Experimental And Numerical Study Of Propane MILD Combustion

With the demand of high efficiency and clean combustion technology in industry,and the advantages of high combustion thermal efficiency and low pollutant emission of MILD combustion,this paper uses propane as the fuel to research the influence mechanism of air preheating temperature,air jet velocity and excessive air coefficient on the mild combustion.An experiment system of 20 kW was designed,manufactured and built,which realized the stable mild combustion of propane under various working conditions.Experiment results present that air preheating can increase the average temperature of the furnace and reduce the temperature fluctuation.The heat of the air and the increased jet velocity caused by preheating together cause the temperature rise in the furnace,and the former has a greater influence.When the air is preheated while its speed is constant,the peak position of oxygen concentration in the furnace will advance.The oxygen concentration of the whole furnace is between 0.4% and 5%.Preheating air will increase NOx emission in flue gas at the end of furnace.In most cases,the CO concentration of the fuel gas emission is 0,and in few cases only 3ppm.Increasing the velocity of air jet can increase the average temperature of furnace and reduce the temperature fluctuation.The high jet velocity makes the oxygen concentration range in the furnace more concentrated,and the oxygen concentration at the end of the furnace is also higher.After preheating the air,the influence of jet velocity on NOx generation is more obvious,and with high jet velocity,NOx generation is also high.There is a strong correlation between the effect of jet velocity on CO concentration and oxygen concentration in the furnace.Increasing the excessive air coefficient α will reduce the average temperature and increase the temperature fluctuation in the furnace,and increase the oxygen concentration in the furnace.With the increase of excessive air coefficient,the NOx concentration in exhaust gas increases linearly.The increase of α results in the increase of NOx production in all parts of the furnace.Increasing α has a significant effect on reducing the local CO peak value in the furnace.Numerical simulations of air preheating temperature with Fluent software were conducted.The results show that there is a low temperature area near the entrance of gas and air jet.In addition,the simulation value of temperature field is in good agreement with the experimental value.Under different preheating air temperature,the prediction of NOx generation by simulation is higher than the experimental value,but its trend is consistent with the experimental value.The phenomenon of high concentration CO at the end of the furnace in the simulation is consistent with the experiment.