Gas extraction device applying hydraulic fracturing mode

Abstract

The invention relates to the technical field of gas extraction, in particular to a gas extraction device applying a hydraulic fracturing mode. Comprising an extraction system, and the extraction system comprises an extraction pipeline and a plurality of extraction pumps; the number of the negative pressure pipelines is the same as that of the extraction pumps, the negative pressure pipelines are communicated with the extraction pipelines, the negative pressure pipelines are communicated with the adjacent extraction pumps through pipelines, the inner walls of the negative pressure pipelines are provided with extraction channels, and the extraction channels are communicated with the positions, away from the adjacent extraction pumps, in the adjacent negative pressure pipelines; and the extraction channel is used for extracting gas and preferentially extracting the gas far away from the extraction pump. According to the method, the gas away from the extraction pump is extracted preferentially through the extraction channel, so that the deeper the gas channel is, the maximum extraction pressure is achieved, the residual quantity of the gas in the deeper position of the gas channel is reduced, the gas extraction efficiency is improved, meanwhile, the risk of gas explosion is reduced, and then the safety of gas extraction is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of gas extraction, and in particular to a gas extraction device using a hydraulic fracturing method. Background Art

[0002] Hydraulic fracturing technology is a method of using high-pressure water jets to form cracks in coal seams. These cracks can enhance the permeability of rock formations, thereby promoting the flow of gas, so as to facilitate the subsequent extraction of gas. A gas extraction device is a device that extracts gas from rock formations. The gas extraction device is generally composed of an extraction pump and a pipeline system. The existing extraction method is generally: first, a gas channel is drilled using a drilling device, and then several cracks are formed in the rock formation near the gas channel through hydraulic fracturing, and then the gas extraction device is used to extract the gas from the rock formation. The pipeline system extracts gas from various cracks simultaneously. Generally speaking, the deeper the pipeline system is laid, the lower the extraction pressure will be at a deeper level. However, the gas pressure deep in the rock formation will increase instead. The above-mentioned extraction method will result in high gas content in the deeper parts of the gas channel and insufficient extraction intensity, while low gas content in the shallower parts of the gas channel and greater extraction intensity. This will make it difficult to extract gas in the deeper parts of the gas channel, resulting in low gas extraction efficiency. In addition, excessive gas residue deep in the gas channel will increase the risk of gas explosion, posing a threat to the safety of personnel in the mine. Summary of the invention

[0003] In order to overcome the shortcomings pointed out in the above background technology, the present invention provides a gas extraction device using a hydraulic fracturing method.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solution: a gas extraction device using hydraulic fracturing, comprising:

[0005] A drainage system, the drainage system comprising a drainage pipeline and a plurality of drainage pumps;

[0006] Negative pressure pipelines, the number of which is the same as the number of the extraction pumps, are connected to the extraction pipeline. The negative pressure pipeline is connected to the adjacent extraction pump through a pipeline. The inner wall of the negative pressure pipeline is provided with an extraction channel. The extraction channel is connected to a position in the adjacent negative pressure pipeline far away from the adjacent extraction pump. The extraction channel is used to extract gas, and preferentially extracts gas far away from the extraction pump.

[0007] Preferably, the extraction channel is located at the lower part of the adjacent negative pressure pipeline.

[0008] Preferably, the negative pressure pipe is provided with a plurality of guide grooves for providing storage space for impurities falling from the upper side of the negative pressure pipe.

[0009] As a preference, it also includes:

[0010] The number of electrically controlled telescopic rods is the same as the number of the negative pressure pipes, and they are fixedly connected to the adjacent negative pressure pipes. The telescopic ends of the electrically controlled telescopic rods are fixedly connected to connecting rods that penetrate into the adjacent negative pressure pipes.

[0011] There are a plurality of sliding rings fixedly connected to the adjacent connecting rods, and the sliding rings are slidingly connected to the adjacent negative pressure pipes.

[0012] Preferably, the sliding ring is located between two adjacent guide grooves.

[0013] As a preference, it also includes:

[0014] Rotating rings, the number of which is the same as that of the sliding rings, are rotatably connected to the adjacent negative pressure pipes, a limiting groove is provided inside the rotating ring, and the rotating ring is provided with an air extraction hole that communicates and cooperates with the adjacent extraction channel;

[0015] The limit pins, the number of which is the same as the number of the rotating rings, are fixedly connected to the adjacent sliding rings, and the limit pins are limitedly matched with the adjacent limit grooves.

