Coal-series gas multi-layer co-mining device

Abstract

The invention discloses a coal-series gas multi-layer co-mining device, and relates to the technical field of coal-series gas mining, the coal-series gas multi-layer co-mining device comprises an extraction pipe and a sealing assembly, the extraction pipe is arranged in an extraction hole, a rock layer and a coal-series gas layer are arranged around the extraction hole, a space, flush with the coal-series gas layer, in the extraction hole is an extraction space, and the sealing assembly is arranged in the extraction hole. Sealing assemblies are fixed outside the pipe wall of the extraction pipe, the space between every two vertically adjacent sealing assemblies corresponds to the extraction space of the coal series gas layer, each sealing assembly comprises a sealing ring and an annular bag, and the annular bags are fixed to the peripheral sides of the sealing rings. The section, exposed in the extraction space, of each extraction pipe is provided with a valve body for controlling extraction coal gas. According to the method, the technical problem of low commingling production capacity caused by interlayer interference during multi-layer co-production of coal-series gas can be well solved, and the extraction efficiency of multi-layer co-production can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of coal-measure gas mining, and more specifically to a coal-measure gas multi-layer mining device. Background Art

[0002] Coal-bearing gas refers to all natural gas, mainly methane, generated during the coal-forming process of the source rock parent material in the entire coal-bearing strata. It can be divided into coalbed methane, shale gas and tight sandstone gas according to its occurrence lithology. In some areas with multiple coal-bearing gas layers, there are often characteristics such as many coal-bearing gas layers, small interlayer spacing and high gas content. Therefore, multi-layer co-mining technology is often used for targeted extraction. However, multi-layer co-mining will cause inter-layer interference, resulting in low combined production capacity.

[0003] The prior art proposes a Chinese invention patent document with a publication number of CN116696291A and a publication date of September 5, 2023. The patent document discloses a coal-measure gas multi-layer combined production device, method and system, the device comprising a plurality of production components respectively arranged at each target reservoir underground, the production component being arranged in the perforation section of the target reservoir; the production component separates an independent production area corresponding to the perforation section in the underground oil-casing annulus area and a flow channel that maintains continuous connection with the oil-casing annulus area, and the independent production area has a production outlet that is connected to the oil-casing annulus area and is unidirectional. Based on the technical solution of the present invention, it is possible to avoid interference between different reservoirs in coal-measure vertical wells, avoid losing the meaning of combined production due to interlayer interference, provide precise control for gas well extraction, and provide accurate production data in real time, providing reliable technical means for refined drainage and production management of coal-measure gas vertical wells.

[0004] Although the above technology can avoid interference between different reservoirs during actual use, each extraction space is an independent closed space, and the coal-bearing gas layers cannot communicate with each other. When multi-layer combined extraction is carried out, the extraction efficiency is not high. Summary of the invention

[0005] In order to solve the above technical problems, the present invention proposes a coal-bearing gas multi-layer co-mining device, which can effectively solve the technical problem of inter-layer interference in multi-layer co-mining, resulting in low co-mining capacity, and can improve the extraction efficiency of multi-layer co-mining.

[0006] The present invention is achieved by adopting the following technical solutions: A coal-bearing gas multi-layer co-extraction device includes an extraction pipe and a sealing component. The extraction pipe is placed in an extraction hole. The extraction hole is surrounded by a rock layer and a coal-bearing gas layer. A sealing component is fixed to the outside of the pipe wall of the extraction pipe. The sealing component is arranged at the intersection of the rock layer and the coal-bearing gas layer. The space between two sealing components that are adjacent to each other in the upper and lower directions corresponding to the coal-bearing gas layer is the extraction space. The sealing component includes a sealing ring and an annular capsule. The outer peripheral side of the sealing ring is fixed with an annular capsule. A valve body for controlling the extraction of coal-bearing gas is provided in a section of the extraction pipe exposed to the extraction space. During extraction, the expansion of the corresponding annular capsule is utilized to form an extraction space between the two sealing components. The extraction space is simultaneously constructed for two adjacently distributed coal-bearing gas layers so as to extract synchronously. The other annular capsules are in a suffocated state. During extraction by the extraction pipe, the coal-bearing gas layers are processed sequentially from top to bottom.

