1、MARPOL & Pollution PreventionOily Water Separator Bilge SystemsBilge Systemsw The essential purpose of a bilge system, is to clear water from the ships dry compartments, in emergency. w The major uses of the system, are for clearing water and oil which accumulates in machinery space bilges as the re
2、sult of leakage or draining, and when washing down dry cargo holds.w The bilge main in the engine room, has connections from dry cargo holds, tunnel and machinery spaces. International Legislation w Oil/water separators are necessary aboard vessels to prevent the discharge of oil overboard mainly wh
3、en pumping out bilges. w The requirement to fit such devices is the result of international legislation.w Legislation was needed because free oil and oily emulsions discharged in a waterway canninterfere with natural processes such as photosynthesis and re-aeration, and ninduce the destruction of th
4、e algae and plankton so essential to fish life. Oil Density w It is important that an oil/water separator is correctly installed, used and maintained.w It is generally accepted that oil is less dense than water and this is the basis of the design of devices to separate the two liquids.w Some of the
5、modern heavy fuels however, have a density nat 15 which approaches, is the same as or is even higher than that of water and nthis has added to the problems of separation in oil/water separators and in centrifuges. Two Separating Waysw The operation of oil/water separators relies heavily on gravity a
6、nd a conventional difference in densities. w Centrifuges by their speed of rotation, exert a force many times that of gravitational effect and the heater reduces density in comparison with that of water.w Oil/Water Separationw Oil/water separators and centrifuges are both employed for the purpose of
7、 separating oil and water but there are major differences.w Oil/water separators are required to handle large quantities of water from which usually, small amounts of oil must be removed.w Various features are necessary to aid removal of the oil from the large bulk of water particularly when the dif
8、ference in densities is small. Centrifugal Separationw Centrifuges are required to remove (again usually) small quantities of water from a much larger amount of oil. w Additionally the centrifuge must separate solids and it must, with respect to fuel, handle large quantities at the rate at which the
9、 fuel is consumed. Bilge Water Separation w The main principle of separation by which commercially available oil/water separators function, is the gravity differential between oil and water. w In oily water mixtures, the oil exists as a collection of globules of various sizes.w The force acting on s
10、uch a globule, causing it to move in the water is proportional to the difference in weight between the oil particle and a particle of water of equal volume. Bilge Water Separationw The relationship of the terminal velocity of the oil globule with viscosity, relative density and particle size can be
11、expressed as: w In general, a high rate of separation is encouraged by na large size of oil globule, nelevated temperature of the system and nthe use of sea water.w Turbulence or agitation should be avoided since it causes mixing and re-entrainment of the oil. w Laminar or streamlined flow is benefi
12、cial. 2188dvowImprove the Separationw In addition to the heating coils provided to optimize separation, there are various other means used to improve and speed up operation. nThe entrance area in the separators is made large so that flow is slow and large slugs of oil can move to the surface quickly
13、. nAlternation of flow path in a vertical direction continually brings oil near to the surface, where separation is enhanced. nAngled surfaces provide areas on which oil can accumulate and form globules, which then float upwards. nFine gauze screens are also used as coalescing or coagulating surface
14、s.w The Simplex-Turbulo oil/water separator consists of a vertical cylindrical pressure vessel containing a number of inverted conical plates. w The oily water enters the separator in the upper half of the unit and is directed downwards to the conical plates.w Large globules of oil separate out in t
15、he upper part of the separator. w The smaller globules are carried by the water into the spaces between the plates. The Simplex-Turbulo oil/water separator w The rising velocity of the globules carries them upwards where they become trapped by the under-surfaces of the plates and coalesce until the
16、enlarged globules break away at the periphery.w The oil rises, is caught underneath an annular baffle and is then led up through the turbulent inlet area by risers to collect in the dome of the separator. w The water leaves the conical plate pack via a central pipe which is connected to a flange at
17、the base of the separator.The Simplex-Turbulo oil/water separatorw To meet the requirement of legislation, a second stage coalescer was added. w Filter elements in the second stage remove any small droplets of oil in the discharge and cause them to be held until they form larger droplets (coalesce).
18、 w As the larger globules form, they rise to the oil collecting space. The Simplex-Turbulo oil/water separatorCentrifuge Feed Pumpw The water is sucked up from the oily water tank or engine room bilge and fed by the variable rate feed pump through the automatic filter. w The rate of the feed pump is
19、 controlled by the oil in water monitor and the automatic filter serves to protect the disk stack of the separator bowl from solid particles larger than 0.5 mm.w A differential pressure switch controls the cleaning of the automatic filter.Centrifuge Heaterw The bilge water then goes through a pre-he
20、ater where it is heated to about 85, and via the feed valve to the separator.w During the start-up or ejection program the flow is directed back into the oily water tank.Centrifuge Separationw The water is separated from the finest oil particles and then conveyed under pressure by a centrifugal pump
21、 to the discharge.w It may be necessary to use chemical dosing with conditioning polymers to handle difficult emulsions.Centrifuge Dischargew To ensure a ppm value under 5 ppm, the bilge water can be directed to an optional absorption filter before it is discharged overboard.w The separated impuriti
22、es accumulated in the sludge space are discharged into the sludge tank periodically.w The oil discharge is directed to the waste oil tank.Centrifuge Variable Floww The clean water discharge is supervised by an oil content meter and discharged into the sea.w If the oil content exceeds 15 ppm, the wat
23、er is recirculated into the oily water tank.w An intellingent process control adapts the capacity of the system to the changes of the oily water.Centrifuge Variable Floww The variable speed feed pump runs at maximum capacity when the oil content of the discharge water is less than 8 ppm.w As the oil content rises, the feed pump capacity is reduced and will be at minimum when the oil content rises to 13 ppm.The end Thank you
