Clean hydrogen production and electricity from coal via chemical looping: Identifying a suitable operating regime

In this paper, a chemical looping combustion (CLC) system, using haematite (Fe₂O₃) as an oxygen carrier, has been simulated in conjunction with a steam–coal gasification process. The analysis has assumed thermodynamic equilibrium throughout. Full heat integration was considered for a range of operating conditions (e.g. by varying oxygen carrier recycle rate). It was found that for low to moderate flows of oxidising steam, it was possible to operate within a regime which could be fully heat-integrated. Furthermore, the size of this operating regime increases with the recycle rate of oxygen carrier. The peak exergetic efficiencies achieved for fully heat-integrated systems were 48.4% and 58.3% at operating pressures of 1 atmosphere and 10 atmospheres respectively, and these were increased respectively to 53.7% and 59.7% when a bottoming steam turbine cycle was included to utilise waste heat. These values compare favourably with those achieved by hydrogen production via steam reformation of methane. The range of suitable operating conditions available at both pressures was encouraging, and showed considerable promise for the successful coupling of a chemical looping system with a gasifier.