Liquid nitrogen filling method and system

Abstract

The invention provides a liquid nitrogen filling method and system, and the method comprises the steps: firstly releasing the pressure of a to-be-filled liquid nitrogen storage tank to a preset pressure, enabling the pressure in the to-be-filled liquid nitrogen storage tank to be lower than the pressure of an external liquid nitrogen storage tank device, forming a pressure difference, and then filling liquid nitrogen. And when higher pressure is reached, an alarm is given and operation risks are brought. And finally, the storage tank to be filled with the liquid nitrogen is pressurized through the external liquid nitrogen storage tank device, the pressure in the storage tank to be filled with the liquid nitrogen is directly pressurized to the standard air pressure, and the storage tank to be filled with the liquid nitrogen does not need to be slowly adjusted for pressurization. According to the method, a pressure relief mode is adopted firstly, then an external liquid nitrogen tank car is used for pressurizing the liquid nitrogen storage tank to the standard air pressure, the internal pressure of the liquid nitrogen storage tank does not need to be manually adjusted in the filling process, the internal pressure of the to-be-filled liquid nitrogen storage tank is controlled within a safe range, and stable operation is achieved; and the working intensity of engineers and the risk caused by uncontrollable factors of manual operation are reduced.

Description

Technical Field

[0001] The present invention belongs to the field of nuclear power technology, specifically relates to the field of liquid nitrogen filling technology, and in particular relates to a liquid nitrogen filling method and system. Background Art

[0002] Liquid ammonia is the main source of nitrogen production in nuclear power plants. Nitrogen is used in nuclear power plants through system protection, safety protection, auxiliary operation and reactor applications to ensure the safety of nuclear power plant equipment, stable operation and personnel environment.

[0003] In nuclear power plants, the downstream systems of liquid nitrogen storage tanks involve numerous nuclear safety-related equipment, such as medium-pressure injection tanks and pressurizer relief tanks. As the units consume more liquid nitrogen, the liquid nitrogen tanks require refilling every month on average. During refilling, after checking the safety of the equipment, liquid nitrogen is directly transferred from a tank truck to the liquid nitrogen storage tank. Since the temperature of the new liquid nitrogen is slightly lower than that of the liquid nitrogen + nitrogen gas inside the tank, the nitrogen inside the tank condenses, causing the pressure in the tank to decrease accordingly. Due to the self-increasing circuit characteristics of the liquid nitrogen storage tank, boosting the pressure to standard atmospheric pressure takes a long time. This is especially true during unit overhauls and uptime, when downstream system equipment requires significant gas for online purging and cleaning. However, when the pressure in the liquid nitrogen storage tank is boosted back to standard atmospheric pressure, it is difficult to meet the unit's operating requirements, posing a threat to the safe and stable operation of related nuclear safety systems. The current practice is to manually intervene by having the operating personnel notify the maintenance personnel to temporarily adjust the self-pressurization circuit and the pressure reducing valve setting. This is extremely inconvenient for the operation and maintenance of the liquid nitrogen system. In addition, manual control requires manual operation of the valve to adjust the pressure, which has the risk of response lag and misoperation. Summary of the Invention

[0004] In order to solve the above problems, the purpose of the present invention is to provide a liquid nitrogen filling method and system, which can completely replace manual labor and abandon human intervention in the self-pressurization circuit and pressure reducing valve during liquid nitrogen filling, bringing safety and convenience to the operation and maintenance of the unit.

[0005] Based on this, the present invention provides a liquid nitrogen filling method, comprising the following steps:

[0006] Connect the external liquid nitrogen storage tank device to the liquid nitrogen storage tank to be filled through a delivery pipeline;

[0007] Depressurizing the liquid nitrogen storage tank to be filled so that the air pressure in the liquid nitrogen storage tank to be filled is lower than the air pressure of the external liquid nitrogen storage tank device, forming a pressure difference between the liquid nitrogen storage tank to be filled and the external liquid nitrogen storage tank device, and making the pressure difference within a pressure difference threshold; after the pressure difference threshold is reached, connecting the external liquid nitrogen storage tank device and the liquid nitrogen storage tank to be filled, and filling the liquid nitrogen storage tank to be filled through the delivery pipeline;

[0008] After the filling is completed, the liquid nitrogen storage tank to be filled is pressurized to increase the pressure of the liquid nitrogen storage tank to be filled to the standard atmospheric pressure.

[0009] Furthermore, the liquid nitrogen storage tank to be filled is provided with a relief valve and a first pressure gauge. When the delivery pipeline connects the external liquid nitrogen storage tank device and the liquid nitrogen storage tank to be filled, the pressure relief valve is opened to relieve pressure, and the pressure of the liquid nitrogen storage tank to be filled is detected by the first pressure gauge. When the pressure displayed by the first pressure gauge reaches a preset pressure, the relief valve is closed, and the preset pressure is less than the standard air pressure.

[0010] Furthermore, the liquid nitrogen storage tank to be filled is provided with a liquid phase inlet, and the external liquid nitrogen storage tank device is provided with a liquid phase outlet. After the pressure of the liquid nitrogen storage tank to be filled is released, the liquid phase inlet and the liquid phase outlet are opened to connect the liquid nitrogen storage tank to be filled and the external liquid nitrogen storage tank device for filling.

[0011] Furthermore, the liquid nitrogen storage tank to be filled is provided with a gas phase air inlet, and the external liquid nitrogen storage tank device is provided with a gas phase air outlet. After a sufficient amount of liquid nitrogen is added to the liquid nitrogen storage tank to be filled, the liquid phase inlet and the liquid phase outlet are closed, and the gas phase inlet and the gas phase outlet are opened. The liquid nitrogen storage tank to be filled and the external liquid nitrogen storage tank device are connected again, and the external liquid nitrogen storage tank pressurizes the gas nitrogen filled into the liquid nitrogen storage tank to be filled to the standard air pressure.

