Air Filter

Abstract

A filter for separation of suspended substances from a flow of air or gas comprises a contaminated gas duct, a filtered-gas duct, each duct having a stub, a disposable filtering assembly having an inlet stub and an outlet stub intended to be attached to the contaminated-gas stub and the filtered stub respectively, and two tubes of flexible sheet material attached to the inlet and outlet stubs respectively. Each duct stub has two gas-tight securing means, the first securing means allowing attachment of the corresponding tube the second securing means allowing addition of successive replacement filtering assemblies, after sealing and cutting of the tube, in such a manner that the remnant of tube attached to the duct stub may be detached from the first securing means after being surrounded by a new tube attached to the second securing means. The new tube is subsequently secured by the first securing means and released from the second securing means.

Description

The present invention relates to a filter device for separation of suspended and in particular radioactive substances from a flow of air or gas.

The filter devices normally employed for separation of suspended substances consist of a filter housing traversed by the gas to be purified, this housing having arranged in it in a sealed manner filter elements situated transversely to the gas flow. Openings closable by means of a cover and externally operated clamping elements for sealing contact, pressing on the filter elements within the housing, are provided in the filter housing for replacement of the filter elements, as required after saturation of the same.

The application of devices of this nature to the separation of suspended radioactive substances in nuclear plants, for example, entails the requirement that the necessary replacement of a filter element saturated with dust by a fresh filter element should be performed in such manner that the personnel is protected reliably against injury by radioactive suspended substances. To this end, the saturated filter element must be stowed in a sealed protective bag during removal from the filter housing. At the same time, the opening must be reliably sealed off circumferentially during the replacement, that is, by the protective bag, so that the personnel is protected against direct contact with radioactively contaminated substances. The time required for the exchange of filter elements must be as short as possible, so that the personnel may be protected against radiation damage at high levels of activity.

In the case of air filter devices of this kind, employed in nuclear plants, an oval marginal ring having several uninterrupted grooves in its surface has been conventionally arranged around the opening of the filter housing. During replacement of the filter element, a bag of synthetic material is secured in the grooves of the marginal ring. The cover of the housing opening must be opened initially, in many instances through the bag itself, and the clamping device for the filter element must be freed. The filter element saturated with dust is then pulled into the bag. The protective bag is sealed off by welding, so that the filter element is situated within a sealed plastic bag, whereas a portion of the plastic bag sealed by the severing weld, is left on the marginal ring. A fresh filter element stowed in another plastic bag is inserted into the opening of the housing in such manner that the protective bag containing the filter element is initially secured in an unoccupied groove of the marginal ring, whereupon the weld-sealed remainder of the previous plastic bag situated on an anterior groove is pulled off the marginal ring, the filter element is pushed into the opening, the clamping device accessible from the outside is operated, and the opening is sealed off by means of a cover. The same procedure must be applied for replacement of the next filter element. This known device causes considerable risks, owing to the structure of the air filter housing and to the application of the plastic bag to the filter element. There is the risk that the unwieldy filter element, possessing a rectangular shape as a rule, may damage a protective bag made of plastic sheet, so that radioactively contaminated suspended substances may spread the contamination to the environment through the protective bag. Even if the most stringent precautions are applied, damage of this kind cannot always be prevented from occurring to the plastic bag during the extraction of the filter element, particularly since the filter elements are of relatively great size and the plastic bags must be dimensioned accordingly. A substantial further disadvantage resides in that a relatively long period elapses owing to the unwieldy handling operations required for replacement of the filter element, so that the personnel must be relieved several times in plants of great size during the replacement operation in view of the radiation danger existing at the high levels of activity. In view of the reasons stated, the operation for replacement of a filter element is dangerous to the personnel, in the case of this known device. The relatively large sealing area between the filter element and the housing is considered to be yet another disadvantage, involving correlatively great contact thrust forces to be exerted by the sealing or clamping elements.

In the case of nuclear plants of greater size in particular, air filters of special structure, such as pot filters have accordingly been employed, in which the contaminated filter elements are removed from the filter housing by means of remotely controlled manipulators, and conveyed to a storage or combustion section. These systems, which assure excellent protection for the personnel, are extremely costly in view of the equipment, labor and structural expense involved, so that the general demand prevails in this sphere of application for arrangements allowing the radioactively contaminated filter elements saturated with dust to be replaced in a minimum of time by the personnel without requiring unwieldy, and possibly dangerous, servicing operations.