[0016] Preferably, the angle formed between the two sides of the air extraction hole and the axis of the adjacent rotating ring is α, and the relative rotation angle between two adjacent rotating rings is β, α=β, so that two adjacent air extraction holes are staggered.

[0017] As a preference, it also includes:

[0018] The first shell has the same number as the number of the rotating rings and is slidably connected to the adjacent negative pressure pipe. The first shell is provided with an air inlet and a flow hole. The air inlet and the adjacent flow hole are both connected and matched with the adjacent extraction channel.

[0019] The sliding rods, the number of which is the same as the number of the first shells, are fixedly connected to the adjacent first shells.

[0020] As a preference, it also includes:

[0021] The second shells, the number of which is the same as that of the first shells, are fixedly connected in the adjacent negative pressure pipes, the sliding rod is slidably connected to the adjacent second shells, an elastic member is fixedly connected between the sliding rod and the adjacent second shells, the second shells are provided with exhaust holes, the exhaust holes are communicated and cooperated with the adjacent air inlet holes, and the exhaust holes are communicated with the adjacent negative pressure pipes.

[0022] As a preference, it also includes:

[0023] The limit rods, the number of which is the same as that of the first shells, are slidably connected to the adjacent first shells, the limit rods are limitedly matched with the adjacent negative pressure pipes, the limit rods are fixedly connected with a first magnet, and the first shells are fixedly connected with a second magnet that is magnetically matched with the adjacent first magnet.

[0024] The advantages and positive effects of the present invention compared with the prior art are as follows: 1. The present invention preferentially extracts gas far away from the extraction pump through the extraction channel, so that the deeper the gas channel is, the greater the extraction pressure is, and the amount of gas residue in the deep gas channel is reduced, thereby improving the gas extraction efficiency and reducing the risk of gas explosion, thereby ensuring the safety of gas extraction;

[0025] 2. Push impurities into the guide groove through the sliding ring to collect impurities, prevent coal blocks and coal powder from moving and blocking rock cracks after falling off, thereby blocking gas discharge and affecting gas extraction efficiency;

[0026] 3. By rotating the rotating ring, different gas extraction holes are connected to the extraction channel in sequence, and the gas in several rock formation cracks is extracted separately in sequence, thereby increasing the local extraction intensity and reducing the gas residue in the local area to ensure the safety of gas extraction;

[0027] 4. The air inlet and the flow hole move upward by the upward movement of the first shell. When the gas pressure at a crack in the gas channel is too high, the air inlet moves upward to be connected with the exhaust hole, so that part of the gas does not need to enter the extraction channel, but directly enters the negative pressure pipeline through the exhaust hole, and directly extracts the gas in the crack, thereby increasing the extraction pressure of the crack and reducing the residual gas at the crack, thereby ensuring the safety of gas extraction. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the three-dimensional structure of the present invention;

[0029] Figure 2 It is a three-dimensional structural cross-sectional view of the negative pressure pipeline of the present invention;

[0030] Figure 3 It is a schematic diagram of the three-dimensional structure of the extraction channel of the present invention;

[0031] Figure 4 It is a schematic diagram of the three-dimensional structure of the guide groove of the present invention;

[0032] Figure 5 It is a schematic diagram of the three-dimensional structure of the connecting rod of the present invention;

[0033] Figure 6 It is a three-dimensional structural cross-sectional view of the rotating ring of the present invention;

[0034] Figure 7It is a schematic diagram of the three-dimensional structure of the first shell and the second shell of the present invention;

[0035] Figure 8 It is a schematic diagram of the three-dimensional structure of the air extraction hole of the present invention;

[0036] Fig. 9 It is a three-dimensional structural sectional view of the first shell, the second shell and the limiting rod of the present invention.

[0037] Names and serial numbers of parts in the figure: 1-extraction system, 101-extraction pipeline, 102-extraction pump, 2-negative pressure pipeline, 201-extraction channel, 3-guide groove, 4-electrically controlled telescopic rod, 401-connecting rod, 402-sliding ring, 5-rotating ring, 501-limiting groove, 502-limiting pin, 503-extraction hole, 6-first shell, 601-air inlet, 602-circulation hole, 603-sliding rod, 7-second shell, 701-exhaust hole, 8-limiting rod, 801-first magnet, 802-second magnet. DETAILED DESCRIPTION

[0038] The present invention will be further described below in conjunction with the embodiments shown in the accompanying drawings.

