Research On Low Nitrogen Combustion Technology Of Layer Combustion Boiler Based On Semi-char Reduction And Forced Partition

A large number of layer-fired coal boilers are used for industrial energy consumption and heating in northern regions,and the largest single unit has reached140 MW.Economical and efficient nitrogen oxide control technology for layer-fired coal-fired boilers is an important technical direction for clean and efficient use of coal.Due to the use of wide sieving particle size fuel and burn-out enhancement measures under the condition of no ash shell,the design excess air coefficient of the layer-fired boiler is generally greater than 1.4,which may be higher in actual operation.How to achieve nitrogen oxide control without reducing combustion efficiency in combustion equipment where the total amount of air exceeds 40%has become the key and difficult point in the low-nitrogen combustion technology of layer-fired boilers.In view of the typical sectional combustion characteristics of the layer-fired combustion process,the grate wind speed in the design of the combustion equipment is generally limited to the 3mm particle size and the specific characteristics of the particle coal crushing during the combustion process.This dissertation proposes a low-nitrogen combustion technology for a layer-fired boiler combining semi-coke reduction and zoning enhancement.Laboratory experiments,numerical simulations,and industrial test verifications were used to study the generation characteristics of nitrogen oxides in stratified semi-coke combustion,the characteristics of semi-coke reduction of nitrogen oxides,and the use of partition screens to achieve zoning enhancement low-nitrogen combustion technology in the furnace.Firstly,the influence of reaction temperature,oxygen concentration,coke particle size,seim-coke mass and HCl concentration on the release of nitrogen oxides was studied by using the fixed bed test.Considering that the particle size of the semi-coke during the stratified combustion process is significantly larger than that of the pulverized coal combustion,the particle size of the semi-coke in the experiment is selected to be 0.1-0.5 mm;considering that the position of the semi-coke cycle reaction of the layer-fired boiler is generally in front of the furnace outlet window and above the front and rear furnace arch,the influence characteristics in the temperature range of 800-950℃was emphatically investigated.The results show that the increase in oxygen concentration increases the peak concentration and total amount of NOx,and the increase in reaction temperature increases the peak concentration,but the total amount of NO production decreases,the particle size of coal char increases,and HCl gas will reduce the peak and total NOx concentration.Secondly,based on the fixed bed test and microwave radiation enhanced reduction test,the basic characteristics of reducing nitrogen oxides by coal char is analyzed,the mechanism and degree of influence of factors such as reaction temperature,oxygen concentration,particle size of semi-coke,the mass of semi-coke and HCl addition or not on the reduction process are obtained.The mechanism and degree of influence of the process clarify the strengthening effect of microwave radiation on the reduction effect.The research results show that the increase in temperature is conducive to NO reduction,and the increase in oxygen concentration reduces the NO reduction effect of semi-coke.HCl gas promotes the reduction of NO by semi-coke,but inhibits the reduction effect of N₂O.In an oxidizing atmosphere,the NO reduction capacity per unit mass of coal char increases with the increase of coal char particle size.Based on this conclusion,the semi-coke cutting particle size in engineering applications can be optimized.On the basis of the aforementioned research,the coal seam combustion process is decomposed into two parts:fire bed combustion and furnace combustion,and the“FLIC”and“FLUENT”software are combined.Numerical simulation studies the influence of enhanced zoning technology on boiler nitrogen oxide emissions when the layout angle of the deflector screen,boiler load and coal type change,and an engineering simulation calculation method of a 65 MW reciprocating grate boilers and a 90 MW reciprocating grate boilers that can optimize and guide engineering design is obtained.Finally,industrial demonstration assessments were conducted on four 29 MW chain grate boilers,two 65 MW reciprocating grate boilers,and one 90MW reciprocating grate boiler.The test results of the demonstration project show that the semi-coke cycle can reduce the NO concentration by more than 13%,the deflector screen can reduce the NO concentration by 34-40%,and the combination of the two can reduce the NO concentration by more than 50%,and the lowest average NOx concentration is less than 175 mg/m³.The technology developed in this research can be used as a pre-source control technology for ultra-low emissions of layer-fired boilers,significantly reducing the original NOx emissions.