Method for refilling a hydrogen tank

Abstract

Proposed is a method for refilling a hydrogen tank (2A), in particular of a vehicle (2), with a gas, in particular hydrogen, having the steps of: filling a first hydrogen store (4) with the gas; filling a working fluid store (7) with a working fluid; connecting the first hydrogen store (4) to the hydrogen tank (4) such that gas is transferred from the first hydrogen store (4) into the hydrogen tank (2A); connecting the working fluid store (7) to the first hydrogen store (4) such that working fluid (8) is transferred from the working fluid store (7) into the first hydrogen store (4); and cooling the gas in the first hydrogen store (4) by isentropic expansion before the working fluid (8) is transferred from the working fluid store (7) into the first hydrogen store (4), such that gas that has been cooled as a result of the isentropic expansion is transferred from the first hydrogen store (4) into the hydrogen tank (2A).

Description

[0001]Method for refueling a hydrogen tank The invention relates to a method for refueling a hydrogen tank, in particular a vehicle, with hydrogen, comprising the steps of: providing a first hydrogen storage device with a hydrogen volume filled with hydrogen, providing a working fluid storage device with a working fluid, connecting the first hydrogen storage device to the hydrogen tank so that hydrogen is transferred from the first hydrogen storage device into the hydrogen tank in a first outflow phase, and connecting the working fluid storage device to the first hydrogen storage device so that working fluid is transferred from the working fluid storage device into the first hydrogen storage device in a first post-compression phase overlapping in time with the first outflow phase, whereby the hydrogen volume filled with hydrogen in the first hydrogen storage device is reduced and a working fluid volume filled with working fluid in the first hydrogen storage deviceis enlarged. Furthermore, the invention relates to a refueling system, in particular a mobile refueling system, for refueling a hydrogen tank, in particular of a vehicle, with hydrogen, comprising: a first hydrogen storage device containing the hydrogen, a working fluid storage device containing a working fluid, a control device, in particular with a valve control, for controlling a first discharge connection for discharging hydrogen from the first hydrogen storage device to the hydrogen tank and for controlling a first inlet connection between the working fluid storage device and the first hydrogen storage device, a pump with which working fluid is pumped from the working fluid storage device to the first hydrogen storage device. Finally, the invention relates to a tank vehicle with such a preferably mobile, i.e., non-stationary, refueling system. WO 2021 / 191636 A1 discloses a method which is suitable for transferring and coolinga compressed gas. A fuel gas, in particular hydrogen (see paragraph 28), is transferred from a source container to a receiving container. Cooling takes place in an intermediate container. The source container is connected to the intermediate container via a first fluid path, wherein the fluid connection can be interrupted via a valve in order to isolate the intermediate container. The intermediate container contains a positive displacement expander, which can be formed by a fluid column, a piston compressor, or another component responsible for expanding the fluid located there. The intermediate container is connected to the receiving container, which can be the fuel tank of a vehicle or machine, via a second fluid path, wherein the fluid connection can also be interrupted via a valve. The transfer and cooling of the fuel gas is carried out in three steps in this prior art.phases. In the first phase, the source vessel is brought into fluid communication with the intermediate vessel, which is completely filled with fluid at this point, by opening the valve. The fuel gas now flows into the intermediate vessel and displaces the fluid, which leaves the intermediate vessel via a valve. During the first phase, the pressure in the source vessel and the intermediate vessel is essentially the same. Due to the expansion of the fuel gas into the intermediate vessel, the fuel gas in the source vessel and the intermediate vessel cools down. As soon as a sufficient amount of fuel gas has been transferred to the intermediate vessel, the inlet valve is closed to separate the intermediate vessel from the source vessel. In the second phase, all of the fluid is withdrawn from the intermediate vessel via a valve. This causes isentropic expansion, which cools the fuel gas. In the third phase, a valve is opened tocontainer and the receiving container in fluid communication with each other. Since the same pressure prevails in the intermediate container and the receiving container, it is necessary to force the cooled fuel into the receiving container by introducing fluid into the intermediate container. During this phase, the hydrogen is no longer cooled. This method therefore differs from the invention described below. In the invention described below, the hydrogen is cooled during the transfer of hydrogen from the first hydrogen storage device to the hydrogen tank, depending on the design, before and / or during the recompression phase, in which working fluid is pumped from the working fluid storage device into the first hydrogen storage device. According to the invention, the cooling can occur through the partial pressure equalization between the first hydrogen storage device and the hydrogen tank. Depending on the design, the cooling can also occur during the recompression phase.be continued. In WO 2021 / 191636 A1, however, the hydrogen is cooled exclusively before being transferred to the receiving container. According to WO 2021 / 191636 A1, no cooling takes place during the transfer of the hydrogen to the receiving container. According to the invention, the working fluid is not used for the expansion of the hydrogen, but for recompression in the first hydrogen storage device. Furthermore, the invention preferably does not provide an intermediate container. DE 102015 016327 A1 describes a filling station for filling storage containers in mobile vehicles with a gas, in particular with hydrogen. The hydrogen is stored in one or more constant-pressure accumulators, with which the gas is made available at a specific, constant pressure. For this purpose, the constant-pressure accumulator has a cylinder which is divided into two areas by a movable separating piston. The first area receives theHydrogen. The second area holds a liquid, for example a hydraulic fluid. During the storage phase, the pressure of the hydrogen in the first area is kept constant by moving the separating piston, whereby the first area is enlarged and the second area is reduced. During the discharge phase, the volume of the first area is reduced by pumping more liquid into the second area and the volume of the second area is increased so that the pressure in the first area is kept constant. This design is intended to reduce the number of load changes and thereby increase the service life of the filling station. A disadvantage of this state of the art, however, is that a complex gas conditioning unit is required to prepare the gas from the constant pressure storage for the consumer. In practice, it has been shown in particular that the temperature of the gas from theConstant pressure storage had to be lowered with a refrigeration machine in order not to exceed the maximum permitted temperature of the vehicle tank. The object of the present invention is to alleviate or eliminate at least some of the disadvantages of the prior art. The invention preferably aims to create a method for refueling a hydrogen tank, with which overheating of the hydrogen tank is prevented with the least possible equipment expenditure. This object is achieved by a method according to claim 1, a refueling system according to claim 12 and a refueling vehicle according to claim 15. Preferred embodiments are specified in the dependent claims. According to the invention, the method comprises the following step: Cooling the hydrogen in the first hydrogen storage device by isentropic expansion before the recompression phase