PURIFICATION(??) OF FUEL OILS

1
LESSON 6

• PURIFICATION(??) OF FUEL OILS

2

• Fuels vary considerably in viscosity, quality and
  chemical composition. They also contain
  impurities from producing, transferring and
  storage.

3

• All heavy fuels contain insoluble(?????)
  impurities such as mineral salts, asphalt(??),
  foreign matter and some liquids not
  miscible(????).

4

• These impurities can to a great degree(extend) be
  removed by centrifugal(???) and filtration(??)
  treatments.

5

• Failure of any cleaning equipment could cause
  very serious troubles to the mechanical parts of
  the fuel injection equipment,

6

• therefore standby duplicate cleaning equipment
  must be provided and so arranged that continuous
  operation can be maintained should the working
  unit fail.

7

• The most common method of cleaning fuel is by
  centrifuging and there are various makes of
  purifiers(???) and clarifiers(???) in use

8

• such as Alfalaval, Titan, Sharpies, etc., the
  basic principles of operation and design are
  similar.

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Dirty oil
Clean oil
water
gravity disc
Separation disc
Cylindrical interface
bowl
10

• The separation discs(???) in purifiers and
  clarifiers are conical in shape and are made of
  stainless steel,

11

• the outer periphery(??) is perforated(??) 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.

12

• When the fuel is pumped into an operating
  centrifuge the centrifugal force generated causes
  the heavier fractions(??) such as sludge and
  water to be forced along the underside of the
  discs to the outer periphery.

13

• A cylindrical interface(?????) 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.

14

• The impurities and sludge can be collected in the
  bowl(???), sludge space, or in some designs
  discharged at regular intervals to a sludge tank.

15

• 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(??) areas.

16

• The specific gravity of the fuel determines the
  size of the gravity rings(???) to be fitted and
  it is important to refer to the makers
  instruction manual for verification.

17

• A higher throughput(????) and more efficient
  process can be achieved if the fuel is heated to
  reduce its viscosity.

18

• Heaters are, therefore, installed in the system.
  Recommended temperatures for high viscosity fuels
  are between 80 to 95? depending on the viscosity
  of the fuel.

19

• If the purifying of relatively clean fuel is
  needed, a centrifuge fitted with a clarifier bowl
  should be used.

20

• There is only one outlet for clean oil, no
  gravity discs(rings) are fitted for the
  separation of water.

21

• Consequently, the maximum cleaning efficiency is
  achieved, as the oil feed will at all time be
  outside the disc stack zone.

22

• Experience has shown excellent results from a
  two-stage centrifuge treatmentpurifying followed
  by clarifying.

23

• The fuel is pumped into the purifier fitted with
  gravity rings and with separate discharges for
  oil, water and sludge.

24

• The relatively clean oil is then pumped into a
  clarifier which extracts(???) any small amount of
  water or impurities still left in the oil.

25

• Unacceptably large quantities of impurities are
  left in the oil after the purifying process if
  the oil is insufficiently heated, or the
  throughput is too high or the wrong type of
  gravity disc is fitted.

26

• Improvements 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 control, heaters,
  flood alarms and other ancillary equipment.

27

• A further development has been the self-cleaning
  purifier which operates unattended(???????, )
  for long periods and discharges its own sludge.

28

• The self cleaning unit can be stopped and started
  at any time without dismantling(??) for manual
  cleaning which is a dirty and time consuming
  job.

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• If the unit is not self-cleaning, then a strict
  maintenance routine must be followed.

30

• Poorly maintained units are a continuous 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.

31

• The efficiency of centrifugal unit decreases
  rapidly when the accumulation of impurities
  reaches a certain point.

32

• For self-cleaning purifiers used in unmanned
  machinery spaces controls are arranged that if a
  centrifuge fails the standby unit will
  automatically comes into operation.

33

• The purifiers are fitted with electric timers for
  controlling the period between bowl emptying
  operations and sequential regulating devices
  control the various' emptying operations

34

• The units must incorporate an audio-visual alarm
  system which come into operation when any running
  condition is out of order.

35

• When an alarm 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.

36

• In order to control the interface zone of the
  bowl a constant pressure control valve is fitted
  at the clean oil outlet.

37

• By applying a high back pressure the interface
  moves outward and with a low back pressure the
  opposite results.

