FUEL CELL SYSTEM WITH A STORAGE DEVICE FOR STORING LIQUID HYDROGEN

Abstract

The invention relates to a fuel cell system (300) with a storage system (200) which includes a storage device (100) for storing liquid hydrogen. The storage device (100) has an outer pressure vessel (110) and an inner pressure vessel (120) configured to store the liquid hydrogen. A first fluid line (145) for supplying liquid hydrogen and a second fluid line (160) for removing liquid hydrogen are provided.Additionally, a pipeline (150) is provided, extending from outside the outer pressure vessel (110) into the inner pressure vessel (120) and reaching a bottom area within the inner pressure vessel (120). This pipeline is designed to be fluidically connected to a suction device (210) located outside the storage device (100) in order to suction condensed impurities (125) from the bottom area of ​​the inner pressure vessel (120) via the pipeline (150). The storage system (200) includes a suction device (210) connected to the pipeline (150) of the storage device (100). The fuel cell system (300) includes a control device configured to initiate a suction process when the fuel cell stack (310) is not in operation.

Description

[0001] The present invention relates to a fuel cell system with a storage system comprising a storage device for storing liquid hydrogen and an electrically driven system.

[0002] Several types of fuel cells are known, for example, those with a polymer electrolyte membrane (PEM) fuel cell, to which hydrogen is supplied as fuel. A fuel cell consists of electrodes, an anode, and a cathode, between which an electrolyte, in particular in the form of a proton-conducting membrane, is arranged. These components form a so-called membrane electrode assembly (MEA).

[0003] The hydrogen required for the fuel cell can be stored as liquid hydrogen (LH2) in a suitable tank, particularly a cryogenic tank, and supplied to the fuel cell as gaseous hydrogen as needed for operation. Storing hydrogen in liquid form allows for more hydrogen to be stored per unit volume than in gaseous form. However, hydrogen only condenses at very low temperatures (-252 °C or -21 K). Therefore, technically suitable cryogenic tanks are required for storing liquid hydrogen.

[0004] Liquid hydrogen can contain impurities that, when used in its gaseous state, can damage fuel cells or impair their performance. These impurities or harmful gases include sulfur dioxide (SO2), ammonia (NH3), carbon dioxide (CO2), carbon monoxide (CO), ozone (O3), and methane (CH4).

[0005] A thermal separation of gases is known for the purification of hydrogen, in which the different melting and / or boiling points of these gases and the hydrogen are used for separation. The hydrogen can be passed through a suitably cooled device along with these gases, where the gases then condense according to their respective boiling and / or condensation temperatures, whereas the hydrogen remains gaseous because it has a lower condensation temperature compared to the other gases.

[0006] This requires a separate device in which the harmful gases and the hydrogen should be cooled at least to the point where the harmful gases can be separated from the hydrogen, as well as a fluid piping system that transports the liquid hydrogen from an LH2 tank to the device and then to the fuel cell, or from the device to the LH2 tank and from there as a gas to the fuel cell.

[0007] US 2022 / 0146047A1 discloses a device for storing and supplying liquid fuel, comprising a tank for liquefied fuel gas balanced with a gas phase, in particular a hydrogen gas phase, a circuit for filling the tank, at least one circuit for extracting liquid from the tank, at least one circuit for controlling the pressure in the tank, wherein the circuits for filling, extracting and pressure control include a valve arrangement located in a housing separate from the tank.

[0008] DE 693 08 355 T2 discloses a method and a device for transferring volatile liquids, in particular liquefied gases, from a container to a pump. The present invention is based on the objective of providing a device that enables improved, and in particular simplified, separation of harmful gases from hydrogen.

[0009] A solution to this problem is achieved according to the teaching of the independent claims. Various embodiments and further developments of the invention are the subject of the dependent claims.

