

Model works well Improvement of adsorption (experimental data) • Adsorption isotherm • Adsorption kinetics

SEWGS Model validation

• Model validation: adsorption exotherms at 3 positions

395

400

405

410

415

420

425

430

435

440

0 500 1000 1500 2000

Tem

pera

ture

[°C]

Time [s]

T4 (2 m) [°C]

T5 (1 m) [°C]

T6 (0.5 m) [°C]

0.5

1

2

H2O adsorption (2 m)

CO2 adsorption (2 m)

Temperature equations must be incorporated (lab-scale) Adsorption, specifically for H2O (in presence of CO2)

― Model

··· Experiment

SEWGS for

Pre-Combustion CO2 Capture

• Process – SEWGS: high-temperature CO2 adsorption, CO2/H2 separation

– Cyclic steady-state, cycle design key to process economics

• Model – SEWGS model describing pellet, reactor, cycle under construction

– Validation study shows more data is required (adsorption isotherm)

• Outlook – Acquire additional experimental data and refine current adsorption models

– Extend the model validation to cyclic cases

– Optimise SEWGS process for pre-combustion CO2 capture cases, other cases

Thank you for your attention

Acknowledgements

E.R. van Selow, C. Hoogland, P.D. Cobden (ECN)

M. van Sint Annaland (TU/e)

This research has been carried out in the context of the CATO-2-program. CATO-2 is the Dutch national research program

on CO2 Capture and Storage technology (CCS). The program is financially supported by the Dutch government (Ministry of

Economic Affairs) and the CATO-2 consortium parties.

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