Note: Descriptions are shown in the official language in which they were submitted.
WO 99/57378 PCT/GB99/01327
WEIR SKIMMER AND FLOTATION SYSTEM
Technical Field
The present invention relates to an improved weir skimmer for removing a
floating liquid
from the surface of another liquid of higher density. Its main application
lies in the
separation of floating pollutants, for example oil or algae layers from the
surface of water.
Other applications of the invention are mentioned below. In an advantageous
application
of the invention, a novel buoyancy support system is provided for use in
conjunction with
the weir skimmer of the invention. Such support system facilitates the
attainment of
accurate horizontal settings of the first operative weir means over which the
floating liquid,
accompanied by a supporting layer of the liquid of higher density, enters the
weir skimmer
device. Furthermore, by the use of the said buoyancy support system, the
adverse elect of
wave and swell motion on the weir skimmer during operation may be mitigated.
The said novel buoyancy support system may also be used with like advantages
in
conjunction with weir skimmers at large. Its advantageous properties are not
limited to the
case of its use with weir skimmers of the present invention.
The floating weir skimmer of the present invention also provides a simple
method for
achieving substantially turbulence free removal of floating pollutants
encountered in
relatively elevated locations, e.g. in a tank, reservoir or canal.
In the interests of clarity and simplicity, the present invention will be
described in detail
herein largely by reference to the removal of floating oil from the surface of
water. In
general, however, such description is to be taken to apply, mutatis mutandis,
to the removal
of any floating first liquid from the surface of any second liquid of higher
density where the
context so admits. The reader is respectfully invited to bear this
qualification in mind.
Either or both such liquids may be an oil. In some circumstances, the floating
liquid layer
may owe its relatively lower density to the presence of discrete, foamed or
aggregated
particulates or fluid droplets. It may, for example, be a layer comprising
surface algae
floating on water. Likewise, it may be a layer of curds formed in a
cheesemaking operation,
or else a layer comprising relatively low density constituents in suspension
encountered in
the treatment of waste or other water.
Other applications of the weir skimmer of the invention will be found in the
oil,
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manufacturing, marine, agricultural, food, chemical and mining or extractive
industries. In
the dairy industry, example, it may be used to remove surface floating cream
so as to leave
behind cream depleted milk or, as already touched upon, by the cheesemaker to
remove the
curds. Elsewhere, the skimmer may be used to remove floating oils and molten
fats from
the surfaces of aqueous compositions in the human and animal food
manufacturing industry.
Background Art
There is a substantial body of published patent literature which relates to
skimmer devices
for the separation and removal of surface liquid pollutants, in particular
oil. Reference is
made to the following specifications : US Nos. 3884807 Heddon, 3762556 Penton,
4851133 Rymal, and 4372854 Szereday; Czechoslovak No. 2412008; European EP
Nos.
0533871 Weinem, 0547184 Leone, 0581837 Brown, 0559639 Koblanski, 0679767
Meyer,
0687330 Lechelon, 0712457 Bronnec, 0731862 Blomberg, 0807196 Gyftonikolos and
0883716 Gustafsson; GB Nos. 2239819A Pearson and 9800679 Allen-Jones; and
PCT/GB
Nos. 91/01881 Maddock and 94/01203 Dorey.
Disclosure of the Invention
According to the present invention, there is provided a weir skimmer for
removing a floating
liquid ("first liquid") from the surface of another liquid of higher density
("second liquid")
characterised by:
i. an outer vessel the rim of which is adapted to act as a first weir to
separate from the
surface of the body of the second liquid and to admit into the vessel floating
first
liquid together with a supporting layer of the second liquid;
ii. an inner dish located within the outer vessel with its rim spaced from the
first weir
rim and arranged to provide a second weir to separate from an underlying mass
of
second liquid within the interior of the outer vessel and to admit into the
inner dish
floating first liquid together with a supporting layer of the second liquid;
iii. aperture means located in the lower part of the inner dish communicating
with the
interior of the outer vessel;
iv. aperture means communicating between the interior of the outer vessel and
its
exterior.
In its preferred embodiment, the weir skimmer of to invention is further
characterised by:
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v. third weir means located within the inner dish to separate from an
underlying layer
of second liquid in the inner dish an enriched mixture of first liquid and
second
liquid, and
vi. means adapted to withdraw the enriched mixture from the weir skimmer.
