WO1983000890A1

WO1983000890A1 - Method and apparatus for controlling oil pollution on water

Info

Publication number: WO1983000890A1
Application number: PCT/GB1982/000268
Authority: WO
Inventors: John Watt West
Original assignee: John Watt West
Priority date: 1981-09-11
Filing date: 1982-09-10
Publication date: 1983-03-17
Also published as: NO831644L; PT75547A; JPS58501436A; GB2105603A; PT75547B; IT8223162A0; IT1152810B; ES515651A0; ES8401168A1; EP0087450A1; ZA826653B

Abstract

A method of substantially removing oil spilt on salt or fresh water includes the steps of: confining the spilt oil with a small mesh net (18) of substantial length which is connected to floats (30) and supports (36, 38) in such a way that the net (18) is maintained substantially vertical, causing or permitting the oil to move to a region adjacent to a selected portion of the net, and picking up the oil in said region off the surface of the water and feeding it into a suitable container. A suitable net has a mesh size of maximum dimension of about 2.5 millimetres and is connected at intervals to dan buoys designed to hold it vertical. The net may be deployed from vessels or aircraft, in a loop shape as seen in plan.

Description

METHOD AND APPARATUS FOR CONTROLLING OIL POLLUTION ON WATER

This invention relates to a method and apparatus for controlling oil pollution on open or coastal water.

The invention is particularly although not exclusively applicable to containing oil spills and recovering the spilt material from the surface of the sea in off-shore oil fields such as the North Sea, the Gulf of Mexico, off Alaska, and elsewhere.

There have been many prior proposals for dealing with oil pollution. These can be classified as (a) use of detergents and dispersants,

(b) attempts to sink the spilt oil, and

(c) attempts to contain the oil on the surface and then remove it therefrom.

The use of detergents and dispersants is costly with large oil spills as copious quantities of possibly expensive chemicals have to be transported and then accurately applied to the spill. This method also involves a danger to wild life. The attempts to sink the oil have not proved satisfactory up to the present and have the disadvantage of hazard to fish and other marine life which breeds on or occupies the sea bed. Numerous prior proposals have been made under heading (c) but most have not satisfactorily resolved numerous practical problems.

According to the invention, there is provided a method of substantially removing oil spilt on salt or fresh water . which includes confining the spilt oil with a small mesh net of substantial length which is connected to floats and supports in such a way that the net is maintained substantially vertical, causing or permitting the oil to move to a region adjacent to a selected portion of the net, and picking up the oil in said region off the surface of the water and feeding it into a suitable container. In a case when the oil is spilt on open water, the oil is confined by encircling it with an elongated small mesh net, one end of which is attached to a suitable vessel, and, by gradually reeling in the net, the oil is brought near to the vessel so that it can be transferred by one or more pumps carried on the vessel into a suitable container such as a tank of the vessel or an adjacent tanker.

In a case where the oil is spilt near a coastline, and particularly near a beach, the elongate net is deployed a short distance to seaward of the coastline in such a configuration that the effect of wind or tide (or both if they assist each other) is to bring the oil to a region adjacent to a selected portion of the net; the oil in said region is then transferred to a suitable container, for example by pumping or a mechanical scoop.

According to one embodiment of the invention, there is provided a method of containing oil spilt on open water whichincludes encircling the spilt oil with a small mesh net of substantial -length which is connected to floats and supports in such a way that the net is maintained approximately vertical and acts to confine the oil.

In a preferred method according to this embodiment of the invention, one end of the net is paid out from a ship which carries it. The ship follows a course while the net is paid out so as to form a loop of net with an open mouth (in other words a U-shaped configuration of net seen from above) whose open mouth (or top of the "U") is nearest to the source of the oil spillage, with the loop extending either down-wind or down-tide. In a case where the wind direction and the tide stream are not the same the net will be positioned according to whether the spilt oil is tide-borne or wind-borne.