[0010] A first aspect of the solution concerns a fuel cell system comprising a storage system. The storage system includes a storage device, in particular a cryogenic tank, for storing liquid hydrogen. The storage device comprises the following: an outer pressure vessel; an inner pressure vessel arranged inside the outer pressure vessel, in which the liquid hydrogen can be stored; a vacuum chamber is formed between the inner pressure vessel and the outer pressure vessel; a first fluid line through which liquid hydrogen can be supplied from outside the outer pressure vessel to the inner pressure vessel; and a second fluid line through which liquid hydrogen can be discharged from the inner pressure vessel to the outside of the outer pressure vessel.a pipeline extending from outside the outer pressure vessel into the inner pressure vessel and into a bottom area within the inner pressure vessel, wherein the pipeline can be fluidically connected to a suction device arranged outside the storage device, such that condensed impurities can be suctioned from the bottom area of ​​the inner pressure vessel via the pipeline.

[0011] The storage device in the fuel cell system, as described in the first aspect, allows for the extraction of condensed impurities from the bottom of the inner pressure vessel during operation (i.e., when the inner pressure vessel is filled with liquid hydrogen). This is achieved by a pipe extending into the bottom of the inner pressure vessel, which can be connected to an extraction system. Extracting these condensed impurities purifies the liquid hydrogen. The first fluid line then allows the liquid hydrogen to be discharged from the inner pressure vessel to the outside of the outer pressure vessel for use in an application, such as via a vaporizer to a fuel cell.Purified liquid hydrogen can prevent potential damage caused by impurities in the respective application, particularly in a fuel cell. Furthermore, the efficiency of the fuel cell can be increased because the impurities are not present in the total volume of fuel supplied to the fuel cell, resulting in a higher overall hydrogen content for the same volume. Additionally, the present storage device can be configured to both store liquid hydrogen and extract impurities, thus purifying the liquid hydrogen. Therefore, a single compact storage device with both of these functions cannot be achieved.

[0012] The storage system also features a suction device connected to the storage device's piping. This allows condensed impurities to be extracted from the storage device's inner pressure vessel, particularly from the bottom of the vessel. This purifies the hydrogen of these impurities.

[0013] The fuel cell system further comprises: a fuel cell stack; an evaporator; the second fluid line of the storage device being fluidically connected to the evaporator; and a fourth fluid line through which the evaporator is fluidically connected to the fuel cell stack. This allows liquid hydrogen from the internal pressure vessel of the storage device to be supplied to the evaporator via the second fluid line of the storage device. The hydrogen converted to gaseous form in the evaporator can then be supplied to the fuel cell stack via the fourth fluid line. This enables the supply of liquid hydrogen, previously purified of impurities, from the storage device to a fuel cell stack of a fuel cell system via an evaporator.

[0014] The fuel cell system has a control unit that is configured to initiate and control a suction process for removing condensed impurities through the storage system's suction device, depending on a predefined criterion being met. This enables automated suction when the criterion is fulfilled.

[0015] The control unit is configured to start the extraction process when the criterion that the fuel cell stack is not in operation is met. This enables automated extraction while simultaneously ensuring that the fuel cell stack is not in operation during extraction.

[0016] Any terms used herein, such as "comprises," "includes," "includes," "features," "has," "with," or any other variant thereof, are intended to cover non-exclusive inclusion. For example, a method or apparatus that includes or features a list of elements is not necessarily limited to those elements but may include other elements not expressly listed or inherent in such method or apparatus.

[0017] Furthermore, unless explicitly stated otherwise, "or" refers to an inclusive "or" and not an exclusive "or". For example, a condition A or B is satisfied by one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).

[0018] The terms "ein" or "eine," as used here, are defined as "one or more." The terms "ein anderer" and "ein Weitere," as well as any other variant thereof, are to be understood as "at least one more."

[0019] The term "plural", as used here, is to be understood in the sense of "two or more".

[0020] The terms "configured" or "set up" to perform a specific function (and their respective variations), as used here, mean that the device in question is already in a configuration or setting in which it can perform the function, or at least that it is adjustable—i.e., configurable—so that it can perform the function after appropriate adjustment. Configuration can be achieved, for example, by adjusting parameters of a process sequence or by using switches or similar devices to activate or deactivate functionalities or settings. In particular, the device can have several predefined configurations or operating modes, allowing configuration to be performed by selecting one of these configurations or operating modes.

