WO2003033110A1

WO2003033110A1 - Method for purifying a gas in a system

Info

Publication number: WO2003033110A1
Application number: PCT/FI2001/000897
Authority: WO
Inventors: Göran Sundholm
Original assignee: Marioff Corporation Oy
Priority date: 2001-10-16
Filing date: 2001-10-16
Publication date: 2003-04-24
Also published as: WO2003033110A8

Abstract

The invention relates to a method for purifying a gas in an exhaust gas system comprising an exhaust duct comprising a filter for filtering fine particles, said method comprising spraying of water mist into said exhaust duct upstream of said filter for purifying said gas, said spraying being effected by at least one spray nozzle causing a negative pressure for sucking the gas into the sprayed spray and by guiding said mixture aside from said filter and guiding thus purified gas into the filter. Due to the method gases can be continuously purified without the filter of the exhaust gas system being clogged. When applied to a room having a fire the method simultaneously enables purification of flue gases, sucking of heat out from the room and enables small particles to be captured by the filter. The present invention also relates to an exhaust gas system.

Description

METHOD FOR PURIFYING A GAS IN A SYSTEM

BACKGROUND OF THE INVENTION

[0001] The invention relates generally to a method for purifying gases in an exhaust gas system. [0002] The invention further relates generally to an exhaust gas system for purifying gases.

[0003] Although the present method and the exhaust gas system can be applied for purifying gases in environments of very different character, the present method and the exhaust gas system are especially well suited for purifying flue gases formed in a room during a fire. The expression "room" refers here generally to closed rooms and/or units comprising exhaust gas systems, such as exhaust air systems, for removing/extracting exhaust gas, such as air, from the rooms/units. Examples of such rooms/units include nuclear power plants, e.g. turbine rooms thereof, and chemical plants. The present invention relates particularly to these nuclear power plants and chemical plants, but also to other plants comprising exhaust gas/air systems with fine filters, which prevent harmful fine particles from escaping along with the exhaust air from the plants.

[0004] If a fire breaks out in such enclosed rooms having fine filters, flue gases generated from the fire will easily block/clog said fine filters. The filters are clogged when particles of different size enter the filters, which become therefore incapable of letting air or other gases pass through. As a result of the clogging, also the hot flue gases cannot leave the room and therefore the temperature inside the room rises. The temperature rise in the room/plant may have devastating effects, because it typically makes the fire spread fast and it may cause explosions especially in chemical plants. Chemical plants typically contain huge amounts of chemical substances, which may react violently in elevated temperatures. Elevated temperatures and overheating may cause major economical and material losses. [0005] WO 93/21997 and WO 94/26356 disclose fire fighting installations adapted to spray water mist into ventilation ducts in order to remove flue gases from a room. However, these known installations do not provide a gas purification system which enables air and flue gases to be continuously purified in an environment where there is additionally a need to filter the outgoing air/gases from very small particles, such as radioactive particles.

BRIEF DESCRIPTION OF THE INVENTION

[0006] In order to provide a solution to the above problems and risks, the present invention provides a method for purifying a gas in an exhaust gas system comprising an exhaust duct comprising a filter for filtering at least part of fine particles from the gas in the exhaust duct, said method comprising spraying of water mist into said exhaust duct upstream of said filter for purifying said gas by producing a mixture of said gas and water, said spraying being effected by at least one spray nozzle causing a negative pressure in an immediate vicinity of said nozzle for sucking the gas into the sprayed spray and by guiding said mixture aside from said filter and guiding thus purified gas into the filter.

[0007] The sucking causes the gas to be entrained into the sprayed spray. The negative pressure draws the gas toward the spray head and guides the gases into the water spray coming from the spray head. This enables an efficient reaction between the gas and water.

[0008] A preferred embodiment of the method comprises the steps of purifying flue gases from a room during a fire, said room comprising said exhaust gas system and said method comprising sucking of the flue gases into the sprayed spray, forming a mixture of flue gases and water and guiding said mixture aside from said filter and guiding thus purified flue gases into the filter.

[0009] Preferably said spraying is effected by a pressure of 10 -

300 bar. Such a high pressure causes a strong negative pressure that is able to effectively suck out flue gases from the room and the high pressure causes a strong spray from the spray nozzle, the spray effectively pushing out purified flue gases from the room through said filter.

