Method and system for fire suppressing

Abstract

 The invention relates to a method and a system for providing a fire suppression agent comprising a fire suppressant (20) and an inert gas stream (5c, 10). The inert gas stream is formed by expansion of a liquid gas (1a, 1b, 1c) and said fire suppressant (20) is added to said inert gas stream after the expansion of said liquid gas.

Description

[0001] The invention relates to a method for providing a fire suppression agent comprising a fire suppressant and an inert gas stream. Further, the invention is directed to a system for providing a fire suppression agent comprising a liquid gas supply, a liquid gas supply line connected to said liquid gas supply, a fire suppressant supply to provide a fire suppressant, and a fire suppressant supply line connected at one end to said fire suppressant supply and at the other end to a fire suppressant ejector having at least one outlet opening.

[0002] Several methods for extinguishing fires are known. The most common way of suppressing fires is by using water or foam. Further, inert gases have been used as means for extinguishing fires.

[0003] From WO 97/02863 a fire extinguisher is known where carbon dioxide is supplied from a CO₂ cylinder to a nozzle, mixed with water and then dispersed as a mist jet with water droplets in it. In use of that fire extinguisher a high pressure drop might occur in the CO₂ cylinder. Further, the water is cooled down to such an extent that the water-droplets freeze which might cause blocking of the nozzle.

[0004] In WO 95/24274 a method for providing a gas/liquid jet is disclosed wherein an inert gas and a fire-extinguishing liquid are fed to a mixing device where the liquid is mixed with the gas. The gas liquid mixture flows along an outlet tube and enters a nozzle as a plug flow with separated liquid and gas portions. The flow emerging from the nozzle is then subjected to an acoustic field. That method only works with inert gas in gaseous form, since in case liquid inert gas is used there is the risk that the liquid fire suppressant will freeze in the inert gas stream and block the nozzle.

[0005] It is an object of the present invention to provide a method and a system which avoids the problems of the prior art.

[0006] This object is achieved by a method for providing a fire suppression agent comprising a fire suppressant and an inert gas stream, wherein said inert gas stream is formed by expansion of a liquid gas and that said fire suppressant is added to said inert gas stream after the expansion of said liquid gas.

[0007] The inventive system for providing a fire suppression agent comprises:

• a liquid gas supply,
• a liquid gas supply line connected to said liquid gas supply,
• a fire suppressant supply to provide a fire suppressant, and
• a fire suppressant supply line connected at one end to said fire suppressant supply and at the other end to a fire suppressant ejector having at least one outlet opening,
• wherein said liquid gas supply line comprises an expansion nozzle and
• said outlet opening of said fire suppressant ejector and the outlet of said expansion nozzle are located close to each other in order to be able to form a combined stream of said expanded liquid gas and said fire suppressant.

[0008] The basic idea is to produce a high velocity gas jet with a long throwing length and to keep that long range even if an additional fire suppressant is added. Therefore, according to the invention a liquid inert gas is expanded in a nozzle to produce a high velocity gas stream followed by the introduction of a fire suppressant into that gas stream.

[0009] According to the invention a gas in the liquid phase is supplied to the nozzle in order to maximize the gas flow. Further at the expansion the inert gas is cooled down and that cooling effect helps to cool the fire to some extent. Another benefit of the inventive mixing in front of the nozzle is that the inert gas flow and the fire suppressant flow can be varied and turned off independently of each other.

[0010] Since the fire suppressant, which is preferably water, is carried by the inert gas it can permeate and expand into all or most of the space or volume to be protected and thus provide a total flooding capability. The fire suppressant will extinguish the fire as well as cool the items in the fire.

[0011] When using water as fire suppressant the high speed of the gas stream causes the water to be divided into small droplets forming a high velocity mist. Due to the small size of the water droplets they will follow the highly turbulent inert gas stream around distant corners of the fire area.

