PostPost-Combustion Capture of carbon dioxide by Clathrate

Hydrate crystallization

Rajnish Kumar1, Praveen Linga1, Adebola Adeyemo1, Peter Englezos1 and John

Ripmeester2

1. Clean Energy Research CenterDepartment of Chemical and Biological

EngineeringThe University of British Columbia

Vancouver, BC2. Steacie Institute for Molecular Sciences

National Research Council of Canada100 Sussex Drive

Ottawa, ON

2

Post-combustion capture of CO2 from

power plants involves separation of CO2

from flue gas

Fossil Fuels COMBUSTION Flue Gas

AirCOCO22

capturecapture

CO2, N2, O2

MIXTURE

CO2

3

Flue gas from a coal-fired power plant

• 15-20% CO2, 5% O2 and balance N2

• Low concentration of CO2

• Absorption in MEA solutions: “most

promising current method”

• “Development of ceramic

membranes could be more efficient”Aaron, D and C. Tsouris, Separation Science and Technology, 40: 321–348, 2005

The clathrate hydrate process

Hydrate formation is a very new

concept for CO2 Capture that is still in lab

testing (Aaron and Tsouris, 2005).

5

Gas Hydrates are Crystals

• Formed by waterwater and

small molecules like

(CH4, C2H6, C3H8, CO2,

N2, O2, H2)

• No chemical reaction

only physical bondingCO2 hydrate 277.1K and 4.1 MPa

H2O forms cagescages enclosing CH4

6

FEED

CO2/N2

Composition of Hydrate

CrystalsDifferent than Feed

Gas Hydrate Formation from gas mixtures

Treated flue gas (CO2, N2, O2) is considered a CO2/N2 mixture

Basic Idea/Concept

Kang S.P. and H. Lee (2000),Environ. Sci. Technol.,Vol. 34, No. 20, pp. 4397-4400.

7

Laboratory scale CO2 capture

Temperature controlled water bath

T2

Crystallizer (CR)

GCD P

GAS

SUPPLy

Motor

SV

RV

CR – Crystallizer DP – Differential Pressure

RV – Reference Vessel GC – Gas Chromatography

SV – Supply Vessel CV – Control Valve

CV

DAQ& PC Crystallizer volume: 323

cm3

Semi-batch operation at constant T & P

We can determine,

• Operating P-T conditions for hydrate crystallization

• Rate of hydrate formation

• Split fraction or CO2 recovery

Post-combustion CO2 capture

CO2/N2 separation via hydrate formation

Flue gas mixture: 17 mol% COFlue gas mixture: 17 mol% CO22 and rest and rest NN22

9

Hydrate crystal formation P & T

0

5

10

15

20

25

30

35

40

45

50

270 272 274 276 278 280 282 284

Temperature (K)

Pre

ssu

re (

MP

a)

Pure N2 (van Cleef et al., 1960)CO2 - 17.61% (Kang et al., 2001)CO2 - 16.9%, This work

Pure CO2 (Adisasmito & Sloan,1992)Pure CO2 (Englezos & Hall, 1994)

Min pressure toform crystals

At T = 0.6 C, P = 7.7 MPa

Pure N2

hydrate

Hydrate from Flue Gas (17% CO2)

phase equilibriumphase equilibrium

Pure CO2

hydrate

10

16.9%16.9%

55.1%57.3%

9.7% 10.9%

0

20

40

60

80

100

Pressure (MPa)

Car

bon

diox

ide

(mol

%)

Initial Flue Gas CompositionHydrate CompositionFinal Flue Gas Composition

10 11

CO2 prefers hydrate phase

Hydrate formation experiments were carried out at 0.6 0C and at two pressures 10 MPa and 11 MPa (Peq = 7.7 MPa)

