GB2323048A

GB2323048A - Oil-water separation using a gas

Info

Publication number: GB2323048A
Application number: GB9805174A
Authority: GB
Inventors: Robert Michael Fielding; Colin Thomas Billiet; Paul Anthony Feather
Original assignee: Domnick Hunter Ltd
Current assignee: Domnick Hunter Ltd
Priority date: 1997-03-13
Filing date: 1998-03-12
Publication date: 1998-09-16
Anticipated expiration: 2018-03-12
Also published as: GB2323048B; GB9705261D0; GB9805174D0

Abstract

Apparatus for separating an oil-water mixture comprises a heat exchange vessel 2 with inlet 12 and a outlet (at lower end 6) between which the liquid oil-water mixture can flow and a gas inlet 18 arranged so that gas supplied to the vessel can flow in the opposite direction to the liquid towards the gas outlet at upper end 4 of vessel 2, a reservoir 8 for collecting the liquid discharged from vessel 2, ad a conduit 10 allowing liquid from reservoir 8 to be returned into vessel 2. The liquid supplied from reservoir 8 to the inlet 12 is heated. This may be achieved by including a heat exchanger along conduit 10. The liquid exiting vessel 2 is discharged into the reservoir 8 over a smaller cross sectional area than the that of the oil-water layer within the reservoir. Using baffle plate 16, liquid exiting vessel 2 may be made to flow down the inner wall of vessel 6 into reservoir 8. By preventing agitation of the oil-water mixture within reservoir 8, it can function as a settling tank allowing the oil-water mixture to separate into distinct layers which can be removed from vessel 2 using valve 24. Vessel 2 preferably includes means, such as Pall rings 14, to disturb the downward flow of the oil-water mixture and ensure maximum contact with the upwardly flowing gas. It may also include means, such as inlet 12, to ensure a even distribution of liquid onto the top of the column packing. The gas supplied from compressor 20 through inlet 18, may be heated using heater 22 or a source of waste heated gas may be connected directly to the vessel. A filter or condensor may be included for the treatment of the heated gas-water vapour mixture exiting vessel 2.

Description

OIL-WATER SEPARATION This invention relates to apparatus for separating components of an oil-water mixture, and to a method of separating components of an oil-water mixture.

Techniques for separating components of an oil-water mixture by allowing the components to separate in a reservoir lead only to partial separation. Such techniques can leave concentrations of organic components in the aqueous system at levels which cannot be tolerated for waste water discharge.

The present invention provides a technique for separating components of an oil-water mixture by causing the mixture to flow through a vessel, generally in the form of a column, countercurrently with a gas. Water in the mixture is discharged from the vessel with the gas, concentrating the oil in the mixture for collection from the reservoir.

Accordingly, in one aspect, the invention provides apparatus for separating components of an oil-water mixture, which comprises: (a) a heat exchange vessel with an inlet and an outlet for the oil-water mixture between which the mixture can flow, and a gas inlet arranged so that gas supplied through it to the vessel can flow through the vessel, in a direction from the mixture outlet towards the mixture inlet, (b) a reservoir for collecting the mixture discharged from the mixture outlet in the vessel, (c) a conduit through which liquid in the reservoir can be supplied to the mixture inlet in the vessel, and (d) means for heating liquid supplied from the reservoir to the mixture inlet so that its temperature when received in the inlet is higher than ambient temperature.

The apparatus of the invention has the advantage that it allows oil components in an oil-water mixture to be concentrated by controlled removal of water from the mixture, so that the oil components separate from the mixture and can be collected for disposal. The separation can be achieved economically; the circulation of the oil-water mixture through the vessel and the reservoir requires little energy. It has been found that the application of heat to raise the temperature of the liquid supplied to the vessel enables water to be evaporated from the oil-water mixture particularly efficiently, and more efficiently than with equipment in which the gas supplied to the heat exchange vessel is heated. Equipment of this type (but for concentrating human waste) is disclosed in US-5207869.

Preferably, the cross-sectional area over which the oil-water mixture is discharged from the heat exchange vessel into the reservoir is significantly less than the cross-sectional area of the surface of the oil-water mixture in the reservoir at its normal operating level. The discharge from the heat exchange vessel into the reservoir will generally be arranged relative to the reservoir such that liquid in the reservoir is left substantially undisturbed by liquid that is discharged into the reservoir from the heat exchange vessel. This has been found to have the advantage of facilitating separation of oil and water in the mixture. For example, the ratio of the crosssectional area over which the oil-water mixture is discharged from the heat exchange vessel into the reservoir, to that of the surface of the oil-water mixture in the reservoir at its normal operating level, is not more than about 0.8, preferably not more than about 0.65, more preferably not more than about 0.5.

