页岩气燃烧器燃烧特性的数值模拟

Numerical simulation of combustion characteristics of shale-gas burners

研究页岩气的清洁燃烧特性并设计优化其燃烧器对页岩气的推广应用具有重要意义。根据页岩气的特点,设计了供小型工业炉使用的200kW页岩气燃烧器,采用数值模拟的方法,研究了过量空气系数(1.05～1.35)、钝体等对页岩气燃烧的温度分布、燃烧产物、NO排放等特性的影响规律。结果表明:①随着过量空气系数增大,炉膛的峰值温度降低;②过量空气系数较大时,容易在燃烧器根部形成高温区域;③未加装钝体时,NO的生成量较大,NO的生成量随过量空气系数的增加而减小;④在燃气管出口处增加钝体后,可实现甲烷的完全转化;⑤与未加装钝体相比,炉膛温度峰值下降,钝体后形成回流区,回流的高温烟气能够有效预热喷出的燃气,减少了着火时间,温度分布较均匀,燃烧状况稳定,产生的NO浓度较低。综合考虑的结论认为,增加钝体优化后的燃烧器,当过量空气系数为1.25时的工况性能最优。

Recent studies have started not only to study the clean combustion features of shale gas but to design and optimize shale-gas burners. This will be of a great value to stimulate the wide application of shale gas. According to the unique properties of shale gas, we designed a 200 kW shale gas burner for a small-scale industrial furnace. The numerical simulation was adopted to discuss what impact the excess air coefficient （1.05 - 1.35） and the bluff body have on the combustion characteristics such as burning temperature distribution, combustion products, NO emission, etc. The following findings were concluded, a. With the increase of excess air co- efficient, the peak temperature in the furnace decreases; when the excess air coefficient is rather higher, a high-temperature zone is easily formed at the bottom of the burner, b. Without a bluff body being installed, the amount of NO yield decreases with the in- crease of the excess air coefficient, c. When a bluff body is installed at the outlet of the gas pipe, the methane in shale gas can be completely consumed and the maximum furnace temperature declines; a backflow zone is also formed in the downstream of the bluff body, where the high-temperature flue gas will preheat the gushing gas, thus to reduce the ignition time. Comparatively, when the bluff body is installed, the combustion condition is stable and the burning temperatures are evenly distributed in the furnace; and the NO yield is rather low. Also, it is pointed out that the optimal combustion condition will be achieved when the excess air coefficient is 1.25.