目前我国工业锅炉保有量超60万台，其中燃煤工业锅炉占现役工业锅炉总数的80%以上，并作为主要热力供应设备被广泛应用于生产生活的各领域。燃煤工业锅炉作为我国仅次于火电厂的第二大燃煤型污染源，推进其清洁高效运行、有效节能减排，是实现经济效益、环境效益和社会效益共赢的必然途径。设计了一种预热解式低氮旋流燃烧器，在低氮旋流燃烧器的基础上添加预燃室可实现稳定燃烧，并使煤粉经过预热解后产物送入炉膛燃烧，通过控制热解气氛引导热解气中生成的NO还原成N2，控制NOx排放。使用CFD模拟方法研究了内外二次风配比和内二次风旋流强度对预热解式低氮旋流燃烧器燃烧性能及污染物排放特性的影响，通过速度场、温度场和烟气组分分布的多工况对比分析，对燃烧器运行参数的优化提出建议。模拟结果表明：内二次风率增至54%时，内二次风破坏了预燃室内的回流区，使燃烧器无法实现稳定燃烧，该预热解式低氮旋流燃烧器存在一个稳定燃烧的最大内二次风率，约为50%；在保证燃烧稳定的范围内提高二次风率，预燃室内的低氧区域面积增大，内二次风与一次风的混合延迟，NOx排放降低，但高风速使煤粉的停留时间降低，出口截面焦炭燃尽率略降低；内二次风旋流叶片角度减至30°时，预燃室内的环形燃烧区消失，使燃烧器无法实现稳定着火，在30°～45°存在一个燃烧器稳定燃烧的最小内二次风旋流叶片角度；内二次风旋流叶片角度增大，燃烧器出口火焰刚性降低并在轴向上被压缩，炉膛前段温度提高、高温区集中，使焦炭充分燃尽，但炉膛出口截面NOx浓度略有升高。

At present, the total number of industrial boilers in China exceeds 600 000, among which the coal-fired indus trial boilers account for more than 80% of the total number of active industrial boilers, and are widely used in various fields of production and life as the main heat supply equipment. As the second largest coal-fired pollution source in China, coal-fired industrial boilers are  an inevitable way to achieve win-win economic, environmental and social benefits by promoting their clean and efficient operation, effective energy conservation and emission reduction. A low-nitrogen swirl burner capable of preheating was designed. On the basis of the low-nitrogen swirl burner, a precombustion chamber was added to achieve stable combustion, and the products of pulverized coal after preheating solution were sent into the furnace for combustion. By controlling the pyrolysis atmosphere, NO generated in the pyrolysis gas can be reduced to N2 to further control the emission of NOx. In this paper, CFD simulation method was used to study the influence of internal and external secondary air ratio and secondary air swirl intensity on combustion performance and pollutant emission characteristics of preheating solution low-nitrogen swirl burner. Through the comparative analysis of multi-working conditions of velocity field, temperature field and component distribution, suggestions were put forward for the optimization of burner operation parameters. The simulation results show that when the internal secondary air rate increases to 54%, the internal secondary air destroys the backflow zone in the precombustion chamber, making the burner unable to achieve stable combustion. The maximum internal secondary air rate of the preheating solution low-nitrogen swirl burner is about 50%. In the range of ensur-ing combustion stability, the secondary air rate is increased, the area of low oxygen area in the precombustion chamber is increased, the mixing of secondary air and primary air is delayed, NOx emission is reduced, but the residence time of coal powder is reduced by high wind speed, and the burnout rate of exit section coke is slightly reduced. When the internal secondary air swirl blade angle decreases to 30°, the annular combustion zone in the precombustion chamber disappears, making the burner unable to achieve stable ignition. There is a minimum internal secondary air swirl blade angle for stable combustion of the burner between 30° and 45°. The angle of the internal secondary wind cyclone blade increases, the flame rigidity of the burner outlet decreases and is compressed in the axial direction, the temperature in the front part of the furnace increases, and the high temperature zone is concentrated, so that the coke is fully burned, but the NOx concentration in the cross-section of the furnace outlet increases slightly.

0 引言

1 燃烧器、炉膛数值模拟设置及验证

2 燃烧器、炉膛数值模拟工况设置

3 模拟结果与讨论

   3.1 内外二次风配比的影响

   3.2 内二次风旋流强度的影响

4 结论