Marine Fuel Oil Centrifugal Purifier on Ship | Centrifuge

Marine Fuel Oil Purifier is one the most important Auxiliary machinery on board a ship. It is also known as a centrifugal purifier or Centrifuge.

After Bunkering, Fuel oil is to first storage tanks and then to the settling tank for gravity separation so that over a gradual period solids impurities such as sludge, dirt, etc., will settle out at the bottom of the tank.

Then Fuel oil is transferred through the centrifugal purifier to the service tank for daily operational use.

Fuel oil centrifugal purifier working principle:

The centrifugal Fuel Oil purifier uses the principle of density difference to separate water and other contaminants from the oil mixture.

Oil, water and other impurities are of different densities. Whenever the oil is subjected to centrifugal force heavier particles such as water and solid will be forced outward and lighter particles will remain near to the centre.

Here, the gravitational force is by centrifugal force that results in better separation.

While the separating force of these mixtures under gravity separation is defined by formula Fs = ∏/6*D3*(ρw-ρo)*g. Now by replacing gravity (g) with centrifugal force ω2r we are able to simply increases the rate of separation by a significant factor; making it a better way of purification.

What is the difference between Purifiers and Clarifiers?

Purifiers	Clarifiers
1. Purifiers Remove water and suspended solids particles from oils	1. Remove finer and lighter particles from the oil
2. Two outlets water and clean oil	2. One outlet for clean oil
3. Gravity disc on top	3. No gravity disc only sealing ring
4. Blind disc on the top of the disc stack	4. Blind disc at the bottom.
5. Sealing water required	5. Sealing water not required

Parts of Fuel Oil Centrifugal Purifier:

Gravity disc:

The gravity disc is an important part of the purifier as it maintains the interface between oil and water. It is done by the inner diameter of the gravity disc.

Centripetal impeller (pump): 

Oil collected from purifiers will be drawn inside and delivered by this impeller.

Vertical shaft:

The Vertical shaft is used to transform the electrical motor output into rotational motion for rotating the bowl at high speed through spur gear and horizontal shaft or belt. The material used for vertical shaft construction is an alloy of steel.

Purifier rpm and motor rpm:

Motor runs at an rpm of 2000-2500 rpm and purifier bowl rotates around 15000-18000 rpm. This is done by increased the gear mechanism of the horizontal shaft.

Horizontal shaft:  

It is connected with the motor via a frictional block arrangement. Bearings in the bearing housings are provided at two ends of the shaft. Between them, spiral gear is fitted.

Water supply device:

 Underneath the bowl body cylinder, a water supply device is fitted to supply low and high pressure operating water.

Factors influencing the interface:

1. Feed Rate:

An increase in feed rate will increase the mass of fuel entering and will push the water out of the bowl and this will cause the oil-water interface to move towards the periphery.

So it’s important to run the purifier at optimum feed rate as a high feed rate decrease the efficiency.

Running with a low feed rate will cause the fuel oil service tank level to decrease. If the feed rate not adjusted for a long time

The pump should run at a feed rate of 110 per cent of the fuel consumption.

2. Diameter of Gravity disc (dam ring):

The inner diameter of the gravity disc determines the amount of sealing water inside the bowl and thus determines the position of the oil-water interface.

If the diameter increases interface moves toward the periphery of the bowl and if the diameter reduces interface moves toward the centre.

3. Density of oil:

An increase in density will also result in an increase in mass and centrifugal force to push more water out of the bowl. i.e. interface will move towards the periphery.

To handle with high-density oil gravity disc diameter has to be decreased and the temperature has to be maintained.

4. Temperature of the fuel:

Temperature plays an important role to maintain the oil-water interface.

• If temperature increases the density of oil reduces which reduces the force exerting by oil and Oil-water interface tend to move towards center.

Sludge discharge/ De-sludge mechanism:

For more reference: https://www.maritimeinformations.com/2020/08/purifier-explained%20.html