DE102023117842A1 - boil-off management system and storage unit - Google Patents

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 to 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), which is less than a response pressure of the boil-off valve (1) but greater than the pressure of the provided oxygen source (60). In addition or as an alternative, 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) to the ejector flow outlet (20) of the Venturi nozzle (7).

Description

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.

In addition to a legally required emergency pressure relief device using simple overpressure safety valves, vehicles or stationary applications with liquid hydrogen tanks can 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 increases, for example, due to heat input from the environment, before the emergency pressure relief device is activated, or to reduce it during a corresponding boil-off event.

The main 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 into the environment untreated. Specifically, the boil-off management system renders the vented hydrogen harmless before it is released in order to counteract a possible risk of explosion due to the formation of an explosive air-hydrogen mixture (oxyhydrogen gas).

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

Conventional boil-off management systems are either actively or passively operated. Actively operated boil-off management systems require an external power supply in order to be able to actively operate different components of the boil-off management system. Passively operated 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 rendered harmless.

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

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

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 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 with oxygen from a separate oxygen source to water. The catalyst can be connected to the liquid hydrogen tank via the boil-off valve and to the oxygen source in parallel to the boil-off valve. A venturi nozzle is provided between the boil-off valve and the catalyst. The venturi nozzle comprises a drive flow inlet which is connected to the boil-off valve, a suction flow inlet which is connectable to the oxygen source, and an ejector flow outlet which is 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.

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 causes an essentially straight-line flow of oxygen from the suction flow inlet to the ejector flow outlet. This special flow guidance enables the addition of oxygen to a superstoichiometric gas mixture and thus the prerequisite for avoiding the risk of explosion, since the hydrogen concentration in the resulting gas mixture is below the lower explosion limit of approx. 4 vol.% and thus no explosive detonating gas is formed, insofar as sufficient mixing of the gas components to form a homogeneous mixture is ensured.

Preferably, the drive flow outlet extends at least along a portion of the circumference of the rectilinear fluid channel portion. In particular, the drive flow outlet extends along several portions or along the entire circumference of the rectilinear fluid channel portion.

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

Preferably, the Venturi nozzle comprises a, in particular tubular, Coanda effect component, which is designed to form a substantially to redirect the 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.

The Coanda effect component mentioned has the advantage that the diverted flow of hydrogen gas from the liquid hydrogen tank creates a suction effect, which causes a particularly large amount of oxygen to be sucked into the Venturi nozzle from the oxygen source. The Coanda effect also ensures that the resulting gas mixture is propelled more intensively into the catalyst to be converted there. The suction effect allows a quantity of oxygen to be sucked in, which results in a superstoichiometric gas mixture. A superstoichiometric gas mixture is understood to be a gas mixture that is no longer explosive. In particular, so much oxygen is sucked 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 approx. 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 outlet which has a hydrogen concentration below the lower explosion limit.

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 with one another in such a way that the check valve only opens when the pressure and the quantity of hydrogen subsequently flowing into the motive flow inlet cause the venturi nozzle to operate, resulting in the output of a flow of superstoichiometric gas mixture.

In other words, the flow limiter and the check valve are designed in such a way 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 response pressure of the check valve is at least at the level of the pressure that the driving flow must have in order to generate the desired Coanda effect. The flow limiter limits the amount of driving flow in such a way that the resulting flow of hydrogen gas does not detach prematurely from a guide surface of the Coanda effect component.

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 can be connected to the liquid hydrogen tank via the boil-off valve and to the oxygen source in parallel to the boil-off valve. The boil-off valve is designed as a backpressure-compensated pressure relief valve. Between the boil-off valve and the catalyst, a check valve is provided with a response pressure which is lower than the response pressure of the boil-off valve but higher than the pressure of the oxygen source to be used.

By designing the boil-off valve as a backpressure-compensated pressure relief valve, the response 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 & reset point) via the check valve with the response pressure specified here. This means that it can open comparatively quickly and completely, like a full-stroke safety valve, while undergoing a valve hysteresis. In the event of a boil-off event, i.e. when the check valve opens, a flow of hydrogen gas with a specified minimum pressure and a specified minimum mass flow can be generated in order to immediately ensure optimal function of the components of the boil-off management system downstream of the check valve. In particular, this represents a safe and complete neutralization of the released free hydrogen. Furthermore, the valve hysteresis obtained enables the pressure in the liquid hydrogen tank to be reduced not only to the response pressure of the boil-off valve, but also below the response pressure of the boil-off valve. This prevents the boil-off valve from opening, at least for the period until the pressure in the liquid hydrogen tank reaches the response pressure of the boil-off valve again, which leads to reduced wear on the boil-off valve and the components of the boil-off management system as a whole.

