method

Abstract

Proposed is a method for operating a storage container (1A) for a cryogen (H2), in particular for hydrogen, wherein the cryogen (H2) can be changed from a liquid phase (LH2) into a gaseous phase (GH2) and vice versa by way of phase transitions, the method having the following steps: a) filling (S1) the storage container (1A) with the liquid phase (LH2), b) introducing (S2) heat (Q) into the liquid phase (LH2), resulting in a pressure increase from an initial pressure (p1) to an operating pressure (p3), wherein the operating pressure (p3) is higher than the critical pressure (pc) of the cryogen (H2), and c) removing (S3) the cryogen (H2) from the storage container (1A), wherein heat (Q) is supplied to the cryogen (H2) with the result that, during step c), the operating pressure (p3) is kept above the critical pressure (pc) at all times and a phase change material accommodated in a latent heat store of the storage container is caused to undergo a phase transition from liquid to solid by way of a transfer of heat from the phase change material to the cryogen, or wherein the phase change material remains solid during step c).

Description

[0001]November 19, 2024 - Claudia Meilinger1 Description Method The invention relates to a method for operating a storage container for a cryogen, in particular for hydrogen. US 3062017 A discloses a method according to the preamble of claim 1. Against this background, an object of the present invention is to provide an improved method for operating a storage container for a cryogen, in particular for hydrogen. Accordingly, a method for operating a storage container for a cryogen, in particular for hydrogen, is proposed. The cryogen can be convertible from a liquid phase to a gaseous phase and vice versa with the aid of phase transitions.The method comprises the following steps: a) filling the storage container with the liquid phase, b) introducing heat into the liquid phase, whereby a pressure increase from an initial pressure to an operating pressure is achieved within the storage container, and whereby the operating pressure is higher than the critical pressure of the cryogen, and c) removing the cryogen from the storage container, whereby heat is supplied to the cryogen so that the operating pressure is always kept above the critical pressure during step c). According to the invention, during step c), a phase change material accommodated in a latent heat storage device of the storage container undergoes a phase transition from liquid to solid by transferring heat from the phase change material to the cryogen, or whereby the phase change material remains solid during step c). The latent heat storage device can also be referred to as a phase change storage device or PCN storage device.A "latent heat storage device" is understood here, in particular, to be a special type of heat storage device that stores a large portion of the thermal energy supplied to it in the form of latent heat, for example, for a phase transition from solid to liquid. Nitrogen is preferably used as the phase-change material. Therefore, the term "phase-change material" can also be replaced by the term "nitrogen" in this context. However, argon, for example, can also be used as the phase-change material. In particular, however, a phase-change material is used that has a melting point that lies above a transport temperature of the cryogen contained in the storage container. The phase-change material can be part of the latent heat storage device and thus also part of the storage container.The phase change material can undergo a phase transition from solid to liquid and from liquid to gaseous and vice versa. Preferably, during step c), only a phase transition between liquid and solid is provided. Alternatively, no phase transition takes place during step c), and the phase change material remains solid. The phase change material absorbs heat during the phase transition from solid to liquid and releases heat during the phase transition from liquid to solid. By always keeping the operating pressure above the critical pressure during step c), it can be ensured that a two-phase state of the cryogen cannot develop within the storage vessel. A pressure drop as previously mentioned, which results from mixing of the liquid and gaseous phases, is prevented.By controlling the conditions within the storage vessel and thus avoiding sudden pressure fluctuations, reliable operation of a consumer can always be ensured, even when the storage vessel is moving, for example, due to sea waves. The cryogen is preferably hydrogen. The terms "cryogen" and "hydrogen" can therefore be interchanged. In principle, however, the cryogen can also be any cryogen other than hydrogen. Examples of cryogenic fluids or liquids, or cryogens for short, include the aforementioned hydrogen, liquid helium, liquid nitrogen, or liquid oxygen. In this context, a "cryogen" can refer to both the liquid and gaseous phases of the cryogen. Furthermore, the term "cryogen" also includes the supercritical state of the cryogen.The liquid phase can, in particular, be evaporated and thus converted into the gaseous phase. Conversely, the gaseous phase can condense and thereby be converted into the liquid phase. After evaporation, the cryogen is a gas19.11.2024 – Claudia Meilinger3 or can be referred to as gaseous or evaporated cryogen. If both the gaseous phase and the liquid phase are present simultaneously, there is a phase boundary between the liquid phase and the gaseous phase. The cryogen is thus located in the two-phase region. However, the method is carried out in such a way that preferably no phase boundary forms within the storage vessel. The method is thus carried out in particular in such a way that the two-phase region is not crossed, at least during step c). The method is thus carried out in particular without forming a two-phase state of the cryogen in the storage vessel.The fact that the cryogen can be converted from the liquid phase to the gaseous phase with the help of phase transitions means in particular that the liquid phase can change from liquid to gaseous into the gaseous phase through a phase transition. The liquid phase evaporates in the process. Conversely, the gaseous phase can change from gaseous to liquid into the liquid phase through a phase transition. The gaseous phase