[0039] In order to solve the problem that the gas content in the deep gas channel is high but the extraction force is insufficient, and the gas content in the shallow gas channel is low but the extraction force is large, the present invention proposes a gas extraction device using hydraulic fracturing, such as Figure 1-Figure 3 As shown, it includes: an extraction system 1, the outside of the extraction system 1 is provided with a control terminal not shown in the figure, the extraction system 1 includes an extraction pipeline 101 and a plurality of extraction pumps 102 electrically connected to the control terminal; negative pressure pipelines 2, the number of which is the same as the number of the extraction pumps 102, connected to the extraction pipeline 101, the negative pressure pipeline 2 is connected to the adjacent extraction pumps 102 through the pipeline, the negative pressure pipeline 2 is inserted into the gas channel of the coal mine tunnel when in use, the negative pressure pipeline 2 is a stainless steel pipe, and the surface of the negative pressure pipeline 2 is coated with an epoxy coating to ensure the support strength and corrosion resistance of the negative pressure pipeline 2, the inner wall of the negative pressure pipeline 2 is provided with an extraction channel 201, the extraction channel 2 01 is located at the lower part of the adjacent negative pressure pipe 2 to prevent impurities on the upper side of the negative pressure pipe 2 from falling into the adjacent extraction channel 201, thereby preventing coal ash from clogging the extraction channel 201, causing the negative pressure pipe 2 to be blocked, and further affecting the extraction intensity of the negative pressure pipe 2 for gas, and affecting the gas extraction efficiency. The right end of the extraction channel 201 is connected to the right end of the adjacent negative pressure pipe 2. The extraction channel 201 is used to extract gas, and gives priority to extracting gas away from the extraction pump 102, so that the extraction pressure at the deepest part of the gas channel is the largest, reducing the amount of gas residue deep in the gas channel, thereby reducing the risk of gas explosion, and thus ensuring the safety of gas extraction.

[0040] like Figure 4As shown, the negative pressure pipe 2 is provided with a plurality of guide grooves 3 for providing storage space for impurities dropped from the upper side of the negative pressure pipe 2. At the hydraulic fracturing site, the structural integrity of the rock formation is damaged, which will cause the structural support force at that site to be weakened, and easily cause coal blocks and coal powder in local areas to fall off. The fallen structures are collected through the guide grooves 3 to prevent the coal blocks and coal powder from moving and clogging the cracks in the rock formation after falling off, thereby causing the discharge of gas to be blocked, thereby affecting the gas extraction efficiency.

[0041] like Figure 2-Figure 5 As shown, it also includes: electrically controlled telescopic rods 4, the number of which is the same as the number of negative pressure pipes 2, which are fixedly connected to adjacent negative pressure pipes 2, the electrically controlled telescopic rods 4 are electrically connected to the control terminal, the telescopic ends of the electrically controlled telescopic rods 4 are fixedly connected to connecting rods 401 that penetrate into the adjacent negative pressure pipes 2, and the movement form of the telescopic ends on the electrically controlled telescopic rods 4 is cyclic reciprocating telescopic movement, which is used to drive the adjacent connecting rods 401 to move back and forth left and right; a plurality of sliding rings 402 are fixedly connected to adjacent connecting rods 401, the sliding rings 402 are slidably connected to the adjacent negative pressure pipes 2, and the sliding rings 402 are located between two adjacent guide grooves 3, which are used to push impurities into the guide grooves 3, thereby collecting the impurities and preventing the coal blocks and coal powder from moving and blocking the rock formation cracks after falling off, thereby causing the gas discharge to be blocked, thereby affecting the gas extraction efficiency.

[0042] The specific working principle is as follows: before extracting the gas, the operator processes the inside of the rock formation through hydraulic fracturing, and creates several cracks by injecting high-pressure fluid (usually water plus sand or other additives) into the underground rock formation, so that the gas can be discharged from the rock formation through the cracks. The operator then inserts the negative pressure pipe 2 and its upper parts into the rock formation to extract the gas discharged from the cracks in the rock formation.