Accordingly, in another aspect, the invention provides apparatus for separating components of an oil-water mixture, which comprises: (a) a heat exchange vessel with an inlet and an outlet for the oil-water mixture between which the mixture can flow, and a gas inlet arranged so that gas supplied through it to the vessel can flow through the vessel, in a direction from the mixture outlet towards the mixture inlet, (b) a reservoir for collecting the mixture discharged from the mixture outlet in the vessel, (c) a conduit through which liquid in the reservoir can be supplied to the mixture inlet in the vessel, in which the cross-sectional area over which the oil-water mixture is discharged from the end of the heat exchange vessel into the reservoir is significantly less than the crosssectional area of the surface of the oil-water mixture in the reservoir at its normal operating level.

Preferably, the said apparatus includes means for heating liquid supplied from the reservoir to the mixture inlet so that its temperature when received in the inlet is higher than ambient temperature.

Preferably, the liquid heating means is arranged to heat the liquid at a point between the reservoir and the inlet to the vessel so that the temperature of the liquid in the inlet is higher than that of the liquid leaving the reservoir. The liquid can be heated by passing the liquid through a heat exchanger as it flows from the reservoir to the inlet to the vessel. The heat source for the heat exchanger can be a source of waste heat, especially a heated gas.

The liquid is preferably heated to a temperature of at least about 450C, more preferably at least about 550C. The temperature of the liquid that is discharged into the heat exchange vessel is preferably not more than about 650C, more preferably not more than about 600C.

The apparatus can use heated gas for supply to the heat exchange vessel to facilitate evaporation of the water in the oil-water mixture. An in-line heat exchanger can be included, for example taking heat from a compressor. The fact that the gas need only be heated for many applications to a temperature no higher than say 700C means that the power requirement of the water heater is not unacceptably high. Alternatively or in addition, warm gas supply means can comprise a conduit for connection to a source of waste warm gas, when an appropriate source is available conveniently close to the vessel. For example, the waste warm gas can be supplied from refrigeration equipment, possibly associated with the apparatus of the invention.

The apparatus can also include means for heating gas which is supplied to the vessel at the gas inlet.

The apparatus can include means for controlling the temperature of gas that is heated before supply to the vessel. The apparatus can be operated so that the temperature of the heated gas is at least about 450C, preferably at least about 550C.

The apparatus can be operated so that the temperature of the heated gas is not more than about 950C, preferably not more than about 750C.

Heated gas, when used, can be supplied from equipment from which heated gas is discharged as waste; even if such a source for the gas is not available, the energy required to heat gas, especially air, at ambient temperature is small.

Preferably, the apparatus includes means for optimising the mixing of the gas and the oil-water mixture. The apparatus can include means for distributing the flow of the oil-water mixture across the cross-sectional area of the vessel.

Preferably, the distributing means provides a transversely dispersed flow of the oil-water mixture across the top of the vessel. This might be achieved by, for example, a perforated member (such as a disc or hollow vessel) through which the mixture is made to flow, or one or more baffles. The apparatus can include means for disturbing the flow of the oil-water mixture through the vessel, to facilitate mixture of the oilwater mixture and the gas, and therefore heat exchange between them, as they flow counter-currently through the vessel. This is preferably achieved by increasing the surface area of the oil-water mixture as it flows through the vessel. For example, the vessel might contain a plurality of beads which the oilwater mixture flows over. Particularly preferred for this is an array of Pall rings, as used to disturb flow of liquids through vessels for other applications.

The apparatus can include means for supplying gas to the vessel at the gas inlet. Preferably, the gas supply includes a compressor. A relatively low power compressor can be used since the back pressure imposed on the gas as it enters the vessel is low. This can help to keep the power requirements of the apparatus low. In some applications, the apparatus can be connected to an external source of compressed air (or other gas), thereby possibly avoiding the need for a compressor as part of the apparatus.

The apparatus can include detectors in the reservoir to detect levels of liquid that have collected in it. For example, a detector can determine when the level of liquid in the reservoir has dropped to or below a minimum level as might occur for example when a desired proportion of the volume of an oil-water mixture has vaporised due to the action of the gas.

When the level drops to that level, the detector can provide an indication that more of the oil-water mixture can be added to the apparatus for separation, possibly after draining the accumulated separated layer of oil from the reservoir.

A detector can be provided to determine when the level of liquid in the reservoir reaches a maximum level, for example to ensure that the amount of liquid in the apparatus does not exceed safe operating limits. The level might be set for example to ensure that oil-water mixture in the reservoir does not flow into the gas inlet in the vessel.