condenses in the process. The cryogen thus has at least two states of matter, namely liquid and gaseous. The cryogen can also change into a solid phase, for example in the form of ice. However, the solid phase is not relevant for the described method. The storage container preferably has an inner container for holding the cryogen and an outer container in which the inner container is accommodated. The storage container is therefore in particular double-walled.A gap can be provided between the inner container and the outer container. A thermal insulation element that completely encloses or surrounds the inner container can be provided in the gap. The insulation element serves for thermal insulation. The insulation element is multi-layered. This means that the insulation element comprises a large number of layers. In particular, the insulation element is so-called multilayer insulation (MLI). During step a), the storage container is filled with the liquid phase in such a way that the storage container, in particular the inner container of the storage container, is completely filled with the liquid phase. This means in particular that the cryogen is preferably single-phase after step a). However, this is not absolutely necessary. After step a), the storage container19.11.2024 – Claudia Meilinger4 may also be filled to a small extent with the gaseous phase in addition to the liquid phase. During step a), i.e. during the filling of the storage vessel, the cryogen can thus be two-phase. In particular, the two-phase region can be passed through during step a), whereas the two-phase region is not passed through during step c). During step b), the heat is introduced into the liquid phase, for example with the help of a heating element. By introducing the heat, the pressure within the storage vessel quickly rises from the initial pressure to the operating pressure. Because the storage vessel, in particular the inner vessel, is completely or at least almost completely filled with the liquid phase after step a), the pressure within the storage vessel rises very quickly when heat is introduced.As previously mentioned, the operating pressure is higher than the critical pressure of the cryogen. In thermodynamics, the critical point is a thermodynamic state of a substance, in this case cryogen, characterized by an equalization of the densities of the liquid and gaseous phases. At the critical point, a phase boundary no longer exists. The differences between the two aforementioned states of matter cease to exist at the critical point. The cryogen is then in its supercritical state. At the critical point, the cryogen exhibits a characteristic critical pressure and a critical temperature. For example, hydrogen has a critical pressure of 12.3 bara and a critical temperature of -239.9 °C.Because the operating pressure during step c) is always higher than the critical pressure, the cryogen is present either in the liquid phase or in the supercritical state during step c). During step c), heat is added to the cryogen, in particular to the liquid phase or to the cryogen in the supercritical state. This allows the operating pressure during step c) to be maintained preferably at a constant operating pressure above the critical pressure. "Always" in this context means, in particular, that the critical pressure is maintained above the critical pressure throughout the entire duration of step c).19.11.2024 – Claudia Meilinger5 According to one embodiment, during step a), a filling level of the storage container with the liquid phase of more than 90%, preferably more than 95%, more preferably more than 96%, more preferably more than 97%, more preferably more than 98%, more preferably more than 99%, more preferably 100% is achieved. The "filling level" is understood here as a ratio of a receiving volume of the aforementioned inner container of the storage container to a volume of the liquid phase accommodated in the receiving volume. If the filling level is 100%, the volume of the liquid phase corresponds to the receiving volume of the inner container. In this case, there is no phase boundary and no gaseous phase within the storage container. If the filling level is less than 100%, a slight gas zone containing the gaseous phase can be provided within the storage container.However, this gas zone no longer exists at the latest when the cryogen is brought into the supercritical state. According to a further embodiment, the cryogen becomes supercritical during step c). This means in particular that the cryogen is brought from the liquid phase into the supercritical state during step c). If the cryogen is in the supercritical state, it is removed from the storage container during step c) even in the supercritical state. According to a further embodiment, the density of the cryogen is increased during step a), wherein the density of the cryogen is kept constant during step b), and wherein the density of the cryogen is reduced during step c). During step a), the density of the cryogen is increased by completely or almost completely filling the storage container with the liquid phase.After step a), the storage vessel is completely filled, so that no change in the density of the cryogen occurs during step b). As previously mentioned, the pressure buildup during step b) occurs by introducing heat into the cryogen, particularly into the liquid phase. Since the cryogen is removed from the storage vessel during step c) and heat is simultaneously added, the density of the cryogen decreases again. According to a further embodiment, after step c), the cryogen is expanded to a minimum supply pressure of a consumer without introducing heat into the cryogen, wherein the minimum supply pressure is below the critical pressure. In this context, the "minimum supply pressure" is understood to mean, in particular, a pressure below which trouble-free operation of the consumer can no longer be guaranteed.In this case, the supercritical state is preferably left and the cryogen is gaseous at the latest at the minimum supply pressure. For example, the consumer which must be supplied with the gaseous phase at a defined supply pressure and a defined supply temperature is assigned to the storage vessel. This latter supply pressure can be above the minimum supply pressure. The cryogen is expanded to a maximum of the minimum supply