On Measurement And Simulation Of Flow In Mixer-settlers

Mixer-settler is one of the most widely used extraction equipment in rare earthindustry with the advantages such as stable operation, high stage-efficiency, simplestructure and easy scale-up. Study on fluid dynamic performance of mixer-settlerhelps to intensify the extraction process, improve the separation efficiency and carryout the design of new high-efficient extraction equipments. In this paper, PIV(Particle Image Velocimetry) measurement for the flow field and CFD(Computational Fluid Dynamics) simulations are used to investigate the box-typemixer-settlers for fluid flow. The influence of many factors on impeller performanceis discussed and a novel impeller is proposed to improve suction and mixingcapability.Firstly, the mixer-settler in rare earth industry is simulated by Fluent software.Velocity vectors are used to reveal the flow characteristics and analysis for turbulentenergy is carried out. And power, head and mixing time is calculated to evaluate theperformance of BSTRRB used in industry. The results show that the phenomenon thatthe fluid at the top of mixer flows at low velocities and mixing time is too muchlonger exists in the industrial mixer-settler, which is the question to be resolved in thelaboratorial study.Secondly, PIV measurements for flow field in the laboratorial mixer-settler arecarried out. The effect of baffles and the upper plate, impeller diameter and impellertype on the flow field is studied. Results show that baffles increases the turbulenceeffectively and impeller diameter has a direct influence on the range of circulation.Impeller type decides the structure of flow field. Under the same installation heightcondition, BSTRTB makes the mixer to be an axial flow field, while TSTRTB leadsto a radial flow field. Meanwhile，PIV results can be used for the validation of CFDsimulation in the subsequent work.Finally, CFD simulations for the laboratorial mixer-settler are performed. Theeffect of baffles and the upper plate on flow filed and the effects of different factorssuch as impeller type, impeller installation height, impeller diameter, the number andheight of blades, inlet flow rate and the diameter and height of antechamber outlet onimpeller performance are investigated. Power number, flow number and head number are used as evaluation parameters and mixing time is calculated by simulations. Basedon all results, a new impeller is proposed. Results show that baffles effectivelyrestrain the vortex flow in the mixer and improve the mixing, reducing mixing timeby39.86%. The reason why impeller type decides the structure of flow field isexplained on aspects of pressure contours and lower circulation flow rate. Bycomparisons, BSTRTB can provide the most suction capability than other impellertype under the same power input condition, while TSTRTB and TSTRRB are theworst ones. However, TSTRTB is better for mixing than BSTRTB under the sameinstallation height. Impeller diameter and impeller installation height have animportant influence on impeller performance. When installation height of BSTRTB israised to27mm, the flow field becomes radial-flow from an axial flow field, and theimpeller has no suction capability but an improved mixing efficiency. Based on thestructure of BSTRTB, a new impeller is proposed. Through validation, the newimpeller can keep the good suction capability under the higher installation locationand intensify the mixing, which other impeller types cannot reach.