WO2015060776A1

WO2015060776A1 - Filter arrangement

Info

Publication number: WO2015060776A1
Application number: PCT/SE2014/051243
Authority: WO
Inventors: Sabina KRISTENSSON; Arto Suoniemi; Per Olof Nilsson; Yann LE MOIGNE
Original assignee: Westinghouse Electric Sweden Ab
Priority date: 2013-10-25
Filing date: 2014-10-22
Publication date: 2015-04-30
Also published as: SE1351270A1

Abstract

The present invention relates to a filter arrangement which comprises a distribution pipe (12) receiving the gaseous medium from the inlet opening (1 1 ) and leads it through a longitudinal flow passage inside the container (10), a plurality of filter units (18) which are mounted around the distribution pipe (12) in different positions which each comprises a filter material (23) and passages receiving the gaseous medium from the distribution pipe (12) and leading it through the filter material (23) and in a substantially transverse direction radially outwardly in the container (10), and outlet passages (26) receiving the gaseous medium in a periphery area of the container (10) after it has passed through the filter units (18) and leading it towards the outlet opening (13).

Description

Filter arrangement BACKGROUND OF THE I NVENTI ON AN D PRI OR ART

The present invention relates to a filter arrangement for filtering of a gaseous medium , wherein the filter arrangement comprises a container, an inlet opening where the gaseous medium is led into the container, a filter material which is adapted to be flown through by the gaseous medium inside the container, and an outlet opening where the gaseous medium is led out from the container. It is known to arrange different types of safety filters in connection with a reactor containment for nuclear power plants which comprises a reactor tank enclosed by a reactor containment consisting of gas tight walls. The main part of the radioactive material in a nuclear power plant is concentrated in the fuel el- ements. During a severe accident, radioactive substances can be released in the reactor containment and the pressure inside the reactor containment can rise. In order to ensure the integrity of the containment, the containment can be pressure relieved via a safety filter which is adapted to reduce the amount of radi- oactive material released into the environment.

In Swedish nuclear power plants, a safety filter is used in the form of a wet filter, called FI LTRA-MVSS. This wet filter reduces, at filtered pressure relief, radioactive substances which may exist in the gas. Also the quantity of methyl iodide is reduced but not in a sufficient degree. EP 2 584 565 shows a filter device absorbing radioactive iodine. The filter device comprises a container having an inlet and an outlet for a gas to be filtered . A number of filters to absorb the iodine are arranged inside the container where they extend across the container. In this solution , the inner volume of the container is not used in an effective manner.

SUM MARY OF THE I NVENTI ON

The object of the present invention is to provide a filter arrangement having capacity to filtrate a large amount gaseous medium at the same time as it has a very compact construction . This object is achieved by the initially mentioned filter arrangement which is characterized in that it comprises a distribution pipe receiving the gaseous medium from the inlet opening and leading it through a longitudinal flow passage inside the container, a plurality of filter units which are mounted around the distribution pipe in different longitudinal positions which each comprises a filter material and passages receiving the gaseous medium from the distribution pipe and leading it through the filter material and in a substantially transverse direction radially outwardly in the container, and outlet passages receiving the gaseous medium , after it has passed through the filter units in a periphery area of the container and leading it towards the outlet opening . In this filter arrangement, the gaseous medium is led into a distribution pipe which preferably has a central position inside the container. Advantageously, the distri bution pipe has a length as nearly corresponds to the length of the container in a longitudinal direction . Thus, a relatively large number of annular filter units may be arranged around the distribution pipe along substantially the entire longitudinal extension of the container. In this case, the gas from the distribution pipe is in led radially outwardly from the distribution pipe to the periphery of the container via the filter units which comprise a filter material cleaning the gas from radioactive substances. Thereafter, the outlet passages may lead the gas to the outlet opening via the inner surfaces of the container. With such a construction , the inner volume of the container may mainly be occupied by filter units which are responsible for the filtering of the gaseous medium. Since the flow is distributed over a relatively large filter material area , a suitable flow velocity is obtained through the filter material . Thus, the gaseous medium may pass through the filter material with a relatively low flow velocity which favors the treat- ment of the gaseous medium in the filter units.

