Wednesday, 16 November 2011


Filter Separators : 
General — This type of separator has a higher separation efficiency than the centrifugal separator, but it uses filter elements, which must periodically be replaced. An example filter separator is shown in Fig. Gas enters the inlet nozzle and passes through the filter section where solid particles are filtered from the gas stream and liquid particles are coalesced into larger droplets. These droplets pass through the tube and are entrained into the second section of the separator, where a final mist extraction element removes these coalesced droplets from the gas stream.

 The most common and efficient agglomerator is composed of a tubular fiber glass filter pack which is capable of holding the liquid particles through submicron sizes. Gas flows into the top of the filter pack, passes through the elements and then travels out through the tubes. Small, dry solid particles are retained in the filter elements and the liquid coalesces to form larger particles. Liquid agglomerated in the filter pack is then removed by a mist extractor located near the gas outlet. The approximate filter surface area for gas filters can be estimated from Fig. given below. The figure is based on applications such as molecular sieve dehydrator outlet gas filters. For dirty gas service the estimated area should be increased by a factor of two or three. The efficiency of a filter separator largely depends on the proper design of the filter pack, i.e., a minimum pressure drop while retaining an acceptable extraction efficiency. A pressure drop of approximately 1-2 psi is normal in a clean filter separator. If excessive solid particles are present, it may be necessary to clean or replace the filters at regular intervals when a pressure drop in excess of 10 psi is observed. However, as a rule, 25 psi is recommended as a maximum as the cartridge units might otherwise collapse. Removal of the filter pack is easily achieved by using a quick-opening closure. Various guarantees are available from filter separator manufacturers such as one for 100 percent removal of liquid droplets 8 microns and larger and 99.5 percent removal of particles in the 0.5-8 micron range. However, guarantees for the performance of separators and filters are very difficult to verify in the field. While most dry solid particles about ten microns and larger are removable, the removal efficiency is about 99 percent for particles below approximately ten microns. For heavy liquid loads, or where free liquids are contained in the inlet stream, a horizontal filter separator with a liquid sump, which collects and dumps the inlet free-liquids separately from coalesced liquids, is often preferred.

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