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LabLab--scale studies for regenerable scale studies for regenerable sorbent selection for COsorbent selection for CO22 capture capture
with Hwith H22 production in IGCC production in IGCC processesprocesses
Marta Marta MaroMaroññooIFC2012IFC2012--LeipzigLeipzig
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Available COAvailable CO22 capture technologies with Hcapture technologies with H22production applicable to IGCC processesproduction applicable to IGCC processes
CO2 capture with AMINES + H2 purification by PSA
COMBINEDCYCLE
COAL + COKE
GASIFICATION
Raw gas FILTRATION
SYSTEM
Syngas
PURIFICATION &
DESULPHURATION
Tail gas1,3 bar
IP STEAMSHIFT REACTOR
CO2
CO2 & H2separation
(Chemical, aMDEA)
100 t/d
CO + H 2O ? CO2 + H 2
Raw H2 (80% of purity)
40%
H2 rich gas
37,5 % CO250,0 % H23,0 % CO
HYDROGENPURIFICATION
(PSA)
Recycle compressor
Pure H2 (2 t/d)
99,99% H2 @ 15 bar
SWEET/SOUR
+H2S (1,44%)
2%2%
CO2 Capture Pilot PlantELCOGAS (with permission)
3
Advantages:
- Commercially available
- Good capture/separation efficiencies
Challenges:
- Amine waste handling
- Reduce volume/energy costs
Available COAvailable CO22 capture technologies with Hcapture technologies with H22production applicable to IGCC processesproduction applicable to IGCC processes
Alternative technologies under studyAlternative technologies under study
Only adsorbents can be used under WGS conditions• Adsorption
• Cryogenics• Absorption based on carbonates
• Chemical looping
For CO2 capture
For H2 separation/purification H2 Selective membranes
For CO2 capture with H2separation/purification
SORPTION-ENHANCED WGS PROCESS
4
SorptionSorption--enhanced WGS reaction approachenhanced WGS reaction approach
Steam
CO2 ready to be compressed or
stored
H2>50% CO<3%
H2 Separation/Purification
MEMBRANESPure H2
Tail gas
Syngas
CO, CO2, H2
Steam
SEWGS reactor
CO + H2O = CO2 + H2
Removal
5
Capture mechanisms:
Adsorption (physical or/and chemical)
SorptionSorption--enhanced WGS reaction approachenhanced WGS reaction approach
Physisorption is favoured:
- Availability of basic centers for capturing CO2 .Beneficial effect of promoters.
- High temperature, high CO2 and steam partial pressures.
Chemisorption is favoured:
- Sorbents with high surface area and pore size distribution
- Operating conditions: low temperature and high pressure
SEWGS operating conditions:
aaTemperatures 300Temperatures 300ººCC--500500ººCCaaSteamSteamaaPPCO2 CO2 <1<1
-High CO2 capture capacity and selectivity
-Easy regenerable
-Mechanical strength
-Low cost
Requisites of sorbents:Requisites of sorbents:
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SorptionSorption--enhanced WGS reaction approachenhanced WGS reaction approachMaterials: CO2 selective sorbents
under WGS conditions
Hydrotalcites M2+1-x M3+
x(OH)2Am-x/m·y H2O
Mg Al (OH)2 CO3
“Memory effect”: Upon calcination structure results destroyed and oxides are formed releasing water and CO2. In presence of CO2 and steam, structure is re-formed capturing CO2.
Upon calcination the structure is destroyed forming the oxides and releasing CO2. In presence of CO2and steam carbonates are formed capturing CO2
Dolomites Mg Ca (CO3)2
Mg Ca (CO3)2 MgO + CaO + CO2
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Thermo balance and saturation system
Micro-Activity Pro Unit
SorptionSorption--enhanced WGS reaction approachenhanced WGS reaction approach
Facilities
PrecursorsMaterial Sample ID Mg/Al K2CO3 Form Pre-treatment
Hydrotalcite Puralox MG30-K2CO3 0.5 17% wt Pellets Calcined 3 h at 550ºCHydrotalcite Puralox MG61-K2CO3 2 20%wt Pellets Calcined slightly at
550ºC Hydrotalcite Puralox MG70-K2CO3 3 20%wt Pellets Hydrated, not calcinedMaterial Sample ID Ca/Mg Colour Form Pre-treatment
Dolomite DolomiteES (Spain) 1.2 White < 1 mm None Dolomite DolomiteIT (Italy) 1 Light
grey <0.8 mm None
Gas Chromatography
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Thermal characterization: TGA and XRDThermal characterization: TGA and XRDHydrotalcites.Hydrotalcites. TGA and DTG resultsTGA and DTG results
Samples have different calcination history: only Mg70 was supplied in its hydrated form.
Mass loss observed at T>600ºC might correspond to decomposition of carbonates and bulk K2CO3.
100 200 300 400 500 600 700 800 900 1000 1100
T (ºC)
MG61-K2CO
3
% M
ass
Loss
MG70-K2CO
3
MG30-K2CO3
Thermal decomposition pathway:
-Dehydration (release of superficial and interlayered water at T<150ºC-De-hydroxylation and de-carbonation (250ºC<T<400ºC)
Calcination at T=600ºC guarantees that all structural
CO2 has been released
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(? ) MgO;
(?) KAl(CO3)2(OH)2,
(? ) K2CO3;
(n) Spinel (Mg2Al2O4)
Thermal characterization: TGA and XRDThermal characterization: TGA and XRD
- As T increases carbonated species disappear and spinel phase is formed
- Formation of K-dawsonite is detected: it is still present at 600ºC
Hydrotalcites. XRD resultsHydrotalcites. XRD results
Results:0 20 40 60 80 0 20 40 60 80
700ºC 700ºC
MG70-K2CO3
700ºC
MG61-K2CO3 MG30-K2CO3
600ºC 600ºC
Inte
nsity
(u.
a.)
