CN116571365A

CN116571365A - High-pressure multi-pipe type double-volute cyclone separator

Info

Publication number: CN116571365A
Application number: CN202310352455.9A
Authority: CN
Inventors: 陶怡慧; 周杰; 黄全全
Original assignee: Changshu Feiao Pressure Vessel Manufacture Co ltd
Current assignee: Changshu Feiao Pressure Vessel Manufacture Co ltd
Priority date: 2023-04-04
Filing date: 2023-04-04
Publication date: 2023-08-11

Abstract

The application discloses a high-pressure multi-pipe double-volute cyclone separator, which relates to the technical field of steam and water, and comprises the following components: a housing having a plurality of gas risers installed therein; the cleaning piece is arranged on the shell and is used for cleaning the riser pipe in the shell; the cleaning piece comprises a scraping plate sleeved with the riser, the scraping plate is arranged in the shell and is attracted with an external magnet outside the shell through magnetic force; the outer magnet is driven to translate by a driver mounted to the outer wall of the housing. According to the high-pressure multi-tube double-volute cyclone separator, the driver is adopted to drive the outer magnet to move, and the scraping plate is driven to slide on the outer wall of the gas lift pipe under the action of attractive force between the inner magnet and the outer magnet, so that the technical problem that the gas lift pipe cannot be cleaned when the conventional multi-tube cyclone separator is used is effectively solved, and the outer wall of the gas lift pipe is cleaned.

Description

High-pressure multi-pipe type double-volute cyclone separator

Technical Field

The application relates to the technical field of steam-water separation, in particular to a high-pressure multitube double-volute cyclone separator.

Background

In the natural gas pipeline transportation process, if liquid phase water exists in the pipeline, corrosion can be accelerated, if solid phase impurities exist, equipment can be blocked, and in order to avoid pipeline corrosion and equipment blockage, a cyclone separator is often adopted to realize separation of gas phase, liquid phase and some solid phase impurities in mixed fluid under the working conditions of high pressure and high dust concentration.

The multi-pipe cyclone separator is a cyclone separator group formed by combining a plurality of cyclone separators with small diameters, and is suitable for working conditions with large gas treatment capacity and high separation efficiency. The multi-tube cyclone separator adopts a vertical cylinder structure, the inside of the multi-tube cyclone separator is axially divided into a liquid collecting area, a cyclone separation area, a purifying chamber area and the like, a plurality of cyclone tubes with small diameters are arranged in the cyclone separation area, are uniformly distributed along the circumferential direction and are fixed through an upper tube plate and a lower tube plate.

At present, the prior published Chinese patent document, namely a multi-cyclone separator (publication number: CN 110947531B), discloses a multi-cyclone separator, and belongs to the technical field of petrochemical equipment. The device comprises: a gas inlet pipe, an elbow, a cylinder, a cyclone assembly, a gas outlet pipe and a cleaning pipe; the gas inlet pipe is used for flowing in dust-containing gas; the elbow is welded with the gas inlet pipe; the cyclone assembly comprises a round upper tube plate, anti-blocking tubes, cyclone tube bundles and a round lower tube plate; the cyclone component is welded in the inner cavity of the cylinder body; the gas outlet pipe is used for cleaning gas; the purge tube includes a first stub and a circular conduit welded to the first stub. Through setting up anti-blocking pipe to the preliminary filtration of dusty gas, under cyclone tube bank's effect, liquid and dust flow out from first dust exhaust pipe, and the washing pipe is in time washed away the interior impurity of drum, has avoided multitube cyclone inner chamber impurity deposit, has avoided this solid particle to block up cyclone entry, has prolonged multitube cyclone's life.

However, in the implementation process of the technical scheme, at least the following technical problems are found:

the riser cannot be cleaned: when the existing multi-pipe cyclone separator is used, dust, impurities and moisture are very easy to adhere to the outer wall of the gas lift pipe due to the fact that the gas entering the device is very easy to adhere to the outer wall of the gas lift pipe, so that the separation effect is reduced, cleaning is required regularly, and when the cleaning is required, the gas does not only enter the device, but also the device is required to stop working;

the water collected inside the device is prone to splash: when the existing multi-pipe cyclone separator is used, as liquid is converged at the bottom of the device, when a certain amount of liquid is converged, newly converged water drops fall on the liquid of the device, the converged liquid is re-excited, so that the liquid can splash, the liquid can be easily re-enter into gas, and secondly, when air enters into the device, the air can blow to the bottom of the device under the action of a riser and a cyclone tube bundle, and the deposited liquid can splash.

