径向移动床反应器内贴壁现象的研究

STUDY OF PINNING IN A RADIAL MOVING BED REACTOR

在径向移动床反应器内,径向气流通量被一种称之为贴壁的现象所限制,从而成为连续式催化重整工艺设计中的一个重要问题.本文对贴壁现象进行了理论与实验研究,建立了一个新的数学模型.该模型不仅指出了贴壁发生的多种机制(渐进型、同时型和空腔型),提出了不同机制的判别准则,并且给出了贴壁发生时床层压降的计算式.对于渐进型贴壁,模型预测贴壁层厚度将随床层压降增加而呈线性增大,并得到了较好的实验结果.

In a radial moving bed reactor, the radial flow rate of gas is limited by a phenomenon called 'pinning'. When radial flow rate of gas increases, the normal stress imposing upon the downstream face, which is produces by the gas flow, will increase. When the stress increases to some value large enough, the friction force between particle bed and downstream face may support some particles, so these particles won't move down again and pinning occurs. In this paper, a new model of pinning has been established. It serves mainly for the rectangular moving bed reactor with cross-flow of gas, but for the industrial radial moving bed reactor, as in the continuous catalytic reforming process, it also provides some insight. From the model, we deduce that there are three types of pinnlng, i. e. progres sive, simultaneous and cavity. In progressive pinning the pinning width extends linearly with the bed pressure drop of cross flowing gas. The initial pressure drop of pinning of cavity has also been given. Satisfactory results are obtained by experiments.