Methods for emptying liquid hydrogen tanks

Abstract

This technology provides a highly energy-efficient way to discharge residual hydrogen from tanks. [Solution] The present invention relates to a method for emptying a tank (13) for liquid hydrogen using a tank heater (15) in a vehicle (1) equipped with at least one hydrogen-driven drive unit (2). The present invention is characterized in that the drive unit (2) does not operate while the tank (13) for liquid hydrogen is being emptied, and a coolant is circulated to a cooling circuit (3) of the drive unit (2) or a cooling circuit (3) indirectly heat-conductively connected to the cooling system of the drive unit (2), and the heat in the coolant and the heat received by the coolant from the ambient air are supplied directly or indirectly to the tank heater (15).

Description

Technical Field

[0001] The present invention relates to a method for emptying a liquid hydrogen tank using a tank heater in a vehicle equipped with at least one hydrogen-driven drive unit. A hydrogen-driven drive unit in the sense of the present invention can be, for example, a fuel cell of a fuel cell system or a machine that burns hydrogen. The hydrogen-driven drive unit can be, for example, a hydrogen-driven combustion engine or a gas turbine.

Background Art

[0002] During the operation of a vehicle equipped with such a tank, in order to extract liquid hydrogen, generally, heat is applied to the liquid phase of hydrogen to vaporize it. Then, the vaporized pressurized gas can be removed from the tank. Various heat sources can be used for this purpose. Patent Document 1 below describes a system that extracts heat for liquefying hydrogen from either the environment or the cooling circuit of a fuel cell according to the season. Its configuration is correspondingly complex and suitable only for fixed installations. The same is also described in Patent Document 2 below.

[0003] In addition to the hydrogen extraction described in these two patent documents, emptying liquid hydrogen tanks for maintenance purposes plays an important role, particularly in the field of vehicle technology, for supplying hydrogen to fuel cell systems or, in principle, other hydrogen-consuming devices. Vehicles generally have separate tank circuits equipped with an electric resistance heater or refrigerant (Kuhlmedium) to operate a tank heater. For this purpose, a liquid refrigerant with a temperature higher than the boiling point of hydrogen flows through the tank circuit. When it is necessary to completely empty a liquid hydrogen tank for maintenance purposes, energy is generally supplied to this tank circuit to heat the refrigerant and vaporize the hydrogen in the tank so that it can be extracted. Since all other systems of the vehicle are no longer operating in such a situation, this energy is generally supplied via an electric heater, for example, an electric heating resistor. In practice, heating resistors are mainly used in vehicles in case the battery is already fully charged when regenerative braking is activated during driving and the resulting power cannot be received. In this case, the surplus power is consumed in the heating resistor. When completely emptying a liquid hydrogen tank for maintenance purposes, this heating resistor can be used to supply heat. However, this method has a significant drawback: it requires a relatively large amount of power, which is typically supplied by a battery. Therefore, after the tank is completely empty, the battery often has a very low or unstable charge level, or requires an external supply of electrical energy. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] U.S. Patent Application Publication No. 2020 / 0298651, Specification A1 [Patent Document 2] Chinese Patent Application Publication No. 115 224 306 Specification A1 [Overview of the project] [Problems that the invention aims to solve]

[0005] The object of the present invention is to provide an improved method for emptying a liquid hydrogen tank using a tank heater for maintenance purposes, which discharges residual hydrogen from the tank with high energy efficiency. [Means for solving the problem]

[0006] This problem is solved by the method of the present invention described in claim 1. Advantageous embodiments and variations will become apparent from the dependent claims.