A net of considerable length, e.g. one or two miles, is preferably employed and this advantageously has a mesh size such that the holes therein have a maximum dimension of about 2.5 mm., i.e. one-tenth inch. Any mesh size may be used that does not allow the spilt oil to pass therethrough, and this is the meaning to be attached to the words "small mesh net" as used herein. Optionally, the net may have a series of floats connected to it at approximately its half height and these floats may be substantially cylindrical or elongated block floats connected end-to-end by rope or cable. The rope or cable may extend through the floats.

At suitable intervals along the net it is supported by a dan buoy, namely a buoy having an upstanding pole or stick. The net is secured at intervals to these poles and is held by them in a substantially vertical orientation so serving to largely or wholly prevent escape of the confined oil. The dan buoys have downwardly extending rods with weights at their lower ends and these ensure that the poles or sticks normally point upwardly. The dan buoys are preferably spaced at about 0.8 to 2.0 metre intervals, and more preferably at one-metre intervals. The poles of the dan buoys may extend through the floatation members thereof.

The net preferably has a total height of about 1½ to 4 metres, of which about 1 to 2 metres or one fathom is below the water level about 1 to 2 metres is above water level. In contrast to the kind of net used for fishing by purse seineing, there is no need to have any substantial height of net below the water level nor is there any need to have the rope or cable "drawstring" at the lower edge of the net which is an essential feature of purse seineing. Also according to the invention, there is provided a small nesh net for use in control of oil spills, the net having a length of over two hundred times its width, a series of floats connected t-o the ncl , at least some of which are dan buoys, the arrangement being such that the net can be held substantially vertical when streamed in the open water. The net may have a width (i.e. a vertical height when streamed) of from 2 to 5 and preferably from 1½ to 4 metres..

The invention will be better understood from the following non-limiting description of examples thereof given with reference to the accompanying drawings in which:- Figure 1 is a diagrammatic plan view illustrating an early stage in a method in accordance with the invention; Figure 2 is a plan view illustrating a later stage in the method according to the invention;

Figure 3 is a front elevation of a portion of one example a net useful in the method according to the invention;

Figures 4 and 5 are cross-sections on the lines IV IV and V-V of Figure 3;

Figure 6 is a side elevation of a net-supporting dan buoy which can be used in place of the floats and the dan buoys shown in 'Figs. 3-5;

Figure 7 is a diagrammatic illustration of a method of recovering a net;

Figures 8 and 9 are respectively end elevation and side elevation of a net recovery roller; Figure 10 is an illustration showing the use of a method in accordance with the invention to pick up oil in a coastal inlet; and Figure 11 illustrates the deployment of nets according to the invention by coastal boats to protect a coastline. Figure 1 is a diagraπznatic plan view of an area of sea or open water in which is located an • oil producing installation 10.from which there is an undesired escape of oil, which lies on the sea as a slick 12 and is blown to leeward of the installation 10, the wind direction being indicated by the arrow 14. A ship or other vessel 16 is equipped for streaming and recbvering a net 18. To confine the slick 12 the ship first drops an anchored buoy 20 which is fixed by its anchor in relation to the sea-bed. The ship then follows a looped path around the leeward side of the slick 12, and streams the net 18 as it does so. The course followed by the ship is approximately U-shaped and is substantially the same as the position occupied by the net 18. There has thus been formed a loop with an open mouth 22 positioned so that all the escaping oil blows into the loop. During collection and confinement of the escaping oil the ship 16 may be anchored at the position illustrated in Figure 1 or may be held relatively steady in this position by the use of its engines. The length of net 18 used may for example be 2 miles and the distance between ship 16 and anchored buoy 20 may be between a half and one mile.

In the above description it has been assumed that the wind is the major influence on the movement of the oil slick hut if the tide was the major influence then a similar procedure would be adopted as illusirated, except that 14 would then denote the tide stream direction.

