METHOD FOR OPERATING A CRYOPERATING TANK

Description

[0001] A method for operating a cryogenic pressure tank, in particular a CcH2 CRYOGAS tank, a control unit for operating a cryogenic pressure tank, a hydrogen storage system, and a motor vehicle are provided. The disclosure thus relates in particular to the field of cryogenic pressure tanks for hydrogen for use in a motor vehicle.

[0002] Methods and cryogenic pressure tanks for storing cryogenically compressed hydrogen (CcH 2 ) are known in the prior art, and are designed for use in light motor vehicles, such as passenger cars. Although the functionality of this technology was demonstrated by BMW in a prototype of the Hydrogen 7 model, it has not yet been commercially applied. Individual cryogenic pressure tanks are used, which can store a quantity of hydrogen of approximately 7 kg. Such cryogenic pressure tanks and methods for their operation are described, for example, in WO 2009 / 071208 A1, WO 2013 / 143773 A1, WO 2013 / 143774 A1, and WO 2022 / 150474 A1. One challenge when using cryogenic pressure tanks, particularly in light motor vehicles, such as passenger cars, is the often long downtimes such vehicles face, which can amount to several hours, several days, or even several weeks.During such downtimes, heat input into the stored hydrogen leads to a steady increase in pressure. To avoid exceeding the permissible maximum pressure of the cryogenic pressure tank, a controlled release of a portion of the stored hydrogen is the result, which can be accompanied by other problems.

[0003] In order to achieve the largest possible buffer until the maximum permissible pressure of the hydrogen is reached, even during long downtimes, the hydrogen is traditionally withdrawn from cryogenic pressure tanks in normal operation in such a way that the pressure is reduced as quickly as possible by withdrawing hydrogen from a (nearly) full cryogenic pressure tank in order to achieve the greatest possible distance from the maximum permissible pressure of the cryogenic pressure tank and in this way to be able to complete long downtimes without reaching the maximum permissible operating pressure.However, the rapid reduction in pressure during the withdrawal of hydrogen from a (nearly) full cryogenic pressure tank can lead to the thermodynamic state of the hydrogen stored in the cryogenic pressure tank approaching or even reaching the two-phase boundary, beyond which at least a portion of the stored hydrogen transitions into the liquid phase and is therefore initially no longer available as gaseous, cryogenically compressed hydrogen. This can make the withdrawal of hydrogen difficult due to the insufficient tank pressure, as well as the determination of the remaining amount (storage capacity) in the container due to the insufficiently accurate temperature measurement near the two-phase boundary. In the two-phase region, the coupling of temperature and pressure without additional sensors in the tank can even make it impossible.Separation of the phases of the hydrogen stored in the cryogenic pressure tank can thus make it impossible to determine the remaining tank contents solely based on temperature and pressure. Furthermore, as the tank becomes increasingly empty, heat supply can become significantly more difficult, so that, in some cases, continuing the journey may no longer be possible due to insufficient tank pressure, even if there is sufficient remaining hydrogen in the cryogenic pressure tank.

[0004] In addition to the use of stored hydrogen in a cryogenic pressure tank to supply a consumer with energy, WO 2013 / 143773 A1 describes with reference to Figure 4 also introducing waste heat from the consumer into the cryogenic pressure tank in order to cool the consumer if necessary.

[0005] Against the background of this prior art, the object of the present disclosure is to provide an improved method for operating a cryogenic pressure tank, which is suitable for expanding the prior art. A specific embodiment of the disclosure can solve the problem of reliably reducing the risk of liquefaction of hydrogen in the cryogenic pressure tank (CcH2 CRYOGAS tank), optionally improving the determination of the hydrogen capacity in the tank through simple temperature and pressure measurements, and optionally ensuring the provision of sufficient tank pressure even when the tank is emptying.

[0006] The object is achieved by a method for operating a cryogenic pressure tank, a control unit for operating a cryogenic pressure tank, a hydrogen storage system, and a motor vehicle having the features of the respective independent claims. Optional embodiments are specified in the subclaims and in the description.

[0007] In a first aspect, a method is provided for operating a cryogenic pressure tank in which cryogenic hydrogen is stored at a supercritical initial pressure and an initial density, for supplying a consumer with hydrogen withdrawn from the cryogenic pressure tank. The method comprises planning a desired pressure profile over a process for completely withdrawing the hydrogen stored in the cryogenic pressure tank at the initial pressure and the initial density to a predetermined minimum density at a predetermined minimum pressure of the hydrogen in the empty state of the cryogenic pressure tank, such that a pressure decrease of the hydrogen in the cryogenic pressure tank to the minimum pressure extends over the entire process for complete withdrawal.Furthermore, the method comprises controlling a heat supply to the cryogenic pressure tank during at least 70% of the complete removal process such that the pressure profile of the hydrogen in the cryogenic pressure tank does not deviate by more than 10% from the desired pressure profile.

[0008] In a further aspect, a control unit is provided for operating a cryogenic pressure tank for storing cryogenic hydrogen at a supercritical pressure for supplying a consumer with hydrogen taken from the cryogenic pressure tank, wherein the control unit is configured to carry out a method according to the disclosure.

[0009] In another aspect, a hydrogen storage system for storing cryogenic hydrogen to supply a consumer with hydrogen is provided. The hydrogen storage system comprises at least one cryogenic pressure tank configured to store hydrogen at a supercritical initial pressure and with an initial density. Furthermore, the hydrogen storage system comprises a heat supply element configured to supply heat to the hydrogen stored in the cryogenic pressure tank.The hydrogen storage system also comprises a control unit configured to perform the following steps: (i) planning a desired pressure profile over a process for complete removal of the hydrogen stored in the cryogenic pressure tank at the initial pressure and the initial density to a predetermined minimum density at a predetermined minimum pressure of the hydrogen in the emptied state of the cryogenic pressure tank, such that a decrease in the pressure of the hydrogen in the cryogenic pressure tank to the minimum pressure extends over the entire process for complete removal. (ii) regulating a heat supply to the cryogenic pressure tank by means of the heat supply element during at least 70% of the process for complete removal, such that the pressure profile of the hydrogen in the cryogenic pressure tank deviates from the desired pressure profile by no more than 10%.

[0010] In a further aspect, a motor vehicle is provided. The motor vehicle comprises an internal combustion engine, such as a hydrogen combustion engine and / or one or more fuel cells, as well as a hydrogen storage system according to the disclosure, which is designed to store cryogenic hydrogen and supply the internal combustion engine or the hydrogen combustion engine and / or the fuel cell with the cryogenic hydrogen. A hydrogen combustion engine can be configured, for example, as a turbine or as a reciprocating piston engine.

