Study On Characteristics And NO_x Emission Of Gas Reburning In A 660MW Coal-fired Boiler

Gaseous fuel reburning is an efficient technology for reducing NOx emissions which can also reduce the consumption of fossil fuels and protect the environment.A 660 MW subcritical coal-fired boiler is taken as the research object,and Fluent software is used to carry out the numerical simulation to study the combustion process and combustion products in the gas fuel reburning boiler.The main contents are as followings:?1?Based on a 660 MW subcritical tangentially coal-fired boiler in a power plant,the impact of biomass gas reburning and nozzle position on the coupled boiler combustion process and NO_x emissions.Under the condition that the input heat of the boiler does not change,the models of pure coal combustion model and biomass gas co-combustion are established.The research conditions are:pure coal condition,and three biomass gas reburning conditions,which are the reburning nozzles are located in the lower,middle and upper part of the reburning zone.The results show that the reburning of biomass gas cause the temperature of the flue gas at flue gas outlet to rise with the height of the biomass gas nozzle.And biomass gas reburning reduces NO_x emissions.Compared with pure coal combustion,when the biomass gas nozzles are located in the upper,middle,and lower parts of the reburning zone,the average mass concentration of NO_x emissions at the outlet has decreased by 63.64mg/m³,81.77mg/m³,52.38 mg/m³.Therefore,the effect of the biomass gas nozzle located in the middle of the reburning zone is the best,which has decreased by28.01%.?2?In order to improve the combustion effect of biomass gas reburning,the influence of excess air coefficient in the reburning zone on the combustion characteristics and combustion products of the coupled boiler was studied.The research conditions are the biomass gas nozzle is located in the lower part of the reburning zone,and an air nozzle is added below the biomass gas nozzle,while increasing the air intake in the burnout zone;The excess air coefficients in the reburning zone are 0.7,0.85,and 1.0,and theco-firing ratio of biomass gas is 10%.The results show that the reburning of biomass gas reduces the temperature of the main combustion zone,and the temperature of the reburning zone changes with the change of the excess air coefficient in the reburning zone.When the excess air coefficient in the reburning zone is 0.85,the temperature in the reburning zone increases,and when the excess air coefficient in the reburning zone is 0.7 and 1.0,the temperature in the reburning zone decreases.Compared with pure coal without reburning conditions,when the excess air coefficient in the reburning zone is 0.7,0.85,and 1.0,the average mass concentration of NO_x in the flue gas at the furnace exit has decreased by 17.69%,24.18%,and 15.37%,respectively.The excess air coefficient in the reburning zone too large and too small are not conducive to reducing NO_x emissions.With the increase of the excess air coefficient in the reburning zone,the outlet CO volume fraction decreases gradually.?3?Based on the 660 MW pure coal combustion conditions,the effects of different gas fuel reburning on the combustion characteristics and combustion products of the boiler were studied.The four operating conditions are:pure coal burning,reburning of biomass gas,blast furnace gas,and natural gas.The co-firing ratio is 10%.Studies have shown that:the more non-combustible components in the gaseous fuel,the smaller the rise in temperature in the reburning zone,and even decline the temperature of the reburning zone.The ability of gaseous fuel reburning to reduce NO_x emissions is related to the composition of gaseous fuels.The more CH4,hydrocarbons,and H2 content,the stronger the ability to reduce NOx emissions.The average mass concentrations of NO_x emissions from biomass gas,blast furnace gas,and natural gas are:308.97mg/m3,328.96mg/m3,290.35mg/m3,of which the natural gas reburning effect is the best,which is 28.75%lower than the average mass concentration of NO_x emission of the pure coal burning condition of 407.53mg/m³.The greater the CO content in the gaseous fuel,the greater the CO₂ content in the flue gas.