APPARATUS AND METHOD FOR SEAFLOOR STOCKPILING
An apparatus for seafloor stockpiling that has a slurry inlet that receives slurry from a seafloor tool via a slurry transfer pipe and walls that, together with the seafloor, define a cavity having a stockpiling volume. The walls are made substantially of a water permeable material, such as a filter fabric or geotextile, that captures and contains seafloor material present in slurry received from the slurry inlet, while permitting egress of water from the slurry. In a preferred form the seafloor stockpiling device is a hood with an open bottom that is located on a seafloor surface.
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The present invention relates generally to underwater mining, and in particular relates to an apparatus for seafloor stockpiling. In particular the invention relates, but is not limited, to a seafloor stockpiling device which receives seafloor material, typically ore slurry, from at least one seafloor tool, and from which the seafloor material can be gathered for transfer to a surface vessel.
BACKGROUND OF THE INVENTIONSeabed excavation is often performed by dredging, for example to retrieve valuable alluvial placer deposits or to keep waterways navigable. Suction dredging involves positioning a gathering end of a pipe or tube close to the seabed material to be excavated, and using a surface pump to generate a negative differential pressure to suck water and nearby mobile seafloor sediment up the pipe. Cutter suction dredging further provides a cutter head at or near the suction inlet to release compacted soils, gravels or even hard rock, to be sucked up the tube. Large cutter suction dredges can apply tens of thousands of kilowatts of cutting power. Other seabed dredging techniques include auger suction, jet lift, air lift and bucket dredging.
Most dredging equipment typically operates only to depths of tens of metres, with even very large dredges having maximum dredging depths of little more than one hundred metres. Dredging is thus usually limited to relatively shallow water.
Subsea boreholes such as oil wells can operate in deeper water of up to several thousand metres depth. However, subsea borehole mining technology does not enable seafloor mining.
Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
SUMMARY OF THE INVENTIONAccording to an aspect the present invention provides a seafloor stockpiling device that is located on the seafloor in use, the device comprising:
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- a slurry inlet for attachment of a slurry transfer pipe and for receiving slurry from a seafloor tool; and
- walls that substantially define a cavity having a stockpiling volume, the walls being configured to capture and contain seafloor material present in the slurry in the device while permitting egress of water present in the slurry from the device.
Preferably, the seafloor stockpiling device is a hood. Preferably the hood has an open bottom. Preferably the cavity is defined by the walls together with a seafloor surface on which the seafloor stockpiling device is located. Preferably the hood is relocatable and at least a portion of the walls are movable sections that reduce drag loads during movement of the seafloor stockpiling device. The movement may be deployment, seafloor relocation, or recovery of the seafloor stockpiling device.
Preferably, at least a portion of the walls are water permeable. Preferably at least a portion of the walls comprise a filter material, such as a geotextile, and/or a filter structure, such as an inclined plate or tube settler, which permits egress of water while containing the desired seafloor material. In a preferred form the walls of the seafloor stockpiling device comprise both a filter material portion and a filter structure portion, preferably a geotextile portion and an inclined plate or tube settler portion, respectively.
The filter material is preferably reversibly mounted such that reversing the mounting of the filter material causes an inward facing surface of the filter material to become outward facing. Reversible mounting of the filter material may present a number of advantages, for example the ability for the filter material to be selectively cleaned when fine seafloor material accumulates on the filter material, as further stockpiling operations will tend to flush such accumulations off the outside surface.
The seafloor stockpiling device preferably further comprises a friction reduction mechanism which may be utilised to reduce static friction (stiction) between the seafloor stockpiling device and a seafloor surface on which the seafloor stockpiling device is located when lifting the device from the seafloor. The friction reduction mechanism may comprise one or more fluid outlets adjacent a bottom portion of the device. The fluid outlets are preferably directed generally towards the seafloor. In use, the fluid outlets preferably fluidise sediment and seafloor material adjacent the seafloor stockpiling device.
