Marine Fuel Oil Purifier: Working Principle of Centrifugal Separator

Video No. 1 of "Marine Centrifugal Separator Video Series"
#Purifier #Centrifuge #Fuelseparator
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A high-speed centrifuge is a type of separator which is used on a ship to remove contamination from liquids such as fuel and lube oils. It is imperative to carry out this treatment in order to remove solid impurities and water before they are supplied to the marine engine. Thus, the task of the centrifuge is to remove solid contamination from liquid and to remove undesirable liquid (water) from useful liquids (fuel).

Principle of Working:

The separation principle of high-speed centrifuge depends on the difference in the specific gravity of two different liquids. To understand, let’s take a settling tank where fuel is stored and because of the difference in the gravity of water and fuel (water is heavier) the water gets collected at the bottom part of the due to the effect of gravity.

Mathematically this process can be represented by:

Fs = ∏/6x D3 (ρw-ρo) g

Where Fs is the separating force, ρw is the density of water, ρo is the density of oil and “g” is gravitational force.

Now if we convert the tank into a conical rotating object, then the gravitational factor g will be replaced by the centrifugal force ω2 r, where ω2 is angular velocity of rotation and r is the effective radius.

Fs = ∏/6x D3 (ρw-ρo) ω2 r.

Now the separating force will be much higher in the centrifuge as compare to a settling tank.

There are normally two types based on the application:

1) Purifier: When a centrifuge is arranged for separating two liquids of different densities, for e.g. water from oil, it is known as a purifier. The main component of purifier is correct size gravity disc or dam ring which is responsible for creating an interface between the oil and water.

2) Clarifier: When a centrifugal is arranged to remove only impurities and a small amount of water, it is called as the clarifier. Since it is used mainly for that fluid were mostly solid impurities are to be removed, gravity disc is not used in clarifier; instead, a sealing ring is used to keep the impurities intact unless desludged.