基于EMMS的循环流化床三维全循环CFD模拟

EMMS-based 3D full-loop CFD simulation of a circulating fluidized bed

对于循环流化床内气固两相流动,三维全循环计算流体力学(Computational Fluid Dynamics,CFD)模拟是最直观可靠的模拟方式。然而,受计算资源和模型的限制,目前的模拟工作大多对构体进行简化,如仅考虑提升管段,或采用二维长方形代替三维构体,或对实际装置几何尺寸进行成比例缩小等等。对几何结构的简化,忽略了出入口、周向结构或返料装置等因素对流动行为的影响,因而计算结果不能准确反映真实流场。采用基于结构的多流体模型(the Structure-dependent multi-Fluid Model,SFM)耦合能量最小多尺度模型(the Energy-Minimization Multi-Scale model,EMMS)修正曳力,完全依据实验参数建立构体和设定边界条件,对中试规模循环流化床进行三维全循环动态模拟。计算结果表明,三维全循环模拟不仅能定性预测快速流态化中典型的上稀下浓和边壁浓中心稀的非均匀分布,定量对比颗粒循环通量、浓度和速度信息与实验值也吻合较好。由于三维全循环模拟不存在几何结构简化,能直接表征真实工况和流场,特别适合于结构复杂的大尺寸工业装置模拟。

3D full-loop CFD simulation is the most reliable method to explore the gas-solid flow behavior in CFB（Circulating Fluidized Bed）. Most of the current work simplifies the geometry to reduce the calculation amount on account of the limitation of computing resource and model ability. However, those simplifications neglect the effect of local equipment structures, so the simulations can not predict the fluid flow successfully. The SFM （Structure-dependent multi-Fluid Model） coupled with a drag coefficient based on the EMMS （Energy-Minimization Multi-Scale） model was employed to perform a 3D full-loop simulation of a pilot-scale CFB without geometry simplification. The results revealed that such simulation can not only predict the heterogeneous distribution phenomena qualitatively, but also have a reasonable agreement with experiment data, such as the solids flux, the profile of pressure, the distribution of solids volume fraction and axial velocity. Consequently, this method is more suitable for the simulation of large-size industrial devices with complicated structure.