[0010] In order to provide a solution to the above described problems and risks, the present invention further provides an exhaust gas system for purifying a gas, said system comprising an exhaust duct comprising a filter for filtering at least part of fine particles from the gas, and a purifying apparatus comprising at least one spray nozzle for spraying of water mist into said exhaust duct upstream of said filter, said spray being adapted to cause a negative pressure in an immediate vicinity of said nozzle for sucking the gas into the sprayed spray. [0011] The purifying apparatus thus functions as a coarse filter positioned before the fine filter.

[0012] Preferably the system is for a room, for removing gases from the room and for purifying the gas to be removed from, wherein the purifying apparatus comprises a support structure for holding said at least one spray nozzle, first guiding means for guiding a mixture of said gases and water aside from the filter, and second guiding means for guiding purified gases against the filter.

[0013] A preferred embodiment of the system comprises a detector for indication of fire, whereby said purifying apparatus is for purifying flue gases from a room during a fire.

[0014] Preferably the spray nozzle of the system is arranged inside a reaction chamber of the purifying apparatus, said reaction chamber comprising an inlet opening for directing a flow of said unpurified gases into the suction of the spray nozzle, inside the reaction chamber. [0015] The present invention provides also a nuclear power plant comprising an exhaust air system of a room for removing exhaust air and for purifying flue gases from the room during a fire, said exhaust air system comprising an exhaust duct comprising a filter for filtering fine particles from air to be removed from said room, and at least one spray nozzle for spraying of water mist into said exhaust duct upstream of said filter said spray being adapted to cause a negative pressure in an immediate vicinity of said nozzle for sucking flue gases into the sprayed spray.

[0016] Still further the present invention provides a chemical plant comprising an exhaust air system of a room for removing exhaust air and for purifying flue gases from the room during a fire, said exhaust air system comprising an exhaust duct comprising a filter for filtering fine particles from air to be removed from said room, and at least one spray nozzle for spraying of water mist into said exhaust duct upstream of said filter, said spray being adapted to cause a negative pressure in an immediate vicinity of said nozzle for sucking flue gases into the sprayed spray

[0017] Preferred embodiments of the apparatus of the invention are disclosed in the appended claims.

[0018] An important advantage of the method and the system for purifying gases is that it enables continuous purification of gas without the filter being clogged. When applied to a room for purification o flue gases formed in the room during a fire, the method and the system enable the extraction of flue gases from the room and also filtering of fine particles during the fire owing to the fact that the exhaust duct and filter, do not become clogged. Thus, and while extracting poisonous gases from the room the invention enables very small particles, such as radioactive particles and very small chemical particles to be captured by the filter of the exhaust gas system. In such a case, the method and system of the present invention sucks out heat from the room and prevents the temperature from rising in the room as high as it would without the method/system. Such a temperature-lowering effect is suitable for preventing fire from spreading and for avoiding the occurrence of explosions of chemical substances - if such substances are present. The present invention has a simple construction and can be installed very easily in existing exhaust air systems.

[0019] The nuclear power plant and the chemical plant according to the invention are expected to be safer than prior art nuclear plants and chemical plants for the reasons set out above.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In the following, the invention will be described in greater detail with reference to two embodiments and the accompanying drawings, in which Figure 1 illustrates the basic principle of the invention;

Figure 2 illustrates a first embodiment of the exhaust air system according to the invention;

Figure 3 illustrates a second embodiment of the exhaust air system according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0021] Figure 1 illustrates the main steps of the method according to the present invention. When the method is applied to a closed room having an exhaust air system including an exhaust duct comprising a fine filter, which catches fine particles from the air which is removed from the room, spraying of water mist is initiated in case of fire. The spraying of water mist can be initiated as a response to a signal received from a smoke alarm detector or a temperature detector, which has detected elevated, abnormal temperatures. The signal which activates/initiates the spraying may alternatively be effected manually or by other means that are obvious to a person skilled in the art. Said spraying is carried out upstream of said filter, so that flue gases that enter the exhaust air system mix or react with the water mist forming a mixture or reaction products and are thus purified before entering the filter. The flue gases are purified in the water mist to such an extent that the purified flue gases are not capable of blocking or clogging the filter. Thus the filter may work as intended, i.e. it catches more or less only very small particles, which do not block the filter. Air and flue gases purified from big and small particles leave the exhaust air system downstream of said filter.

