FIELD OF INVENTION This invention is concerned with a method and apparatus for separation of liquids of differing densities and in particular to separation of oleaginous materials from water.

BACKGROUND ART

Effective separation of oil/water mixtures and aqueous emulsions of water has long been a problem in many industries such as on shore and off shore oil drilling operations, petroleum refining operations and waste water treatment processes associated with the chemical industry municipal sewage treatment etc.

Although many prior art processes for separation of oil from waste water have been crudely efficient, increasing environmental concerns have imposed stringent requirements on waste water quality in an endeavour to reduce environmental pollution.

Whereas hitherto the dumping into the ocean of relatively small quantities of oily substances such as bilge water from marine vessels, primary water separated from extracted oil on an offshore drilling platform, treated primary sewage outflows and the like has been considered unacceptable but to some extent inevitable due to relatively inefficient separation systems, current environmental considerations require more cost efficient and effective systems.

Moreover, in order to reduce the contamination by oil wastes of storm water drains, local government regulations increasingly require oil separation units to be incorporated with storm water drainage systems of all commercial premises. This is a particular requirement in the case of engineering shops, auto service stations and the like where lubricant spillage

and washing of oily components is likely to occur.

The plethora of prior art references relating to separation of oil from water demonstrates a continuing need for improvement in apparatus and methods of this kind.

Probably the simplest and most commonly employed means for separation of oil from water is a plate separator of the type generally described in British patent specification GB-A-2116060. A conventional plate separator system typically comprises a gravitational separation zone, a plate pack separation zone and a final polishing filter to achieve a high level of separation below, say, 15 parts per million of oil/water. The system of GB-A-2116060 offers a more efficient plate pack separator by recognising that the positioning of a flow pump on the upstream side of the system increases shear on the oil/water mix with a consequent reduction in oil droplet size. By placing the flow pump on the downstream side of the system, oil droplet size in the delivery flow is not reduced.

Plate separators are generally suited to mixtures where the oil droplet size is relatively large. A major difficulty with plate separators however is a low throughput rate and the requirement for frequent cleaning of the plates. If a final polishing filter is employed, this must also be replaced on a frequent basis.

Another type of oil/water separator is a gravitational separation which selectively recirculates differing dispersion phases of an oil/water emulsion to achieve separation of the oil and water. International Patent Application No. PCT/US91 /02887 describes such an apparatus. Coalescence separators are a variation on a plate separator system which provides a plurality of surfaces upon which very small oil droplets can

collect and coalesce.

United States Patent No. 4129500 describes a porous coalescing apparatus while the apparatus of International Patent Applications PCT/NO92/0065 and PCT/GB91 /01867 provide a series of concentrically arranged downwardly divergent conical surfaces for coalescence. Australian patent specification AU-B- 58674/80 describes a coalescer having a series of concentrically arranged upwardly divergent conical surfaces.

A major disadvantage associated with the above coalescence separators is that they are contained in sealed chambers and thus are difficult and inconvenient to clean on a regular basis. Australian patent specification No. AU-B-71705/81 describes a cylindrical container where an oil/water mixture is delivered tangentially to create a vortex in the container with an air column extending to an outlet in the centre of the floor of the container. Separation of the oil from water is achieved by centrifugal force as the mass of liquid rotates in the container.

It is considered that the energy requirements to maintain a stable air column in the vortex are excessive but in any event another separation means such as a hydrocyclone is required downstream to effect a further separation of oil from the output of the vortex separation.

Hydrocyclones are a well known means for separation of oil and water mixtures under the influence of centrifugal force. International Patent Applications PCT/US91 /02888 and PCT/US92/03642 are illustrative of recent developments in this field and demonstrate clearly the complexity and capital expense required to improve the efficiency of hydrocyclones to separate oil and water.

Yet another method for separation of oil from

water utilises gas bubbles which adhere to oil droplets to form a froth on the surface of the liquid being treated.

