GB2260133A - Apparatus for separating oil from an oil/water mixture - Google Patents

Abstract

Apparatus for separating oil from an oil water mixture comprises an entry port 8 into a gas release region, within wall 10. An impermeable liquid feed tube 12 extends from the interior of the gas release region to open into the lower part of a separation chamber 3 having an outlet 5 only in an upper part thereof. The outlet opens into a settlement chamber 4, and an oil outlet 22 opens from an upper region of the settlement chamber above the level of the outlet 5 and below the level of the gas release region. A sorbent bed 33 is contained in a further separation chamber. A water outlet 30 leads from a lower region of the settlement chamber, and water may flow therethrough to the sorbent bed. A final water outlet 38 leads from the sorbent bed at a level below the oil outlet 22. <IMAGE>

Description

APPARATUS FOR SEPARATING OIL FROM AN OIL/WATER MIXTURE This invention relates to apparatus for separating oil from an oil/water mixture.

Oil/water separators are known which rely on settlement of the mixture to allow oil to be drawn off at a higher level than water, but these have limited efficiency as they are unable effectively to separate the oil/water emulsion which is also present in these mixtures.

It is becoming increasingly important to separate oils from contaminated water before discharging the water to the sewage system, in order to reduce pollution levels.

Furthermore, if effective oil separation can be carried out by simple, on-site apparatus then the site operator's need for specialised waste collection can be significantly reduced.

It is known from GB-A-2084480 that an oil/water mixture can be separated by feeding the mixture through a coalescing filter into a settlement chamber having an oil outlet opening from an upper region thereof and a water outlet from a lower region thereof. Water from this outlet passes to a sorbent bed contained in a second chamber and flows through the sorbent bed. Our co-pending British application No 9114689.4 describes a more sophisticated separator utilising a similar principle.

Oils traditionally used in compressor lubrication are able to separate reasonably readily from an oil/water mixture.

Some oils which are now seeing increasing use are designed to emulsify in water, and separation is therefore much more difficult. This invention seeks to provide separation apparatus that is effective for a wide range of oils.

According to the present invention, apparatus for separating oil from an oil water mixture comprises an entry port into a gas release region, an impermeable liquid feed tube extending from the interior of the gas release region to open into the lower part of a separation chamber having an outlet only in an upper part thereof, said outlet opening into a settlement chamber, an oil outlet opening from an upper region of the settlement chamber above the level of the outlet from the separation chamber and below the level of the gas release region, a sorbent bed contained in a further separation chamber, a water outlet from a lower region of the settlement chamber through which water may flow to the sorbent bed, and a final water outlet from the sorbent bed at a level below the oil outlet.

Most surprisingly, it has been found that replacing the coalescing filter by the gas release region and separation chamber in the relationship specified leads to more effective operation. In particular more oil can be separated from the mixture before the liquid passes to the sorbent bed, and the life of that bed can be prolonged accordingly.

In operation, the oil/water mixture enters the device.

Entrained air or other gas is released to atmosphere either directly or indirectly from the gas release region. The oil/water emulsion passes to the separation chamber and the oil and water commence separating in that chamber, and rise through that chamber. The materials then pass into the settlement chamber, where free oil rises to the surface of the liquid within the chamber and flows therefrom through the oil outlet.

Water with a very low level of contaminant leaves the lower part of the settlement chamber from which it passes through the sorbent bed and thence from the device. The sorbent bed is effective to remove most remaining traces of oil, together with other impurities, and the water is sufficiently clean to enable it to be discharged directly to the sewage system without any significant pollution resulting therefrom.

The oil can simply be allowed to accumulate until a sufficient quantity has been collected for economic disposal by a specialist.

It has been found that the level of contaminant remaining in the waste water leaving the device is typically less than 5mg/l, a level that is significantly lower than previously achieved.

In one embodiment of the invention the settlement chamber is defined within a vessel, the gas release region is located within the vessel above the level of the oil outlet opening, the vessel has gas vent means from space within the vessel above the level of the oil outlet opening, the separation chamber is located within the vessel, the oil outlet is connected through the vessel wall to an oil collection region and the water outlet is connected through the vessel wall to the further separation chamber. The gas release region may then be a region with a permeable wall through which gas may pass to the exterior thereof.

