双层格栅桨搅拌容器内气液两相混合

Gas-liquid mixing in a dual grid-disc impeller stirred vessel

为了提高搅拌容器内的气液混合效果,在标准Rushton桨的基础上,用格栅圆盘代替实体圆盘,设计一种格栅搅拌桨。采用计算流体力学的方法,研究双层格栅桨的气液混合性能,并与标准Rushton桨进行了对比。研究结果表明:在所研究的工况条件下,双层格栅桨搅拌容器内的流型仍为典型的双循环流动结构,但搅拌桨附近流体的轴向速度和泵送能力得到了提高,改善了搅拌桨附近、上下两层桨之间以及搅拌容器上方区域内气体的分散状态。就搅拌功率而言,双层格栅桨通气前的功率准数比标准Rushton桨约低5%,具有一定的节能效应;通气后双层格栅桨的相对功率需求约大8%,气液混合效率略高。

In order to improve the gas-fluid mixing efficiency in the stirred vessel, by replacing the solid disc of standard Rushton impeller(RT) with a grid disc, the grid-disc Rushton impeller(RT-G) was designed. Grid independence test was completed. Gas holdup distributions of dual RT were numerically studied by the computational fluid dynamics(CFD) technique and compared with the literature data so as to validate the reliability of the numerical model and simulation method. The same numerical strategy was used to investigate the gas-liquid hydrodynamics of dual RT-G. Results were compared with those of dual RT and it was found that, under the operating condition studied here, dual RT-G had the same double-circulation flow field structure as RT. However, fluid axial velocity around the two RT-G impellers and axial pumping capacity could be enhanced, which contributed to improve the gas distribution state especially in regions adjacent to the impellers, between the upper and lower impeller, as well as in the top area of the stirred vessel. In terms of power consumption, the power number of dual RT-G before gassing was about 5% lower than that of dual RT, which indicated that RT-G was more energy-saving. The relative power demand(RPD) of dual RT-G after gassing was about 8% higher than dual RT, and accordingly was more efficient in gas dispersing.