CN116829811A - Acquisition method of underwater resources - Google Patents

Abstract

An extraction pipe (2) is extended toward the underwater crust (B), and the lower part of an insertion pipe (3) connected to the lower part of the extraction pipe (2) is inserted into the underwater crust (B). A rotation shaft (4) extending in the tube axis direction inside the extraction tube (2) and the insertion tube (3) and stirring blades (6) attached to the lower part of the rotation shaft (4) are rotated inside the insertion tube (3) while supplying a liquid (L) inside the insertion tube (3), and soil (S) inside the insertion tube (3) is excavated and decomposed by the stirring blades (6). Then, the mud S decomposed into slurry is lifted up to the upper part of the insertion pipe 3 by the stirring flow generated by the rotation of the stirring blade 6, and the lifted mud S is pumped up to the water by the pumping unit through the pumping pipe 2. At this time, in the initial step of the excavation, the rotation speed of the stirring blade (6) is made slower than the subsequent steps after the initial step. Thus, the underwater resources contained in the soil of the underwater crust can be efficiently collected.

Description

Acquisition method of underwater resources

Technical Field

The present invention relates to a method for collecting underwater resources, and more particularly, to a method for collecting underwater resources which can efficiently collect underwater resources contained in soil of an underwater crust.

Background

In the development of ocean resources, earth of a submarine earth crust containing a submarine resource such as rare earth existing in a deep sea is extracted together with a liquid such as water by extraction means such as pump lifting and air lifting to an extraction ship on the water. The larger the mass of earth, the more liquid volume is required for extraction. The more the amount of liquid that is extracted together with the soil, the more man-hours for the operations of extracting and separating the soil from the liquid, and the more the cost required for the collection of the underwater resources. Therefore, in order to collect the water bottom resources contained in the soil of the water bottom crust efficiently, it is important to finely decompose the soil of the water bottom crust and extract the soil with a smaller liquid amount.

Conventionally, various systems for excavating and extracting soil from a submarine earth crust have been proposed (see patent document 1). In the marine resource mining apparatus of patent document 1, a recovery hopper provided at a lower portion of a suction pipe portion is opposed to a surface of a submarine earth crust. Next, the rotating cutter head is penetrated into the underwater crust, and soil of the underwater crust is excavated by spraying an emulsion (oil mixed with a surfactant) lighter in specific gravity than seawater from a nozzle provided at a lower end portion of the cutter head. Then, the soil and the emulsion rising from the underwater crust to the upper part of the recovery hopper are extracted to the water through the extraction pipe part. In this method, much of the earth in the underwater crust excavated by the cutter head spreads in the underwater crust, and thus the earth cannot be finely decomposed. In this marine resource mining apparatus, therefore, an emulsion having a lighter specific gravity than seawater is sprayed into the underwater crust in order to raise the soil. However, since a large amount of emulsion is required to be sprayed and extracted into the underwater crust, the working time for separating the extracted soil from the emulsion increases, and the cost required for collecting underwater resources increases. In addition, there is a concern that the aquatic environment is damaged by the emulsion flowing out into the water.

Prior art literature

Patent literature

Patent document 1: japanese patent application laid-open No. 2019-11568

Disclosure of Invention

Problems to be solved by the invention

The invention aims to provide a method for collecting underwater resources, which can efficiently collect underwater resources contained in soil of underwater crust.

Means for solving the problems

In order to achieve the above object, a method of collecting underwater resources according to the present invention is a method of collecting underwater resources, in which soil of an underwater crust in an unexcavated state containing underwater resources is excavated and extracted onto water, characterized in that an extraction pipe is provided so as to extend from above water toward the underwater crust, at least a lower portion of an insertion pipe connected to a lower portion of the extraction pipe is inserted into the underwater crust, liquid is supplied into the interior of the insertion pipe while a rotation shaft extending in a pipe axis direction in the extraction pipe and the interior of the insertion pipe and a stirring blade attached to a lower portion of the rotation shaft are rotated in the interior of the insertion pipe, the soil in the interior of the insertion pipe is excavated and decomposed by the stirring blade, the soil in a slurry state resulting from the decomposition is lifted to an upper portion of the insertion pipe by a stirring flow generated by the rotation of the stirring blade, the lifted slurry soil is extracted onto water by the extraction pipe, and in an initial step of excavating the soil, and a step subsequent to the initial step of rotating the stirring blade is slowed down.

Effects of the invention

According to the present invention, in the subsequent steps after the initial step, the soil in the insertion tube can be efficiently granulated into a slurry by excavating and decomposing the soil in the insertion tube by the stirring blade rotating at a relatively high speed. Further, by rotating the stirring blade at a high speed, a stirring flow in which the fine-grained soil is easily lifted up can be generated inside the insertion tube. On the other hand, in the initial step of excavating, the stirring blade is rotated at a relatively low speed, so that the risk of clogging of the suction pipe due to the rising of the soil having large soil blocks to the upper portion of the insertion pipe can be reduced. Therefore, the soil of the underwater crust can be efficiently extracted with a relatively small amount of liquid, and the underwater resources contained in the soil can be efficiently collected.

Drawings

Fig. 1 is an explanatory diagram illustrating an outline of an embodiment of a method for collecting underwater resources according to the present invention.

Fig. 2 is an explanatory view illustrating the interior of the insertion tube of fig. 1 in a plan view.

Fig. 3 is an explanatory view illustrating the inside of the insertion tube in a view from the direction a in fig. 2.

Fig. 4 is an explanatory view illustrating the inside of the insertion tube in a view from the side B of fig. 2.

Fig. 5 is an explanatory view illustrating a state in which the insertion pipe of fig. 1 is inserted into the underwater crust.

Fig. 6 is an explanatory view illustrating a state in which the agitation She Guanru in a state of relatively low-speed rotation is brought to a predetermined depth shallower than the target depth of the underwater crust from the state of fig. 5.

Fig. 7 is an explanatory view illustrating a state in which the agitation She Guanru in a state of relatively rotating at a high speed is brought to a target depth of the underwater crust from the state of fig. 6.

Fig. 8 is a graph illustrating the time lapse of the penetration depth of the stirring blade.

Fig. 9 is an explanatory view illustrating a state in which the agitation She Guanru in a state of relatively low-speed rotation is brought to a target depth of the underwater crust from the state of fig. 5.

Fig. 10 is an explanatory view illustrating a state in which the stirring blade in a state of relatively rotating at a high speed is reciprocated in the tube axis direction inside the insertion tube from the state of fig. 9.

Fig. 11 is an explanatory view illustrating an interior of an insertion tube according to another embodiment of the underwater resource collection method of the present invention in a plan view.

Fig. 12 is an explanatory view illustrating a cross-sectional manner of an interior of an insertion tube of still another embodiment of a method for collecting underwater resources according to the present invention.

Fig. 13 is an explanatory diagram illustrating an outline of another embodiment of the underwater resource collection method of the present invention.

