NL2012578C2

NL2012578C2 - Transport system for the recovery of mineral deposits from a sea bed.

Info

Publication number: NL2012578C2
Application number: NL2012578A
Authority: NL
Inventors: Johan Heiler; Pieter Abraham Lucieer; Kris Bruyne; Harmen Derk Stoffers
Original assignee: Oceanflore B V
Priority date: 2013-12-02
Filing date: 2014-04-07
Publication date: 2015-06-03

Description

Transport system for the recovery of mineral deposits from a sea bed

FIELD OF THE INVENTION

The invention relates to a transport system for the recovery of mineral deposits from a sea bed. The invention also relates to a pump module for use in the transport system, and to an assembly of the transport system and a subsurface mining equipment attached to an upstream end of the transport system. The invention finally relates to a method for the recovery of mineral deposits from a sea bed using said transport system.

BACKGROUND OF THE INVENTION

Deep sea mining involves collecting mineral deposits, such as polymetallic nodules, diamonds, gold, and rare soils from (below) the sea floor 4,000 - 6,000 m. Polymetallic nodules may for instance comprise nickel, copper, cobalt and manganese nodules. In deep sea mining, the sea floor may be a distance of up to 5000 m and more away from the sea surface, and developing equipment for deep sea mining imposes many challenges.

Deep sea mining devices need to bring subsurface mining equipment to the sea floor and recover the same from the sea floor after termination of a mining operation. A deep sea mining device further typically comprises a transport system such as a riser string that extends from a vessel to the mining equipment and is adapted to recover mineral deposits that have been collected from the sea bed. The vessel may further comprise a support arrangement for the mining equipment that also carries umbilical’s and the like for transferring electrical control signals to instrumentation and visualization devices present on the vessel. A lift system is usually operational in raising and launching the riser string.

The known transport system for bringing the usual slurry of mined mineral deposits and sea water from the sea floor at great depths to a floating vessel storage hold at the surface typically comprises a string of interconnected transport system units through which the mined mineral deposits can be conveyed from the sea bed to a surface vessel by pumping means adapted to pump mineral deposits from a unit upstream of the pumping means to a unit downstream of the pumping means.

Considering the depths at which the mineral nodules need to be collected and pumped up to the sea surface, a transport system needs to be reliable. In case of failure of a pumping means fir instance and subsequent shut down of the transport system, a lot of effort is required for repair and restart, and valuable production time is lost. Collateral damage to the transport system may also occur in which case even more time is lost.

An aim of the present invention therefore is to provide a transport system for the recovery of mineral deposits from a sea bed that is more reliable than the known transport system and reduces the risk for damage to the transport system as a result of failure of a component thereof. A further aim is to provide a more reliable method for the recovery of mineral deposits from a sea bed.

SUMMARY OF THE INVENTION

The present invention thereto provides a transport system for the recovery of mineral deposits mined from a sea bed in accordance with claim 1. In particular, the transport system comprises a string of interconnected transport system units through which the mined mineral deposits can be conveyed from the sea bed to a surface vessel by a plurality of pump modules provided in the string at a number of positions, a pump module comprising an inlet section and an outlet section that connect to a transport system unit, and a pump arranged in between the inlet and outlet sections and adapted to pump mineral deposits from a unit upstream of the pump module to a unit downstream of the pump module, a pressure relief valve positioned upstream of the pump module in the string, and a dump valve positioned downstream of the pump module in the string.

Since the slurry of mineral deposits and water is pumped upwards from the sea bed to the sea surface, an upstream position is defined as a position at a greater depth than a downstream position. The pressure relief valve associated with a pump module is therefore positioned at a greater depth than said module, i.e. below said pump in the string, whereas the dump valve associated with a pump module is positioned at a lesser depth than said pump module, i.e. above said pump in the string. A blockage in the transport system at a position downstream of a pump module may cause water hammering and damage to pump modules and/or transport system units. In such case, a pressure release valve in the string (downstream of the blockage position) is opened, and water enters the transport system units. A pump failure in the transport system at a position downstream of a pump module may cause nodules falling down, blockage, and a negative pressure in the units, causing collapse of units. In such case, a dump valve is opened to allow nodules to escape from the transport system. A pressure release valve in the string is opened to let water in and relieve the negative pressure.

