The effect of hydrogen containing fuel blends upon flashback in swirl burners
The effect of hydrogen containing fuel blends upon flashback in swirl burners
复制标题
含氢燃料混合物对旋流燃烧器回火的影响
DOI：
10.1016/j.apenergy.2011.01.057
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发表时间：
2012
期刊：
影响因子：
11.2
通讯作者：
P. Bowen
中科院分区：
文献类型：
--
作者：
N. Syred;M. Abdulsada;A. Griffiths;T. O’Doherty;P. Bowen
稀薄预混旋流燃烧由于具有良好的火焰稳定性和吹脱极限以及较低的NOx排放等优点而被广泛应用于燃气轮机和许多其他燃烧过程中。虽然回火通常不是天然气燃烧的问题，但有一些关于现有燃气涡轮机回火损坏的报道，而富氢燃料混合物，特别是源自煤和/或生物质/工业过程（如炼钢）的气化的那些富氢燃料混合物，引起了该领域的关注。因此，本文描述了一种实用的实验方法，以研究和减少回火的影响，在一个紧凑的设计，通用旋流燃烧器的代表许多系统。一系列不同的燃料混合物的回火和吹出的限制进行了研究，这些燃料混合物包括甲烷，甲烷/氢混合物，纯氢和焦炉煤气。通过改变进气道的数量或进气道的结构来研究旋流数的影响。著名的刘易斯和冯易北河临界边界速度梯度表达式被用来消除闪回，并使比较与其他可用的数据。这里遇到了两种闪回现象。第一个在较低的涡流数涉及通过外壁边界层的回火，其中的关键参数是临界边界速度梯度，Gf。Gfare值与刘易斯和von Elbe报道的层流条件下的值大小相似，并且可以认识到，在湍流条件下，薄旋流边界层中的实际梯度比层流条件下的梯度高得多。在较高的涡流数，中央回流区（CRZ）变得扩大，并向后延伸到燃料喷射器的燃烧器基板，并导致回火发生在较高的速度更早。CRZ的这种延伸是复杂的，受涡流数、当量比和雷诺数的控制。在这些条件下，当CRZ周围的圆柱形火焰前缘迅速向外加速到切向入口和更远时，尤其是在含氢燃料混合物的情况下，发生回火。相反，在具有修改的排气几何形状的较低涡流数（因此限制CRZ）下，当燃料混合物的氢含量不超过30%时，会以低得多的流速通过外部薄边界层发生回火。这项工作表明，它是可能的运行预混旋流燃烧器与广泛的氢燃料混合物，以大大减少回火行为，从而允许更广泛地使用该技术，以减少氮氧化物排放。
Lean premixed swirl combustion is widely used in gas turbines and many other combustion Processes due to the benefits of good flame stability and blow off limits coupled with low NOxemissions. Although flashback is not generally a problem with natural gas combustion, there are some reports of flashback damage with existing gas turbines, whilst hydrogen enriched fuel blends, especially those derived from gasification of coal and/or biomass/industrial processes such as steel making, cause concerns in this area. Thus, this paper describes a practical experimental approach to study and reduce the effect of flashback in a compact design of generic swirl burner representative of many systems. A range of different fuel blends are investigated for flashback and blow off limits; these fuel mixes include methane, methane/hydrogen blends, pure hydrogen and coke oven gas. Swirl number effects are investigated by varying the number of inlets or the configuration of the inlets. The well known Lewis and von Elbe critical boundary velocity gradient expression is used to characterise flashback and enable comparison to be made with other available data. Two flashback phenomena are encountered here. The first one at lower swirl numbers involves flashback through the outer wall boundary layer where the crucial parameter is the critical boundary velocity gradient, Gf. Values of Gfare of similar magnitude to those reported by Lewis and von Elbe for laminar flow conditions, and it is recognised that under the turbulent flow conditions pertaining here actual gradients in the thin swirl flow boundary layer are much higher than occur under laminar flow conditions. At higher swirl numbers the central recirculation zone (CRZ) becomes enlarged and extends backwards over the fuel injector to the burner baseplate and causes flashback to occur earlier at higher velocities. This extension of the CRZ is complex, being governed by swirl number, equivalence ratio and Reynolds Number. Under these conditions flashback occurs when the cylindrical flame front surrounding the CRZ rapidly accelerates outwards to the tangential inlets and beyond, especially with hydrogen containing fuel mixes. Conversely at lower swirl numbers with a modified exhaust geometry, hence restricted CRZ, flashback occurs through the outer thin boundary layer at much lower flow rates when the hydrogen content of the fuel mix does not exceed 30%. The work demonstrates that it is possible to run premixed swirl burners with a wide range of hydrogen fuel blends so as to substantially minimise flashback behaviour, thus permitting wider used of the technology to reduce NOx emissions.