lab-scale studies for regenerable sorbent selection for co...

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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)

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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

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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

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Capture mechanisms:

Adsorption (physical or/and chemical)


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


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

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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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(? ) 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.

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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.

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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.

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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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