Liquid hydrogen system

Abstract

To provide a liquid hydrogen system that can further improve energy efficiency.SOLUTION: A liquid hydrogen system 10 includes: a hydrogen tank 12 that stores liquid hydrogen inside a vehicle; a supply circuit 20 that extracts the liquid hydrogen from the hydrogen tank 12, then converts it into hydrogen gas, and supplies it to a hydrogen engine 100; a boil-off flow path 40 that directs boil-off gas inside the hydrogen tank 12 to the outside of the tank; and a fuel cell 50 that is provided in the boil-off flow path 40 and generates electricity using the boil-off gas and air.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This specification discloses a liquid hydrogen system for storing liquid hydrogen in a vehicle equipped with a hydrogen engine. [Background technology]

[0002] In recent years, vehicles equipped with hydrogen engines have been proposed. Such vehicles are required to carry large amounts of hydrogen. Therefore, it has been proposed to store hydrogen in a liquid state inside the vehicle. For example, Patent Document 1 discloses a liquid hydrogen system having a hydrogen tank for storing liquid hydrogen. The liquid hydrogen system of Patent Document 1 further includes a first flow path connecting the hydrogen tank to the outside of the vehicle, and a safety valve provided in the first flow path. With this configuration, boil-off gas that naturally vaporizes inside the hydrogen tank is released outside the vehicle, preventing excessive pressure buildup in the hydrogen tank. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2024-006562 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in Patent Document 1, the boil-off gas is released outside the vehicle after reacting with air or directly, and therefore the boil-off gas is not effectively utilized. Therefore, the technology of Patent Document 1 leaves room for improvement in terms of energy efficiency.

[0005] Therefore, this specification discloses a liquid hydrogen system that can further improve energy efficiency. [Means for solving the problem]

[0006] The liquid hydrogen system disclosed in this specification is characterized by comprising a hydrogen tank for storing liquid hydrogen inside a vehicle, a supply circuit for extracting the liquid hydrogen from the hydrogen tank, converting it into hydrogen gas, and supplying it to a hydrogen engine, a boil-off flow path for directing boil-off gas inside the hydrogen tank to the outside of the tank, and a fuel cell provided in the boil-off flow path for generating electricity using the boil-off gas and air. [Effects of the Invention]

[0007] According to the liquid hydrogen system disclosed in this specification, the boil-off gas is used to generate electricity in a fuel cell, thereby further improving energy efficiency. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing the configuration of a portion of a liquid hydrogen system. [Figure 2] FIG. 10 is a diagram showing the configuration of another part of the liquid hydrogen system. DETAILED DESCRIPTION OF THE INVENTION

[0009] The configuration of the liquid hydrogen system 10 will be described below with reference to the drawings. Figures 1 and 2 are schematic diagrams showing the configuration of the liquid hydrogen system 10. The liquid hydrogen system 10 is mounted on a vehicle and stores hydrogen in a liquid state. The vehicle is a hydrogen engine automobile equipped with a hydrogen engine 100.

[0010] The liquid hydrogen system 10 has a hydrogen tank 12 for storing liquid hydrogen. The hydrogen tank 12 stores the liquid hydrogen in an insulated manner. For example, the hydrogen tank 12 may be a container with a double-tube structure, with a vacuum insulation layer between an inner tank made of stainless steel and an outer tank covering the inner tank. The hydrogen tank 12 is spherical or bale-shaped as shown in Figure 1 in order to maintain uniform pressure on the inner wall.

[0011] In the hydrogen tank 12, the liquid hydrogen is kept at a low temperature. The pressure of the liquid hydrogen in the hydrogen tank 12 is approximately the same as or slightly higher than atmospheric pressure, for example, 1 MPa or less. A hydrogen pump 16 is attached to the hydrogen tank 12. The hydrogen pump 16 pumps up the liquid hydrogen in the hydrogen tank 12 and sends it to the hydrogen engine 100. In this example, the hydrogen pump 16 is a booster pump that pumps up the liquid hydrogen while pressurizing it. The hydrogen pump 16 is driven by a pump motor 18. As shown in FIG. 1, the pump motor 18 is located outside the hydrogen tank 12.

[0012] The liquid hydrogen discharged from the hydrogen pump 16 is supplied to the hydrogen engine 100 through a supply circuit 20 shown in Figure 2. The supply circuit 20 has a supply flow path 22, a vaporizer 24, a pressure chamber 26, and a supply pressure reducing valve 28. The supply flow path 22 is a flow path that guides the hydrogen discharged from the hydrogen pump 16 to the hydrogen engine 100.

[0013] Vaporizer 24 is a heat exchanger that converts liquid hydrogen into hydrogen gas by exchanging heat between liquid hydrogen and a refrigerant. Pressure chamber 26 is located downstream of vaporizer 24. Pressure chamber 26 is a container that temporarily stores the hydrogen gas output from vaporizer 24. The capacity of pressure chamber 26 is set to a level that can cover the response delay in hydrogen gas supply control. By providing such pressure chamber 26, it is possible to prevent a shortage of hydrogen gas even if the amount of hydrogen gas consumed by hydrogen engine 100 suddenly changes.

