Numerical Simulation Of Gas-Solid Two-Phase Flow In Frustrated System Of The Third Stage Separator Of FCCU

In this dissertat ion a detailed st udy on ga s-solid two-phase flow behavior, which includes three type s of structure of the fourth st age separation system s, gas flow field distribution in two type s of critical nozzle struct ures and catal yst particle motion chara cteristics, i n frustrated sys tem of the third st age separator of FC CU, was made wi th Fluent software. The study provides valuable guida nce for further improvement i n frustrated system structure. Validity of the simulat ed re sults has been substantiat ed by compar ison with theoretic al ca lc ul ation resul ts.The results indicate that, for Type 1 of the tradit ional fourth stage separation system, the rece iving tank has t he function of pre-separa ti on t o catalys t particl es in the fl ue gas. However,pressure in the receiving tank is much highe r than that in dipleg of the fourth stage s eparator,which is prone to reve rse flow from the receiving tank to the fourth stage separat or and blocking in the dipleg. The structure is suitable for working conditions where particle concentrati on is dense. Compared wi th Type 1 of the traditional fourth stage separ ation sys tem, Type 2 is more stabl e in working condit ion. R egularity is relatively st rong for gas flow field in the fourth stage separator tube. The operation i n the fourth stage separator tube is normal. Periodic secondary vortex, making particle residenc e time longe r, happens in the dipleg, the ex istence of which may lead to wear of the wall. When part icle concentration is very dense, dipleg can block up easily. The working condition in new typ e of the buil t-in fourth stage separ ation system is safer than the t raditional ones, sol ving the problem of wear of the wall and blocking in the dipleg. The fourth stage separator has a higher separation efficiency than the fourth stage separator tube. But escape of part icles at the balance tube low the separation efficiency of the fourth stage separat ion system, which can be solved by adding a conical ash dam per in t he receivi ng tank. The dense particle concentration in annular space and conical section of the ash hopper is prone t o wear out the wall of t he fourth st age separa tor. For the orifi ce plate type critical nozzle, high speed compres sible flow comes into bei ng under pressure difference of 0.14 MPa. Gas flow jets in t he main flue collector through throat and at a speed of 84 m/s on the wall. The wear z one of the nozzle is mainly on the wall of the main flue collector, with a distance of 1000~1500 mm from the critical nozzle insertionpoint along the main flue collector ax ially. The worn-out parti cles are larger than 5 μm.Reducti on of parti cle diameter in t he flue ga s can decrease erosion of particles t o the flue col lector of the critical noz zle. For the Laval type critical nozzle, shock wave phenomenon happens i n t he diffuser. Rotary eddy ex ists on the wall, the cent er of whi ch locates at x=-254 mm, away from the wall about 13 mm. Particl es smaller than 10 μm wear the wall more severe ly. The wear zone is on the back end of the di ffuser of the nozz le, at the zone of 0~500mm. Particle abrasion doesn’t happen in the main flue collect or for the La val type critical noz zle. The nozzl e can be protected by decreasing particle concentration in the flue gas.