[0021] The term "fuel cell," as used here, refers specifically to a device in which chemical energy is directly converted into electrical energy through an electrochemical reaction of a fuel with an oxidant. For this purpose, an electrolyte layer may be provided between two layers acting as electrodes within the fuel cell. This electrolyte layer is, for example, a polymer electrolyte membrane (PEM), which must be moist during operation to conduct protons. At an electrode designated as the anode, a fuel, such as hydrogen, is dissociated. The resulting protons can diffuse through the PEM to the electrode used as the cathode and react there with an oxygen atom of the oxidant that has been reduced by the cathode, forming water (formally: 2H₂). + + ½O2 → H2O).

[0022] The term "vacuum," as used here, refers specifically to a gas pressure in a closed volume that is below atmospheric pressure of 1013 hPa under standard conditions. In particular, this vacuum can be a so-called rough vacuum with a gas pressure of 1013 hPa to 100 Pa, a so-called fine vacuum with a gas pressure between 100 Pa and 100 mPa, or a high vacuum with a gas pressure of 100 mPa to 0.1 µPa.

[0023] Preferred embodiments of the fuel cell system are described below, which, unless expressly excluded or technically impossible, can be combined with each other and with the other aspects described.

[0024] In some embodiments, the pipeline extends from the bottom area through the inner pressure vessel to an opposite side of the bottom area and from this opposite side out of the storage device. In an inner pressure vessel filled with liquid hydrogen, an area opposite its bottom may be free of liquid hydrogen. This may occur because the inner pressure vessel was not completely filled with liquid hydrogen, or because some of the liquid hydrogen has evaporated into gaseous hydrogen in the meantime. In this case, the pipeline on the opposite side may prevent liquid hydrogen from exerting force in the same direction as any extraction, which could make it more difficult to separate the impurities to be extracted from the liquid hydrogen.

[0025] In some embodiments, the base area has a concave shape. This allows for a collection effect of the condensed contaminants within this concave area. This enables more effective extraction of the contaminants, as they can collect in a smaller area compared to a solution without a concave shape.

[0026] In some embodiments, the inner pressure vessel is designed as an elongated hollow body, in particular cylindrical or cuboid, and the bottom region is formed on one end face of the inner pressure vessel. This can be advantageous if the storage device is installed vertically during operation, since this end face then has the bottom region where the contaminants can collect.

[0027] In some embodiments, the inner pressure vessel is designed as an elongated hollow body, in particular cylindrical or cuboid, and the bottom region is formed on one longitudinal side of the inner pressure vessel. This can be advantageous if the storage device is installed in a transverse direction during operation, since this longitudinal side then has the bottom region where the contaminants can collect.

[0028] In some embodiments, the storage device has a third fluid line designed to discharge gaseous hydrogen from the inner pressure vessel to the outside of the outer pressure vessel. This allows the discharged gaseous hydrogen to be supplied to a fuel cell for its operation. This eliminates the need, at least temporarily, for an evaporator to vaporize the liquid hydrogen.

[0029] In some embodiments, the inner pressure vessel has a level sensor configured to detect the liquid hydrogen level within the vessel. This allows the system to determine whether liquid hydrogen should be added to the inner pressure vessel via a first fluid line when the level falls below a predetermined value. Furthermore, the level reading can be used to determine whether the volume of gaseous hydrogen present in the inner pressure vessel is sufficient to operate a fuel cell, with the gaseous hydrogen being supplied to the fuel cell via a third fluid line.

[0030] A second aspect of the solution concerns an electrically powered system, comprising a fuel cell system according to the first aspect.

[0031] In some embodiments, the electrically driven system is designed as a motor vehicle, emergency power generator or energy supply system.

[0032] The features and advantages explained in relation to the first aspect of the solution also apply to the other aspects described.

[0033] Further advantages, features and application possibilities will result from the following description of preferred embodiments in connection with the figure.

[0034] The figure schematically shows a hydrogen tank 100, a hydrogen tank system 200 and a fuel cell system 300 according to one embodiment.

[0035] The hydrogen tank system 200 includes the hydrogen tank 100 and a suction pump 210.

[0036] The fuel cell system 300 has a fuel cell stack 310 and a control unit 320, which is connected to the hydrogen tank system 200 and the fuel cell stack 310 via signal technology.

