WO1998042615A1

WO1998042615A1 - Drop tube with gas separator for refilling liquid storage tanks

Info

Publication number: WO1998042615A1
Application number: PCT/GB1998/000853
Authority: WO
Inventors: Carl Denby
Original assignee: Carl Denby
Priority date: 1997-03-20
Filing date: 1998-03-20
Publication date: 1998-10-01
Also published as: GB2323355A; GB9705747D0; AU6738498A

Abstract

A filling conduit of a liquid storage tank (2) includes a gas removal conduit (20) which is attached to the inside surface of a wall of a removable drop tube (12) forming part of the filling conduit. The outlet (16) of the drop tube is immersed in the liquid contents of the tank when it is partially filled. When filling takes place, the gaseous contents of the filling conduit are removed via the gas removal conduit (20), and via a gas exit aperture (30) formed in the wall of the drop tube, without those gaseous contents being ejected into the liquid contents of the tank. The gas removal conduit comprises a flame retardant mesh (46) for prevention of combustion of vapours within the headspace of the tank. A diffusing sleeve (18) is located adjacent the gas exit aperture of the internal drop tube.

Description

DROP TUBE WITH GAS SEPARATOR FOR REFILLING LIQUID STORAGE TANKS

This invention relates to the refilling of liquid storage tanks, in particular but not exclusively to the refilling of storage tanks for petroleum fuels or chemicals.

In the following, the discussion will relate to petrol storage tanks, although it is to be appreciated that the invention is similarly applicable to deliveries made to other petroleum fuel, chemical or other liquid storage tanks remains the same. Petrol storage tanks generally have a filling entry at the top of the tank, and have either a direct fill point, or an offset fill point to which a tanker delivery vehicle connects for the delivery of liquid product to the tank.

A fixture in the form of a sealed internal drop tube is supported at the filling entry. The liquid outlet of the drop tube is suspended a short distance above the base of the storage tank. This arrangement is intended to reduce disturbance caused by the incoming liquid when liquid is delivered into the tank. Rather than falling uncontrolled from the top of the tank on entering, the liquid mixes directly with the stored liquid remaining in the tank as it exits from the outlet at the end of the drop tube. However, the filling conduit, which includes the pipeline connecting the offset fill point if present to the top of the drop tube and the drop tube itself, normally contains an air/vapour mixture which is locked in the filling conduit between the inlet and the stored liquid surface inside the drop tube. On delivery of liquid into the filling conduit, these gaseous contents are, in the conventional arrangement, forced downwards through the drop tube and out of the lower outlet of the drop tube. If, as is normally the case, the lower outlet of the drop tube is immersed in the remaining stored liquid, this gaseous mixture travels through the remaining stored liquid in bubbles, the bubbles bursting as the gases reach the surface of the stored liquid. This bubbling of the existing gaseous content of the drop tube through the remaining stored liquid causes a great amount of disturbance within the tank.

This disturbance is problematic not only because it can cause damage to the tank and the fill pipe itself, but also because the disturbance causes an unnecessary amount of vapour emission from the tank during liquid delivery. In its ambient state, the storage tank contains its liquid product, for example, petrol, and a shallow layer of saturated vapour above the liquid surface. The remainder of the tank is filled with unsaturated vapour. However, after a disturbance is caused as described above by the initial stages of delivery, the saturated vapour layer is disrupted and the remaining space in the tank receives a greater concentration of vapour. As the liquid level rises during a delivery, the pressure within the tank is reduced by venting gas from the top of the storage tank. The greater concentration of vapour at the top of the tank after a disturbance as described above leads to an unnecessary about of emission of vapour from the tank during each delivery. Vapour emissions from a tank are undesirable as they lead to waste of product and, often more importantly, an environmental hazard insofar as the vapour may be poisonous or otherwise damaging to the environment.

British patent application GB 2301347 describes an arrangement in a liquid storage tank in which a pipe with a plurality of gas outlet apertures is inserted inside the fill pipe of the liquid storage tank. The fill pipe includes a permanent drop tube which has an outlet normally covered by the tank contents. The gas pipe conveys the gaseous contents of the fill pipe to a separate outlet as refilling liquid is introduced into the fill pipe. This allows the gas inside the fill pipe to be separately vented from the fill pipe without disturbing the liquid contents of the tank. In accordance with one aspect of the invention there is provided a liquid storage tank comprising a removable drop tube having a wall defining a liquid flow path leading to a liquid outlet which is covered by the liquid contents of the tank when the tank is partially filled, and means, attached to said wall, for defining a gas flow path leading to a gas exit aperture, gaseous contents being conveyed from said liquid flow path along said gas flow path during refilling of said tank via said liquid flow path.