Desirably the vessel is formed with first and second reentrant sections in the sides thereof, the first re-entrant section accommodates an oil collection receptacle therein to receive oil from the oil outlet, and the second re-entrant section accommodates a housing within which is defined the further spearation chamber. The oil collection receptacle and the housing may each be removably mounted in their respective re-entrant section.

The separation chamber is preferably defined within the lower part of a casing extending downwardly from the top of the vessel, the gas release region is located within the upper part of the casing, and the upper part of the casing has a gas outlet opening into space within the vessel above the level of the oil outlet opening.

The casing containing the gas release region, liquid feed tube and separation chamber may be a unit designed to be replaceable, and therefore releasably mounted in the vessel.

In another embodiment the gas release region comprises an exhaust chamber isolated from space within the vessel above the level of the oil outlet opening. This is advantageous in that entrained air is separated and discharged, preferably to the atmosphere by way of filter means, without entering the space above the liquid in the settlement chamber; thus there can be no disturbance of that liquid. The exhaust chamber desirably has a curved wall, the entry port being aligned so that the incoming mixture impinges substantially tangentially on to the curved wall.

The sorbent bed may be of any suitable material that will effect the required removal action. The preferred material will usually be activated carbon, but materials such as an activated alumina, zeolite or hydrophobic polyurethane foam may be used.

Conveniently the oil outlet comprises a funnel having an open upper end and connected to an outlet pipe. The funnel may be adjustable in height to allow oil drainage into the funnel at different levels.

Preferably water is directed from the lower region of the settlement chamber to flow to a delivery level above the level of the sorbent bed, and the water level from the sorbent bed comprises an outlet pipe extending upwardly from a lowermost part of the sorbent bed. Desirably the outlet pipe extends upwardly to a level above the top of the sorbent bed but below the delivery level.

In order that the invention may be better understood, specific embodiments of apparatus in accordance therewith will now be described in more detail, by way of example only, with reference to the accompanying drawing, in which: Figure 1 is a schematic sectional drawing of the apparatus; and Figures 2 to 4 show alternative embodiments of part of the apparatus of Figure 1.

The apparatus shown in Figure 1 comprises a vessel 1, which may desirably be seamless and formed, for example, by rotational moulding of a suitable plastics material. The vessel is divided by an inserted cylindrical casing 2 into a separation chamber 3 lying within the casing and a chamber 4 lying outside the casing and forming a settlement chamber. The separation chamber 3 communicates with chamber 4 by way of openings 5 cut in the upper part of the wall of the casing 2.

The top of the vessel is fitted with an inlet manifold 7 which includes entry ports 8 for introducing air/oil/water mixture to be separated. An exit port 9 from the inlet manifold opens into the interior of a gas release region having a gas permeable wall 10 mounted in the first chamber with its axis extending vertically within that chamber. The upper end cap of the wall 10 is secured to the inlet manifold. The gas release region is located wholly above the level that will be the steady state liquid level when the apparatus is in use. An impervious liquid feed tube 12 extends downwardly from the lower end cap of filter 10 to the lower part of the separation chamber 3.

The wall 10 of the gas release region is desirably designed to impose a very low pressure drop on gas passing therethrough to ensure a steady gas flow that will not disturb liquid settling in the apparatus and to ensure that no gas is forced down the liquid feed tube 12. The wall 10 may, for example, simply be a length of open weave fabric wound around a perforated metal cylinder, or may be any suitable form of coalescing filter.

Above the wall 10, the inlet manifold 7 may optionally incorporate a visually indicating pressure relief valve 13 comprising a clear plastic housing 14 within which a ball valve 15 is urged onto a seat by a compression spring 16. The vessel 1 has a gas vent hole in the top thereof.

An oil outlet pipe 18 is located within the settlement chamber 4 and extends downwardly through a sliding seal secured by a bulkhead fitting 19 in a re-entrant section 20 of the vessel wall. The pipe can drain into an oil collection tank 21, desirably of a translucent plastics material, removably supported in the re-entrant section. A funnel 22 is secured to the upper end of the outlet pipe 18 and a support bar 23 extends across the open top of the funnel. A support rod 24 extends upwardly from the support bar 23 through a locking gland 25 in the upper wall of the vessel. A "T" bar 26 is secured to the upper end of the support rod 24 and protected by a removable cap 27. The height of the funnel may be adjusted by removing the cap 27, unlocking the gland 25, grasping the"T" bar to manually move the rod 24 and then re-locking the gland 25.