Detectors provided for liquid levels in the reservoir can be used to control the supply of oil-water mixture to the apparatus for separation, for example automatically through appropriately controlled valves or by providing appropriate signals to an operator.

Preferably, the apparatus includes means for minimising agitation of the surface of liquid in the reservoir as a result of discharge into the reservoir of the oil-water mixture from the vessel outlet. This feature can prevent mixing of separated layers of liquids in the reservoir, in particular between an aqueous layer and a layer of concentrated organic material on the surface of the aqueous layer. The means for minimising agitation of the surface of liquid in the reservoir can cause oil-water mixture discharged into the reservoir to flow into the reservoir preferentially down the walls of the reservoir. For example, a baffle can be provided centrally in the vessel with a gap between the edge of the baffle and the internal wall of the vessel, possibly around the entire periphery of the baffle, through which liquid draining from the vessel can flow.

The flow rate of the oil-water mixture through the vessel will be selected according to the size of the vessel, the amount of the gas that is supplied to the vessel and the desired rate at which it is desired to perform the separation. It has been found that a flow rate of at least about 60 l.h-l can be appropriate for operation of the apparatus, preferably at least about 100 l.h-l, for example at least about 145 l.h1.

When the vessel is a column, especially when arranged substantially vertically, the mixture inlet will often be at or towards the top of the column and the outlet at or towards the bottom, so that the mixture flows generally downwardly. The gas inlet will generally be towards the bottom of the column and so that the gas flows upwardly, in countercurrent relationship with the flow of the mixture.

The apparatus can be used to separate oil-water mixtures containing a variety of organic materials. Generally, the apparatus will be used to separate organic materials with boiling points above 1000C from an oil-water mixture. Such materials might be derived from oils used in compressors. They might be used as lubricants, such as white oils used in machining industries. The apparatus can be used for example to separate components of oil-water mixtures containing esters, such as glycol based esters including polyoxyalkylene glycol/ pentaerythritol ester blends The apparatus can include means for condensing vapour discharged from the vessel with the gas leaving the vessel, at or towards its upper end when it is a column. The incorporat ion of a condenser has the advantage that contaminants that are carried from the vessel with the gas can be collected and separated from water that is collected after condensation, generally by a technique other than that relied on in the apparatus of the invention, selected according to the nature of the contaminant.

The apparatus can include a filter for material discharged from the vessel with the gas leaving the column (at or towards its upper end when it is a column). A filter can be used to collect contaminants that are carried from the vessel with the gas, which might be solid particulate materials, or possibly liquid materials carried as aerosol particles.

The incorporation of a condenser or a filter can be advantageous when the vapour discharged from the column carries bacteria with it.

The apparatus can include a settlement tank which can be used to isolate materials in an oil-water mixture to be treated by the apparatus, in particular solids and immiscible liquids (such as heavy organic materials) . It can also be used to allow compressed air or other gas to escape from the liquid.

In another aspect, the invention provides a method of separating components of an oil-water mixture, which comprises circulating an oil-water mixture through (a) a vessel in which the mixture flows countercurrently with a gas, and (b) a reservoir into which the mixture is discharged from the vessel and from which the mixture is abstracted for supply to the vessel, the mixture being heated during the circulation so that its temperature when discharged into the vessel is higher than its temperature when discharged from the vessel into the reservoir.

The method can be operated using the apparatus of the invention; features of the apparatus that are discussed above can be used in the method of the invention, singly or in combination.

The present invention will now be described, by way of example only, with reference to the accompanying drawing, which is a schematic sectional elevation through apparatus according to the invention.

Referring to the drawing, apparatus for separating components of an oil-water mixture comprises a vessel 2 in the form of a column which is open at its upper end 4 to admit the mixture to be separated. It is connected at its lower end 6 to a reservoir 8, into which the mixture flows from the column. The oil-water mixture to be separated is supplied to the column 2 through a tube 10. Mixture is discharged from the tube 10 into the column through a perforated vessel 12 which distributes the mixture over the area of the top of the column.

The column 2 contains a plurality of Pall rings 14 (of which some are shown schematically) of a material which is inert to exposure to the components of the oil-water mixture to be separated. The Pall rings disturb the flow of the oil-water mixture through the column, from the upper end 4 towards the lower end 6 and into the reservoir 8.

