摘要
针对流化床内部流体结构的复杂性和缺乏有效放大设计理论的问题,以漏斗型导流内构件强化的内循环流化床的气液运动为研究对象,利用欧拉-欧拉双流体模型构建了能描述其复杂流动的CFD数学模型,通过宏观流场、气含率分布、液体速度分布解析内构件对气液混合传质的作用原理.数值模拟结果表明：双流体模型能较好地揭示流化床内气液流场结构,流化床中漏斗型导流内构件的置入能够稳定流场和增加气泡的停留时间,明显提高相际间的混合与传质效果;通过数值分析的直观与量化获知,特定条件下上升区气含率增加10%~25%,下降区气含率的峰值增大约10倍,液体循环速度被一定程度降低,下降区的气泡较多地聚集于顶部,形成了气含率接近于1的区域而构成分布上的不均匀.数值分析的结果启示,在实际废水处理中应该寻求合适的操作区域与内构件型式,以达到液体循环速度和气含率等流体力学特性的数值结构优化,最终实现反应器的功能化与优化设计的结合.
The development of fluidized bed reactors suffers from drawbacks including a poor understanding of the complexity of internal fluid flow and the lack of an efficient theory for scale-up of the design.A computational fluid dynamics（CFD） simulation using the Eulerian-Eulerian double-phase model was used for predicting the complex two-phase flow in a reactor which was enhanced by implanting an funnel-shaped internal in the internal-loop fluidized bed reactor.The role of the conical baffle in improving the gas-liquid mixing was explored by investigating the flow field,the gas holdup distribution and the liquid velocity distribution.The simulation results demonstrate that the Eulerian-Eulerian model reasonably predicts the two-phase flow in the fluidized bed.The cone-shaped baffle is favorable for improving gas-liquid mass transfer by increasing the flow conductivity of both gas and liquid and extending the bubble retention time.The presence of the conical baffle results in an increase in the gas holdup by 10%~25% in the rising area and by a maximum of ten times in the downcomer area,but also a noticeable decrease in the liquid circulation velocity.Non-uniform distribution of bubbles is also observed in the downcomer area,and specifically the gas holdup in some areas is found to approach 1.The simulation results imply that the appropriate range of gas velocity and type of the implanted baffle should be rationalized to achieve the optimal liquid circulation velocity and gas holdup,thus leading to the optimization of reactor function and system design.
出处
《环境科学学报》
CAS
CSCD
北大核心
2011年第6期1212-1219,共8页
Acta Scientiae Circumstantiae
基金
国家自然科学基金重点项目(No.21037001)
国家科技支撑计划重点项目(No.2008BAC32B06-1)~~
关键词
废水处理
生物流化床
内构件
流体力学
数值模拟
CFD
wastewater treatment
internal-loop fluidized bed
cone-shaped baffle
hydrodynamics
numerical simulation
CFD（computational fluid dynamics）
