Automatic fire-extinguishing device for energy storage system

Abstract

The present invention relates to an automatic fire-extinguishing device, and more specifically, to an automatic fire-extinguishing device for an energy storage system, the device being capable of effectively suppressing thermal runaway in the event of a fire in the energy storage device. The automatic fire-extinguishing device for an energy storage system, according to the present invention, comprises a liquefied nitrogen supply means, a level measurement means, a vent valve, a spray means, an opening / closing means, a sensor means and a control means. The liquefied nitrogen supply means includes: a liquefied nitrogen storage tank part in which liquefied nitrogen is stored; and a pressure vessel for accommodating the high-pressure nitrogen gas so as to supply the nitrogen gas to the liquefied nitrogen storage tank in order for the liquefied nitrogen to be sprayed at each battery module in the event of a fire. The level measurement means is mounted in the liquefied nitrogen storage tank part so as to measure the level of the liquefied nitrogen. The vent valve is mounted on the liquefied nitrogen storage tank part so as to be open when the pressure of the liquefied nitrogen storage tank part is lower than a predetermined pressure, and to be closed when the pressure of the liquefied nitrogen storage tank part is higher than the predetermined pressure, so that the gas generated in the liquefied nitrogen storage tank part can be discharged to the outside. The spray means includes: pipes connected such that the liquefied nitrogen can be supplied from the liquefied nitrogen storage tank part to the respective battery modules; and nozzles each mounted on the pipe. The opening / closing means opens / closes the liquefied nitrogen supply means so that the liquefied nitrogen can be supplied from the liquefied nitrogen storage tank part to the pipe. The sensor means includes a temperature detection sensor for detecting the temperature of the battery module, and a fire detection sensor for detecting flames, gas or smoke generated in the battery module, and is mounted on each battery module. The control means opens the opening / closing means so that the liquefied nitrogen can be sprayed through the nozzle when a predetermined temperature or higher is detected by the temperature detection sensor or a fire signal is detected by the fire detection sensor, and has a transmission / reception part for transmitting the state of the battery module so that an external manager can be notified of overheating or a fire outbreak of the battery module. According to the present invention, by spraying cryogenic liquid nitrogen, the temperature of the battery undergoing thermal runaway is rapidly cooled in a primary stage, and in a secondary stage, the sprayed liquid nitrogen vaporizes to extinguish the fire, thereby effectively suppressing a fire caused by thermal runaway. In addition, the fire can be suppressed without damaging electronic components, and thus recovery costs after fire suppression can be reduced. Furthermore, the present invention has the vent valve so that the pressure of the storage tank for storing the liquefied nitrogen can be maintained to be constant, and the liquefied nitrogen can be quickly sprayed in the event of a fire outbreak. Moreover, the present invention has the level measurement means so as to check the level of the liquefied nitrogen such that the lost liquefied nitrogen can be filled back up before a fire breaks out. Therefore, problems caused by a lack of liquefied nitrogen for suppressing a fire can be prevented.

Description

Automatic fire extinguishing device for energy storage devices

[0001] The present invention relates to an automatic fire extinguishing device, and more particularly, to an automatic fire extinguishing device for an energy storage device that can effectively suppress thermal runaway in the event of a fire in the energy storage device.

[0002] An energy storage system (ESS) is a device that stores electricity and supplies it when power is needed. It is equipped with multiple battery packs, and each battery pack has multiple battery modules.

[0003] Battery modules housed in energy storage devices are repeatedly charged and discharged. Repeated charging and discharging can lead to thermal runaway, which can lead to fire and even explosion. Therefore, it is crucial to detect and prevent thermal runaway in batteries.

[0004] Therefore, a fire extinguishing system capable of preventing thermal runaway or fire in energy storage devices is essential. Conventional fire extinguishing systems install sensors in battery modules. If thermal runaway or fire occurs at the sensor, extinguishing agents stored in the extinguishing agent tank are sprayed to extinguish the battery module's thermal runaway or fire.

[0005] Publication date of patent No. 10-2023-0166015 (published on December 6, 2023)

[0006] Conventional fire extinguishing systems typically use extinguishing agents with excellent electrical insulation, which can cause damage not only to the battery packs at the point of application but also to electronic components installed nearby. This can significantly increase restoration costs after fire suppression. Furthermore, even if a fire is extinguished immediately, the risk of re-ignition exists in battery modules if chemical reactions continue to occur within the module.