[0007] The method according to the present invention is intended to operate a coolant supply device in the cooling circuit of a drive unit, or a coolant supply device in a cooling circuit that is indirectly heat-conductively connected to the cooling system of the drive unit, even when the drive unit is not operating, i.e., when the drive unit is not generating any mechanical or electrical output. In this case, the heat present in the coolant (Kuhlmittel) can be utilized through this coolant supply device, and once the coolant is cooled to a temperature lower than the ambient temperature, heat from the environment can be utilized. For this purpose, heat from the ambient air is introduced into the coolant via a cooling heat exchanger that would otherwise be used to cool the coolant. This allows heat to be supplied at a temperature level that best corresponds to the ambient air temperature. This temperature, generally in the range of 5 to 25°C, is sufficient to vaporize the cryogenic liquid hydrogen in the tank, so that residual hydrogen can be removed before tank maintenance. Therefore, the method according to the present invention utilizes the cooling circuit to supply, directly or indirectly, the heat first in the coolant in the cooling circuit, and then the heat absorbed from the ambient air into the cooled coolant, to the tank heater.

[0008] In that case, the cooling circuit may be, for example, the cooling circuit of a fuel cell system or a hydrogen engine itself. If multiple cooling circuits are to be operated, for example, at different temperature levels, it is a cooling circuit that includes a cooling heat exchanger for dissipating waste heat into the environment. In that case, this makes it possible to take heat from the ambient air through the cooling heat exchanger into the coolant.

[0009] For this purpose, it is only necessary to operate the coolant supply device and, if necessary, the fan, to allow ambient air to flow through the cooling heat exchanger. This is possible with much higher energy efficiency than electrically heating the tank heater to extract residual hydrogen. Thus, the method according to the present invention makes it possible to completely empty the tank with very high energy efficiency for maintenance purposes.

[0010] In this case, according to a highly advantageous development of the method according to the present invention, heat received from the ambient air is transferred to the refrigerant in the tank circuit via a heat exchanger, and the refrigerant is used to heat and vaporize the liquid hydrogen in the tank heater. This configuration utilizes a configuration very common in fuel cell vehicles, which on the one hand comprises a cooling circuit for the fuel cell system and on the other hand a further refrigerant tank circuit for heating and extracting hydrogen during operation. Generally, these two circuits are coupled to each other via a heat exchanger, and in many cases, the aforementioned electric brake resistor is part of the tank circuit. In particular, an air conditioning circuit can also be coupled to this tank circuit to transfer heat.

[0011] Therefore, in this particular embodiment of the method according to the present invention, contact between the coolant and ambient air can be established by utilizing a cooling circuit equipped with a large-area cooling heat exchanger, also colloquially referred to as a radiator. Thus, when the coolant is cooled to a temperature lower than the ambient temperature by heating liquid hydrogen, the coolant can acquire heat from the ambient air in the cooling circuit and transfer this heat to the refrigerant in the tank circuit via a heat exchanger between the two circuits, which in turn transfers this heat to the tank heater, for which only one supply device needs to be activated. The medium cooled in the tank heater is then heated again in the heat exchanger. For this purpose, both supply devices are activated not only in one circuit but also in the other circuit, and fans are activated as needed to supply a sufficient amount of ambient air to the area of ​​the cooling heat exchanger in the cooling circuit. Hydrogen can be vaporized and extracted from the tank with very high energy efficiency, as no further energy is required.

[0012] In addition, heat for heating the tank may be supplied using further heat sources that are connected to or can be connected to the cooling circuit and / or tank circuit. Such heat sources are generally areas or circuits with a medium that has a temperature above the level of ambient air, the air in the passenger compartment, etc., in a vehicle with the power off. In this way, heat from the air conditioning circuit of an air conditioning system, which is generally connected to the tank circuit, may also be included. If further cooling circuits are in thermal conduction contact with the cooling circuit, these can also be operated together.

[0013] In a more highly advantageous embodiment of the method according to the present invention, an electric resistance heater is provided in at least one of the circuits, which can be further intended to operate when additional heat is needed. Thus, for example, if the ambient temperature is so low that the refrigerant freezes in at least one of the circuits, or if one of these cooling circuits is no longer available or not available at all due to a vehicle malfunction, such as after an accident, it is always possible to completely empty the residue via electric auxiliary heating (electric resistance heater) as in the conventional manner.

[0014] The method according to the present invention can be applied to various tank systems that can be used in a variety of vehicles, such as commercial vehicles, light commercial vehicles, and passenger cars, as well as ships, railway vehicles, and the like.

