Influence Of Annular Separation Secondary Air Of Burner On Flow And Combustion Characteristics Of 29MW Pulverized Coal Fired Industrial Boiler

Coal occupies a dominant position in China’s energy structure.However,burning coal produces NOx and other pollutants,causing environmental problems such as acid rain and photochemical pollution.In response to the problem of excessively high pollutant emissions from coal-fired boilers,Harbin Institute of Technology has proposed a new type of low-nitrogen pulverized coal combustion technology.Its unique separation secondary air layout structure can achieve radial air combustion in the furnace and can effectively control the NOx emission of the boiler.However,there is still little research on the layout of the separation secondary air.In this paper,Fluent software is used to numerically simulate a 29 MW industrial pulverized coal furnace using a new type of high-efficiency and low-nitrogen pulverized coal combustion technology,and the rationality of the model is verified through industrial experiments.This article mainly aims at four cases: the number and position of the nozzles are different when the single-layer arrangement of the separated secondary air nozzles is different,the nozzle positions are different when the two-layer staggered arrangement,and the air ratio of the inner and outer two layers is different when the two-layer staggered arrangement.And it studied the effects of these four conditions on boiler flow,combustion,and NOx generation characteristics.When the single-layer arrangement of the secondary air nozzles is separated,the simulation results show that the circumferential diameter d of the nozzles and the number of nozzles n have a great influence on the furnace.The increase of the circumferential diameter d of the separation secondary air nozzle will increase the area of the high-temperature region above 1300 k in the furnace and reduce NOx emissions.When the d increases from 1.15 D to 2.14 D,the nitrogen oxide content at the furnace outlet decreases by 8.47mg/m³（O₂=9%）.However,if the value of d is too large,the high temperature area is too close to the water wall,which may cause slagging and high temperature corrosion of the water wall.For comprehensive consideration,when 16 nozzles are arranged in a single layer,it is recommended to set the diameter of the nozzle to be between 1.57 D and 1.71 D.The increase in the number n of secondary air separation nozzles is beneficial to control the formation of nitrogen oxides.n changes from 16 to 32,the nitrogen oxide content at the outlet of the furnace decreases by 12%（O₂=9%）,and the peak temperature will also drop by 3m,which is easy to damage the water wall at the bottom of the furnace.It is recommended that when the nozzle is arranged at 1.57 D,the number of nozzles is 24 or 28.When the two layers of nozzles are staggered,the separated secondary air is mixed into the precombustion chamber jet in two stages,which is helpful to reduce NOx emissions.Compared with 16 single-layer arrangements,the 32 nozzles in the two-layer staggered arrangement have a nitrogen oxide drop of 33.12 mg/m³（O₂=9%）.Compared with the 32 nozzles in the single-layer arrangement,the location distribution in the high-temperature area is more reasonable.When the circumferential diameter of the separation secondary air nozzle is different,the structure with a larger d value is more beneficial to reduce the concentration of nitrogen oxides at the outlet of the furnace,but the circumferential diameter of the nozzle is too large,which is easy to cause damage to the water cooling wall.When d₁=1.57 D and d₂=1.86 D,the nitrogen oxide concentration at the furnace outlet is 184.3mg/m³（O₂=9%）,which is the most recommended choice.When the air rates of the inner and outer layers of the separated secondary air are different,the air mixing in the furnace is more uniform when the inner and outer layers are 1:1,the area of the high temperature area is relatively largest,and the nitrogen oxide content at the furnace outlet is the lowest.Taking all factors into consideration,it is recommended that the split secondary air nozzles be arranged in two layers staggered,with the inner layer nozzles arranged at 1.57 D and the outer layer nozzles arranged at 1.86 D,keeping the air ratio between the inner and outer layers at 1:1.