基于微火焰燃烧的新型低氮燃烧器模拟优化

Optimization simulation of anovel low NOxburner based on micro flame combustion

为应对大气污染严重问题,我国近年来加速了“煤改气”政策的推行,燃煤锅炉逐渐被燃气锅炉替代,开发和设计新型低氮燃气燃烧器具有重要意义。为响应国家“低氮环保”号召,提出了一种新型微火焰燃气低氮燃烧器。采用数值模拟方法对该燃烧器进行了相应的孔径结构优化,并在此基础上进行燃烧工况模拟,以选出燃烧的最优工况。结果表明:随着空气入口口径由16 mm增大到22 mm,由于口径增大,空气流速变慢,燃气甲烷与空气混合反应燃烧时间变长,燃烧释放出更多热量,继续增大口径时,由于小火焰具有更大的散热面积,热量向四周散失,故火焰中心高温区温度先升高后降低,而燃烧器燃烧原料为清洁燃料甲烷,生成NOx主要为受温度影响较大的热力型NOx,故NOx生成量亦先升后降;随着过量空气由1.1增大到1.4,火焰中心高温区明显变小,温度也由2270 K降低到2042 K,由于炉膛内高温区温度降低且空气在高温区停留时间变短,NOx生成量也由412 mg/m 3降低到52 mg/m 3。因此该新型低氮燃烧器燃烧效果良好,能有效降低NOx排放。在甲烷入口口径设计为2 mm,空气入口口径设计为16 mm,过量空气系数设置为1.4时,该新型低氮燃烧器可以达到很低的NOx排放量。

In response to solve serious problems of air pollution,China has accelerated the implementation of the"coal-to-gas"policy in recent years.Coal-fired boilers have been gradually replaced by gas-fired boilers.It is important to develop and design the new low-nitrogen gas burners.In response to the national call of"low nitrogen and environment protection",a new micro flame low nitrogen burner was proposed.Numerical simulation method was used to optimize the corresponding aperture structure of the burners,and on this basis,the combustion conditions were simulated to select the optimal combustion conditions.The results show that as the air inlet diameter increases from 16 mm to 22 mm,the air flow rate slows down due to the diameter increase,the combustion time of the mixed reaction of gas methane and air becomes longer,and the combustion releases more heat.When the diameter continues to increase,because the small flame has a larger heat dissipation area and the heat is dissipated to the surroundings,the temperature in the high-temperature area at the center of the flame first increases and then decreases.The burner burns clean fuel methane,and the produced NOxis mainly thermal NOxthat is greatly affected by temperature.Therefore,the amount of NOxgenerated first rises and then falls.With the increase of excess air from 1.1 to 1.4,the high temperature area in the center of theflame obviously decreases,the temperature also decreases from 2270 K tO2042 K.As the temperature in the high temperature zone in the furnace decreases and the residence time of air in the high temperature zone becomes shorter,the production of NOxdecreases from 412 mg/m 3 to 52 mg/m 3.In conclusion,the new low nitrogen burner has a good combustion effect and can effectively reduce NOxemission.Moreover,when the methane inlet diameter is designed to be 2 mm,the air inlet diameter is designed to be 16 mm,and the excess air coefficient is set to be 1.4,the new low-nitrogen burner can achieve low NOxemission.