GB2260917A

GB2260917A - Automatic vent system

Info

Publication number: GB2260917A
Application number: GB9123238A
Authority: GB
Inventors: Jeffrey Stamp; Claude Louis Denis Broussy
Original assignee: Pall Corp
Current assignee: Pall Corp
Priority date: 1991-11-01
Filing date: 1991-11-01
Publication date: 1993-05-05
Anticipated expiration: 2011-11-01
Also published as: FR2687829B1; FR2687829A1; GB9123238D0; ES2070683A2; ES2070683B1; GB2260917B; BE1006903A3; ES2070683R

Abstract

An automatic vent system can be used, for example, in a contaminant 28 of a nuclear reactor so that when pressure in the contaminant rises as a result of an accident, gas and contaminant (particles) pass into inertial separators 17 in a chamber 18 into where contaminant is separated and exhausted within the contaminant from chamber 18 by a pump impeller 26, while clean gas passing from the separators into a duct 12 drives a turbine 24 to power the impeller 26. The system requires no external power source and can thus remain dormant until an emergency occurs and then provide high extraction of contaminant with minimum pressure drop with maximum extraction of contaminants. Coalescer/mist eliminators 30, 31 may be located upstream and/or downstream of separators 17. In an alternative arrangement, the pump impeller (or other pump) can be driven from an external power source. <IMAGE>

Description

AUTOMATIC VENT FILTERS The invention relates to automatic vent filters.

Some enclosures can contain, intermittently, fluid at a pressure higher than normal and containing contaminants.

In order not to damage the enclosure, it is necessary to release the fluid pressure to atmosphere but to try and ensure as far as possible that the contaminants are not vented with the fluid.

An example of such a situation is prevention of the escape of irradiating matter and particulate contaminant from a nuclear power station in the event of a reactor failure.

Reactors, such as pressurized water nuclear reactors, are housed in concrete buildings, known as containments, whose purpose is to retain any radioactive material close to the reactor. In the event of a nuclear accident, such as a reactor core meltdown, it is likely that extremely high temperatures will be generated within the reactor. In order to control such an accident, water would be sprayed on to the containment to provide cooling. The effect of the temperature and the water evaporation is to raise the gas pressure in the containment. In order to prevent rupture of the containment, a vent is installed to allow gas to be vented at some pressure below the burst pressure of the containment. Since the burst pressure is typically in the region of 12 bar.g., the vent is usually designed to operate at pressures in the region of 5-7 bar.g.

It is desirable that such a vent will fit inside the containment so that the radiation hazard is controlled in one area that should have high capacity for contaminant, since the contaminant level cannot be accurately predicted.

It has been proposed to provide a barrier filter in such a vent. A barrier filter is a filter in which it presents a barrier to the passage of particulate through the filter.

Such a filter might be formed, for example, of fibrous material. However, such barrier filters have the problem that they are readily blocked by particulate (they have a low contaminant capacity) and that such blockage would lead to a possible over-pressurization of the containment. This can to a certain extent be mitigated by increasing the size of such a barrier filter, but there are plainly limits on an acceptable size.

According to a first aspect of the invention, there is provided an automatic vent filter comprising a housing having an inlet and an outlet for the passage of fluid therethrough, a chamber being provided in the housing and dividing the housing into upstream and downstream sections, the chamber including at least one inertial separator having an inlet communicating with the upstream end of the housing, a fluid outlet communicating with a downstream end of the housing and a contaminant outlet leading to the interior of the chamber, the chamber also having an outlet in which is provided a pump for drawing contaminant from the chamber to exhaust.

Since, following any accident, the gas in the containment would be heavily contaminated with radioactive particulate material, the vent must filter this gas to remove the radiation hazard. Such a filter may thus be required to be passive, because power supplies may be disrupted by the accident.

The housing may have, located between the chamber and the housing outlet, a converter for converting kinetic energy of fluid passing through the housing into power which drives the pump so that contaminant laden fluid entering the housing inlet has the contaminant separated therefrom by the separator and exhausted by the pump, the fluid downstream of the chamber driving the converter to power the pump.

In this way, blockage is avoided since contaminant is continuously removed from the separator by the pump. No external power source is, however, required because the kinetic energy of the gas is used to drive the pump.