and / or during the recompression phase, so that by the isentropic expansioncooled hydrogen is transferred from the first hydrogen storage unit to the hydrogen tank. When the first hydrogen storage unit is connected to the hydrogen tank, in particular by opening a first gas outlet valve, hydrogen flows from the first hydrogen storage unit into the hydrogen tank due to the pressure difference between the first hydrogen storage unit and the hydrogen tank. In the process, a (partial) pressure equalization takes place between the first hydrogen storage unit and the hydrogen tank. By feeding the working fluid, which is different from hydrogen, from the working fluid storage unit into the first hydrogen storage unit over the duration of the recompression phase, the hydrogen in the first hydrogen storage unit is recompressed. As a result, the mass flow of hydrogen from the first hydrogen storage unit into the hydrogen tank is determined exclusively by the pressure difference compared to a free overflow of the hydrogen.between the first hydrogen storage device and the hydrogen tank. Unlike the prior art, however, the first hydrogen storage device is not operated as a constant-pressure storage device, but rather the gas pressure of the hydrogen in the first hydrogen storage device is reduced before the recompression phase and / or during the recompression phase, preferably over the entire duration of the recompression phase. The hydrogen tank heats up due to the pressure increase during refueling with hydrogen. In the prior art with refueling via constant-pressure storage devices, it was only possible to avoid exceeding the maximum temperature of the vehicle tank, which can be between 80°C and 115°C, through special measures, in particular a refrigeration machine. In contrast, the method according to the invention cools the hydrogen in the first hydrogen storage device by at least partially isentropic expansion of the hydrogen in the first hydrogen storage device.This results in hydrogen cooled by isentropic expansion being increasingly transferred from the first hydrogen storage device to the hydrogen tank after refueling begins. This has the advantageous effect that the tank temperature increases less sharply over the refueling cycle. The invention therefore utilizes the isentropic expansion of the hydrogen in the first hydrogen storage device in order to be able to maintain the maximum temperature of the vehicle tank at the end of refueling. In a first embodiment, the connection between the working fluid storage device and the first hydrogen storage device is opened substantially simultaneously with the connection between the first hydrogen storage device and the hydrogen tank. In this embodiment, the first post-compression phase begins substantially simultaneously with the first outflow phase, in which the hydrogen flows from the first hydrogen storage device into the hydrogen tank.However, the pump's volumetric delivery capacity is not sufficient to maintain the pressure in the first hydrogen storage tank, so that partially isentropically expanded hydrogen is transferred from the first hydrogen storage tank into the hydrogen tank during the recompression phase. The first recompression phase can end before, simultaneously with, or after the end of the first discharge phase (i.e., before, simultaneously with, or after the connection between the first hydrogen storage tank and the hydrogen tank is closed). In a particularly preferred embodiment, the first discharge phase begins before the first recompression phase, i.e., the connection between the working fluid storage tank and the first hydrogen storage tank is only opened after a waiting period from the beginning of the first discharge phase. Thus, the cooling of the hydrogen in the first hydrogen storage tank by isentropic expansion begins before the transfer of the working fluid from the working fluid storage tank into thefirst hydrogen storage. By observing the waiting time before opening a first inlet connection to the working fluid storage, various effects can be achieved. Even a waiting time of at least 5 seconds (s), in particular of at least 10 seconds, for example of at least 20 seconds, alleviates or eliminates the problem that the first outlet connection, for example a pipeline, between the first hydrogen storage and the hydrogen tank has a thermal capacity and must first be cooled down, which is caused by the escaping hydrogen. To maximize the effect of the pressure ratio between the first hydrogen storage and the hydrogen tank, it is advantageous to start the first recompression phase first (i.e., to start the pump and reduce the pressure drop by displacing the hydrogen in the first hydrogen storage with working fluid, thereby maintaining the absolute temperature difference between thehydrogen in the first hydrogen storage tank and the hydrogen in the hydrogen tank) if the first storage connection has been pre-cooled. With a longer waiting time of at least 30 seconds, in particular of at least 60 seconds, the cooling effect due to the pressure difference between the first hydrogen storage tank and the hydrogen tank can be utilized even more effectively. In these embodiments, the hydrogen in the first hydrogen storage tank is cooled due to isentropic expansion even before the start of the first post-compression phase, so that cooled hydrogen flows from the first hydrogen storage tank into the hydrogen tank. This cooling effect counteracts the heating caused by the pressure increase in the hydrogen tank. After the waiting time has elapsed, the working fluid is pumped into the first hydrogen storage tank, which is designed as a pressure reservoir, whereby the hydrogen volume available for the hydrogen in the first hydrogen storage tankis reduced. In this case, the volumetric delivery capacity of the (high-pressure) pump is not sufficient to maintain the pressure in the first hydrogen storage device. In a preferred embodiment, the first discharge connection is closed, preferably with further flow of working fluid into the first hydrogen storage device, as soon as the vehicle tank and the first hydrogen storage device have equalized their pressures to a pressure difference preferably selected from a range of 20 bar to 200 bar, preferably 30 bar to 100 bar, in particular 40 bar to 70 bar, so that the first discharge phase from the first hydrogen storage device is terminated. The subsequent supply of the cooled gas counteracts the temperature increase in the hydrogen tank, which results from the pressure increase during refueling with the gas. Advantageously, the final temperature of the hydrogen tank can thus be reduced at the end of the refueling process. It is particularly advantageous if the final temperature of theHydrogen tanks can be kept below a predetermined maximum temperature without the need for additional cooling of the gas flowing out of the first hydrogen storage device (or from the second or third hydrogen storage device described below). This eliminates the need for a refrigeration machine between the first hydrogen storage device and the hydrogen tank. Thus, preferably, no refrigeration machine is connected between the first hydrogen storage device and the hydrogen tank (and optionally also no refrigeration machine between the second hydrogen storage device and the hydrogen tank or between the third hydrogen storage device and the hydrogen tank, see below). For the purposes of this disclosure, "hydrogen" always refers to molecular hydrogen (H2). With the method according to the invention, in particular, the hydrogen tank of a vehicle with a fuel cell, for example, a construction vehicle such as an excavator, can be fueled with hydrogen.When opening the first inlet connection to the working fluid reservoir after the waiting time has elapsed, the gas remaining in the first hydrogen reservoir can have a temperature of less than minus 20 degrees Celsius (°C), in particular less than minus 30 degrees Celsius, for example less than minus 35 °C. Preferably, the initial pressure of the hydrogen in the first hydrogen reservoir, i.e. the nominal pressure of the hydrogen before opening the first outlet connection to the hydrogen tank, is more than 500 bar, preferably more than 600 bar, in particular more than 700 bar and / or less than 