(515e) Oxygen Carriers for Chemical-Looping Combustion with Solid Fuels

Chemical-looping combustion (CLC) is a novel combustion technology with inherent CO2 separation, and uses an oxygen carrier instead of air to burn the fuel to CO2 and H2O. In this way, the CO2 is inherently separated from the nitrogen in the air, and no energy is needed to perform this separation. As most CCS technologies are burdened with high costs and efficiency losses mainly due to gas separation, CLC is a potential break-through technology for CO2 capture. The main economic advantage of CLC is likely realized for combustion of solid fuels such as coal, petroleum coke and biomass. The solid fuel is burnt in the fuel reactor together with the oxygen carrier particles, and there are three main routes for converting solid fuel: i) The solid fuel is gasified by H2O/CO2 to CO/H2, which reacts with the oxygen carrier particles to CO2 and H2O, i.e. conventional chemical-looping combustion ii) The oxygen carrier particles release gaseous oxygen which reacts with the solid fuel through normal combustion, i.e. chemical-looping with oxygen uncoupling (CLOU) and iii) The fuel reacts via a combination of CLC and CLOU. The role of the oxygen carrier is thus different and depends upon the process which is used above. For route i) the oxygen carrier needs to convert the intermediate syngas and volatiles at a sufficient rate to achieve high gaseous yield to carbon dioxide. For route ii), or CLOU, the oxygen carrier needs to supply oxygen to the fuel at a sufficient rate to achieve a high rate of solid conversion. Finally, some oxygen carriers may only be able to supply a small amount of oxygen via CLOU, and thus may react in the fuel reactor via a combination of CLOU and CLC. The paper proposes quantitative criteria for evaluating reactivity data of the three processes above, and analytical expressions for obtaining oxygen carrier inventories in the fuel reactor are presented.