[0007] The present invention aims to solve the above problems. The purpose of the present invention is to provide an automatic fire extinguishing device for an energy storage device that can effectively suppress a fire caused by thermal runaway by first cooling a battery module using liquid nitrogen and secondarily extinguishing the fire by vaporizing the injected liquid nitrogen.

[0008] An automatic fire extinguishing device for an energy storage device according to the present invention comprises a liquid nitrogen supply means, a level measuring means, a vent valve, an injection means, an opening / closing means, a sensor means, and a control means. The liquid nitrogen supply means comprises a liquid nitrogen storage tank for storing liquid nitrogen therein, and a pressure vessel for receiving high-pressure nitrogen gas so as to supply nitrogen gas to the liquid nitrogen storage tank for injecting the liquid nitrogen to each battery module in the event of a fire. The level measuring means is mounted on the liquid nitrogen storage tank and measures the level of the liquid nitrogen. The vent valve is mounted on the liquid nitrogen storage tank so as to open when the pressure of the liquid nitrogen storage tank is lower than a certain pressure and close when the pressure is higher than the certain pressure, thereby allowing gas generated inside the liquid nitrogen storage tank to be discharged to the outside. The injection means has a pipe connected to supply the liquid nitrogen from the liquid nitrogen storage tank to each of the battery modules, and a nozzle mounted on the pipe. The opening / closing means opens and closes the liquid nitrogen supply means so that the liquid nitrogen can be supplied from the liquid nitrogen storage tank to the pipe. The sensor means has a temperature detection sensor for detecting the temperature of the battery module, and a fire detection sensor for detecting flames, gas, or smoke generated from the battery module, and is mounted on each of the battery modules. The control means opens the opening / closing means so that the liquid nitrogen can be sprayed through the nozzle when a temperature above a certain level is detected by the temperature detection sensor or a fire signal is detected by the fire detection sensor, and has a transceiver for transmitting the status of the battery module so as to notify an external manager of overheating or a fire occurrence in the battery module.

[0009] In addition, in the automatic fire extinguishing device for the energy storage device, it is preferable that the vent valve has a valve body, a valve spool, and a spring. The valve body has a passage formed therein so that gas inside the liquid nitrogen storage tank can be discharged to the outside. The valve spool is slidably mounted on the passage so as to close the passage by the pressure inside the liquid nitrogen storage tank. The spring is mounted on the valve body so as to support the valve spool so as to open the passage when the pressure inside the liquid nitrogen storage tank is lower than the predetermined pressure.

[0010] In addition, in the automatic fire extinguishing device for the energy storage device, it is preferable that the liquid nitrogen storage tank section includes an inner tank, an outer tank, and an insulating material, and the level measuring means includes a buoyancy member, an elastic member, and a level display unit. The inner tank stores the liquid nitrogen therein. The outer tank accommodates the inner tank by being spaced apart from the inner tank by a predetermined distance so that a vacuum layer is formed between the outer tank and the inner tank. The insulation is filled in the vacuum layer. The buoyancy member is accommodated in the inner tank so as to rise and fall according to the level of the liquid nitrogen. The pressure of the elastic member changes linearly according to the height of the buoyancy member. The level display unit indicates the level of the liquid nitrogen by the pressure of the elastic member.

[0011] In addition, in the automatic fire extinguishing device for the energy storage device described above, it is preferable that the opening / closing means include an opening / closing valve and a rupture plate. The opening / closing valve opens / closes the pressure vessel so as to supply high-pressure nitrogen gas to the liquid nitrogen storage tank when a fire is detected by the sensor means. The rupture plate ruptures when the liquid nitrogen storage tank is pressurized, thereby closing the outlet of the liquid nitrogen storage tank so as to supply the liquid nitrogen to the pipe.

[0012] According to the present invention, by spraying ultra-low-temperature liquid nitrogen, the temperature of a battery undergoing thermal runaway is first rapidly cooled, and secondly, the injected liquid nitrogen vaporizes and extinguishes the fire, effectively extinguishing the fire caused by thermal runaway. Furthermore, since the fire can be extinguished without damaging electronic components, post-fire recovery costs can be reduced.

[0013] In addition, according to the present invention, by providing a vent valve, the pressure of a storage tank storing liquid nitrogen can be maintained at a constant level, and liquid nitrogen can be quickly sprayed in the event of a fire.