With this aspect of the invention, an arrangement for reducing the disturbance within the tank during the initial stages of delivery of a liquid via the liquid flow path can be achieved by modification of an existing removable drop tube.

According to a further aspect of the invention there is provided apparatus for refilling a liquid storage tank, said apparatus comprising a filling conduit defining a liquid flow path leading from a liquid inlet to a liquid outlet, said liquid outlet being covered by the liquid contents of the tank when the tank is partially filled, a separate gaseous outlet for allowing the removal of gaseous contents from said liquid flow path via a gas flow path during delivery of liquid to the tank via said liquid flow path, and flame retardant means, arranged in said gas flow path, for preventing a combustion of gases within said liquid flow path passing through said gaseous outlet.

When the liquid stored in the tank is volatile, there is a danger of an explosion being caused within the filling conduit by sparking, occurring for example when a tanker hose is attached to the tank. With this aspect of the invention, such a potential combustion can be localised substantially within the filling conduit itself. According to a further aspect of the invention there is provided apparatus for refilling a liquid storage tank, said apparatus comprising a filling conduit for defining a liquid flow path leading from a liquid inlet to a liquid outlet, said liquid outlet being covered by the liquid contents of the tank when a tank is partially filled, and an aperture for allowing the removal of gaseous contents from said liquid flow path, said filling conduit comprising means for causing liquid flowing therein to spiral, and said aperture being directed tangentially away from said spiralling fluid flow.

It has been found that, by causing such spiralling fluid flow within the filling conduit, delivery speeds can be increased. By arranging the apertures to be directed tangentially away from the spiralling fluid flow, ingress of the flowing liquid into the gas removal aperture can be reduced. According to a yet further aspect of the invention there is provided apparatus for refilling a liquid storage tank, said apparatus comprising a filling conduit for defining a liquid flow path leading from a liquid inlet to a liquid outlet, said liquid outlet being covered by the liquid contents of the tank when the tank is partially filled, and a gas exit aperture for conveying gaseous contents from said liquid flow path into a headspace above the liquid contents of the tank, and further comprising means, located adjacent said gas exit aperture, for diffusing the exiting gases passing into said headspace.

With this aspect of the invention, the disturbance within the headspace during the initial stages of the delivery of refilling liquid into the tank can be reduced. The diffusing means reduces the force and/or the speed at which the gases enter the headspace.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying diagrams, wherein:

Figure 1 shows a liquid storage tank being refilled in accordance with an embodiment of the invention; Figure 2 shows a cross-sectional detail of the arrangement shown in Figure 1; and

Figure 3 shows a side view of a gaseous conduit illustrated in Figure 2.

Figure 1 shows an underground fuel storage tank 2 having a direct fill point 4 to which a road tanker hose 6 is connectable. The direct fill point 4 is defined by a fill pipe section 8 which is connected at its lower end, by a clamp 10, to the upper end of a manually removable drop tube 12. The clamp 10 is provided with an internal thread which engages with an external thread provided on a clamping sleeve 18 which extends from above and into the storage tank 2. An annular space is provided between the drop tube 12 and the clamping sleeve 18.

When the tank is partially filled, as shown in Figure 1, the inside of the tank 2 is filled partially by its liquid contents 14 and partially by a headspace 22 above the liquid contents. The drop tube 12 has a liquid outlet 16 at its lower end which is immersed in the liquid contents 14, and an overfill prevention mechanism 21 spaced some distance from its upper end. A gas removal conduit 20 is attached to the wall of the drop tube 12, located above the overfill prevention mechanism 21. The gas removal conduit 20 leads to a gas exit aperture 30 formed in the wall of the drop tube 12. The gas removal conduit 20 passes gases from inside the drop tube 12 into the headspace 22 during the initial stages of delivery of liquid via the filling conduit defined by the tanker hose 6, the fill pipe section 8 and the internal drop tube 12. Thus, the gases removed by the gas removal conduit 20 are not ejected into the liquid contents 14 of the tank during a delivery of liquid. The refilling liquid meanwhile passes into the storage tank 2, substantially free of gases, via the liquid outlet 16 of the drop tube 12.

