The Investigation On Non-Switching High Temperature Air Combustion Technology

A set of non-switching high temperature air combustion system was designed in this paper. It was mainly composed of the flue gas auto-circulation burner, furnace body as well as shell and tube heat exchanger. Numerical simulation and experiment were used to investigate temperature distribution, NOx emission and concentration distribution of flue gas auto-circulation furnace.There was a small combustion zone between fuel nozzle and annular air nozzle at the head of burner which played a positive role in the ignition and flame retention. This zone could gradually decrease with fuel nozzle extending distance and fuel preheating temperature increasing, while increase with increasing distance between fuel nozzle and air nozzle. When fuel nozzle extended into10mm there was a maximum high temperature zone and average temperature would rise. However if the extending distance exceeded10mm, high temperature zone in the furnace would gradually decrease and temperature distribution would become uneven. With the furnace length increasing, the average temperature and maximum temperature would also increase, smaller temperature difference, more uniform temperature distribution in the furnace. When fuel preheating temperature was400K, there was a minimum high temperature zone and lowest temperature in the furnace. When it was over400K, high temperature zone and average temperature in the furnace would gradually increase. The average temperature would increase when distance between fuel nozzle and air nozzle d was30mm. However the average temperature would decrease when d was40mm. The maximum temperature in the furnace would increase linearly with increasing distance d. Thermal NOx was the main pollution in the furnace, and the trend of NOx distribution was similar to the average temperature distribution. We could conclude that fuel combustion needed three zones:pyrolysis zone, transition zone and combustion zone through concentration analysis.In this paper an experimental system of high temperature air combustion was established. Effect of air preheated temperature and excess air coefficient on combustion was analyzed through the experiment. At different air preheated temperature, temperature distribution of each measuring point in the furnace had consistent temperature distribution trend. With air preheated temperature increasing, temperature of each measuring point would rise and the flame would gradually become irregular and flame volume would also gradually become larger. With temperature rising, thermal NOx increased and CO emission would gradually reduce and combustion was improved. At different excess air coefficient, temperature distribution of each measuring point in the furnace kept consistent. With excess air coefficient increasing, temperature of each measuring point would gradually rise, and flame color would gradually change from blue to yellow. Meanwhile flame volume would become smaller and the flame became regular. The oxygen concentration of diverging mouth and NO concentration of outlet increased as the excess air coefficient increased. It could be concluded that experiment and simulation were basically consistent through numerical simulation of the experimental model. Combustion stability was also analyzed in this paper and a curve was drawn which air preheated temperature as the abscissa and excess air coefficient as the ordinate. Upper right area of the curve was the stable combustion zone and the lower left area of the curve was the non-combustion zone.