The oil escaping from an oil rig 10 is thus confined by the net 18 and once the escape is stopped, the net loop is closed. The ship 16 is manoeuvredto pick up the end 24 of the net while the end 26 is still attached to the ship. ILhe anchored buoy 20 is also recovered. The ship 16 and the net 18 enclosing the oil may then be allowed to drift downwind or downtide, while the oil is agglomerated (if desired) into a thick sludge or jelly by the progressive addition of a suitable agglomerating agent. Such agents are known. Once agglomerated,' the resulting sludge or Jelly is transferred into the ship 16, and thence, if the quantity of sludge or jelly exceeds the capacity of the ship 16, into a tanker or a series of tankers which would be brought alongside the ship 16. As seen in Figure 2 they would be brought alongside the port side of the ship 16. The agglomerated oil can be taken abroad the ship 16 using scoops or.brails, or in a case where agglomeration is not needed, a mixture of oil and water is pumped aboard and passed to oil-water separators, the separated water being returned overside.

One suitable design of net 18 is illustrated in Figures 3 - 5, the intended water level being shown at WL. The net 18 is of a long thin rectangular shape having a length of say 2 miles and a width of about 3 metres. It is secured at intervals to bolster-shape floats 30. These have a central longitudinal hole 32 through which passes a rope or cable 33. 3)an buoys 34 each having an upstanding rod 36 and a downwardly—extending rod 38 bearing a weight 40 are also secured to the net at intervals and the top 42 and bottom 44 of the net are suitably fixed to the respective rods 36, 38, for example by ties 46. The height-of the net is not critical, but it is expected that best results will be obtained if the height h, in Figure 3 is from one to 2 metres and the height h~ is from 2 to 4 metres. However the invention should not be regarded as limited to any particular dimensions. It can be seen with this arrangement that the net 18 is held approximately vertical so as to function as a retaining

"fence" around the oil slick. Of course in heavy weather some oil will be thrown outside the net 18 by agitated seas, but in heavy weather, to the best of Applicants knowledge and belief, none of the presently known methods of handling substantial oil escapes are satisfactory either, and it is expected that the method disclosed herein will be able to operate satifactorily in worse weather than can the presently-known procedures. The method disclosed herein employs techniques which in essentials have been proved practical through experience of purse-seineing fishing, and it is anticipated that the disclosed method will prove successful and economic in containing and recovering oil spills or escapes involving hundreds or thousands of tons of oil.

According to a preferred embodiment of the invention, it can be arranged that the floats 30 are made of or coated with an oil-absorbent material. The central floats 34 (Figure 4) dan buoys can also be made of or coated with such material.

An alternative design of dan buoy used for net flotation is shown in Figure 6. This is a simple dan buoy having an upstanding rod or stick 41, e.g. of frors 1 to 4 metres in length which has a float 43 secured thereto intermediate its ends. The lower end 45 is formed by or carries weights so that the dan buoy will float in a vertical orientation in the water. A pair of loops 47 may optionally be attached to the rod 41 to facilitate the fixing of the dan buoys to the net. The float 43 may be located about § of the way up the rod 41 but its exact height will be chosen in accordance with the dimensions and material of the net with which the dan buoys are to be used. The dan buoys may be pre-attached to the net, in the manufacture of the net, or may be attached one-by one as the net is streamed into, the water from the vessel which is carrying it. In the latter case the loops 47 on the dan buoy may be attached to the net by clips of the snapshut type.

Figure 8 shows a net 50 streamed to largely encircle an oil slick 52. A vessel 54 is about to haul in the net and pump the oil into its hull tanks. In the case of a large volume of oil, it would of course be pumped into a series of tankers. The vessel 54 has a winch 56 to haul in, through a fairlead 57, a rope or a pair of ropes connected to one end of the net 50, so bringing one end of the net adjacent to the hull of the vessel, to which it is then attached by suitable ropes or cables. The vessel also carries a net-hauling roller assembly 56. This is a power-driven roller around which the net 50 is wound, so hauling in the net 50 and decreasing the perimeter of the oil slick. It is shown in greater detail in Figures 8 and 9.