11

CO2/N2 separation & recovery at 0.6 oC

Split fraction or CO2 recovery 0.42 0.32 0.38

Separation factor

13.20 7.27 36.66 2 2

2 2

H gasCO N

H gasN CO

n nSF

n n

Gas

Hydrate

83.1 mol% N2

16.9 mol%

CO2

2

2

HCO

feedCO

nSpFr

n

Stage 1 Stage 2 Stage 3

12

“Post-Combustion” Capture of CO2

water

Flue Gas

Residual flue gas removal

Hydrate layer Hydrate

decomposition

Gas released from hydrate decomposition(CO2 enriched)

Hydrate formation

Water

Hydrate Layer

Water

Single Stage Hydrate Process

13

“Post-Combustion” Capture of CO2

MembraneProcess

CO2

N2

T = 0.6 oC

P = 10 MPa

T = 0.6 oC

P = 5 MPa

T = 0.6 oC

P = 2.5 MPa

Gas

Hydrate

Process

17% CO2

83% N2

H2O57% CO2

10% CO2

First Stage

50% CO2

83% CO2

Gas

Hydrate

Process

H2O

Second Stage

Gas

Hydrate

Process

H2O98-99% CO2

70% CO2

Third Stage

14

Process Drawbacks

• Flue gas requires compression to high pressure (~10 MPa) for hydrate formation

• ~385MW (77%) of the output of a 500MW power plant required for compression alone

15Temperature (K)

273 274 275 276 277

Pre

ssur

e (k

Pa)

0

1000

20006000

8000

10000

120000.5 mol% THF (This work)1.0 mol% THF (This work)1.5 mol% THF (This work)Water (Linga et al.,2006c)

Hydrate formation pressure decreases in presence of THF

16.9 % CO2 and rest N2 gas mixture

Min pressure to form crystals

At T = 0.6 C, P = 0.35 MPa

At T = 0.6 C, P = 7.7 MPa

16

CO2/N2 separation & recovery at 0.6 oC (in presence of THF)

Split fraction or CO2 recovery 0.460.46 0.470.47 0.370.37

Separation factor

7.597.59 6.776.77 7.737.732 2

2 2

H gasCO N

H gasN CO

n nSF

n n

1.0% THF Solution

Gas

Hydrate

83.1 mol% N2

16.9 mol%

CO2

2

2

HCO

feedCO

nSpFr

n

Stage 1 Stage 2 Stage 3

17

.

GasHydrateProcess

(1)

GasHydrateProcess

(2) GasHydrateProcess

(3)

MembraneProcess

17 % CO2

83 % N2

1 mol% THF

94 % CO2

for Disposal/Storage

10 % CO2

37 % CO2

28 % CO2

62 % CO2

70 % CO2

CO2

N2

CO2 -lean

CO2 -rich

1 mol% THF1 mol% THF

T = 0.6 oC

P = 2.5 MPa

T = 0.6 oC

P = 2.5 MPa

T=0.6oCP= 2.5 MPa

First Stage

Second Stage Third

Stage

“Post-Combustion” Capture of CO2

in presence of THF and lower pressure

18

Concluding Remarks

• CO2 can be separated from flue gas by hydrate

formation

– CO2 prefers the hydrate phase

• High purity CO2 can be recovered from a flue

gas mixture in three hydrate formation stages

– Coupled with a single stage membrane process

• Additives such as THF (1mol% solution) reduce

the hydrate formation pressure

– Making it more suitable for industrial application

19

• Slow kinetics due to mass transfer restriction

Current Challenges

water

Hydrate layer

Gas Slow gas diffusion through hydrate layer

20

Current challenges: work underway

• To determine the best contact mode between water and gas in order to speed up hydrate formationHydrate formation with water

adsorbed on silica gel

Hydrate formation with micro water droplets

21

Acknowledgements

• Natural Resources Canada- Greenhouse Greenhouse Gas Mitigation ProgramGas Mitigation Program

• Canada Foundation for Innovation (CFI)– Clean Energy Research Center

22

Compression Cost

• Calculated for a 500MWe PC power plant

• ~2,439,000kg/hr flue gas produced*

• Compression from atmospheric pressure to 10 MPa was considered with 4 staged compressor with equal compression ratio for each stage

• ~385MW would be required to achieve compression

*MIT Report on The Future of Coal http://web.mit.edu/coal/