pressure. This makes it possible to empty the storage vessel as completely as possible. According to a further embodiment, the cryogen is converted into the gaseous phase when the pressure is expanded to the minimum supply pressure. Here, too, the two-phase region is not passed through. In particular, the cryogen is converted from the supercritical state into the gaseous phase when the pressure is expanded. A two-phase state of the cryogen is thus reliably prevented.According to a further embodiment, the density of the cryogen is reduced to the minimum supply pressure during the expansion. This reduction in density results from the fact that the cryogen continues to be removed from the storage vessel during the expansion. November 19, 2024 – Claudia Meilinger7 According to a further embodiment, the phase-change material undergoes a phase transition from solid to liquid when step c) is interrupted. An "interruption" of step c) is understood here to mean that the cryogen is no longer removed from the storage vessel unintentionally or unexpectedly. Normal operation of the storage vessel is thus irregularly or undesirably interrupted or terminated.In order to keep the introduction of heat from the environment into the storage container as low as possible, the phase change material undergoes a phase transition from solid to liquid, which in the process absorbs heat introduced into the storage container from the environment. According to a further embodiment, heat is extracted from a shield of the storage container during the phase transition from solid to liquid with the aid of the phase change material, wherein the shield encloses an inner container of the storage container, and wherein the cryogen is accommodated in the inner container. The latent heat storage device is in particular connected to the shield in a heat-conducting manner. The shield encloses or encloses the inner container. In particular, the shield is arranged between the inner container and the outer container of the storage container. The heat introduced into the storage container from the environment is introduced into the shield and transferred to the latent heat storage device.This prevents heat from being introduced into the inner container and thus into the cryogen. The holding time of the cryogen in the storage container can thereby be increased. "One" is not necessarily to be understood as limiting it to exactly one element. Rather, multiple elements, such as two, three, or more, can also be provided. Any other counting term used here should not be understood as implying a precise limitation to the corresponding number of elements. Rather, numerical deviations upwards and downwards are possible. 19.11.2024 – Claudia Meilinger8 Further possible implementations of the method also include combinations of features or embodiments not explicitly mentioned above or below with regard to the exemplary embodiments.In doing so, the person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the process. Further advantageous embodiments of the process are the subject of the dependent claims and the exemplary embodiments of the process described below. The process is explained in more detail below using preferred embodiments with reference to the accompanying figures. Fig. 1 shows a schematic sectional view of an embodiment of a storage container; Fig. 2 shows a pressure-density diagram of hydrogen stored in the storage container according to Fig. 1; Fig. 3 shows a schematic sectional view of the embodiment of the storage container from Fig. 1 with a latent heat storage device; Fig. 4 shows a schematic sectional view of an embodiment of a latent heat storage device for the storage container according to Fig. 3; and Fig.Figure 5 shows a schematic block diagram of an embodiment of a method for operating the storage container. In the figures, identical or functionally equivalent elements have been provided with the same reference numerals unless otherwise stated. Figure 1 shows a schematic sectional view of an embodiment of a storage container 1A. The storage container 1A can also be referred to as a storage tank. The storage container 1A is preferably suitable for holding hydrogen H2 (boiling point: 1 bara: 20.268 K = -252.882 °C). Therefore, the storage container 1A can also be referred to as a hydrogen storage container or a hydrogen storage tank. However, the storage container 1A can also be used for other cryogenic liquids.Examples of cryogenic fluids or liquids, or cryogens for short, in addition to the aforementioned hydrogen H2, include liquid helium He (boiling point at 1 bara: 4.222 K = -268.928 °C), liquid nitrogen N2 (boiling point at 1 bara: 77.35 K = -195.80 °C), or liquid oxygen O2 (boiling point at 1 bara: 90.18 K = -182.97 °C). In the following, it is assumed that hydrogen H2 is used as the cryogen. Accordingly, the terms "hydrogen" and "cryogen" can be interchanged arbitrarily. The storage container 1A can be a transport container. For example, liquid hydrogen LH2 can be transported using the storage container 1A. The storage container 1A can be part of a vehicle, in particular a watercraft. In this case, the storage container 1A is suitable for mobile applications. However, the storage tank 1A can also be used stationary, for example in building technology.The storage container 1A is constructed rotationally symmetrically to a symmetry or central axis 2. The central axis 2 is oriented perpendicular to a direction of gravity g. The storage container 1A comprises a first container or inner container 3, which is also constructed rotationally symmetrically to the central axis 2. The inner container 3 comprises a tubular or cylindrical base section 4, which is also constructed rotationally symmetrically to the central axis 2. The base section 4 can have a circular or approximately circular geometry in cross-section. The base section 4 is closed on both sides by means of a cover section 5, 6. The cover sections 5, 6 are curved. A first cover section 5 and a second cover section 6 are curved in opposite directions, so that the cover sections 5, 6 are curved outwards with respect to the base section 4. The inner container 3 is fluid-tight, in particular gas-tight.The inner container 3 is made of stainless steel. The inner container 3 contains the liquid hydrogen LH2. As long as the hydrogen H2 is in the