Chemical-looping combustion of solid fuels – Design and operation of a 100 kW unit with bituminous coal

Reviewartikel, 2013

Chemical-looping combustion is a novel technology with inherent capture of CO2 when burning gaseous, liquid or solid fuels. By using two interconnected fluidised beds with a bed material capable of transferring oxygen from air to the fuel, a nitrogen-free stream of CO2 can be obtained with no direct efficiency loss. Here, approximately 20 h of experimental results from a 100 kW unit for solid fuels are presented. Using ilmenite oxygen carrier and a Colombian bituminous coal (Cerrejón coal), five periods of operation were conducted at 940-980°C in the fuel reactor for 1.5-6 h. The unit worked well and stable operation was easily reached. The investigation involves variations of operational parameters to see the effect on performance. It was shown that an oxygen demand below 16% and a CO2 capture above 99% can be reached during extended periods at close to optimal conditions. By replacing the steam fluidisation with inert nitrogen, the influence of the carbon stripper with respect to the steam gasification was tested. It was shown that CO2 capture decreased from 98.5% to 95.5% without the gas conversion provided by the carbon stripper. Finally, pressure profiles from two experiments are presented and compared to a pressure profile predicted from cold-flow model experiments. The work shows the first extended operation of chemical-looping combustion with solid fuels in the 100 kW scale and the operational experience gives strong indication that the process is viable.