GB2116060A

GB2116060A - Oil-water separator

Info

Publication number: GB2116060A
Application number: GB08206522A
Authority: GB
Inventors: Alan Virrill
Original assignee: Hamworthy Engineering Ltd
Current assignee: Hamworthy Engineering Ltd
Priority date: 1982-03-05
Filing date: 1982-03-05
Publication date: 1983-09-21

Abstract

A separator for separating oil from water comprises a multi-stage coalescing corrugated plate pack 10, preferably combined with a gravity separator 5 at its inlet end and connected to receive the oil/water mixture without pumping on the inlet side. The mixture is fed to the separator by gravity or is sucked into the separator by a pump 1 connected to the separated water outlet. A pump 2 for separated oil may also be provided. The absence of a pump on the inlet side ensures that the oil reaches the separator as relatively large droplets which are easy to separate. <IMAGE>

Description

SPECIFICATION Oil-water separator This invention relates to devices for separating oil from water. The invention has particular but not exclusive reference to oil-water separators for use aboard ship, to prevent oil from being in advertently discharged overboard during the pumping of a ship's bilge or ballast tank; legislation is in prospect, to control the discharge of oil from the bilges and ballast tanks of ships and therefore improved separation is desirable. The invention is however also applicable to the separation of oil from waste water or effluent on land.

In a conventional separator system the water/oil mixture is pumped from a bilge or other reservoir through a separator which typically might consist of a gravity section followed by a plate pack or other form of coalescer followed in turn by a polishing filter in order to achieve a high level of separation below, say, 15 parts per million.

The disadvantage of these systems is that the pump, being upstream of the separator and feeding the separator at a positive pressure, creates shearing forces in the oil/water mixture which reduce oil droplet size, especially at high shaft speeds, and make subsequent oil separation very difficult.

According to the present invention, in apparatus for separating oil from water, the oil/water mixture is not pumped into the separator. Accordingly the mixture is not subjected to shearing forces before entering the separator, and the latter can therefore operate more efficiently and/or be made smaller than in conventional oil/water separating apparatus, because it can be designed to operate on relatively large oil droplets.

Flow of the mixture can be provided for example by means of a pump of which the suction side is connected to the separator, instead of the delivery side as in conventional systems. The pump operator on the separated water. A further pump may be provided to withdraw the separated oil. In such an arrangement, the separator, which is on the suction side of the pump or pumps; accommodates the varying conditions of the suction lines. It enables high pump speeds to be used than in conventional systems, producing greater suction lift and head characteristics from the pumps to be used.

Alternatively, flow through the separator can be produced by gravity, for example using a header tank with gravity discharge to the separator, the direction of flow being controlled for example by valves in the oil and water discharge lines. Again, as the oil/water mixture does not pass through a pump, the oil droplets are not sheared and reduced in size before reaching the separator.

According to another aspect of the present invention, an oil/water separator comprises a multi-stage coalescing corrugated plate pack. Such a separator is particularly suitable for use on the suction side of a pump or pumps or for receiving a gravity feed as set forth above. It may be combined with a gravity separator. in the plate pack, smaller oil droplets coalesce to form large globules which rise into a collection chamber.

The present invention is illustrated by the accompanying drawings, in which: Figure 1 is a diagram of oil/water separating apparatus embodying the invention, and Figure2 is a perspective view of a separator plate pack.

Figure 1 shows a separator including a fabricated steel vessel 30 containing a horizontal three-stage coalescing corrugated plate pack made from oleophilic pvc, polypropylene or similar material.

The plate pack 10 is shown in Figure 2 and comprises three packs of corrugated pvc plates 31 and suitable supports 32, the plate spacing being about 10 mm.

The crest and troughs of the corrugations are horizontal and the individual plates are vertical, although other configurations are possible, e.g.

vertical corrugations and vertical or tilted plates.

The plate pack is combined with a gravity separator Sat its inlet end. The mixture of oil and water to be separated is drawn into the gravity separator from a reservoir 33 through a strainer 3 and a non-return solenoid or motorised valve 4.

The mixture of oil and water is caused to flow through the gravity separator 5 and plate pack 10 by an oil pump 2 and a water pump 1. These are positive displacement pumps mounted on the separator unit and connected to the latter on the suction sides of the pumps. Alternatively, suitable pumps producing the correct oil and water flow rate can be mounted remotely from the separator. Becaue the separator is on the suctin side of the pumps, it operates under partial vacuum and the oil in the mixture is not subjected to any shearing action before it enters the separator.