[0012] Furthermore, the liquid nitrogen storage tank to be filled is provided with a pressure stabilizing circuit. The external liquid nitrogen storage tank device inflates and pressurizes the liquid nitrogen storage tank to be filled. After the pressure of the liquid nitrogen storage tank to be filled is pressurized to the standard air pressure, the pressure stabilizing circuit is used to maintain the pressure of the liquid nitrogen storage tank to be filled at the standard air pressure.

[0013] Furthermore, the pressure stabilizing circuit includes a first boosting circuit and a pressure reducing valve. When the air pressure in the liquid nitrogen storage tank to be filled is greater than the standard air pressure, the pressure reducing valve is opened to release the pressure. When the air pressure in the liquid nitrogen storage tank to be filled is lower than the standard air pressure, the first boosting circuit is opened to increase the pressure.

[0014] Furthermore, the first pressurizing circuit includes a heat exchanger and a pressurizing valve. When the air pressure in the liquid nitrogen storage tank to be filled is lower than the standard air pressure, the heat exchanger converts the liquid nitrogen into nitrogen gas, and the nitrogen gas is passed into the liquid nitrogen storage tank to be filled through the pressurizing valve.

[0015] Furthermore, the external liquid nitrogen storage tank device includes a second pressurizing circuit. After the filling is completed, the step of pressurizing the liquid nitrogen storage tank to be filled to increase the pressure of the liquid nitrogen storage tank to be filled to the standard atmospheric pressure includes:

[0016] pressurizing the external liquid nitrogen storage tank device to a preset threshold value through the second pressurizing circuit, wherein the preset threshold value is greater than the standard air pressure;

[0017] Open the gas phase analysis valve to connect the second pressurizing circuit to the delivery pipeline to pressurize the liquid nitrogen storage tank to be filled to the standard gas.

[0018] Furthermore, the standard air pressure is 13 bar, and the pressure difference threshold is greater than 5 bar.

[0019] The present invention also provides a liquid nitrogen filling system comprising an external liquid nitrogen storage tank device and a liquid nitrogen storage tank to be filled, wherein the external liquid nitrogen storage tank device and the liquid nitrogen storage tank to be filled are connected via a delivery pipeline, wherein

[0020] The liquid nitrogen storage tank to be filled includes a pressure relief valve, a liquid phase inlet and a gas phase inlet, and the pressure relief valve is connected to the internal tank space of the liquid nitrogen storage tank to be filled, and is used to relieve pressure before filling the liquid nitrogen storage tank to be filled with liquid nitrogen, and the liquid phase inlet and the gas phase inlet are both connected to the delivery pipeline;

[0021] The external liquid nitrogen storage tank device includes a second pressurizing circuit, a liquid phase outlet, and a gas phase outlet, wherein the liquid phase outlet and the gas phase outlet are both connected to the delivery pipeline, and the second pressurizing circuit is connected to the liquid nitrogen storage space in the external liquid nitrogen storage tank device. When the liquid nitrogen storage tank to be filled is depressurized so that the air pressure in the liquid nitrogen storage tank to be filled is lower than the air pressure of the external liquid nitrogen storage tank device and the pressure difference formed between the liquid nitrogen storage tank to be filled and the external liquid nitrogen storage tank device reaches a pressure difference threshold, the liquid phase outlet is connected to the liquid phase inlet through the delivery pipeline;

[0022] After the filling is completed, the liquid phase outlet and the liquid phase inlet are closed and connected, and the gas phase outlet and the gas phase inlet are connected to inflate and pressurize the liquid nitrogen storage tank to be filled.

[0023] Beneficial effects:

[0024] The present invention provides a liquid nitrogen filling method and system. The method is to first relieve the pressure of the liquid nitrogen storage tank to be filled to a preset pressure, so that the pressure in the liquid nitrogen storage tank to be filled is lower than the pressure of the external liquid nitrogen storage tank device, and then fill the liquid nitrogen after reaching the preset pressure difference. The pressure relief can prevent the pressure of the liquid nitrogen storage tank from directly filling exceeding the safety threshold, reaching a higher pressure to alarm and bring operational risks. After the liquid nitrogen filling is completed, the liquid nitrogen storage tank to be filled is pressurized by the external liquid nitrogen storage tank device, and the pressure in the liquid nitrogen storage tank to be filled is directly pressurized to the standard air pressure, without the need for the liquid nitrogen storage tank to be filled to slowly adjust the pressurization. The present invention adopts a method of first relieving the pressure, and then uses an external liquid nitrogen tank truck to pressurize the liquid nitrogen storage tank to the standard air pressure. There is no need to manually adjust the internal pressure of the liquid nitrogen storage tank during the filling process. The internal pressure of the liquid nitrogen storage tank to be filled can be controlled within a safe range and run smoothly. The filling method is simple and efficient, reducing the workload of engineers and the risks brought by uncontrollable factors of manual operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0026] Figure 1 is an exemplary system architecture diagram in which embodiments of the present invention may be applied;

[0027] Figure 2 is a schematic diagram of a liquid nitrogen charging method provided in an embodiment of the present invention;

[0028] Figure 3 Schematic diagram of the structure of the liquid nitrogen storage tank to be filled provided by an embodiment of the present invention;

[0029] Figure 4 It is a structural schematic diagram of an external liquid nitrogen storage tank device provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0030] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0031] like Figure 1As shown, the liquid nitrogen system 100 includes a liquid nitrogen storage tank 101, a pressure stabilizing circuit 102, a pressurized vaporization component 103, a delivery pipeline 104 and a control component 105. The liquid nitrogen system provides stable nitrogen for safety systems, equipment maintenance, etc. through storage, pressurization, vaporization, delivery and precise control.

