EP0048158A2

EP0048158A2 - Interceptor tank

Info

Publication number: EP0048158A2
Application number: EP81304205A
Authority: EP
Inventors: Norman Wilfrid Purtell
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-09-17
Filing date: 1981-09-15
Publication date: 1982-03-24
Also published as: GB2083850A; EP0048158A3

Abstract

The invention is concerned with an interceptor tank, of the kind installed in drainage systems such as at garages, to prevent liquid of low specific gravity such as oil or petrol from being discharged with surface water into the sewage system. In accordance with the invention an interceptor tank (6) is divided into three generally superposed separation chambers (8,10,12) by partitions (14,16). Inlet means (42) is provided by which water containing petrol or oil is delivered to the lowermost chamber (8), the partitions being provided with apertures (26, 28) whereby water may pass upwardly from the lowermost to successively higher chambers, and through an outlet (38). A supplementary compartment (18) is provided, which is connected to the chambers in a manner whereby liquid of a specific gravity less than 1 may flow therefrom into the supplementary compartment, the supplementary compartment having an outlet (48) through which low s.g. liquid may flow, which is positioned at a level higher than the outlet (38) from the uppermost chamber. Liquid from the supplementary chamber (18) flows through the outlet (48) into a collection chamber (50) from which water may be removed from the lower part, and low s.g. liquid from the upper part.

Description

This invention is concerned with improvements relating to interceptor tanks, particularly of the kind (hereinafter referred to as being of the kind specified) which are installed in drainage systems, such as at petrol filling stations, to prevent liquid of low specific gravity (such as oil or petrol) from being discharged with surface water.
Interceptor tanks of the kind specified conventionally comprise a number of laterally adjacent compartments, separated by downwardly-extending partitions, so that when a mixture of water and oil is ducted into the interceptor, the oil (being of lower specific gravity than the water) is trapped in upper parts of the compartments and water relatively free from oil is discharged into the sewage system.
Such conventional interceptor tanks suffer from some at least of the following major disadvantages:-

1. To obtain acceptable freedom of the discharged water from liquid of low specific gravity, such ' such interceptors are necessarily large having five or more laterally adjacent compartments, and these require large holes to be excavated for their installation.
2. Difficulty is encountered in removing oil from the compartments, since this must be done separately for each compartment.
3. The oil removed from the compartments will necessarily be included with a significant quantity of water, which makes any reclamation of the oil difficult of expensive.
4. When water flows into the tank at a high rate, such as in consequence of a sudden storm, the turbulence which is created within the tank tends to cause oil which has previously separated out to be re-mixed with the water, and water carrying a significant quantity of oil flows from the tank.