Fig. 14 is an explanatory view illustrating an interior of the insertion tube of fig. 13 in a longitudinal section.

Fig. 15 is an explanatory view illustrating a state in which the insertion pipe of fig. 13 is inserted into the underwater crust.

Fig. 16 is an explanatory view illustrating a state in which the stirring blade is inserted into the deepest insertion position of the underwater crust from the state of fig. 15.

Fig. 17 is an explanatory view illustrating a state in which the stirring blade is reciprocated in the tube axis direction inside the insertion tube from the state of fig. 16.

Fig. 18 is a graph illustrating the time lapse of the penetration depth of the stirring blade.

Detailed Description

Hereinafter, a method for collecting underwater resources according to the present invention will be described based on the illustrated embodiment. In the present invention, using the collection system 1 (hereinafter referred to as collection system 1) for underwater resources illustrated in fig. 1, soil S of the underwater crust B in an unexcavated state containing underwater resources (mineral resources) such as rare earth is excavated and extracted on water.

The collection system 1 includes an extraction pipe 2 extending from above water toward the underwater crust B, an insertion pipe 3 connected to the lower portion of the extraction pipe 2, and a rotation shaft 4 extending in the pipe axis direction inside the extraction pipe 2 and the insertion pipe 3. The collection system 1 further includes a stirring blade 6 attached to the lower part of the rotation shaft 4 and a liquid supply mechanism 8 for supplying a liquid L (seawater or fresh water) into the insertion tube 3. In this embodiment, the case where the extraction pipe 2 is connected to the extraction vessel 20 on the water is exemplified, but the extraction vessel 20 is not limited thereto, and for example, the extraction pipe 2 may be connected to an extraction facility or the like provided on the water.

The extraction tube 2 communicates with the insertion tube 3. The inner diameter of the insertion tube 3 is set larger than the inner diameter of the extraction tube 2. The inner peripheral surface of the connecting portion between the extraction tube 2 and the insertion tube 3 has a smoothly continuous curved shape. The inner diameter of the extraction tube 2 is set to be in the range of, for example, 0.2m to 1.0m, and the inner diameter of the insertion tube 3 is set to be in the range of, for example, 0.5m to 5 m. A pumping unit for pumping the soil S rising to the upper portion of the insertion pipe 3 upward through the pumping pipe 2 is connected to the pumping pipe 2. The pumping unit is constituted by, for example, an air lift pump, a slurry pump, or the like.

The length of the insertion pipe 3 in the pipe axis direction is set appropriately according to the depth of the stratum where the water bottom resources are distributed, but is set in a range of, for example, 2m to 20 m. In this embodiment, a stopper 3a having an annular shape in a plan view is provided on the outer peripheral surface of the insertion tube 3. The area of the insertion tube 3 below the stopper 3a is inserted into the underwater crust B, and the area of the insertion tube 3 above the stopper 3a is projected upward from the surface of the underwater crust B, with the stopper 3a as a boundary.

The rotation shaft 4 is suspended by inserting the extraction tube 2 and the insertion tube 3 from the extraction vessel 20, and is rotated by a driving mechanism. As illustrated in fig. 2 to 4, in this embodiment, a stirring blade 6 is attached to a head 5 detachably connected to a lower portion of the rotary shaft 4. A digging cutter 7 for digging soil S of the underwater crust B is provided at the lower end portion of the head 5. A stirring blade group including a plurality of stirring blades 6 is provided on the outer peripheral surface of the head 5 above the digging blade 7. Each stirring blade 6 extends toward the inner peripheral surface of the insertion tube 3. The plurality of stirring blades 6 constituting the same stirring blade group are arranged at intervals in the circumferential direction of the rotary shaft 4.

Each stirring blade 6 of this embodiment is formed in a flat plate shape, and has a tapered shape that tapers from a root portion connected to the rotary shaft 4 (head 5) toward the tip end. The tip of the stirring blade 6 in the rotation direction has a sharp shape. For example, the tip portion of the stirring blade 6 may be formed into a zigzag shape having continuous peaks and valleys. The stirring blade 6 is not limited to a flat plate shape, and may be formed into a curved shape such as a blade of a propeller, for example.

In this embodiment, a stirring blade group composed of 2 stirring blades 6 arranged at opposing positions is provided with 3 layers in the axial direction of the rotary shaft 4. Each stirring blade 6 constituting the stirring blade group at the lowest layer is inclined downward as going to the rotation direction. Each stirring blade 6 of the stirring blade group constituting the middle layer and the stirring blade group of the uppermost layer is inclined upward as going to the rotation direction. As illustrated in fig. 4, the angle θ (depression angle) between the axial direction of the rotary shaft 4 and the extending direction of the stirring blade 6 is set to be, for example, in a range of 10 degrees to 80 degrees, preferably 20 degrees to 70 degrees, more preferably 25 degrees to 40 degrees.

The stirring blades 6 adjacent to each other in the axial direction of the rotary shaft 4 are arranged at positions offset from each other in the circumferential direction of the rotary shaft 4 in a plan view. A gap (clearance) of about 50mm to 500mm is provided between the inner peripheral surface of the insertion tube 3 and the tip of the stirring blade 6.

The number of layers of the stirring blade group provided in the axial direction of the rotary shaft 4, the number of stirring blades 6 constituting the stirring blade group of each layer, and the like are not limited to this embodiment, and may be different. For example, a stirring blade group consisting of 3 stirring blades 6 may be configured such that 2 layers or the like are provided in the axial direction of the rotary shaft 4. The stirring blades 6 constituting each stirring blade group are preferably arranged so as to be point-symmetrical with respect to the axial center of the rotary shaft 4 in a plan view. The direction of inclination of the stirring vanes 6 constituting the stirring vane group of each layer is not limited to this embodiment, and for example, the stirring vanes 6 constituting the stirring vane group of the uppermost layer and the stirring vane group of the intermediate layer may be configured to be inclined downward as going to the rotation direction.

The liquid supply means 8 supplies water (sea water, fresh water) as the liquid L, for example. It is convenient to use field water (sea water, fresh water) that can be obtained on site. In addition, the liquid L may be, for example, a liquid in which an additive is added to water or a liquid other than water. The liquid supply mechanism 8 of this embodiment has an injection nozzle 8a provided at the distal end portion of the stirring blade 6. The liquid supply device provided on the water (extraction vessel 20) is configured to supply the liquid L to each of the injection nozzles 8a through a main pipe extending inside the rotary shaft 4 and a plurality of pipes 8b branched at the lower part of the main pipe.

The injection nozzle 8a and the pipe 8b are attached to a surface on the rear side of the stirring blade 6 with respect to the rotation direction of the stirring blade 6. For example, the injection nozzle 8a and the pipe 8b may be provided in the stirring blade 6 to inject the liquid L from the tip of the stirring blade 6. In this embodiment, the injection nozzles 8a are provided in each of all the stirring blades 6, but the injection nozzles 8a may be selectively provided in some of the stirring blades 6. That is, for example, the injection nozzles 8a may be provided only for the stirring vanes 6 constituting the stirring vane group at the lowest layer.

