AU2818701A - Separation of liquids - Google Patents

Description

WO 01/54788 PCT/AUO1/00078 Separation of Liquids This invention relates to an apparatus for the separation of mutually immiscible liquids and to a process for separation of liquids using the apparatus. The 5 apparatus and process will be described with reference to the separation of water and oil from mixtures thereof. The term oil is herein used to refer to water immiscible liquids which may be in the form of silicones or organic liquids such as hydrocarbon, lubricant and wastes. 10 A number of types of separators are being produced which rely on a variety of separation techniques including gravity separation, air flotation and filtration using a variety of filters such as paper filters or polymeric cartridges. Many of these separators suffer from a number of disadvantages. 15 The passage of oil-water liquor through the apparatus can lead to the generation of new oil droplets which are much finer than oil droplets originally present in the oil-water liquor. These ultra-fine oil droplets are much harder to separate from the water phase, for example in coalescing devices based on the use of parallel or conical plates, or high surface area oleophilic surfaces. The 20 presence of these fine oil droplets may in many cases limit the performance of the apparatus. The passage of liquor through separators is non-uniform. This is often apparent from streaming, channelling or tracking. Fine oil droplets are swept along in 25 these streaming flow patterns, and the performance limit of the apparatus is defined by high streaming flow velocities rather than by the average flow velocity through the apparatus. In this way poor apparatus performance may occur even at low flow rates. 30 The ingress of significant quantities of clay or other fine particulates suspended in water often also comprises the performance of the apparatus. The use of filters in the apparatus provides limited oil holding capacity and these filters frequently need replacement and maintenance.

WO 01/54788 PCT/AUO1/00078 2 The size of the unit required to process a given flow rate of oil-water influent is frequently large. This often prevents installation of the oil-water separator in limited available space such as onboard a small boat or underneath a shelf. 5 The range of oil types which can be separated from an aqueous stream is limited, for example used engine oil or viscous oil may be problematic to separate. 10 The purpose of this invention is to overcome one or more disadvantages associated with prior art. In a first aspect, this invention provides an apparatus for the separation of water and oil from a mixture thereof comprising: 15 e a separation vessel within which oil and water are to be separated; e an inlet for the mixture to be separated; e an outlet for separated water disposed below the inlet and providing a downward flow of mixture within the vessel; and * at least one cross-plate extending across the vessel in the flow path 20 between the inlet and outlet and provided with a plurality of holes for controlled passage of the mixture. The apparatus may be used in separation of a wide range of oil/water mixtures but is particularly suited in application where water is predominant. 25 Nonetheless the apparatus may handle mixtures which change composition from substantially water to substantially oil. Variation in the influent mixture may be encountered in oil spill clean up or on board ships. Particular embodiments of the invention will be described with reference to the preferred embodiment in which the influent stream is, on average, predominantly aqueous. 30 The cross-plate will generally provide a more uniform flow below the plate and will reduce turbulence from the influent stream. We have found that the performance of the apparatus is improved if the dimension of the holes and distribution of holes is within certain limits.

WO 01/54788 PCT/AUO1/00078 3 Accordingly it is preferred that the diameter of the holes in the plate is greater than 0.5 millimetres. Preferably the diameter of the holes in the plate is less than one-fifth of the plate diameter, more preferably less than one-tenth of the 5 plate diameter, even more preferably less than one-twentieth of the plate diameter. Preferably the sum of the area of the holes in the plate is less than 70% of plate area (including holes) and more preferably less than 55% of plate area 10 (including holes). Preferably the sum of the area of the holes in the plate is greater than 5% of the plate area, more preferably greater than 10%. Preferably the thickness of the cross-plate is greater than 0.25 mm, more preferably greater than 1mm. Preferably the thickness of the cross-plate is less 15 than 10 mm, more preferably less than 5 mm. The linear velocity of liquor flow with the vessel will have an effect on the performance of the apparatus. Preferably the maximum linear average down flow velocity of liquid with the apparatus, designated Vmax which may be 20 calculated according to the equation: influent flow rate Vmax= plate surface area is less than 200 cm per minute, more preferably less than 100 cm per minute, 25 even more preferably less than 20 cm per second. Preferably the material from which the cross-plates are made does not swell in oil. For example the cross-plates may be made from epoxy-powder coated aluminium or perfluorinated polymer (eg Teflon-coated aluminium. Preferably 30 the contact angle of oil drops on the surface of the cross-plate or plates in a water medium is greater than 200 more preferably greater than 500.

WO 01/54788 PCT/AUO1/00078 4 Where a single plate is used the flow may still lead to some turbulence particularly where the inlet is in the side of the vessel. A side inlet tends to produce more rapid flow through holes closest to the point of inlet and also through holes which are the most remote from the inlet. When the flow rate is 5 non-uniform across the plate it may be difficult to achieve a optimal separation. We have found that it is preferred to use at least one further plate comprising a multiplicity of holes in the flow path. Accordingly it is preferred to use two or more perforated cross-plates in the 10 apparatus. When two cross-plates are used, it is preferred that the minimum distance between the first (or upper) cross-plate and the second (lower) cross plate is 10 mm, and it is preferred that the distance between the first and second plate is no more than twice the diameter of the first plate, more preferably less than one-half the plate diameter, even more preferably less than 15 one-quarter plate diameter. The use of this combination significantly enhances the uniformity of the liquid flow by inhibiting the process of fluid tracking or streaming. Preferably an oil reservoir is provided within the vessel and the aqueous 20 component of the influent stream passes through the oil reservoir. Frequently when the influent stream is substantially aqueous in nature the stream passes through the reservoir as droplets of aqueous phase. Preferably a significant oil reservoir is maintained at the top of the apparatus 25 and influent oily-water liquor is fed into the oil reservoir. An oil-water interface exists where the oil reservoir encounters the substantially water phase in the lower part of the oil-water separator. Preferably the influent oil-water liquid enters the oil reservoir at a distance 30 10mm or greater above the oil-water interface, more preferably 20mm or greater.

