WO2022191712A1 - System for mining subsea metallic crusts - Google Patents

Abstract

The invention relates to a system for mining of metal-containing crusts on the seabed. At least one vehicle is provided to travel on the seabed to crush the metallic-rich rock. The rock is then pumped via an umbilical to a subsea station and then via a riser to a surface vessel. The surface vessel (1) having ore treatment and storage facilities. There may be several vehicles all controlled together. The vehicles may also be arranged for autonomous operation.

Description

Description

Title of Invention: System for mining subsea metallic crusts

Technical Field

[0001] The present invention relates to a system for mining subsea mineral crusts.

Background Art

[0002] It is widely known that there are valuable minerals on the seafloor, but it hasn’t been technologically or economically feasible to go after them until the past decade. Widespread growth of battery-driven technologies such as smartphones, computers, wind turbines and solar panels is changing this calculation as the world runs low on land-based deposits of copper, nickel, aluminium, manganese, zinc, lithium and cobalt.

[0003] There are three main types of marine mineral deposits: polymetallic nodules in the form of potato-shaped “nodules” on the seafloor; polymetallic or seafloor massive sulphides in and around hydrothermal vents; and cobalt-rich ferromanganese crusts. The present invention is directed to the latter type.

[0004] Cobalt crusts are rock-hard, metallic layers that form on the flanks of submarine volcanoes, called seamounts. Similar to manganese nodules, these crusts form over millions of years as metal compounds in the water are precipitated.

[0005] Because the cobalt crusts are firmly attached to the rocky substrate, they cannot simply be picked up from the bottom like manganese nodules. They will have to be separated and removed from the underlying rocks. A main challenge in mining these crust deposits is that the seamounts often have steep sides, creating difficulties for machinery to crawl along the slopes. Cobalt-rich crust mining vehicles need to walk on complex terrain with high and low undulations in the mining area. The mining head needs to adapt to micro-topography changes and break up a thin layer of cobalt-rich crust from the hard bedrock and ensure the collection rate and depletion rate. [0006] At present, the exploitation of cobalt-rich crusts on the seabed mostly stays in the technical feasibility of the mining method and the laboratory simulation test. It fails to combine the complex topographical features of the cobalt-rich crust mine area and the characteristics of the fracture collection. It is the design scheme of the crushing collection and walking system. The existing mining equipment is difficult to adapt to the complex terrain changes of the mining area, and does not consider the joint matching operation function of the cutting and crushing and collecting of the cobalt-rich crust.

[0007] CN 102080543 describes an undersea mining with a crust stripping shovel having a scraper bucket with relieving teeth using an electric hoist to supply power to the stripping shovel via cable wires so that the stripping shovel can strip the cobalt crust on level or inclined surface. After the shovel finishes stripping, the cable wires lift the stripping shovel from the sea level, opens a side door and the scraper bucket inclines a certain degree so that the cobalt crust is poured in the mining carrying vehicle on a dredger

[0008] CN 106014417 describes a seabed crust mining vehicle having mining heads, collecting heads and a collecting device. The vehicle is mounted on a base that is fixed to a walking device. The mining heads are fixed to a support and make contact with the ground to broke cobalt-rich crusts. The collecting heads are fixed to the base and are arranged on the mining heads in the advancing direction of the mining vehicle, and the collecting device is fixed to the base and connected with the collecting heads and provides negative pressure for the collecting heads to suck cobalt-rich crust pulp generated after the mining heads broke the cobalt- rich crusts.

Summary of Invention

[0009] The purpose of the invention is to overcome the above-mentioned obstacles and provide an efficient system for harvesting the marine crusts and bring them to the surface. This is achieved in that the system comprises a surface vessel having ore treatment and storage facilities as well as control systems, a subsea station comprising a garage for at least one ore mining vehicle, a riser system extending between the subsea station and the vessel, a pumping unit, and at least one mining vehicle connected to the subsea station with an umbilical.

[0010] The individual vehicles can be operated independently and in such away that a failure in one vehicle will not stop the operation.

[0011] The main advantage of the system is that it the cutting tool will be able to remove the metallic-containing crust from uneven bed-rock surface.