two-phase region, a gas zone 7 with gaseous hydrogen GH2 and a liquid zone 8 with liquid hydrogen LH2 can be provided in the inner container 3. Thus, after being filled into the inner container 3, the hydrogen H2 can have two phases with different aggregate states, namely liquid and gaseous. This means that a phase boundary 9 is located in the inner container 3 between the liquid hydrogen LH2 and the gaseous hydrogen GH2. The gaseous hydrogen GH2 can also be referred to as the gaseous phase in the present case. Accordingly, the terms "gaseous hydrogen" and "gaseous phase" can be interchanged arbitrarily. The liquid hydrogen LH2 can also be referred to as the liquid phase in the present case.Accordingly, the terms "liquid hydrogen" and "liquid phase" can be interchanged arbitrarily in the present case. The inner container 3 is arranged entirely within a second container or outer container 10. The storage container 1A is thus double-walled. The outer container 10 is also constructed rotationally symmetrically to the central axis 2. The outer container 10, like the inner container 3, comprises a tubular or cylindrical base section 11, which is constructed rotationally symmetrically to the central axis 2. The base section 11 can have a circular or approximately circular geometry in cross-section. The base section 11 is closed at each end by a cover section 12, 13. In particular, a first cover section 12 and a second cover section 13 are provided. The cover sections 12, 13 are curved in opposite directions, so that the cover sections 12, 13 are curved outward relative to the base section 11.The outer container 10 is fluid-tight, in particular gas-tight. The outer container 10 is also made of stainless steel. A gap 14 that completely surrounds or encloses the inner container 3 is provided between the inner container 3 and the outer container 10. The gap 14 is subjected to a vacuum. A "vacuum" in this case is defined in particular as a pressure of less than 300 mbar, preferably less than 10. -3 mbar, more preferably less than 10 -7mbar. The storage container 1A is thus vacuum-insulated or vacuum-insulated. The fact that the gap 14 completely "encloses" or "envelops" the inner container 3 means, in this case, that the gap 14, on the one hand, completely surrounds the base section 4 and, on the other hand, is also provided between the two first lid sections 5, 12 and between the two second lid sections 6, 13. A thermal insulation element (not shown) that completely encloses or surrounds the inner container 3 is provided in the gap 14. This means that the insulation element encloses both the base section 4 and the lid sections 5, 6 of the inner container 3. The insulation element serves for thermal insulation. The insulation element is multi-layered. This means that the insulation element comprises a plurality of plies or layers.The insulation element can therefore also be referred to as a multi-layer insulation element or a multi-layer thermal insulation element. In particular, the insulation element is a so-called multilayer insulation (MLI). The outer container 10 borders an environment 15 of the storage container 1A. A withdrawal line 16 opens out of the liquid zone 8, with the aid of which liquid hydrogen LH2 can be withdrawn from the storage container 1A. The withdrawal line 16 leads to an evaporator 17, with the aid of which the liquid hydrogen LH2 can be evaporated to gaseous hydrogen GH2. The evaporator 17 can evaporate the liquid hydrogen LH2 electrically or with the aid of a heating medium. A valve 18 can be connected into the withdrawal line 16 between the storage container 1A and the evaporator 17. The withdrawal line 16 leads from the evaporator 17 to a consumer 19. The consumer 19 is preferably a fuel cell.A "fuel cell" is understood here to be a galvanic cell that converts the chemical reaction energy of a continuously supplied fuel, in this case gaseous hydrogen GH2, and an oxidizing agent, in this case oxygen, into electrical energy. With the help of the evaporator 17, the gaseous hydrogen GH2 can be made available to the consumer 19 at a suitable supply pressure and a suitable supply temperature. The storage container 1A further comprises a heating element 20. The heating element 20 is arranged in the liquid zone 8. With the help of the heating element 20, heat Q can be introduced into the liquid hydrogen LH2. The heating element 20 can be, for example, an electric heater or. Alternatively, the heating element 2019.11.2024 – Claudia Meilinger12 can introduce the heat Q into the liquid hydrogen LH2 with the help of a heat transfer medium.In this case, the heating element 20 can be a helium circuit, for example. With the help of the heating element 20, a pressure buildup or a pressure increase can be achieved within the inner container 3, in particular in the gas zone 7. The storage container 1A, the extraction line 16, the evaporator 17, and the valve 18 can form a gas supply device 21, in particular a hydrogen supply device, which is suitable for providing the consumer 19 with the gaseous hydrogen GH2 at the aforementioned supply pressure and supply temperature. The gas supply device 21 can have a control and regulation unit 22, which can control the evaporator 17, the valve 18, and / or the heating element 20. This control can be based on sensor signals from a sensor system 23.The sensor system 23 can, for example, comprise temperature and / or pressure sensors arranged in or on the inner container 3, the extraction line 16, the evaporator 17, the valve 18, and / or the consumer 19. Particularly in maritime applications, movement of the liquid hydrogen LH2 contained in the storage container 1A caused by sea waves must be expected. If the storage container 1A is arranged horizontally, as shown in Fig. 1, the inertia of the liquid hydrogen LH2 and the curvature of the storage container 1A caused by the horizontal installation promote extensive sloshing of the liquid hydrogen LH2 both on its cylindrical outer wall and at its ends.This sloshing, also known as sloshing, leads to the cooling of the gaseous hydrogen GH2 above the liquid hydrogen LH2, resulting in an abrupt pressure drop in the gas cushion of the gaseous hydrogen GH2 that has formed above the liquid hydrogen LH2. Depending on the current sea state, this can have adverse effects on the supply pressure available for the operating components of consumer 19, which can lead to unstable operation of consumer 19. 