The friction reduction mechanism may alternatively, or additionally, comprise movable walls. The movable walls are preferably contained inside the walls of the device and enclose seafloor material contained within the device. The movable walls preferably pivot relative to the walls of the device during lifting of the device. As the movable walls pivot they preferably swing away from the seafloor material contained, within the device.
The device preferably has at least one lifting attachment for lifting and manoeuvring the device. The lifting attachment is preferably engaged with a movement system that can at least lift the device. An offset lifting attachment which is offset from a central axis of the device, preferably located on or adjacent an outer edge of the device, may be provided. The offset lifting attachment preferably causes the device to be lifted on an angle during relocation of the device.
Preferably the seafloor stockpiling device is formed from at least two modules configured for separate deployment from a surface vessel and for underwater interconnection. The maximum deployment capacity of surface vessel deployment systems may present a constraint to the size of the seafloor stockpiling device and, accordingly, in some embodiments the seafloor stockpiling device is formed in two or more modules configured for separate surface deployment, and configured for interconnection once submerged and/or on the seafloor. For example, such a modular seafloor stockpiling device may, in some embodiments, be up to 25 m in diameter and up to 100 T submerged weight once formed from the two or more modules.
In embodiments of the invention, the seafloor stockpiling device may comprise a stockpile removal device enabling material stockpiled within the seafloor stockpiling device to be removed in slurry form. The stockpile removal device may comprise an opening port, such as a door in the seafloor stockpiling device, which when open permits a boom mounted suction inlet of a seafloor machine to be introduced into the seafloor stockpiling device to gather stockpiled material, preferably in slurry form, and which when closed restrains stockpiled material. Alternatively or additionally the stockpile removal device of the seafloor stockpiling device may comprise a suction inlet and slurry transfer pipe mounted on and extending into the seafloor stockpiling device, so that the suction inlet of the seafloor stockpiling device is placed in a suitable position to mobilise and extract stockpiled material.
Such embodiments of the present invention recognise that slurry flow rates desired for capturing seafloor material can be significantly different to the slurry flow rates desired for lifting slurry to a surface vessel, such as by a riser and lift system, and thus provides for decoupling of these flow rates by use of a seafloor stockpiling device. The respective flow rates may thus be separately optimised. For example, a slurry flow rate into the seafloor stockpiling device may for example be about 3,000 m3/hour, with an ore concentration of about 3%, while a slurry flow rate to the surface vessel may be around 1,000 m3/hour at an average ore concentration of about 12%.
In embodiments of the invention, the seafloor stockpiling device is preferably configured such that, when positioned on a relatively flat portion of the seafloor, the seafloor stockpiling device forms a hood which completely encloses a stockpiling volume in a manner to minimise the loss of slow-settling fine particles (referred to herein as “fines”). In such embodiments, to accommodate large volumes of slurry inflow, the hood preferably permits the egress of water from the stockpiling volume so as to filter and capture the seafloor material from the slurry. To this end, preferably a significant surface area of the walls of the hood are formed of filter material which contains fines while permitting egress of water from the hood. A grade of the filter material, being a dimension below which solid particles can pass through the filter material, is preferably selected in order to maximise fines containment while permitting the necessary water flow rate out of the hood to accommodate slurry inflows into the hood. For example the filter material may comprise a silt curtain of 50 micron grade. The seafloor hood preferably comprises a space frame supporting the filter material, with the walls of the hood being formed by the filter material.
Capture of fines from a slurry inflow into the hood can be advantageous both environmentally in avoiding escape of plumes of the seafloor material, and operationally as such fines may represent 30% or more of the seafloor material desired to be gathered.
The stockpile hood may have angled walls forming a substantially frustoconical shape, the walls being at an angle to approximate the expected rill angle of an ore heap so as to avoid a stockpiled ore heap exerting significant outward pressure on the walls.