The dump and pressure release valves are preferably opened when building up a string of interconnected transport system units. This ensures and promotes water supply to the units.

An embodiment of the transport system according to the invention comprises a pump bypass conduit that connects a pump inlet to a pump outlet and is arranged in parallel to a pump inlet and outlet tubing, the pump bypass conduit being provided with a bypass valve.

Due to the presence of a bypass circuit for the pumps, proper slurry transport is ensured, even in case of failure of one of the pumps or pump modules. Each pump can also be serviced without having to discontinue the whole operation, and redundancy is build into the system.

In another embodiment of the invention, a transport system is provided wherein the inlet and/or the outlet tubing of a pump is provided with a gate valve. Closing such gate valve in case of a failed pump for instance will effectively redirect the flow of slurry to the bypass circuit. A practical embodiment provides a transport system wherein at least one of the pressure relief valve and the dump valve opens passively against a spring force. Such embodiment allows an ‘automatic’ opening of at least one of said valves, and preferably both valves, in case of an emergency or failure situation.

Yet another embodiment of the invention relates to a transport system wherein at least one of the pressure relief valve and the dump valve closes actively under the intervention of a hydraulic force. Such embodiment ensures a relatively straightforward start-up of a failed pump module. The valves may be conveniently actuated from a control room on the vessel. A further useful embodiment of the transport system according to the invention is characterized in that a pressure relief valve is positioned upstream of about any pump module in the string, and, even more preferred, in that a dump valve is positioned downstream of about any pump module in the string. These embodiments increase reliability and safety even further.

In an embodiment of the transport system according to the invention, a pump module comprises a plurality of pumps arranged in series. Another embodiment of the invention relates to a transport system wherein a pump module comprises two pumps arranged in series.

Yet another embodiment of the invention provides a transport system comprising pump modules wherein each pump comprises a pump bypass conduit that connects said pump inlet to said pump outlet and is arranged in parallel to said pump inlet and outlet tubing, the pump bypass conduit being provided with a bypass valve.

Another useful embodiment of the transport system in accordance with the invention is characterized in that a pump module comprises at least one of the pressure relief valve, the dump valve, a pump bypass conduit with bypass valve and a gate valve. Such an embodiment is apart from other advantages easily build up from a number of transport system units and pump modules. The build-up string will comprise all required valves for a good operation.

In an embodiment of the transport system, the pressure relief valve in the pump module is positioned upstream from the pump bypass conduit. In another embodiment of the transport system, the dump valve in the pump module is positioned downstream from the pump bypass conduit.

Although any type of pump may be used in the pump module according to the invention, an embodiment wherein the pump comprises a centrifugal pump has proved to be particularly useful.

In a preferred embodiment of the invention, the transport system units of the transport system comprise rigid pipe sections.

The invention further relates to a pump module for use in a transport system in accordance with the invention, and comprising an inlet section and an outlet section that is connectable to a transport system unit, a pump arranged in between the inlet and outlet sections and adapted to pump mineral deposits from a unit upstream of the pump module to a unit downstream of the pump module, and a pressure relief valve positioned upstream of the pump, and a dump valve positioned downstream of the pump in the pump module. Other embodiments of the pump module have already been described hereinabove and in the appended claims. A particularly useful embodiment of the pump module according to the invention has end couplings for coupling to end sections of a transport system unit. Such pump modules are coupled in series to transport system units to form the string, and therefore represent load bearing structural units.

In yet another embodiment of the invention, the end couplings have about the same dimensions as the end sections of the transport system units, such that a pump module can be handled with the same or similar pick-up equipment as a transport system unit. This allows readily building up the string of interconnected transport system units and pumping modules. A further aspect of the invention provides an assembly of any embodiment of the transport system and subsurface mining equipment attached to an upstream end of the transport system. The notion upstream relates to the flow direction of a slurry of mineral deposits in sea water being transported to the surface of the sea. A useful embodiment of the assembly is equipped with subsurface mining equipment comprising a mining vehicle.

