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Marine Fuel Oil Blenders

Blending is the mixing of two fuels, usually a heavy fuel and marine diesel oil. The intention is to produce an intermediate-viscosity fuel suitable for use in auxiliary diesels. The fuel cost savings for intermediate fuel grades are sufficient to justify the cost of the blending plant. Furthermore no supply problems exist since the appropriate mixture can be produced by the blender from available heavy and marine diesel oils.

The blending unit thoroughly mixes the two fuels in the appropriate proportions before supplying it to a blended fuel supply tank. Compatibility can be a problem and tests should be conducted on any new fuel before it is used. Incompatible fuels may produce sludge or sediment. The cracked residues presently supplied from many refineries are very prone to incompatibility problems when blended with marine diesel oil.


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Fuel oil supply system prior blending process – This system supplies the fuel from the service tank to the diesel engine. The system consists of: a supply flow meter, supply pumps, circulating pumps, preheaters, the final filter, a viscosity controller, a FO venting box. The pressurised system is preferable while operating the diesel engine on high viscosity fuels. It can be delivered as a modular unit (fuel oil supply module), tested and ready for service supply connections

The temperature of fuel oil is raised before burning to reduce the high viscosity of the fuel to a value at which correct atomisation can take place by the fuel injectors. This will allow correct mixing and burning for efficient combustion. Viscosity of fuel oil can be reduced by passing it through a heater.

Correct temperature is maintained by the viscotherm which automatically regulates the temperature of the heater to a constant temperature to maintain controlled viscosity.

The density of fuel oil burned in a diesel engine is important because some fuels of different densities are not compatible and formation of heavy sludges can occur in tanks.

The viscosity is important because it is required to be able to calculate temperatures at which fuel is treated and injected into the engine for correct combustion. Viscosity control for the temperature of a fuel oil heater is considered more superior because it is possible that oils stored in the ship's tanks or even one tank could have come from different sources and have different properties, therefore viscosity control is considered more superior.

The flash point in a fuel system is important for safety reasons. The flash point of any fuels onboard ship must not be less than 60°C.

Solid contaminants that might be found in fuels are rust, sand, dirt or refinery catalysts which are all abrasive materials and cause wear. Liquid contaminants found in a fuel oil system may be salt or fresh water.

Fuel oil tank protection

Old vessels, but unfortunately also many new ones, have bunkers in double hull and any shell damage can result in oil spill. This common practice has been stopped by new revised MARPOL Annex I, Regulation 13A. This regulation applies to all ships with an aggregate oil fuel capacity of 600m3 and above for which the building contract is placed on or after 1 August 2007, or the delivery of which is on or after 1 August 2010.

According to the new regulation, individual oil fuel tanks shall not have a capacity of over 2500m3. The provisions of this regulation will apply to all oil fuel tanks except small tanks with an individual capacity not greater than 30m3, provided that the aggregate capacity of such excluded tanks is not greater than 600m3.

For ships having an aggregate oil fuel capacity of 600m3 and above, oil fuel tanks shall be located above the moulded line of the bottom shell plating nowhere less than the distance h as specified: h = B/20m or h = 2.0m, whichever is the lesser. The minimum value of h = 0.76m.

For ships having an aggregate oil fuel capacity of 600m3 or more but less than 5000 m3, oil fuel tanks shall be located inboard of the moulded line of the side shell plating, nowhere less than the distance w which is measured at any cross-section at right angles to the side shell as specified: w = 0.4 + 2.4C/20,000m, “C” is the vessel’s total volume of oil fuel, in m3, at 98% tank filling.
The minimum value of w = 1.0m, however for individual tanks with an oil fuel capacity of less than 500m3 the minimum value is 0.76m.

For ships having an aggregate oil fuel capacity of 5000m3 and over, oil fuel tanks shall be located inboard of the moulded line of the side shell plating, nowhere less than the distance w which is measured at any cross-section at right angles to the side shell as specified below:
w = 0.5 + C/20,000m, or w = 2.0m, whichever is the lesser. The minimum value of w = 1.0m.



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