[0012] The presence of the inert gas increases the efficiency of the fire extinguishing and suppression action. The inert gas will be drawn into the fire by the negative pressure and choke the fire. Further the inert gas will cool the hot air in the fire area and to some extent the fire, too. Smoke as well as hot, flammable or combustible gases will be ventilated and removed from the fire area by the inert gas. The risk of personal injuries for the firemen is reduced and the spreading of the fire slowed down. Further the view for the firemen is cleared thus facilitating the firefighting.

[0013] In addition to water all fire suppressants are preferred which are substantially liquid or solid at ambient temperature and pressure. For example, powder can be pushed to the nozzle by a gas stream and is then injected into the expanded inert gas stream.

[0014] Another preferred embodiment is to use foam to suppress the fire. In that case a foam additive and water are injected into the inert gas stream after the expansion of the liquid gas. The foam will be created within the inert gas stream with the inert gas within the foam bubbles. The so created foam will have a low oxygen content and in that respect will be more efficient than ordinary foam used by the fire brigade. When the mixture of inert gas and foam reaches the fire, the inert gas will expand. Thus, the bubbles in the foam will also expand and the volume of the fire suppression agent will increase.

[0015] It is advantageous to form the inert gas stream by the expansion of liquid nitrogen or liquid carbon dioxide. In particular the use of liquid carbon dioxide is preferred due to its physical properties. Carbon dioxide is heavier than air and will, therefore, easier stay in the fire area. When the fire extinguishing action is stopped the items in the fire area are normally still hot or warm and there is the risk that new oxygen reaches those items and the fire will start again. This is effectively prevented by the use of carbon dioxide.

[0016] Liquid carbon dioxide has the further advantage that it can be easily stored in high pressure cylinders or tanks. And compared to other gases as liquid nitrogen or liquid argon it is quite easy to keep the liquid carbon dioxide more or less subcooled in the whole liquid gas supply line between the liquid gas supply and the expansion nozzle, which is necessary in order to get a high flow of gas into the expansion nozzle.

[0017] For fighting fire it is advantageous to form a high velocity inert gas stream, in particular to form a gas stream having supersonic speed. This is achieved by introducing the liquid inert gas into a nozzle designed to increase the gas velocity when the gas is expanding in the outlet of the nozzle. In particular, the use of a conical nozzle or a Laval nozzle is preferred.

[0018] In some cases it might be necessary not to throw the fire suppressant agent over large distances but to spread out the fire suppressant mist, for example to inert a room or volume with the inert gas in order to blow away the smoke and to clear the way for the firemen. This could be achieved by a spray distributor placed in front of the nozzle outlet. The distributor may be permanently fixed to the nozzle or better be a movable part of the nozzle which could be moved in front of the nozzle when needed. The distributor may be arranged to deflect the inert gas stream only or to deflect the combined inert gas and fire suppressant stream.

[0019] The nozzle can be further improved in several ways: The nozzle can be provided with valves, for example manual valves, for the inert gas as well as for the fire suppressant stream or with handles to carry the nozzle and to support the fireman during use. Larger nozzles could be used together with some dedicated mechanical equipment as for example a steering-arm operated by a fireman from a control box.

[0020] Normally hoses will be used for the liquid gas supply line and the fire suppressant supply line. Hoses with small internal diameter which might be used with low capacity gas nozzles could for example be arranged in hose cassettes which are carried by the firemen. For larger hoses other solutions as a hose reel on a wagon with swivel couplings might be used.

[0021] For the supply of the liquid inert gas and of the fire suppressant a multiple hose could be used or two separate hoses bounded together.

[0022] To maximize the flow rate through the liquid gas supply line it is preferred to control the pressure of the liquid inert gas during its feed to the nozzle. For example a noncondensed gas is used to keep the pressure in the liquid inert gas supply system stable and also to subcool more or less all the way from the liquid gas supply to the nozzle. When using liquid carbon dioxide as the fire suppressing inert gas it is advantageous to pressurize the liquid carbon dioxide storage vessel with gaseous nitrogen.

