Boil-off management system and bearing unit

Abstract

The present invention relates to a boil-off management system (100) for a liquid hydrogen tank (50). The boil-off management system (100) comprises a boil-off valve (1) and a catalyst (11). The catalyst (11) can be connected to the liquid hydrogen tank (50) via the boil-off valve (1) and to the oxygen source (60) in parallel with the boil-off valve (1). The boil-off valve (1) can be designed as a backpressure-compensated pressure relief valve, wherein a check valve (5) with a response pressure is provided between the boil-off valve (1) and the catalyst (11). This response pressure is lower than the response pressure of the boil-off valve (1) but higher than the pressure of the oxygen source (60). Additionally or alternatively, a Venturi nozzle (7) can be provided between the boil-off valve (1) and the catalyst (11).The Venturi nozzle is designed such that hydrogen from the liquid hydrogen tank (50) is introduced laterally, in particular radially, into a substantially straight fluid channel section (17), which connects the suction flow inlet (19) with the ejector flow outlet (20) of the Venturi nozzle (7).

Description

[0001] The present invention relates to a boil-off management system for a liquid hydrogen tank and a storage unit for liquid hydrogen with a corresponding boil-off management system.

[0002] Vehicles or stationary applications with liquid hydrogen tanks can, in addition to a legally required emergency pressure relief device using simple overpressure safety valves, also include a so-called boil-off management system. One task of the boil-off management system is to limit the pressure level in the cryogenic liquid hydrogen tank, which may increase due to, for example, heat input from the environment, before the emergency pressure relief device is triggered, or to reduce it during a corresponding boil-off event.

[0003] The key difference between the boil-off management system and the emergency pressure relief device is that the boil-off management system does not release the vented hydrogen untreated into the environment. Specifically, the boil-off management system renders the vented hydrogen harmless before its release to counteract the potential risk of explosion due to the formation of an explosive air-hydrogen mixture (oxyhydrogen gas).

[0004] The elimination of free hydrogen can be achieved using a catalytic converter (catalyst), which oxidizes the hydrogen with oxygen, especially with ambient oxygen, to water vapor and thus renders it harmless.

[0005] Conventional boil-off management systems are either actively or passively operated. Actively operated boil-off management systems require an external power supply to actively operate various components of the boil-off management system. Passive boil-off management systems, in contrast, require a certain start-up phase during which an explosive hydrogen-air mixture is formed in the boil-off management system and / or the released hydrogen is not completely neutralized.

[0006] Against this background, it is an object of the present invention to further develop and improve the known boil-off management systems.

[0007] This task is solved by the boil-off management systems of the independent claims. Beneficial further training can be found in the dependent claims.

[0008] According to a first aspect of the present invention, a boil-off management system for a liquid hydrogen tank comprises a boil-off valve and a catalyst. The boil-off valve is configured to connect the boil-off management system to the liquid hydrogen tank. The catalyst is configured to oxidize hydrogen from the liquid hydrogen tank to water using oxygen from a separate oxygen source. The catalyst is connectable to the liquid hydrogen tank via the boil-off valve and to the oxygen source in parallel with the boil-off valve. A Venturi nozzle is provided between the boil-off valve and the catalyst. The Venturi nozzle comprises a motive flow inlet connected to the boil-off valve, a suction flow inlet connectable to the oxygen source, and an ejector flow outlet connected to the catalyst.The motive flow inlet of the Venturi nozzle is connected to a motive flow outlet, which opens laterally, in particular radially, into a substantially straight fluid channel section which connects the suction flow inlet to the ejector flow outlet.

[0009] According to the invention, the Venturi nozzle is integrated into the boil-off management system in such a way that a laterally introduced flow of hydrogen gas from the liquid hydrogen tank creates a substantially straight-line flow of oxygen from the suction flow inlet to the ejector flow outlet. This special flow pattern enables the admixture of oxygen to a superstoichiometric gas mixture and thus provides the prerequisite for avoiding the risk of explosion, since the hydrogen concentration in the resulting gas mixture is below the lower explosion limit of approximately 4 vol.%, thus preventing the formation of explosive oxyhydrogen gas, provided sufficient mixing of the gas components into a homogeneous mixture is ensured.

[0010] Preferably, the drive flow outlet extends at least along a portion of the circumference of the rectilinear fluid channel section. In particular, the drive flow outlet extends along multiple portions or along the entire circumference of the rectilinear fluid channel section.

[0011] These designs enable a compact yet efficient introduction of the hydrogen gas from the liquid hydrogen tank into the straight fluid channel section.

[0012] Preferably, the Venturi nozzle comprises a, in particular tubular, Coanda effect component which is designed to redirect a substantially radial flow of hydrogen gas from the drive flow outlet towards the ejector flow outlet in order to suck oxygen into the Venturi nozzle via the suction flow connection and to discharge it together with the hydrogen gas as a gas mixture through the ejector flow outlet.

