Active exhaust control system of hydrogen fuel storage tank

Abstract

The invention provides an active exhaust control system of a liquid hydrogen storage tank. The active exhaust control system allows safe storage of greater mass of hydrogen for a longer period of time. The system is configured to actively monitor, control, and expel hydrogen as a function of a combination of pressure and fill level within the tank. When the tank reaches a predetermined fill level, the active exhaust control system is configured to exhaust the tank for a predetermined period of time. The active exhaust control system is configured to repeat the process during shipping and storage to allow the tank to be filled at a higher initial fill level and contain a greater mass of hydrogen compared to the passive pressure relief system.

Description

[0001] Cross-reference to related applications This application is a PCT international patent application claiming priority to U.S. Provisional Patent Application No. 18 / 545,971, filed December 19, 2023, entitled "ACTIVE VENTING CONTROL SYSTEM FOR HYDROGEN FUEL TANKS", and claiming the benefit and priority to U.S. Provisional Patent Application No. 63 / 515,059, filed July 21, 2023, entitled "ACTIVE VENTING CONTROL SYSTEM FOR HYDROGEN FUEL TANKS", all of which are incorporated herein by reference in their entirety. Technical Field

[0002] This disclosure relates to an exhaust control system for hydrogen fuel storage tanks, and more specifically, to an active exhaust control system for modular liquid hydrogen fuel storage tanks for vehicles. Background Technology

[0003] Hydrogen is a clean energy source that can be used to power various modes of transportation, including aircraft and other vehicles. Hydrogen fuel is typically stored as a gaseous fuel in tanks or other preferred containers, or as a liquid under cryogenic conditions. Hydrogen fuel offers significant advantages over other types of power sources. For example, the specific energy of aviation fuel, such as jet fuel, is generally in the range of approximately 43 MJ / kg to approximately 48 MJ / kg. In contrast, the specific energy of hydrogen is generally in the range of approximately 120 MJ / kg to approximately 140 MJ / kg. Therefore, using hydrogen as a fuel source for vehicles can reduce the fuel weight on the vehicle while providing energy comparable to other conventional fuel sources. Furthermore, burning carbon-based fuels produces exhaust gases with various atmospheric pollutants, such as carbon dioxide. However, consuming hydrogen as fuel releases only benign or non-toxic byproducts, such as water, thus reducing the environmental impact of various transportation modes that use hydrogen as a fuel source.

[0004] During the storage and transportation of hydrogen fuel in tanks to hydrogen-powered aircraft or other vehicles, and during storage, ambient heat from outside the tanks will seep into the tanks due to inadequate insulation. This heat causes the liquid hydrogen to expand, increasing the pressure inside the tanks. Therefore, the tanks must be vented to prevent overpressure. However, each time the fuel tank is vented, some gaseous hydrogen is released, meaning fuel loss. Furthermore, aircraft or other vehicles may have operational requirements that maintain hydrogen at certain pressures. Therefore, a hydrogen storage tank and venting system that minimizes fuel loss and meets operational requirements safely and efficiently is needed. Summary of the Invention

[0005] The technology disclosed herein overcomes the aforementioned disadvantages and provides additional benefits. For example, one or more embodiments of the technology provide a liquid hydrogen storage tank module assembly, including a liquid hydrogen fuel storage tank located within a module housing. The tank is configured to contain liquid hydrogen under cryogenic conditions and gaseous hydrogen in a top space above the liquid hydrogen. A plurality of sensors are operatively coupled to the hydrogen fuel storage tank and configured to measure liquid temperature, vapor temperature, tank pressure, and hydrogen mass. Hydrogen mass is the total mass of liquid and gaseous hydrogen in the internal volume of the tank. The assembly has a passive pressure relief valve and an active venting control system. The passive pressure relief valve is coupled to the interior of the hydrogen fuel storage tank and configured to automatically move to an open position when the tank pressure exceeds a pressure relief threshold. The active venting control system has an active venting valve movable between a closed position and an open position and operatively coupled to the hydrogen fuel storage tank to communicate with the gaseous hydrogen.

[0006] The controller is coupled to the sensor and configured to receive the sensor's output. The controller is also configured to calculate vapor density based on vapor temperature and tank pressure, liquid density based on liquid temperature and tank pressure, average density based on hydrogen mass and tank volume, and effective fill level based on vapor density, liquid density, and average density. The controller is configured to move the active vent valve from the closed position to the open position when the effective fill level exceeds an initial fill level threshold, and to move the active vent valve to the closed position when a secondary threshold is reached after the initial fill level threshold.

[0007] Other embodiments of this technology provide a liquid hydrogen storage tank assembly, including a liquid hydrogen fuel tank configured to contain liquid and gaseous hydrogen fuel. A passive pressure relief valve is coupled to the interior of the hydrogen fuel tank and configured to automatically move to a first open position when the internal pressure within the tank exceeds a pressure relief threshold. A plurality of sensors are operatively coupled to the liquid hydrogen fuel tank and configured to measure conditions within the liquid hydrogen fuel tank. The sensors include a pressure sensor and a fill level sensor, the pressure sensor being configured to determine the internal pressure within the tank volume, and the fill level sensor being configured to acquire data to determine the liquid hydrogen fill level within the tank volume. The assembly also includes an active venting control system coupled to the liquid hydrogen fuel tank and the plurality of sensors. The active venting control system has an active venting valve and a controller. The active venting valve is movable between a closed position and an open position and is operatively in communication with gaseous hydrogen in the top space above the liquid hydrogen in the tank volume. The controller is coupled to the sensors and the active venting valve. The controller is configured to receive output from sensors and determine the effective fill level of liquid hydrogen and the pressure within the tank volume. The controller is configured to move the active vent valve from a closed position to an open position when the effective fill level exceeds an initial fill level threshold, and is configured to move the active vent valve to a closed position when a secondary threshold is reached after the initial fill level threshold. Attached Figure Description

[0008] The features and advantages of this disclosure can be better understood by referring to the following detailed description, which illustrates illustrative embodiments utilizing the principles of this disclosure, along with the accompanying drawings.

[0009] Figure 1 This is a perspective view of a modular hydrogen fuel storage assembly having one or more liquid hydrogen storage tanks according to one embodiment of the present technology, the liquid hydrogen storage tanks being configured for use with an active exhaust control system.

[0010] Figure 2 This is an enlarged perspective view of a liquid hydrogen storage tank with a controllable active exhaust control system according to an embodiment of the present technology.