According to an embodiment of the present invention , the distribution pipe comprises openings leading out the gaseous medium to the respective filter units. The openings are here arranged in connection with the respective the filter units. The distri bution pipe of the filter arrangement is adapted to distribute the gas flow such that all filter units receive a substantially uniform flow of the gaseous medium . It can be occurred by providing the openings of the distri bution pipe with a varying size such that the flow of the gaseous medium in the distribution pipe is uniformly distri buted to the filter units. However, it is possible to distribute the gas flow from the distribution pipe to the filter units in other ways such as by means of suitably shaped flow members provided with guiding surfaces leading the gas uni- formly into the filter units.

According to an embodiment of the present invention , the distribution pipe has an extension between a first end which comprises the inlet opening and an opposite end which is closed by a stop element. Thus, the gaseous medium entering the distribution pipe via the inlet opening can only be led out via the openings in the distribution pipe. Advantageously, the distribution pipe has a straight extension between said ends. According to an embodiment of the present invention , each of the filter units comprises an inner periphery opening leading the gaseous medium from the distribution pipe to an inner space defined by a wall element and a filter space which comprises the filter material . Thus, the inner space is closed in that the gaseous medium which is received from the distribution pipe can only be led out from the inner space via the filter material . Advantageously, said wall element has an inclination such that the inner space obtains a decreasing volume in en direction radially outwardly in the container. Thus, the inclined wall element leads the gaseous medium towards the filter material when it is led radially outwardly in the inner space.

According to an embodiment of the present invention , the filter material consists of loosely arranged particles which may be balls/pellets. In this case, the filter material is arranged in a fil- ter space in the form of a bed which has a substantially horizontal extension such that the loose balls/pellets are maintained in a layer which has a uniform thickness in all parts of the bed . The filter material may consist of zeolites which are coated with silver. Zeolites are a porous substance having a large contact sur- face with surrounding medium . A chemical reaction may occurs due to the presence of silver when the gaseous medium is led through the filter material at which iodine compounds, for example, methyl iodide is removed from the gaseous medium . According to an embodiment of the present invention , filter arrangement comprises an outer space where the gaseous medium is received after that it has passed through the filter material of a filter unit, wherein the outer space is defined by the filter space of said filter unit and a wall element of an adjacent filter unit. Consequently, the outer space is located between the outer surfaces of two adjacent filter units. There is here no way back but the gaseous medium is led in the outer space radially outwardly in direction towards the inner periphery surface of the container. According to an embodiment of the present invention , the container has a round cross sectional shape in a transverse plane and the filter units have a periphery edge surface which at least partly is located at a distance from the inner surface of the con- tainer such that flow passages is formed radially outwardly of the filter units which constitutes outlet passages leading the gaseous medium along the inner surface of the container in a direction towards the outlet opening . Thus, outlet passages for the gaseous medium are created in a simple manner which lead it in a direction towards the outlet opening . The filter units may have a periphery edge surface which is circular. Advantageously, the edge surface of the filter units forms a somewhat lesser circle than the inner surface of the container in a transverse plane. Thus, a gap-shaped space is formed between the periph- ery edge surface of the filter units and the inner surface of the container which is used as outlet passage for the gaseous medium . Alternatively, the filter units may have a periphery edge surface which comprises a plurality of straight portions which forms an angle to each other. In this case, the periphery edge surface of the filter units may form a plurality of separate gap- shaped spaces in relation to the inner circular surface of the container which are used as outlet passages for the gaseous medium. According to an embodiment of the present invention , at least one of the filter units is built of a plurality of filter components constituting segment of the annular filter unit. The filter arrangement is intended to be able to filter a large amount of gaseous medium which is pressure released/ventilated from a reac- tor containment. Even if the filter arrangement, according to the invention , is compact, a large amount of gaseous medium implies that the filter units have to be made rather large. Therefore, they may be built up by a suitable number of smaller filter components which in a connected state form a filter unit. According to an embodiment of the present invention , the inlet opening is arranged at a lower portion of the container and the outlet opening is arranged at an upper portion of the container. In this case, the gaseous medium is mainly led upwardly in the container except when it is led radially outwardly through the filter units and downwardly through the filter material . With such a design , the filter arrangement may easily be combined with another filter arrangement and be attached on the top of an existing container of such a filter arrangement. Alternatively, the inlet opening may be arranged at an upper portion of the container and the outlet opening may be arranged at a lower portion of the container. In this case, the gaseous medium is thus led substantially downwardly in the container except when it is led radially outwardly through the filter units. At least when the filter units comprise loose filter material , the filter spaces ought to have a horizontal extension . Furthermore, the flow direction of the gas through the filter material ought to be directed downwardly and the distri bution pipe to have a vertical extension . In these cases, it is suitable that the inlet and outlet of the con- tainer are arranged in the above mentioned positions on the container.