The description below continues by reference to removal of oil from the
surface of water.
The aperture means communicating between the interior of the outer vessel and
its exterior
are preferably in the form of conduits which extend inwardly from or through
the sides of
the outer vessel, such conduits having decreased cross sectional areas at
their inner ends.
In the preferred form of the invention, tapered conduits extend inwardly from
apertures in
the sides of the outer vessel. In another embodiment of the invention, one or
more conduits
may be in the form of a tube, e.g. a cylindrical tube which extends through
the side of the
vessel and has at its outer end an expanded opening or a junction to two or
more tubular
elements (e.g. as in the case of a T junction) which between them provide an
outer aperture
that is of larger cross sectional area than that at the inner end of the
conduit within the
vessel.
During operation, the final product withdrawn from the skimmer device of the
invention will
in the great majority of cases be an enriched mixture of oil and water. For
the purposes of
this specification, such product will be referred to as "enriched oil/water
mixture".
In exceptional cases, the invention may be put to work to provide "oil" alone
as the final
product. Reference is made below to the case where the invention is used to
remove part
of a layer of floating cream leaving behind semi skimmed milk. In such a case,
the references
below to "enriched oil/water mixture" are to be read as references to oil
alone.
In the case of the aforesaid preferred embodiment of the invention, withdrawal
of the
enriched oil/water mixture from the skimmer device may be effected in the
downward
direction or in the upward direction.
Where the withdrawal is in the downward direction, the third weir is provided
by the rim
of the inlet of a downwardly extending extraction pipe which constitutes the
means for
withdrawal. The pipe extends through the base of the dish and onwardly through
the base
of the outer vessel.. The third weir is adapted to separate enriched oil/water
mixture from
underlying water within the inner dish. The rim of the extraction pipe inlet
is
advantageously encircled by an horizontal baffle plate the upper surface of
which is at at the
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same level as, or close to and just below the level of the weir rim. The
presence of the
horizontal baffle plate promotes turbulence free separation of the enriched
mixture from
underlying water within the inner dish.
Where the withdrawal is effected in an upward direction, an extraction pipe
which
constitutes the means for withdrawal extends upwardly from a sump disposed
within the
inner dish. The rim of the sump provides the third weir which is adapted to
separate
enriched oi1/water mixture from underlying water within the inner dish. The
rim of the sump
is advantageously encircled by an horizontal baffle plate in the same manner
and for the
same purpose as has been described above, mutatis mutandis in relation to the
rim of the
extraction pipe inlet.
The construction of the skimmer device may be varied by interposing
intermediate weir
means between the first weir that faces outwardly ("the outer weir") and the
second weir
provided by the rim of the inner dish. This may be brought about by the use of
an
intermediate dish, or else a series of intermediate dishes, the upper rim of
each such dish
providing an intermediate weir. In this case, the intermediate dishes are
arranged and
located so that oil and a supporting layer of water may flow over the rims of
each one in
sequence between the first weir and the innermost weir. Aperture means are
located in the
lower part of each intermediate dish. In the case of the first dish closest to
the first weir,
such aperture means allow flow of water into the interior of the vessel. In
the case of each
other dish including the innermost dish, the aperture means are adapted to
allow flow of
water into the next dish in line upstream, and ultimately from the last dish
in line upstream
into the interior of the vessel.
Flotation Support System
The operation of a floating weir skimmer device can be adversely affected by
wave and
swell motion, especially where use is made of flotation means which are
integral with or
rigidly connected to the skimmer device.
The novel flotation support system described below serves to mitigate the
effect of wave
and swell motion on floating weir skimmers. It brings about a reduction in
shaking and
vibration resulting from to the impact of small waves. It also promotes a
closer relationship
between the rim of the skimmer's outer weir and the changing contours of the
surface of
the body of water when the skimmer encounters a swell.