[0011] Figure 3 This is a schematic diagram of an active exhaust control system according to an embodiment of the present technology.

[0012] Figure 4 An operational flowchart of an active exhaust control system according to an embodiment of the present technology is shown.

[0013] Figure 5A , Figure 5B and Figure 5CThe diagrams illustrate the changes in hydrogen mass, fill level, and tank pressure over time in a liquid hydrogen fuel storage tank having a passive pressure relief valve and an active venting valve of an active venting control system according to one or more embodiments of the present technology.

[0014] Figure 6 A schematic diagram of hydrogen saturation curves in a liquid hydrogen fuel tank having a passive pressure relief valve and an active exhaust valve of an active exhaust control system according to an embodiment of the present technology is shown.

[0015] Figure 7A and Figure 7B The image shows a side view and schematic diagram of a catalytic converter configured to be coupled to one or more active exhaust control systems according to various embodiments of the present technology.

[0016] Those skilled in the art will understand that the features shown in the accompanying drawings are for illustrative purposes, and variations including different and / or additional features and arrangements are possible. Detailed Implementation

[0017] This technology relates to an active exhaust control system configured for use with a liquid hydrogen fuel storage tank, or a tank filled with other fuels stored in a liquid state at cryogenic temperatures. Specific details of this technology are described herein. Figures 1 to 7B Description. While many embodiments are described with respect to liquid hydrogen fuel tank assemblies or systems, it should be noted that other applications and embodiments besides those disclosed herein are also within the scope of this technology. Furthermore, embodiments of this technology may have constructions, components, and / or processes different from those shown or described herein. Moreover, those skilled in the art will understand that embodiments of this technology may have other constructions, components, and / or processes besides those shown or described herein, and these and other embodiments may not have certain constructions, components, and / or processes shown or described herein without departing from this technology.

[0018] While various embodiments of the present technology have been shown and described herein, it will be apparent to those skilled in the art that these embodiments are provided by way of example only. Many variations, modifications, and substitutions will occur to those skilled in the art without departing from the scope of the present technology. It should be understood that various alternatives to the embodiments described herein may also be employed. Furthermore, even if not specifically shown or described, components disclosed in connection with one described embodiment may be included in or used in other embodiments. Some components described or shown in connection with the embodiments may not be essential and may be excluded while still remaining within the scope of the applicant's inventive technology.

[0019] In one aspect, this disclosure provides an active exhaust control system located in or coupled to one or more modular liquid hydrogen fuel tank assemblies configured for use on a vehicle such as an aircraft. In some embodiments, the modular tank assembly may be configured to be stored remotely from the vehicle, transported to the vehicle, and removably installed within the vehicle to supply hydrogen fuel to the vehicle's powertrain (e.g., a fuel cell system) or other hydrogen-based power units. The tank assembly can then be removed from the vehicle and transported to a remote location for refilling and storage until the vehicle requires it again. The active exhaust control system may be configured to actively vent gaseous hydrogen from the tank based on tank pressure and fill level to maintain a maximum amount of liquid hydrogen in the tank during filling, storage, transport, and installation on a hydrogen-powered aircraft, while maintaining the pressure in the tank at or below a selected maximum or operating pressure. In some cases, the liquid hydrogen tank in the assembly is configured to contain a volume of hydrogen that is liquid at cryogenic conditions, as well as a portion of gaseous hydrogen filling the top space above the liquid hydrogen within the tank assembly. As the temperature inside the tank rises and some liquid hydrogen converts to gas, the pressure inside the tank increases. An active venting system monitors temperature, pressure, liquid volume, and / or other internal conditions, and is configured to actively vent hydrogen from the tank to carefully control the amount of hydrogen released, while maintaining as much hydrogen fuel as possible at a safe pressure for subsequent use once the tank is coupled to an aircraft or other vehicle. In addition to the active venting system, the tank assembly includes a conventional passive pressure relief valve configured to open if the gas pressure inside the tank exceeds a specified level.

[0020] In some embodiments, a liquid hydrogen fuel storage tank assembly with an active venting control system according to the present technology is configured to monitor conditions within the tank, including liquid fill level, temperature, and pressure, and during storage and / or transport storage, to actively open a valve via a controller whenever a predetermined fill level is reached, the predetermined fill level being determined based on the tank pressure and the characteristics (e.g., volume, density, and / or temperature) of the liquid hydrogen stored within the tank. The effective fill level is the effective percentage of the total tank volume occupied by liquid hydrogen. The active venting control system is configured to allow the hydrogen fuel storage tank to be filled at a higher initial fill level than a hydrogen fuel storage tank using a conventional passive valve (which opens upon reaching a predetermined venting pressure). The active venting control system is also configured to provide substantial mass savings by venting less hydrogen from the tank than a conventional passive venting system.

[0021] For example, a hydrogen fuel tank with appropriate volume and using only a conventional 9-bar passive venting system can be filled with an initial mass of only 148 kg of liquid hydrogen, at an initial fill level of 70% of the tank volume, and after storage and passive venting to maintain an internal pressure equal to or less than 9 bar for 200 hours, it can only retain 114 kg of hydrogen. In contrast, a similar modular liquid hydrogen fuel tank with the same volume and 9-bar pressure limit, but equipped with an active venting control system according to embodiments of the present technology, can be filled with an initial mass of up to 195 kg and an initial fill level of 92% of the same tank volume, such that after 200 hours of storage under the same environmental conditions, the tank can retain 158 kg of hydrogen for subsequent use by aircraft or other vehicles after the modular tank assembly is installed and the fuel system is activated. Therefore, the active venting system allows for an increase of approximately 31.8% in the initial mass of stored hydrogen, and an increase of approximately 38.6% in the hydrogen retained after 200 hours.

