ENHANCEMENT OF PERMEATE FLUX BY GAS SLUGS FOR CROSS-FLOW ULTRAFILTRATION IN TUBULAR MEMBRANE MODULE

Flux enhancements by gas slugs for dextran T500 solutions ultrafiltrat ed in a ZrO2/carbon tubular membrane module were measured and are disc ussed for various resistances of the concentration boundary layer. The se resistances are functions of the liquid velocity, the transmembrane pressure, and the feed concentration in the liquid-phase ultrafiltrat ion. When the boundary layer resistance is low, the flux enhancement b y gas slugs is limited. For a liquid ultrafiltration system with a sev ere concentration polarization, or operated in conditions of low liqui d velocity, high transmembrane pressure, and high feed concentration, flux enhancement by gas slugs is very significant if the gas velocity exceeds a certain threshold. This threshold gas velocity depends on th e extent of the concentration polarization in the single liquid-phase ultrafiltration system. It is concluded that the same permeate flux ob tained in single liquid-phase ultrafiltration with a higher crossflow velocity can also be achieved with a lower liquid velocity by introduc ing gas slugs of moderate velocity, and lead to reduced energy consump tion.