Co2 capture and storage in IGCC plants

8/6/2019 Co2 capture and storage in IGCC plants

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CO2 Capture and storage inIGCC plants

Abhiram Kukunuri

M.Tech (Thermal)

Advanced Energy Conversion

Seminar on


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Contents

Introduction On IGCC

Objective

CO2 capture technologies

Physical absorption of CO2 by SelexolPerformance of IGCC with Selexol based CO2

capture

Storage of Captured CO2Conclusions

References


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IGCC Plant (without CO2 capture)


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Advantages of IGCC

Higher efficiencies and loweremissions (low NOxand SO2also)

Higher output

Product flexibility - includingcarbon capture and hydrogenproduction


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Objective

To find the suitable carbon capture and storage

technologies, their effects on efficiencies of IGCC plants.

COCO22 CaptureCaptureCO2 capture is the separation ofCO2 from emissionssources or the atmosphere and the recovery of aconcentrated stream ofCO2 that is amenable tosequestration or conversion .

In general CO2 capture can be divided into

three categories:

1. Post-combustion Capture2. Oxy-fuel combustion3. Pre-combustion Capture (applied to IGCC plants)


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CO2 capture Technologies


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In an IGCC power plant, coal is converted to anintermediate synthesis gas.

The carbon can be recovered from this synthesis gas inthree steps (Pre combustion capture):

1. conversion of the carbon monoxide to carbon dioxide

(by shift reactor),2. extraction of the carbon dioxide by a physical

absorption process (using selexol) and

3. Desorption, compression and drying of the carbondioxide.

The method reduces the emission of carbon dioxide byabout 88%.


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Physical absorption

Physical absorption occurs by mass transfer of gas molecules intoa solvent.

This process is governed by Henry's law, which states that theamount of absorbed gas is proportional to the partial pressure of

the gas.

Selexol is a 95% solution of the dimethyl ether of polyethyleneglycol in water.

CH3-O-(CH2-CH2-O)N -CH3 where N = 2 to 9

This process can also be used to remove sulfur products (H2S)

during gas clean up.

Physical Solvents are mostly suited for the removal ofCO2 fromPhysical Solvents are mostly suited for the removal ofCO2 from

gases with high vapour pressures.gases with high vapour pressures.


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Shift Reactor CO from Syngas (CO+H2), is converted into CO2.

This is done by reacting the CO with steam in a catalyst-packed tubular reactor.

Water gas shift reaction

CO + H2O(g) H2+ CO2 (exothermic)

Catalysts Used:

Iron oxide catalyst (340C - 590C).

Copper oxide catalyst (Below that temperature).

High CO2 recovery is best achieved by staged reactorsthat allow for cooling between stages.

About 90% conversion and a decrease of approximately9% in the lower heating value of the synthesis gas, (11.3

to 10.3 MJ/m3

).


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Process used to recoverCO, from the

synthesis gas.


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Absorption Process by selexol


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After the shift reaction, the gas-mixture containing CO2, H2and a small amount of CO flows countercurrent through the

selexol (unit No. 1 in Fig.). After absorbing the CO2, thesolvent is collected at the bottom of the unit.

The CO2-rich solvent flows into a recycle flash drum (3),where essentially all the H2 and CO are flashed.

The CO2 is recovered by reducing the pressure. Thesechanges are accomplished in several, serially-connecteddrums (4) and (5).

The CO2 is partly released at high pressure and partly atatmospheric pressure. After the desorption stages, the selexolstill contains 25-35% of the originally dissolved CO2. ThisCO2 is recycled back to the absorber and is recovered in a

later cycle.


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In the selexol recovery process, energy is required forpumping of the selexol. The solubility of CO2 is 20 Nm3/m3selexol. In order to absorb 500 t CO2/h, the circulation rate ofselexol must be 5.5 m3/sec if the selexol has a desorption

ratio of 0.65.

The power demand for pumping may be calculated from therelation

Pp=qv*p/p wherePP = power demand (W), qv= flux(m3/sec),

p = pressure difference (bar) and p=pumping efficiency.

Assuming p, = 0.70, the power demand will be approximately17 MW,.

About 50% of this energy is recovered by reducing thepressure of the selexol, which leaves a net power

consumption of 9 MW,


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About 13% reduction in the net plant output of 711MWe plant due to carbon capture(Here it is assumed that the gas turbine has the same performance with H2

gas as it has

With synthesis gas).


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Study by Jacobs consultancy in cooperation with General Electric (Texaco sponsored)


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CO2Storage


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IGCC Plant (with CO2 capture and storage)


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Conclusions

Gasification under high pressures allow the useof physical solvents (like selexol) to capture CO2efficiently.

Pre combustion capture of CO2 can be done inIGCC plants and only H

2can be send to Gas

turbines.

Reduction in efficiencies of IGCC plant willdepend on amount of CO2 capture required andthe technology used.

Usage of selexol in KRW IGCC plant reducedthe output of the plant by 25% for 88% CO2recovery.


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References

1) GASIFICATION COMBINED CYCLE: CARBON DIOXIDERECOVERY,TRANSPORT, AND DISPOSAL ,R.D. Doctor, l.C. Molburg, P.

Thimmapuram,G.F. Berry, C.D. Livengood, and R.A. Johnson, Energy

Conversion.MgmtVol. 34, No. 9-11, pp. 1113-1120, 1993.

2) TECHNOLOGY AND COST OF RECOVERING AND STORING CARBON

DIOXIDE FROM AN INTEGRATEDGASIFIER, COMBINED-CYCLE PLANT ,C. A.

HENDRIKS,~ K. BLOK, and W. C. TURKENBURG, Energy Vol. 16, N o. 11/12p,p. 1277-1293 1991.

3) Purification and Recovery Options for Gasification D.J. Kubek,E. Polla ,F.P.

Wilcher 2000 UOP LLC, Des Plaines, Illinois.

4) COUPLING CO2 CAPTURE AND STORAGE WITH COAL GASIFICATION:

DEFINING SEQUESTRATION-READY IGCC, Jennie C. Stephens, Energy

Technology Innovation Project a joint project of the Science, Technology andPublic Policy Program and the Environment and Natural Resources Program

Belfer Center for Science and International Affairs, Sept 2005.

5) CARBON DIOXIDE CAPTURE AND STORAGE, IEA/OECD, 2000

Co2 capture and storage in IGCC plants

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