One such process is described in United States patent No. 4790944 wherein a stream of contaminated liquid containing a dissolved gas is mixed with an induced gas, the multi-phase flow so produced then being subjected to turbulence and shearing to disperse the gas and then allowing the gas to expand below the surface of the contaminated liquid. The bubbles of gas rise to the surface of the liquid with contaminant particles adhering thereto.

While all of the prior art references referred to above are effective to varying degrees, none combine a high level of oil removal efficiency with compactness, low energy requirements and low capital requirements and none are really suited to separation of oil from water where the oil to water ratio in the separator may reach extreme levels. Moreover, with the sole exception of the plate separation apparatus described in GB-A-2116060 referred to above, none of the prior art references appear to have addressed the problems associated with shear and turbulent flow in oil/water separation systems. In United States patent No. 4948517 separation efficiency (%) of a water/oil mixture is defined as:

Eff = (mfcf - MwCw)/mfcf, where mf = mass flow rate of feed

Mw = mass flow rate of separated water cf = concentration of oil in feed ( g/litre) and Cw = concentration of oil in separated water

(mg/litre) . Figure 2 of U.S. 4948517 shows that with a conventional hydrocyclone separator separation efficiency decreases dramatically with a reduction in oil droplet size. In the example given, separation efficiency dropped from 97% to about 45% with a

reduction of only 40 microns in oil droplet size.

The use of an unpowered progressive cavity hydraulic motor as a throttling device is proposed in U.S. 4948517 as an alternative to a conventional metering or dump valve which imparts substantial shear to the oil/water feed in a conventional hydrocyclone, centrifuge, settling tank or a combination thereof. Control of the unpowered progressive cavity motor is achieved by a braking system to limit the rate of rotation of the rotor with minimum shear being applied to the oil/water mixture.

While generally effective for its purpose in increasing the separating efficiency (or perhaps, more correctly, preventing a reduction in efficiency) of a conventional hydrocyclone, centrifuge or settling tank, the apparatus of U.S. 4948517 is nevertheless unable to overcome inefficiencies otherwise inherent in such prior art separators.

SUMMARY OF INVENTION

It is an aim of the present invention to overcome or alleviate at least some of the disadvantages of prior art separators for removing a layer of oleaginous materials from the surface of a body of water.

According to one aspect of the invention there is provided an apparatus for separating mixtures of liquids of differing densities, said apparatus comprising:- a hollow upright chamber; an inlet port intermediate an upper and lower end of said chamber; an outlet port for one component separated from said liquid mixture, said outlet port being located adjacent said lower end of said chamber below said inlet port; a collection skimmer for collection of a less

dense component of said liquid mixture, said collection skimmer including an upper edge spaced from an interior wall of said chamber and above said inlet port, said collection skimmer including a discharge port in fluid communication with an exterior wall of said chamber to discharge said less dense component of said mixture; and, head control means for controlling, in use, a head of liquid in said chamber at a predetermined position relative to said upper edge of said collection skimmer.

The inlet port may comprise a single opening in fluid communication with the interior of said chamber or a plurality of openings. Said single opening or plurality of openings may comprise a flow path aligned radially or tangentially relative to an upright axis of said chamber.

The chamber may comprise any suitable length and cross sectional wall shape. Preferably the chamber has a circular cross sectional wall shape.

If required the chamber may be telescopically adjustable in length.

The collection skimmer suitably includes a recessed portion located inwardly of said upper edge thereof, said recessed portion being in fluid communication with said discharge port.

Suitably the collection skimmer includes an upwardly divergent lower wall surface. Preferably the lower wall surface of said collection skimmer has an upwardly divergent frusto- conical shape.

If required the recessed portion of said collection skimmer comprises a downwardly convergent frusto conical shape.

Suitably the discharge port of said collection skimmer is in fluid communication with an upright

tubular discharge conduit located centrally of said chamber to define a chamber having an annular cross section.

Preferably said discharge conduit extends through a floor of said chamber.

The upper edge of the collection skimmer may be axially adjustable relative to said chamber to selectively vary a fluid flow path in said chamber.