[0032] The liquid nitrogen storage tank 101 is a double-layer container, including an outer wall and an inner liner, and the annular space between the outer layer and the inner liner is evacuated to a vacuum (≤3Pa.a) to reduce heat transfer. The inner liner is used to store liquid nitrogen, which is connected to a safety valve to prevent overpressure of the liquid nitrogen, and the outer wall is connected to a bursting disk to prevent damage caused by too low a vacuum.

[0033] The pressurized vaporization assembly 103 includes a high-pressure nitrogen vaporizer and a low-pressure nitrogen vaporizer. It utilizes ambient air heat to heat and vaporize cryogenic liquid nitrogen, transporting the nitrogen to various downstream nitrogen application systems via delivery pipeline 104. The high-pressure vaporizer operates intermittently, using a single tank structure; the low-pressure vaporizer, which requires continuous supply, typically utilizes two parallel tanks.

[0034] Delivery pipeline 104 is equipped with multiple pipes and valves, forming a gas supply network, including high-pressure and low-pressure gas supply networks. Pressure in the network is controlled by pressure regulating valves. Through various valve controls, gaseous nitrogen is delivered to various users, such as injection tanks for the passive core cooling system, reactor coolant drain tanks, equipment purification, power plant maintenance / coverage, and pressurization.

[0035] Control assembly 105 is equipped with temperature and pressure sensors and other monitoring equipment to monitor the temperature, pressure, and other parameters of the liquid nitrogen system in real time and transmit this data to the control system. Based on set values and actual monitoring data, the control system automatically adjusts the opening of relevant valves and the operating status of pumps to ensure stable and safe operation of the liquid nitrogen system.

[0036] Pressure stabilization circuit 102 uses a pressure-stabilizing vaporizer to heat and vaporize the small amount of liquid nitrogen at the bottom of the liquefied liquid tank. This gas circulates naturally into the upper portion of the liquefied liquid tank, pressurizing the tank and maintaining internal pressure. The pressure balancing logic of the pressure stabilization circuit is as follows: when the pressure in the tank drops due to liquid nitrogen consumption, the vaporized nitrogen is used to replenish the pressure. If the pressure is too high, the pressure is released through the tank safety valve or return valve to prevent overpressure.

[0037] It should be understood that Figure 1 The structure of the liquid nitrogen system 100, which includes a liquid nitrogen storage tank 101, a pressure stabilizing circuit 102, a pressurized vaporization component 103, a delivery pipeline 104, and a control component 105, is merely illustrative. The connection and layout of the liquid nitrogen storage tank, the pressurized vaporization component, the delivery pipeline, and the control component can be designed according to implementation requirements.

[0038] It should be noted that the pressure stabilizing circuit 102 is provided with a self-pressurizing circuit and a pressure reducing valve to maintain the pressure inside the liquid nitrogen tanker at 13 bar. Specifically, the self-pressurizing circuit is provided with a pressure increasing valve and a heat exchanger. The heat exchanger is used to absorb the heat of the air to heat the liquid nitrogen and convert it into gaseous nitrogen, and then the internal pressure of the liquid nitrogen storage tank is maintained together by two regulating valves. Specifically, when the pressure inside the liquid nitrogen storage tank is greater than 13 bar, the pressure increasing valve is closed and the pressure reducing valve is opened to discharge the excess gas outside the liquid nitrogen storage tank, such as the downstream nitrogen application system and other storage tank devices. When the pressure inside the liquid nitrogen storage tank is lower than 13 bar, the pressure reducing valve is closed and the pressure increasing valve is opened to pressurize the storage tank by inputting gaseous nitrogen. In addition, the liquid nitrogen system is also provided with a safety warning pressure. When the pressure inside the liquid nitrogen storage tank is lower than 9 bar, the downstream nitrogen application system will be shut down. When the pressure inside the liquid nitrogen storage tank is higher than 17 bar, an alarm will be sounded and the safety valve will be closed.

[0039] It should be understood that the operating pressure of 13 bar and the warning pressures of 9 bar and 17 bar are the pressures required for stable operation of the liquid nitrogen system in the embodiment of the present invention. In other embodiments, the pressures can be designed as needed according to operational requirements. However, during the liquid nitrogen filling process, the liquid nitrogen vaporizes and absorbs heat, causing temperature changes, and the gas in the tank condenses and liquefies. This causes the pressure in the tank to gradually decrease. The liquid nitrogen in the self-pressurizing system is derived from the liquid nitrogen storage tank, and then converted into nitrogen gas through heat exchange or vaporizer. It takes a long time to restore the pressure in the tank to the operating pressure of 13 bar by setting up a self-pressurizing circuit in the liquid nitrogen system.

[0040] To this end, the present invention provides a liquid nitrogen filling method, such as Figure 2 As shown, the method comprises the following steps:

[0041] 201: Connect the external liquid nitrogen storage tank device to the liquid nitrogen storage tank to be filled through a delivery pipeline.

[0042] 202: Depressurize the liquid nitrogen storage tank to be filled so that the air pressure in the liquid nitrogen storage tank to be filled is lower than the air pressure of the external liquid nitrogen storage tank device, and a pressure difference is formed between the liquid nitrogen storage tank to be filled and the external liquid nitrogen storage tank device, and the pressure difference is within a pressure difference threshold.

[0043] 203: After the pressure difference between the liquid nitrogen storage tank to be filled and the external liquid nitrogen storage tank device reaches a pressure difference threshold, the external liquid nitrogen storage tank device and the liquid nitrogen storage tank to be filled are connected, and liquid nitrogen is added to the liquid nitrogen storage tank to be filled through the delivery pipeline.