[0013] The Coanda effect component has the advantage that the redirected flow of hydrogen gas from the liquid hydrogen tank creates a suction effect, which draws a particularly large amount of oxygen from the oxygen source into the Venturi nozzle. Furthermore, the Coanda effect ensures an intensified propulsion of the resulting gas mixture into the catalyst for conversion. The resulting suction effect enables the intake of a quantity of oxygen, resulting in a superstoichiometric gas mixture. A superstoichiometric gas mixture is defined as a gas mixture that is no longer explosive. In particular, such a quantity of oxygen is drawn into the Venturi nozzle and mixed with the hydrogen from the liquid hydrogen tank that the average volume fraction of hydrogen is below the lower explosion limit of approximately 4% of the volume fraction.In other words, the flow guidance and the Coanda effect in the Venturi nozzle result in the discharge of a gas mixture at the ejector flow outlet which has a hydrogen concentration below the lower explosion limit.

[0014] Preferably, a flow restrictor and a check valve are provided between the boil-off valve and the Venturi nozzle. The Venturi nozzle, the flow restrictor, and the check valve are coordinated such that the check valve only opens when the pressure and quantity of hydrogen subsequently flowing into the motive stream inlet cause the Venturi nozzle to operate, resulting in the discharge of a stream of superstoichiometric gas mixture.

[0015] In other words, the flow restrictor and the check valve are designed such that opening the check valve in the Venturi nozzle always generates a flow of hydrogen gas from the liquid hydrogen tank, which triggers the Coanda effect described above. Specifically, the set pressure of the check valve is at least equal to the pressure the propellant flow must have to generate the desired Coanda effect. The flow restrictor limits the amount of propellant flow such that the resulting flow of hydrogen gas does not prematurely detach from a guide surface of the Coanda effect component.

[0016] According to another aspect of the present invention, a boil-off management system for a liquid hydrogen tank comprises a boil-off valve and a catalyst. The boil-off valve is designed to connect the boil-off management system to the liquid hydrogen tank. The catalyst is designed to oxidize hydrogen from the liquid hydrogen tank to water using oxygen from a separate oxygen source. The catalyst is connectable to the liquid hydrogen tank via the boil-off valve and, in parallel to the boil-off valve, to the oxygen source. The boil-off valve is designed as a backpressure-compensated relief valve. A check valve with a response pressure that is lower than the response pressure of the boil-off valve but higher than the pressure of the oxygen source to be used is provided between the boil-off valve and the catalyst.

[0017] By designing the boil-off valve as a backpressure-compensated relief valve, the set pressure of the boil-off valve is no longer dependent on the pressure in a boil-off line downstream of the boil-off valve. The boil-off valve can be operated in its end positions (flow point and reset point) via the check valve with the set pressure specified here. This means that, like a full-lift safety valve, it can open relatively quickly and completely, undergoing a valve hysteresis during which it undergoes a valve hysteresis. This allows a flow of hydrogen gas with a specified minimum pressure and a specified minimum mass flow to be generated in the event of a boil-off event, i.e., when the check valve opens, to immediately ensure optimal function of the components of the boil-off management system downstream of the check valve.This, in particular, ensures safe and complete neutralization of the released free hydrogen. Furthermore, the resulting valve hysteresis allows the pressure in the liquid hydrogen tank to be reduced not only to the set pressure of the boil-off valve, but also below the set pressure of the boil-off valve. This prevents the boil-off valve from opening, at least until the pressure in the liquid hydrogen tank returns to the set pressure of the boil-off valve, resulting in reduced wear on the boil-off valve and the components of the boil-off management system as a whole.

[0018] Preferably, a Venturi nozzle is provided between the boil-off valve and the catalyst. The Venturi nozzle comprises, in particular, a drive flow inlet connected to the boil-off valve, a suction flow inlet connectable to the oxygen source, and an ejector flow outlet connected to the catalyst. The drive flow inlet of the Venturi nozzle is connected to a drive flow outlet, which opens laterally, in particular radially, into a substantially rectilinear fluid channel section connecting the suction flow inlet to the ejector flow outlet.

[0019] The previously described valve hysteresis enables the operation of the provided Venturi nozzle, which always produces a lean gas mixture with a superstoichiometric oxygen-to-hydrogen ratio. Specifically, the Venturi nozzle is integrated into the boil-off management system in such a way that a laterally introduced flow of hydrogen gas from the liquid hydrogen tank creates an essentially straight-line flow of oxygen. This special flow pattern enables the admixture of oxygen to a superstoichiometric gas mixture, thus avoiding the risk of explosion.

[0020] Preferably, the Venturi nozzle comprises a, in particular tubular, Coanda effect component which is designed to redirect a substantially radial flow of hydrogen gas from the drive flow outlet towards the ejector flow outlet in order to suck oxygen into the Venturi nozzle via the suction flow connection and to discharge it together with the hydrogen gas as a gas mixture through the ejector flow outlet.

[0021] As already described above, the Coanda effect component serves to generate sufficient suction for the oxygen that is to be mixed with the hydrogen gas from the liquid hydrogen tank.

[0022] Preferably, a flow restrictor is provided between the boil-off valve and the Venturi nozzle. The Venturi nozzle, the flow restrictor, and the check valve are coordinated such that the check valve only opens when the pressure and quantity of hydrogen gas subsequently flowing into the motive stream inlet causes the Venturi nozzle to operate, resulting in the discharge of a stream of a superstoichiometric gas mixture.

[0023] The flow restrictor limits the amount of propulsion flow when the check valve opens, preventing the resulting hydrogen gas flow from prematurely detaching from a guide surface of the Coanda effect component. This ensures the required suction effect.

