NO emission characteristic during fluidized combustion of biomass with limestone addition

Abstract

Abstract The emission characteristics of NOx and N2O during fluidized combustion of rice straw (RS) and pine sawdust (PS) were investigated following limestone addition at 800\xa0°C. The dominant N-containing pollutant during biomass combustion was NO. Only a small amount of N2O was detected whereas no NO2 was found in any cases. The contributions of volatile-N to the total emissions of NO and N2O were 82.5% and 67.4% for RS and PS, respectively, which were highly consistent with the volatile content in the fuel types (82.9% and 69.1%, respectively). The emission of NO was not affected by limestone addition in a bubbling fluidized bed (BFB) reactor, whereas it was reduced in a circulating fluidized bed (CFB) reactor. The reduction rates for NO were 11.8%, 15.1%, and 24.9% at Ca/S molar ratios of 2:1, 5:1, and 10:1, respectively. These differences were mainly attributed to the catalysis of CaO on the reduction of NO to N2 by CO in the dilute phase zone. To our knowledge, this is the first study to experimentally investigate the effects of limestone addition on NOx and N2O emissions during biomass combustion.