Oily Water Separation


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The engineers on our vessels are having trouble with adequately maintaining the 15ppm via the coalescer type OWS, although it is only 3 years old. I have sailed for 30 years and had the same problems. Has anyone had any experience with ULTRAFILTRATION onboard ships? If so, any contacts please?


Ultrafiltration will not necessarily solve your problem. To separate water and oil there a few things to bear in mind. First choose the correct separating equipment - which means that you have to tailor the equipment to the specific density of the oil/water mixture as closely as possible - and that density is temperature related. Therefore also the temperature of the mixture is important: a higher temperature will generally assist in separation since the specific densities of oil and water will be somewhat wider apart at elevated temperatures.

A second point of consideration is the types of additives used in the oil. If the oil uses lots of ash-containing dispersants (as usually is the case for heavy-duty engine oils for trucks and other wheeled equipment) it is very difficult to separate water and oil. Therefore in engine oils for vessels usually another type of ashless dispersant is used that is better suited for separation of water and oil on the basis of centrifugal forces.

Ultrafiltration is something quite different. If you have water in the oil (and therefore a certain amount of emulsion) ultrafiltration will usually not help because the fine pores in the filter will readily be clogged by the emulsion.

In hydraulics, where ultrafiltration is used quite often, usually non-detergent types of hydraulic oil are employed that readily shed water. Just traces of engine oil will usually destroy the water shedding properties, and so will small amount of Ca-based additives.