Process and system for converting energy

Abstract

The invention presented relates to a method (100) for operating a system (200) for converting energy. The presented method (100) comprises operating (101) an energy converter (205) of the system (200) by extracting liquid hydrogen from at least one hydrogen tank (203) of a hydrogen tank system (201) for storing hydrogen, determining (103) an expected shutdown time of the energy converter (205), and operating (105) the energy converter (205) by extracting gaseous hydrogen from the at least one hydrogen tank (203) from a switching time before the expected shutdown time in order to vaporize liquid hydrogen accumulated in an evaporator (217) of the hydrogen tank system.

Description

[0001] The presented invention relates to a method for operating a system for converting energy, a system for converting energy and a vehicle. State of the art

[0002] Especially for commercial vehicle applications, hydrogen-based powertrains, both based on fuel cells and on a hydrogen combustion engine, are characterized by higher energy densities and thus longer ranges and shorter refueling times compared to purely battery-based powertrains.

[0003] This essentially results from hydrogen storage in the vehicle in the form of compressed hydrogen at pressures of up to 700 bar. Liquid hydrogen storage is attracting increasing interest, particularly for long-haul truck applications, as the density of liquid hydrogen, at > 60 kg / m3, is significantly higher than the density of compressed hydrogen, at approximately 40 kg / m3 at 700 bar.

[0004] In addition to the range advantage that can be achieved in this way, a more flexible hydrogen tank design option also results in packaging advantages in the vehicle as well as cost advantages for the hydrogen tank and hydrogen distribution.

[0005] On the other hand, there is the hurdle of the high investment costs required for highly efficient liquefaction plants and a so-called boil-off behavior.

[0006] In a hydrogen tank system for cryogenic liquid hydrogen, the actual hydrogen tank is connected to a hydrogen consumer via a pipe or pipe system.

[0007] Also part of this connection is a hydrogen vaporizer, which vaporizes the hydrogen, preferably taken in liquid form from the hydrogen tank, and then further heats it to the temperature required for supply to the hydrogen consumer, typically around 65°C.

[0008] When the hydrogen consumer is shut down, the hydrogen contained in a line between the hydrogen tank and the energy converter, as well as in the evaporator—i.e., in a respective line system—heats up, leading to a huge isochoric pressure increase at a constant volume. Once this pressure reaches the maximum permissible operating pressure of the line and evaporator, hydrogen must be vented, which is both environmentally harmful and detrimental to the energy efficiency of the entire system.

[0009] Since liquid hydrogen is present in the inlet area of ​​the evaporator when liquid hydrogen is withdrawn from a respective hydrogen tank, the pressure increase due to evaporation of hydrogen in a volume “locked” in the pipe system is particularly strong. Disclosure of the invention

[0010] Within the scope of the invention presented, a system for converting energy and a method for operating the system, as well as a vehicle, are presented. Further features and details of the invention emerge from the respective subclaims, the description, and the drawings. Features and details described in connection with the method according to the invention naturally also apply in connection with the system according to the invention or the vehicle according to the invention, and vice versa, so that with regard to the disclosure of the individual aspects of the invention, reference is always made to each other.

[0011] The invention presented serves in particular to minimize a loss of hydrogen by blowing off from a hydrogen tank and to maximize the energy efficiency of a corresponding system for converting energy.

[0012] Thus, according to a first aspect of the invention presented, a method for operating a system for converting energy is presented.

[0013] The presented method comprises operating an energy converter of the system by withdrawing liquid hydrogen from at least one hydrogen tank of a hydrogen tank system for storing hydrogen, determining an expected shutdown time of the energy converter, and operating the energy converter by withdrawing gaseous hydrogen from the at least one hydrogen tank from a switchover time before the expected shutdown time in order to evaporate liquid hydrogen accumulated in an evaporator of the hydrogen tank system.

[0014] In the context of the present invention, an energy conversion process is understood to mean, in particular, a process in which chemical energy stored in a quantity of hydrogen is converted into electrical energy. For this purpose, the hydrogen can be burned or oxidized by an energy converter, e.g., in the form of an internal combustion engine, in particular a piston engine, and / or by a fuel cell system, i.e., converted into water by reacting with oxygen to generate electrical energy.