WO 01/54788 PCT/AUO1/00078 5 Preferably the distance from the oil-water interface to the first cross-plate is greater than one-eighth the plate diameter, more preferably greater than one quarter the plate diameter. 5 The oil in the oil reservoir should be compatible with the oil to be separated. Preferably the oil should be non-viscous. Preferably the initial charge of oil in the reservoir should not support a stable water-in-oil emulsion. The oil may be chosen from the group of used motor oil, diesel and vegetable oil. 10 Preferably compacted netting or mesh is installed in the space below a cross plate. When a plurality of cross-plates are used the netting or mesh is preferably below the lowermost cross-plate. The compacted netting may extend to the point of discharge of clean water. 15 In a particularly preferred embodiment the invention thus provides an apparatus for separation of oil from a mixture of oil and water including: a separation vessel having a side wall and bottom wall; an inlet for oily water; an outlet for purified water disposed below said inlet for oily water and 20 providing a downward flow of the mixture within the vessel; at least two cross-plates extending across the flow path of the mixture and comprising a plurality of holes said plates being vertically separated within the vessel; and hydrophobic netting packed within the vessel and disposed between the 25 lower of the two perforated plates and the outlet for purified water. The apparatus will preferably include a top wall and an outlet for oil in or adjacent the top wall. The vessel is preferably a cylindrical vessel with a vertically disposed axis. 30 In operation a layer of oil is preferably provided adjacent the top of the vessel and the inlet for oily water is disposed within the oil layer. We have found that by introducing the oily water to the oil layer the process of coalescence is assisted.

WO 01/54788 PCT/AU01/00078 6 The oily water flows through the apparatus in a downward direction and through the perforated plates which extend across the flow path of the oily water. The plates are perforated and coagulated oil particles may rise through the plate 5 against the down flow of the mixture to join the oil layer at the top of the vessel. Introduction of the oily water to the oil layer may produce turbulence within the region above the first plate. However below the plates the turbulence of the oily water liquid is reduced. The plates thereby produce zones of progressively 10 lower turbulence in the passage of the oily water. The introduction of oily water into the oil layer at the top of the vessel produces a relatively turbulent zone. The first of the perforated plates produces a zone of less turbulence between the first and second plate and below the second plate a relatively still zone is produced. 15 The oil layer at the top of the vessel forms a discrete phase separated from a predominantly water phase by an oil/water interface which is preferably spaced above the upper plate. An oil outlet may be provided for the outlet oil from the oil layer. The outlet may be actuated in response to the oil/water interface 20 falling to a predetermined level. A suitable oil/water detection means is described in our copending International Application PCT/AU00/00199 the contents which are herein incorporated by reference. The oil/water detection means is responsive to a change in condition from 25 immersion in water to immersion in oil. The oil water detection means may be a probe or part of a probe spaced below the vertical level of the inlet. When the oil reservoir reaches its maximum volume it extends to the oil/water detection means producing a change in condition of the detection means from immersion in water to immersion in oil to activate delivery of oil from the outlet. Oil is 30 delivered from the outlet until a predetermined lesser volume is provided. Generally the predetermined lesser volume will provide a reservoir of oil extending from adjacent the top of the vessel to below the inlet for the mixture to be separated.