In the case where the injection nozzles 8a are selectively provided to some of the stirring blades 6, the injection nozzles 8a provided in each layer are preferably arranged so as to be point-symmetrical with respect to the axial center of the rotary shaft 4 in a plan view. The liquid supply mechanism 8 is not limited to the structure of this embodiment, as long as it can supply the liquid L into the insertion tube 3.

Next, an example of the operation steps of the method for acquiring the underwater resources using the acquisition system 1 will be described below. In the present invention, an initial process and a post process are performed.

An insertion tube 3 is connected to the lower portion of the extraction tube 2, and a head 5 is detachably fixed to the inside of the upper portion of the insertion tube 3. In the initial step, as illustrated in fig. 5, the extraction pipe 2 is extended from the water (extraction vessel 20) toward the underwater crust B, and at least the lower portion of the insertion pipe 3 is inserted into the underwater crust B in the non-excavated state. For example, 50% or more of the entire length of the insertion pipe 3 is inserted into the underwater crust B. The upper part of the insertion pipe 3 accommodating the head 5 is not inserted into the underwater crust B, and the head 5 is placed above the surface of the underwater crust B. At this stage, the inside of the lower portion of the insertion tube 3 inserted into the underwater crust B is filled with soil S of the underwater crust B. The inside of the upper part of the insertion pipe 3 which is not inserted into the underwater crust B is filled with water W in the water area.

In this embodiment, when the insertion pipe 3 is inserted into the underwater crust B to a position where the stopper 3a provided on the outside of the insertion pipe 3 is in contact with the surface of the underwater crust B, the lower portion of the insertion pipe 3 is inserted to the depth of the stratum where the underwater resources are distributed. The upper portion of the insertion tube 3 in which the head 5 is housed is in a state protruding upward from the surface of the underwater crust B.

Next, the rotary shaft 4 is lowered from the water (extraction vessel 20) toward the underwater crust B while being inserted into the extraction pipe 2 and the insertion pipe 3, and the head 5 (stirring blade 6) is connected to the lower end of the rotary shaft 4. When the rotary shaft 4 is moved downward further toward the underwater crust B in a state where the head 5 is connected to the lower end portion of the rotary shaft 4, the head 5 is detached from the insertion tube 3. As a result, the head 5 (stirring blade 6) integrated with the rotation shaft 4 is movable in the tube axis direction.

Next, as illustrated in fig. 6, the liquid L is supplied into the insertion tube 3 by the liquid supply mechanism 8, and the stirring blade 6 rotating in the insertion tube 3 is inserted into the surface of the underwater crust B in the non-excavated state, so as to excavate and decompose the soil S in the insertion tube 3. In the initial step of the excavation, the rotation speed of the stirring blade 6 is made slower than the subsequent steps after the initial step. The rotation speed (revolutions per minute) of the stirring blade 6 in the initial step is set to be, for example, in the range of 5rpm to 20 rpm.

Next, in the subsequent step, as illustrated in fig. 7, the liquid L is supplied to the inside of the insertion tube 3 by the liquid supply mechanism 8, and the soil S in the inside of the insertion tube 3 is excavated and decomposed by the stirring blade 6 in a state where the rotation speed is relatively faster than in the initial step. Then, the mud S decomposed into slurry by the rotation of the stirring blades 6 is lifted up to the upper portion of the insertion pipe 3 by the stirring flow, and the lifted mud S is pumped up to the water by the pumping means through the pumping pipe 2.

The rotational speed of the stirring blade 6 in the subsequent step is set to, for example, 1.5 to 4.0 times the rotational speed of the stirring blade 6 in the initial step. Specifically, in order to generate a stirring flow for raising the soil S, the rotation speed of the stirring blade 6 needs to be set to be 20rpm or more, more preferably 30rpm or more, and still more preferably 40rpm or more, because the rotation speed (rotations per minute) of the stirring blade 6 in the subsequent step is required to be correspondingly high. On the other hand, since there is a limit to rotating the stirring blade 6 at a high speed, the upper limit of the rotation speed is set to, for example, about 80rpm or 60 rpm. In the initial step and the subsequent step, the rotation speed of the stirring blade 6 is not necessarily constant throughout the entire period of the step, and therefore, if not constant, the average rotation speed is calculated. The calculated average rotation speed is set to 1.5 to 4.0 times the rotation speed in the subsequent step with respect to the initial step.

In this embodiment, the soil S between the tip of the stirring blade 6 and the inner peripheral surface of the insertion tube 3 is excavated and decomposed by injecting the liquid L at high pressure from the injection nozzle 8a toward the inner peripheral surface of the insertion tube 3. As illustrated in fig. 6, in the initial step of making the rotation speed of the stirring blade 6 relatively slow, the stirring blade 6 is penetrated from the surface of the unglazed underwater crust B to a predetermined depth PD shallower than the target depth TD of the underwater crust B, and the soil S inside the insertion pipe 3 up to the predetermined depth PD is excavated and decomposed.

The target depth TD can be set appropriately according to the depth of the stratum where the underwater resources are distributed, but is set to a depth of about 1.5m to 9m from the surface of the underwater crust B, for example. The target depth TD is set to a depth at a position halfway the insertion pipe 3 in a state of being inserted into the underwater crust B. The predetermined depth PD can be set appropriately according to the hardness of the soil S of the underwater crust B, but is set to a depth of about 0.5m to 2m from the surface of the underwater crust B or a depth range of 20% to 60% of the target depth TD from the surface of the underwater crust B, for example.

In a subsequent step of relatively increasing the rotational speed of the stirring blade 6, the stirring blade 6 is inserted from the predetermined depth PD to the target depth TD, and the soil S inside the insertion tube 3 from the predetermined depth PD to the target depth TD is excavated and decomposed. The soil S decomposed in the initial step is stirred in the insertion pipe 3 together with the soil S excavated and decomposed in the subsequent step by the stirring flow generated by the high-speed rotation of the stirring blade 6, and is decomposed more finely. The fine-grained soil S in the insertion tube 3 floats in a state of being mixed with the liquid (including the water W in the water area and the liquid L supplied by the liquid supply mechanism 8) in the insertion tube 3, and the interior of the insertion tube 3 is filled with the slurry-like soil S.

Then, by supplying new liquid L from the liquid supply mechanism 8 (the injection nozzle 8 a) into the interior of the insertion tube 3, replacement of the water W and soil S in the interior of the insertion tube 3 with the newly supplied liquid L is promoted. Then, by using the stirring flow generated by the high-speed rotation of the stirring blade 6, the slurry-like soil S rising to the upper portion of the insertion pipe 3 is sequentially extracted by the extracting means through the extracting pipe 2 to the water (extracting boat 20).