[0022] Figure 2 shows a first embodiment of an exhaust air system for performing the method described above. The exhaust air system includes an exhaust duct 500' provided with a fine filter 600'. The filter 600' is designed to catch radioactive small particles, because the system is intended for purifying air of a nuclear power plant. Alternatively, the exhaust air system is a system for a chemical plant or some other unit/room. Depending on the application, the filter is chosen according to required filtering properties. [0023] The exhaust air system comprises a purifying apparatus, generally indicated by reference numeral 900'. In Figure 2, the purifying apparatus 900' is mounted upstream of the filter 600', which is always the case. The purifying apparatus 900' is mounted in series with the exhaust duct 500'. The apparatus 900' comprises flanges 1', 2' enabling easy mounting of the apparatus into the exhaust duct 500'. The apparatus 900' can be mounted at the end of the exhaust duct 500', as shown in Figure 2, or in an intermediate part of the exhaust duct. The total height of the apparatus is relatively small and therefore it is easy to find a mounting space for it and to fit it also into existing air exhaust systems. A small height is possible when the gases to be purified are deviated sideways out of their principal flow direction at the inlet.

[0024] The inlet flange 1', which is shown partly in section in Figure 2, comprises a number of holes for fastening the purifying apparatus 900' to the exhaust duct 500' of the exhaust air system by utilizing bolts (not shown) to be inserted into the holes. The discharge flange 2 comprises a corresponding perforation, by which the apparatus 900' can be attached to another part of the exhaust duct.

[0025] Between the flanges 1' and 2' there is provided a connection that allows air and flue gases to be guided from the inlet flange 1' to the discharge flange 2'. The arrows show the flow direction of air and possible flue gases when the apparatus 900' is in use. In use, exhaust air passes through the apparatus and is removed (i.e. extracted) from the room/unit. In case of fire in the room/unit, unpurified flue gases, which have been created as a consequence of the fire, are received at the inlet flange V and are purified in the apparatus. The purified flue gases are discharged through the flange 2' against the filter 600'. The purifying apparatus 900' functions like a coarse filter, i.e. filter for filtering coarse particles.

[0026] Reference numeral 800' shows an optional filter adapted to allow passage of bigger particles than the filter 600'. The filter 800' is not a necessity, but, it may improve the working characteristics of the invention in some applications. However, filter 800' does not possess the capability of filtering bigger amounts of particles and hence, the purifying apparatus 900' is solely responsible for absorbing big amounts of particles.

[0027] The apparatus 900' comprises a support structure, generally referred to with reference numeral 3', with a number of spray heads 4' attached thereto. The number of the spray heads 4' varies according to the application; in the solution of Figure 2 there are seven of them, but a solution where one spray head is sufficient is also possible (in which case suction and spreading ducts may be arranged to produce a larger area of suction), whereas some solutions may comprise dozens of spray heads. The spray heads 4' are of a type that can be used at a high pressure causing strong suction in their immediate vicinity. The pressure to be used is within 10 to 300 bar, typically from about 20 to 100 bar. Each spray head 4' comprises preferably at least two nozzles arranged in a diverging position with respect to each other, and the structure of the head may be for example similar to the one disclosed in WO 92/20453. In principle only one nozzle may be enough, although one nozzle does not provide as strong suction effect as if there were two or more nozzles in the spray head. Due to the risk of clogging, the spray head 4' is preferably simple in structure. The spray heads are arranged in a circle at a distance from one another, and they are directed to produce substantially parallel sprays. The pipe system for supplying water to the spray heads 4' is not shown for the sake of simplicity, because it is very easy for a person skilled in the art to accomplish. The water is supplied from a water source (not shown) which may be constituted by the water mains to which a high pressure pump is connected in order to supply the spray heads with high pressure water. Alternatively, the water source may consist of a number of hydraulic high pressure accumulators. The water source should be able to provide a pressure of at least 10 bar to the spray heads. The pressure source is preferably a high-pressure source able to provide a pressure of at least 20 bar and up to 100 - 300 bar.

