Bypass separator

Abstract

A bypass separator 30 for separating contaminants such as hydrocarbons and particulates from water. The separator comprises an inlet 12 connected to a first chamber 13 and a second chamber 17 connected to an outlet 28. A first flow path connects the first chamber to the second chamber and a second flow path connects the second chamber to the outlet. There is a third flow path connecting the first chamber to the outlet with a relief valve 36 in the third flow path. The third flow path enables bypass of inflowing water during high flow conditions such as heavy rain and storms.

Description

Field The subject of the present disclosure is a bypass separator for separating contamination such as hydrocarbons and particulate matter from surface water for safe discharge. Background In certain countries, there is legislation requiring that surface water drainage systems for areas such as car parks and petrol station forecourts are provided with means for separating pollutants, which may include hydrocarbons (such as diesel, petrol, or oil) from water, such that only water with a hydrocarbon content below a certain threshold is discharged into surface water drains. Similar systems may be employed in areas in which there is a similar risk of contamination of surface water, such as through a chemical spill. Bypass separators are vessels designed to separate contamination (such as particulate matter and hydrocarbon contamination) from surface water before discharging the treated surface water through an outlet. When untreated surface water enters the separator, the retention time of the water in the bypass separator facilitates the separation of different components based on their different densities. Hydrocarbons rise to the top of the vessel as their density is lower than that of the surface water, while silt and heavy particulate matter sinks as a result of its comparatively high density. In periods of heavy rain, this bypass separator may reach capacity. A bypass feature diverts the liquid entering the inlet to the outlet without treating much of the liquid entering the inlet. This is usually permissible since the bulk of the contaminants enter the bypass separator during the initial stages of rainfall and are treated, while the subsequent storm water flow (which is transported to the outlet via the bypass feature) is generally free of contaminants and therefore acceptable to discharge to drains without treatment. The usage of known bypass separators in coastal areas may be ineffective if the outlet discharges treated surface water to a region which may be periodically submerged, such as estuarial riverbanks subject to tidal level changes. There is therefore a need for a bypass separator which is better adapted for use in tidal areas. Summary The present disclosure provides a bypass separator for use in tidal areas as set out in claim 1. The bypass separator comprises a relief valve between a first chamber and an outlet for preventing backflow of fluid from the outlet into the first chamber. Brief Description of the Drawings The present specification makes reference, by way of example only, to the accompanying drawings in which: Figure 1 shows a bypass separator as is known in the art; Figure 2 shows a bypass separator as is known in the art, in normal operating conditions; Figure 3 shows the bypass separator of Figure 2 in storm operating conditions; Figure 4 shows a bypass separator with a relief valve according to an embodiment of the present disclosure; Figure 5 shows a schematic of a relief valve according to an embodiment of the present disclosure from the upstream side; and Figure 6 shows a side view of the valve of Figure 5. Detailed Description of the Drawings Figures 1-3 show bypass separators 10 as are known in the art. The known bypass separator 10 comprises: a tank 11; an inlet 12 through which untreated fluid can enter the bypass separator 10; a first chamber 13; a second chamber 17; an outlet 28 for discharging treated fluid or bypassing fluid; a first passage 18 for permitting fluid flow between the first chamber 13 and second chamber 17; and a bypass feature 14. In the known bypass separator 10 of Figures 1-3, the bypass feature 14 is a weir 35, formed by an upper portion of a dividing wall 15 which separates the first chamber 13 from the second chamber 17. Bypass separator 10 is substantially horizontal, with the inlet 12 situated near the top of the bypass separator 10. The outlet 28 is similarly situated near the top of the bypass separator 10, on the opposite side of the tank 11 to the side of the inlet 12. The outlet 28 is situated slightly lower than the inlet 12 to facilitate fluid flow from the inlet to the outlet in use. Further features of the bypass separator 10 shown in Figures 1-3 include: a filter 22 in the second chamber 17, connected to a second passage 24, through which fluid is conducted to the outlet 28, via an outlet reservoir 26. The filter 22 is connected to an entrance 25 to the second passage 24 at the bottom of the second chamber 17. The outlet reservoir 26 is a compartment connected to the upstream end of the outlet 28. The outlet reservoir 26 is further connected to the first chamber 13 via the bypass feature 14. As best seen in Figures 2 and 3, the known bypass separator 10 further comprises a first manhole, 62 to facilitate access to the bottom of the first chamber 13 to allow for the extraction of a silt 56 layer. The bypass separator 10 further comprises a second manhole 64 to facilitate access to the second chamber 17 for extraction of a hydrocarbon layer 58, or for general cleaning and maintenance. The second manhole 64 is large enough to facilitate removal and replacement of the filter 22. The filter 22 in the known bypass separator 10 may be a coalescing filter, on which small globules of hydrocarbon are trapped and coalesce with other globules until a globule of sufficient size to detach and float upwards due to buoyant forces is formed. The filter 22 in the known bypass separator 10 is mounted near the bottom of the second chamber 17. However, as the skilled person would understand, other locations for the filter 22 are possible. Although the embodiment shown in Figures 1-3 has the first chamber 13 and the second chamber 17 as substantially horizontally aligned, the skilled person would understand that this is not a limiting requirement, and other alignments are possible, such as a substantially vertical alignment as disclosed in WO 2008 / 090384. The general operating principles of the bypass separator 10 are now explained with reference to the embodiment shown in Figures 1-3. Contaminated water enters the first chamber 13 through the inlet 12. Within the bypass