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Fuel blenders for auxiliary diesels- procedure for motor ships
Conventionally, the lower cost residual fuels are used for large slow speed diesel main engines and generators are operated on the lighter more expensive distillate fuel. The addition of a small amount of diesel oil to heavy fuel considerably reduces its viscosity and if heating is used to further bring the viscosity down then the blend can be used in generators with resultant savings.
The in-line blender shown in Figure below takes fuels from heavy oil and light diesel tanks, mixes them and supplies the mix directly to auxiliary diesels. Returning oil is accepted back in the blender circulating line. It is not directed back to a tank where there would be the danger of the two fuels settling out.
Figure : In-line fuel blender (Sea-Star)
Fuel is circulated around the closed loop of the system by the circulating pump against the back pressure of the p.s. (pressure sustaining) valve. Thus there is supply pressure for the engine before the valve and a low enough
pressure after it, to allow returning oil back into the loop. Sufficient light diesel is injected into the loop by the metering pump for light load running. As increased load demands more fuel, this is drawn in from the heavy oil tank by a drop in loop pressure on the suction side of the circulating pump. The extra fuel made necessary as the load increases is supplied from the residual fuel tank.
At full load the ratio may be 30% diesel with 70% heavy fuel, A viscotherm monitors viscosity and controls it through the heater. The hot filter removes particles down to 5 micron size and there are other filters on the tank suctions. Constant circulation and remixing of the blend and the returning fuel prevents separation. The diesel is started and runs light on distillate fuel. As the load increases, heavy fuel is added.
Summarized below some of the basic procedure of machinery service systems and equipment :
- Marine air compressor
A single stage compressor used to provide air at the high pressures required for diesel engine starting, would unfortunately generate compression temperatures of a level similar to those in a diesel. Such heat would be sufficient to ignite vaporized oil in the same way as in a compression-ignition engine. The heat produced in a single stage of compression would also be wasteful of energy.....
- Air starting system
Air at a pressure of 20 to 30 bar is required for starting main and auxiliary diesel engines in motorships and for the auxiliary diesels of steamships. Control air at a lower pressure is required for ships of both categories and whether derived from high pressure compressors through reducing valves or from special control air compressors, it must be clean, dry and oil free.....
- automatic-operation-air-compressor
Before the general introduction of control equipment, air compressors were stopped and started by engine room staff, as necessary, to maintain air receiver pressure. In port or at sea, this usually meant operating one compressor for about half an hour daily unless air was being used for the whistle (during fog), for work on deck or for other purposes. ....
- Compressed air systems for steamships
A compressed air system is necessary to supply air for boiler soot-blower air motors, hose connections throughout the ship and possibly diesel generator starting. A general service air compressor would supply air at 8 bar but greater pressure (as for diesel ships) would be necessary for diesel starting.....
- Two stage starting air compressor
Hamworthy 2TM6 type which was designed for free air deliveries ranging from 183 m3 per hour at a discharge pressure of 14 bar to 367m3 per hour at 42 bar. The crankcase is a rigid casting which supports a spheroidal graphite cast iron crankshaft in three bearings.....
- Fuel handling
Fuels and lubricating oils are obtained from crude primarily by heating the crude oil, so that vapours are boiled off and then condensed at different temperatures. The constituents or fractions are collected separately in a
distillation process.....
- Fuel transfer and fire risk
The oil fuel system provides the means for delivering fuel from the receiving stations at upper deck level, port and starboard, to double-bottom or deep bunker tanks. Sampling cocks are fitted at the deck connections to obtain a representative specimen for (a) shore analysis; (b) on board testing; and (c) retention on the ship.....
- High density fuel treatment
The density of a fuel tested at 15 deg C may approach, be equal to or greater than that of water. With high density fuels, the reduction in density differential between fuel and water can cause a problem with separation but not with the usual solid impurities.....
- Viscosity controller
A continuous sample of the fuel is pumped at a constant rate through a fine capillary tube. As the flow through the tube is laminar, pressure drop across the tube is proportional to viscosity. In this unit an electric motor drives the gear pump through a reduction gear, at a speed of 40 rpm......
- Fuel blenders
Conventionally, the lower cost residual fuels are used for large slow speed diesel main engines and generators are operated on the lighter more expensive distillate fuel. The addition of a small amount of diesel oil to heavy fuel considerably reduces its viscosity and if heating is used to further bring the viscosity down then the blend can be used in generators with resultant savings.....
- Fuel heaters
The system which delivers residual fuel from the daily service tank to the diesel or boiler, must bring it to the correct viscosity by heating.For burning heavy fuel oil in a boiler furnace, or a compression-ignition engine, it is necessary to pre-heat it....
- Homogenizer
The homogenizer provides an alternative solution to the problem of water in high density fuels. It can be used to emulsify a small percentage for injection into the engine with the fuel. This is in contradiction to the normal aim of removing all water, which in the free state, can cause gassing of fuel pumps, corrosion and other problems......
- Package boiler combustion system
The elementary automatic combustion system based on a two flame burner is used for many auxiliary boilers. The burner is drawn oversize to show detail. Various different control systems are employed for the arrangement.....
- Lubricating oil treatment
Mineral oils for lubrication are, like fuel, derived from crude during refinery processes. Basic stocks are blended to make lubricants with the desired properties and correct viscosity for particular duties. ....
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