In this way, in the present invention, in the initial step of excavating, by rotating the stirring blade 6 at a relatively low speed, the risk of the suction pipe 2 being clogged due to the soil S having large soil blocks, which are not sufficiently decomposed, rising to the upper portion of the insertion pipe 3 can be reduced. On the other hand, in the subsequent step, the soil S in the insertion tube 3 can be efficiently granulated into a slurry by excavating and decomposing the soil S in the insertion tube 3 by the stirring blade 6 rotating at a relatively high speed. Further, by rotating the stirring blade 6 at a high speed, a stirring flow in which the fine-grained soil S easily rises can be generated inside the insertion pipe 3. Thus, the soil S of the underwater crust B can be efficiently extracted with a relatively small liquid amount, and the underwater resources contained in the soil S can be efficiently collected.

When the soil S having a relatively shallow depth is excavated and decomposed, the soil S retained above is relatively small, and therefore the soil S excavated and decomposed by the stirring blade 6 is relatively easy to rise. Therefore, as in this embodiment, when the stirring blade 6 is inserted into the surface of the unglazed underwater crust B to a predetermined depth PD shallower than the target depth TD in a state where the rotational speed is relatively low in the initial step, the risk of clogging of the suction pipe 2 due to the soil S at a shallow depth rising to the upper portion of the insertion pipe 3 with the soil mass large can be reduced.

After the stirring blade 6 is inserted to the predetermined depth PD, the amount of soil S remaining above the stirring blade 6 becomes relatively large, and the soil S is less likely to rise to the upper portion of the insertion tube 3 in a state where the soil mass is large. Accordingly, in the subsequent step, the stirring blade 6 is inserted from the predetermined depth PD to the target depth TD with a relatively high rotation speed, whereby the soil S inside the insertion pipe 3 can be efficiently excavated and decomposed. Further, by rotating the stirring vane 6 at a high speed to generate a stirring flow which flows quickly inside the insertion pipe 3, the slurry-like soil S can be efficiently lifted up to the upper portion of the insertion pipe 3.

Next, another example of the steps of the underwater resource collection method will be described below. The procedure until the insertion pipe 3 is inserted into the non-excavated underwater crust B and the head 5 (stirring blade 6) is connected to the lower end portion of the rotation shaft 4 is the same as that previously exemplified.

The horizontal axis of the graph of fig. 8 shows the elapsed time from the penetration of the stirring vane 6 into the underwater crust B, and the vertical axis shows the penetration depth of the stirring vane 6 with respect to the surface of the underwater crust B (0 m). As shown in the graph of fig. 8, in this embodiment, in the initial step, the stirring blade 6 is inserted into the surface of the unglazed underwater crust B to the target depth TD. Then, in the subsequent step, the stirring vane 6 is reciprocally moved in the pipe axis direction within a predetermined depth range (a range shallower than the target depth TD) between the target depth TD and the surface of the underwater crust B inside the insertion pipe 3.

As illustrated in fig. 9, in the initial step, if the stirring blade 6 is inserted from the surface of the underwater crust B to the target depth TD in a state where the rotation speed is relatively low, the risk of the suction pipe 2 being clogged due to the soil S having large soil blocks rising to the upper portion of the insertion pipe 3 can be further reduced.

Further, as illustrated in fig. 10, in the post-process, if the stirring blade 6 is reciprocated in the pipe axis direction within a predetermined depth range between the target depth TD and the surface of the underwater crust B in the interior of the insertion pipe 3 in a state where the rotation speed is relatively high, the soil S in the interior of the insertion pipe 3 can be more reliably atomized by repeatedly decomposing the soil S in the interior of the insertion pipe 3. Further, by reciprocating the stirring blade 6 rotating at a high speed in the pipe axis direction, the soil S decomposed inside the insertion pipe 3 is more difficult to settle down to the lower portion of the insertion pipe 3. Thus, it is more advantageous to efficiently extract the soil S of the underwater crust B with a relatively small liquid amount. The stirring vane 6 is preferably moved from the target depth TD to the upper portion of the insertion tube 3. The number of times of reciprocating the stirring blades 6 can be appropriately determined according to the hardness of the soil S of the underwater crust B, the number of stirring blades 6, and the like, but it is preferable to reciprocate the stirring blades about 2 to 15 times, for example.

In the initial step and the subsequent step, the rotation speed of the stirring blade 6 may be set to be constant, but for example, the rotation speed of the stirring blade 6 may be set to be faster as the penetration depth of the stirring blade 6 is deeper. By setting the rotation speed of the stirring blade 6 to be higher as the penetration depth becomes deeper, the soil S can be excavated and decomposed more efficiently while avoiding clogging of the extraction pipe 2 by the soil S having large soil blocks rising to the upper portion of the insertion pipe 3.

The speed at which the stirring blade 6 is moved in the pipe axis direction can be appropriately set according to the hardness of the soil S of the underwater crust B, and the like. Specifically, for example, the movement speed of the stirring blade 6 in the tube axis direction is preferably set to be in the range of 1 mm/sec to 100 mm/sec, more preferably 1 mm/sec to 10 mm/sec. Preferably, in the initial step, the movement speed of the stirring blade 6 in the tube axis direction is preferably made slower than in the subsequent step.

In the initial step of penetrating the stirring blade 6 into the unglazed underwater crust B, the load applied to the stirring blade 6 is also relatively large. Therefore, in the initial step, by setting the movement speed of the stirring blade 6 in the pipe axis direction to a relatively slow speed of about 1 mm/sec to 5 mm/sec, even if the rotation speed of the stirring blade 6 is low, the soil S of the underwater crust B can be decomposed relatively finely while avoiding the application of an excessive load to the stirring blade 6. In the subsequent step, since the rotation speed of the stirring blade 6 is made faster than in the initial step, the soil S in the insertion tube 3 can be efficiently excavated and decomposed by making the movement speed of the stirring blade 6 in the tube axis direction faster than in the initial step. The movement speed of the stirring blade 6 in the tube axis direction in the subsequent step is set to, for example, about 5 mm/sec to 100 mm/sec, and more preferably about 5 mm/sec to 10 mm/sec.

When the liquid L is injected from the injection nozzle 8a provided at the distal end portion of the stirring blade 6 toward the inner peripheral surface of the insertion tube 3, the soil S between the distal end of the stirring blade 6 and the inner peripheral surface of the insertion tube 3, which is not reached by the stirring blade 6, can be excavated and decomposed. Thus, the soil S inside the insertion tube 3 can be thoroughly extracted. Further, by disposing the injection nozzle 8a at the tip end portion of the stirring blade 6 near the inner peripheral surface of the insertion tube 3, the injection pressure of the liquid L required for cutting the soil S between the tip end of the stirring blade 6 and the inner peripheral surface of the insertion tube 3 can be made relatively low.

In addition, since the liquid (water W and liquid L in the water area) flows inside the insertion tube 3 by the liquid L ejected from the ejection nozzle 8a at high pressure, the soil S inside the insertion tube 3 is more likely to be fine-grained, and the soil S is more likely to be settled to the lower portion of the insertion tube 3. The soil S remaining after the completion of the extraction of the soil S in the insertion tube 3 is less adhered to the inner peripheral surface of the insertion tube 3. Therefore, when the insertion pipe 3 is inserted into the new position of the underwater crust B, the insertion pipe 3 can be smoothly inserted without increasing the resistance when the soil S is extracted a plurality of times by changing the position of the insertion pipe 3. The labor required for maintenance of the insertion tube 3 after completion of the extraction operation can be reduced.