[0012] According to a main aspect of the invention the milling of the crust is performed while the vehicle is moving in a continuous movement along the seamount slope

[0013] The cutting tool will consist of several, individually adjustable elements, each element will clear a narrow path. The neighbouring cutting tool elements will cover their own narrow path such that together they will clear the full width. The cutting tool will smash or grind the loosened crust pieces to sizes that can be pumped to surface without further preparation. There is also provided for control of the depth of cutting. The depth control for the cutting tool will be based on a combination of sensor and response data (torque, speed of penetration, change in speed of penetration etc). Depth control will be automated

[0014] Depth control may be based on the difference in hardness of crust and bed rock - the tool will mill down to the hard rock and stop

[0015] Depth control may also be based on hydroacoustic or other sensor data, indicating crust thickness and bed-rock surface

[0016] The autonomous control system may adjust the speed or stop temporarily to overcome obstacles.

Brief Description of Drawings

[0017] The invention will now be described in more detail in relation to the enclosed figures, where

[0018] [Fig.1 ] is a sketch showing an overview of the system,

[0019] [Fig.2] is a drawing of a vehicle according to the invention,

[0020] [Fig.3] shows a cutting tool inside the vehicle, [0021] [Fig.4] shows a cutting tool

[0022] [Fig.5] shows a cutting tool

[0023] [Fig.6] illustrates how the cutting tool can be moved in different positions,

[0024] [Fig.7] shows a set of cutting tools inside the vehicle.

[0025] [Fig.8] illustrates the independent movement of each cutting tool.

[0026] [Fig.9] shows a cutting tool with a skirt.

Detailed Description of Invention

[0027] In Fig. 1 there is shown the principal arrangement of the mining system. The system broadly consists of a mining production vessel 1 and connected elements for carrying out the mining operation. In the vessel there is main control facilities for control and operation of a subsea mining system. The vessel also has means for ore collection and storage, including de-watering of the produced slurry from the mining operation. The vessel is also the starting point for launch and recovery of the various components of the system.

[0028] On the seabed there is located a subsea station 2. The station preferably is designed as a template that is located on and anchored to the seabed. It includes at least one garage (not shown) that will host mining vehicles during launch and recovery. Each garage should also be equipped with a reel for an umbilical 5, the purpose of which will be explained later. The station also comprises a pumping system. The pumping system is used for pumping ore cuttings from the mining vehicles to the subsea station. Further pumps provide vertical transportation of the cuttings to the mining production vessel

[0029] The subsea station 2 is connected to the vessel 1 with a riser system 4. The riser system provides for vertical transportation of ore cuttings from subsea pump station to vessel as well as return water from de-watering system. The riser system also includes cables for the supply of electrical power to the subsea station and the mining vehicles as well as cables for fiber optic and electrical communication between vessel and the subsea elements. This will provide control of navigation, monitoring of sensors. Preferably this also comprises video connection. [0030] At least one mining vehicle 6 is shown located at the seabed. There may be more than one vehicle as shown in Fig. 1 . They are each connected to the subsea station with the umbilical 5. The umbilical provides for the transfer of cuttings from the vehicles to the riser base/garage as well as providing communication and power as necessary. The reel located in the subsea garage will allow «reeling in» of the vehicle to docking and lock positions. The hose/umbilical reel will simplify launch and recovery of the mining vehicle.

[0031] The umbilical may also include a pipe for the supply of water to the mining vehicle.

[0032] The umbilical may be provided with buoyancy elements (not shown) for neutral buoyancy. This will facilitate the launch and recovery of the mining vehicles.

[0033] In Fig. 2 there is shown a preferred embodiment of a mining vehicle. The vehicle has a body 20 enclosing the equipment for carrying out the mining operations. The vehicle has a skirt 21 that reaches down to the ground. The vehicle has a separate traction mechanism for forward movement along the seamount in the form of wheels 22 preferably located at each corner of the vehicle. The wheels are preferable mounted on an articulated axle 23 so that the wheels can follow the uneven ground on the seabed. The wheels are preferably independently controlled and powered. This enables continuous, controlled movement of mining tool when cutting. The moving path of the vehicle can is preferably controlled by steering of the wheels. Alternatively, a differential braking system can be used.

[0034] The vehicle may also be equipped with buoyancy elements (not shown). These elements can be configured to achieve neutral or near neutral buoyancy. This enables the vehicle to be free-swimming for positioning of vehicle prior to crust cutting.

[0035] The vehicle preferably has a common center of gravity and center of buoyancy

[0036] The vehicle has a number of thrusters 24 mounted on the body. Although four are shown on Fig. 2 it should be understood for a person of skill that there may be more or less as needed for the operation of the vehicle. The thrusters can be rotated to various positions to enable control of yaw, pitch, roll and lateral movements in any orientation. The thrusters may also be used to provide additional downward or perpendicular contact force for more efficient traction of the wheels against the ground. The control of the thrusters will allow navigation and free-swimming functionality within the length of cutting transfer umbilical.

