EP0052132A1

EP0052132A1 - Method and device for separating immiscible liquids

Info

Publication number: EP0052132A1
Application number: EP81901487A
Authority: EP
Inventors: Ake Oskar Vilhelm Hellovist; Göran HELLMAN
Original assignee: Cinderella / SFS (Swede Filter System) AB; Cinderella AB
Current assignee: Cinderella / SFS (Swede Filter System) AB; Cinderella AB
Priority date: 1980-06-02
Filing date: 1981-06-02
Publication date: 1982-05-26
Also published as: WO1981003434A1

Abstract

Procede de separation de liquides sensiblement non miscibles (A, B) ayant des densites differentes telles que des melanges huile-eau, caracterise par l'introduction de ce melange dans un conteneur ouvert de preference, ou un tube (4) s'etend au-dessus et sous la surface (12) du liquide dans le conteneur, etablissant une interface entre ces liquides de densites differentes dans ce tube, et par la recuperation du liquide moins dense par la partie superieure du tube de preference a un niveau (7) au-dessus du liquide plus lourd se trouvant dans le conteneur, cette introduction s'effectuant de telle maniere que le materiau moins dense s'ecoule dans le tube, le tube faisant de preference un angle par rapport a la verticale.Method for separating substantially immiscible liquids (A, B) having different densities such as oil-water mixtures, characterized by the introduction of this mixture into an open container preferably, or a tube (4) extends to the -above and under the surface (12) of the liquid in the container, establishing an interface between these liquids of different densities in this tube, and by the recovery of the less dense liquid by the upper part of the tube preferably at a level (7) above the heavier liquid in the container, this introduction being carried out in such a way that the less dense material flows into the tube, the tube preferably making an angle with respect to the vertical.

Description

METHOD AND DEVICE FOR SEPARATING IMMISCIBLE LIQUIDS.

This invention relates to a method of an apparatus for separating substantially immiscible -liquids of differing densities and is of particular use for purifying water and especially for separating oil from water, or water from oil.

BRIEF SUMMARY OF THE INVENTION.

Industrial wastewater invariably contains impurities . It has been found particularly troublesome in the past to separate oil from wastewater. Using conventional filters, the oil to be separated has a tendency to clog the filter medium and frequent replacement or reversal of the flow cycle is required to maintain an efficient flow rate.

It is the object of the' invention to provide an improved method and apparatus for separating liquids and, in particular, separating oil from water, or water from oil without the use of a filtering medium.

THE PRIOR ART.

For the separation of sludge from water, there have been numerous proposals in which sedimentation is effected by passing the contaminated water in a downward flowing stream through a series of parallel tubes inclined at angles in excess of 45 degrees. The sludge settles at the bottom of the filter vessel whilst the clean effluent is discharged at the top of the fluent after rising along a generally upwardly inclined path parallel to but separate from the downwardly flowing contaminated stream.

This concept has been incorporated in so-called lamella separators in which the flow is downward through a series of parallel plates or tubes. One of these separators, made by Parkson Corporation, is illustrated on page 45 of "Handbook of Advanced Wastewater Treatment" (Section Edition) by Russell C. Culp, George Mack Wesner and Gordon L. Culp published 1978 by Van Nostrand Reinhold Company of New York.

In the Parkson-Lamella separator, the flow of contaminate water is downward through a series of parallel plates. The sludge is collected at the bottom of the basin, with the sludge water flowing in the same direction. The clarified water is conveyed to the top of the basin by return tubes.

From one aspect, the invention provides a method for separating substantially immiscible liquids of differing densities which comprises introducing said mixture into an open container wherein there is positioned a tube extending above and below the surface of liquid in said container, establishing an interface between said liquids of differing densities in said tube and recovering the less dense liquid from the upper portion of said tube at a level above that of liquid in said container, said introduction being effected in such manner that the less dense material flows into said tube. From another aspect it provides an apparatus for separating substantially immiscible liquids of differing densities which comprises an apparatus for separating substantially immiscible liquids of differing densities which comprises a container having an open top, a tube positioned in said container in such a way as to have a substantial vertical component, means for introducing a mixture of liquids into said container and means for recovering the less dense liquid from the upper portion of said tube.

