哈工程轮机英语lesson6

1、Harbin Engineering universityLESSON 6PURIFICATION(净化净化) OF FUEL OILSProf. Song ZhouHarbin Engineering universityNew Words and Expressions in Text viscosity 粘度 composition 组成 storage 存储 insoluble 不溶解的 impurity 杂质 asphalt 沥青 miscible 易混合的 filtration 过滤 purifier 分水机 clarifier 分杂机 conical 圆锥形的 periphery

2、 外围，用边 perforate 穿(钻，冲)孔 cylindrical 圆柱形的 bowl 分离筒Harbin Engineering university ancillary 辅助的 centrifuge 离心分离机 accumulation 积聚 consume 消耗 agitation 搅动 circumstance 环境，详情Harbin Engineering universityFuels vary considerably in viscosity, quality and chemical composition. They also contain impurities f

3、rom producing, transferring and storage. Harbin Engineering universityA l l h e a v y f u e l s c o n t a i n insoluble(不能溶解的不能溶解的) impurities such as mineral salts, asphalt(沥沥青青), foreign matter and some liquids not miscible(易混合的易混合的). Harbin Engineering universityThese impurities can to a great de

4、gree(extend) be removed by c e n t r i f u g a l ( 离 心 的离 心 的 ) a n d filtration(过滤过滤) treatments. Harbin Engineering universityF ailure of any c le aning equipment could cause very s e r i o u s t r o u b l e s t o t h e mechanical parts of the fuel injection equipment, Harbin Engineering universit

5、ytherefore standby duplicate cleaning equipment must be provided and so arranged that continuous operation can be maintained should the working unit fail.Harbin Engineering universityThe most common method of cleaning fuel is by centrifuging and there are various makes of purifiers(分离机分离机) and clari

6、fiers (分杂机分杂机) in useHarbin Engineering universitysuch as Alfalaval, Titan, Sharpies, etc., the basic principles of operation and design are similar.Harbin Engineering universitygravity discDirty oilClean oilwaterbowlCylindrical interfaceSeparation discHarbin Engineering universityThe separation dis

7、cs(分离盘分离盘) in purifiers and clarifiers are conical in shape and are made of stainless steel, Harbin Engineering universitythe outer periphery(外围外围) is perforated(打孔打孔) by a series of holes through which the fuel passes, the distance between each disc is approximately 0.5 mm and the thickness is abou

8、t 1 mm.Harbin Engineering universityWhen the fuel is pumped into an operating centrifuge the centrifugal force generated causes the heavier fractions(部分部分) such as sludge and water to be forced along the underside of the discs to the outer periphery. Harbin Engineering universityA cylindrical interf

9、ace(圆柱分界圆柱分界面面) 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. Harbin Engineering universityThe impurities and sludge can be collected in the bowl(分离筒分离筒), sludge space, or in some designs dischar

10、ged at regular intervals to a sludge tank. Harbin Engineering universityThe best results are obtained when the interface zone is close to the periphery of the bowl and it must be outside the disc stack(堆叠堆叠) areas. Harbin Engineering universityThe specific gravity of the fuel determines the size of

11、the gravity rings(比重环比重环) to be fitted and it is important to refer to the makers i n s t r u c t i o n m a n u a l f o r verification. Harbin Engineering universityA higher throughput(处理能力处理能力) and more efficient process can be achieved if the fuel is heated to reduce its viscosity. Harbin Engineer

12、ing universityHeaters are, therefore, installed in the system. Recommended temperatures for high viscosity fuels are between 80 to 95 depending on the viscosity of the fuel. Harbin Engineering universityIf the purifying of relatively clean fuel is needed, a centrifuge fitted with a clarifier bowl sh

13、ould be used. Harbin Engineering universityThere is only one outlet for clean oil, no gravity discs(rings) are fitted for the separation of water. Harbin Engineering universityConsequently, the maximum cleaning efficiency is achieved, as the oil feed will at all time be outside the disc stack zone.