According to the invention there is provided a filter for separation of suspended substances from a flow of air or gas, comprising a contaminated-gas duct, a filtered-gas duct, each duct having a stub, a disposable filtering assembly having an inlet stub and an outlet stub intended to be attached to the contaminated-gas stub and the filtered-gas stub respectively, and two tubes of flexible sheet material attached to the inlet and outlet stubs respectively, each duct stub having two gas-tight securing means, the first securing means allowing attachment of the corresponding tube, the second securing means allowing addition of successive replacement filtering assemblies, after sealing and cutting of the tube, in such a manner that the remnant of tube attached to the duct stub may be detached from the first securing means after being surrounded by a new tube attached to the second securing means, the new tube being subsequently secured by the first securing means and released from the second securing means.

A feature of the invention is that the securing means may be continuous grooves formed in the duct stub.

Another feature resides in that the filter assembly consists of a middle portion open at both ends, corresponding to the cross-sectional shape of the filter element, and of two funnel-shaped covering portions, each carrying a connector stub, and overlapping the middle portion with intercalation of seals placed on the filter element, and joined to the central portion, e.g., by means of liquid hardenable substances, to form an integral structural unit.

Owing to the arrangement of the filter element within a filter assembly possessing connector stubs, according to the invention, it becomes superfluous to employ the onerous arrangement and operation of complex gas-proof clamping devices for sealing the filter elements, since sealing is now directly effected in a simpler manner on the filter unit. It is no longer necessary to extract the filter elements from the filter housing, since the filter assembly receiving the filter element may have its connecting flanges disconnected externally from the flanges of the duct.

Owing to the incorporation of the two connector stubs with the overlapping flexible protective tubes, and thanks to the displaceable arrangement of the filter assemblies in a guide beam of the duct, it is possible by displacement of the filter assembly relative to the duct to sever and weld the stretched plastic tubes in the middle, so that the connecting flanges of the filter unit as well as the flanges of the duct are sealed off in gas-tight and safe manner. The filter assembly containing the saturated filter element is then withdrawn from the beam on the duct and carried away for destruction by storage of incineration. A fresh filter assembly is inserted into the beam on the air duct, fresh protective tubes being connected between the connector stubs of the filter assembly and of the duct at the same tine. The assembly is then pushed into the operating position and the flanges situated at the extremities of the connector stubs are joined to one another in sealed manner by means of resilient clamping elements releasable from the outside.

An embodiment of the filter according to the invention is characterized in that the connector stubs of the filter assembly are arranged coaxially relative to each other, and that the filter assembly has projecting pegs on opposite sidewalls of the middle portion arranged displaceably in transverse direction relative to the axis of the connectors in a frame built up from channel sections. The connector stubs of the ducts and the connector stubs of the filter assembly are equipped terminally with matching sealing flanges which may be closed in hermetic manner by means of rapid-release clamps engaging same. In this embodiment, the filter assembly is intercalated between the two spaced flanges of an air duct. The displacement of the filter assembly for the purpose of replacing the same should occur transversely to the axis of its connector stubs.

In the case of filter plants of greater size in which it is mandatory to employ several filter assemblies of this nature, a relatively great floor or installation space is necessary in view of the required transverse displaceability of the filter assemblies. A modified embodiment possesses the advantage of requiring a minimum of space for installation purposes. It is characterized in that the filter assembly connector stubs are situated parallel to each other on one side of the filter assembly, and that a main air-duct has a partition situated between its connector stubs for division into contaminated-air and pure-air passages. Rows of connector stubs for reception of a row of filter assemblies, arranged one beside the other, may be provided at one or both sides of the main air duct.

Channel-section beams may be arranged on the duct, bearing the filter assembly in a manner enabling their displacement relative to the axial direction of the connector stubs. This embodiment offers the possibility that a multiplicity of rows of connector stubs may be provided, adjoining the two opposed sides of a box-like duct divided by a partition into a contaminated-gas passage and a pure-gas passage, so that a multiplicity of filter assemblies containing filter elements may be arranged on one duct. The filter assemblies may be arranged contiguously, since a single displacement perpendicular to the side of the duct is necessary for replacement of the filter assemblies, owing to the presence of the connector stubs.

Another feature of this embodiment resides in that pivoted latch means in the form of spring-loaded or analogous screw clamps, which are downwardly tippable, are employed to establish the sealed joint between the connector stubs of the filter assemblies and the connector stubs of the duct, and secure the filter assemblies at the extremities of the beams or rails. In this case the connector stubs of the filter assemblies each possess a sealing flange, and the connector stubs of the duct each possess a contact surface equipped with a seal and receiving the sealing flange. The application of clamping elements engaging the flanges of the connector stubs becomes superfluous, thanks to the provision of the spring-loaded screw clamps, since the latter themselves ensure that the filter assembly is pressed in sealing manner against the duct. These clamps have the additional advantage that they are self-adjusting, thanks to their spring-loading, to take up any give of the seals.