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According to this aspect of the present invention, there is provided an
arrangement which
comprises a weir skimmer device
i. that is adapted to be buoyantly supported in water or other fluid by a
plurality of
flotation units located outwardly of the device and connected to the device by
way
of associated connecting support means, and
ii. where each connecting support means is so arranged as to permit free
upward and
downward movement relative to the device of its associated flotation unit
between
a. an upper position at which further upward relative movement of the
flotation
unit is arrested or restrained so that the flotation unit and its associated
connecting
support means provide upward buoyancy support to the skimmer device, and
b. a lower relative position at which the flotation unit will provide no such
support.
In the preferred form of this aspect of the invention, the arrangement
comprises a weir
skimmer device according to the invention as earlier referred to and described
above.
For operation on open water and in other locations where space permits, it is
preferred to
arrange for the buoyant support of the skimmer device by way of three or more
flotation
units. Such flotation units may advantageously be disposed symmetrically
around the
skimmer device. The buoyant support provided by such units should be such that
the outer
weir is set horizontally, i.e. to be parallel to the water surface in calm
conditions and at a
predetermined level in relation to the level of the water surface. This may be
achieved by
simple adjustment of stops adapted to define the upper limit of the relative
movement of
the flotation units in relation to the skimmer device. Further or in the
alternative, the
relevant relative level of the outer weir may be set using suitable ballast
weights. In
practice, both expedients may be put to use simultaneously.
For operation within narrow spaces, the skimmer device may be arranged to be
buoyantly
supported by two flotation units arranged on opposite sides of the skimmer
device. In this
way, the skimmer arrangement may be put to use, e.g. within tanks or
containers that are
fitted with vertically disposed baffle plates that extend downwardly for part
or all of their
depth. Such baffle plates are generally located parallel to each other. In
certain cases, (as
e.g. in oil tankers and other liquid container ships) their distances apart
are set in accordance
with prescribed standards or regulations, and may be of the order of one metre
or less.
In the preferred embodiment of this aspect of the invention, outwardly
extending arms
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constitute the connecting support means between the skimmer device and the
flotation units
when the arrangement is in its operating mode. Such arms may be provided with
"elbows"
adapted for pivotal movement in the horizontal plane. By appropriate
horizontal pivotal
movement of one or more such an outwardly extending arm, the overall area
within which
the skimmer arrangement can operate may be reduced. In practice, such
horizontal pivotal
movement will call for adjustment and/or the use of weights as mentioned above
in order
to restore the desired horizontal disposition and the relative level of the
outer weir rim.
In a useful embodiment of the present invention, each or any of the flotation
units may be
mounted by way of a pivotal trunnion type of mounting onto the forked outer
end of its
associated support arm which is connected at its other end to the skimmer
device. The
trunnion axis is arranged to be horizontal. Preferably it is located in the
zone of the centre
of buoyancy of the flotation unit. This will enable it to oscillate freely in
response to the
shorter wave length wave motions without unduly affecting the angular
disposition of its
associated support arm.
If desired, when a support arm approaches its upper relative position, bias
means (e.g.
spring loaded means) may be used to exert a progressive restraint upon its
further upward
movement and cushion its impact against its appropriate stop means.
The level of the first or outer weir rim in relation to the level of the
surface of the
surrounding body of water is set so that some water accompanies the oil drawn
over the
outer weir into the outer vessel. This water forms a supporting layer for the
oil and
facilitates or lubricates its passage over the outer weir. A progressively
diminishing quarnity
of water perfocins the same function as the oil flows over succeeding weirs.
In the case where an oil pollutant that is to be removed floats on the water
as a thin layer
of low viscosity, the outer weir rim will be positioned very near to the water
surface. On
the other hand, when dealing with a thick layer of oil, particularly oil of
greater viscosity,
a lowered level of the outer weir rim will be called for. The precise setting
of the level of
the outer weir rim in the manner described above calls for care and precision.
The best
guide to the optimum level in any particular circumstances will be trial and
error.
In an advantageous embodiment of the arrangement, the skimmer support arms are
pivotally
connected to the skimmer device so as to be freely movable until they hang
vertically
downwards when the skimmer is taken out of water. By suitable location of the
pivot
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mountings, the support arms together with their respective associated
flotation units may,
when the skimmer is out of use, be disposed so that they are located
substantially or entirely
within the outer perimeter of the first or outer weir rim when seen in plan
view. This
facilitates the introduction of the skimmer device together with its flotation
units through
relatively small sized manholes, inspection holes and the like. On
encountering the surface
of the body of water at the operating zone, the support arms together with
their respective
associated flotation units extend outwardly freely to their respective
operating positions to
give appropriate buoyant support to the skimmer device.
