Study On The Mixing Performance Of Multi-stage Impeller In The Mixing Of Pseudoplastic Fluid

Stirred vessels with multiple impellers are very common existed in the industrial process and are more often used for liquid-gas mixing, solid suspensions, heat transfer and the mixing of viscous fluids. In the gelling mixing process of FCC catalyst, lots of gelatinous pseudoplastic fluids with high consistency will be generated. It is a difficult work to mixing the pseudoplastic fluid due to its high viscosity and shear-thinning features, and the multiple impeller system used in the factory can’t give a good mixing property. Here, numerical simulation method was used to study the cavern, flow flied and mixing performance of multi-stage impeller in the mixing of pseudoplastic fluid.Software Fluent is used to study the cavern formation in a1/10zoomed gelling mixing tank. The cavern size as a function of agitation speed is obtained and when the speed reaches to360r/min, the fluid can be agitated in the whole tank. In addition, according to the research for shear rate distribution and apparent viscosity distribution, it can be found that, the apparent viscosity distribution is closely related to the shear rate distribution, and with the agitation speed increases the apparent viscosity declines rapidly and distributes evenly in the whole tank.Four type of impeller combinations are used to study the influence of combination type on the flow field. The combination type has a great effect on the flow field. Parallel flow formed in the tank with radial flow impeller and other type can produce a merging flow on the bottom region of the tank. Take six-blade PBT combination for instance, the effect of impeller spacing on flow regime is investigated and the impeller spacing value is obtained when the merging flow formed in the whole tank for all types of impeller combination.Based on the calculation of steady-flow field, numerical simulation of the mixing process is finished. The results show that, PBT impeller combination is most suitable for the mixing of pseudoplastic fluid and it can provide enough shear stress and axial circulation. The mixing efficiency of PBT impeller combination is57%higher than the original combination, and the mixing efficiency of axial flow impeller combination is only48%higher than the original combination due to its lower shear property. Radial flow impeller combination can’t obvious improve the mixing efficiency.