Numerical Simulation Of The Combustion And NOx Formation In A 300MWe Down-fired Boiler With Swirl Burner

In China, the abundant anthracite reserves led to a capacity explosion in power plant. Down-fired boiler is the main furnace burning anthracite, owing to good fire conditions, longer flame journeys, fuel and air classification. At present, so many urgent problems such as poor combustion and high NOx emissions needed to be solved in power plant. In recent years, chinese scholars study the boiler by various experimental methods, and owing to the limitations of experiment, a novel research technique "computer simulation" is widely used.In this paper, the comprehensive numerical simulation of combustion process in a 300MWe down-fired boiler with swirling burner in a power plant was studied by the CFD software—FLUENT. I calculated the combustion process with different ratio of secondary air quantity and tertiary air quantity, different vane angle of the outer and inner secondary air in boiler under full load operation, comtrasted the flow field, temperature, the distribution of gas ingredients and pollution in furnace, compared the temperature, the component concentration variation , NOx emissions and the size of carbon of fly ash along the furnace height direction,then analysed the combustion characteristics in furnace.Comparing the data from thermal industrial test under actual operation parameters with the result from simulation under the same parameter settings, the error bewteen simulation and experiment is within 20%, validate the model selection and simulation method. According to the numerical simulation results, it can be obtained that the ratio of secondary air and staged air has no effect on the ignition, increasing the air ratio appropriately contribute to higher furnace temperature and lower flame center, but the changes are small, the amount reducing of staged air cause the bad combustion. The impact about vane angle of the outer and inner secondary air to the combustion process is consistent, but the degree of the outer secondary air is more bigger. Increasing the vane angle appropriatly contribute to advance ignition and flame expansion, it contribute to higher furnace temperature and higher flame center, the effect of staged combustion is bad.Considering combustion state, slagging risk, NOx emissions, carbon content of fly ash and other factors, I recommend the parameters of the power station boiler in actual operations: the ratio of secondary air and staged air is between 6:1 and 7:1, the vane angle of inner secondary air is about 45°, the vane angle of outer secondary air is between 25°and 35°.