[0022] Figures 1 to 3 This is a view of a hydrogen fuel module 20 including a liquid hydrogen fuel tank assembly 30 with an active exhaust control system 100, according to an embodiment of the present invention. The hydrogen fuel tank module 20 can be configured to be removably loaded into and securely held in an aircraft or other vehicle with a hydrogen-powered system. The fuel storage module 20 may include modules and components described in U.S. Patent No. 11,525,544 entitled “Fuel Storage Module Assembly” and / or U.S. Patent Application No. 18 / 311,209 entitled “Modular Hydrogen-Fuel Storage Assembly”, filed May 2, 2023, the entire contents of which are incorporated herein by reference. The hydrogen fuel tank assembly 30 may include fuel tanks and components as disclosed in U.S. Patent Application Publication No. 2022 / 0136656 entitled “Systems and Methods for Storing Liquid Hydrogen,” the entire contents of which are incorporated herein by reference. The liquid hydrogen fuel storage tank assembly 30 is configured to be filled with hydrogen fuel, for example, at a filling location remote from aircraft or other vehicles. The fuel tank module 20, equipped with an active exhaust control system 100, can be remotely stored and / or transported to aircraft or other vehicles for installation and connection to the vehicle's fuel and power system. The active exhaust system 100 is configured to actively monitor and control the pressure and conditions within the tank to reduce the amount of hydrogen fuel that needs to be vented from the tank, while maintaining target internal pressure, temperature, and fill volume during module filling, storage, and transport to aircraft or other vehicles.

[0023] like Figure 2As shown, the illustrated active exhaust system 100 includes an active exhaust valve 140 and a controller 150. The active exhaust valve 140 is coupled to the tank assembly 30 and configured to be actuated to selectively and precisely release gaseous hydrogen from the tank 30 to reduce internal pressure within the liquid hydrogen fuel tank assembly 30. A sensor 130 and the active exhaust valve 140 are connected to the controller 150, which may be located within the module 20 and adjacent to the tank 30. In other embodiments, the controller 150 may be attached externally to the tank module 20. The controller 150 may be configured to communicate with the sensor 130, the active exhaust valve 140, and / or the active exhaust control system 100 or other components of the hydrogen tank assembly 30 via a wired communication link or wirelessly. The controller 150 may be configured to communicate with more than one active exhaust valve 140 and sensor within or on multiple liquid hydrogen fuel tank assemblies 30 (such as multiple tank assemblies within a module). The controller 150, the active exhaust valve 140, and / or the sensor 130 may be coupled to a power source (such as a battery or other selected onboard or external power source).

[0024] The liquid hydrogen fuel storage tank assembly 30 has a fillable insulated multi-walled tank with an interior 105 for containing liquid hydrogen fuel under cryogenic conditions. A piping system 180 is attached to the tank and in fluid communication with the interior 105. The piping system 180 has an inlet fuel line and an outlet fuel line, allowing the tank to be filled with liquid hydrogen to a selected fill level via one or more inlet lines, and allowing hydrogen fuel to be removed from the tank via one or more outlet lines during use in an aircraft (or other vehicle). The piping system 180 also includes a passive pressure relief valve 160, configured to remain in a closed, sealed position until the internal pressure exceeds a threshold level above the desired storage and operating internal pressure. In the event that the pressure inside the tank exceeds the threshold pressure, the passive pressure relief valve 160 is automatically pushed to an open position to release some hydrogen from the tank 30, thereby reducing the internal pressure of the tank below the threshold level. It should be noted that the active venting system 100 is configured to actively and carefully control the internal pressure of the liquid hydrogen storage tank, and the passive pressure relief valve 160 can be directly used as an automatic backup valve for the active venting system 100 if internal or external conditions require it.

[0025] In the illustrated embodiment, the liquid hydrogen fuel storage tank assembly 30 is configured to be filled or refilled with liquid hydrogen to a selected fill level, such that the space above the liquid inside the tank (i.e., the top space) is filled with gaseous hydrogen. The liquid hydrogen fuel storage tank assembly 30 of the illustrated embodiment is configured to be filled or refilled with liquid hydrogen under cryogenic conditions and within a selected pressure range (e.g., approximately 4 to 6 bar or preferably up to approximately 7 bar). In other embodiments, the liquid hydrogen fuel storage tank assembly 30 may be configured to retain hydrogen within other temperature and pressure ranges for the selected configuration during storage and / or transportation after filling and before installation on an aircraft or other vehicle. The liquid hydrogen fuel storage tank assembly 30 retains liquid hydrogen fuel for a selected period of time during storage / transportation, and the active venting system 100 closely monitors and controls the internal pressure of the tank to maximize the allowable initial fill level and internal pressure, thereby maximizing the storage or holding time while minimizing hydrogen fuel loss due to venting. In some embodiments, the tank can be held for up to approximately 200 hours after initial filling and before installation of module 20 into an aircraft (or other vehicle) while minimizing losses from venting. Other embodiments may also provide additional maximum holding times. In some embodiments, tank module 20 is also configured with a hydrogen leak and fire detection system 110 for additional protection.

[0026] The hydrogen fuel module 20 is stored, transported, used, or otherwise present in most of the surrounding environment. When the liquid hydrogen fuel storage tank assembly 30 is filled or refilled with cryogenic liquid hydrogen fuel, heat from outside the tank is slowly transferred through the tank to the liquid hydrogen inside. As a result, if left uncontrolled, the liquid hydrogen will slowly expand, and the tank pressure will increase over time. The sensors 130 of the active exhaust system 100 may include multiple different sensors, such as a liquid temperature sensor, a vapor temperature sensor 131, a tank pressure sensor 133, a hydrogen mass sensor, a fill level sensor 135, a health monitoring sensor, and other types of sensors. Sensors 130 can transmit various measurement results to the controller 150.

[0027] In some embodiments, controller 150 may be a hardware controller with a central processing unit (CPU) that receives and interprets signals (e.g., digital signals) from sensor 130 using conventional communication protocols. The CPU may be a single processing unit or multiple processing units located in a single device or distributed across multiple devices. The CPU may be mounted on the hydrogen fuel module 20, or it may be located remotely from the module. The CPU may use sensor information to calculate internal conditions within the tank and communicate with the active venting assembly to move the active venting valve 140 between an open and closed position based on a combination of sensor information regarding fill level, temperature, and / or pressure. Controller 150 may be or include a computing device that accesses a computer-readable medium, including computer-readable storage media and data transmission media. A computer-readable storage medium is a tangible storage device that does not include transiently propagating signals. Examples of computer-readable storage media include memories such as main memory, cache memory, and secondary storage (e.g., DVDs), and include other storage devices. The computer-readable storage medium may contain computer-executable instructions, or may be encoded using computer-executable instructions. Additionally, the stored information may be encrypted. Data transmission media are used to transmit data via wired or wireless connections using transiently propagating signals or carrier waves (such as electromagnetic waves). Additionally, the transmitted information can be encrypted.