WO 01/54788 PCT/AUO1/00078 7 The preferred apparatus of the invention preferably includes netting or mesh packed beneath the second plate. We have found that mesh, particularly plastic mesh, significantly improves the efficiency with which fine droplets of oil coalesce. The mesh is preferably formed of a hydrophobic material such as a 5 polyolefin or PVC. Polyolefins are particularly preferred. The net or mesh is preferably formed of strands of diameter in the range of from 10 to 1000 microns and the spacing between strands is preferably at least 1 mm and more preferably from 1 to 50 mm. The strands may be multi component strands formed by plaited or interlaced fibres or sub-strands. 10 The mesh or net is preferably located beneath the second plate to provide a tortuous flow path immediately upstream of the outlet. The net or mesh will generally extend across the flow passage. It is particularly preferred that the mesh is spaced below the second plate so that a relatively still zone of liquor 15 water is provided between the second plate and the mesh. Preferably the distance from the lower cross-plate to the top of the compacted netting is more than 5 mm, preferably more than one-quarter of a plate diameter. 20 The bottom of the netting or mesh may extend to the bottom of the vessel. The mesh is preferably coated with a coating comprising fluorinated compounds such as fluoro alkyl polymers sold under the trade name 'SCOTCHGUARD' by 25 the 3M Company. The mesh is compressed to ensure that fluid streaming or tracking does not occur. An internal or external polishing module may preferably be provided. The internal polishing module may comprise a woven fibre mat firmly contained 30 between two anchored perforated holding plates. The woven fibre mat typically includes an oleophilic fibre of high surface area. The fibres may be greasy wool or kapok, a silky fibre obtained from a number of tropical plants and which is also known as Java cotton. Such oleophilic fibres may become fragile when WO 01/54788 PCT/AUO1/00078 8 they absorb oil, and it is advantageous that the mat formed by oleophilic fibre is intermingled with a structural fibre such as sisal. It may advantageous to provide an oleophilic surface treatment to one or more 5 fibre types using methods known to the art. It may be advantageous to provide fibres which are biodegradable. It is advantageous to provide a loosely intermingled mat of fibres which is permeable to water at lower pressures, but which also presents a high surface area of oleophilic fibre to the percolating aqueous stream. 10 Preferably the internal polishing module is located immediately above the compacted mesh or netting. The external polishing module should preferably be located in the clean water discharge line. The external module may contain a woven fibre filtering mat of similar composition to the mat of the internal 15 polishing module, or the module may comprise a commercial cartridge filter e.g. the Microclean range of cartridge filters provided by CUNOT of Melbourne, Australia. The pump which drives oily water liquid through the apparatus may be located 20 in the influent line. Preferably the pump has low-shear characteristics and is self priming. The pump may be a diaphragm pump such as the Johnson P120 or P50 pump made by Johnson Pumps of Melbourne, Australia. Preferably the pump can sustainably operate in water containing clay or other dispersed particulates. 25 In order to provide for a capacity for automatic oil discharge it is advantageous to insert a probe capable of differentially sensing oil and water through the oil reservoir in the upper part of the apparatus. This probe may comprise a POINTEK capacitative probe model CLS100 sold by Milltronics 30 (http:/www.milltronics.com). The probe typically includes sensing means responsive to a change in condition from immersion in water to immersion in oil. The sensing means is disposed within the vessel so as to detect the maximum oil volume allowed. On reaching the maximum oil volume the sensing means activates the oil discharge line for example by activating a solenoid switch on WO 01/54788 PCT/AUO1/00078 9 the oil discharge line. At the same time the probe preferably causes the discharge of clean water to be arrested. When the probe detects the presence of water, part of the oil has been 5 removed. Preferably after the elapse of a set time lag, the probe causes the discharge of oil to be arrested. At the same time, the probe preferably causes the discharge of clear water to recommence. It is preferred that the oily water inlet is elongated and extends laterally. 10 If the top of the apparatus is closed, the vessel may also include an air bleed to allow any gas which collects in the vessel to be removed adjacent the top of the vessel. 15 In an alternative though less preferred embodiment a reservoir of oil in the form of a layer is retained below a perforated cross-plate and adjacent the underside thereof by the downward flow of liquid through the plate. The size of the holes in the plate and the flow rate through the plate are such that said layer of oil is retained below the plate and oily water passes through the layer of oil as 20 discrete water-in-oil droplets formed on the underside of the plate adjacent the holes. When a plurality of such water in oil droplets is formed on the underside of the cross-plate, the continuous oil phase surrounding these water-in-oil droplets 25 may be very thin, and the shape of said droplets may be influenced by the close proximity of other droplets, possibly leading to the formation of a honeycomb effect wherein the boundaries of the cells comprise oil and the discrete inner part of the cells comprise water. The water-in-oil droplets or globules have the appearance of bubbles and may be visible on the underside of the oil layer 30 which is located beneath the oil-retaining plate. The improved performance of the apparatus is due at least in part to the passage of oily water through the oil layer in the form of water-in-oil droplets or WO 01/54788 PCT/AUO1/00078 10 globules. Without wishing to be bound by theory we, believe this provides a high surface area across which oil and water separation occurs within each droplet. A number of embodiments of the invention will now be described and 5 exemplified with reference to the accompanying drawings. Figure 6 and the accompanying description relate to the most preferred embodiments of the invention. In this embodiment the oil reservoir is located adjacent the top of the vessel. Figures 1 to 5 relate to less preferred embodiments in which oil is retained below a plate. 10 In the drawings: Figure 1 is a schematic vertical section of an apparatus according to the invention. 15 Figure 2 is a cross section of the apparatus of Figure 1 at the Line AA'. Figure 3 is a schematic vertical section of a further embodiment of an apparatus according to the invention. 20 Figure 4 is a cross section of the apparatus of Figure 3 at the Line B-B' with the top wall (20) cutaway. Figure 5 is a schematic vertical section of an apparatus according to 25 another embodiment of the invention which includes netting. Figure 6 is a schematic vertical section of a particularly preferred embodiment of the apparatus of the invention. 30 Referring to Figures 1 and 2 drawing there is shown an apparatus of the invention (1) including a vessel (2) having a closed top end (3) and closed bottom end (4) and provided with an inlet for oily water (5) and an outlet for separated water (6) disposed below the inlet (5).

