Chemical-looping combustion of solid fuels - Operation in a 10 kW unit with two fuels, above-bed and in-bed fuel feed and two oxygen carriers, manganese ore and ilmenite

摘要

Chemical-looping combustion (CLC) is a combustion concept with inherent separation of CO_2. The process uses a solid oxygen carrier, which consists of metal oxide, to transfer the oxygen from air to fuel. The chemical-looping combustor used in the present experiments features two interconnected fluidized beds; a fuel reactor (FR) and an air reactor (AR). In the FR, fuel is gasified with steam whereupon gasification products react with the oxygen carrier to form, ideally, CO_2 and H_2O. This study concerns CLC of solid fuels in a continuously operating 10 kW unit using two natural ores as oxygen carrier: (a) ilmenite, an iron-titanium mineral and (b) a manganese ore containing smaller amounts of Fe, Al and Si. The fuel feed was re-designed in order to increase contact between oxygen carrier and fuel. The new in-bed fuel feed was found to significantly improve gas conversion, mainly caused by increased contact between the oxygen carrier and volatile gases released in the fuel chute. Two fuels were used to evaluate the effect of fuel feed; a bituminous coal and a pet coke. The in-bed fuel feed was used when ilmenite and manganese ore were compared. The use of a manganese ore as oxygen carrier was shown to significantly enhance the rate of char gasification and also improve gas conversion. A concern with the manganese ore is the large production of fines.