[0028] The controller 150 can be configured to operatively move the active vent valve 140 between an open position and a closed position based on calculations performed by the controller 150 using measurements received from the sensor 130. When the controller 150 moves the active vent valve 140 to the open position, the valve 140 releases gaseous hydrogen from the storage tank at a fixed or variable rate. When the controller 150 moves the active vent valve 140 to the closed position, the release of gaseous hydrogen stops until the valve reopens.

[0029] Active venting valve 140 may include a valve actuator 142 and a vacuum jacket 146. The valve actuator 142 is operatively coupled to a controller and may be configured to actuate valve 140 to move the valve between an open and closed position in response to a command from controller 150. The vacuum jacket 146 may be configured to reduce heat transfer between active venting valve 140 and liquid hydrogen to maintain an appropriate operating temperature. Because liquid hydrogen is stored at cryogenic temperatures, active venting valve 140 and / or other components (e.g., sensor 130) must be capable of cryogenic operation. In some embodiments, active venting valve 140 may be at least partially located in a cold box 144 within the tank module. Cold box 144 provides a thermally controlled environment for active venting valve 140 and other piping or hydrogen fuel lines coupled to the tank. This controlled environment can help maintain the temperature and pressure around active venting valve 140 to reduce the potential impact of the temperature and / or pressure of the surrounding environment around the tank module.

[0030] Figure 4 A flowchart 400 of an active exhaust control system according to one embodiment is shown. This active exhaust control system monitors pressure, temperature, and hydrogen fill level within a storage tank to determine when to actuate an active exhaust valve 140 to selectively release a minimum amount of hydrogen from the storage tank while maximizing the amount of hydrogen maintained in the tank during module storage and / or transport to an aircraft or other vehicle. In step 411, one or more sensors 130 measure the temperature (“vapor temperature”) of gaseous hydrogen fuel within the storage tank module 20. In step 412, one or more sensors 130 measure the tank pressure within the storage tank module 20. In step 413, one or more sensors 130 measure the temperature (“liquid temperature”) of liquid hydrogen fuel within the storage tank module 20. In step 414, one or more sensors 130 measure the mass (“hydrogen mass”) of hydrogen fuel within the storage tank module 20. The measurement results obtained in steps 411, 412, 413, and 414 can be transmitted to controller 150, for example, in real time, at fixed time intervals, or upon request from controller 150. The number or timing of measurement results acquired by sensor 130 and transmitted to controller 150 can be adjusted by the controller according to the needs of a specific tank module or the environment to which the tank module will be exposed.

[0031] In step 421, the controller 150 calculates the vapor density within the tank module 20 based on, for example, the vapor temperature measured in step 411 and the tank pressure measured in step 412. In step 422, the controller 150 calculates the liquid density within the tank module 20 based on, for example, the tank pressure measured in step 412 and the liquid temperature measured in step 413. In step 423, the controller calculates the average hydrogen density within the tank module 20 by, for example, dividing the hydrogen mass measured in step 414 by the known volume of the tank module 20. In some embodiments, the controller 150 uses various other sensor measurements to calculate the vapor density, liquid density, average density, and / or other parameters related to the hydrogen fuel within the tank module 20.

[0032] In step 431, controller 150 uses vapor density, liquid density, and average density to calculate the effective fill level (i.e., the effective percentage of the total tank volume occupied by liquid hydrogen). For example, the effective fill level is equal to the quotient of (1) the difference between average density and vapor density and (2) the difference between liquid density and vapor density, or Effective fill level = Where ρ is the average density, ρ v ρ is the vapor density, and ρl is the liquid density. Still in step 431, the controller 150 can then compare the calculated effective fill level with an initial fill level threshold (e.g., in the range of approximately 90% to 97%, and in some embodiments, in the range of approximately 90% to 95%). In other embodiments, the fill level can be measured directly (e.g., via the fill level sensor 135). In some embodiments, the initial fill level threshold may be predetermined or calculated and adjusted over time.

[0033] If the calculated effective fill level is greater than the initial fill level threshold, controller 150 proceeds to step 441, in which the controller moves active vent valve 140 from the closed position to the open position. When active vent valve 140 is in the open position, tank module 20 is vented in a controlled manner to release some gaseous hydrogen, thereby reducing the internal pressure and / or effective fill level in the tank below the initial fill level threshold. However, to prevent unnecessary fuel loss due to excessive venting time in tank module 20, controller 150 moves active vent valve 140 back to the closed position in step 442 once a predetermined condition is met. In some embodiments, the predetermined condition may be the elapsed time (e.g., 30 seconds, 60 seconds) or the recalculated effective fill level being lower than a secondary fill level threshold (e.g., in the range of approximately 80% to 85%). In the illustrated embodiment, the secondary fill level threshold is a selected or determined amount smaller than the initial fill level threshold. If the initially calculated effective fill level in step 431 is less than the initial fill level threshold, controller 150 proceeds directly to step 442, in which active vent valve remains in the closed position.

[0034] The active exhaust control system 100 is configured to continuously repeat the measurements, calculations, and determinations in flowchart 400 at selected intervals during the storage or transport of the tank module with the filling tank, and before the module is loaded onto an aircraft or other vehicle and connected to the fuel system and powertrain. In some embodiments, different combinations of sensor measurements are used to calculate the effective filling level. If the controller 150, sensor 130, and active exhaust valve 140 fail and the pressure inside the tank is not adequately released, the passive pressure relief valve 160 provides a backup valve that opens and releases gas from the tank if the internal pressure of the tank exceeds an emergency pressure upper limit threshold, thereby providing automatic pressure relief.

[0035] Figures 5A to 5C Schematic diagrams illustrating changes in hydrogen mass, fill level, and tank pressure over time in a liquid hydrogen fuel storage tank module 20 having a passive pressure relief valve 160 and an active venting valve 140 of an active venting control system 100 according to one or more embodiments of the present technology. Figure 5A In the figure, hydrogen mass schematic graph 501 shows the change of total hydrogen mass over time in a liquid hydrogen storage tank using the active venting control system 100 module, compared to a conventional storage tank with only a passive pressure relief valve, as shown in graph 511, as shown in graph 512. Figure 5B In the diagram, fill level schematic graph 502 shows the change in fill level over time (where 1.00 represents 100% capacity) in a liquid hydrogen storage tank using the active venting control system 100 module, compared to a conventional storage tank with only a passive pressure relief valve, as shown in curve 521. Figure 5CIn the diagram 503, the tank pressure schematic shows the change of tank pressure over time in a liquid hydrogen tank using the active venting control system 100 module, compared to a conventional tank with only a passive pressure relief valve, as shown in curve 531. As shown in curve 532, the tank pressure is as follows.