Disclosure of Invention

(one) solving the technical problems

Aiming at the defects of the prior art, the application provides a high-pressure multi-tube double-volute cyclone separator, which solves the technical problems that the existing multi-tube cyclone separator cannot clean a riser and water collected in the device is easy to splash when in use.

(II) technical scheme

In order to achieve the above purpose, the application is realized by the following technical scheme:

the utility model provides a high-pressure multitube formula double-volute cyclone, this cyclone includes the casing, and is located the inside riser of casing, after gas enters into the device inside from the air inlet, with the contact of riser, liquid in the gas adheres to the outer wall at the riser, and the air enters into the below of device from the clearance between riser and the cyclone tube bank, enters into the riser again from the below of device and gathers to the gas outlet to discharge, accomplish the separation of gas and liquid:

a housing having a plurality of gas risers installed therein;

the cleaning piece is arranged on the shell and is used for cleaning the gas lift pipe in the shell, and impurities outside the gas lift pipe are scraped by sliding the gas lift pipe back and forth on the outer wall of the gas lift pipe, so that the cleanliness of the outer wall of the gas lift pipe is ensured, and the gas lift pipe is convenient to clean;

the cleaning piece comprises a scraping plate sleeved with the gas lift pipe, so that impurities on the outer wall of the gas lift pipe can be cleaned when the scraping plate moves (like an automobile windscreen wiper, the outer wall of the gas lift pipe can be scraped clean), the scraping plate is arranged in the shell and is mutually attracted with an outer magnet outside the shell through magnetic force, and the outer magnet and the scraping plate can be linked, so that the impurities on the outer wall of the gas lift pipe can be cleaned;

the outer magnet is driven by a driver arranged on the outer wall of the shell to translate, so that the power for moving the outer magnet is provided.

Preferably, the driver comprises a motor arranged outside the shell, and an output shaft of the motor is connected with a screw rod, and the extending direction of the screw rod is consistent with the length direction of the riser;

the screw rod is in threaded connection with the external magnet, so that the external magnet can be driven to lift when the screw rod rotates, and moving power is provided for the external magnet.

Preferably, the surface of the scraper is provided with a plurality of through holes, and the outer magnet is inserted into the through holes on the surface of the scraper, so that the scraper corresponds to the riser;

the scraping strip is arranged on the inner wall of the through hole and is attached to the outer wall of the outer magnet through the scraping strip, so that impurities on the outer wall of the gas lift pipe can be cleaned when the scraping plate moves.

Preferably, the inner magnet is arranged on the outer side of the scraper, the scraper is mutually attracted with the outer magnet through the inner magnet, so that the outer magnet and the scraper are mutually attracted through magnetic force, and the outer magnet and the scraper can be linked at the moment, so that impurities on the outer wall of the gas lift pipe are cleaned.

Preferably, a cyclone assembly is arranged in the shell, the cyclone assembly comprises an upper tube plate and a lower tube plate which are vertically corresponding, cyclone tube bundles are inserted into the outer part of the lower tube plate, and the cyclone tube bundles are in one-to-one correspondence with the gas risers;

the cyclone tube bundle is sleeved at the end part of the gas lift pipe, so that liquid falling along the gas lift pipe is converged at the bottom of the device.

Preferably, the shell comprises an upper sleeve and a lower sleeve which are mutually butted, the top of the upper sleeve is provided with an air outlet, and the outer wall of the upper sleeve is provided with an air inlet.

Preferably, a spiral casing pipe is arranged on the inner wall of the upper sleeve, and is communicated with the air inlet, so that air entering along the air inlet enters the device along the spiral casing pipe, and the spiral casing pipe can enable the air to rotate on the inner wall of the device, thereby being in contact with a gas lift pipe in the device and avoiding being in contact with a local gas lift pipe only;

the tail end of the volute pipe corresponds to a riser pipe between the upper pipe plate and the lower pipe plate.

Preferably, the scraper is located between the upper tube plate and the lower tube plate, and when the scraper is attached to the upper tube plate, the tail end of the volute tube is located below the scraper, so that the scraper is prevented from affecting the flow of gas between the gas risers, and the stability of the device is ensured.

