WO2001038648A1

WO2001038648A1 - Methods and means of carrying off contaminated materials

Info

Publication number: WO2001038648A1
Application number: PCT/NO2000/000375
Authority: WO
Inventors: Åge KYLLINGSTAD
Original assignee: Hitec AS; National Oilwell Norway AS
Current assignee: Hitec AS; National Oilwell Varco Norway AS
Priority date: 1999-11-26
Filing date: 2000-11-08
Publication date: 2001-05-31
Anticipated expiration: 2002-05-26
Also published as: AU2411501A; NO995834L; NO314851B1; NO995834D0

Abstract

An account is given of a method and means of carrying off contaminated, particulate solid materials such as drill cuttings from a seabed location. This is done through a hose/pipeline (16, 18) running from a mound (14) of said materials on the seabed (10) to a surface location, where a suction effect is created at the lower materials suction end of the hose/pipeline (16, 18) by a transport liquid being injected in the intended transport direction of said materials, and where the hose/pipeline (16, 18) at a somewhat higher level is connected to a feed hose (28) for compressed gas that, upon upward flow in the hose/pipeline (16, 18), pulls the mixture of transport liquid and particulate solid materials along. The mixture is fed out of the hose/pipeline (16, 18) and ends in a tank (22) in which the solid particles are separated from said mixture, the liquid fraction of which - the transport liquid - is recycled while contaminated from its contact with contaminated materials, by first being fed to the suction end opening of the hose/pipeline (16, 18) and then continuing to flow in the essentially vertically oriented loop of the means.

Description

METHODS AND MEANS OF CARRYING OFF CONTAMINATED MATERIALS

The present invention regards a method of carrying off contaminated, e.g. particulate materials that are present on the seabed. The method is thereby of the type that is stated in the introductory part of claim 1.

The invention also regards means that may among other things be used to implement operations covered by the method according to the invention, but which it will also be possible to use in order to achieve particular advantages associated with this invention, in connection with similar methods of removing various contaminated materials from the seabed, in which the aspect of the method does not fully come under the definition of this method, but rather represents modifications and variants of this.

The means according to the invention is of the type that shows a constructive structure as stated in the introductory part of the first appliance claim. Both the method and the means, which are technically related and inventively uniform, may be applicable and useful for a range of carrying-off operations in which contaminated, in particular particulate materials are to be taken up from the 5 sea bed and transported off, among other things for environmental purposes by raising the quality of the seabed and the seawater, for the purpose of improving conditions for marine fauna and flora. The present invention is however primarily linked to two main tasks, that is the removal of ιo drill cuttings from the seabed around marine platforms and the removal of other contaminated, particulate materials from the seabed in fjords and harbours.

However these specifically stated applications do not limit the extent of the patent protection, which is defined in the is first method claim and in the first appliance claim, which still presupposes that settled materials to be removed are contaminated and that a liquid/gas based transport medium is used for removal.

It is thus an objective to provide, in accordance with the ₂o invention, a method of the type stated in the preamble of the following claim 1, and also provide means of the type stated in the preamble of the first appliance claim, in which considerable benefits are achieved in comparison with conventional and other technology, both financially and in _5 terms of capacity and efficiency.

According to the present invention, these objectives are realised by, in the case of the method, proceeding in accordance with the characterising part of claim 1, and by the means being erected constructively in accordance with the ₃o characterising part of the first independent appliance claim. In accordance with the method of the invention, the procedure is thereby to recycle a liquid, or possibly gaseous transport medium for removal of said contaminated materials from the seabed to a dump site that may be temporary, normally above 5 the surface of the sea, which transport medium has become contaminated through contact with said contaminated materials, an upwardly directed jet of return liquid or gas being injected into the free, lower end of a suction hose for carrying off materials from the seabed, at a short distance o from the extreme end of said suction hose, which hose is manipulated by e.g. a remote-operated vehicle (ROV) and is connected at the top to a riser for further upward transport of contaminated, particulate solid materials by use of, except in the case of the first circulation, similarly 5 contaminated transport liquid (or gas). Using recycled contaminated transport medium has proven to have no negative effect whatsoever on the process. According to the invention, the conditions are made right for control/adjustment of the mixing ratio of materials to transport medium (normally o liquid) . At the surface location, the mixture of particulate materials and transport liquid will be subjected to screening and separation, and the contaminants contained in the recycled transport liquid will thus have a smaller particle size than those retained by the screens of the vibrating 5 sieve, and will normally consist of liquid contaminants.

