CFD优化大型浅层鼓泡塔管式气体分布器结构

分布器结构影响大型浅层鼓泡塔反应器性能,采用CFD模拟研究了5种四管气体分布器,各分布器的通气管均匀布置在不同的分布环上（0.3/0.4/0.5/0.6/0.7＊DT）,模拟采用了双流体方法和多气泡簇MUSIG模型。文中较全面的考察了高表观气速下（Ug=0.1m/s）管式分布器分布环直径对反应器流型、相含率、液速、湍b流、气泡大小以及混合时间的影响;模拟结果表明整体气含率和混合时间均随环径比先增大后减小,气含率的最佳环径比在0.4左右,而混合时间最大值出现在0.5d/DT附近,当环径比小于时0.5,鼓泡塔内为单循环流动,大于此值,鼓泡塔内将形成双循环流动,不利于混合。

Application of CFD simulation for optimisation of the multi-pipe gas distributors in a large-scale shallow bubble column

It has been generally acknowledged that the configuration of a gas distributor has significant impact on fluid dynamics and mixing in shallow bubble column reactors.This study employs computational fluid dynamics （CFD）-based models to simulate transient gas-liquid flow in a large-scale shallow cylindrical bubble column of 800mm in diameter at the superficial gas velocity of 0.1m/s.An Eulerian-Eulerian two-fluid model along with the stand k-ε turbulence model is adopted to simulate flow generated by gas sparged through five different multiple-pipe gas distributors which the four pipes are uniformly mounted at different distribution rings with ring to bubble column diameter ratios of 0.3,0.4,0.5,0.6 and 0.7.Multiple-Size-Group （MUSIG） model is also employed in the simulation to account for bubble break-up and coalescence.The effects of the diameter of distribution rings for allocating gas sparging pipes in the gas distributor on hydrodynamics,gas hold-up,mixing,turbulence and bubble size is systematically investigated.The simulation results clearly show that gas hold-up and mixing characteristics in the bubble column are affected by the ring to bubble column diameter ratio.It is demonstrated that the mixing time and overall gas hold-up increase with the increase of ring to bubble column diameter ratio initially but decrease with further increasing such ratio.It is found from the simulation that the optimum ring to bubble column diameter ratio is about 0.4 for the best gas hold-up distribution and such a ratio of 0.5 corresponds the longest mixing time.The CFD modelling results also reveal that the flow pattern inside the bubble column is dominated by single circulation when ring to bubble column diameter ratio is smaller than 0.5 while double-circulation flow appears when the ratio is larger than 0.5,thus impairing the mixing in the bubble column.A comparison has been presented between the simulation and the experimental data.