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Fe−Co/Al2O3多孔介质催化剂催化低浓度瓦斯燃烧特性

Catalytic combustion properties of Fe−Co/Al2O3 porous media catalysts for low-concentration coal mine gas

  • 摘要: 针对8%以下煤矿低浓度瓦斯利用率低与大量排空造成能源浪费和温室效应问题,采用超声辅助浸渍法制备了负载Fe2O3与Co3O4双活性组分的Fe−Co/Al2O3双金属多孔介质催化剂,在渐变孔密度燃烧器中开展低浓度甲烷催化燃烧性能研究,重点考察了过量空气系数φa和流量f对燃烧特性的影响,并测试了长期燃烧稳定性。结果表明:Fe−Co/Al2O3中的Fe、Co双金属协同参与了CH4催化反应,Fe3+和Co3+在反应中被部分还原为Fe2+和Co2+物种,CoFe2O4尖晶石结构的形成提高了催化剂的热稳定性和抗烧结能力,使其在高温贫燃过程中保持良好的催化活性。CH4氧化反应遵循MvK机制,晶格氧参与CH4中C—H键断裂与活化,其消耗形成氧空位;吸附氧动态补充晶格氧,在维持氧物种迁移与循环的同时进一步促进中间产物氧化。过量空气系数和流量显著影响温度分布与火焰迁移,低过量空气系数或低流量易引发燃烧回火,高过量空气系数或高流量则会导致脱火风险;多孔介质渐变孔结构的热缓冲作用与催化反应的持续放热减缓了温度波动并提高了火焰稳定性。在φa = 2.44 ~ 2.56与f = 50 ~ 65 L/min,火焰锚定于燃烧器中游,燃烧温度维持在800 ℃以上,且NOx排放极低。在φa = 2.56下,燃烧持续72 h预热区温度仍保持在220 ℃左右,CH4转化率接近100%,表明渐变多孔介质与催化反应的耦合显著提高了贫燃特性和稳定性。本研究为煤矿低浓度瓦斯的清洁高效利用提供了新的思路和技术支撑。

     

    Abstract: Addressing the low utilization and massive venting of low-concentration methane (LCM) in coal mines (< 8%), which results in energy waste and greenhouse effect. Fe−Co/Al2O3 bimetallic porous media catalyst loaded with Fe2O3 and Co3O4 as dual active components was prepared using ultrasonic-assisted impregnation method to investigate the combustion performance of LCM. The effects of excess air ratio φa and flow rate f on combustion characteristics were examined, and long-term combustion stability was tested. The results indicated that the Fe and Co in Fe−Co/Al2O3 synergistically engaged in CH4 catalytic reaction. Fe3+ and Co3+ were partially reduced to Fe2+ and Co2+ species, and the formation of CoFe2O4 spinel structure improved thermal stability and resistance to sintering of the catalyst, enabling it to maintain good catalytic activity during high-temperature lean combustion. CH4 oxidation reaction followed the MvK mechanism, in which lattice oxygen participated in the cleavage and activation of the C—H bond in CH4, with its consumption forming oxygen vacancies. Adsorbed oxygen dynamically replenished lattice oxygen to maintain the migration and cycling of oxygen species, while further promoting the oxidation of intermediates. Excess air ratio and flow rate significantly influenced temperature distribution and flame migration, low excess air ratio or low flow rate tended to cause combustion flashback, whereas high excess ratio or high flow rate could lead to the risk of blow off. The thermal buffering effect generated by the gradient pore structure of the porous media, combined with the sustained heat release of the catalytic reaction, alleviated temperature fluctuation and enhanced flame stability. Within the range of φa = 2.44—2.56 and f = 50—65 L/min, the flame was anchored in the middle of the burner, the combustion temperature was maintained above 800 ℃, and NOx emissions were extremely low. At φa = 2.56, the preheating zone temperature remained around 220 ℃ even after 72 h of combustion, and the CH4 conversion approached 100% throughout the process, confirming that the coupling of gradient porous media and catalytic reaction significantly improved lean-burn performance and stability. This study provides a novel insights and technical support for the clean and efficient utilization of coal mine LCM.

     

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