[0007] A gas equalization component is arranged between the two sealing components corresponding to each extraction space, and the gas equalization component includes a guide sleeve, an air inlet, an air outlet and a connecting pipe. The guide sleeve is fixed between two adjacent sealing components, and a plurality of air inlets are provided on the outer surface of the guide sleeve. The air inlet is connected to the air outlet through a connecting pipe, and the air outlet is located on the inner surface of the guide sleeve. The gas equalization component can adjust the coal-bearing gas flow pressure entering the extraction pipe from the coal-bearing gas layer, and when two adjacently distributed coal-bearing gas layers are synchronously extracted, the coal-bearing gas flow pressure of the relatively lower coal-bearing gas layer is slightly greater than the coal-bearing gas flow pressure of the upper coal-bearing gas layer.

[0008] The outer diameter of the guide sleeve is smaller than the diameter of the extraction hole, and the inner diameter is larger than the diameter of the extraction pipe.

[0009] A plurality of baffle components are arranged on the connecting pipe; the baffle component comprises a driving rod, a mounting seat, a return spring and a baffle plate, the mounting seat is fixed to the outer wall of the connecting pipe, a through hole is arranged at the mounting seat and the connecting pipe position corresponding to the mounting seat, the driving rod extends into the connecting pipe, a limited end is arranged at one end of the driving rod, a return spring is arranged between the limited end and the mounting seat, the driving rod is a through pipe structure, and a baffle plate is connected to one side of the driving rod located in the connecting pipe, and when the baffle plate is filled with liquid, the baffle plate is in an arc state.

[0010] The driving rod is connected with an external hydraulic control pipe.

[0011] The driving rod is provided with magnets distributed in an array along its axial direction.

[0012] An electromagnetic seat is fixed on the mounting seat, and an electromagnet corresponding to the magnet is fixed on the electromagnetic seat.

[0013] An auxiliary pipe is also provided in the extraction pipe. An air hole is opened on the auxiliary pipe. Sealing rings are provided on the upper and lower sides of the air hole so that the auxiliary pipe and the extraction pipe form a separate annulus at the air hole.

[0014] A sealing head is arranged on the top of the extraction hole, and a through hole for the extraction pipe to pass through is arranged on the sealing head.

[0015] An interception net is embedded on the air inlet.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. During extraction, the present invention utilizes the expansion of the corresponding annular sacs to simultaneously construct extraction spaces for two adjacent coal-bearing gas layers for synchronous extraction, while the other annular sacs are in a shrunk state. This can improve the extraction efficiency and facilitate mutual communication between other coal-bearing gas layers, thereby allowing the coal-bearing gas in the high-permeability coal-bearing gas layer to enter the low-permeability coal-bearing gas layer for fracture-assisted transformation, thereby improving subsequent extraction efficiency.

[0017] 2. In the present invention, a gas equalizing component is arranged between the two sealing rings corresponding to each of the coal-bearing gas layers. The gas equalizing component can adjust the coal-bearing gas flow pressure entering the extraction pipe from the coal-bearing gas layer, and make the coal-bearing gas flow pressure of the relatively lower coal-bearing gas layer slightly greater than the coal-bearing gas flow pressure of the upper coal-bearing gas layer when two adjacent coal-bearing gas layers are extracted synchronously, so as to minimize the disturbance between the two coal-bearing gas layers.

[0018] 3. In the present invention, the damping between the mounting seat and the driving rod is adjusted by magnetic force to position the driving rod, thereby improving the accuracy of flow resistance and further reducing the disturbance between the two coal-bearing gas layers.

[0019] 4. The present invention is also provided with an auxiliary pipe to inject carbon dioxide into each coal-bearing gas layer to displace the coal-bearing gas adsorbed in the rock, thereby further improving the extraction efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, wherein: Figure 1 It is a structural schematic diagram of a coal-measure gas multi-layer co-mining device; Figure 2 It is a structural schematic diagram of a gas homogenizing component in a coal-measure gas multi-layer co-mining device; Figure 3 It is a structural schematic diagram of a flow-blocking component in a coal-measure gas multi-layer co-mining device; Figure 4 It is a structural schematic diagram of an auxiliary pipe in a coal-measure gas multi-layer co-mining device; Markings in the figure: 1. extraction hole, 2. coal-bearing gas layer, 3. rock layer, 4. extraction pipe, 5. head, 6. sealing ring, 7. ring bag, 8. auxiliary pipe, 9. gas equalization component, 10. valve body, 81. air hole, 82. sealing ring, 91. guide sleeve, 92. air inlet, 93. air outlet, 94. connecting pipe, 95. baffle assembly, 951. driving rod, 952. mounting seat, 953. reset spring, 954. electromagnetic seat, 955. magnet, 956. baffle. DETAILED DESCRIPTION