A baffle 16 is provided towards the lower end 6 of the column, extending across most of the cross-sectional area of the column leaving a small gap between the edge of the baffle and the internal wall of the column. Preferably, the baffle is domed so that it is slightly higher towards its centre than at its edge (for example by an appropriate forming process or by being thicker at its centre), causing liquid flowing onto it to flow towards its edge. The shape of the baffle and the gap between it and the internal wall of the column are arranged so that liquid flowing off the baffle at its edge flows down the internal wall of the column, into the reservoir. This minimises agitation of the surface of liquid in the reservoir as a result of discharge into the reservoir of the oil-water mixture from the column outlet.

The tube 10 by which liquid is supplied to the upper end 4 of the column 2 is connected to the reservoir, allowing liquid to be recycled between the reservoir and the column, at a rate of between about 15 and 25 l.h-1. Liquid flowing through the tube 10 passes through a heater 13 by which heat can be supplied to the liquid in the tube. This can raise the temperature of the liquid to about 600C.

The column 2 has an inlet 18 for air, located towards the lower end 6 of the column. The air is supplied from a compressor 20 and can be heated by an appropriate heater 22 to a temperature of about 700C. Air supplied to the column through the inlet 18 flows upwardly through the column, towards the upper end 4, in countercurrent flow with the oil-water mixture as it flows downwardly towards the reservoir. The disturbance of the flow of the oil-water mixture through the column by the Pall rings 14 facilitates mixing of the oil-water mixture and the air.

The flow of gas through the liquid mixture causes water in the mixture to vaporise and to be carried from the column at its upper end with the gas. The vaporisation of the water is encouraged by the heating of the liquid between the reservoir and the inlet to the column (and the heating of the gas if used).

The vaporisation of the water in the oil-water mixture leads to concentration of the organic components in the mixture which collects in the reservoir. This leads to formation of a separated layer containing the organic components, on the aqueous layer. The reservoir can include a valved outlet 24 for the collected organic components, through which they can be removed from the apparatus for disposal.

The separation of oil from the oil-water mixture can be facilitated by arranging for a "quiet" region in the liquid in the reservoir, around a central region into which liquid is discharged into the reservoir from the heat exchange column.

For example, the cross-sectional area over which the oil-water mixture is discharged from the heat exchange vessel into the reservoir can be significantly less than the cross-sectional area of the surface of the oil-water mixture in the reservoir at its normal operating level. This result can be achieved with a column with a circular cross-section of area 300 cm2, discharging liquid centrally over a circular cylindrical reservoir of cross-sectional area about 1000 cm2.

The reservoir can include a lower level sensor 26 which can provide a signal to an operator that the volume of liquid in the apparatus has diminished to a level which permits recharging of the apparatus, probably after removal of a layer of separated organic material from the reservoir.

The reservoir can include an upper level sensor 28 to control supply of liquid to the apparatus, for example by providing a signal to an operator that sufficient liquid has been supplied, or by providing a signal to a valve to prevent supply of liquid. The sensor might also cause an emergency drain 30 to open. The upper level sensor 28 can prevent liquid reaching a level in the reservoir which might lead to it flowing into the gas inlet 18.

A condenser or a filter or both can be provided for gas products leaving the column 2 from its upper end, to allow contaminants in the liquid to be separated from the gas products, such as bacterial contaminants, organic components in aerosols.

Suitable operating parameters for apparatus of the type described above are as follows: Inlet air temperature (at position 6): c 210C Inlet air humidity (at position 6): 43.2% Outlet air temperature (at position 4): 450C Outlet air humidity (at position 4): 93.9% Reservoir temperature: 300C Liquid inlet temperature (at position 12): 550C Circulating water flow rate (in pipe 10): 148.5 l.h1 Air flow rate (through column 2): 90 m3.h1 Operation of apparatus according to the above operating parameters resulted in loss of water from a mixture of water and a polyoxyalkylene glycol/pentaerythritol ester at a rate of 5.0 l.h-1.

As water vapour was lost from the top of the column, the liquid in the reservoir tended to separate to form a saturated aqueous layer and an oily layer on the surface of the aqueous layer.

The oily layer can be drained from the reservoir for disposal.

Claims

CLAIMS:

1. Apparatus for separating components of an oil-water mixture, which comprises: (a) a heat exchange vessel with an inlet and an outlet for the oil-water mixture between which the mixture can flow, and a gas inlet arranged so that gas supplied through it to the vessel can flow through the vessel, in a direction from the mixture outlet towards the mixture inlet, (b) a reservoir for collecting the mixture discharged from the mixture outlet in the vessel, (c) a conduit through which liquid in the reservoir can be supplied to the mixture inlet in the vessel, and (d) means for heating liquid supplied from the reservoir to the mixture inlet so that its temperature when received in the inlet is higher than ambient temperature.