WO 01/54788 PCT/AUO1/00078 11 A cross-plate (7) is provided which in operation accumulates and retains a reservoir of oil (8) adjacent the underside. This embodiment is less preferred. The oil retaining plate extends across the vessel in the downward flow path of liquid between the oily water inlet (5) and separated water outlet (6). The cross 5 plate has a multiplicity of holes (9) spaced apart across the plate. A distributor plate (11) is provided immediately below the inlet and above the oil retaining plate. The distributor plate has holes (12) offset from the flow path of holes (9) of the cross-plate (7) and operates to provide a more uniform down 10 flow of oily water from the oily water inlet (5) through plate (7). An upper plate extends across the vessel adjacent the upper extremity of the oily water inlet (5). The upper plate is provided with holes (14) which allow passage of oil to form a reservoir (15) adjacent the top of the vessel (3). The 15 upper plate reduces turbulence created at the oil water interface by the influent stream at the oily water inlet. It therefore significantly reduces and generally avoids formation of an oil haze. The region in which oil collects below the cross-plate (7) may be provided with an outlet (16) to allow excess oil to be removed. 20 In operation the vessel is filled with oily water and a flow rate established to retain a reservoir of oil adjacent the underside of the cross-plate (7). The reservoir (8) may be established by running this system for a period of time under the appropriate conditions or by introducing oil. When the appropriate 25 flow rate and conditions are achieved the oily water will form water-in-oil droplets adjacent the holes (9) in the oil retaining plate on the underside 7(a) of the plate (7). The appropriate flow rate will depend on the size and number of the holes but can be determined without undue experimentation using the procedure described in the examples of series A below, or a similar procedure. 30 Referring to Figure 3 and Figure 4 there is shown another embodiment of the apparatus of the invention. In this embodiment the oil reservoir is retained under the cross-plate but means is provided for the oil (32) under the cross plate to move to another reservoir at the top of the apparatus. The vessel (2) WO 01/54788 PCT/AUO1/00078 12 has a top wall (20) provided with an oil outlet (21). The separation vessel (2) includes a partition wall (22) which extends from the top wall (20) and between one portion of side wall (23a) and another portion of the side wall (23b). 5 The partition wall may be straight or curved to increase the relative size of the oil retaining plate. An inlet (24) for the mixture to be separated is adjacent the top wall (20) and an outlet (25) for purified water is provided below the partition wall (22) to provide a 10 down flow passage (26) on the inlet (24) side of the partition (22). An oil retaining plate (27) extends across the down flow passage (26) between the partition wall (22) and vessel wall on the facing side (28). The partition wall (22) extends below the oil retaining plate (27) to provide a submerged weir (29). 15 During operation an oil layer (32) builds up on the underside of the oil retaining plate (27) as a result of coalescence of oil droplets and the oil layer builds up until it reaches the bottom (30) of partition wall (22). Further coalescence of oil causes the oil layer to pass beneath the partition wall (22) and rise into an oil collection space (31) on the side of the partition wall (22) remote from inlet (24). 20 Oil floats into the oil collection space (31) and may be collected in a header tank (34) through an oil outlet (21) in the top wall. Referring to Figure 5 there is shown an embodiment of the invention including a 25 vessel (40) having closed top (41) and closed bottom wall (42) a side wall (43) provided with an inlet (44) for oily water and in the upper portion and an outlet for purified water (45) in the lower portion of the side wall (43). An oil retaining plate (46) extends across the vessel (40). The oil retaining plate 30 retains a layer or reservoir of oil (47) on the underside thereof. Netting (48) in the oil layer (47) creates a tortuous path for the mixture to be separated but freely allows passage of fine grit which tends to clog conventional oil filters. The netting (33) is "SARLON" brand polypropylene netting of strands WO 01/54788 PCT/AU01/00078 13 each comprising three plaited filaments of 0.3 mm diameter and having mesh dimensions of 20 mm x 20 mm. The netting (48) is folded and compressed between the oil retaining plate (46) 5 and a lower perforated plate (49). The lower perforated plate is provided with holes which allow free passage of fluid. The size of holes in the perforated plate (49) is not critical as its primary function is to retain the netting (48) in a compressed state. The netting significantly improves the efficiency with which oil coalesces particularly when the netting is coated with a coating which 10 includes a fluoro alkyl polymer. In a specific embodiment the vessel of Figure 5 is 250 mm in diameter 400 mm deep and there is a separation of 200 mm between the oil retaining plate (46) and lower perforated plate (49). Oily water may be fed into the inlet at 6.5 L per 15 minute to provide effective oil/water separation. In the drawings Figure 6 shows a particularly preferred apparatus in accordance with the invention (51) which includes a vessel (52) having a sidewall (53) top wall (54) and bottom wall (55). The side wall (53) is provided with an inlet (56) 20 for oily water adjacent top wall (54), an outlet (57) for purified water adjacent the bottom wall (55) and an outlet (58) for oil in the top wall (54). A first perforated plate (59) extends to the housing wall (53) and is disposed between in inlet (56) for oily water and the outlet for purified water (57). A second perforated plate (60) disposed beneath the first perforated plate (59) and spaced below the 25 second plate (60) is a volume of netting (61) packed firmly into the bottom portion of the vessel (52). A probe (62) is provided extending into the vessel and including a oil detection means (63) for producing a signal when the water phase which it contacts under normal operating conditions is replaced by oil as the volume of separated oil increases. 30 To operate the apparatus a volume of oil (64) is established having an oil/water interface (65) below the oily water inlet (56) and above .the oil detection means and oily water mixture to be separated is fed into the inlet (56) to produce a flow of oily water downward through the plates (59, 60) netting (61) and the purified WO 01/54788 PCT/AU01/00078 14 water is delivered through outlet (57). The oil/water interface (65) is spaced above the first plate (59) to provide a zone of predominantly water between the first plate (59) and oil/water interface (65). The flow of oily water into the vessel (52) from inlet (56) produces turbulence in this zone and this zone may contain 5 up to 20% oil. The flow rate and the hole diameter of the first plate may be correlated to achieve optimum performance. The function of the first plate (59) is to confine the high turbulence regime above the first plate and to create a relatively quiet, 10 lower turbulence region between the first (59) and the second plate (60), which permits coalesced droplets between the plates to rise by density difference back to the upper region. If the flow rate is too high and/or the hole diameter too small then oil will be prevented from rising through the plate. On the other hand the holes should provide some impediment to turbulent flow. A further function 15 of the first plate is to provide a uniform velocity profile across the apparatus. The zone (67) between the first and second plates is substantially less turbulent as is evident from relatively uniform gentle flow. 20 The size of the holes in the second plate is less critical but they will generally be large enough to allow a steady flow and to allow oil droplets to rise through the plate. The second plate (60) produces a relatively still zone (68) immediately beneath. 25 The invention will now be described with reference to the following examples. It is to be understood that the examples are provided by way of illustration of the invention and that they are in no way limiting to the scope of the invention. In the following examples series A including experiments Al to A13 relate to 30 less preferred embodiments wherein the reservoir of oil is located underneath a cross-plate. Examples I to 3 relate to the more preferred embodiment where an oil reservoir is provided at the top of the vessel.