The storage tank 2 is also provided with a vent pipe 24, having a pressure release valve 26 formed therein. As the refilling liquid enters the storage tank, and as the gaseous contents of the filling conduit are removed into the headspace 22, the pressure within the headspace 22 rises. When the pressure rises above a predetermined threshold, the pressure release valve 26 operates to allow the escape of some of the air/vapour mixture within the headspace 22 from the tank. Although not illustrated, a vapour return hose may be connected to the tank vent 24, for conveying the vented gases back to the road tanker for allowing subsequent vapour recovery therefrom.

Figure 2 shows the arrangement of the gas removal conduit 20 within the drop tube 12 in greater detail. The gas removal conduit 20 includes a vertically- extending pipe section 28, which is fluidly connected to a gas exit aperture 30 formed in the wall of the internal drop tube 12, via a horizontal pipe section 32 which spaces the vertical pipe section 28 from the drop tube wall. The gas removal conduit 20 also comprises an attachment plate 34 for attaching the gas removal conduit 20 to the wall of the drop tube 12.

The gas removal conduit 20 comprises a plurality of vertically-extending elongate gas inlet apertures 36 located along the length of the vertical pipe section 28. The inside of the vertical pipe section 28 comprises a waisted section 38, located above the gas inlet apertures 36. A float valve, in the form of a ball 40, is located within the lower section of the vertical pipe portion 28 below the waisted section 38. A non-return valve, in the form of a second ball 42, is located within the upper section of the vertical pipe portion 28 above the waisted section 38. When refilling liquid begins to be delivered from the road tanker into the filling conduit, the air/vapour mixture within the filling conduit, caught between the incoming liquid and the liquid level in the drop tube 12, begins to increase in pressure. This pressure increase causes the air/vapour mixture to enter the gas removal conduit 20 via the inlet apertures 36. The non-return valve ball 42 moves upwards to allow the gases to enter the horizontal pipe section 32 from the vertical pipe section 28, and to enter the headspace 22 via the gas exit aperture 30. Rather than the gases passing directly into the headspace 22, the gases pass into an annular space formed between the top end of the drop tube 12 and the clamping sleeve 18, and are redirected by the clamping sleeve, which thus acts as a diffuser to reduce the force and speed of entry of the gases into the headspace 22. As the refilling liquid continues to enter the filling conduit, the amount of gases within the filling conduit is gradually reduced until substantially no gaseous contents remain within the filling conduit. As liquid enters the gas removal conduit 20, the float valve ball 40 floats upwards within the lower section of the vertical pipe 28, until it reaches the waisted portion 38, and there forms a seal to prevent the exit of liquid via the gas exit aperture 30. The non-return valve ball 42 then falls back into place at the waisted section 38 to prevent the return of gases from the headspace 22 into the gas filling conduit, in case of a reduced pressure being created within the filling conduit during refilling. Figure 3 shows a side view of the gas removal conduit 20 before attachment to the inside surface of the drop tube 12 as shown in Figure 2. As can be seen, the attachment plate 34 comprises two bolt holes 44 and defines a gas outlet aperture 46. The gas outlet aperture 46 is covered by a flame retardant fine metal gauze to prevent any potential combustion of the air/vapour mixture within the filling conduit from extending into the headspace 22.

Referring again to Figure 2, the drop tube 12 is provided at its upper end with a pull bar 48 whereby the drop tube 12 is manually removable from the tank 2. In order to remove the drop tube 12, the clamp 10 is unscrewed, and the fill pipe section 8 is removed. The pull bar 48 is then manually grasped and the drop tube 12 is lifted from its mounting.

In order to modify an existing removable drop tube 12 to provide the gas removal arrangement of this embodiment of the invention, the drop tube 12 is first removed from the tank 2 and a template is applied at the upper end of the drop tube at the point at which the gas exit aperture 30 is to be formed. The template includes apertures corresponding to the locations of the bolt holes 44 and the gas outlet aperture 46 in the attachment plate 34 of the gas removal conduit 20. The gas exit aperture 30, and bolt holes corresponding to those on the attachment plate 34, are then drilled into the wall of the drop tube 12. The gas removal conduit 20 is then simply bolted into place to form an arrangement as illustrated in Figure 2. A rubber seal may be located between the attachment plate 34 and the wall of the drop tube 12.