[0015] The invention presented is based on the principle that an increase in pressure in a line system between a hydrogen tank and an energy converter supplied with hydrogen by the hydrogen tank, which leads to a blow-off of hydrogen, is prevented or at least delayed by switching from a normal operation of the energy converter by removing liquid hydrogen from the hydrogen tank to a preventive operation during a control operation of the energy converter, wherein during the preventive operation the energy converter is operated by removing gaseous hydrogen from the hydrogen tank.

[0016] To switch between the withdrawal of liquid hydrogen and the withdrawal of gaseous hydrogen, a respective hydrogen tank can have two tank valves, wherein a first tank valve is arranged on an upper side of the hydrogen tank in the direction of gravity and a second tank valve is arranged on a lower side of the hydrogen tank in the direction of gravity. Since gaseous hydrogen accumulates on the upper side of the hydrogen tank in the direction of gravity, opening the first valve causes only gaseous hydrogen to flow out, while opening the second valve causes only liquid hydrogen to flow out. Accordingly, switching between the withdrawal of gaseous hydrogen and liquid hydrogen can be achieved by alternately opening the first valve and the second valve.

[0017] The inventive removal of only gaseous hydrogen during normal operation, particularly in an operating phase shortly before the energy converter is shut down, prevents the entrapment of liquid hydrogen in a line system between a respective hydrogen tank and the energy converter and, as a result, a significant increase in pressure in the line system due to hydrogen changing from the liquid state to the gaseous state. As a result, the amount or density of hydrogen in the line system is lower than when only liquid hydrogen is removed, so that a critical load on the line system or its components and the resulting release of hydrogen from the line system is delayed, and in particular prevented.

[0018] By operating the energy converter as provided according to the invention by removing gaseous hydrogen from the at least one hydrogen tank before the expected shutdown time, the gaseous hydrogen is consumed or removed from the line system by the energy converter, so that a density of hydrogen and, as a result, a pressure in the line system is minimized by the operation of the energy converter.

[0019] It can be provided that respective hydrogen tank valves of the at least one hydrogen tank are completely closed until all liquid hydrogen has evaporated in an evaporator of the hydrogen tank system and / or a temperature of the hydrogen downstream of the respective hydrogen tank valves is greater than or equal to an ambient temperature.

[0020] By closing hydrogen tank valves of the at least one hydrogen tank, a supply of liquid hydrogen into a line system between a respective hydrogen tank and the energy converter is blocked, so that the energy converter minimizes a density of hydrogen in the line system and, as a result, a pressure in the line system particularly quickly.

[0021] It can further be provided that, in the event that, after the switch-off time of the energy converter, a pressure in a line system between the at least one hydrogen tank and the energy converter is greater than a predetermined reactivation threshold value, the energy converter is reactivated in a storage mode in which hydrogen from the at least one hydrogen tank is consumed by the energy converter and converted into electrical energy, and electrical energy provided by the energy converter is stored in an electrical energy storage device of the system.

[0022] To minimize or delay damage to the piping system or the release of hydrogen into the environment, a safety function can be used that is activated when, after the energy converter has been switched off, the pressure in a piping system between the at least one hydrogen tank and the energy converter is greater than a predetermined reactivation threshold. For rapid and reliable reduction of the pressure in the piping system, the energy converter can be activated specifically to reduce hydrogen stored in the piping system. To maintain the system's energy efficiency, electrical energy provided while the safety function is being executed is stored in an electrical energy storage device, such as a battery.

[0023] It can further be provided that the switch-off time is selected such that liquid hydrogen accumulated in the evaporator is completely evaporated by the switch-off time.

[0024] To prevent a pressure increase due to evaporating hydrogen in the piping system, the shutdown time can be selected such that liquid hydrogen accumulated in the evaporator is completely evaporated by the shutdown time. For this purpose, the shutdown time or a time at which the extraction of gaseous hydrogen is started can be selected, for example, depending on the hydrogen consumption of the energy converter and a known volume of the piping system.

[0025] It may further be provided that the switch-off time is determined on the basis of route information about a route to be traveled by a vehicle comprising the energy converter.

[0026] In order to determine the switch-off time or a switch-over time for switching from a withdrawal of liquid hydrogen to a withdrawal of gaseous hydrogen in such a way that the energy converter is supplied with liquid hydrogen for as long as possible and with gaseous hydrogen only for as long as necessary, route information from, for example, a navigation system of a vehicle comprising the energy converter can be evaluated.

