摘要
采用多孔介质模型描述两床层间的气体分布板,开发了一种多层流化床典型结构单元的计算流体动力学(CFD)模拟方法,研究了操作气速对多层流化床床层流化状态及其溢流管内颗粒流动特性的影响。结果表明:层间溢流管内颗粒料位具有缓冲作用,使得颗粒进入下床层后被迅速均匀分散,保证了下床层固相均匀性。流化气速增大,下床层进入溢流管的气体量增加,导致管内密相区范围增大、浓度降低、浓度梯度增大,密相区与稀相区间的过渡区范围增大,密相区内逐渐出现气泡或气体栓塞,同时使溢流管内上升气流的阻挡作用增强,上流化床层向溢流管的间歇进料难度变大,溢流管上方出现料位积累。颗粒溢流状态的改变和间歇进料难度的加剧可能是颗粒溢流失稳的原因。
By using the porous media model to simulate the gas distributer,a method was established to simulate the typical structural unit of the multi-stage fluidized bed via computational fluid dynamics(CFD).Based on it,the effect of operating gas velocity on the fluidization state in adjacent bed layers and particle flow behaviors in the downcomer was studied.The results showed that the particle bed in the downcomer had a buffering effect which made the particles quickly dispersed after entering the lower bed and ensured the homogeneity of solid phase in the lower bed.With the increase of operating gas velocity,the gas short-circuited into the downcomer from the lower bed increased,resulting in two effects on particle overflow.Firstly,in the downcomer,the solid concentration of dense phase zone decreased,the concentration gradient,the length of dense phase zone and the length of transition zone increased,then bubbles and gas embolism started to appear in the dense phase zone.Secondly,due to the enhanced blocking effect of the ascending airflow in the downcomer,the intermittent solid flow from the upper bed to the downcomer became more difficult,and the particle accumulation occurred above the downcomer.The change of particle flow state and the increasing difficulty of intermittent particle flow from the upper bed to the downcomer may be the possible reasons for the instability of particle overflow.
作者
陈城
杨遥
黄正梁
孙婧元
王靖岱
阳永荣
李金安
CHEN Cheng;YANG Yao;HUANG Zhengliang;SUN Jingyuan;WANG Jingdai;YANG Yongrong;LI Jinan(State Key Laboratory of Chemical Engineering,College of Chemical and Biological Engineering,Zhejiang University,Hangzhou 310027,China;Chenzhou Sinochem Fuyuanxincailiao Company,Chenzhou 424202,China)
出处
《化学反应工程与工艺》
CAS
2021年第5期446-456,共11页
Chemical Reaction Engineering and Technology
基金
浙江省自然科学基金(LY19B060015)。
关键词
多层流化床
溢流管
颗粒下料
计算流体力学
multi-stage fluidized bed
downcomer
particle overflow
overflow-cup
computational fluid dynamics