The transport system, assembly and pump module in accordance with the invention can be used with advantage in a method for the recovery of mineral deposits from a sea bed, the method comprising providing a transport system or an assembly in accordance with the invention, conveying mined mineral deposits from the sea bed to a surface vessel through the string of interconnected transport system units by pumping mineral deposits from any unit upstream of a pump module to a unit downstream of the pump module, and, in case of failure of a pressure module, opening a pressure relief valve positioned downstream of the failed pump module in the string, and optionally a dump valve positioned downstream of the failed pump module in the string. The method prevents damage to the system in case of failure or malfunction of a component in the string, and allows to continue the recovery operation which saves considerable production time.

In case of failure of one or a limited amount of pump modules, or other local failure, an embodiment of the method comprises opening a pressure relief valve positioned downstream of the failed pump module or other failure in the string to prevent vacuum collapse of a downstream part of the string.

In case of failure of a substantial amount of pump modules or other near total failure of the string, which causes nodules to fall back in the upstream direction, an embodiment of the method is provided wherein a pressure relief valve of some or all pump modules opens to let in water, and a dump valve of some or all pump modules opens to let out falling nodules. This prevents blockage of upstream equipment, such as pumps, by falling nodules.

Another embodiment of the invented method comprises, in case of failure of a pump in a pump module, opening a bypass valve in a bypass conduit that connects the failed pump inlet to the failed pump outlet and is arranged in parallel to the failed pump inlet and outlet tubing.

Yet another embodiment provides a method comprising closing a gate valve provided in the inlet and/or the outlet tubing of the failed pump.

In another embodiment, a method is provided wherein at least one of the pressure relief valve and the dump valve is opened passively against a spring force.

In yet another embodiment, a method is provided wherein at least one of the pressure relief valve and the dump valve is closed actively under the intervention of a hydraulic force after the failure has been resolved.

It should be noted that any combination of the above described embodiments can be made within the scope of the invention, each having its own usefulness and merits.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be elucidated in more detail with reference to the accompanying figures, without otherwise being limited thereto. In the figures:

Fig. 1 is a side view of an assembly of a subsurface mining vehicle and a riser to which it is attached, comprising pomp modules in accordance with an embodiment of the invention;

Fig. 2 is a schematic diagram of an embodiment of a pump module according to the invention;

Fig. 3a, 3B and 3C represent schematic diagrams of the embodiment of the pump module shown in figure 2 in different operational states;

Fig. 4 is a side view of an embodiment of a pump module according to the invention; Fig. 5 is a partly worked open side view of the embodiment of a pump module shown in figure 4; and finally

Figures 6A and 6B illustrate the operation of relief and dump valves in case of failure. DETAIDED DESCRIPTION

With reference to figure 1 is shown part of a typical arrangement used in deep sea mining of mineral deposits, such as polymetallic nodules. The arrangement typically comprises a transport system in the form of a tubular riser string 2 (which may have a length of several thousands of meter and connects to a deep sea mining vessel 1 to which is attached some mining equipment such as mining vehicle 3. A flexible interconnection hose assembly 4 is typically arranged between the lower end 7 of the riser string 2 and the mining vehicle 3 which is adapted to move on a deep sea bottom 5 and collect mineral deposits there from.

The interconnection assembly 4 comprises a flexible submarine hose 40 that is adapted to transport mineral nodules collected by the vehicle 3 to the rigid riser 2, and is provided with buoyancy blocks 41 that compensate the components own weight and generate an upward force in a part of the hose to create an S-shape. Having a rigid connection between the vehicle 3 and the riser 2 would imply that forces are transferred from one to the other, and that both are subjected to the same motions. The flexible interconnection hose assembly 4 allows the mining vehicle 3 to have a certain degree of freedom for moving around on the seabed 5, and ensures that the vehicle is not affected by the movements of the riser string 2. In order to support and lift the vehicle 3, steel lifting cables (not shown) may be provided between vessel and vehicle 3.

The transport system in the form of a tubular riser string 2 of extreme length comprises a plurality of pump modules 10 arranged over its length. The pump modules 10 are adapted to pump up mineral deposits (nodules) from the sea bed 5 in an upward direction 6, that points away from the sea bed 5 towards the sea surface.