Preferably, an inner pipe is arranged in the shell, the inner pipe is attached to the inner wall of the shell, and a floating net is connected to the bottom opening of the inner pipe;

the buoyancy of the floating net is larger than the sum of the gravity of the inner pipe and the floating net, so that the floating net can always float above the liquid, when newly condensed liquid drops, the newly condensed liquid firstly contacts with the surface of the floating net, and then the liquid enters the lower part along the meshes of the floating net, so that the newly condensed liquid is prevented from colliding with the condensed liquid.

(III) beneficial effects

1. Because the driver is adopted to drive the outer magnet to move, and then the scraping plate is driven to slide on the outer wall of the gas lift pipe under the action of attractive force between the inner magnet and the outer magnet, the technical problem that the gas lift pipe cannot be cleaned when the conventional multi-pipe cyclone separator is used is effectively solved, and further the cleaning of the outer wall of the gas lift pipe is realized, meanwhile, the cleaning difficulty of the gas lift pipe can be reduced, impurities are prevented from adhering to the outer wall of the gas lift pipe, and the cleaning of the device is influenced.

2. Because the double-volute structure is adopted, gas is fed into the device, the technical problem that the gas is unevenly distributed when the conventional multi-pipe cyclone separator is used is effectively solved, the rotation of the gas is further realized, the condition that the gas can only contact with a local riser is avoided, and the steam-water separation effect is improved.

3. Because the conical seat is adopted to disperse the gas entering the device, the technical problem that the gas distribution is uneven when the traditional multi-pipe cyclone separator is used is effectively solved, the rotation of the gas is further realized, the gas is prevented from contacting with a local riser, and the steam-water separation effect is improved.

4. Because the floating net is adopted to cover the outside of the liquid, the technical problem that the water collected in the device is easy to splash when the traditional multi-pipe cyclone separator is used is effectively solved, the isolation between the liquids is further realized, the deposited liquid is prevented from colliding with the newly generated liquid, and the liquid collection stability is improved.

Drawings

The foregoing description is only an overview of the present application, and is intended to provide a better understanding of the present application, as it is embodied in the following description, with reference to the preferred embodiments of the present application and the accompanying drawings.

FIG. 1 is an overall block diagram of an embodiment of the present application;

FIG. 2 is a cross-sectional view of the housing in embodiment 1 of the present application;

FIG. 3 is a block diagram of a cyclone assembly according to embodiment 1 of the present application;

FIG. 4 is an exploded view of the cyclone assembly of example 1 of the present application;

FIG. 5 is a sectional view of the housing in embodiment 2 of the present application;

FIG. 6 is a structural view of a cleaning member in embodiment 1 of the present application;

FIG. 7 is a sectional view of the case in embodiment 3 of the present application;

FIG. 8 is a block diagram of a cyclone assembly in accordance with embodiment 3 of the present application;

FIG. 9 is an exploded view of the cyclone assembly of example 3 of the present application;

FIG. 10 is a view showing the structure of an air inlet and a conical seat in embodiment 3 of the present application;

FIG. 11 is a partial cross-sectional view of the housing in embodiment 3 of the present application;

FIG. 12 is a partial cross-sectional view of the housing in embodiment 4 of the present application;

fig. 13 is a structural view of a floating net in embodiment 4 of the present application.

Legend description: 11. an upper sleeve; 12. a lower sleeve; 13. a base; 14. an air outlet; 15. an air inlet; 16. a volute pipe; 2. a cleaning member; 21. a motor; 22. a screw rod; 23. an outer magnet; 24. a scraper; 25. an inner magnet; 3. a cyclone assembly; 31. an upper tube sheet; 32. a riser; 33. a lower tube sheet; 34. a cyclone tube bundle; 41. a conical seat; 42. a connecting rod; 51. an inner tube; 52. a floating net.

