Integrated modular shielding type filtering device

Abstract

The invention provides an integrated modular shielding type filtering device, and relates to the technical field of nuclear facility air purification, the device comprises: a filtering shell, the side wall of which is provided with an air inlet and an air outlet; the pre-filter assembly is arranged in the filtering shell, and the pre-filter assembly comprises a pre-filter cylinder and a pre-filter installed in the pre-filter cylinder; the high-efficiency filter assembly is arranged in the filtering shell, and the high-efficiency filter assembly comprises an HEPA filter cylinder and an HEPA filter installed in the HEPA filter cylinder; wherein the pre-filter and the HEPA filter are both of a cylindrical structure with the top end open and the side wall and the bottom closed, and the top ends of the pre-filter and the HEPA filter are both communicated with an air inlet channel formed by air inlets. By optimizing airflow organization and a sealing structure and integrating an on-line monitoring system, the industrial problem that radioactive substances escape when the filter element is replaced is fundamentally solved, and meanwhile the device has the advantages of being precise in maintenance, reliable in shielding and convenient and fast in modular layout.

Description

Technical Field

[0001] This invention belongs to the field of air purification technology for nuclear facilities, specifically relating to an integrated modular shielded filter device. Background Technology

[0002] With the rapid development of nuclear isotopes, the construction of highly radioactive and tightly sealed hot chambers is increasing. To meet the operational requirements of these hot chambers and ensure the normal operation of equipment and the safety of personnel, a hot chamber exhaust purification system is necessary. Traditional nuclear radiochemical plant exhaust systems typically use metal purification devices or small, civil-built purification chambers, which occupy significant floor space and pose radiation hazards to personnel. To overcome these shortcomings, an innovative pit-type air filtration and purification device has been designed. This device incorporates two-stage filters within an integrated cylindrical shell. An external air inlet pipe connects to the inlet of the first-stage filter, and an external exhaust pipe connects to the outlet of the second-stage filter. Contaminated air within the plant is filtered through both stages before being discharged. A shielding cover and plug seal the pit. Although this type of pit-type purification device does not occupy the floor space of the factory, the first-stage filter has air intake at the bottom and air outlet at the radial direction, while the second-stage filter has air intake at the radial direction and air outlet at the bottom. The filtered radioactive substances are prone to adhere to the inner wall of the filter. There is a risk of a large amount of radioactive material escaping and falling off during the filter element replacement process. In addition, the shielding cover is prone to leakage due to poor sealing between the shielding cover and the factory floor base. The device requires a high level of skill in equipment installation and filter replacement, which is not conducive to actual operation in the production process. Summary of the Invention

[0003] To address the critical technical problem of easy escape of radioactive materials during filter replacement as described in the background art, this invention provides an integrated modular shielded filtration device. This device solves the problem of safe containment of radioactive materials during filtration and replacement by adopting a top-inlet cylindrical filter structure, an integrated status monitoring system, and a modular overall design, and improves the reliability and maintainability of the device.

[0004] This invention is achieved using the following technical solution: an integrated modular shielded filter device, comprising: The filter housing has an air inlet and an air outlet on its side wall; A pre-filter assembly is disposed inside the filter housing, the pre-filter assembly including a pre-filter cartridge and a pre-filter installed therein; A high-efficiency filter assembly is disposed inside the filter housing, the high-efficiency filter assembly including a HEPA filter cartridge and a HEPA filter installed therein; Both the pre-filter and the HEPA filter are cylindrical structures with an open top and closed side walls and bottom, and the top of both are connected to the air inlet channel formed by the air inlet.

[0005] Furthermore, it also includes a monitoring system, which comprises: The dose monitoring probe is fixed inside the housing by a shielding sleeve located at the top of the filter housing; At least one differential pressure monitoring port is provided on the wall surface of the filter housing.

[0006] Furthermore, the monitoring system also includes an online radiation monitor connected to the dose monitoring probe signal.

[0007] Furthermore, the bottom end of the pre-filter is fixed inside the pre-filter cartridge by a locking device, and the bottom end of the HEPA filter is fixed inside the HEPA filter cartridge by a locking device.