[0036] As an example, in Figure 5A In the middle, when time = 0 and the liquid and vapor temperatures are close to saturation, there is an active exhaust control system 100 ( Figure 3 The module's storage tank is initially filled with an initial mass of approximately 185 kg of liquid hydrogen. For a storage tank of the same size with only a passive pressure relief valve 160, when time = 0, the tank can only be filled with an initial mass of approximately 169 kg of liquid hydrogen over the same storage duration. The following will discuss... Figure 6 In further detail, the use of the active venting valve 140 allows the storage tank to be filled with a larger initial mass of hydrogen than a storage tank using only the passive pressure relief valve 160. For the illustrated embodiment, the maximum storage tank capacity is 209 kg. Figure 5B As shown, it has an active exhaust control system 100 ( Figure 3 The initial fill level of the tank with the passive pressure relief valve 160 at time = 0 is approximately 0.89 (i.e., 89%), while the initial fill level of the tank with only the passive pressure relief valve 160 at time = 0 is approximately 0.81 (i.e., 81%). As ambient heat is transferred to the module's tank (e.g., due to inadequate insulation), the internal liquid hydrogen expands, causing an increase in both the fill level (i.e., the percentage of total tank volume occupied by liquid hydrogen) and the tank pressure. Figure 5B and Figure 5C As shown. However, as Figure 5A As shown, for a period of time after time = 0, both the active venting valve 140 and the passive pressure relief valve 160 in each storage tank are closed, the corresponding storage tanks do not vent, and the hydrogen mass remains constant, even though the actual filling level in the storage tanks initially begins to increase, such as... Figure 5B As shown.

[0037] like Figure 5C As shown in curve 531, for a tank with only a passive pressure relief valve 160, the valve remains closed until a predetermined fixed venting pressure, approximately 620 kPa, is reached. This passive venting pressure is reached at approximately time = 320,000 seconds. Once the passive venting pressure is reached, the passive pressure relief valve 160 opens to allow the tank pressure to remain at the fixed venting pressure. As a result, gaseous hydrogen is released at a rate proportional to the expansion of hydrogen in the tank caused by heat transfer from the environment to the tank module 20, and the mass of hydrogen in the tank decreases linearly, for example, from time = 320,000 seconds. Figure 5AAs shown. When liquid hydrogen is converted into gaseous hydrogen due to heat transfer, and released through the passive pressure relief valve after time = 320,000 seconds, the actual liquid hydrogen fill level stops rising and begins to decrease, for example, linearly decreasing after time = 320,000 seconds, as... Figure 5B As shown.

[0038] In contrast, for a storage tank with this technology module featuring an active venting control system 100, the active venting valve 140 is configured to selectively open and close based on data from sensor 130 and in response to commands from controller 150. Controller 150 can, according to... Figure 4 The flowchart 400 shows the operation, and the active vent valve 140 is opened when the effective fill level reaches the initial fill level threshold. Figures 5A to 5C In the examples shown (curves 512, 522, and 532, respectively), the tank is filled with an initial mass of approximately 185 kg at t=0. Pressure and fill level begin to increase after t=0 when the valve is closed. The initial fill level threshold is approximately 0.925 (i.e., 92.5%) when the hydrogen in the tank first reaches the initial fill level threshold at approximately time = 115,000 seconds. Figure 5B As shown. The standby passive pressure relief valve remains closed, but the active vent valve 140 opens briefly, thereby releasing gaseous hydrogen from the tank and reducing the internal pressure of the tank, as... Figure 5C As shown in curve 532. Hydrogen is released by opening the active vent valve, allowing the hydrogen quality and fill level to drop rapidly, as... Figure 5A (Curve 512) and Figure 5B (Curve 522) As shown. After a predetermined amount of time or when other conditions are met, the controller 150 moves the active exhaust valve 140 back to the closed position. In the schematic diagrams 501, 502, and 503 shown, the amount of time the active exhaust valve is in the open position is very short (e.g., at most a few minutes) compared to the overall storage time of approximately 200 hours in the illustrated embodiment, making the amount of time the active exhaust valve is in the open position difficult to perceive. Therefore, curve 512 shows the hydrogen mass curve 501 for multiple cycles of controlled opening and closing of the active exhaust valve 140, which is a step function. This arrangement makes it possible to achieve hydrogen mass from time = 0 to time = 1,00,000 seconds (>200 hours) in short time intervals except for about 300,000 seconds (see Figure 501). Figure 5A For almost all other times, tanks with active exhaust control systems can store more hydrogen than tanks using only conventional passive pressure relief valves.

[0039] After the controller moves the active vent valve 140 back to the closed position, as described above, ambient heat continues to be transferred to the tank module 20, causing the fill level and tank pressure to rise again. Whenever the effective fill level reaches the initial fill level threshold, the controller 150 reopens the active vent valve 140. In the illustrated example, the initial fill level threshold remains constant (e.g., 92.5%). In other embodiments, the controller can be configured to redefine the initial fill level threshold over time. In the illustrated example, after each opening and closing cycle of the active vent valve 140, when the active vent valve 140 moves to the open position, the tank pressure increases, such as... Figure 5C As shown in curve 532. However, as Figure 5C As shown, from approximately time = 0 to time = 580,000 seconds, the pressure in the tank using the active venting control system 100 remains equal to or lower than the pressure in a similar tank using only a passive pressure relief valve (when the active venting valve 140 is used, the tank pressure can exceed the fixed venting pressure of the passive pressure relief valve 160).

[0040] In the example shown, curve 532 surpasses curve 531 at approximately time = 580,000 seconds (approximately 160 hours). Figure 5A It was also shown that after an extended storage period of approximately 200 hours (i.e., 720,000 seconds), the amount of hydrogen fuel remaining in tank module 20 (i.e., hydrogen mass) was still significantly higher than the remaining hydrogen mass in a tank using only a conventional passive pressure relief valve. Therefore, during the extended storage period (i.e., >200 hours), the actual hydrogen fill level in the tank with the active venting control system 100 was significantly greater than the fill level in the tank using only a passive pressure relief valve, as... Figure 5B As shown. This means that compared to a liquid hydrogen storage tank that only uses the passive pressure relief valve 160, the tank system with the active venting control system 100 of this technology significantly reduces hydrogen fuel loss. Furthermore, the active venting valve 140 vents the hydrogen fuel storage tank module 20, ensuring that the tank pressure exceeds the venting pressure of the passive pressure relief valve 160 without causing safety issues.