[0024] Preferably, the response pressure of the check valve is between 4 bar and 8 bar, in particular 6 bar, and / or the response pressure of the boil-off valve is between 15 bar and 25 bar, in particular 20 bar.

[0025] These values ​​for the response pressure of the check valve or the boil-off valve have proven to be particularly suitable for implementing the inventive concept.

[0026] Preferably, a heat exchanger is provided between the boil-off valve and the catalyst, in particular between the boil-off valve and further components which are arranged upstream of the catalyst, which heat exchanger is designed to transfer heat from exhaust gases from the catalyst to the hydrogen gas from the boil-off valve.

[0027] This heat exchanger results in a heating of the comparatively cold hydrogen gas from the liquid hydrogen tank and thus makes it possible to avoid or at least reduce unwanted ice formation within components of the boil-off management system that are located upstream of the catalyst.

[0028] The boil-off management system preferably comprises a merging component in which the hydrogen from the boil-off valve is combined with the oxygen from the oxygen source. In particular, the merging component is a Venturi nozzle or the previously described one.

[0029] Such a combination component enables efficient combination of hydrogen and oxygen to form the desired gas mixture. As described above, a Venturi nozzle, or the previously described one, represents a particularly advantageous choice for the design of such a combination component.

[0030] Preferably, a hydrogen filter is provided between the boil-off valve and the merging component.

[0031] The hydrogen filter in question essentially serves to filter out unwanted impurities from the gas stream passing through it.

[0032] Preferably, a mixing chamber, in particular with mixing elements contained therein, is provided between the combining component and the catalyst.

[0033] Such a mixing chamber enables optimized mixing of the hydrogen gas with the oxygen, thus forming the most homogeneous gas mixture possible for the reaction in the catalyst. Mixing elements are understood to be, in particular, elements that impede the flow of the gas mixture, generating swirl and turbulent flows in the gas mixture. Various designs for such mixing elements are well known to those skilled in the art and include, for example, baffles, (mono-)swirl mixers, and / or other types of projections along an inner wall of the mixing chamber.

[0034] Preferably, a substrate permeable to the gas mixture is provided between the combining component and the catalyst, in particular behind a provided mixing chamber. Additionally or alternatively, the catalyst is reactively coated only in a rear region, and a front region of the catalyst is designed as a substrate permeable to the gas mixture.

[0035] Such substrates can fulfill a variety of functions to optimize the oxidation reaction within the catalyst and / or the safety of the boil-off management system. The use of a separate substrate from the catalyst allows for particularly flexible substrate selection and adaptation. The combined design of the catalyst and substrate enables particularly compact overall designs with fewer individual components.

[0036] Preferably, the substrate is designed as a guide component, heat shield and / or flame arrester.

[0037] The substrate acts as a guide component when it optimizes the flow of the gas mixture directed onto the catalyst in a desired manner, for example, by evenly distributing it. Designing it as a heat shield prevents excessive heating of the gas mixture before entering the catalyst and the resulting reduced efficiency of the exothermic reaction in the catalyst and / or backpressure that reduces the flow of gas mixture into the catalyst. Designing it as a flame arrester serves to prevent an unexpected ignition of the gas mixture in the catalyst from spreading into upstream areas of the boil-off management system.

[0038] Preferably, an inlet funnel is provided upstream of the catalyst, which increases the cross-section of the fluid channel upstream of the catalyst. Alternatively or additionally, an outlet funnel is provided downstream of the catalyst, which reduces the cross-section of the fluid channel downstream of the catalyst.

[0039] The inlet funnel reduces the flow velocity of the gas mixture due to its larger flow cross-section. This allows more time for the components of the gas mixture to mix homogeneously on their way to the catalyst. The outlet funnel increases the flow velocity of the gas mixture due to its smaller flow cross-section. This allows the exhaust gases to be directed away from the catalyst particularly efficiently.

[0040] Preferably, a condensate trap is provided behind the catalyst.

[0041] The condensate trap serves to prevent or at least reduce the contamination of the catalyst with condensate, which forms behind the catalyst from the exhaust gases of the catalyst.

[0042] The boil-off management system is preferably designed to use the environment of the boil-off management system as an oxygen source. In particular, the boil-off management system comprises an air filter for filtering ambient air before it is combined with the hydrogen gas from the liquid hydrogen tank.

[0043] In other words, the hydrogen gas from the hydrogen tank is mixed with oxygen from the ambient air to form the gas mixture for reaction in the catalyst. The air filter serves to filter out unwanted components from the inducted air stream.

[0044] Preferably, the boil-off management system is designed in such a way that it operates completely passively, i.e. without the need for external control and / or without the need for an additional energy supply.

[0045] In other words, the boil-off management system requires no power supply beyond the components described here and is self-powered. Each of the components operates completely autonomously, without the need for manual or automated control. Consequently, the boil-off management system also does not require any separate pressure and / or temperature sensors to collect the information necessary to control the individual components. The specific function of the boil-off management system results solely from the characteristics and specific combination of the previously described components of the boil-off management system.

[0046] Preferably, the boil-off valve is a valve with a metal bellows, in particular a stainless steel bellows valve.

[0047] This type of boil-off valve design is particularly robust and therefore reliable and durable.