[0011] A cryogenic pressure tank is a tank designed to store cryogenic or cryogenically compressed hydrogen at a supercritical pressure, allowing the hydrogen to be withdrawn from the tank in a controlled manner to supply one or more consumers. Further features that a cryogenic pressure tank may have are described, for example, in WO 2013 / 143773 A1.

[0012] A cryogenic pressure tank can, in particular, be a tank that is suitable and / or designed for storing cryogenically compressed gaseous hydrogen under high pressure. A cryogenic pressure tank can also be referred to as a CcH2 CRYOGAS tank.

[0013] The initial density and the initial pressure are those values ​​of the density and the pressure of the hydrogen which the stored hydrogen has in its current state, in particular when filled. The predetermined minimum pressure can be a measure of the pressure of the hydrogen which the withdrawn hydrogen must have in order to be able to supply it to one or more consumers. To supply a fuel cell with hydrogen, a predetermined minimum pressure in a range from 5 bar to 15 bar may optionally be required. To supply an internal combustion engine, such as a hydrogen combustion engine, a predetermined minimum pressure in a range from 8 bar to 50 bar may optionally be required.For example, at least one fuel cell and / or at least one internal combustion engine can be connected as consumers, which require a supply of hydrogen at a system-specific minimum pressure for correct operation. This can represent the predetermined minimum pressure or influence it. If a pressure drop is to be expected between the hydrogen outlet from the cryogenic pressure tank and the one or more consumers, the predetermined minimum pressure for the hydrogen stored in the cryogenic pressure tank can depend on the system-specific minimum pressure of the consumer(s) and on the expected pressure drop. If the hydrogen stored in the cryogenic pressure tank falls below the predetermined minimum pressure, this can therefore result in the withdrawn hydrogen not being able to be consumed by the consumer(s) or not being able to be consumed completely.This may result in the consumer no longer being able to operate properly and / or being damaged, as described by way of example in the following publication.

[0014] CM Rangel et al.: "Fuel Starvation: Irreversible Degradation Mechanisms in PEM Fuel Cells", WHEC 2010, Essen, Germany, Session Title / No. Electrochemistry of PEM Fuel Cells / FC. 1 (June 4, 2014).

[0015] Regulating the heat input into the cryogenic pressure tank serves to heat the cryogenic hydrogen stored in the cryogenic pressure tank in a controlled manner, causing it to expand and thus increasing the hydrogen pressure. By regulating the heat input, the pressure profile of the stored hydrogen in the cryogenic pressure tank can be influenced. A heat exchanger can optionally be incorporated into the cryogenic pressure tank for heat input, as described, for example, in WO 2013 / 143773 A1.

[0016] A heat supply element can optionally comprise a heat exchanger or be designed as such. The heat exchanger can be arranged within the cryogenic pressure tank to transfer heat from a fluid flowing through the heat exchanger to the hydrogen stored in the cryogenic pressure tank.

[0017] The method for operating the cryogenic pressure tank can in particular comprise a method for the controlled removal of hydrogen from the cryogenic pressure tank or for a controlled emptying of the cryogenic pressure tank.

[0018] Planning the desired pressure curve can include determining a target for regulating the heat supply in order to provide a measure of the desired pressure curve of the hydrogen in the cryogenic pressure tank as the tank is gradually emptied. Planning the desired pressure curve also means actively determining a desired pressure curve and providing targets for the control system to achieve the desired pressure curve, rather than allowing the pressure curve to develop uncontrollably.

[0019] Regulating the heat supply can comprise regulating and / or controlling the heat supply. In particular, regulating the heat supply can comprise regulating and / or controlling an opening of a valve unit, which regulates a flow of a heat transfer medium through the heat exchanger optionally arranged in the cryogenic pressure tank. The valve unit can be designed to gradually adjust the flow of the heat transfer medium through the valve unit, i.e. to regulate a flow rate through a variable opening of the valve unit. Alternatively, the valve unit can be designed such that it only has an open and a closed state. In this case, regulating the heat supply can be achieved by temporally controlling or regulating the opening of the valve unit.

[0020] The fact that the heat supply to the cryogenic pressure tank is controlled during at least 70% of the complete extraction process can mean that the pressure of the hydrogen in the cryogenic pressure tank is regularly measured as a controlled variable for at least 70% of the complete extraction process and the heat supply is adjusted as needed. The fact that the heat supply to the cryogenic pressure tank is controlled during the complete extraction process can further mean that the desired pressure profile is specified for at least 70% of the complete extraction process and optionally for the entire complete extraction process and that the heat supply is controlled to achieve this, instead of only being activated when a predetermined minimum pressure is reached or for other reasons, such as to absorb external waste heat, as is conventional.However, the fact that the heat supply to the cryogenic pressure tank is regulated during at least 70% of the complete removal process does not necessarily mean that the heat supply must be continuously varied during at least 70% of the complete removal process.

[0021] The disclosure also offers the advantage of reducing the risk of unwanted liquefaction of the stored hydrogen. Liquefaction can typically occur if the pressure during withdrawal falls below the critical pressure of 12.84 bar without regulation while the hydrogen is still cryogenically cold. The stored hydrogen could then typically transition from the single-phase supercritical CRYOGAS to a two-phase gas-liquid mixture by falling below the two-phase saturation limit, which would be associated with the disadvantages of two-phase formation. This can be avoided by the subject matter of the independent claims. The disclosure also offers the advantage of eliminating the need for an expensive and difficult-to-maintain level sensor. This allows the complexity of the hydrogen storage system and the costs of manufacturing, operating, and / or maintaining it to be kept to a minimum.In particular, the disclosure also offers the advantage that there is no rapid pressure drop during the initial withdrawal of hydrogen from the filled cryogenic pressure tank, and accordingly, the thermodynamic state of the stored hydrogen can be at a safe distance from the two-phase boundary, at which a transition of at least a portion of the stored hydrogen into the liquid phase occurs. Furthermore, the disclosure offers the advantage that, due to a safe distance of the thermodynamic state of the hydrogen from the two-phase boundary and, in particular, from the critical point, measurement errors in the temperature measurement do not lead to a significant underestimation or overestimation of the storage capacity, as would otherwise conventionally occur due to the high dependence of the density on the temperature in the region of the two-phase boundary and, in particular, the critical point.

