Clean combustion of solid fuels

A chemical-looping process is proposed for the clean combustion of solid fuels for electric power or heat generation. The process is based on coal gasification with CO2 to produce CO. The CO then reduces CaSO4, which is used as an oxygen carrier, in a separate reactor to give CaS and CO2. A portion of the CO2 is recycled for the gasification stage and the rest can be sent for sequestration. The CaS is sent to another reactor for oxidation with air and to generate heat or power. The overall thermal effect is the same as direct combustion, but separation of CO2 and other pollutants, such as sulphur, is achieved. In comparison with conventional chemical-looping combustion of natural gas, much less water is present in the CO2 product, and hence the loss of heat energy and corrosion of the fuel–reactor system can be reduced.