Preferably, a Venturi nozzle is provided between the boil-off valve and the catalyst. The Venturi nozzle comprises in particular a drive flow inlet which is connected to the boil-off valve, a suction flow inlet which can be connected to the oxygen source, and an ejector flow outlet which is 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 straight fluid channel section which connects the suction flow inlet to the ejector flow outlet.

The previously described valve hysteresis enables the operation of the provided Venturi nozzle, which always produces a lean gas mixture with a superstoichiometric oxygen-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 causes an essentially straight-line flow of oxygen. This special flow guidance enables oxygen to be added to a superstoichiometric gas mixture, thus avoiding the risk of explosion.

Preferably, the Venturi nozzle comprises a, in particular tubular, Coanda effect component which is designed to divert 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.

As already described above, the Coanda effect component serves to generate sufficient suction for the oxygen to be added to the hydrogen gas from the liquid hydrogen tank.

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 with one another in such a way that the check valve only opens when the pressure and the quantity of hydrogen gas subsequently flowing into the motive flow inlet causes the venturi nozzle to operate, resulting in the output of a flow of a superstoichiometric gas mixture.

The flow limiter limits the amount of drive flow when the check valve is opened in such a way that the resulting flow of hydrogen gas does not detach prematurely from a guide surface of the Coanda effect component. This makes it possible to ensure the required suction effect.

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.

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.

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 connected 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.

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 undesirable ice formation within components of the boil-off management system which are located upstream of the catalyst.

Preferably, the boil-off management system comprises a combining component in which the hydrogen from the boil-off valve is combined with the oxygen from the oxygen source. In particular, the combining component is a Venturi nozzle or the one described above.

Such a merging component enables efficient merging of the 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 merging component.

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

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

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

Such a mixing chamber enables an optimized mixing of the hydrogen gas with the oxygen and thus the formation of a gas mixture that is as homogeneous as possible for the reaction in the catalyst. The mixing elements used are in particular other elements which impede the flow of the gas mixture and generate a swirl and turbulent flows in the gas mixture. Various designs for such mixing elements are well known to the person skilled in the art and include, for example, baffle plates, (mono) swirl mixers and/or other types of projections along an inner wall of the mixing chamber.

Preferably, a substrate permeable to the gas mixture is provided between the combining component and the catalyst, in particular behind a provided mixing chamber. In addition or as an alternative to this, 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.

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 substrate separate from the catalyst enables particularly flexible selection and adaptation of the substrate. The combined design of the catalyst and the substrate enables particularly compact overall designs with fewer individual parts.

Preferably, the substrate is designed as a guide component, heat shield and/or flashback arrester.

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 distributing it evenly. The design as a heat shield prevents excessive heating of the gas mixture before it enters the catalyst and a resulting reduced efficiency of the exothermic reaction in the catalyst and/or a back pressure which reduces the flow of gas mixture into the catalyst. The design as a flashback arrester serves to prevent an unexpected ignition of the gas mixture in the catalyst from spreading into areas of the boil-off management system upstream.

Preferably, an inlet funnel is provided in front of the catalyst, which increases a cross-section of the fluid channel in front of the catalyst. Alternatively or additionally, an outlet funnel is provided behind the catalyst, which reduces a cross-section of the fluid channel behind the catalyst.

The inlet funnel reduces the flow speed of the gas mixture due to the increased flow cross-section. This gives more time for the components of the gas mixture to mix homogeneously on the way to the catalyst. The outlet funnel increases the flow speed of the gas mixture due to the reduced flow cross-section. This means that the exhaust gases are guided away from the catalyst particularly efficiently.

Preferably, a condensate trap is provided behind the catalyst.

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.

Preferably, the boil-off management system is 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.

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 incoming air stream.

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.

In other words, the boil-off management system does not require any energy supply beyond the components described here and is self-powered. Each of the components provided operates completely autonomously, without the need for manual or automated control. Consequently, the boil-off management system 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 the specific combination of the previously described components of the boil-off management system.

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

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

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

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

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

This makes it possible to reduce 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.

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 according to the above description. Each liquid hydrogen tank provided is connected to the other components of the boil-off management system via its own boil-off valve but via a common boil-off line.