In the gravity separator 5, most of the oil in the oil/water mixture separates out due to the difference in density between the oil and water, and the oil collects in the top of the gravity separator vessel.

Solids can collect in a sump 7 at the bottom of the gravity separator, which sump also communicates with the bottom of the plate pack 10.

The water and residual oil passes from the gravity separator 5 through the coalescing corrugated plate pack 10, in which the remaining smaller droplets of oil coalesce as they pass through the plate pack, and form larger globules which rise through the plate pack and eventually into the oil collection chamber 6 which comprises the upper part of the gravity separator. The outlet end 12 of the plate pack communicates with an oil transfer pipe 11 so that any oil which has passed through the plate pack to its outlet end can collect and travel upwards to the oil collection chamber 6, particularly when the separator is tilted, for example aboard ship when pitching or rolling.

Depending on the amount of oil collected in the chamber 6, flow is drawn in one orthe other of two directions, by one or the other of the suction pumps.

The oil chamber 6 is provided with lower and upper oil level probes or sensors 8. 9, which can for example capacitive, conductive or ultrasonic probes.

The control system is so arranged that, when both probes 8 and 9 detect water, the water pump 1 will run, drawing the flow through the three-stage coalescing plate pack 10. Oil particles will coalesce on the plates until the globules are large enough to rise off the plates and through the pack 10 into the oil chamber 6. The oil transfer pipe 11, allows oil collected at the outlet end 12 to travel to the oil chamber 6. Water is drawn from the outlet pipe 13 to the water pump 1, which then pumps the water through a non-return valve 14to a discharge outlet 15. Asampling point 16 is positioned along this pipe.

When both probes 8 and 9 detect oil, the water pump 1 stops and the oil pump 2 starts drawing oil through oil outlet 17 of chamber 6 into the oil pump 2. This pumps the oil through a non-return valve 18, and into an oil collecting tank 19, until the upper probe 9 detects water: the oil pump 2 then stops and the water pump 1 starts. That sequence continues until the unit is stopped manually or is controlled by a high/low level float switch 20, in the mixture reservoir 33.

The pumps 1 and 2 are protected from dry running by an automatic priming system. If air enters the unit it will rise to an air collection chamber 21 at the top of the oil chamber 6, and drop a magnetic float switch 22, which will stop the pumps 1 and 2, open an air vent solenoid valve 23, and a water prime solenoid valve 24. When all the aid has been expelled through the vent 23, the valves 23 and 24 will close and the pump will start.

Oil discharge due to faulty probes 8 or 9 is prevented by an oil alarm probe 25, stopping the water pump 1 if oil is detected at the outlet 13.

The oil chamber is fitted with an immersion heater 28 to deal with very viscous oils and oil slugs, and for cleaning.

Plate packs are cleaned in situ by reverse flushing, as follows. Oil is drawn from the unit using pump 2.

Water suction valve 26 is closed, and valve 24 and a recirculation valve 27 are opened; the unit is then primed with clean water via the water supply valve 24. The immersion heater 28 and oil pump 2 are switched on for a specified time. The heater 28 and pump 2 are switched off and the sump drain valve 29, and vent valve 23, are opened to drain back to the reservoir or bilge.

The drain valve 29 also serves for removal of solids from the sump 7.

The control circuitry between the oil-sensing devices 8, 9 and 25, and the pumps is not shown; similarly the control circuitry incorporating the float switch 22 and the float switch 20 is not shown. Any suitable control circuitry can be provided.

Because the oil does not pass through a pump before separation, the oil globules entering the separator are relatively large and therefore easy to separate. Furthermore, because it is not necessary to design or operate the pumps in such a way as to reduce shearing of oil globules, high pump speeds can be used, producing greater suction lift and head characteristics from the pumps. The separator can therefore operate more efficiently than a conventional separator with an upstream pump.

As already mentioned, shear-free flow can be produced by using a gravity feed to the separator instead of pumps. The direction of flow can be controlled by suitable valves in the oil and water discharge lines.

CLAIMS (Filed on 4/3/83) 1. Apparatus for separating oil from water, comprising an oil/water separator and means for effecting flow therethrough of an oil/water mixture, characterised in that the means for effecting flow is pumping means downstream of the separator and/ or a gravity flow system, whereby the mixture is not subjected to shearing upstream of the separator.

