Producing hydrogen and power using chemical looping combustion and water-gas shift

Niall R. McGlashan, Peter R. N. Childs, Andrew L. Heyes, Andrew J. Marquis

Research output: Contribution to journalArticle

12 Citations (Scopus)

Abstract

A cycle capable of generating both hydrogen and power with "inherent" carbon capture is proposed and evaluated. The cycle uses chemical looping combustion to perform the primary energy release from a hydrocarbon, producing an exhaust of CO. This CO is mixed with steam and converted to H2 and CO2 using the water-gas shift reaction (WGSR). Chemical looping uses two reactions with a recirculating oxygen carrier to oxidize hydrocarbons. The resulting oxidation and reduction stages are preformed in separate reactors-the oxidizer and reducer, respectively, and this partitioning facilitates CO2 capture. In addition, by careful selection of the oxygen carrier, the equilibrium temperature of both redox reactions can be reduced to values below the current industry standard metallurgical limit for gas turbines. This means that the irreversibility associated with the combustion process can be reduced significantly, leading to a system of enhanced overall efficiency. The choice of oxygen carrier also affects the ratio of CO versus CO2 in the reducer's flue gas, with some metal oxide reduction reactions generating almost pure CO. This last feature is desirable if the maximum H2 production is to be achieved using the WGSR reaction. Process flow diagrams of one possible embodiment using a zinc based oxygen carrier are presented. To generate power, the chemical looping system is operated as part of a gas turbine cycle, combined with a bottoming steam cycle to maximize efficiency. The WGSR supplies heat to the bottoming steam cycle, and also helps to raise the steam necessary to complete the reaction. A mass and energy balance of the chemical looping system, the WGSR reactor, steam bottoming cycle, and balance of plant is presented and discussed. The results of this analysis show that the overall efficiency of the complete cycle is dependent on the operating pressure in the oxidizer, and under optimum conditions exceeds 75%.

LanguageEnglish
Article number031401
Number of pages10
JournalJournal of Engineering for Gas Turbines and Power
Volume132
Issue number3
Early online date3 Dec 2009
DOIs
Publication statusPublished - 31 Mar 2010
Externally publishedYes

Fingerprint

Water gas shift
Steam
Hydrogen
Oxygen
Gas turbines
Hydrocarbons
Carbon capture
Redox reactions
Energy balance
Flue gases
Zinc
Oxidation
Oxides
Metals
Industry
Temperature

Keywords

  • carbon capture
  • chemical looping combustion
  • hydrogen economy
  • water-gas shift
  • zinc

Cite this

McGlashan, Niall R. ; Childs, Peter R. N. ; Heyes, Andrew L. ; Marquis, Andrew J. / Producing hydrogen and power using chemical looping combustion and water-gas shift. In: Journal of Engineering for Gas Turbines and Power. 2010 ; Vol. 132, No. 3.
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Producing hydrogen and power using chemical looping combustion and water-gas shift. / McGlashan, Niall R.; Childs, Peter R. N.; Heyes, Andrew L.; Marquis, Andrew J.

In: Journal of Engineering for Gas Turbines and Power, Vol. 132, No. 3, 031401, 31.03.2010.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Producing hydrogen and power using chemical looping combustion and water-gas shift

AU - McGlashan, Niall R.

AU - Childs, Peter R. N.

AU - Heyes, Andrew L.

AU - Marquis, Andrew J.

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N2 - A cycle capable of generating both hydrogen and power with "inherent" carbon capture is proposed and evaluated. The cycle uses chemical looping combustion to perform the primary energy release from a hydrocarbon, producing an exhaust of CO. This CO is mixed with steam and converted to H2 and CO2 using the water-gas shift reaction (WGSR). Chemical looping uses two reactions with a recirculating oxygen carrier to oxidize hydrocarbons. The resulting oxidation and reduction stages are preformed in separate reactors-the oxidizer and reducer, respectively, and this partitioning facilitates CO2 capture. In addition, by careful selection of the oxygen carrier, the equilibrium temperature of both redox reactions can be reduced to values below the current industry standard metallurgical limit for gas turbines. This means that the irreversibility associated with the combustion process can be reduced significantly, leading to a system of enhanced overall efficiency. The choice of oxygen carrier also affects the ratio of CO versus CO2 in the reducer's flue gas, with some metal oxide reduction reactions generating almost pure CO. This last feature is desirable if the maximum H2 production is to be achieved using the WGSR reaction. Process flow diagrams of one possible embodiment using a zinc based oxygen carrier are presented. To generate power, the chemical looping system is operated as part of a gas turbine cycle, combined with a bottoming steam cycle to maximize efficiency. The WGSR supplies heat to the bottoming steam cycle, and also helps to raise the steam necessary to complete the reaction. A mass and energy balance of the chemical looping system, the WGSR reactor, steam bottoming cycle, and balance of plant is presented and discussed. The results of this analysis show that the overall efficiency of the complete cycle is dependent on the operating pressure in the oxidizer, and under optimum conditions exceeds 75%.

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KW - hydrogen economy

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