WO2008090384A1

WO2008090384A1 - Improved separator

Info

Publication number: WO2008090384A1
Application number: PCT/GB2008/050054
Authority: WO
Inventors: Damone Armstrong
Original assignee: Tanks And Containers Group Limited
Priority date: 2007-01-26
Filing date: 2008-01-28
Publication date: 2008-07-31
Also published as: GB0701521D0; GB2447723B; GB2447723A; GB0801501D0

Abstract

A hydrocarbon / water separator comprises an inlet (4), a cleaned water outlet (5) and a retention chamber (2), wherein a hydrocarbon coalescing means (12) is situated in the retention chamber. The hydrocarbon coalescing means is buoyant and rises and falls with the level of liquid in the retention chamber. A secondary filter (11) removes any remaining hydrocarbon to the extent that the concentration of hydrocarbon in the cleaned water is within statutory limits.

Description

Improved Separator

Field of the Invention

The present invention relates to separators, and in particular to separators for separating hydrocarbons from water, examples for the use of such separators being in the collection of run-off surface water from hard-standings such as car parks, fuel station forecourts, airport runways, roadways, etc .

Background of the Invention

From time to time cars parked in car parks leak oil. There is also the possibility that petrol and diesel may leak from vehicles. Such leaked oil/fuel is in the course of time washed away from the site of the initial spill by rain water, ultimately finding its way into surface water drains. Contamination of surface water by hydrocarbons is not desirable and in the United Kingdom legislation has been introduced requiring the surface water drainage systems of car parks to be provided with means for separating oil/fuel from water, such that only water containing less than a certain threshold (5mg/litre) of oil/fuel is discharged into the surface water drains. Whilst there is a risk of contamination of surface water by oil/fuel in car parks, hence the legislation, there is nevertheless recognition that the risk is low. For this reason the separator is required to be able to capture and retain all surface water run -off from a car park when rainfall is up to 5mm / hour.

Separators have been developed and are in use in hard-standing areas, such as car parks. These separators include a tank, and mounted inside the tank a filter. These separators include a filter and are designed to capture all surface water run-off when rainfall is up to 5mm / hour, but in storm conditions to switch to a by-pass mode whereby no water passes through the filter. In use, these tanks are buried in the ground. Surface water run-off enters the tank where oil/fuel fraction migrates to the top of the liquid in the tank and small particles suspended in the liquid fall out of suspension to the bottom of the tank. An outlet from the tank is connected to an outfall to a main surface water drain. The path between the tank and the outfall includes the filter. Any water exiting the tank must pass through the filter before entering the sewage system. The type of filter commonly used is a coalescent filter.

As mentioned above, a factor which must be taken into account when designing a separator for collecting oil/fuel entrained with surface water is that small particles are held in suspension with the surface water. These small particles will be referred to herein as silt. Once in the separator a large proportion of entrained silt will tend to fall out of suspension with the water. This poses problems insofar as the separator must be emptied of silt periodically. Also, commonly used separators mount the coalescent filter for extracting the oil/fuel fraction from the water at the bottom of the tank. The build up of silt in the bottom of the separator can render the filter ineffective. A number of proposals have been made for dealing with the problem associated with silt. In some separators silt traps are provided up stream of the separator. In other separators additional access manholes are provided to allow vacuum tanks to suck silt laden sludge from a separate silt chamber in the tank.

In known separators, the coalescent filter consists of a sleeve of filter material which is mounted on the outer surface of a perforated tube. The downstream end of the perforated tube connects directly or indirectly to a sewage outfall. Any oil/fuel not separated from the water must pass through the filter in order to reach the sewage outlet.

One problem associated with known arrangements of the filter is that their exposure to the contents of the tank results in large amounts of silt falling out of suspension with the water collecting on the surface of the filter material. This can lead to the sleeve of filter material being dragged down by the weight of silt giving rise to two undesirable effects. First, the filter material does not work as effectively, and second the perforations of the pipe may be exposed allowing potentially contaminated water to be discharged to the outfall without the filtration required by environmental regulations.

Another problem associated with current separator designs is that of access to the filter unit. As mentioned above, the type of filter used is usually a coalescent filter. This type of filter must be either cleaned or replaced from time to time. Location of the filter at the base of the separator tank makes access thereto difficult. Some proposals have been made to mount the filter unit on a lift mechanism, but this adds complexity and can be difficult to achieve within the restricted dimensions of a separator tank.

One solution to this problem is proposed in International patent application number WO 2006/035224. In the separator described in this publication the coalescing filter is situated in a housing into which silt cannot enter. The filter material is located such that any water in which hydro-carbon is entrained passes through a filter from the inside of the filter material to the outside thereof.

Whilst the configuration described in international patent application number WO 2006/035224 functions well in a lower range of flow rates, when the flow rate is increased there can be a problem with the coalescing filter becoming overloaded. When this occurs the coalescing filter fails and hydrocarbon entrained in the water does not coalesce on the filter, and passes through the outflow to a surface water drain.