[0044] 204: After the filling is completed, the liquid nitrogen storage tank to be filled is pressurized, and the pressure of the liquid nitrogen storage tank to be filled is increased to the standard air pressure.

[0045] It should be noted that in step 201, the external liquid nitrogen storage tank device can be a liquid nitrogen tank truck for transporting cryogenic liquid nitrogen. The liquid nitrogen storage tank is the liquid nitrogen storage equipment of the nuclear power plant. The delivery pipeline is a low-temperature resistant metal hose (such as a stainless steel bellows) or a composite insulated hose. One end of the delivery pipeline is connected to the liquid phase outlet of the external liquid nitrogen storage tank device, and the other end is connected to the liquid phase inlet of the liquid nitrogen storage tank. Before delivery, the delivery pipeline needs to be pre-cooled to avoid deformation of the delivery pipeline due to excessive temperature differences.

[0046] In this embodiment, after completing the safety inspection of the external liquid nitrogen storage tank device and the liquid nitrogen storage tank to be filled before the filling operation, in step 202, the air relief valve in the liquid nitrogen storage tank to be filled is opened to relieve the pressure of the liquid nitrogen storage tank to be filled, so that the air pressure in the liquid nitrogen storage tank to be filled is lower than the air pressure of the external liquid nitrogen storage tank device, and a pressure difference is formed between the liquid nitrogen storage tank to be filled and the external liquid nitrogen storage tank device, and the pressure difference is within the pressure difference threshold.

[0047] Specifically, the liquid nitrogen storage tank to be filled is equipped with a first pressure gauge and a relief valve. When a delivery pipeline connects the external liquid nitrogen storage tank device and the liquid nitrogen storage tank to be filled, the relief valve is opened to relieve the pressure of the liquid nitrogen storage tank to be filled, discharging the gaseous nitrogen in the liquid nitrogen storage tank to the downstream nitrogen application system or other nitrogen storage device, thereby creating a low-pressure environment in the liquid nitrogen storage tank to be filled. Simultaneously with the venting, the pressure of the liquid nitrogen storage tank to be filled is detected by the first pressure gauge, monitoring the pressure of the liquid nitrogen storage tank to be filled in real time. When the pressure displayed by the first pressure gauge reaches a preset pressure, the relief valve is closed.

[0048] It should be noted that the air relief valve can be a separately provided valve, or it can be a pressure reducing valve or air relief valve provided in other nitrogen branches in the liquid nitrogen storage tank to be filled. As long as it is connected to the liquid nitrogen storage tank to be filled, it can discharge the nitrogen in the liquid nitrogen storage tank to be filled, so that the liquid nitrogen storage tank to be filled forms a low-pressure environment and can be used as an air relief valve.

[0049] It should be noted that to ensure that the liquid nitrogen in the external liquid nitrogen storage tank can be charged into the liquid nitrogen storage tank to be filled at a sufficient speed and flow rate, the pressure difference between the liquid nitrogen storage tank to be filled and the external liquid nitrogen storage tank must be greater than 5 bar. If the pressure difference is less than 5 bar, the time it takes to charge the liquid nitrogen in the external liquid nitrogen storage tank to the liquid nitrogen storage tank to be filled will be prolonged, the heat exchange between the liquid nitrogen and the outside world will increase, and the amount of liquid nitrogen vaporized will increase, resulting in a decrease in the effective charge volume.

[0050] Furthermore, a preset pressure is set before the liquid nitrogen storage tank to be filled is depressurized. The preset pressure is the pressure inside the tank after the liquid nitrogen storage tank to be filled is depressurized. Specifically, the pressure relief is monitored by a first pressure gauge. When the reading of the first pressure gauge reaches the preset pressure, the pressure relief valve is closed to stop the pressure relief.

[0051] It should be noted that the preset pressure is lower than standard atmospheric pressure. Furthermore, since the external liquid nitrogen storage tank device may operate at a pressure with smaller specifications, the preset pressure may be lower than the lower limit of the operating pressure of the liquid nitrogen storage tank to be filled, so that the pressure difference between the liquid nitrogen storage tank to be filled and the external liquid nitrogen storage tank device is greater than 5 bar. Specifically, the preset pressure range is 5 bar to 10 bar.

[0052] It should be noted that the liquid nitrogen storage tank to be filled has an upper pressure limit and a lower pressure limit. The upper pressure limit is higher than the standard pressure, and the lower pressure limit is lower than the standard pressure. That is, the standard pressure is between the upper pressure limit and the lower pressure limit. Generally, the standard pressure is the midpoint of the upper pressure limit and the lower pressure limit. When the pressure in the liquid nitrogen storage tank to be filled exceeds the upper pressure limit, the safety valve automatically opens and sounds an alarm. When the pressure in the liquid nitrogen storage tank to be filled falls below the lower pressure limit, the liquid nitrogen cannot flow to the downstream nitrogen application system due to insufficient pressure.

[0053] Preferably, the preset pressure is 9 bar. The external liquid nitrogen storage tank device is generally a liquid nitrogen tank truck, and its operating pressure is generally between 8-16 bar, mostly 14 bar. Relieving the pressure in the liquid nitrogen storage tank to be filled to 9 bar can easily meet the condition that the pressure difference between the liquid nitrogen storage tank to be filled and the external liquid nitrogen storage tank device is greater than 5 bar. While ensuring stable filling, the pressure in the liquid nitrogen storage tank to be filled can be maintained at a higher operating pressure to avoid the pressure in the liquid nitrogen storage tank to be filled being too low, which will slow the flow of liquid nitrogen to the downstream nitrogen application system and fail to meet the supply of the downstream nitrogen application system.