[0048] Preferably, the catalyst is oriented substantially vertically and / or a chimney is arranged downstream of the boil-off management system.

[0049] Such designs allow the chimney effect to be used to efficiently remove exhaust gases from the catalyst.

[0050] Preferably, the catalyst and / or components downstream of the catalyst are surrounded by insulation.

[0051] This enables the reduction of the formation of condensate from the hot exhaust gases in and / or behind the catalyst and thus the negative impact of such condensate on the functioning of the boil-off management system.

[0052] According to a further aspect of the present invention, a storage unit for liquid hydrogen comprises at least one, in particular two, liquid hydrogen tanks and a boil-off management system as described above. Each provided liquid hydrogen tank is connected to the remaining components of the boil-off management system via its own boil-off valve but via a common boil-off line.

[0053] Such a storage unit benefits from the previously described advantages obtained by the boil-off management system according to the invention.

[0054] Preferably, each liquid hydrogen tank is provided with at least one, preferably two, pressure relief valves which have a higher response pressure than the boil-off valve assigned to the respective liquid hydrogen tank.

[0055] These pressure relief valves function as emergency pressure relief devices, releasing untreated hydrogen from the corresponding hydrogen tank into the atmosphere in the event of a dangerous overpressure in the liquid hydrogen tank. This prevents the liquid hydrogen tank from bursting due to overpressure in the corresponding liquid hydrogen tank. A single pressure relief valve is sufficient for this purpose. However, at least one additional redundant pressure relief valve is provided for additional safety.

[0056] The invention will now be described by way of example with reference to the accompanying drawings, in which: FIG. 1 is a schematic representation of the process consisting of an exemplary storage unit with a boil-off management system according to the present invention; and FIG. 2 is an example of a Venturi nozzle used in the FIG. 1shown boil-off management system can be used.

[0057] Accordingly FIG. 1 An embodiment of a storage unit 200 according to the invention for liquid hydrogen comprises at least one liquid hydrogen tank 50, which is connected to a boil-off management system 100 according to the invention. In particular, the storage unit comprises several, in particular as in FIG. 1 shown two separate liquid hydrogen tanks 50, each coupled to its own boil-off valve 1 of the boil-off management system 100.

[0058] The liquid hydrogen tanks 50 shown here each comprise an inner container 51 for the hydrogen and an outer container 52 surrounding the inner container 51. In the present case, a vacuum is provided between the inner container 51 and the associated outer container 52 to insulate the inner container 51. Alternatively or additionally, insulating materials could also be provided at least partially between the two containers 51 and 52. In the case shown, the interior of the inner containers 51 of the two liquid hydrogen tanks 52 is each connected to at least one, specifically even two, pressure relief valves 53. These pressure relief valves 53 form the emergency pressure relief device described above. They are designed to release untreated hydrogen gas from the associated liquid hydrogen tank 50 to the environment 60 as soon as a critical pressure in the liquid hydrogen tank 50 is exceeded.To ensure uninterrupted and safe release of excess pressure, no further components, such as a catalyst or the like, are connected downstream of the provided pressure relief valves 53 other than a line. Instead, the released hydrogen is released directly into the environment 60 of the storage unit 200.

[0059] This emergency protection is supplemented by the boil-off management system 100, which is described in more detail below.

[0060] Each liquid hydrogen tank 50 is coupled to a separate boil-off valve 1 of the inventive boil-off management system 100. The two boil-off valves 1 are each designed as backpressure-compensated pressure relief valves, in particular with a metal bellows, for example made of stainless steel. They each have a response pressure that is lower than the response pressure of the provided pressure relief valves 53. Thus, the boil-off valves 1 respond upstream of the pressure relief valves 53 and discharge gaseous hydrogen from the liquid hydrogen tanks 50 even before the maximum permissible operating pressure in the liquid hydrogen tanks 50 is reached.

[0061] Both boil-off valves 1 flow into a common boil-off line 2, which in the illustrated embodiment leads to a heat exchanger 14. The function of the heat exchanger 14 is described below.

[0062] A hydrogen filter 3 follows the heat exchanger 14 to filter unwanted impurities from the hydrogen gas. A flow restrictor 4 and a check valve 5 are arranged in series behind the hydrogen filter 3. The check valve has a set pressure that is below the set pressure of the boil-off valve 1 but above the pressure that prevails or is to be expected in the intended oxygen source 60, for example, in the form of the environment 60 of the storage unit 200. The function of these components is also described in more detail below.

[0063] The check valve 5 is coupled to a drive flow inlet 18a of a merging component 7, in this case in the form of a Venturi nozzle 7. The merging component 7, i.e., in this case the Venturi nozzle 7, further comprises a suction flow inlet 19, which is connected to the environment 60 of the storage unit 200 as an oxygen source via an air filter 6. In this case, oxygen from the ambient air is used to react with the hydrogen gas discharged from the liquid hydrogen tanks 50.

[0064] The concrete structural design of this merging component 7 as a Venturi nozzle 7 is shown in FIG. 2 shown and is described in detail below.

[0065] Returning to FIG. 1, the Venturi nozzle 7 is followed by a mixing chamber 8 as a merging component. This serves to improve the mixing of the gas flows merged in the merging component 7 by flow processes / momentum exchange and can optionally be equipped with corresponding mixing elements and / or swirl elements (not shown but well known per se).