2. Apparatus as claimed in claim 1, in which the crosssectional area over which the oil-water mixture is discharged from the heat exchange vessel into the reservoir is significantly less than the cross-sectional area of the surface of the oil-water mixture in the reservoir at its normal operating level.

3. Apparatus for separating components of an oil-water mixture, which comprises: (a) a heat exchange vessel with an inlet and an outlet for the oil-water mixture between which the mixture can flow, and a gas inlet arranged so that gas supplied through it to the vessel can flow through the vessel, in a direction from the mixture outlet towards the mixture inlet, (b) a reservoir for collecting the mixture discharged from the mixture outlet in the vessel, (c) a conduit through which liquid in the reservoir can be supplied to the mixture inlet in the vessel, in which the cross-sectional area over which the oil-water mixture is discharged from the end of the heat exchange vessel into the reservoir is significantly less than the crosssectional area of the surface of the oil-water mixture in the reservoir at its normal operating level.

4. Apparatus as claimed in claim 3, which includes means for heating liquid supplied from the reservoir to the mixture inlet so that its temperature when received in the inlet is higher than ambient temperature.

5. Apparatus as claimed in claim 1 or claim 4, in which the liquid heating means is arranged to heat the liquid at a point between the reservoir and the inlet to the vessel so that the temperature of the liquid in the inlet is higher than that of the liquid leaving the reservoir.

6. Apparatus as claimed in any one of claims 1 to 5, which includes means for distributing the flow of the oil-water mixture across the cross-sectional area of the vessel.

7. Apparatus as claimed in claim 6, in which the said distributing means provides a transversely dispersed flow of the oil-water mixture across the top of the vessel.

8. Apparatus as claimed in any one of claims 1 to 7, in which the vessel contains means for disturbing the flow of the oil-water mixture through the vessel, to facilitate mixture of the oil-water mixture and the gas as they flow countercurrently through the vessel.

9. Apparatus as claimed in any one of claims 1 to 8, which includes means for supplying warm gas to the vessel at the gas inlet.

10. Apparatus as claimed in claim 9, in which the warm gas supply means comprises a conduit for connection to a source of waste warm gas.

11. Apparatus as claimed in any one of claims 1 to 9, which includes means for heating gas which is supplied to the vessel at the gas inlet.

12. Apparatus as claimed in any one of claims 9 to 11, which includes means for controlling the temperature of the heated gas supplied to the vessel.

13. Apparatus as claimed in claim 12, in which the temperature controlling means controls the temperature of the heated gas so that it is at least about 450C.

14. Apparatus as claimed in claim 12 or claim 13, in which the temperature controlling means controls the temperature of the heated gas so that it is not more than about 950C.

15. Apparatus as claimed in any one of claims 1 to 14, which includes a detector for an upper level of liquid in the reservoir.

16. Apparatus as claimed in any one of claims 1 to 15, which includes a detector for an lower level of liquid in the reservoir.

17. Apparatus as claimed in any one of claims 1 to 16, which includes means for minimising agitation of the surface of liquid in the reservoir as a result of discharge into the reservoir of the oil-water mixture from the vessel outlet.

18. Apparatus as claimed in claim 17, in which the means for minimising agitation of the surface of liquid in the reservoir causes oil-water mixture discharged into the reservoir to flow into the reservoir preferentially down the walls of the reservoir.

19. Apparatus as claimed in any one of claims 1 to 18, in which the reservoir has an outlet for removing one of a plurality of separated layers of immiscible liquids.

20. Apparatus as claimed in any one of claims 1 to 19, which includes means for condensing vapour discharged from the vessel with the heated gas leaving the vessel at or towards its upper end.

21. Apparatus as claimed in any one of claims 1 to 20, which includes a filter for material discharged from the vessel with the heated gas leaving the vessel at or towards its upper end.

22. Apparatus as claimed in any one of claims 1 to 21, in which the mixture flows between the mixture inlet and the mixture outlet under gravity.

23. A method of separating components of an oil-water mixture, which comprises circulating an oil-water mixture through (a) a vessel in which the mixture flows countercurrently with a gas, and (b) a reservoir into which the mixture is discharged from the vessel and from which the mixture is abstracted for supply to the vessel, the mixture being heated during the circulation so that its temperature when discharged into the vessel is higher than its temperature when discharged from the vessel into the reservoir.

24. A method as claimed in claim 23, in which oil-water mixture discharged from the vessel is collected in a reservoir, and oil-water mixture that is supplied to the vessel is supplied from the reservoir.