[0021] Example 1 As a preferred embodiment of the present invention, a coal-bearing gas multi-layer co-mining device includes an extraction pipe 4 and a sealing assembly, wherein the extraction pipe 4 is placed in an extraction hole 1, and the extraction hole 1 is surrounded by a rock layer 3 and a coal-bearing gas layer 2. A sealing assembly is fixed to the outside of the pipe wall of the extraction pipe 4, and the sealing assembly is arranged at the intersection of the rock layer 3 and the coal-bearing gas layer 2. The space between two sealing assemblies that are adjacent to each other in the upper and lower directions corresponding to the coal-bearing gas layer 2 is the extraction space, and the sealing assembly includes a sealing ring 6 and an annular capsule 7, and an annular capsule 7 is fixed to the outer peripheral side of the sealing ring 6. A valve body 10 for controlling the extraction of coal-bearing gas is provided in a section of the extraction pipe 4 exposed to the extraction space. During extraction, the corresponding annular capsule 7 is expanded to form an extraction space in the space between the two sealing assemblies, and the extraction space is simultaneously constructed for two adjacently distributed coal-bearing gas layers 2 for synchronous extraction, and the other annular capsules 7 are in a suffocated state.

[0022] Example 2 As another preferred embodiment of the present invention, based on Example 1, this embodiment is provided with a gas equalization component 9 between two sealing components corresponding to each extraction space, and the gas equalization component 9 includes a guide sleeve 91, an air inlet 92, an air outlet 93 and a connecting pipe 94. The guide sleeve 91 is fixed between two adjacent sealing components, and a plurality of air inlets 92 are provided on the outer surface of the guide sleeve 91. The air inlet 92 is connected to the air outlet 93 through the connecting pipe 94, and the air outlet 93 is located on the inner surface of the guide sleeve 91. The outer diameter of the guide sleeve 91 is smaller than the diameter of the extraction hole 1, and the inner diameter is larger than the diameter of the extraction pipe 4.

[0023] A plurality of baffle components 95 are arranged on the connecting pipe 94; the baffle component 95 includes a driving rod 951, a mounting seat 952, a return spring 953 and a baffle plate 956, wherein the mounting seat 952 is fixed to one side of the connecting pipe 94, and a driving rod 951 is slidably connected through the mounting seat 952, and the driving rod 951 also seals and slides into the connecting pipe 94, and one side of the driving rod 951 is connected to the mounting seat 952 by a return spring 953, and the driving rod 951 is a through-tube structure, and one side of the driving rod 951 located in the connecting pipe 94 is connected to a baffle plate 956, and the baffle plate 956 is made of a deformable and non-retractable material, and when the baffle plate 956 is filled with liquid, the baffle plate 956 is in an arc state.

[0024] The gas equalization component 9 can adjust the coal-bearing gas flow pressure from the coal-bearing gas layer 2 into the extraction pipe 4, and when two adjacently distributed coal-bearing gas layers 2 are synchronously extracted, the coal-bearing gas flow pressure of the relatively lower coal-bearing gas layer 2 is slightly greater than the coal-bearing gas flow pressure of the upper coal-bearing gas layer 2. Thereby, the disturbance between the two coal-bearing gas layers 2 is minimized. It should be explained that the baffle 956 is a deformable and non-retractable material. When the baffle 956 is filled with liquid, the baffle 956 is in an arc state, so that the loading of the baffle 956 can be realized. The drive rod 951 can be connected to an external hydraulic control pipe to control the liquid pressure in the drive rod 951. In this embodiment, the flow pressure can be controlled by loading different numbers of baffles 956. The baffle 956 can not only control the flow pressure, but also block the flow in a gentler way.

