Process concepts for combined CO2 and

SO2 removal

CSIRO: Erik Meuleman, Paul Feron

EnBW: Denise Lübbren, Sven Unterberger

TNO: Christina Sanchez Sanchez, Patricia van den Bos, Mark Roelands, Monique Oldenburg, Earl Goetheer

June 6th 2011

Aim:

Traditional powerplant with CCS versus co2/so2 integrated system

pictures illustrating this will be made

Process Design routes

DECASOX

DOUBLE LOOPED CAPTURE PROCESS

Modified DECASOX

2June 6th 2011

Absorber

Loadedsolvent

Separator

Pump

Stripper

Regenerated solvent

Pump

Crystallizer

Crystallizer

Pump

Calcium carbonate (aq)

CO2

Crystallized solvent

Air

CO2

Clean flue gas

Gypsum)(CaSO4)

Flue gas 90oC

30oC

40oC

30oC

Cooler35oC

35%

65%

40 - 50oC

Compressor

Limestone(CaCO3)

Heat exchanger

Carbamate (aq)

DECASOx Conceptual Process Design

3June 6th 2011

DECASOx Experimental Results & Conclusions

June 6th 20114

Experimental results of CaCO3 recrystallization to CaSO3/CaSO4 by applying pressurized CO2

Feasible CaCO3 recrystallization to CaSO3/CaSO4 by CO2 pressure, but CaCO3 conversion not very high due to:

At pH ~6, most sulphite converted to bisulphite → calcium bisulphite

soluble compound has higher solubility than sulphite.

CaCO3 extremely low solubility.

exp. Potassiumtaurate

(kmol.m-3)

K2SO4

(kmol.m-3)

K2SO3

(kmol.m-3)

CaCO3

(kmol.m-3)

CO2

pressure (bar)

Final pH

Reaction time

(hh:mm)

CaCO3

converted (%)

A 0.10 0.35 0.35 0.25 7.15 6.27 2:22 22.56%B 0.03 0.13 0.13 0.25 7.20 6.37 2:29 3.14%C 0.03 0.13 0.12 0.25 38.86 5.88 18:19 30.83%

Conclusion: DECASOx is complex and has a high operational cost

Double Looped Capture Process

June 6th 20115

Thermodynamics K2CO3 – SO2 – CO2 System

Vapour phase

Liquid phase

CO2

CO2

H2O

H2O

SO2

SO2

R1: 2 H2O ↔ H3O+ + OH-

R2: CO2 + 2 H2O ↔ H3O+ + HCO3-

R3: HCO3- + H2O ↔ H3O+ + CO3

2-

R4: SO2 + 2 H2O ↔ H3O+ + HSO3-

R5: HSO3- + H2O ↔ H3O+ + SO3

2-

Speciesconcentrationfunction of pH

6June 6th 2011

Sulfite-Carbonate Equilibrium

0,0

0,5

1,0

1,5

2,0

6 7 8 9 10 11 12

Dom

inan

t spe

cies

(m)

pH

CO3=HCO3-

SO3=

CO2 (g)

HSO3-

At pH ~ 8 recycled solvent enters absorber → CO2 mostly found in bicarbonate (HCO3

-) form. pH < 6 is required for limestone (CaCO3) scrubbing.

7June 6th 2011

Limestone scrubbing

Limestone Dissolution:CaCO3 + H+ ↔ Ca2+ + HCO3

-

Reaction with Dissolved SO2:Ca2+ + HSO3

- ↔ CaSO3 + H+

Ca2+ + SO32- ↔ CaSO3 (↓)

Precipitation of solid species governed primarily by solubility:Salt Solubility product (M2)

CaSO3•½H2O 2.76 x 10-7 (40oC)

CaSO4•2H2O 1.20 x 10-6 (40oC)

CaCO3 0.87 x 10-8 (25oC)Source: Kohl, Nielsen, Gas Purification, 1997.

8June 6th 2011

CaCO3 addition

CaCO3 starts precipitating above pH ~ 7.5.Sulfur found in solution in sulfite (SO3

2-) form.Almost no Ca2+ remains in solution → no CaCO3 precipitation expected in the absorber.