[0008] Furthermore, sealing gaskets are provided between the top of the pre-filter and the pre-filter cartridge, and between the top of the HEPA filter and the HEPA filter cartridge.

[0009] Furthermore, a cover plate is provided on the top of the filter housing, and a shielding cover plate is embedded in the cover plate.

[0010] Furthermore, the cover plate is provided with an embedded lifting ring and bolt fasteners for connecting with the support.

[0011] Furthermore, the filter housing is an integrated cylindrical structure, with its bottom fixedly supported by a support member.

[0012] Furthermore, the device has a modular structure, which allows at least two of the filter devices to be combined and installed, with the covers of adjacent devices connected by an L-shaped structure that fits together.

[0013] Furthermore, the top perimeters of both the pre-filter cartridge and the HEPA filter cartridge are welded and fixed to the filter housing via sealing ring plates.

[0014] Compared with the prior art, the integrated modular shielded filter device provided by the present invention has the following beneficial effects: (1) Addressing the core safety issue of radioactive material escaping during filter replacement, the filtration device provided by this invention features a cylindrical structure with an open top, closed side walls and bottom, and a top-to-air inlet channel, creating a unique airflow path of axial intake and radial exhaust. This structure allows contaminated air to enter from the top of the filter, flow through the filter media, and exit from the side walls, while all trapped radioactive particles are contained within the internal cavity of the filter element. During replacement, due to gravity and the absence of reverse airflow disturbance, radioactive material will not escape from the bottom mounting port, thus achieving complete containment of radioactive material and greatly improving operational safety.

[0015] (2) The monitoring system provided by this invention, through the coordinated setting of dose monitoring probe and differential pressure monitoring port, realizes real-time online monitoring of cumulative radiation dose and working resistance of filter. This enables maintenance personnel to scientifically formulate filter replacement strategies based on accurate dose and differential pressure data, avoiding waste caused by premature replacement or filter failure and leakage risk caused by late replacement, and realizing accurate replacement of filter element and early warning of radionuclide leakage.

[0016] (3) Based on the positioning device and sealing gasket, the present invention establishes a reliable mechanical fixing and sealing scheme. The positioning device ensures that the filter element can be installed quickly and accurately into the preset slot, avoiding bypass leakage caused by misalignment; at the same time, in conjunction with the sealing gasket set at the top, an effective static seal is formed under the action of the pressing mechanism, which isolates the possibility of unfiltered air leaking through the interface gap, thus structurally ensuring filtration efficiency and system sealing.

[0017] (4) The integrated cylindrical structure, modular structure and L-shaped connection design provided by the present invention offer a compact and flexible layout scheme. The integrated cylindrical structure reduces the amount of on-site welding and assembly work; the modular design allows for flexible combination of multiple units according to air volume requirements; the L-shaped connection structure between the cover plates not only facilitates installation and positioning, but also effectively saves the overall floor space of the assembly and ensures the continuity of shielding, greatly reducing the cost and difficulty of installation and subsequent operation and maintenance. Attached Figure Description

[0018] The accompanying drawings, which form part of this disclosure, are used to provide a further understanding of this disclosure. The illustrative embodiments of this disclosure and their descriptions are used to explain this disclosure and do not constitute an undue limitation of this disclosure.

[0019] Figure 1 This is a schematic diagram of the integrated modular shielded filter device provided by the present invention. Figure 2 A top view of the integrated modular shielded filter device provided by the present invention; Figure 3This is a schematic diagram of the integrated module combination provided by the present invention; Figure 4 This is a cross-sectional view of AA. Figure 5 This is a cross-sectional view of BB. Figure 6 This is a CC cross-sectional view.

[0020] In the diagram: 101, pre-filter cartridge; 102, pre-filter; 201, HEPA filter cartridge; 202, HEPA filter; 3, filter housing; 4, cover plate; 5, shielding cover plate; 6, shielding sleeve; 7, air inlet; 8, air outlet; 9, support component; 10, dose monitoring probe; 11, online radiation monitor; 12, differential pressure monitoring port; 13, locking device; 14, sealing gasket; 15, embedded lifting ring; 16, bolt fasteners. Detailed Implementation

[0021] It should be noted that the following detailed descriptions are exemplary and intended to further illustrate the technical solutions provided by the present invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0022] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, unless otherwise expressly indicated by the invention, the singular form is also intended to include the plural form. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof. For ease of description, the terms "upper," "lower," "left," "right," "front," and "rear" appearing in this invention only indicate their relationship to the appendix. Figure 1 The fact that the top, bottom, left, and right directions are consistent does not limit the structure. It is only for the purpose of describing the invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of the invention.

