WO2000002637A1

WO2000002637A1 - Apparatus and methods for separating immiscible fluids

Info

Publication number: WO2000002637A1
Application number: PCT/CA1999/000624
Authority: WO
Inventors: Paul Costinel
Original assignee: Paul Costinel
Priority date: 1998-07-10
Filing date: 1999-07-09
Publication date: 2000-01-20
Also published as: CA2243142A1; CA2243142C; AU4596299A

Abstract

A compact multi-stage oil-water separator (20) has application in removing oily contaminants from bilge water in ships. The oil-water separator has a final stage (36) in which the flow of fluid is repeatedly reversed. The separator preferably has two toroidal mechanical separation stages (31, 32) on the suction side of a feed pump (27), and a cyclone separation stage (34) and a polishing stage (36) on the output side of the pump. The cyclone separation and polishing stage (34, 36) may be located inside the mechanical separation stages (31, 32) for compactness. The oil-water separator (20) has built-in-fail-safe operation to prevent the accidental discharge of water in the case of contaminated sensors. The oil-water separator (20) has a novel stage (36) that avoids the need for standard coalescing filters.

Description

APPARATUS AND METHODS FOR SEPARATING IMMISCIBLE FLUIDS

FIELD OF THE INVENTION

This invention relates to a method and apparatus for separating immiscible fluids having different densities. The invention may be used for separating oily substances from water and has particular application in separating waste oil from bilge water in ships

BACKGROUND OF THE INVENTION

Oil-water separators are used to remove hydrocarbons from water. Oil-water separators are used, for example, on board ships to remove oils from bilge water before the bilge water is discharged from the ship In such applications it is important to minimize the amount of oil released into the environment One complication arises because bilge water often contains oil-water emulsions Prior art separators capable of separating oil and water from an oil water emulsion are complicated and expensive Centrifuge type separators comprise rotating parts which are susceptible to wear and break down Such separators can require expensive servicing to keep them running efficiently. Hydrocyclone type separators can be used to separate oils from water but most commonly available hydrocyclones are not capable of reducing oil content to below about 50 parts per million The International Maritime Organization (LMO) specifies that ships should not discharge effluents having an oil content in excess of 15 parts per million Two or more hydrocyclones may be used in series to produce an effluent with an acceptably low oil content If this is done then the recovered oil tends to contain a substantial amount of water This tends to make the recovered oil difficult to store or reuse Injecting pure water or chemical substances to improve the performance of hydrocyclones can be done but is wasteful Moreover, hydrocyclones are prone to becoming eroded In an extreme case an eroded hydrocyclone could rupture and cause an oil spill

U.S Patent No 5,603,825 describes an oil-water separator which is effective for separating oil from water in various applications This oil-water separator has significant advantages over many other prior oil-water separators The initial stages in the oil-water separator patent do not use filters These stages include centrifugal separation stages and are capable of reducing oil levels in water to a level below 15 parts per million (PPM) The system of U.S. patent 5,603,825 includes a final filtering stage to effectively treat effluent water which contains significant amount of high density hydrocarbons. This is because the centrifugal forces and the vortex effects utilized by the initial stages of the system described in this U.S. patent have a reduced effectiveness in separating two liquids with close densities. One disadvantage of the system of U.S. patent No. 5,603,825 is therefore that it includes filters which must be periodically replaced. This increases the cost of operation both in terms of downtime and parts. Another disadvantage of this device is that the filters must generally be back flushed to discharge oil which the filters have collected. The flow of liquid through the filters must be reversed to accomplish back flushing. During the back flushing sequence the oil-water separator must be shut down. This also results in undesirable downtime.

There is an ongoing demand for oil-water separation devices which are more cost effective to operate and have less down time than prior art devices, including the system described in U.S. patent No. 5,603,825.

SUMMARY OF THE INVENTION

This invention provides a multi-stage apparatus for separating an immiscible fluid, such as oil, from a fluid, such as oily water from the bilge of a ship. The apparatus may be made in a compact form which is easy to install and operate. Furthermore, the apparatus may be constructed so that its operation is not significantly affected by the movement of a ship.

The apparatus and methods permit the removal of oils from water to the low parts-per-million level without the necessity of filters. Thus the requirements that filters be periodically back flushed and eventually replaced can be avoided through use of the invention.

Accordingly, the invention provides a separator for separating a less dense fluid from a denser fluid which is immiscible with the less dense fluid. The less dense fluid may, for example, be oil, or a collection of oils. The denser fluid may, for example, be water. The separator provides a fluid path extending from an effluent inlet upstream to a discharge port downstream. In a preferred embodiment the separator comprises one or more initial separation stages in the fluid path downstream from the effluent inlet The initial separation stages typically reduce the concentration of the less dense fluid to a level of about 10 PPM in normal operating conditions The separator also has a polishing stage downstream in the path from the initial separation stages In this specification,

"polishing" refers to refining, improving or adding finishing touches to The polishing stages refines the effluent from the initial separation stages by removing oils which were not removed in the initial separation stages The polishing stage comprises a chamber containing oleophilic particles The chamber has a fluid inlet in a lower portion thereof, a fluid outlet in an upper portion thereof and a first collection area for the less dense fluid above the fluid outlet, a channel in fluid connection with the fluid outlet, the channel comprising a plurality of generally vertically oriented sections, each section having a fluid inlet, a fluid outlet and a second collection area for the less dense fluid in an upper end of the section, and, one or more passages for carrying less dense fluid from the first collection area and each of the second collection areas to a collection zone Fluid entering the polishing stage passes from the fluid inlet upwardly through the chamber to the fluid outlet and then passes through the channel reversing its direction of flow each time that it passes from one of the sections into another one of the sections Preferably the oleophilic particles comprise a plurality of polyethylene beads having diameters in the range of 1 to 10 millimeters