A plurality of uprightly spaced liquid mixture inlet ports may be associated with said chamber to selectively vary a fluid flow path in said chamber.

If required, means may be provided to selectively vary a spaced between said skimmer upper edge and said interior wall of said chamber to modify a flow of liquid therebetween.

The head control means may comprise any suitable means for maintaining the level of said one component at a predetermined position relative to said skimmer upper edge. The head control means may comprise flow control means coupled to a sensor means, said sensor means being selectively positionable in association with said chamber.

The head control means may comprise a pressure control means in use associated with a source of pressurised liquid mixture entering said chamber.

Alternatively the pressure control means may be associated with said outlet port in use to apply a predetermined pressure to said one component. If required a plurality of apparatuses according to the invention could be connected in series with the outlet port of an upstream apparatus being in fluid communication with an inlet port of a downstream apparatus. According to another aspect of the invention there is provided a method of separating layers of liquids of differing densities, said method comprising

the steps of : - introducing into the inlet port of an apparatus according to the invention a mixture of liquids of differing densities at a predetermined pressure whereby one component of said mixture flows in a generally downward direction at a predetermined velocity such that at least a major portion of a less dense second component is allowed to rise to the surface of said one component countercurrent to the flow of said one component; and, allowing said less dense component to flow over the upper edge of said collection skimmer for collection via said discharge port.

If required the method may be carried out on a plurality of apparatuses according to the invention, the outlet port of an upstream apparatus being in fluid communication with the inlet port of a downstream apparatus.

Suitably the method comprises a continuous process.

Alternatively the method comprises a batch process or semi-continuous process wherein the one component obtained from the outlet port is recycled to the inlet port.

BRIEF DESCRIPTION OF DRAWINGS In order that the invention may be more readily understood and put into practical effect, reference will now be made to preferred embodiments illustrated in the accompanying drawings in which FIGS 1-3 show schematically a side elevational cross sectional view of one embodiment of the apparatus during differing phases of operation.

FIG 4 shows a cross sectional view of an alternative embodiment to the apparatus of FIGS 1-3.

FIG 5 shows an oil separation system according to yet another embodiment of the invention.

DETAILED DESCRIPTION In FIGS 1-3 the apparatus comprises a cylindrical chamber 1 having an open upper end and a lower end closed by floor 2. A generally frusto conical collection skimmer 3 having a recessed inner portion 4 is located within the upper part of chamber 1. A discharge conduit 5 connects with a discharge port 6 associated with recessed inner portion 4. Discharge conduit 5 extends through the floor 2 of chamber 1 to form a generally annular cavity 7 therein.

Located intermediate the upper and lower ends of chamber 1 is an inlet port 8 to receive a mixture of at least two liquids having differing densities. An outlet port 9 is provided towards the lower end of chamber 1 to allow egress of one component separated from the feed mixture.

The outlet port 9 of chamber 1 is connected adjacent the base of a liquid head control means 10. Head control means 10 comprises a tubular body 11 with a height adjustable overflow conduit 12 located within body 11.

As shown in FIGS 1-3, the outlet of overflow conduit 12 is in fluid communication with a pump 13 the outlet of which is connected to inlet port 8 thereby providing a closed system for recirculating the more dense underflow while the less dense overflow collected by collection skimmer 3 is collected via conduit 5. The system is initially charged with say an oil/water mixture scavenged from a ships's bilges via conduit 14. When the system is initially filled with liquid, valve 15 is closed to enable recirculation of the underflow from outlet port 9. Initially, as shown in FIG 1, the oil feed mixture will contain a high oil/water ratio as typically scavenging is achieved via a floating inlet

nozzle (not shown) adapted to float just below the oil/water interface.

The high oil/water ratio initially enters chamber 1 as large oil particles which readily coalesce and float to the top of oil/water mixture as a layer 16 of substantially pure oil.

The velocity of the recirculating underflow is adjusted to achieve a laminar flow such that Stokes' law is applicable to droplets of oil endeavouring to rise under the influence of buoyancy due to specific gravity differences but against viscous drag of a downwardly directed flow of water.

