Sea water is a common contaminant in marine fuels.
Comment:
It should be noted that the centrifuge is unable to remove water if it is emulsified. See also section 4.2.
The graph shows water distribution for residual fuel.
Below: The Kittiwake Water in Oil Test .
Info Centre >> Fuel and Lube Oil Technical Manual >> 4. Fuel Oil - Test Results >> 4.6 Test Parameters - Water
Water in Fuel
The vast majority of fuels contain less than 0.2% water. More than 90% contain less than 0.5% and about 1% exceed the present ISO 8217 of 1%. It is anticipated that the next revision of ISO 8217 will include a water limit of 0.5%.
Do not pay for any water in the fuel over and above the limit stated in the appropriate standard. Water can be introduced into the fuel supply chain from a number of sources including tank condensation, tank leakage or deliberate contamination. In practice, the nature of the water present may be fresh, brackish or salt. The world-wide salt content of sea water varies, however. In first order terms, 100 mg/kg (PPM) is associated with 1% sea water contamination in the fuel.
Excessive water represents a triple loss. Firstly, there is the loss of specific energy in the fuel which will affect the fuel consumption; secondly, there is the cost of disposal of the water removed by the treatment system. Such water is unlikely to pass through a 15 mg/kg (PPM) oily water separator, so it has to be retained for disposal later, with a cost to the ship operator. Thirdly, water will damage fuel injection equipment, cause corrosion and failure to exhaust valves and turbochargers.
The settling tank will remove gross water as long as it is not emulsified. Warm fuel will shed water faster than cold fuel in the settling tanks. The drains should be checked regularly, especially on first use of a new fuel delivery.
A well-operated centrifuge should achieve water removal efficiency of above 90%. However, the effectiveness will be less for very viscous fuels.
Operation in series as a purifier and clarifier assures maximum water removal. Operating temperatures in the centrifuge should be maintained as high as possible, usually around 95° - 98°C. Up to 5% fresh water or 3% salt water can be removed in an effective fuel treatment system provided the water is not emulsified.