In the initial step, when the liquid L is rapidly supplied into the insertion tube 3, the soil S having large soil blocks rises to the upper portion of the insertion tube 3, and the risk of clogging of the extraction tube 2 increases. Therefore, in the initial step, the amount of liquid per unit time to be supplied into the insertion tube 3 is preferably smaller than in the subsequent step. In the subsequent step, the amount of liquid per unit time supplied into the insertion tube 3 is made larger than in the initial step, so that the decomposed slurry soil S is advantageously efficiently lifted up to the upper portion of the insertion tube 3.

As in another embodiment of the present invention illustrated in fig. 10, the liquid L may be ejected obliquely forward with respect to the rotation direction of the stirring blade 6 from the ejection nozzle 8a provided at the distal end portion of the stirring blade 6. The injection angle of the injection nozzle 8a with respect to the extending direction of the stirring blade 6 can be appropriately set according to the rotation speed of the stirring blade 6 or the like, but is set in a range of, for example, 10 degrees to 45 degrees.

When the liquid L is ejected obliquely forward from the ejection nozzle 8a with respect to the rotation direction of the stirring blade 6 in this way, the ejected liquid L more easily and forcefully reaches the inner peripheral surface of the insertion tube 3. Thus, the soil S between the tip of the stirring blade 6 and the inner peripheral surface of the insertion tube 3 can be more efficiently excavated and decomposed. For example, a variable mechanism capable of changing the injection angle of the injection nozzle 8a with respect to the extending direction of the stirring blade 6 may be provided, and the injection angle of the injection nozzle 8a may be changed in accordance with the rotation speed of the stirring blade 6.

As in the further embodiment of the present invention illustrated in fig. 11, a discharge nozzle 8c for discharging the liquid L may be provided as the liquid supply means 8 at the lower portion (head 5) of the rotary shaft 4 disposed inside the insertion tube 3. When the liquid L is discharged from the discharge nozzle 8c toward the surface of the stirring blade 6 in this way, the soil S adhering to the surface of the stirring blade 6 can be removed. Thus, the soil S can be prevented from accumulating on the surface of the stirring blade 6, and the soil S inside the insertion tube 3 can be extracted more easily. In addition, since the liquid L is more likely to spread over the soil S in the range where the stirring blade 6 reaches, the soil S is more likely to flow inside the insertion tube 3. Thus, it is more advantageous to fine-grain the soil S inside the insertion tube 3 efficiently.

Next, another example of the steps of the underwater resource collection method will be described below.

As illustrated in fig. 13 and 14, the acquisition system 1 used in this embodiment includes an extraction pipe 2 extending from above water toward the underwater crust B, an insertion pipe 3 connected to the lower portion of the extraction pipe 2, and a rotation shaft 4 extending in the pipe axis direction inside the extraction pipe 2 and the insertion pipe 3. The collection system 1 further includes a stirring blade 6 attached to the lower portion of the rotation shaft 4 and a liquid supply mechanism 8 for supplying the liquid L into the insertion tube 3. The acquisition system 1 of this embodiment further includes an intensity sensor 9 and a pressure sensor 10 provided in the insertion tube 3. The structures of the extraction tube 2, the insertion tube 3, the rotation shaft 4, the stirring blade 6, and the liquid supply mechanism 8 are the same as those of the previously exemplified embodiment.

The intensity sensor 9 measures the intensity of the underwater crust B in the non-excavated state. Examples of the index indicating the strength of the underwater crust B include uniaxial compressive strength, N value, and cone index in the tube axis direction of the soil S of the underwater crust B. As the strength sensor 9, for example, a soil hardness tester, a soil layer strength check rod, or the like is used. The strength sensor 9 is provided at a position of the insertion pipe 3 to be inserted into the underwater crust B. The strength sensor 9 is preferably provided near the lower end opening 3c of the insertion tube 3 (at a position within 30cm from the lower end opening 3c in the tube axis direction). In this embodiment, the strength sensor 9 is provided at a position not in contact with the stirring blade 6 on the inner peripheral surface of the insertion tube 3, but may be provided on the outer peripheral surface and the lower end surface of the insertion tube 3, for example.

The pressure sensor 10 measures the pressure inside the insertion pipe 3 inserted into the underwater crust B. The pressure sensor 10 is provided in a range of the region R1 to be excavated for excavating and decomposing the soil S by the stirring blade 6, for example. The pressure sensor 10 is preferably disposed at a position spaced from the lower end 3b of the insertion tube 3 upward by a distance of 100cm or more and 500cm or less, for example. In this embodiment, the pressure sensor 10 is provided at a position of the inner peripheral surface of the insertion tube 3 that is not in contact with the stirring blade 6. The measurement data of each of the intensity sensor 9 and the pressure sensor 10 is transmitted to the management unit on the water (extraction vessel 20) in sequence, and the measurement data can be grasped by the manager. The intensity sensor 9 and the pressure sensor 10 can be provided arbitrarily.

Next, an example of the operation steps of the method for acquiring the underwater resources using the acquisition system 1 will be described below.

An insertion tube 3 is connected to the lower portion of the extraction tube 2, and a head 5 is detachably fixed to the inside of the upper portion of the insertion tube 3. As illustrated in fig. 15, the extraction pipe 2 is extended from the water (extraction vessel 20) toward the underwater crust B, and at least the lower portion of the insertion pipe 3 is inserted into the underwater crust B in an unexcavated state. The upper part of the insertion pipe 3 accommodating the head 5 is not inserted into the underwater crust B, and the head 5 is placed above the surface of the underwater crust B. The insertion tube 3 is inserted into the underwater crust B at least at the lower portion thereof, and the upper portion of the insertion tube 3 protrudes upward from the surface of the underwater crust B. For example, 50% or more of the entire length of the insertion pipe 3 is inserted into the underwater crust B.

At this stage, the inside of the lower portion of the insertion pipe 3 inserted into the underwater crust B is filled with soil S of the underwater crust B in an unexcavated state. The inside of the upper part of the insertion pipe 3 which is not inserted into the underwater crust B is filled with water W in the water area. In the process of inserting the insertion pipe 3 into the underwater crust B, the strength of the underwater crust B is successively measured by the strength sensor 9.

In this embodiment, when the insertion pipe 3 is inserted into the underwater crust B to a position where the stopper 3a provided on the outside of the insertion pipe 3 is in contact with the surface of the underwater crust B, the lower portion of the insertion pipe 3 is inserted to the depth of the stratum where the underwater resources are distributed. The upper portion of the insertion tube 3 in which the head 5 is housed is in a state protruding upward from the surface of the underwater crust B.

