Study On Combustion Characteristic And Pollutant Emission Of Biomass Gas Co-firing With Coal In A 300 MW Coal-fired Boiler

Biomass gas co-firing with coal in coal-fired boiler can not only reduce the consumption of coal and effectively utilize biomass fuel,but also reduce the emission of pollutants.Based on the numerical simulation software Fluent,it takes a 300 MW power plant boiler as the research object to analyze the co-firing process of biomass gas with coal and the variation of combustion flow field and combustion product.The main research contents are as follows:(1)The co-firing process of biomass gas with coal is designed based on the design parameters and structural dimensions of a 300 MW subcritical natural circulation boiler which model is DG1025/17.5-II4.Gambit software is used to divide the grid and the combustion condition of biomass gas co-firing with coal is simulated by the software of Fluent.The biomass gas co-firing with coal is calculated by the two mixture fraction method.Two kinds of fuels are defined respectively: the pulverized coal flow is defined as the combustion flow and the biomass gas is defined as the secondary flow.(2)Research on four cases of combustion process of pure coal combustion and coal co-firing with 10% three kinds of biomass gas(pine gas,straw gas and sawdust gas).The velocity field,temperature field,flue gas compositions and NOx distribution were acquired under different conditions.The results show that biomass gas co-firing with coal can significantly reduce the temperature at combustion area and the NOx content at the furnace exit.(3)Research on the co-firing process of coal co-firing with biomass gas at different power loads.Under the three conditions of 100%,90% and 80% loads,the co-firing process of coal co-firing with 10% pine gas are studied.The results show that the content of pollutants in the furnace drops,with the decrease of boiler load,but it has little effect on the volume fraction of O2,CO and CO2 in the furnace.(4)Research on the co-firing process of coal co-firing with different proportion of biomass gas.Based on the 300 MW boiler unit,the four cases of pure coal,co-firing 10%,20% and 30% pine gas with coal were studied.The results show that with the increase of the proportion of co-firing biomass gas,the decrease of the temperature in the boiler furnace is more and more obvious,the pollutant content in the furnace is obviously reduced,and the residence time of pulverized coal is decreased.