Mechanical coalescers, which are the more common type of coalescers, operate by physically altering a droplet by mechanical means. They are commonly applied in the global oil and gas industries for the removal of water or hydrocarbon condensate. While coalescers by definition function as a separation tool for liquids, they are also used, and mistakenly referred to, as filters.
In the area of compressed air purification, coalescing filters are used to separate liquid water and oil from compressed air using a coalescing effect. Coalescence (physics) shows how coalescing filters operating at lower temperatures and high pressures work better. These filters additionally remove particles. The most commonly used media in this case is borosilicate micro-fiber.
In the Oil and Gas, Petrochemical and Oil Refining industries, liquid-gas coalescers are widely used to remove water and hydrocarbon liquids to less than 0.011 mW (plus particulate matter to less than 0.3 µm in size) from natural gas to ensure natural gas quality and protect downstream equipment such as compressors, gas turbines, amine or glycol absorbers, molecular sieves, PSA's, metering stations, mercury guard beds, gas fired heaters or furnaces, heat exchangers or gas-gas purification membranes.
In the natural gas industry, gas/liquid coalescers are used for recovery of lube oil downstream of a compressor.  All liquids will be removed but lube oil recovery is the primary reason for installing a coalescer on the outlet of a compressor.  Liquids from upstream of the compressor, which may include aerosol particles, entrained liquids or large volumes of liquids called "slugs" and which may be water and/or a combination of hydrocarbon liquids should be removed by a filter/coalescing vessel located upstream of the compressor. Efficiencies of gas/liquid coalescers are typically 0.3 µm (0.3 micron) liquid particles, with efficiencies to 99.98%.
Liquid-liquid coalescers can also be used to separate hydrocarbons from water phases such as oil removal from produced water. They have been also used in pyrolysis gasoline (benzene) removal from quench water in ethylene plants, although in this application, the constant changing of cartridges can lead to operator exposure to BTX (benzene, toluene and xylene), as well as disposal issues and high operating costs from frequent replacement.