United Kingdom patent application published under no 2423299 describes a separator for separating oil from water in which an oil-coalescing means is positioned upstream of an oil retention chamber. The separator described in this patent application claims to require a smaller volume than other separators. However, in one embodiment there is no specific sedimentation filtration upstream of the coalescing means, which would result in the coalescing material being sub_ject to the same sediment problems as described above with reference to other prior art separators. The present invention seeks to provide an improved separator capable of handling large volumes of water in which hydrocarbons are entrained.

Use of separators according to the invention is not limited to the separation of oils and oil products used in vehicles. The separators may be deployed in any scenario where there is a requirement to separate fluids of different densities, where one of the fluids is capable of coalescing on a coalescent material. For example, the separator may be used as a grease separator by food production or catering businesses.

Summary of the Invention

According to the invention, there is provided a separator as specified in Claim 1.

According to another aspect of the invention, there is provided a method of separating hydrocarbon from water as specified in Claim 14.

Preferred embodiments of the invention are set out in the claims dependent on Claims 1 and 14, and in the drawings and description.

Brief Description of the Drawings

In the drawings, which illustrate a preferred embodiment of the invention, and are by way of example:

Figure 1 is a schematic representation of an embodiment of a separator according to the invention in a first condition;

Figure 2 is a schematic representation of the embodiment of a separator illustrated in Figure 1 in a second condition; Figure 3 is a parts view of some of the components of the separator illustrated in Figures 1 and 2,

Figure 4 illustrates the test to which a separator according to the invention was subjected,

Figure 5 illustrates in cross-section a separator according to another aspect of the invention, and

Figure 6 is a plan view of the separator illustrated in Figure 5.

Detailed Description of the Preferred Embodiments

Figure 1 illustrates an embodiment of the invention in a condition where no water is flowing through the separator 1.

Figure 2 illustrates the embodiment of the invention shown in Figure 1 in a condition where water is flowing through the separator at a flow rate resulting from rainfall at up to 6.5mm per hour. The separator illustrated in Figures 1 and 2 is a bypass separator, hence when rain falls at a rate exceeding 6.5 mm per hour the flow rate of surface water into the separator functions in its "bypass" mode, i.e. incoming water passes from the separator inlet to the separator outlet without entering the retention chamber.

Referring now to Figure 1, a separator 1 comprises a retention chamber 2 in the upper portion of which is mounted a bypass chamber 3. The bypass chamber 3 includes an inlet 4, an outlet 5, a skim pipe 6 and a dip pipe 7. The dip pipe 7 extends from the base of the retention chamber 2, through the bypass chamber 3 to the top of the filter housing 9. Located within the retention chamber is a body of coalescing material 12.

The lower portion of the dip pipe 7 includes a plurality of openings 8 through which fluid may pass. When rain falls water collected on the surface served by the separator 1 is delivered to the inlet 4. When rain falls at a rate up to 6.5 mm/hour the water flowing through inlet 4 is retained within the bypass chamber 3 until it reaches the level of the top of the skim pipe 6, whereupon the water in the bypass chamber 3 overflows through skim pipe 6 which debouches into the retention chamber 2. The body of coalescing material 12 is buoyant and rises and falls with the water level in the retention chamber.

Referring now to Figure 2, the body of coalescing material 12 has risen to the top of the retention chamber 2. Any hydrocarbon entrained in the water entering the retention chamber 2 through skim pipe 6 coalesces on the material 12. As such the water below the level of the coalescing material 11 is therefore substantially free of hydrocarbon.

The head of water forces water in the retention chamber 2 out via the outlet 5. Water enters the dip pipe 7 via openings 8 which comprise a plurality of spaced apart elongate slots 8. The configuration of the openings 8 prevents clogging with silt. Water exits the dip pipe 7 via openings 10 which are surrounded by a coalescing filter material 11. The coalescing filter material removes any remaining small amounts of hydrocarbon and fine silt particles.

The body of coalescing material 12 consists of multiple strands and is buoyant. The buoyant nature of the material ensures that as soon as the retention chamber has filled the lower half thereof, the material 12 sits in the upper half of the chamber. In the configuration shown in Figure 2 (the coalescing material is shown clear of the outlet 6a in order not to obscure the said outlet 6a) the outlet 6a of the skim pipe 6 debouches directly into the coalescing material, which surrounds the said outlet 6a and ensures that the incoming water must pass through a bulk of the material 12 before it may enter the lower half of the retention chamber 2, thereby ensuring opportunity for any hydrocarbon entrained in the incoming water to coalesce on the material 12. As the mixture of hydrocarbon and water debouches into the retention chamber 2 its flow is turbulent. The coalescent material 12 captures any oil entrained in the mixture. Hydrocarbon floats to the top of the retention chamber where is trapped away from the turbulent area in the region of the outlet 6a.