875 bar, for example substantially 800 bar. The same preferably also applies to the second or third hydrogen reservoir described below. In practice, a polytropic expansion of the hydrogen takes place in the first hydrogen reservoir (and of course also in the second or third hydrogen reservoir described below). If in thisWhen the description refers to isentropic expansion, the isentropic component of the polytropic expansion due to the opening of the first discharge connection from the first (to nth) hydrogen storage to the hydrogen tank is to be understood. In a preferred embodiment, when the first discharge connection is open, the gas is pumped from the first pressure accumulator to the hydrogen tank solely due to the pressure difference between the first hydrogen storage and the hydrogen tank, i.e., passively, without an additional compressor. In the refueling system according to the invention, the control device is configured to control the first inlet connection and / or the pump such that hydrogen in the first hydrogen storage is cooled by isentropic expansion and hydrogen cooled by the isentropic expansion is discharged from the first hydrogen storage via the first discharge connection into the hydrogen tank. In a preferred embodiment,The control device is configured to open the first inlet connection after a waiting time has elapsed from the connection of the first hydrogen storage device to the hydrogen tank. In order to give the gas in the first pressure storage device sufficient time for isentropic expansion, in a preferred embodiment with the control device, a waiting time of at least 5 seconds, in particular at least 10 seconds, preferably at least 15 seconds, is maintained from the time the first hydrogen storage device is connected to the hydrogen tank until the time the working fluid storage device is connected to the first hydrogen storage device. With this embodiment, the first outlet connection can be cooled by utilizing the maximum pressure difference between the first hydrogen storage device and the hydrogen tank. In order to ensure that hydrogen is discharged from the first hydrogen storage device into the hydrogen tank in a more isentropically cooled state, theWaiting time may be at least 30 seconds, in particular at least 60 seconds. Depending on the design, the waiting time may be less than 15 minutes, in particular less than 10 minutes, preferably less than 5 minutes. In a preferred embodiment, the working fluid in the first hydrogen storage device is in direct contact with the hydrogen. The working fluid is therefore designed as a liquid piston. The working fluid therefore forms a liquid volume inside the first hydrogen storage device, in particular a liquid column, which borders the hydrogen directly, i.e. without any intermediate machine components, in particular without a solid piston. By further feeding working fluid into the first hydrogen storage device, the working fluid volume occupied by the working fluid inside the first hydrogen storage device is increased and the hydrogen volume occupied by the hydrogen is reduced, which is accompanied by a corresponding increase in the hydrogen pressure.A polyalphaolefin is preferably used as the working fluid. The use of a polyalphaolefin (PAO) as the working fluid is surprising, as it achieves particular advantages without having to accept the disadvantages typical of PAO. Practical tests have shown that a particular advantage of PAO for the inventive application is its low viscosity. This can, for example, avoid the problem that gases released into the fluid due to pressure changes lead to foaming of the fluid upon re-expansion. Such foaming could, for example, increase the tendency to cavitation in a pump supplying the working fluid, thereby increasing pump wear. When refueling the vehicle with hydrogen, the foaming of the working fluid could also cause fluid to be carried over into the hydrogen tank, which, however, should be avoided. In the prior art, highly viscous working fluids were used.Working fluids, such as ionic liquids, have been proposed, which have a high foaming tendency, which should be compensated by very low gas solubility. In practice, however, the required low gas solubility has not been achieved. Other working fluids such as mineral oils, synthetic oils, and hydraulic oils are so viscous that foam formation would make their use in the applications according to the invention very disadvantageous or even impossible. On the other hand, thermal oils, due to their tendency to carry over, are unsuitable for use in systems that provide hydrogen for fuel cell-powered vehicles. The inventive use of PAO is based on the finding that the low foaming tendency of PAO can reliably prevent foam formation without requiring extremely low gas solubility. In the applications according to the invention, the low foaming of PAO can be optimally utilized., even if the gas solubility of the PAO is quite low in absolute terms, but higher than that of ionic liquids. A "polyalphaolefin" is understood to mean a poly-1-olefin produced by polymerizing alpha-olefins. The term "polyalphaolefin" encompasses polyalphaolefin homopolymers, polymers composed of two or more different monomer units (e.g., polyalphaolefin copolymers, polyalphaolefin terpolymers), and mixtures thereof. The working fluid preferably comprises the polyalphaolefin in an amount of 80 wt% or more, more preferably 90 wt% or more, even more preferably 95 wt% or more, particularly preferably 99 wt% or more, based on the total weight of the working fluid. This allows the positive properties of the polyalphaolefin with regard to low gas solubility and low foaming tendency to be effectively utilized. Depending on the design, the working fluid can comprise exactly one polyalphaolefin. In aIn a preferred embodiment, the working fluid comprises a mixture of two or more polyalphaolefins. The physical properties of the working fluid (e.g., viscosity, boiling point) can then be adapted to the respective conditions. The polyalphaolefin can have a straight or branched chain structure (n-alkane or isoalkane). A mixture of a straight polyalphaolefin and an isomer of the same polyalphaolefin or of a polyalphaolefin with a different number of carbon atoms can also be used. This allows the boiling point of the working fluid to be adjusted. In a preferred embodiment, at least 90% by weight of the polyalphaolefin has 19 or fewer carbon atoms per molecule, preferably 14 to 18 carbon atoms per molecule, particularly preferably 16 to 18 carbon atoms per molecule, based on the total weight of the polyalphaolefin. Preferably, at least 95% by weight of thePolyalphaolefins have such a number of carbon atoms, more preferably at least 99% by weight, based on the total weight of the polyalphaolefin. Polyalphaolefins with such a number of carbon atoms have particularly low gas solubility and a particularly low foaming tendency, making them particularly suitable as a working fluid. If the working fluid comprises two or more polyalphaolefins, preferably all polyalphaolefins have such a number of carbon atoms. Preferably, a maximum of 10% by weight of the polyalphaolefin has 20 or more carbon atoms, in particular 20 to 30 carbon atoms, based on the total weight of the polyalphaolefin. Preferably, a maximum of 5% by weight of the polyalphaolefin has such a number of carbon atoms, more preferably a maximum of 3% by weight, based on the total weight of the polyalphaolefin. This allows the viscosity to be kept low, which is associated with a low foaming tendency. The working fluid haspreferably a proportion of an aromatic hydrocarbon of a maximum of 1 wt%, preferably a maximum of 0.5 wt%, based on the total weight of the working fluid. This also allows the viscosity and consequently the foaming tendency to be kept low. The proportion of a sulfur compound in the working fluid is preferably a maximum of 10,000 ppm, more preferably a maximum of 1,000 ppm, based on the total weight of the working fluid. This can in particular prevent an effect as a cell poison in vehicles with fuel cell drive. In a preferred embodiment, the hydrogen in the first hydrogen storage unit is at a nominal pressure, also referred to as the initial pressure, before being connected to the hydrogen tank. The nominal pressure is preferably