Most preferably the initial separation stages comprise a toroidal separation chamber in the fluid path downstream from the effluent inlet, the separation chamber having a tangentially disposed inlet for causing the fluid to swirl within the separation chamber and a pump in the path, the pump having a suction port and a discharge port, the suction port in fluid communication with and downstream from the separation chamber The initial separation stages preferably further comprise a bed of buoyant oleophilic plastic beads in the path downstream from the separation chamber and upstream from the polishing stage

The polishing stage is preferably downstream from a pump in the fluid path The pump is connected to cause fluid to flow through the fluid path in a direction from the effluent inlet to the discharge port Because the polishing stage is on the discharge side of the pump, there is a pressure differential between the polishing stage and stages on the suction side of the pump. This pressure differential may be used to transfer oils collected in the polishing stage to a collection zone located on the suction side of the pump. A specific embodiment of the invention provides an oil water separator comprising: a first toroidal separation chamber having a tangentially disposed fluid inlet on an outer wall thereof an oil collection zone above said fluid inlet and an annular outlet at a lower end thereof; a second toroidal chamber generally coaxial with and inside said first toroidal separation chamber, said second toroidal chamber having a second oil collection zone at an upper end thereof an outwardly inclined perforated plate at a lower end thereof, and a toroidal bed of polyethylene beads floating between said perforated plate and a fluid permeable member above said plate; a settling chamber in fluid communication with said second toroidal chamber; a pump having a suction port in fluid communication with said settling chamber and a discharge port; a hydrocyclone chamber disposed generally coaxially inside said second toroidal chamber, said hydrocyclone chamber having a larger diameter end and a smaller diameter end, a tangential fluid inlet in fluid communication with said pump discharge port at said larger diameter end, a tube axially disposed within said chamber, said tube having a perforated wall in a region toward said larger diameter end of said hydrocyclone chamber an annular outlet at said smaller diameter end of said hydrocyclone chamber and a diffuser plate extending outwardly from said tube and spaced apart from said annular outlet; an oil collection area above said diffuser and above an upper end of said tube; a conduit extending from said oil collection area to said second oil collection zone; a third chamber below said diffuser plate extending around said hydrocyclone; a conduit for carrying fluid from said third chamber to a polishing stage comprising a channel having a plurality of locations within the channel wherein a direction of flow of the fluid is reversed at each of the locations as fluid flows along the channel from a channel inlet to a channel outlet; a plurality of oil collection areas in the channel; a conduit extending from the polishing stage to said second oil collection zone for carrying oil collected in the oil collected areas to the second oil collection zone; and, an effluent outlet in fluid connection with and downstream from the channel outlet. Another aspect of the invention provides a polishing unit for use in an oil-water separator. The polishing unit may be used in combination with various initial separation stages. The polishing unit comprising a channel having a channel inlet, a channel outlet a plurality of oil collection areas within the channel and a plurality of locations within the channel. When a fluid is caused to flow through the channel from a channel inlet to a channel outlet, a direction of flow of the fluid is reversed at each of the locations. The polishing unit preferably comprises a member having a generally vertically oriented passage in fluid connection with the channel inlet, the passage containing a bed of oleophilic particles, the passage having an inlet below the bed of oleophilic particles and an outlet connected to the channel inlet above the bed of oleophilic particles. Most preferably the channel surrounds the member. This provides a compact polishing unit.

In a preferred embodiment, the member comprises a cylindrical tube and the channel is defined by a plurality of walls extending radially from the tube to an outer wall of the polishing unit. The channel inlet comprises an aperture in a wall of the member and the radially extending walls are apertured to provide a continuous sinuous flow path between the channel inlet and the channel outlet. In this embodiment, the polishing unit preferably comprises a cavity overlying the member and the channel, wherein a wall between the cavity and the member is punctured by an orifice located above the passage and an orifice located above the space defined by each adjacent pair of radially extending walls.

Another aspect of the invention provides a method for separating a less dense fluid from a denser fluid which is immiscible with the less dense fluid. The method comprises the steps of: passing the fluid through a first channel segment in which the fluid flows generally vertically downward while collecting particles of the less dense fluid in an upper portion of the first channel segment; passing the fluid through a second channel segment wherein the fluid flows generally vertically upward while collecting particles of the less dense fluid in an upper portion of the second channel segment; passing the fluid through a third channel segment in which the fluid flows generally vertically downward while collecting particles of the less dense fluid in an upper portion of the third channel segment; and, passing the fluid through a fourth channel segment wherein the fluid flows generally vertically upward while collecting particles of the less dense fluid in an upper portion of the fourth channel segment

Preferably the method comprises the step of passing the fluid through a bed of oleophilic particles before the step of passing the fluid through the first channel segment The step of passing the fluid through the bed of oleophilic particles may comprise passing the fluid in an upward direction The less dense fluid may comprise an oil or a mixture of oils and the less dense fluid may comprise water

Another aspect of the invention provides a method for separating a less dense fluid from a denser fluid which is immiscible with the less dense fluid The method comprises the step of passing the fluid through a channel in such a manner that a direction of flow of the fluid alternates between upward and downward while collecting the less dense fluid at a plurality of collection areas in upper portions of the channel

BRIEF DESCRIPTION OF THE DRAWINGS In drawings which illustrate specific embodiments of the invention, but which should not be construed as restricting the spirit or scope of the invention in any way

FIG 1 is a block diagram of a preferred embodiment of the invention,

FIG 2 is an elevational section through an oil-water separator according to the invention, FIG 3 is an elevational section through the second stage of the oil-water separator of

