Establishment Of Model And Study On Crossflow Microfiltration With Gas-sparging Using Tubular Membranes

Based on the analysis on membrane fouling in crossflow microfiltration (CFMF) with gas-sparging using tubular membranes, the status of gas-liquid mixture fluid is well revealed by the calculation of slug flow which has the profoundest effects on permeate flux enhancement. A model which can calculate the time dependant flux during gas-liquid two-phase CFMF is advanced for the first time by combining the calculation of velocity profile of falling film with single particle model. And the calculated results obtained by this model were validated with the experimental data achieved in gas-liquid two-phase CFMF of titanium dioxide suspensions, achieving a satisfactory agreement.In this paper, the course of gas-liquid two-phase CFMF is divided into two stages by analysis on the formation and development of membrane fouling: pore blocking stage and cake formation and development stage. Some studies have come to the conclusion that it is not related to the introduction of gas that the permeate flux declines rapidly in the first stage. However, gas sparging leads to a big change in the status of gas-liquid mixture fluid in the second stage, which is well revealed by the velocity calculation of Taylor bubble, falling film and liquid slug in this paper. For the purpose to get the liquid velocity acting on the particles deposited on cake, a method that can calculates the velocity profile of falling film is deduced. Thus it is allowed to get the accurate drag force acting on particles deposited on cake. Then combining it with single particle model, the critical particle size at different time is achieved by analysis on force balance. After that, it is available to calculate the deposited particle mass, cake thickness and specified cake resistance during a specified intermittence. So the time dependant permeate flux during gas-liquid two-phase CFMF using tubular membranes is achieved by iterating the procedure mentioned above.To achieve the highest permeate flux under same operating conditions, experimental studies were also carried out on effects of membrane inclination angles and flow directions on permeate flux. The results show that: the steady state flux is found to be the highest when membrane inclination is 45°from horizontal among all angles examined, and the flux for 30°or 60°is smaller than 45°but higher than that when membrane module is vertically reposed, minimum steady state flux is achieved when membrane module is horizontally reposed; Flux with downwards flow of gas-liquid mixture fluid is higher than upwards.