[0041] Figure 6 A schematic diagram 600 shows the hydrogen saturation curve 602 of a liquid hydrogen fuel storage tank with the active exhaust control system 100 of the present technology as described above, and a conventional liquid hydrogen fuel storage tank with only a passive pressure relief valve. When the pressure and density of hydrogen create the plotted point below the saturation curve 602, hydrogen is in the liquid + gas phase. When the pressure and density of hydrogen create the plotted point on the curve above the saturation curve, hydrogen is in the saturated liquid phase or saturated gas phase.

[0042] When hydrogen is stored in liquid hydrogen tanks, it is highly desirable to maintain the pressure and density of the hydrogen within the tank below saturation curve 602 (e.g., through venting, temperature control, etc.). If the hydrogen fuel is above curve 602 in the saturated liquid phase, several problems can arise. For example, a saturated liquid may have a greater density variation, making it more difficult to control fill levels and reducing the efficiency of the fuel system. As another example, a saturated liquid is more difficult to cool, leading to increased vaporization and subsequent overpressure.

[0043] Compared to a liquid hydrogen storage tank with only a conventional passive pressure relief valve, as shown in curve 610, the liquid hydrogen storage tank and active venting control system 100 of this disclosure allow for the storage of a larger mass of hydrogen while maintaining it below saturation curve 602, as shown in curve 620. For comparison purposes, when using a conventional liquid hydrogen storage tank with only a passive pressure relief valve 160, the pressure and density of hydrogen follow curve 610. Conventional tanks can store hydrogen at a density just greater than about 55 kg / m³. 3 The initial density filling is approximately 7.5 bar with a passive depressurization level. As ambient heat is transferred to the tank, the tank pressure increases, and the hydrogen density remains constant as long as the passive depressurization valve 160 remains closed. Once the pressure in the conventional tank reaches the 7.5 bar level, the hydrogen in the tank will essentially reach the saturation curve 602, and the passive depressurization valve will open, preventing the hydrogen from exceeding the saturation curve 602 and allowing the tank pressure to remain at 7.5 bar. This results in a continuous linear loss of hydrogen fuel from the conventional tank, especially over extended storage periods. Therefore, the pressure threshold level of the conventional passive depressurization valve essentially determines the maximum initial mass of hydrogen fuel that can be placed in a conventional liquid hydrogen tank for extended storage (following the vertical portion of the downward-sloping curve 610). Furthermore, once the conventional tank is connected to the fuel system, the pressure threshold level of the conventional depressurization valve should not exceed the operating pressure of the hydrogen fuel. Otherwise, the hydrogen fuel pressure will need to be gradually reduced through the fuel system to reach the desired operating pressure, increasing the complexity and cost of the fuel system.

[0044] In contrast, the liquid hydrogen storage tank of the module with the active venting control system 100 of this technology allows more hydrogen to be added to the tank during filling and allows more hydrogen to be maintained in the module's tank over extended storage periods (e.g., >200 hours), while also ensuring that the hydrogen in the tank remains below the saturation curve. This is because the pressure, temperature, and fill level within the tank are actively monitored, and the active control valve 140 can be opened and closed multiple times depending on the conditions within the tank, as shown by curve 620. The active monitoring and control of the active venting valve 140 also allows the hydrogen in the tank to substantially follow the saturation curve 602, while remaining below the saturation curve during extended storage and / or transport to aircraft or other vehicles for subsequent use in fuel and powertrain systems. In the illustrated embodiment, the hydrogen content is exactly greater than about 55 kg / m³ compared to a conventional liquid hydrogen storage tank of similar size as described above. 3 Compared to the hydrogen density of [other materials], storage tanks with active exhaust control systems can initially operate at approximately 64 kg / m³. 3 The hydrogen density filling. This also means that for the storage tank of the module of the active exhaust control system 100 with this technology, the maximum initial mass of hydrogen fuel that the storage tank can accept is not determined solely based on the operating pressure requirements of the vehicle's fuel cell system, but also based on the frequency and speed at which the controller 150 opens and closes the active exhaust valve 140. The controller 150 can also be configured to maximize the hydrogen density in the storage tank during storage and to regulate the hydrogen pressure to the operating pressure before or during the process of the module being prepared for loading into the aircraft to connect to the aircraft's hydrogen fuel system. For example, the controller 150 can be configured to set the storage tank pressure to a value between approximately 6 bar and 8 bar at the end of the transport and storage period. It should be noted that while more frequent opening and closing of the active exhaust valve 140 can allow curve 620 to be closer to the "bend" of the saturation curve 602 and produce a larger maximum initial mass, this benefit must be balanced against the operational requirements and cycle life of the active exhaust valve 140 and other components of the active exhaust control system. For example, the controller 150 can be configured to move the active exhaust valve 140 from the closed position to the open position at least three times during transport and storage, such as Figure 6 As shown.

[0045] When the module 20 of the liquid hydrogen storage tank has an active exhaust control system 100 according to various embodiments of the present technology Figure 7B When stored or transported to aircraft or other vehicles, as described above, some hydrogen fuel may be actively released from the storage tank. This gaseous hydrogen fuel must be released safely and correctly. In one embodiment, the gaseous hydrogen fuel to be released can be released and directed via a catalyst to prevent the fuel from evaporating. For example, Figure 7A and Figure 7BThese are side views and schematic diagrams of a catalyst 700, configured to be coupled to one or more modules 20 comprising a liquid hydrogen storage tank having an active exhaust control system 100. Figure 7B The catalyst 700 is configured to receive exhaust gaseous hydrogen 720 and ambient air 710 through nozzle 730. Ambient air 710 and gaseous hydrogen 720 are mixed in mixing chamber 740, and the resulting mixture is converted into water in catalyst housing 750, thereby releasing waste 760 such as water and heat. The catalyst 700 allows for the safe and rapid processing of the released hydrogen and prevents its combustion, while hydrogen storage tanks remain for storage or transportation.

[0046] During transport and / or storage of the module and / or tank with active exhaust control system 100, module 100 may be secured within an enclosed space, such as trailer 770 or other storage facility. Catalyst 700 may be coupled to an exhaust line that delivers discharged hydrogen, and catalyst waste may be safely directed to the surrounding environment outside the trailer or other enclosed space containing the module, tank, and active exhaust control system.

