煤矿超低浓度瓦斯蓄热燃烧特性及其关键影响因素分析

Analysis on the Properties of Coal Mine Ultra-low Concentration Methane Combustion and Its Key Influencing Factors

为研究超低浓度瓦斯蓄热燃烧特性及其关键影响因素,搭建多孔介质燃烧测试平台,研究不同孔隙率多孔介质蓄热体及其组合条件下的超低浓度瓦斯燃烧特征,探讨烟气热量回流对燃烧稳定的影响。研究发现,基于多孔介质的超低浓度瓦斯蓄热燃烧状态包括表面燃烧和浸没燃烧,相同工况下表面稳定燃烧的火焰传播速度小于浸没燃烧状态下的火焰传播速度,当多孔介质孔隙内火焰传播速度大于孔内的气体轴向流速时,表面燃烧将向浸没燃烧模式进行转变,以此为基础确定其燃烧模式转变的临界条件。超低浓度瓦斯蓄热燃烧所表现出的燃烧区分层、热斑及燃烧区破裂等非稳定性的燃烧特征在传输过程中相互耦合且不断演化,其形成与存在与燃烧波及热波的传播密切相关。当临界准则数(贝克莱数)Pe≥65时,多孔介质内可实现稳定传播的燃烧波。在该实验条件下,20PPI的多孔介质有利于超低浓度瓦斯的稳定燃烧,合理组合的多孔介质界面有助于燃烧火焰的稳定和温度分布的均匀。由此提出烟气逆流用于强化进气预热的自回热新思路,与无热量回流相比,烟气逆流可显著强化进气预热,有效改善超低浓度瓦斯的蓄热燃烧状态,使得床内温度场的分布更趋均匀,显著降低床内各区域间的温度梯度,有效抑制火焰倾斜、热斑、破裂等非稳定燃烧特征。

In order to study the characteristics of ultra-low-concentration gas regenerative combustion and its key influencing factors,a porous media combustion test platform was built.The characteristics of ultra-low-concentration gas combustion and its combustion stability has been investigated under different porosity porous media regenerators and their combinations.Results show that the combustion mode of ultra-low-concentration methane based on porous media includes surface combustion and submerged combustion state.Under the same burning conditions,the flame propagation speed of the surface combustion is lower than that of the submerged combustion.When the flame propagates in the pores of the porous media is higher than the gas axial flow velocity,the combustion mode of ultra-low concentration methane will transit from surface combustion to submerged combustion.And,the critical conditions for the transition of the combustion mode are determined on this basis.Unstable combustion characteristics such as combustion stratification,hot spots and combustion zone rupture are usually coupled with each other and evolve continuously during the flame transmission process.Also,their formation and development are closely related to the flame propagations and heat waves.The stable combustion wave can be propagated in the porous medium only when the critical criterion number(Bekeley's number)Pe≥65.Under present experimental conditions,20PPI porous medium is suitable to the stable combustion for the ultra-low-concentration gas.Based on the above results,a new self-heating regenerative by the flue gas counterflow for strengthening intake-air preheating is proposed.Compared with non-heat recovery,flue gas counterflow can significantly strengthen intake air preheating and effectively improve the heat storage of ultra-low concentration gas combustion.It makes the temperature distributions in the porous medium much more uniform,and significantly reduces the temperature gradient between each area.Besides,the new method effectively suppresses the unstable combustion characteristics.