The present invention utilizes the fact that a greater head of liquid of lower density is required to generate the same pressure as a given head of liquid of higher density. Thus, for an oil having a density 10% less than that of water a column of oil will stand approximately 10% higher than a column of water above an oil-water interface. Thus, if one inserts a tube containing oil, open to the atmosphere at its upper end, into a tank of water to a depth of 40 cm the oil level in the tube will be approximately 4 cm above that of the surrounding water.

The establishment of an interface between the more and less d.ense liquids in the tube can be affected in any convenient manner, for example, providing a constriction in the tube. Of course, if the tube is extending to a sufficient depth beneath the surface of the surrounding liquid, an interface will inevitably be formed in due course as a result of droplets of the less dense liquid rising in the tube thereby establishing a region containing only the less dense liquid in the upper portion of the tube. The rate at which the less dense liquid is taken off from the top of the tube can be used to control this process and produce an interface at an appropriate depth below the surface of the ambient liquid.

It is, of course, necessary that the less dense liquid be caused to flow into the tube. This can be ensured among other ways by proper positioning of the feed of the liquid mixture and shaping of the lower portion of the tube, for example, the lower portion of the tube can be shaped as an inverted funnel and positioned immediately above the mixed liquid feed pipe.

Thus, in one particular embodiment of the invention there is provided a method of separating liquids by passing a mixture of immiscible liquids of differing densities down a downwardly inclined passageway situated beneath the surface of an ambience- composed of the more dense liquid so that the less dense liquid in the feed mixture can creep back along the upper limit of said passageway and be collected therefrom by use of riser tubes rising above the surface of the ambient liquid. An apparatus for implementing this method comprises a) a container fitted with b) means for maintaining the level of liquid in said container at a predetermined level, said container having positioned therein c) a set of at least one downwardly inclined passage¬ ways, said passageways being open at their lower ends and being so positioned that their upper ends are below the intended level of liquid in said container, said down- wardly inclined passageways having connected thereto at the upper ends d) riser tubes of substantially smaller bore than said downwardly inclined passageways rising to a level above that intended for liquid in said container, said downwardly inclined passageways further having connected thereto in their upper portion but spaced from said riser tubes e) feed means for introducing said mixture of liquids into said downwardly inclined passageways.

In such an embodiment the present invention is implemented by situating the upper end of the downwardly inclined passageways substantially below the intended surface of the liquid of higher density, for example, in a tank in which they are mounted. This then enables one to take advantage of the differential pressure head effect of liquids of different densities so as to facilitate separation of the liquids.

It is, of course, necessary that the feed into the upper end of said downwardly inclined passageway be sufficiently distant from the riser tubes that only the less dense material passes into these. Furthermore, the rate at which liquid mixture is fed into the downwardly inclined passageways must not be so great as to preclude the creeping passage of the less dense material back up the upper limit of said passageways. Appropriate speeds can readily be computed by use of a simple vector diagram as

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SUBSTITUTE SHEET N /?NAT will be hereinafter described.

Typically the interface between the two liquids will be at the junction of the downwardly inclined passageway and the riser tubes. The exact rate of feed required to ensure this can be calculated or determined by simple experiment.

The assembly of downwardly inclined passageways, riser tubes and feed means will normally be mounted in a fixed position in the container. It is, however, also possible that such an assembly could be mounted on a float so as to enable the apparatus to be used in situations where the surface- level of the surrounding liquid ma ^'vary, for example, to permit direct discharge of wastewater con¬ taining oil into, a lake or river should the nature of the effluent and the local environmental protection regulations permit this..

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS.

Fig. 1 shows a single tube immersed into a column of water to explain the principle of the invention;

Fig. 2 shows a simple apparatus for putting the invention into effect;

Fig. 3 shows in a cross-sectional view, partly diagrammatic of an apparatus constructed in accordance with the invention for separating oil from an oil-water mixture;

Fig. 4 is a vector diagram of use. in computing flow rates for use with given liquids and angles of downwardly inclined passageways in Fig. 3.

