WO1996029238A1

WO1996029238A1 - Transport of oil

Info

Publication number: WO1996029238A1
Application number: PCT/GB1996/000699
Authority: WO
Inventors: Angus Lamberton Jamieson
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-03-22
Filing date: 1996-03-22
Publication date: 1996-09-26
Anticipated expiration: 1997-09-22
Also published as: AU5152596A

Abstract

A tanker (10) has a number of cargo tanks (12) each of which is provided with a grid (16) of apertured pipes. In the event of a breach in a tank, or in anticipation of an incident which may cause a breach, a gellant may be pumped from a deck tank (14) through a selected grid (16). The grid (16) moves through the cargo injecting gellant into the cargo and gelling the oil, substantially preventing spillage.

Description

"Transport of Oi.-t "

This invention relates to the storage and transport of oil, especially (but not exclusively) to the transport of crude oil, and to the safety of tanker ships used for the transport of oil.

In recent years the search for oil to sustain modern industry and transport has reached into increasingly environmentally sensitive areas, and tankers have become larger and more numerous.

In UK waters, exploration is moving into Atlantic waters where the use of fixed platforms is not possible, and it will be necessary to use floating production facilities and tanker transport, with attendant risks of spillage and pollution in remote and unspoilt areas.

A number of approaches have been made to limiting spillage from tankers in the event of collision or stranding, for example the use of double bottoms, or a variety of constructional arrangements to ensure that any breach results in ingress of water rather than egress of oil. However, all of these suffer from the limitation that in sufficiently extreme circumstances the vessel will suffer a level of damage in which these structural precautions are overwhelmed.

One aspect of the present invention is based upon the concept of addressing these risks by modifying, not the vessel, but the cargo.

The invention, from this aspect, provides a method of handling oil in which oil is placed in a tank which is provided with means for injecting a liquid into the contents of the tank; and, in the event that an emergency occurs or is though to be imminent, a gellant is injected via said means into the oil within the tank.

Typically, the oil is placed in one or more cargo tanks of a transport vehicle, most commonly a tank ship.

The oil may subsequently be de-gelled by mechanical agitation, or by the addition of acid.

Another aspect of the invention provides a transport vehicle, most preferably a tank ship, having one or more cargo tanks, one or more storage tanks for a gellant, and injection means for injecting the gellant from the storage tanks (s) into the cargo tank(s) .

In a particularly preferred arrangement, the injection means comprises a perforated pipe device in each cargo tank, each said pipe device being connected to the gellant tank(s) via a flexible hose to permit the device to be permanently mounted above, at the side or on the bottom of the tank in normal use but to be movable vertically or horizontally within the tank, and means for pumping gellant from the gellant tank(s) through a selected one or more of the pipe devices. Each of the perforated pipe devices may suitably be in the form of a grid or matrix of perforated pipes. The pipes may be located on either side of a plate member which is formed with passages shaped to promote turbulence in the oil as the plate member moves therethrough.

In a particularly preferred arrangement, a tank ship with a number of cargo tanks has a single gellant tank on deck, and the gellant tank may have a capacity of sufficient gellant to treat one cargo tank.

The term "gellant" is used herein to refer to any additive which causes the oil to become a solid or semi-solid mass. For example, the gellant may cause the oil to become gelatinous or to adopt a rubbery consistency. Generally, exposure to the gellant causes the viscosity of the oil to increase, this hindering egress of the treated oil from the tank.

The term "gel" is used herein to describe the oil following treatment with the gellant and refers to the solid or semi-solid physical state of the treated oil.

Suitable gellants are know per se. for example in the form of polymer additives used for the purpose of thickening oil-based drilling muds, for example "Geltone" (trade mark) of National Lead Company which is conventionally used as a thickener for drilling muds. Other chemicals which cause the oil to gel may be used, for example polyacrylamides, carboxymethyl celluloses, carboxyethyl celluloses, alginates, dextrans, and derivatives of such substances.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a schematic perspective view of an oil tanker incorporating the invention; Fig. 2 is an enlarged detail of part of Fig. 1; Fig. 3 illustrates a modification of Fig. 2, Fig. 3A being a partial cross-sectional side view and Fig. 3B a partial plan view; and Fig. 4 is a schematic pictorial view illustrating an optional feature of the embodiment.

