What Factors Affect Separation in Oily Water Separator on Ships?

Oily Water Separators are one of the most important yet neglected equipment on board ships. Revered and feared alike, marine engineers are often afraid to use it, and want to keep it unused and working so that they can show it to the Port State Control Officer (PSCO) and stay on the safer side.

Based on simple working principles and designed to be reliable and less labor intensive, oil water separators are however troublesome and demanding to engineers due to later’s lack of knowledge, proper training, operational negligence and sometimes apathy. However proper care, maintenance, correct trouble shooting and efficient starting/stopping can keep it working properly and make life easier and safer. With stricter control and PSC inspections combined with stringent penalties including criminal action against the operating crew, it ‘s in the interest of the marine engineers to keep the OWS working properly.

A lot has been said and written about the inadequacy of some of the market equipment and especially those that have been retrofitted in old ships in seminars and forums. However, the seagoing marine engineers do not have access to these seminars and their voices are often unheard. In the absence of a sympathetic ear, marine engineers just endeavor to keep the equipment running during their “contract time” and abstain from complaining for the fear of victimizing.

The oil water separator (OWS) is designed to work properly under ideal conditions; however the ship is not one and there are various sources of contamination in the bilge water. The bilge water is a mixture of various grades of oil in water, along with suspended solids, rust, chemicals, detergents, soot, paint chips and cargo dust etc.

In view of such a complex scenario it is necessary to have the knowledge of the various parameters and factors that influence the satisfactory operation of OWS. The satisfactory operation of the oily water separator (OWS) is dependent on the knowledge of the following:

In these series of articles we shall endeavor to discuss the various ways to optimize the performance of OWS such as the design factors, operational limitations, efficient bilge management, training requirements and some good working practices.

Oily Water Separator is used to remove oil from the bilge water prior to discharging it overboard. It works on theprinciple of Stokes law and basically separates the two components utilizing their difference in specific gravity. The OWS for marine use are optimized to make them smaller in size due to space constraints. Additional components are fitted to help with the separation process but the knowledge of the basic design factors is beneficial.

The Stoke’s Law generally states that the velocity or rise and hence the separation rate is directly proportional to the difference in density of the oil and the continuous fluid and the size of the droplets of oil. It is also states that rate of rise is inversely proportional to the viscosity of the surrounding fluid. We infer from the famous law the following:

Chief Engineer Mohit Sanguri is a Marine Chief Engineer (Class I Unlimited Power). He has 12 years of experience as Marine Engineer. He is currently working with Dynacom Tankers Ltd on their Bulk Carriers division and has served in the past with Wallems Ship Mgmt on Car Carriers and PCTC’s, MSC Ship Mgmt on Containers, Univan Ship Mgmt on RoRo’s and Five Stars Shipping on Bulkers and SNP Ship Mgmt on General Cargo at various designations.

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