过量空气系数及旋流数对天然气燃烧特性的影响研究

Study on the Influence of Excess Air Coefficient and Swirl Number on Combustion Characteristics of Natural Gas

针对天然气在O_(2)/N_(2)氛围下扩散燃烧时,过量空气系数和旋流数对WNS型燃气锅炉燃烧室内的温度分布、速度分布及NOx生成的影响,利用CFD软件,采用标准k-ε湍流模型、P-1辐射模型和涡耗散模型进行数值模拟。基于旋流对流动特性的影响,采用旋流数S来表示入口空气的旋流强度。结果表明:在过量空气系数α从1.0增大到1.3的过程中,火焰直径逐渐变小,排烟温度降低,燃烧室出口处NOx的质量分数逐渐减小;在空气旋流数从0提高到0.8的过程中,燃烧室内形成了中心回流区,火焰的径向流动分布逐渐改善,燃烧室内的温度分布更加均匀;旋流燃烧的火焰中心轴线温度分布高于直流射流燃烧,提高空气旋流数可以有效降低NOx的质量分数。

The effects of excess air coefficient and swirl number on temperature distribution,velocity distribution and NO_(x) generation in the combustion chamber of WNS gas boiler when natural gas diffused and burned in O_(2)/N_(2)atmosphere were addressed.The numerical simulations were carried out by using CFD software,the standard k-ε turbulence model,P-1 radiation model and eddy dissipation model.Based on the swirling effect on dynamic flow behavior,the swirl number S was used to express the swirling intensity of the inlet air.The results show that in the process of increasing the excess air coefficient α from 1.0 to 1.3,the diameter of the flame gradually decreases,the exhaust gas temperature decreases,and the mass fraction of NO_(x) at the outlet of the combustion chamber gradually decreases;in the process of increasing the number of air swirls from 0 to 0.8,a central recirculation zone is formed in the combustion chamber,the radial flow distribution of the flame is gradually improved,and the temperature distribution in the combustion chamber is more uniform;the temperature distribution of the central axis of the swirling combustion flame is higher than that of the straight-flow jet combustion,and increasing air swirl number can effectively reduce NO_(x) mass fraction.