射流环流反应器中颗粒悬浮的数值模拟

Numerical Simulation of Suspension of Solid Particles in a Jet Loop Reactor

为确定射流环流反应器中射流所能驱动的环流速度的大小,以此来确定催化剂颗粒的粒度。在二维轴对称假定下,采用雷诺应力模型(RSM)模拟考察了导流筒与反应器直径比(De/D)、反应器底部型式、射流口与导流筒下缘距离(Hn)的变化对环流流量与射流流量比(RQ)的影响,并结合离散相模型(DPM),模拟了不同几何结构,不同射流速度下,不同粒径催化剂颗粒的悬浮情况。研究表明,De/D为0.67时RQ最大,而不同底部型式和Hn下的RQ相差均低于3.6%,影响可以忽略;但反应器底部的锥形设计以及较低的Hn值有助于改善催化剂颗粒的悬浮状况;按给定的设备结构参数和物性参数,得出了低体积浓度(约0.1%)下实现催化剂完全悬浮于整个设备的临界射流速度(Vnc),建立了Vnc与催化剂颗粒粒径的关联式。通过模拟方法实现了催化剂粒径的设计、射流速度的选择和设备结构的优化。

Suspension of the catalyst particles was studied in a jet loop reactor with computational fluid dynamics method. A 2-dimensional axisymmetry model was adopted with Reynolds Stress Model（RSM） to analyse the effect on the flow rate ratio （RQ） of circulation to jet from the diameter ratio of draft tube to reactor （De/D）, geometric structure of the reactor, axial distance of the nozzle and the draft tube （Hn）. Then the Discrete Phase Model was used to describe particle suspension against various bottom type, jet velocity and diameter of particles. Conclusions can be drawn from the simulation results： RQ is largest when De/D is 0.67 and the deviation of Ro is below 3.6% when bottom type and Hn vary. With cone bottom and lower Hn, particle suspension can be smoothly achieved. With the specified geometric parameters of the equipment and physical property of the two phases, the critical jet velocity（Vnc） that can suspend particles, of low concentration by volume （about 0.1%）, in the whole device is obtained through numerical prediction and correlation of Vnc and catalyst particle size is suggested from numerical results.