Properties of Bilge in Marine Vessels

The properties of bilge in actual marine vessel will vary from case to case depending on vessels, one of which reasons is inclusion in bilge of various chemicals for use in maintenance of the engine and others. Not only lubrication oil but also fuel oil has various additives put in. However, the effect of chemicals directly dumped in bilge is considered more influential than those to be added in oil.

Bilge Well Covered with Grill, for Collecting Bilge from Various Places in Engine Room
Bilge Well Covered with Grill, for Collecting Bilge from Various Places in Engine Room

Detergents with Surface Active Agent

Detergent containing surface active agent is produced with the base material of petroleum or animal vegetable oil. In some cases, the oil content of almost 100% can be detected even from a single substance. The action of these detergents to water and oil is so complicated that some are soluble well in water but not so well in oil, or vice versa, or others are soluble in both water and oil. In all cases, however, their effect on bilge will be significant, and grains of detergents and oil grains melted in detergents are both so fine as approximately 5 micrometer or smaller in size as are mixed in bilge.

Chemicals to be Used as Prescribed by the Manufacturer
Chemicals to be Used as Prescribed by the Manufacturer

The maximum grain size which the existing oily water separators can separate by using any physical method is no larger than 10 to 20 micrometer. Therefore, it will be almost impossible to treat these detergents or oil grains melted in detergents, and some types have a great bonding power, even if a least amount, or others are to be fine-grained. For such reasons, detergents with surface active agent, if used, will require careful attention not to be mixed in bilge. To solve this problem, a quick separation type detergent has been developed. (e.g. Drew Clean 2000, or Ameroid OWS by Drew Aameroid). Use these detergent according to the manufacturer's instructions.

Flushings, Rust Preventives and Antiscales

Flushings, agents as well as rust preventives, antiscales or other cleaning compounds for cleaning heat exchangers are used in various ways depending on application. Any of these can affect the properties of bilge when mixed in the bilge tank, making the PH value higher or lower one side to thereby refine the grains of the oil contents of bilge, which will be a significant effect on the oil-water separation performance. Therefore, any of these should be necessary not to be mixed in bilge as much as possible.

Compressor Drain

The drained oil from the compressor is such as the water content of compressed air is emulsified with oil grains, with light milk colour, and apparently is very much like detergents with surface active agents as dissolved in water: it is most difficult to distinguish one from the other. Oil grains from the drained oil from the compressor is finer than those formed in detergents and exist in negative ions, and therefore cannot be removed by any physical treating method. It follows that it should be necessary to treat such drained oil separately in order to prevent mixing of it in bilge.

Oily Water Separator
Oily Water Separator

Sludge

Sludge contained in the bilge includes such heavy matters as iron rust, sediment, metal carbon, floating carbon, etc. In such type of sludge, the light matters may be bonded with oil grains and become loose with specific gravity equal to that of water, and will float in an intermediate layer of the bilge. These grains are hard to be separated when supplied in the oily water separator. The heavy matters will be separated in the oily water separator and can be the cause of damaging the equipment indirectly. Therefore , the input of such sludge to bilge should be cautioned for the prevention of inclusion of it in the bilge tank as it can adversely affect the performance as well as the maintenance of the separator.

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