In operation, oil together with a supporting layer of water flows from the
surface of the
body of water over the first or outer weir rim. Some of the water flows
downwardly under
the the rim of the inner dish and into the body of the outer vessel. The
floating oil passes
over the rim together with the remainder of the water. Such water again
provides a
supporting and lubricating layer, and the oil cascades into the inner dish
over the second
weir provided by its rim.
Some of this water gravitates to the lower part of the inner dish. There, it
encounters the
apertures leading to the body of the outer vessel. It flows through them to
join the water
that has flowed in below the rim of the inner dish.
The floating oil supported by a diminished amount of water flows over the
horizontal bale
plate to the rim of the extraction pipe inlet or, in the case of upward
extraction, the rim of
the sump. The horizontal baffle plate acts to stabilise the fluid in the inner
dish.. The third
weir provided by the inlet rim or sump rim (as the case riiay be) allows the
oil to cascade
into the extraction pipe or sump. With it goes a much diminished amount of
water. This
water yet again provides a supporting and lubricating layer. It accompanies
the oil through
the extraction pipe. Together with the oil, it forms the "enriched oiUwater "
mixture which
is the final product.
The water that has been denied access to the extraction pipe by the third weir
rim joins the
water that has gravitated to the lower part of the inner dish. It then runs
out through the
apertures into the body of the outer vessel.
The interior of the body of the outer vessel is directly connected to the
outside body of
water through apertures in its side walls. Preferably, such apertures take the
form of
conduits extending inwardly from or through the sides of the outer vessel,
their cross
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_g_
sectional areas at their inner ends being less than their cross sectional
areas at their outer
ends. Such apertures ensure that the fluid pressure inside the vessel is
maintained in
equilibrium with the fluid pressure within the body of water outside. The
presence and
shape of the conduits mitigate against the disruption that can result from a
sudden swge of
flow of oil bearing water into the skimmer device or of water out of it.
Connection of a vacuum pump or a suction pipe to the extraction pipe promotes
a smooth
non turbulent withdrawal of the enriched oil/water mixture. Where turbulent
mixing of the
enriched oil/water mixtwe is not a matter of concern or consequence, an
ordinary pump may
be employed.
It is advantageous to withdraw the enriched oil/water mixture from the inner
dish of the
skimmer device by way of gravity flow where circumstances allow. In this way,
there may
be secured a smooth substantially non turbulent flow of the enriched oil/water
mixture
through the extraction pipe to an outlet located at a level that is below the
level of the
surface of the water on which the device operates.
When taking advantage of gravity flow to withdraw the enriched oil/water
mixture from the
inner dish of the skimmer device, it is desireable to minimise the occurrence
of "gulping".
"Gulping" is a common phenomenon that occurs when fluids are withdrawn from
surface
skimmers through an extraction pipe. The expression relates to what happens
when air is
entrapped and passes into the extraction pipe together with the fluid that is
being
withdrawn. Such gulping action results in turbulence. That in turn causes
internal agitation
within the fluid. Where the fluid has more than one component, there will be
mixing. In the
case of the skimmer device of the invention, gulping can also disrupt the
smooth operation
of one or more of the skimmer's weirs.
The occurrence and the frequency of gulping may be mitigated by providing the
extraction
pipe or an extension of it along its length with a part that has a smaller
cross sectional area
than the inlet through which the oil/water mixture leaves the inner dish. The
optimum extern
of the relative reduction of the cross sectional area is best ascertained by
trial and error.
It will depend upon the circumstances in any particular case. The larger the
difference
between the skimmer operating level and the level of the extraction pipe final
outlet, (- the
drop in level), the greater will be the speed at which fluid will be drawn
through the inlet,
and hence the greater will be the tendency towards gulping. Hence, also, the
greater should
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be the extent of the reduction in cross sectional area. Other relevant
considerations are the
viscosity and the density of the liquids being withdrawn and their feed rate
into the
extraction pipe. In general, the extraction pipe or a continuation of it
should be reduced
in cross sectional area to below 80 per cent of the cross sectional area of
the inlet, and
preferably to from less than i per cent to 50 per cent, and, depending on the
conditions,
advantageously to from less than 1 per cent to 25 per cent.