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

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.

These pressure relief valves act as an emergency pressure relief device to release untreated hydrogen from the corresponding hydrogen tank into the environment in the event of a dangerous overpressure in the liquid hydrogen tank in order to reduce the pressure. This prevents the respective liquid hydrogen tank from bursting due to overpressure in the corresponding liquid hydrogen tank. A single pressure relief valve is sufficient for this. However, at least one additional redundant pressure relief valve is provided for additional safety.

• 1 eine schematische Darstellung des Prozesses bestehend aus einer beispielhaften Lagereinheit mit einem Boil-off-Managementsystem gemäß der vorliegenden Erfindung; und
• 2 ein Beispiel für eine Venturi-Düse, welche in dem in 1 gezeigten Boil-off-Managementsystem einsetzbar ist.

The invention is described below by way of example with reference to the accompanying drawings.

• 1 a schematic representation of the process consisting of an exemplary storage unit with a boil-off management system according to the present invention; and
• 2 an example of a Venturi nozzle, which is used in the 1 can be used with the boil-off management system shown.

Accordingly 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 1 shown two separate liquid hydrogen tanks 50, each of which is coupled to its own boil-off valve 1 of the boil-off management system 100.

The liquid hydrogen tanks 50 shown here each comprise an inner container 51 for the hydrogen and an outer container 52 which surrounds 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 in addition to this, insulating materials could also be provided between the two containers 51 and 52, at least in some areas. 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. In order to ensure an undisturbed and safe release of the 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.

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

Each liquid hydrogen tank 50 is coupled to a separate boil-off valve 1 of the boil-off management system 100 according to the invention. 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 which is lower than the response pressure of the provided pressure relief valves 53. The boil-off valves 1 therefore respond to the overpressure pressure valves 53 and discharge gaseous hydrogen from the liquid hydrogen tanks 50 before the maximum permissible operating pressure in the liquid hydrogen tanks 50 is reached.

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

The heat exchanger 14 is followed by a hydrogen filter 3 to filter out unwanted impurities from the hydrogen gas. A flow restrictor 4 and a check valve 5 are provided in series behind the hydrogen filter 3. The check valve has a response pressure which is below the response pressure of the boil-off valve 1 but above the pressure which 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.

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, also has a suction flow inlet 19, which is connected here via an air filter 6 to the environment 60 of the storage unit 200 as an oxygen source. In this case, oxygen from the ambient air is used to react with the hydrogen gas discharged from the liquid hydrogen tanks 50.

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

Coming back to 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).

Behind the mixing chamber 8, a catalyst 11 is provided between an inlet funnel 9a that increases 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 to form water. In this way, only water vapor is ultimately released into the environment of the storage unit 200. The risk of an oxyhydrogen reaction therefore no longer exists.

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 1 shown, be provided as a separate substrate 10 or be formed by a front non-reactively coated area of the catalyst 11. A combination of these two possibilities would also be conceivable.

In order to reduce or even prevent 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.

The aforementioned optional heat exchanger 14 is provided behind the catalyst 11, in particular behind the outlet funnel 9b. Since the intended oxidation of hydrogen with oxygen to water in the catalyst 11 is an exothermic reaction and the hydrogen gas coming from the boil-off valves 1 is relatively cold, the heat exchanger 14 transfers heat from the exhaust gases of the catalyst 11 to the hydrogen gas from the boil-off valves 1. After the oxidation reactions in the catalyst 11 have started, this leads to a preheating of the hydrogen gas and thus reduces, among other things, the formation of condensate or mist and/or ice within the combination component 7 when the hydrogen gas is mixed with the ambient air.

The exhaust gases from the catalyst 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 be able to optimally use the chimney effect to discharge the exhaust gases and/or to reduce condensate formation within the boil-off management system, the catalyst 11 and components of the boil-off management system 100 downstream of the catalyst 11 are provided with insulation 12.

In the embodiment shown, 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.

In the following, with reference to 2 the concrete design of the proposed The Venturi nozzle 7 is described as the merging component 7.

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.

The main body 21 forms a suction flow inlet 19 and a driving flow inlet 18a aligned substantially perpendicularly thereto. A gap 18b between the main body 21 and the Coanda effect component 22 functions as a driving flow outlet 18b, while the Coanda effect component 22 forms an ejector flow outlet 20. The said driving flow outlet 18b extends at least around sections 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. The driving flow outlet 18b thus opens laterally, in particular radially, into the substantially rectilinear fluid channel section 17.