FIG 2,

FIG 4 is an elevational section through the hydrocyclone-dispersion plate assembly and the fifth stage of the oil-water separator of FIG. 2,

FIG. 5 is a ghost, partially cut away view of the final polishing stage of the oil-water separator of FIG 2 with its upper portion removed for clarity ,

FIG 6 is a block diagram showing the electrical circuitry of the oil-water separator of

FIG 2,

FIG 7 is a block diagram showing the oil discharge sequence for the oil-water separator of FIG 2, and, FIGS 8 A, 8B and 8C show the configuration of the valves in the oil-water separator of

FIG 2 respectively during various phases of operation DETAILED DESCRIPTION

The operation of the invention will be described in the context of an oil-water separator 20 for separating oil from water on board a ship However, the method and apparatus of the invention may be used to separate other immiscible liquids having different densities as will be apparent from the following explanation

As shown in FIG 1, water contaminated with oil enters oil-water separator 20 through pipe 21 and inlet valve 25 Feed pump 27 draws the oil-water mixture through a preliminary mechanical separation stage 31 a first mechanical coalescent separation stage 32 and a second mechanical separation stage 33. Feed pump 27 then expels the oil- water mixture through a centrifugal separation stage 34, a second mechanical coalescent separation stage 35 and a final flow-reversing polishing stage 36 Cleaned water exiting from polishing stage 36 is discharged through outlet 40 It will be appreciated that the preferred embodiment described herein has initial stages similar to the separator described in U S patent No 5,603,825 in combination with a novel polishing stage 36

Waste oil separated in stages 32 through 36 is collected in a secondary collection zone 42 First stage 31 separates the coarsest globules of oily substances from the contaminated water and effects a preliminary mechanical separation of entrained particles which are denser than water Waste oil collected by primary mechanical separation stage 31 is collected in a primary collection zone 44 As described below, waste oil in secondary collection zone 42 and primary collection zone 44 can be purged through one-way valves 46 and 47 to a holding tank 170 (not shown in FIG. 1)

As shown in FIG 2, oil-water separator 20 typically comprises a tank 55 Tank 55 may comprise a pair of domed flanged shells bolted together around their flanges Tank 55 is supported on legs 49

First stage 31 includes annular chamber 51 between the side walls of tank 55 and a cylindrical concentrically mounted baffle wall 63 Water enters annular chamber 51 tangentially through check valve 25 Check valve 25 prevents the flow of water from being reversed when separator 20 is in stand-by mode Water introduced through valve 25 swirls downward through chamber 51 and then flows around the bottom end of a frusto-conical wall 60 as indicated by arrows 62 Wall 60 extends downwardly and inwardly from the lower edge of baffle wall 63

Chamber 51 permits large globules of oily substances to float upwardly through perforations in an annular plate 68 into primary collection zone 44 from where they can be drawn off through a conduit 73 to holding tank 170 Plate 68 keeps flow in primary collection zone 44 to a minimum and helps oily substances which accumulate in primary collection zone 44 to settle before being evacuated into holding tank 170 A check valve 47 is provided in conduit 78 to prevent air from being drawn into first stage 31 during the separation process Oil sensor probes 70 which are preferably conductance-type probes may be provided to alert an operator when primary collection zone 44 is nearly full and/or to trigger an automatic sequence for evacuating collected oily substances from primary collection zone 44 Probes 70 may be threaded into the lid 72 of tank 55 through a nipple 71 welded to the top of tank 55 As water flows around plate 60 coarse particles entrained in the water which are denser than water are deflected toward collector 43 on the bottom of tank 55 where they settle as a layer of sludge Removing such dense coarse particles in first stage 31 prevents the coarse particles from entering subsequent stages of separator 20 (which are discussed below) This reduces erosion of parts of those subsequent stages, such as hydrocyclone 95 A drain pipe 153 is connected to the bottom of sludge collector 43 Valve 154 on drain pipe 153 can be opened to draw off sludge which has collected in sludge collector 43

Apparatus according to the invention may be very compact This may be accomplished by constructing separator 20 so that first stage 31 (comprising chamber 51 and primary collection zone 44) surrounds subsequent stages of the apparatus Compact apparatus saves space and is simple to install

As water follows arrow 62 around the bottom of wall 60 it enters second stage 32 of FIG 1 Second stage 32 occupies a chamber 80 between a cylindrical baffle wall 64 and an inverted frusto-conical baffle 86. Baffle wall 64 lies inside of and is concentric with baffle wall 63 As water enters second stage 32 it encounters a slanted perforated plate 78. Oil which collects on perforated plate 78 moves upwardly and outwardly along plate 78 to baffle 64 The lower portion of baffle 64 has perforations 61 around its circumference to allow the passage of oil into the annular space between baffle 63 and baffle 64. The oil can float upwardly through this annular space into primary collection zone 44 without being disturbed by the water flow in chamber 51. Baffle 86 and wall 60 assist this process by deflecting part of the flow of water entering chamber 80 toward the periphery of chamber 80 as indicated by arrows 62. Perforations 61 in baffle wall 64 help to maintain the thickness of an oil layer on perforated plate 78 constant. As a less preferred alternative to baffle wall 64 a pipe may be connected to perforations 61 for withdrawing oil from the oil layer and carrying the oil upward to primary collection zone 44. As shown in FIG. 3, second stage 32 further includes an arrangement for absorbing emulsified oil. A bed of polyethylene beads 77 is provided in a generally toroidal region between plate 78 and a second annular perforated plate 79. Beads 77 are buoyant in water and float against a perforated plate 79. Preferably beads 77 have a density of less than 0.95 that of water. The diameter of the beads 77 is preferably in the range of 1 mm to 10 mm and is most preferably approximately 3 mm so that beads 77 have a relatively large surface area for collecting oil particles. Beads 77 are preferably not tightly packed. Beads 77 should be able to move relative to each other as liquid flows among them. As discussed below, the movement of beads 77 helps to clean beads 77 and promotes the coalescence of small oil particles into larger particles. Polyethylene beads 77 aid in coalescing small droplets of oil into larger droplets of oil. The larger oil droplets float up through region 80 into secondary collection area 42. A conduit 74 is connected to the top of the secondary collection zone 42 to drain accumulated oil into holding tank 170. Conduit 74 preferably has a diameter approximately 4 times smaller than the diameter of conduit 73 due to the reduced amount of oil collected in the secondary zone 42. A check valve 46 is provided in conduit 74 to prevent air ingress into second stage 32.

