Numerical Simulation Of Combustion Characteristic And NO_x Emission Reduction For Pulverized Coal Boiler

As a leading producer of coal, the thermal power takes of a pivotal position in China either today or in the foreseeable future. The equipped capacitor of power plant has to argument with the development of economy, the rapid increase of population and power consumption per hand, environment pollution from thermal power plant will increase,where the NO_X emissions has had a huge impact on the environment, how to improve boiler efficiency and reduce emissions of NO_X are serious problems of thermal power enterprises have to consider.In this paper, taking a 660 MW coal-fired boiler of one power plant for study, the grid model of the boiler furnace established by GAMBIT and the simulation of boiler combustion uses FLUENT. Models select as follows, k-e two equations model is selected for gas turbulence model, P1 model is selected for radiation model, nonpremixed combustion model is selected for combustion model, stochastic trajectory model is selected for particulate phase tracking, power / diffusion-limited model is selected for coke combustion model, these models are used for the numerical simulation of design condition. The study around high efficiency and low emissions, predicts the furnace temperature, gas composition of each substance and the generation amount and the concentration distribution of NO, on this basis, the optimum combustion program is determined and compared to the actual operation of power plant, verified the validity of the simulation.This paper is based on the mainly NO_X control theory, under the following factors of boiler combustion to simulation. 1)At a certain air rate of per layer, control the excess air ratio of furnace in 1.10, 1.15, 1.20 and 1.25, comparing the results of simulation and find the better excess air ratio for the boiler. 2)Under a certain excess air ratio, control the OFA rate of furnace in 10%, 20% and 30%, comparing the results of simulation and find the better OFA rate for the boiler.The simulation results showed that the optimal excess air ratio is 1.15 and the optimal OFA rate is 20%, when the excess air ratio is increased, the CO concentration in outlet is decreased, but the NO concentration is increased, and the shortage of oxygen leads to low temperature in primary combustion zone, and when the OFA rate is 20%, the NO emissions are controlled in 298.82mg/m3, when the OFA rate is reduced to 10%, the NO emissions increased to 332.76mg/m3, when the OFA rate is increased to 30%, the burnout rate is decreased and the boiler efficiency is reduced.Through the analysis and comparison of the results, obtained optimum combustion program, and can play a guiding role in the operation of this boiler.