Referring to Figs. 1 and 2, crude oil is transported from a loading point to a delivery terminal in a substantially conventional tanker 10 having a number of cargo tanks 12. At the loading point, the crude oil is pumped into the cargo tanks 12.

The oil is loaded into the cargo tanks in conventional manner. A quantity of gel-forming polymer (gellant) is loaded into a gellant tank 14 on deck. The oil is transported and unloaded in conventional manner so long as the voyage is uneventful. In the event that a potentially dangerous situation arises, however, the gellant is mixed with the cargo.

The mixing of gellant and cargo would ideally be by spraying the surface of the crude with a mixture which increased the density of the crude ensuring that the specific gravity does not exceed that of water but allowing it to sink as the gel formed, exposing fresh liquid at the surface. It may not be possible to find a suitable chemistry to achieve this but the following mechanical mixing method is proposed as an alternative.

Each of the cargo tanks 12 is provided with a matrix of perforated pipes 16 which are secured together to form a raft-like structure. In normal use, the pipe matrix 16 lies in position in its tank and is connected via a flexible hose and suitable valves to the gellant tank 14. If an emergency occurs or is imminent, gellant is pumped through the flexible hose to the pipe matrix 16. Gellant is expelled in finely divided streams into a section of the tank contents. At the same time, the pipe grid moves either by natural buoyancy, gravity or a mechanical horizontal movement through the fluid creating an even dispersion of gellant throughout the tank.

Fig. 3 shows a modification of the matrix of Figs. 1 and 2. The pipes 16 are disposed on either side of a planar sheet member 17, which may for example be moulded from GRP. The sheet member 17 is formed with through passages 19, suitably with two passages 19 in diagonally opposite corners of each square of the matrix, as shown. Each of the passages 19 extends from an aperture 21 in the lower face of the sheet member 17 to an aperture 23 in its upper face, with the passage 19 turning through 90 degrees clockwise between the two, thus forming part of a helix.

This arrangement of passages has the effect that, as the pipe matrix moves through the cargo, the oil is forced through the passages and is caused to exit with a swirling motion, thus inducing turbulence and mixing between the oil and the gellant.

The initiation of gellant injection may be controlled manually, for example by operation of a panic button on the bridge of the ship. Alternatively, automatic control may be used. Most cargo tanks are already fitted with tank sensors for determining the liquid volume and/or the pressure within the tank. Either of these parameters may be used, since rupture of a tank will cause a loss of both volume and pressure. The above embodiment provides mixing in a timescale of minutes or tens of minutes and therefore provides a high degree of cargo containment even if the gelling procedure is initiated only after the tank is ruptured.

This arrangement provides a very thorough and rapid mixing of oil and gellant in a manner which is simple to operate and requires minimal alteration to the tanker.

To minimise space and cost requirements, it is proposed that the gellant tank should be large enough only to carry sufficient gellant to treat one cargo tank. In most situations of stranding and collision, the immediate risk is loss of the contents of one particular tank, and thus such a limited quantity of gellant is sufficient to deal with the immediate emergency. Thereafter, additional gellant can be pumped on board the vessel from a support vessel to allow further cargo tanks to be treated.

Fig. 4 shows an optional feature for facilitating the transfer of further gellant. The tanker 10 has a spar 18 at the top of which a ring 20 is releasably mounted. A messenger line 22 secured to the ring 20 can be fixed to a flexible hose (not shown) . If the ship is in danger of breaking up, a helicopter 24 can use a lowered hook 26 to engage the ring 20 and transfer the messenger line 22 to a support vessel 28. Thereafter the support vessel 28 hauls in on the messenger line 22 to bring the hose on board to permit transfer of additional gellant from a safe distance. A similar line arrangement can be used to transfer a hawser for later towing. A normal deployment of a light line and buoy is still highly recommended in case helicopter access is restricted.