Water from chamber 80 exits second stage 32 and enters third stage 33 by flowing in the direction of arrows 84 over the upper lip of baffle 86, through an annular passage between baffle 86 and a cone-shaped wall 87, and into a region 88 inside baffle 86. Region 88 is relatively large so that the velocity of water inside baffle 86 is relatively small. Oil droplets may separate from the water inside region 88 and float upwardly into secondary collection zone 42

Water is withdrawn from the interior of baffle 86 through a conduit 91 by a pump 27. Pump 27 is preferably a positive displacement feed pump, such as a progressing cavity pump, having a capacity matched to the size of separator 20 The water discharged from pump 27 is fed through pipe 92 to fourth stage 34. Fourth stage 34 comprises inverted hydrocyclone 95, an axial tube 100 secured to the bottom of hydrocyclone 95 and a dispersion plate 109

As shown in FIG 4, hydrocyclone 95 comprises a chamber 101 defined by a frusto-conical plate 99a joined to a cylindrical wall 99b, and a tube 100 axially located within chamber 101 Chamber 101 is generally symmetrical with respect to tube 100 Pipe 92 delivers water through a flattened nozzle 93 which enters chamber 101 tangentially through wall 99b Water flowing into chamber 101 through nozzle 93 causes the water inside chamber 101 to flow in a high velocity vortex Chamber 101 preferably has a diameter to length ratio of approximately 1 to 5 The height of wall 99b is preferably equal to the diameter of chamber 101 inside wall 99b

Oil particles entrained in the water inside chamber 101 tend to move away from plate 99a and wall 99b and are concentrated around tube 100 The lower part of tube 100 is perforated to allow oil particles to migrate into the bore of tube 100. Preferably the bore of tube 100 is filled with polyethylene beads of the type described above Tube 100 extends out of chamber 101 through an aperture at the upper end of plate 99a The upper end of tube 100 is enlarged and supports a circular dispersion plate 109 Oil particles inside the bore of tube 100 float upwardly, leave tube 100 through orifices located in the central region of dispersion plate 109, and emerge into region 104 from where the oil is drawn through pipe 106 to secondary collection area 42. While it is desirable, to a point, to increase the velocity of water in chamber 101 in order to increase the centripetal forces acting on the water in chamber 101 if those forces are too high then oil drops entrained in the water may be sheared and made more difficult to remove from the water It has been determined experimentally that, for best operation of hydrocyclone 95, the size of nozzle 93 and the flow rate through chamber 101 should be set so that the centripetal forces acting on water particles near the outside of chamber 101 are approximately 4 to 5 times the force of gravity.

Water leaves chamber 101 through annular aperture 107 between tube 100 and plate 99a. As water leaves chamber 101 it enters stage 35. The components of stage 35 are located in a chamber 110 inside wall 87. The oil-water mixture exiting hydrocyclone 95 is extremely diluted, containing minute droplets of oil. Some oil droplets which may remain in the water leaving chamber 101 are projected against plate 109. Oil droplets coalesce further on plate 109. The resulting oil flows to the edges of plate 109 and floats into region 104 above plate 109. Oil is drawn out of region 104 through pipe 106 as described below.

After leaving chamber 101, water flows downwardly through region 110 between the outer wall 99a of chamber 101 and wall 87. As the influent water leaves chamber 101 in a spinning motion it is drawn downwards to the periphery of region 110. The combined effect of centrifugal and gravitational forces in region 110 prevents most of the oil which is still entrained in the water from reaching the bottom of region 110

A second bed 111 of polyethylene granules retained inside a mesh wall 112 is preferably provided inside region 110. Water must flow through bed 111 to leave region 110. Oil particles may coalesce on the polyethylene beads in bed 111 and become large enough to float upwardly into region Water passes through bed 111 into region 115 at the bottom of the chamber 110.

From region 115 the water passes to final polishing stage 36. Final polishing stage 36 removes most remaining traces of oils from the water without the use of filters. Water from region 115 is forced through a conduit 119 into a manifold 223 which lies within a chamber 226 as shown in FIG. 2. The wall forming the bottom of chamber 226 may also form the roof of area 104. Chamber 226 houses a hollow cylindrical body 236 which is mounted concentrically inside chamber 226. The region 230 lying outside of body 236 in chamber 226 is divided into a plurality of sectors 230a, 230b, 230c, and 230d by division plates 240 which extend radially from cylindrical body 236. Cylindrical body 236 has a perforated plate 228 in its upper portion. A bed of oleophilic particles, such as coalescing beads 229 is confined within the bore of cylinder 236 under plate 228 Beads 229 are preferably polyethylene beads having diameters in the range of about 1 millimeter to about 10 millimeters Water is introduced into the bottom of the bore of cylindrical body 236 from manifold 223 The water flows up through beads 229 to an opening 231 above plate 228. Opening 231 communicates with sector 230a of region 230

