When removal of micron and submicron sized particles is difficult or impossible with conventional clarifiers or flow through filters, cross-flow micro-filtration systems are capable of virtually complete removal. The cross-flow micro-filtration process also breaks oil water emulsions without chemical addition. Additionally the porous polypropylene construction enhances the coalescing of submicron droplets of free oil.
Cross-flow micro-filtration, unlike dead-end filtration, has a filtration surface which is continuously swept by flowing liquid. The shear of the flowing liquid along the tube wall minimizes the buildup of the solids on the filtration surface; thus, cross-flow filtration affords the possibility of nearly steady state operation. With conventional dead-end filtration, the filtrate rate decays as the solids layer builds up. In cross-flow micro-filtration, the direction of the feed flow is parallel to the filter surface so that accumulated solids are continuously swept away by the force of the flow.
The cross-flow micro-filter modules contain multiple porous polypropylene tubes, which have a nominal pore size of 0.2 microns. With this small pore size, large colloidal particles, and bacteria can be filtered from a process stream, but not molecular level substances. The system also has the ability to reject and
concentrate high molecular weight emulsified materials such as petroleum based oils, animal fats vegetable oil, turpenes and other compounds.
The maximum pressure used for processing a liquid stream is generally 30-40 PSID with cross-flow micro-filtration systems.