more than 500 bar, preferably more than 600 bar, in particular more than 700 bar, and / or less than 875 bar, for example substantially 800 bar. At the end of the refueling process, the hydrogen can beconnecting the first (and / or the second or third described below) hydrogen storage device to the working fluid storage device, the hydrogen can be substantially recompressed to the nominal pressure. To achieve high filling pressures in the hydrogen tank by sequentially refueling the hydrogen tank via multiple hydrogen storage devices, the method in a preferred embodiment also comprises the following steps: providing a second hydrogen storage device with a second hydrogen volume filled with hydrogen, connecting the second hydrogen storage device to the hydrogen tank, preferably with the first discharge connection closed, so that hydrogen is transferred from the second hydrogen storage device to the hydrogen tank in a second discharge phase, feeding working fluid into the second hydrogen storage device in a second recompression phase, preferably by connecting the second hydrogen storage device to the first hydrogen storage device, andTransferring working fluid from the first hydrogen storage device to the second hydrogen storage device, so that the hydrogen in the second hydrogen storage device is cooled by isentropic expansion before the second post-compression phase and / or during the second post-compression phase, and hydrogen cooled by the isentropic expansion is transferred from the second hydrogen storage device to the hydrogen tank. The connection between the second hydrogen storage device and the hydrogen tank is preferably opened 1 to 20, in particular 2 to 10, for example essentially four, minutes after the first hydrogen storage device is connected to the hydrogen tank, so that hydrogen is discharged from the second hydrogen storage device via a second discharge connection in the direction of the hydrogen tank. To achieve even higher filling pressures by sequentially refueling the hydrogen tank via several hydrogen storage devices, the method in a preferredEmbodiment also comprises the following steps: providing a third hydrogen storage device with a third hydrogen volume filled with hydrogen, connecting the third hydrogen storage device to the hydrogen tank, preferably in the closed state of the first and second discharge connection, so that hydrogen is transferred from the third hydrogen storage device into the hydrogen tank in a third discharge phase, feeding working fluid into the third hydrogen storage device in a third post-compression phase, preferably by connecting the third hydrogen storage device to the second hydrogen storage device and transferring working fluid from the second hydrogen storage device into the third hydrogen storage device, so that the hydrogen in the third hydrogen storage device is cooled by isentropic expansion before the third post-compression phase and / or during the third post-compression phase, and hydrogen cooled by the isentropic expansion is transferred from the thirdHydrogen storage is transferred into the hydrogen tank. The connection between the third hydrogen storage and the hydrogen tank is preferably opened 1 to 20, in particular 2 to 10, for example essentially four, minutes after the second hydrogen storage is connected to the hydrogen tank, so that hydrogen is discharged from the third hydrogen storage via a third discharge connection in the direction of the hydrogen tank. In order to achieve effective recompression of the hydrogen in the respective hydrogen storage, the working fluid is pumped, in a preferred embodiment, with the aid of a high-pressure pump, in particular an axial piston pump, a radial piston pump, a gear pump or a positive displacement piston pump, in particular a plunger piston pump, from the working fluid storage to the first hydrogen storage, preferably also from the first hydrogen storage to the second hydrogen storage and / or from the second hydrogen storage to thethird hydrogen storage and / or from the third hydrogen storage to the working fluid storage. With the aforementioned designs of the high-pressure pump for the working fluid, high hydrogen pressures of more than 500 bar, in particular more than 600 bar, preferably more than 700 bar and / or a maximum of 875 bar, for example, substantially 800 bar, can be achieved in the respective hydrogen storage. The pump is preferably coupled to a drive, in particular to a drive motor. The drive provides the drive power with which the high-pressure pump is operated in order to pump the working fluid under pressure into the first hydrogen storage, preferably also into the second hydrogen storage, and in particular also into the third hydrogen storage. In a particularly preferred embodiment, the drive is coupled to a hydraulic connection of the vehicle, so that the drive is operated via the hydraulic connection of the vehicle.Thus, the drive power for the drive can be provided by the vehicle, which has a hydraulic connection for providing hydraulic fluid, preferably at a pressure of 50 to 420, in particular 100 to 300 bar, for example 150 to 250 bar. Such hydraulic connections are found, for example, in construction vehicles. Advantageously, the vehicle to be refueled can thus itself provide the drive power for operating the high-pressure pump. This allows the refueling system itself to be simplified or made smaller. This advantage is particularly significant for a mobile refueling system, preferably as part of a tanker vehicle. For continuous operation of the high-pressure pump via a hydraulic circuit, it is advantageous if the drive is connected to the vehicle's hydraulic connection via a bidirectional hydraulic coupling, so that hydraulic fluid under high pressure is supplied to the drive.is supplied and hydraulic fluid is returned under low pressure from the drive to the vehicle's hydraulic connection. In a preferred embodiment, the hydrogen in the hydrogen tank is compressed during refueling to a filling pressure of more than 500 bar, in particular more than 600 bar, preferably more than 650 bar, preferably up to 875 bar. All pressure specifications in this disclosure refer to an ambient temperature of 288.15 Kelvin. As described above in connection with the method for refueling the hydrogen tank, in a preferred embodiment of the refueling system, a second hydrogen storage device is provided, which can be connected to the hydrogen tank via a second discharge connection. An embodiment with a third hydrogen storage device, which can be connected to the hydrogen tank via a third discharge connection, is particularly preferred. The second and / or the third hydrogen storage device are preferablyidentical to the first hydrogen storage device. The first and / or the second and / or the third hydrogen storage device can have a capacity of 50 to 1000 liters (l), in particular of 200 to 500 l, for example, essentially 400 l. When fully filled, 5 to 130 kilograms (kg) of hydrogen, for example, essentially 20 kg of hydrogen, can be stored in the first, second, or third hydrogen storage device. In order to be able to release and block the gas and working fluid flows described above at different times, the refueling system, in a preferred embodiment, has: a first gas outlet valve in the first discharge connection, and / or a second gas outlet valve in the second discharge connection, and / or a third gas outlet valve in the third discharge connection, and / or a first inlet valve in the first inlet connection from the working fluid storage device to the first hydrogen storage device,and / or a second inlet valve in the second inlet connection from the working fluid reservoir to the second hydrogen reservoir, and / or a third inlet valve in the third inlet connection from the working fluid reservoir to the third hydrogen reservoir, and / or a first gas inlet valve for filling the first pressure reservoir with the hydrogen, and / or a second gas inlet valve for filling the second pressure reservoir with the hydrogen, and / or a third gas inlet valve for filling the third pressure reservoir with the hydrogen, and / or a first return valve in a first return line from the first hydrogen reservoir to the second hydrogen reservoir for transferring working fluid from the first hydrogen