[0028] The spray heads 4' are fastened to the ends of rods 6', which are in turn fastened to a flange 7' of the support structure, the spray heads being suspended from the flange so that they produce a downward spray. The direction of the spray is thus opposite to the direction of flow of unpurified flue gases. The spray heads 4' can be easily detached from the flange 7' for cleaning. This is carried out by opening the fastening means 60', which are nuts, screws or the like, to which the rods 6' are fastened: the nuts 60' are unscrewed and the rods 6' are lifted up together with the spray heads 4'.

[0029] The apparatus comprises a mantle construction in the form of a cylindrical housing 8'. Inside the housing 8' there is a cylindrical wall 910' concentric with the housing. [0030] Between the housing 8' and the cylindrical wall 910' there is a flow space 11' for unpurified flue gases.

[0031] Between the housing 8' and the cylindrical wall 910' there are seven reaction chambers 13' formed of tubes 130', each reaction chamber being provided with a spray head 4'. Unpurified exhaust gases enter each reaction chamber 13' through an inlet opening 14'. The reaction chambers 13' are formed of tubes 130' provided with said inlet openings 14' which allow unpurified exhaust gases to be sucked into the reaction chambers by the effect/impact of the spray heads 4' (a suction effect/impact). The tubes 130' are curved, i.e. they comprise a curved portion, owing to which the water sprays from the spray heads 2' hit the curved wall of the tubes. The tubes 130' are connected to a space enclosed by the wall 910', the bottom end of which is formed to be conical so as to allow reaction products to be guided from the reaction chambers 13' and from said space into a discharge conduit 15'. The discharge conduit 15' is supplied through a hole 16 in the flange 8 to guide the reaction products out of the apparatus. The, reaction products are guided to a place where they do not cause any harm. The purified exhaust gases flow inside the wall 910', i.e. inside the space, in the same direction as unpurified exhaust gases have when they enter the inlet flange 1'. The exhaust duct 500' may be provided with a fan (not shown) in order to secure the flow of purified gases from the space inside the wall 910' against the filter 600'. [0032] Because the reaction products may be highly corrosive, a suitable material for the walls 8', 910', the tubes 13' and the discharge conduit 15' is for example austenitic stainless steel.

[0033] In the following, the operation of the apparatus of Figure 2 will be described.

[0034] When there is no fire in the room/unit, the spray heads 4' are not activated, and air flows through the inlet flange 1' and the inlet openings 14' into the space inside the wall 910' and from there against and through the filter 600'. [0035] In case of fire in the room/unit, the spray heads 4' are activated by a signal from a detector, e.g. a smoke detector of a fire extinguishing installation (not shown). Due to the suction effect of the spray heads 4', air and unpurified flue gases forcefully drawn through the inlet flange 1' and through the inlet openings 14' into the reaction chambers 13'. The flue gases are effectively purified in the reaction chambers 13' and they travel further from the space inside the wall 910' through the flange 2' against and through the filter 600. The air and flue gases are guided into the mist-like water spray of the spray heads 4'. The droplet size in the water spray is very small, thereby enabling for an efficient reaction between the flue gases and the water. 90 % of the volume of water (Dv90) constitutes of droplets that are typically smaller than 200 μm, preferably smaller than 100 μm and most preferably smaller than 50 μm.

[0036] Figure 3 shows a second embodiment of an exhaust air system for performing the method described above. In Figure 3, like reference numerals refer to like parts as in Figure 2. The purifying apparatus 900" of Figure 3 deviates from that of Figure 2 in that the apparatus is meant to be fastened to the side of an air exhaust duct 500" of a room/unit, in parallel with the exhaust duct. For this purpose the inlet flange 1" and the outlet flange 2" are in the same plane. The discharge flange 2" and the discharge conduit 15" are thus made separate from the exhaust duct 500". Therefore the purifying apparatus 900" is extremely easily mountable into existing air exhaust ducts 500".

