Oil removal (in compressor)

During the compression cycle of the typical lubricated compressor, oil vapour is generated in the compressor by the high temperature and mechanical shearing of the lubricating oil film.

The quantity and fineness of the size of the oil vapor particles are determined by mechanical factor in the compression chamber- piston speed, clearance, oil viscosity etc.

For example rotary compressors, which have much higher shear rates in the lubricant film. produce much large quantities of oil vapour and in a more finely disperse state.

If the oil vapour is not removed from the compressed air, it slowly coalesces into droplets large enough to settle out in the piping system as liquid oil. This occurs in orifice plates, pressure reducers, nozzles. 

Coalesence is a function of air flow turbulence and is not influenced by temperature reduction in the lines, as in the case of water vapour condensation.

The oil particles vary in size from 5 microns and under and will pass through conventional air line filters design to remove much larger water droplets and dirt particles.

This automatically eliminates by many types of mechanical filters or separators since   gravitational inertial impingement  and other similar separators don't effectively remove droplet smaller than 3 microns.

The natural application of this characteristics is creation of a turbulent flow in the presence of oil absorbent material to accomplish oil removal.

For vapours under 0.01 micron in size, sufficient  Brownian motion exists for them to be effectively absorbed by activated carbon or alumina, with carbon  exhibiting the greater oil capacity.

Filters of these type should be followed by an afterfilter to avoid any dusting problem. venting to atmosphere  prior to absorber startup also helps eliminate dusting problems.