提升管内气固流动行为的数值模拟

应用计算流体力学软件Fluent,对空气为连续相、固相为催化裂化反应催化剂的循环流化床提升管内的气固流动行为进行模拟。采用用户自定义函数引入颗粒与壁面的恢复系数和颗粒的镜面反射系数,对颗粒在边壁处的部分滑移运动进行描述。采用不同的计算动力学模型及参数,数值模拟了径向颗粒浓度、轴向床层压降的空间分布,以及用以描述颗粒脉动动能的颗粒温度与固含率的关系,并与文献报道的实验和数值模拟结果进行对比分析。结果表明,选取的颗粒动力学理论模型及参数、颗粒部分滑移边界条件及气固曳力模型,可计算得到合理的颗粒轴向及径向分布,验证了提升管中存在典型的径向环核流动结构和轴向压降分布。进一步分析表明固含率显著影响颗粒温度,当固含率为0.05~0.1,颗粒温度存在转折区。

CFD Simulation of Gas and Solid Flow Behavior in a Riser

Gas-particle flow behavior in the riser section of a circulating fluidized bed(CFB) was simulated using computational fluid dynamics(CFD) software-Fluent.The kinetic theory of granular flow(KTGF) was applied to describe the granular pressure and stress to close the governing equations.Fluid catalytic cracking(FCC) particles and air were used as the solid and gas phases,respectively.The part-slip boundary condition of solid was described using the user defined function in the Fluent.To identify the validity of the model and various conditions adopted in this simulation,gas and particle flow profiles were obtained for time-averaged radial solid volume fraction and axial bed pressure drop.Furthermore,the typical core-annular flow structure was observed.The granular temperature which is the scale of the fluctuant energy of single particle could be predicted by simulation.It was investigated that the granular temperature was related with solid volume fraction.When solid volume fraction ranged from 0.01 to 0.05,granular temperature was in the transition region from dispersed values to well-regulated ones.