| At present,the non-standard emission of nitrogen oxide concentration in the flue gas of most gas boilers and the high temperature flue gas contain sensible heat and a large amount of latent heat of vaporization.Therefore,the study of gas boilers with low temperature and low nitrogen oxide flue gas emission heating system is of great significance to improve boiler efficiency and reduce environmental pollution.In the flue gas waste heat recovery technology:the heat exchanger type flue gas waste heat recovery technology cannot perform deep condensation recovery of the high temperature flue gas waste heat,while the absorption heat pump is not suitable for the flue gas waste heat recovery system of small gas boiler.The compression heat pump is selected to recover the waste heat of the high-temperature flue gas in the system process.In low-nitrogen combustion technology,air humidified combustion can reduce the concentration of nitrogen oxides in the flue gas after boiler combustion.Therefore,by establishing a model of flue gas waste heat recovery system with compression heat pump and air humidification combustion technology,this paper analyzes the nitrogen reduction effect under air humidification and flue gas recirculation combustion mode and the main factors affecting the waste heat recovery effect of the system.First,through the Gibbs reactor model to simulate the combustion process under gas boiler air humidification and flue gas recirculation,combustion air humidification and flue gas recirculation will reduce the boiler combustion temperature and NO content in the combustion product,thereby improving the nitrogen reduction rate.When the combustion air is not humidified,the combustion temperature of the gas boiler has a maximum of 1971°C when the excess air coefficient is 1.15.When humidifying,the increase in moisture content will reduce the combustion temperature of the boiler,when the excess air coefficient is 1.15,the air humidity content is 0g/kg dry airand 150g/kg dry air,the combustion temperature difference can reach 307°C.The increase of air moisture content and excess air coefficient will reduce the CO content in the product.For the H2 content of the intermediate product generated by combustion,when the excess air coefficient is lower than 1.1,the H2 content in the product increases with the increase of air moisture content,and the H2 content gradually decreases with the increase of air moisture content after the excess air coefficient is greater than 1.1.Combustion air humidification and an appropriate excess air coefficient facilitate the full reaction in the furnace.At the same time,when the flue gas recirculation rate is 15%,the nitrogen reduction rate can reach more than 70%,and the increase of flue gas recirculation will increase the CO and H2content in the flue gas.Secondly,when the humidified water volume is the same as 200L/h,the heat gain of humidified water under the simulated working conditions is slightly higher than the experimental test results.Under this working condition,the moisture content of the combustion air was 32.25g/kg dry air and 32.5g/kg dry air,the nitrogen reduction rate was 24.1%and 35.2%,and the COP difference of heat pump was 2.67.Third,the increase in combustion air in the simulation system process can improve the heat supply of the system.When the high temperature flue gas temperature is 150°C and the excess air coefficient is 1.05,the system heat supply is 57.21k W,the waste heat recovery efficiency is 21.3%,and the boiler efficiency can reach 103.5%.The amount of humidification water in the humidification tower is greater than 200L/h,which no longer affects the moisture content of the combustion air.At the same time,the increase in exhaust gas temperature does not affect the heat supply of the boiler in the simulation process,but it will reduce the heat supply of the system.At the exhaust gas temperature of 25°C and 40°C,the heat supply of the system is 56.74k W and 55.82k W,respectively. |
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