Abstract: A 2D numerical model was developed to describe the flow of liquid and gas phases in a novel triplet loop fluidized bed and multiplex loop fluidized bed,which had been developed in authors' early research.Local flow field,gas holdup distribution and liquid velocity distribution were analyzed to investigate the influence of internal loop numbers on hydrodynamic characteristics of the fluidized bed,in order to explore the best internal structure and operation factors for energy saving of fluidized bed.The simulation results showed that triplet loop and multiplex loop mostly affected the mixing of fluid from the riser and the downcomer compared with the simplex loop.Increasing internal loop number could shorten circulation distance and time consumed of the internal loop,which was beneficial to enhancing interface mixing and reaction.However the flow pattern in triplet loop and multiplex loop fluidized bed was still similar to plug flow,while microcirculation was scarely observed.Multiplex loop fluidized bed had better hydrodynamic characteristics than triplet loop fluidized bed,which meant that radial and axial homogenization of liquid velocity and higher oxygen transformation efficiency could be observed with larger internal loop numbers.This research implied that flow field reconstruction by means of structure reconstruction was favorable for the improvement of hydrodynamic characteristics,which should be one of the research and development tools of aerobic biological treatment of high organic load wastewater.

Key words: internal loop fluidized bed, triplet loop, multiplex loop, computational fluid dynamics

摘要： 针对前期研究开发的新型三重环流与多重环流流化床,构建气液两相流的二维数值模型,分析微观流场、液体运动速度和气相含率,剖析环流数对流化床流体力学特性的影响和对内循环过程的改善,寻找反应器运行过程节能的结构与优化的操作条件。通过数值模拟发现:基于单重环流,多重环流作用主要改变流体在上升区和下降区之间的相互混合和交汇,增大环流数可缩短流体运动的循环路程和时间,有利于加强相际之间的混合,但床内整体流态仍接近推流,微循环的存在所占比例较小;多重环流流化床的流体力学性能优于三重环流,随着环流次数的增多,液速在径向和轴向上分布更均匀,气泡逆流进入下降区,有利于反应器整体氧传质效率的提高。通过流化床结构改变实现的流体重构支持流体力学性能的改善,是高负荷有机废水好氧生物处理期待选择的开发方向。

关键词: 内循环流化床, 三重环流, 多重环流, 计算流体力学