The invention will now be described in detail with reference to the accompanying drawing, which illustrates the invention in a non-restrictive sense. In the drawing:

FIGS. 1A to 1F are diagrammatical illustrations of different stages of operation of one embodiment, showing the substitution of a fresh filter unit for a contaminated one;

FIGS. 1A to 1F are sectional detail views relating to FIGS. 1A-1F, respectively;

FIG. 2 is an illustration of a modified embodiment of an air duct, in elevation;

FIG. 2A is a section along the line IIA-IIA of FIG. 2;

FIG. 3 is an illustration corresponding to FIG. 2 of a complete apparatus with filter units installed, in side view;

FIG. 3A is an elevational view of the apparatus of FIG. 3;

FIG. 4 illustrates a single filter unit comprising a filter element in side view;

FIG. 4A is a plan view of the filter element of FIG. 4;

FIG. 5 is an enlarged illustration of a detail of FIG. 4;

FIG. 6 is an illustration of the filter unit according to FIG. 4 coupled to the air duct;

FIG. 7 is an illustration of another modified embodiment in the disconnected condition;

FIG. 8 is an illustration corresponding to FIG. 7, showing the connected condition;

FIG. 9 is an illustrated in perspective of an air duct according to FIG. 2; and

FIG. 10 is an illustration in perspective of an air duct, with a filter unit disconnected.

A filter unit 1 comprising two coaxial connector stubs 2 and 3 is shown in FIGS. 1A to 1F. A filter element 26 corresponding to FIG. 1A, is situated in the unit 1. The filter unit 1 has its connector stubs 2 and 3 connected to the connector stubs 4 and 5 of an air duct. To this end, the stubs 2 and 3 each possess a sealing flange 6, and the connector stubs 4 and 5 each possess a sealing flange 7. The two corresponding sealing flanges 6 and 7 are held in sealing contact by means of a coupling clamp 8 which is releasable from inside or outside the protective tube.

Circumferential rings or collars 9 and 10 are situated on the stubs 2, 3 and 4, 5, a plastic tube 11 being fastened on each of these rings, to envelop the two stubs 2, 4 and 3, 5. As shown by the enlarged detail views of FIGS. 1A-1F, the circumferential ring 10 has two peripheral grooves 12 and 13 extending parallel to each other, the tube 11 being clipped in these grooves by means of elastic bands and being made of transparent plastic. The filter unit 1 has projecting pegs 14 engaged in a frame 15 made of channel sections. FIG. 1A shows the filter unit 1 coupled to the stubs 4 and 5 of the air duct.

When the filter element situated in the filter unit 1 is saturated with dust and must be replaced, the coupling clamp 8 of the sealing flanges is freed initially by action through the tube 11, whereupon the filter unit 1 is displaced towards the right in the frame 15 according to FIG. 1B, with stretching of the plastic tube 11.

As is apparent from FIG. 1C, the plastic tube 11 is severed and welded shut at the same time at the point 16 by means of welding shears. The filter unit 1 is then pulled out of the frame 15, towards the right, its two connector stubs 2 and 3 being sealed off in gas-tight manner by the two welded plastic hose portions 11.

A new filter unit 1 is inserted into the frame 15 according to FIG. 1D. A new plastic tube 17 is clipped on to each of the circumferential rings 9, in each case, the other extremities of these tubes being secured in the outer grooves 13 of the circumferential rings 10 of the stubs 4 and 5.

According to FIG. 1E, the remainder of the tube 11 present on the inner groove 12 of the circumferential ring 10 is then pulled off and, according to FIG. 1F, the filter unit 1 is then brought into the coupled position corresponding to FIG. 1A. During replacement of this filter unit 1, the remainder of the plastic tube 11 is received in the part of the tube 17 which envelops the connector stubs 2 and 3 of the filter unit in gas-tight manner.

FIGS. 2 to 10 show other embodiments, FIGS. 2 and 2A showing a duct 18 of rectangular cross-section divided into an upper chamber 20 and a lower chamber 21 by a central partitioning plate 19. At the right-hand end of the upper chamber the central air inlet 20a for the dust-laden air is situated, the air outlet 21a for pure air being situated at the opposite end of the lower chamber 21. Projecting stubs 2 and 3, forming an upper row leading into the chamber 20 and a lower row leading into the chamber 21, are situated on both sides of the duct 18. I-beams 22 are situated on the sidewalls of the duct 18, between the stubs 2 and 3.

FIGS. 3 and 3A show filter units 23 equipped with connector stubs 24 and 25 parallel to each other and connected to the stubs 2 and 3 in the manner specified in the foregoing, description with plastic tubes affixed to the circumferential rings. The filter units 23 may be displaced on the beams 22 and removed, at right angles to the sidewalls of the air duct 18.