BRI EF DESCRI PTION OF THE DRAWI NGS In the following preferred embodiments of the invention are described with reference to the attached drawings, on which :

Fig . 1 shows a filter arrangement according to the present invention in combination with a known filter arrange- ment,

Fig . 2 shows a longitudinal section of the filter arrangement in Fig 1 ,

Fig . 3 shows a cross section view in a plane A-A of filter arrangement in Fig 2 ,

Fig . 4 shows a filter arrangement according to an alternative embodiment and Fig . 5 shows a cross section view in a plane B-B of the filter arrangement in Fig 4.

DETAI LLED DESCRI PTION OF PREFERRED EM BODI MENTS OF THE I NVENTI ON

Fig . 1 shows a filter arrangement 1 according to the present invention . In this case, the filter arrangement 1 constitutes a supplementary filter to an ordinary filter arrangement 2. The ordi- nary filter arrangement 2 is, in this case, a wet filter. The ordinary filter arrangement 2 comprises a container 3. The container 3 has a circular shape in a transverse plane. A schematically shown pressure relief line 4 extends from a reactor containment 5 to an inlet opening in the container 3 of the ordinary filter ar- rangement 2. The line 4 comprises one or several valves 6 and/or one or several frangi ble discs which are opened at occasions when a filtered pressure relief is to be performed . The ordinary filter arrangement 2 comprises an outlet opening 7 defined by an outlet pipe 8 which is arranged at an upper portion of the container 3. I n this case, the supplementary filter arrangement 1 has been applied on an upper surface of the container 3 of the ordinary filter arrangement by aid of a leg construction 9. The supplementary filter arrangement 1 comprises a container 10 which is manufactured of a material which may be resistant against pressure and corrosion . The container 10 has a circular cross sectional shape in a transverse plane and is otherwise designed without sharp edges such that it has capacity to with- stand high internal pressure. The supplementary filter arrangement 1 comprises, at a lower end , a distribution pipe 12 with an inlet opening 1 1 for receiving of gas from the ordinary filter arrangement 2. The distribution pipe 12 of the supplementary filter arrangement has been mounted together with the distri bution pipe 8 of the ordinary filter arrangement by means of a suitable connection such that the gas, in this case, can be directly trans- ferred from the outlet opening 7 of the ordinary filter arrangement to the inlet opening 1 1 of the supplementary filter arrangement. Components such as frangible discs and orifice plates may be arranged between the outlet opening 7 and the inlet opening 1 1 . The supplementary filter arrangement 1 comprises an outlet opening 1 3 at an upper end which is formed by an outlet pipe 14. Components such as frangible discs may be arranged downstream of the outlet pipe. Downstream of the outlet pipe, the cleaned gas is further led in order to be released into the environment in an appropriate manner, for example, via a chimney.