[0023] Since nitrogen is to some extent soluble in carbon dioxide which might lead to a two-phase-flow in the liquid gas supply line, it is preferred to connect at least two carbon dioxide storage vessels in series and to enter the gaseous nitrogen at one end of the combined storage vessels and to take out the liquid carbon dioxide at the opposite end. Thus the carbon dioxide will be pressurized and subcooled during most of the emptying process of the storage vessels and less nitrogen is dissolved in the carbon dioxide.

[0024] In a preferred embodiment of the invention the liquid inert gas is stored in high pressure storage vessels. The pressure in these vessels can be as high as 190 bars. Normally such high pressure vessels are not provided with any insulation. A single storage vessel will improve the total weight of the gas supply system, but one drawback is the above described risk that nitrogen used for subcooling will be dissolved in the liquid inert gas. In practice it depends on the situation whether it is better to use a single storage vessel or a bundle of for example gas cylinders.

[0025] Instead of using nitrogen to pressurize the liquid carbon dioxide it is also possible to subcool the liquid carbon dioxide by helium. If using a single storage vessel it is also possible to use a pump to feed the liquid inert gas from the storage vessel to the nozzle. The pump could be used for un-insulated tanks but also for insulated tanks in which the liquid carbon dioxide is stored at a lower temperature. The pump should give such a high pressure that during the way through the liquid gas supply line as little as possible of the inert gas is vaporized. Otherwise a two-phase-flow will occur and the mass flow in the liquid gas supply line will be decreased. Of course such a large storage vessel could also be used with two or more liquid gas supply lines.

[0026] The invention has several advantages compared to the prior art methods for firefighting. The inventive method and system can be used at short and long distances, even if the fire brigade cannot locate the center of the fire or cannot come close to the fire. The inert gas stream pushes smoke and gases out of the fire area which reduces the risk of personal injuries and helps the firemen to better see the place of fire. The inert gas sprayed into the fire area decreases the overall oxygen concentration whereby reducing and extinguishing the fire. The inert gas is sucked into the fire and thus it is not necessary to directly hit the flames with the fire suppressant, as with conventional methods.

[0027] The inventive method to spray a mixture of small droplets of a liquid fire suppressant and a high velocity gas stream into the fire is very efficient since it combines the positive firefighting effects of the liquid suppressant, namely to extinguish the fire and to cool the items in the fire area, with the advantages of the inert gas stream, which not only produces the fine liquid droplets, but also reduces the oxygen level.

[0028] The invention has particular advantages when used as a mobile fire extinguishing system. The equipment comprises a liquid gas storage vessel, a liquid fire suppressant supply a nozzle and the respective supply lines, all being installed on a motorized frame or truck. Such a mobile system allows to produce the fire extinguishing mist at demand.

[0029] Another benefit of the invention is the possibility to switch between different fire suppression agents. A fire extinguishing system using carbon dioxide as the inert gas and water and a foam additive as additional fire suppressants can be easily switched between pure water, pure carbon dioxide, a mixture of carbon dioxide and water and a combined stream of carbon dioxide, water and foam. Since the fire suppressants, in that case water and/or a foam additive, are added to the inert gas stream after its expansion, there is no risk of blocking the expansion nozzle, even if it is switched from a pure carbon dioxide mode to a pure water mode.

[0030] The invention as well as further details and preferred embodiments of the invention are disclosed in the following description and illustrated in the accompanying drawings, in which

figure 1

schematically shows a mobile fire suppression system according to the invention,

figure 2

an inventive nozzle,

figure 3

an after-native fire suppression system including a foam additive injection system, and

figure 4

another embodiment which uses powder instead of water as fire suppressant.

[0031] The invention is preferably carried out using carbon dioxide as inert gas and water as liquid fire suppressant. The carbon dioxide and the water supply for such a system is shown in figure 1.