The matters set out above in relation to the use and advantages of gravity
flow and the
reduction of the internal cross sectional area of the extraction pipe apply
equally, mutatis
mutandis in the case of weir skimmer devices in general where the design
permits or calls
for the withdrawal of the pertinent liquid or liquid mixture from the device
through an
extraction pipe.
The arrangement comprising the novel flotation support system and the weir
skimmer of the
present invention provides for flexible methods of operation when dealing with
a wide range
of different floating pollutants under a wide range of different conditions
and
circumstances. A particularly useful application of the arrangement lies in
the removal of
a floating layer of algae from an aqueous substrate. Other floating pollutants
that may
succesfully be removed manifest large variations in properties, e.g. by reason
of differing
specific gravities and/or viscosities. The properties of floating crude oil
may change daily.
The adaptation of the arrangement comprising the novel flotation support
system for
satisfactory operation in any particular case may involve any one or more of
the following
activities:
Varying the "stop" or upward support position of one or more of the flotation
units
in relation to the body of the skimmer device so that such skimmer body is
raised or
lowered as the case may be in relation to the surface of the body of water.
Screw
mounted means provide a ready means of achieving an accurate setting.
2. Varying the level of the inner dish rim weir in relation to the outer weir
rim. This
again may be done accurately using screw mounted means.
3. Varying the level of the horizontal baffle plate surrounding the inlet to
the drainage
pipe in relation to the level of the inlet. Again, screw mounted means may be
used
to ensure a precise difference of respective levels. In one embodiment, the
drainage
pipe itself may be threaded on the outside and the horizontal baffle plate
screw
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mounted onto it.
4. Varying the level of the inlet to the drainage pipe in relation to the
level of the weir
rim of the inner dish. The inner dish itself rnay be screw mounted onto the
threaded
drainage pipe so that vertical adjustment of the one in relation to the other
is readily
and accurately effected.
5. Varying the ballast weight. A standard set of pre-determined ballast
weights will
advantageously provide a sequence of standard settings for the differences
between
the respective levels of the outer weir rim and the water or other fluid on
which the
skimmer device is buoyantly supported. Fine adjustment is achieved by using
the
expedient mentioned under I . above and/or by the use of ballast weights of
lower
denomination.
In this way, the buoyantly supported skimmer device of the invention may be
readily
adapted for effective use over a range of operating conditions. Trial and
error will provide
guidance to the most satisfactory settings for the variants mentioned under 1.
to 4. above.
The invention and its further aspect will now be described by reference to the
accompanying schematic drawings in which:
Fig. I represents in plan view an embodiment of the skimmer device of the
present invention
which is arranged for the withdrawal of the enriched oil/water mixture
downwardly through
an extraction pipe. Also illustrated schematically are three flotation units
connected to the
skimmer device and arranged in accordance with the further aspect of the
present invention.
Fig 2 represents a cross-sectional view of the skimmer device of Figure I and
of its
connection to one such flotation unit.
Fig 3B represents the flotation unit of Fig 2 pivotally mounted on one end of
a rigid arm that
has been allowed to swing downwardly around its pivotal connection at its
other end to the
skimmer device.
Fig 3A represents the features of Fig 3B when looking in the direction of the
centre of the
skimmer device.
Fig 4 represents in cross-section another embodiment of the skimmer device of
the invention
which is arranged for upwardly directed withdrawal of enriched oil/water
mixture. Also
illustrated schematically is one of the skimmer device's flotation units made
to a different
design that provide flotation support of the kind described above. This
flotation unit is
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slidably mounted for upward and downward movement around a guide rod that
terminates
with an adjustable stop connected to the skimmer device.
Fig 5 represents in cross-section an alternative flotation unit arrangement in
which the
flotation unit is free to move upwardly or downwardly within a cage attached
to the
skimmer device, there being an adjustable stop at the top of the cage.
Fig 6 represents in plan view an embodiment of the invention in which the
skimmer device
is arranged to be buoyantly supported by two flotation units, one on each
side.
Fig 7 represents a skimmer device floating in its operating mode on the
surface of a body
of water with the outlet to its extraction pipe located at a lower level than
the surface of the
body of water.