Recycling contaminated transport liquid results in large financial savings. Not least, it is costly to handle and treat/remove contaminated transport liquid when using known techniques. An essentially closed loop for flowing transport o liquid is beneficial to the capacity and efficiency of the method. The material suction process at the seabed can be subjected to audio-monitoring. This can be implemented by arranging a hydrophone on the suction hose, positioned at a certain distance from the suction end.

The means in accordance with the invention comprises a hose/tube shaped transport device with a longitudinal extent that corresponds to the approximate distance from the point on the seabed from which the materials are being carried off, to a temporary discharge/disposal site, which transport device is preferably based on the so-called "gas lift principle" (where pressurised air may be used). The transport device preferably comprises an ROV manipulated suction hose that is designed to suck in contaminated materials from the seabed by its free end, which suction hose should be coupled to a riser at a suitable distance from the site of operation on the seabed, particularly when operating at great depths.

When operating at great depths, which corresponds to great lifting heights for said riser, the riser should be designed with an increasing diameter (gradual or in steps) towards the outlet, which is located above the surface location. By this means, the velocity and pressure drop due to gas expansion is reduced (gas introduced into the riser from the gas lift pipeline) .

As an example, a gas lift in the form of a feed hose for compressed gas, e.g. pressurised air, may be connected at the transition between the suction hose below and the riser above that forms the extension of the suction hose. The upper end of the feed hose is connected to a compressor that is located above the water surface. A lower end portion of a return hose for contaminated transport liquid (or gas) projects into the lower end portion of the material transport hose (the suction hose). The end of the return hose may be equipped with a jet nozzle.

A conduit/tube/hose for recycled gas for the gas lift may lead to the compressor from an accumulation/separation tank. This conduit etc. may if desired be left out if recycling of this gas is not required.

From the accumulation tank, which is either designed as a separator or comprises a separation device, there is partly an outlet for contaminated materials that have been transported up, which materials may consist of particles of dissimilar size, and partly an outlet for excess liquid, connected to said return liquid hose for contaminated transport liquid.

The return hose may, immediately below the accumulation and separation tank, be connected to a branch line having a shut- off valve in close proximity to the return hose.

If the gas used for the gas lift is not to be recycled, the accumulation and separation tank, which may consist of several parts, may have an open top.

A pump may if desired be installed in the return hose for contaminated transport liquid, above the surface of the sea.

This pump may be left out if the hydrostatic pressure due to the difference in height is sufficient to feed contaminated transport liquid downwards so as to make it arrive at said nozzle at a satisfactory velocity of flow.

The above mentioned nozzle for injection of contaminated transport liquid into the end portion of the suction hose for materials on the seabed may be positioned at a restriction in the end portion of the suction hose, at a distance from the free end thereof. By so doing, a venturi effect may be achieved in order to increase the suction effect on the materials. The nozzle may also be positioned eccentrically relative to the axis of the end of the suction hose or at an angle, so as to establish and maintain a helical flow that facilitates the materials feed.

A non-limiting example of a preferred embodiment is represented in a highly schematic form in the appended sole drawing figure, in which means of removal of contaminated materials from the seabed is shown in one applicable working position.

In the drawing figure 10 denotes the seabed and 12 denotes the surface of the sea, while 14 indicates a mound of contaminated particulate materials that display mutually divergent particle sizes, for instance drill cuttings.