DETAILED DESCRIPTION.

Referring first to Fig. 1 of the drawing, there is shown

a column of water 1 in which is immersed a vertical tube 2 containing oil. By virtue of the difference in specifi gravity, the level of the oil in the tube rises about 4 c above the water level 3. The specific gravity of oil varies from 0.85 for pure naphtha to 0.88 for petroleum. Contaminated wastewater discharged from industrial plants contains a mixture of different oil impurities with varying specific gravities . All industrially used oils are, however,- lighter than water so that the principle of the invention applies regardless of the particular industry although the heat of oil above water may vary slightly from case to case.

Fig. 2 shows an inclined tube 4 mounted so as to project above and below the surface level (l-) of a liquid. A means 5 is provided for introducing a mixture of two immiscible liquids of differing densities A and B. A is more dense than B. The tube 4 is provided with an inverted funnel 6 to aid in collection of the less dense liquid B.

An interface between liquids A and B is established in tube 4 at level 1, . As a result of the differing densities of A and B the surface of liquid B will be above that of the ambient liquid which is composed of liquid A. This will be at level 1,. The distance between 1- and ~ is designated S, and that between 1, and L as S.

Thus,

PR ^{S =} PB ^{(S + S}l^} where p. is the density of liquid A and P„ the density of liquid^' 3.

Liquid B is recovered by flow along tube 7 for collection in collector 8.

Referring now to Fig. 3, the tank 16 containing the lamella type separator may be cylindrical, square, rectangular or oblong in section.

The lamella unit consists of a series of inclined, parallel passages 18. The passages 18 are made from parallel flat plates ur tubes. The tubes and plates and the tank proper are made from stainless steel or PVC or some other known corrosive material. The tubes or plates are welded together or held in the tank by a suitable support not shown. The upper portion 18 of the lamella separator is inclined at 25-45 degrees to the vertical. By increasing the inclination of the tubes or passages 18, the performance and throughput can be increased depending on the character of the wastewater being treated.

The influent wastewater containing the oil-water mixture is collected in a raised trough 20. A series of vertical tubes 22 lead from the bottom of trough 20 to a point within and below the upper end of the passage in the lamella separator. The lamella separator stops short from the bottom 24 of the tank. The water leaving the lower open ends of passages 18 is substantially pure and decontaminated. The separated oil creeps along the upper wall of the passages in an upward direction and collects in vertical risers 26 which are connected to a horizontal fixed manifold 28. The oil is discharged towards the right of the tank by first passing through a flexible joint 30 and then into a horizontal floating discharge pipe 32. The discharge pipe 32 rests on a float 34 suspended on the surface level of the tank 16. Of course, the permitted difference between the surface level of-the tank and the discharge pipe will depend upon the difference in density of the contents of the tank and that of the liquid being discharged, and the depth below the surface at which an interface between the two liquids is established (i.e. at the junction of the riser tubes and the downwardly inclined passageways) . The oil discharge pipe 32 is strapped to float 34 by bands 36 or secured thereto in any other suitable manner.

The purified water is laterally discharged from the top of tank 16 through an outlet 38 which in the form shown is located beneath oil discharge pipe 32 , but could also be located at any other part of the vessel's surface.

The separation of liquids such as oil from water in the passages of the lamella separator is explained by the small vector diagram of Fig. 4.

The upper vector (a) represents the floatation speed of the less dense liquid (e.g. oil) which must be of the order of 30 cm/sec. or 300 m/hour.

The downwardly pointing vector (b) (whose angle corres¬ ponds to the inclination of passages 18) represents the speed of the more dense liquid (e.g. water) passing down through the lamella separator.

The third vector (c) which points in an upward direction represents the flow of separated out oil towards the upper surface of the passages 18.

The lamella separator is a very efficient unit which operates well without motor or other moving parts or pump. It has been calculated that if the lamella is 0.8 meters long, and the floatation speed of oil is of the order of 30 cm/sec, then each lamella can be loaded with 22.5 cubic meters per hour of an oil-water mixture.

