6.7.2 Static oil purifiers/coalescers
An alternative system which is now coming into use is the static purifier, which is shown diagrammatically on Fig 2.64.
Oil is taken from the main oil tank at a rate of of the oil inventory per hour. The oil initially passes through a series arrangement of fine-mesh sloping screens. The water coalesces on the screens in water droplets which run down to the bottom of each screen and are led to drain. The oil then passes through a series of polyolefinic bags which filter out the particulate matter. Finally, the oil is pumped through a 5 micron pressure filter and delivered back into the main oil tank. The oil passes through the purifier at its operating temperature and because it is not heated the risk of bacterial/fungal growth may be greater (see Section 6.8 of this chapter).
Provision is made for the regeneration of used oil within the station oil transfer system. Oil for regeneration is taken from the unit oil tank or the station dirty-oil tank at around l.lm3 per hour and processed in the plant shown schematically on Fig 2.65.
The oil is heated to 54.4°C and is then sprayed into a chamber with a vacuum maintained at 913 mbar below atmospheric. Under these conditions the water boils off, is removed by the vacuum pump and condensed. The dry oil is then pumped out of the vacuum chamber and through a filter. The filter comprises a pack of nylon-backed filter papers clamped between perforated steel plates, and filters the oil to 10 microns. From the filter, the oil is taken into the clean oil tank prior to being pumped back into the unit oil tank after it has been cleaned.