[0022] The disclosure further offers the advantage that, during a large part of the process for completely removing the hydrogen from the cryogenic pressure tank, the pressure can be kept at a safe distance from the minimum pressure, thus preventing the pressure from falling below the minimum pressure. Furthermore, this can offer the advantage that continuous intervention by the heat supply control is not necessarily required to prevent the pressure from falling below the minimum pressure. Thus, the disclosure can offer the additional advantage that the number of valve switching operations for heat supply control can be reduced or even minimized. This can reduce any wear on the valve unit and accordingly extend the required maintenance interval and / or the service life of the valve unit.This can be particularly advantageous if the valve unit is arranged in a vacuum area and maintenance of the valve unit would require flooding or venting the vacuum area. A safe pressure distance from the two-phase boundary is understood to be a pressure difference between the prevailing hydrogen pressure and the pressure at which the two-phase boundary is reached or exceeded, which allows a pressure change of 10% without the two-phase boundary being reached. A safe pressure distance from the minimum pressure is understood to be a pressure difference between the prevailing hydrogen pressure and the predetermined minimum pressure, which allows a pressure change of 10% without the minimum pressure being reached or exceeded.

[0023] The disclosure thus allows the desired pressure profile to be planned optionally in such a way that the distance between the thermodynamic state of the hydrogen stored in the cryogenic pressure tank and the two-phase boundary of the hydrogen is sufficiently high or even maximum and / or does not fall below a predetermined threshold. In this context, the disclosure can offer the advantage that temperature fluctuations pose a lower risk of slipping into the two-phase region.Since small deviations in the measurement of the pressure and / or temperature of the hydrogen stored in the cryogenic pressure tank can typically result in significant deviations in the determination of the residual amount of hydrogen stored in the cryogenic pressure tank in the two-phase region and near the boundary line to the two-phase region, the separation of the thermodynamic state of the hydrogen according to the disclosure offers significant advantages for the reliable determination of the residual amount and thus for the determination of the remaining range of a vehicle whose propulsion is supplied with the hydrogen. By keeping the thermodynamic state of the hydrogen separated from the two-phase region, the occurrence of significant measurement errors in the determination of the residual amount of hydrogen stored in the cryogenic pressure tank can be avoided.

[0024] The disclosure can also offer the advantage of avoiding the risk of entering a thermodynamic range in which the technical means for supplying heat are insufficient to supply the hydrogen with the required heat. While with conventional control methods at low densities close to the empty tank state (i.e. close to a minimum density of the stored hydrogen) a case can arise in which the required heat inflow and the available heat inflow develop in opposite directions and thus the required heat inflow can exceed the available heat inflow, this is not necessarily the case when using a control method according to the disclosure. This is because with the control method according to the disclosure, the required heat inflow and the available heat inflow develop qualitatively similarly even at low densities due to early heat supply even at higher densities.

[0025] Furthermore, the disclosure can offer the advantage that at low filling levels and in particular at the end of an emptying process, a pressure drop can be avoided and in this way the amount of hydrogen available for withdrawal can be increased or the density can be reduced.

[0026] Furthermore, the disclosure can offer the advantage that a hydrogen withdrawal flow from the cryogenic pressure tank can be reliably maintained above a minimum value. Optionally, the withdrawal flow can be maintained at or above a minimum value of 2.5 g / s throughout the entire withdrawal process. Optionally, the withdrawal flow can be maintained at or above a value of 5 g / s or 9 g / s throughout the entire withdrawal process.

[0027] Furthermore, the disclosure may offer the advantage that, according to the disclosed control method, most of the heat is supplied when the cryogenic pressure tank is full (unlike conventional methods, where most of the heat is supplied when the tank is almost empty). This facilitates heating the hydrogen, since the stored hydrogen is colder in a full tank than in a largely empty tank, and thus the heat can be transferred more effectively. Furthermore, the hydrogen has a higher density when the cryogenic pressure tank is almost full than when it is almost empty, which may also promote heat supply.

[0028] Optionally, the heat supply can be controlled such that the pressure curve of the hydrogen in the cryogenic pressure tank deviates by no more than 5% from the desired pressure curve. This offers the possibility of precise design and / or control of the pressure curve. In addition, the desired pressure curve can be planned and / or the heat supply controlled such that the pressure curve of the hydrogen in the cryogenic pressure tank is always within a range of ± 20 bar around the desired pressure curve when the cryogenic pressure tank is at least half full, i.e. when the density of the stored hydrogen in the cryogenic pressure tank is at least 35 g / L. In addition, the desired pressure curve can be planned and / or the heat supply controlled such that the tolerated deviations of the pressure curve of the hydrogen in the cryogenic pressure tank from the desired pressure curve decrease from ± 20 bar to ± 1 bar as the cryogenic pressure tank is progressively emptied.The progressive emptying of the cryogenic pressure tank can be accompanied by an optional linear decrease in the density of the stored hydrogen in the cryogenic pressure tank from approximately 35 g / L to approximately 8 g / L. This offers the advantage that even with pressure curves that deviate from the desired pressure curve, exceeding the permissible maximum pressure of the cryogenic pressure tank and falling below the specified minimum pressure can be avoided.

[0029] Optionally, the process for complete removal comprises one or more partial removal processes. In other words, the complete removal of hydrogen from the cryogenic pressure tank or the complete emptying of the cryogenic pressure tank down to the minimum pressure does not take place in a single, continuous removal process, but in several separate partial removal processes. Optionally, the one or more removal processes can be interrupted by phases in which no hydrogen is removed from the cryogenic pressure tank and the motor vehicle in which the cryogenic pressure tank is optionally installed is at rest. Optionally, the heat supply to the cryogenic pressure tank is controlled in such a way that the pressure curve of the hydrogen in the cryogenic pressure tank does not deviate by more than 10% from the desired pressure curve during the one or more partial removal processes. In other words, the heat supply orThe aim of achieving the desired pressure curve should be limited to the partial withdrawal processes. This offers the advantage that heat supply regulation to achieve the desired pressure curve can be omitted during phases in which no hydrogen is being withdrawn. The heat supply to the cryogenic pressure tank can optionally be regulated in such a way that any deviation of the hydrogen pressure curve in the cryogenic pressure tank from the desired pressure curve is minimal. In other words, the control can be optimized so that the actual pressure curve is as close as possible to the desired pressure curve.