Further, the present invention provides a seafloor stockpiling device adaptable in some embodiments to deployment at significant water depths. For example some embodiments may be operable at depths greater than about 400 m, more preferably greater than 1000 m and more preferably greater than 1500 m depth. Nevertheless it is to be appreciated that some embodiments of the present invention may also present a useful seafloor mining option in water as shallow as 100 m or other relatively shallow submerged applications. Accordingly is to be appreciated that references .to the seafloor or seabed are not intended to exclude application of the present invention to mining or excavation of lake floors, estuary floors, fjord floors, sound floors, bay floors, harbour floors or the like, whether in salt, brackish, or fresh water, and such applications are included within the scope of the present specification.
An example of the invention will now be described with reference to the accompanying drawings, in which:
The present embodiment provides a system 100 operable to around 2500 m depth, however alternative embodiments may be designed for operation to 3000 m depth or greater. During production operations, one or more seafloor mining tools (SMTs) 112 are used to excavate seafloor material, preferably ore, from the seabed 110.
Ore mined by the seafloor mining tool 112 is gathered upon being cut and pumped, in the form of slurry, from the seafloor mining tool 112 through a stockpile transfer pipe (STP) 128 to a seafloor stockpiling device 124. The seafloor stockpiling device 124 captures ore from the slimy while permitting egress of water from the slurry.
A gathering tool 114 inserts a boom-mounted suction inlet into the seafloor stockpiling device 124 via a door 220 (see
The stockpiling hood 124 has walls comprising panels 208 that, together with the seafloor 110, define a cavity for stockpiling seafloor material (as illustrated in
The panels 208 are removable and formed of a frame 212 with a water permeable skin in the form of a geotextile covering 214.
Due to the large geometry of the stockpiling hood 124 there is a large in water added mass associated with the device due to the geotextile covering 214. This added mass causes in water lifting drag to increase dramatically over that of conventional lifts. As a result in this embodiment the geotextile covering 214 is able to be rotated to align with a direction of movement before any lifting operations occur. The panels 208 are able to be opened to reduce water resistance during movement of the stockpiling hood 124. The geotextile covering 214 reduces the outflow velocity to allow settlement of larger spoil particles and retain fines larger than 30-60 microns. In case of differential pressure across the filter material rising due to filter pore blockages, a relief valve or flap is provided to avoid rupture of the filter material.
As shown in
During lifting and lowering operations the drag of the hood is substantial. To reduce this it is desirable to allow water to flow through the structure.
Provision is made in the design of the stockpiling hood 124 for access by the gathering machine 300 via doors in the form of flaps 220, which comprises a rubber panel with suitably arranged slits to permit a gathering portion in the form of a boom mounted suction inlet 302 of the gathering machine 300 to be inserted through flap 220. Flaps 220 are provided at several locations to provide gathering from all sides of the stockpile, and do not require any power to function. The flaps 220 are designed to avoid excessive leakage of slurry when not in use by gathering machine 300.
This embodiment thus filters the flow of ore slurry being pumped from one or more sea floor production tools. This slurry is a high volume flow and the slurry velocity needs to be reduced to allow the ore to settle out of the flow onto the sea floor. The stockpiling hood 124 reduces the amount of ore lost from such a slurry flow and is designed to minimise the disturbance of the ore pile created when the stockpiling hood 124 is relocated. The stockpiling hood 124 is able to be shifted by an overhead crane on a vessel so as to be re-useable.
An inflow of ore slurry is slowed inside the stockpiling hood ,124 due to the large volume of the stockpiling hood 124, and the large surface area covered in the geotextile covering 214. Larger ore particles in the slurry are fast setline and settle to the stockpile in a slow flow region. A large volume slurry flow moves through the geotextile covering 214 at low velocity with the geotextile covering 214 filtering slow-settling particles from the flow.
By lifting the stockpiling hood 124 from the offset lifting point, the side of the stockpiling hood 124 that is below the offset lifting point 218 is lifted first, reducing the total break force required to overcome the stiction. Once the stiction has been overcome, the stockpiling hood 124 can then be raised and manoeuvred using a central lift gear 206.
It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.
