Numerical Simulation Of Low NO_x Burner In High Temperature Furnace

With the development of economy in our country,the standard for the emission of industrial furnaces gaseous pollution have been improved.The huge amount of industrial furnace in China caused a large amount of nitrogen oxides.Therefore,the development of low NOx combustion technology in industrial furnace is very important.The investigation found that the coke oven gas used in the heating furnace of iron and steel enterprises contains ammonia,which has a certain influence on the nitrogen oxide produced by its burner.Therefore,it is of great significance to study the low NOx combustion technology of industrial gas under the condition of ammonia.In this paper,chemical reaction kinetics software and FLUENT were used to study the causes of NOx and the structure optimization of low NOx burner in the process of coke oven gas mixed with ammonia combustion.The combustion in the constant temperature of coke oven gas and coke oven gas mixed with ammonia in the air were simulated through chemical reaction kinetics software.It is found that from the aspect of chemical reaction kinetics,the primary reaction affecting NO generation in the combustion process mainly included 179th,180th,189th,208th and 214th elementary reaction.There was little NOx generation at the outlet of the combustion process of coke oven gas under 1000-1300℃,and with the increase of the temperature and the ratio of primary and secondary air,the outlet NOx concentration increased.When the coke oven gas was mixed with ammonia,the NOx concentration at the outlet of the range of 1000-1500℃ increased first and then decreased with the increase of the temperature and the ratio of the primary and secondary air.At the range of 1500-1700℃,the NOx concentration at the outlet increased with the increase of the temperature and the ratio of the primary and secondary air.For the coke oven gas mixed with ammonia burned at constant temperature in O2+Ar atmosphere,with the increase of temperature and the ratio of primary air and secondary air,the NOx at the outlet of the range of 1000-1500℃ increased first and then decreased.There was no NOx at the range of 1500-1700℃.Therefore,no NOx was produced when NH3 burned at high temperature.Coke oven gas mixed with ammonia was suitable for combustion at the temperature range from 1400 to 1500℃ and the ratio of primary air and secondary air was about 7:3.According to the sensitivity analysis of NO and N2,the 38th elementary reaction promoted NO formation and inhibited N2 formation,and the 35th elementary reaction promoted N2 formation and inhibited NO formation.A simplified mechanism with 56 step elementary reaction and 19 components was obtained by chemical reaction kinetics software.FLUENT software was used to simulate and compare the new burner structure before and after the structural improvement.After the improved structure,the high temperature zone was reduced,the temperature distribution was relatively uniform,the residence time of flue gas was shortened,and the NOx concentration at the outlet was about 18.1ppm,which was about 30ppm less than that before the structural improvement.The results showed that with the increase of the amount of mixed ammonia,the NOx concentration at the outlet increased,which was consistent with the chemical reaction kinetics software simulation results,and the accuracy of the simulation results was verified by experiments.