The filter unit 23 is shown in detail in FIGS. 4, 4A and 5. This unit comprises a prismatic central portion or casing 26 open at both ends, and containing a coarse filter 30 and a fine filter 31. A frustoconical cover 27 is arranged above the central portion 26, and a similar cover 28 is arranged under the central portion 26. The edges of the covers 27 and 28 overlap the middle portion 26 with seals 32 intercalated between the filters 30, 31 and the cover portions 27, 28. The parts 26, 27 and 28 are combined into a gas-tight unit by sealing the overlapping edges of each a covers 27 and 28. The connector stubs 24 and 25 carrying the circumferential ring 9 and a sealing flange 6, at their front extremity, are arranged on the sides of the covers 27 and 28.

FIG. 6 shows the filter unit 23 connected to the duct 18. The filter unit 23, carried by the beam 22, is connected to the duct 18 by means of the stubs 2 and 3 which lead into the duct chambers 20 and 21. To this end, clamps 8 straddling the sealing flanges 6 and 7 are situated inside or outside the plastic tube 11 which is secured in the circumferential rings 9 and 10.

To replace the filter unit 1, the clamping elements 8 are freed by action through the tube 11 or from the outside of the tube 11, whereupon the filter unit 23 is drawn off the stubs 2 and 3 along the beam 22. The filter unit 23 is guided by means of pegs 33. The protective tubes 11, stretched by the removal of the filter unit 23, are severed in the manner shown in FIG. 1C, whereupon a filter unit 23 saturated with dust is pulled out of the beam 22, a new filter unit 23 then being inserted and brought into sealing contact with the stubs 2 and 3 with replacement of a new plastic tube.

FIGS. 7 and 8 show a further embodiment of the filter unit 23 in which it is unnecessary to fit clamping elements on the sealing flanges of the stubs. A beam 39 carries at its end a downwardly tippable or foldable screw clamp 34 equipped with a compression spring 35. As is apparent from FIGS. 3 and 3A, the screw clamps 34 bear on the rear side of the central portion 26 of the filter unit 23 whose upper and lower guiding flanges 40 bracket the beam 39. The filter unit 23 has an upper and a lower stub 36, these stubs carrying each a circumferential ring 9. An upper and a lower connector stub 37, each carrying a circumferential ring 10 and a comprising an annular contact surface 38 designed for sealing engagement with the confronting flange 6 of a corresponding connector stub 36, are connected to the duct chambers 20 and 21 of the air duct 18. When the filter unit 23 has had its connector stub 36 brought into contact with the stub 37, the screw clamps 34 are raised and tightened, so that the flanges of the filter unit 23 are pressed in sealing manner against the seat 38. The give of the seal is taken up continuously by the spring 35.

FIG. 9 illustrates in perspective of the air duct 18 according to FIG. 2, comprising beams 22 and spring-loaded screw clamps 34. FIG. 10 is a similar illustration showing a duct case 41 divided by partitions 42 into an upper dust-laden-air portion and a lower pure-air portion. The filter unit 23, arranged on this case 41 in the manner described above, is illustrated prior to having its guiding pegs 33 inserted in the rails 22 which in this case form part of a single channel beam bent into U-shape.

Claims

I claim:

1. A gas-purification filter comprising: an incoming duct for dust-laden gas terminating in a first stub; an outgoing duct for purified gas terminating in a second stub parallel to said first stub; a filter casing provided with an inlet stub and an outlet stub coaxially confronting said first and second stubs, respectively; rail means parallel to the axes of all said stubs supporting said casing for displacement between an operative position proximal to said ducts and a withdrawn position remote therefrom, said inlet and outlet stubs sealingly engaging said first and second stubs, respectively, in said operative position; a pair of accordion-pleated flexible synthetic resin tubes with extremities releasably clamped to the confronting ends of said inlet and first stubs and of said outlet and second stubs, respectively, said tubes being sufficiently deformable to permit removal of said casing to said withdrawn position with disengagement of said stubs yet without unclamping of said tubes; and pivoted latch means on said rail means for alternately locking said casing in said operative position and facilitating detachment of said casing from said rail means upon removal to said withdrawn position.

2. A filter as defined in claim 1 wherein each of said stubs is provided with an external collar having two parallel grooves, further comprising a pair of elastic bands for each stub receivable in said grooves thereof for alternate engagement with respective tube extremities during replacement of a remnant of a severed tube by a fresh tube.

3. A filter as defined in claim 1 wherein said ducts are formed by respective compartments of a common housing, said rail means being secured to said housing.

4. A filter as defined in claim 3 wherein said rail means comprises a pair of channel beams bracketing said casing.

5. A filter as defined in claim 4 wherein said channel beams are end portions of a single rail member bent into U-shape.

6. A filter as defined in claim 1 wherein said latch means comprises a swingable holder and a clamping screw on said holder.

7. A filter as defined in claim 1 wherein said casing comprises a prismatic box with frustoconical covers on opposite sides thereof respectively bearing said inlet and outlet stubs.