OILY WATER SEPARATER

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All designs use at least two stages to separate the oil and water:-

Stage 1 separates the large particles of oil, usually using either gravity or coalescing.

Stage 2 completes the separation by removing the smaller particles of oil, either coalescing, coagulating, flocculation, biologically or centrifugally.

(1)   Separation by gravity ‑ depends upon the density difference between oil and water.

Since the rate of change in density, with respect to temperature, is greater for oil than water, the rate of separation will increase with temperature as the specific gravity difference between the two increases with temperature. For this reason, and because separation improves as the viscosity of the water decreases, heating of the oil‑water mixture is beneficial and is usually carried out before the mixture enters the separator. Although some separators are fitted with heaters in their lower part to assist separation, some others are provided only with a heater in the oil space, which facilitates discharge of the oil from the separator.

(2)   The use of coalescing devices which encourages the formation of large oil droplets.

Coalescing      ‑           To gather together or unite

Most Separators use some form of coalescing arrangement which can be a series of plates that smooth out flow, limit the maximum distances that separates oil particles and provide an extended surface on which oil particles can deposit.

Plates encourage laminar flow and act as coalescing surfaces. The rate of separation depends upon the difference between the viscous drag at the oil/water interface and the effect of gravity. The formation of larger globules is accelerated at the coalescing surfaces.

Meshes and filters use material that is oleophilic (attractive to oil) and during the passage through the coalescer all of the fluid comes into contact with the material. As the oil molecules then attract each other they enlarge and eventually float free

.(1)   Separation by Coagulator.

The oleophillic material attracts oil which sticks to the surface similar to a coalescer. The oil droplets, however, do not merge and the coagulator has to be backflushed to remove the oil.

(2)   Separation by flocculation.

Chemicals are added to which cause the oil to stick together in large floccs which can be easily removed.

(3)   Separation by biological means.

The fluid is passed through a chamber containing bacteria which consume the oil.

(4)   Separation by centrifuge.

Similar to fuel oil separators.

The Oily Water Separator Pump should be matched to its duty, i.e. should not exceed the intended capacity of the separator.

Vane or screw type pumps are the best if the pump is placed before the separator due to the fact that they do not break up the oil droplets and cause emulsification