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High density fuel treatment (ALCAP System) & fuel handling procedure for motor ships
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.
Heating of the fuel (Figure 1 below) will reduce the density and this may be sufficient in itself to obviate the problem of water separation. The change in density of water with temperature (dotted line) is not so pronounced, as can be seen from the graph, so that heating produces a differential Some caution must be exercised in heating the fuel.
Figure 1: Temperature/density graph (courtesy Alpha-Laval)
The Alfa-Laval design of centrifuge (Figure 2) intended for dealing with high density residual fuels, is a self-sludging machine which has a flow control disc that makes it virtually a clarifier. There are no gravity discs to be changed to make the machine suitable for fuels of different specific gravity/density. Heating is used to reduce the density (and viscosity) of the fuel so that water
and sludge accumulate in the outer part of the bowl, as the result of the centrifugal effect.
Figure 1: FOPX separator
As the interface moves inwards, but before reaching the disc stack, water droplets flow through to reach a water sensing transducer (Figure 3). Via micro-processor circuitry, the transducer causes the bowl to self-sludge or the water to be discharged through the water drain valve. The system is said to be capable of handling fuels with densities as high as 1010 kg/m3 at 15 deg C
Figure 3: water-sensing-transducer
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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