(573f) Process of Chemical Looping Combustion of Coal

Coal is commonly processed by combustion/gasification using oxygen to produce electricity. Coal, however, can be processed using, instead of oxygen, an oxygen carrier. Metal oxides such as Fe2O3 can act as suitable oxygen carriers. However, unlike combustion of coal with air/oxygen, there is a relatively pure sequestration ready CO2 stream produced on combustion with metal oxide carriers. The reduced form of metal oxide can then be reacted with air to liberate heat to produce electricity or reacted with steam to form a relatively pure stream of hydrogen, which can then be used for a variety of purposes. The process requires two reactors, one for combustion of coal and the other for regeneration of the used metal oxide. The developed process is capable of transforming close to 80% of the thermal energy of coal into hydrogen. This is much higher than the 62% envisaged for coal gasification technologies. Sulfur cleanup may be necessary in order to attain a highly purified hydrogen stream. The high efficiencies and flexibility to produce desired products, coupled with the integrated environmental benefits in terms of a readily sequestrable CO2 stream make chemical combustion looping combustion of coal an attractive technology for energy management.

Chemical looping combustion experiments were conducted with Fe2O3 particles as oxygen carriers. Fe2O3 was supported to provide mechanical strength and immunity towards sintering at high temperatures. It was found that most of the Fe2O3 was converted to Fe and product gases comprised mainly of CO2. Cyclic looping studies revealed that the composite particles retain their activity over multiple reduction/oxidation cycles.