Numerical Simulation Of NO Reduction By Natural Gas Reburnning

Developing the technology of clean combustion of coal and solving the NOx pollution which come from coal-fired power generation is one of the most concerned issues in current energy field. Brought out in the 1980s, natural gas reburning technology is a fuel-staged combustion technology which can reduce NOx emissions effectively.Because of the unique technical and ecnomical advantages in reducing NO emissions, natural gas reburning technology has been extensively studied by many scholars and researchers of different countries.Based on inducing,conclueding and analysising the previous work, the paper takes a 35t/h tangential fired boiler as study object,conducting full-scale three-dimensional numerical simulation on the process of natural gas reburning using Fluent software. The major contents of this paper are as follows:(1) Establish mathematic models of the furnace combstion. The gas-phase turbulent flow was described by Realizable k-εturbulence model, component transport model was employed to describe the process of gas-phase combustion, the stoichastic tracking model was applied to describe the discrete phase flow, the devolatilization was simulated by two competing reaction model, char combustion was described by diffusion-kinetics model, radiation heat transfer was depicted by P-1 model, the post-treatment method was employed to calculate the generation and reduction of NO.(2) Based on the above model, the three-dimensional simulation on the process of natural gas reburning was performed. The results give out the distribution of velocity,temperature,reaction and the concetration of components and NO in furnace. In this base, the paper analyzed the effects of the reburning zone length, the position of fuel nozzle, excess air coefficient in reburning zone, natural gas amount on the output NO concentration. The simulation results conclued:the increase of reburning zone length is beneficial to reduce NO emission but against the combustion of primary combustion zone,considered comprehensively, the best value is 800mm; the position of natural gas is not suitable to be too high or too low, the best position is 800mm; excess air coefficient in reburning zone has an optimum range 0.8～0.9, in view of the study conditions in this paper, the best value is 0.9; natural gas amount has an important influence on NO emission, the optimum range is 15%～20%.The numerical simulation study of this paper gives out the furnace combustion characteristics of natural gas reburning condition and analyzes the effects of variable parameters on output NO concentration, provides reference for actual engineering application.