As shown in FIG 1 there is a distribution in the diameters of oil droplets in the chamber 1. Clearly, larger diameter droplets are more concentrated towards the oil/oil-water mixture interface 17 as they are more buoyant but also due to the greater population density of larger droplets in this region coalescence occurs more readily to create even larger, more buoyant droplets.

Towards the floor of chamber 1 , the droplet distribution is more sparse and droplet diameter becomes progressively smaller.

In a theoretical model oil droplets above a certain size should rise and coalesce due to buoyant forces whereas droplet sizes below a certain value should be swept towards outlet 9 by their inability to resist the viscous drag of the downward flow of water. Similarly, in such a theoretical model there should be a critical droplet diameter where buoyant forces balance viscous drag such that droplets of that critical diameter will remain suspended in chamber 1.

There are however a number of factors which in practice mitigate against a "stationary layer" of droplets and these factors serve to improve oil separation efficiencies.

While certain "critical diameter" particles

remain "suspended" in a substantially stationary state, smaller diameter droplets move through this stationary layer.

Coalescence due to collision between small and critical diameter particles occurs such that these coalesced particles begin to move under the influence of buoyancy forces. This in turn increases the possibility of coalescence due to collision with other critical diameter particles to form relatively large particles.

It can be seen therefore that this theoretical stationary critical layer acts to a large degree as a screen or filter to prevent small diameter particles passing to the outlet 9. In practice it can be shown that a stationary band of fluid having a higher degree of turbidity than the water above and below is attained by careful control of the velocity of fluid through the separation chamber under conditions of lamina flow. The stability of the theoretical stationary critical layer and the presence of laminar flow is supported by the presence of this band.

An apparatus according to the invention may thus comprise separation chamber(s) comprised of a transparent material or including optical viewing or other detection means to ascertain and/or control the position of the boundaries of this layer.

If required a further outlet port associated with a collection means located in the chamber could be employed to specifically remove this "band" which contains oil droplets of 20 microns or less. The portion removed could be recirculated or treated eg. by heating, centrifuging or the like to coalesce the oil droplets to assist separation before returning it to the system.

Another factor which must be taken into account is that even under ideal laminar flow conditions, the

velocity of the water diminishes to almost zero in the multi molecular layer immediately adjacent the inner wall of chamber 1 and the outer wall of conduit 5. Accordingly, as viscous drag is a function of the relative velocities of water and oil droplets in chamber 1 the effective viscous drag at the inner wall surfaces of the chamber is zero and thus even oil droplets having a diameter less than the critical diameter will be subject to buoyant forces. In practice this is manifested by the formation of an oily film caused by coalescence, the oily film creeping upwardly under the influence of buoyancy forces. As the film moves up the walls of chamber 1 and conduit 5, it increases in thickness and forms droplets which rise rapidly to the interface 17. To assist in droplet formation and removal of the slowly moving oil film from the chamber walls, one or more inwardly projecting ribs or a helical rib may be formed on the inner wall. In the initial separation stage shown by FIG 1 , there is an accumulation of "pure" oil in a layer 16. Depending upon the viscosity of the oil, this accumulated layer can displace the interface layer 17 downwardly such that the liquid in chamber 1 is pressurised by a force equal to the value of the pressure head "A" less the mass of the oil layer 16.

Depending upon the nature and viscosity of the oil to be separated from the water, the space between the upper edge of collection skimmer 3 and the inner wall of chamber 1 can be selectively varied to permit the internal pressure developed in chamber 1 to force the oil into skimmer 3 for collection via conduit 5.

FIG 2 illustrates an intermediate phase in the recirculating system of fig 1. The distribution of small oil droplets returning as underflow from outlet is diminishing and the amount of oil accumulated around the skimmer diminishes as

does the pressure head "B".

FIG 3 shows the final stage of separation of the oil water mix wherein substantially all of the oil has been removed from the mass of water contained in the system. The pressure head "C" in this case is substantially zero.