[0027] To determine the switchover point from liquid hydrogen to gaseous hydrogen, a time for supplying the energy converter with gaseous hydrogen can be assigned to a route length, for example. This assignment can be made using a predefined assignment scheme or using an appropriately trained machine learner.

[0028] Alternatively or additionally, further information, such as operating parameters of the energy converter and / or environmental information, such as an ambient temperature, can be provided to a machine learner to determine a time at which the energy converter is to be supplied with gaseous hydrogen in order to reduce the pressure in the line system, for example, to a predetermined value.

[0029] Alternatively, it may also be provided that the switching time is determined based on a fixed time range for the removal of gaseous hydrogen.

[0030] A fixed time range minimizes the computational effort required to calculate the switching time and is particularly reliable in operation.

[0031] It can further be provided that when operating the energy converter by removing gaseous hydrogen from the at least one hydrogen tank, a heating power of a heating element in the at least one hydrogen tank is increased compared to an operation of the energy converter by removing liquid hydrogen from the at least one hydrogen tank and a heating power of the evaporator is reduced in order to keep a working pressure for supplying the energy converter constant.

[0032] Since an energy converter must be supplied with hydrogen at a substantially constant pressure for error-free operation, a pressure fluctuation in a line system between the hydrogen tank and the energy converter caused by the switching from a withdrawal of liquid hydrogen to gaseous hydrogen provided according to the invention can be compensated by an adapted temperature or heating output.

[0033] According to a second aspect, the presented invention relates to a system for converting energy.

[0034] The presented system comprises a hydrogen tank system with at least one hydrogen tank for storing hydrogen, an energy converter for converting chemical energy into electrical energy and a computing unit, wherein the computing unit is configured to carry out a possible embodiment of the presented method.

[0035] In the context of the invention presented, a computing unit is understood to mean a computer, a processor, a control unit or any other programmable circuit.

[0036] It can be provided that the energy converter comprises an internal combustion engine and / or a fuel cell system.

[0037] It may further be provided that the hydrogen tank system is configured to store hydrogen in saturated form or subcooled form or in cryostatically compressed form.

[0038] Since subcooled or cooled fluids expand particularly strongly in response to heat input, the presented invention is particularly suitable for tank systems for storing such fluids.

[0039] According to a third aspect, the presented invention relates to a vehicle comprising a possible embodiment of the presented system.

[0040] Advantages described in detail for the method of operating an energy conversion system according to the first aspect of the invention apply equally to the energy conversion system according to the second aspect of the invention and the vehicle according to the third aspect of the invention.

[0041] Further advantages, features, and details of the invention will become apparent from the following description, which describes exemplary embodiments of the invention in detail with reference to the drawings. The features mentioned in the claims and in the description may be essential to the invention individually or in any combination. Drawings

[0042] They show: Fig. 1 a possible design of the presented procedure, Fig. 2 a possible design of the presented system, Fig. 3 a possible design of the presented vehicle. Description of the embodiments

[0043] In Fig. 1 shows a method 100 for operating an energy conversion system.

[0044] The presented method 100 comprises a first operating step 101 in which an energy converter of the system is operated by withdrawing liquid hydrogen from at least one hydrogen tank of a hydrogen tank system for storing hydrogen, a determination step 103 in which an expected shutdown time of the energy converter is determined, and a second operating step 105 in which the energy converter is operated by withdrawing gaseous hydrogen from the at least one hydrogen tank from a switching time before the expected shutdown time in order to evaporate liquid hydrogen accumulated in an evaporator of the hydrogen tank system.

[0045] In Fig. 2 shows a system 200 for converting energy.

[0046] The system 200 comprises a tank system 201 with a hydrogen tank 203 for storing hydrogen, an energy converter 205 in the form of a fuel cell system for converting chemical energy into electrical energy, and a computing unit 207.

[0047] The computing unit 207 is configured to carry out the method 100 according to Fig. 1 to execute.

[0048] Optionally, the system 200 comprises an electrical energy storage device 209 in the form of a battery for storing electrical energy provided by the energy converter 205, for example in the event that a pressure in a line system 211 between the hydrogen tank 203 and the energy converter 205 rises above a predetermined safety threshold and the energy converter 205 is activated in a safety mode to consume hydrogen located in the line system 211.