Referring now to Figures 8 and 9, the hauling roller assembly 56 has a net-carrying roller 60 of an axial length about 2 metres, that is to say slightly more than the height of the net. The net-carrying roller 60 co-operates with a a pair of pressure rollers 62, one at each end of the roller 60. In conjunction with the roller 60, each of the rollers 62 defines a nip. In use, a head cable and a tail cable extend along the top and bottom of the net, and are attached to or threaded through the loops 47 on each dan buoy. When the net is being hauled from the water by the hauling roller assembly 56, the head and tail ropes and the adjacent portions of the net are gripped in the respective nips between the rollers. The rollers 62 are of short axial length so that they do not impede the winding on of the net on the roller, the net becoming "fatter" at its half-height region due to the presence of the floats 43. The roller 60 is carried to rotate on a shaft 63 extending between end-supports 64 and is in the form of a hollow cylinder. At each end it contains motors and gearing 66 whereby the roller can be rotated, in either direction, relative to the supports, 64. The motors 66 may be electrical, pneumatic, or hydraulic or may be mechanically driven from the prime mover of the vessel 54.

As stated, a pair of pressure rollers 62 form respective nips 68 with the roller 60. Each pressure roller 62 is mounted on a swinging arm 70, pivoted for movement about a horizontal axis 72. A piston-cylinder ram 74 is mounted between a fixed bracket 76 and the free end 78 of each arm 70. The function of the rams 74 is to apply pressure to the respective nip 68 so that it firmly grips the net and the tail or head cable as the case may be so that the net can be hauled in, even against the very considerable resistance arising from the inertia of the oil slick 52.

Figure 10 illustrates the use of several elongate small mesh nets 80-88 in a coastal inlet to prevent oil from fouling beaches or rocky coastline. These nets 80-88 may be of the kind shown in Figures 3-5 but a simpler net of the kind described with reference to Figure 6 may equally well be employed, as illustrated. A boat 90 is seen streaming the net 80 in a position where it is interposed between an oil slick 92 and the coastline, and the ends of nets 82 and 84 are anchored at 96 and these nets are being streamed by respective boats 98 and 100. These nets are streamed to prevent the oil reaching a headland 102. Other nets 86,88 streamed by vessels 104, 106 serve to confine the oil slick against moving away from the coastline if the wind or tide should change direction. A motor-driven suction pump 108 having a motor 110, and a suction nozzle 112 at the end of a boom 114 is located on a suitable quay or jetty in a position where it can pick up oil from within the confining net and transfer it to an offtake pipe 116. Instead of the pump 108, a mechanical scoop could be used to pick up the oil.

Figure 11 illustrates the streaming of an elongate smallmesh net 120 from a coastal boat 122 near to the shore of an inlet. Other nets are shown being streamed from other vessels and the intended course of the boat 122 is shown by arrow 124. The individual nets will be joined, once streamed, and serve to protect the coastline 125. Depending on the direction of wind and tide, the oil of the slick 126 can be picked up at a suitable region adjacent to a downwind (leeward) or down—tide portion of the net by a small tanker (not shown) carrying one or more suction pumps. .As seen in Figure 11, one end of the net 120 is anchored by an anchor 128 and buoyed by a buoy 130. According to an important but optional feature of the invention, an elongate small mesh net such as is described in the foregoing text may be deployed in the desired location from an aircraft such as a slow-flying freight aeroplane or a helicopter, in order to confine spilt oil. The net (with dan buoys attached thereto) may be carried in the hold of the aeroplane or the helicopter, and dispensed therefrom as tKe aircraft flies along, out of an open door or hatchway of the aircraft. Alternatively a roll of net, already having dan buoys attached thereto, may be carried on a rotatable shaft supported on suitable mountings in the aircraft. As another alternative, a tray (or other net-containing item of equipment) may be suspended, e.g. on cables, below the aircraft and an elongate net, having dan buoys already attached thereto, may be laid in folds on the tray, in a serpentine arrangement with a free end of the net secured to an anchor. The anchor is carried on the tray at a location where it can be readily tipped or pulled off the tray, e.g. by a trip rope operated by a crewman in the helicopter. The net is arranged so that it will run freely out once the anchor is tipped off the tray, and this is done when the helicopter is in the desired position in relation to the oil slick. The anchor fixes one end of the elongate net and the helicopter is then flown around the oil slick, causing the net to be progressively pulled off the tray and deployed in the water around the oil slick. When all the net is deployed, a second helicopter may take over to deploy a further net in a similar way, if the slick is of a size to require this. Otherwise the end of the net is dropped and is also anchored. A second anchor, on the other end of the net, may be tripped similarly if desired. The oil slick thus confined can then be dealt with, that is to say, the oil can be agglomerated if necessary and mechanically picked up, or it can be pumped into a tanker vessel.