The pipe matrix arrangements illustrated in Figs. 1, 2 and 3 are also useful in de-gelling the cargo after an incident. The effect of polymer gellants can be reversed by treating the gelled oil with an acid, which breaks down the gel. The pipe matrixes 14 simplify this procedure, as the required acid can be pumped through each matrix 14, causing liquefaction of the neighbouring oil which allows the matrix to move through the tank again, degelling the contents as it goes .

In an alternative arrangement (not illustrated), the polymer and oil may be mixed by using the circulating pumps which are conventionally provided on board for use in tank washing procedures, to circulate the cargo oil via a mixing chamber.

With the use of the invention, in the event of the tanker suffering a major breach or spillage, the mobility of the cargo is severely reduced, and the oil will float and be washed ashore as relatively large pieces of gel which are easier to collect than crude oil, and which cause very little seepage into beaches and coastal soil.

The safety of a tanker ship incorporating the present invention may be further enhanced by incorporating one or more of the following features:

1. A flexible boom is carried aboard which, in the event of a spillage, will be deployed around the vessel to contain the worst of the spillage. 2. The tanks are lined with fibre reinforced tarpaulin or sheeting so that a hull-penetrating collision will not damage the "bag" containing the oil. 3. Use of grounding alarms (known per se) . 4. Remote control of major functions by telemetry so that personnel can safely leave the ship without stopping all ship operations (not new per se) . 5. Black box recorders and collision warning systems using intelligent radar (not new per se) .

By using a combination of such features a much safer "green tanker" can be achieved.

Although the present invention is described above primarily with reference to tanker ships, the invention may also be applied to other situations where oil is stored or transported, for example in road or rail vehicles, or in tank farms.

Claims

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1. A method of handling oil in which oil is placed in a tank which is provided with means for injecting a liquid into the contents of the tank; and, in the event that an emergency occurs or is though to be imminent, a gellant is injected via said means into the oil within the tank.

2. The method of claim 1, in which the oil is placed in one or more cargo tanks of a transport vehicle.

3. The method of claim 2, in which the vehicle is a tank ship.

4. The method of any preceding claim, in which the oil is subsequently de-gelled by mechanical agitation.

5. The method of any of claims 1 to 3, in which the oil is subsequently de-gelled by the addition of acid.

6. A transport vehicle having one or more cargo tanks, one or more storage tanks for a gellant, and injection means for injecting the gellant from the storage tanks(s) into the cargo tank(s) .

7. A vehicle according to claim 6, in the form of a tank ship.

8. A vehicle according to claim 6 or claim 7, in which the injection means comprises a perforated pipe device in the or each cargo tank, the or each said pipe device being connected to the gellant tank(s) via a flexible hose to permit the device to be permanently mounted above, at the side or on the bottom of the tank in normal use but to be movable vertically or horizontally within the tank, and means for pumping gellant from the gellant tank(s) through a selected one or more of the pipe devices.

9. A vehicle according to claim 8, in which the or each perforated pipe device is in the form of a grid or matrix of perforated pipes.

10. A vehicle according to claim 9, in which the pipes are located on either side of a plate member which is formed with passages shaped to promote turbulence in the oil as the plate member moves therethrough.

11. A tank ship according to claim 7 or any claim dependent thereon, having a number of cargo tanks and a single gellant tank on deck.

12. A tank ship according to claim 11, in which the gellant tank has a capacity of sufficient gellant to treat one cargo tank.

13. A tank ship according to any of claims 7, 11 and 12, including means for connecting a hose between the ship and a support vessel to receive additional gellant.

14. A tank ship according to claim 13, in which said means comprises a mast on the ship mounting a member (for example, a ring) engageable by a helicopter and having a messenger line attached thereto.