π型锅炉“煤改气”后的低氮燃烧器易发生火炬“刷墙”和积碳问题，而旋流预混燃烧方法因火炬短、燃尽快等优势备受关注。将贫预混旋流燃烧与钝体相结合，设计带有位移钝体的贫预混旋流燃烧器，通过移动钝体位置，可改变燃烧器出口流速。使用此燃烧器研究了不同旋流数、热功率、钝体位置工况下，旋流预混火焰污染物生成特性，并利用激光颗粒成像测速技术测量燃烧器喷嘴出口处流场。研究发现，NOx生成量随旋流数增加呈先减小后增加的趋势，旋流数为0.25时，NOx生成量最低；钝体位置固定时，由于此时流速随热功率的增加而增大，导致NOx生成量随热功率的增加而降低，CO生成量随热功率的增加而增加；改变钝体位置保证出口流速不变时，NOx和CO生成量均保持较低水平，NOx生成量<12 mg/m3，CO生成量<7 mg/m3，且仅在最低热功率下有少量CO生成。通过分析流场和火焰可知，旋流数由0增至0.25时，火焰宽度增加，对周围烟气卷吸作用增强，NOx生成量降低；旋流数由0.25增至0.83时，火焰宽度基本维持不变，但轴向回流增强，热烟气停留时间增加，NOx生成量升高。因此，优化位移钝体位置和旋流数，可以使燃烧器出口流场和火焰结构更加合理，使污染物维持在较低水平。

In a π-type boiler,the low NOx coal-to-gas transition may result in the problems of the "wall brush" of the flame torch and carbon deposition, and the swirl premixed combustion method is attractive as it provides short flame length and fast burn-out. Combining the advantages of both lean premixed swirl combustion and bluff-body combustion,a lean premixed swirl burner integrated with a displacement bluff-body was designed. By moving the position of the bluff-body,the burner outlet flow velocity could be tuned. The swirl premixed flames pollutant generation characteristics under different swirl numbers,thermal power and bluff-body position conditions were studied and the flow field at the outlet of the burner nozzle was measured using particle image velocimetry technology. Results show that the amount of NOx generated first decreases and then increases with the increase of the swirl number,the NOx concentration is lowest at the swirl number of 0.25. When the bluff-body height is fixed,since the flow velocity increases with the increase of thermal power at this time,the NOx concentration decreases while the CO concentration increases as a function of the thermal power. If the bluff-body position is varied to keep a fixed outlet flow velocity,both the NOx and CO concentrations are maintained at a relatively low level,as NOx<12 mg/m3,CO<7 mg/m3,and only a small amount of CO is generated at the lowest thermal power. Based on the flow field and flame analysis,as the swirl number increases from 0 to 0.25,the flame width increases,strengthening the flue gas entrainment,and resulting in a decrease in the NOx emission. As the swirl number further increases from 0.25 to 0.83,the width of the flame hardly changes but the axial flue gas recirculation is enhanced,increasing the residence time of the hot flue gas and the NOx formation. Therefore,optimized bluff body position and swirl number lead to a reasonable flow field and flame structure,and thereby keep the emissions at a relatively low level.

0 引言

1 试验

   1.1 旋流燃烧器

   1.2 试验系统

2 结果与讨论

   2.1 旋流数对燃烧污染物生成的影响

   2.2 定钝体高度变功率对污染物生成的影响

   2.3 变钝体高度变功率对污染物生成的影响

   2.4 旋流数对燃烧器出口流场的影响

3 结论