14、Harbin Engineering universityExperience has shown excellent results from a two-stage centrifuge treatmentpurifying followed by clarifying. Harbin Engineering universityThe fuel is pumped into the purifier fitted with gravity rings and with separate discharges for oil, water and sludge. Harbin Engine

15、ering universityThe relatively clean oil is then pumped into a clarifier which extracts(分离出分离出) any small amount of water or impurities still left in the oil. Harbin Engineering universityUnacceptably large quantities of impurities are left in the oil after the purifying process if the oil is insuff

16、iciently heated, or the throughput is too high; or the wrong type of gravity disc is fitted.Harbin Engineering universityImprovements in oil, oil purifying techniques and centrifuges have led to the development of single phase purifiers which have in themselves been aided by improved temperature con

17、trol, heaters, flood alarms and other ancillary equipment.Harbin Engineering universityA further development has been the self-cleaning purifier which operates unattended(无人照管无人照管监视监视的的, ) for long periods and discharges its own sludge. Harbin Engineering universityThe self cleaning unit can be stop

18、ped and started at any time without dismantling(拆卸拆卸) for manual cleaning which is a dirty and time consuming job. Harbin Engineering universityIf the unit is not self-cleaning, then a strict maintenance routine must be followed. Harbin Engineering universityPoorly maintained units are a continuous

19、source of trouble and allowing a machine to run beyond its recommended time can result in a choked bowl, especially if very dirty fuel is being purified. Harbin Engineering universityThe efficiency of centrifugal unit decreases rapidly when the accumulation of impurities reaches a certain point. Har

20、bin Engineering universityFor self-cleaning purifiers used in unmanned machinery spaces controls are arranged that if a centrifuge fails the standby unit will automatically comes into operation. Harbin Engineering universityThe purifiers are fitted with electric timers for controlling the period bet

21、ween bowl emptying operations and sequential regulating devices control the various emptying operations; Harbin Engineering universityThe units must incorporate an audio-visual alarm system which come into operation when any running condition is out of order. Harbin Engineering universityWhen an ala

22、rm condition prevails with the unit, it should be arranged to shut down or the fuel oil recycling valve should open and the oil flow should be passed to the outer circle thus preventing the loss of oil. Harbin Engineering universityIn order to control the interface zone of the bowl a constant pressu

23、re control valve is fitted at the clean oil outlet. Harbin Engineering universityBy applying a high back pressure the interface moves outward and with a low back pressure the opposite results. Harbin Engineering universityIt is important to note that when an excessive amount of water is present in t

24、he fuel the temperature for centrifuging must be kept below the boiling point of water, otherwise foaming(起泡起泡) and, agitation(搅拌搅拌) of the fuel takes place.Harbin Engineering universityUnder these circumstances it will be necessary to purify at a very low rate to achieve a reasonable efficiency. Ha

25、rbin Engineering universityREADING MATERIAL A. OIL TREATMENT Harbin Engineering universityBoth fuel oils and lubricating oils require treatment before passing to the engine. Harbin Engineering universityThis will involve storage and heating to allow separation of water present, coarse and fine filte

26、ring to remove solid particles and also centrifuging. Harbin Engineering universityThe centrifugal separator is used to separate two liquids, for example oil and water, or a l i q u i d a n d s o l i d s a s i n contaminated oil. Harbin Engineering universitySeparation is speeded up by the use of ce

27、ntrifuge and can be arranged as a continuous process. Where a centrifuge is arranged to separate two liquids, it is known as a purifier. Harbin Engineering universityWhere a centrifuge is arranged to separate impurities and small amounts of water from oil it is known as a clarifier. Harbin Engineeri

28、ng universityThe separation of impurities and water from fuel oil is essential for good combustion. The removal of contaminating impurities from lubricating oil will reduce engine wear and possible breakdowns. Harbin Engineering universityCentrifugingA centrifuge consists of an electric motor drive