38

• It is important to note that when an excessive
  amount of water is present in the fuel the
  temperature for centrifuging must be kept below
  the boiling point of water, otherwise foaming(??)
  and, agitation(??) of the fuel takes place.

39

• Under these circumstances it will be necessary to
  purify at a very low rate to achieve a reasonable
  efficiency.

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READING MATERIAL

• A. OIL TREATMENT

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• Both fuel oils and lubricating oils require
  treatment before passing to the engine.

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• This will involve storage and heating to allow
  separation of water present, coarse and fine
  filtering to remove solid particles and also
  centrifuging.

43

• The centrifugal separator is used to separate two
  liquids, for example oil and water, or a liquid
  and solids as in contaminated oil.

44

• Separation is speeded up by the use of centrifuge
  and can be arranged as a continuous process.
  Where a centrifuge is arranged to separate two
  liquids, it is known as a 'purifier'.

45

• Where a centrifuge is arranged to separate
  impurities and small amounts of water from oil it
  is known as a clarifier.

46

• The 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.

47
Centrifuging

• A centrifuge consists of an electric motor drive
  to a vertical shaft on the top of which is
  mounted the bowl assembly.

48

• An outer framework(??) surrounds the assembly and
  carries the various feed and discharge
  connections.

49

• The bowl can be a solid assembly which retains
  the separated sludge 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.

50

• The dirty oil is admitted into the center of the
  bowl, passes up through a stack of discs and out
  through the top.

51
The Purifying Process

• The centrifugal separation of two liquids such as
  oil and water, results in the formation of a
  cylindrical interface between the two.

52

• The position of this interface within the
  centrifuge is very important for correct
  operation.

53

• The setting or positioning of the interface is
  achieved by the use of dam ring(???) or gravity
  disc at the outlet of the centrifuge.

54

• Various diameter rings are available for each
  machine when different densities of oil are used.

55
The Clarifying Process

• Cleaning oil that contains little or no water is
  achieved in a clarifier bowl where the impurities
  and water collect at the bowl periphery.

56

• A clarifier bowl has only one outlet. No gravity
  disc is necessary since no interface is formed.

57

• The bowl therefore operates at maximum separating
  efficiency since the oil is subjected to the
  maximum centrifugal force.

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The Bowl Discs

• Purifier and clarifier bowls each contain a stack
  of conical discs. The discs may number up to 150
  and are separated from one another by a small
  gap.

59

• Separation of impurities and water from the oil
  takes place between these discs. A series of
  aligned(???) holes near the outside edge permits
  entry of the dirty oil.

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• The action of centrifugal force causes the
  lighter components (the clean oil) to flow,
  inwards and the water and impurities flow
  outwards.

61

• The water and impurities form a sludge which
  moves outwards along the undersides of the discs
  to the periphery of the bowl.

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Selection of Gravity Disc

• The interface between the liquid seal (water) and
  the oil should be positioned as close as possible
  to the bowl periphery.

63

• However, the interface must not be located so far
  from the bowl center that the oil will pass the
  outer edge of the top disc, breaking the liquid
  seal and discharging with the water.

64

• Factors 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.

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• Throughput 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.

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• The same effect is produced by a high back
  pressure, and a low one respectively, in the
  clean oil outlet.

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• Gravity disc. The location of the interface is
  adjusted by altering the outlet for the water,
  i.e. exchanging the gravity disc.

68

• Changing to a gravity disc with larger hole
  diameter will move the interface towards the bowl
  periphery,

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• whereas a disc with smaller hole diameter will
  position the interface closer to the bowl center.

70

• The nomogram(???) is an aid to select a
  tentative(???) gravity disc when the density of
  the oil at a given temperature is known.

71

• The hole diameter of the disc to be tried first
  appears directly from the nomogram.

72

• However, 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
  emulsification(??)in the water outlet.

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Discharge of Sludge

• Modern centrifuge designs enable continuous
  operating, over a considerable period of time.

74

• This is achieved by an ejection process which is
  timed to discharge the sludge at regular
  intervals.

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• The sludge deposits build up on the bowl
  periphery as separation-continues, and the
  ejection process is timed to clear these deposits
  before they begin to affect the separation
  process.

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• To start the ejection process the oil feed to the
  centrifuge is first shut off and the oil
  remaining in the bowl removed by admitting
  flushing water(???).

77

• Water is then fed into the hydraulic system in
  the bottom of the bowl to open a number of
  spring-load valves.