[0037] The thrusters may also be used to exert downward pressure of the vehicle should the suction force be insufficient.

[0038] An outlet 26 is arranged for connecting to the umbilical 6. A sensor arrangement 26 is used to monitor the path of the vehicle. The sensor may include a camera.

[0039] The arrow 26 indicates the direction of travel.

[0040] In the vehicle there is arranged a number of cutting tools 30 as illustrated in Fig. 3. As shown in Figs. 4 and 5 each cutting tool 30 has a cutter head similar to drill bits that can be rotated by a motor 34.

[0041] The cutting tool is fixed to a transverse axle 36. This enables the cutting tool to be moved in a vertical plane inside the vehicle. A Cylinder 32 attached to the opposite end of the cutting tool (related to the cutting bit) is used to push the cutting tool towards contact with the ground 40. This also enables control of the force that the cutting bit exerts against the ground 40. The cylinder will also be used to lift the cutting tool off the ground when not in use. As the vehicle moves along the slope 40 the cutting tool will mill out the crust. The cutting tool can crush the crust and grind the loosened crust pieces to sizes that can be pumped to surface without further preparation.

[0042] Fig. 6 illustrates how the cutting tool can take many different positions for more effective milling out of crust.

[0043] As a person skilled in the art will know, there exists many types of the cutting tools that can be used for the operation. In a preferred embodiment the rotary cutting tool can have hardened cutting teeth. Axis of rotation is perpendicular to the bed-rock surface. The cutting tool is rotated at a speed such that small bits with linear size maximum 10mm will be chipped off the crust. [0044] The rotary tool can be lifted and lowered automatically such that the bed-rock surface is followed, as explained earlier.

[0045] In another embodiment the rotary cutting tool has its axis of rotation parallel with the bedrock surface.

[0046] In yet another embodiment a linear chisel tool with a pointy tip can be used. This can then be operated by a hammering mechanism. The linear tool will operate at relatively high frequency such that small chips are removed from the crust. In that case a hydraulic hammering mechanism can be utilized to drive the chisel

[0047] Alternatively, a linear magnet mechanism can be utilized to drive the chisel. Local electrical storage such as an «Ignition Coil», a Super Capacitor or a battery may be utilized to support high impact energy by the magnet mechanism. A mechanical spring-loaded feature will provide feeding the movement of the chisel until it hits the bed-rock which slows the movement. Alternative feeding mechanisms can be used such as a hydraulic spring feature.

[0048] Milling will be performed while the mining vehicle is moving in a continuous movement along the steep slope. Depth control for the cutting tool will be based on a combination of sensor and response data (torque, speed of penetration, change in speed of penetration etc.). Depth control will be automated. Depth control may be based on the difference in hardness of crust and bed-rock - the tool will mill down to the hard rock and stop. Depth control may also be based on hydroacoustic or other sensor data, indicating crust thickness and bed-rock surface.

[0049] The cutting tool will consist of several, individually adjustable elements, each element will clear a narrow path. The neighbouring cutting tool elements will cover their own narrow path such that together they will clear the full width

[0050] The autonomous control system may adjust the speed or stop temporarily to overcome obstacles

[0051] Preferably more than one cutting tool is arranged in the mining vehicle. This is illustrated in Fig. 7. The assembly may consist of several, individually controllable cutting tools, each tool clearing a narrow path. The neighbouring cutting tool elements will cover their own narrow path such that together they will clear the full width. Two neighbouring cutting tools are preferable arranged so that they are contra-rotating. All the cutting tools are preferably connected on the transverse axle 36. Preferably the cutting teeth are not lined up with a tooth on a neighbouring bit but offset by one tooth to allow for said contra-rotating.

[0052] There will be a trade-off between the number of cutting tools and the need for keeping the vehicle as small and compact as possible. As an example, each cutting head is 10 cm in diameter. It will then be possible to have 10 cutting tools inside each vehicle. In this example the distance from the axle 36 to the cutter head is 60 cm and length of a cutter head is 30 cm.

[0053] With the cutting teeth offset as explained earlier, the teeth from one cutter head can pass between the teeth of the neighbouring cutter head. The cutter heads is preferably contra-rotating to minimize the net force exerted on the tool.

[0054] Each cutting tool may be independently controlled for position. In Fig. 3 there was shown how a cutting tool could follow the contours of the ground 40. With all the tools independently controlled as shown in Fig. 8 they can follow the uneven ground even adjusting for terrain differences within the vehicle’s envelope.