Sectors 230a, 230b, 230c, and 230d form a channel When water flows along this channel its direction of flow alternates between going upward and going downward As shown in Fig 5, water flows sequentially downward through sector 230a, upward through sector 230b, downward through sector 230c, and upward through sector 230d The water reverses direction each time it passes into the next sector Water passes between adjacent sectors through apertures 233 in division plates 240 Apertures 233 alternate between being near the bottom edges of the division plates 240 and being slightly below the top edges of division plates 240 Each sector has an oil collection area in its portion above the upper edges of apertures 233 Region 230 and cylindrical body 236 are capped at their upper ends by the lower wall 235 of a cylindrical chamber 235a Wall 235 is perforated by an orifice above each sector of region 230 and an orifice above cylindrical body 236 The orifices allow oils which have floated to the top portions of the sectors of region 230 or body 236 to enter chamber 235a where they can be collected Each orifice is large enough to allow oily substances to flow upwardly into chamber 235a The dimensions of the orifices are a design variable which may change with the dimensions and design of the oil water separator in question The orifices are typically on the order of about Vi inch in diameter

Chamber 235a allows the segregation of the separated oil from the water in region 230 and body 236 A conduit 237 is provided for extracting the oil from chamber 235a into collection zone 42 Oil from chamber 235a is carried together with some water through conduit 237 by the pressure differential which results from the fact that the inlet of conduit 237 is on the discharge side of pump 27 whereas the outlet of conduit 237 is on the suction side of pump 27 The cleanliness of chamber 226 is maintained by means of a duct 238 Water carrying any traces of oil which collect at the top of chamber 226 are carried through duct 238 (Fig. 2) into oil collection zone 42 by the pressure differential between oil collection zone 42 and chamber 226.

Cleaned water exits from sector 230d through pipe 144 and valve 54 to discharge port 40 where it exits oil-water separator 20. Preferably the amount of oil in the water is monitored continuously by an oil content meter 150 to ensure that the quality of the cleaned water is acceptable at all times. Oil content meter 150 may, for example measure the concentration of oil in the effluent water by detecting the increase in turbidity after ultrasonic emulsification. Oil content meter 150 may be connected between pipe 144 and pipe 21. Because the pressure is higher in pipe 144 than it is in pipe 21, small amounts of treated water will flow through oil content meter 150 where the oil content is measured.

Oil content meter 150 may provide a signal to alert an operator whenever the oil content in the clean discharge water is greater than the selected level. The alarm signal may also actuate valve 54 to cause the effluent liquid to be directed into the ship's bilge via conduit 181 whenever the oil content exceeds the limits imposed by any applicable local regulations. As described below, valve 54 is preferably an electrically actuated 3- way valve. Preferably, valve 54 is in its normal working position when electrical power is applied to the valve actuator and returns under the force of a spring to its "off '(standby) position in which water from pipe 144 is directed into the bilge through conduit 181 when electrical power is shut off.

FIG. 8A shows separator 20 in its stand-by mode with pump 27, positive displacement pump 90, oil meter 150 and valve 54 de-energized. Valve 54 is positioned to block the flow of the effluent water from the separator to the overboard discharge port 40. As described below, oil accumulated in primary collection zone 44 and secondary collection zone 42 is periodically discharged into a waste oil tank (not shown) and stored for recycling or reuse. It can be appreciated that oil-water separator 20 can be made very compact by nesting the apparatus for separation stages 34, 35 and 36, which act on water exiting pump 27, inside the apparatus for stages 31, 32, and 33 which act on water being drawn into pump 27. The operation of the separator is coordinated by means of a control unit 160 (Fig 6) which includes a conductance probe-type relay CPR and a timer (TMR) 161 Timer 161 is preferably an on-delay timer which, when energized, actuates a pair of contacts after a delay interval Control unit 160 receives signals from the sensors and controls the operation of pump 27 and pump 90

Operation

Separator 20 is initially filled with clean water As shown in FIG 8B, a water level sensor 169, which maybe, for example, a mercury level float switch, is mounted in the bilge of the ship Sensor 169 signals control unit 160 when the liquid in the bilge rises to a predetermined level In response to the signal from sensor 169, control unit 160 energizes oil meter 150 and feed pump 27 which begins to circulate the liquid through separator 20 At the same time the actuator for valve 54 is energized so that effluent processed by separator 20 is discharged overboard through line 40 As shown in detail in FIG 2, the oil-water mixture is drawn from the bilge through line 21 and check valve 25 and into the first stage of separator 20 As the water enters annular chamber 51 tangentially oil particles in the water undergo a preliminary separation due to gravity and centrifugal force created by the circular motion of the water Larger oil droplets float upwards in annular chamber 51 against the generally descending water flow Most oil entrained in the water entering separator 20 is collected in primary collection zone 44 where it accumulates as a continuously growing oil layer

Under the influence of the centrifugal force some oil drops are displaced inwardly toward baffle 63 where they can merge The resulting bigger drops have an enhanced buoyancy and can float upwardly along baffle 63 into primary collection zone 44 When the flowing liquid reaches the bottom of annular chamber 51 it flows around plate 60 As liquid flows around plate 60 contaminants which are denser than water are deposited in sludge collector 43

The water enters the second stage 32 as indicated by the arrows 62. In the second stage, polyethylene beads 77 attract oil droplets due to their oleophilic nature Preferably, oil droplets coalesce and gradually from an oil layer on plate 78 The upper region of the oil layer extends into the mass of polyethylene beads 77 As more oil droplets are admitted into second stage 32, the thickness of the oil layer tends to increase Consequently the lower region of the oil layer can migrate towards the periphery of second stage 32 assisted by the water flow When the oil layer is sufficiently thick, excess oil exits second stage 32 through orifices 61 and is funneled by baffle 63 towards primary collection zone 44 The thickness of the oil layer is maintained relatively constant