In Figures 1 and 2, 1 refers to the skimmer device generally which consists of
the outer
vessel 2. Its upper rim 3 forms the outer first weir during operation and
floating oil
together with a supporting layer of water flows over it from the surface of
the body of
water and into the outer vessel 2.
Within the outer vessel 2 is located the dish 4. During operation, the outer
rim 5 of dish 4
forms the second weir. Floating oil together a supporting layer of water flows
over the
second weir from the outer vessel and into the dish 4. The respective levels
of the weirs are
set so as to ensure that the proportion of oil in the liquid flowing over the
second weir is
higher than the proportion of oil in the liquid flowing over the outer or
first weir. Within
dish 4, oil and a diminished supporting layer of water flows in a continuous
stream over the
horizontal baflie plate 9 towards the centrally located inlet to the
extraction pipe 7. The
rim 8 to the inlet provides the third weir. Oil and a much diminished
supporting layer of
water cascades over the inlet 8 and into the extraction pipe 7. The remainder
of the water
gravitates to the lower part of dish 4 below the floating oil and escapes
through apertures
6 in the base of dish 4 into the interior of the outer vessel 2. Extraction
pipe 7 extends
downwardly from the inlet rim 8 through the base of dish 4 and then through
the base of
vessel 2. Inlet rim 8 is set at a pre-determined level in relation to the rim
5 of the inner dish
which provides the second weir. The horizontal baffle plate 9 which encircles
inlet 8 is
adjustably located so that its upper surface is at or is just below the level
of the rim 8. The
finai enriched oiUwater mixture is withdrawn through the extraction pipe 7.
The interior of vessel 2 communicates through conduits 10 with the body of
water from the
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surface of which the oil is separated. Conduits 10 are located at a level
below the underside
of dish 4. Preferably, such conduits extend from the sides of the outer vessel
2 inwardly
part of the distance towards the centre of outer vessel 2 and have decreased
cross-sectional
areas at their inner ends.
In exceptional circumstances, the weir skimmer of the invention may be put to
use in such
a way that oil alone will flow into the extraction pipe 7. In circumstances
where no more
than partial separation of the floating liquid is called for, for example in
the separation of
part of a layer of floating cream that is intended to leave behind semi-
skimmed milk, the
operation may be adapted by way of the expedients mentioned above so that
cream alone
is withdrawn through the extraction pipe 7. In this context, the description
of the invention
as set out herein should be read as including the case where the expression
"oil",
(interpreted according to the qualification appearing near the beginning of
this specification)
replaces the expression "enriched oiUwater mixture".
Apertures 6 in the base of dish 4 permit part of the water that has flowed
over the second
weir to flow directly into the outer vessel 2. The dimensions of apertures 6
can be made
variable, e.g. by suitable throttle means so as to control the rate of flow of
water
therethrough. The conduits 10 connecting the interior of vessel Z and the
surrounding body
of water provide a substantial equilibrium between the water pressure within
vessel 2 and
that obtaining in the outside body of water. The configurations and dimensions
of the
conduits 10 are designed to minimise the incidence and the effect of sudden
surges of water
between the interior of the vessel 2 and the main body of water upon the
occurrence of
factors tending to disturb such equilibrium, e.g.wave motion.
Oil or an enriched oil/water mixture is withdrawn through extraction pipe 7
for storage or
further treatment.
As already mentioned above, one or more additional weirs may be interposed
between the
first or outer weir and the second weir of the skimmer device described above.
The weirs
result from the interposing of one or a series of intermediate concentric
dishes between the
first or outer weir and the second weir. Their respective rims form weirs that
are disposed
in appropriate stepped configuration between the level of the first or outer
weir and that of
the second weir. The base of each such intermediate dish is provided with
aperture means
to permit flow of water into the interior of its predecessor in the series.
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In operation, oil and a progressively diminishing quantity of water flow over
each weir in
turn and eventually over the baffle plate 9 and into inlet 8.
