This article discusses about the oily water separator, 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
4) Regular cleaning of the valves which are used to
regulate the flow.