reservoir to the second hydrogen reservoir, and / or a second return valve in a second return line from the second hydrogen reservoir to the third hydrogen reservoir for transferring working fluid from the second hydrogen reservoir to the thirdHydrogen storage, and / or a third return valve in a third return line from the third hydrogen storage to the working fluid storage for returning working fluid from the third hydrogen storage to the working fluid storage. In a preferred embodiment, the refueling system has an axial piston pump, a radial piston pump, a gear pump, or a positive displacement piston pump, in particular a plunger piston pump, as a high-pressure pump, with which working fluid can be pumped from the working fluid storage to the first hydrogen storage, preferably also from the first hydrogen storage to the second hydrogen storage and / or from the second hydrogen storage to the third hydrogen storage and / or from the third hydrogen storage to the working fluid storage. In a preferred embodiment of the refueling system, the high-pressure pump is coupled to a drive. The drive is preferably coupled to a hydraulic connection of the vehicle. As a result,The drive can be operated, i.e., supplied with drive power, via the vehicle's hydraulic connection. In a preferred embodiment of the refueling system, the drive is connected to the vehicle's hydraulic connection via a bidirectional hydraulic coupling. This allows hydraulic fluid to be supplied to the drive under high pressure, and hydraulic fluid to be returned from the drive to the vehicle's hydraulic connection under low pressure. According to the invention, a refueling vehicle is also provided with a cargo space in which a mobile refueling system in one of the embodiments described above is accommodated. In a preferred embodiment, a hydrogen vehicle, in particular a fuel cell vehicle, is provided as the refueling vehicle, which has a hydrogen vehicle tank, with which the energy for the refueling vehicle's movement is provided. It is particularly advantageous if theThe hydrogen vehicle tank of the refueling vehicle is connected to the first hydrogen storage device, and optionally also to the second and / or third hydrogen storage device, via a fluid line, in particular one provided with an openable and closable valve. Thus, the range of the refueling vehicle can be increased by transferring hydrogen from the first, and optionally from the second or third, hydrogen storage device into the hydrogen vehicle tank of the refueling vehicle. In this embodiment, the refueling vehicle can supply itself with hydrogen as needed. At the site of use, however, another vehicle can be refueled with hydrogen using the refueling vehicle. The invention is explained in more detail below using a preferred embodiment in the drawings. Fig. 1 schematically shows a mobile refueling system for refueling a hydrogen tank of a vehicle. Figs. 2 to 5 show various steps of aMethod for refueling the hydrogen tank, wherein individual inactive gas and working fluid lines have been hidden for the sake of clarity. Fig. 6 schematically shows several characteristic curves of the method for refueling the hydrogen tank. Fig. 1 schematically shows a refueling system 1 for refueling a hydrogen tank 2A ​​(symbolically shown in Fig. 1) of a vehicle 2 with hydrogen. The vehicle 2 to be refueled can have a fuel cell 2B which is operated with the hydrogen from the hydrogen tank 2A. Fig. 1 shows a mobile version of the refueling system 1 which can be carried in the cargo space of a refueling vehicle 3 (different from the vehicle 2 to be refueled). The mobile refueling system 1 has a first hydrogen storage unit 4, a second hydrogen storage unit 5 and a third hydrogen storage unit 6, which are each filled with hydrogen, i.e. have a first, second and third hydrogen volume respectively.In addition, the refueling system 1 has a working fluid reservoir 7, which is filled with a working fluid 8, here polyalphaolefin. The first 4, second 5, and third hydrogen reservoirs 6, as well as the working fluid reservoir 7, are arranged essentially vertically (i.e., their longitudinal axes extend in the vertical direction). All location and direction information in this disclosure refers to the intended operating state of the refueling system 1 in the cargo space of the tank vehicle 3 on a horizontal surface. The fill level of the working fluid reservoir 7 is monitored by a fill level measuring element 9. The pressure and temperature of the working fluid reservoir 7 are monitored by a pressure and temperature measuring element 10. The first hydrogen reservoir 4 is connected to a gas inlet 12 via a first storage connection 11. The second hydrogen reservoir 5 is connected to the gas inlet 12 via a second storage connection 13. The thirdHydrogen storage 6 is connected to the gas inlet 12 via a third storage connection 14. The first storage connection 11 has a first gas inlet valve 15, the second storage connection 13 has a second gas inlet valve 16, and the third storage connection 14 has a third gas inlet valve 17. When the first 15, the second 16, or the third gas inlet valve 17 is open, gas provided at the gas inlet 12 is transferred to the first 4, second 5, or third hydrogen storage 6, so that hydrogen is stored in the first 4, second 5, and third hydrogen storage 6 at a nominal pressure of, for example, substantially 800 bar. The first 4, second 5 or third hydrogen storage 6 can be connected via a first 18, second 19 or third discharge connection 20 to a gas outlet 21, to which the vehicle 2 to be refueled can be connected. In the first 18, second 19 or thirdA first 22, second 23, and third gas outlet valve 24 are arranged at the discharge connection 20. The first 18, second 19, and third discharge connection 20 are combined in a common outlet line 25, in which a temperature measuring element 26 for measuring the gas temperature and a gas pressure measuring element 27 for measuring the gas pressure are arranged. The outlet line 25 is connected to the gas outlet 21 via a fuse 28, a gas line 29, and a tank coupling 30. The working fluid reservoir 7 has a supply line 51 with a supply valve 52, which is connected to the first hydrogen reservoir 4 via a first inlet connection 31, to the second hydrogen reservoir 5 via a second inlet connection 32, and to the third hydrogen reservoir 6 via a third inlet connection 33. The first 31, second 32 and third inlet connection 33 each open into the bottom of the first 4, second 5 and third hydrogen storage 6, respectively, sothat the first 4, second 5 or third hydrogen storage unit 6 is filled with working fluid 8 from below. A first 34, second 35 or third inlet valve 36 as well as a first 37, second 38 or third inlet check valve 39 are arranged in the first 31, second 32 or third inlet connection 33. The first hydrogen storage unit 4 is connected via a first return line 40 with a first return valve 41 to the second inlet connection 32, by means of which the second hydrogen storage unit 5 is supplied with working fluid. The second hydrogen storage unit 5 is connected via a second return line 42 with a second return valve 43 to the third inlet connection 33, by means of which the third hydrogen storage unit 6 is supplied with working fluid. The third hydrogen storage 6 is connected via a third return line 44 with a third return valve 45 with a return line 53, which is parallel to theSupply line 51 runs. A return valve 54 and an orifice 55 are arranged in the return line 53. The return line 53 leads back to the working fluid reservoir 7, so that working fluid 8 can be returned from the third hydrogen reservoir 6 to the working fluid reservoir 7. In the embodiment shown, the refueling system 1 has a (high-pressure) pump 46, which can be designed in particular as an axial piston pump, radial piston pump, gear pump, or plunger piston pump. This high-pressure pump 46 serves to pump the working fluid from the working fluid reservoir 7 to the first hydrogen reservoir 4, from the first hydrogen reservoir 4 to the second hydrogen reservoir 5, from the second hydrogen reservoir 5 to the third hydrogen reservoir 6, and from the third hydrogen reservoir 6 back to the working fluid reservoir 7. The high-pressure pump 46 is connected to a drive 47. In the embodiment shown, the