[0032] Liquid carbon dioxide is stored in three high pressure uninsulated storage vessels 1a, 1b, 1c. Typically about 1500 kg of liquid carbon dioxide is stored in storage vessels 1a, 1b, 1c. The storage vessels 1a, 1b, 1c are mounted on a scale 2 which is used to determine the amount of carbon dioxide stored in the storage vessels 1a, 1b, 1c. In addition the storage vessels 1a, 1b, 1c are provided with liquid level indicators 3. When filling or re-filling the storage vessels 1a, 1b, 1c with liquid carbon dioxide the liquid indicators 3 and/or the scale 2 are used to stop the filling procedure when a predetermined liquid level respectively predetermined weight has been reached.

[0033] Storage vessel 1a is provided with tubes 4a, 4b connected to the gas phase of the stored carbon dioxide. Tubes 5a, 5b, 5c are extending into the liquid phase of each storage vessel 1a, 1b, 1c. The liquid phases of storage vessels 1a, 1b, 1c are connected in series, i. e. liquid tube 5a connects the liquid phases in storage vessels 1a and 1b, and liquid tube 5b the liquid phases in storage vessels 1b and 1c.

[0034] Tube 4a connected to the gas phase of storage vessel 1a is further connected to a gas cylinder 6 filled with gaseous nitrogen at a pressure of about 200 bars. Tube 4a is provided with a pressure regulated valve 7 having a set pressure of about 5 to 10 bars above the boiling point of the liquid carbon dioxide in the storage vessels 1a, 1b, 1c.

[0035] Instead of the serial connection of storage vessels 1a, 1b, 1c it is also possible to connect them in parallel or to use one single storage vessel. It is also an advantage to use helium instead of nitrogen, but due to the higher price of helium nitrogen might still be preferred. Further instead of nitrogen cylinder 6 a liquid carbon dioxide pump located in liquid tube 5c may be used to increase the pressure of the liquid carbon dioxide and to pump the liquid carbone dioxide from the storage vessel 1a, 1b, 1c to the nozzle 12. It will be apparent to one skilled in the art that then the piping has to be changed somewhat.

[0036] Liquid tube 5c extending into the liquid phase of storage vessel 1c is at its other end provided with an outlet valve 8 and a connection point 9 which is used for connecting a liquid carbon dioxide hose 10. Liquid carbon dioxide hose 10 is arranged in a hose cassette 11 and at its end provided with an ejector 12.

[0037] Gas tube 4a leads to a gas line 13 which is connected to the liquid tube 5c downstream outlet valve 8. The gas flow through gas line 13 can be regulated by means of gas valve 14. Gas valve 14 as well as outlet valve 8 can be controlled by an operating system 15. Valve 14 is used to pressurize the carbon dioxide line and the liquid carbon dioxide hose 10 in order to avoid dry-ice formation in the line.

[0038] To refill the liquid carbon dioxide storage vessels 1a, 1b, 1c a fill line 16 comprising a fill pump 17 is connected to liquid tube 5c. To avoid over-pressure during the filling of the storage vessels 1a, 1b, 1c a venting line 18, which is provided with a filling regulator 19, branches from the gas tube 4a.

[0039] However, it will be apparent to one skilled in the art that the liquid gas supply system and liquid supply line could be arranged in other versions that depart from these specific details.

[0040] Water is supplied in the conventional way, for example from a tank 20, and if necessary a pump, not shown in figure 1, is used to increase the feed pressure. At connection point 21 a water hose 22 is connected to the water supply system. Water hose 22 and carbon dioxide hose 10 are bound together. Water hose 22 also leads to the ejector 12 which in the following will be described with reference to figure 2.

[0041] In figure 2 the carbon dioxide and water ejector 12 is shown in greater detail. Liquid carbon dioxide hose 10 is connected to a nozzle 23. The liquid carbon dioxide flow to nozzle 23 can be manually regulated by valve 24. Nozzle 23, for example a Laval nozzle, is designed to achieve a gas stream of high velocity, especially to increase the gas velocity above sonic speed.

