The Research Of NO_x Emission Characteristics In The Combustion Of Densified Biomass Solid Fuels

As a renewable energy resource,biomass fuel can achieve near zero carbon emissions.Biomass fuels have been widely used for their large reservation and good availability.Densified biomass solid fuels are produced by crushing and pressing raw biomass in the form of granules or briquettes.Compared with raw biomass,they have higher energy density and are easier for transportation,so they are the main form for concentrated utilization of biomass.However,the high nitrogen content in the biomass fuels leads to high NO_x concentrations in the flue gas.In order to study the NO_x emissions of the biomass combustion,a small grate combustion reactor was built in laboratory.The corn stalk pellets were burned under different combustion conditions and the NO_x concentrations were analyzed with a real-time flue gas analyzer.Through simulating the flue gas recirculation conditions,the effects of flue gas recirculation on NO_x emissions were studied.Emission tests were carried out on a 0.5t/h biomass-fired chain industrial boiler,which were compared with the results obtained in the laboratory.Through experiments on the small grate combustion reactor in laboratory,the following conclusions can be drawn.Firstly,the generation of NO_x can be effectively controlled by adjusting the air distribution.The staged air combustion could reduce the NO_x by about 100 ppm compared with the non-staged combustion.With the increasing of the excess air ratio or the primary air scale in total air,the NO_x emissions increased linearly.The position of secondary air blowing has little effect on the NO_x emissions.Secondly,the research on the influence of flue gas recirculation was carried out.Part of NO gas passing into the middle of the furnace with the primary air was reduced to N₂ and the conversion rate of this reaction followed a logarithmic variation law.The primary air was diluted with N₂ to reduce the oxygen concentration in the primary air.With the decrease of oxygen content in the primary air,NO_x emissions decrease linearly.The tests on a 0.5t/h biomass-fired chain industrial boiler that used the peanut shell pellets as fuels show that the NO_x emissions changed linearly with excess air ratio of the boiler,which verified the conclusions obtained from the experiments in the laboratory.