A. Mechanical Action – the shearing action
of pumps, non-laminar flow (that can impinge or press together or
apart particles under pressure) inherent in transfer operations, and
turbulent conditions in general will cause dispersion of oil in water.
It is difficult to form stable emulsions with purely mechanical means
(these will separate in a tank after some hours); however, such mechanical
factors greatly enhance the efficacy of small amounts of other emulsifying
agents, which can be present in the bilge. In many cases, the presence
of materials such as soot, rouge, soap and diesel (all emulsifying
agents) is inevitable and, in small amounts, greatly enhances emulsification
when oil is caused to disperse by aggressive mechanical action (high
agitation of the bilge water). Certain types of pumps are more prone
to disperse oil in water than others. Diaphragm and progressive cavity
pumps are the least shearing. Centrifugal pumps are fairly aggressive
and can cause shearing and become problematic in cases of cavitation
due to insufficient NPSH (net positive suction head).
B. Emulsifying Agents – The following materials
all enhance emulsification of oil in water:
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▸ Particulate matter:
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▸ Chemicals:
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• Soaps and detergents – reduce the surface tension
of the oil/ water interface and cause formation of stable droplets.
• Solvents – diesel, kerosene, and benzene greatly
enhance the effectiveness of soaps/detergents and shearing action.
They can cause stable emulsions themselves in high quantities (>1%
to approximately 5% of the total weight of the bilge water), especially
when sheared.
• Cleaners – Industrial cleaners usually contain
detergents and solvents and are formulated to emulsify oil. Introduction
of these types of materials into the bilge is the most common cause
of o/w emulsion formation.
• Microbial contamination – It is rare but microbial
contamination can cause oil emulsification. More often when microbial
contamination is present, rouge produced by microbes is being detected.