Chemical Looping Combustion: A Technology for the Clean Utilisation of Coal

Coal is used for around 39% of global production of electricity. Despite being one of the most polluting fossil fuels, in terms of mass of CO2 emitted per unit of power generated, the use of coal is projected to increase from present day levels by ~ 80% by 2030. It is, therefore, important to find ways of using it for power generation whilst avoiding the release of CO2 into the atmosphere. The currently-available technology for CO2 separation is by scrubbing the flue gases with, e.g. monoethylamine (MEA): however, this technique comes with a large energy penalty because of the large heat requirement for regeneration of the solvent, reducing the efficiency of the power plant by up to one-third. This presentation will survey, briefly, current methods for separating CO2. It will then present some research being conducted at Cambridge on Chemical-looping combustion (CLC), which has the inherent property of separating CO2 from flue gases without the energy penalty associated with amine scrubbing. Instead of air, it uses an oxygen-carrier, usually in the form of a metal oxide, to provide oxygen for combustion. If time permits, further work on a modification of chemical looping will be described, involving the oxides of iron in packed bed reactors, to produce hydrogen of high purity from low-grade synthesis gas. This offers substantial benefits in terms of the distributed production of hydrogen, avoiding costly transport of the gas by a dedicated grid.