11 / 19 / 2024 – Claudia Meilinger13 In order to provide the supply pressure for consumer 19, it is possible, according to internal company knowledge, to use a liquid-cooled and liquid-bearing pump to pump the liquid hydrogen LH2. However, such a pump has moving parts.Furthermore, intermittent operation of the pump can lead to bubbles forming in the liquid hydrogen LH2 due to its heating. This can cause the pump to malfunction. Alternatively, the liquid hydrogen LH2 can also be first evaporated and then brought to the required supply pressure with the help of a compressor. However, this is energetically unfavorable. Furthermore, the storage tank 1A can also be operated directly at the supply pressure. In this case, an equilibrium is established in the storage tank 1A between the liquid zone 8 and the gas zone 7 layered above it. However, due to the low surface tension of liquid hydrogen LH2, movement of the storage tank 1A leads to the liquid hydrogen LH2 and the gaseous hydrogen GH2 mixing with one another, and the liquid hydrogen LH2 thus cools the warmer gaseous hydrogen GH2.Maintaining the supply pressure is then not possible until equilibrium is restored between the temperature of the liquid hydrogen LH2 and the gaseous hydrogen GH2. This needs to be improved. Figure 2 shows a pressure-density diagram of hydrogen H2 stored in the storage container 1A. Using this pressure-density diagram according to Figure 2, a method for operating, in particular for filling and emptying, the storage container 1A is explained below, in which the previously mentioned disadvantages do not occur or at least only occur to a reduced extent. In Figure 2, the density ϱ is plotted on the right-hand axis or abscissa axis and the pressure p is plotted on the vertical axis or ordinate axis. In Figure 2, a denotes the two-phase region in which the gaseous hydrogen GH2 and the liquid hydrogen LH2 are present simultaneously. This means that in the two-phase region a, the hydrogen H2 is two-phase. The supercritical region is denoted by b.The pure gas phase is designated c. The pure liquid phase is designated d.19.11.2024 – Claudia Meilinger14 In Figure 2, the two-phase line 24 with the critical point Pc is drawn. In thermodynamics, the critical point Pc is a thermodynamic state of a substance, in this case hydrogen H2, which is characterized by the equalization of the densities of the liquid phase and the gaseous phase. The differences between the two states of matter cease to exist at the critical point Pc. The hydrogen H2 is then in its supercritical state. At the critical point Pc, the hydrogen H2 has a critical pressure pc of 12.3 bara and a critical temperature Tc of -239.9 °C. A minimum supply pressure p2 for the consumer 19, for example, is approximately 6 bara.The "minimum supply pressure" in this case is understood to mean a pressure p below which trouble-free operation of the consumer 19 can no longer be guaranteed. The minimum supply pressure p2 can, for example, also be 7 bara, 5 bara, 4 bara, or 3 bara. Starting from a point A, the filling of the storage container 1A with liquid hydrogen LH2 begins below the critical pressure pc at an initial pressure p1 and a density ϱ1. During the filling of the storage container 1A, it is ensured that the storage container 1A, in particular the inner container 3, is filled to at least 95%, preferably to at least 98%, more preferably to at least 99%, more preferably to 100%. This means, in particular, that after the filling of the storage container 1A, preferably no gas zone 7 with gaseous hydrogen GH2 is provided in the inner container 3, but only the aforementioned liquid zone 8 with liquid hydrogen LH2.The storage container 1A, in particular the inner container 3, is completely filled up to a point B, as indicated by a filling line 25 running parallel to the abscissa axis. At point B, the liquid hydrogen LH2 still has the initial pressure p1. Furthermore, at point B, the liquid hydrogen LH2 has a density ϱ2 that is greater than the density ϱ1. Starting from point B, conditioning takes place up to a point C. The conditioning is indicated by a conditioning line 26 running parallel to the ordinate axis. This means that the density ϱ2 of the liquid hydrogen LH2 does not change during conditioning from point B to point C. 11 / 19 / 2024 - Claudia Meilinger15 Conditioning is carried out by increasing the pressure p from the initial pressure p1 to a higher operating pressure p3. The operating pressure p3 is higher than the critical pressure pc.Thus, a pressure build-up occurs from point B to point C. The pressure build-up is achieved by introducing heat Q into the liquid hydrogen LH2 with the aid of the heating element 20. However, due to the high or even complete filling level of the storage container 1A, in particular the inner container 3, with the liquid hydrogen LH2, only a very small supply of heat Q is required to quickly increase the pressure p from point B to point C or from the initial pressure p1 to the operating pressure p3. Once point C with the operating pressure p3 and the density ϱ2 is reached, the hydrogen H2 can be withdrawn, which is then evaporated with the aid of the evaporator 17 and supplied to the consumer 19. The withdrawal of the hydrogen H2 is indicated by a first withdrawal line 27, which runs parallel to the abscissa axis or the filling line 25.The hydrogen H2 is withdrawn up to a point D, whereby the operating pressure p3 does not change from point C to point D. At point D, the hydrogen H has a density ϱ3 which is lower than the density ϱ2 at point C. Point D lies in the supercritical region b. In order to keep the operating pressure p3 constantly above the critical pressure pc during the withdrawal of the hydrogen H2, heat Q continues to be supplied to the hydrogen H2 from point C to point D. During the withdrawal of the hydrogen H2, however, only so much heat Q is supplied to it that the operating pressure p3 remains at a constant level above the critical pressure pc even during the withdrawal. During the step from point C to point D, the process changes from the supercooled liquid state of the liquid hydrogen LH2 at point C to the supercritical fluid state of the hydrogen H2 at point D, without passing through the two-phase region a.From point D, the hydrogen H2 can finally be expanded without any input of heat Q to a point E at the minimum supply pressure p2, which is below the operating pressure p3 and below the critical pressure pc, and a density ϱ4 that is below the density ϱ3. 