Chemical-looping combustion or CLC, as defined by Ishida in the nineties, involves the transfer of oxygen from air to fuel by means of an oxygen-carrier material. The technology uses two different reactors, an air reactor and a fuel reactor. The fuel is oxidized to CO2 and H2O in the fuel reactor and the oxygen carrier is regenerated in the air reactor. Thus, the process is able to deliver a stream of highly concentrated CO2without any active gas separation. This provides a possibility to avoid the large costs and energy penalties of gas separation which are seen in other CO2 capture technologies. Consequently, the process has a potential for dramatic reduction of CO2 capture costs.
The concept can also be used for conversion of fuel to hydrogen, e.g. through partial oxidation of the fuel, often referred to as chemical-looping reforming. An additional application of chemical looping is for treating raw gas from biomass gasification. In recent years, research has mainly been focused on oxygen carrier materials, reactor concepts and potential applications.
The process has been investigated in several pilot plants at different scales, from lab scale test rigs to a semi-industrial scale of 1 MWth. The research involves gaseous, liquid and solid fuels, and a number of different oxygen-carrier materials have been used.