separator 10, the first passage 18 defines a first flow path for allowing fluid to flow from the first chamber 13 into the second chamber 17. The first flow path is indicated on Figure 1 by the arrows 20. A second flow path is defined by the second passage 24 for allowing fluid to flow from the second chamber 17 to the outlet 28. A distinct third flow path is provided from first chamber 13 via the weir 35, to the outlet reservoir 26 and the outlet 28, as indicated by the arrow 16 in Figure 1. The third flow path is for allowing fluid to flow from the inlet 12 to the outlet 28, bypassing the second chamber 17. The first and second flow paths in sequence define the flow of fluid entering the bypass separator 10 via inlet 12 and leaving the bypass separator 10 via the outlet 28 under normal operating conditions. The third flow path 16, defines the flow of fluid entering the inlet 12 and leaving the outlet 28 under high flow conditions, such as during a storm. In normal operating conditions (i.e. non-storm conditions), fluid flows through the inlet 12, into the first chamber 13. Sediment / silt 56, which has a higher density than water, accumulates at the bottom of the first chamber 13, as best seen in Figure 2. A hydrocarbon layer 50 forms at the top of the fluid in the first chamber 13. On reaching the height of the entrance to the first passage 18, the fluid in the first chamber 13 flows through the first passage 18, into the second chamber 17, through an opening 19 in internal wall 15, as indicated by the arrows 20 in Figure 1. Further separation occurs in the second chamber 17, resulting in the formation of a hydrocarbon layer 58 at the top of the fluid, as best seen in Figure 2. Driven by hydrostatic pressure, fluid in the second chamber 17 passes through a filter 22 at the bottom of the second chamber 17 and travels up a second passage 24 into the outlet reservoir 26. Once the level of fluid in the outlet reservoir 26 reaches the bottom of the outlet 28, it can then exit the separator 10 via the outlet 28. The hydrocarbon layer 58 remains trapped in the second chamber 17. The inlet 12 of the bypass separator 10 is curved to direct the incoming flow down into the first chamber 13, so as to minimise the re-entrainment of hydrocarbon layer 50 in the first chamber 13 and improve separation. In storm operating conditions when larger volume flow rates of fluid enter the separator 10, the fluid level in the first chamber 13 may exceed the height of the weir 35 formed by the top portion of the internal wall 15, as shown in Figure 3. The excess fluid flow exits the first chamber by the third flow path 16, exiting the first chamber 13 by flowing over the weir 35, into the outlet reservoir 26, and then discharging through the outlet 28. However, if the outlet 28 becomes submerged (submerged outlet operating conditions), fluid can flow from the outlet 28 side back into the first chamber 13 over the weir 35. This could give rise to undesirable contamination of the outlet 28 flow with the hydrocarbon layer 50 which floats at the top of the first chamber 13. Figure 4 shows an embodiment of the bypass separator 30 of the present disclosure. As many features are common to the bypass separator 10 of the prior art, in the following description of the bypass separator 30 of the present disclosure, where appropriate, the same reference numerals are used in Figure 4 as in the previous Figures. Thus, the bypass separator 30 of the present disclosure also comprises a tank 11 with an inlet 12, a first chamber 13, a second chamber 17, an outlet 28 and a bypass feature 14. In this case, the bypass feature 14 is a relief valve 36. The bypass separator 30 may further comprise a first passage 18 to allow fluid flow from the first chamber 13 to the second chamber 17, and flow from the second chamber 17 may pass via a filter 22 and second passage 24 to an outlet reservoir 26 and subsequently to the outlet 28. The first chamber 13 and the second chamber 17 may be separated by an internal wall 15, with an opening 19 for the first passage 18. In the bypass separator 30, a relief valve 36 is positioned between the inlet 12 and the outlet 28. Preferably, the relief valve 36 is located between the first chamber 13 and the outlet reservoir 26. In the event of heavy rainfall, excess fluid flows through the relief valve 36, in the direction indicated by arrow 34. Positioning the relief valve 36 between the inlet 12 and the outlet 28, as opposed to at the outlet 28, prevents flooding upstream from the inlet 12 in submerged outlet operating conditions. The relief valve 36 may be a flap valve 70, or any other suitable form of valve. The relief valve 36 may be a flap valve 70, as shown in Figure 5. The flap valve 70 may comprise a support structure 72, a plate 74, and a hinge 76. The plate 74 may rest on the support structure 72 when the flap valve 70 is in the closed position and may rotate about the hinge 76 to open. The support structure 72 may be on the upstream side of the bypass separator 30 relative to the plate 74. The flap valve 70 may be arranged to be parallel with the flow when in the closed position (i.e. it may be substantially horizontal), as is the case for the arrangement of Figure 4, moving upwardly as shown by reference 32 in order to open. Alternatively, the flap valve 70 may be at an angle to the flow in the closed position. For example, the flap valve 70 may be arranged to be perpendicular to the flow when in the closed position, such that the outlet reservoir 26 filling with fluid from the outlet 28 (e.g. if the outlet 28 is submerged) may force the flap valve 70 into a closed position. The relief valve 36 may be connected to a relief valve control mechanism 38. The relief valve control mechanism 38 may bias the relief valve 26 to a closed position. The relief valve control mechanism 38 may be at least one weight located on the upstream side of the relief valve 36, calibrated to bias the relief valve 36 into the closed position and to allow the relief valve 36 to open at a set pressure difference between the inlet / upstream side of the relief valve 36 and outlet / downstream side of the relief valve 36. This pressure difference may be the pressure difference between the first chamber 13 (at the height of the relief valve 36) and the outlet reservoir 26 (at the height of the relief valve 36). Alternatively or additionally, the relief valve control mechanism 38 may comprise at least one spring. The (or each) spring may be calibrated to bias the relief valve 36 into the closed position and to allow the relief valve 36 to open at a set pressure difference between the inlet / upstream side of the relief valve 36 and outlet / d own stream side of the relief