Research Of Ultrafiltration System With Reciprocating Rotating Tubular Membrane And Enhancement Mechanism

The membrane separation technology has been developed rapidly and used widely. Butthe membrane fouling problem has been a bottleneck restricting membrane separationtechnology. So how to solve the membrane fouling problem become increasingly urgent. Atpresent, high cost, complicated operation and large membrane damage as the major problemin controlling the membrane fouling. To reduce membrane fouling by the hydraulic shear ofmembrane surface, with great potential, can achieve continuous filtration, wide application,easy operation. The reciprocating rotary tubular membrane system can reduce the fouling andconcentration polarization and delay the permeate flux decline by creating the shear rate at themembrane surface.This paper aims to conduct experiments of the reciprocating rotary tubular ceramicmembrane system. First, the influences of different operation parameters were discussed onthe filtration flux to reveal the mechanism of enhanced filtration. On this basis, orthogonalexperiments were designed to determine the optimum operating conditions and theimportance order of influential factors. And using mathematical and statistical softwareestablished the steady-state membrane filtration flux model. Then a Computational FluidDynamics, CFD, with realizable κ-ε model was therefore developed to predict the complexflow field in the filtration system. Using Gambit, the processor of the Fluent software, to buildtwo-dimensional geometric model. Use Fluent software for numerical calculations. Thissection focuses on the distribution of the flow field at different rotational speed, thedevelopment of flow field with time and distribution of the shear stress on membrane surfacewith time. Finally, took into account the influence of the rotation speed and the reciprocatingrotation cycle on the concentrated filtration test and researched the difference betweenconcentrated filtration and the whole loop filtration and made a technical evaluation ofmembrane filtration systems.The results of experiments showed that compared with the unidirectional rotatingfiltration and dead-end filtration under the same conditions, the reciprocating rotary filtrationsystem showed superiority in reducing membrane fouling. Ultrafiltration skim milk solution tests for investigating the influences of operating parameters revealed that, increasing of feedconcentration could lead to the decrease of membrane permeate flux, and membrane fluxcould be reduced once the TMP was too high. The increasing of rotating speed could inducethe increasing of shear enhancement and membrane permeate flux. As the reciprocatingrotating cycle increased, the quasi steady membrane permeate flux firstly increases and thendecreases. When the feed fluid velocity come to the membrane module velocity, rotated themembrane module in the opposite direction instantaneously, generating the largest shear rateon the membrane surface and gaining the largest permeate flux. The results of orthogonalexperiments showed that the order of importance was rotating cycle> feed concentration>rotating speed> TMP. It was also found that the optimum reaction conditions is rotatingcycle2s, feed concentration4g/L, rotating speed100rpm, TMP100kPa. Usingmathematical and statistical software established the steady-state membrane filtration fluxmodel.The simulation results demonstrated that the greater the rotation speed, the greater thevelocity of the fluid around the surface of the membrane, the faster the speed of the flow fieldreach to a stable state, and when the rotation speed was at low speed, the flow field was notsignificantly change with time. The shear stress of the membrane surface showed a gradualdecreasing trend with time. The greater the speed, the greater the shear stress on membranesurface; The closer the fluid velocity and the membrane module velocity, the smaller the shearstress on the membrane surface; When the rotational speed is low, the shear stress onmembrane surface hardly change with time. Realizable κ-ε model, hope to be the microscopicunderstanding tools, reasonably predicts the complex flow field in the filtration system, whichhence saving time and money of experiment.Furthermore, the concentrated filtration test results demonstrated the influence of therotation speed and the rotation cycle was similar to the whole loop filtration. The specificenergy consumption per m3permeate of the reciprocating rotary filtration system was lowerthan the unidirectional rotating filtration under the same conditions.