Thus, the invention permits the separation of two immiscible, e.g. mutually insoluble liquids, such as emulsions and dispersions, especially an. oleophilic or hydrophobic liquid and a h drophilic or oleophilic liquid, either of said liquids forming the dispersed phase in the other liquid, especially a dispersion of oil in water. The invention will in the following be explained especially with reference to a method and a device for separating an oilly phase from an aqueous phase, especially in combination with the cleaning of oil tanks in ships and similar use.

Such cleaning of oil tanks and similar treatments are usually performed by spraying high pressure water against an oil contaminated surface, the result being a mixture, optionally an emulsion, of an oil phase and an aqueous phase.

According to the invention said separation^" is performed by using density differences of said phases , the less dense phase being permitted to rise through an elongated column or a similar device in which said less dense phase forms a liquid column subjected to the boyant force of an optionally shorter column of the heavier phase so that said less dense phase can be withdrawn at a level above the upper level of said denser phase.

Optionally the density of said less dense phase may be obtained or influenced by the addition of a lighter auxiliary medium, especially a gas, such as air or combustion exhaust gas which forms bubbles in the liquid and contributes to increasing the upper level of the liquid in said less dense phase column in a communicating system formed by said heavier phase and said lighter phase.

Embodiments of the invention are in the following explained with reference to Figures 5-8.

Figure 5 shows schematically a section through a tanker 1. The figure is not in scale, and broken lines 2 indicate interruptions in the drawing. The centre of the section shows an elongated tanker room 3 extending from the bottom 4 to the deck 5 with vertical side walls 6. In the lower part of the room 3 there is an inlet tube 7 through which a mixture of oil and water, obtained e.g. by tank cleaning, discharges. Said water-oil mixture is introduce into a device 8 which enhances separation of said mixture, e.g. a turbulency restricting or emulsion breaking device. Examples of such devices are a downwardly open bell-shaped means and/or a lamella separator, e.g. of the type disclos above and with reference to Figures 1-4.

According to the invention there is achieved in the lower part of said room 3 or at least at a substantial distance from the deck 6 or an intended upper level 9 of the more dense phase, i.e. water, introduced into the room 3, a separation of oil and water so that the oil can flow up through a column or a tube 10 and form therein a column, the lower level of the liquid in said column being indicated with a broken line 11 on Figure 5. In order to improve the collection of said less dense phase the lower part of the tube 10 is constructed with larger diameter than the upper part and is on Figure 5 shown as an inverte funnel-shaped extended part 12. The heavier phase, the water, flows away from the lower part of said extended part 12 as indicated with an arrow 13. Although not indicated on the figure the room 3 is provided also with an outlet for the separated water.

The separated less dense phase can be withdrawn from the tube 10 through a branch conduit 14 provided with a valve

15 and, if desired, arranged above the deck 5, said branching conduit if desired can be arranged at a level above the upper level of the water 9 corresponding to the difference in density between the separated phases and the distance from the lower level 11 of the oil phase to the upper level 9 of the water phase and the branch conduit 14, resp. In order to increase the lifting power of buoyancy one may also add a lighter phase, such as air or combustion exhaust gas into the tube 10 through a tube

16 indicated with broken lines. The upper level of the oil phase is indicated with a broken line 17. Optionally a superatmospheric pressure may be maintained in the room 3, and/or the collecting means for the less dense phase may be provided with a pump aiding the discharge of said less dense phase from the water after separation.

The separating aqueous phase may be used again for cleaning tanks, e.g. by spraying under high pressure against the tank walls or may be recovered for storing and disposal, etc.

Figure 6 shows a further embodiment of a device according to the. invention. Those parts which are equivalent with those of Figure 5 have obtained the same reference numerals. The oil column forming part 10 with the collecting means 11 are in this embodiment enclosed in an enclosure 18 which receives the separated aqueous phase. An outlet 19 for said aqueous phase is arranged in the lower part of the enclosure 18, but said outlet may, of course, be arranged at any desired level. Furthermore, the enclosure 18 may be terminated at a lower level as indicated with the broken line 20. The upper part of the enclosure 18 may then be substituted with a riser conduit or a similar device for the aqueous phase or with any other suitable means, e.g. an adjustable check valve in the conduit 19 or a similar device for maintaining a sufficiently high pressure in the aqueous phase and thus in the oil column in the tube 10 so that the upper oil level 17 rises to a desired level.