2. Apparatus as claimed in claim 1 in which the separator has an outlet for separated water and the said pumping means is connected to the said outlet.

3. Apparatus as claimed in claim 2 including further pumping means for withdrawing separated oil from the separator.

4. Apparatus as claimed in claim 1,2 or 3 in which the separator comprises a multi-stage coalescing corrugated plate pack.

5. Apparatus as claimed in claim 1,2,3 or 4 in which the separator comprises a gravity separation chamber.

6. Apparatus as claimed in claim 4 in which the separator has a gravity separation chamber immediately upstream of the plate pack.

7. Apparatus as claimed in claim 6 in which the plate pack and gravity separation chamber are in a common housing.

8. An oil/water separator comprising a multistage coalescing corrugated plate pack.

9. A separator as claimed in claim 8 in which the multi-stage plate pack is mounted in a housing having at an inlet and thereof a chamber for initial gravity separation of oil from water, which chamber communicates directly with the first stage of the plate pack.

10. An oil/water separator substantially as herein described with reference to the accompanying drawings.

11. Oil/water separating apparatus substantially as herein described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. coalescing plate pack 10. Oil particles will coalesce on the plates until the globules are large enough to rise off the plates and through the pack 10 into the oil chamber 6. The oil transfer pipe 11, allows oil collected at the outlet end 12 to travel to the oil chamber 6. Water is drawn from the outlet pipe 13 to the water pump 1, which then pumps the water through a non-return valve 14to a discharge outlet 15. Asampling point 16 is positioned along this pipe. When both probes 8 and 9 detect oil, the water pump 1 stops and the oil pump 2 starts drawing oil through oil outlet 17 of chamber 6 into the oil pump 2. This pumps the oil through a non-return valve 18, and into an oil collecting tank 19, until the upper probe 9 detects water: the oil pump 2 then stops and the water pump 1 starts. That sequence continues until the unit is stopped manually or is controlled by a high/low level float switch 20, in the mixture reservoir 33. The pumps 1 and 2 are protected from dry running by an automatic priming system. If air enters the unit it will rise to an air collection chamber 21 at the top of the oil chamber 6, and drop a magnetic float switch 22, which will stop the pumps 1 and 2, open an air vent solenoid valve 23, and a water prime solenoid valve 24. When all the aid has been expelled through the vent 23, the valves 23 and 24 will close and the pump will start. Oil discharge due to faulty probes 8 or 9 is prevented by an oil alarm probe 25, stopping the water pump 1 if oil is detected at the outlet 13. The oil chamber is fitted with an immersion heater 28 to deal with very viscous oils and oil slugs, and for cleaning. Plate packs are cleaned in situ by reverse flushing, as follows. Oil is drawn from the unit using pump 2. Water suction valve 26 is closed, and valve 24 and a recirculation valve 27 are opened; the unit is then primed with clean water via the water supply valve 24. The immersion heater 28 and oil pump 2 are switched on for a specified time. The heater 28 and pump 2 are switched off and the sump drain valve 29, and vent valve 23, are opened to drain back to the reservoir or bilge. The drain valve 29 also serves for removal of solids from the sump 7. The control circuitry between the oil-sensing devices 8, 9 and 25, and the pumps is not shown; similarly the control circuitry incorporating the float switch 22 and the float switch 20 is not shown. Any suitable control circuitry can be provided. Because the oil does not pass through a pump before separation, the oil globules entering the separator are relatively large and therefore easy to separate. Furthermore, because it is not necessary to design or operate the pumps in such a way as to reduce shearing of oil globules, high pump speeds can be used, producing greater suction lift and head characteristics from the pumps. The separator can therefore operate more efficiently than a conventional separator with an upstream pump. As already mentioned, shear-free flow can be produced by using a gravity feed to the separator instead of pumps. The direction of flow can be controlled by suitable valves in the oil and water discharge lines. CLAIMS (Filed on 4/3/83)

1. Apparatus for separating oil from water, comprising an oil/water separator and means for effecting flow therethrough of an oil/water mixture, characterised in that the means for effecting flow is pumping means downstream of the separator and/ or a gravity flow system, whereby the mixture is not subjected to shearing upstream of the separator.