By way of illustration only, the following examples show extraction of oil from an oil/water mixture for grossly contaminated and mildly contaminated samples. EXAMPLE A

An apparatus of the type shown generally in FIG 5 was employed except three separation chambers were connected in series with the inlet of each downstream chamber connected to the outlet of an adjacent upstream chamber. The outlet of the downstream chamber was returned to a large storage tank which in turn was connected via a surface skimmer therein to the inlet of the upstream chamber to form a closed circuit.

Separation chambers 1 , 2 and 3 respectively positioned upstream, intermediate and downstream comprised the following characteristics.

Chamber Chamber Chamber

1 2 3

Diameter 210 mm 240 mm 240 mm

Height 106 mm 106 mm 106 mm

Height of skimmer ) 102.8 mm 99.9 mm 99.3 mm Lip from chamber base)

Skimmer lip diameter 195 mm 205 mm 205 mm

Height inlet from base 800 mm 800 mm 800 mm

Each skimmer was formed as a shallow frusto conical member having a sharp outer junction between the concave and convex walls. When viewed cross- sectionally, the included angle between the inner

walls was about 104° and the included angle between the outer walls was 76°.

All connecting conduits as well as the discharge conduit were 32 mm in diameter. The pump employed was a "MONO" (Trade Mark) model CP11 helical rotor pump operated at 1140 rpm with a theoretical output of 850 litres/hour actual output measured at the outlet of chamber 3 was 720 litres/hour and the difference between theoretical and actual values was ascribed to friction losses in the system and the pressure head of the separation chambers.

Initially the storage tank contained 480 litres of clean fresh water before the addition of oil. For testing purposes, valves were provided in the outlet ports of chambers 1 and 2 to facilitate taking of samples and the outlet of chamber 3 was tested at its point of re-entry into the storage tank.

With the fresh water recirculating through the system, 8 litres of fresh, unused 20w 40 motor oil was poured into the storage tank and the following concentrations of oil in water were measured from samples taken from the outlets of chambers 1 , 2 and 3. The layer of oil floating on the surface of the water was removed entirely in 10 minutes which equated to an oil/water ratio of 8 litres/120 litres.

TIME CHAMBER 1 CHAMBER 2 CHAMBER 3

1 min 31 ppm 16 ppm 23 ppm

5 min — - 90 ppm

10 min — - 620 ppm

30 min - - 400 ppm

The grossly oil contaminated sample of water equated to about 66,600 ppm, far in excess of a typical baffle plate separator designed to operate at a contamination level of about 1000 ppm of oil in

water .

Although these results show that with continued recirculation the residual oil content of the water could be reduced even further, it should be appreciated that even at the peak oil content in the outlet water at 10 minutes, ie. 8 litres oil/120 litres water, the separation efficiency is 99.07%.

This efficiency compares favourably with a conventional plate separator which is claimed to reduce an influent oil/water concentration from 1000 ppm to 30 ppm or 97% separation efficiency. A favourable comparison is also made with the lower shear hydrocyclone of U.S. Patent No. 4948517 which claims a 97% efficiency with an influent oil concentration of 1000 ppm under ideal operating conditions.

The 10 minute and 30 minute samples were characterised by a fine pearly turbidity. After allowing both samples to stand undisturbed for about 3 days, there was clearly visible a film of oil on the surface of the 10 minute sample whereas the 30 minute sample showed a barely discernible surface oil film. Both samples showed the same degree of turbidity which remained stable in intensity. It is believed that the turbidity, and hence the relatively high oil concentrations, in the 10 minute and 30 minute samples is a function of partially soluble oil arising from the detergents added to motor oils. EXAMPLE 2

Using the same apparatus as EXAMPLE 1 and operating under the same conditions, 120 ml of distillate was added to the surface of the water in the storage tank to obtain a contamination level of 1000 ppm of oil in water. Again, the distillate layer was removed after about 10 min which corresponded to 120 litres of water being removed from the tank.