[0043] When the operator needs to use the device to extract gas, the operator turns on the extraction pump 102 through the control terminal. The extraction pump 102 extracts the gas in the negative pressure pipe 2, so that negative pressure is formed in the negative pressure pipe 2. The gas in the extraction channel 201 flows into the negative pressure pipe 2. The extraction channel 201 extracts the gas in the rock fractures, so that the gas located on the right side of the extraction channel 201 is extracted first. The deeper the gas channel is, the greater the extraction pressure is, thereby preventing the extraction force in the deep part of the channel with more gas content from being less than that in the shallow part of the channel, thereby preventing the pressure in the deep part of the gas channel from being too high and posing a risk of explosion, posing a threat to the safety of personnel in the tunnel.

[0044] During the gas extraction process, the operator turns on the electric telescopic rod 4 through the control terminal. The telescopic end of the electric telescopic rod 4 drives several adjacent sliding rings 402 to move back and forth left and right through the connecting rod 401, pushing impurities into the guide grooves 3 on the left and right sides of the sliding ring 402 to collect the impurities, preventing the coal blocks and coal powder from falling off and moving to block the rock cracks, thereby blocking the gas discharge and affecting the gas extraction efficiency.

[0045] When it is necessary to stop using the device, the operator turns off the extraction pump 102 and the electric telescopic rod 4 through the control terminal, and inspects the device to facilitate the next use of the device.

[0046] In order to solve the problem that simultaneous extraction of gas from various rock fractures in the gas channel will lead to insufficient overall extraction pressure and uneven extraction pressure distribution, such as Figure 2 , Figure 3 and Figure 6 As shown, the present invention also includes: rotating rings 5, the number of which is the same as the number of sliding rings 402, which are rotatably connected to the adjacent negative pressure pipeline 2, and a limiting groove 501 is arranged in the rotating ring 5, and the rotating ring 5 is provided with an exhaust hole 503 which is connected and matched with the adjacent extraction channel 201; limiting pins 502, the number of which is the same as the number of rotating rings 5, which are fixed to the adjacent sliding rings 402, and the limiting pins 502 are limited and matched with the adjacent limiting grooves 501, and the angle formed between the two sides of the exhaust hole 503 and the axis of the adjacent rotating ring 5 is α, and the relative rotation angle between the two adjacent rotating rings 5 ​​is β, α=β, so that the two adjacent exhaust holes 503 are staggered, which is used to make different exhaust holes 503 alternately connected with the adjacent extraction channel 201 in turn, thereby increasing the extraction pressure of the extraction channel 201 on the local position in the gas channel, and avoiding that when multiple positions in the gas channel are extracted at the same time, the extraction pressure of the extraction channel 201 is insufficient, thereby affecting the extraction efficiency.

[0047] The specific working principle is as follows: in the process of the sliding ring 402 moving back and forth, the sliding ring 402 drives the limit pin 502 to move back and forth, and the limit pin 502 moves back and forth along the limit groove 501, so that the rotating ring 5 rotates back and forth, and the rotating ring 5 drives the exhaust holes 503 thereon to rotate, and the positions of different exhaust holes 503 on adjacent rotating rings 5 ​​are different, so that different exhaust holes 503 are alternately connected to the extraction channel 201 during the rotation process, and the gas in several rock formation cracks is extracted separately in turn, thereby increasing the local extraction force, thereby preventing the insufficient extraction force in some areas from causing a large amount of gas residue for a long time, which in turn affects the safety of the mine.

[0048] In this embodiment, the operator can control the extension amount and extension speed of the telescopic end of the electric-controlled telescopic rod 4 through the control terminal. For example, the extension speed of the telescopic end of the electric-controlled telescopic rod 4 is gradually slowed down when it is extended, so that the connection time between the right-side exhaust hole 503 and the extraction channel 201 is increased to control the extraction time of different areas in the gas channel.