29、to a vertical shaft on the top of which is mounted the bowl assembly. Harbin Engineering universityAn outer framework(机 壳机 壳 ) surrounds the assembly and carries the various feed and discharge connections. Harbin Engineering universityThe bowl can be a solid assembly which retains the separated slud

30、ge and operates non-continuously, or the bowl can be arranged so that the upper and lower parts separate and the sludge can be discharged while the centrifuge operates continuously.Harbin Engineering universityThe dirty oil is admitted into the center of the bowl, passes up through a stack of discs

31、and out through the top. Harbin Engineering universityThe Purifying ProcessThe centrifugal separation of two liquids such as oil and water, results in the formation of a cylindrical interface between the two. Harbin Engineering universityThe position of this interface within the centrifuge is very i

32、mportant for correct operation. Harbin Engineering universityThe setting or positioning of the interface is achieved by the use of dam ring(阻水环阻水环) or gravity disc at the outlet of the centrifuge. Harbin Engineering universityVarious diameter rings are available for each machine when different densi

33、ties of oil are used. Harbin Engineering universityThe Clarifying ProcessCleaning oil that contains little or no water is achieved in a clarifier bowl where the impurities and water collect at the bowl periphery. Harbin Engineering universityA clarifier bowl has only one outlet. No gravity disc is n

34、ecessary since no interface is formed. Harbin Engineering universityThe bowl therefore operates at maximum separating efficiency since the oil is subjected to the maximum centrifugal force. Harbin Engineering universityThe Bowl DiscsPurifier and clarifier bowls each contain a stack of conical discs.

35、 The discs may number up to 150 and are separated from one another by a small gap. Harbin Engineering universitySeparation of impurities and water from the oil takes place between these discs. A series of aligned(排列的排列的) holes near the outside edge permits entry of the dirty oil. Harbin Engineering

36、universityThe action of centrifugal force causes the lighter components (the clean oil) to flow, inwards and the water and impurities flow outwards. Harbin Engineering universityThe water and impurities form a sludge which moves outwards along the undersides of the discs to the periphery of the bowl

37、. Harbin Engineering universitySelection of Gravity DiscThe interface between the liquid seal (water) and the oil should be positioned as close as possible to the bowl periphery. Harbin Engineering universityHowever, the interface must not be located so far from the bowl center that the oil will pas

38、s the outer edge of the top disc, breaking the liquid seal and discharging with the water. Harbin Engineering universityFactors influencing the interface position are:Oil viscosity and density. A high oil density will position the interface closer to the bowl periphery than will a low density. Harbi

39、n Engineering universityThroughput and back pressure. As a rule the interface will be located closer to the bowl periphery at a high throughput than at a low one. Harbin Engineering universityThe same effect is produced by a high back pressure, and a low one respectively, in the clean oil outlet. Ha

40、rbin Engineering universityGravity disc. The location of the interface is adjusted by altering the outlet for the water, i.e. exchanging the gravity disc. Harbin Engineering universityChanging to a gravity disc with larger hole diameter will move the interface towards the bowl periphery, Harbin Engi

41、neering universitywhereas a disc with smaller hole diameter will position the interface closer to the bowl center.Harbin Engineering universityThe nomogram(诺莫图诺莫图) is an aid to select a tentative(暂定的暂定的) gravity disc when the density of the oil at a given temperature is known. Harbin Engineering uni

42、versityThe hole diameter of the disc to be tried first appears directly from the nomogram.Harbin Engineering universityHowever, in practical operation the best result is obtained by using the gravity disc with largest hole diameter that will not cause a break in the liquid seal in the bowl or an emu

43、lsification(乳化乳化)in the water outlet. Harbin Engineering universityDischarge of SludgeModern centrifuge designs enable continuous operating, over a considerable period of time. Harbin Engineering universityThis is achieved by an ejection process which is timed to discharge the sludge at regular inte