[0025] Example 3 As another preferred embodiment of the present invention, based on Example 2, this embodiment is provided with magnets 955 distributed in an axial array on the driving rod 951, an electromagnetic seat 954 is fixed on the mounting seat 952, and a plurality of electromagnets 955 corresponding to the magnets 955 are fixed on the electromagnetic seat 954, and the electromagnets 955 can attract the magnets 955.

[0026] The magnetic force of the electromagnet 955 is adjustable. In practice, the damping between the mounting seat 952 and the driving rod 951 is adjusted by controlling the magnetic force of the electromagnet 955 , and the driving rod 951 can also be positioned.

[0027] Example 4 As the best embodiment of the present invention, the present invention includes an extraction pipe 4 and a sealing assembly, wherein the extraction pipe 4 is placed in an extraction hole 1, and the extraction hole 1 is surrounded by a rock layer 3 and a coal-bearing gas layer 2. A sealing assembly is fixed to the outside of the pipe wall of the extraction pipe 4, and the sealing assembly is arranged at the intersection of the rock layer 3 and the coal-bearing gas layer 2. The space between two sealing assemblies that are adjacent to each other in the upper and lower directions corresponding to the coal-bearing gas layer 2 is the extraction space, and the sealing assembly includes a sealing ring 6 and an annular capsule 7, and an annular capsule 7 is fixed to the outer peripheral side of the sealing ring 6. A valve body 10 for controlling the extraction of coal-bearing gas is provided in a section of the extraction pipe 4 exposed to the extraction space. During extraction, the corresponding annular capsule 7 is expanded to form an extraction space in the space between the two sealing assemblies, and the extraction space is simultaneously constructed for two adjacently distributed coal-bearing gas layers 2 for synchronous extraction, and the other annular capsules 7 are in a suffocated state. It should be explained that, in the present embodiment, two coal-bearing gas layers 2 are extracted each time, which can improve the extraction efficiency, and the two coal-bearing gas layers 2 are two adjacent coal-bearing gas layers 2. The two adjacent coal-bearing gas layers 2 here mean that there are no other coal-bearing gas layers 2 between the two coal-bearing gas layers 2, but there may be rock layers 3 and the like. Since two adjacent coal-bearing gas layers 2 are extracted each time, the other coal-bearing gas layers 2 may communicate with each other. Therefore, during extraction, the corresponding annular capsules 7 are used to expand to simultaneously construct extraction spaces for two adjacently distributed coal-bearing gas layers 2 for synchronous extraction, and the other annular capsules 7 are in a shrunk state, which facilitates the communication between the other coal-bearing gas layers 2. An air equalization component 9 is arranged between two sealing components corresponding to each extraction space, and the air equalization component 9 includes a guide sleeve 91, an air inlet 92, an air outlet 93 and a connecting pipe 94. The guide sleeve 91 is fixed between two adjacent sealing components, and a plurality of air inlets 92 are provided on the outer surface of the guide sleeve 91. The air inlet 92 is connected to the air outlet 93 through the connecting pipe 94, and the air outlet 93 is located on the inner surface of the guide sleeve 91. The outer diameter of the guide sleeve 91 is smaller than the diameter of the extraction hole 1, and the inner diameter is larger than the diameter of the extraction pipe 4.

[0028] The connecting pipe 94 is provided with a plurality of flow-blocking components 95; the flow-blocking components 95 include a driving rod 951, a mounting seat 952, a return spring 953 and a flow-blocking plate 956. The mounting seat 952 is fixed to the outer wall of the connecting pipe 94. The mounting seat 952 and the connecting pipe 94 position corresponding to the mounting seat 952 are provided with a through hole. The driving rod 951 extends into the connecting pipe 94. A limited end is provided at one end of the driving rod 951. A return spring 953 is provided between the limited end and the mounting seat 952. The driving rod 951 is a through-tube structure. The side of the driving rod 951 located in the connecting pipe 94 is connected with a flow-blocking plate 956. The driving rod 951 is connected to an external hydraulic control pipe. The flow-blocking plate 956 is a deformable and non-retractable material. When the flow-blocking plate 956 is filled with liquid, the flow-blocking plate 956 is in an arc state.