valve 36. This pressure difference may be the pressure difference between the first chamber 13 (at the height of the relief valve 36) and the outlet reservoir 26 (at the height of the relief valve 36). The springs may be connected to a fixed part of the tank 11 and the relief valve 36. The springs may be connected to the outlet side of the bypass separator 30, and / or the inlet side of the bypass separator 30, and / or the internal wall 15. Alternatively or additionally, the relief valve control mechanism 38 may comprise at least one piston. The (or each) piston may be connected to an override feature, whereby the piston can maintain the valve in a shut position and / or an open position. The override feature may be an external input from an operator, such as the pressing of a button. The override feature may be an input from a monitoring system, which may monitor any of: the hydrocarbon level in the first chamber 13; the hydrocarbon level in the second chamber 17; the hydrocarbon content of the flow through the outlet 28; the hydrocarbon content of the flow entering the bypass separator 30 through the inlet 12; the flow rate entering the bypass separator 30 through the inlet 12; the quantity of silt 56 in the first chamber 13; the overall fluid level in the first chamber 13; the overall fluid level in the second chamber 17; and / or the condition of the filter 22. The override feature may be suitable for preventing bypass from occurring in the event of a spill (such as if the tank were mostly filled with spilled hydrocarbons). The override feature may be connected to an external system monitoring the hydrocarbon level in a connected vessel or vessels. The relief valve control mechanism 38 may comprise a feature for indicating to an operator above ground the status of the relief valve 36. This may comprise a transmitter for sending a signal over a network to a remote monitoring station, or to an indicator, such as a light, in the proximity of the bypass separator 30. The feature for indicating to an operator above the ground the status of the relief valve may be mechanical, such as moving an indicator on a manhole 62, 64. The relief valve 36 and / or the relief valve control mechanism 38 facilitates the use of such a bypass separator 30 in locations in which the outlet 28 is periodically or temporarily submerged. Bypass separators 10 known in the art with a submerged outlet 28 could not guarantee acceptable discharges, owing to fluid flowing into the separator through the outlet 28. This back-flowing fluid would then mix with fluid in the bypass separator 10, such as the hydrocarbon layer 50 in the top of the first chamber 13, which would then be discharged through the bypass system 14, effectively untreated. As the skilled person would understand, compatible features of known bypass separators 10 may also be included in a separator 30 of the present disclosure. For example, the bypass separator 30 may further comprise at least one manhole 62, 64. A manhole may be provided to facilitate access to the tank for cleaning, emptying, and general maintenance. Advantageously, the first manhole 62, 64 may be wide enough to facilitate access to the bottom of the first chamber 13 and / or second chamber 17 to allow for silt extraction and access for inspection / maintenance of the relief valve and / or relief valve control mechanism 38. The bypass separator 30 may comprise two manholes 62, 64. The first manhole 62 may be wide enough to facilitate access to the bottom of the first chamber 13 to allow for silt extraction, and the second manhole 64 may be positioned to provide access for cleaning, emptying, and otherwise maintaining the second chamber 17. Advantageously, the second manhole may be positioned and sized so as to facilitate the easy removal of the filter 22. Either the first or second manhole may be positioned to provide access to the relief valve and / or relief valve control mechanism 38 for maintenance. The bypass separator 30 may comprise more than two manholes (62, 64). The first manhole 62 may be wide enough to facilitate access to the bottom of the first chamber 13 to allow for silt extraction, and the second manhole 64 may be positioned to provide access for cleaning, emptying, and otherwise maintaining the second chamber 17. Advantageously, the second manhole may be positioned and sized so as to facilitate the easy removal of the filter 22. Further manholes may be positioned as desired, such as to provide access to the relief valve and / or relief valve control mechanism 38 for maintenance. The bypass separator 30 of the present disclosure may be sized to be larger than the maximum anticipated spillage, to prevent the bypass being used during a spill. The total volume of the bypass separator 30 may be between 1000 and 300,000 litres. The length of a bypass separator 30 of the present disclosure may be between 1 metre and 30 metres. The diameter of a bypass separator 30 of the present disclosure may be between 0.3 metres and 5 metres. The filter 22 of bypass separator 30 may be a coalescing filter. The inlet 12 of bypass separator 30 may be curved to create a region of turbulence on the inlet side of the tank and in so doing, encourage the formation of a longer region of laminar flow through the first chamber 13, which improves separation. The inlet 12 of bypass separator 30 may further function as a flame trap. The bypass separator 30 may comprise a hydrocarbon skimmer 60, for removing the hydrocarbon layer 58 from the second chamber 17. The hydrocarbon skimmer 60 may remove the hydrocarbon layer 58 periodically. The hydrocarbon skimmer 60 may pump the hydrocarbon layer 58 into a connected vessel. The bypass separator 30 may further comprise a system for monitoring the hydrocarbon level in the first chamber 13 and / or the second chamber 17 and / or a connected vessel. The bypass separator 30 may further comprise a transmitter for sending a signal over a network to a remote monitoring station, or to an indicator, such as a light, in the proximity of the bypass separator 30. Alternatively or additionally, the monitored hydrocarbon level may by communicated by mechanical means, such as moving an indicator on a manhole 62, 64, 66. The outlet 28 of the bypass separator 30 may further comprise monitoring equipment for monitoring outlet flow condition, which may comprise any of: the frequency of discharge; the volume of discharge; the volume flow rate of discharge; the duration for which the outlet is submerged; the timings when the outlet is submerged. The monitoring equipment may be connected to a transmitter for sending this information to a monitoring station. The monitoring station may be remote from the bypass separator 30.