The oil layer on plate 78 helps to break down emulsified oil entrained in the flowing water Emulsified oil otherwise tends to remain in suspension and is hard to separate When a particle of oil/water emulsion carried by the flow encounters the oil layer on plate 78 it tends to become entrapped within the mass of oil Eventually the oil layer absorbs the emulsified oil

Some oil droplets will float upwards with the water flow through polyethylene beads 77 An oil droplet adhering to a polyethylene bead 77 will tend to coalesce with other droplets which are adhering to the same polyethylene bead or an adjoining bead The resulting larger oil droplet has an enhanced buoyancy which overcomes the attraction between the polyethylene bead and the oil droplet As the oil droplet rises it will encounter other polyethylene beads and the process continues Eventually the oil droplet leaves beads 77 and floats upwardly with the water flow into secondary collection zone 42 The water flow causes beads 77 to move freely against perforated plate 79 This speeds up the coalescing process by bringing together oil droplets adhering to adjacent beads 77 At the same time the action of the polyethylene beads 77 rubbing against each other and against plate 79 releases the oil droplets and other contaminants in a self- cleaning process The water ascending through region 80 follows arrows 84 into region 88 of stage 33 through an annular passage In most parts of region 88 the velocity of the flowing water is reduced and so smaller oil droplets can float upwardly toward secondary collection zone 42 Pump 27 transfers the liquid from region 88 into stage 34 It can be appreciated that the oil content of the water is greatly reduced by the time the water reaches pump 27 so that pump 27 does not cause emulsification of any significant quantities of oil In stage 34 the liquid swirls at high velocity Any oil droplets entrained in the water experience a radially directed inward force because they are less dense than water This causes oil droplets to migrate towards tube 100 which lies on the axis of hydrocyclone 95 Some liquid and oil droplets enter tube 100 through perforations in the lower part of tube 100 If there are polyethylene beads inside tube 100, which is preferred, the beads help oil droplets to coalesce with each other as described above The flow inside tube 100 carries oil particles upwardly through any beads inside tube 100. Larger oil droplets leave tube 100 into region 104 through orifices in dispersion plate 109 From region 104 oil droplets are drawn into secondary collection zone 42 through conduit 106

There is a pressure differential between the ends of pipe 106 which tends to drive oils through pipe 106 into secondary collection zone 42 The pressure differential arises because the inlet to pipe 106 is in region 104 which is on the discharge side of pump 27 and the outlet of pipe 106 is in secondary collection zone 42, which is on the suction side of pump 27

Liquid which does not enter tube 100 is accelerated towards the cone shaped end of chamber 101 from where it is ejected through an annular opening into chamber 110 As shown in FIG 4, the water emerging from hydrocyclone 95 is deflected by the enlarged frusto-conical upper end of tube 100 and dispersion plate 109 as it enters the chamber 110 It should be appreciated that, because hydrocyclone 95 is completely inside separator 20, damage to hydrocyclone cannot directly result in an oil spill Rather, a failure of hydrocyclone 95 would merely degrade the performance of separator 20 In chamber 110, there are few oil particles still remaining The water passes through screen 112 (which, as noted above is preferably filled with beads 111) and into region 115 Oil particles still entrained in the water in chamber 110 are prevented from descending into region 115 by their own buoyancy, the forces exerted on them by the spinning motion of the water and by beads 111 The water reaching region 115 is delivered to chamber 126 through pipe 119 that is connected to manifold 223 The oil content of water entering manifold 223 is typically not more than about 10 parts per million Water is directed through conduit 223 into a passage formed by a bore in cylindrical body 236 Oil is separated from the water through the coalescing effect of beads 229, as described above Oil floats to the top of the bore of cylindrical body 236 and exits into chamber 235a through orifice 234b Cleaned water exiting cylinder 236 through port 231 enters sector 230a and flows downwardly in sector 230a The water then flows through sectors 230b, 230c, and 230d, changing direction each time that it enters another sector The inventor has discovered that further oil-water separation is promoted by causing water to flow in a path which repeatedly reverses its direction as occurs in sectors 230a through 230d The cross sectional shapes of sectors 230a through 230d may be varied without departing from the broad scope of the invention However, the configuration shown in the drawings is preferred because it leads to a very compact arrangement of polishing stage 36 The configuration shown in the drawings is adapted to fit within the central bore of a toroidal, or annular, separation chamber 51 with little wasted space The cross sectional area and lengths of sectors 230a through 230d depends upon the volume of water to be treated by oil water separator 20 Preferably these dimensions are such that a residence time of water in polishing stage 36 is at least about 20 seconds The number of sectors may be varied, however, the inventor has determined that 4 sectors generally provides acceptable results The minute amounts of oil separated in each sector rise toward the top portion of each of the sectors The oil then passes through the orifices into collection chamber 235a from where it is extracted through conduit 237 into secondary collection zone 42 as described above The oil leaving sector 230d preferably has an oil content of not more than about 5 parts per million The provision of polishing stage 36 achieves good final oil-water separation but avoids the use of filters Since no filters are used it is not necessary to perform a back flushing step as would be necessary to keep filters clean Because no back flushing is required, the water pressures developed within oil-water separator 20 can be kept low If the water pressures are kept low enough then it ceases to be necessary to design separator 20 to meet the standards of design and construction required for "pressure vessels". This, in turn, reduces the weight of separator 20 and also reduces the cost of construction of separator 20

