NOx formation of biomass co-firing with coal in two-stage drop-tube furnace

HOU Yan; YANG Fuxin; TAN Houzhang; XIONG Xiaohe; CHEN Falin

doi:10.13225/j.cnki.jccs.2024.0134

Abstract：The co-firing of biomass with coal is one of the technologies to reduce the carbon emission from the coal-fired power plant.The position of biomass co-firing has a significant impact on NOx emission during the co-firing process.Therefore,in order to study the effect of the biomass co-firing position and the temperature on the NOx emission,a two-stage drop-tube furnace was used to study the NOx emission of biomass co-firing with coal from the primary combustion zone and the burnout zone as well as the migration of fuel N.The results show that NOx emission behaviors are signific-antly different when biomass is mixed from the primary combustion zone and the burnout zone.When biomass is mixed from the primary combustion zone,NOx emission at studied temperature shows a decreasing trend with the increase of the biomass co-firing ratio from 0 to 40％,with the increase of the over-fire air ratio,the lowest NOx emission occurs when the ratio is 0.33.When biomass is mixed from the burnout zone,the NOx emission decreases continuously with the increase of the biomass co-firing ratio from 0 to 40％at the burnout temperature of 1 000 ℃.At the burnout temperatures of 1 200 and 1 400℃,the NOx emission is lowest when the biomass co-firing ratio is 10％.There is a significant difference in the con-version of fuel N to intermediate products of HCN and NH3 during biomass co-firing in the burnout zone.At the studied burnout temperature,when biomass is mixed in the burnout zone,the conversion rate of fuel N to HCN always increases with the increase of biomass co-firing ratio.The conversion of fuel N to NH3 increases with the increase of biomass co-fir-ing ratio at the burnout temperature of 1 000℃;when the burnout temperatures is 1 200 and 1 400 ℃,the conversion rate of NH3 is the highest at biomass co-firing ratio of 10％.When the primary zone temperature is 1 200 ℃ and the burnout temperature is 1 400 ℃,about 94％of the fuel N is converted to N2 and ash N,about 5％is converted to NOx,and less than 1％is converted to HCN and NH3.The co-firing of biomass can reduce the conversion of fuel N to NOx compared to pure coal combustion.However,as the biomass co-firing ratio increases,the conversion rate of fuel N to NOx and ash N increases,and the conversion rate of fuel N to N2 decreases.