[0054] It should be noted that the pressure stabilizing circuit is also used to maintain the pressure of the liquid nitrogen storage tank to be filled at the standard air pressure, so as to ensure that the liquid nitrogen in the liquid nitrogen storage tank to be filled can be normally supplied to the downstream nitrogen application system. Specifically, the pressure stabilizing circuit includes two branches, a first boosting circuit and a pressure reducing valve. The pressure of the liquid nitrogen storage tank to be filled is monitored in real time by the above-mentioned first pressure gauge. When the air pressure in the liquid nitrogen storage tank to be filled is greater than the standard air pressure, that is, when the first pressure gauge shows a reading higher than 13 bar, the first boosting circuit is closed, the pressure reducing valve is opened, and the liquid nitrogen storage tank to be filled is vented. When the air pressure in the liquid nitrogen storage tank to be filled is lower than the standard air pressure, that is, when the first pressure gauge shows a reading lower than 13 bar, the first boosting circuit is opened, the pressure reducing valve is closed, and the liquid nitrogen storage tank to be filled is inflated and pressurized.

[0055] In this embodiment, after the pressure of the liquid nitrogen storage tank to be filled is relieved, the liquid phase outlet of the external liquid nitrogen storage tank device and the liquid phase inlet of the liquid nitrogen storage tank are opened, and the delivery pipeline is connected. Since the pressure of the external liquid nitrogen storage tank device is higher than that of the liquid nitrogen storage tank to be filled, the external liquid nitrogen storage tank device drives the liquid nitrogen therein to flow according to the pressure, and starts to fill the liquid nitrogen into the liquid nitrogen storage tank to be filled.

[0056] It should be noted that during the filling process, the vaporization of liquid nitrogen will cause the volume of the gas to expand. According to the principle of the gas state equation PV = nRT, the pressure in the liquid nitrogen storage tank will also rise for a period of time. However, as the liquid nitrogen storage tank is fully cooled by liquid nitrogen, the subsequent liquid nitrogen vaporization amount decreases, and the original gas in the storage tank is cooled by the low-temperature liquid nitrogen, condensing into liquid nitrogen regardless of gas, which greatly reduces the volume and the pressure in the tank. Ultimately, after the liquid nitrogen filling is completed, the tank pressure is lower than the standard atmospheric pressure. Therefore, after the liquid nitrogen filling is completed in step 203, it is necessary to pressurize the liquid nitrogen storage tank to be filled, and increase the pressure in the liquid nitrogen storage tank to the standard atmospheric pressure to maintain the smooth operation of the liquid nitrogen system.

[0057] It should be noted that the standard air pressure is a preset working pressure. In order to avoid the liquid nitrogen storage tank to be filled from rupture or explosion due to excessive pressure, and to avoid negative pressure damage to the structure due to excessively low pressure, the standard air pressure is set as a fixed working pressure for the liquid nitrogen storage tank to be filled.

[0058] In this embodiment, the standard atmospheric pressure is set to 13 bar. If the operating pressure of the liquid nitrogen storage tank to be filled is too low, the tank may inhale air, contaminating the liquid nitrogen or damaging the tank structure. The first booster circuit maintains a positive pressure to fill the liquid nitrogen storage tank with nitrogen, ensuring that the liquid nitrogen storage tank is at the standard atmospheric pressure and is isolated from external impurities. If the operating pressure of the liquid nitrogen storage tank to be filled is too high, it may cause the tank to rupture or explode, threatening the safety of operators and equipment.

[0059] In this embodiment, the external liquid nitrogen storage tank device includes a second pressurizing circuit, which pressurizes the external liquid nitrogen storage tank device to a preset threshold value. The external liquid nitrogen storage tank device still forms a pressure difference with the liquid nitrogen storage tank to be filled, and the pressure of the external liquid nitrogen storage tank device is higher than the pressure of the liquid nitrogen storage tank to be filled.

[0060] Specifically, the second boosting circuit includes a second pressure gauge, a vaporizer and a return valve. The preset threshold value is greater than the standard atmospheric pressure. The second boosting circuit converts the liquid nitrogen in the external liquid nitrogen storage tank device into gaseous nitrogen through the vaporizer, thereby increasing the pressure in the external liquid nitrogen storage tank device. The return valve is used to control the nitrogen entering the external liquid nitrogen storage tank. The external liquid nitrogen storage tank device connects the second boosting circuit to the delivery pipeline to pressurize the liquid nitrogen storage tank to be filled to the standard atmospheric pressure through the gas phase analysis valve. In this embodiment, the preset threshold value is 15 bar, that is, when the reading of the second pressure gauge shows 15 bar, the external liquid nitrogen storage tank device and the liquid nitrogen storage tank to be filled are connected again, and the nitrogen in the external liquid nitrogen storage tank device is filled into the liquid nitrogen storage tank to be filled, and the liquid nitrogen storage tank to be filled is directly pressurized to the standard atmospheric pressure, without the need to slowly adjust the boost pressure through the first boosting circuit in the liquid nitrogen storage tank to be filled.

[0061] It is understandable that before the liquid nitrogen storage tank to be filled is filled with liquid nitrogen, the pressure in the external liquid nitrogen storage tank device can be increased by the second boosting circuit to ensure that the pressure in the external liquid nitrogen storage tank device is higher than the pressure in the liquid nitrogen storage tank to be filled.