The means of carrying off contaminated materials from the seabed comprises a suction hose 16 that may consist of a relatively long, flexible hose, and which constitutes the lower portion of a continuous passage that similarly comprises a riser 18, the upper portion of which projects above the surface of the sea 12, where it incorporates a portion twice angled at 90°, so as to direct the outlet of the riser 18 (and thereby of the common passage 16, 18) down into the upper zone of an accumulation and separation tank 22.

When operating at great depths, which corresponds to great lifting heights, the riser 18 may be designed with an increasing diameter towards the outlet. Thereby, the velocity of flow and the pressure drop due to gas expansion is restricted.

The tank is equipped with a vibrating sieve (shown simplified in the form of an inclined screen) 24 for separation of the mixture of transport liquid and contaminated materials from the mound 14.

Reference number 26 indicates a transition piece between the suction hose 16 and the riser 18. The most important thing is to establish one passage 16, 18 that extends from the site of operation on the seabed 10 to a processing site, e.g. the tank 22 above the surface 12.

The gas lift in the riser 18 is implemented by means of a feed hose 28 for compressed gas, for example and preferably in the form of pressurised air, from a compressor 30. The principle of the gas lift is well known: As a result of its specific gravity, the gas flows upwards in a defined passage (18) and carries with it liquid and other matter that may be present in/is introduced into said passage.

If this compressed air is to be retained and recycled upon arrival in the tank 22, the tank 22 must be designed with a closed top, and a conduit 32 (broken line) must be established between the tank 22 and the compressor 30. An outlet 34 for the contaminated mass of particulate solids such as drill cuttings leads out of the vibrating sieve in the tank 22, which sieve is in the form of an inclined screen 24. The contaminated particles have been brought up to the surface location, and the further transport is, as far as it goes, irrelevant to the present invention. In the drawing figure, such materials are shown as they leave the tank 22 and proceed out through the outlet 34. Naturally, these materials will be taken care of via e.g. an underlying channel for further transport.

It is assumed that the lower zone of the tank 22 at the outset is filled with a suitable volume of transport liquid.

The lower zone of the tank 22, which at the outset is filled with transport liquid, is connected to a bottom outlet 36 that is first of all connected to a suspended, very long hose/pipeline 38 for transport liquid. After the first circulation through the means the transport liquid is contaminated by its contact with contaminated materials, and subsequently represents recycled transport liquid.

The hose 38 is therefore termed a return hose for contaminated transport liquid.

The lower end portion of the return hose 38 is angled twice and projects, through its extreme end 40, into the end portion of the suction hose 16. The suction hose 16 is shown at a suitably inclined position relative to the seabed 10, corresponding to an expedient position in relation to the mound 14 of materials, and the extreme end portion 40 of the return hose may have a corresponding inclination so that the mouth of the return hose 38 is placed coaxially in the lower section of the suction hose 16.

The nozzle in the angled end portion 40 of the return hose 38 may be located in a restriction (venturi) 42 in the surrounding portion of the suction hose 16, in order to increase its suction effect.

In said free end portion 40 of the return hose, a nozzle has been installed for injection of the transport liquid. The nozzle may be made up of a mouth piece into which has been inserted a jet pump, in order to implement efficient feeding of materials from the mound 14, at least up to a point in the suction hose/riser at which the gas from the feed hose for compressed air in the gas lift starts to have an effect.

A hydrophone 44 has been mounted on the suction hose 16 near the transition 26 to the riser 18, which hydrophone is an underwater listening device for audio monitoring of the suction process.

A branch line 46 with a shut-off valve 48 is connected to the return hose 38 immediately below the bottom of the tank 22, through which branch line any excess liquid may be drawn off.

Immediately downstream of the branch line 46, the return hose 38 is connected to a pump 50. This pump may be left out if the hydrostatic pressure due to the difference in height is sufficiently high.