According to a second aspect of the invention, there is provided a method of separating contaminants from fluid comprising passing the fluid through an inertial separator to separate the contaminant from the fluid and then passing the fluid through a converter to convert the kinetic energy of the fluid into power to drive a pump, the pump acting to draw separated contaminant from the separator and pass the contaminant to exhaust.

The following is a more detailed description of an embodiment of the invention, by way of example, reference being made to the accompanying drawing in which: Figure 1 is a front elevation of an automatic vent filter Figure 2 is a section on the line II-II of Figure 1, Figure 3 is a similar view to Figure 2, but showing the additional coalescer/mist eliminator panels.

Figure 4 is a partial section of a second form of automatic vent filter incorporating a first form of ejector pump, and Figure 5 is a partial section of a third form of automatic vent filter incorporating a second form of ejector pump.

Referring to both Figure 1 and Figure 2, the vent filter comprises a housing 10 which may, for example, be manufactured from light gauge stainless steel sheet which is completely airtight with airtight sealed joints. The housing 10 has a rectangular inlet 11 followed by a duct 12 which reduces in cross-section to connect to a tube 13 whose downstream end provides an outlet 14.

Two parallel but spaced rectangular panels 15,16 are mounted in the inlet 11 of the housing 10 to divide the housing into upstream and downstream portions. The edges of the panels 15,16 are completely airtight with the adjacent housing.

The panels 15,16 and the portion of the housing 10 between them define a chamber 18. A plurality of inertial separators 17 are arranged within the chamber extending between the panels 15,16. As best seen in Figure 2, each separator includes a tube having an inlet 19 which opens on the upstream panel 15 and an outlet 20 which opens on to the downstream panel 16. The inlets 19 and the outlets 20 are welded to the associated panels 15,16.

Each inertial separator 17 comprises a tube and a swirl generator at 21 arranged within the tube. A contaminant outlet 22 leads into the chamber 18 at a point intermediate the inlet 19 and the outlet 20 of each inertial separator 17.

The inertial separator 17 may take any convenient form.

One such inertial separator is sold by Pall Corporation under the trade mark CENTRISEP and is described in UK Patent Specifications Nos. 1236941 and 1207208. In such a separator, a fluid/contaminant mixture entering the tube is acted on by the swirl generator which causes the mixture to swirl and hence imparts a centrifugal force to the contaminant. This causes the contaminant to collect in an annular space adjacent the inner surface of the tube. The outlet 22 is sized to remove fluid/contaminant from this annular zone while the remaining fluid in the centre of the tube (not containing contaminant) passes to the tube outlet 20.

It will be appreciated that the size and performance of the inertial separator 17 will be arranged to meet expected operating requirements.

A kinetic energy converter 23 is mounted in the tube 13 and comprises a fluid driven turbine 24 connected to one end of a drive shaft 25. The drive shaft 25 passes through the duct 12 (with appropriate seals to prevent passage into the duct 12 of contaminant) and carries at its opposite end a pump in the form of an impeller 26.

The impeller 26 is located in the sealed outlet passage 27 leading from the chamber 18 to exhaust.

In use, the filter is mounted on, for example, a wall 28 of a containment, such as a chamber for housing a nuclear reactor (not shown). The outlet 14 to the tube 13 is connected to an aperture 29 in the wall.

While the pressure within the containment remains at or close to atmospheric pressure, the filter is dormant. If, however, the pressure rises above a predetermined level explosive discs or valves in the inlets to inertial separators 17 will open and allow fluid flow through the separators 17. The turbine 24 will start to operate thus operating the impeller 26. Fluid within the containment, which will usually be air, will, as a result of the pressure difference between the interior and exterior of the containment, pass into the inertial separators 17 where contaminants will be separated out by centrifugal forces and removed by a scavenge air flow created by a suction pressure provided by the impeller 26 and pass into the chamber 18 and out through the outlet passage 27.

During this operation, the duct 12 performs a function of controlling the air flow distribution through the panels 15,16 to achieve a uniform flow per separator 17. By reducing its cross-section in a downstream direction, the duct 12 accelerates the air flow to provide the correct velocity vector to suit the turbine 24. It also decelerates the air flow from the turbine 24 with minimal pressure loss.

The duct 12 incorporates drainage slopes to collect any liquid that passes into the housing 10 and directs it to the outlet passage 27 via a connecting scavenge hole provided between the duct 12 and the passage 27. Flow through this hole will be induced by a small pressure differential between the duct 12 and the passage 27.