The following results were obtained at the outlet of chamber 3:-

10 min: 21 ppm

30 min: 26 ppm 60 min: 25 ppm.

The relative consistency of the results suggests that although separation of the oil from the influent water was quite effective, even in a single pass, the recirculation of the contents of the storage tank approximately twice through the system shows the formation of a relatively stable emulsion. By utilising a pump having a lower shear, it is expected that these results could be improved significantly.

Nonetheless, the results obtained were an improvement over baffle plate separators and hydrocyclones operating with a similar influent oil/water ratio to obtain an effluent ratio of 30 ppm compared with 25 ppm for the present invention.

EXAMPLE 3 A 120 ml sample of light crude oil obtained from the "Jabiru" offshore platform in north western

Australia was subjected to the same separation conditions as the distillate sample of example 2.

Although no quantitative measurements of residual oil content in the outlet water were taken, a qualitative visual inspection suggests that the degree of separation was slightly better than that for distillate.

Experiments conducted to date show the efficacy of the invention to extraction of a wide variety of oil types, viscosities etc. from water at differing oil/water concentrations.

With suitable modifications the apparatus and method of the invention may be adapted for a wide range of applications including:

Waste or process water treatment in the petroleum, chemicals, food industries.

Recovering of oil from oil water mixtures in on shore and off shore drilling operations.

Bilge water treatment for marine vessels.

Waste water treatment in commercial and agricultural processes.

Municipal sewage treatment facilities

Waste oil recovery and purification processes.

Purification of water contaminated by oil spills.

Although with refinement it is believed that the apparatus and method according to the invention may be effective in separation of oil/water mixtures rather than layered mixtures, it is considered that the primary application will be for separation of layered mixtures. In particular, the present invention may provide an alternative to settling ponds where water is drawn off at a low level and oil drawn off the surface. By utilising a storage tank (which may be heated to break emulsions or assist separation) the present invention may provide a more compact, more effective alternative to separation methods requiring settling.

By employing the present invention upstream of other oil separation systems, a very effective separation of grossly contaminated water can be achieved which enables use of an apparatus downstream for removal of small quantities of oil from water.

It will be clear to a skilled addressee that the apparatus is applicable to separation of liquids of differing densities where recovery of either or both of the high and low density liquids is required.

It will be equally apparent to a skilled addressee that many modifications and variations may be made to the invention without departing from the spirit and scope thereof. For example, FIG 4 shows some of the modifications which may be made to the apparatus of FIGS 1-3.

In FIG 4 the main separation chamber 20 may have a plurality of inlet ports 21 spaced to provide varying path distances between a given iniet port, the outlet port 22 and the upper edge of skimmer 23. Skimmer 23 is located in an outwardly divergent region 24 of chamber 20 and is axially moveable relative thereto to selectively vary the overflow gap 25 between the upper edge 26 of skimmer 23 and the inner wall surface 27 of region 24. Selective adjustment may be achieved by a screw threaded connection 28a between skimmer 23 and discharge conduit 28.

Alternatively, the chamber 20 may be cylindrical and a plurality of skimmers of differing diameter may be employed for this purpose.

The liquid head 29 in chamber 20 may be adjusted as required by a telescopically adjustable overflow conduit 30 in head control means 31.

In other modifications of the invention, the or each separation chamber may include two inlet ports, one port to introduce a grossly oil contaminated mixture and another inlet port located below the first port to introduce water to act as a "carrier" for the oil layer thereabove. In this manner, the separation chamber cannot fill entirely with oil and a pressure differential is maintained with a downstream separation chamber as shown in FIG 5 or a head control means as shown in FIGS 1-5.

An upwardly convergent frusto-conical flow diverter with a central aperture may be provided in association with the second inlet port to direct the water flow initially upwardly and otherwise to maintain a laminar flow in the separation chamber.

FIG 5 illustrates yet further adaptation of the conduit 30 in head control means 31 of FIG 4.

FIG 5 illustrates yet further adaptations of the invention.

