Manganese Minerals as Oxygen Carriers for Chemical Looping Combustion of Coal

In this paper, four different manganese minerals were tested in a batch fluidized bed reactor to evaluate their performance in the chemical looping combustion (CLC) of solid fuels. The char gasification rate in the experiments with the manganese minerals tested was higher than the corresponding values for ilmenite and iron ore, which were taken as benchmark materials. This phenomenon was attributed to the deposition of K, Na, and Ca from the manganese minerals on char particles so that they catalyzed char gasification. The char gasification rate observed using manganese minerals decreased with the number of cycles until a stable value was reached. Under these conditions, one of the materials presented higher char gasification rates than those observed for benchmark materials even when most of the K was already released. An estimation of the CO2 capture efficiency in a continuous unit using one of the selected manganese minerals showed that around 99% CO2 capture efficiency could be reached at 1000 degrees C with a solid inventory in the fuel reactor as low as 300 kg/MWth if an efficient carbon stripper was present.