[0037] The hydrogen tank 100 comprises an outer pressure vessel 110 and an inner pressure vessel 120, the inner pressure vessel 120 being arranged inside and spaced apart from the outer pressure vessel 110. The inner pressure vessel 120 and the outer pressure vessel are connected to each other by means of a plurality of spaced-apart crossbeams and are also spaced apart from each other by the crossbeams. The inner pressure vessel 120 is suitable for storing liquid hydrogen.

[0038] A vacuum-controlled space 115 is formed between the inner pressure vessel 120 and the outer pressure vessel 110. This provides thermal insulation of the liquid hydrogen stored in the inner pressure vessel 120 from a region outside the outer pressure vessel 110 or outside the hydrogen tank 100.

[0039] The temperature in the inner pressure vessel 120 can be adjusted via a fluid line 170 for a temperature compensation fluid. The fluid line 170 is routed in a closed manner into and out of the inner pressure vessel 120, for example through a U-shaped section of the line, so that heat exchange via the temperature compensation fluid occurs only through the line and not directly with the fluid itself.

[0040] The inner pressure vessel 120 is fluidically connected to a fluid line 140 for the removal of gaseous hydrogen (H₂). 2(g)), a fluid line 145 for supplying liquid hydrogen (H 2(l) ), a pipeline 150 for removing condensed impurities and a fluid line 160 for removing liquid hydrogen to an evaporator 330.

[0041] Through the fluid line 140 for the discharge of gaseous hydrogen, hydrogen that has transitioned into the gaseous state within the inner pressure vessel 120 can be discharged from the inner pressure vessel 120 or from the hydrogen tank 100.

[0042] Liquid hydrogen can be supplied to the inner pressure vessel 120 via fluid line 145. Liquid hydrogen can be discharged from the inner pressure vessel 120 via fluid line 160. This liquid hydrogen can then be supplied to the fuel cell stack 310 via a corresponding fluid line 340 for its operation, using an evaporator 330, where the liquid hydrogen is converted into gaseous hydrogen.

[0043] The control unit 320 allows the fuel cell stack to be operated either with gaseous hydrogen directly from the inner pressure vessel 120 via fluid line 140 or with liquid hydrogen vaporized by the evaporator 330 via fluid line 340. A flow divider valve 345 is provided for this purpose. A level sensor 130 located in the inner pressure vessel 120 determines the level of liquid hydrogen within that vessel. Pressure sensors 260 are also provided on fluid lines 140 and 340 to measure the gaseous hydrogen pressure. Pressure relief valves 250 are also provided downstream of these lines to prevent excessive pressure.

[0044] For pressure regulation and for regulating the transport of hydrogen in liquid or gaseous form, one or more shut-off valves 220, control valves 230, pressure relief valves 245, overflow valves 250, a discharge valve 350, and a pressure reducing valve 355 are additionally provided in the respective flow paths. These are marked accordingly in the figure.

[0045] During processing and transport, liquid hydrogen can become contaminated with gaseous impurities. These impurities, or harmful gases, include sulfur dioxide (SO2), ammonia (NH3), carbon dioxide (CO2), carbon monoxide (CO), ozone (O3), and methane (CH4). These impurities condense at the temperature of the liquid hydrogen. Since the hydrogen is in liquid form in the inner pressure vessel 120, these impurities condense within the inner pressure vessel 120. These condensed impurities then sink to the bottom of the inner pressure vessel 120. Through a pipeline 150 connected to the inner pressure vessel 120, particularly to its bottom, these impurities can be extracted using the extraction pump 210.This allows the liquid hydrogen to be purified, so that the hydrogen used from it in gaseous form is also purified of these impurities 125.

[0046] The control unit 320 can control the extraction process and, in particular, start or not start it depending on the operation of the fuel cell stack 310.