[0015] Further advantageous embodiments of the method according to the present invention can also be obtained from exemplary embodiments shown in more detail below with reference to the drawings. [Brief explanation of the drawing]

[0016] [Figure 1] This is a schematic diagram of a vehicle equipped with a fuel cell system and a liquid hydrogen tank. [Modes for carrying out the invention]

[0017] In Figure 1, vehicle 1 is schematically represented by a dashed line. This vehicle 1 may be, for example, a commercial vehicle electrically driven via a fuel cell system. In the embodiment illustrated herein, two parallel fuel cells 2, so-called fuel cell stacks or fuel cell arrays, are shown for this fuel cell system. These form a drive unit 2 in the sense of the present invention. However, the drive unit may be replaced with an internal combustion engine, a gas turbine, or the like, in which case vehicle 1 would be driven mechanically or in a serial hybrid manner via them. In that case, the remaining configuration will obviously be the same as the example described below in relation to fuel cell vehicle 1.

[0018] In this case, the fuel cell 2 is located together with the fuel cell cooling circuit 3 and can be cooled in parallel by the volumetric flow rate of the coolant supplied (transported) via the coolant supply device (coolant transport device) 4 during normal operation. Furthermore, a fuel cell bypass 5 is provided. This makes it possible for the coolant to flow through the fuel cells 2 individually or simultaneously, or not to flow through at all, and for this purpose, a bypass valve 6 is provided to control the flow of coolant according to the desired operating state. The waste heat of the fuel cell 2 is dissipated through a cooling heat exchanger 7 during normal operation. The cooling heat exchanger 7, often also called a radiator, may consist of one or more elements, one or more of which are generally located in the vehicle 1 so that sufficient cooling air flows through it while the vehicle 1 is running. If this cooling air is insufficient, an additional or enhanced airflow can be generated through the cooling heat exchanger 7 via the fan propeller 8 shown herein. This cooling heat exchanger 7 also has a radiator bypass 9 with a bypass valve 10, which, for example, in a cold start scenario of a fuel cell system, does not cool the slowly warming refrigerant but heats the fuel cell 2 as quickly as possible. All of this is generally known to engineers of fuel cell systems. Instead of one cooling circuit 3, multiple cooling circuits connected to each other by heat conduction may be provided.

[0019] Through a heat exchanger 11, this at least one fuel cell cooling circuit 3 is connected to a refrigerant circuit 12 of a tank for liquid hydrogen 13. This tank circuit (refrigerant circuit) 12 also includes a supply device 14 for the refrigerant circulating within the tank circuit 12. Furthermore, a tank heater 15 is part of this tank circuit 12. The tank heater 15 extends through the tank 13 so as to flow around it via a bypass valve 16 and, if necessary, via a bypass 17, and more specifically, preferably extends within a section of the tank 13 that is located downward in the direction of gravity during specified use. The tank heater 15 comes into contact with the liquid hydrogen and heats the liquid hydrogen accordingly. The bubbles then rise to the upper region of the tank 13 during specified use and are discharged from the tank via a extraction device 18, and become available as a reactant in the fuel cell 2, for example, during the normal operation of the vehicle 1. In most cases, an electric heating resistor (electric heating heater) 19, which may be provided to heat the coolant within the tank circuit 12, is also in thermal conduction contact with this tank circuit 12. This allows the electric heating resistor 19 to assist the tank heater 15. Often, this heating resistor 19 is also used when more power is generated during regenerative braking of the vehicle 1 than can be received by the battery (not shown). The excess power is then consumed in the electric heating resistor 19.

[0020] Further heat sources may be placed within the tank circuit 12 or on the fuel cell cooling circuit 3. Just as an example, box 20 may symbolize further heat sources such as power electronics to be cooled, an electric motor to be cooled, or an air conditioning system, which are connected to one of the circuits 3, 12, or in this case, the tank circuit 12, to transfer heat.

[0021] The operation of such a system in a vehicle 1 during normal operation is generally known and well-known to those skilled in the art, and therefore does not require further explanation here.