[0037] The duct 500" comprises a baffle 700". The baffle 700" enables air and flue gases to be guided alternatively through the purifying apparatus 900", or air and flue gases may enter the filter 600" without passing the purifying apparatus 900". When there is no fire, the baffle 700 is normally kept open; and in case of fire the baffle is automatically (or manually) turned in a closed position, c.f. arrows indicating that the baffle may be turned. A signal from a smoke detector 950", or some other detector capable of detecting a fire, can be applied to close the baffle 700". [0038] In the above specification, the invention is illustrated with reference to only two examples, on the basis of which it can be understood that the details of the invention may vary in many ways within the scope of the accompanying claims. Thus, e.g. the shape of the purifying apparatus may deviate from what is shown in the figures, although from the point of view of the gas flows and the manufacturing and the cleaning of the purifying apparatus, a cylindrical shape is preferable. There may be a plurality of discharge conduits 15', 15", although it is recommended that the reaction products are guided in a centralized manner from the reaction chambers to a single discharge conduit, so that the construction is simple and the reaction products can be removed from one and the same place. The direction of the spray heads 4', 4" may vary, although they preferably point downward, because then the sprays facilitate the removal of the reaction products from the apparatus. This does not naturally mean that the spray heads would need to point directly downward. In addition, downward directed spray heads enable an apparatus of small dimensions and easy mounting. The system shown in the drawings can advantageously be applied for purifying gases and air of a chemical plant.

Claims

1. A method for purifying a gas in an exhaust gas system comprising an exhaust duct (500', 500") comprising a filter (600', 600") for filtering at least part of fine particles from the gas in the exhaust duct, said method comprising spraying of water mist into said exhaust duct upstream of said filter for purifying said gas by producing a mixture of said gas and water, said spraying being effected by at least one spray nozzle causing a negative pressure in an immediate vicinity of said nozzle for sucking the gas into the sprayed spray and by guiding said mixture aside from said filter and guiding thus purified gas into the filter.

2. A method according to claim 1 for purifying flue gases formed in a room during a fire, said room comprising said exhaust gas system and said method comprising sucking of the flue gases into the sprayed spray, forming a mixture of flue gases and water and guiding said mixture aside from said filter and guiding thus purified flue gases into the filter.

3. A method according to claim 1 or 2, wherein said spraying is effected by a pressure of 10 - 300 bar.

4. A method according to claim 2, wherein said spraying is initiated as a response of a signal from a fire detection apparatus.

5. A method according to claim 1 or 2, wherein said spraying of water mist is initiated as a response of a signal from a smoke detector.

6. A method according to claim 1 or 2, comprising deviating at least part of said gas to be purified out of a principal exhaust flow path by the suction provided by the spray head.

7. An exhaust gas system for purifying a gas, said system comprising an exhaust duct (500', 500") comprising a filter (600', 600") for filtering at least part of fine particles from the gas, and a purifying apparatus (900', 900") comprising at least one spray nozzle (4', 4") for spraying of water mist into said exhaust duct upstream of said filter, said spray being adapted to cause a negative pressure in an immediate vicinity of said nozzle for sucking the gas into the sprayed spray.

8. A system according to claim 7 for a room, for removing gases from the room and for purifying the gases to be removed from the room, wherein the purifying apparatus (900', 900") comprises a support structure (3', 3") for holding said at least one spray nozzle (4¹, 4"), first guiding means (130', 130") for guiding a mixture of said gases and water aside from the filter (600¹, 600"), and second guiding means (910', 100", 910") for guiding purified gases against the filter (600', 600"). (Figs. 2, 3)

9. A system according to claim 8 for purifying flue gases from the room during a fire, comprising a detector (950") for indication of fire. (Figs. 2,

3)

10. A system according to claim 7 or 8, wherein the spray nozzle (4', 4") is arranged inside a reaction chamber (13', 13") comprising an inlet opening (14', 14") for directing a flow of said unpurified gas into the suction of the spray nozzle, inside the reaction chamber. (Fig. 2, 3)

11. A system according to claim 10, comprising a discharge conduit (15', 15"), connected to the reaction chamber (13', 13") for receiving said mixture and reaction products formed of water and said gas from the reaction chamber (13', 13") and for guiding the mixture and reaction products out of the purifying apparatus (900¹, 900"), and a gas discharge port for discharging purified gas against the filter (600', 600 "). (Figs. 2, 3)

12. A system according to claim 10, comprising a coarse filter (800', 800") for filtering coarser particles, positioned between the reaction chamber (13', 13") and the filter (600', 600") for filtering at least part of fine particles.