WO 01/54788 PCT/AUO1/00078 15 Examples: Series A Specifying the parameters of the apparatus of the invention 5 The apparatus of the invention is characterised by such parameters as: - the number of holey plates used - the material of construction of the holey pates - the separation between the plates - the positions of the plates relative to the flow entry and flow exit ports 10 - the geometry of the influent pipe (which may be drawn out to a rectangular cross-section to direct influent flow between the holey plates - the diameter of the holes in the plates (which may or may not be uniform) - the spatial distribution of holes in the plates - the degree of alignment or non-alignment of holes in the proximal plates 15 - the recommended flow rate of influent liquor - the spatial dimension and shape of the chamber in which oil-water separation occurs - the properties of the oil to be separated from the aqueous phase - the properties of the aqueous phase (e.g. concentration of salt or suspended 20 solids). In the following examples of Series A, a diagnostic method is provided to establish appropriate choices for the parameters of the apparatus of the invention. The diagnostic method is based on: 25 e Forming a cavity in which the oil-in-water separation will take place, said cavity comprising a liquor inlet port in the side of the cavity and a liquor outlet port, located below the inlet port in the cavity. Conveniently the top of the cavity is open to air and the material defining the cavity is transparent. 30 e Adding a quantity of water and a quantity of oil to the cavity. 0 Forming a plate stack, comprising one or more horizontally disposed holey plates which are secured on an all-thread stand comprising three vertical supporting all-thread members. 35 WO 01/54788 PCT/AUO1/00078 16 Inserting the plate stack into the cavity so that a snug fit is obtained and so that the great majority of fluid flow occurs through the holes of the plates, rather than through the peripheral space where the plates encounter the inner wall of the cavity. When the plate stack has been inserted into the 5 cavity, the floating oil layer in the cavity should (a) cover the top plate by 10mm or more, and (b) extend down to the bottom plate and preferably below the bottom plate for a further 10-20mm or more. 10 The water in the cavity should extend from the bottom of the oil phase to the base of the cavity. At least one plate should be located underneath the inlet port, and other plates may be located above the inlet port, or underneath the inlet port. The liquor outlet port should be positioned below the lowermost plate, and preferably at least 30cm below the lowermost plate. 15 * Pumping water in through the liquor inlet port at the design flow rate, and taking the liquor leaving through the outlet port and re-circulating to the inlet port. 20 The following criteria may be used to specify the parameters of the apparatus of the invention, using the diagnostic method : C1 (the defining criterion): Under the influence of water pumping into the oil separation cavity from the inlet port at the design flow rate, a 25 continuous oily region should be maintained in the region proximal to and below at least one of the plates located underneath the inlet port, and the transit of aqueous phase through said continuous oily region should be substantially in the form of water-in-oil globules. 30 C2 (a criterion of improvement): Under the influence of water pumping into the oil separation cavity at the design flow rate, and with respect to the plates below the inlet port the oil initially present in the region above and proximal to said plates should be displaced by the aqueous phase.