It is necessary to periodically discharge oil which has accumulated in oil- collection zones 42 and 44 The oil discharge sequence (Figure 8C) operates as follows As oil accumulates in primary collection zone 44 the oil-water interface moves downwards until it reaches the lowermost probe of oil sensor 70 The signal provided by sensor 70 to control unit 160 energizes pump 90 Pump 90 starts operating and removes oil from the collection zones 42 and 44 into holding tank 170 as shown in Figure 8C

As the oil is discharged the oil-water interface in the primary collection zone 44 rises The probes of sensor 70 sense clean water When the uppermost probe of sensor 70 senses clean water, its signal to control unit 160 changes and control unit 160 stops pump 90 It is undesirable to continue pumping the liquid out from collection zones 44 and 42 after the oil is evacuated To prevent the transfer of water into waste oil tank 170 which would occur if one of the probes in sensor 70 was not operating properly, timer 161 begins counting a fixed time interval at the start of the oil discharge sequence. If the probes in sensor 70 fail to detect the rise of the oil-water interface before timer 161 finishes counting its time interval then timer 161 terminates the oil evacuation by stopping pump 90 and indicates "probe fault" by means of a pilot light on the control unit 160 The cycle of separation and oil discharge ends when the liquid level In the bilge drops to a predetermined level as detected by sensor 169 Control unit 160 then places separator 20 in stand-by mode as shown in FIG 8A and as described above.

As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible In the practice of this invention without departing from the spirit or scope thereof For example, while the above example has discussed the use of the invention for separating oil from water, the invention could be used to separate mixtures of other immiscible fluids. While the above example has discussed a separator for separating oils from bilge water on a ship, separators according to the invention could be used in other contexts. While the polishing stage of the invention has been described as the final stage in a system which incorporates several specific preliminary stages, the polishing stage of the invention could be used in separators having different initial separation stages. Additional stages or filters could be added after the polishing stage without departing from the broad scope of the invention.

While a feature of the invention is that it provides a final polishing stage for an oil-water separator which does not require the use of filters, filters could be added to a separator according to the invention without departing from the invention.

The polishing stage has been described as having a cylindrical body surrounded by a plurality of wedge-shaped sectors. This is the preferred configuration. This configuration has several advantages over other possible configurations. These advantage include being very compact. However, the shape of the sectors and body could be changed without departing from the broad scope of the invention. What is necessary is that there be provided a path along which water can flow wherein the water reverses direction between flowing generally upwardly and flowing generally downwardly several times as it flows along the path. Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.

Claims

What is claimed is

1 A separator (20) for separating a less dense fluid from a denser fluid which is immiscible with the less dense fluid, the separator providing a fluid path extending from an effluent inlet (21) upstream to a discharge port (40) downstream, the separator comprising a) one or more initial separation stages(31, 32, 33) in the fluid path downstream from the effluent inlet (21), characterized by b) a polishing stage (36) downstream in the path from the initial separation stages, the polishing stage (36) comprising i) a chamber (236) containing oleophilic particles (229), the chamber having a fluid inlet in a lower portion thereof, a fluid outlet in an upper portion thereof and a first collection area for the less dense fluid above the fluid outlet, ii) a channel in fluid connection with the fluid outlet, the channel comprising a plurality of generally vertically oriented sections (230a, 230b, 230c, 23 Od), each section having a fluid inlet, a fluid outlet and a second collection area for the less dense fluid in an upper end of the section, and, iii) one or more passages for carrying less dense fluid from the first collection area and each of the second collection areas to a collection zone (235a), wherein fluid entering the polishing stage passes from the fluid inlet upwardly through the chamber (236) to the fluid outlet and then passes through the channel reversing its direction of flow each time that it passes from one of the sections (230a, 230b, 230c, 23 Od) into another one of the sections (230a, 230b, 230c, 230d)

2 The separator of claim 1 wherein the oleophilic particles (229) comprise a plurality of polyethylene beads

3. The separator of claim 2 wherein the beads (229) are in the range of 1 to 10 millimeters in diameter.

4. The separator of any one of claims 1, 2 or 3 wherein the initial separation stages (31 , 32, 33) comprise a toroidal separation chamber (51) in the fluid path downstream from the effluent inlet, the separation chamber (51) having a tangentially disposed inlet (25) for causing the fluid to swirl within the separation chamber and a pump (27) in the path, the pump having a suction port and a discharge port, the suction port in fluid communication with and downstream from the separation chamber (51) .

5. The separator of any one of claims 1, 2, 3 or 4 wherein the initial separation stages comprise a bed of buoyant oleophilic plastic beads (77) in the path downstream from the separation chamber and upstream from the polishing stage (36).

6. The separator of any one of claims 1, 2 or 3 wherein the polishing stage (36) is downstream from a pump (27) in the fluid path and the pump is connected to cause fluid to flow through the fluid path in a direction from the effluent inlet (21) to the discharge port (40).

7. The separator of any one of claims 1, 2, 3, 4, 5, or 6 wherein the channel (230) surrounds the chamber (236) and the segments (230a, 230b, 230c, 23 Od) of the channel each comprise a wedge shaped sector separated from adjacent segments by radially extending walls (240).

8. The separator of any one of claims 1, 2, 3, 4, 5, 6 or 7 wherein the chamber (236) comprises a member having a generally vertical cylindrical bore and the oleophilic particles (229) are in the bore.