[0066] Behind the mixing chamber 8, a catalyst 11 is provided between an inlet funnel 9a that enlarges the cross-section of the line and an outlet funnel 9b that reduces the cross-section of the line. This catalyst 11 is designed to oxidize the hydrogen discharged from the liquid hydrogen tank 50 with oxygen from the ambient air, forming water. Thus, ultimately, only water vapor is released into the environment of the storage unit 200. The risk of an oxyhydrogen reaction thus no longer exists.

[0067] To optimize the flow and mixing of the gas streams in the reactive area of ​​the catalyst 11, a substrate 10 can be provided. This can, as in FIG. 1 shown, be provided as a separate substrate 10 or be formed by a front non-reactively coated region of the catalyst 11. A combination of these two possibilities would also be conceivable.

[0068] In order to reduce or even avoid contamination of the catalyst 11 with condensate from the exhaust gases of the catalyst, a condensate trap 13 is connected downstream of the catalyst 11.

[0069] The aforementioned optional heat exchanger 14 is provided downstream of the catalytic converter 11, in particular downstream of the outlet funnel 9b. Since the intended oxidation of hydrogen with oxygen to water in the catalytic converter 11 is an exothermic reaction and the hydrogen gas emerging from the boil-off valves 1 is relatively cold, the heat exchanger 14 transfers heat from the exhaust gases of the catalytic converter 11 to the hydrogen gas emerging from the boil-off valves 1. This leads to a preheating of the hydrogen gas after the oxidation reactions in the catalytic converter 11 have begun, thus reducing, among other things, the formation of condensate or mist and / or ice within the converging component 7 when the hydrogen gas mixes with the ambient air.

[0070] The exhaust gases from the catalytic converter 11 are finally discharged to the environment 60 via a chimney 15, which is provided at its outlet, in particular, with a wind and / or rain protection 16. In order to optimally utilize the chimney effect for discharging the exhaust gases and / or to reduce condensate formation within the boil-off management system, the catalytic converter 11 and components of the boil-off management system 100 downstream of the catalytic converter 11 are provided with insulation 12.

[0071] In the illustrated embodiment, the components, and in particular the catalyst 11, of the boil-off management system are arranged or aligned essentially vertically. Alternatively, however, a horizontal arrangement or alignment is also possible.

[0072] In the following, with reference to FIG. 2 the concrete design of the Venturi nozzle 7 provided here as a merging component 7 is described.

[0073] In the embodiment shown, the Venturi nozzle 7 comprises a tubular main body 21 and a tubular Coanda effect component 22 at least partially inserted therein, wherein the main body 21 and the Coanda effect component 22 can be designed as a single combined Venturi nozzle 7.

[0074] The main body 21 forms a suction flow inlet 19 and a propulsion flow inlet 18a oriented substantially perpendicular thereto. A gap 18b between the main body 21 and the Coanda effect component 22 functions as a propulsion flow outlet 18b, while the Coanda effect component 22 forms an ejector flow outlet 20. Said propulsion flow outlet 18b extends at least around portions of the circumference of a substantially rectilinear fluid channel section 17 formed in the Venturi nozzle 7, from the suction flow inlet 19 to the ejector flow outlet 20. Thus, the propulsion flow outlet 18b opens laterally, in particular radially, into the substantially rectilinear fluid channel section 17.

[0075] In the following, with reference to the two Figures 1 and 2 The functionality of the illustrated boil-off management system 100 is described with respect to a single hydrogen tank 50. The same functionality applies to the second liquid hydrogen tank 50.

[0076] A heat input from the environment 60 of the liquid hydrogen tank 50, which cannot be completely avoided, leads to a continuous heating of the hydrogen in the liquid hydrogen tank 50 and thus to a continuously increasing pressure of the stored hydrogen.

[0077] This pressure increases until the set pressure of the backpressure compensated boil-off valve 1 is reached and this opens to release hydrogen gas into the boil-off line 2. This means that at the set pressure of the backpressure compensated boil-off valve 1, the first release of hydrogen from the liquid hydrogen tank into the boil-off line 2 takes place. As a result, the pressure in the liquid hydrogen tank 50 does not reach the higher set pressure of the pressure relief valves 53, so that these never open to release untreated hydrogen into the environment 60, at least when the boil-off management system 100 is functioning properly.

[0078] Due to the repeated release of hydrogen gas into the boil-off line 2, a pressure systematically builds up in the boil-off line 2 due to the defined set pressure of the check valve 5. Due to the design of the boil-off valve 1 as a backpressure-compensated pressure relief valve, this backpressure does not lead to a systematic increase in the set pressure of the boil-off valve 1.

[0079] As soon as the pressure in the boil-off line 2 reaches the response pressure of the check valve 5, the check valve 5 opens and allows a flow of hydrogen gas, limited by the flow restrictor 4, from the boil-off line 2 into the merging component 7 or into the Venturi nozzle 7. This causes a sudden opening of the boil-off valve 1, in particular into its maximum intended opening position or stroke, and thus a surge of hydrogen gas is released from the liquid hydrogen tank 50 into the boil-off line 2. As a result, more hydrogen gas is released into the boil-off line 2 through the boil-off valve 1 than would be necessary to bring the pressure in the liquid hydrogen tank 50 into line with the response pressure of the boil-off valve 1. In other words, the boil-off valve 1 undergoes a valve hysteresis.