drive 47 is connected to a hydraulic connection 48 of the vehicle 2connected. A feed hose 50 is connected to the drive 47 via a bidirectional hydraulic coupling 49. If hydraulic fluid is fed through the drive 47, the drive 47 converts the volume flow into mechanical work and in turn drives the high-pressure pump 46. The hydraulic flow, released after work has been performed, is transferred via a return hose 51 to the bidirectional hydraulic coupling 49 and finally to the hydraulic connection 48. The valves described above can be magnetically, hydraulically, or pneumatically actuated, i.e., in particular, transferred between an open and a closed position. Pneumatic actuation of the valves is particularly preferred. In this embodiment, an air compressor 56 can be provided, which supplies the supply air for switching the pneumatically actuated valves. An electrical unit 57 allows the storage and release of electrical energy to and from the drive 47 and theCompressed air compressor 56. The refueling system 1 also has an (electronic) control device 58, with which the valves described above can be controlled, in particular opened and closed. The control device 58 has a timer 59 (described in more detail below). With this refueling system 1, the vehicle 2 can be refueled with compressed gas, here hydrogen, as follows. At least the following steps are carried out. In a first step, the first 4, second 5 and third hydrogen storage units 6 are filled with the gas via the gas inlet 12. In a further step, the refueling vehicle 3 with the refueling system 1 is brought to the site where the vehicle 2 to be refueled, for example an excavator, is parked. In a further step, the vehicle 2 is connected to the refueling system 1 via the tank coupling 30. In a further step, the drive 47 is connected via the hydraulic connection 48 or the electrical unit57 is supplied with energy. In a further step, the first hydrogen storage unit 4 is connected to the gas outlet 21 by opening the first gas outlet valve 22 by means of the control device 58, whereby hydrogen is transferred into the hydrogen tank of the vehicle 2 in a first outflow phase. Due to the isentropic component of the expansion in the first hydrogen storage unit 4, the hydrogen transferred into the vehicle 2 cools down. With the timer 59 of the control device 58, a waiting time from the opening of the first gas outlet valve 22 can be recorded, so that a first recompression phase by pumping working fluid 8 from the working fluid storage unit 7 into the first hydrogen storage unit 4 by means of the high-pressure pump 46 only begins after the start of the first outflow phase. Depending on the design, the first recompression and the first outflow phase can overlap with each other in a time period selected from a range of 5 seconds to 4 minutes. BeforeOnce pressure equalization is achieved between the first hydrogen storage 4 and the vehicle 2 at the gas outlet 21, the valves are switched by the control device 58 such that the first discharge connection 18 is shut off. Working fluid 8 can be fed into the first hydrogen storage 4 for a certain time (in particular until the start of the second discharge phase, see below) via the high-pressure pump 46 from the working fluid storage 7. In a further step, the second hydrogen storage 5 is connected to the gas outlet 21 by opening the second gas outlet valve 23 by means of the control device 58, so that a second discharge phase begins. With the timer 59 of the control device 58, a second waiting time can be maintained from the opening of the second gas outlet valve 23, so that a second recompression phase by pumping working fluid 8 into the second hydrogen storage 5 by means of the high-pressure pump 46 only begins after the start of the secondThe discharge phase begins. Depending on the design, the second recompression and the second discharge phase can overlap with each other for a period of time selected from a range of 5 seconds to 4 minutes. Before pressure equalization is achieved between the second hydrogen storage unit 5 and the vehicle 2 at the gas outlet 21, the valves are switched by means of the control device 58 such that the second discharge connection 19 is shut off. Working fluid 8 can be fed from the first hydrogen storage unit 4 into the second hydrogen storage unit 5 for a certain time (in particular until the start of the third discharge phase, see below) via the high-pressure pump 46. In a further step, the third hydrogen storage unit 6 is connected to the gas outlet 21 by opening the third gas outlet valve 24 by means of the control device 58, so that a third discharge phase begins. A third waiting period fromthe opening of the third gas outlet valve 24, so that a third recompression phase by pumping working fluid 8 into the third hydrogen storage device 6 by means of the high-pressure pump 46 only begins after the start of the third outflow phase. Depending on the design, the third recompression and the third outflow phase can overlap with each other in a time duration selected from a range of 5 seconds to 4 minutes. Before pressure equalization between the third hydrogen storage device 6 and the vehicle 2 at the gas outlet 21 is achieved, the valves are switched by means of the control device 58 such that the third discharge connection 20 is closed. In a further step, see Fig. 5, the valves can be switched by means of the control device 58 such that working fluid 8 is returned from the third hydrogen storage device 6 to the working fluid storage device 7. Finally, by replenishing the working fluid 8, the nominal orInitial pressure in the first 4 and / or second 5 and / or third hydrogen storage 6 can be restored. Fig. 6 shows a diagram with several characteristic curves in which the effect of the method described above is symbolically illustrated. A first characteristic curve 60 shows the mass flow of hydrogen in g / s. A second characteristic curve 61 shows the filling pressure of the hydrogen tank 2A ​​in barA. A third characteristic curve 62 shows the temperature of the hydrogen tank 2A ​​in °C. At the beginning of the first outflow phase, the temperature in the hydrogen tank 2A ​​rises rapidly until the temperature reaches a first (local) maximum. Then, the cooling effect through the isentropic expansion of the hydrogen takes effect, which is particularly pronounced in the first outflow phase due to the high pressure difference between the inertial pressure of the first hydrogen storage 6 and the low initial pressure of the hydrogen tank 2A. In the second outflow phase and in the third outflow phase,Significantly lower cooling occurs due to the isentropic expansion of the hydrogen. It is important that the temperature in the hydrogen tank 2A ​​does not rise (quasi-)continuously during the refueling process, but rather that cooling occurs temporarily due to the isentropic expansion of the hydrogen, which contributes to maintaining the specified maximum temperature of the hydrogen in the hydrogen tank 2A, for example, 110°C. Reference numbers: 1 refueling system 2 vehicle 2A hydrogen tank 2B fuel cell 3 tank vehicle 4 first hydrogen storage 5 second hydrogen storage 6 third hydrogen storage 7 working fluid storage 8 working fluid 9 level measuring element 10 temperature measuring element 11 first injection connection 12 gas inlet 13 second injection connection 14 third injection connection 15 first gas inlet valve 16 second gas inlet valve 17 third gas inlet valve 18 first discharge connection 19 second discharge connection 20 thirdDischarge connection 21 Gas outlet 22 First gas outlet valve 23 Second gas outlet valve 24 Third gas outlet valve 25 Common outlet line 26 Temperature measuring element 27 Gas pressure measuring element 28 Breakaway device 29 Gas line 30 Tank coupling 31 First inlet connection 32 Second inlet connection 33 Third inlet connection 34 First inlet valve 35 Second inlet valve 36 Third inlet valve First inlet check valve Second inlet check valve Third inlet check valve First return line First return valve Second return line Second return valve Third return line Third return valve High pressure pump Drive Hydraulic connection Hydraulic coupling Supply hose Supply line Supply valve Return line Return valve Orifice Air compressor Electrical unit Electronic control device Timer

