为了提升直流煤粉燃烧器在促进煤粉着火稳燃及降低NOx生成方面的性能，哈尔滨锅炉厂设计开发了一种中心富燃料直流煤粉燃烧器，通过设置两级煤粉浓缩并结合钝体回流及稳燃齿稳燃，强化煤粉浓淡分级燃烧、稳燃及降低NOx生成效果，利用ANSYS Fluent数值计算方法获得该类型燃烧器的整体燃烧性能，通过调整风量配比系统研究了该燃烧器的气固流动、燃烧特性及NOx生成特性。结果表明：一次风煤粉气流经两级浓缩后，可将大部分煤粉（占总煤粉量的80%～90%）浓缩于中间浓煤粉气流通道，浓煤粉气流喷出速度在12～16 m/s，能在燃烧器出口形成低速、富燃料区，促进煤粉气流的快速升温及着火，着火位置距燃烧器出口约300 mm。同时，稳燃板的设置可在燃烧器出口处形成2处对称高温回流区，对应回流区长度在160 mm附近。减小一次风量并增大二次风量，将降低挥发分的反应速率，延长CO及固定碳的反应时间，火焰高温区长度增大，且不利于抑制NOx生成。而当增大二次风量同时减小燃尽风量时，高速二次风对煤粉气流的引射作用增强，为后续煤粉燃烧持续补氧，促进了后续煤粉的持续燃烧放热，同时由于空气分级燃烧效果进一步减弱，削弱了主燃区还原性效果，使NOx质量浓度保持在237.3 mg/m3 (O2体积分数6%)。通过该燃烧器基准工况下的NOx生成特性可知，由于燃烧器出口高温回流区加低速富燃料区的共同作用，燃烧器出口形成贫氧富燃料的强还原性氛围，从而明显抑制NOx生成，使NOx质量浓度降至162.34 mg/m3(O2体积分数6%)。

In order to improve the performance of direct-flow pulverized coal burner in promoting the coal ignition and stable combustion,and simultaneously reducing the NOx generation,Harbin Boiler Co.,Ltd. developed a central fuel-rich direct-current pulverized coal burner. In this burner,a combination of two stages of pulverized coal concentration,a blunt body and combustion stabilization teeth were used to enhance fuel rich/lean organization,stabilize combustion and reduce NOx generation. The overall combustion performance of this type of burner was obtained by using ANSYS fluent numerical calculation method,and the gas/solid flow,combustion and NOx generation characteristics of the burner were studied by adjusting the air distribution. The research results show that after the primary coal/air flow is concentrated in two stages,most of the coal particles (about 80%-90% of the total coal particles) can be concentrated in the middle fuel-rich flow channel,and the corresponding flow velocity is between 12 and 16 m/s. Therefore,a low-velocity and fuel-rich zone can be formed near the burner nozzle,which is beneficial to promote the timely ignition of the coal/air flow,and the ignition location is about 300 mm away from the burner nozzles. At the same time,the setting of the combustion stabilizing plate can form two symmetrical high-temperature recirculation zones at the burner outlet,and the corresponding recirculation zone length is around 160 mm. by decreasing the primary air flux and increasing the secondary air flux,the volatile reaction rate is reduced,the reaction time of CO and fixed carbon is prolonged,and the flame length area is simultaneously increased,which is not conducive to suppressing NOx generation. When the secondary air flux increases and the overfire air flux reduces,the entrainment effect of the high-velocity secondary air on the coal/air flow is enhanced,so as to continuously provide oxygen for the subsequent coal combustion and promote the further heat release. At the same time,due to the further weakening of the effect of air staged combustion,the reducing effect of the main combustion area is weakened,and the NOx emission concentration is maintained at a high level of 237.3 mg/m3 at 6% O2. According to the NOx generation characteristics of the burner under the reference working condition,under the benchmark conditions,due to the combined effect of the high-temperature recirculation zone and the low-velocity fuel-rich zone,an oxygen-lean and fuel-rich strong reducing atmosphere is formed near the burner nozzles,which obviously inhibits the NOx production,and a low NOx emission concentration of 162.34 mg/m3 at 6% O2 is achieved.

0 引言

1 中心富燃料直流煤粉燃烧器

2 数值计算方法

   2.1 流动及燃烧模拟理论模型

   2.2 计算域及边界条件

   2.3 数值计算模型验证

3 结果与讨论

   3.1 气流流动特性

   3.2 煤粉浓缩特性

   3.3 挥发分释放及温度分布

   3.4 CO生成及固定碳燃尽特性

   3.5 NO生成特性

4 结论