[0062] In this embodiment, after the pressure of the liquid nitrogen storage tank to be filled is increased to the standard atmospheric pressure in step 204, the liquid nitrogen storage tank to be filled is automatically adjusted by the pressure stabilizing circuit to maintain the pressure inside the tank at the standard atmospheric pressure. Specifically, a pressure stabilizing circuit is provided in the liquid nitrogen storage tank to be filled, and the pressure stabilizing circuit is used to balance the pressure inside the liquid nitrogen storage tank to be filled during operation, so that the pressure inside the liquid nitrogen storage tank to be filled is maintained at the standard atmospheric pressure. When the pressure inside the liquid nitrogen storage tank to be filled exceeds or falls below the standard pressure, the pressure stabilizing circuit performs operations such as pressure relief or pressure boosting to maintain the pressure inside the liquid nitrogen storage tank at the standard atmospheric pressure, thereby ensuring the safe operation of the liquid nitrogen storage tank to be filled.

[0063] Specifically, the pressure stabilizing circuit includes a first boosting circuit and a pressure reducing valve. The pressure reducing valve is directly connected to the liquid nitrogen storage tank to be filled, and can exhaust and reduce the pressure of the liquid nitrogen storage tank to be filled, while the first boosting circuit is used to pressurize the gaseous nitrogen filled into the liquid nitrogen storage tank to be filled.

[0064] More specifically, the first pressurizing circuit and the pressure reducing valve are controlled by the control assembly 105 to automatically maintain a balance in the pressure in the liquid nitrogen storage tank to be filled. When the reading displayed by the first pressure gauge is greater than the standard atmospheric pressure, the pressure relief valve automatically opens to discharge the gas nitrogen in the liquid nitrogen storage tank to be filled. When the reading of the first pressure gauge is less than the standard atmospheric pressure, the first pressurizing circuit increases the pressure of the gas nitrogen in the liquid nitrogen storage tank to be filled.

[0065] It should be noted that, in one possible implementation of this embodiment, the pressure stabilizing circuit can also be used to relieve pressure before filling the liquid nitrogen storage tank to be filled, that is, the pressure reducing valve can also be used as a pressure relief valve to relieve pressure before filling the liquid nitrogen storage tank to be filled, and the pressure reducing valve can be opened by manual operation or program setting.

[0066] More specifically, the first pressurization circuit includes a boost valve and a heat exchanger. The heat exchanger absorbs heat from the air to convert liquid nitrogen from the liquid nitrogen storage tank to gaseous nitrogen. This gas is then passed through the boost valve into the liquid nitrogen storage tank, thereby increasing the pressure. The pressure reducing valve, when opened, directly connects the liquid nitrogen storage tank to the gaseous nitrogen, discharging it.

[0067] In another embodiment of the present invention, see Figure 3-Figure 4 , provides a liquid nitrogen filling system, the system comprising:

[0068] The liquid nitrogen storage tank 300 to be filled is a liquid nitrogen storage device used in nuclear power plants to store liquid nitrogen and provide liquid nitrogen to the downstream nitrogen application system of the nuclear power plant.

[0069] The external liquid nitrogen storage tank device 400 is also a liquid nitrogen storage device, which can be used to transport and load liquid nitrogen and to replenish liquid nitrogen to the liquid nitrogen storage tank to be filled.

[0070] It should be noted that the external liquid nitrogen storage tank device and the liquid nitrogen storage tank to be filled are connected by a delivery pipeline. The liquid nitrogen storage tank to be filled includes a first boosting circuit, a liquid phase inlet and a gas phase inlet. The first boosting circuit is connected to the internal tank space of the liquid nitrogen storage tank to be filled, and is used to relieve pressure before the liquid nitrogen storage tank to be filled is filled with liquid nitrogen. The liquid phase inlet and the gas phase inlet are both connected to the delivery pipeline.

[0071] The external liquid nitrogen storage tank device includes a second boosting circuit, a liquid phase outlet and a gas phase outlet, the liquid phase outlet and the gas phase outlet are both connected to the delivery pipeline, the second boosting circuit is connected to the liquid nitrogen storage space in the external liquid nitrogen storage tank device, when the liquid nitrogen storage tank to be filled is depressurized, so that the air pressure in the liquid nitrogen storage tank to be filled is lower than the air pressure of the external liquid nitrogen storage tank device and the pressure difference formed between the liquid nitrogen storage tank to be filled and the external liquid nitrogen storage tank device reaches a pressure difference threshold, the valve of the external liquid nitrogen storage tank device is opened, so that the liquid phase outlet is connected to the delivery pipeline and the liquid phase inlet, and the liquid nitrogen is added to the liquid nitrogen storage tank to be filled through the delivery pipeline.

[0072] After the filling is completed, the liquid phase outlet and the liquid phase inlet are closed, the second boosting circuit vaporizes the liquid nitrogen in the external liquid nitrogen storage tank device, the gas phase outlet and the gas phase inlet are opened, and the liquid nitrogen storage tank to be filled is inflated and pressurized through the conveying pipeline, and the pressure of the liquid nitrogen storage tank to be filled that has been completed is boosted to the standard air pressure.

[0073] In this embodiment, if Figure 3 As shown, the liquid nitrogen storage tank 300 to be filled includes a storage tank 8SGZ801EV, equipped with valves V3 (829VZ) and V3' (830VZ) for controlling the opening and closing of the liquid phase inlet, and valves V2 (828VZ) and V2' (821VZ) for controlling the opening and closing of the gas phase inlet. A pressure relief valve E1 (833VZ) is used for degassing. The pressure stabilizing circuit includes a heat exchanger Pr (804RE), a boosting valve V5 (836VZ), and a pressure reducing valve V10 (837VZ). The heat exchanger Pr (804RE) and the boosting valve V5 (836VZ) form a boosting branch - the first boosting circuit, and the pressure reducing valve V10 (837VZ) forms a pressure reducing branch.