[0042] Water hose 22 is connected via tube 25 to a water distributor 26. The water flow can also be regulated by the fireman by using water valve 27. The water is transferred through tube 25 to the water distributor 26 which surrounds nozzle 23 and which has several outlet openings 28. An insulation 29 is provided between the nozzle 23 and the water distributor 26 to avoid freezing of the water.

[0043] A spray distributor 30 is movably arranged in front of the outlet of the nozzle 23. If necessary the fireman can push the spray distributor 30 directly in front of nozzle 23 and thus deflect the carbon dioxide gas jet in order to create a broad gas stream

[0044] In the following a preferred mode of operation of the invention is described. The system shown in figures 1 and 2 is mounted on a fire truck. At the fire station storage vessels 1a, 1b, 1c are filled with liquid carbon dioxide. A source of liquid carbon dioxide is connected to the fill line 16. Fill pump 17 is started and liquid carbon dioxide is pumped through liquid tubes 5c, 5b, 5a into storage vessels 1a, 1b, c. The filling procedure is stopped when scale 2 or liquid level indicator 3 show a pretermined weight or predetermined liquid level indicating that storage vessels 1a, 1b, 1c are completely filled. In case the pressure within storage vessels 1a, 1b, 1c increases above the set value of filling regulator 19, filling regulator 19 opens and gaseous carbon dioxide is blown via venting line 18 to the atmosphere.

[0045] In case of alarm the fire truck is moved to the place of fire. Carbon dioxide hose 10 and water hose 22 are connected to the respective connection points 9 and 21 on the fire truck and hose cassette 11 is wheeled away in the direction to the fire. When being close enough to the fire, ejector 12 is connected to hoses 10, 22.

[0046] Operating system 15 opens valve 14 to allow gaseous carbon dioxide to flow into carbon dioxide hose 10 in order to pressurise the hose 10. Then valve 14 is closed and the liquid carbone dioxide valve 8 is opened. Nitrogen gas is fed from nitrogen cylinder 6 into the storage vessels 1a, 1b, 1c at a pressure of about 5 bars above the boiling point of liquid carbon dioxide. Pressure regulator 7 ensures that during emptying the storage vessels 1a, 1b, 1c the gas pressure is kept stable.

[0047] The gaseous nitrogen pushes liquid carbon dioxide out of storage vessels 1a, 1b, 1c via liquid tube 5c and hose 10 to the carbon dioxide ejector 12. Due to the serial connection of storage vessels 1a, 1b, 1c and due to the fact that gaseous nitrogen enters the storage vessels at one end and the liquid carbon dioxide is withdrawn at the opposite end, the amount of nitrogen fed into liquid tube 5c and hose 10 is minimized.

[0048] Water is supplied from tank 20 via water hose 22 to the ejector 12, either by use of a high pressure pump not shown in figure 1 or any other suitable means.

[0049] The fireman at the ejector 12 opens valve 24 and liquid carbon dioxide flows into nozzle 23. The liquid carbon dioxide expands in nozzle 23, forms a mixture of gaseous, liquid and solid carbon dioxide and leaves the nozzle 23 with very high speed.

[0050] When needed water valve 27 is opened and water flows into water distributor 26 which is coaxially arranged with nozzle 23. The water is pushed out through outlet openings 28, thus creating water jets surrounding the central high speed carbon dioxide jet. The water jets and the carbon dioxide leave ejector 12 as essentially parallel gas streams. However, for certain applications it might be advantageous to adjust the ejection angle of the water and/or the carbon dioxide jet as well as their respective angles α, β of jet spread.

[0051] The water is sprayed into the carbon dioxide jet and by the large speed of the carbon dioxide the water is divided into fine droplets forming a high speed carbon dioxide-water-mist which has a long throwing length.