44、rvals. Harbin Engineering universityThe sludge deposits build up on t h e b o w l p e r i p h e r y a s separation-continues, and the ejection process is timed to clear these deposits before they begin to affect the separation process. Harbin Engineering universityTo start the ejection process the o

45、il feed to the centrifuge is first shut off and the oil remaining in the bowl removed by admitting flushing water(置换水置换水). Harbin Engineering universityWater is then fed into the hydraulic system in the bottom of the bowl to open a number of spring-load valves. Harbin Engineering universityThis oper

46、ating water causes the sliding bowl bottom to move downwards and open discharge ports in the bowl periphery. Harbin Engineering university The sludge is discharged through these ports by centrifugal force. Closing operating water is now feed in to raise sliding bowl up again and close the discharge

47、ports. Harbin Engineering universityWater is fed into the bowl to remake the liquid seal, the oil feed reopened, and separation continues. Harbin Engineering universityMaintenanceThe bowl and the disc stack will require periodical cleaning whether or not an ejection process is in operation. Harbin E

48、ngineering universityCare should be taken in stripping(拆卸拆卸) down the bowl, using only the special tools provided and noting that some left-hand threads are used. Harbin Engineering universityThe centrifuge is a perfectly balanced piece of equipment, rotating at high speeds; all parts should therefo

49、re be handled and treated with care. Harbin Engineering universityB. OPERATION OF AN OIL SEPARATOR Harbin Engineering universityBefore StartingThe bowl should be well cleaned and assembled according to the instruction. Check particularly: The brake is released. Harbin Engineering universityThe colle

50、cting covers (frame hood respectively) are clamped(夹紧夹紧) with the hinged(装铰链装铰链) bolts. The oil level in worm gear (蜗轮蜗轮) housing is somewhat above the middle of the gauge glass. Harbin Engineering universityThe operating liquid tank is full and the control valves are closed (operating liquid feed t

51、urned off; bowl open). Harbin Engineering universityNote: The oil level must never be allowed to sink below the lower edge of the gauge glass. If the g l a s s i s p r o v i d e d w i t h corrugation(沟纹沟纹) they should be vertical. Harbin Engineering universityKeep the gauge glass clean, otherwise a

52、line, which could be mistaken for the oil level, will in time build upon the inside of the glass. Harbin Engineering universityIf the machine has been idle (for instance during a night), screw out the drain screw some turns and drain off any water. Harbin Engineering universityStarting the MotorIf t

53、he process liquid is to be preheated, circulate it through the preheating until suitable temperature is reached. Harbin Engineering universityShortly after starting it may occur that the bowl begins to vibrate more than normal. Harbin Engineering universityThe cause is generally lack of balance due

54、to bad cleaning of the bowl. Stop the machine and clean the bowl if the vibrations are very heavy. Harbin Engineering universityHeat is always generated in the clutch(离合器离合器) coupling during the running-up period. Harbin Engineering universityThis will be noticeable, especially when the pads(垫垫, 衬垫衬

55、垫) on the friction block are new, through smoke and smell of burning. Like the sliding sound, this is quite normal and has no importance. Harbin Engineering universityDuring acceleration the power consumption is higher than in normal operation.Harbin Engineering universityThe acceleration time may v

56、ary somewhat depending, for instance, on the condition of the friction pads in the clutch coupling(离合器离合器).Harbin Engineering universityBowl ClosingAfter attaining the right speed, the bowl should be closed. Harbin Engineering universityBefore starting the closing operation, the number of revolution

57、s of the speed indicator must be checked against the speed table in the instruction book.Harbin Engineering universityThe acceleration time can vary somewhat depending, i.e. on the wear of the friction pads.Close the bowl by opening the corresponding control valve. Wait till the bowl has closed. The

58、n fill it.Harbin Engineering universityFillingThe filling procedure differs for purification, clarification and concentration(浓缩分离浓缩分离), i.e. for machines provided with purifier, clarifier and concentrator bowl respectively.Harbin Engineering universityClarification (clarifier bowl)Set the flow regulator t