Numerical Study On Nitrogen Oxides Control Of Co-firing Biomass With Coal In A 670MW Boiler

Biomass combustion process has ecologically significant zero carbon emissions,so it has always been an ideal alternative to fossil fuels such as coal.Co-firing of biomass and pulverized coal on large power plant boilers is one of the current research hotspots.In this paper,a 670MW four-corner tangential boiler is taken as the research object,with method of numerical simulation,which mainly considers the injection position,particle size,gas fuel reburning,and analyzes the influence of these factors on combustion and NOx emissions.In this paper,the numerical simulation method is combined with the actual operating data of the boiler,and the combustion process under the original working conditions of the boiler is analyzed.It is found that there are problems such as high nitrogen oxide emission and high temperature corrosion of water wal.and then the simulation calculation of 11%biomass co-firing is carried out,and the influence of the parameters such as the position of biomass injection and the particle size of biomass is deeply studied.The results show that after biomass replaces lower layer pulverized coal,the overall temperature of the lower part of the furnace decreases,and it has the effect of reducing NOx emissions,but it will lead to the backward movement of the burnout position,which may cause overheating of the superheater.At the same time,the situation that the biomass fuel replaces the pulverized coal fuel of the first layer primary air nozzle and the second layer primary air nozzle respectively is compared,since the time to participate in the combustion is earlier,and the release of volatiles and other components of the reduction will be earlier,it is better to replace the first layer of working conditions to reduce NOx emissions.Then,the influence of the particle size of the biomass was investigated.The particle size was 0.5mm,1mm,and 2mm.When the biomass particles changed from 2mm to 1mm,the particle size change had little effect,but after changing from 1mm to 0.5mm,NOx emissions have dropped significantly.After gasification of the same biomass,send gas into the furnace,then continue to study the effect of combustion.Studies have shown that after replacing the co-firing fuel,the overall temperature drop in the lower part of the furnace is more obvious,and NOx emissions are also reduced.Similarly,after comparing the data of biomass gas replacement of different nozzle pulverized coal fuels,the conclusion is the same as that of biomass.Finally,numerical simulation of reburning using biomass gas.Compared with the previous simulation data,the effect of biomass gas reburning to reduce NOx emissions is very obvious,from the original612 mg/Nm~3 can be reduced to 402mg/Nm~3,approximately 34%reduction,it can be considered that biomass gas reburning is the best solution to reduce NOx emissions.The research methods and conclusions of this paper have certain realistic reference significance for the research and application of biomass and coal blending utilization in large coal-fired boilers.