[0049] To achieve self-regulation of gas extraction intensity, Figure 7-Figure 9 As shown, the present invention also includes: a first shell 6, the number of which is the same as the number of the rotating rings 5, which is slidably connected to the adjacent negative pressure pipe 2, the first shell 6 is provided with an air inlet 601 and a flow hole 602, the length of the air inlet 601 is greater than the length of the flow hole 602, and the length of the air inlet 601 is greater than the diameter of the extraction channel 201. When the gas pressure at a certain point in the rock formation fracture increases, the first shell 6 moves upward due to the gas pressure, causing the flow hole 602 to lose the connection with the adjacent extraction channel 201, the air inlet 601 can still be connected with the adjacent extraction channel 201, and the air inlet 601 moves upward to directly connect with the adjacent negative pressure pipe 2, and the gas at this point is directly extracted through the negative pressure pipe 2, thereby increasing the gas extraction intensity at the place with higher pressure to prevent the risk of explosion due to excessive gas pressure, and the air inlet 601 and the adjacent flow hole 602 are both connected and coordinated with the adjacent extraction channel 201; sliding rods 603, the number of which is the same as the number of the first shell 6, are fixedly connected to the adjacent first shell 6.

[0050] like Figure 7-Figure 9 As shown, it also includes: a second shell 7, the number of which is the same as that of the first shell 6, fixed in the adjacent negative pressure pipeline 2, a sliding rod 603 is slidably connected to the adjacent second shell 7, an elastic member is fixed between the sliding rod 603 and the adjacent second shell 7, wherein the elastic member is a tension spring, the greater the pressure on the first shell 6, the greater the distance the adjacent sliding rod 603 is driven to move upward, so that the stretching length of the elastic member is greater, and after the flow hole 602 loses communication with the adjacent extraction channel 201, the elastic member is stretched to the limit, and the second shell 7 is provided with an exhaust hole 701, the exhaust hole 701 is communicated and cooperated with the adjacent air inlet hole 601, the exhaust hole 701 is communicated with the adjacent negative pressure pipeline 2, after the first shell 6 moves upward, and the air inlet hole 601 is still connected to the adjacent extraction channel 201, the negative pressure pipeline 2 extracts the gas in the adjacent air inlet hole 601 through the adjacent exhaust hole 701.

[0051] like Figure 8 and Fig. 9As shown, it also includes: a limit rod 8, the number of which is the same as the number of the first shell 6, which is slidably connected to the adjacent first shell 6, and a protrusion is set on the left side of the limit rod 8 for hooking the negative pressure pipe 2. The limit rod 8 and the adjacent negative pressure pipe 2 are limited and cooperated. After the flow hole 602 loses communication with the adjacent extraction channel 201, the first shell 6 and the adjacent limit rod 8 cooperate to block the adjacent extraction channel 201, so that the extraction channel 201 is divided into two left and right parts, temporarily losing the extraction of the left half of the extraction channel 201, and increasing the extraction force of the right half of the extraction channel 201. The limit rod 8 is fixedly connected to the first magnet 801, and the first shell 6 is fixedly connected to the second magnet 802 which is magnetically matched with the adjacent first magnet 801, which is used to fix the limit rod 8 to prevent the limit rod 8 from sliding downward.

[0052] The specific working principle is as follows: In this embodiment, the gas at the cracks in the gas channel enters the extraction channel 201 through the air inlet 601.

[0053] When the gas pressure at a crack in the gas channel is too high, causing the first shell 6 to move upward, the first shell 6 drives the sliding rod 603 to move upward, and the elastic part of the sliding rod 603 stretches. At the same time, the air inlet 601 moves upward to communicate with the exhaust hole 701, so that part of the gas does not need to enter the extraction channel 201, but directly enters the negative pressure pipeline 2 through the exhaust hole 701, directly extracting the gas in the crack, increasing the extraction pressure of the crack, and preventing the risk of explosion due to excessive gas pressure. The pressure in the channel continues to increase, causing the first shell 6 to continuously move upward, and the flow hole 602 gradually moves to lose communication with the extraction channel 201. The first shell 6 drives the second magnet 802 to move upward, and the second magnet 802 loses contact with the first magnet 801. The extraction channel 201 is divided into two left and right parts by the first shell 6 and the limit rod 8. The extraction channel 201 no longer extracts gas from the left part, so that the extraction force at this location is further increased, reducing the gas residue at this location, thereby ensuring the safety of gas extraction.

[0054] In summary, the invention includes but is not limited to the above embodiments. Any equivalent substitution or partial improvement made under the spirit and principle of the invention shall be deemed to be within the protection scope of the invention.

