Performance of Industrial Mist Collectors Over Time

Abstract

Effective, economical control of metalworking fluid mists at the source is important, because exposure to these mists may cause adverse health effects. This study investigated performance changes over time for industrial collectors that removed metalworking fluid mist in the laboratory and in a transmission plant. Aerosizers were used to measure the efficiency of each stage in several multistage collectors as a function of mist droplet diameter, for up to one year of continuous operation. Metal-mesh, first-stage filters operated at low pressure drops and were effective at removing droplets larger than 3 to 5 microns in diameter. Some second-stage filters worked better than others. Both "65 percent" and "95 percent" cartridge filters failed after only a few weeks; their efficiencies decreased substantially over that time. Pocket filters and cylindrical cartridges used as second-stage filters also decreased in efficiency for submicron droplets. Whereas filters for solid particles load continuously to form a dust cake that increases efficiency, mist filters form no cake and load only to the point where collection equals drainage. As a mist filter loads, the interstitial gas velocity increases, so that efficiency decreases for small droplets that collect by diffusion. Although a third-stage 95 percent DOP filter showed important decreases in efficiency over time for submicron droplets, third-stage HEPA filters operated with efficiencies that consistently approaches 100 percent for droplets of all sizes, even after one year of operation. These results suggest that the performance of second-stage filters can be improved if they can be made to drain collected liquid more effectively. For high efficiency, mist collectors should use a HEPA filter as a final stage.

Experimental and modelled efficiencies during the filtration of a liquid aerosol with a fibrous medium

“…Thus, the same consequences as an increase in filtration velocity are observed, i.e. an increase of efficiency for micron-sized particles and a decrease for submicron liquid particles (Boundy et al, 2000;Contal et al, 2004;Frising et al, 2005;Leith et al, 1996;Payet et al, 1992;Peters et al, 2001;Raynor and Leith, 1999).…”

“…Joining the comments of different authors (Boundy et al, 2000;Raynor and Leith, 1999), these two effects result from a liquid accumulation in the filter volume during clogging and thus an increase in the interstitial velocity. Nevertheless, re-entrainment is also measured during the drainage stage because of the bubble bursting on the downstream side of the filter.…”

“…Liquid aerosols can be generated in several industrial machining processes (Boundy et al, 2000;Cooper and Leith, 1998;Gunter and Sutherland, 1999;Simpson et al, 2000). These mists can be formed by different mechanisms.…”

Validation of a new phenomenological “jump-and-channel” model for the wet pressure drop of oil mist filters

“…Aerosols consisting of sub-micrometer oil droplets ("mist") are an undesirable contaminant of effluent air from engine crankcases, oil lubricated compressors and other industrial processes (Brink et al, 1966;Leith et al, 1996;Boundy et al, 2000). A very common way of eliminating oil mist is by fibrous filters (Fairs, 1958;Mohrmann, 1970).…”

Influence of the test emulsion on filtration efficiency and pressure drop of mist separators for cooling lubricants

“…Filter elements consisting of fine fibres, e.g. coalesce-filter, HEPA-filter…, can have a very high liquid holdup with enormous pressure drop increase [4,5].…”