Claims
1. A seafloor stockpiling device that is located on the seafloor in use, the device comprising:
- a slurry inlet for attachment of a slurry transfer pipe and for receiving slurry from a seafloor tool; and
- a hood with an open bottom comprising walls that substantially define a cavity having a stockpiling volume, the walls being configured to capture and contain seafloor material present in the slurry in the device while permitting egress of water present in the slurry from the device.
2. (canceled)
3. The seafloor stockpiling device of claim 1, wherein the walls define the cavity together with a seafloor surface that the seafloor stockpiling device is located on.
4. The seafloor stockpiling device of claim 1, wherein the walls are water permeable.
5. The seafloor stockpiling device of claim 1, wherein at least a portion of the walls comprise a filter material.
6. The seafloor stockpiling device of claim 5, wherein the filter material is reversibly mounted such that reversing the mounting of the filter material causes an inward facing surface of the filter material to become outward facing.
7. The seafloor stockpiling device of claim 5, wherein the filter material is a geotextile.
8. The seafloor stockpiling device of claim 1, wherein at least a portion of the walls comprise a filter structure.
9. The seafloor stockpiling device of claim 8, wherein the filter structure is an inclined plate or tube settler.
10. The seafloor stockpiling device of claim 1, further comprising movable sections that can be moved to between a storage position and a travel position, wherein the drag load during movement of the seafloor stockpiling device is reduced in the travel position.
11. The seafloor stockpiling device of claim 1, further comprising at least one friction reduction mechanism that reduces static friction between the seafloor stockpiling device and the seafloor.
12. The seafloor stockpiling device of claim 11, wherein the friction reduction mechanism comprises one or more fluid outlets adjacent a bottom portion of the seafloor stockpiling device.
13. The seafloor stockpiling device of claim 12, wherein the one or more fluid outlets are fluidly connected via a conduit to a diverter valve in the slurry inlet.
14. The seafloor stockpiling device of claim 12, wherein the one or more fluid outlets are directed generally towards the seafloor.
15. The seafloor stockpiling device of claim 12, wherein the one or more fluid outlets comprise nozzles.
16. The seafloor stockpiling device of claim 11, wherein the friction reduction mechanism comprises movable walls.
17. The seafloor stockpiling device of claim 16, wherein the movable walls are preferably contained inside the walls of the seafloor stockpiling device and enclose seafloor material contained within the device.
18. The seafloor stockpiling device of claim 16, wherein the movable walls pivot relative to the walls of the seafloor stockpiling device.
19. The seafloor stockpiling device of claim 1, further comprising a lifting attachment.
20. The seafloor stockpiling device of claim 1, further comprising an offset lifting attachment that is offset from a central axis of the seafloor stockpiling device.
21. The seafloor stockpiling device of claim 20, wherein the offset lifting attachment is located adjacent an outer edge of the seafloor stockpiling device.
22. The seafloor stockpiling device of claim 1, wherein the seafloor stockpiling device is formed from at least two modules configured for separate deployment from a surface vessel and for underwater interconnection.
23. The seafloor stockpiling device of claim 1, further comprising a stockpile removal device.
24. The seafloor stockpiling device of claim 23, wherein the stockpile removal device comprises an opening port in at least one of the walls of the seafloor stockpiling device.
25. The seafloor stockpiling device of claim 1, wherein the walls are angled forming a substantially frustoconical shape.
26. The seafloor stockpiling device of claim 1, further comprising a rigid skirt around the periphery of the seafloor stockpiling device.
Type: Application
Filed: Jun 15, 2012
Publication Date: May 22, 2014
Applicant: NAUTILUS MINERALS PACIFIC PTY LTD (Milton, Queensland)
Inventors: Glen Robert Jones (Milton), Daal Hallam Jaffers (Milton), Roland Gunter Berndt (Milton), Paul David Griffiths (Wallsend), David Edward Milburn (Wallsend)
Application Number: 14/125,946
International Classification: E21C 50/00 (20060101); E02F 5/00 (20060101);