The vessel 1 has a second re-entrant section 28, with an opening in which a seal 29 is located. The upper end of a dip pipe 30 extends through the seal 29 and the pipe is secured to the wall of the re-entrant section 28 by a nut screwed on to a threaded end of the pipe. The dip pipe extends vertically downwardly within the settlement chamber 4 to the lower portion thereof.

An activated carbon filter 31 forming a further separation chamber is supported in the reentrant section 28.

The activated carbon filter comprises a housing 32 packed with a sorbent bed 33 of activated carbon between perforated end plates and mounted with its axis substantially vertical. An inlet 36 is formed in the upper part of the filter and can be located as a push fit on to the projecting end of the dip pipe 30. A discharge pipe 37 extends upwardly through the sorbent bed from the bottom thereof to a clean water outlet level 38 that lies below the opening 39 from pipe 30 and above the level 40 of the top of the sorbent bed. This arrangement ensures a constant level of water above the sorbent bed, so that if there should be any small transfer of oil through dip pipe 30 this will float within the housing 32 in which the sorbent bed is contained and will not contaminate that bed.The bed may be maintained in a compressed state by a porous disc 41 located on top of the bed and held by a locking washer 42 secured on the outside of discharge pipe 37. The pipe 37 may be connected to drain into the sewage system.

A sample tap 43 is located part way up the activated carbon filter, and can be used to draw a water sample from the filter for analysis.

The lower part of the opening 39 from the dip pipe 30 lies below the level of the upper rim of the funnel 22, and the top of the discharge pipe 37 lies below the level of the opening from the dip pipe 30.

The top of the vessel is provided with removable inspection caps such as 44, and has a gas vent opening 45, which is above the level of the oil outlet opening.

Operation of the apparatus will readily be understood.

The apparatus is initially primed with clean water until steady state flow from the water outlet is attained. Thereafter, an air/oil/water mixture discharged, for example, from a compressor aftercooler or a compressed air ring main, enters the system into the inlet manifold 7 and passes into the gas release region. Any air that is with the liquid escapes through the wall 10 of this region above the liquid level within the settlement chamber 4, and leaves the vessel through vent opening 45. The wall 10 may also act to remove some airborne aerosol and to have a silencing effect on the escaping air. The liquid mixture passes from the gas release region down feed tube 17 into separation chamber 3, wherein the oil begins to separate from the water. The liquid rises through the chamber 3 and emerges into the settlement chamber 4 through the openings 5.Within the settlement chamber 4 the liquids continue separating into three fractions, a lower fraction of water, an intermediate fraction of emulsion and an upper fraction of oil. The lower fraction of water passes through the dip pipe 30 into the activated carbon filter 31, and after passage through the carbon bed the water passes to discharge pipe 37.

Following initial charging of the device with clean water the level of liquid in the settlement chamber 4 will be determined by the height of the water outlet 38. As oil builds up in the settlement tank the average specific gravity reduces and the level increases, eventually resulting in a flow of oil from the upper fraction in settlement chamber 4 outwardly through the pipe 18 and into the oil collection tank 21, together with a constant flow of water from the lower fraction in chamber 4 into and through the activated carbon filter to the discharge pipe 37 and so to the sewage system.

The water flowing from chamber 4 is left with a low level of remaining contamination, and that contamination is reduced still further by passage of this water through the activated carbon filter 21. As a result of this action the water leaving the system can exhibit contamination levels less than 5mug/1, well within acceptable standards for direct discharge into the sewage system.

In a modified form of the apparatus in Figure 1 the lower end of the liquid feed tube 12 may open into the interior of a coalescing filter 50 as indicated in broken lines in Figure 1. The filter 50 may be a conventional coalescing filter, for example of a construction similar to that described in GB-B-2128497 or GB-A-2198739. Such filters comprise an upper end cap and a lower end cap between which extend inner and outer perforated metal cylinders. A cylinder of filter medium is sandwiched between the metal cylinders, the filter medium being, for example, non-woven polypropylene fibre or boro-silicate glass microfibre. Filter 50 could simply be a body of plastics foam or other open material providing a high internal surface area onto which oil droplets may coalesce.

