Effect of operating conditions in Chemical-Looping Combustion of coal in a 500 Wth unit

Chemical-Looping Combustion, CLC, is one of the most promising processes to capture CO2 at low cost. It is based on transferring the oxygen from air to the fuel by using a solid oxygen-carrier that circulates between two interconnected fluidized-bed reactors: the fuel- and the air-reactor. In this work, CLC with coal was investigated in a continuous 500 W-th using ilmenite as oxygen-carrier and Colombian bituminous coal as fuel. In the fuel-reactor the oxygen-carrier is reduced by the volatile matter and coal gasification products. The effect of operating conditions such as the solids circulation rate and oxygen-carrier residence time, the coal flow feed and the steam flow as gasification agent were investigated on the combustion efficiency and extent of gasification. The influence of using CO2 as gasification agent was assessed by doing experiments with different CO2-H2O mixtures. The results obtained are valid for the scale-up of a CLC process with coal. They indicate that it is feasible to decrease the gasification agent flow to lower values than the corresponding stoichiometric for the gasification, and that some of the steam as gasification agent can be replaced by CO2 recirculated from the fuel-reactor outlet. Low circulation rate of solids improved coal conversion. (C) 2011 Elsevier Ltd. All rights reserved.