[0030] Optionally, the method further comprises measuring the temperature and pressure of the hydrogen in the cryogenic pressure tank, as well as determining the initial pressure and initial density based on the measured temperature and pressure. The determined values ​​of the initial pressure and initial density can then be used as a basis for planning the desired pressure profile. In this way, the desired pressure profile can be planned with high precision.

[0031] Optionally, the target pressure curve can be planned such that the pressure decrease of the hydrogen in the cryogenic pressure tank towards the minimum pressure is monotonic throughout the entire process for complete extraction. Optionally, the target pressure curve can be planned such that the pressure decrease of the hydrogen in the cryogenic pressure tank towards the minimum pressure is linear throughout the entire process for complete extraction. This offers the advantage that a safe distance of the thermodynamic state from the two-phase boundary can be maintained throughout the entire process for complete extraction, thus reducing the risk of a portion of the hydrogen transitioning into the liquid phase.Furthermore, this can offer the advantage that the pressure of the stored hydrogen can be kept at a safe distance from the minimum pressure for most of the process until it is completely withdrawn, thus reducing the risk of the minimum pressure being exceeded. Furthermore, this can offer the advantage that the linear pressure curve allows the highest possible mass flow rate of hydrogen from the cryogenic pressure tank to be achieved while being limited by a predetermined maximum heat input. Furthermore, the linear pressure curve means that the available maximum heat input and the heat input required to regulate the pressure curve have the same or similar curves, rather than the conventional opposing curves at low densities, thus avoiding bottlenecks in the available heat input.

[0032] Planning the desired pressure curve can optionally include specifying a desired change in pressure depending on the density and / or temperature of the hydrogen in the cryogenic pressure tank. In particular, the desired change in pressure depending on the density and / or temperature can optionally be specified as a constant pressure gradient. Controlling the heat supply can optionally use the desired change in pressure depending on the density and / or temperature and, if available, the constant pressure gradient as a reference variable. This offers the possibility of implementing the monotonic or linear pressure curve into the control system with little effort and, accordingly, implementing a suitable control system for achieving the desired pressure curve without additional hardware expenditure.The dependence of the change in pressure on the density and / or temperature can optionally also be taken into account by a dependence of the pressure on another quantity, which in turn is related to the density or temperature or depends on the density or temperature.

[0033] The desired pressure curve can optionally be planned such that the pressure decrease of the hydrogen in the cryogenic pressure tank towards the minimum pressure throughout the entire process for complete extraction follows a predetermined polynomial function or a predetermined exponential function. This offers the advantage of ensuring a safe distance between the pressure of the stored hydrogen and the two-phase boundary and / or the minimum pressure during the process for complete extraction.

[0034] The desired pressure curve can optionally be planned in such a way that the number of heat supply phases into the cryogenic pressure tank is minimized. This offers the advantage of minimizing the number of switching operations of a valve unit for heat supply. This can minimize any wear on the valve unit and thus extend the maintenance intervals and / or the service life of the valve unit. This can be particularly advantageous if the valve unit is difficult to access, for example, if the valve unit is located in a vacuum area and the vacuum area must be vented or flooded for maintenance of the valve unit.

[0035] The desired pressure curve can optionally be planned in such a way that the pressure decrease of the hydrogen in the cryogenic pressure tank down to the minimum pressure follows a gradual progression throughout the entire process for complete extraction. This can offer the advantage of minimizing the number of heat supply phases and / or the number of valve unit switching operations.

[0036] Optionally, the heat supply to the cryogenic pressure tank can also be controlled in such a way that the pressure profile of the hydrogen in the cryogenic pressure tank does not exceed a predetermined maximum pressure of the cryogenic pressure tank and / or does not fall below the minimum pressure. This offers the advantage of preventing damage to the cryogenic pressure tank and ensuring the supply of hydrogen at a pressure suitable for the consumer.

[0037] Planning the desired pressure curve can comprise specifying a tolerance range around the desired pressure curve, wherein the tolerance range includes the desired pressure curve and is limited upwards by the predetermined maximum pressure of the cryogenic pressure tank in the initial pressure range and downwards by the minimum pressure in the minimum pressure range. In other words, a tolerance range can be specified which extends asymmetrically around the desired pressure curve. At high fill levels in the cryogenic pressure tank and correspondingly high pressures, the desired pressure curve can lie in the upper range of the tolerance range, while at low fill levels in the cryogenic pressure tank and correspondingly lower pressures, the desired pressure curve lies in the lower range of the tolerance range.This offers the advantage that a deviation of the pressure curve is tolerated more generously in the direction in which the pressure curve does not approach a critical pressure range.

[0038] The features and embodiments mentioned above and explained below are not only to be considered as disclosed in the explicitly stated combinations, but are also encompassed by the disclosure content in other technically meaningful combinations and embodiments. In particular, the disclosures relating to the method are also to be considered as disclosed for the control unit, the hydrogen storage system, and the motor vehicle, and vice versa.

[0039] Although the present disclosure is directed in part to the storage and withdrawal of cryogenically compressed hydrogen, it is also to be considered directed to the storage and withdrawal of other cryogenically compressed gases.

[0040] Further details and advantages will now be explained in more detail using the following examples and optional embodiments with reference to the figures.

[0041] They show: Figure 1 shows a motor vehicle in a schematic representation with a hydrogen storage system according to an optional embodiment; Figure 2 shows a hydrogen storage system according to an optional embodiment in a detailed view; Figure 3 shows a method for operating a cryogenic pressure tank using a schematic sketch; Figures 4A to 4C show a schematic comparison between conventional changes in pressure and a pressure curve when applying a method for operating a cryogenic pressure tank according to an optional embodiment of the disclosure; Figures 5A and 5B show a schematic comparison between a conventional regulator ( Figure 5A) and a pressure regulator according to an optional embodiment for regulating the heat supply; Figure 5C: an illustration of an iteration method; Figure 5D: an illustration of a control system; Figure 5E: a graph illustrating a control system; Figure 5F: a pictorial representation of a control system; Figures 6A to 6D show various optional curve shapes of the desired pressure curve by way of example; Figure 7 shows an explanation of an optional embodiment of a method according to the disclosure for regulating the heat supply using a temperature-density diagram; Figures 8A and 8B show a comparison of the heat flow versus the density of the hydrogen stored in the cryogenic pressure tank 16 with inverted sign; Figures 9A and 9B show the corresponding temperature curve of the hydrogen in the cryogenic pressure tank for the Figures 8A and 8B comparison shown.

[0042] In the following figures, identical or similar elements in the various embodiments are designated by identical reference numerals for the sake of simplicity.