19.11.2024 - Claudia Meilinger16 This is indicated in Fig. 2 by a second extraction line 28, which runs diagonally to the first extraction line 27. The second extraction line 28 also does not run through the two-phase region a. Once point D is reached, at which a reduction in pressure p no longer leads to a crossing of the two-phase region a, the pressure can be expanded to the minimum supply pressure p2 below the critical pressure pc. At the same time, further input of heat Q is dispensed with. As soon as the hydrogen H2 falls below the critical pressure pc, the hydrogen H2 is no longer in supercritical form, but in gaseous form.The hydrogen H2 can be expanded to a maximum of the previously mentioned minimum supply pressure p2, at which stable operation of the consumer 19 can just be guaranteed. A very small residual amount of hydrogen H2 remains unused in the storage vessel 1A, in particular in the inner vessel 3. Because the operation of the storage vessel 1A is designed to avoid the formation of a two-phase state, fluctuations in the pressure p within the storage vessel 1A, in particular within the inner vessel 3, due to sloshing can be avoided and stable operation of the downstream consumer 19 can be ensured. Optimal utilization of a storage vessel volume is possible by filling the storage vessel 1A preferably with 100% liquid hydrogen LH2.Since the gaseous hydrogen GH2 is present at the minimum supply pressure p2 at point E, almost the entire amount of the tanked hydrogen H2 can be utilized. Due to the lack of a gas cushion, rapid conditioning to the operating pressure p3 is possible, since the storage vessel 1A is preferably 100% filled with liquid hydrogen LH2. Unlike in the two-phase region a, a small change in the enthalpy of the liquid hydrogen LH2 leads to a strong change in the pressure p in the storage vessel 1A. In other words, with a relatively small supply of heat Q, a rapid pressure increase from the initial pressure p1 to the operating pressure p3 can be achieved. Therefore, only a small amount of heat is required to keep the operating pressure p3 constant from point C to point D. The heating element 20 can be dimensioned accordingly small.19.11.2024 – Claudia Meilinger17 A sudden pressure drop within the storage vessel 1A due to the mixing of a supercooled liquid phase with a superheated gas phase – resulting from the aforementioned sloshing – is not to be feared, since a two-phase state of the hydrogen H2 can never develop at any time during the operation of the storage vessel 1A. By controllable conditions within the storage vessel 1A and the associated avoidance of sudden pressure fluctuations, reliable operation of the consumer 19 can be ensured even during movements of the storage vessel 1A, for example due to sea waves. Figure 3 shows a schematic sectional view of the storage vessel 1A from Figure 1 with a latent heat accumulator 33. A screen or shield 29, in particular a so-called soft shield, can be provided between the inner vessel 3 and the outer vessel 10. The shield 29 is thus placed in the gap 14.The shield 29 is preferably made of a material with good thermal conductivity, such as copper or aluminum. The shield 29 is preferably fluid-permeable, in particular gas-permeable. The shield 29 encloses or surrounds the inner container 3. The shield 29 preferably has a cylindrical base section 30 that is rotationally symmetrical to the central axis 2. The base section 30 is closed at the end by means of a first cover section 31 and a second cover section 32. The latent heat accumulator 33 is preferably placed within the shield 29. In the orientation of Fig. 3, the latent heat accumulator 33 is placed next to the inner container 3. In particular, the latent heat accumulator 33 is arranged between the cover sections 6, 13. The latent heat accumulator 33 is preferably filled at least in sections with a phase change material N2 (PCM), as will be explained below.The phase change material N2 is nitrogen in the present case. However, the phase change material N2 can also be argon, for example. It is assumed below that the phase change material N2 is nitrogen. Therefore, the phase change material N2 is referred to below as nitrogen. The latent heat accumulator 33 is preferably connected to the shield 29, in particular to the base section 30 of the shield 29, via a heat-conducting element 34 running around the central axis. The heat-conducting element 34 can be disc-shaped. A heat exchanger 35 can be arranged within the latent heat accumulator 33. The heat exchanger 35 is preferably thermally conductively connected to the extraction line 16, which opens into the inner container 3, is guided through the latent heat accumulator 33, and is guided through the shield 29 and the outer container 10.The heat exchanger 35 is connected in particular to the extraction line 16, so that the extraction line 16 can transfer heat Q to the heat exchanger 35 or vice versa. The heat exchanger 35 can be a metal plate, in particular an aluminum plate or a copper plate, welded or soldered to the extraction line 16. The heat exchanger 35 can also be constructed from several such metal plates. A blow-off line 36 with a blow-off valve 37 generally opens out of the latent heat accumulator 33. The blow-off line 36 can be routed within the shield 29. The blow-off line 36 can be thermally conductively connected to the shield 29. The blow-off line 36 can run helically or helically around the central axis 2 and be attached to the inside or outside of the shield 29. The blow-off valve 37 can release vaporized nitrogen N2 into the environment 15. Fig.4 shows a schematic sectional view of an embodiment of a latent heat accumulator 33 as mentioned above. The latent heat accumulator 33 functions as a thermal buffer for the storage container 1A. The latent heat accumulator 33 has a housing 38, which is connected to the shield 29 by means of the heat-conducting element 34. The blow-off line 36 leads out of the housing 38. The housing 38 encloses an interior space 39 in which the heat exchanger 35 is accommodated, which