[0055] During operation the ore cuttings will be pumped to the subsea station. This creates an suction effect in the vehicle for transporting crushed ore to the subsea station and to the vessel. This suction effect also will provide a perpendicular force and as a result help the vehicle grip the ground. As explained earlier the vehicle body is equipped with a skirt so that this suction force can be maintained during operations. In this there may be a problem since the suction force can be so large as to preclude the vehicle from moving. To mitigate this a check valve (not shown) may be installed in the vehicle to allow for inflow of water. Alternatively, the umbilical may include a return line for water. This is preferable since it will result in a better control of the suction force. On the other hand, if the suction force is not enough to keep the vehicle on a steady trajectory, the thrusters may be used to provide additional downward force.

[0056] In an alternative embodiment shown in Fig. 9 a smaller skirt 42 is installed inside the body surrounding the cutting tool(s). This has the advantage of making the space for circulating water smaller so that a smaller volume of water can be circulated around the cutting tools. The skirt can be in two parts forming a channel between them. Water will flow into the space via opening 44. This opening may be either connected to the check valve mentioned earlier or to the umbilical 3 via the outlet 26.

[0057] Each vehicle can be equipped with individual, independent autonomous driving functionality with the control path determined by steering of wheels or by differential braking. Video cameras is used for monitoring of driving conditions and for positioning along the edge of previous cutting lines. The autonomous control system may adjust the speed or stop temporarily to overcome obstacles.

[0058] Position references and steering input for autonomous algorithms will have several sensor systems:

[0059] The system may be equipped with several sensors to allow for steering and control. Sensors can be located either in the vehicles, in the subsea station or in an observation ROV used to monitor operations. Sensors may include accurate depth sensors for allowing driving along a line at constant depth on a steep slope. Depth calculation can for example be corrected for tidal variations allowing sideways position accuracy in the decimeter range.

[0060] Hydroacoustic transponders may be positioned along the route for help with navigation.

[0061] Hydroacoustic system may be used for monitoring of relative positions between vehicle, subsea station and vessel.

[0062] A hydro acoustic communication link may be used as back-up in case of fiber optic and/or electrical communication failures.

[0063] The vehicle is preferably equipped with depth control means for the cutting tool. This can be based on a combination of sensor and response data (torque, speed of penetration, change in speed of penetration etc.) if desired, depth control can be automated.

[0064] The depth control feature may be based on the difference in hardness of crust and bed-rock -such that the tool will mill down to the hard rock and stop. Depth control may also be based on hydroacoustic or other sensor data, indicating crust thickness and bed-rock surface. [0065] As stated earlier the vehicles may be equipped with autonomous drive functionality. This functionality may also be used to control several vehicles driving in formation. An example with three vehicles is shown on Fig. 1. j

Claims

Claims

1. j System for mining of metal-containing crusts on the seabed, comprising a surface vessel (1) having ore treatment and storage facilities as well as control, a subsea station (4) comprising a garage for at least one ore mining vehicle, a riser system extending between the subsea station (4) and the vessel (1), a subsea pumping unit, and at least one mining vehicle (5) connected to the subsea station with an umbilical (3), characterized in that the mining vehicle comprises a body (20) having a skirt (21 ) defining an enclosed interior space with at least one cutting tool (30). 2. System according to claim 1 characterized in that the cutting tool is a milling tool having a rotary motor for rotation around its own axle.

3. System according to claim 1 and 2 characterized in that the cutting tool

(30) is rotatable around an axle (36) mounted transversely in the vehicle enabling the tool to be movable in a vertical plane. 4. System according to claim 3 characterized in that the cutting tool is connected to a hydraulic cylinder (32).

5. System according to claim 3 characterized in that several cutting tools are mounted in parallel on the transverse axle (36).

6. System according to claim 5 characterized in that each cutting tool has a hydraulic cylinder so that each tool can be independently operated.

7. System according to claim 1 , characterized in that the cutting tool is a linear chisel tool with a pointy tip operated by a hammering mechanism.

8. System according to claim 1 characterized in that the vehicle comprises thrusters 9. System according to claim 1 characterized in that the vehicle comprises four wheels, each mounted on an articulated axle and capable of independent motion.

10. System according to claim 1 characterized in that it comprises a control system for autonomous operation.

11. Method for mining metal-rich crusts on the seabed, comprising the following steps:

Providing a vehicle able to travel transversely along the side of a seamount, the vehicle having cutting tools,

Cutting ore crusts while travelling, and

Pumping the crushed ore to a surface vessel

12. Method according to claim 11 , wherein several mining vehicles are controlled to travel as a group

13. Method according to claim 12 where the vehicles are under autonomous control j