Foam is the presently preferred medium as in addition to providing the required surface area it also does not impose any significant pressure drop to the liquid flowing therethrough.

A filter in the position 50 will in due course commence to become blocked and will accordingly impose an increasing back pressure on the liquid flowing through tube 12. If the optional valve 13 is incorporated in the inlet manifold then a visual indication will be given of this increasing pressure, by lifting of the ball valve 15 and the filter 50 can thereafter be replaced.

Figures 2 and 3 show alternative arrangements for the separation chamber 3, and parts corresponding to those in Figure 1 are indicated by the same reference numerals with the suffix a. In the embodiment of Figure 2 the liquid feed tube 12a supports a series of baffles or vanes 51, the edges of which may be located closely to the internal surface of the casing 2. Baffles 51 may also be formed with openings such as 52 through which the liquid may pass. The baffles are desirably of fibreglass or a suitable plastics material such as polyethylene. The presence of the baffles will aid removal of suspended oil droplets due to impaction and surface tension effects. These droplets will attach temporarily to the surfaces of the baffles, will coalesce and will then float upwardly through the tortuous path defined by the baffles to the upper section of the separation chamber 3.

In the embodiment of Figure 3 the liquid feed tube 12a supports a spiral baffle 53, which again may be formed of fibreglass or a suitable plastics material, and which will again assist in separation the oil and water phases. In each of the Figures 2 and 3 embodiments the lower end of the liquid feed tube 12 may open into an optional coalescing filter 50a.

Baffle arrangements other than those of Figures 2 and 3 can be incorporated in the separation chamber 3.

Figure 4 illustrates a further arrangement of initial separating means. In this embodiment the inlet manifold 7 is replaced by a gas exhaust chamber 60 designed to be mounted on top of the vessel 1. The exhaust chamber has an inlet 61 for the incoming air/oil/water mixture, the inlet being directed substantially tangentially towards a curved wall 62 of the chamber. A central annular partition 63 has an inwardly directed lower flange 64 on which rests a first filter 65 and an upper section 66 of greater diameter forming a rim on which rests a second filter 67. The partition 63 may be a separate structure secured within an opening of the exhaust chamber 60 or may be moulded as an integral part thereof.

The first filter 65 is of such a nature that it is effective to remove any oil/water mist that is present in air passing through the filter out of the exhaust chamber and to remove any larger particles, without imposing any significant pressure drop. The second filter 67 should be similarly effective. It may, for example, be a foam pad and it is possible for this to be impregnated with activated carbon in order that any residual oil vapour is adsorbed from the air before discharge to the atmosphere.

The lower wall 68 of the exhaust chamber 60 opens into a basin 69, from the bottom of which extends an impervious liquid feed tube 70. The exhaust chamber 60 is mounted on the container 1 so that the basin 69 and tube 70 extend downwardly within a cylindrical partition 71 having a closed lower end and openings 72 towards its upper end, equivalent to the partition 2 of the embodiment of Figure 1. If desired, the lower end of tube 70 may open into the interior of a coalescing filter (not shown) similar to the filter 50 indicated in Figure 1.

In operation, the mixture to be separated enters the exhaust chamber and impinges substantially tangentially on to the curved wall thereof. The liquids separate from the air on the wall of the chamber and drain into the basin 69 and thus into the separation chamber formed by the interior of cylindrical partition 71. The separated air leaves the exhaust chamber 60 through the filters 65 and 67 and passes to atmosphere, any liquid mist being coalesced from the air by these filters and draining into the basin 69. In the separation chamber within partition 71 the oil begins to separate from the water and the liquid rises through the chamber and emerges through the openings 72 into the settlement chamber within the vessel 1. There the liquids continue separating, contaminant is discharged and the activated carbon filter 37 functions as already described.This embodiment is advantageous in that entrained air is separated and discharged without entering the space above the liquid in the settlement chamber. No disturbance of that liquid is possible and the apparatus can thus effectively handle higher air and liquid volumes and irregular inputs.

The activated carbon filter will need changing at intervals. Checks can be made by periodically taking samples from sample tap 43 and the filter should be changed when the water quality is still above acceptable values. This change is extremely simple, due to the location of the filter externally of the vessel 1. The carbon filter may alternatively be a filter comprising any other suitable sorbent bed, for example activated alumina, zeolite or hydrophobic polyurethane foam.

