| Biomass energy is a kind of renewable energy,and its development potential is huge.The layer burner has strong adaptability and is widely used in the field of biomass combustion.The nitrogen oxide emission standards of biomass layer burners are becoming stricter.The performance of single NOx control technology continues to be improved.Due to the excessive pursuit of pollutants and ultra-low emissions,the problems of corrosion,clogging and ammonia slip of existing environmental protection equipment are intensified.Constantly innovating and developing new denitrification technologies,solving existing denitrification technical problems,and improving the efficiency of denitrification are of great significance to the reduction of NOx emissions in China.In this paper,a complete numerical simulation of a 500t/d biomass layer furnace is carried out.Firstly,the combustion in the solid space of the bed is calculated by the FLIC software.The radiation temperature and other boundary conditions are preset to obtain the temperature,velocity and composition distribution of the gas in the overflow bed,and this is used as the entrance of the combustion gas space combustion calculation condition.Then use FLUENT to calculate the gas velocity field,temperature field,concentration of each component and pollutant emission of the entire boiler,and then use the calculated gas phase space and the radiation temperature of the furnace wall to the bed as the entrance condition for bed calculation,so that the solid phase space of the bed and the gas phase space of the furnace are coupled to complete the special delivery process of matter and energy.In terms of NOx,the NOx calculation module is added to the bed solid-phase space simulation,and the NOx post-processing model is used in the furnace gas-phase space simulation.The two interact with each other.Through the above coupling method,the basic working conditions are calculated in this paper,the effect of primary air on bed combustion is studied,the combustion status of the furnace and the NOx emission characteristics are described,and then whether it is suitable for over-burning is explored.The effects of different flue gas recirculation rates and different SNCR parameters on the combustion characteristics and NOx emissions of the boiler are discussed.The proposed results show that:in terms of primary air distribution in the bed,the design air distribution method in this paper can meet the air volume required for each combustion process compared to the forward,average,and rearward air distribution methods,and at the same time improve the utilization of the grate combustion area Rate and combustion efficiency;in the gas-phase space combustion under basic working conditions,the temperature distribution above the grate is consistent with the calculation results of the Flic bed,indicating the correctness of the bed furnace model coupling,the final NOx concentration of the boiler outlet is calculated to be 258.2mg/Nm3;in the burnout wind,the burnout wind is injected to make the combustion area move up,the outlet temperature is as high as 1417K,and the outlet NOx concentration is as high as 338.7mg/Nm3,It shows that this layer of burner is not suitable for igniting exhaust air;in the numerical simulation of flue gas recirculation,as the flue gas recirculation rate increases,the flue gas outlet temperature and outlet NO concentration both decrease,and the flue gas recirculation rate is selected as 20%is more reasonable,the NOx concentration of the boiler outlet is 232.1mg/Nm3;in terms of SNCR denitration technology,the NOx concentration at the boiler outlet by single SNCR technology is 188.3mg/Nm3,ammonia slip is 3.5mg/Nm3.SNCR denitration technology is added on the basis of 20%flue gas recycling conditions,and the simulated NOx concentration at the outlet will reach 163.1 mg/Nm3,ammonia slip is 3.5mg/Nm3,denitration efficiency is 36.8%,which proves the feasibility of combined denitration technology;in terms of SNCR reducing agent nozzle parameters,improper matching of injection velocity and particle size will result in too large or too small injection range of urea solution;in terms of NSR,As the NSR increases,the denitration efficiency and ammonia slip will increase.NSR selection 1.5 can maintain a low ammonia slip while maintaining a high denitration rate.This study is helpful to fill the blank of biomass combustion furnace combined NOx control technology,which has certain guiding significance for reducing NOx emission of boiler. |
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