is in contact with solid nitrogen N2. The latent heat accumulator 33 can be completely or partially filled with the solid nitrogen N2. The interior space 39 is at least partially or completely filled with a highly heat-conducting knitted fabric 40. The knitted fabric 40 can be made of aluminum and / or copper threads. In particular, the knitted fabric 40 can be copper and / or aluminum wool. The knitted fabric 40 is connected to the heat exchanger 35 in a heat-conducting manner.The knitted fabric 40 is impregnated with nitrogen N2. The highly thermally conductive knitted fabric 40 ensures good heat transfer between the heat exchanger 35 and the solid nitrogen N2. Since the pressure p within the storage vessel 1A, as previously explained with reference to the storage vessel 1A, reacts very sensitively to the addition of heat Q, it can happen that, during the standby mode of the storage vessel 1A, due to an undesired introduction of heat Q from the environment 15, hydrogen H2 is released via a pressure relief device (not shown) in order to stabilize the pressure p. This leads to a reduced holding time of the hydrogen H2 and is therefore undesirable. For this reason, the storage vessel 1A has the latent heat storage device 33. The latent heat storage device 33 utilizes the enthalpy of fusion of nitrogen N2.In the event of a withdrawal stop, the latent heat storage device 33 minimizes the introduction of heat Q from the environment 15 to the hydrogen H2, which is accompanied by a low rate of pressure increase and thus an extension of the holding time. Optionally, a buffer tank for gaseous hydrogen GH2 can be integrated downstream of the evaporator 17 in order to further minimize pressure fluctuations. The functionality of the latent heat storage device 33 is explained below. During normal operation of the storage container 1A, an essentially constant withdrawal of liquid hydrogen LH2 from the inner container 3 takes place via the withdrawal line 16. When the liquid hydrogen LH2 is passed through the latent heat storage device 33, it extracts heat Q from the nitrogen N2 via the heat exchanger 35 and the knitted fabric 40. If the nitrogen N2 is liquid, it undergoes a phase transition from liquid to solid. In the process, the nitrogen N2 releases heat Q.In the event that the nitrogen N2 is already solid, it is kept in the solid state. This means that the nitrogen N2 stored in the latent heat storage device 33 is solid during normal operation of the storage container 1A. The latent heat storage device 33 is at least partially thermally separated from the inner container 3. If the liquid hydrogen LH2 is no longer extracted for a short time, the solid nitrogen N2 melts with a moderate increase in pressure in the latent heat storage device 33. As the solid nitrogen N2 melts, it extracts heat Q from the shield 29 via the heat-conducting element 34. Because the latent heat storage device 33 is connected to the shield 29 via the heat-conducting element 34, the shield 29 is cooled down.If the withdrawal of liquid hydrogen LH2 is subsequently resumed, a reverse phase transition of the nitrogen N2 from liquid to solid occurs, since the liquid hydrogen LH2 flowing through the withdrawal line 16 extracts heat Q from the liquid nitrogen N2. Thus, during normal operation of the storage vessel 1A, the system is closed. This means that during normal operation, no nitrogen N2 is vented via the vent line 36. If no more liquid hydrogen LH2 is withdrawn for an extended period of time, for example during standby operation of the storage vessel 1A, the solid nitrogen N2 melts, begins to boil, and ultimately evaporates. The gaseous nitrogen N2 can then be vented into the environment 15 via the vent line 36 and the vent valve 37.The vent line 36, as previously mentioned, can circulate helically around the shield 29, with the cold, gaseous nitrogen N2 further extracting heat Q from the shield 29. During normal operation, the phase transition of the nitrogen N2 from solid to liquid and vice versa prevents a loss of nitrogen N2 via the vent line 36 and the vent valve 37 and / or prevents an excessively high maximum permissible pressure within the latent heat storage device 33. The input of heat Q into the inner vessel 3 is significantly reduced by the shield 29, which is cooled by the nitrogen N2. This increases the holding time of the liquid hydrogen LH2. During normal operation of the storage vessel 1A, the latent heat storage device 33, together with the heat exchanger 35, thus forms a closed system in which a phase transition from solid to liquid alternately occurs.Only if no more liquid hydrogen LH2 is removed for an extended period of time does the nitrogen N2 evaporate and is released into the environment 15. Figure 5 shows a schematic block diagram of an embodiment of a method for operating the storage container 1A, 1A. In the method, in a step S1, the storage container 1A, 1A is filled with the liquid hydrogen LH2. During step S1, a filling level of the storage container 1A, 1A, in particular of the inner container 3, with the liquid hydrogen LH2 of more than 90%, preferably more than 95%, more preferably more than 96%, more preferably more than 97%, more preferably more than 98%, more preferably more than 99%, more preferably 100%, can be achieved. This means in particular that the storage container 1A, 1A, in particular the inner container 3, is filled with the liquid hydrogen LH2 in such a way that no gas zone 7 is formed in the inner container 3.Step S1 is carried out from point A to point B. During step S1, the density ϱ of the hydrogen H2 is increased. In step S1, the two-phase region a can be passed through. In a step S2, heat Q is introduced into the liquid hydrogen LH2, whereby a pressure increase from the initial pressure p1 to the operating pressure p3 is achieved within the storage container 1A, 1A. The operating pressure p3 is higher than the critical pressure pc of the hydrogen H2. During step S2, the density ϱ of the hydrogen H2 is kept constant. Step S2 can also be referred to as conditioning, conditioning step or conditioning process. The heat Q is introduced with the aid of the heating element 20. Step S2 is carried out from point B to point C. Point C lies in the liquid phase d. Point B can lie in the two-phase region a. However, this is not absolutely necessary.In