内外二次风量比对逆喷旋流燃烧器特性的影响

Effect of inner/outer secondary air mass flow ratio on the characteristics of the reverse-swirl burner

逆喷旋流燃烧器是一种同时将逆向射流稳燃技术和旋流稳燃技术耦合的适用于烟煤的低氮燃烧器,具有良好的节能减排效果,但是,目前该燃烧器的稳燃机理研究不深入限制了其进一步推广应用。其中内外二次风量比、逆向一次风率、旋流强度等是影响逆喷旋流燃烧器基本性能的关键因素。为了探究不同内外二次风量比对该燃烧器流场特性和燃烧特性的影响,通过等温模化原理,建立与原14 MW逆喷旋流燃烧器比例为1∶2的燃烧器模型,使用飘带网格方法测量了耦合回流区边界,使用Dantec Multichannel热线风速仪测量了平均速度分布和RMS(Root-Mean-Square)速度分布,根据耦合回流区边界和平均速度计算得出相对回流率,然后在燃用神府东胜烟煤的14MW逆喷旋流燃烧器上使用Testo 340烟气分析仪测量了预燃锥内沿程气体中NOx质量浓度和O_(2)体积分数分布。试验结果表明:随着内外二次风量比增加,耦合回流区的面积增大,长度不变,最大直径从0.67 D增加到0.87 D,相对回流率峰值从0.83增加到1.23,测量截面b的O_(2)体积分数增大,靠近预燃锥壁面附近NO_(x)质量浓度降低;在0.3≤X/D≤0.8的耦合回流区内平均速度较低但是湍动强烈,内外二次风量比2∶5在截面X/D=0.8附近脉动速度峰值达到最大,内外二次风量比10∶23和内外二次风量比10∶28均在截面X/D=0.75附近火焰稳定且强度较高,因此从流场特性和燃烧特性2个角度均表明,耦合回流区内0.3≤X/D≤0.8的区域起到稳定火焰的作用;靠近预燃锥壁面附近形成一个高速低湍流的空气保护层,且该区域O_(2)体积分数均大于7%,有利于防止壁面出现高温腐蚀现象。

The reverse-swirl(RS)burner is a kind of low-nitrogen burner which is suitable for bituminous coal.It couples reverse jet and swirl flow for the stabilization of flame and has the advantages of energy-saving and emission-reduction.However,the further application of RS burner is limited by the lack of in-depth research on its combustion stabilization mechanism.The basic performance of RS burner is influenced by the key factors,i.e.,inner/outer secondary air mass flow ratio,reverse primary air ratio and swirling intensity,etc.In order to explore the effect of different inner/outer secondary air mass flow ratios on the flow and combustion characteristics of RS burner,a burner model with a ratio of 1∶2 to the original 14 MW RS burner was established using the isothermal modeling theory.The boundary of coupled recirculation zone was measured using the coordinate frame which a short yarn was tied to the each grid of the frame.The distributions of mean velocity and RMS velocity were measured by Dantec Multichannel hot wire anemometer.The relative reverse flow rate was calculated based on the boundary and mean velocity of the coupled recirculation zone.The NO_(x)and O_(2)concentration in the pre-combustion cone was measured by Testo 340 flue gas analyzer on a 14 MW RS burner burning Shenfu Dongsheng bituminous coal.The results showed that with increasing of the inner/outer secondary air mass flow ratio,the area of the annular coupled recirculation zone increased,the length remained unchanged,and the maximum diameter increased from 0.67 D to 0.87 D.The peak value of reverse flow rate increased from0.83 to 1.23.In addition,the O_(2)concentration of the measurement section-b increased,and by contrast the concentration of NOxdecreased near the pre-combustion cone.In the coupled recirculation zone of 0.3≤X/D≤0.8,the mean velocity was low but the turbulence was strong.For case-2∶5,the peak of RMS velocity reached the maximum near the section X/D=0.8.For case-10∶23 and case-10∶28,the flame was stable and the intensity was high near the section X/D=0.75.Therefore,from the viewpoint of aerodynamic field characteristics combined with combustion characteristics,the coupled recirculation zone in the range of 0.3≤X/D≤0.8 would take action in terms of flame stabilization.Furthermore,a high-speed,low-turbulence air protection layer was formed near the pre-combustion cone,and the O_(2)concentration in this area was more than 7%,which was expected to inhibit high temperature-corrosion on the wall.