[0043] Figure 1shows a schematic representation of a motor vehicle 10 with a hydrogen storage system 12 according to an optional embodiment and a consumer 14. The consumer can optionally comprise one or more fuel cells and / or one or more internal combustion engines. The hydrogen storage system 12 is equipped for storing cryogenic hydrogen to supply the consumer 14 with hydrogen. The hydrogen storage system 12 comprises a cryogenic pressure tank 16, which is designed to store hydrogen at a supercritical initial pressure and with an initial density. In addition, the hydrogen storage system 12 has a heat supply element 18, which is designed to supply heat to the hydrogen stored in the cryogenic pressure tank 16.In addition, the hydrogen storage system 12 has a control unit 20 which is configured to perform the following steps: (i) setting a desired pressure profile over a process for the complete removal of the hydrogen stored at the initial pressure and the initial density in the cryogenic pressure tank 16 up to a predetermined minimum density at a minimum pressure of the hydrogen in the emptied state of the cryogenic pressure tank 16 such that a decrease in the pressure of the hydrogen in the cryogenic pressure tank 16 down to the minimum pressure extends over the entire process for the complete removal. (ii) regulating a heat supply to the cryogenic pressure tank 16 by means of the heat supply element 18 during at least 70% of the process for the complete removal such that the pressure profile of the hydrogen in the cryogenic pressure tank 16 deviates from the desired pressure profile by no more than 10%.

[0044] Figure 2shows a hydrogen storage system 12 according to an optional embodiment in a more detailed view. This has a cryogenic pressure tank 16, which is shown including optional additional components. The hydrogen storage system can be based on a conventional cryogenic pressure tank 16, as described in WO 2013 / 143773 A1. Cryogenic hydrogen can be stored in the cryogenic pressure tank 16 to supply a consumer 14, for example an internal combustion engine, which can optionally be designed as a hydrogen combustion engine, and / or a fuel cell of the motor vehicle 10, at absolute pressure values ​​of the internal tank pressure in the order of 150 bar or more, but at least under supercritical pressure at 13 bar and more.This cryogenic pressure tank 16 can have a pressure-resistant inner tank 20, within which the cryogenic hydrogen is in the supercritical state, as well as an insulation layer 22 surrounding the inner tank 20, in which a vacuum can essentially be present, i.e. a pressure of less than 1 mbar, and an outer shell 24 enclosing this vacuum. The inner tank 20 can be filled with cryogenic hydrogen in the supercritical state via a combined and thus single-flow filling and removal line 26, and hydrogen can be removed from the inner tank 20 via this filling and removal line 26, which opens into a cryogenic valve unit 28. For this purpose, a first orAn external heat exchanger 30 may be connected through which, on the one hand, a first heat transfer medium circuit 32 and, on the other hand, a supply line 34 leading from the cryogenic valve unit 28 and connecting to the filling / withdrawal line 26 are routed, which ultimately leads to the aforementioned consumer 14. Via the heat exchanger 30, the supply line 34 can be in heat-transfer connection with the first heat transfer medium circuit 32, so that the hydrogen carried in the supply line 34 is heated in the external first heat exchanger 30.

[0045] Following the external first heat exchanger 30, the supply line 34 can be led into a second valve unit 36, through which the supply line 34 is led, passing a control valve 38 and a pressure adjustment unit 40, before reaching the consumer 14. A branch line 42 can branch off from the control valve 38, through which hydrogen extracted from the cryogenic pressure tank 16 and heated in the first (external) heat exchanger 30 can be introduced into a second (internal) heat exchanger 44 provided within the inner tank 20 of the cryogenic pressure tank 16.After flowing through this second heat exchanger 44, located within the cryogenic pressure tank 16, more precisely within its inner tank 20, this hydrogen can be introduced via a return line 46 into the supply line 34 downstream of the branch of the branch line 42. This return line 46 is previously routed through a third (external) heat exchanger 48, connected in parallel to the first (external) heat exchanger 30 and supplied by the same heat transfer medium circuit 32, in which the hydrogen cooled in the second internal heat exchanger 44 is reheated by heat exchange with the aforementioned heat transfer medium circuit 32. Thus, the hydrogen conducted through the branch line 42, the second internal heat exchanger 44, and the return line 46 can serve as a heat transfer medium for heating the hydrogen stored in the cryogenic pressure tank 16.

[0046] The control or regulation of this heating can be controlled or regulated by the supply of said heat transfer medium or hydrogen to the internal heat exchanger 44 and thus by a suitable switching strategy of the control valve 38. The control or regulation of the control valve 38 and thus the heat supply into the cryogenic pressure tank can be carried out by means of a control unit 20 according to the disclosure. The control unit 20 can be configured to control a Figure 3 to carry out the procedure described.

[0047] Figure 3 shows, by means of a schematic sketch, a method 300 for operating a cryogenic pressure tank 16 in which cryogenic hydrogen is stored at a supercritical initial pressure and an initial density, for supplying a consumer 14 with hydrogen taken from the cryogenic pressure tank 16.

[0048] The method comprises, in a step 302, measuring a temperature and a pressure of the hydrogen in the cryogenic pressure tank 16.

[0049] In a further optional step 304, the method comprises determining the initial pressure and the initial density based on the measured temperature and the measured pressure.

[0050] Furthermore, in a further step 306, the method 300 comprises planning a desired pressure profile over a process for completely removing the hydrogen stored in the cryogenic pressure tank 16 at the initial pressure and initial density to a predetermined minimum density at a minimum pressure of the hydrogen in the emptied state of the cryogenic pressure tank 16, such that a decrease in the pressure of the hydrogen in the cryogenic pressure tank 16 to the minimum pressure extends over the entire complete removal process. The complete removal process may comprise one or more partial removal processes.

[0051] Furthermore, in a further step 308, the method 300 comprises regulating a heat supply to the cryogenic pressure tank 16 during at least 70% of the complete removal process such that the pressure profile of the hydrogen in the cryogenic pressure tank 16 deviates by no more than 10% from the desired pressure profile. Regulating 308 the heat supply to the cryogenic pressure tank 16 can be carried out such that the pressure profile of the hydrogen in the cryogenic pressure tank 16 deviates by no more than 10% from the desired pressure profile during the one or more partial removal processes.

[0052] The planning 306 of the desired pressure curve can be carried out such that the pressure decrease of the hydrogen in the cryogenic pressure tank 16 towards the minimum pressure is monotonic throughout the entire process for complete removal. Optionally, the planning 306 of the desired pressure curve can be carried out such that the pressure decrease of the hydrogen in the cryogenic pressure tank 16 towards the minimum pressure is linear throughout the entire process for complete removal.