Referring to figure 2, an embodiment of a transport system in accordance with the invention is shown. The pump module 10 comprises an inlet 11 and an outlet 12 for connection to riser 2 units (pipe segments), two centrifugal pumps (13, 14) arranged between the inlet 11 and the outlet 12 and adapted for pumping mineral deposits from the inlet 11 to the outlet 12. A pump bypass conduit 13c that connects a pump inlet to a pump outlet is arranged in parallel to a pump inlet tubing 13a and outlet tubing 13b, the pump bypass conduit 13c being provided with a bypass valve 13d. In the embodiment shown, the inlet tubing (13a, 14a) and the outlet tubing (13b, 14b) of each centrifugal pump (13, 14) are both provided with a gate valve 15 to regulate or close of the flow to a pump (13, 14).

Further, the inlet 11 of the pump module 10 is provided with a pressure relief valve 20 provided upstream from the pump bypass conduit 13c. When one of more pump modules 10 below a certain pump module 10 in the riser break down or fail for some reason, pressure relief valve 20 is opened against a resisting force provided by a spring element to let (sea) water in (see arrow 21) the system tubing and prevent collapsing thereof by the lowered pressure (partial vacuum) in the tubing as a result from said failure.

Further, the outlet 12 of the pump module 10 is also provided with a dump valve 22 provided downstream from the pump bypass conduit 14c. When one of more pump modules 10 above a certain pump module 10 in the riser string break down or fail for some reason, dump valve 22 is opened against a resisting force provided by a spring element to let slurry comprising mineral nodules and (sea) water out (see arrow 23).

This prevents damage to the system tubing and/or collapse thereof by the increased pressure in the tubing resulting from said failure.

The slurry velocity in the riser system 2 is preferably selected based on the settling behavior of the mined mineral solids in the mineral/sea water slurry. The settling velocity of the mineral solids depends among others on the density, and their shape and diameter. The density of wet mineral nodules is typically around 2000 kg/m3, their shape is typically round, and nodules with diameters up to 130 mm are to be expected in the slurry. A slurry velocity of between 2 and 6 m/s represents a safe and economical choice and the pump(s) in an embodiment of the pump module 10 should be able to produce such a velocity.

With a riser diameter of about 355 mm for instance, the slurry flow in the transport system would be around 0.4 m3/s for instance. The pressure required to transport the nodules up to the surface is then typically of the order of 100 bar; this is the hydrostatic head loss due to the slurry density (approx. 82%) and the dynamic head loss due to friction (approximately 18%). The hydraulic power required to transport the nodules to the surface is the product of the flow and the required pressure. This is approximately 4.1 MW for the example given.

The mining transport system is preferably designed with a double redundancy. In such an embodiment of the transport system, operations can continue safely with one single failure, and with a second failure it can be shut down safely.

To reduce the number of umbilicals in the riser system 2, two or more pump units (13, 14) are preferably combined into one pump module 10. Pump modules 10 are preferably positioned evenly along the riser string 2.

As shown in figures 3A, B and C, every pump module 10 may be designed around a pair of electrically driven centrifugal pumps (13, 14). In order to ensure proper slurry transport even during failure of a pump unit (13, 14), valves (13d, 14d) are installed to bypass the pump. During normal operation (figure 3A) the bypass valves (13d, 14d) are closed, and all flow will be directed through the pumps (13, 14). When a pump fails (figure 3B), the corresponding bypass valve (13d and/or 14d) will be opened, and the flow will be redirected around the corresponding pump (13 and/or 14). Subsequently the two gate valves 15 positioned on both sides of the pump (13 and/or 14) will be closed. This prevents clogging up of the pump with nodules and sediment. It also ensures that the full flow is going through the bypass tubing 13c. If both pump and bypass would remain open the velocity in both will be lower, which means that the bypass may be clogged as well.

In case of a complete pumping system failure (e.g. a blackout on the vessel, see figure 3C) the slurry would fall down, as the density of the slurry in the riser is higher than the surrounding water. This may create a very dangerous situation, as the falling slurry would create a high vacuum high up the riser, which could lead to collapse of the riser pipe. In theory this could be avoided by closing of the riser at the bottom thereof so no water could exit. This would however not restrain the nodules from falling down and clogging the pumps, the nodule collector, the flexible hose and the complete lower end of the riser 2.