Fig . 2 shows the supplementary filter arrangement 1 more in detail . The distribution pipe 12 has a straight extension in a verti- cal direction in a central position inside the container 10. The distribution pipe 12 has an extension from a lower end which is defined by the inlet opening 1 1 to an upper end which is arranged a small distance below the upper end portion of the container 10. The distribution pipes 12 is at the upper end closed by a stop element 15. The distribution pipe 12 is provided with openings 16 arranged at different high levels. In this case, the openings 16 are arranged at five different high levels of the distribution pipe 12. An annular filter unit 18 is arranged in connection with each of the respective the openings 16. In this case, five annular filter units 18 are arranged around the distribution pipe 12 in connection with the radially openings 16. The annular units 18 comprise a central through hole such that they can be attached around the distri bution pipe 12. The annular filter units 18 are arranged around the distri bution pipe 12 vertically above each other in the form of a stack. The annular filter units 18 comprises inner arranged radially openings 19 which are adapted to be arranged in a corresponding high level as radially openings 16 of the dis- tribution pipe 18. The radially openings 19 of the filter units 18 lead a gas flow to an inner space 20 inside the filter units 18 which is defined by an upper wall element 21 and a lower filter space 22 which is filled with a filter material 23 of loosely arranged particles/balls/pellets. The loose filter material is in this case ball-shaped zeolites (aluminum silicate). The zeolites are coated with silver.

The filter arrangement 1 comprises outer spaces 25 which are located between two adjacent filter units 18 where the gas is received after it has passed through the filter units 18. The outer spaces 25 are defined by the filter space 22 of the filter unit 18 which the gas has passed through and a wall surface 21 of an adjacent filter unit 18. This concerns all outer spaces 25 apart the lowest located one which is defined downwardly by an inner lower surface of the container 10. The gas is led radially out- wardly in the outer spaces 25 until it substantially comes in contact with an inner side surface of the container 10.

Fig . 3 shows a section in a transverse plane A-A in Fig . 2. One of the annular filter units 18 are here shown from the above in a mounted state around the distribution pipe 12. I n this case, the annular filter unit 18 is manufactured of eight connected filter components 24 in the form of segment which each covers an angle range of 45° around the distribution pipe 12. The upper wall element 21 of the respective filter segment 24 consists a flat wall which slopes downwardly from a radially inner position to an outer periphery edge portion 24a of the respective filter segment 24. The container 10 has en circular cross sectional shape while the periphery edge portion 24a of the filter segment 24 are straight. Thus, it is formed a gas passage 26 in en posi- tion radially outwardly of each of the respective filter segments 24.

At times when a filtered pressure relief is to occur, gas flows through the pressure release line 4. Thus, the gas in the reactor containment 5 is led , via the line 4, to the ordinary filter arrangement 2. After that the gas passed through the ordinary fil- ter arrangement 2 , it is led to the supplementary filter arrangement 1 . The gas, which flows into the supplementary filter arrangements is led , via the distribution pipe 12 , in a vertical direction in the container 10. The gas is led substantially uniform from the distribution pipe 12 , via de radially outlet openings 16, to the respective the filter units 18. Initially, the gas is received in the inner spaces 20 of the filter units 18. When the gas is led radially outwardly in de inner spaces 20, the inclined walls elements 21 lead the gas downwardly towards the filter space 22 with the filter material 23. Thereby, the gas is led through the filter material 23 such that it comes in contact with the silver doped zeolites. Thus, a chemical reaction occurs at which , for example, iodine in the form of methyl iodide, is captured and cleaned .