Figure 7 discloses a modification of the device according to Figure 6 in which the i pper part of the enclosure 18 is shaped as a tank 21, the volume of which may contribute to level-out fluctuations in the inflow through the conduit 7. Figures 6 and 7 show an upper level 9 of the aqueous phase which is situated above the level of the deck 5 in order to improve the discharge of relatively dense oil phase above the level of said deck.

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0Λ1P1 Figure 8 shows schematically a lamella separator which can be used in the process of the invention. Figure 8 shows a section through a number of lamellas 1 consisting of oblique parallel plates or sheets. Between said lamellas 1 there are in the upper part of the interspaces between the lamellas 1 arranged a number of auxiliary lamellas 2, according to Figure 8 one auxiliary lamella 2 between each couple of lamellas 1. The auxiliary lamellas disclosed on the figure are arranged parallel with the lamellas 1 and essentially centrally between said lamellas When a mixture of oil and water (or another mixture of a heavy phase and a light phase) is introduced into the lower part of said lamella separator, the lighter phase will accumulate at the lower side surface of the lamellas, i.e. on the^* upper surface side of the auxiliary lamellas in the spaces between the lamella and the adjacent under¬ lying auxiliary lamella and form a column with a lower surface level 5 and an upper surface level 4 which is higher than the level of the upper surface 3 of said heavier phase if the outflow of said lighter phase is arranged at said higher level by using the buoyance lift pressure of said heavier phase on said lower surface 5 of the solumn of said lighter phase. The lamella separator according to Figure 8 can be used instead of the devices according to Figures 5-7 for separating e.g. oil and water or used together with said devices in which case the lamella separator can be arranged below the tube 10 and collecting means 11 if said means is used.

In the following a number of embodiments of the invention is disclosed with reference to the drawings. Figures 5-7.

1. A process and a device for separating and collectin a light phase, especially oil, from a mixture of said light phase and a heavy phase, especially an aqueous phase e.g. obtained by cleaning oil tanks in tankers, etc., comprising the introduction of said mixture of light and heavy phases in the lower part of a column 10 or a similar device and bringing said mixture to separate into a lighter phase (oil phase) which is permitted or brought to rise in said column and form an oil column therein, and a heavy phase which is removed from the lower part of said column and maintained under a pressure in said column which exerts a buoyance pressure on said oil column,

2. A process according to embodiment 1 in which the oil phase is withdrawn from the column at a discharge 14 e.g. arranged above or close to the deck 5 of a ship, especially tanker, and transferring oil from said mixture of oil and water to the lower part of said column at a distance of at least 5 m, preferably at least 10 m, especially at least 15 m, at least 20 m or at least 25 m below said discharge 14 or the level of said deck 5.

3. A process according to embodiment 1 or 2 which comprises adding the mixture of oil and water to an extended, preferably inverted funnel-shaped lower part 12 of said column 10, preferably to a device arranged in said part which improves separation of the light and heavy phases, e.g. a turbulency decreasing device 8.

4. A process or a device according to any of embodi- ments 1-3, said oil column forming a means 10 being enclosed in an enclosure 18 in which a pressure head of said heavy phase, especially aqueous phase, is maintained, said pressure head being sufficient to rise the upper level of said oil column in the column 10 to the desired discharge opening 14.

As stated above separation of the light phase from the heavy phase may be performed in a device of the type disclosed above with reference to Figures 1-4 or 8.