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

An unavoidable heat input from the environment 60 of the liquid hydrogen tank 50 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.

This pressure increases until the response pressure of the back pressure 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 response pressure of the back pressure compensated boil-off valve 1, hydrogen is first released from the liquid hydrogen tank into the boil-off line 2. As a result, the pressure in the liquid hydrogen tank 50 does not reach the higher response pressure of the pressure relief valves 53, which means that they never open to release untreated hydrogen into the environment 60, at least when the boil-off management system 100 is functioning properly.

By repeatedly releasing hydrogen gas into the boil-off line 2, a pressure systematically builds up in the boil-off line 2 due to the defined response 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 response pressure of the boil-off valve 1.

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 enables a flow of hydrogen gas, limited by the flow limiter 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 to 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.

Referring to 2 the different 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 drive flow inlet 18a of the Venturi nozzle 7 is in a pressure and mass range which causes sufficient deflection of the flow from the drive flow outlet 18b in the direction of 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 limiter 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 drive 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 towards 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.

The described deflection of the propulsion flow creates a suction at the suction flow inlet 19, through which ambient air is sucked 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 the amount of the propulsion flow of hydrogen subsequently formed at the Venturi nozzle 7 are sufficient for suction. an amount of oxygen, so that the gas mixture output at the ejector flow outlet 20 is overstoichiometric with ambient air. In concrete terms, this means that the volume fraction of hydrogen is below 4% of the volume fraction in the resulting gas mixture. The risk of an explosive oxyhydrogen reaction within the boil-off management system 100 can thus be reduced or eliminated, while ensuring that the hydrogen is oxidized as completely as possible in the downstream catalyst 11.

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 line is widened. This widening leads to an expansion of the gas mixture and thus to a slowing of the flow rate, 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 flashback arrester to prevent an unexpected ignition of the gas mixture in or in front of the catalyst 11 from breaking through into the areas of the boil-off management system 100 in front 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.

An exothermic reaction takes place in the catalyst 11 in the form of the oxidation of the hydrogen gas in the gas mixture with free oxygen gas in the gas mixture to form 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 emits this as "exhaust gases".

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

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.

As soon as the boil-off valve 1 closes again, the pressure in the boil-off line 2 decreases rapidly until the pressure in the boil-off line 2 falls below the response pressure of the check valve 5, causing it to close again. This leads to a break in the driving flow for the Venturi nozzle 7 and thus to a cessation of the processes behind the Venturi nozzle 7.

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.

Due to the interaction of the boil-off valve 1, which is designed as a back-pressure compensated pressure relief valve, with the specially coordinated check valve 5, the boil-off valve 1 undergoes a valve hysteresis each time the hydrogen gas is released, through which a quantity of hydrogen gas is released from the liquid hydrogen tank 50 which significantly exceeds the quantity required to reach the response pressure of the boil-off valve 1. This prevents hydrogen gas from constantly "hissing out" through the boil-off valve 1 once the response pressure is reached for the first time. Rather, this excessive release of hydrogen gas provides a rest period for the boil-off valve 1 until the response 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.

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 6 bar, and a response pressure for the boil-off valve 1 of 15 bar to 25 bar, in particular 20 bar, has proven to be particularly suitable.

The lateral introduction of the hydrogen gas as a driving stream into the Venturi nozzle 7 means that a comparatively small stream of hydrogen gas sucks 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 the support of active devices such as heaters or blowers. Furthermore, the full suction effect and thus the desired mixing ratio in the gas mixture output is achieved via the described Venturi nozzle 7 almost immediately upon admission of the drive stream. A start-up phase and at least partial return 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 outset when hydrogen is blown off.

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 to be particularly advantageous.

A further advantage of the present design is that all components work completely passively, meaning they do not require any 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 interference, for example from heaters or fans. This allows for a simplified overall structure that reliably performs its task even without an external power supply and/or control.

list of reference symbols

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 protection

17

straight fluid channel section

18a

drive current inlet

18b

drive current outlet/gap

19

suction flow inlet

20

ejector flow outlet

21

main body

22

Coanda effect component

50

hydrogen tank

51

inner container

52

outer container

53

pressure relief valve

60

oxygen source/environment

100

boil-off management system

200

storage unit

Claims (24)