[0080] Referring to FIG. 2The various components of the boil-off management system 100 are coordinated with one another in such a way that the flow of hydrogen gas fed into the motive flow inlet 18a of the Venturi nozzle 7 lies in a pressure and mass range that causes sufficient deflection of the flow from the motive flow outlet 18b toward the ejector flow outlet 20 along the Coanda effect component 22. In other words, the corresponding components, in particular the boil-off valve 1, the boil-off line 2, the flow restrictor 4, and the check valve 5, are coordinated with one another, for example by testing and / or simulation, in such a way that the flow of hydrogen gas from the motive flow outlet 18b follows a convexly curved inner surface of the Coanda effect component 22, at least over a certain pressure range, and is thus deflected toward the ejector flow outlet 20.Both too low and too high a pressure of the drive flow results in a premature detachment of the drive flow from the Coanda effect component 22 or in a collapse of the suction effect at the suction flow inlet 19. The same applies to a mass flow that is too low or too high.

[0081] The described redirection of the propulsion flow creates a suction at the suction flow inlet 19, through which ambient air is drawn into the Venturi nozzle 7 and discharged together with the hydrogen gas from the liquid hydrogen tank 50 at the ejector flow outlet 20. The check valve 5 only opens when the pressure and quantity of the hydrogen propulsion flow subsequently formed at the Venturi nozzle 7 results in the intake of a quantity of oxygen, so that the gas mixture discharged at the ejector flow outlet 20 is overstoichiometric with ambient air. Specifically, this means that the volume fraction of hydrogen is below 4% of the volume fraction in the resulting gas mixture. Thus, the risk of an explosive oxyhydrogen reaction within the boil-off management system 100 can be reduced or eliminated, while ensuring the most complete oxidation of the hydrogen possible in the downstream catalyst 11.

[0082] From the Venturi nozzle 7, the gas mixture formed therein is passed through the mixing chamber 8 into the inlet funnel 9a, where the cross-section of the conduit is widened. This widening leads to an expansion of the gas mixture and thus to a slowing of the flow velocity, which promotes the subsequent exothermic reaction in the catalyst 11. The gas mixture is passed via the substrate 10 into the catalyst 11 or into a reactive rear region of the catalyst 11 if a front region of the catalyst 11 is designed as a non-reactive substrate 10.The substrate acts as a guide component for the targeted distribution of the gas flow over the entire surface of the catalyst 11, as a heat shield to reduce heating of the gas mixture before entering the catalyst 11 and / or as a flame arrester to prevent the penetration of an unexpected ignition of the gas mixture in or upstream of the catalyst 11 into the areas of the boil-off management system 100 upstream of the substrate 10. Several individual substrates 10 and / or substrate areas in the catalyst 11 can also be combined with one another in order to fulfill one or more of these or other tasks.

[0083] In the catalyst 11, an exothermic reaction occurs in the form of the oxidation of the hydrogen gas in the gas mixture with free oxygen gas in the gas mixture, forming water or water vapor. In other words, in the present embodiment, the catalyst 11 converts the hydrogen-air mixture introduced into it into a water vapor-air mixture and discharges this as "exhaust gases."

[0084] These exhaust gases are fed through the condensate trap 13 into the outlet funnel 9b, where the cross-section of the line is reduced. This leads to an increase in the flow velocity of the exhaust gases (i.e., the water vapor-air mixture from the catalyst 11). In the downstream heat exchanger 14, heat is then transferred from the exhaust gases to the hydrogen gas in the boil-off line 2 to preheat it.

[0085] Finally, the exhaust gases, in the form of a no longer explosive water vapor-air mixture, are discharged via the chimney 15 into the environment 60 of the storage unit 200.

[0086] As soon as the boil-off valve 1 closes again, the pressure in the boil-off line 2 rapidly decreases until the pressure in the boil-off line 2 falls below the set pressure of the check valve 5, causing it to close again. This leads to a disruption of the drive flow for the Venturi nozzle 7 and thus to a cessation of the processes downstream of the Venturi nozzle 7.

[0087] Due to the operation described above, hydrogen gas is repeatedly released through the boil-off management system 100, converting the hydrogen gas into water or water vapor, without the need to release untreated hydrogen gas to the environment through the pressure relief valves 53.

[0088] Due to the interaction of the boil-off valve 1, designed as a backpressure-compensated relief valve, with the specially tuned check valve 5, the boil-off valve 1 undergoes a valve hysteresis each time the hydrogen gas is released. This causes a quantity of hydrogen gas to be released from the liquid hydrogen tank 50 that significantly exceeds the amount required to reach the set pressure of the boil-off valve 1. This prevents hydrogen gas from continuously "hissing" through the boil-off valve 1 once the set pressure is first reached. Rather, this excessive release of hydrogen gas ensures a rest period for the boil-off valve 1 until the set pressure of the boil-off valve 1 is reached again. This effectively reduces the wear of the boil-off valve 1 and gives the components of the boil-off valve 1 the opportunity to relax as much as possible between the release processes.

