Numerical Simulation On Combustion Optimization For A300MW Pulverized Coal-fired Boiler Based On SOFA

Coal is the most important primary energy in China, but the burning of coal causes great damage to the environment, and nitrogen oxides (NOx) which produced from coal burning is a major source of air pollution in China. The released nitrogen oxides may lead to acid rain, photochemical smog and other pollution, also seriously endanger human health.Tangentially fired boiler is one of the world’s most commonly used types of power plant boiler due to its’good burning adaptability and evenly mixture of air and pulverized coal. Since the characteristics of tangentially fired boiler are adapted with the wide distribution of coal, it is also the most widely used and the most mature combustion method in China. With more attention is being paid to environmental problems and pollutant emissions requirements becomes increasingly strict, China has been strengthen the pollutant emission standards of power plants. Reducing NOx emissions has become an urgent issue for the development of power industry.This thesis takes the present application status of a300MW tangentially coal-fired boiler of Jiaxing Power Plant as the research background, applying air-staged combustion technology and to get furnace temperature fields and chemical components distributions through numerical methods in order to study the combustion process of pulverized coal in the furnace and search the optimal conditions for the low NOx emissions in different combustion conditions.First of all, the current operating condition of this300MW tangentially coal-fired boiler is simulated after introducing the basic ideas of numerical calculation and the method of modeling and meshing of the boiler. It turns out that the calculated results flow field, temperature field and material components’distribution in the furnace are almost in accordance with measured values. This means that the selected model is correct and the numerical results are reliable.Then, the boiler is modified with air-staged combustion technology and simulated to determine the best location, best air volume and best nozzle arrangement of separate over fire air (SOFA). This thesis researches the combustion conditions of furnace with different SOFA position (SOFA nozzle is high from the top primary air nozzle by3m,6m or9m), different SOFA distribution ratio (SOFA nozzle’s air distribution ratio vary among15%,20%,25%and30%), and different air-staged forms of SOFA respectively to find the influence of combustion and NOx emission of the boiler. The simulation results show the flow field, temperature distribution, each species concentration as well as NOx emission, providing some useful reference to understand the combustion process and its rules of tangentially fired pulverized coal boiler furnace and improving the design, operation and transformation level of the same type of boiler.