旋涡式低NO_x煤粉燃烧器燃烧特性的数值模拟

Numerical Simulation on Combustion Characteristics of Low NO_x Swirling Coal-fired Furnace

在冷态实验和数值研究的基础上,采用STAR-CD软件对旋涡式低NOx煤粉燃烧器进行了热态模拟,分别得出了燃烧器内还原区和燃尽区的燃烧特性.还原区流场呈涡旋状,颗粒处在高速旋转、燃烧、破碎的状态,其内严重缺氧,温度较低且分布均匀.燃尽区内氧气浓度相对较高,温度较高,有利于颗粒的燃尽.对于0.5mm以下颗粒,本燃烧器能够稳定地燃烧,并得到较低的氮氧化物排放.对燃烧器优化设计的计算结果表明,将一次风单管进风改为多口进风能够较好地将大颗粒压制在下部的旋流区内,在保证低氮氧化物排放的同时,有利于阻止颗粒逃逸、提高燃烧效率.在优化的计算工况下,其NOx的排放量仅为118mg/Nm3,远低于固态排渣炉650mg/Nm3的国家排放标准.

Based on the previous studies of cold experiment and modeling, the numerical simulation of combustion characteristics of low NOx swirling coN-fired furnace was carried on using the CFD software, STAR-CD3.15. Two zones, swirling reductive zone and burnout zone, appear obviously in the furnace with different features. Coal particles swirl and break up continuously in the reducing zone, which results in low temperature and even temperature distribution. While in the burnout zone, the local stoichiometric ratio is higher than that in the reducing zone, which makes the temperature high and is helpful to particle burnout. The simulation results show that the furnace is able to operate stably with low NOx emission for coal particles with the sizes less than 0.5 ram. Furthermore, the fiwnace design is optimized by modification of primary air injection. Using the uniform multi-inlet instead of the single inlet, the particle residence time in the swirling reducing zone can be increased. The structural change can prevent the particles from escaping and improve the combustion efficiency as well as decrease the NO~ emission sharply. With the injection improved, the NOx emission is only 8.99×10^-5 kg/kg （118 mg/Nm^3）, which is much less than that of the national NOx emission standard for solid-bath furnace, 650 mg/Nm^3.