[0029] The gas equalization component 9 can adjust the coal-bearing gas flow pressure from the coal-bearing gas layer 2 into the extraction pipe 4, and when two adjacently distributed coal-bearing gas layers 2 are synchronously extracted, the coal-bearing gas flow pressure of the relatively lower coal-bearing gas layer 2 is slightly greater than the coal-bearing gas flow pressure of the upper coal-bearing gas layer 2. Thereby, the disturbance between the two coal-bearing gas layers 2 is minimized. It should be explained that the baffle 956 is a deformable and non-retractable material. When the baffle 956 is filled with liquid, the baffle 956 is in an arc state, so that the loading of the baffle 956 can be realized. The drive rod 951 can be connected to an external hydraulic control pipe to control the liquid pressure in the drive rod 951. In this embodiment, the flow pressure can be controlled by loading different numbers of baffles 956. The baffle 956 can not only control the flow pressure, but also block the flow in a gentler way.

[0030] The driving rod 951 is provided with magnets 955 distributed in an array along its axial direction, the mounting seat 952 is fixed with an electromagnetic seat 954, and the electromagnetic seat 954 is fixed with an electromagnet 955 corresponding to the magnet 955. The electromagnet 955 can attract the magnet 955. In this embodiment, the magnetic force of the electromagnet 955 is adjustable. During implementation, the damping between the mounting seat 952 and the driving rod 951 is adjusted by controlling the magnetic force of the electromagnet 955, and the driving rod 951 can also be positioned.

[0031] The extraction pipe 4 is also provided with an auxiliary pipe 8, which is provided with a gas hole 81, and sealing rings 82 are provided on the upper and lower sides of the gas hole 81, so that the auxiliary pipe 8 and the extraction pipe 4 form a separate annulus at the gas hole 81. Carbon dioxide can be injected into each coal-bearing gas layer 2 through the auxiliary pipe 8 to displace the coal-bearing gas adsorbed in the rock. At the initial stage of implementation, the first coal-bearing gas layer 2 and the second coal-bearing gas layer 2 are extracted first, at which time the annular capsules 7 corresponding to the first coal-bearing gas layer 2 and the second coal-bearing gas layer 2 expand for sealing, and the annular capsules 7 corresponding to the third coal-bearing gas layer 2 and the fourth coal-bearing gas layer 2 shrink, so that the third coal-bearing gas layer 2 and the fourth coal-bearing gas layer 2 communicate with each other. At the same time, the valve bodies 10 corresponding to the first coal-bearing gas layer 2 and the second coal-bearing gas layer 2 are opened, and the valve bodies 10 corresponding to the third coal-bearing gas layer 2 and the fourth coal-bearing gas layer 2 are closed; at this time, the annular capsule 7 corresponding to the fifth coal-bearing gas layer 2 expands and the valve body 10 corresponding to the fifth coal-bearing gas layer 2 is opened, and the auxiliary pipe 8 is lowered into the extraction pipe 4, and the sealing ring 82 is located at the valve body 10 corresponding to the fifth coal-bearing gas layer 2, to ensure that the gas provided by the auxiliary pipe 8 can enter the fifth coal-bearing gas layer 2 through the valve body 10 corresponding to the fifth coal-bearing gas layer 2 without affecting other coal-bearing gas layers 2.

[0032] A sealing head 5 is provided at the top of the extraction hole 1 , and a through hole for the extraction pipe 4 to pass through is provided on the sealing head 5 .

[0033] An interception net is embedded in the air inlet 92 .

[0034] In this embodiment, during extraction, the corresponding annular capsules 7 are used to expand to simultaneously construct extraction spaces for two adjacent coal-bearing gas layers 2 for synchronous extraction, while other annular capsules 7 are in a shrunk state, which can improve the extraction efficiency and facilitate mutual communication between other coal-bearing gas layers 2, thereby allowing the coal-bearing gas in the high-permeability coal-bearing gas layer 2 to enter the low-permeability coal-bearing gas layer 2 for fracture-assisted transformation, thereby improving subsequent extraction efficiency. In addition, a gas equalization component 9 is provided between the two sealing rings 6 corresponding to each of the coal-bearing gas layers 2, and the gas equalization component 9 can adjust the coal-bearing gas flow pressure from the coal-bearing gas layer 2 to the extraction pipe 4, and when two adjacent coal-bearing gas layers 2 are synchronously extracted, the coal-bearing gas flow pressure of the relatively lower coal-bearing gas layer 2 is slightly greater than the coal-bearing gas flow pressure of the upper coal-bearing gas layer 2, thereby minimizing the disturbance between the two coal-bearing gas layers 2. When the present invention uses the multi-layer co-mining technology to extract the coal-bearing gas layer 2 area, the disturbance between the coal-bearing gas layers 2 can be reduced and the extraction efficiency can be improved.

