锥形下行床内流动行为的CFD数值模拟

CFD Study of Flow Pattern in Conical Downers

针对传统圆柱形下行床中固含率较低的问题,提出采用锥形下行床作为褐煤热解反应器。采用CFD软件进行数值模拟,考察了颗粒循环通量、密度、粒径等因素对锥形下行床中径向和轴向流动规律的影响。结果表明:增加颗粒循环通量或降低颗粒密度均可显著提高床层固含率平均水平,并强化颗粒对浓相环形区峰值的影响;颗粒粒径对固含率影响较弱,主要影响浓相环形区出峰位置;颗粒循环通量显著影响着反应器内轴向压力的变化幅度。通过考察气固轴向速度分布发现,减小颗粒密度和粒径可降低气固间滑移速度,有效提高颗粒的跟随性。与传统圆柱形下行床相比,锥形下行床可显著提高床层平均固含率,适合于褐煤热解等以颗粒相作为反应物的快速反应。

Conical downer,which is expected to replace conventional cylindrical downer as pyrolyzer,was proposed to address the issue of low solid holdup.Through computational fluid dynamics(CFD)simulation,the effects of solids flux,density and diameter on the radial and axial flow behaviors in conical downers were systematically investigated.The results show that,high solid flux and low particle density are beneficial for the enhancement of solids holdup and can strengthen the effect of solids phase on the peak value of dense ring,while particle diameter mainly affects the radial position of dense ring.In addition,it is found that changing solid flux can significantly affect the variation amplitude of pressure along axial direction.According to axial velocity distribution,it is concluded that lowering particle density and size can reduce slip velocity.From the comparison with conventional cylindrical downers,it is found that conical downer can improve solid holdup and fit for the ultra-fast reactions with particles as reactants,such as lignite pyrolysis.