[0047] In some embodiments, in addition to the active exhaust valve 140, the catalyst 700 may also be coupled to receive exhaust gaseous hydrogen from the passive pressure relief valve 160. In the illustrated embodiment, a single catalyst 700 is coupled to a plurality of tank modules 20. In some embodiments, tank modules 20 are coupled to a plurality of catalysts 700. In some embodiments, the catalyst 700 is decoupled from the hydrogen fuel active exhaust control system 100 before it is installed on the aircraft 10.

[0048] While preferred embodiments of the present disclosure have been shown and described herein, it will be apparent to those skilled in the art that these embodiments are provided by way of example only. This disclosure is not intended to be limited by the specific examples provided in the specification. Although the present disclosure has been described with reference to the foregoing description, the description and illustration of the embodiments herein are not intended to be construed as limiting. Many variations, alterations, and substitutions will occur to those skilled in the art without departing from this disclosure. It should be understood that all aspects of this disclosure are not limited to the specific descriptions, constructions, or relative proportions set forth herein, as this depends on various conditions and variables. It should be understood that various alternatives to the embodiments of the present disclosure described herein may be employed in the practice of this disclosure. Therefore, it is contemplated that this disclosure will also cover any such alternatives, modifications, variations, or equivalents. The appended claims are intended to define the scope of this disclosure and thereby cover the methods and structures within the scope of these claims and their equivalents.

Claims

1. A liquid hydrogen storage tank assembly comprising: a liquid hydrogen fuel storage tank configured to contain liquid and gaseous hydrogen fuel, wherein the hydrogen fuel storage tank has a tank volume; a passive pressure relief valve coupled to an interior of the liquid hydrogen fuel storage tank and configured to automatically move to a first open position when an internal pressure within the tank volume exceeds a pressure relief threshold; a plurality of sensors operatively coupled to the liquid hydrogen fuel storage tank and configured to measure conditions within the liquid hydrogen fuel storage tank, wherein the plurality of sensors includes a first pressure sensor configured to determine an internal pressure within the tank volume and a second fill level sensor configured to acquire data to determine a fill level of the liquid hydrogen within the tank volume; an active vent control system coupled to the liquid hydrogen fuel storage tank and the plurality of sensors, the active vent control system comprising: an active vent valve in operative communication with the gaseous hydrogen above the liquid hydrogen in the tank volume, the active vent valve movable between a closed position and a second open position; a controller coupled to the plurality of sensors and the active vent valve, the controller configured to determine an effective fill level of the liquid hydrogen within the tank volume and a pressure within the tank volume using information from the plurality of sensors, configured to move the active vent valve from the closed position to the second open position when the effective fill level exceeds an initial fill level threshold, and configured to move the active vent valve to the closed position upon a secondary threshold after the initial fill level threshold is reached, wherein the secondary threshold is different than the initial fill level threshold.

2. The assembly of claim 1, wherein, the plurality of sensors are operatively coupled to the hydrogen fuel storage tank and configured to measure at least one of a liquid temperature, a vapor temperature, a tank pressure, and a hydrogen mass within the tank volume, wherein the liquid temperature is a temperature reading of the liquid hydrogen, wherein the vapor temperature is a temperature reading of the gaseous hydrogen, wherein the tank pressure is a pressure reading of the internal pressure within the hydrogen fuel storage tank, and wherein the hydrogen mass is a total mass of the liquid hydrogen and the gaseous hydrogen.

3. The assembly of claim 1, wherein, the controller is configured to calculate a hydrogen vapor density based on the vapor temperature and the tank pressure, a liquid density based on the liquid temperature and the tank pressure, an average density based on the hydrogen mass and the tank volume, and the controller calculates the effective fill level based on the hydrogen vapor density, the liquid density, and the average density.

4. The assembly of claim 3, wherein, the controller is configured to compare the calculated effective fill level to the initial fill level threshold.

2. The liquid hydrogen storage tank assembly of claim 1, wherein the passive pressure relief valve is configured to move to the first open position when the internal pressure within the tank volume exceeds the pressure relief threshold.

3. The liquid hydrogen storage tank assembly of claim 1, wherein the passive pressure relief valve is configured to move to the first open position when the internal pressure within the tank volume exceeds the pressure relief threshold.

4. The liquid hydrogen storage tank assembly of claim 1, wherein the passive pressure relief valve is configured to move to the first open position when the internal pressure within the tank volume exceeds the pressure relief threshold.

5. The liquid hydrogen storage tank assembly of claim 1, wherein the passive pressure relief valve is configured to move to the first open position when the internal pressure within the tank volume exceeds the pressure relief threshold.

6. The liquid hydrogen storage tank assembly of claim 1, wherein the passive pressure relief valve is configured to move to the first open position when the internal pressure within the tank volume exceeds the pressure relief threshold.

7. The liquid hydrogen storage tank assembly of claim 1, wherein the passive pressure relief valve is configured to move to the first open position when the internal pressure within the tank volume exceeds the pressure relief threshold.

8. The liquid hydrogen storage tank assembly of claim 1, wherein the passive pressure relief valve is configured to move to the first open position when the internal pressure within the tank volume exceeds the pressure relief threshold.

9. The liquid hydrogen storage tank assembly of claim 1, wherein the passive pressure relief valve is configured to move to the first open position when the internal pressure within the tank volume exceeds the pressure relief threshold.

10. The liquid hydrogen storage tank assembly of claim 1, wherein the passive pressure relief valve is configured to move to the first open position when the internal pressure within the tank volume exceeds the pressure relief threshold.

11. The liquid hydrogen storage tank assembly of claim 1, wherein the passive pressure relief valve is configured to move to the first open position when the internal pressure within the tank volume exceeds the pressure relief threshold.

12. The liquid hydrogen storage tank assembly of claim 1, wherein the passive pressure relief valve is configured to move to the first open position when the internal pressure within the tank volume exceeds the pressure relief threshold.

13. The liquid hydrogen storage tank assembly of claim 1, wherein the passive pressure relief valve is configured to move to the first open position when the internal pressure within the tank volume exceeds the pressure relief threshold.

14. The liquid hydrogen storage tank assembly of claim 1, wherein the passive pressure relief valve is configured to move to the first open position when the internal pressure within the tank volume exceeds the pressure relief threshold.