It will be seen that there has been disclosed a practical and relatively inexpensive method and apparatus for dealing with oil slicks of considerable area. Compared to the prior method of NYFELDT (British patent application Serial No.

2 044 623 A published on 22nd October 1980) the difficulties of operating the pursing-up ropes 26, detaching, and then towing the oil-filled sections are avoided, and the method is better adapted for dealing with large oil volumes. In practice, to tow any large volume of oil would involve great expense for fuel for the towing vessels; also in the use of the Applicant's method the expense of specil hose shaped net sections does not arise. Compared to the proposal of

REID (British patent application Serial No. 2 074 887 A published 11th November 1981) the problems of steering a ship in bad weather impeded by a trawling net and a dracone are avoided, as is the need to sequentially release filled dracones and attach empty ones. The present Applicant believes his method is better suited for dealing with large volumes of oil, e.g. a slick one mile or more in diameter.

Claims

1. A method of substantially removing oil spilt on salt or fresh water which includes confining the spilt oil with a small mesh net of substantial length which is connected to floats and supports in such a way that the net is maintained substantially vertical, causing or permitting the oil to move to a region adjacent to a selected portion of the net, and picking up the oil in said region off the surface of the water and feeding it into a suitable container.

2. A method according to claim 1 in which the small mesh net is deployed to separate an oil slick from adjacent coastline.

3. A method according to claim 2 in which the elongate net is deployed a short distance to seaward of the coastline in such a configuration that the effect of wind or tide (or both if they assist each other) is to bring the oil to a region adjacent to a selected portion of the net; the oil in said region is then transferred to a suitable container, for example by pumping or a mechanical scoop.

4. A method of containing oil spilt on open water which includes encircling the oil with a small mesh net of substantial length which is connected to floats and supports in such a way that the net is maintained approximately vertical and acts to confine the oil.

5. A method according to claim 4 in which one end of the net is anchored and the net is streamed (paid out) from a ship in such a way as to form a loop with an open mouth.

6. A method according to claim 4 or 5 in which the net used has a mesh size such that the holes therein have a maximum dimension of approximately of 2.5 mm.

7. A net for use in confining oil on the surface of open water characterised in that (1) it has a small mesh as specified herein, (2) it is of a length greater than 1000 metres, and (3) it is connected to dan buoys in such a way that it can float approximately vertical with a substantial portion of its height above and a substantial portion of its height below the water level.

8. A net according to claim 7 which is also connected to floats.

9. A net according to claim 7 or 8 in which at least 33% of the height of the net is above water level when it floats.

10. A net according to claim 9 in which at least 45% of the height of the net is below water level when it floats.

11. A net according to any of claims 7 to 10. which has a mesh size such that the holes therein have a maximum dimension of approximately 2.5 mm.

12. A net according to claim 8 in which the floats are made of or coated with an oil-absorbent material.

13. A net according to any of claims 7 to 12 in which the dan buoy floats are made of or coated with oil-absorbent material.

14. A net according to claim 13 including a head cable and a tail cable connected to the dan buoys and to the net.

15. A method according to any of claims 1 to 6 in which the net is recovered from the sea using a net roller assembly carried by a vessel and having rollers defining a pair of nips through which the net is drawn", during recovery, by driving one or both of the rollers.

16. A method according to claim 15 which includes applying a force to one of the rollers in a direction transverse to the net, to increase the grip applied to the net by the rollers.

17. A method according to any one of claims 1-6, 15 and 16 in which the net, with dan buoys attached, is deployed from an aircraft.

18. A method according to claim 17 in which the net is deployed from a helicopter.