[0014] A supply pressure reducing valve 28 is provided downstream of the vaporizer 24. The supply pressure reducing valve 28 reduces the pressure of the hydrogen gas to a pressure suitable for the hydrogen engine 100. The reduced pressure hydrogen gas is supplied to the hydrogen engine 100 via an injector 30. The flow rate of the hydrogen gas supplied to the hydrogen engine 100 is detected by a flow meter 32.

[0015] As shown in Figure 1, there is always a space (hereinafter referred to as the "upper space") above the hydrogen tank 12 that is equal to or larger than a predetermined volume. This upper space is where hydrogen gas, which is generated when the liquid hydrogen stored in the tank vaporizes, accumulates. Naturally, as the amount of accumulated hydrogen gas increases, the pressure inside the hydrogen tank 12 increases. To prevent the pressure inside the tank from rising excessively, the liquid hydrogen system 10 is further provided with a release flow path 34 and a boil-off flow path 40.

[0016] The boil-off flow path 40 is a flow path that guides the hydrogen gas inside the tank, i.e., boil-off gas, out of the tank when the internal pressure of the hydrogen tank 12 is reduced. Releasing a portion of the hydrogen gas out of the tank prevents the internal pressure of the hydrogen tank 12 from becoming excessively high. As shown in FIG. 1 , in this example, the boil-off flow path 40 branches into two systems: a first flow path 42 and a second flow path 44. The configurations of the first flow path 42 and the second flow path 44 will be described in detail later.

[0017] The release flow path 34 is a flow path that directs hydrogen gas outside the tank when a large amount of hydrogen gas is generated in a short period of time. This release flow path 34 opens when the tank internal pressure exceeds a predetermined allowable pressure, directing hydrogen gas from the hydrogen tank 12 outside the vehicle. Such a release flow path 34 may be a single system or multiple systems. The release flow path 34 illustrated in FIG. 1 includes a first release flow path 34a equipped with a solenoid valve 66 and a second release flow path 34b equipped with a rupture disk 68. The solenoid valve 66 opens and closes depending on the tank internal pressure. Meanwhile, the rupture disk 68 is irreversibly destroyed and remains open when the tank internal pressure exceeds the predetermined allowable pressure. By providing such a release flow path 34, an increase in tank internal pressure can be prevented even when a large amount of hydrogen gas is generated in a short period of time that cannot be handled by the boil-off flow path 40 alone.

[0018] Next, the configuration of the boil-off flow path 40 will be described in detail. As described above, the boil-off flow path 40 in this example branches into a first flow path 42 and a second flow path 44. As shown in FIG. 1 , a fuel cell 50 is provided in the first flow path 42. The fuel cell 50 is a generator that generates electricity through an electrochemical reaction between hydrogen gas and air (more specifically, oxygen gas contained in air). In this example, boil-off gas (i.e., hydrogen gas) is supplied to the fuel cell 50 through the first flow path 42. This causes the fuel cell 50 to generate electricity and water. The electricity generated by the fuel cell 50 is stored in the on-board battery 110. The electricity from the on-board battery 110 is used to drive vehicle accessories (e.g., air conditioning) and a starter motor (not shown) of the hydrogen engine 100. In addition, water generated as a by-product is separated into gas and liquid by a gas-liquid separator 52 and then discharged outside the vehicle.

[0019] Conventional liquid hydrogen systems also have a boil-off flow path that directs hydrogen gas (i.e., boil-off gas) from the hydrogen tank 12 to the outside of the tank. However, in conventional liquid hydrogen systems, the boil-off gas is simply discharged outside the vehicle. This results in poor hydrogen utilization efficiency in conventional liquid hydrogen systems. On the other hand, in this example, as described above, the hydrogen gas (boil-off gas) discharged from the hydrogen tank 12 is not simply discarded, but is effectively utilized as energy to drive the vehicle's auxiliary machinery, etc. As a result, this example can improve hydrogen utilization efficiency compared to conventional technology.

[0020] A pressure reducing valve 48 and a shutoff valve 46 are provided in the first flow path 42 upstream of the fuel cell 50. The pressure reducing valve 48 reduces the pressure of the boil-off gas discharged from the hydrogen tank 12 to a pressure suitable for power generation in the fuel cell 50. In principle, the shutoff valve 46 is always open. The shutoff valve 46 is closed only when it is desired to actively stop power generation by the fuel cell 50, for example, when the fuel cell 50 breaks down.

[0021] The second flow path 44 is a flow path that guides excess boil-off gas that cannot be completely discharged through the first flow path 42 to the outside of the vehicle. For example, when the amount of boil-off gas generated per unit time is greater than the amount of hydrogen consumed by the fuel cell 50, or when the on-board battery 110 is fully charged and power generation by the fuel cell 50 cannot continue, the boil-off gas flows into the second flow path 44. The second flow path 44 is provided with a check valve 62 and a reaction section 56. The check valve 62 opens only when the back pressure is equal to or greater than a predetermined opening pressure. The opening pressure of the check valve 62 is sufficiently higher than the output pressure of the pressure reducing valve 48. Therefore, the boil-off gas flows preferentially to the fuel cell 50, and only the excess boil-off gas that cannot be completely consumed by the fuel cell 50 is sent to the reaction section 56.