Detailed Description

The embodiment of the application solves the technical problems that the existing multi-pipe cyclone separator cannot clean the gas lift and water collected in the device is easy to splash when in use, and the existing multi-pipe cyclone separator adopts a driver to drive an outer magnet to move and then drives a scraper to slide on the outer wall of the gas lift under the action of attractive force between the inner magnet and the outer magnet, so that the cleaning of the outer wall of the gas lift is realized, the cleaning difficulty of the gas lift is reduced, and impurities are prevented from adhering to the outer wall of the gas lift to influence the cleaning of the device; because of adopting the double-volute structure, the gas is sent into the device, thereby realizing the rotation of the gas, avoiding that the gas can only contact with a local riser, and improving the steam-water separation effect; the conical seat is adopted, so that the gas entering the device is dispersed, the rotation of the gas is realized, the gas is prevented from being contacted with a local riser, and the steam-water separation effect is improved; because the floating net is adopted to cover the outside of the liquid, the isolation between the liquids is realized, and the collision between the deposited liquid and the newly generated liquid is avoided, so that the liquid collection stability is improved.

Example 1

The technical scheme in the embodiment of the application is to effectively solve the technical problem that the riser 32 cannot be cleaned when the conventional multi-tube cyclone separator is used, and the general thought is as follows:

in view of the problems existing in the prior art, the present application provides a high-pressure multi-pipe type double-volute cyclone separator, which comprises a housing, and a gas lift pipe 32 positioned in the housing, wherein when gas enters the interior of the device from a gas inlet 15, the gas lift pipe 32 is contacted, liquid in the gas adheres to the outer wall of the gas lift pipe 32, air enters the lower part of the device from a gap between the gas lift pipe 32 and a cyclone tube bundle 34, and enters the gas lift pipe 32 from the lower part of the device to be converged at a gas outlet 14, so that the gas is discharged, and separation of the gas and the liquid is completed:

a housing having a plurality of chimneys 32 mounted therein as shown in fig. 2;

the cleaning piece 2 is arranged on the shell and is used for cleaning the gas lift tube 32 in the shell, and impurities outside the gas lift tube 32 are scraped by sliding back and forth on the outer wall of the gas lift tube 32, so that the cleanliness of the outer wall of the gas lift tube 32 is ensured, and the cleaning is convenient;

the cleaning member 2 includes a scraper 24 sleeved with the riser 32, so that impurities on the outer wall of the riser 32 can be cleaned (like a car wiper, the outer wall of the riser 32 can be scraped clean) when the scraper 24 moves, the scraper 24 is arranged in the shell and corresponds to an outer magnet 23 outside the shell, and the outer magnet 23 and the scraper 24 are attracted to each other through magnetic force, so that the outer magnet 23 and the scraper 24 can be linked, and impurities on the outer wall of the riser 32 can be cleaned;

the outer magnet 23 is driven to translate by a driver mounted to the outer wall of the housing to provide motive force for the movement of the outer magnet 23.

In some examples, the driver comprises a motor 21 mounted outside the shell, and a screw rod 22 is connected to an output shaft of the motor 21, and an extending direction of the screw rod 22 is consistent with a length direction of the riser 32;

the screw 22 is in threaded connection with the outer magnet 23, so that the screw 22 can drive the outer magnet 23 to lift when rotating, thereby providing power for the outer magnet 23 to move.

In some examples, the surface of the scraper 24 is provided with a plurality of through holes, and the external magnet 23 is inserted into the through holes on the surface of the scraper 24, so that the scraper 24 corresponds to the riser 32;

wherein, the scraping strip is installed to the inner wall of through-hole, and through scraping strip and the laminating of outer magnet 23's outer wall, so when scraper 24 motion, can clear up the impurity of riser 32 outer wall.

In some examples, the inner magnet 25 is mounted on the outer side of the scraper 24, and the scraper 24 is attracted to the outer magnet 23 through the inner magnet 25, so that the outer magnet 23 and the scraper 24 are attracted to each other through magnetic force, and at the moment, the outer magnet 23 and the scraper 24 can be linked, so that impurities on the outer wall of the riser 32 are cleaned.

In some examples, as shown in fig. 3 and 4, the cyclone assembly 3 is installed inside the shell, the cyclone assembly 3 comprises an upper tube plate 31 and a lower tube plate 33 which are vertically corresponding, a cyclone tube bundle 34 is inserted outside the lower tube plate 33, and the cyclone tube bundles 34 are in one-to-one correspondence with the gas risers 32;

wherein the cyclone tube bundle 34 is sleeved on the end of the gas riser 32, so that the liquid falling along the gas riser 32 is converged at the bottom of the device.