The apparatus comprises two separation chambers 32, 33 connected in series with the outlet port 34 of chamber 32 connected to the inlet port 35 of chamber 33. Oily waste water 36 is delivered to a sump 37 by conduit 38 by any suitable pump means or the like (not shown). A flexible conduit 39 is connected to a floating scavenger head 40 to collect a water/oil mixture at the interface of a layer of oil 41 floating on the body of water in sump 37.

The oil/water mixture is delivered to the inlet port 42 of separation chamber 32 by a low shear pump 43 such as a helical rotor pump. Between pump 43 and inlet port 42 is a valve 44 coupled to a liquid level detector 45 to maintain a water level in chamber 32. Alternatively, as shown in phantom, liquid level detector 45 may be coupled to pump 43 for the purposes of maintaining a desired water level in chamber 32.

In a manner similar to the embodiments illustrated in FIGS 1-4, frusto conical skimmers 46 are located in chambers 32 and 33 and their respective discharge ports 47, 48 are coupled in fluid communication with a discharge conduit 49 leading to an oil collection container 50. The outlet port 51 of downstream chamber is connected via valve 52 to a water outlet 53 for discharge of de-oiled water to a waste drain 54 or the like. Valve 52 is coupled to a liquid level detector 55 associated with chamber 33 to maintain head of water at a desired height therein.

Although not shown, valve 52 may be coupled to a water return conduit connected to sump 37 to selectively recycle water stripped of oil in separation chambers 32, 33. Although the fluid mechanics of the oil separation process according to the invention are not fully understood, it is believed that the frusto-

conical configuration of the oil skimmer device, in combination with the restricted annular gap between the skimmer and surrounding chamber wall play a large part in the efficiency of the system. The annular gap provides a controlled region of back pressure through which the upper layer of relatively viscous oil must pass. In so doing, a large proportion of the oil is brought into contact with the undersurface of the skimmer or the wall of the separating chamber.

In this region the oily mass undergoes extreme shear without the risk of breaking up into droplets, or, in the case of emulsions, without reducing the size of oil droplets in this region. An additional shear force is applied to the oil as it passes over the relatively sharp edge of the skimmer.

Yet another factor which is considered to contribute to efficient oil separation is that while the body of water in the separation chamber between the inlet and outlet ports undergoes a generally laminar flow, the body of water between the inlet port and the top of the skimmer is effectively static thus allowing undisturbed separation and coalescence of oil droplets in this region.

In yet further modifications to the invention, the outlet port associated with the or each separation chamber may comprise a plurality of outlet apertures spaced about the peripheral wall surface of the chamber near the base or a plurality of spaced apertures in the base. These apertures are manifolded to provide a single connection to a conduit communicating with the head control means.

Alternatively certain of the outlet apertures may be in fluid communication with the head control means and one or more other outlet apertures may be in fluid communication with the pump or inlet port to provide a

controlled recirculation of part of the more dense fluid from near the base of the separation chamber. A plurality of outlet apertures assists in maintaining laminar flow in the chamber at higher flow rates. Still further, the inlet port may be adapted to include spaced upwardly convergent frusto conical flow diverters located on the inner wall of the chamber with a plurality of inlet apertures in fluid communication with the space therebetween. The frusto conical flow diverters have a large central aperture and act to divert influent liquid in a generally upward direction.

In another embodiment of the invention, particularly where circumstances or the nature of the liquids to be separated dictate a low flow velocity in the separation chamber, one or more downwardly convergent frusto conical ribs may be located on the inner wall of the chamber below the inlet port to provide one or more narrowings in the flow path in the chamber. The rib surfaces act as collectors of fine droplets of oil and serve to selectively increase fluid velocity in selected regions of the chamber.

Although the invention has been exemplified with reference to separation of oil from water, it will be clear to a skilled addressee that the apparatus and process of the invention will have other useful applications .

Apart from separation of mixtures of liquids of differing densities, the apparatus, with suitable modifications, may be applicable to solvent extraction processes in such industries as oilseed production, pharmaceuticals, mineral extraction and the like.