[0022] The reaction unit 56 converts the hydrogen gas flowing through the second flow path 44 into water by reacting it with air (more precisely, oxygen gas contained in the air), and releases the water outside the vehicle. To cause this hydrogen gas reaction, the reaction unit 56 is provided with a catalyst 58 and a fan 60 that sends air to the catalyst 58. The catalyst 58 induces a reaction that generates water from hydrogen and oxygen (hereinafter referred to as the "water generation reaction") and is made of, for example, copper. When the check valve 62 is opened, the fan 60 rotates and sends air to the catalyst 58. The water generated in the reaction unit 56 is released outside the vehicle. In this way, by converting the excess boil-off gas into water in the reaction unit 56, the excess boil-off gas can be more safely released outside the vehicle. Furthermore, the second flow path 44 can release the boil-off gas outside the vehicle regardless of the charging rate of the on-board battery 110. Therefore, by providing the second flow path 44 in addition to the first flow path 42, an excessive increase in tank internal pressure can be more reliably prevented.

[0023] Here, we will explain the circumstances under which boil-off gas is generated. When the hydrogen pump 16 and, ultimately, the pump motor 18 are driven to drive the hydrogen engine 100, the amount of boil-off gas generated increases due to the heat generated by the drive. The boil-off gas generated at this time can be used to generate electricity in the fuel cell 50, thereby reducing the power supplied to the alternator (not shown). That is, an alternator that generates electricity using power is typically installed inside a vehicle. To ensure sufficient power for the vehicle, a portion of the output power of the hydrogen engine 100 is supplied to the alternator. However, in this case, a portion of the power of the hydrogen engine 100 is used for power generation, which reduces the efficiency of hydrogen utilization. In this example, boil-off gas is used to generate power in the fuel cell 50, thereby reducing or eliminating the amount of power required by the alternator. As a result, the alternator can be made smaller, or even eliminated entirely.

[0024] Furthermore, the hydrogen tank 12 is typically well insulated, and the amount of boil-off gas generated per unit time is small. However, if the vehicle is left parked for a long period of time, a small amount of boil-off gas continues to be released. If the fuel cell 50 continues to generate power using this boil-off gas, the on-board battery 110 may become fully charged during this period. To effectively utilize the boil-off gas that continues to be generated even after the on-board battery 110 is fully charged, the fuel cell 50 may be electrically connected to the external battery 112 while the vehicle is parked. That is, the vehicle may be provided with a detachable connector for the external battery 112, and the fuel cell 50 and the external battery 112 may be electrically connected via this connector while the vehicle is parked. The external battery 112 typically has a larger capacity than the on-board battery 110, and the power of the external battery 112 can also be used to power electrical appliances outside the vehicle. By electrically connecting the external battery 112 to the fuel cell 50, the boil-off gas generated while the vehicle is parked can be converted into electricity without being wasted. As a result, the hydrogen utilization efficiency can be further improved.

[0025] As is clear from the above description, in this example, the fuel cell 50 is provided in the boil-off flow path 40, thereby further improving the efficiency of hydrogen utilization. The configuration described above is merely an example, and other configurations may be modified as appropriate as long as the configuration of claim 1 is included. For example, in the above description, the reaction section 56 is provided in the second flow path 44. However, the reaction section 56 may not be provided, and the excess boil-off gas may be directly released outside the vehicle. Furthermore, a low temperature of the boil-off gas reduces the efficiency of power generation by the fuel cell 50. Therefore, a configuration for heating the boil-off gas may be provided between the hydrogen tank 12 and the fuel cell 50. For example, a heater for heating the boil-off gas may be provided. Alternatively, the boil-off flow path 40 may pass through the vaporizer 24, and the boil-off gas may be heated in the vaporizer 24. [Explanation of symbols]

[0026] 10 liquid hydrogen system, 12 hydrogen tank, 16 hydrogen pump, 18 pump motor, 20 supply circuit, 22 supply flow path, 24 vaporizer, 26 pressure chamber, 28 supply pressure reducing valve, 30 injector, 32 flow meter, 34 discharge flow path, 34a first discharge flow path, 34b second discharge flow path, 40 boil-off flow path, 42 first flow path, 44 second flow path, 46 shut valve, 48 pressure reducing valve, 50 fuel cell, 52 gas-liquid separator, 56 reaction section, 58 catalyst, 60 fan, 62 check valve, 66 solenoid valve, 68 rupture disk, 100 hydrogen engine, 110 on-board battery, 112 external battery.

Claims

[Claim 1] a hydrogen tank for storing liquid hydrogen inside the vehicle; a supply circuit that extracts the liquid hydrogen from the hydrogen tank, converts it into hydrogen gas, and supplies it to a hydrogen engine; a boil-off flow path that guides boil-off gas from the hydrogen tank to the outside of the tank; a fuel cell provided in the boil-off flow path for generating electricity using the boil-off gas and air; A liquid hydrogen system comprising:

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