To prevent riser collapse and clogging during total system failure, dump valves 22 and relief valves 20 are provided in the pump module 10. In case of loss of slurry transport, the dump valves 23 will open automatically (spring actuated) and will allow the slurry in the riser section 2 above the module 10 to fall back and out of the riser 2 in the direction 23. The relief valves 20 will preferably open at the same time and supply water to the riser section below the pump module 10, thereby preventing high vacuum and riser collapse.

The relief valve 20 may also be used in normal operations. In an embodiment, it is automatically opened when the pressure at the inlet 11 of a module 10 is lower than a preset threshold value. This protects the pumps (13, 14) and pipeline sections downstream of the pump module 10 from water hammering in case of clogging upstream in the riser string 2.

The dump and relief valves (22, 20) are preferably opened during deployment and recovery of the riser 2 to ensure inflow of water and thereby levelling the pressures inside and outside the riser.

Figure 4 shows the outside of a pump module 10. The structure of the pump module 10 is such as to be able to transfer forces and mount equipment. In order to provide the pump module 10 with sufficient strength, openings in the outer shell 17 are kept as small as possible. The shell 17 may be segmented in order to provide access for maintenance of the equipment inside. The pump modules 10 are preferably kept as compact as possible to keep their mass low as well as drag forces due to currents.

To preferably direct all forces through the housing 17 of the pump module 10 and not through the pumps (13, 14) or piping, expansion pieces 25 are fitted before and after the pumps (13, 14). Pumps and electric motors are preferably mounted to a lantern piece that is integrated into the housing 17 of the pump module 10. Maintenance of the pumps and motors is made easy as the housing can be split close to both sides of the lantern pieces.

Dump valves 22 and pressure relief valves 20 preferably exit close to the outside ends of the module 10. The dump valve 22 in an embodiment exits on the side of the module 10 opposite the pressure relief valve 20. Sediment therefore will not accumulate inside the pump housing 17 nor be sucked into lower sections of the riser pipe through the relief valve 20. Pump modules are preferably also equipped with a junction box that is easily accessible.

The pump modules 10 are provided with flanges (not shown) on both ends to connect to adaptor pieces. Such pieces comprise small lengths of riser pipe that make the total length of a module 10 about equal to the length of a standard riser joint for ease of handling. In this way, a pump module 10 easily fits on any location in the riser string 2.

As shown in figure 6A, failure of a pump 13 of an upstream pump module 10U, or another local failure such as a blockage 50 of one of the conduits has occurred. In an embodiment of the method a pressure relief valve 20 positioned downstream in the string of the failed pump module 10U or blockage 50 is then opened to let in water in accordance with arrow 51 and prevent vacuum collapse of a downstream part of the string.

As shown in figure 6B, failure of a substantial amount of pump modules or other near total failure of the string causes nodules to fall back in the upstream direction according to arrow 53. In order to prevent blockage of upstream equipment, such as pumps (13, 14) in upstream pump module 10U, by the falling nodules, an embodiment of the method is provided wherein pressure relief valve 20 of some or all pump modules opens to let in water in accordance with arrows 52, and dump valve 22 of some or all pump modules opens to let out falling nodules in accordance with arrows 52.

Claims

CLAIMS 1. A transport system for collecting mineral deposits extracted from a seabed, wherein the transport system comprises a strand of interconnected transport system units through which the extracted mineral deposits can be brought from the seabed to a surface vessel by a quantity of pump modules provided in a number of positions, wherein a pump module comprises an inlet section and an outlet section which are each connected to a conveyor system unit, and a pump arranged between the inlet and outlet sections and which is adapted to pump mineral deposits from a relative to the pump module upstream unit to a downstream unit relative to the pump module, the conveyor system further comprising a pressure relief valve positioned upstream in the strand, and an overflow valve positioned downstream in the strand relative to the pump module p.

Transport system as claimed in claim 1, comprising a pump by-pass which connects a pump inlet to a pump outlet and which is arranged parallel to a pump inlet and pump outlet line, the by-pass being provided with a by-pass valve.