According to this invention there is provided an interceptor tank of the kind specified comprising two vertically-spaced partitions dividing the tank into three generally superposed separation chambers, and inlet means by which water may be delivered to the lowermost chamber, the partitions being provided with apertures whereby water may pass upwardly from the lowermost to successively higher chambers, and through an outlet from the uppermost chamber, a supplementary compartment being provided which is connected at least to the two lower chambers in a manner whereby liquid of a specific gravity less than one may flow therefrom into the supplementary compartment, the supplementary compartment having an outlet through which low specific gravity liquid may flow, which is positioned at a level higher than the outlet from the uppermost chamber.
Preferably, the outlet from the supplementary compartment extends to a collection chamber into which liquid of low specific gravity flows from the supplementary compartment. In this manner, such low specific gravity liquid may be removed from the collection chamber without disturbance to the conditions pertaining in the interceptor tank itself.
Preferably the lowest point of the outlet from the supplementary compartment is at a level higher than the highest point of the outlet from the highermost chamber. In this manner, liquid (water) will flow preferentially through the outlet from the uppermost chamber and will not flow through the outlet from the supplementary compartment until the head of liquid of low specific gravity in the supplementary compartment is sufficiently high. In this manner, a large head of liquid of low specific gravity in the supplementary compartment may be obtained, tending to ensure that the liquid which flows through the outlet from the supplementary compartment is contaminated with water to a minimal extent only.
Preferably, the partitions are inclined to the horizontal. In this manner the highermost positions of the chambers will be at specific locations, providing for a concentration of liquid of lower specific gravity and a convenient ducting of such liquid into the supplementary compartment.
Most conveniently the partition separating the lowermost chamber from the intermediate chamber is inclined to the horizontal at a relatively small: angle, whilst the partition which divides the intermediate from the highermost chamber is or comprises a part which is inclined to the horizontal at a greater angle. Thus, the partition dividing the intermediate chamber from the highermost chamber may comprise a part which extends vertically.
Preferably the supplementary compartment is tapered, decreasing in cross-sectional area in the upward direction. In this manner, a greater criticality may be obtained at the point of discharge of low specific gravity liquid from the supplementary compartment in relation to the quantity of liquid entering the supplementary compartment.
Additionally, in the use of conventional interceptor tanks of the kind specified, difficulty is encountered in removing solid materials which may flow into the tank with the surface water, and usually this must also be done separately for each compartment.
Thus, preferably the partitions provide surface sloping downwardly within the tank and towards a central of the tank whereby solid materials which may be carried into the tank and which pass upwardly through the communi cation apertures in the partitions may fall away from said communication apertures towards the central part.
Preferably each of the partitions comprises, at the central part of the tank, an opening through which solid materials may fall from the uppermost and intermediate chambers into the lowermost chamber, whereby such solid materials may be removed from the tank in a single operation. Preferably the tank comprises a single valve member which, when in position, closes these openings, and which may be removed therefrom when it is desired to remove such solid materials from the tank.
Preferably both partitions comprise frusto-conical portions, said partitions extending upwardly and outwardly from a central vertical axis of the tank, and preferably the central axis of at least the lowermost partition is inclined to the vertical axis.
There will now be given a detailed description, to _'be read with reference to the accompanying drawing, of an interceptor tank which is a preferred embodiment of this invention and which has been selected for the purposes of illustrating the invention by way of example.
The accompanying drawing is a schematic vertical sectional view of the interceptor tank which is the preferred embodiment of this invention.
The interceptor tank comprises a generally spherical body 6, divided into lower, intermediate and upper separation chambers 8, 10, 12 respectively, by vertically-spaced partions 14, 16. The partition 14 comprises a main portion which is frusto-conical in form, the axis of the frustrume thereof being inclined to the vertical, the lowermost chamber 8 extending, at the location where the junction between the partition 14 and the peripheral wall of the body 6 is highest, into a supplementary compartment 18 which extends upwardly to ground level, terminating in a vent pipe 33.
The partition 16 comprises a lowermost part 15, which similarly is generally frusto-conical, but with axis vertical, and a vertical part 17, said vertical part 17 extending upwardly beyond the confines of the spherical body 6.
Each of the partitions 14 and 16 is provided with a central opening 20, 22 respectively, the tank comprising a valve member 24 which, when in operative position, seats against lips bounding the openings 20 and 22, to close the openings.
The partition 14 is provided at radially outer portions with a plurality of circumferentially spaced communication apertures or slots 26, and the vertical part of the partition 16 is provided with a plurality of circumferentially spaced communication apertures or slots 28. As is shown in the drawings, the communication apertures 28 are thus at radially inner locations, compared with the location of the apertures 26.
Extending from the uppermost region of the intermediate chamber 10 (as defined by the junction between the partition 18 and the peripheral wall of the body 6) into an upper portion of the supplementary compartment 18 is a transfer conduit 30.
The vertical wall 17 extends upwardly beyond the confines of the wall of the body 6, and provides a generally cylindrical upper portion 34 of the interceptor tank. Extending through the upper portion 34 and in communication with a vertical pipe 36 which extends from the portion 34 into the uppermost chamber 12, is an outlet 38, which is connected to an outlet pipe 40.
The interceptor tank also comprises an inlet pipe 42, which extends through the body and downwardly through the superposed compartments 12, 10 and 8, and opens into a lowermost part of the interceptor tank.
The supplementary compartment 18 comprises an outlet 32, through which liquid may flow from the compartment 18 and which is positioned at a level higher than the level of the outlet 38 through which liquid flows from the uppermost chamber 12.
In use, the interceptor tank which is the preferred embodiment of this invention will be mounted at a position below ground level (indicated G/L in the drawings) as is shown. Liquid, comprising generally water, low specific gravity liquid such as oil, and suspended solids, will be delivered to the lowermost chamber 8 through the inlet pipe 42. Displaced water will flow through the communication apertures 26 into the chamber 10, whilst oil will travel up the slope of the partition 14 towards and into the supplementary compartment 18, some oil however being carried through the communication openings 26 into the chamber 10. Such latter oil will float to the top of the intermediate chamber 10 to the junction between the partition wall 17 and the peripheral wall of the body 6, from which it will flow through the duct 30 into the upper part of the compartment l8, whilst further displaced water will flow through the communication openings 28 into the uppermost chamber 12. It will be appreciated that oil passing through the openings 26 will tend only to a minimal extent to be carried through the communication openings 28.
Since the lowermost point of the outlet 32 is higher than the highermost point of the outlet 38_, displaced liquid in the interceptor tank will normally flow through the outlet 38, through the pipe 40 into the sewage system. However when the quantity of liquid of low specific gravity in the supplementary compartment 18 increases to a sufficient extent, such low specific gravity liquid will flow through the outlet 32 and into the collection chamber 50. It will be appreciated that the occurrence of this will depend upon the specific gravity of the liquid trapped in the compartment 18, and its height. Desirably, such transference through the outlet 32 into the chamber 50 does not take place until a considerable quantity of low specific gravity liquid has been collected within the supplementary compartment 18, as is shown in the drawing, since this ensures that the low specific gravity liquid will have had a sufficient residence time in the compartment 18, to ensure that most at least of the water contained in suspension therein will have fallen therefrom, ensuring a minimum pollution of such liquid with water.
In the preferred embodiment shown in the accompanying drawing, the distance between the lowermost point of the outlet 32 and the highermost point of the outlet 38 (shown X) is in the order of two to three inches. However if desired, the oil transfer pipe 48 extending between the outlet 32 and the collection chamber 50 may be provided with means to facilitate variation of this distance to enable the distance to be adjusted in accordance with the specific gravity of the liquid being collected. Thus, where a spillage of liquid of lower specific gravity than normal takes place, the point of transference of such liquid from the supplementary compartment 18 into the collection chamber 50 may be increased.
Whilst the apparatus above described reliably separates low specific gravity liquid from water flowing through the inlet 42, nonetheless a film of liquid of low specific gravity may collect on the upper surface of water shown at the level W/L in the uppermost compartment 12. Desirably therefore, an opening 44, which may be a venturi opening, is located in the inlet pipe 42 at a position, about one inch below the water level. Thus, water entering the interceptor tank through the inlet pipe 42 will draw the surface layer of water from the uppermost chamber 12 back into the inlet pipe, for recirculation. In this manner, the freedom of the water being discharged to the sewage system through the outlet pipe 40 may be further reduced.
Non-bouyant solid material which may be carried into the interceptor tank with the inflowing water will initially settle at the base of the lowermost chamber 8. However, some suspended solids will initially be carried through the communication apertures 26 into the intermediate chamber 10; since the turbulance within the tank decreases in proportion to the distance from the termination of the inlet pipe, on passing through the communication apertures 26 and entering more quiescent liquid, some at least of the suspended solids will fall from suspension towards the central opening 20. Other solids will remain in suspension, to fall therefrom subsequent to passage through the communication apertures 28, where they will fall towards the central opening 22 of the partition 16.
When it is desired to remove such solid materials from the interceptor tank, it is merely necessary to remove the manhole cover M/C1 to lift the plug 24 by use of the rope 25 connected thereto, and to insert a suction hose downwardly through the openings 22, 20 and into the lowermost chamber 8, to evacuate by suction such solid material.
When it is necessary to remove low specific gravity liquid from the collection chamber 50, it is merely necessary to remove the manhole cover M/C2, and to suck out low specific gravity liquid from the collection chamber 50 by the use of a suction hose. It will of course be appreciated that this should be effected before the level of liquid in the collection chamber 50 reaches the level of the outlet pipe 48.