[0023] Terminology Explanation: The terms “connection,” “installation,” “fixing,” and “setting” in this invention are interpreted broadly. For example, “connection” can mean a fixed connection or an indirect connection through an intermediate component without affecting the relationship between components and the technical effect. It can also mean an integral connection or a partial connection. In such cases, those skilled in the art can understand the specific meaning of the above terms in this invention or invention according to the specific circumstances.

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0025] Example 1 The integrated modular shielded filter device provided by this invention optimizes the airflow structure of traditional pit-type filter purification devices, avoiding the possibility of radioactive substances escaping from the filter; it optimizes the filter differential pressure and online dose monitoring functions, allowing for precise replacement of the filter element based on the differential pressure and dose monitoring values; and its integrated modular construction facilitates on-site construction, greatly reducing installation and subsequent operation and maintenance costs.

[0026] In this embodiment, the present invention provides an integrated modular shielded filter device comprising: Pre-filter cartridge (101): Set inside the filter housing to secure the pre-filter.

[0027] Pre-filter (102): Set inside the pre-filter cylinder.

[0028] HEPA filter cartridge (201): Set inside the filter housing to secure the HEPA filter.

[0029] HEPA filter (202): Installed inside the HEPA filter cartridge.

[0030] Filter housing (3): Used to install pre-filters, HEPA filters, shielding sleeves, dose monitoring probes, etc.

[0031] Shielding cover (5): Used to shield the accumulated dose within the filter.

[0032] Shielding sleeve (6): Used to fix the dose monitoring instrument.

[0033] Online radiation monitor (11): used to display measured values ​​and high alarms in real time on-site, and transmit measurement data to the control center.

[0034] Specifically, the device includes: a filter housing (3) with an air inlet (7) and an air outlet (8) provided on its side wall; A pre-filter assembly is disposed inside the filter housing (3), the pre-filter assembly including a pre-filter cylinder (101) and a pre-filter (102) installed therein. A high-efficiency filter assembly is disposed inside the filter housing (3), the high-efficiency filter assembly including a HEPA filter cartridge (201) and a HEPA filter (202) installed therein. The pre-filter (102) and the HEPA filter (202) are both cylindrical structures with open tops and closed side walls and bottoms, and the tops of both are connected to the air inlet channel formed by the air inlet (7).

[0035] The integrated modular shielded filter device provided in this embodiment optimizes the internal airflow organization, ensuring that the airflow enters axially from the top of the filter element, exits radially, and converges into the lower ventilation channel. Radioactive materials are completely contained within the filter element and will not escape into the ventilation channel. Based on the cylindrical shape with an open top and a closed bottom, the forced airflow enters axially from the top of the filter, penetrates the filter material, and flows radially out from the side wall. This flow direction design works in conjunction with the direction of gravity to ensure that the trapped radioactive particles are "locked" in the cavity inside the filter element. When replacing the filter element, since the bottom is closed and fixed, only the connection at the top needs to be disconnected to lift the entire contaminated filter element as a sealed unit. This fundamentally eliminates the problem of radioactive dust falling and escaping caused by bottom openings or complex flow channels in existing technologies, achieving intrinsic safety.

[0036] Specifically, it also includes a monitoring system, which comprises: The dose monitoring probe (10) is fixed inside the housing by a shielding sleeve (6) set on the top of the filter housing (3); At least one differential pressure monitoring port (12) is provided on the wall of the filter housing (3).