[0089] When using the environment 60 of the storage unit 200 as an oxygen source 60 with a pressure of approximately 1 bar as described above, a response pressure for the check valve of 4 bar to 8 bar, in particular of 6 bar, and a response pressure for the boil-off valve 1 of 15 bar to 25 bar, in particular of 20 bar, has proven particularly suitable.

[0090] The lateral introduction of the hydrogen gas as a propulsion stream into the Venturi nozzle 7 causes a comparatively small stream of hydrogen gas to draw in a large stream of oxygen or air. This makes it possible to use the ambient air as an oxygen source, which is particularly cost-efficient. It is not necessary to rely on the support of active devices such as heaters or fans. Furthermore, the described Venturi nozzle 7 establishes the full suction effect and thus the desired mixing ratio in the output gas mixture almost immediately upon inlet of the propulsion stream. A start-up phase and at least partial recirculation of the exhaust gases from the catalyst 11 into the gas mixture upstream of the catalyst 11 to achieve the desired operating parameters for the catalyst 11 is therefore not necessary.This leads to increased safety of the overall system, since the formation of a superstoichiometric mixture and thus non-explosive gas mixture in the boil-off management system 100 is possible essentially from the beginning when hydrogen is blown off.

[0091] A combination of the above-described design for maintaining the valve hysteresis with the above-described specific integration of a Venturi nozzle 7 into the boil-off management system is considered particularly advantageous.

[0092] A further advantage of this design is that all components operate completely passively, requiring no external control or additional power supply. In other words, the entire system is driven by automatically generated pressure and temperature differences without the need for external intervention, such as heaters or fans. This allows for a simplified overall design that reliably performs its function even without an external power supply and / or control system. List of reference symbols

[0093] 1 Boil-off valve 2 Boil-off line 3 Hydrogen filter 4 Flow restrictor 5 Check valve 6 Air filter 7 Venturi nozzle / merging component 8 Mixing chamber 9a Inlet funnel 9b Outlet funnel 10 Substrate 11 Catalyst 12 Insulation 13 Condensate trap 14 Heat exchanger 15 Chimney 16 Wind and / or rain shield 17 Straight fluid channel section 18a Propellant inlet 18b Propellant outlet / gap 19 Suction inlet 20 Ejector outlet 21 Main body 22 Coanda effect component 50 Hydrogen tank 51 Inner vessel 52 Outer vessel 53 Pressure relief valve 60 Oxygen source / ambient 100 Boil-off management system 200 Storage unit

Claims

1. A boil-off management system (100) for a liquid hydrogen tank (50), the boil-off management system (100) comprising: a boil-off valve (1) configured to connect the boil-off management system (100) to the liquid hydrogen tank (50); and a catalyst (11) configured to oxidize hydrogen from the liquid hydrogen tank (50) to water using oxygen from a separate oxygen source (60); the catalyst (11) being connectable to the liquid hydrogen tank (50) via the boil-off valve (1) and to the oxygen source (60) in parallel with the boil-off valve (1);wherein a Venturi nozzle (7) is provided between the boil-off valve (1) and the catalyst (11), wherein the Venturi nozzle (7) comprises a drive flow inlet (18a) which is connected to the boil-off valve (1), a suction flow inlet (19) which is connectable to the oxygen source (60), and an ejector flow outlet (20) which is connected to the catalyst (11); characterized in that the drive flow inlet (18a) of the Venturi nozzle (7) is connected to a drive flow outlet (18b) which opens laterally, in particular radially, into a substantially rectilinear fluid channel section (17) which connects the suction flow inlet (19) to the ejector flow outlet (20).

2. Boil-off management system (100) according to claim 1, characterized in thata) the drive flow outlet (18b) extends at least along a portion of the circumference of the rectilinear fluid channel section (17), wherein the drive flow outlet (18b) extends in particular along several portions or along the entire circumference of the rectilinear fluid channel section (17); and / or b) the Venturi nozzle (7) comprises a, in particular tubular, Coanda effect component (22) which is designed to redirect a substantially radial flow of hydrogen gas from the drive flow outlet (18b) towards the ejector flow outlet (20) in order to suck oxygen into the Venturi nozzle (7) via the suction flow connection (19) and to discharge it together with the hydrogen gas as a gas mixture through the ejector flow outlet (20).

3. Boil-off management system (100) according to claim 1 or 2, characterized in thata flow restrictor (4) and a check valve (5) are provided between the boil-off valve (1) and the Venturi nozzle (7), wherein the Venturi nozzle (7), the flow restrictor (4) and the check valve (5) are coordinated with one another in such a way that the check valve (5) only opens when the pressure and the quantity of the hydrogen gas subsequently flowing into the drive stream inlet (18a) causes the Venturi nozzle (7) to operate, resulting in the output of a stream of a superstoichiometric gas mixture.

4. A boil-off management system (100) for a liquid hydrogen tank (50), the boil-off management system (100) comprising: a boil-off valve (1) configured to connect the boil-off management system (100) to the liquid hydrogen tank (50); and a catalyst (11) configured to oxidize hydrogen from the liquid hydrogen tank (50) to water using oxygen from a separate oxygen source (60); the catalyst (11) being connectable to the liquid hydrogen tank (50) via the boil-off valve (1) and to the oxygen source (60) in parallel with the boil-off valve (1); characterized in that the boil-off valve (1) is designed as a backpressure-compensated pressure relief valve and a check valve (5) with a response pressure is provided between the boil-off valve (1) and the catalyst (11), which is lower than the response pressure of the boil-off valve (1) but higher than the pressure of the oxygen source (60) to be used.

