Application of CFD simulation for optimisation of the multi-pipe gas distributors in a large-scale shallow bubble column
Journal Title: Science Paper Online - Year 2008, Vol 3, Issue 12
Abstract
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 800 mm in diameter at the superficial gas velocity of 0.1 m/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.
Authors and Affiliations
Guang LI , Xiaogang YANG , Qingbai CAI, Gance DAI
Keywords
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