Effect Of Fuel Nitrogen And Flue Gas Recirculation On NO_x Concentration At The Outlet Of MSW Incinerator

With the gradual advancement of industrialization and urbanization in all countries of the world,the total amount of Municipal solid waste and the amount of per capita production have been increasing year by year,leading to the booming development of MSW incineration industry.The grate incinerator can adapt to the characteristics of low calorific value and high moisture content of MSW in China.It has the advantages of reliable technology,large capacity,strong adaptability and convenient operation,which makes it become the main type of incinerator used worldwide at present.NOx is a harmful flue gas pollutant during the MSW incineration.The composition of MSW is complex,in this paper,soybean powder and nylon 66 were used to represent the components of biomass nitrogen and synthetic polymer nitrogen in waste,respectively.The effects of fuel nitrogen on NO_x concentration at the outlet of incinerator were studied by using computational fluid dynamics technology.The influence of flue gas recirculation on the concentration of NO_x at the outlelet of incinerator was also studied.These studies can provide reference value for controlling NO_x emissions during the operation of waste incinerators.The main results and conclusions are summarized as follows:（1）The pyrolysis experiments of Soybean powder and nylon 66 were carried out in a horizontal fixed bed tube furnace.With the increase of temperature,the HCN conversion of fuel nitrogen increases,while the NH₃ conversion increases first and then decreases.With the increase of temperature,the proportion of NH₃ to volatile nitrogen in nylon 66 decreases,while the proportion of NH₃ in soybean powder decreases slightly.（2）A 750 t/d moving-grate incinerator was modeled to simulate the solid phase combustion process on the bed and the gas phase combustion process in the furnace,and the accuracy of the calculation is verified by the process.The numerical calculation of HCN,NH₃ and NO_x produced by combustion of two fuels mixed with biomass nitrogen（soybean powder）and synthetic polymer nitrogen（nylon 66）on grate was carried out,the proportion of NH₃ in waste mixed with biomass nitrogen to volatile nitrogen was 81.8%,and that of NH₃ in waste mixed with synthetic polymer nitrogen was 74.9%.The average concentration of NO_x at the outlet of the incinerator of waste blended with biomass nitrogen and synthetic polymer nitrogen is 213.99 ppm and239.44 ppm（converted based on dry flue gas）.Combustion of biomass nitrogen can lead to lower NO_x concentration at incinerator outlet.（3）The emission of NO_x was influenced by flue gas recirculation.With the increase of the flue gas recirculation ratio,the concentration of NO_x at the outlet of incinerator showed a downward trend.When the recirculation ratio is 25%,the NO_x concentration at the outlet of incinerator decreased by 10.5%.The denitrification effect of flue gas recirculation is affected by the optimization of air distribution.When the air distribution ratio is kept constant at 7:3,the lowest concentration of NO_x at the outlet of incinerator is 211.8 ppm under the condition of excess air ratio of 1.8 and recirculation ratio of 25%.When the excess air ratio is kept constant at 1.7,the concentration of NO_x at the outlet of incinerator decreases by 30.79%under the condition of air distribution ratio of 8:2.The denitrification effect of flue gas recirculation is also affected by fuel nitrogen.When the flue gas recirculation ratio is 25%,the NO_x concentration at outlet of waste mixed with biomass nitrogenthe decreased from 213.99 ppm to 166.47 ppm,with a decrease of 22.2%;the NO_x concentration at outlet of waste mixed with synthetic polymer nitrogen decreased from 239.44 ppm to 180.82 ppm,with a decrease of 24.5%.