In situ gasification of coal using steam with chemical looping: a technique for isolating CO₂ from burning a solid fuel

In chemical looping combustion (CLC), a metal oxide ( generalised as MeO) is used to oxidise a gaseous fuel in: (2n+m) MeO+CnH₂m–>(2n+m) Me+mH(2)O+nCO(2). Pure CO₂ can then be obtained by cooling the off-gases to condense the steam. The reduced form of the metal oxide, Me, is then transferred to a different reactor, where it is re-oxidised by air in: Me+1/2O(2)–>MeO. The gas from this reactor is N-2 containing unused O-2. The net effect of these reactions is that the fuel has been burned, with the total heat evolved being the same as for combustion of the fuel in air; however, the resulting CO₂ is now pure and not mixed with the nitrogen from the air. This paper shows how it is possible to use CLC with a solid fuel, such as coal char, provided a gasification agent like steam is introduced into the reactor. The gasification agent transfers solid carbon to gaseous CO, which, like the H-2 also formed, can be reacted with a solid, e. g. Fe2O3, carrying oxygen, to yield CO₂ and H₂O. On the basis of a limited series of experiments, the reaction of sintered compacts of Fe2O3 appears to be sufficient to make a semi-batch process feasible when used with steam.