Note: Descriptions are shown in the official language in which they were submitted.
CA 02243142 1998-07-10
FILTERLESS MULTI-STAGE APPARATUS AND METHODS
FOR SEPARATING IMMISCIBLE FLUIDS
FIELD OF THE INVENTION
This invention relates to a method and apparatus for
separating immiscible Iluids 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 (IMO) 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
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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
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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.
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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, "poli.shing" 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
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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
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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
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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 ori~.ce 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
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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:
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FIG. 1 is a block diagram of a preferred embodiment of the
inve ntion;
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. 8A, 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
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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
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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 llow 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 fi0 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
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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 88 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 82. 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.
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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 ?7 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 ?7 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
7? 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 1?0. 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
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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
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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 beset 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
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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
Moat 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.
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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 1/ inch in
diameter.
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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
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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'(stand-by) 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.
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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.
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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 ?7. 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
CA 02243142 1998-07-10
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beads 77 and floats upwardly with the water flow into secondary
collection zone 42.
The water flow causes beads 7? 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.
CA 02243142 1998-07-10
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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
CA 02243142 1998-07-10
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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
CA 02243142 1998-07-10
- 25 -
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 hushing 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 any'
44 into holding tank 170 as shown in Figure 8C.
CA 02243142 1998-07-10
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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 knishes 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.BA 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 t'
invention could be used in other contexts. While the polishing sta.
CA 02243142 1998-07-10
-27-
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
inve ntio n.
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.