Figure 9 shows a separating device which is similar to the device according to Figure 6. A housing 1 shaped essentially as an inverted funnel comprises an internal funnel-shaped separating wall 2, the outline of which is indicated with a broken dot line. Said separating wall seals against the inner surface of the walls of the housing 1 leaving passages 3 between the lower edges of the separating wall 2 and the bottom of the housing 1. A mixture of two liquid phases which are to be separated, e.g. oil and water, is introduced through an inlet 4 into the space in the housing 1 formed by the inverted funnel- shaped separating wall 2. In said space the lighter phase rises and is removed through a tube 5 extending from the upper part of the separating wall 2. The heavier phase, water, passes through the passages 3 below said separating wall 2 as indicated with arrows 6 and is withdrawn through an outlet 7 from the housing 1. The separating device according to Figure 9 may be arranged as indicated on Figure 10 which shows a section through a tanker vessel. The housing 1 with the separating device is indicated schematically on Figure 10 with the inlet tube 2 and the oil outlet tube 5 which extends to an oil outlet 3 above the deck 4. The upper level of the heavier phase, water, in the tank compartment 6 in which the separating device is arranged is also indicated on the figure. Preferably the heavier phase in the tank compartment 6 communicates with the internal of the housing 1 and with the tube 3 containing the separated light phase, e.g. oil, so that the weight of the heavier phase lifts the lighter phase up through the tube 3 to a level above the deck 4.

Examples of lighter phases which are usually treated as mixtures with a heavier phase consisting of water or an aqueous solution of e.g. inorganic salts are petroleum products such as crude oil or petroleum fractions having a density calculated as grams per cubic centimeter of below 0.70, below 0.72, below 0.74, below 0.76, below 0.78, below 0.8, below 0.9 or below 0.96, below 1.0 or below 1.10, e.g. a density within the range 0.70-0.76, 0.75-0.80, 0.80-0.90 or 0.85-1.0. Examples of such

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0Λ1 products are gasoline, e.g. aviation gasoline, motor-car gasoline, kerosene, white spirit, diesel oil, fuel oil or heating oil, e.g. fuel oil No. 1, No. 2, No. 3, No. 4, bunker C oil, stabilized crude, topped crude, reduced crude, spiked crude, synthetic crude oil, jet fuel, wide cut jet fuel, petroleum ether, petroleum spirit, special boiling point naphtha, e.g. 80/110, light virgin naphtha, virgin naphtha, kerosene, kerosene stock, paraffin, Stoddard solvent, petroleum naphtha, heating oil, domestic fuel, heavy fuel oil, bunker fuel, marine gas oil, marine diesel fuel, marine intermediate fuel, marine heavy fuel, marine residual fuel, lubricant oils, metal working oil, cutback asphalt, asphalt emulsion and other asphalt products, etc., tar and tar oil. All said petroleum products may be based on paraffin-base, naphthenic base, alphalt base or mixed base and may consist of bitumen or bitumenous materials.

The heavier phase may especially consist of water, such as sweet water, or water with a content of inorganic dissolved constituents of at most 0.5%, preferably at most 0.2% or 0.1% or at most 0.05%. The heavier phase may also consist of a salt solution, such as sea water or brackish water having a content of inorganic consti- tuents of at least 0.3%, preferably at least 0.7%, at least 1%, at least 2% or at least 3% or 3.5%, by weight, or even contents above the concentration in ordinary ocean sea water, e.g. at least 5% or at least 10% soluble inorganic constituents. The heavier phase may also consist of a water containing minor quantities of organic constituents, such as alcohols, e.g. methanol or ethanol or various detergents, froth control consti¬ tuents, emulsion breaking constituents, etc., e.g. in a quantity of at least 0.001% or at least 0.1% or at least 1%, optionally together with inorganic soluble consti¬ tuents as mentioned above.

Claims

1. A method for separating substantially immiscible liquids of differing densities such as oil-water mixtures, characterized by introducing said mixture into a preferably open container wherein there is positioned a tube extending above and below the surface of liquid in said container, establishing an interface between said liquids of differing densities in said tube and recovering the less dense liquid from the upper portion of said tube preferably at a level above that of the heavier liquid in said container, said introduction being effected in such a manner that the less dense material flows into said tube, said tube preferably being disposed at an angle to the vertical.

2. A method according to claim 1, wherein the establis ment of an interface in said tubes is encouraged by a constriction in said tube and/or wherein the mixture of immiscible liquids is fed into said container at a level below and adjacent the bottom of said tube, the bottom of said tube preferably being shaped so as to collect the less dense liquid.