a step S3, the hydrogen H2 is withdrawn from the storage container 1A, 1A, wherein heat Q is supplied to the hydrogen H2 so that the operating pressure p3 can always be kept above the critical pressure pc during step S3. During step S3, the density ϱ of the hydrogen H219.11.2024 – Claudia Meilinger22 is reduced. Step S3 is carried out from point C to point D. Point D lies in the supercritical region b. This means that the hydrogen H2 becomes supercritical during step S3. When point D is reached, after step S3, the hydrogen H2 is expanded to the minimum supply pressure p2 without introducing heat Q into the hydrogen H2, wherein the minimum supply pressure p2 can be below the critical pressure pc. The supercritical region b is left again and the hydrogen H2 becomes gaseous.Liquid hydrogen LH2 is not present at this time, so that no phase boundary 9 exists. The expansion takes place up to point E to the minimum supply pressure p2. During the expansion, the density ϱ of the hydrogen H2 is reduced. During step S3, the phase change material accommodated in the latent heat storage 33 of the storage container 1A, here nitrogen N2, undergoes a phase transition from liquid to solid by transferring heat Q from the phase change material to the cryogen, here the hydrogen H2. Alternatively, the phase change material, here the nitrogen N2, remains solid during step S3. After an irregular or undesired interruption of step S3, the phase change material can now undergo a phase transition from solid to liquid. This means in particular that the phase change material, here the nitrogen N2, melts. In the process, the phase change material absorbs heat Q.With the help of the phase-change material (nitrogen N2), heat Q can be extracted from the shield 29 during the phase transition from solid to liquid. This allows the inner container 3 to be protected from the ingress of heat Q. Although the present invention has been described using exemplary embodiments, it is versatile and can be modified. 19.11.2024 - Claudia Meilinger23 Reference numerals used: 1A Storage container 2 Central axis 3 Inner container 4 Base section 5 Lid section 6 Lid section. 7 Gaszone 8 Liquid zone 9 Phase boundary 10 Outer container 11 Base section 12 Lid section 13 Lid section 14 Spalt 15 Environment16 Extraction line17 Evaporator 18 Ventil 19 Consumer20 Heating element21 Gas supply device22 Control unit23 Sensors24 Two-phase line25 Filling line26 Conditioning line27 Withdrawal line28 Withdrawal line 29 Schild30 Base section 31 Cover section 32 Cover section 33 Latent heat storage 19.11.2024 – Claudia Meilinger 24 34 Heat conducting element 35 Heat exchanger 36 Blow-off line 37 Blow-off valve 38 Housing 39 Interior 40 Knitted two-phase area A Punkt b supercritical region B Punkt c Gas phase C Punkt d liquid phase D Punkt E Punkt g Gravity directionGH2 Gaseous hydrogen / gaseous phase H2 Hydrogen / cryogen LH2 Liquid hydrogen / liquid phase N2 Nitrogen / phase change material p Druck pc critical pressurePc critical pointp1 outlet pressurep2 supply pressurep3 operating pressure Q Wärme S1 Step S2 Step S3 Step ϱ Dichte ϱ1 Dichte ϱ2 Dichte November 19, 2024 – Claudia Meilinger25 ϱ3 Dichte ϱ4 Dichte

Claims

19. 11.2024 – Claudia Meilinger26 patent claims 1. Method for operating a storage container (1A) for a cryogen (H2), in particular for hydrogen, wherein the cryogen (H2) can be converted from a liquid phase (LH2) into a gaseous phase (GH2) and vice versa by means of phase transitions, with the following steps: a) filling (S1) the storage container (1A) with the liquid phase (LH2), b) introducing (S2) heat (Q) into the liquid phase (LH2), whereby a pressure increase from an initial pressure (p1) to an operating pressure (p3) is achieved within the storage container (1A), wherein the operating pressure (p3) is higher than the critical pressure (pc) of the cryogen (H2), and c) removing (S3) the cryogen (H2) from the storage container (1A), wherein heat (Q) is supplied to the cryogen (H2) whereby the operating pressure (p3) is always kept above the critical pressure (pc) during step c), characterized in thatthat during step c) a phase change material (N2) accommodated in a latent heat storage device (33) of the storage container (1A) undergoes a phase transition from liquid to solid by transferring heat (Q) from the phase change material (N2) to the cryogen (H2), or wherein the phase change material (N2) remains solid during step c).

2. The method according to claim 1, wherein during step a) a filling level of the storage container (1A, 1A) with the liquid phase (LH2) of more than 90%, preferably more than 95%, more preferably more than 96%, more preferably more than 97%, more preferably more than 98%, more preferably more than 99%, more preferably 100%, is achieved.

3. The method according to claim 1 or 2, wherein during step c) the cryogen (H2) becomes supercritical.

4. A method according to any one of claims 1-3, wherein during step a) the density (ϱ) of the cryogen (H2) is increased,wherein during step b) the density (ϱ) of the cryogen (H2) is kept constant, and wherein during step c) the density (ϱ) of the cryogen (H2) is reduced., November 19, 2024 - Claudia Meilinger27 5. The method according to any one of claims 1-4, wherein after step c), the cryogen (H2) is expanded to a minimum supply pressure (p2) of a consumer (19) without introducing heat (Q) into the cryogen (H2), and wherein the minimum supply pressure (p2) is below the critical pressure (pc).

6. The method according to claim 5, wherein the cryogen (H2) is converted into the gaseous phase (GH2) during the expansion to the minimum supply pressure (p2).

7. The method according to claim 5 or 6, wherein the density (ϱ) of the cryogen (H2) is reduced during the expansion to the minimum supply pressure (p2).

8. The method according to any one of claims 1 to 7, wherein upon interruption of step c), the phase-change material (N2) undergoes a phase transition from solid to liquid.Method according to one of claims 1 to 8, wherein heat (Q) is extracted from a shield (29) of the storage container (1A) with the aid of the phase change material (N2) during the phase transition from solid to liquid, wherein the shield (29) encloses an inner container (3) of the storage container (1A), and wherein the cryogen (H2) is accommodated in the inner container (3).

Images