WO 01/54788 PCT/AUO1/00078 17 C3 (a further criterion of improvement): Under the influence of water pumping into the oil separation cavity at the design flow rate, and with respect to the plate immediately above the inlet port, and the plates below the inlet port, the oil initially present in the region between said plates 5 should be substantially displaced by the aqueous phase. Apparatus Used for Experiments in Series A Plates were made from polypropylene, polyethylene, nylon and PVC. The plates 10 were of circular cross section with diameters of 189cm, and were 3mm thick. The plates were perforated with equally spaced holes on a square lattice with the centers of the holes 13mm apart. The diameters of the holes were uniform for each plate. In various experiments plates having holes of different diameters from 4 - 6mm were used. In each plate, 3 additional 6mm holes were cut to 15 enable the plates to be threaded on a 3-member all-thread stand. The oil-water separation cavity was defined by a cylindrical perspex pipe glued to a flat perspex base. The cavity (formed by the inner diameter of the pipe) was 189cm in diameter and the height was 280mm. The top of the cavity was open 20 to the air. The inlet to the cavity was located 35mm from the top, and comprised a rectangular slit which was 4mm high and 50mm wide. The outlet from the cavity was 10mm from the bottom of the cavity. The stack comprised 3 plates with adjacent faces spaced 5mm apart. The plates were located on the 3 member all-thread stand and the gaps between the plates were maintained by 25 polycarbonate 5mm sleeve tubing sections which were inserted over the stainless steel all-threads between the plates. The top plate was positioned 0.25mm above the top of the inlet rectangular slit and the middle plate was positioned 0.25mm below the bottom of the inlet rectangular slit. The middle plate was offset (rotated) by 1200 from the top plate, so that the holes were not 30 aligned. The bottom plate was spaced 5mm below the bottom face of the middle plate, and offset (rotated) by a further 1200. Note: the middle plate was designed to act as a flow equalizer plate, and the bottom plate was designed to act as the oil retaining plate.

WO 01/54788 PCT/AUO1/00078 18 A. Johnson P.75 diaphragm pump was run from a 12V DC source, and operated at a fixed flow rate of 6.5 litres/minute. 5 Experimental Process - Experiment Al According to the diagnostic method discussed previously, water and diesel oil were added to the cavity of the apparatus described above, and the 3-plate stack described above was inserted into the cavity. All plates were made from 10 nylon, and the diameter of the holes in each of the plates was 4mm. After insertion of the stack, and before the pump was switched on, the top of the diesel oil layer was 10mm above the upper face of the top plate, and the bottom of the layer was 35mm below the lower face of the bottom plate (total height of oil layer =60mm). 15 The purpose of the experiment was to determine whether or not the apparatus as described meets the defining criteria of the invention (Cl), and whether or not the apparatus meets the criteria of improvement (C2) and (C3). 20 Within 20 seconds of commencing the pumping of water through the inlet slit at 6.5 L/minute, (i) a uniform layer of water-in-oil globules was formed under the continuous oil layer located under the third plate. This result means that criteria C1 was satisfied; and 25 (ii) substantially all of the oil phase between the plates had been displaced by influent aqueous phase. This result mean that criteria C2 and C3 were satisfied. Experiment A2 30 Conditions were as for experiment Al except that the three plates were fabricated from high density polyethylene (HDPE) and the hole sizes in all the plates was 5mm.

WO 01/54788 PCT/AUO1/00078 19 Within 20 seconds of commencing the pumping of water through the inlet slit at 6.5 L/minute, (i) a uniform layer of water-in-oil globules was formed under the third plate this result means that criteria C1 was satisfied; 5 (ii) oil initially present above and proximal to the second and third plates was displaced by aqueous phase. This result means that criteria C2 was satisfied; and (iii) significant quantity of oil phase remained underneath the second plate. This result mean that criteria C3 was not satisfied. 10 Thus in A2, the apparatus was configured according to the invention at a flow rate of 6.5 L/minute, however optimal behaviour was not achieved. Experiment A3 15 PVC plates, 5mm hole diameters in each plate. Criterion C1 and C2 were satisfied but a distinct layer of diesel remained in place underneath the second plate (less than in A2). Thus in A3, the apparatus was configured according to the invention at a flow rate of 6.5 L/minute, however optimal behaviour was not achieved. 20 Experiment A4 PVC plates, 6mm hole diameters in each plate. Criteria C1 and C2 were satisfied but considerable quantities of diesel remained in place underneath the second plate (more than in A2). Thus in A4, the apparatus was configured 25 according to the invention at a flow rate of 6.5 L/minute, however optimal behaviour was not achieved. Experiment A5 HDPE plates, 4mm hole diameters in each plate. Criteria C1, C2 and C3 were 30 satisfied. Experiment A6 HDPE plates, 6mm hole diameters in each plate. Criteria C1 and C2 were satisfied, however C3 was not satisfied.

