【作者】 杨鹏；

【导师】 杨仲卿；

【作者基本信息】 重庆大学 ， 动力工程及工程热物理， 2016， 硕士

【摘要】 超低浓度甲烷广泛存在于矿井抽采的煤层气和化工废气中,它的浓度通常随着开采条件的变化而波动,通常其体积浓度不超过3%,热值很低,利用难度较大。在我国煤炭开采过程中,大量超低浓度甲烷不经处理直接排放到外界环境中,不仅污染环境而且浪费资源,因此,研究利用超低浓度甲烷具有节能和环保双重意义。流态化燃烧技术具有燃料适应性广、热容量大等优点,适用于低热值气体的燃烧利用,当超低浓度甲烷流化床内催化燃烧时,反映其流态化催化燃烧特点的反应模型需要进一步研究和建立。针对此问题,本文根据超低浓度在鼓泡流化床中催化燃烧特点,建立分区模型并进行耦合,并采用实验研究和理论分析相结合的方法研究了0.15~3 vol.%超低浓度甲烷在以0.5%Pd/Al2O3作为催化剂颗粒床料的鼓泡流化床反应器中催化燃烧特性并对反应模型进行了验证,最后通过模型计算,对甲烷在流化床反应器的变化进行了预测。基于超低浓度甲烷在鼓泡流化床催化燃烧特性,在流化床流动、反应和质量平衡的基础上,根据气固两相流理论,在密相区与稀相区分别建立反应模型,在密相区中考虑了气泡相与乳化相之间的传质以及甲烷在催化颗粒表面的催化反应;在稀相区,根据超低浓度甲烷燃烧的特点,又进一步划分为飞溅颗粒区和均相反应区,并分别建立反应模型。采用实验研究的方法对所建立的反应模型在不同工况下进行了验证,考察了床层温度、进气浓度、流化风速以及静态床层高度等因素对低浓度甲烷流态化催化燃烧的影响,并与常见流态化反应模型活塞流、混合流及K-L反应模型进行了对比分析,研究表明本文建立的反应模型与实验数据吻合较好,误差在5%以内。同时研究发现,床层温度增加到650℃时,甲烷的转化率可达100%,减小甲烷进气浓度和流化风速以及增加床层温度均可提高低浓度甲烷的转化率,并使反应向着床层下方移动;甲烷在密相区床层的反应主要发生在乳化相,气泡相甲烷浓度的变化主要是通过气泡相和乳化相间的传质来实现。本文根据超低浓度甲烷在鼓泡流态化燃烧反应不同区域的特点,建立了催化燃烧的反应模型,并对反应模型进行了实验验证,考察了操作条件等对低浓度甲烷流态化催化燃烧的影响规律,研究结果可为低热值气体的高效利用与转化提供理论支撑与依据。更多还原

【Abstract】 It is common knowledge that ultra-low concentration methane is prevalent in coal bed methane and exhaust gases; its concentration varies depending on the operating conditions and always is not more than 3%. However, its low calorific value makes it difficult to use, and therefore, most untreated low-concentration methane is simply released to the atmosphere in our country. This not only causes air pollution, but also represents a colossal waste of energy resources. Therefore, to study the use of ultra-low concentration methane has an important significance of energy conservation and environmental protection. Fluidized bed catalytic combustion has been widely used for the combustion of inferior grade gases because of its wide scope of application, high heat capacity. However, the reaction model of fluidized combustion need to study and establish while ultra-low methane catalytic combustion in a fluidized bed.For this problem, the partition model was established and coupled on the basis of the characteristics of ultra-low concentration methane catalytic combustion characteristics in the bubbling fluidized bed, then the catalytic combustion characteristics of low concentration(0.15–3 vol. %) methane combustion in a lab-scale fluidized bed with 0.5 wt. % Pd/Al2O3 as catalytic particles were studied experimentally and analyzed theoretically. Finally the axial distribution of low concentration methane in the fluidized bed was predicted using the mathematical model.Based on the known characteristics of low concentration catalytic combustion in a bubbling fluidized bed, the models of dense and freeboard zone were established respectively according to the flow characteristics, reaction and mass balance and gas-solid two phase flow theory. Mass transfer between emulsion phase and bubble phase and the surface reaction of methane absorbed in the catalyst particle was taken into account for dense zone. Based on the characteristics of ultra-low concentration catalytic combustion in the freeboard zone, freeboard zone was divided into two zones: a splash zone and a homogeneous zone, then the models were developed respectively. The reaction model was verified by the experimental study at different conditions. The influences of bed temperature, inlet concentration, fluidized velocity and static bed height on ultra-low concentration methane fluidized catalytic combustion were analyzed, then a comparative analysis was done for the methane conversion predicted by the established model, plug flow, mixed flow and K-L model under different conditions. The research showed the reaction model was agreed with the experimental data, with a deviation within 5%. Meanwhile, it was found that methane conversion reached approximately 100 % as the bed temperature increased to 650 ℃.Methane conversion increased and the reactions moved toward the lower part of the bed while bed temperature increased and inlet methane concentration and fluidized velocity decreased. Reactions of methane combustion in dense zone mainly occurs in the emulsion phase. And this variation of methane concentration in the bubble phase is largely dependent on mass transfer between the bubble phase and emulsion phase.Based on the characteristics of ultra-low concentration methane fluidized catalytic combustion in these different zones of the bubbling fluidized bed, the model was developed and verified by the experimental study, the effects of operating conditions on ultra-low concentration methane catalytic combustion were investigated. The results can provide theoretical support and basis for the efficient use and conversion of low calorific value gas.更多还原