[0053] Optionally, the heat supply to the cryogenic pressure tank 16 can also be regulated 308 such that the pressure profile of the hydrogen in the cryogenic pressure tank 16 does not exceed a predetermined maximum pressure of the cryogenic pressure tank and / or does not fall below the minimum pressure. The heat supply can be regulated 308 to the desired pressure profile depending on the density and / or temperature. If the planning 306 is carried out in such a way that a constant pressure gradient is specified, this can be used as a reference variable. Optionally, the heat supply to the cryogenic pressure tank can be regulated 308 such that any deviation of the pressure profile of the hydrogen in the cryogenic pressure tank from the desired pressure profile is minimal.

[0054] The Figures 4A to 4Cshow schematically a comparison between conventional changes in the pressure P of the hydrogen stored in the cryogenic pressure tank 16 as a function of the density of the hydrogen in the cryogenic pressure tank 16 ( Figures 4A and 4B ) and a pressure profile when applying a method 300 for operating a cryogenic pressure tank 16 according to an optional embodiment of the disclosure ( Figure 4C ).

[0055] According to the Figure 4A In the conventional pressure curve 400 shown, in a first phase 402 of the hydrogen extraction, an uncontrolled pressure reduction initially occurs until the pressure P reaches a predetermined minimum pressure. In a subsequent second phase 404, the heat supply to the cryogenic pressure tank 16 is then regulated so that the pressure P does not fall below the predetermined minimum pressure.

[0056] The Figure 4BThe conventional pressure curve 406 shown corresponds to a pressure curve that can be achieved using a conventional method for supplying heat, which is described in WO 2009 / 071208 A1. At low fill levels, the control valve is kept continuously open, causing the pressure in the cryogenic pressure tank to rise. Nevertheless, this pressure curve 406 also initially includes a first phase 408 in which the pressure P continuously drops to the predetermined minimum value, and a second phase 410 in which the pressure is maintained at the minimum pressure by regulating the heat supply. The control valve is then fully opened in the third phase 412.

[0057] Figure 4Cshows an advantageous pressure curve 414, which can be achieved with a disclosed heat supply method according to an optional embodiment. According to the embodiment shown, the pressure is regulated over the entire density range 416, so that the pressure does not initially drop to the minimum value, but rather drops in a controlled manner in a monotonous or even linear manner to the minimum pressure at the minimum density. This ensures that the hydrogen is always in a thermodynamic range that is safely spaced from the two-phase boundary.

[0058] In this case, planning 306 of the desired pressure profile can include specifying a desired change in pressure as a function of the density and / or temperature of the hydrogen contained in the cryogenic pressure tank 16 and / or variables closely related thereto. The desired change in pressure as a function of the density and / or temperature can optionally be specified as a constant pressure gradient.

[0059] In this context, the Figures 5A and 5B a schematic comparison between a conventional controller ( Figure 5A ) and a pressure regulator according to an optional embodiment for regulating the heat supply to the cryogenic pressure tank 16. As in Figure 5A As can be seen, a fixed pressure value, known as P setpoint, is conventionally given to the control loop as a reference variable, whereby the pressure in the cryogenic pressure tank P tank is controlled. Such a control loop can also form the basis for the Figure 5Bshown regulator according to the optional embodiment of the disclosure, as shown by the dashed line. In addition, the regulator according to Figure 5B designed to dynamically determine the reference variable to be transferred to the conventional controller by means of the controller C1, whereby in this case a constant pressure gradient (via the density) dP dρ constant is used as a reference variable.

[0060] Determining the constant pressure gradient as a reference variable in the controller C 1 according to Figure 5B can optionally be done by the following iterative procedure, which is also Figure 5C is shown pictorially: gradient = − P i + 1 − P i ρ i + 1 − ρ i = dP dρ constant P i + 1 = P i − dP dρ constant ρ i + 1 − ρ i ρ i + 1 − ρ i ≅ ρ i − ρ i − 1 P i + 1 = P i − dP dρ constant ρ i − ρ i − 1

[0061] The variables P stand for the pressure and ρ for the density of hydrogen in the cryogenic pressure tank 16. The index i stands for the respective iteration step. Figure 5D illustrates the control. The density ρof the hydrogen in the pressure tank is determined and fed to the controller C 1. This controller also receives the predetermined constant gradient as a specification and, using the iteration method explained above, dynamically determines the pressure value P setpoint , which is then supplied to the conventional control loop as a reference variable. This optional method for controlling the heat supply can be determined based on measured values ​​from the cryogenic pressure tank, namely the pressure and density and / or the temperature of the hydrogen stored in the cryogenic pressure tank 16.

[0062] Alternatively or additionally, the heat supply can be controlled by specifying a constant pressure gradient based on measured values ​​relating to the consumer 14, such as a fuel cell. The mass flow ṁ of hydrogen flowing from the cryogenic pressure tank 16 to the consumer 14 and the determined time period Δ tas measured variables. This form of control is explained below and in Figure 5E shown using a graph ρ i + 1 − ρ i = 1 V tank m i + 1 − m i m i + 1 − m i = dm dt Δ t dm dt = − m ˙ ρ i + 1 − ρ i = − m ˙ Δ t V tank P i + 1 = P i − dP dρ constant ρ i − ρ i − 1 P setpoint i + 1 = P setpoint i + dP dρ constant m ˙ Δ t V tank

[0063] V tank indicates the capacity of the cryogenic pressure tank 16, m the mass of hydrogen and ṁ the mass flow of hydrogen flowing to the consumer (change in mass per time), and t is the time. Figure 5F illustrates this form of regulation.

[0064] According to other optional embodiments, the target pressure curve can be planned such that the pressure decrease of the hydrogen in the cryogenic pressure tank 16 to the minimum pressure throughout the entire process for complete removal follows a different monotonic curve. For example, the target pressure curve can follow a predetermined polynomial function 600, as shown in Figure 6Ashown by way of example, or follow a predetermined exponential function 602, as in Figure 6B shown.