WO 01/54788 PCT/AUO1/00078 20 Experiment A7 Nylon plates 5mm hole diameters. Criteria C1 and C2 were satisfied, however C3 was not satisfied. 5 Experiment A8 PVC plates, 4mm hole diameters. Criteria C1, C2 and C3 were satisfied. Experiment A9 10 PVC plates, top plate with 5mm hole diameters, middle and bottom plate with 4mm hole diameters. Criteria C1 and C2 were satisfied. Criteria C3 was not satisfied. Experiment A10 15 PVC plates, top plate with 4mm hole diameters, middle plate with 5mm hole diameters, bottom plate with 4mm hole diameters. Criteria C1, C2 and C3 were satisfied. Experiment Al1 20 PVC plate, top plate with 6mm hole diameters, middle plate with 5mm hole diameters, bottom plate with 4mm hole diameters. Criteria C1 and C2 were satisfied, C3 was not satisfied. Experiment A12 25 PVC plates, top plate with 4mm hole diameters, middle plate with 6mm hole diameters, bottom plate with 4mm hole diameters. Criteria C1 and C2 satisfied. C3 not satisfied. Experiment Al 3 30 In this experiment, an oil water separator according to the current invention (configured as in experiment A8) was used to separate an oily-water influent stream (no recycling was carried out). 200mis per minute of diesel oil was dosed into an aqueous stream to provide a total influent flow rate of 6.5 Litre/minute. Water-in-oil globules formed underneath the third plate and as WO 01/54788 PCT/AUO1/00078 21 more oil was added in the influent stream, the thickness of the globular layer increased from 1cm to 20cm. The aqueous exit stream from the apparatus contained less than 20ppm of oil in water. 5 Example 1 An apparatus was constructed in accordance with the embodiment of Figure 6 of the drawings and above description. 10 The vessel was constructed as a vertical cylinder of diameter 188 mm and 500 mm height. Prior to commencing flow of oily water the vessel was filled with water and a volume of oil added at the top to produce an oil zone or reservoir (64). The 15 initial oil charge was 2 Litres, and comprised 20W40 brand motor lubrication oil (Shell Australia). A zone (66) primarily of water was provided separating the oil reservoir from the first plate (59) by about 50mm. The first plate had holes of 8 mm diameter and a pitch (hole to hole) distance of 13mm. The separation of the first and second plate was about 50mm. The second plate had holes of 4mm 20 diameter and a pitch distance of 13mm. Polypropylene bird netting was cut into a 15m x 2m portion and was dipped into a "Ricaphob EP 191" brand liquor comprising 5% perfluorinated polymer in white spirit. This liquor, Ricaphob EP 191, was provided by RCA International of 25 3 Pilgrim Court, Ringwood, Melbourne, Victoria 3134 Australia. After dipping, the netting was allowed to drain overnight and the hydrophobic coating was dried on the netting in an oven at 60 0 C for 2 hours. The coated netting was then packed with random folds into the vessel and compressed downward to form a tight packing which abutted the vessel bottom wall and side wall to a 30 level within the vessel about one third to a half of the vessel volume. Oily water containing "20W40" brand motor lubrication oil (Shell Australia) at 0.5 - 5% was pumped into the oily water inlet at a rate of 4-8 litres per minute. The oily water also contained clay particles of up to 4mm diameter.

WO 01/54788 PCT/AUO1/00078 22 The apparatus provided progressively less turbulent zones along the flow path of liquid within the vessel. The zone (66) above the first plate (59) was relatively turbulent, the zone (67) between the first plate (59) and the second 5 plate (60) was relatively quiet. The oil content of these zones (66, 67, 68) was approximately 20%, 2% and 0.2% by weight respectively. The clay particles passed through the netting and therefore did not interfere with flow or operation of the apparatus. These particles may be removed by filtration 10 or flocculation if desired and are generally much easier to remove after oil/water separation. An oil detection probe was used to produce a signal which actuated delivery of oil from the oil reservoir (64) at the top of the vessel. The probe provided a 15 signal in response to cessation of contact with water so that on complete immersion in oil it caused oil to be delivered to a predetermined level. The treated water contained less than 10 ppm of oil. 20 Example 2 An apparatus for separation of oil and water from mixtures thereof was constructed in accordance with Figure 6 of the accompanying drawings. 25 The inlet for oil water was 60 mm below the top (54) of the vessel and the first plate (59) was spaced 150 mm below the top wall (54). The first plate (59) was 1mm thick and contained holes of 4mm diameter providing a fraction hole surface area of 10%. 30 A second plate (60) also of 1mm thickness was provided 50mm below the first plate and had a hole size of 8mm diameter and fraction hole surface area of 20%.

WO 01/54788 PCT/AUO1/00078 23 The bottom wall (55) of the vessel was spaced at 450mm below the second plate and netting was packed adjacent the bottom wall (55) of the vessel (52). The packing of netting extended from the bottom wall to 50 mm below the second plate. 5 The netting (61) was 750 g of white "SARLON" brand polypropylene bird netting sold by Hoogies of Yarra Glen, Melbourne. The netting comprises strands comprising three plaited filaments at 0.3 mm diameter with mesh dimensions (extended ) of 20 mm x 20 mm. 10 To operate the apparatus a reservoir of oil (64) at the top vessel and extending below the top wall (54) was used to provide an oil/water interface (65) about 90mm below the top wall (54). 15 The polluted influent stream contained 2% w/w Corena CH46 compressor oil (sold by Shell Australia) in 98% water. The polluted stream was contained in a collector vessel and delivered to the apparatus of the invention by a Johnson P75 diaphragm pump driven by a 12V DC power source and running at 5 litres per minute. 20 The diameter of the apparatus was 188mm. At a flow rate of 5 litres per minute, this corresponds to a value of Vmax = 18 cm/minute. The oil reservoir (64) in the apparatus comprised Corena CH46 compressor oil. 25 After intermittent operation over a period of 6 weeks the level of total oil and grease in the clean water discharge liquor was less than 7ppm (solvent extraction methodology). Example 3 30 An apparatus in accordance with Example 2 was constructed having the following dimensions: (a) diameter 380mm; (b) inlet (56) spaced 40mm below top wall (54); WO 01/54788 PCT/AUO1/00078 24 (c) an oil reservoir (54) extending to provide an oil/water interface about 50 mm below the inlet (56) for oily water; (d) a first perforated plate (59) about 60mm below the oil/water interface and being constructed of 1.2mm thick stainless steel and having 4mm 5 holes providing a hole fraction area of 10%; (e) a second perforated plate (60) was spaced 150mm below the first plate (59); (f) the netting was packed to a height of 600mm above the bottom wall (55) which was spaced 1.2 metres below the second plate (60); 10 The polluted influent stream comprised 5% of brand Diala BX transformer oil as supplied by Triton Petrochem of Melbourne, Australia, in 93% water and 2% clay. 15 The polluted stream was contained in a collector vessel and delivered to the apparatus of the invention by a Johnson P75 diaphragm pump driven by a 12V DC power source and running at 5 litres per minute. The oil reservoir (54) in the apparatus comprised Diala BX transformer oil. After 20 intermitted running for 24 hours the level of oil in the clean water discharge was less than 2 ppm. Those skilled in the art will appreciate that there may be many variations and modifications of the configuration described herein which are within the scope of 25 the present invention.