5. Boil-off management system (100) according to claim 4, characterized in that a Venturi nozzle (7) is provided between the boil-off valve (1) and the catalyst (11); wherein the Venturi nozzle (7) comprises in particular a drive flow inlet (18a) which is connected to the boil-off valve (1), a suction flow inlet (19) which is connectable to the oxygen source (60), and an ejector flow outlet (20) which is connected to the catalyst (11), wherein the drive flow inlet (18a) of the Venturi nozzle (7) is connected to a drive flow outlet (18b) which opens laterally, in particular radially, into a substantially rectilinear fluid channel section (17) which connects the suction flow inlet (19) to the ejector flow outlet (20).

6. Boil-off management system (100) according to claim 5, characterized in thatthe Venturi nozzle (7) comprises a, in particular tubular, Coanda effect component (22) which is designed to divert a substantially radial flow of hydrogen gas from the drive flow outlet (18b) towards the ejector flow outlet (20) in order to suck oxygen into the Venturi nozzle (7) via the suction flow connection (19) and to discharge it together with the hydrogen gas as a gas mixture through the ejector flow outlet (20); wherein a flow restrictor (4) is preferably provided between the boil-off valve (1) and the Venturi nozzle (7), and the Venturi nozzle (7), the flow restrictor (4) and the check valve (5) are coordinated with one another in such a way that the check valve (5) only opens when the pressure and the quantity of the hydrogen gas subsequently flowing into the drive stream inlet (18a) causes the Venturi nozzle (7) to operate, resulting in the output of a stream of a superstoichiometric gas mixture.

7. Boil-off management system (100) according to one of claims 3 to 6, characterized in that the response pressure of the check valve (5) is between 4 bar and 8 bar, in particular 6 bar and / or the response pressure of the boil-off valve (1) is between 15 bar and 25 bar, in particular 20 bar.

8. Boil-off management system (100) according to one of the preceding claims, characterized in that between the boil-off valve (1) and the catalyst (11), in particular between the boil-off valve (1) and further components which are connected upstream of the catalyst (11), a heat exchanger (14) is provided which is designed to transfer heat from exhaust gases from the catalyst (11) to the hydrogen gas from the boil-off valve (1).

9. Boil-off management system (100) according to one of the preceding claims, characterized in thatthe boil-off management system (100) comprises a combining component (7) in which the hydrogen from the boil-off valve (1) is combined with the oxygen from the oxygen source (60), wherein the combining component (7) is in particular a Venturi nozzle (7).

10. Boil-off management system (100) according to claim 9, characterized in thata) a hydrogen filter (3) is provided between the boil-off valve (1) and the combining component (7); and / or b) a mixing chamber (8), in particular with mixing elements contained therein, is provided between the combining component (7) and the catalyst (11); and / or c) a substrate (10) permeable to the gas mixture is provided between the combining component (7) and the catalyst (11), in particular behind a provided mixing chamber (8); and / or d) the catalyst (11) is reactively coated only in a rear region and a front region of the catalyst is designed as a substrate (10) permeable to the gas mixture; wherein said substrate (10) is preferably designed as a guide component, heat shield and / or flashback arrester.

11. Boil-off management system (100) according to one of the preceding claims, characterized in thata) an inlet funnel (9a) is provided upstream of the catalyst (11), which enlarges a cross-section of the fluid channel upstream of the catalyst (11); and / or b) an outlet funnel (9b) is provided downstream of the catalyst (11), which reduces a cross-section of the fluid channel downstream of the catalyst (11); and / or c) a condensate trap (13) is provided downstream of the catalyst (11).

12. Boil-off management system (100) according to one of the preceding claims, characterized in that the boil-off management system (100) is designed to use the environment of the boil-off management system (100) as an oxygen source (60), wherein the boil-off management system (100) in particular comprises an air filter (6) for filtering ambient air before it is combined with the hydrogen gas from the liquid hydrogen tank (50).

13. Boil-off management system (100) according to one of the preceding claims, characterized in thata) the boil-off management system (100) is designed such that it operates completely passively, i.e. without the need for external control and / or without the need for an additional energy supply; and / or b) the boil-off valve (1) is a valve constructed with a metal bellows, in particular made of stainless steel.

14. Boil-off management system (100) according to one of the preceding claims, characterized in that a) the catalyst (11) is oriented substantially vertically; and / or b) a chimney (15) is arranged downstream of the boil-off management system (1) and / or c) the catalyst (11) and / or components arranged downstream of the catalyst (11) are surrounded by insulation (12).

15. A storage unit (200) for liquid hydrogen (50), comprising: at least one, in particular two, liquid hydrogen tank(s) (50); and a boil-off management system (100) according to one of the preceding claims; wherein each provided liquid hydrogen tank (50) is connected to the other components of the boil-off management system (100) via its own boil-off valve (1) but via a common boil-off line (2); wherein preferably each liquid hydrogen tank (50) is provided with at least one, preferably two, pressure relief valve(s) (53), which has / have a higher response pressure than the boil-off valve (1) assigned to the respective liquid hydrogen tank (50).

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