0

0,5

1

1,5

2

0 0,5 1 1,5 2

CaCO3 added (m)

Spec

ies

conc

entr

atio

n (m

)

5,5

6

6,5

7

7,5

8

pH

pH

HSO3-

CaSO3 (s)

CaCO3 (s)

Ca2+

SO3=

9June 6th 2011

Expected Recycled Solvent Composition

CaCO3added (m) pH

HCO3-

(m)CO3

2-

(m)SO3

2-

(m)HSO3

-

(m)Ca2+

(m)0 6.09 0.05 1.3 x 10-5 1.55 0.45 0

0.2 6.58 0.15 1.2 x 10-5 1.65 0.15 3.2 x 10-5

0.4 7.05 0.45 0.001 1.55 0.05 3.4 x 10-5

0.6 7.32 0.82 0.004 1.38 0.02 3.7 x 10-5

0.8 7.50 1.20 0.007 1.19 0.01 4.1 x 10-5

1 7.56 1.40 0.01 1.09 0.01 4.4 x 10-5

1.2 7.56 1.40 0.01 1.09 0.01 4.4 x 10-5

CaCO3precipitation

* 1.8 m K2CO3; 2 m SO2 @25 C,1 atm

10June 6th 2011

low Ca2+

concentration inrecycled solvent

Proof of principle

Proof of Principle K2CO3-SO2 System

20 wt% K2CO3

H2OSO2 (g)

pH ~ 6

Filtrate

Solids

Strong indications that high recovery of sulfurous components is possible

filtrate

solid

Compound %CaCO3 35CaSO3•0.5H2O 55K2SO4 10

Composition of solid sample:

12June 6th 2011

CaCO3 (s)

Yield on Sulfur is around 70%

Proof of concept (Continuous processing )Microplant experiments

SO2 absorption section CO2 absorption section

stripper

13June 6th 2011

CO2 absorber

SO2 absorber

SO2 scrubbing liquid

14June 6th 2011

Thermodynamics H2O-K2CO3-PZ-CO2 System

Molecular structuresof piperazine species

Source: Hilliard M., Thermodynamics of Aqueous Piperazine/Potassium Carbonate/Carbon Dioxide Characterized by the Electrolyte NRTL Model within Aspen Plus, 2005.

15June 6th 2011

VLE data H2O-K2CO3-PZ-CO2 System

Enthalpy of CO2Absorption

CO2 Solubility in 6 m K+ + 1.2 m PZ from20 – 120oC. Points: 40oC, 60oC, 80oC,

100oC, 120oC.Lines: elecNRTL Model Predictions.

Comparison of the Enthalpy of CO2 Absorption in 6 m K+ + 1.2 m PZ at 40 and 120oC from Kim (2007) to Predictions from this work.

16June 6th 2011

CO2 absorption rates in different solvents

CO2 absorption rates in K2CO3 and MEAsolutions at 60 C.

Source: Cullinane J.T., Rochelle G.T., Carbon dioxide absorption with aqueous potassium carbonate promoted by piperazine, 2004

Comparison of promoted K2CO3 solutions

17June 6th 2011

Comparison to MEA process: Conditions

Source: Oexmann J., Hensel C., Kather A., Post-combustion CO2-capture from coal-fired power plants: Preliminary evaluation of an integrated chemical absorption process with piperazine-promoted potassium carbonate, 2008.

Boundary conditions for MEA and K2CO3/PZ CO2-capture process comparison

18June 6th 2011

Comparison to MEA process: Results

Source: Oexmann J., Hensel C., Kather A., Post-combustion CO2-capture from coal-fired power plants: Preliminary evaluation of an integrated chemical absorption process with piperazine-promoted potassium carbonate, 2008.

Results for MEA and K2CO3/PZ CO2-capture process comparison

19June 6th 2011

Double looped process - Preliminary conclusions

Proof of Principle delivered

Proof of concept in progress

However, operational benefits can be debated

20June 6th 2011

Modified DECASOx Conceptual Process Design

21June 6th 2011

Absorber

K2SO3/K2SO4

Rich solvent

Stripper

Lean solvent

K2SO4

CO2

CaSO4

Air/O2

CaCO3

Flue gas

To stack

Modified DECASOx

K2SO4

CO2 CaCO3 (sus)

CaSO4/CaCO3

K2CO3 (aq. sol)

22June 6th 2011

Proof of Principle of Modified DECASOx concept

First route scouting modified DECASOx shows promising results

filtrate

solid

K+ AAS-

H2OSO2 (g)

pH ~ 6

Filtrate

Solids

K2SO3/K2SO4

23June 6th 2011

CaCO3 (s)

Yield sulfur 80%

Promising route, warrants further investigations

Endproduct sulfur containing species (K2SO4 or CaSO4) dependent on the market needs

Economics should be further investigated

24June 6th 2011

Modified DECASOx - Preliminary conclusions

Acknowledgement