Chemical looping is a special kind of combustion technology which is based on the splitting of global chemical reactions into two or more sub-reactions which take place in different reactors. Intermediate products are reacted and regenerated when sub-reactions occur.

Since intermediate products are produced in separate reactors, chemical looping allows sep­aration of more easily unwanted components which are formed during the combustion process. A particular interest for this kind of combustion/separation technology is for cleaning up the flue gases from pollutants or from greenhouse gases, thus allowing having efficient and cost-effective reduced emissions combustion. Chemical looping is also interesting to split a chemical reaction with high irreversibility into more reactions which have a global lower entropy generation.

The basic feature of chemical looping is to use a medium which can participate in the reactions and facilitate the reaction of the reactants and the production of the products. Such a medium should be highly reactive at process temperature and pressure conditions and physically and chemically stable, should allow an easy separation from the reactants and the products and have moderate exothermic to endothermic heat of reactions. A medium with these features should behave as a fluid, either a liquid or a fluidized solid, being the latter more often employed.

Chemical looping combustion is a technology that can be used with any kind of fuel, either gaseous or liquid or solid, but it is more interesting with solid fuels where conventional combustion systems do not allow easy separation of intermediate products and chemical reactors are less easy to be built and operated as efficiently as for liquid and gaseous fuels.