Claims

1. A gas extraction device using hydraulic fracturing, characterized in that: include: A drainage system (1), the drainage system (1) comprising a drainage pipeline (101) and a plurality of drainage pumps (102); a negative pressure pipeline (2), the number of which is the same as the number of the drainage pumps (102), which is connected to the drainage pipeline (101); the negative pressure pipeline (2) is connected to an adjacent drainage pump (102) through a pipeline; an drainage channel (201) is provided on the inner wall of the negative pressure pipeline (2); the drainage channel (201) is connected to a position in an adjacent negative pressure pipeline (2) far from the adjacent drainage pump (102); the drainage channel (201) is used to drain gas, and preferentially drains gas far from the drainage pump (102).

2. A gas extraction device using hydraulic fracturing according to claim 1, characterized in that: The extraction channel (201) is located at the lower portion of the adjacent negative pressure pipeline (2).

3. A gas extraction device using hydraulic fracturing according to claim 2, characterized in that: The negative pressure pipe (2) is provided with a plurality of guide grooves (3) for providing storage space for impurities dropped from the upper side of the negative pressure pipe (2).

4. A gas extraction device using hydraulic fracturing according to claim 3, characterized in that: include: The number of electrically controlled telescopic rods (4) is the same as the number of the negative pressure pipes (2), and they are fixedly connected to the adjacent negative pressure pipes (2); the telescopic ends of the electrically controlled telescopic rods (4) are fixedly connected to connecting rods (401) that penetrate into the adjacent negative pressure pipes (2); There are a plurality of sliding rings (402) which are fixedly connected to the adjacent connecting rods (401), and the sliding rings (402) are slidingly connected to the adjacent negative pressure pipes (2).

5. A gas extraction device using hydraulic fracturing according to claim 4, characterized in that: The sliding ring (402) is located between two adjacent guide grooves (3).

6. A gas extraction device using hydraulic fracturing according to claim 5, characterized in that: include: Rotating rings (5), the number of which is the same as the number of the sliding rings (402), and are rotatably connected to the adjacent negative pressure pipe (2), wherein a limiting groove (501) is provided in the rotating ring (5), and the rotating ring (5) is provided with an air extraction hole (503) that is in communication with the adjacent extraction channel (201); The number of the limiting pins (502) is the same as the number of the rotating rings (5), and is fixedly connected to the adjacent sliding rings (402). The limiting pins (502) are in limiting cooperation with the adjacent limiting grooves (501).

7. A gas extraction device using hydraulic fracturing according to claim 6, characterized in that: The angle formed between the two sides of the air extraction hole (503) and the axis of the adjacent rotating ring (5) is α, and the relative rotation angle between the two adjacent rotating rings (5) is β, α=β, so that the two adjacent air extraction holes (503) are staggered.

8. A gas extraction device using hydraulic fracturing according to claim 6, characterized in that: include: The first shell (6) has the same number as the rotating ring (5), and is slidably connected to the adjacent negative pressure pipe (2). The first shell (6) is provided with an air inlet (601) and a flow hole (602). The air inlet (601) and the adjacent flow hole (602) are both connected and matched with the adjacent extraction channel (201); The sliding rods (603) are the same in number as the first shells (6) and are fixedly connected to the adjacent first shells (6).

9. A gas extraction device using hydraulic fracturing according to claim 8, characterized in that: include: The second shell (7) has the same number as the first shell (6) and is fixedly connected in the adjacent negative pressure pipe (2). The sliding rod (603) is slidably connected to the adjacent second shell (7). An elastic member is fixedly connected between the sliding rod (603) and the adjacent second shell (7). The second shell (7) is provided with an exhaust hole (701). The exhaust hole (701) is communicated and matched with the adjacent air inlet hole (601). The exhaust hole (701) is communicated with the adjacent negative pressure pipe (2).

10. A gas extraction device using hydraulic fracturing according to claim 9, characterized in that: include: The limiting rod (8) is the same in number as the first shell (6), and is slidably connected to the adjacent first shell (6). The limiting rod (8) is limitedly matched with the adjacent negative pressure pipe (2). The limiting rod (8) is fixedly connected with a first magnet (801), and the first shell (6) is fixedly connected with a second magnet (802) that is magnetically matched with the adjacent first magnet (801).

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