Claims

Claims:

1. A method for refueling a hydrogen tank (2A), in particular a vehicle (2), with hydrogen, comprising the steps of: providing a first hydrogen reservoir (4) with a hydrogen volume filled with hydrogen, providing a working fluid reservoir (7) with a working fluid, connecting the first hydrogen reservoir (4) to the hydrogen tank (4) so that hydrogen is transferred from the first hydrogen reservoir (4) into the hydrogen tank (2A) in an outflow phase, and connecting the working fluid reservoir (7) to the first hydrogen reservoir (4) so that working fluid (8) is pumped from the working fluid reservoir (7) into the first hydrogen reservoir (4) in a post-compression phase overlapping the outflow phase, whereby the hydrogen volume filled with hydrogen in the first hydrogen reservoir (4) is reduced,characterized by cooling the hydrogen in the first hydrogen storage device (4) by isentropic expansion before the post-compression phase and / or during the post-compression phase, so that hydrogen cooled by the isentropic expansion is transferred from the first hydrogen storage device (4) to the hydrogen tank (2A).

2. The method according to claim 1, characterized in that a waiting time of at least 30 seconds, preferably at least 60 seconds, in particular at least 2 minutes, for example at least 3 minutes, is observed from the connection of the first hydrogen storage device (4) to the hydrogen tank (2A) until the connection of the working fluid storage device (7) to the first hydrogen storage device (4).

3. The method according to claim 1 or 2, characterized in that the working fluid in the first hydrogen storage device (4) is in direct contact with the gas.

