【作者】 王鹏；

【导师】 王天宇；

【作者基本信息】 哈尔滨工业大学 ， 动力工程及工程热物理， 2022， 硕士

【摘要】 随着国际及国内对环保问题的重视,发展绿色能源成为人们关注的重点。近年来随着氢燃料电池技术的快速发展,氢能逐渐成为研究的热点。但受工业化大规模制氢效率的限制,氢气产能存在较大缺口,影响其发展。微通道反应器具有反应速度快、传热性能好等优点成为解决方案之一。微通道反应器的操作参数及其几何结构特征均会对内部气流的流动及反应过程产生影响,改变出口处的反应物产率和氢碳比等结果。国内外学者对微通道甲烷干重整反应器进行了大量研究。但受限于实验方法的特有缺陷及不同类型微通道的结构差异,难以具体分析微通道反应器内部流动及反应情况。而甲烷干重整反应的数值模拟研究中涉及微通道反应器的较少,且很少关注反应器结构对制氢性能的影响。因此本文基于微通道反应器,借助数值模拟软件Fluent并耦合的反应动力学机理,对微通道反应器的操作参数及几何结构影响特性进行了模拟研究,考察对转化率、产氢率、氢碳比和抗积碳性能的影响,优化了反应器操作条件及结构参数。利用三维建模软件UG建立了微通道反应器三维物理模型。基于微动力学反应模型及单相流动模型,建立了相应的基本控制方程及催化反应控制方程,并通过编写Chemkin机理文件将详细的甲烷干重整反应机理耦合至Fluent组分输运模型。在划分网格并完成网格无关性验证后,模拟了反应温度对出口结果的影响,与文献中实验结果吻合良好。研究了反应器操作参数对反应结果的影响特性。主要考察了反应温度、入口流量、入口碳烷比及催化剂负载密度等参数,综合分析了这些参数对反应物转化率、氢气及一氧化碳产率、催化表面积碳率的影响,研究了甲烷及氢气质量分数沿流动路程变化的情况,并分析了造成以上影响的原因。结果表明提高反应温度对反应有促进作用;较低或过高入口流量均会降低转化率及产率;改变入口碳烷比会较大程度影响氢气选择性及出口氢碳比;增大催化剂负载密度会有效提高反应速率但会增大积碳率。通过以上研究确定反应温度800℃、入口流量12 ml/min、入口碳烷比1、催化剂负载密度4.387 g/m~2为最佳操作条件,为进一步优化反应器结构奠定基础。研究了反应器几何结构对反应结果的影响。通过模拟不同的微通道高宽比、微通道布局结构和微通道截面形状,考察对反应物转化率、氢气及一氧化碳产率、催化表面积碳率的影响。其中改变微通道布局结构是将直线式微通道改为正弦波式,改变微通道截面形状是将矩形截面改为三角形及半椭圆形,分析并确定反应器结构对反应过程的影响规律。结果显示,降低微通道高宽比能有效增强反应器制氢效果,但同时会极大提升进出口压降;改变微通道布局结构一定程度上能增大反应速率及转化率;改变微通道截面形状对反应结果影响较小。更多还原

【Abstract】 With the international and domestic attention to environmental protection,the development of green energy has become the focus of people’s attention.In recent years,with the rapid development of hydrogen fuel cell technology,hydrogen energy has gradually become a research hotspot.However,limited by the efficiency of large-scale hydrogen production in industrialization,there is a large gap in hydrogen production capacity,which affects its development.Microchannel reactor is one of the solutions because of its fast reaction speed and good heat transfer performance.The operating parameters and geometrical characteristics of the microchannel reactor will affect the flow of internal air and the reaction process,and change the reaction product yield and hydrogen carbon ratio at the outlet.Domestic and foreign scholars have carried out a lot of research on the microchannel methane dry reforming reactor.However,due to the unique defects of the experimental method and the structural differences of different types of microchannels,it is difficult to analyze the flow and reaction in the microchannel reactor.Numerical simulation method lacks accurate reaction dynamics model,and the accuracy of results is deficient.Therefore,based on the microchannel reactor,with the aid of numerical simulation software Fluent and the coupling reaction kinetics mechanism of the operating parameters and geometric structure of the microchannel reactor impact characteristics are simulated research,investigation on conversion rate,production rate,ratio of hydrogen to carbon and carbon deposition resistance,the effect of reactor operating conditions and structure parameters was optimized.A 3d physical model of microchannel reactor was established by UG.Based on the microkinetic reaction model and single-phase flow model,the corresponding basic governing equation and catalytic reaction governing equation were established,and the detailed methane dry reforming reaction mechanism was coupled to Fluent component transport model by writing Chemkin mechanism file.After meshing and meshing independence verification,the effect of reaction temperature on outlet results is simulated,which is in good agreement with experimental results.The influence of reactor operation parameters on reaction results was studied.Parameters such as reaction temperature,inlet flow rate,inlet carbon-alkane ratio and catalyst load density were investigated.The effects of these parameters on reactant conversion,hydrogen and carbon monoxide production,and carbon ratio of catalytic surface area were comprehensively analyzed.The change of mass fraction of methane and hydrogen along the flow path was studied,and the reasons for the above effects were analyzed.The results show that increasing the reaction temperature can promote the reaction.Lower or higher inlet flow will reduce the conversion rate and yield.The selectivity of hydrogen and the ratio of hydrogen to carbon at the outlet will be greatly affected by changing the ratio of carbon to carbon at the inlet.Increasing the catalyst load density can effectively improve the reaction rate but increase the carbon deposition rate.Based on the above studies,the optimal operating conditions were determined as reaction temperature800℃,inlet flow rate 12m L/min,inlet carbon to alkane ratio 1 and catalyst load density 4.387g/m~2,which laid a foundation for further optimization of reactor structure.The effect of reactor geometry on reaction results was studied.The effects of different microchannel height-to-width ratio,microchannel layout structure and microchannel cross section shape on reactant conversion,hydrogen and carbon monoxide production and catalytic surface area carbon ratio were investigated.To change the layout structure of the microchannel is to change the linear microchannel to sine wave type,and to change the cross-section shape of the microchannel is to change the rectangular section to triangle or semi-oval shape.The influence of the reactor structure on the reaction process is analyzed and determined.The results show that reducing the aspect ratio of microchannels can effectively enhance the hydrogen production efficiency of the reactor,but also greatly improve the inlet and outlet pressure drop.Changing the microchannel layout can increase the reaction rate and conversion rate to some extent.Changing the shape of the microchannel cross section has little effect on the reaction results.更多还原