[0037] The integrated modular shielded filtration device provided in this embodiment is equipped with differential pressure and online dose monitoring instruments for both the pre-filter and HEPA filter. These instruments can monitor the differential pressure and cumulative dose values ​​before and after each stage of the filter in real time, enabling precise filter replacement. The dose monitoring probe extends deep into the filter housing through a shielded sleeve to directly monitor the accumulated radiation on the filter surface, providing direct data for determining whether the filter has reached saturation and providing a basis for replacement. The differential pressure monitoring port is used to connect to a differential pressure transmitter, reflecting the changes in filter resistance caused by particulate matter accumulation in real time. Together, these two components constitute the device's condition monitoring network, upgrading traditional periodic or experience-based maintenance to predictive maintenance based on the actual condition of the equipment.

[0038] Specifically, the monitoring system also includes an online radiation monitor (11) that is connected to the dose monitoring probe (10) via signal.

[0039] The online radiation monitor processes, displays, and transmits the analog signals collected by the dose monitoring probe. It features local display and high-alarm capabilities, enabling operators in both the field and remote control rooms to monitor the filter's radioactivity containment status in real time. An immediate alarm is triggered in case of an abnormally high dose, providing early warning and rapid response to potential leakage risks.

[0040] Specifically, the bottom end of the pre-filter (102) is fixed inside the pre-filter cylinder (101) by a locking device (13), and the bottom end of the HEPA filter (202) is fixed inside the HEPA filter cylinder (201) by a locking device (13).

[0041] The integrated modular shielded filter device provided in this embodiment uses a locking device to fix the bottom of the filter element, ensuring that the filter element is installed in the accurate slot, and that the filter element sealing ring and sealing gasket are effectively compressed for a reliable seal. The locking device (such as the cooperation of a buckle, positioning pin, and slot) provides precise axial and radial positioning for the filter element. This ensures that the filter element can automatically align during installation, so that the sealing surface at its top accurately fits the corresponding sealing surface of the filter cartridge, laying the foundation for subsequent application of pressure to form an effective seal, while preventing the filter element from shaking or shifting due to airflow impact during operation.

[0042] Specifically, sealing gaskets (14) are provided between the top of the pre-filter (102) and the pre-filter cartridge (101), and between the top of the HEPA filter (202) and the HEPA filter cartridge (201).

[0043] Sealing gaskets are crucial components for ensuring filtration efficiency. After the filter element is positioned by the locking device and pressed down by the upper mechanism, the sealing gasket undergoes elastic deformation under pressure, tightly filling the microscopic gap between the filter element flange and the filter cartridge interface, forming a reliable sealing barrier. This barrier ensures that all air to be treated must pass through the filter media without short-circuiting through the interface gaps, thus guaranteeing the filter's filtration efficiency and preventing the leakage of radioactive aerosols.

[0044] Specifically, a cover plate (4) is provided on the top of the filter housing (3), and a shielding cover plate (5) is embedded on the cover plate (4).

[0045] The cover plate, serving as the top enclosure of the entire device, has a shielding cover (usually made of heavy metals such as lead and steel) facing the part of the filter below where the accumulated radioactivity is strongest. It constitutes the main shield against penetrating radiation such as gamma rays, significantly reducing the radiation dose level outside the device, especially in the upper operating area, and protecting the safety of maintenance personnel.

[0046] Specifically, the cover plate (4) is provided with an embedded lifting ring (15) and bolt fasteners (16) for connecting with the support (9).

[0047] The embedded lifting rings provide a convenient and safe point of leverage for the transportation, installation, and subsequent filter replacement of the entire device. Bolts are used to securely connect the cover plate to the lower support or adjacent modules, ensuring the stability of the overall structure and the integrity of the sealed cavity.

[0048] Specifically, the filter housing (3) is an integrated cylindrical structure, and its bottom is fixedly supported by a support member (9).

[0049] The integrated cylindrical shell reduces unnecessary welds and flanges, lowers manufacturing complexity and potential leakage points, and enhances structural strength and airtightness. The bottom support evenly distributes the weight of the entire unit to the foundation, ensuring operational stability.

[0050] Specifically, the device is a modular structure that can combine at least two of the filter devices, and the cover plates (4) of adjacent devices are connected by an L-shaped structure that cooperates with each other.