In order to reduce the volume of liquid passing into the housing 10 and exiting from the housing 10, coalescer/mist eliminators may be placed upstream and/or downstream of the chamber 17.

An example of this is shown in Figure 3 in which parts common to Figure 3 and Figure 2 are given the same reference numerals and will not be described in detail.

In this example two coalescers/mist eliminators 30,31 are provided - one upstream of the separators 17 and one downstream of the separators 17 within the chamber 12.

Each coalescer/mist eliminator 30,31 comprises a frame 32 holding upstream and downstream meshes 33,34 between which is sandwiched a knitted pad of wire 35 having a predetermined density and thickness. The wire diameter may, for example, be between 0.1mum to 0.3mm. The lower point of the frame 32 is connected to a duct 36 which leads to the outlet passage 27.

The upstream coalescer/mist eliminator 30 is connected to the duct 12 by a cowling 37 which is proivded with gaps, one of which is shown at 38 to allow fluid flow to the separators 27 in the event that the coalescer/mist eliminator is blocked by contaminant.

In use, water and contaminant laden air impinges on the upstream coalescer/mist eliminator 30, small droplets of water impact on the wires and coalesce into larger droplets which pass down through the wires to the duct 36 from where they are scavenged into the passage 27 by the pressure differential created by the impeller 26. In this way, the volume of water passing to the separators 17 is reduced substantially.

The downstream coalescer/mist eliminator 31 works in the same way, removing water from the air passing from the separators 17 into the chamber 12.

The use of coalescer/mist eliminator panels 30,31 can provide an overall water removal efficiency of 99.6% or better.

The outlet passage 27 is designed to collect efficiently air and contaminant from the chamber 17 and to ensure that a good air flow distribution is achieved at the impeller 26 with the minimum pressure drop and with the minimum risk of low flow areas where the contaminant may be deposited. This outlet 27 may be connected to a duct which directs fluid and contaminant to a corner of the containment where fluid is static and hence the fluid and particulate can be dumped with the minimum risk of it being reintrained by the filter. This duct can be designed also to decelerate the air flow to recover kinetic energy and to provide a baffle system to maximize contaminant retention in the correct location.

A filter such as that described above with reference to the drawings can operate at, for example, a pressure of 1.8 bar and above and at air temperatures up to 3000C.

For a 7 micrometre median sized dust distribution, between 90-92% of dust particulate can be separated from air. An efficiency for water separation of between 60-90% can also be achieved.

The pressure drop across the housing 10 is minimal and remains constant throughout operation, thus eliminating the risk of over pressurization of the containment.

There are a number of variations that can be made to the filter. A second chamber formed by two panels and the housing 10 may be provided downstream of the first chamber 18 and including further inertial separators arranged as the inertial separators 17 described above. The second chamber may have an outlet connected to the impeller passage 27.

The inertial separators in the second chamber can have different characteristics to the inertial separators 17 in the first chamber 18.

The impeller 26 can be replaced by scavage fans, or compressed air ejectors or water/oil jet pumps powered from an external power source. Two such proposals are shown in Figures 4 and 5 and will now be described in greater detail. Parts common to Figures 1 to 3 and to Figures 4 and 5 will be given the same reference numerals and will not be described in detail.

In the embodiment of Figure 4, the turbine 24, the impeller 26 and the connecting drive shaft 25 are omitted. The outlet passage 27 is formed with a chamber 45 from which leads a vertical ejector tube 46 terminating in a diverging outlet 47. A pipe 48 terminates within the chamber 45 in a nozzle 49 which is directed into the tube 46. The pipe 48 is connected to a source 50 of high pressure gas or liquid (which may be air or water).

In use, the fluid from the source 50 emerges from the nozzle 49 and creates a zone of reduced pressure in the chamber 45. This draws separated contaminant from the separators 17 and water from the coalescers/mist eliminators 30,31, where such are provided. The contaminant and water are entrained in the fluid flow from the nozzle 49 and pass with the fluid through the tube 46 and the outlet 47 to the containment.

The embodiment of Figure 5 is similar, except that the ejector tube 46 and the diverging outlet 47 are horizontally arranged. The nozzle 49 is connected to a source 51 of liquid/gas mixture under pressure which, in use, exits the nozzle at sonic or supersonic velocity to create a low pressure zone in the chamber 45 and to entrain contaminant and water and pass them to the containment.