[0014] Furthermore, the present invention provides a liquid nitrogen level measuring device, enabling the liquid nitrogen level to be checked and liquid nitrogen lost before a fire occurs to be replenished. Thus, problems arising from a lack of liquid nitrogen for extinguishing a fire can be prevented in advance.

[0015] Figure 1 is a conceptual diagram of one embodiment of an automatic fire extinguishing device for an energy storage device according to the present invention.

[0016] Figure 2 is an operation diagram of the vent valve of the embodiment illustrated in Figure 1,

[0017] Figure 3 is a conceptual diagram of the operation of the embodiment illustrated in Figure 1.

[0018] 10: Liquid nitrogen supply means 11: Liquid nitrogen storage tank

[0019] 12: Inner tank 14: Outer tank

[0020] 16: Insulation 17: Pressure vessel

[0021] 20: Water level measuring device 21: Buoyancy member

[0022] 23: Elastic member 25: Water level indicator

[0023] 30: Vent valve 31: Valve body

[0024] 33: Valve spool 35: Spring

[0025] 40: Injection means 41: Piping

[0026] 43: Nozzle 50: Opening / closing means

[0027] 51: Shut-off valve 53: Rupture disc

[0028] 60: Sensor means 61: Temperature detection sensor

[0029] 63: Fire detection sensor 70: Control means

[0030] 71: Transmitter and receiver 100: Battery pack

[0031] 110: Battery module

[0032] Referring to FIGS. 1 to 3, one embodiment of an automatic fire extinguishing device for an energy storage device according to the present invention is described.

[0033] An automatic fire extinguishing device for an energy storage device according to the present invention includes a liquid nitrogen supply means (10), a water level measuring means (20), a vent valve (30), an injection means (40), an opening / closing means (50), a sensor means (60), and a control means (70).

[0034] The liquid nitrogen supply means (10) serves to supply liquid nitrogen so that it can be sprayed to each battery module (110) in the event of a fire. To this end, the liquid nitrogen supply means (10) is equipped with a liquid nitrogen storage tank (11) and a pressure vessel (17).

[0035] The liquid nitrogen storage tank (11) is equipped with an inner tank (12), an outer tank (14), and an insulating material (16) to store liquid nitrogen inside.

[0036] The inner tank (12) stores liquid nitrogen within it. The temperature of liquid nitrogen is extremely low, at -196°C. That is, if the temperature of the inner tank (12) is higher than -196°C, the liquid nitrogen vaporizes, increasing the pressure of the inner tank (12). In this case, the vaporized gas must be released, resulting in a loss of liquid nitrogen. Therefore, insulation of the inner tank (12) is important.

[0037] The outer tank (14) is exposed to the atmosphere and serves to prevent the inner tank (12) from being exposed to the outside in order to insulate the inner tank (12). To this end, the outer tank (14) is spaced apart from the inner tank (12) by a certain distance to accommodate the inner tank (12). At this time, a vacuum layer is formed in the space between the inner tank (12) and the outer tank (14) which are spaced apart by a certain distance.

[0038] The insulation (16) serves to reduce heat transfer to the inner tank (12). To this end, the insulation (16) is filled in the space between the inner tank (12) and the outer tank (14).

[0039] The pressure vessel (17) supplies nitrogen gas to the liquid nitrogen storage tank (11) to pressurize the liquid nitrogen stored in the liquid nitrogen storage tank (11) so that it can be sprayed, and for this purpose, high-pressure nitrogen gas is stored inside.

[0040] The water level measuring means (20) is mounted on the liquid nitrogen storage tank (11) and serves to measure the water level of the liquid nitrogen stored inside the internal tank (12). To this end, the water level measuring means (20) is provided with a buoyancy member (21), an elastic member (23), and a water level display unit (25).

[0041] The buoyancy member (21) is housed inside the internal tank (12) and rises and falls depending on the level of liquid nitrogen.

[0042] The elastic member (23) changes pressure linearly according to the height of the buoyancy member (21), and one end is connected to the buoyancy member (21), and the other end is connected to the water level indicator (25).