Claims (25)

1. An apparatus for the separation of water and oil from a mixture thereof comprising: 5 0 a separation vessel within which oil and water are to be separated; * an inlet for the mixture to be separated; e an outlet for separated water disposed below the inlet and providing a downward flow of mixture within the vessel; and at least one cross-plate extending across the vessel in the flow path between 10 the inlet and outlet and provided with a plurality of holes for controlled passage of the mixture.

2. An apparatus according to claim 1 wherein the diameter of the holes is in the range of from 0.5mm to less than one fifth the diameter of the plate and the 15 sum of the area of the holes in the plate is in the range of from 5 to 70% of the plate area.

3. An apparatus according to claim 1 wherein the maximum linear average down flow velocity of the mixture is less than 100cm per minute. 20

4. An apparatus according to claim I wherein the cross-plate has a thickness in the range of from 0.25mm to 10mm.

5. An apparatus according to claim 1 wherein at least one cross-plate is 25 formed of metal or surface coated metal.

6. An apparatus according to claim 5 wherein the plate is formed of a metal coated with powder coating or perfluoropolymer. 30

7. An apparatus according to claim 1 wherein the contact angle of oil droplets on the surface of the cross-plate in a water medium is greater than 200.

8. An apparatus according to claim I wherein the vessel has a cylindrical side wall and vertical axis. WO 01/54788 PCT/AUO1/00078 26

9. An apparatus according to claim 1 comprising a first cross-plate and a second cross-plate. 5

10. An apparatus according to claim I wherein the inlet for the mixture is elongate and extends laterally.

11. An apparatus according to claim 1 including a first cross-plate and a second cross-plate below the first cross-plate and separated therefrom by a 10 distance of from a minimum of 10mm to a maximum of twice the diameter of the first plate.

12. An apparatus according to claim 1 further comprising an oil reservoir through which the mixture passes. 15

13. An apparatus according to claim 12 wherein the oil reservoir extends from above to below the vessel inlet.

14. An apparatus according to claim 12 wherein a layer of oil is retained 20 below a cross-plate adjacent to the underside thereof by downward flow of the mixture.

15. An apparatus according to claim 1 wherein the vessel comprises a top wall, a bottom wall and a side wall and at least two said cross-plates are 25 present including a first cross-plate and a second cross-plate vertically spaced below the first cross-plate and the apparatus further comprises hydrophobic netting packed with the vessel between the second cross-plate and the outlet for purified water. 30

16. An apparatus according to claim 15 wherein the mixture is introduced to a reservoir of oil and the cross-plates produce zones of progressively less turbulence toward the outlet for purified water. WO 01/54788 PCT/AUO1/00078 27

17. An apparatus according to claim 1, claim 11 or claim 15 including an oil reservoir adjacent the top wall separated from a predominantly aqueous phase by an oil water interface spaced above the first cross-plate and wherein the top wall includes an outlet for delivery of oil from the oil reservoir. 5

18. An apparatus according to claim 1, claim 11 or claim 15 further comprising a probe for detecting a maximum volume of oil, wherein the probe includes sensing means disposed within the vessel the sensing means being responsive to a change in condition from immersion in water to immersion in oil 10 to cause discharge of oil from the oil outlet.

19. An apparatus according to claim 18 wherein the sensing means produces an arrest in the lower outlet flow during oil discharge. 15 20. An apparatus according to claim 18 wherein the probe is responsive to a change in condition from immersion in oil to immersion in water to cause the discharge of oil to be arrested and the discharge of purified water from the lower outlet to recommence.

20

21. An apparatus according to claim 1, claim 11 or claim 18 wherein the top wall is provided with an air bleed to allow gas collecting within the vessel to be removed.

22. An apparatus according to claim 15 or claim 18 wherein the netting is 25 formed of a plastics material selected from the group consisting of PVC, polyolefins and mixtures of two or more thereof and the net includes strands of diameters in the range of from 10 to 1000 microns and spacing between strands of from 1mm to 50mm. 30

23. An apparatus according to claim 15 or claim 18 wherein the netting has a coating of fluorinated compounds for increasing the hydrophibicity of the netting. WO 01/54788 PCT/AUO1/00078 28

24. An apparatus according to claim 18 further including a polishing module comprising a fibre mat extending across the flow path of the vessel the fibre mat being formed of an oleophilic fibre material. 5

25. An apparatus according to claim 24 wherein the fibre mat includes a oleophilic fibre and a structural fibre and is anchored between a pair of opposing porous plates.