[0065] Optionally, the desired pressure curve can be planned in such a way that the number of heat supply phases into the cryogenic pressure tank is minimized. This can be particularly advantageous in that the heat supply can be effected via a valve that only has one closed and one open state, but cannot gradually change the flow rate. Furthermore, reducing or minimizing the number of heat supply phases can be advantageous in that the number of required valve switching operations is reduced, thus reducing valve wear and, accordingly, increasing the duration of a maintenance interval and / or the valve's service life. Figure 6Cshows, by way of example, a process in which the pressure curve is planned in such a way that only three phases of heat supply are provided, during which the pressure is increased. Between the phases of the planned heat supply, the pressure can optionally be monitored without any active heat supply being provided. The desired pressure curve can therefore be planned in such a way that the pressure decrease of the hydrogen in the cryogenic pressure tank towards the minimum pressure has a stepped progression 604 over the entire process for complete removal.

[0066] The planning 306 of the desired pressure profile may optionally comprise specifying a tolerance range around the desired pressure profile, wherein the tolerance range includes the desired pressure profile and is limited upwards by the predetermined maximum pressure of the cryogenic pressure tank in the range of the initial pressure and is limited downwards by the minimum pressure in the range of the minimum pressure. Figure 6C shows an example of a desired pressure curve. Furthermore, the planning 306 of the desired pressure curve can be carried out such that the distance between the thermodynamic state of the hydrogen stored in the cryogenic pressure tank 16 and the two-phase boundary of the hydrogen is maximum and / or does not fall below a predetermined threshold. Figure 6Dshows, by way of example, a desired pressure curve 606 together with a tolerance range formed by an upper limit 608 and a lower limit 610. The desired pressure curve does not run parallel to the tolerance range. Rather, at high fill levels, the tolerance range is limited by the upper limit 608, which can correspond to or be derived from a predefined permissible maximum pressure, while at low fill levels, the tolerance range is limited by the lower limit 610, which can correspond to or be derived from a predefined permissible minimum pressure.

[0067] Based on Figure 7A further advantage of an optional embodiment of a method according to the disclosure for regulating the heat supply is described using a temperature-density diagram. The temperature in Kelvin is shown on the horizontal axis and the density of the hydrogen in the cryogenic pressure tank 16 in kg / m 3 is shown on the vertical axis. The lines 700 indicate isobars along which the pressure is constant. The curve 702 of the density versus the temperature corresponds to the curve that can be achieved with a conventional method for regulating the heat supply, i.e. with a method in which no heat supply is regulated initially at high fill levels. It can be seen that the density already drops rapidly at low temperatures and the thermodynamic state of the hydrogen very closely approaches the thermodynamic range of saturation 704, in which the hydrogen at least partially transforms into the liquid state.This has the disadvantage that even small temperature fluctuations can lead to an error in the calculation of the density and thus the residual capacity of the hydrogen in the tank. The curve 706f, on the other hand, represents a curve that can be achieved with a heat supply control according to the disclosure. This differs from the conventional curve, among other things, in that the temperature is increased even at high densities, and in this way, a safe distance (indicated by arrow 708) of the thermodynamic state of the hydrogen from the two-phase boundary 704 can be maintained for the entire density range. As a result, in the event of temperature measurement inaccuracies, there is no risk of a major error in the determination of the density and thus the residual capacity of the hydrogen in the cryogenic pressure tank (CcH2 CRYOGAS tank) 16. This can increase the reliability of the operation of the cryogenic pressure tank 16.

[0068] The Figures 8A and 8Bshow a comparison of the heat flow versus the density of the hydrogen stored in the cryogenic pressure tank 16 with inverted sign (the progress on the horizontal axis to the right thus corresponds to a progressive emptying of the cryogenic pressure tank) for a conventional control of the heat supply ( Figure 8A ), in which the pressure initially drops to the minimum pressure and the control then maintains the pressure at the minimum pressure, with a control according to an optional embodiment in which a linear pressure curve from the initial pressure to the minimum pressure is specified over the entire emptying process ( Figure 8B The horizontal axis shows the density of the hydrogen stored in the cryogenic pressure tank in g / L and the vertical axis the heat flow in kW.

[0069] As in Figure 8AAs can be seen, in the conventional case, for a wide range of fill levels in the cryogenic pressure tank, the available heat flow 800 is significantly higher than the required heat flow 802 needed to maintain a pressure of 15 bar for the stored hydrogen. However, at low densities below approximately 10 g / L, the required heat flow increases rapidly, while the available heat flow that can be introduced into the hydrogen by means of the heat exchanger decreases. At the intersection point 804 of the two curves 800 and 802, the required heat flow 802 even exceeds the available heat flow, so that maintaining the pressure of 15 bar cannot be guaranteed. This can result in the pressure of the hydrogen falling below a predetermined minimum pressure and the consumer can no longer be adequately supplied with the remaining hydrogen in the cryogenic pressure tank.

[0070] As in Figure 8BAs can be seen, this problem does not occur in the case of linear control according to an optional embodiment of the disclosure, in which a linear pressure curve (between initial pressure and minimum pressure) is specified. With such a control, heat is supplied even before the point at which the pressure reaches the minimum pressure. This offers the advantage that the available heat flow 806 is always greater than the required heat flow 808 and that these have a qualitatively similar curve. Accordingly, in this case, the critical case in which the required heat flow 808 can exceed the available heat flow 806 does not arise. Thus, when using such a control according to an optional embodiment of the disclosure, there is no risk that the pressure will drop below the minimum pressure and the consumer can no longer be supplied with the hydrogen available.

[0071] In addition, the presence of hydrogen stored in the cryogenic pressure tank 16 in a cryogenic temperature range of 35 K to 60 K can be avoided. Figures 9A and 9B show for the in the Figures 8A and 8B The comparison shown shows the corresponding temperature profile of the hydrogen in the cryogenic pressure tank 16, with the density of the hydrogen stored in the cryogenic pressure tank being plotted in g / L on the horizontal axis with inverted sign and the temperature in Kelvin on the vertical axis. In the conventional case (as described with reference to Figure 8A described), which is in Figure 9A As shown, the initial pressure decrease is accompanied by a temperature decrease, with the temperature of the hydrogen initially falling from about 60 K to about 35 K. Only when heat is added, with the aim of maintaining the pressure at the minimum pressure, does the temperature rise again.