It will be appreciated that the particular arrangement of the apparatus may vary from that shown in the drawings. Using re-entrant sections of the main settlement vessel to accommodate the activated carbon filter and the oil collection tank leads to a particularly compact and elegant design.

However, these are not necessary and other arrangements could be used. Leading the discharge pipe from the activated carbon filter upwardly for virtually the full height of that filter increases dwell time of water in the carbon bed for higher filtering efficiency. A similar effect could be achieved by having upward flow through the filter, water being led from the settlement vessel at a lower part thereof for connection to the filter. In such arrangement a valve would be necessary in that connection to prevent drainage from the settlement chamber during replacement of the activated carbon filter.

In general, separation performance increases with longer residence time, i.e., improves inversely in relation to flow velocity through the apparatus, so that design to encourage low flow velocities is advantageous.

Claims (16)

1. Apparatus for separating oil from an oil water mixture comprising an entry port into a gas release region, an impermeable liquid feed tube extending from the interior of the gas release region to open into the lower part of a separation chamber having an outlet only in an upper part thereof, said outlet opening into a settlement chamber, an oil outlet opening from an upper region of the settlement chamber above the level of the outlet from the separation chamber and below the level of the gas release region, a sorbent bed contained in a further separation chamber, a water outlet from a lower region of the settlement chamber through which water may flow to the sorbent bed, and a final water outlet from the sorbent bed at a level below the oil outlet.

2. Apparatus according to claim 1 in which the settlement chamber is defined within a vessel, the gas release region is located within the vessel above the level of the oil outlet opening, the vessel has gas vent means opening from space within the vessel above the level of the oil outlet opening, the separation chamber is located within the vessel, the oil outlet is connected through the vessel wall to an oil collection region and the water outlet is connected through the vessel wall to the further spearation chamber.

3. Apparatus according to claim 2 in which the vessel is formed with first and second re-entrant sections in the sides thereof, the first re-entrant section accommodates an oil collection receptacle therein to receive oil from the oil outlet, and the second re-entrant section accommodates a housing within which is defined the further separation chamber.

4. Apparatus according to claim 3 in which the oil collection receptacle and the housing are each removably mounted in their respective re-entrant section.

5. Apparatus according to any one of the preceding claims in which the oil outlet comprises a funnel having an open upper end and connected to an outlet pipe extending through a wall of the settlement chamber.

6. Apparatus according to any one of the preceding claims in which the sorbent bed comprises activated carbon.

7. Apparatus according to any one of the preceding claims in which water is directed from the lower region of the settlement chamber to flow to a delivery level above the level of the sorbent bed, and the water level from the sorbent bed comprises an outlet pipe extending upwardly from a lowermost part of the sorbent bed.

8. Apparatus according to claim 7 in which the outlet pipe extends upwardly to a level above the top of the sorbent bed but below the delivery level.

9. Apparatus according to any one of the preceding claims in which the gas release region is a region with a permeable wall through which gas may pass to the exterior thereof.

10. Apparatus according to claim 9 in which the separation chamber is defined within the lower part of a casing extending downwardly from the top of the vessel, the gas release region is located within the upper part of the casing, and the upper part of the casing has a gas outlet opening into space within the vessel above the level of the oil outlet opening.

11. Apparatus according to claim 10 in which the casing containing the gas release region, liquid feed tube and separation chamber is a unit designed to be replaceable, and is releasably mounted in the vessel.

12. Apparatus according to any one of claims 1 to 8 in which the gas release region comprises an exhaust chamber isolated from space within the vessel above the level of the oil outlet opening.

13. Apparatus according to claim 12 in which the exhaust chamber opens to atmosphere by way of filter means.

14. Apparatus according to claim 12 or 13 in which the exhaust chamber has a curved wall, and the entry port is aligned so that the incoming mixture impinges substantially tangentially on to the curved wall.

15. Apparatus for separating oil from an oil water mixture substantially as herein described with reference to Figures 1 to 3 of the accompanying drawings.

16. Apparatus for separating oil from an oil water mixture substantially as herein described with reference to Figure 1 as modified by Figure 4 of the accompanying drawings.