Continuous Self-Cleaning Membrane Enhanced Filters for Aerosol and Smoke Filtration

摘要

A novel filter system has been developed for filtering mist and smoke particles by combining a centrifugal prefilterrnwith an integral high efficiency micro-porous membrane filter. Mist-laden air flows radially inward into arncylindrical assembly of stacked, but slightly separated, annular disks which constitutes the inertial prefilter, and arnmembrane filter element within the hollow core defined by the disk stack. The assembly rotates at high speed,rncausing multiple boundary layers to develop at the perimeter entrance of the disk pack. The momentum of thernrotation is transferred to entrained particles in the incoming air stream. As a result, coarse particles with sufficientrnmass are separated by the centrifugal force and collected within the filter housing. Any fine particles that penetraternthe boundary layers are collected on the surface of the high efficiency membrane filter. The centrifugal forcernprevents the membrane from fouling by continuously expelling coalesced/agglomerated particles on the membranernsurface. Thus, this unique filter system is self-cleaning and offers a constant pressure drop. A prototype wasrnchallenged with mist and smoke particles generated from an oil-based metalworking fluid. The prototype was testedrnat a maximum rotation speed of 3450 RPM, with airflow rates up to 400 CFM. The membrane air-to-cloth ratiornaveraged over 30 ft/min. Filtration test results indicated a collection efficiency over 95% for 0.5 μm diameterrnparticles. The device was operated continuously for more than one day, and challenged with high concentrations ofrnoil mist and smoke particles to evaluate long-term performance. The results showed that the system pressure droprnand volumetric airflow rate were constant (i.e., no blinding of the filtration media). Conversely, when rotation wasrnterminated, the membrane filter blinded immediately, but completely recovered after reinitiation of disk rotation.rnThe attributes of this filtration methodology are high collection efficiency, stable pressure drop and flow rate, highrnparticulate loading and low maintenance. The integrated filter system is called a NovaFilter?.