WEIR SKIMMER AND FLOTATION SYSTEM

Abstract: A weir skimmer (1) for removing a floating liquid ("first liquid" exemplified in this abstract by floating oil) from the surface of another liquid of higher density ("second liquid" exemplified in this abstract by water) comprising: i) an outer vessel (2) the rim (3) 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 (2) floating oil together with a supporting layer of water; ii) an inner dish (4) located within the outer vessel (2) with its rim (5) spaced from the first weir rim (3) and adapted to act as a second weir to separate from an underlying mass of water within the interior of the outer vessel (2) and to admit into the inner dish (4) floating oil together with a supporting layer of water; iii) aperture means (6) located in the lower part of the inner dish (4) communicating with the interior of the outer vessel (2); iv) aperture means (10) communicating between the interior of the outer vessel (2) and its exterior. Buoyant support for the weir skimmer device (1) during use is provided by a plurality of outwardly located flotation units exemplified in the drawing accompanying this abstract by flotation unit (11). Each flotation unit (11) is connected to the weir skimmer device (1) by associated support means, e.g. a rigid support arm (12), each arm being pivotally connected at (13) to the skimmer device (1).

Description: 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 effect 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, 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 te invention is further characterised by: 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 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 oil/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. 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 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 quantity of water performs 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 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 baffle 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 may 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 oil/water " 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 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 surge 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 mixture 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 extent 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 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 1 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: 1. 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 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 may 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 1. 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.1 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 1 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 3 A 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 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 baffle 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 final enriched oil/water mixture is withdrawn through the extraction pipe 7. The interior of vessel 2 communicates through conduits 10 with the body of water from the 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 oil water 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 2 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 rninimise 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. 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 rim 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 predetermined level in relation to the second weir rim 25. Such rim 28 is encircled by an horizontal baffle 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 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 1 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 1 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 slάmmer 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 11. 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 11 is pivotally mounted on pivotal mountings or trunnions 16 at the forked end 17 of its associated support arm 12. See Figures 1 and 3 A. 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. 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 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 1 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.

Claims: CLAIMS 1. 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 and 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 adapted to act as a second weir to separate from an underlying mass of second liquidwithin 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, and iv. aperture means communicating between the interior of the outer vessel and its exterior. 2. A weir skimmer as claimed in claim 1 characterised by: 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 the first liquid and the second liquid, and vi. means adapted to withdraw the said enriched mixture from the weir skimmer. 3. A weir skimmer as claimed in either preceding claim characterised by aperture means in the form of conduits which extend inwardly from or through the sides of the outer vessel. 4. A weir skimmer as claimed in claim 3 in which the conduits have decreased cross sectional areas at their inner ends. 5. A weir skimmer as claimed in any of claims 2 to 4 in which the rim of the inlet of a downwardly extending extraction pipe is adapted to act as a third weir to separate the enriched mixture of the first liquid and the second liquid from the underlying layer of second liquid. 6. A weir skimmer as claimed in any of claims 2 to 4 in which the rim of a sump is adapted to act as a third weir to separate the enriched mixture of the first liquid and second liquid from the underlyig layer of second liquid A weir skimmer as claimed in either of claims 5 and 6 in which the third weir nm is encircled by an horizontal baffle plate the upper surface of which is located at or just below the level of the third weir rim A weir skimmer as claimed in any preceding claim that is adapted to separate i floating oil from water, or ii a floating of algae from an aqueous substrate. A weir skimmer as claimed in claim 5 and any dependent claim in which the extraction pipe or an extension thereof is provided along its length with a part that has a smaller cross sectional area than the pipe inlet. A modification of the invention as claimed in any preceding claim in which one or more mtermediate dishes are interposed between the first weir rim and the nm of the inner dish, the rim of each interposed dish providing an intermediate weir adapted to separate oil and a supporting layer of water from the underlying water layer in the adjacent dish upstream, or in the case of the first dish in line, in the vessel interior, aperture means being provided in the lower part of each dish connecting with the interior of the next dish in line upstream or, in the case of the first dish in line, with the interior of the vessel An arrangement which comprises a weir skimmer device l 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 wherein each connecting support means is arranged so as to permit free upward and downward movement relative to the device of its associate 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 position at which the flotation unit will provide no such support An arrangement as claimed in claim 11 where the weir skimmer device is as claimed in any of claims 1 to 10 RECTIFIED SHEET RULE 91 13. An arrangement as claimed in either of claims 11 and 12 which includes stop means adapted to define and control the limits of the upward relative movements of the respective flotation units. 14. An arrangement as claimed in any of claims 11 to 13 in which the connecting support means comprise support arms adapted to extend outwardly from the weir skimmer device to the flotation units. 15. An arrangement as claimed in claim 14 in which the connections between the support arms and the flotation units permit oscillatory movement of the flotation units in response to wave motion. 16. An arrangement as claimed in either of claims 14 or 15 in which the flotation units and their associated support arms are connected to the weir skimmer device in such a manner that they can be hung freely downwardly from the weir skimmer device within the area bounded by the outer rim of the weir skimmer device when seen in plan view. 17. An arrangement as claimed in any of claims 14 to 16 in which the support arms together with their respective flotation units are adapted to assume automatically their respective buoyancy providing dispositions when the arrangement is placed on water. 18. An arrangement as claimed in any of claims 15 to 17 in which one or more of the support arms comprise means whereby it may be horizontally and pivotally flexed whereby the overall width of the arrangement may be varied. 19 A modification of the invention as claimed in claim 13 and each dependent claim in which the arrangement is adapted to provide for the withdrawal of cream alone without accompanying milk in the case where the weir skimmer is put to use to separate cream from a substate of cream depleted milk. 20. A method for the removal of a first liquid floating on the surface of another liquid of higher density by the use a weir skimmer as claimed in any of claims 1 to 10. 21. A method as claimed in claim 20 in which use is made of a buoyantly supported weir skimmer that is comprised within an arrangement as claimed in any of claims 11 to 19. 22. Amethod as claimed in either of claims 20 or 21 when applied to the separation of i. Floating oil from water, or ii. A floating layer of algae from an aqueous substrate, or iii. Floating cream from a substrate of cream depleted milk. RECTIFIED SHEET (RULE 91 23. Weir skimmers of the invention substantially as described herein by reference to the accompanying drawings. 24. Arrangements comprising weir skimmers and flotation support systems substantially as described herein by reference to the accompanying drawings. 25. Methods for removing floating liquids from the surfaces of liquids of higher density substantially as described herein.

Inventors: MADDOCK THOMAS MERLIN, MADDOCK, THOMAS, MERLIN
Applicants: MADDOCK THOMAS MERLIN, MANTIS OIL SEPARATION LTD, MADDOCK, THOMAS, MERLIN, MANTIS OIL SEPARATION LIMITED
Application year: 1999
Main classification: E02B15
IPC codes: E02B15