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 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.

N₂O Reduction and NOx Adsorption in Carbonator of Calcium Looping CO₂ Capture Process

“…Because the gas leakage between the carbonator and the regenerator was negligible (Table 2), the presence of NOx in the regenerator flue gas is attributable to the transportation of NOx from carbonator associated with solid transportation. Since reversible adsorption of NO on CaO surface was observed using thermogravimetric analysis in the previous work 34) , this transportation is explained by adsorption-desorption of NO on CaO surface.…”

“…However, the presence CO2 was found to inhibit NO adsorption by CaO 34) . Thus it is still unclear whether the transportation of NO from the carbonator to the regenerator by adsorption on CaO occurs under actual carbonator conditions in the presence of CO2…”

“…In the authors' previous work 34) , a batch fluidized bed of CaO particles was operated under a carbonator temperature condition, feeding gas containing CO2, N2O, and NO. It was found that N2O decomposition occurred when CaO had activity to capture CO2.…”

“…In addition, it is expected that a part of NO is adsorbed by CaO in the carbonator and transported to the regenerator, because CaO was found to adsorb NO under a carbonator condition 34) . However, the presence CO2 was found to inhibit NO adsorption by CaO 34) .…”

A thermochemical reaction and kinetic characteristic study of municipal sludge in the atmosphere of treated flue gas from calcium looping (Ca‐L)

“…To realize the excess heat utilization and NO x reduction, Shimizu et al 10 . investigated the reaction pathways of NO x and N 2 O over CaO under carbonator conditions of the Ca‐L process using a laboratory‐scale fluidized bed.…”