Oily Water Separator Construction and Working

Oily Water Separator Construction
and Working

Which is very important auxiliary machinery on board ship. Basically, oily

water separator is used in order to treat the bilge waters, so as to avoid any

type of oil getting into the sea with water. It can be considered as waste water

treatment. So let’s see what we have here.

Marpol Annex 1 says that you cannot discharge water with oil content more

than 15 PPM (Parts per million) in open sea. And the reason why they have

made this rule is that, oily water makes a layer above the water surface and

stops the flow of oxygen into the water. This harms the flora and fauna of the

sea and hence dangerous for the marine life. In order to comply with the

standards of Marpol, oily water separator has been installed on board ship to

treat waste water which may contain oil. Generally the bilge of the ship, below

the engine room accounts for maximum waste oil and water, and it is like

storage place for it.

The oil and water come from leaks occurring at various pumps, engine

machinery etc. So, this bilge water has to be drained out timely and this is the

reason oily water separator is installed to take out the oil present in the water.

Only 15 PPM of oil in water is allowed to go and if it does not meet the

conditions, it is again contained back. So let’s study more about this apparatus

in much detail like principal, construction etc.

Construction of Oily water separator

The construction of oily water is simple and there are very less moving parts

in this device. Below diagram shows you the arrangement of the oily water

separator on board ship. As you can see that there are two separate

compartments in this system. First compartment is like accumulator, and it

accumulates the small oil particles. And other compartments are just for

removing these accumulated oil pockets.

There are several probes which are fitted on the oily water separator like oily

water monitoring system, oil level probe etc. Sometimes in order to facilitate

the oil separation, steam line passes through the oily water separator. In the

first compartment baffle plates are installed and these plates serve as the

means for providing the surface for oil getting collected in larger volumes. A

pump from bilge gives supply to the oily water separator.

Working of oily water separator

Working of oily water separator is quite simple and easy to understand. You

just have to see the diagram once and you will be able to understand the

whole working of the oily water separator. The whole process of separation

starts with the pumping of bilge waters from bilges by the bilge pump. The

discharge of this pump goes to the first compartment. Here there are several

baffle plates are arranged and they act as the surface for accumulation of very

small oil droplets to accumulate and make large mass oil.

When the oil droplets gets bigger they have to be removed from the chamber,

and for this a valve is provided on the right hand compartment to remove the

oil content. This oil sent to the waste oil tank and later it is used in the

incinerator for burning.

But in the first compartment oil is only taken out till the 100 PPM content but

our requirements is to drop the oil content in the water to 15 PPM. So, for this

purpose we pass the remaining liquid into the second chamber. In the second

chamber we have a separate mechanism of taking out the remaining oil. These

materials are like oil absorbing or water absorbing. Generally we have an oil

absorbing material. Now as you can see in the fugue that the oil is entering the

second chamber from the bottom. As oil passes upwards to the chamber, oil

particles start getting absorbed and the oil quantity in the water decreases as it

goes upwards. At the outlet we get the oil which has the oil content less than

the 15PPM.

But this water is not thrown directly into the sea. At the outlet line, we have

an oil monitoring device and this device guarantees us with exact PPM which

we want. Actually oil monitoring is set at a level of around 15PPM and it

allows the liquid to go through till it has the oil content less than 15 PPM. Any

amount more than this will leads to bypass action of the signal control valve

and whole discharge will divert back to the first chamber. And an alarm is

also sounded automatically when this condition occurs.

So you can see that this system is a totally automated system and no moving

part is involved in this process. We just take the help of the gravity and

special absorbing material, and our work is done.

Maintenance required on the oily water separator

There are no specific maintenance required on the oily water separator

because the moving parts in this machinery are very less and hence less wear

and tear, but still some maintenance is always required for running

machinery. Following are the checks and maintenance which are carried out

in the oily water separator:

1) Periodic changes of oil absorbing material.

2) Regular cleaning of the surface of the chambers as oil sticks to them.

3) Regular checking and troubleshooting of the oil monitoring system.

4) Regular cleaning of the valves which are used to regulate the flow.