In the specific implementation process, after entering the device from the air inlet 15, the air contacts with the air lift pipe 32, the liquid in the air is adhered to the outer wall of the air lift pipe 32 and slides down along the air lift pipe 32 to be converged at the bottom of the device, while the air enters the lower part of the device from the gap between the air lift pipe 32 and the cyclone tube bundle 34 and enters the air lift pipe 32 from the lower part of the device to be converged at the air outlet 14, so that the air is discharged, and the separation of the air and the liquid is completed.

When the impurity on the outer wall of the gas lift tube 32 needs to be cleaned, the motor 21 is controlled to drive the screw rod 22 to rotate, and the screw rod 22 is in threaded connection with the outer magnet 23, and the outer magnet 23 is arc-shaped and is attached to the outer wall of the device, so that when the screw rod 22 rotates, the outer magnet 23 can be driven to move, the inner magnet 25 in the device and the outer magnet 23 are attracted mutually, and at the moment, the outer magnet 23 and the scraping plate 24 can be linked, so that the impurity on the outer wall of the gas lift tube 32 is cleaned, and the impurity on the outer wall of the gas lift tube 32 is attached to the outer wall of the outer magnet 23 through the scraping strip, so that the impurity on the outer wall of the gas lift tube 32 can be cleaned when the scraping plate 24 moves.

Example 2

Based on the embodiment 1, the embodiment of the application effectively solves the technical problem of uneven gas distribution when the traditional multi-tube cyclone separator is used, and the general thought is as follows:

the housing comprises an upper sleeve 11, a lower sleeve 12 and a base 13 for supporting the device, which are butted with each other, an air outlet 14 is arranged at the top of the upper sleeve 11, and an air inlet 15 is arranged at the outer wall of the upper sleeve 11, as shown in fig. 1 and 2.

In some examples, the inner wall of the upper sleeve 11 is provided with a spiral casing pipe 16, and the spiral casing pipe 16 is communicated with the air inlet 15, so that the air enters the interior of the device along the air inlet 15 and enters the interior of the device along the spiral casing pipe 16, and the spiral casing pipe 16 can enable the air to rotate on the inner wall of the device so as to be in contact with the riser 32 in the device, and avoid being in contact with only a partial riser 32;

wherein the ends of the spiral casing tubes 16 correspond to the riser tubes 32 between the upper tube sheet 31 and the lower tube sheet 33, as shown in fig. 2.

In some examples, the scraper 24 is positioned between the upper tube sheet 31 and the lower tube sheet 33, and when the scraper 24 is in engagement with the upper tube sheet 31, the end of the volute tube 16 is positioned below the scraper 24, thereby avoiding the scraper 24 from affecting the flow of gas between the risers 32, thereby ensuring stability of the device.

Example 3

the housing comprises an upper sleeve 11 and a lower sleeve 12 which are butted with each other, an air outlet 14 is arranged at the top of the upper sleeve 11, and an air inlet 15 is arranged on the outer wall of the upper sleeve 11, as shown in fig. 1 and 2.

The ends of the air inlets 15 extend between the upper tube sheet 31 and the lower tube sheet 33 as shown in fig. 8 and 9;

wherein, the bottom of the upper tube plate 31 is provided with a conical seat 41, and the opening at the top of the conical seat 41 corresponds to the end of the air inlet 15, so when air is discharged from the air inlet 15, the top of the conical seat 41 is firstly impacted, and the air is diffused through the blocking of the top of the conical seat 41, thereby enabling the air to be in contact with all the gas risers 32, and improving the separation effect;

the edge of the conical seat 41 is connected with a connecting rod 42, and the conical seat 41 is connected with the bottom of the upper tube plate 31 through the connecting rod 42, so that the position of the conical seat 41 is ensured to be fixed.

Example 4

Based on the embodiment 1, the embodiment of the application effectively solves the technical problem that water collected in the device is easy to splash when the traditional multi-tube cyclone separator is used, and the general thought is as follows:

an inner pipe 51 is arranged in the shell, the inner pipe 51 is attached to the inner wall of the shell, and a floating net 52 is connected to the bottom opening of the inner pipe 51;

the buoyancy of the floating net 52 is greater than the sum of the gravity of the inner pipe 51 and the floating net 52, so that the floating net 52 can always float above the liquid, when newly condensed liquid drops, the newly condensed liquid firstly contacts with the surface of the floating net 52, and then the liquid enters below along the meshes of the floating net 52, so that the newly condensed liquid is prevented from colliding with the condensed liquid.