Claims

C l a i m s

1. A method for carrying off contaminated, for example particulate materials from the seabed, in which a flow of materials and transport medium is effected to a

5 higher position through a hose or a pipe (passage) (16, 18), and in which the flow is established and maintained by compressed gas being introduced into said passage (16, 18) at a distance above the lower suction end of the passage (16, 18), and brings about a so-called gas o lift inside the passage (16, 18), which lift affects the mixture of materials and transport medium, c h a r a c t e r i z e d i n that said transport medium, normally liquid, but possibly gaseous, after having transported a certain amount of materials up s under the influence of the lift gas and thereby having become contaminated by its contact with the contaminated materials, is recycled in a contaminated condition to the seabed (10) materials suction end of the passage (16, 18), where recycled, contaminated transport liquid 0 is introduced in the form of a directional jet, preferably at an increased velocity of flow, in order to increase the suction effect in relation to the materials on the seabed (10), a mixture of transport medium and materials being led to a tank (22) having a sieve/screen 5 (24) for separating out the solid particles, while the contaminated transport medium is caused to leave the tank (22) in order to be introduced into the suction end of said passage (16, 18).

2. Means of carrying off contaminated, for example o particulate materials from a seabed location, comprising means (16, 18, 28, 38, 40) of effecting a flow of materials and a transport medium through an upward passage (16, 18) to a higher position, preferably above the surface of the sea, where the upward passage of a hose/pipeline design (16, 18) has associated with it 5 means (28, 40) comprising at least a gas feed hose/pipeline (28) connected to the hose/pipeline (16, 18) at a distance above the lower suction end of this, and causes an ejector/gas lift effect in the hose/pipeline (16, 18), particularly in order to o implement the method as stated in claim 1, c h a r a c t e r i z e d i n that the means comprises a tank (22) having a sieve/screen (24) for separating out contaminated, particulate materials that have been transported up, which tank (22) has a hose s shaped tubular, downward return passage (38) for contaminated transport medium (fluid), which return passage (38) has its in the operating position bottom end (40) located inside the suction end of said hose/pipeline (16, 18).

0 3. Means according to claim 2, c h a r a c t e r i z e d i n that the return passage (38) that transports contaminated transport medium for the purpose of recycling is provided with a nozzle at the outflow end (40) located in its said suction end, for injection of 5 said return liquid with a directional jet effect.

4. Means according to claim 3, c h a r a c t e r i z e d i n that said nozzle is made up of a mouth piece with a built-in jet pump.

5. Means according to claim 2, 3 or 4, o c h a r a c t e r i z e d i n that an underwater listening device in the form of a hydrophone (44) is mounted on a lower portion of said hose/pipeline (16, 18) for the purpose of audio monitoring of the materials suction process.

6. Means according to one or more of the claims 2-5, c h a r a c t e r i z e d i n that the lower part of said materials/transport medium-uptransporting passage (16, 18) of a hose/pipeline design is a flexible, relatively long hose (16), the upper end of which is coupled to a riser (18) that exhibits an increasing diameter towards the outlet (20) located at the top, particularly in the case of great depths/lifting heights .

7. Means according to one or more of the claims 2-6, c h a r a c t e r i z e d i n that a channel (32), a pipe or a hose, runs between said tank (22), which is designed with a closed top, and a compressor (30) for delivery of compressed gas, e.g. air, for recycling of pressurised gas used in the gas lift.

8. Means according to claim 3 or 4 , c h a r a c t e r i z e d i n that said nozzle/mouth piece is located in a restriction (42) in the lower end portion of the suction hose (16).

9. Means according to claim 3, 4 or 8, c h a r a c t e r i s e d i n that the nozzle/mouth piece is eccentric and/or inclined relative to the longitudinal axis of the end portion of the suction hose (16).

0. Use of a contaminated transport medium, preferably a liquid transport medium, in a process for transporting up contaminated, particulate solid materials that are present on the seabed (10), in which contaminated transport liquid is recycled in an essentially closed loop that is essentially oriented in the vertical direction.