Numerical Simulation Of NO_x Formation And Reduction Mechanism In Coke Oven Combustion Chamber

The demand for coke is increasing with the development of Chinese industry.Coke oven as an important equipment for coke refining,its use is increasing year by year.However,the extensive use of coke ovens has caused serious air pollution,and the traditional flue gas denitrification technology is less economical as the low concentration of NO_x in the flue gas.It is very important to reduce the NO_x production in the coke oven.At present,in order to reduce the production of NO_x in the coke oven,the staged combustion or flue gas recirculation is usually used alone in China.The combined technology of staged combustion and flue gas recirculation has not been reported.Meanwhile,due to the complexity of coke oven thermal process,the NO_x generation and reduction mechanism,and the influencing factors have not been fully considered.In this study,a large volume 7m coke oven was taken as the research object,and CFD numerical simulation software was used to explore the influence of coke oven structure parameters,air distribution ratio,flue gas circulation ratio,and secondary fuel supply mode on combustion characteristics.The NO_x generation and reduction mechanism was also elaborated.By changing the air supply position,adjusting the air supply ratio and other influencing factors,the results show that the air staged combustion technology can inhibit the combustion level of the main combustion zone,and reduce the temperature in the furnace,and change the size of the reducing atmosphere zone in the furnace.Then the NO_x production and reduction are affected,and the flame height is stretched to improve the uniformity of temperature distribution in the furnace.Air divided into three parts is better than that of two parts.The optimal condition of air fractional combustion: primary air accounts for 50% of the total air volume,the position parameter of secondary air inlet is 0.5,the proportion of tertiary air to secondary air volume is 7:3,and the position parameter of tertiary air inlet is0.84.Under the conditions of optimal operating conditions and flue gas recirculation technology,the combination of air staged combustion and flue gas recirculation technology is realized.Adjusting the feeding position and circulating ratio of recirculated flue gas,the combination of staged combustion and flue gas recirculation can increase the velocity of flue gas and dilute the concentration of O2 in the furnace which can suppress the combustion intensity and reduce the temperature in the furnace,and thereby reduce the production amount of NO_x.When the locationparameter of the inlet of the recirculated flue gas is 0.33,and the recirculation rate is2%,NO_x emission is lower than 64 ppm,which meets the national standard requirements.Finally,basis on the air staged combustion,an innovative idea of using coke oven gas as a secondary fuel to achieve staged combustion of fuel to reduce NO_x emissions was proposed.The simulation results show that by adding fuel staged combustion technology basis on air staged combustion,not only the temperature field disturbance in the combustion chamber is small,but also the intermediate substances such as CH3 and CH2 generated by incomplete combustion of secondary fuel can greatly reduce and decompose the nitrogen oxides generated in the vertical fire passage.When the ratio of secondary fuel and main fuel is 0.01 and the NO_x emission at the outlet is less than 30 ppm,the NO_x reduction is up to 95%.This research work has certain reference value and practical significance to study the mechanism of NO_x generation and reduction in coke oven and optimization of coke oven structure.It can promote the application and development of low nitrogen combustion technology in coke oven.