After the gas has flown through the filter material 23, it is received in the outer space 25 which is located between two filter units 18. The gas is led radially outwardly in the outer space 25 until it comes in contact with an inner surface of the container 10. Thereafter, the gas is led upwardly via one of the outlet passages 26 where it successively is mixed with gas from the vertically above located filter units 18. The gas is led further upwardly along the inner surface of the container and then radially inwardly to a position substantially directly above the closed end of the distri bution pipe 1 2. Thereafter, the gas is led out, via the outlet pipe 14 and the outlet opening 13. The gas which leaves the supplementary filter arrangement 1 is thus cleaned .

Fig . 4 shows an alternative embodiment of the filter arrangement 1 according to the invention . I n this case, the filter arrangement 1 comprises distribution pipe 12 with an inlet opening 1 1 at an upper end for receiving of a gas to be cleaned . The filter arrangement 1 comprises an outlet opening 13 at a lower end defined by an outlet pipe 14. The distribution pipe 12 has a vertical extension in a central position in the container 10. The distribution pipe 12 has an extension from an upper end which is de- fined by the inlet opening 1 1 to a lower end which is arranged at a smaller distance above a lower end portion of the container 10. The lower end of the distri bution pipe 12 is closed by a stop element 15. The distribution pipe 12 is provided with openings 16 which are arranged at predetermined high levels.

A plurality of annular filter units 18 are arranged around the distribution pipe 12 in connection with the openings 16. The annular filter units 18 comprise a centrally arranged through hole such that they can be arranged around the distri bution pipe 12 whereupon they are moved to a predetermined mounting position on the distribution pipe 12. Thus, the annular filter units 18 can be arranged vertically above each other in the form of a stack. The filter units 18 comprise internally arranged radially openings 19 in connection with the radially openings 16 of the distribution pipe 18. The filter units 18 comprise an inner space

20 defined by an upper wall element 21 and a lower filter space 22 which is filled with a loose filter material 23. The wall element

21 inclines downwardly from en radially inner position to an out- er periphery edge portion 18a of the filter unit 18.

Fig . 5 shows a section in a transverse plane B-B in Fig . 4. One of the filter units 18 is here shown from the above in a mounted state around the distribution pipe 12. In this case, the filter unit 18 is manufactured as a unitary circular filter component. In this case, the container 10 as well as the filter units 18 have a circular cross-sectional shape. However, the periphery edge portion 18a of the filter unit 18 has a smaller radius than the container 10 at a corresponding level such that it is formed an outlet pas- sage 26 radially outwardly of each of the annular units 18.

During operation , gas is led into the filter arrangement 1 via the inlet opening 1 1 . The gas is led vertically downwardly in the distribution pipe 12. The openings 16 lead out the gas substantially uniformly from the distribution pipe 12 to the filter units 18. Thus all filter units 18 receive, via its inlet opening 19, a substantially equal amount of gas. The gas is led into the inner spaces 20 of the filter units 18. The downwardly inclined wall element 21 guides the gas downwardly towards the lower filter space 22 when the gas is led radially outwardly in the inner space 20. Thereafter, the gas is led downwardly through the filter material 23. Thus, a chemical reaction occurs at which iodine such as methyl iodide is captured from the gas. Thus, the gas leaving the filter material 23 is cleaned . After the gas has flown through the filter material 23, it is received in an outer space 25 which is located below the filter unit 18. The outer space 25 is defined downwards by a wall surface 21 of a below located filter unit 18. However, for the lowest located filter unit 1 8, the outer space 25 is defined by an inner lower surface of the container 10. The gas is led radially outwardly in the outer space 25 until it substantially comes in contact with an inner surface of the container 10. Thereafter, the gas is led downwardly through flow passage 26 where it successively is mixed with gas from vertically below located filter units 18. When the downwardly flowing gas approaches the lower level of the containers, it is led radially inwardly to a position which is located below the stop element 15 for the lower end of the distribution pipe 12. Thereafter, the gas is led out via the outlet pipe 14 and the outlet opening 13.