[0043] The level indicator (25) displays the level of the liquid nitrogen by the pressure of the elastic member (23), and is installed in the external tank (14) so ​​that the level of the liquid nitrogen can be checked from the outside. Therefore, when the liquid nitrogen vaporizes into gas and a loss of the liquid nitrogen occurs, the buoyancy member (21) descends along with the level of the liquid nitrogen. Then, as the pressure of the elastic member (23) changes, the changed level of the liquid nitrogen is displayed on the level indicator (25). The liquid nitrogen stored in the internal tank (12) is at an extremely low temperature of -196°C, and when the temperature of the internal tank (12) is higher than -196°C, it vaporizes into gas and increases the pressure of the internal tank (12). In this case, if the vaporized gas is released to maintain the pressure of the internal tank (12) constant, a problem occurs in which the liquid nitrogen is insufficient to extinguish the fire when a fire breaks out. In the present embodiment, a water level measuring means (20) is mounted on the liquid nitrogen storage tank (11) so that the water level of the liquid nitrogen can be checked, thereby preventing problems arising from a lack of liquid nitrogen in advance.

[0044] The vent valve (30) discharges gas generated inside the liquid nitrogen storage tank (11) to the outside to maintain the internal pressure of the liquid nitrogen storage tank (11) at a constant level. To this end, the vent valve (30) is provided with a valve body (31), a valve spool (33), and a spring (35).

[0045] The valve body (31) is mounted on the liquid nitrogen storage tank (11), and a passage (32) is formed inside so that the gas generated by vaporizing the liquid nitrogen stored inside the inner tank (12) can be discharged to the outside. Here, one end of the passage (32) is connected to the liquid nitrogen storage tank (11) so that gas can flow in, and the other end of the passage (32) is connected to the outside so that gas can be discharged.

[0046] The valve spool (33) serves to close the flow path (32) with the pressure inside the liquid nitrogen storage tank (11). For this purpose, the valve spool (33) is mounted so as to be able to slide on the flow path (32). Here, the valve spool (33) is formed so as to slide to close the flow path (32) when the pressure inside the liquid nitrogen storage tank (11) is greater than a certain pressure, and to be supported by a spring (35) so as to open the flow path (32) when the pressure inside the liquid nitrogen storage tank (11) is less than a certain pressure.

[0047] A spring (35) is mounted on the valve body (31) to support the valve spool (33). Here, the spring (35) elastically supports the valve spool (33) so that the valve spool (33) can open the passage (32) when the pressure inside the liquid nitrogen storage tank (11) is lower than a certain pressure. When the liquid nitrogen stored in the inner tank (12) of the liquid nitrogen storage tank (11) vaporizes and generates gas, the generated gas is supplied to one end of the passage (32). At this time, since the pressure inside the inner tank (12) is lower than a certain pressure, the valve spool (33) is supported by the spring (35) as shown in (a) of Fig. 2 to open the passage (32). Then, the gas supplied to the passage (32) of the vent valve (30) is discharged to the outside through the opened passage (32). Therefore, the internal pressure of the inner tank (12) can be maintained at a constant level. Meanwhile, when a fire occurs and liquid nitrogen is sprayed into the battery module (110), high-pressure nitrogen gas is supplied from the pressure vessel (17) to the inner tank (12). At this time, since the pressure inside the inner tank (12) is greater than a certain pressure, the valve spool (33) is pressurized by the high-pressure gas as shown in (b) of Fig. 2 to close the flow path (32). When the flow path (32) is closed, the pressure inside the inner tank (12) rapidly increases, so that the liquid nitrogen can be pressurized and quickly sprayed by the injection means (40).

[0048] The injection means (40) is equipped with a pipe (41) and a nozzle (43) and serves to inject liquid nitrogen into each battery module when a fire occurs.

[0049] The pipe (41) branches out from the liquid nitrogen storage tank (11) to flow into the interior of each battery pack (100) so that when liquid nitrogen is supplied from the liquid nitrogen storage tank (11), it can be sprayed into each battery module (110), and branches out again from the battery pack (100) to each battery module (110).

[0050] The nozzle (43) is mounted on the pipe (41) and sprays liquid nitrogen into the battery module (110).

[0051] The opening / closing means (50) serves to open the liquid nitrogen supply means (10) so that liquid nitrogen can be supplied from the liquid nitrogen storage tank (11) to the pipe (41). For this purpose, the opening / closing means (50) is provided with an opening / closing valve (51) and a rupture plate (53).

[0052] The opening / closing valve (51) is mounted on the pressure vessel (17) so as to open / close the pressure vessel (17).