3. A method according to claim 1 or 2, which comprises introducing a mixture of said liquids into the upper portion of a downwardly inclined passageway, said passage¬ way being positioned beneath the surface of an ambience, e.g. a tank, comprising the more dense of said liquids, said passageway being open at the bottom end and having at its upper end a riser tube of narrower bore than said passageway, said riser tube rising to a level above the surface of said ambient liquid and said introduction being effected in the upper portion thereof but below the uppermost point thereof so that in passing down said inclined passageway the less dense liquid separates from the more dense liquid and moves against the upper limit

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„ _rr-_^^-.c»_f3 ι--^* E^» •r_;i_^,.r^*r~^* ψ Wi of said passageway towards the top thereof and thence through said riser tube to a level above that of the ambient liquid whence it is collected, said downwardly inclined passageways preferably being disposed at an angle of 25-45° to the vertical, said less dense liquid preferably having a floatation speed in said more dense liquid of at least 30 cm/sec.

4. An apparatus for separating substantially immiscible liquids of differing densities which comprises a container, preferably having ah open top, at least one tube- positioned in said container in such a way as to have a substantial vertical component, means for introducing a mixture of liquids into said container and means for recovering the less dense liquid .from the upper portion of said tube.

5. An apparatus according to claim 4, wherein said container is fitted with an outlet thereby enabling control of the level of liquid therein, said tube preferably being positioned so as to extend above and below the level at which liquid is controlled in said container, said tube preferably being arranged at an angle to the vertical, said means for introducing a mixture of liquids into said container preferably being positioned at a level below that of the bottom of said tube, especially adjacent the bottom of said tube.

6. An apparatus according to either of claims 4 and 5, wherein said tube is provided with a constriction, preferably at a level substantially below the level of the surface which liquid will adopt in said container.

7. An apparatus according to any of the preceding claims, wherein the lower end of said tube is in the shape of an inverted funnel.

8. An apparatus according to any of the preceding claims for separating substantially immiscible liquids of differing densities which comprises: a) a container fitted with b) means for maintaining the level of liquid in said container at a predetermined level, said container having positioned therein c) a set of. at least one downwardly inclined passage¬ ways, said passageways being open at their lower ends and being so positioned that their upper ends are below the intended level of liquid in said container, said down- wardly inclined passageways having connected thereto a their upper ends d) riser tubes of substantially smaller bore than said downwardly inclined passageways rising to a level above that intended for liquid in said container, said down- wardly inclined passageways further having connected thereto in their upper portion but spaced from said riser tubes e) feed means for introducing said mixture of liquids into said downwardly inclined passageways, said assemblage of downwardly inclined passageway, riser tubes and feed means preferably being mounted in a fixed position in said container, said downwardly inclined passageways preferably being disposed at an angle of from 25 to 45 to the vertical, said riser tubes especially being connected to a lateral discharge tube from which liquid may be discharged at a level above the level of liquid in said container.

9. An apparatus according to claim 4 for separating substantially immiscible liquids of differing densities which comprises: a) a tank having b) in the upper portion thereof an outlet and having mounted therein c) a set of downwardly inclined passageways open at the lower ends, the upper ends of said inclined passage¬ ways being substantially below the level of said outlet, said passageways being at an angle of from 25 to 45° to the vertical, d) the upper ends of said passageways being connected to substantially vertical riser tubes of smaller bore than said downwardly inclined passageways, said passageways further being provided with e) feeder tubes which are positioned so as to be able to introduce a liquid mixture into said downwardly inclined passageways at a point below the top thereof, f) said riser tubes being connected at their upper end through a manifold to a lateral run-off tube, said tube being^' positioned at a level just above the outlet to said tank.

10. An apparatus according to claim 4 for separating substantially immiscible liquids of different densities which comprises: a) a float having mounted therebeneath b) a set of one or more downwardly inclined passage¬ ways, said passageways being fitted at their upper ends with c) riser tubes of smaller bore than said downwardly inclined passageways, said passageways further being provided with d) feed- means for introducing liquids into the downwardly inclined passageways at a position in the upper portion thereof but spaced from said riser tubes.