[0049] To switch from the first operating step 101 to or to the second operating step 105, for example, a first tank valve 213 on an upper side of the hydrogen tank 203 in the direction of gravity can be opened so that gaseous hydrogen accumulated at the top of the hydrogen tank 203 escapes from the hydrogen tank 203 into the line system 211, and a second tank valve 215 on a lower side of the hydrogen tank 203 in the direction of gravity, on which liquid hydrogen collects, can be closed.

[0050] An evaporator 217 is arranged in or on the line system 211, which is freed of liquid hydrogen by switching from the first operating step 101 to the second operating step 105, since in the second operating step 105 it is only supplied with gaseous hydrogen.

[0051] Alternatively, the energy converter 205 may be operated when both the first tank valve 213 and the second tank valve 215 are closed to remove hydrogen from the line system 211 and, thereby, minimize a pressure in the line system 211.

[0052] In Fig. 3, a vehicle 300 is shown. The vehicle 300 includes the system 200 according to Fig. 2.

Claims

[1] A method (100) for operating a system (200) for converting energy, the method (100) comprising: - operating (101) an energy converter (205) of the system (200) by withdrawing liquid hydrogen from at least one hydrogen tank (203) of a hydrogen tank system (201) for storing hydrogen, - determining (103) an expected switch-off time of the energy converter (205), - Operating (105) the energy converter (205) by withdrawing gaseous hydrogen from the at least one hydrogen tank (203) from a switchover time before the expected switch-off time in order to evaporate liquid hydrogen accumulated in an evaporator (217) of the hydrogen tank system. [2] Method (100) according to claim 1, characterized bythat respective hydrogen tank valves (213, 215) of the at least one hydrogen tank (203) are completely closed until all liquid hydrogen in the evaporator (217) has evaporated and / or a temperature of the hydrogen downstream of the respective hydrogen tank valves (213, 215) is greater than or equal to an ambient temperature. [3] Method (100) according to claim 1 or 2, characterized byin that, in the event that, after the switch-off time of the energy converter (205), a pressure in a line system (211) between the at least one hydrogen tank (203) and the energy converter (205) is greater than a predetermined reactivation threshold value, the energy converter (205) is reactivated in a storage mode in which hydrogen from the at least one hydrogen tank (203) is consumed by the energy converter (205) and converted into electrical energy, and electrical energy provided by the energy converter (205) is stored in an electrical energy store (209) of the system (200). [4] Method (100) according to one of the preceding claims, characterized by that the switch-off time is selected such that liquid hydrogen accumulated in the evaporator (217) is completely evaporated by the switch-off time. [5] Method (100) according to one of the preceding claims, characterized bythat the switch-off time is determined on the basis of route information about a route to be traveled by a vehicle (300) comprising the energy converter (205). [6] Method (100) according to one of the preceding claims, characterized by that the switching time is selected depending on an operating point of the energy converter (205). [7] Method (100) according to one of claims 1 to 5, characterized by that the switching time is determined on the basis of a fixed time range for removing gaseous hydrogen from the at least one hydrogen tank (203). [8] Method (100) according to one of the preceding claims, characterized bythat when operating the energy converter (205) by removing gaseous hydrogen from the at least one hydrogen tank (203), a heating power of a heating element in the at least one hydrogen tank (203) is increased compared to an operation of the energy converter (205) by removing liquid hydrogen from the at least one hydrogen tank (203) and a heating power of the evaporator (217) is reduced in order to keep a working pressure for supplying the energy converter (205) constant. [9] System (200) for converting energy, wherein the system (200) comprises: - a hydrogen tank system (201) with at least one hydrogen tank (203) for storing hydrogen, - an energy converter (205) for converting chemical energy into electrical energy, - a computing unit (207), wherein the computing unit (207) is configured to execute a method (100) according to one of claims 1 to 8. [10] System (200) according to claim 9, characterized by that the energy converter (205) comprises an internal combustion engine and / or a fuel cell system. [11] System (200) according to claim 9 or 10, characterized by that the hydrogen tank system (201) is configured to store hydrogen in saturated form or subcooled form or in cryostatically compressed form. [12] Vehicle (300), wherein the vehicle (300) comprises a system (200) according to any one of claims 9 to 11.

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