Claims

1. An automatic vent filter comprising a housing having an inlet and an outlet for the passage of fluid therethrough, a chamber provided in the housing and dividing the housing into upstream and downstream sections, the chamber including at least one inertial separator having an inlet communicating with the upstream end of the housing, a fluid outlet communicating with a downstream end of the housing and a contaminant outlet leading to the interior of the chamber, the chamber also having an outlet in which is provided a pump for drawing contaminant from the chamber to exhaust.

2. An automatic vent filter according to claim 1 wherein the housing has located between the chamber and the housing outlets, a converter for converting kinetic energy of fluid in the housing into power which drives the pump so that contaminant laden fluid entering the housing inlet has the contaminant separated therefrom by the separator and exhausted by the pump, the fluid downstream of the chamber driving the converter to power the pump.

3. An automatic vent filter according to claim 1 wherein the converter comprises a turbine rotated by the fluid, the rotation of the turbine being used to drive the pump.

4. An automatic vent filter according to claim 3 wherein rotation of the turbine rotates a shaft which, at an end thereof, remote from the turbine, is connected to the pump to drive the pump.

5. An automatic vent filter according to claim 3 wherein the turbine is connected to an electrical generator whose electrical output is connected to an electric motor which drives the pump.

6. An automatic vent filter according to claim 3 wherein the turbine is connected to a fluid compressor having an outlet for compressed fluid connected to a fluid motor for driving the pump.

7. An automatic vent filter according to any one of claims 3 to 6 wherein the housing includes a tubular section, the turbine being mounted in said tubular section at a downstream end of said tubular section forming the housing inlet.

8. An automatic vent filter according to claim 1 and including a source of external power connected to the pump.

9. An automatic vent filter according to claim 8 wherein the pump is a fluid ejector pump connected to a source of fluid under pressure.

10. An automatic vent filter according to any one of claims 1 to 9 wherein the chamber is formed by two parallel but spaced panels lying in respective planes normal to the direction of flow of fluid through the housing, the at least one inertial separator extending between said panels.

11. An automatic vent filter according to claim 10 wherein a plurality of inertial separators are provided, the separators extending parallel to one another between said panels.

12. An automatic vent filter according to any one of claims 1 to 11 wherein the at least one inertial separator comprises a tube forming the inlet and the fluid outlet and a swirl generator arranged within the tube for imparting a centrifugal force to fluid and contaminant entering the tube so that the contaminant flows around a radially outer annular section of the tube, the contaminant outlet removing the fluid and contaminant from said section while the remainder of said fluid leaves the tube through the fluid outlet.

13. An automatic vent filter according to any one of claims 10 to 12 and including a second chamber downstream of the first chamber and formed by two parallel but spaced panels lying in respective planes normal to the direction of fluid flow through the housing, at least one further inertial separator extending between an inlet formed in an upstream panel and an outlet formed in a downstream panel, the second chamber leading to the outlet of the first-mentioned chamber.

14. An automatic vent filter according to any one of claims 1 to 7 wherein the pump comprises a centrifugal impeller.

15. An automatic vent filter according to any one of claims 1 to 14 wherein a mist eliminator is provided in the housing upstream of the chamber for separating water from fluid entering the housing.

16. An automatic vent filter substantially as hereinbefore described with reference to the accompanying drawings.

17. A method of separating contaminants from a fluid comprising passing the fluid through an inertial separator to separate the contaminant from the fluid and then passing the fluid through a converter to convert kinetic energy of the fluid into power to drive a pump, the pump acting to draw separated contaminant from the separator and pass the contaminant to exhaust.

18. A method of separating contaminants substantially as hereinbefore described with reference to the accompanying drawings.

Amendments to the claims have been filed as follows 1. A containment including a nuclear reactor and an automatic vent filter comprising a housing having an inlet within the containment and an outlet without the containment for the passage of fluid therethrough, a chamber provided in the housing and dividing the housing into upstream and downstream sections, the chamber including at least one inertial separator having an inlet communicating with the upstream end of the housing, a fluid outlet communicating with a downstream end of the housing and a contaminant outlet leading to the interior of the chamber, the chamber also having an outlet in which is provided a pump for drawing contaminant from the chamber to exhaust within the containment.