[0074] Before filling with liquid nitrogen, open the pressure relief valve E1 (833VZ) to relieve the pressure of the storage tank 8SGZ801EV, reducing the air pressure in the storage tank 8SGZ801EV from the standard air pressure of 13 bar to 5 bar-10 bar, so that the pressure in the storage tank 8SGZ801EV is lower than the pressure of the external liquid nitrogen storage tank device 400 by more than 5 bar, forming a pressure difference for filling with liquid nitrogen. The purpose of pressure relief is to prevent direct filling from causing the pressure of the storage tank 8SGZ801EV to exceed 13 bar and reach the pressure alarm.

[0075] It should be noted that when the liquid nitrogen system is operating, the pressure stabilization circuit is also used to maintain the air pressure balance in the storage tank 8SGZ801EV, automatically maintaining the pressure in the tank at 13 bar. Specifically, the heat exchanger Pr (804RE) absorbs heat from the air to heat the liquid nitrogen into gaseous nitrogen, and then the pressure in the storage tank 8SGZ801EV is maintained at the operating pressure of 13 bar through the booster valve V5 (836VZ) and the pressure reducing valve V10 (837VZ). When the pressure in the storage tank 8SGZ801EV exceeds 13 bar, the booster valve V5 (836VZ) will close, and the pressure reducing valve V10 (837VZ) will open and discharge the excess gas to the user to reduce the pressure of the storage tank 8SGZ801EV. When the pressure of the storage tank 8SGZ801EV is lower than 13 bar, the boost valve V5 (836VZ) will open and the pressure reducing valve V10 (837VZ) will close, and the nitrogen generated by the heat exchanger PR (804RE) will be charged into the storage tank 8SGZ801EV for boosting.

[0076] Furthermore, in order to facilitate the maintenance of the boost valve V5 (836VZ) and the heat exchanger Pr (804RE), the first boost circuit is also provided with valve V1 (834VZ) and valve V7 (862VZ). Valve V7 (862VZ) is directly connected to the storage tank 8SGZ801EV. During maintenance, valve V1 (834VZ) and valve V7 (862VZ) are closed, so that the boost valve V5 (836VZ), the heat exchanger Pr (804RE) and the storage tank 8SGZ801EV are disconnected to prevent nitrogen or liquid nitrogen from entering the maintenance channel.

[0077] Furthermore, a warning device is installed inside tank 8SGZ801EV. If the pressure in the liquid nitrogen storage tank SGZ801EV drops below 9 bar, the start signal for the downstream compressor of tank 8SGZ801EV will be blocked. If the pressure in tank 8SGZ801EV reaches 17 bar, the safety valves SGZ802VZ and SGZ832VZ will trip, triggering an alarm.

[0078] It should be noted that since the temperature of the newly injected liquid nitrogen is slightly lower than the temperature of the medium (liquid nitrogen + nitrogen gas) inside the storage tank 8SGZ801EV, the nitrogen inside the liquid nitrogen storage tank SGZ801EV to be filled is condensed after the new liquid nitrogen is filled, and the tank pressure decreases accordingly.

[0079] Therefore, after the new liquid nitrogen is filled, it is necessary to increase the pressure of gaseous nitrogen through the storage tank 8SGZ801EV to the operating voltage. In this embodiment, the external liquid nitrogen storage tank device 400 is provided with a second boosting circuit. The second boosting circuit vaporizes the liquid nitrogen through the heat exchanger PB to increase the pressure within the external liquid nitrogen storage tank device 400, and then pressurizes the liquid nitrogen storage tank 300 to be filled with nitrogen.

[0080] Specifically, if Figure 4 As shown, the external liquid nitrogen storage tank device 400 is provided with a loop inlet valve (V3, V3'), and the return valve (V4) realizes its self-pressurization. When the pressure gauge (P1-2) of the external liquid nitrogen storage tank device 400 shows that the pressure reaches 15 bar, the gas phase analysis valve (AV2) is operated to control the gas phase outlet to open, and the hose is connected to the filling valve E3 (803VZ) of the liquid nitrogen storage tank 300 to be filled. At this time, the valves SGZ829VZ and SGZ830VZ for controlling the liquid phase inlet in the liquid nitrogen storage tank 300 to be filled remain closed, and the valves SGZ828VZ and SGZ821VZ for controlling the opening and closing of the gas phase inlet remain open. The gas phase pipe (pressure 15 bar) of the external liquid nitrogen storage tank device 400 is used to continue to pressurize the liquid nitrogen storage tank to the standard air pressure of 13 bar, which can meet the unit operation requirements without human intervention.

[0081] It should be noted that the liquid nitrogen filling system of this embodiment belongs to the same concept as that of the method embodiment. Its specific implementation process is detailed in the method embodiment, and the technical features in the method embodiment are applicable to this embodiment and will not be repeated here.

[0082] Throughout this specification, reference to terms such as "one embodiment," "some embodiments," "examples," "specific examples," or "some examples" means that a specific feature, structure, material, or characteristic described in conjunction with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0083] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to the embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the claims and their equivalents.

[0084] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and substitutions can be made without departing from the technical principles of the present invention. These improvements and substitutions should also be regarded as the scope of protection of the present invention.

Claims

1. A liquid nitrogen filling method, characterized in that: The following steps are involved: Connect the external liquid nitrogen storage tank device to the liquid nitrogen storage tank to be filled through a delivery pipeline; Depressurizing the liquid nitrogen storage tank to be filled so that the air pressure in the liquid nitrogen storage tank to be filled is lower than the air pressure of the external liquid nitrogen storage tank device, forming a pressure difference between the liquid nitrogen storage tank to be filled and the external liquid nitrogen storage tank device, and ensuring that the pressure difference is within a pressure difference threshold; After the pressure difference between the liquid nitrogen storage tank to be filled and the external liquid nitrogen storage tank device reaches the pressure difference threshold, connecting the external liquid nitrogen storage tank device and the liquid nitrogen storage tank to be filled, and filling the liquid nitrogen storage tank to be filled through the delivery pipeline; After the filling is completed, the external liquid nitrogen storage tank device is kept connected to the liquid nitrogen storage tank to be filled according to the delivery pipeline, and the external liquid nitrogen storage tank device inflates and pressurizes the liquid nitrogen storage tank to be filled, and pressurizes the liquid nitrogen storage tank to be filled to the standard air pressure.

