lesson 6　PURIFICATION(净化) OF FUEL OILS 轮机英语课件.ppt

LESSON 6 PURIFICATION(净化) OF FUEL OILS Fuels vary considerably in viscosity, quality and chemical composition. They also contain impurities from producing, transferring and storage. All heavy fuels contain insoluble(不能溶解的) impurities such as mineral salts, asphalt(沥青), foreign matter and some liquids not miscible(易混合的). These impurities can to a great degree(extend) be removed by centrifugal(离心的) and filtration(过滤) treatments. Failure of any cleaning equipment could cause very serious troubles to the mechanical parts of the fuel injection equipment, therefore standby duplicate cleaning equipment must be provided and so arranged that continuous operation can be maintained should the working unit fail. The most common method of cleaning fuel is by centrifuging and there are various makes of purifiers(分水机) and clarifiers(分杂机) in use such as Alfalaval, Titan, Sharpies, etc., the basic principles of operation and design are similar. The separation discs(分离盘) in purifiers and clarifiers are conical in shape and are made of stainless steel, the outer periphery(外围) is perforated(打孔) by a series of holes through which the fuel passes, the distance between each disc is approximately 0.5 mm and the thickness is about 1 mm. When the fuel is pumped into an operating centrifuge the centrifugal force generated causes the heavier fractions(部分) such as sludge and water to be forced along the underside of the discs to the outer periphery. A cylindrical interface(圆柱分界面) is formed between the heavier fractions (water) and the lighter fractions (oil). The lighter fraction is forced inward and up to the clean oil outlet. The impurities and sludge can be collected in the bowl(分离筒), sludge space, or in some designs discharged at regular intervals to a sludge tank. The best results are obtained when the interface zone is close to the periphery of the bowl and it must be outside the disc stack(堆叠) areas. The specific gravity of the fuel determines the size of the gravity rings(比重环)