[0022] The basic scenario in this case is as follows. Vehicle 1 is malfunctioning, for example, or at least has a defect in the area of the hydrogen supply line and / or the area of tank 13. When Vehicle 1 is stopped and the fuel cell 2 is no longer operating or is inoperable, the residual hydrogen in tank 13 is assumed to be extracted with high energy efficiency. Instead of making available the heat required to vaporize the residual liquid hydrogen via the electric heating resistor 19 as was the conventional practice, it is possible at this time to operate both the supply device 4 for the coolant in the fuel cell circuit 3 and the supply device 14 for the refrigerant in the tank circuit 12. The fuel cell circuit 3 can be operated, in the embodiment illustrated here, to flow through, for example, only the heat exchanger 11, the cooling heat exchanger 7, the fuel cell bypass 5, and the coolant supply device 4. Although it is basically possible to flow through the fuel cell 2 itself, it is generally not necessary here if there is an appropriate fuel cell bypass 5, which is the case generally applied. Thus, by operating the supply device 14 in the tank circuit 12 and appropriately adjusting the bypass valve 16, the refrigerant is supplied at this time through the tank heater 15, the residual liquid hydrogen in tank 13 is vaporized, and is cooled at that time. At this time, this coolant in the tank circuit 12 receives heat again in the area of the heat exchanger 11 and can vaporize further residual liquid hydrogen in tank 13. This heat can be supplied simply by circulating the coolant in the fuel cell cooling circuit 3 in the aforementioned manner, so that when the coolant is cooled to a temperature lower than the ambient temperature in the heat exchanger 11, it can receive heat from the ambient air in the cooling heat exchanger 7 and be transported to the heat exchanger 11. Then, this heat is transmitted to the coolant in the tank circuit 12 and serves to vaporize the residual liquid hydrogen that can be extracted via the extraction device 18.

[0023] Aside from the operation of the two supply units 4 and 14, and the operation of fan 8 as needed, no additional energy is required here to make a larger volume of ambient air, and therefore more heat, available, and in particular, energy-intensive electric heating is not needed. If a further heat source, symbolized by box 20, is available, the residual heat present in the region of this heat source can also be used to heat the refrigerant in tank circuit 12 to vaporize the residual liquid hydrogen.

[0024] Furthermore, if necessary, heat may be supplied to this refrigerant in the tank circuit 12 via an electric heating resistor 19, but this should only be done if all other measures fail, for example, due to a failure in the fuel cell cooling circuit.

Claims

1. A method for emptying a tank for liquid hydrogen (13) using a tank heater (15) in a vehicle (1) equipped with at least one hydrogen-powered drive unit (2), While the liquid hydrogen tank (13) is empty, the drive unit (2) does not operate, and the coolant is circulated through the cooling circuit (3) of the drive unit (2) or through a cooling circuit (3) that is indirectly connected to the cooling system of the drive unit (2) by heat conduction, thereby supplying the heat in the coolant and the heat that the coolant receives from the ambient air to the tank heater (15) directly or indirectly. A method characterized by the following features.

2. The heat from the coolant in the cooling circuit (3) is transferred to the coolant in the coolant circuit (12) of the tank (13) via the heat exchanger (11), and then the residual liquid hydrogen is heated and vaporized by the tank heater (15) using the heat. The method according to claim 1, characterized in that

3. A further heat source (20) in contact with the cooling circuit (3) and / or the refrigerant circuit (12) of the tank (13) is used to heat the refrigerant in the refrigerant circuit (12) of the tank (13). The method according to claim 2, characterized in that...

4. At least one of the circuits (3, 12) is provided with an electric heating resistor (19) that operates when additional heat is needed. The method according to claim 2 or claim 3, characterized in that it is the method according to claim 2 or 3.

5. At least one fuel cell (2) is used as the drive unit (2). The method according to any one of claims 1 to 4, characterized in that

6. At least one hydrogen combustion machine is used as the drive unit (2). The method according to any one of claims 1 to 4, characterized in that

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