Study On Flow And Nitrogen Oxide Emission Reduction Characteristics In A 350MW Pulverized Coal Boiler

With the emphasis on environmental protection in China,the nitrogen oxide emission standards of coal-fired power plants are becoming increasingly strict,and many power plant boilers must be retrofitted with low nitrogen.In view of the expensive operation and maintenance costs of flue gas denitration systems,most power plants choose low-nitrogen combustion in the furnace.The low-nitrogen combustion reform is mainly carried out in two aspects:burner reform and air-fuel staged combustion reform.In this paper,a 350MW four-corner round pulverized coal furnace is taken as the research object,and the characteristics of low-nitrogen combustion technology in the furnace are numerically analyzed.Based on this,the boiler burner reformation and the fuel and air classification system are reformed.The thesis first briefly introduces the development and classification of boiler denitration technology,then uses 3D software to reasonably simplify and model the boiler geometry,and divides the appropriate grid according to the characteristics of the boiler,and then uses Ansys Fluent software to select reasonable numerical calculations for the boiler The model uses the Euler method to calculate the gas,the Lagrangian method to track the pulverized coal particles,the standard k-εmodel deals with turbulence,and the Arrhenius formula calculates the chemical reaction,pulverized coal volatilization and combustion models are two-step competitive reaction and multi-surface reaction,respectively.Then simulates and analyzes the velocity vector field,temperature field,concentration field of each component and the trajectory of pulverized coal particles in the furnace,which provides theoretical basis and technical support for boiler reformation.The simulation results show that when the furnace temperature is low and the pulverized coal particle residence time is moderate,the NOx concentration decreases.The low secondary air rate in the main combustion zone can reduce the combustion temperature and increase the combustion height.The higher SOFA air rate can reduce the outlet smoke temperature,reducing the temperature deviation of the furnace outlet,but at the same time will reduce the coal burnout rate and combustion efficiency.Therefore,after reforming the boiler pulverized coal burner and the secondary air and nozzle system,through experiments to determine the appropriate ratio of secondary air and SOFA air,so that it can meet the performance requirements of equipment such as boiler SCR,superheater and reheater.Boiler test experiment the working performance of boilers of different coal types at 350MW,263MW,and 210MW.The boiler efficiency is between 94%and 95%,which is higher than the guaranteed value of 93%.Below the guaranteed value of 260 mg/m~3,the SCR inlet NOx is between213.4 and 254.4 mg/m~3,and the smoke temperature is between 329.2℃～365.1℃,which is within the guaranteed value of 320～380℃.