[0053] The rupture disc (53) ruptures when the liquid nitrogen storage tank (11) is pressurized, thereby closing the outlet of the liquid nitrogen storage tank (11) so that liquid nitrogen can be supplied to the pipe (41). Therefore, when the sensor means (60) detects overheating of the battery module (110) or a fire signal, the on-off valve (51) opens, and the high-pressure nitrogen gas stored in the pressure vessel (17) is supplied to the liquid nitrogen storage tank (11). Then, when the internal pressure of the liquid nitrogen storage tank (11) increases and the liquid nitrogen is pressurized, the rupture disc (53) ruptures, and the liquid nitrogen stored in the liquid nitrogen storage tank (11) is supplied to the pipe (41).

[0054] The sensor means (60) comprises a temperature detection sensor (61) and a fire detection sensor (63). Here, the temperature detection sensor (61) is mounted on each battery module (110) to detect whether the battery module (110) is overheated. In addition, the fire detection sensor (63) is mounted on each battery module (110) to detect fire signals such as flames, gas, or smoke generated from the battery module (110).

[0055] When the sensor means (60) detects overheating or thermal runaway of the battery module (110) or a fire signal, the control means (70) opens the opening / closing valve (51) so that liquid nitrogen can be sprayed through the nozzle (43) and serves to notify the outside of the battery status. To this end, the control means (70) is equipped with a transceiver (71) and receives data from a temperature detection sensor (61) and a fire detection sensor (63). Here, the transceiver (71) transmits the status of the battery module (110) to an external manager via a wireless communication network so as to notify the outside manager of overheating or thermal runaway of the battery module (110) and the occurrence of a fire. Therefore, when a temperature exceeding a certain level is detected by the temperature detection sensor (61) mounted on the battery module (110) or a fire signal is detected by the fire detection sensor (63), it is determined that the battery module (110) is overheated or has runaway heat and is in a fire state, and the opening / closing valve (51) is opened. Then, the high-pressure nitrogen gas stored in the pressure vessel (17) is supplied to the liquid nitrogen storage tank (11) to pressurize the liquid nitrogen stored in the liquid nitrogen storage tank (11). When the liquid nitrogen storage tank (11) is pressurized, the rupture plate (53) mounted on the outlet of the liquid nitrogen storage tank (11) ruptures, and the liquid nitrogen is supplied to the pipe (41). Then, the liquid nitrogen is sprayed onto the battery module (110) through the nozzle (43) to cool the battery module (110) and extinguish the fire.

[0056] In the present embodiment, a vent valve (30) and a level measuring means (20) are installed in the liquid nitrogen storage tank (11). The liquid nitrogen stored in the inner tank (12) is at an extremely low temperature of -196°C. When the temperature of the inner tank (12) is higher than -196°C, it vaporizes into gas, thereby increasing the pressure of the inner tank (12). Therefore, when the liquid nitrogen vaporizes and the pressure of the inner tank (12) increases, the vaporized gas is discharged to the outside through the vent valve (30). At this time, the vaporized gas supplied to the vent valve (30) has a pressure lower than a certain pressure, so it is discharged to the outside through the open passage (32) of the vent valve (30). Therefore, the pressure of the inner tank (12) can be maintained at a constant level. However, in this case, since the liquid nitrogen is lost, there is a problem that the liquid nitrogen to extinguish the fire in case of a fire is insufficient, making it impossible to extinguish the fire. In the present embodiment, since a level measuring means (20) is installed, the liquid nitrogen level can be checked. Therefore, if liquid nitrogen is lost, liquid nitrogen can be refilled before a fire occurs, thereby preventing problems arising from a lack of liquid nitrogen in advance.

[0057] Meanwhile, when a temperature exceeding a certain temperature is detected by the temperature detection sensor (61) or a fire signal is detected by the fire detection sensor (63), the control means (70) opens the opening / closing valve (51) so that liquid nitrogen can be sprayed into the battery module (110) where overheating or a fire has occurred. Then, the high-pressure nitrogen gas stored in the pressure vessel (17) is supplied to the internal tank (12) of the liquid nitrogen storage tank unit (11) to pressurize the liquid nitrogen stored in the internal tank (12). At this time, a pressure greater than a certain pressure is applied to the vent valve (30) mounted on the liquid nitrogen storage tank unit (11), so that the valve spool (33) is pressurized and slides to close the flow path (32). Then, the vaporized gas generated in the inner tank (12) cannot be discharged to the outside, and high-pressure nitrogen gas is supplied to the inner tank (12), so the pressure inside the inner tank (12) increases more quickly to pressurize the liquid nitrogen. When the liquid nitrogen is added, the rupture plate (53) mounted on the outlet of the liquid nitrogen storage tank (11) ruptures, and the liquid nitrogen is supplied to the pipe (41). When the liquid nitrogen is supplied to the pipe (41), it is sprayed to the battery module (110) through the nozzle (43) to extinguish the fire.