4. The method according to claim 3, characterized inthat a polyalphaolefin is used as the working fluid., 5. Method according to one of claims 1 to 4, characterized in that the hydrogen in the first hydrogen storage device (4) is present at a nominal pressure of more than 500 bar, preferably more than 600 bar, in particular more than 700 bar and / or less than 875 bar, for example substantially 800 bar, before being connected to the hydrogen tank (2A).Method according to one of claims 1 to 5, characterized by: providing a second hydrogen storage device (5) with a hydrogen volume filled with hydrogen, connecting the second hydrogen storage device (5) to the hydrogen tank so that hydrogen is transferred from the second hydrogen storage device (5) into the hydrogen tank (2A) in a second outflow phase, feeding working fluid into the second hydrogen storage device (5) in a second post-compression phase overlapping in time with the second outflow phase, preferably by connecting the second hydrogen storage device (5) to the first hydrogen storage device (4), so that the hydrogen in the second hydrogen storage device (5) is cooled by isentropic expansion before the second post-compression phase and / or during the second post-compression phase, and hydrogen cooled by the isentropic expansion is transferred from the second hydrogen storage device (5) to the hydrogen tank (2A). 7.Method according to claim 6, characterized by: providing a third hydrogen storage device (6) with a hydrogen volume filled with hydrogen, connecting the third hydrogen storage device (6) to the hydrogen tank (2A) so that hydrogen is transferred from the third hydrogen storage device (6) into the hydrogen tank (2A) in a third outflow phase, feeding working fluid into the third hydrogen storage device (6) in a third post-compression phase which overlaps in time with the third outflow phase, preferably by connecting the third hydrogen storage device (6) to the second hydrogen storage device, so that the hydrogen in the third hydrogen storage device (6) is expanded by isentropic expansion before the third post-compression phase and / or during the third. post-compression phase, and hydrogen cooled by isentropic expansion is transferred from the third hydrogen storage device (6) to the hydrogen tank (2A).

8. The method according to one of claims 1 to 7, characterized in that the working fluid (8) is pumped from the working fluid storage device (7) to the first hydrogen storage device (4), preferably also from the first hydrogen storage device (4) to the second hydrogen storage device (5) and / or from the second hydrogen storage device (5) to the third hydrogen storage device (6) and / or from the third hydrogen storage device (6) to the working fluid storage device (7) by means of a high-pressure pump (46), in particular an axial piston pump, a radial piston pump, a gear pump, or a positive displacement piston pump, in particular a plunger piston pump.

9. The method according to claim 8, characterized in that the high-pressure pump (46) is coupled to a drive (47).Method according to claim 9, characterized in that the drive (47) is coupled to a hydraulic connection (48) of the vehicle (2), so that the drive (47) is operated via the hydraulic connection (48) of the vehicle (2).

11. Method according to claim 10, characterized in that the drive (47) is connected to the hydraulic connection (48) of the vehicle (2) via a bidirectional hydraulic coupling (49), so that hydraulic fluid is supplied to the drive (47) under high pressure and hydraulic fluid is returned from the drive (47) to the hydraulic connection (48) of the vehicle (2) under low pressure.Refuelling system (1), in particular a mobile refueling system, for refueling a hydrogen tank (2A), in particular of a vehicle (2), with hydrogen, comprising: a first hydrogen reservoir (4) which contains the hydrogen, a working fluid reservoir (7) which contains a working fluid (8), a control device (58), in particular with a valve control, for controlling a first discharge connection (18). for discharging hydrogen from the first hydrogen storage device (4) to the hydrogen tank (2A) and for controlling a first inlet connection (31) between the working fluid storage device (7) and the first hydrogen storage device (4), a pump (46) with which working fluid can be pumped from the working fluid storage device (7) to the first hydrogen storage device (4), characterized in that the control device (58) is designed to control the first inlet connection (31) and / or the pump (46) such that hydrogen in the first hydrogen storage device (4) is cooled by isentropic expansion and hydrogen cooled by the isentropic expansion is discharged from the first hydrogen storage device (4) via the first discharge connection (18) into the hydrogen tank (2A). 13.Fuelling system (1) according to claim 12, characterized by: a second hydrogen storage (5) which can be connected to the hydrogen tank (2A) via a second discharge connection (19), preferably a third hydrogen storage (6) which can be connected to the hydrogen tank (2A) via a third discharge connection (20).

14. Refueling system (1) according to claim 12 or 13, characterized by a first gas outlet valve (22) in the first discharge connection (18), and / or a second gas outlet valve (23) in the second discharge connection (19), and / or a third gas outlet valve (24) in the third discharge connection (20), and / or a first inlet valve (34) in the first inlet connection (2) from the working fluid reservoir (7) to the first hydrogen reservoir (4), and / or a second inlet valve (35) in the second inlet connection (32) from the working fluid reservoir (7) to the second hydrogen reservoir (5) and / or. a third inlet valve (36) in the third inlet connection (33) from the working fluid reservoir (7) to the third hydrogen reservoir, and / or a first gas inlet valve (15) for filling the first pressure reservoir (4) with hydrogen, and / or a second gas inlet valve (16) for filling the second pressure reservoir (5) with hydrogen, and / or a third gas inlet valve (17) for filling the third pressure reservoir (6) with hydrogen, and / or a first return valve (41) in a first return line (40) from the first hydrogen reservoir (4) to the second hydrogen reservoir (5) for transferring working fluid (8) from the first hydrogen reservoir (4) to the second hydrogen reservoir (5), and / or a second return valve (43) in a second return line (42) from the second hydrogen reservoir (5) to the third hydrogen reservoir (6) for transferring working fluid (8) from the second Hydrogen storage (5) into the third hydrogen storage (6),and / or a third return valve (45) in a third return line (44) from the third hydrogen storage device (6) to the working fluid storage device (7) for returning working fluid (8) from the third hydrogen storage device (6) to the working fluid storage device (7).

15. A refueling vehicle (3) with a cargo space in which the mobile refueling system (1) according to claim 13 or 14 is accommodated, wherein the refueling vehicle (3) preferably has a vehicle tank connected via a fluid line to the first hydrogen storage device (4), preferably also via at least one further fluid line to the second hydrogen storage device (5) and / or the third hydrogen storage device (6).

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