Finally, it should be noted that: it is apparent that the above examples are only illustrative of the present application and are not limiting of the embodiments. Other variations or modifications of the above teachings will be apparent to those of ordinary skill in the art. It is not necessary here nor is it exhaustive of all embodiments. And obvious variations or modifications thereof are contemplated as falling within the scope of the present application.

Claims

1. A high pressure multi-tube twin scroll cyclone separator, comprising:

a housing having a plurality of risers (32) mounted therein;

the cleaning piece (2) is arranged on the shell and is used for cleaning the surface of the riser (32);

the cleaning piece (2) comprises a scraping plate (24) sleeved with the riser (32), the scraping plate (24) is arranged in the shell and corresponds to an outer magnet (23) outside the shell, and the outer magnet (23) and the scraping plate (24) are attracted to each other through magnetic force;

the outer magnet (23) is driven to translate by a driver mounted to the outer wall of the housing.

2. A high pressure multi-tube twin scroll cyclone separator as claimed in claim 1, wherein: the driver comprises a motor (21) arranged outside the shell, a screw rod (22) is connected to an output shaft of the motor (21), and the extending direction of the screw rod (22) is consistent with the length direction of the riser (32);

wherein the screw rod (22) is in threaded connection with the outer magnet (23).

3. A high pressure multi-tube twin scroll cyclone separator as claimed in claim 1, wherein: the surface of the scraping plate (24) is provided with a plurality of through holes, and the outer magnet (23) is inserted into the through holes on the surface of the scraping plate (24);

the scraping strip is arranged on the inner wall of the through hole and is attached to the outer wall of the outer magnet (23).

4. A high pressure multi-tube twin scroll cyclone separator as claimed in claim 1, wherein: an inner magnet (25) is arranged on the outer side of the scraping plate (24), and the scraping plate (24) and the outer magnet (23) are attracted mutually through the inner magnet (25).

5. A high pressure multi-tube twin scroll cyclone separator as claimed in claim 1, wherein: the cyclone assembly (3) is arranged in the shell, the cyclone assembly (3) comprises an upper tube plate (31) and a lower tube plate (33) which are vertically corresponding to each other, a cyclone tube bundle (34) is inserted into the outer part of the lower tube plate (33), and the cyclone tube bundles (34) are in one-to-one correspondence with the gas risers (32);

wherein the cyclone tube bundle (34) is sleeved at the end part of the riser (32).

6. A high pressure multi-tube twin scroll cyclone separator as claimed in claim 5, wherein: the shell comprises an upper sleeve (11) and a lower sleeve (12) which are in butt joint with each other, an air outlet (14) is arranged at the top of the upper sleeve (11), and an air inlet (15) is arranged on the outer wall of the upper sleeve (11).

7. A high pressure multi-tube twin scroll cyclone separator as claimed in claim 6, wherein: the inner wall of the upper sleeve (11) is provided with a spiral volute pipe (16), and the volute pipe (16) is communicated with the air inlet (15);

wherein the end of the spiral case pipe (16) corresponds to a riser pipe (32) between the upper tube plate (31) and the lower tube plate (33).

8. A high pressure multi-tube twin scroll cyclone separator as claimed in claim 7, wherein: the scraper (24) is positioned between the upper tube plate (31) and the lower tube plate (33), and when the scraper (24) is attached to the upper tube plate (31), the tail end of the volute tube (16) is positioned below the scraper (24).

9. A high pressure multi-tube twin scroll cyclone separator as claimed in claim 6, wherein: the tail end of the air inlet (15) extends between the upper tube plate (31) and the lower tube plate (33);

wherein, the bottom of the upper tube plate (31) is provided with a conical seat (41), and an opening at the top of the conical seat (41) corresponds to the tail end of the air inlet (15);

the edge of the conical seat (41) is connected with a connecting rod (42), and the conical seat (41) is connected with the bottom of the upper tube plate (31) through the connecting rod (42).

10. A high pressure multi-tube twin scroll cyclone separator as claimed in any one of claims 1 to 9, wherein: an inner pipe (51) is arranged in the shell, the inner pipe (51) is attached to the inner wall of the shell, and a floating net (52) is connected to the bottom opening of the inner pipe (51);

wherein the buoyancy of the floating net (52) is greater than the sum of the weights of the inner tube (51) and the floating net (52).