2. An automatic vent filter, containment and nuclear reactor according to claim 1 wherein the housing has located between the chamber and the housing outlet, a converter for converting kinetic energy of fluid in the housing into power which drives the pump so that contaminant laden fluid entering the housing inlet has the contaminant separated therefrom by the at least one separator and exhausted by the pump into the containment, the fluid downstream of the chamber driving the converter to power the pump.

3. An automatic vent filter comprising a housing having an inlet and an outlet for the passage of fluid therethrough, a chamber provided in the housing and dividing the housing into upstream and downstream sections, the chamber including at least one inertial separator having an inlet communicating with the upstream end of the housing, a fluid outlet communicating with a downstream end of the housing and a contaminant outlet leading to the interior of the chamber, the housing having located between the chamber and the housing outlet, a converter for converting kinetic energy of fluid in the housing into power which drives a pump so that contaminant laden fluid entering the housing inlet has the contaminant separated therefrom by the at least one separator and exhausted by the pump, the fluid downstream of the chamber driving the converter to power the pump.

4. An automatic vent filter according to claim 2 or claim 3 wherein the converter comprises a turbine rotated by the fluid, the rotation of the turbine being used to drive the pump.

5. An automatic vent filter according to claim 4 wherein rotation of the turbine rotates a shaft which, at an end thereof remote from the turbine, is connected to the pump to drive the pump.

6. An automatic vent filter according to claim 4 wherein the turbine is connected to an electrical generator whose electrical output is connected to an electric motor which drives the pump.

7. An automatic vent filter according to claim 4 wherein the turbine is connected to a fluid compressor having an outlet for compressed fluid connected to a fluid motor for driving the pump.

8. An automatic vent filter according to any one of claims 4 to 7 wherein the housing includes a tubular section, the turbine being mounted in said tubular section, a downstream end of said tubular section forming the housing outlet.

9. An automatic vent filter according to claim 1 and including a source of external power connected to the pump.

10. An automatic vent filter according to claim 9 wherein the pump is a fluid ejector pump connected to a source of fluid under pressure.

11. An automatic vent filter according to any one of claims 1 to 10 wherein the chamber is formed by two parallel but spaced panels lying in respective planes normal to the direction of flow of fluid through the housing, the at least one inertial separator extending between said panels.

12. An automatic vent filter according to claim 11 wherein a plurality of inertial separators are provided, the separators extending parallel to one another between said panels.

13. An automatic vent filter according to any one of claims 1 to 12 wherein the at least one inertial separator comprises a tube forming the inlet and the fluid outlet and a swirl generator arranged within the tube for imparting a centrifugal force to fluid and contaminant entering the tube so that the contaminant flows around a radially outer annular section of the tube, the contaminant outlet removing the fluid and contaminant from said section while the remainder of said fluid leaves the tube through the fluid outlet.

14. An automatic vent filter according to any one of claims 11 to 13 and including a second chamber downstream of the first chamber and formed by two parallel but spaced panels lying in respective planes normal to the direction of fluid flow through the housing, at least one further inertial separator extending between an inlet formed in an upstream panel and an outlet formed in a downstream panel, the second chamber leading to the outlet of the first-mentioned chamber.

15. An automatic vent filter according to any one of claims 1 to 8 wherein the pump comprises a centrifugal impeller.

16. An automatic vent filter according to any one of claims 1 to 15 wherein a mist eliminator is provided in the housing upstream of the chamber for separating water from fluid entering the housing.

17. An automatic vent filter according to any one of claims 1 to 15 wherein a mist eliminator is provided in the housing downstream of the chamber for separating water from fluid leaving the chamber.

18. A containment including a nuclear reactor and an automatic vent filter substantially as hereinbefore described with reference to the accompanying drawings.

19. An automatic vent filter substantially as hereinbefore described with reference to the accompanying drawings.

20. A method of separating contaminants from a fluid comprising passing the fluid through an inertial separator to separate the contaminant from the fluid and then passing the fluid through a converter to convert kinetic energy of the fluid into power to drive a pump, the pump acting to draw separated contaminant from the separator and pass the contaminant to exhaust.

21. A method of separating contaminants from a fluid substantially as hereinbefore described with reference to the accompanying drawings.