[0058] Traditionally, fire extinguishing agents with excellent electrical insulation have been used to extinguish fires. However, this method has the disadvantage of causing damage not only to the battery pack at the point of injection but also to electronic components installed in the vicinity, significantly increasing the recovery time after extinguishing the fire. Furthermore, in the case of battery modules, even if a fire is extinguished immediately, the fire can break out again if a chemical reaction continues within the battery module. In contrast, the present invention injects ultra-low-temperature liquid nitrogen. This first rapidly cools the temperature of the battery module (110) undergoing thermal runaway, and secondarily, the injected liquid nitrogen vaporizes, further cooling the battery module (110) to extinguish the fire. Therefore, even if chemical reactions remain within the battery module (110), the battery module (110) can be extinguished, effectively extinguishing fires caused by thermal runaway. Furthermore, since the fire can be extinguished without damaging electronic components, the cost of post-fire extinguishment can be reduced.

Claims

1. A liquid nitrogen supply means having a liquid nitrogen storage tank section storing liquid nitrogen inside, and a pressure vessel containing high-pressure nitrogen gas to supply nitrogen gas to the liquid nitrogen storage tank section in order to spray the liquid nitrogen to each battery module in the event of a fire; A level measuring means mounted on the above liquid nitrogen storage tank section and capable of measuring the level of the liquid nitrogen, A vent valve mounted on the liquid nitrogen storage tank section so that the gas generated inside the liquid nitrogen storage tank section can be released to the outside by opening when the pressure of the liquid nitrogen storage tank section is lower than a certain pressure and closing when the pressure is higher than the above pressure, A pipe connected to supply the liquid nitrogen from the liquid nitrogen storage tank to each of the battery modules, and a spraying means equipped with a nozzle mounted on the pipe, An opening / closing means for opening / closing the liquid nitrogen supply means so that the liquid nitrogen can be supplied from the liquid nitrogen storage tank to the pipe, A sensor means mounted on each of the battery modules, comprising a temperature detection sensor for detecting the temperature of the battery module and a fire detection sensor for detecting flames, gas or smoke generated from the battery module, An automatic fire extinguishing device for an energy storage device, characterized in that it includes a control means having a transmitter and receiver that opens the opening / closing means so that the liquid nitrogen can be sprayed through the nozzle when a temperature exceeding a certain level is detected by the temperature detection sensor or a fire signal is detected by the fire detection sensor, and transmits the status of the battery module so as to notify an external manager of overheating or fire in the battery module.

2. In the first paragraph, the vent valve A valve body having a path formed so that gas inside the liquid nitrogen storage tank can be discharged to the outside, A valve spool that is slidably mounted on the passage so that the passage can be closed by the pressure inside the liquid nitrogen storage tank, An automatic fire extinguishing device for an energy storage device, characterized in that it has a spring mounted on the valve body to support the valve spool so that the passage can be opened when the pressure of the liquid nitrogen storage tank is lower than the predetermined pressure.

3. In paragraph 2, The above liquid nitrogen storage tank section comprises an inner tank for storing liquid nitrogen therein, an outer tank for accommodating the inner tank at a predetermined distance from the inner tank so that a vacuum layer is formed between the inner tank and the outer tank, and an insulating material filled in the vacuum layer. An automatic fire extinguishing device for an energy storage device, characterized in that the water level measuring means comprises a buoyancy member accommodated in the internal tank to rise and fall according to the water level of the liquid nitrogen, an elastic member whose pressure changes linearly according to the height of the buoyancy member, and a water level display unit that displays the water level of the liquid nitrogen with the pressure of the elastic member.

4. In the third paragraph, the opening and closing means An opening / closing valve that opens / closes the pressure vessel to supply high-pressure nitrogen gas to the liquid nitrogen storage tank when a fire is detected by the above sensor means, An automatic fire extinguishing device for an energy storage device, characterized in that it comprises a rupture plate that closes the outlet of the liquid nitrogen storage tank so that the liquid nitrogen storage tank can be ruptured when pressurized and the liquid nitrogen can be supplied to the pipe.

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