[0047] While at least one exemplary embodiment has been described above, it should be noted that a large number of variations exist. It should also be noted that the described exemplary embodiments are merely non-limiting examples, and it is not intended to restrict the scope, applicability, or configuration of the devices and methods described herein. Rather, the preceding description will provide the person skilled in the art with guidance for implementing at least one exemplary embodiment. It is understood that various modifications to the function and arrangement of the elements described in an exemplary embodiment can be made without derogating from the subject matter defined in the appended claims and their legal equivalents. REFERENCE MARK LIST 100 hydrogen tank 110 Outer pressure vessel 115 Room area with vacuum 120 Inner pressure vessel 125 impurities 130 Level sensor 140 Fluid line for the removal of gaseous hydrogen 145 Fluid line for supplying liquid hydrogen 150 Pipeline for removing condensed impurities 160 Fluid line for the removal of liquid hydrogen 170 Fluid line for temperature compensation fluid 200 hydrogen tank systems 210 Suction pump 220 Shut-off valve 230 Control valve 245 Pressure relief valve 250 overflow valve 260 pressure sensor 300 fuel cell systems 310 fuel cell stacks 320 Control unit 330 evaporators 340 Fluid line for supplying hydrogen 345 Flow divider valve 350 discharge valve 355 Pressure reducing valve

Claims

[1] Fuel cell system (300), comprising: a storage system (200), comprising: a storage device (100) for storing liquid hydrogen, comprising: an external pressure vessel (110); an inner pressure vessel (120) arranged and configured inside the outer pressure vessel (110) to store liquid hydrogen therein; wherein a space (115) is formed between the inner pressure vessel (120) and the outer pressure vessel (110) in which a vacuum prevails; a first fluid line (145) which is designed to supply liquid hydrogen from outside the outer pressure vessel (110) to the inner pressure vessel (120); a second fluid line (160) which is designed to discharge liquid hydrogen from the inner pressure vessel (120) to the outside of the outer pressure vessel (110); and an additional pipeline (150), distinct from the first fluid line (145) and the second fluid line (160), which extends from outside the outer pressure vessel (110) into the inner pressure vessel (120) to a bottom area within the inner pressure vessel (120), wherein the pipeline (150) is configured to be fluidically connected to a suction device (210) arranged outside the storage device (100) in order to suction condensed impurities (125) from the bottom area of ​​the inner pressure vessel (120) via the pipeline (150), wherein the storage system further comprises a suction device (210) which is connected to the pipeline (150) of the storage device (100), the fuel cell system further features: a fuel cell stack (310); an evaporator (330); wherein the second fluid line (160) of the storage device (100) is fluidically connected to the evaporator (330); a fourth fluid line (340) through which the evaporator (330) is fluidically connected to the fuel cell stack (310); and a control device (320) which is configured to start and control an extraction process for the extraction of the condensed impurities (125) through the extraction device (210) of the storage system (200) depending on a predetermined fulfilled criterion, wherein the control device (320) is configured to start the extraction process when the criterion is met that the fuel cell stack (310) is not in operation. [2] Fuel cell system (300) according to claim 1, wherein the pipeline (150) extends from the bottom area through the inner pressure vessel (120) to an opposite side of the bottom area and from this opposite side out of the storage device (100). [3] Fuel cell system (300) according to claim 1 or 2, wherein the bottom area has a concave shaped area. [4] Fuel cell system (300) according to one of claims 1 to 3, wherein the inner pressure vessel (120) is designed as an elongated hollow body, and the bottom area is formed on an end face of the inner pressure vessel (120). [5] Fuel cell system (300) according to one of claims 1 to 3, wherein the inner pressure vessel (120) is designed as an elongated hollow body, and the bottom area is formed on a longitudinal side of the inner pressure vessel (120). [6] Fuel cell system (300) according to one of the preceding claims, wherein the storage device (100) has a third fluid line (140) which is configured to discharge gaseous hydrogen from the inner pressure vessel (120) and outside the outer pressure vessel (110). [7] Fuel cell system (300) according to one of the preceding claims, wherein the inner pressure vessel (120) has a level sensor (130) which is configured to detect a level value of the liquid hydrogen in the inner pressure vessel (120). [8] Electrically powered system comprising a fuel cell system according to any of the preceding claims. [9] Electrically powered system according to claim 8, which is designed as a motor vehicle, emergency power generator or power supply system.

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