In the skimmer device schematically represented in Figure 4, the first or
outer weir is formed
over the upper rim 23 of vessel 22 over which oil and a supporting layer of
water flows into
vessel 22 during operation. The outer rim 25 of dish 24 within the vessel 22
forms the
second weir over which floating oil together a supporting layer of water flows
from the
vessel 22 into the dish. Within dish 24, oil and a diminished amount of water
mixture flows
in the direction of the iim 28 of the centrally located sump 30. The rim 28
provides the
third weir. Water gravitates to the lower part of dish 24 below the floating
oil, and escapes
through apertures 26 in the base of dish 24 into the interior of the outer
vessel 22.
Extraction pipe 27 extends upwardly from the sump 30. The inlet rim 28 is set
at a pre-
determined level in relation to the second weir rim 25. Such rim 28 is
encircled by an
horizontal battle plate 29 the upper surface of which is adjustably located so
as to be at or
just below the level of the rim 28.
In like manner to the embodiment described by reference to Figures 1 and 2,
the interior of
vessel 22 communicates through the inwardly directed conduits 20 with the
outside body
of water. The cross sectional areas of the conduits decrease in the inward
direction.
During operation, enriched oil/water mixture is drawn upwardly from the sump
30 through
the extraction pipe 27 after cascading over weir rim 28. The other features of
operation
are the same, mutatis mutandis as those already described in relation to
Figures 1 and 2.
Flotation Support System
The further aspect of the present invention that relates to the provision of
buoyant support
for weir surface skimmer devices is illustrated schematically in the drawings
referred to
below.
In Figure 1, three flotation units 11 are adapted to provide buoyant support
for the skimmer
device 1. Each of these flotation units is mounted on a support arm 12
pivotally connected
at 13 to the skimmer device. The pivot connection 13 is located within the
slot or recess
15 which is designed to allow vertical arcuate movement of the support arm 12
and its
associated flotation unit 11 in relation to the skimmer device 1 up to but not
beyond an
upper stop position defined by stop member 14. See Figure 2. Below that stop
position, the
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support arm 12 with its associated flotation unit 11 swings freely downwards
and gives no
buoyant support to the skimmer.
It is particularly advantageous in practice to provide means whereby each
pivoted support
arm 12 may be pivoted until it hangs freely together with its associated
flotation unit 11
below the skimmer device I within the area bounded by the outer rim 3 when
looked at in
plan view. See Figure 3B. This enables the arrangement of skimmer device and
flotation
system to be easily transported and stored. In particular, this expedient
enables the
arrangement to be lowered through limited apertures or access means into
tanks,
subterranean reservoirs and the like. On reaching the surface of the liquid,
there occurs a
relative outward an upward movement of the arms 12 and their associated
flotation units
1 I until the arms encounter the stop means 14 when the flotation units 11
provide the
skimmer device 1 with buoyant support.
An additional advantage of this arrangement is that it enables the skimmer
device together
with its attendant flotation units to be inserted into and cleaned and stored
in a container
of easily managed dimensions. The container may contain a cleaning fluid and,
if desired,
a heating element. Depending on the dimensions of the skimmer device, the
container may
also be mounted on wheeled transport means ranging in size and approximate
weight down
to a "golf club trolley" type device or smaller.
Referring to Figure 2, the screw mounting of the stop member 14 may be
employed to
adjust as desired the upper limit of the pivotal movement of the rigid arm 12.
In this way,
the level of the first or outer weir over rim 3 may be varied in relation to
the flotation units
i I . In this way also, by appropriate adjustment, it is possible to ensure
that the outer weir
rim 3 is set in a substantially horizontal plane, (i.e., parallel to the
surface of the external
body of water in calm conditions) for operation of the arrangement.
In the preferred embodiment of the present invention, each flotation unit I 1
is pivotally
mounted on pivotal mountings or trunnions 16 at the forked end 17 of its
associated support
arm 12. See Figures 1 and 3A. Preferably, such pivotal support 16 is located
at or near
the centre of buoyancy of the flotation unit. This enables the flotation unit
to respond more
readily to surface waves and ripples. The rocking motion of the flotation unit
around its
pivotal mounting serves to diminish the oscillatory forces otherwise exerted
on the rigid
arm 12.
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If desired, the rigid arms 12 or any of them may be provided with "elbows" 18,
that is to say
pivotal means whereby they may be pivotally moved horizontally so as to reduce
(if
desired) the overall width of the arrangement. See Figure 1. In this way, the
skimmer
device together with its flotation units may be adapted for use within
relatively narrow
spaces, e.g. between tank or container baffle plates.