[0051] The integrated modular shielded filter device provided in this embodiment adopts an integrated modular construction and allows for remote replacement of the internal filter elements using a shielded trolley. Its compact structure makes installation and replacement more convenient. The modular design and L-shaped connection method are key features that enable the invention to achieve engineering applicability. Users can combine multiple standard filter units in parallel, like building blocks, according to actual airflow requirements. The L-shaped interface facilitates quick alignment and installation, and forms effective shielding overlap at the connection points, avoiding the weakness of radiation leakage between modules. Simultaneously, this compact connection method maximizes space savings. Furthermore, filter element replacement can be performed remotely using a dedicated shielded trolley, minimizing the operator's contact time and radiation dose with radioactive components, further improving operational safety and convenience.

[0052] Specifically, the top periphery of both the pre-filter cartridge (101) and the HEPA filter cartridge (201) is welded and fixed to the filter housing (3) by a sealing ring plate.

[0053] Each filter cartridge is permanently and airtightly fixed within the main housing, forming a non-removable internal partition structure. This ensures strict isolation between the filter chambers at each stage, prevents airflow short-circuiting, and ensures that air flows along the designed path of pre-filtration followed by high-efficiency filtration, guaranteeing the effectiveness of staged filtration.

[0054] In one specific embodiment, such as Figure 1 As shown: 1. Pre-filter cartridge (101): The pre-filter cartridge (101) is cylindrical and is installed inside the filter housing (3). The top circumference is welded and fixed to the filter housing (3) by a sealing ring plate, and the bottom end is provided with a locking device to lock and fix the pre-filter (102).

[0055] 2. Pre-filter (102): The pre-filter (102) is cylindrical and is installed inside the pre-filter cylinder (101). The top end is connected to the air inlet channel, and the bottom end is fixed inside the pre-filter cylinder (101) by a locking device.

[0056] 3. HEPA filter cartridge (201): The HEPA filter cartridge (201) is cylindrical and is installed inside the filter housing 3. The top circumference is welded and fixed to the filter housing (3) by a sealing ring plate, and the bottom end is provided with a locking device to lock and fix the HEPA filter (202).

[0057] 4. HEPA filter (202): The HEPA filter (202) is cylindrical and is installed inside the HEPA filter cartridge (201). The top end is connected to the air inlet channel, and the bottom end is fixed inside the HEPA filter cartridge (201) by a locking device.

[0058] 5. Filter housing (3): The filter housing (3) is an integral cylindrical type with a rectangular cover plate (4) at the top. The two sides of the housing are respectively provided with an air inlet (7) and an air outlet (8). The inside of the housing is used to install a pre-filter cartridge (101), a pre-filter (102), a HEPA filter cartridge (201), a HEPA filter (202), a shielding sleeve (6), a dose monitoring probe (10), etc.

[0059] 6. Shielding cover (5): The shielding cover (5) is disposed inside the rectangular cover (4) for shielding the accumulated dose inside the pre-filter (102) or HEPA filter (202).

[0060] 7. Shielding sleeve (6): The shielding sleeve (6) is installed inside the rectangular cover plate (4) and is used to fix the dose monitoring instrument (10).

[0061] 8. Air inlet (7): The air inlet (7) is located at the air inlet end of the filter housing (3) and is used to connect the air inlet pipe.

[0062] 9. Air outlet (8): The air outlet (8) is located at the air outlet end of the filter housing (3) and is used to connect the air outlet pipe.

[0063] 10. Support component (9): The support component (9) is a steel component used to support and fix the integrated modular shielded filter device.

[0064] 11. Dose monitoring probe (10): The dose monitoring probe (10) is a tubular radiation detector used to measure the cumulative dose value in filters (102) and (202).

[0065] 12. Online radiation monitoring instrument (11): The online radiation monitoring instrument (11) is used to display the measured value and high alarm in real time on the spot, and transmit the measurement data to the control center.

[0066] 13. Differential Pressure Monitoring Port (12): The differential pressure measuring port (12) is respectively installed on the air inlet (7), air outlet (8) and filter housing (3), and is equipped with a cap. After being connected to the differential pressure monitoring instrument, it is used to monitor the differential pressure values ​​before and after the pre-filter and HEPA filter in real time.