Next, the rotary shaft 4 is lowered from the water (extraction vessel 20) toward the underwater crust B while being inserted into the extraction pipe 2 and the insertion pipe 3, and the head 5 (stirring blade 6) is connected to the lower end of the rotary shaft 4. When the rotary shaft 4 is moved downward further toward the underwater crust B in a state where the head 5 is connected to the lower end portion of the rotary shaft 4, the head 5 is detached from the insertion tube 3. As a result, the head 5 (stirring blade 6) integrated with the rotation shaft 4 is movable in the tube axis direction.

Next, as illustrated in fig. 16, the liquid L is supplied into the insertion tube 3 by the liquid supply mechanism 8, and the rotation shaft 4 and the stirring blade 6 attached to the lower portion (head 5) of the rotation shaft 4 are rotated in the insertion tube 3. Then, the stirring blade 6 in a rotated state is penetrated from the surface of the underwater crust B to the soil S of the underwater crust B to excavate the soil S inside the insertion pipe 3, and the soil S is decomposed into a slurry. In this embodiment, by injecting the liquid L at a high pressure from the injection nozzle 8a toward the inner peripheral surface of the insertion tube 3, the soil S between the tip of the stirring blade 6 and the inner peripheral surface of the insertion tube 3 can be excavated and decomposed while supplying the liquid L to the inside of the insertion tube 3. The pressure inside the insertion tube 3 (hereinafter, referred to as the internal pressure of the insertion tube 3) is successively measured by the pressure sensor 10.

When the stirring blade 6 is inserted into the underwater crust B, the deepest insertion position D1 of the stirring blade 6 (stirring blade 6 located most downward) is set to be a predetermined distance T upward from the lower end 3B of the insertion tube 3. The lower end opening 3c of the insertion tube 3 is closed by the soil S of the underwater crust B, and the soil S decomposed into slurry by the stirring blade 6 is prevented from flowing out of the insertion tube 3 through the lower end opening 3c of the insertion tube 3.

That is, the soil S in the excavation target region R1 from the surface of the underwater crust B to the deepest penetration position D1 in the insertion pipe 3 is excavated and decomposed by the stirring blade 6, and the non-excavation region R2 having a thickness of a predetermined distance T in the pipe axis direction is left between the deepest penetration position D1 and the depth D2 where the lower end 3B of the insertion pipe 3 is located. Then, the lower end opening 3c of the insertion pipe 3 is closed by the soil S in the non-excavated region R2 which is relatively hard with respect to the decomposed soil S. In the figure, soil S in an unexcavated state is indicated by a diagonal line.

The predetermined distance T is set to a distance that can prevent the soil S in the excavation region R2 that closes the lower end opening 3c of the insertion tube 3 from being disintegrated by the internal pressure of the insertion tube 3 even when the internal pressure of the insertion tube 3 becomes maximum when the soil S in the insertion tube 3 is excavated and decomposed by the stirring blades 6. The greater the strength of the underwater crust B (for example, uniaxial compression strength, N value, conical index, etc.), the greater the predetermined distance T, the greater the resistance to the soil S of the non-excavated region R2 of the internal pressure of the insertion tube 3.

Thus, an appropriate predetermined distance T, which can prevent the soil S, which has blocked the lower end opening 3c of the insertion tube 3, from disintegrating due to the internal pressure of the insertion tube 3, can be set based on the strength of the underwater crust B and the internal pressure of the insertion tube 3. By setting the predetermined distance T, the deepest penetration position D1 where the stirring blade 6 is penetrated can also be set according to the relationship with the depth D2 where the lower end 3b of the insertion tube 3 is located.

The strength of the underwater crust B can be obtained by the strength sensor 9 when the insertion pipe 3 is inserted into the underwater crust B as in the present embodiment, or can be obtained in advance before the insertion pipe 3 is inserted into the underwater crust B. Alternatively, the strength of the underwater crust B can be obtained both before and during the insertion of the insertion pipe 3 into the underwater crust B.

In the case where the strength of the underwater crust B is obtained in advance, for example, a known strength test (for example, a uniaxial compression test, a standard penetration test, or the like) is performed in which the soil S of the underwater crust B in an unexcavated state is collected and the strength of the underwater crust B is measured. If the strength sensor 9 is provided as in this embodiment, the strength of the underwater crust B can be measured by the strength sensor 9 when the insertion pipe 3 is inserted into the underwater crust B.

When the strength of the underwater crust B is obtained both before and during the insertion of the insertion pipe 3 into the underwater crust B, the predetermined distance T is preferably set by using the measurement value of the underwater crust B, which is the measurement value of the relatively low strength. In this way, the soil S that has blocked the lower end opening 3c of the insertion pipe 3 can be more reliably prevented from being disintegrated by the internal pressure of the insertion pipe 3, compared with the case where the predetermined distance T is set based on the measured value of either one of before and during insertion of the insertion pipe 3 into the underwater crust B.

The internal pressure of the insertion pipe 3 inserted into the underwater crust B may be obtained by the pressure sensor 10 after the insertion pipe 3 is inserted into the underwater crust B as in the present embodiment, or may be obtained in advance before the insertion pipe 3 is inserted into the underwater crust B. Alternatively, the internal pressure of the insertion pipe 3 may be obtained before and after the insertion pipe 3 is inserted into the underwater crust B.

The internal pressure of the insertion pipe 3 inserted into the underwater crust B can be calculated in advance based on the conditions such as the size of the insertion pipe 3, the amount of liquid per unit time supplied into the insertion pipe 3, and the amount of extraction per unit time by the extraction means. The internal pressure of the insertion tube 3 can be obtained in advance by performing a preliminary test using the collection system 1 or a simulation using a computer. For example, in a preliminary test, the pressure sensor 10 is used to measure the internal pressure of the insertion pipe 3 in the region R1 to be excavated when the stirring blade 6 excavates and breaks down the soil S in the insertion pipe 3 while supplying the liquid L into the insertion pipe 3 inserted into the underwater crust B.

By providing the pressure sensor 10 as in this embodiment, the internal pressure of the insertion pipe 3 in the region R1 to be excavated through which the stirring blade 6 is inserted can be measured by the pressure sensor 10 in the process of inserting the insertion pipe 3 into the underwater crust B and then penetrating the stirring blade 6 into the underwater crust B. The predetermined distance T can be set using the measured value of the internal pressure of the insertion tube 3 obtained by the pressure sensor 10 during penetration of the stirring blade 6.

When conditions such as the rotational speed and the moving speed of the stirring blade 6, the amount of liquid per unit time supplied to the inside of the insertion pipe 3, and the amount of extraction per unit time of the extraction unit are changed during the excavation and the decomposition of the soil S, the internal pressure of the insertion pipe 3 varies to some extent. Therefore, the predetermined distance T is preferably set based on the maximum value of the internal pressure of the insertion tube 3 at the time of excavation and disassembly.