The separator of claim 8 wherein the separator comprises a perforated plate (228) in the bore above the particles (229)

The separator of claim 9 wherein the particles (229) float against an underside of the perforated plate (228) and are free to move relative to one another

The separator of claim 4 wherein the polishing stage (36) is surrounded by the toroidal separation chamber (51)

An oil water separator comprising a) a first toroidal separation chamber (51) having a tangentially disposed fluid inlet (25) on an outer wall thereof an oil collection zone (44) above said fluid inlet (25) and an annular outlet at a lower end thereof, b) a second toroidal chamber generally coaxial with and inside said first toroidal separation chamber (51), said second toroidal chamber having a second oil collection zone (42) at an upper end thereof an outwardly inclined perforated plate (78) at a lower end thereof, and a toroidal bed of polyethylene beads (77) floating between said perforated plate and a fluid permeable member (79) above said plate, c) a settling chamber (88) in fluid communication with said second toroidal chamber, d) a pump (27) having a suction port in fluid communication with said settling chamber (88) and a discharge port, e) a hydrocyclone chamber (95) disposed generally coaxially inside said second toroidal chamber, said hydrocyclone chamber having a larger diameter end and a smaller diameter end, a tangential fluid inlet (93) in fluid communication with said pump discharge port at said larger diameter end, a tube (100) axially disposed within said chamber, said tube (100) having a perforated wall in a region toward said larger diameter end of said hydrocyclone chamber an annular outlet (107) at said smaller diameter end of said hydrocyclone chamber (101) and a diffuser plate (109) extending outwardly from said tube (100) and spaced apart from said annular outlet (107); f) an oil collection area above said diffuser (107) and above an upper end of said tube (100); g) a conduit (106) extending from said oil collection area to said second oil collection zone (42); h) a third chamber below said diffuser plate extending around said hydrocyclone; i) a conduit (119) for carrying fluid from said third chamber to a polishing stage (36) comprising a channel (230) having a plurality of locations within the channel wherein a direction of flow of the fluid is reversed at each of the locations as fluid flows along the channel from a channel inlet to a channel outlet; j) a plurality of oil collection areas in the channel; k) a conduit (237) extending from the polishing stage to said second oil collection zone (42) for carrying oil collected in the oil collected areas to the second oil collection zone (42); and, 1) an effluent outlet (40) in fluid connection with and downstream from the channel outlet.

13. A polishing unit (36) for use in an oil-water separator (20), the polishing unit comprising a channel (230) having a channel inlet, a channel outlet a plurality of oil collection areas within the channel and a plurality of locations within the channel wherein, when a fluid is caused to flow through the channel from a channel inlet to a channel outlet, a direction of flow of the fluid is reversed at each of the locations.

14. The polishing unit of claim 13 comprising a member having a generally vertically oriented passage (236) in fluid connection with the channel inlet, the passage containing a bed of oleophilic particles (229), the passage having an inlet below the bed of oleophilic particles and an outlet above the bed of oleophilic particles and in fluid connection with the channel inlet

The polishing unit of claim 14 wherein the channel (230) surrounds the member.

The polishing unit of claim 15 wherein the member comprises a cylindrical tube and the channel is defined by a plurality of walls (240) extending radially from the tube to an outer wall (227) of the polishing unit, the channel inlet comprises an aperture in a wall of the member and the radially extending walls are apertured to provide a continuous sinuous flow path between the channel inlet and the channel outlet

The polishing unit of claim 16 comprising a cavity (235a) overlying the member and the channel, wherein a wall between the cavity (235a) and the member is punctured by an orifice located above the passage and an orifice located above the space defined by each adjacent pair of radially extending walls

The polishing unit of claim 17 wherein the oleophilic particles (229) float against an underside of a perforated plate (228) located in the passage

The polishing unit of claim 17 wherein the oleophilic particles comprise polyethylene beads (229)

The polishing unit of claim 19 wherein the polyethylene beads (229) have diameters in the range of 1 mm to 10 mm

A method for separating a less dense fluid from a denser fluid which is immiscible with the less dense fluid, the method comprising the steps of a) passing the fluid through a first channel segment (230a) in which the fluid flows generally vertically downward while collecting particles of the less dense fluid in an upper portion of the first channel segment (230a), b) passing the fluid through a second channel segment (230b) wherein the fluid flows generally vertically upward while collecting particles of the less dense fluid in an upper portion of the second channel segment (230b), c) passing the fluid through a third channel segment (230c) in which the fluid flows generally vertically downward while collecting particles of the less dense fluid in an upper portion of the third channel segment (230c), and, d) passing the fluid through a fourth channel segment (23 Od) wherein the fluid flows generally vertically upward while collecting particles of the less dense fluid in an upper portion of the fourth channel segment (230d)

The method of claim 21 comprising the step of passing the fluid through a bed of oleophilic particles (77. 229) before passing the fluid through the first channel segment (230a)

The method of claim 22 wherein passing the fluid through the bed of oleophilic particles (77, 229) comprises passing the fluid in an upward direction

The method of any one of claims 22 and 23 comprising the step of swirling the fluid in a toroidal separation chamber (51) and collecting less dense fluid in an upper portion of the toroidal chamber before passing the fluid through the bed of oleophilic particles (77, 229)

The method of claim 24 comprising passing the fluid through a pump (27) after swirling the fluid in the toroidal separation chamber (51) and before passing the fluid through the bed of oleophilic particles (77, 229)

The method of claim 25 comprising passing the fluid through a hydrocyclone (95) after passing the fluid through the pump (27) and before passing the fluid through the bed of oleophilic particles (229) The method of claim 26 wherein the less dense fluid comprises an oil or a mixture of oils and the less dense fluid comprises water

The method of claim 27 wherein the oil content of water leaving the fourth channel segment (23 Od) is less than 5 parts per million

A method for separating a less dense fluid from a denser fluid which is immiscible with the less dense fluid, the method comprising the step of passing the fluid through a channel (230) in such a manner that a direction of flow of the fluid alternates between upward and downward while collecting the less dense fluid at a plurality of collection areas in upper portions of the channel (230)