Claims

1. A coal-measure gas multi-layer co-mining device, characterized in that: The invention comprises an extraction pipe (4) and a sealing component, wherein the extraction pipe (4) is placed in an extraction hole (1), the extraction hole (1) is surrounded by a rock layer (3) and a coal-bearing gas layer (2), the space in the extraction hole (1) flush with the coal-bearing gas layer (2) is the extraction space, a sealing component is fixed to the outside of the pipe wall of the extraction pipe (4), the sealing component is arranged at the intersection of the rock layer (3) and the coal-bearing gas layer (2), the space between two upper and lower adjacent sealing components corresponds to the extraction space of the coal-bearing gas layer (2), the sealing component comprises a sealing ring (6) and an annular capsule (7), the outer peripheral side of the sealing ring (6) is fixed with the annular capsule (7), and a section of the extraction pipe (4) exposed to the extraction space is provided with a valve body (10) for controlling the extraction of coal-bearing gas.

2. A coal-based gas multi-layer co-mining device according to claim 1, characterized in that: An air equalization component (9) is arranged between two sealing components corresponding to each extraction space, and the air equalization component (9) comprises a flow guide sleeve (91), an air inlet (92), an air outlet (93) and a connecting pipe (94). The flow guide sleeve (91) is fixed between two adjacent sealing components, and a plurality of air inlets (92) are provided on the outer surface of the flow guide sleeve (91). The air inlet (92) is connected to the air outlet (93) through the connecting pipe (94), and the air outlet (93) is located on the inner surface of the flow guide sleeve (91).

3. A coal-based gas multi-layer co-mining device according to claim 2, characterized in that: The outer diameter of the guide sleeve (91) is smaller than the diameter of the extraction hole (1), and the inner diameter is larger than the diameter of the extraction tube (4).

4. A coal-based gas multi-layer co-mining device according to claim 2, characterized in that: A plurality of flow-blocking components (95) are arranged on the connecting tube (94); the flow-blocking components (95) comprise a driving rod (951), a mounting seat (952), a return spring (953) and a flow-blocking plate (956); the mounting seat (952) is fixed to the outer wall of the connecting tube (94); the mounting seat (952) and a through hole are arranged at a position of the connecting tube (94) corresponding to the mounting seat (952); the driving rod (951) extends into the connecting tube (94); a limit end is arranged at one end of the driving rod (951); a return spring (953) is arranged between the limit end and the mounting seat (952); the driving rod (951) is a through-tube structure; one side of the driving rod (951) located in the connecting tube (94) is connected to the flow-blocking plate (956).

5. A coal-based gas multi-layer co-mining device according to claim 4, characterized in that: The driving rod (951) is connected to an external hydraulic control pipe.

6. A coal-based gas multi-layer co-mining device according to claim 4, characterized in that: The driving rod (951) is provided with magnets (955) distributed in an array along its axial direction.

7. A coal-based gas multi-layer co-mining device according to claim 4 or 5, characterized in that: An electromagnetic seat (954) is fixed on the mounting seat (952), and an electromagnet (955) corresponding to the magnet (955) is fixed on the electromagnetic seat (954).

8. A coal-based gas multi-layer co-mining device according to claim 1, characterized in that: An auxiliary pipe (8) is further provided in the extraction pipe (4), and an air hole (81) is provided on the auxiliary pipe (8). Sealing rings (82) are provided on the upper and lower sides of the air hole (81), so that the auxiliary pipe (8) and the extraction pipe (4) form a separate annulus at the air hole (81).

9. A coal-based gas multi-layer co-mining device according to claim 1, characterized in that: A sealing head (5) is provided at the top of the extraction hole (1), and a through hole for the extraction pipe (4) to pass through is provided on the sealing head (5).

10. A coal-measure gas multi-layer co-mining device according to claim 3, characterized in that: An interception net is embedded in the air inlet (92).

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