Fuel oil and lube oil are treated in a centrifugal separator because mechanical separation cannot break emulsified bond between two liquids or two liquids that are immiscible. Where a centrifuge is arranged to separate two liquids, it is known as a ‘purifier’. Where a centrifuge is arranged to separate impurities and small amounts of water from oil it is known as a ‘clarifier’. Most people tend to confuse a purifier and a clarifier.
A purifier removes water from large amount of fuel while the Oily Water Separator (OWS) removes oil from large amount of water. The major difference between a clarifier and a purifier is that the purifier has its gravity disc at the top while the clarifier has its gravity disc at the bottom. Also, the purifier has two outlets (fuel and water/sludge) while the clarifier only has only one outlet for the fuel. The clarifier is an optional mode of operation and is only suitable for oils containing very small amounts of water.
It is recommended that 10% of the oil quantity in the tanks should pass the separator per hour.
Both fuel oil and lubricating oil are needed for the smooth running of the Main engines as well as auxiliary engines but during processes like distillation, storage, bunkering and settling, the oils get contaminated with sludge, metal particles, oxidation products, water impurities as well as carbon deposits. Therefore, a means of separation and purification for oils is required to remove these foreign particles and impurities.
The oil to be purified are first allowed to settle in settling tanks. Settling tanks allow for separation by gravity, allowing the water and deposited particles in the tank to settle at the bottom where they can ejected out through drain cocks (this can be done in every engine room watch duty). The fuel then pass through various pipes in the fuel oil piping system or lubricating oil piping system. These piping systems have fine meshed filters and strainers along its piping network which prevents the passage of coarse particles. After this, the fuel can then be supplied to the purifier through the purifier feed motor for the purification process to commence. The purifier normally purifies to the Fuel Day tanks and the emergency generator fuel storage tank.
The oil purifier rotates at very high RPM in order to use centrifugal force to remove fine solids which cannot be filtered out from the oil. Purification is essential and high recommended especially when the bunker fuel is of poor quality. Purification is essential for good combustion.
The purifier is self-flushing but has to be manually cleaned at intervals (F.O purifier- 7days interval, L.O purifier- 30 days).
IMPORTANCE OF PURIFICATION/ SEPARATION
- To separate two mutually insoluble liquids with different densities while removing any solids present at the same time.
- To concentrate and separate solid particles from a liquid.
- To free a liquid of solid particles.