[0052] If the firemen cannot see the fire it might be advantageous to blow away the smoke using the spray distributor 30. Spray distributor 30 is moved in front of the carbon dioxide outlet in order to deflect the carbon dioxide jet stream. Thus a broad spread mist is created which removes the smoke.

[0053] The embodiment according to figure 3 differs from the system shown in figure 1 that it comprises an additional foam additive injection system. In figures 1 and 3 same reference numbers refer to identical parts.

[0054] In addition to the water supply 20 a foam additive supply 31 is provided. Foam additive supply vessel 31 is connected to the gaseous nitrogen supply via line 32. The nitrogen gas is used to propel the foam additive out of foam additive supply vessel 31 into the water stream. The mixture of water and foam additive is fed to ejector 12 and injected into the carbon dioxide gas stream via distributor 26.

[0055] Figure 4 shows another embodiment of the invention which uses a mixture of carbon dioxide gas and powder to extinguish fires. Same reference numbers again refer to same parts. The powder is stored in a storage vessel 40. The gas phase in the carbon dioxide supply system is used to push the powder via hose 22 to ejector 12. Therefore, powder storage vessel 40 is connected to the gas phase of storage vessel 1a via lines 41 and 4a. The system according to figure 4 works essentially in the same way as the systems according to figures 1 and 3.

[0056] In both embodiments, figure 3 and figure 4, gaseous nitrogen or gaseous carbon dioxide can be used to push the foam additive respectively the powder to the ejector 12, although figure 3 only shows a connection 31 to the gaseous nitrogen supply and figure 4 only shows a connection 41 to the carbon dioxide gas phase.

Claims

1. Method for providing a fire suppression agent comprising a fire suppressant and an inert gas stream, characterized in that said inert gas stream is formed by expansion of a liquid gas and that said fire suppressant is added to said inert gas stream after the expansion of said liquid gas.

2. Method according to claim 1, characterized in that said fire suppressant (20) is substantially liquid or solid at ambient temperature and pressure.

3. Method according to any of claims 1 or 2, characterized in that said inert gas stream is formed by expansion of liquid carbon dioxide (1a, 1b, 1c).

4. Method according to any of claims 1 to 3, characterized in that an inert gas stream is formed having supersonic speed.

5. Method according to any of claims 1 to 4, characterized in that water (20) or powder (40) is added to said inert gas stream.

6. Method according to any of claims 1 to 5, characterized in that water (20) and an additive (30) which could create foam with water are added to said inert gas stream.

7. Method according to any of claims 1 to 6, characterized in that prior to its expansion said liquid gas is pressurized to a pressure above the boiling point of said liquid gas.

8. Method according to any of claims 1 to 7, characterized in that said liquid gas is pressurized with gaseous nitrogen (6) or gaseous helium.

9. Method according to any of claims 1 to 8, characterized in that during a first period of time said fire suppression agent comprises said fire suppressant and said inert gas stream, and that during another period of time only a fire suppressant is provided.

10. System for providing a fire suppression agent comprising:

- a liquid gas supply,

- a liquid gas supply line connected to said liquid gas supply,

- a fire suppressant supply to provide a fire suppressant, and

- a fire suppressant supply line connected at one end to said fire suppressant supply and at the other end to a fire suppressant ejector having at least one outlet opening,

characterized in that said liquid gas supply line (5c, 10) comprises an expansion nozzle (23) and that said outlet opening (28) of said fire suppressant ejector and the outlet of said expansion nozzle (23) are located close to each other in order to be able to form a combined stream of said expanded liquid gas and said fire suppressant.

11. System according to claim 10 characterized in that said expansion nozzle (23) is a conical nozzle or a Laval nozzle.

12. System according to any of claims 10 or 11 characterized in that said fire suppressant ejector comprises a plurality of outlet openings (28) surrounding said expansion nozzle (23).

13. System according to any of claims 10 to 12 characterized in that said expansion nozzle (23) is provided with a spray distributor (30) in front of said nozzle outlet opening.

Drawing