When the internal pressure of the insertion pipe 3 is obtained both before and after the insertion pipe 3 is inserted into the underwater crust B, the predetermined distance T is preferably set by using a measurement value of the maximum value of the internal pressure of the insertion pipe 3 which is relatively high. In this way, the soil S that has blocked the lower end opening 3c of the insertion pipe 3 can be more reliably prevented from being disintegrated by the internal pressure of the insertion pipe 3, compared with the case where the predetermined distance T is set based on the measured value of either one of before and after the insertion of the insertion pipe 3 into the underwater crust B.

After the stirring blade 6 is inserted into the deepest insertion position D1, as illustrated in fig. 7, the stirring blade 6 is reciprocated in the pipe axis direction within a predetermined depth range (a range shallower than the deepest insertion position D1) between the deepest insertion position D1 and the surface of the underwater earth crust B, and the soil S in the excavation target region R1 is repeatedly decomposed. The number of times of reciprocating the stirring blades 6 can be appropriately determined according to the strength of the underwater crust B, the number of stirring blades 6, the rotation speed of the stirring blades 6, etc., but it is preferable to reciprocate it a plurality of times, for example, about 2 to 15 times. The operation of reciprocating the stirring blade 6 can be omitted appropriately, but if this operation is performed, the soil S in the region R1 to be excavated can be more reliably atomized.

The soil S in the region R1 to be excavated in the interior of the insertion tube 3 is mixed with the liquid (including the water W in the water area and the liquid L supplied by the liquid supply means 8) in the interior of the insertion tube 3 and floats, and the interior of the insertion tube 3 above the deepest penetration position D1 is filled with the soil S in the form of a slurry. Then, the soil S in the slurry-like state decomposed into the region R1 to be excavated is lifted up to the upper portion of the insertion pipe 3, and the lifted soil S in the slurry-like state is extracted by the extraction means through the extraction pipe 2 to the water (extraction vessel 20).

By supplying new liquid L from the liquid supply mechanism 8 (the injection nozzle 8 a) into the interior of the insertion tube 3, replacement of the water W in the interior of the insertion tube 3 and the soil S in the region R1 to be excavated with the newly supplied liquid L is promoted. Further, by generating a stirring flow in the interior of the insertion tube 3 by the rotation of the stirring blade 6, the soil S which is fine-grained in the interior of the insertion tube 3 is easily lifted to the upper portion of the insertion tube 3, and is efficiently extracted to the water.

In this way, in this collection method, the liquid L is supplied into the interior of the insertion pipe 3 inserted into the underwater crust B, and the stirring blade 6 is rotated to excavate and decompose the soil S in the interior of the insertion pipe 3. The deepest penetration position D1 of the stirring blade 6 is set to a predetermined distance T upward from the lower end 3B of the insertion tube 3, and the lower end opening 3c of the insertion tube 3 is maintained in a state of being blocked by the soil S of the underwater crust B, so that the soil S decomposed into a slurry is prevented from flowing out of the insertion tube 3 through the lower end opening 3c of the insertion tube 3. Accordingly, the soil S in the insertion tube 3 can be efficiently granulated to be pasty with a relatively small liquid amount, and can be efficiently raised to the upper portion of the insertion tube 3 while avoiding waste caused by outflow of the pasty soil S. Thus, the water bottom resources contained in the soil S of the water bottom crust B can be efficiently collected. By preventing the decomposed soil S from flowing out, the state of the soil S around the outer periphery of the insertion tube 3 can be prevented from being disturbed. Even when water is supplied as the liquid L, the liquid L can be prevented from flowing out into the water outside the insertion tube 3, and thus the risk of damaging the environment in the water is extremely low.

At first sight, it may be considered that: by penetrating the stirring blade 6 to the maximum depth to decompose the soil S by making the predetermined distance T substantially zero, more water bottom resources can be collected. However, the strength of soil S of the underwater crust B containing the underwater resources such as rare earth is relatively low, and the water depth is deep, so that the number of uncertain elements is large. Therefore, when the stirring blade 6 is inserted into the lower end 3b of the insertion tube 3, the risk of the soil S decomposed in the insertion tube 3 and the supplied liquid L flowing out of the insertion tube 3 through the lower end opening 3c of the insertion tube 3 becomes extremely high. When such outflow occurs, the slurry-like soil S is lost, and the internal pressure of the insertion pipe 3 drops sharply. Thus, the extraction efficiency of soil S may be lowered. The present invention is a simple method of intentionally leaving the non-excavation region R2 having a thickness of a predetermined distance T below the insertion pipe 3, but capable of effectively and stably improving the efficiency of extracting soil S. Thus, a method that is highly advantageous to those skilled in the art.

In addition, the inner diameter of the extraction pipe 2 used in the deep sea is small, and the gap between the inner peripheral surface of the extraction pipe 2 and the rotary shaft 4 is relatively narrow, but since the soil S in the insertion pipe 3 flows into the extraction pipe 2 in a fine-grained state with little soil, the soil S is hard to clog the extraction pipe 2. Therefore, it is difficult to cause a trouble in the extraction pipe 2, and the soil S of the underwater crust B can be extracted very smoothly.

In order to decompose the soil S efficiently and generate an effective stirring flow, the rotation speed of the stirring vane 6 is preferably 20rpm or more, more preferably 40rpm or more. In particular, in order to generate a stirring flow for raising the soil S, the rotation speed of the stirring vane 6 needs to be increased correspondingly. On the other hand, since there is a limit to rotating the stirring blade 6 at a high speed, the upper limit of the rotation speed is set to, for example, about 80rpm or 60 rpm.

The movement speed of the stirring blade 6 in the pipe axis direction can be appropriately set according to the strength of the soil S of the underwater crust B, and the like. Specifically, for example, the movement speed of the stirring blade 6 in the tube axis direction is preferably set to be in the range of 1 mm/sec to 100 mm/sec, more preferably 1 mm/sec to 10 mm/sec. The horizontal axis of the graph of fig. 18 shows the elapsed time from the penetration of the stirring vane 6 into the underwater crust B, and the vertical axis shows the penetration depth of the stirring vane 6 with respect to the surface of the underwater crust B (0 m). As shown in the graph of fig. 8, the following movement speed of the stirring blade 6 in the tube axis direction when the stirring blade 6 is reciprocated in the tube axis direction inside the insertion tube 3 is preferably set to be faster than the movement speed of the stirring blade 6 in the tube axis direction when the stirring blade 6 is penetrated from the surface of the underwater crust B to the deepest penetration position D1.

When the stirring blade 6 is inserted into the underwater crust B in the non-excavated state, the soil S of the underwater crust B is not decomposed, and the load applied to the stirring blade 6 is relatively large. In this case, by setting the movement speed of the stirring blade 6 in the tube axis direction relatively slow and gradually penetrating the stirring blade 6, it is possible to avoid applying an excessive load to the stirring blade 6. The soil S once excavated is decomposed to some extent, and the load applied to the stirring blade 6 is relatively small. Accordingly, after the stirring blade 6 is inserted into the deepest insertion position D1, the movement speed of the stirring blade 6 in the pipe axis direction is set relatively fast, and the stirring blade is reciprocated, whereby the soil S in the insertion pipe 3 can be efficiently decomposed.