[0067] 14. Positioning device (13): The positioning device (13) is located in the middle of the filter end cap and the bottom of the filter cylinder, and is used to position and fix the filter.

[0068] 15. Sealing gasket (14): The sealing gasket (14) is placed between the outer sealing ring of the air inlet flange of the filter (102 / 202) and the filter cylinder (101 / 201) to seal and isolate the gas.

[0069] like Figure 2 As shown: 1. Rectangular cover plate (4): The rectangular cover plate (4) is the top cover plate of the entire device, with (2) shielding cover plates (5) embedded inside.

[0070] 1. Embedded lifting ring (15): Installed in the middle of the rectangular cover plate (4), embedded, the lifting ring can rotate 180 degrees.

[0071] 2. Bolt fasteners (16): installed on both sides of the rectangular cover plate (4) and connected to the support (9).

[0072] like Figure 3 , Figure 4 As shown: Modules 1-3: Adopt an integrated modular construction for assembly. The module cover plates use an L-shaped structure, which facilitates quick and easy installation and effectively saves floor space.

[0073] The working principle of this device is as follows: When this device is in operation, polluted air enters the filter housing (3) through the air inlet (7). First, larger particles are removed by the pre-filter (102), and then the air enters the HEPA filter (202), which efficiently traps small particles such as radioactive aerosols. The clean air is finally discharged through the air outlet (8). Throughout the process, axial air intake and radial air exhaust safely contain radioactive materials inside the filter element; the online monitoring system tracks the filter status in real time, providing data support for precise maintenance; the locking and sealing structure ensures the accuracy of installation and the airtightness of the system; and the modular design gives the device good layout flexibility. These technical features work together to achieve the design goals of high safety, high reliability, and convenient maintenance.

[0074] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. An integrated modular shielded filtration device, characterized in that, The device comprises: a filter housing (3) with an air inlet (7) and an air outlet (8) on its side wall; a pre-filter assembly arranged inside the filter housing (3), which comprises a pre-filter cylinder (101) and a pre-filter (102) installed therein; a high-efficiency filter assembly arranged inside the filter housing (3), which comprises a HEPA filter cylinder (201) and a HEPA filter (202) installed therein; wherein the pre-filter (102) and the HEPA filter (202) are both cylindrical structures with open top ends, closed side walls and bottoms, and the top ends of both are in communication with an air inlet channel formed by the air inlet (7).

2. The apparatus of claim 1, wherein, The device further comprises a monitoring system, which comprises: a dose monitoring probe (10) fixed in the housing through a shielding sleeve (6) arranged on the top of the filter housing (3); at least one differential pressure monitoring port (12) arranged on the wall of the filter housing (3).

3. The apparatus of claim 2, wherein, The monitoring system further comprises an online radiation monitor (11) in signal connection with the dose monitoring probe (10).

4. The apparatus of claim 1, wherein, The bottom end of the pre-filter (102) is fixed in the pre-filter cylinder (101) through a clamping device (13), and the bottom end of the HEPA filter (202) is fixed in the HEPA filter cylinder (201) through a clamping device (13).

5. The apparatus of claim 4, wherein, A sealing gasket (14) is arranged between the top end of the pre-filter (102) and the pre-filter cylinder (101), and between the top end of the HEPA filter (202) and the HEPA filter cylinder (201).

6. The apparatus of claim 1, wherein, A cover plate (4) is arranged on the top of the filter housing (3), and a shielding cover plate (5) is embedded in the cover plate (4).

7. The apparatus of claim 6, wherein, An embedded lifting ring (15) and a bolt fastener (16) for connecting with a support (9) are arranged on the cover plate (4).

8. The apparatus of claim 1, wherein, The filter housing (3) is an integrated cylindrical structure, and its bottom is fixed and supported by the support (9).

9. The apparatus of claim 6, wherein, The device is of a modular structure, and at least two filter devices can be combined and installed, and the cover plates (4) of adjacent devices are connected by mutually matched L-shaped structures.

10. The apparatus of claim 1, wherein, The top periphery of the pre-filter cylinder (101) and the HEPA filter cylinder (201) is welded and fixed to the filter housing (3) by a sealing circular ring.

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