2. The liquid nitrogen filling method according to claim 1, characterized in that: The liquid nitrogen storage tank to be filled is provided with a relief valve and a first pressure gauge. When the delivery pipeline connects the external liquid nitrogen storage tank device and the liquid nitrogen storage tank to be filled, the pressure relief valve is opened to relieve pressure, and the pressure of the liquid nitrogen storage tank to be filled is detected by the first pressure gauge. When the pressure displayed by the first pressure gauge reaches a preset pressure, the relief valve is closed, and the preset pressure is less than the standard air pressure.

3. The liquid nitrogen filling method according to claim 2, characterized in that: The liquid nitrogen storage tank to be filled is provided with a liquid phase inlet, and the external liquid nitrogen storage tank device is provided with a liquid phase outlet. After the pressure of the liquid nitrogen storage tank to be filled is released, the liquid phase inlet and the liquid phase outlet are opened to connect the liquid nitrogen storage tank to be filled and the external liquid nitrogen storage tank device for filling.

4. The liquid nitrogen filling method according to claim 3, characterized in that: The liquid nitrogen storage tank to be filled is provided with a gas phase air inlet, and the external liquid nitrogen storage tank device is provided with a gas phase air outlet. After a sufficient amount of liquid nitrogen is added to the liquid nitrogen storage tank to be filled, the liquid phase inlet and the liquid phase outlet are closed, and the gas phase inlet and the gas phase outlet are opened. The liquid nitrogen storage tank to be filled and the external liquid nitrogen storage tank device are connected again, and the external liquid nitrogen storage tank pressurizes the gas nitrogen filled into the liquid nitrogen storage tank to be filled to the standard air pressure.

5. The liquid nitrogen filling method according to claim 1, characterized in that: The liquid nitrogen storage tank to be filled is provided with a pressure stabilizing circuit. After the external liquid nitrogen storage tank device inflates and pressurizes the liquid nitrogen storage tank to be filled and the pressure of the liquid nitrogen storage tank to be filled is increased to the standard air pressure, the pressure stabilizing circuit is used to maintain the pressure of the liquid nitrogen storage tank to be filled at the standard air pressure.

6. The liquid nitrogen filling method according to claim 5, characterized in that: The pressure stabilizing circuit includes a first pressurizing circuit and a pressure reducing valve. When the air pressure in the liquid nitrogen storage tank to be filled is greater than the standard air pressure, the pressure reducing valve is opened to release the pressure. When the air pressure in the liquid nitrogen storage tank to be filled is lower than the standard air pressure, the first pressurizing circuit is opened to increase the pressure.

7. The liquid nitrogen filling method according to claim 6, characterized in that: The first pressurizing circuit includes a heat exchanger and a pressurizing valve. When the air pressure in the liquid nitrogen storage tank to be filled is lower than the standard air pressure, the heat exchanger converts liquid nitrogen into nitrogen gas, and the nitrogen gas is introduced into the liquid nitrogen storage tank to be filled through the pressurizing valve.

8. The liquid nitrogen filling method according to claim 1, characterized in that: The external liquid nitrogen storage tank device includes a second pressurizing circuit. After the filling is completed, the step of pressurizing the liquid nitrogen storage tank to be filled to increase the pressure of the liquid nitrogen storage tank to be filled to the standard atmospheric pressure includes: pressurizing the external liquid nitrogen storage tank device to a preset threshold value through the second pressurizing circuit, wherein the preset threshold value is greater than the standard air pressure; Open the gas phase analysis valve to connect the second pressurizing circuit to the delivery pipeline to pressurize the liquid nitrogen storage tank to be filled to the standard air pressure.

9. The liquid nitrogen charging method according to any one of claims 1 to 8, characterized in that: The standard air pressure is 13 bar, and the pressure difference threshold is greater than 5 bar.

10. A liquid nitrogen filling system, comprising an external liquid nitrogen storage tank device and a liquid nitrogen storage tank to be filled, wherein the external liquid nitrogen storage tank device and the liquid nitrogen storage tank to be filled are connected via a delivery pipeline, characterized in that: The liquid nitrogen storage tank to be filled includes a pressure relief valve, a liquid phase inlet and a gas phase inlet, and the pressure relief valve is connected to the internal tank space of the liquid nitrogen storage tank to be filled, and is used to relieve pressure before filling the liquid nitrogen storage tank to be filled with liquid nitrogen, and the liquid phase inlet and the gas phase inlet are both connected to the delivery pipeline; The external liquid nitrogen storage tank device includes a second pressurizing circuit, a liquid phase outlet, and a gas phase outlet, wherein the liquid phase outlet and the gas phase outlet are both connected to the delivery pipeline, and the second pressurizing circuit is connected to the liquid nitrogen storage space in the external liquid nitrogen storage tank device. When the liquid nitrogen storage tank to be filled is depressurized so that the air pressure in the liquid nitrogen storage tank to be filled is lower than the air pressure of the external liquid nitrogen storage tank device and the pressure difference formed between the liquid nitrogen storage tank to be filled and the external liquid nitrogen storage tank device reaches a pressure difference threshold, the liquid phase outlet is connected to the liquid phase inlet through the delivery pipeline; After the filling is completed, the liquid phase outlet and the liquid phase inlet are closed and connected, and the gas phase outlet and the gas phase inlet are connected to inflate and pressurize the liquid nitrogen storage tank to be filled.

Images