WO1998039520A1

WO1998039520A1 - Apparatus for use in separating and retaining oil from the surface of an area of water

Info

Publication number: WO1998039520A1
Application number: PCT/GB1998/000679
Authority: WO
Inventors: James Allen-Jones
Original assignee: Individual
Current assignee: Individual
Priority date: 1997-03-06
Filing date: 1998-03-06
Publication date: 1998-09-11
Anticipated expiration: 1999-09-06
Also published as: AU6407698A; GB9704660D0

Abstract

Apparatus for use in separating and retaining oil from the surface of an area of water comprises a collection boom (12) towable through water by a towing vessel and a containment area rearwardly of the boom. A portion of the boom is arranged to permit flow of oil over the boom and into the containment area. The oil collects in the containment area and may be recovered from the area.

Description

APPARATUS FOR USE IN SEPARATING AND RETAINING OIL FROM THE SURFACE OF AN AREA OF WATER

This invention relates to apparatus for use in separating and retaining oil from the surface of an area of water.

There are a number of different forms of oil-slick containment booms currently available, and these typically comprise flotation members with weighted skirts depending therefrom, the skirts being intended to minimise the volume of oil that passes beneath the boom. The boom may also include upwardly directed fins, to limit the volume of oil washed over the boom.

Four failure mechanisms have been identified in the use of existing booms: 1) static drainage failure, where the depth of oil on the surface of the water is greater than the depth of the skirt; 2) droplet entrainment failure, where oil droplets entrained in water currents are swept beneath the skirt; 3) failure by viscous accumulation where, under the influence of water currents, the leading edge of a layer of oil "peels off" the surface and passes beneath the boom - the layer of oil may be swept under the skirt or may create a sufficient thickness of oil to cause

"dynamic" drainage failure; and 4) splashover, where wave or wind action carries oil over the boom onto the open sea surface. These failure mechanisms act either individually, or more often in combination, to cause failure of existing containment systems .

It is an object of one aspect of the present invention to minimise the possibility of at least drainage droplet entrainment failure and viscous accumulative failure, and it is an object of another aspect of the invention to minimise the possibility of splashover.

According to a first aspect of the present invention there is provided apparatus for use in separating and retaining oil from the surface of an area of water, the apparatus comprising: a boom comprising a flotation member and a skirt depending therefrom, the member having towing attachments such that, in use, the boom may be towed through water by a towing vessel; and means for defining a containment area rearwardly of the boom, the arrangement being such that a portion of the member permits flow of oil over said portion and into said containment area. According to another aspect of the present invention there is provided a method of separating and retaining oil from the surface of an area of water, the method comprising: providing a first boom comprising a flotation member and a skirt depending therefrom and a containment area rearwardly of the boom; towing the boom through water having a layer of oil thereon; and arranging a portion of the boom to permit oil- flow past said boom portion and into said containment area.

In use, the boom may be arranged such that oil in front of the boom will tend to gather at said portion of the boom, typically a central portion of the boom, and will then flow into the containment area, where the oil will be retained. One of the primary aims of the preferred embodiments of the invention is to thicken the oil layer on the water to facilitate oil recovery; the apparatus will typically be used in combination with a recovery device for pumping the gathered oil from the containment area and means for storing the recovered oil. In open water the oil layer resulting from a spill is typically around 1 cm thick, and recovery is facilitated by thickening of the oil layer; embodiments of the present invention aim to provide an oil layer in the containment area of up to 20 cm, although an oil layer of 3 cm or more facilitates recovery significantly.

Preferably, the boom is configured such that, when the speed of the apparatus relative to the water reaches a predetermined rate, said portion of the boom submerges, allowing oil to flow over the boom and into the containment area; below this speed the boom portion remains on the surface and is effective to retain oil in the containment area. The flotation member may further comprise sections at said portion which are not intended to submerge. Such sections will pierce the water surface and thus enhance the stability of the boom portion. Alternatively, the central portion of the boom may include openings to permit flow of oil into the containment area. The openings may be provided with valves that open only when the boom and skirt are moving relative to the water. In other embodiments, the skirt may be configured to direct water under the containment area.

Typically, the boom will assume a near catenary configuration while being towed.

Preferably also, the boom includes a tension member attached to the skirt and having ends attached to towing points on the boom to ensure that the skirt extends forwardly of the flotation member while the boom is moved through the water.

The containment area may be defined by a further boom comprising a flotation member and skirt, ends of the flotation member being attached to the flotation member of the first boom and a leading edge of the skirt being attached to the skirt of the first boom.

Preferably also, the containment area defines vents, submerged in use, which permit water to escape from the containment area.

Preferably, the boom is of a flexible material and the flotation member may be inflatable. Most preferably, the boom is divided longitudinally into discrete compartments such that an inflated boom will not deflate completely when punctured or damaged. Further, the flotation member preferably has a variable diameter, and variable buoyancy. This permits variation in the height of the flotation member relative to the water surface, to accommodate, for example, different thicknesses of oil layers and the relative speed of the apparatus relative to the water which may vary depending on, for example, the towing vessel and sea conditions.