When each stirring blade 6 constituting the lowermost stirring blade group is inclined downward in the direction of rotation, the soil S excavated and decomposed by the stirring blade 6 constituting the lowermost stirring blade group goes upward and is further decomposed by the stirring blade 6 constituting the upper stirring blade group. Thus, the soil S can be very efficiently fine-grained. Further, the downward pressure of the soil S and the liquid (including the water W and the liquid L in the water area) stirred by the stirring blades 6 constituting the stirring blade group at the lowermost layer becomes relatively small, so that it is advantageous to prevent the soil S in the non-excavated region R2, which blocks the lower end opening 3c of the insertion tube 3, from disintegrating.

In the case where the pressure sensor 10 is provided as in this embodiment, in the step of reciprocating the stirring blade 6 in the tube axis direction after the stirring blade 6 is inserted into the deepest insertion position D1, the amount of liquid per unit time to be supplied into the insertion tube 3 is preferably adjusted based on the measured value of the pressure sensor 10. The more the amount of liquid per unit time is supplied into the insertion tube 3, the more easily the decomposed soil S rises to the upper portion of the insertion tube 3, which is advantageous in improving the extraction efficiency. On the other hand, if the amount of liquid supplied to the inside of the insertion tube 3 becomes excessive with respect to the amount of the soil S and the liquid (including the water W and the liquid L in the water area), the internal pressure of the insertion tube 3 may become larger than the maximum value of the internal pressure of the insertion tube 3 used when the predetermined distance T is set. Accordingly, based on the measurement value of the pressure sensor 10, the amount of liquid per unit time to be supplied to the inside of the insertion tube 3 is preferably adjusted so that the extraction efficiency increases as much as possible within a range not exceeding the maximum value of the internal pressure of the insertion tube 3 used when the predetermined distance T is set.

The method of setting the predetermined distance T is not limited to the above-described method, as long as the predetermined distance T can be set so as to be able to maintain the state in which the lower end opening 3c of the insertion pipe 3 is blocked by the soil S in the non-excavation region R2 of the underwater earth crust B against the internal pressure of the insertion pipe 3. For example, the conditions of the predetermined distance T may be changed by a preliminary test using the acquisition system 1 or a simulation using a computer, and the predetermined distance T may be set appropriately based on the test result.

The method described above with reference to fig. 1 to 12 and the method described below with reference to fig. 13 to 18 can be appropriately combined. For example, in the above-described method, as in the method described later, the deepest penetration position D1 of the stirring blade 6 may be set to a predetermined distance T upward from the lower end 3B of the insertion pipe 3, and the lower end opening 3c of the insertion pipe 3 may be maintained in a state of being blocked by the soil S of the underwater crust B, so that the soil S in the form of slurry may be prevented from flowing out of the insertion pipe 3 through the lower end opening 3c, and the underwater resources may be collected without using the method described later. For example, in the method described later, as in the method described above, the rotation speed of the stirring blade 6 may be made slower in the initial step of excavation than in the subsequent steps after the initial step, and the underwater resources may be collected without using the method described above.

Description of the reference numerals

1 acquisition system of underwater resources

2 drawing tube

3 insert tube

3a stop

3b lower end

3c lower end opening

4 rotation shaft

5 heads

6 stirring blade

7 digger blade

8 liquid supply mechanism

8a spray nozzle

8b piping

8c discharge nozzle

9 intensity sensor

10 pressure sensor

20 extraction ship

B submarine crust

PD predetermined depth

TD target depth

D1 deepest penetration position

Depth of the lower end of the D2 insertion tube

R1 excavation target area

R2 non-excavated region

S soil

L liquid

W water

Claims (12)

1. A method for collecting underwater resources is characterized in that soil of the underwater crust in an unexcavated state containing the underwater resources is excavated and extracted to the water,

in a state where an extraction pipe is provided so as to extend from above water toward the underwater crust, at least a lower portion of an insertion pipe connected to a lower portion of the extraction pipe is inserted into the underwater crust, a liquid is supplied into the insertion pipe, a rotation shaft extending in a pipe axis direction inside the extraction pipe and the insertion pipe and a stirring blade attached to a lower portion of the rotation shaft are rotated inside the insertion pipe, the stirring blade is used to excavate and decompose the soil inside the insertion pipe, the stirring flow generated by the rotation of the stirring blade is used to lift the soil decomposed into a slurry state on an upper portion of the insertion pipe, the lifted slurry state soil is extracted to above water through the extraction pipe by an extraction unit, and in an initial process of excavation, the rotation speed of the stirring blade is made slower than a subsequent process after the initial process.

2. The method for collecting underwater resources according to claim 1,

in the initial step, the stirring blade is inserted from the surface of the underwater crust to a predetermined depth shallower than a target depth, and in the post step, the stirring blade is inserted from the predetermined depth to the target depth.

3. The method for collecting underwater resources according to claim 1,

in the initial step, the stirring blade is inserted from the surface of the underwater crust to a target depth, and in the post step, the stirring blade is reciprocated in a tube axis direction within a predetermined depth range between the target depth and the surface of the underwater crust.

4. A method for collecting underwater resources as claimed in any of claims 1 to 3,

in the initial step, the amount of liquid per unit time to be supplied into the insertion tube is made smaller than in the subsequent step.

5. The method for collecting underwater resources according to any of the claim 1 to 4,

the liquid is ejected from an ejection nozzle provided at a tip end portion of the stirring blade toward an inner peripheral surface of the insertion tube obliquely forward with respect to a rotation direction of the stirring blade.

6. The method for collecting underwater resources according to any of the claim 1 to 5,

the liquid is discharged from a discharge nozzle provided to the rotary shaft toward the surface of the stirring blade.

7. The method for collecting underwater resources according to claim 1 to 6,

the deepest penetration position of the stirring blade is set to a predetermined distance upward from the lower end of the insertion pipe, and the lower end opening of the insertion pipe is maintained in a state of being blocked by soil of the underwater crust, so that the soil in a slurry state is prevented from flowing out of the insertion pipe through the lower end opening.

8. The method for collecting underwater resources according to claim 7,

the predetermined distance is set based on the strength of the underwater crust and the pressure of the inside of the insertion pipe inserted into the underwater crust.

9. The method for collecting underwater resources according to claim 8,

the strength is obtained in advance before the insertion pipe is inserted into the underwater crust.

10. A method for collecting underwater resources as claimed in claim 8 or 9,

the strength is obtained by a strength sensor when the insertion pipe is inserted into the underwater crust.

11. The method for collecting underwater resources according to any of the claim 8 to 10,

The pressure is calculated and obtained in advance before the insertion pipe is inserted into the underwater crust.

12. The method for collecting underwater resources according to any of the claim 8 to 11,

the pressure is obtained by a pressure sensor after the insertion pipe is inserted into the underwater crust.