Boil-off management system (100) for a liquid hydrogen tank (50), the boil-off management system (100) comprising: a boil-off valve (1) which is designed to connect the boil-off management system (100) to the liquid hydrogen tank (50); and a catalyst (11) which is designed to oxidize hydrogen from the liquid hydrogen tank (50) with oxygen from a separate oxygen source (60) to water; the catalyst (11) is connectable to the liquid hydrogen tank (50) via the boil-off valve (1) and to the oxygen source (60) in parallel to 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 can be connected 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). Boil-off management system (100) according to claim 1 , characterized in that the drive current outlet (18b) extends at least along a portion of the circumference of the rectilinear fluid channel section (17), wherein the drive current outlet (18b) extends in particular along several sections or along the entire circumference of the rectilinear fluid channel section (17). Boil-off management system (100) according to claim 1 or 2 , characterized in that the 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 output it together with the hydrogen gas as a gas mixture through the ejector flow outlet (20). Boil-off management system (100) according to one of the preceding claims, characterized in that a flow limiter (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 limiter (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 flow inlet (18a) causes operation of the Venturi nozzle (7), which results in the output of a flow of a superstoichiometric gas mixture. Boil-off management system (100) for a liquid hydrogen tank (50), the boil-off management system (100) comprising: a boil-off valve (1) which is designed to connect the boil-off management system (100) to the liquid hydrogen tank (50); and a catalyst (11) which is designed to oxidize hydrogen from the liquid hydrogen tank (50) with oxygen from a separate oxygen source (60) to water; the catalyst (11) is connectable to the liquid hydrogen tank (50) via the boil-off valve (1) and to the oxygen source (60) in parallel to 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 smaller than the response pressure of the boil-off valve (1) but greater than the pressure of the oxygen source (60) to be used. Boil-off management system (100) according to claim 5 , 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 can be connected 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). Boil-off management system (100) according to claim 6 , characterized in that the 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 output it together with the hydrogen gas as a gas mixture through the ejector flow outlet (20). Boil-off management system (100) according to claim 7 , characterized in that a flow limiter (4) is provided between the boil-off valve (1) and the Venturi nozzle (7), wherein the Venturi nozzle (7), the flow limiter (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 flow inlet (18a) causes operation of the Venturi nozzle (7), which results in the output of a flow of a superstoichiometric gas mixture. Boil-off management system (100) according to claim 4 or one of the Claims 5 until 8 , 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. 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 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). Boil-off management system (100) according to one of the preceding claims, characterized in that the boil-off management system (100) comprises a merging component (7) in which the hydrogen from the boil-off valve (1) is brought together with the oxygen from the oxygen source (60), wherein the merging component (7) is in particular a or the Venturi nozzle (7). Boil-off management system (100) according to claim 11 , characterized in that a hydrogen filter (3) is provided between the boil-off valve (1) and the merging component (7). Boil-off management system (100) according to claim 11 or 12 , characterized in that a mixing chamber (8), in particular with mixing elements contained therein, is provided between the combining component (7) and the catalyst (11). Boil-off management system (100) according to one of the Claims 11 until 13 , characterized in that 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 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. Boil-off management system (100) according to claim 14 , characterized in that the substrate (10) is designed as a guide component, heat shield and/or flashback arrester. Boil-off management system (100) according to one of the preceding claims, characterized in that an inlet funnel (9a) is provided in front of the catalyst (11), which increases a cross-section of the fluid channel in front of the catalyst (11); and/or an outlet funnel (9b) is provided behind the catalyst (11), which reduces a cross-section of the fluid channel behind the catalyst (11). Boil-off management system (100) according to one of the preceding claims, characterized in that a condensate trap (13) is provided behind the catalyst (11). 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). Boil-off management system (100) according to one of the preceding claims, characterized in that 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. Boil-off management system (100) according to one of the preceding claims, characterized in that the boil-off valve (1) is a valve designed with a metal bellows, in particular made of stainless steel. Boil-off management system (100) according to one of the preceding claims, characterized in that the catalyst (11) is aligned substantially vertically and/or a chimney (15) is arranged downstream of the boil-off management system (1). Boil-off management system (100) according to one of the preceding claims, wherein the catalyst (11) and/or components downstream of the catalyst (11) are surrounded by insulation (12). 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 liquid hydrogen tank (50) provided 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). Storage unit (200) after claim 23 , wherein each liquid hydrogen tank (50) is provided with at least one, preferably two, pressure relief valve(s) (53) which have a higher response pressure than the respective liquid hydrogen tank (50) associated boil-off valve (1).

Images