As shown in Figure 2, the vertical pipe portion 28 of the gas removal conduit 20 is located eccentrically within the drop tube 12, and the gas inlet apertures 36 are directed tangentially in a clockwise direction when viewed from above. The tanker hose 6 has, internally, spiralled grooves therein, which cause the incoming refilling liquid to spiral in an anti-clockwise sense, when viewed from above, inside the filling conduit. Accordingly, the incoming spiralling liquid impinges on the side of the vertical pipe section 28 opposite to that in which the gas inlet apertures 36 are formed. This prevents the spiralling incoming liquid entering the gas inlet apertures 36 directly. Of course, where the tanker hose 6 is formed to cause the incoming liquid to spiral in the opposite sense, the filling apertures 36 are to be located on the opposite side of the vertical pipe section 28.

It is envisaged that various variations and modifications can be employed in relation to the above described embodiment without departing from the spirit or scope of the present invention.

Claims

CLAIMS ;

1. A liquid storage tank comprising a removable drop tube having a wall defining a liquid flow path leading to a liquid outlet which is covered by the liquid contents of the tank when the tank is partially filled, and means, attached to said wall, for defining a gas flow path leading to a gas exit aperture, gaseous contents being conveyed from said liquid flow path along said gas flow path during refilling of said tank via said liquid flow path.

2. A liquid storage tank according to claim 1, wherein said gas exit aperture is formed in said wall.

3. A liquid storage tank according to claim 1 or claim 2 , wherein said conveying means is attached to the inside surface of said wall.

4. A liquid storage tank according to any of claims 1 to 3 , wherein said conveying means comprises a vertically-extending conduit.

5. A liquid storage tank according to claim 4, wherein said conduit is provided with a plurality of gas inlet apertures along its length.

6. A liquid storage tank according to claim 5, wherein said apertures are elongate and extend vertically.

7. A liquid storage tank according to any of claims 1 to 6, wherein said conveying means comprises a non-return valve for preventing the entry of gas into said liquid flow path via said gas exit aperture.

8. A liquid storage tank according to any of claims 1 to 7 , wherein said conveying means comprises a flame retardant means arranged in said gas flow path.

9. A liquid storage tank according to any of claims 1 to 8, further comprising means, located adjacent said gas exit aperture, for diffusing or redirecting the exiting gases passing into said headspace.

10. Apparatus for refilling a liquid storage tank, said apparatus comprising a filling conduit defining a liquid flow path leading from a liquid inlet to a liquid outlet, said liquid outlet being covered by the liquid contents of the tank when the tank is partially filled, a separate gaseous outlet for allowing the removal of gaseous contents from said liquid flow path via a gas flow path during delivery of liquid to the tank via said liquid flow path, and flame retardant means, arranged in said gas flow path, for preventing a combustion of gases within said liquid flow path passing through said gaseous outlet.

11. Apparatus for refilling a liquid storage tank according to claim 10, wherein said flame retardant means comprises a fine wire mesh extending across said gas flow path.

12. Apparatus for refilling a liquid storage tank according to claim 10 or 11, wherein said gas flow path leads to a headspace above the liquid contents of the tank.

13. Apparatus for refilling a liquid storage tank, said apparatus comprising a filling conduit for defining a liquid flow path leading from a liquid inlet to a liquid outlet, said liquid outlet being covered by the liquid contents of the tank when the tank is partially filled, and an aperture for allowing the removal of gaseous contents from said liquid flow path, said filling conduit comprising means for causing liquid flowing therein to spiral, and said aperture being directed tangentially away from said spiralling fluid flow.

14. Apparatus for refilling a liquid storage tank, said apparatus comprising a filling conduit for defining a liquid flow path leading from a liquid inlet to a liquid outlet, said liquid outlet being covered by the liquid contents of the tank when the tank is partially filled, and a gas exit aperture for conveying gaseous contents from said liquid flow path into a headspace above the liquid contents of the tank, and further comprising means, located adjacent said gas exit aperture, for diffusing or redirecting the exiting gases passing into said headspace.