[0072] According to the Figure 9BIn the case shown, with heat supply controlled for a linear pressure curve, there is no initial temperature drop; instead, the temperature rises right from the start. Thus, the temperature does not penetrate the extremely cold range between 35 K and 60 K. List of reference symbols

[0073] 10Motor vehicle 12Hydrogen storage system 14Consumer 16Cryogenic pressure tank 18Heat supply element 20Control unit 22Insulation layer 24Outer shell 26Withdrawal line 28Cryogenic valve unit 30Heat exchanger 32Heat transfer circuit 34Supply line 36Secondary valve unit 38Control valve 40Pressure adjustment unit 42Branch line 44Heat exchanger 46Return line 48Heat exchanger 300Procedure for operating a cryogenic pressure tank (CcH2 CRYOGAS tank) 302 - 308Procedure steps 400 Conventional pressure curve 402 First phase of hydrogen extraction 404 Second phase 406 Conventional pressure curve 408 First phase 410 Second phase 412 Third phase 414 Pressure curve according to optional embodiment 416 Total density range 600Polynomial function 602Exponential function 604Step-like curve 606Target pressure curve 608Upper limit of the tolerance range 610Lower limit of the tolerance range 700Isobars 702Conventional density curve 704Two-phase boundary 706Density curve according to optional embodiment 708Arrow (indicates the safe distance from the saturation region) 800 available heat flow 802 required heat flow 804 intersection 806 available heat flow 808 required heat flow

Claims

1. Method (300) for operating a cryo pressure tank (16), in which cryogenic hydrogen is stored at a supercritical initial pressure and an initial density, for supplying a consumer (14) with hydrogen removed from the cryo pressure tank (16), the method (300) characterized by: - planning (306) a desired pressure profile over an operation for the complete removal of the hydrogen, stored at the initial pressure and the initial density in the cryo pressure tank (16), to a predetermined minimum density at a predetermined minimum pressure of the hydrogen in an emptied state of the cryo pressure tank (16) in such a way that a pressure decrease of the hydrogen in the cryo pressure tank (16) to the minimum pressure extends over the entire operation for the complete removal; - regulating (308) a heat supply into the cryo pressure tank (16) during at least 70% of the operation for the complete removal in such a way that the pressure profile of the hydrogen in the cryo pressure tank (16) deviates by no more than 10% from the desired pressure profile.

2. Method (300) according to Claim 1, wherein the operation for the complete removal comprises one or more partial removal operations.

3. Method (300) according to Claim 2, wherein the regulating of the heat supply into the cryo pressure tank (16) is effected during the one or more partial removal operations.

4. Method (300) according to one of the preceding claims, further comprising: - measuring (302) a temperature and a pressure of the hydrogen in the cryo pressure tank (16); and - ascertaining (304) the initial pressure and the initial density on the basis of the measured temperature and the measured pressure.

5. Method (300) according to one of the preceding claims, wherein the planning (306) of the desired pressure profile is effected in such a way that the pressure decrease of the hydrogen in the cryo pressure tank (16) to the minimum pressure is monotonous over the entire operation for the complete removal.

6. Method (300) according to one of the preceding claims, wherein the planning (306) of the desired pressure profile is effected in such a way that the pressure decrease of the hydrogen in the cryo pressure tank to the minimum pressure is linear over the entire operation for the complete removal.

7. Method (300) according to Claim 6, wherein the planning (306) of the desired pressure profile comprises predefining a desired change in the pressure in dependence on the density and / or temperature of the hydrogen in the cryo pressure tank (16), and wherein the desired change in the pressure in dependence on the density and / or temperature is predefined as a constant pressure gradient.

8. Method (300) according to one of the preceding claims, wherein the planning (306) of the desired pressure profile is effected in such a way that the pressure decrease of the hydrogen in the cryo pressure tank (16) to the minimum pressure follows a predetermined polynomial function (600) or a predetermined exponential function (602) over the entire operation for the complete removal.

9. Method (300) according to one of the preceding claims, wherein the planning (306) of the desired pressure profile is effected in such a way that a number of phases of the heat supply into the cryo pressure tank (16) is minimal.

10. Method (300) according to one of the preceding claims, wherein the planning (306) of the desired pressure profile is effected in such a way that the pressure decrease of the hydrogen in the cryo pressure tank (16) to the minimum pressure has a step-like profile over the entire operation for the complete removal.

11. Method (300) according to one of the preceding claims, wherein the regulating (308) of the heat supply into the cryo pressure tank (16) is also effected in such a way that the pressure profile of the hydrogen in the cryo pressure tank (16) does not exceed a predetermined maximum pressure of the cryo pressure tank (16) and / or does not fall below the predetermined minimum pressure, and wherein the planning (306) of the desired pressure profile comprises predefining a tolerance range around the desired pressure profile, wherein the tolerance range includes the desired pressure profile and is upwardly limited in the region of the initial pressure by the predetermined maximum pressure of the cryo pressure tank (16) and is downwardly limited in the region of the minimum pressure by the predetermined minimum pressure.

12. Method (300) according to one of the preceding claims, wherein the planning (306) of the desired pressure profile is effected in such a way that a distance of the thermodynamic state of the hydrogen stored in the cryo pressure tank from a two-phase limit (704) of the hydrogen is maximal and / or does not fall below a predetermined threshold value.

13. Control unit (20) for operating a cryo pressure tank (16) for storing cryogenic hydrogen at a supercritical pressure for the supply of a consumer (14) with hydrogen removed from the cryo pressure tank (16), characterized in that the control unit (20) is configured to carry out a method according to one of the preceding claims.

14. Hydrogen storage system (12) for storing cryogenic hydrogen for the supply of a consumer (14) with hydrogen, the hydrogen storage system (12) comprising: - a cryo pressure tank (16) which is designed to store hydrogen at a supercritical initial pressure and at an initial density; - a heat supply element (18) which is designed to supply heat to the hydrogen stored in the cryo pressure tank (16); - a control unit (20), characterized in that the control unit is configured to carry out the following steps: + planning (306) a desired pressure profile over an operation for the complete removal of the hydrogen, stored at the initial pressure and the initial density in the cryo pressure tank (16), to a predetermined minimum density at a predetermined minimum pressure of the hydrogen in an emptied state of the cryo pressure tank (16) in such a way that a pressure decrease of the hydrogen in the cryo pressure tank (16) to the minimum pressure extends over the entire operation for the complete removal; + regulating (308) a heat supply into the cryo pressure tank (16) by means of the heat supply element (18) during at least 70% of the operation for the complete removal in such a way that the pressure profile of the hydrogen in the cryo pressure tank deviates by no more than 10% from the desired pressure profile.

15. Motor vehicle (10) comprising: - a hydrogen combustion engine and / or one or more fuel cells; and - a hydrogen storage system (12) according to Claim 14 which is designed to store cryogenic hydrogen and to supply the hydrogen combustion engine and / or the fuel cell(s) with the hydrogen from the hydrogen storage system (12).