--- gravity separation of oil from oily effluents

CPI is one kind of high efficient oil-water gravity separator, now is widely used in oily wastewater treatment to remove bulk oil from water.

Gravity separation is the most straightforward method of wastewater treatment and is, therefore, utilized widely in industry for separation of settling and/or floatable impurities from a carrier liquid.

An enlarged separating surface can be achieved by placing various smaller planes on top of each other in the tank. If these planes are subsequently inclined in a tilted position, material separated between the plates is removed by the gravitational force. This is the principle on which the CPI corrugated plate pack is based.

In this plate pack the planes as referred to have been constructed in the shape of corrugated plates. They promote both the coalescence of the intercepted oil particles and, at the same time, their transfer through the plate pack.

If settleable material is present in the liquid, such material is collected and concentrated in the troughs of the corrugations so that it will slide down in the plate pack smoothly and easily.

Very small separating diameters can be obtained in the CPI system, because the

disturbing factors, such as eddies and turbulences, which adversely affect large

conventional separating tanks (e.g. API’s), are eliminated in the CPI.

In formulating a design, the following minimum data are essential:

 the type of pollutants to be intercepted

 the separating diameter of the oil droplet

 the difference in density between the carrier liquid (waste water) and the pollutants to be intercepted

 the maximum amount of water to be treated

 the water temperature

the sedimentation velocity

 origin of the oily liquid

 physical data, chemical analysis of carrier phase.

With the objective of not breaking up the oil droplets unnecessarily, the CPI system is

preferably fed by gravity. The oily water flows into the interceptor through the inlet compartment which has a dual function as a sand trap (1). A double slotted baffle (2) induces incoming water to flow evenly and uniformly to the entrance of the corrugated plate pack (3). In the plate pack the oil droplets are intercepted and coalesce into large droplets. They leave the pack rapidly in counter current mode and move upwards against the liquid flow, to the surface.

The separated oil builds up a floating layer (4) which is removed through a skim pipe (5).