Claims

1. An interceptor tank of the kind which are installed in drainage systems, such as at petrol filling stations, to prevent liquid of low specific gravity (such as oil or petrol) from being discharged with surface water, comprising two vertically-spaced partitions (14,16) dividing the tank .(6) into three generally superposed separation chambers (8,10,12), and inlet means (42) by which water may be delivered to the lowermost chamber (8), the partitions (14,16) being provided with communication apertures (26,28) whereby water may pass upwardly from the lowermost to successively higher chambers, and through an outlet (38) from the uppermost chamber (12), a supplementary compartment (18) being provided which is connected at least to the two lower chambers (8,10) in a manner whereby liquid of a specific gravity less than one may flow therefrom into the supplementary compartment (18), the supplementary compartment having an outlet (32) through which low specific gravity liquid may flow, which is positioned at a level higher than the outlet (38) from the uppermost chamber (12).

2. An interceptor tank according to claim 1 wherein the outlet (32) from the supplementary compartment (18) extends to a collection chamber (50) into which liquid of low specific gravity flows from the supplementary compartment (18).

3. An interceptor tank according to one of claims 1 and 2 wherein the lowest point of the outlet (32) from the supplementary compartment (18) is at a level higher than the highest point of the outlet (38) from the uppermost chamber (12).

4. An interceptor tank according to any one of the preceding claims wherein the partitions (14,16) are inclined to the horizontal.

5. An interceptor tank according to claim 4 wherein the partition (14) separating the lowermost chamber (8) from the intermediate chamber (10) is inclined to the horizontal at a relatively small angle, whilst the partition (16) which divides the intermediate chamber (10) from the uppermost chamber (12) is or comprises a part which is inclined to the horizontal at a greater angle.

6. An interceptor tank according to claim 5 wherein the partition (16) dividing the intermediate chamber (10) from the uppermost chamber (12) comprises a part (17) which extends vertically.

7. An interceptor tank according to any one of the preceding claims wherein the partitions (14,16) provide surfaces sloping downwardly within the tank and towards a central part of the tank whereby solid materials which may be carried into the tank and which pass upwardly through the communication apertures in the partitions may fall away from said communication apertures towards the central part.

8. An interceptor tank according to claim 7 wherein each of the partitions (14,16) comprises, at the central part of the tank, an opening (20,22) through which solid materials may fall from the uppermost and intermediate chambers into the lowermost chamber.

9. An interceptor tank according to claim 8 wherein the tank comprises a single valve member (24) which, when in position, closes these openings, and which may be removed therefrom which it is desired to remove such solid materials from the tank.

10. An interceptor tank according to any one of the preceding claims wherein both partitions (14,16) comprise frusto-conical portions, said partitions extending upwardly and outwardly from a central vertical axis of the tank.

11. An interceptor tank according to claim 10 wherein the central vertical axis of the lowermost partition (14) is inclined to the vertical axis.