Reaction Pathways of NO_X and N₂O over CaO in the Presence of Char under Carbonator Conditions of Calcium-Looping CO₂ Capture Process

Abstract

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 N₂O 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 CO₂ 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.