The present invention is not in any way restricted to the above mentioned embodiments but may be freely modified within the scope of the claims. The filter arrangement is primary adapted to clean gases from methyl iodide which flows out from a reactor containment. The filter arrangement can be used separate or in combination with other types of filter arrangement. It can also be provided with a su bsequently arbitrary filter material .

Claims

1 . A filter arrangement for filtering of a gaseous medium, wherein the filter arrangement comprises a container (10), an inlet opening (1 1 ) where the gaseous medium is led into the container (1 0), a filter material (23) which is adapted to be flown through by the gaseous medium inside the container (10), and an outlet opening (13) where the gaseous medium is led out from the container (10), characterized in that the filter arrange- ment comprises

- a distribution pipe (12) receiving the gaseous medium from the inlet opening (1 1 ) and leading it through a longitudinal flow passage inside the container (10),

- a plurality of filter units (18) which are mounted around the distribution pipe (12) in different longitudinal positions which each comprises a filter material (23) and passages receiving the gaseous medium from the distribution pipe (12) and leading it through the filter material (23) and in a substantially transverse direction radially outwardly in the container (10) and ,

- outlet passages (26) receiving the gaseous medium in a periphery area of the container (10) after it has passed through the filter units (1 8) and leading it towards the outlet opening (13), wherein the distribution pipe (12) comprises radially openings (16) leading out the gaseous medium to the respective filter units (18), that each of the filter units (18) comprises an inner periphery opening (19) leading the gaseous medium from the distribution pipe (12) to an inner space (20) defined by a wall element (21 ) and a filter space (22) comprising the filter material (23), that said wall element (21 ) has an inclination such that the inner space (20) receives a decreased volume in a direction radially outwardly in the container (10) and that the filter material (23) consists of loose particles.

2. A filter arrangement according to claim 1 , characterized in that said openings (16) are designed such that they distribute the gas flow inside the distribution pipe (12) such that all filter units (18) receive a substantially uniform flow of the gaseous medium.

3. A filter arrangement according to claim 1 or 2, characterized in. that the distribution pipe (12) has an extension between a first end which comprises the inlet opening (1 1 ) and an opposite end which is closed by a stop element (15).

4. A filter arrangement according to any one of the preceding claims, characterized in that the filter material (23) consists of zeolites which are coated with silver.

5. A filter arrangement according to any one of the preceding claims, characterized in that it comprises an outer space (25) where the gaseous medium is received after it has passed through the filter material (23) of a filter unit (18), wherein the outer space (25) is defined by the filter space (22) of said filter unit (18) and a wall element (21 ) of an adjacent filter unit (18).

6. A filter arrangement according to any one of the preceding claims, characterized in that the container (10) has a round cross-sectional shape in a transverse plane and that the filter units (18) have a periphery edge surface which at least partly is located on a distance from the inner surface container (10) such that flow passages (26) are formed radially outwardly of the filter units (18) which constitute outlet passages (26) leading the gaseous medium along the inner surface of the container (10) in direction towards the outlet opening (13).

7. A filter arrangement according to claim 6, characterized in that the filter units (18) have en outer periphery edge surface (18a) with a circular shape.

8. A filter arrangement according to claim 6 or 7, characterized in. that the filter units (18) have a periphery edge surface com- prising a plurality of straight portions (24a) which form an angle in relation to each other.

9. A filter arrangement according to claim 7 or 8, characterized in. that at least one of the filter units (18) is built of a plurality of filter components (24) which constitute segment of the annular filter unit (18).

10. A filter arrangement according to any one of the preceding claims, characterized in that the inlet opening (1 1 ) is arranged at a lower portion of the container (10) and that the outlet opening (13) is arranged at an upper portion of the container (10).

1 1 . A filter arrangement according to any one of the preceding claims 1 to 9, characterized in that the inlet opening (1 1 ) is arranged at an upper portion of the container (10) and that the outlet opening (13) is arranged at a lower portion of the container (10).