According to another aspect of the present invention there is provided oil containment apparatus comprising a boom having a flotation member, a splashover member pivotally mounted on an upper portion of the boom, the splashover member comprising a pair of angled arms extending outwardly from a pivot connection and along the boom, each arm carrying a buoyant member towards the free end thereof .

In use, in windy conditions, the wind will act on the arms and cause the splashover member to pivot such that the downwind arm contacts the surface of the water and the other arm is lifted such that it extends above the boom, and minimises the possibility of splashover. The arrangement limits the affect of changes in attitude in the boom on the attitude of the arm, and vice versa.

Each arm may be in the form of a sheet of material . The sheet may be self-supporting but is preferably a flexible membrane or fine mesh net supported by struts or the like. The buoyant members may be discrete members mounted on the angled arms, or may be incorporated into the arms. These and other aspects of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a plan view of apparatus for use in separating and retaining oil from the surface of an area of water in accordance with a preferred embodiment of a first aspect of the present invention;

Figure 2 is a sectional view on line 2 - 2 of Figure l;

Figure 3 is a sectional view on line 3 - 3 of Figure 13; Figure 4 is a sectional view of apparatus for use in separating and retaining oil from the surface of an area of water in accordance with a further embodiment of a first aspect of the present invention, corresponding to a view taken on line 3 - 3 of Figure 1 ; Figure 5 is a perspective view of an oil slick containment arrangement in accordance with an embodiment of another aspect of the present invention;

Figure 6 is a perspective view of the arrangement of Figure 5 and also illustrates a splashover member; and Figures 7 and 8 are enlarged views of portions of the arrangement of Figure 6.

Reference is first made to Figures 1, 2 and 3 of the drawings which illustrate apparatus 10 for use in separating and retaining oil from the surface of an area of water in accordance with a preferred embodiment of a first aspect of the present invention. The arrangement 10 includes a buoyant boom 12 comprising a flotation member 13 with a skirt 14 depending therefrom. A tension member 16 extends along the lower edge of the skirt 14 , the ends of the member 16 being adapted to be connected to suitable towing vessels, typically tugs. Figure 1 illustrates the arrangement 10 as it would appear in use, with the boom 12 assuming a near catenary configuration as the arrangement 10 is towed behind a pair of tugs. As may be seen from Figure 2, the tension member 16 tends to pull the lower end of the skirt 14 inwardly and forwardly to assist in gathering oil and oil containing water within the area defined by the boom 12.

A containment lagoon 18 is formed rearwardly of a central portion of the boom 12, the lagoon 18 being defined by a further boom 20 having a flotation member 21 and a skirt 22 which depends from the boom 20 and extends parallel to the water surface to attach to the skirt 14, as may be seen in Figure 3 of the drawings. The skirt 22 defines vents which allow water to pass from the lagoon 18. The flotation member 13 is not of constant cross- section, and thus buoyancy, over its whole length, the central portion of the member 13a being of smaller cross- section than the remainder of the member 13.

When the apparatus 10 is stationery in the water, or moving at very low speeds, the central portion of the member 13a pierces the surface of the water. However, when the apparatus 10 is moved relative to the water above a predetermined speed, for example, 2 to 4 knots, the flotation member 13 is pulled beneath the water surface, such that any oil on the surface of the water passes over the member 13 and into the containment lagoon 18/ To provide stability, the flotation member central portion 13a includes larger diameter portions 13b which pierce the surface of the water as the apparatus is pulled through the water.

The forward end of the skirt 22 is attached to the boom 12, with cords 30 extending from the skirt 22 to the tension member 16 of the skirt 14.

To attenuate and diffuse high frequency waves, which tend to "slap" the boom 12 and may cause splashover, a number of cords 32 extend across the boom apex, the cords 32 being arranged in groups, within each group the cords 32 being vertically spaced apart at and around the mean water level . In use, the arrangement 10 is towed behind a pair of tugs such that oil on the surface of the water gathers in the area defined by the boom 12. With forward movement the oil will tend to gather at the central portion of the boom 12, and will then pass over the flotation member 13 and into the lagoon 18. As noted above, the skirt 22 which extends beneath the lagoon 18 is provided with a number of sub-surface vents (not shown) which allow water, but not oil, to escape from the lagoon 18.

The apparatus 10 is towed through oil-contaminated water and a volume of oil is collected in the lagoon 18. In open water oil typically forms a layer around 1 cm thick and this is difficult to recover, without also drawing in a significant volume of water. However, the apparatus results in the formation of an oil layer in the lagoon 18 which is significantly thicker in the lagoon (3 - 20 cm) , and is relatively easily recovered.

