天然气柔和燃烧锅炉结构参数影响模拟研究

Numerical study on effects of structure parameters of natural gas fueled MILD combustion boiler

在天然气锅炉中引入柔和燃烧技术将大大降低NOx排放,高速未燃气卷吸高温烟气回流并与之快速掺混再燃烧是柔和燃烧的重要特征,因此,开展天然气锅炉关键结构参数优化设计以组织流场形成柔和燃烧所需的高温低氧反应气氛非常必要。基于天然气锅炉的工况特征,设计了热负荷15kW的模型燃烧室,采用数值模拟手段详细研究了燃烧室高度、喷嘴孔径、喷嘴相对位置及烟气出口尺寸对燃烧室流场、组分场及关键参数——烟气回流比的影响规律,并最终确定了燃烧室结构优选方案,对天然气锅炉柔和燃烧机设计提供理论基础数据。

The application of MILD （Moderate or Intense Low-oxygen Dilution） combustion technology in natural gas fueled boiler could reduce NOx emission.The discrete and high speed fuel/air j ets entrain high temperature flue gases separately, then mixed rapidly to form a high-temperature and low-oxygen environment leading to MILD combustion. Therefore, it is necessary to conduct parametric studies of various structure parameters for a natural gas fueled MILD combustion boiler,including fuel/air nozzle diameter,relative positions between fuel and air nozzles, discharge area of flue gas.According to typical operating conditions of natural gas boiler,a 15kw heat load model combustor was designed and detailed numerical investigations were conducted. The influence of the aforementioned parameters on flow, mixture and temperature field and the recirculation ratio of flue gas were also studied.Finally,an optimized model combustor was obtained.