3. Transport system as claimed in claim 2, wherein the inlet and / or the outlet line of a pump is provided with a valve valve.

4. Transport system as claimed in any of the foregoing claims, wherein at least one of the pressure relief valve and the overflow valve passively opens against a spring force.

A transport system according to any one of the preceding claims, wherein at least one of the pressure relief valve and the overflow valve actively closes under the influence of a hydraulic force.

A conveyor system according to any one of the preceding claims, wherein a pressure relief valve is positioned upstream with respect to approximately each pump module in the string.

7. Transport system as claimed in any of the foregoing claims, wherein an overflow valve is positioned downstream with respect to approximately every pump module in the strand.

8. Transport system as claimed in any of the foregoing claims, wherein a pump module comprises a quantity of pumps arranged in series.

The conveyor system of claim 6, wherein a pump module comprises two pumps arranged in series.

Transport system as claimed in any of the foregoing claims, wherein a pump module comprises at least one of the pressure relief valve, the overflow valve, a pump bypass with bypass valve and a valve valve.

The conveyor system of claim 10, wherein the pressure relief valve is positioned in the pump module upstream of the pump bypass.

12. Transport system according to claim 10 or 11, wherein the overflow valve is positioned in the pump module downstream of the pump bypass.

A conveyor system according to any one of the preceding claims, wherein the pump comprises a centrifugal pump.

A conveyor system according to any one of the preceding claims, wherein the conveyor system units comprise rigid pipe sections.

Assembly of a transport system according to any one of the preceding claims and an underwater mining vehicle connected to an upstream end of the transport system.

A pump module for use in a conveyor system as claimed in any one of the preceding claims, comprising an inlet section and an outlet section, each of which can be connected to a conveyor system unit, a pump arranged between the inlet and outlet sections and adapted to pump mineral deposits from a relative to the pump module upstream unit to a downstream unit relative to the pump module, and a pressure relief valve positioned upstream of the pump, and an overflow valve positioned downstream of the pump in the pump module.

A pump module according to claim 16, comprising a pump bypass which connects a pump inlet to a pump outlet and which is arranged in parallel with a pump inlet and an outlet line, the pump bypass being provided with a by-pass valve.

A pump module according to claim 17, wherein the inlet and / or outlet line of a pump is provided with a valve valve.

A pump module according to any one of claims 16-18, comprising a plurality of pumps arranged in series.

Pump module according to one of claims 16-19, provided with end couplings for coupling to end sections of a conveyor system unit.

A pump module according to claim 20, wherein the end couplings have approximately the same dimensions as the end sections of the conveyor system unit, so that a pump module can be treated in the same way with a pick-up tool as a conveyor system unit.

A method for extracting mineral deposits from a seabed, the method comprising providing a transport system according to any of claims 1-14 or an assembly according to claim 15, bringing recovered mineral deposits from the seabed to a surface vessel through it the strand of interconnected transport system units by pumping mineral deposits from any unit positioned upstream of a pump module to a unit positioned downstream of the pump module, and, in the event of a failure of a pump module or other malfunction, opening a downstream of the pump module failed pump module or other failure in the string positioned pressure relief valve to prevent a downstream part of the string from collapsing under vacuum.

The method of claim 22, wherein, in the event of a failure of a substantial amount of pump modules or other nearly total failure where nodules fall back in the upstream direction, a pressure relief valve of pump modules opens to allow water in, and an overflow valve of pump modules opens to release fallen nodules.

A method according to claims 22 and 23, comprising, in the event of a pump failure in a pump module, opening a by-pass valve in a bypass which connects the failed pump inlet to the failed pump outlet and which is arranged in parallel with failed pump inlet and outlet exhaust pipe.

The method of claim 24, comprising closing a valve valve provided in the inlet and / or outlet line of the failed pump.

The method of any one of claims 22-25, wherein at least one of the pressure relief valve and the overflow valve is passively opened against a spring force.

The method of any one of claims 22-26, wherein at least one of the pressure relief valve and the overflow valve is actively closed with the intervention of a hydraulic force after the failure has been resolved.