Coalescing filters are specialized filter media designed to collect and remove oil and other vapors or mists from process air streams. Similar to mist collectors or eliminators, coalescing filtration systems force air or gas through a series of fibrous panels or films. While the air or gaseous material can permeate the tangle, vapors and other particles adsorb or collect on its surface. These fine particulates merge and drain away.
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Purpose of Coalescing Filters
Common contaminants removed by coalescing filters include condensed water droplets, liquid oil and oil vapor, dust, rust and other ambient air particles. If not removed, these particulates can block valves and passageways, cause seals to swell, corrode piping and result in the overall mechanical failure of pneumatic manufacturing equipment.
Application of Coalescing Filters
Predominantly used in compressed air applications, coalescing-type filters are essential to refrigerant, automotive, ventilation, heating and cooling, transportation, pharmaceutical, food processing and natural gas filtration industries. To accommodate the needs of such a variety of industries, coalescing filters are available in sizes as small as 0.18" inside diameter and as large as 22" outside diameter. With efficiencies ranging from 93% to 99.9999% particulate removal at the 0.3 micron range and similar at the 0.01 micron range, filtering systems such as these not only purify process streams, but they also minimize pollution and downstream corrosion as well as operating and maintenance costs while promoting worker health and safety.
Design of Coalescing Filters
The basic design and operation of coalescing filters is similar to various other air filtration systems. The air sample passes through a filter panel or cartridge. These consist of two or more layers of an extremely fine mesh-like substance. The inner capture layer is a coalescing layer, while the outer layer, made of coarser fibers, is used predominantly for drainage. The fine inner layer collects the droplets and vapors before forcing them to the secondary layer where they merge. The growing matter becomes increasingly heavy and is eventually pulled down by gravity.
These contaminants are manually or automatically retrieved from the collection bowl located below the coalescing panel. In some applications this byproduct is disposed of while in others it is valuable liquids that are retrieved and therefore it is recycled back into processing to increase throughput. When valuable oils or aerosols are to be collected, a third layer is used in the coalescing filter. An inner layer made of fine materials is positioned between the two outer layers, which trap dust and other solids, ensuring that the coalesced material is itself fairly pure. In any event, coalescing filter panels or cartridges are made up of fibrous materials that form a complex matrix or lattice. Examples include borosilicate microglass, fiberglass, closed cell foam or other durable and chemically resistant lattice materials.