13. A system according to claim 10, wherein the reaction chamber

(13') is surrounded by a mantle construction (8'), and between the mantle construction and the reaction chamber there is a flow space (11') for conveying the unpurified gas to the inlet opening (14') of the reaction chamber. (Fig. 2)

14. A system according to claim 10, further comprising a mantle construction (8") and a conduit (910") comprising a first end and a second end, the conduit being arranged inside the mantle construction, the spray head (4") being arranged into a space (11") between the mantle construction and the conduit, the first end of the conduit comprising an opening (100") for directing a flow of purified gas to the second end of the conduit, which is provided with a gas discharge opening. (Fig. 3)

15. A system according to claim 14, comprising a plurality of spray nozzles (4") mounted onto the support structure (3") in the form of a circle between the mantle construction (8") and the conduit (910'") and at a distance from one another, the spray nozzles being arranged inside their respective tubes (130") which form reaction chambers. (Fig. 3)

16. A system according to claim 13, comprising a plurality of spray nozzles (4') mounted onto the support structure (3') in the form of a circle between the mantle construction (8') and the wall (910') and at a distance from one another, the spray nozzles being mounted inside their respective tubes (130') which form reaction chambers (13'). (Fig. 2)

17. A system according to claim 15 or 16, wherein the tubes (130', 130") comprise a curved portion and they lead to a space defined inside the wall (910'), said discharge conduit (15', 15") being in communication with said space. (Figs. 2, 3)

18. A system according to claim 15 or 16, wherein the spray nozzles (4', 4") are detachably fastened to a flange (7', 7") of the support structure (3', 3") from which they are suspended and can be detached by lifting. (Figs. 2, 3)

19. A system according to claim 7 or 8, comprising fastening means (1', 2', 1") for mounting the purifying apparatus (900', 900") to the exhaust duct

(500', 500"). (Figs. 2, 3)

20. A system according to claim 19, wherein the fastening means comprise an inlet flange (1', 1") provided with an opening for conveying the unpurified gases of the room into the purifying apparatus (900', 900"), and a discharge flange (2', 2") provided with an opening for conveying the purified gases out of the apparatus. (Figs. 2, 3)

21. A system according to claim 20, wherein the inlet flange (1") is formed to be fastened to a side of the exhaust duct (500") in parallel with the exhaust duct. (Fig. 3)

22. A system according to claim 21 , further comprising a baffle device (700") for guiding the unpurified gas alternatively directly against the filter (600") or via the purifying apparatus (900") against the filter. (Fig. 3)

23. A nuclear power plant comprising an exhaust air system of a room for removing exhaust air and for purifying flue gases from the room during a fire, said exhaust air system comprising an exhaust duct (500', 500") comprising a filter (600', 600") for filtering fine particles from air to be removed from said room, and at least one spray nozzle (4', 4") for spraying of water mist into said exhaust duct upstream of said filter said spray being adapted to cause a negative pressure in an immediate vicinity of said nozzle for sucking flue gases into the sprayed spray.

24. A nuclear power plant according to claim 23, further comprising a purifying apparatus (900', 900") comprising a support structure (3', 3") for holding said at least one spray nozzle (4', 4"), first guiding means (130', 130") for guiding a mixture of flue gases and water aside from the filter (600', 600") and second guiding means (910', 100", 910") for guiding purified gases against the filter (600', 600").

25. A chemical plant comprising an exhaust air system of a room for removing exhaust air and for purifying flue gases from the room during a fire, said exhaust air system comprising an exhaust duct (500', 500") comprising a filter (600', 600") for filtering fine particles from air to be removed from said room, and at least one spray nozzle (4', 4") for spraying of water mist into said exhaust duct upstream of said filter, said spray being adapted to cause a negative pressure in an immediate vicinity of said nozzle for sucking flue gases into the sprayed spray.

26. A chemical plant according to claim 25, further comprising a purifying apparatus (900', 900") comprising a support structure (3', 3") for holding said at least one spray nozzle (4', 4"), first guiding means (130'. 130") for guiding a mixture of flue gases and water aside from the filter (600', 600") and second guiding means (910', 100", 910") for guiding purified gases against the filter (600', 600").