If desired, the configuration of the front skirt 14 and the rear skirt 22 may be arranged to encourage flow separation, as illustrated in Figure 4 of the drawings, such that water is directed flows below the skirt 22. In this embodiment, a sluice 34 is provided in the skirt 14 below the flotation member 13. Reference is now made to Figures 5, 6, 7 and 8 of the drawings, which illustrate elements of another aspect of the present invention. The arrangement 80 includes a boom 82 having a flotation member formed of a flexible cylinder 84 which accommodates a plurality of separate longitudinally extending inflatable tubes 86. A skirt 85 (not shown in Figure 6) depends from the cylinder 84. Pivotally mounted on the upper surface of the boom 82 is a splashover member 88 (not shown in Figure 5) , as described in greater detail below. The splashover member 88 is mounted on a cable 90 which runs along the upper surface of the boom 82. The member 88 comprises two angled arms 92, 93, each of which comprise a longitudinally extending flexible membrane or fine mesh net 94 and a plurality of radially extending struts 96, and an inflatable floatation tube 98 mounted to the free ends of the rods 96. The connection between the cable 90 and the arms 92, 93 is provided by a joint 100, as illustrated in Figures 7 and 8 of the drawings, comprising a bushing 102 for location over the cable 90 and two sleeves 104, 105 for receiving the ends of the rod stiffeners 96.

The arrangement 80 is intended to minimise splashover of oil from the upwind side of the boom 82. As illustrated in Figure 6, when the wind blows across the boom 82, the wind acts on the arms 92, 93 and pivots the splashover member 88 such that the floatation tube 98 mounted on the downwind arm 93 rests on the surface of the water. The buoyancy of the tube 98 prevents any further rotation of the member 88, such that the upwind arm 92 extends upwardly of the boom 82, and will remain in this attitude unless the wind direction reverses. The provision of a pivot link between the boom and the splashover member 88 permits the boom 82 and member 88 to move independently such that, for example, a change in attitude of the boom 92 would not affect the member 88.

It will be clear to those of skill in the art that the above-described embodiments are merely exemplary of the present invention, and that various modifications and improvements may be made thereto without departing from the scope of the invention.

Claims

1. Apparatus for use in separating and retaining oil from the surface of an area of water, the apparatus comprising: a collection boom towable through water by a towing vessel; and means for defining a containment area rearwardly of the boom, the arrangement being such that a portion of the boom is arranged to permit flow of oil over said portion and into said containment area.

2. The apparatus of claim 1, wherein the boom comprises a flotation member and a skirt depending therefrom.

3. The apparatus of claim 1 or 2 , wherein said portion of the boom is submergible, to allow oil to flow over the boom and into the containment area.

4. The apparatus of claim 3 , wherein the boom is configured such that, when the speed of the apparatus relative to the water reaches a predetermined rate, said portion of the boom submerges, allowing oil to flow over the boom and into the containment area, and below this speed the boom portion remains on the surface and is effective to retain oil in the containment area.

5. The apparatus of claim 3 or 4 , wherein said portion of the boom comprise sections which are not intended to submerge, and thus pierce the water surface and enhance the stability of the boom portion.

6. The apparatus of any of the preceding claims, wherein the boom has a skirt configured to direct water under the containment area.

7. The apparatus of any of the preceding claims, wherein the boom comprises a flotation member and a skirt depending therefrom, and a tension member is attached to the skirt and having ends attached to towing points on the boom to ensure that the skirt extends forwardly of the flotation member while the boom is moved through the water.

8. The apparatus of any of the preceding claims, wherein the containment area may be defined by a further boom comprising a flotation member and skirt, ends of the flotation member being attached to a flotation member of the first boom and a leading edge of the skirt being attached to a skirt of the first boom.

9. The apparatus of any of the preceding claims, wherein the containment area defines vents, submerged in use, which permit water to escape from the containment area.

10. The apparatus of any of the preceding claims, wherein the boom is of a flexible material and includes an inflatable flotation member.

11. The apparatus of claim 10, wherein the flotation member is divided longitudinally into discrete compartments, such that the inflated member will not deflate completely when punctured or damaged.

12. The apparatus of claim 10 or 11, wherein the flotation member has variable buoyancy.

13. The apparatus of any of the preceding claims further comprising a splashover member pivotally mounted on an upper portion of the boom, the splashover member comprising a pair of angled arms extending outwardly from a pivot connection and along the boom, each arm carrying a buoyant member towards the free end thereof .

14. The apparatus of claim 13, wherein each arm comprises a sheet of material .

15. The apparatus of claim 14, wherein the sheet is flexible and supported by struts or the like.

16. A method of separating and retaining oil from the surface of an area of water, the method comprising: providing a first boom and a containment area rearwardly of the boom; towing the boom through water having a layer of oil thereon; and arranging a portion of the boom to permit oil flow past said boom portion and into said containment area.

17. The method of claim 16, wherein said portion of the boom is submerged to permit oil to flow over the boom and into said containment area.

18. The method of claims 16 or 17, further including recovering gathered oil from the containment area and storing the recovered oil.

19. Oil containment apparatus comprising a boom having a flotation member, a splashover member pivotally mounted on an upper portion of the boom, the splashover member comprising a pair of angled arms extending outwardly from a pivot connection and along the boom, each arm carrying a buoyant member towards the free end thereof .

20. The apparatus of claim 19, wherein each arm comprises a sheet of material .

21. The apparatus of claim 20, wherein the sheet is flexible and supported by struts or the like.