15. The liquid hydrogen storage tank assembly of claim 1, wherein the passive pressure relief valve is configured to move to the first open position when the internal pressure within the tank volume exceeds the pressure relief threshold.

16. The liquid hydrogen storage tank assembly of claim 1, wherein the passive pressure relief valve is configured to move to the first open position when the internal pressure within the tank volume exceeds the pressure relief threshold.

17. The liquid hydrogen storage tank assembly of claim 1, wherein the passive pressure relief valve is configured to move to the first open position when the internal pressure within the tank volume exceeds the pressure relief threshold.

18. The liquid hydrogen storage tank assembly of claim 1, wherein the passive pressure relief valve is configured to move to the first open position when the internal pressure within the tank volume exceeds the pressure relief threshold.

19. The liquid hydrogen storage tank assembly of claim 1, wherein the passive pressure relief valve is configured to move to the first open position when the internal pressure within the tank volume exceeds the pressure relief threshold.

20. The liquid hydrogen storage tank assembly of claim 1, wherein the passive pressure relief valve is configured to move to the first open position when the internal pressure within the tank volume exceeds the pressure relief threshold.

5. The assembly of claim 1, wherein, The secondary threshold is a secondary fill level threshold that is less than the initial fill level threshold, and the controller is configured to move the active vent valve to the second closed position when the effective fill level reaches the secondary fill level threshold.

6. The assembly of claim 1, wherein, The controller is configured to move the active vent valve from the open position to the second closed position after a predetermined period of time after moving the active vent valve to the open position.

7. The assembly of claim 1, wherein, The hydrogen fuel tank and the active vent control system are configured to enable the hydrogen fuel tank to be filled with liquid hydrogen having an initial mass of approximately 195 kg, and an initial fill level in a range of about 90% to 95% of an internal volume of the tank, and to allow storage for approximately 200 hours, wherein approximately 158 kg of hydrogen remains in the tank at the end of the storage period after active venting during the storage period.

8. The assembly of claim 7, wherein, The initial fill level is approximately 92% of the internal volume of the tank.

9. The assembly of claim 1, wherein, The predetermined fill level is based on a hydrogen saturation curve.

10. The assembly of claim 1, wherein, The active vent valve is coupled to a catalytic converter, wherein the catalytic converter is configured to convert gaseous hydrogen released through the active vent valve into aqueous exhaust gas.

11. A liquid hydrogen tank module assembly, comprising: a module housing; a liquid hydrogen fuel tank located within the housing and configured to contain liquid hydrogen under cryogenic conditions and gaseous hydrogen within a headspace above the liquid hydrogen, wherein the hydrogen fuel tank has a tank volume; a plurality of sensors operatively coupled to the hydrogen fuel tank and configured to measure a liquid temperature, a vapor temperature, a tank pressure, and a hydrogen mass, wherein the liquid temperature is a temperature reading of the liquid hydrogen, wherein the vapor temperature is a temperature reading of the gaseous hydrogen, wherein the tank pressure is a pressure reading of an interior of the hydrogen fuel tank, and wherein the hydrogen mass is a total mass of the liquid hydrogen and the gaseous hydrogen; a passive pressure relief valve coupled to the interior of the hydrogen fuel tank and configured to automatically move to a first open position when the tank pressure exceeds a pressure relief threshold; and an active vent control system coupled to the hydrogen fuel tank, the active vent control system comprising: an active vent valve operatively coupled to the hydrogen fuel tank and in communication with the gaseous hydrogen, the active vent valve movable between a closed position and a second open position; and a controller configured to receive output from the sensors and to calculate a vapor density based on the vapor temperature and the tank pressure, a liquid density based on the liquid temperature and the tank pressure, an average density based on the hydrogen mass and the tank volume, and an effective fill level based on the vapor density, the liquid density, and the average density, wherein the controller is configured to move the active vent valve from the closed position to the second open position when the effective fill level exceeds an initial fill level threshold, and to move the active vent valve to the closed position when a secondary threshold is reached after reaching the initial fill level threshold.

12. The assembly of claim 11, wherein, The secondary threshold is a secondary fill level threshold that is less than the initial fill level threshold, and wherein the controller is configured to move the active vent valve to the closed position when the effective fill level reaches the secondary fill level threshold.

13. The assembly of claim 11, wherein, The secondary threshold is a predetermined time period, and wherein the controller is configured to move the active vent valve to the closed position after reaching the initial fill level threshold and the predetermined time period has elapsed.

14. The assembly of claim 11, wherein, The initial fill level threshold is between approximately 90% and 95% of the tank volume.

15. The assembly of claim 11, wherein, The initial fill level threshold is based on a hydrogen saturation curve.

16. The assembly of claim 11, wherein, The controller is configured to move the active vent valve from the closed position to the second open position at least three times during transport and storage.

17. The assembly of claim 11, wherein, The controller is configured to set the tank pressure between approximately 6 and 8 bar at the end of the transport and storage period.

18. The assembly of claim 11, wherein, The active vent valve is coupled to a catalytic converter, wherein the catalytic converter is configured to convert gaseous hydrogen released through the active vent valve into aqueous exhaust gas.

19. The assembly of claim 11, further comprising a cold box coupled to the liquid hydrogen fuel tank and configured to house a hydrogen line coupled to the internal volume and a controlled environment different from the ambient environment surrounding the liquid hydrogen fuel tank.

20. A liquid hydrogen tank assembly, comprising: a liquid hydrogen fuel tank configured to contain liquid hydrogen under cryogenic conditions and gaseous hydrogen within a headspace above the liquid hydrogen, wherein the hydrogen fuel tank has a tank volume; a plurality of sensors operatively coupled to the hydrogen fuel tank and configured to measure liquid temperature, vapor temperature, tank pressure, and hydrogen mass within the tank; and an active vent control system coupled to the hydrogen fuel tank, the active vent control system comprising: an active vent valve operatively coupled to the hydrogen fuel tank and in communication with the gaseous hydrogen, the active vent valve movable between a closed position and an open position; and a controller configured to receive output from the sensors and to calculate a vapor density based on the vapor temperature and the tank pressure, a liquid density based on the liquid temperature and the tank pressure, an average density based on the hydrogen mass and the tank volume, and an effective fill level based on the vapor density, the liquid density, and the average density, wherein the controller is configured to move the active vent valve from the closed position to the open position when the effective fill level exceeds an initial fill level threshold, and the controller is configured to move the active vent valve to the closed position upon reaching a secondary threshold after the initial fill level threshold.

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