Reaction pathways of NOX and N2O over CaO under carbonator conditions of the calcium-looping (CaL) process were investigated using a laboratory-scale fluidized bed with calcined limestone (CaO) and inert quartz sand as bed materials. Char particles were fed to the fluidized bed to simulate char transportation to the carbonator. With char feed to the sand bed, slight reduction of NO and N 2O in the feed gas was observed, but considerable CO formation was observed. When NO was fed to the CaO bed, NO was first adsorbed onto the CaO surface. The adsorbed NO was desorbed when char or gaseous CO 2 was fed. Although char feed to the CaO bed decreased NO slightly, the reduction of NO was nearly equal to that in the sand bed. This reduction of NO with char feed was attributable solely to NO reduction by the char. The formation of CO from char oxidation for CaO bed was much less than that for the sand bed. These results suggest that CO was oxidized over CaO before it reduced NO. For N2O decomposition, the CaO bed had high catalytic activity. CaL process is expected as a multifunctional process of CO2 capture and N2O decomposition with low CO emissions.
A dual-fluidized bed solid circulating system that comprised a bubbling bed carbonator and a fast fluidized bed regenerator was operated under a condition of Calcium Looping (CaL) CO2 capture process. Calcined limestone (CaO) was employed as bed material. Gas mixture simulating flue gas from air-blown combustor consisted of CO 2, N2O, NO, O2, and N2 was fed to the carbonator. Most part of the fed CO2 was captured by the calcined limestone particles, then the partially carbonated particles were transported to the regenerator, in which thermal decomposition of CaCO 3 was carried out in air stream. The carbonator of CaL process was found to be effective for N2O reduction when the sorbent particles had activity to capture CO2. A part of NO in the feed gas was also adsorbed by CaO particles, then the adsorbed NO was transported to the regenerator, and released to the gas phase there, though the net decomposition of NOx was not observed. CaL process was revealed to be a multifunctional process of CO 2 capture, N2O decomposition, and removal of a part of NO in the flue gas fed to the carbonator.
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