Claims

1. A bypass separator for separating contamination from water, comprising an inlet connected to a first chamber, and a second chamber connected to an outlet, a first flow path connecting the first chamber to the second chamber, and a second flow path connecting the second chamber to the outlet, wherein the separator further comprises a third flow path connecting the first chamber to the outlet and a relief valve in the third flow path.

2. A bypass separator according to claim 1 wherein the relief valve is a flap valve.

3. A bypass separator according to any preceding claim further comprising a relief valve control mechanism.

4. A bypass separator according to claim 3, wherein the relief valve control mechanism is at least one piston.

5. A bypass separator according to claim 3 or claim 4, wherein the operation of the relief valve control mechanism is actuatable by an external system or user.

6. A bypass separator according to claim 5 wherein the external system is a system for monitoring fluid levels in the bypass separator or a connected vessel.

7. A bypass separator according to claim 3, wherein the relief valve control mechanism comprises at least one weight located on the upstream side of the relief valve, calibrated to bias the relief valve into a closed position and to allow the relief valve to open when pressure on the upstream side of the relief valve exceeds pressure on the downstream side of the relief valve by a predetermined amount.

8. A bypass separator according to claim 3, wherein the relief valve control mechanism comprises at least one spring calibrated to bias the relief valve into a closed position and to allow the relief valve to open when pressure on the upstream side of the relief valve exceeds pressure on the downstream side of the relief valve by a predetermined amount.

9. A bypass separator according to any preceding claim, further comprising an outlet reservoir at an upstream end of the outlet and the relief valve is located between the first chamber and the outlet reservoir.5 10. A bypass separator according to any preceding claim further comprising monitoringequipment for monitoring outlet flow condition.

11. A bypass separator according to claim 10, further comprising a transmitter for transmitting the outlet flow condition to a remote monitoring station.

012. A bypass separator according to claim 2, wherein the flap valve is arranged to be horizontal in the closed position and to open upwardly.

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