600ºC
As-suppliedAs-supplied As-supplied
2Θ
0 20 40 60 80
10
Thermal characterization: TGA and XRDThermal characterization: TGA and XRD
Dolomites.Dolomites. TGA and DTGTGA and DTG
Theoretical thermal decomposition pathway:
CaMg(CO3)2 = Mg O + CO2 + CaCO3CaCO3 = Ca O + CO2
0 200 400 600 800 100050
60
70
80
90
100
50
60
70
80
90
100
Wei
ght l
oss
%
T (ºC)
Dolomite ES
Dolomite IT Dolomite IT required T>800ºC to decompose
Dolomite ES seemed to decomposed in several steps with two main decomposition processes
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Thermal characterization: TGA and XRDThermal characterization: TGA and XRD
(? ) MgO; (n) CaO; (•) CaCO3
20 30 40 50 60 70 80 20 30 40 50 60 70 80
Fresh
600ºC
700ºC
800ºC
Inte
nsity
(a.
u.)
600ºC
Fresh
Dolomite ES Dolomite IT
2Θ2Θ
700ºC
800ºC
Any of the Dolomite samples studied follow the theoretical thermal decomposition pathway.
Dolomites: XRD Dolomites: XRD
Only Dolomite ES decomposed partially at 600ºC providing some opportunities to prepare adequate sorbents to be used in the SEWGS process
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First COFirst CO22 capture screening testscapture screening testsThermobalanceThermobalance--dry gasdry gas
1002003004005006000
1
2
3
4
5
60
1
2
3
% m
ass
incr
ease
T (ºC)
MG30-K2CO3 MG61-K2CO3 MG70-K2CO3
Dolomite IT Dolomite ES
Feed gas: 15% CO2/N2Cooling down from 600ºC to room temperature
Mass increase during cooling of the samples in presence of CO2
Only Hydrotalcite samples have showed efficiency towards the capture of CO2, in the temperature range of 300ºC to 500ºC showed by the slope of the mass increase curve.
Dolomite ES captured CO2 at 600ºC due to the CaO formed during partial calcination. More studies at lower calcination temperature are required.
13
First COFirst CO22 capture screening testscapture screening testsThermobalance Thermobalance -- Effect of calcination temperatureEffect of calcination temperature
100200300400500600
0
2
4
6
0
2
4
60
2
4
6
MG30-K2CO3 600ºC
MG30-K2CO3 700ºC
T (ºC)
MG61-K2CO3 600ºC
MG61-K2CO3 700ºC%
mas
s in
crea
se
MG70-K2CO3 600ºC
MG70-K2CO3 700ºC
CO2 Capture tests for hydrotalcite samples precalcined at both 600ºC and 700ºC
Better results were obtained for samples calcined at 600ºC except for sample Mg70 but the mass increase was lower than for the other two.
14
First COFirst CO22 capture screening testscapture screening testsThermobalanceThermobalance-- Effect of steamEffect of steam
Positive effect of steam in CO2 capture
01002003004005006000
2
4
60
2
4
60
2
4
6
T (ºC)
CO2/N2 sat
CO2/N2
MG30-K2CO3
% m
ass
incr
ease
CO2/N2
CO2/N2 satMG61-K2CO3
CO2/N2
CO2/N2sat
MG70-K2CO3
4%CO2/N21.5%v/v water
Sorbent Mg61-K2CO3seemed to be more selective to CO2 in presence of steam
Detailed studies of the effect of higher water contents have been performed to confirm this behavior.
15
First COFirst CO22 capture screening testscapture screening testsEffect of system pressure and regeneration methodEffect of system pressure and regeneration method
Ads1 Ads2 Ads3 Ads40.0
0.1
0.2
0.3
0.4
0.5
Adsorption after Regeneration at P= 1 bar and T= 500ºC
Adsorption after Depressurisation at P=1 bar
Mol
/kg
P= 1 bar P= 5 bar
Adsorption after Regeneration at 500ºC
0.0 0.2 0.4 0.60.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
mo
l/kg
PCO2
Isotherm at 300ºCMG61-k2CO3 calc 600ºC
High CO2 partial pressures provide better capture
efficiencies
Thermal regeneration more effective than depressurisation
4%CO2/N2- Dry feed gas
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Isothermal tests. Effect of steamIsothermal tests. Effect of steam
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.00
2
4
6
8
10
MG61-K2CO3
MG70-K2CO3
MG30-K2CO
3
mo
l/kg
PH2O
High steam partial pressures provide higher CO2 capture capacities.
PCO2= 0.34 barThe capture mechanism is strongly influenced by PCO2 and PH2O.
At high PH2O and low PCO2 reconstruction of hydrotalcites takes place while at low PCO2 and low PH2O ( or dry feed gas) capture of CO2 takes place via formation of double carbonates K-Al (K-dawsonite).
Capture efficiency:
Mg61 > Mg30 > Mg70
Tad=300ºC
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ConclusionsPotassium carbonate promoted Hydrotalcites have proved to be very promising sorbents to be used under WGS conditions. Material Mg61-K2CO3 selected as the most adequate to continue studies.
The capture mechanism is strongly influenced by PCO2and PH2O.
CO2 Capture efficiencies as high as 9 mol/kg have been obtained at PH2O= 4.5 and PCO2= 0.34 bar
-Optimization of SEWGS process conditions (T and steam) to improve selective capture of CO2.
-Lowering of calcination temperatures and promotion with basic cations are being considered for DolomiteES.
Work continues….
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THANK YOU FOR
YOUR KIND
ATTENTION