78

• This 'operating' water causes the sliding bowl
  bottom to move downwards and open discharge ports
  in the bowl periphery.

79

• 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 ports.

80

• Water is fed into the bowl to remake the liquid
  seal, the oil feed reopened, and separation
  continues.

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Maintenance

• The bowl and the disc stack will require
  periodical cleaning whether or not an ejection
  process is in operation.

82

• Care should be taken in stripping(??) down the
  bowl, using only the special tools provided and
  noting that some left-hand threads are used.

83

• The centrifuge is a perfectly balanced piece of
  equipment, rotating at high speeds all parts
  should therefore be handled and treated with
  care.

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• B. OPERATION OF AN OIL SEPARATOR

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Before Starting

• The bowl should be well cleaned and assembled
  according to the instruction. Check particularly
  The brake is released.

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• The collecting covers (frame hood respectively)
  are clamped(??) with the hinged(???) bolts. The
  oil level in worm gear (??) housing is somewhat
  above the middle of the gauge glass.

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• The operating liquid tank is full and the control
  valves are closed (operating liquid feed turned
  off bowl open).

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• Note The oil level must never be allowed to sink
  below the lower edge of the gauge glass. If the
  glass is provided with corrugation(??) they
  should be vertical.

89

• Keep the gauge glass clean, otherwise a line,
  which could be mistaken for the oil level, will
  in time build upon the inside of the glass.

90

• If the machine has been idle (for instance during
  a night), screw out the drain screw some turns
  and drain off any water.

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Starting the Motor

• If the process liquid is to be preheated,
  circulate it through the preheating until
  suitable temperature is reached.

92

• Shortly after starting it may occur that the bowl
  begins to vibrate more than normal.

93

• The cause is generally lack of balance due to bad
  cleaning of the bowl. Stop the machine and clean
  the bowl if the vibrations are very heavy.

94

• Heat is always generated in the clutch(???)
  coupling during the running-up period.

95

• This will be noticeable, especially when the
  pads(?, ??) on the friction block are new,
  through smoke and smell of burning. Like the
  sliding sound, this is quite normal and has no
  importance.

96

• During acceleration the power consumption is
  higher than in normal operation.

97

• The acceleration time may vary somewhat
  depending, for instance, on the condition of the
  friction pads in the clutch coupling(???).

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Bowl Closing

• After attaining the right speed, the bowl should
  be closed.

99

• Before starting the closing operation, the number
  of revolutions of the speed indicator must be
  checked against the speed table in the
  instruction book.

100

• The 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.
  Then fill it.

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Filling

• The filling procedure differs for purification,
  clarification and concentration(????), i.e. for
  machines provided with purifier, clarifier and
  concentrator bowl respectively.

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Clarification (clarifier bowl)

• Set the flow regulator to wanted throughput and
  open the process liquid feed valve.

103
Purification (purifier bowl)

• Supply liquid, usually water, to form the liquid
  seal. This liquid should preferably have the same
  temperature as the process liquid and must be
  supplied quickly.

104

• Shut off the feed of sealing liquid when this
  begins flowing out and becomes visible in the
  sight glass.

105
Set the Flow Regulator to Desired Throughput

• Slowly open the process liquid feed valve. A
  certain quantity of sealing liquid will now
  escape, until equilibrium is reached.

106

• If the valve is opened too quickly, the liquid
  seal could be forced away to the effect that
  light liquid phase is discharged in the wrong
  way,

107

• i.e. through the outlet for the heavy liquid
  phase. When this occurs with the filling
  procedure has to be repeated.

108

• Adjust to suitable back pressure in the conduit
  for light phase (For machine with equipment for
  interface disposition see Selection of gravity
  disc)

109
Concentration (concentrator bowl)

• The liquid seal builds up automatically. Adjust
  to wanted throughput-see Purification above.

110
Running

• Check particularly that throughput and working
  temperature are constant that oil does not leak
  from the worm gear housing (oil level at
  operative height)

111

• that, in purification, light phase is not
  escaping together with the heavy one, thereby
  indicating that the bowl is clogged or the liquid
  seal is broken.

112

• If so, a sludge discharge must be carried out
  immediately and henceforth the interval between
  discharges be reduced.

113

• If sludge had packed(??) between the bowl discs
  it may be necessary to stop the machine for
  manual cleaning of the bowl.