短接触旋流反应器混合区内气固返混特性模拟研究

Modeling of Gas-Solid Back-Mixing in the Mixing Region of Short-Contact Cyclone Reactors

采用欧拉双流体模型模拟短接触旋流反应器内气固两相流动,加载无反应组分输运方程计算入口混合区内气固停留时间分布（RTD）。根据各截面上下行流率分配,定义了截面返混比,并考察了入口结构型式对气固返混特性的影响。研究结果表明,反应器混合区内固体催化剂的停留时间比气体小;气体在入口混合区内返混程度比固体颗粒显著,颗粒接近平推流;气体截面返混比为0-0.5,且随着轴向位置增大呈现先增加后减小的趋势;轴向入口设导向叶片增大了反应器混合区内气体轴向返混;与直切式和斜上切式结构相比,斜下切式结构反应器混合区气体返混程度较弱,有利于催化裂化反应。

Gas-solid two-phase flow in cyclone reactors was simulated with Euler-Euler model, and the gas-solid residence time distribution （RTD） in the mixing region was studied using species transport equation under no reaction mode. The cross-sectional back-mixing ratio （Rmix） was defined to quantify the gas and solid back-mixing in the mixing region of the reactor. The effects of entrance structure on the back-mixing of gas and solid were also investigated. The results show that the residence time of catalysts is shorter than that of gas. The back-mixing of gas is stronger than that of the catalysts, and the particle flow is close to plug flow. In the mixing region of the reactor, the Rmix values vary from 0 to 0.5, which increases first and then decreases with the increase of axial position. The back-mixing of gas becomes obvious in the mixing region when the guided vane is installed in the axial inlets. Comparing with reactors with upward and straight tangential inlets, the back-mixing of gas in the mixing region is weaker with downward tangential inlets, which indicates that reactors with downward tangential inlets are beneficial to the catalytic cracking reaction.