Research On Low NOx Combustion Based On Air Humidification For Gas Boiler

With the stable development of China’s economy,energy demand is growing,the situation of energy conservation and emission reduction remains severe.The implementation of the"coal-to-gas"policy in northern China has realized the large-scale application of gas boilers,but some unmodified gas boilers still have a nitrogen oxide concentration of up to 150mg/m³in the exhaust gas.In order to respond to my country’s atmosphere pollution control policies to reduce nitrogen oxide emissions from gas boilers are urgently needed.In order to study the influence of air humidification technology on low-nitrogen combustion in the furnace of gas boilers,based on the principle that combustion-supporting air humidification can reduce the combustion temperature and the concentration of CH radicals and other components,from the perspective of experiment and simulation,this paper experimentally investigates the humidity of different combustion-supporting air.The influence of the amount of fuel on the exhaust gas temperature and pollutant emissions of gas boilers,and mainly adopts numerical simulation methods to change the excess air coefficient,boiler load,combustion air preheating temperature and humidification under conventional air atmosphere.The combustion characteristics of the fuel and the concentration of major pollutants in the furnace are analyzed.This paper experimentally studies the effect of boiler exhaust gas and nitrogen oxide emission reduction under different combustion air moisture content.The results show that with the increase of the combustion air moisture content,the gas boiler exhaust gas temperature fluctuates and rises when the combustion air is humidified to 79.04g/kg_{dry air},the average nitrogen oxide concentration of gas boiler exhaust flue gas can be reduced to 38.05 mg/m³,and the nitrogen reduction rate is as high as 71.96%.This paper analyzes the change rule of the NOx concentration at the outlet of the boiler with the operating time under different combustion air moisture content.When the combustion air is humidified to 57.30g/kg_{dry air},the average nitrogen value at the boiler outlet is the most stable with the running time.In this paper,numerical simulation studies the changes of combustion characteristics in the furnace under different excess air coefficients and boiler loads.The maximum combustion temperature in the furnace shows a trend of first increasing and then decreasing with the increase of excess air coefficient,and the average nitrogen oxide emission concentration and the average carbon monoxide emission concentration decrease accordingly.The intensity of the combustion flame is weakened.When the boiler load is reduced by 10%,the nitrogen oxide emission concentration can be reduced by about 6%,and the maximum temperature of the furnace combustion and the length of the combustion flame are also shortened.Based on the experimental results,this paper conducts a numerical simulation to analyze the influence of the preheating temperature and moisture content of the combustion air on the low-nitrogen combustion characteristics of gas boilers.With the increase of the combustion air preheating temperature,the maximum combustion temperature and the average nitrogen oxide emission concentration of the furnace also increase.When the combustion air preheating temperature is 48℃,the maximum combustion temperature of the furnace is 2218K,and the average nitrogen oxides emission concentration is as high as 190.03 mg/m³.As the moisture content of the combustion air increases,the combustion rate,the average temperature of the furnace outlet and the average carbon monoxide emission concentration increase,and the maximum furnace combustion temperature and the average nitrogen oxide emission concentration decrease accordingly.Compared with the average nitrogen oxide emission concentration when the combustion air preheating temperature is 48℃,the nitrogen reduction rate when the combustion air is humidified to 79.04 g/kg_{dry air} can reach 75.64%.The fluctuation of the average carbon monoxide emission concentration can be used as a reference standard for boiler combustion stability.Combining the results of experiment and numerical simulation,the limit value of combustion air humidification can be designed to 57.30 mg/m³.This research can provide a reference for the application of air humidification technology in gas boilers.