Numerical Simulation And Optimization Analysis Of Biomass Gas Mixed Burning In A 300MW Coal-fired Boiler

As a kind of renewable energy with abundant reserves in the non fossil energy category,biomass energy has been paid more and more attention by contries all over the world in recent years.China is definitely a top agricultural country,and the potential of biomass energy utilization is huge.Biomass energy can be used in several ways,including direct combustion and indirect combustion.In recent years,with the development of gasification technology,biomass gas generated from solid biomass pyrolysis has become another new way of utilization,whose application includes coal and biomass gas coupling power generation,etc.The impacts of the blending of the two fuel on the operation of coal-fired boilers are worthy of further discussion.Therefore,the full text will focus on combustion characteristics of the co-firing of biomass gas and the pulverized coal.In this paper,a 300MW subcritical parameter coal-fired boiler is selected,and models of the pure pulverized coal combustion and co-combustion are established by using FLUENT,focusing on the combustion characteristics and optimization analysis of biomass gas and the pulverized coal.The co-combustion characteristics mainly focus on the different locations of the biomass gas nozzle,and contents of combution optimization include the effects of the blending ratio of the biomass gas,the excess air ratio,the over fired air ratio and the inlet velocity of the biomass gas on the co-combustion characteristics.The results of different calculation conditions include velocity field,temperature field and flue gas component field distribution in the furnace,as well as NO_x emission.Through the comparative analysis of the calculation results of pure coal and mixed burning,the following conclusions are finally obtained in this paper（1）The calculation results of pure pulverized coal condition are more reliable,and the model selection is reasonable.（2）Compared with pure pulverized coal combustion,when 20%ratio of the biomass gas is mixed,the peak temperature in the center of the furnace and the flue gas temperature at the outlet will decrease,and the higher the position of the biomass gas is,the lower the peak temperature in the burnout zone of the pulverized coal will be;the volume fraction of O₂,CO and CO₂ in the furnace under mixed combustion vary in the same way of pure pulverized coal combustion,and the volume fraction of O₂ at the outlet will decrease and the volume fraction of CO₂ will increase;the NO emission can be reduced under the condition of mixed combustion,and the higher the position of biomass gas jet is,the lower the NO emission is.However,when the position of biomass gas jet is much lower,the NO emission reduction is not obvious.（3）When the blending ratio of biomass gas changes between 10%,15%and 20%,the higher the ratio is,the lower the peak temperature of the main combustion zone is,the higher the peak temperature in the burnout zone is,the lower the O₂ content is,the higher the CO₂ content is,and the higher NO content in the furnace is.When the excess air ratio changes between 1.20,1.25 and 1.30,the greater the excess air ratio is,the higher the peak temperature in the main combustion zone,the lower the peak temperature in the burnout zone is,the higher the O₂ content and NO emission are,and the lower the CO₂ content is.When the over fired air ratio changes between 20%,22%and 24%,the greater the ratio is,the more intense the flow in the burnout air zone is,the lower the peak temperature of the main combustion zone is,and the higher the peak temperature in the burnout zone is.The volume fraction of CO in the cold ash hopper and main combustion zone increases,while the volume fraction of CO₂ decreases.The NO content decreases.When the inlet velocity of biomass gas varies between 30 m/s,36.9 m/s and 43.8 m/s,the distributions of velocity field,the temperature field,flue gas component field and NO emission are not significantly different.For the selected boiler,when the blending ratio is 20%,the excess air ratio is 1.20,and the over fired air rate is 24%,the NO_x emission reduction effect is the best,and the velocity of the biomass gas has little effect on the co-firing.