填充床中气体流动与气固反应的相互作用

Interaction between flow of gas mixture and gas-solid reaction in a packed bed

对界面化学反应和粒内扩散联合控制的气固反应,考虑到反应造成的混合气体质量和密度的变化,研究了填充床中等温条件下的快速气固反应和气体运动的相互作用,建立了相应的数学模型.数值分析表明,按耦合分析和非耦合分析得到的混合气体速度完全不同;忽略反应造成的混合气体密度变化,相当于增加一个额外的源项或汇项,因此当反应气体与惰性气体摩尔质量相差较大时,不能忽略反应造成的混合气体密度变化;按耦合分析和非耦合分析得到的浓度场也有很大差别,反应气体浓度波(物质波)阵面的差别也很大;化学反应明显地阻滞反应气体浓度波的推进;当平均压力降和其他条件相同时,反应器越长波阵面推进的量纲1距离越短;反应活跃区的发展对速度场的影响极大.

For the case that the overall gas-solid reaction in a pellet in a packed bed is controlled simultaneously by the chemical reaction on the reaction front and the intraparticle diffusion, the interaction between compressible flow and isothermal gas-solid reaction in the packed bed was investigated. On one hand, both the mass and density changes of the gas mixture due to chemical reaction affected the motion of gas mixture considerably, on the other hand, the flow of gas mixture also affected the gas-solid reaction. A coupled model was presented to formulate these interactions. A numerical solution showed that the velocity profiles obtained from the coupled models were very different from those obtained with the existing non- coupled model, not only in magnitude but also in the trend of velocity variation in the packed bed. Because the ignorance of the density change of gas mixture due to reaction would lead to an extra sink of gas mass dissipation or a source of gas mass generation, the effect of the density change of gas mixture on itself flow could not be neglected, especially in the situation where there was an observable difference between the molar masses of reactive gas and inert gas. The numerical results further showed that the concentration profiles obtained from the coupled models differed greatly with those obtained with the non-coupled model, and the progress of the concentration wave front of reactive gas obtained from the coupled models was obviously different from that obtained with the non-coupled model. It was found that chemical reaction blocked greatly the progress of concentration wave front of reactive gas. If the average pressure drop across a packed bed and the other conditions were kept unchanged, the longer the packed bed, the shorter the normalized distance of wave front advance. The evolution of the active reaction zone in a packed bed affected the velocity profile of gas mixture considerably.