Other means may be employed to provide buoyant support for the skimmer device
falling
within the scope of the present invention.
In Fig 4, the skimmer device 22 is represented as being provided with a rigid
arm 60 that
supports a vertical rod or shaft 61 that terminates with an adjustable stop
member 62.
Slidably mounted on rod or shaft 61 is flotation unit 63 which, when it abuts
against
adjustable stop 62 provides (in conjunction with two or more other flotation
units likewise
mounted, but not shown) adjustable buoyancy support for the weir skimmer
device. Such
flotation units may be spring loaded so as to be biased in a downward
direction from the
stop position or towards the optimal level of operation.
In Fig 5 the flotation unit represented by a ball 65 is freely moveable in the
vertical direction
within a cage 66 that is attached to the skimmer device 67. When the skimmer
is in
operating position in the water, the ball bears against an adjustable stop 68
at the top 69 of
the cage and, (in conjunction with two like ball and cage arrangements
disposed around the
skimmer) provides the skimmer with adjustable buoyancy support.
In this case also, the ball may be spring loaded so as to be biased in a
downward direction.
Fig 6 represents a skimmer device 31 adapted to be buoyantly supported by
flotation units
32 and 33 disposed on opposite sides of the skimmer device and connected to
the skimmer
device by rigid forked support arms 34 and 35 which are pivotally mounted at
spaced
mountings 36, 36 and 37, 37 within the slots 38 and 39 which extend inwardly
from the
outer wall of the skimmer device 31. The slots and the dimensions and
mountings of the
support arms are arranged in the manner described above, mutatis mutandis so
as to enable
the flotation units and their respective associated support arms to be folded
down beyond
the outer rim of the skimmer device when seen in plan view. This facilitates
insertion of
the arrangement into a tank through a restricted opening. On alighting on the
fluid surface
below, the arms extend outwardly until they encounter the appropriately
located stop
members when the flotation units 32 and 33 are enabled to provide the skimmer
device 31
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with buoyant support. The arrangement may then operate within the narrow area
bounded
on each side by walls or baffle plates 40 and 41.
In Fig 7, 50 represents a tank or container in which a weir skimmer device 51
as
descriobed herein floats on a body of water 52 the surface of which is
contaminated by a
surface layer of oil (not shown). A flexible extraction pipe 53 extends from
inlet 57 within
the skimmer device 51 through the underside of the device downwardly and
through a point
54 on the outer wall of the tank or container 50 beyond which lies the outlet
56 and an
intermediate valve 55. The cross sectional area of at least part of extraction
pipe 53 is
smaller than that of the cross sectional area of inlet 57. The extent of the
reduction in any
particular case is best determined by experience and trial and error. It
should be at least
down to less than 80 per cent, preferably down to from less than 1 per cent to
50 per cent,
and advantageously, depending on the conditions, down to from less than I per
cent to 25
per cent.
By using the valve 55 to control the rate of flow through the inlet into the
extraction pipe,
the incidence of gulping may be reduced. However, for continuous operation and
as an
added precaution against gulping, it is preferred in addition to limit the
internal cross
sectional area of at least part of the extraction pipe as indicated above.
Where it is not possible or reasonably practicable to provide the extraction
pipe with a
continuously downward gradient between the inlet and the outlet, it may be
disposed over
an intermediate obstacle (e.g. the wall of a tank or the retaining wall of a
reservoir) to
provide a siphon. To initiate the skimming operation, the extraction pipe is
filled with
water, e.g. by suction applied at a level below that of the water surface
within the tank
using a simple low powered suction pump.
In operation, oil bearing water flows into the weir skimmer device 51 and
enriched
oil/water mixture flows out by way of extraction pipe inlet 57 and then down
through
extraction pipe 53, at least part of which has a reduced cross sectional area.
It emerges
from the outlet 56. The rate of flow is controlled by the variable valve 55.
The surface
skimming operation proceeds smoothly and unimpaired by vibration, rocking or,
to a very
large extent, gulping. By the use of gravity alone to extract the enriched
oil/water mixture,
substantial economies are achieved.
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