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