管式加热炉空气分级燃烧器的CFD研究

CFD Study on Air Staged Burner of Tube Furnace

以某炼油厂管式加热炉空气分级燃烧器为研究对象,应用计算流体力学(CFD)软件FLUENT,研究了二次风分级比R(二次空气与总空气体积之比)为0.5、0.6、0.7、0.8和0.85的5种不同工况下,辐射室内速度、温度、组分浓度、火焰高度和NO生成速率的变化规律。结果表明,由于射流卷吸的作用,辐射室内存在较大范围的回流区。当R由0.5增至0.85时,辐射室对称面平均温度基本不变,出口温度升高0.65%,壁面热通量下降1.65%,火焰高度增加0.44倍,NO排放体积分数由214.4μL/L迅速下降至37.9μL/L。在温度和氧气浓度较高的燃气/空气混合接触面上,热力型NO形成较多;在低温富燃的火焰前端区,快速型NO形成较多。当R为0.8时,炉内温度分布均匀、燃烧完全且烟气NO浓度较低,可作为燃烧器设计和现场调节的优化参考值。

A numerical simulation of the combustion process, which was based on the air staged burner of a refinery, was carried out by using the CFD （Computational fluid dynamics） software FLUENT. Some related parameters, such as velocity, temperature, component distribution, flame height, thermal NO production rate, prompt NO production rate and so on, were obtained under the secondary staged air volume rate R of 0.5, 0.6, 0.7, 0.8 and 0.85, respectively. The results showed that there was a large corner recirculation zone in radiation section due to the entrainment. When R increased from 0.5 to 0.85, the furnace symmetry average temperature maintained constant, while the furnace outlet temperature increased by 0.65% , the radiation surface heat flux declined by 1.65%, the flame height increased by 0.44 times and the volume fraction of NO in emission gas declined from 214.4 μL/L to 37.9 μL/L. The thermal NO was formed at the fuel/air mixing surface with high temperature and rich oxygen and the prompt NO was formed at the fuel rich flame front with lower temperature. Among the five experimental cases,R of 0.8 can be used as the optimized reference for design and field regulation of the burner because of the uniform temperature distribution, complete combustion and low NO emission.