Numerical Simulation On Low NO_x Combustion Of 600MW W-shape Flame Boiler

The worldwide environment pollution and energy use problem has been a serious threat to human survival and development, thus the controlling of NOx emissions becomes an important subject of power industry development. The coal-fired units can run with high efficiency and low NOx emission by optimizing the operation. Therefore, the study of the mechanism of NOx production in coal combustion and its control method is of great significance. In order to solve the problems occurring in a 600 MW supercritical W-shape flame boiler of certain power Plant, such as high NOx emissions, numerical simulation on the combustion process of the boiler is conducted with the software of Fluent in researching the effect of combustion and NOx emission on the different position of single-tier OFA nozzles, different OFA ratio of double-tier, different angle of single-tier OFA nozzles, primary air nozzles switching position with exhaust gas nozzles,primary air nozzles switching position with exhaust gas nozzles and adding OFA, and primary air nozzles switching position with exhaust gas nozzles and adding OFA at regular intervals, which provides a basis for a reference of W flame boiler reduce NOx emissions.First of all, mathematical model was built on the combustion process of furnace, including equations of mass conservation, momentum conservation and energy conservation, turbulent flow model, gas and solid two phase flow model, volatile pyrolysis and combustion model, coke combustion model, radiation model and NOx model. Secondly, the boiler structure was introduced and physical model was built, at the same time, boundary condition of inlet, outlet and wall also were set. Finally, the influence of OFA nozzles position on NOx emissions is researched and the optimum position is set 2m, which can obviously reduce NOx emissions by 17.6% compared with the original operating condition. When the OFA ratio of double-tier is 1:1.67, the operating condition is more advantageous for furnace combustion and the NOx emissions is reduced by 10.7% compared with the operating condition of single-tier OFA nozzles. Meanwhile, the experiment on different angle of double-tier OFA nozzles has been conducted to prove that the OFA angle f 10° is optimum to reduce NOx emissions. Furthermore,numerical simulation is performed on furnace combustion condition of primary air nozzles switching position with exhaust gas nozzles, primary air nozzles switching position with exhaust gas nozzles and adding OFA, and primary air nozzles switching position with exhaust gas nozzles at regular intervals, putting forward new modification project of air staged combustion. Combined with simulation data, the operating condition of primary air nozzles switching position with exhaust gas nozzles and adding OFA at regular intervals is better to improve the combustion characteristics.