Figure 3 illustrates some of the parts of the separator shown in Figures 1 and 2. Referring now to Figure 3, the filter housing 9 includes a bracket 14 to which a first part of the dip pipe 7 is attached. One end of an upper part 15 of the dip pip 7 is attached to a lid 13 which is provided with a handle 16. The other end of the upper part 15 sits in the bracket 14. The filter 11 is therefore easily accessible simply by removing a lid 18 from the bypass chamber 3. The filter 11 is then inspected by a service technician who grasps the handle 16 and lifts the upper part 15 of the dip pipe 7 out of the filter housing 9. The filter may be then be inspected, cleaned, or removed and replaced.

The lid 13 of the filter housing 9 includes a plurality of openings 17 which form bypass weir ports. When rainfall is greater than 6.5mm per minute the skim pipe 6 chokes and the separator operates in bypass mode, when inflowing water substantially fills the bypass chamber 3. When the level of water in the bypass chamber 3 rises above the top of the filter housing 9 the water debouches through the openings 17 in the lid 13 of the filter housing 9 into the body of the said filter housing, exiting through the outlet 5 (see Figures 1 & 2).

The lid 13 includes a breather opening 19.

In order to empty the retention chamber the upper part 15 of the dip pipe 7 is removed in the manner described above and a suction hose is dropped into the dip pipe 7.

In use, the mixture of water and hydrocarbon enters the retention chamber 2 via the skim pipe 6.

Figures 5 and 6 illustrate another embodiment of the invention which includes an upstream settlement chamber 20 having an inlet 21 and an outlet 22, the outlet 22 being connected to the inlet 4 of the separator 1. The provision of a large body of coalescing material in the retention chamber vastly reduces the amount of hydrocarbon to be removed by the coalescent filter 11 and allows large scale separators capable of handling large volumes of surface water run-off to be installed.

Example

The example below demonstrates the effectiveness of the separator of the present invention.

In the example a separator having a nominal inlet capacity of six litres per second was tested in accordance with the standard EN 858-1. The test involved first charging the separator with water by introducing potable water at a rate of 6 litres/second for a period of fifteen minutes, then for a period of five minutes introducing potable water again at a rate of six litres per second to which oil was added at a rate of 5 ml/second.

The outflow from the separator is then measured to establish what quantity of the introduced oil remains in the water flowing out of the separator.

The test is illustrated in Figure 4. During the period TE the separator is charged with water and during the period Tp oil is added to the water flowing into the separator.

The results of the test of the separator, which was an example of a separator according to the invention are set out in the table below:

In order for the separator to meet the standard set down in EN 858-1, the concentration of light liquid, i.e. oil, in the water must be less than 5.0 «g// throughout the period of the test. In the present example the maximum concentration of light liquid was 1.4 «g//and the average was 1.3

Whilst the example of the separator illustrated in the drawings is a bypass separator, the separator may equally be configured as a full retention separator. All that is required is an appropriately sized retention chamber and the closing off of bypass weir ports 17.

The separator of the invention provides for extremely effective separation of hydrocarbons and in particular light liquids, such as oils from water, and the secondary oil coalescing means is not affected by silt.

Claims

1. A hydrocarbon / water separator comprising an inlet, a cleaned water outlet and a retention chamber, wherein a hydrocarbon coalescing means is situated in the retention chamber.

2. A hydrocarbon / water separator according to Claim 1, wherein the coalescing means is buoyant and rises and falls with the fluid in the retention chamber.

3. A hydrocarbon / water separator according to Claim 1 or 2, further comprising a secondary filter located downstream of the coalescing means.

4. A hydrocarbon / water separator according to Claim 3, wherein the secondary filter is a coalescent filter.

5. A hydrocarbon / water separator according to Claim 3 or 4, wherein the secondary filter is situated in the upper part of the retention chamber.

6. A hydrocarbon / water separator according to any of Claims 3 to 5, wherein the secondary filter is mounted in a filter housing.

7. A hydrocarbon / water separator according to any of Claim 3 to 6, wherein the secondary filter is mounted in a fluid inlet chamber upstream of the retention chamber.

8. A hydrocarbon / water separator according to any preceding claim, wherein a flow control means is located between the inlet and the retention chamber.

9. A hydrocarbon / water separator according to Claim 8, wherein the flow control means includes a pipe, wherein the pipe is curved so as to direct fluid flowing into the retention chamber to the upper region thereof.

10. A hydrocarbon / water separator according to Claim 7 or any claim dependent thereon, wherein the filter housing is mounted in the inlet chamber.

11. A hydrocarbon / water separator according to Claim 10, wherein the inlet chamber is a bypass chamber and the filter housing includes inlet and outlet weir ports.

12. A hydrocarbon / water separator according to Claim 11, wherein the outlet weir port is the said cleaned water outlet.

13. A hydrocarbon / water separator according to any preceding claim, further including an upstream settlement chamber.

14. A hydrocarbon / water separator according to any preceding claim, wherein the coalescing means is a body of multi-strand coalescing material.

15. A method of separating hydrocarbon from water comprising the step of: i) Passing a mixture including hydrocarbon and water to a separator as claimed in any of Claims 1 to 14.

16. A hydrocarbon / water separator substantially as shown in, and as described with reference to, the drawings.