Numerical Simulation And Optimization Analysis Of Biomass Mixed Burning In A 300MW Lignite Boiler

In recent years,the proportion of clean energy consumption has continued to increase,and its strategic position has become increasingly prominent.As one of clean energy sources,biomass energy is abundant in reserves and widely used.Among them,using biomass power generation is one of the main application ways.At present,people mostly focus on the biomass gasification coupling power generation research,and biomass direct combustion power generation as another generation method,has the advantages of simplicity,efficiency,economy and so on.For this kind of power generation mode,it is found that there are few researches on the mixed burning biomass in lignite boilers.This paper will focus on this research.This paper takes a 300MW lignite boiler as the research object.First,the original operating conditions are numerically simulated based on Fluent software.The results show that the error is within a reasonable range,and the model selection is reasonable.Select cotton,corn,and wheat stalks as biomass objects,set the blending ratio to 15%,and the biological spout position as the lowest primary spout,and conduct an in-depth study on the blending of different biomass.The results showed that when cotton and wheat stalks were blended,the temperature in the main combustion zone was slightly lower than that of pure coal,while the corn stalks had the opposite pattern.When blended with wheat,the pollutant NO has the lowest emission,and wheat straw is the best blended substance.Secondly,in order to further optimize the working conditions of the lignite boiler mixed with biomass,the effects of the position of the biomass nozzle,the mixing ratio,the excess air coefficient,and the over-fire air rate on the combustion characteristics in the furnace and the pollutant NO_x were studied.Through comparative analysis of the simulations under each group of working conditions,the results show that when the biomass nozzle changes in the A～E layer,the higher the position of the biomass nozzle,the higher the peak temperature of the main combustion zone.The position of the biomass spout is arranged in the E layer,and the NO volume fraction is the lowest.When the biological blending ratio is 10%,15%,and 20%,the larger the blending ratio,the greater the peak temperature of the over-fired air zone,the smaller the peak CO volume fraction in the main combustion zone,and the lower the O₂ volume fraction at the furnace outlet.The larger the volume fraction.When the blending ratio is 15%,NO has the best emission reduction effect.When the excess air coefficient is 1.15,1.2 and 1.25,the larger the excess air coefficient,the smaller the peak value of the burnout zone,the greater the O ₂ volume fraction at the furnace outlet,and the lower the CO₂ volume fraction.When the excess air coefficient is 1.15,the NO content of the boiler has Lowest emissions.When the over-fire air rate is 20%,23%,25%,the greater the over-fire air rate,the lower the peak temperature of the main combustion zone and the burn-out zone,the higher the overall CO volume fraction in the furnace,and the lower the CO₂ volume fraction in the furnace.The higher the outlet O₂ volume fraction.When the burn-out air rate is 25%,NO emissions are the lowest.Finally,for the lignite boiler studied in this article,when the admixed material is wheat,the biological nozzles are arranged in layer E,the admixture ratio is 15%,the excess air coefficient is 1.15,and the over-combustion air rate is 25%,NO_x emissions lowest.It provides certain theoretical guidance for the mixed burning of biomass in lignite boilers in engineering practice.