燃尽风喷口位置对燃气锅炉NO_x排放影响的模拟研究

Simulation Research of the Effect of OFA Nozzle Position on the NO_x Emission of a Gas-Fired Boiler

摘要: 针对某台额定蒸发量为75 t/h π型燃气锅炉NO_x排放质量浓度较高的问题，在过量空气系数为1.2的条件下，采用燃尽风风量占比25%的空气分级低氮燃烧方式对其进行改造，分别对原工况以及三种不同燃尽风喷口布置改造方案进行数值模拟研究。综合分析了炉内燃烧温度分布、NO_x生成情况，确定了较优的燃尽风喷口位置。结果表明：方案一的燃尽风喷口布置于折焰角的下方，此处通入新鲜空气会使炉膛高温区域面积大大减小，NO_x排放质量浓度低于无燃尽风方案；方案二的燃尽风喷口布置于CO质量浓度最高的区域，这使得该位置燃烧反应更充分，第一层和第二层燃烧器间的高温区域增大；方案三的分级配风使得下层高温区域面积有所减小，但是扩大了炉膛上部NO_x富集区域面积；方案二、三NO_x排放质量浓度高于无燃尽风方案，方案一表现最佳。

Abstract: To reduce the NO_x emission of a 75t/h π type gas-fired boiler, a retrofit scheme was proposed by adopting the 25% over-fire air (OFA) rate air-staged combustion mode at excess air ratio of 1.2. Numerical simulations were carried out for the original condition and three different OFA retrofit schemes respectively. The distributions of temperature and NO_x emission are comprehensively analyzed to determine the optimum position of OFA nozzle. Results indicated that the OFA nozzle was arranged below the arch nose in scheme 1, which greatly reduced the area of the interior high temperature region due to the introduction of fresh air. The NO_x emission mass concentration is lower than the non-overburned air solution. The OFA nozzle of scheme 2 was arranged in the region with the highest CO mass concentration, and the combustion at the position was more sufficient. The high temperature region between the first layer and the second layer burner increased. The OFA nozzle in scheme 3 decreased the high temperature area in the lower part, but the NO_x enrichment area was enlarged in the upper part of the furnace. The NO_x emission mass concentration of scheme 2 and 3 were higher than the scheme without OFA and scheme 1 was the best.