Combination of h2 storage methods

Abstract

The invention relates to a system (1) for the generation of electric energy, comprising a first oxygen store (2) for oxygen or for an oxygen-containing gas and a first hydrogen store (3) for fluidic hydrogen, a first fuel cell (4) which is connected to the first oxygen store (2) via a first oxygen line (5) and to the first hydrogen store (3) via a first hydrogen line (6), and a first water outlet (7), said system (1) further comprising a second hydrogen store (8) for hydrogen which is bound to a hydrogen carrier and which can be released again by way of the addition of water, a second fuel cell (9) which can be supplied with oxygen via a second oxygen line (10) and which is further connected via a second hydrogen line (11) to the second hydrogen store (8) and has a second water outlet (12), wherein the first and the second water outlet (7, 12) are connected via first and second water lines (13, 14) to a water inlet (15) of the second hydrogen store (8). The invention further relates to a method for the generation of electric energy.

Description

Description TITLE Combination of H2 storage methods TECHNICAL FIELD

[0001] The invention relates to a system for generating electrical energy by means of fuel cells and a corresponding method. BACKGROUND D It is known from the state of the art that when hydrogen (e.g. from a gaseous or liquid hydrogen storage) is fed into a fuel cell together with the appropriate amount of oxygen, water is produced in addition to electrical energy and heat.

[0003] Hydrogen carriers are also known from the state of the art that require liquid water to release hydrogen (e.g., NaBH4). Once this process is initiated and the hydrogen is fed into a fuel cell along with the appropriate amount of oxygen, water is one of the products, in addition to electrical energy and heat. It is particularly important to note that when this hydrogen combines with oxygen in a fuel cell, the corresponding stoichiometric amount of water is again produced, at least theoretically.

[0004] EP 1 880 439 A1 and US 6,864,002 B1 disclose fuel cell systems in which a hydrogen-containing fuel contained in a fuel tank absorbs and reacts with the byproduct water to produce hydrogen, which is supplied to the fuel cell to maintain its operation without the need for external water supply for system operation. This results in a reduction in the weight and volume of the system, as well as internal chemical control of hydrogen production to maintain power generation and internal water management. SUMMARY OF THE INVENTION

[0005] However, there are two problems. First, to initiate this reaction, liquid water is required as a starting material. Second, since reactions generally do not yield 100%, additional water quantities are required within the system boundaries. This means that these additional water quantities (e.g., in additional water tanks) had to be introduced into closed systems from the outset. The object of the invention is therefore to provide a system for generating electrical energy that solves the problems of the initial water supply and the stoichiometrically incomplete water yield. Furthermore, the object of the invention is to provide a corresponding method.

[0007] The object directed to the system is achieved by a system for generating electrical energy, comprising a first oxygen storage device for oxygen or for an oxygen-containing gas and a first hydrogen storage device for fluidic hydrogen, a first fuel cell which is connected to the first oxygen storage device via a first oxygen line and, for supplying hydrogen, to the first hydrogen storage device via a first hydrogen line and has a first water outlet, the system further comprising a second hydrogen storage device for hydrogen bound to a hydrogen carrier and releasable by adding water, characterized in that the first water outlet is connected to a water inlet of the second hydrogen storage device via a first water line and in that a second hydrogen line branches off from the second hydrogen storage device for supplying hydrogen to the system.A fuel cell typically refers to a fuel cell unit or a fuel cell stack.

[0008] By combining different hydrogen storage systems, where one hydrogen storage system produces water in the overall balance and another tends to consume water, the capacity in terms of energy density can be (watt-hours per unit volume or watt-hours per unit mass) of a system.

[0009] In an advantageous embodiment of the invention, the first hydrogen storage device is a compressed gas storage device. By compressing the hydrogen to high pressure (typically 350 to 700 bar), a higher energy density is achieved. This means that more energy can be stored in a smaller volume, which is particularly useful when space is limited or the storage device has to be transported. Furthermore, compressed gas storage devices enable comparatively efficient storage and withdrawal of hydrogen, as the pressure in the storage device can be quickly adjusted as needed. This enables rapid availability of hydrogen for various applications, such as fuel cells in this case. Furthermore, compressed gas storage devices are generally more cost-effective than other storage technologies such as liquid hydrogen storage or metal hydride storage.Finally, compressed gas storage has a lower environmental impact compared to other storage technologies because it does not require chemical reactions or complex cooling processes.

[0010] In an alternative embodiment of the invention, the first hydrogen storage device is a liquefied gas storage device. Hydrogen in liquid form has a higher energy density than gaseous hydrogen at ambient temperature. By converting hydrogen to liquefied gas at extremely low temperatures, more hydrogen can be stored in a given volume. This can be particularly useful when space is limited or the storage device must be transported. Furthermore, liquid hydrogen has a lower risk of leakage than gaseous hydrogen because it can be stored at lower pressures. This reduces the risk of accidents and explosions compared to compressed gas storage devices.

[0011] It is advantageous if the system comprises, in addition to the first fuel cell, a second fuel cell which can be supplied with oxygen or with oxygen-containing gas via a second oxygen line, which is further connected via the first hydrogen line to the first hydrogen storage or via the second Hydrogen line connected to the second hydrogen storage unit or to both hydrogen storage units and having a second water outlet connected to the water inlet of the second hydrogen storage unit via a second water line. The presence of a second fuel cell allows the system to continue generating energy if one of the cells fails, increasing the reliability and availability of the system. Two fuel cells can also help increase the efficiency of the system, as they can be operated in parallel to increase power or maintain the individual cells operating at optimal performance. With two fuel cells, the system can also respond more flexibly to changing energy demands by controlling and adjusting the power of each cell separately.Furthermore, a second fuel cell, connected via a second hydrogen and oxygen line and a second water outlet, can help optimize the system's heat and water management. For example, the waste heat from a fuel cell can be used to heat the water in the second hydrogen storage tank, thus increasing the system's efficiency.

[0012] It is also important that fuel cells are not permanently assigned to a specific hydrogen storage device, but can be supplied with hydrogen from both hydrogen storage devices. In particular, this allows the fuel cells to operate with hydrogen primarily from, for example, the second hydrogen storage device, which can then also be designed larger.

[0013] This has several advantages. Hydrogen as a fluid is highly flammable and can pose a safety risk when stored under pressure or at low temperatures. In a bound hydrogen storage system, the hydrogen is bound to a carrier substance, reducing the risk of ignition or explosion.

[0014] The storage density of hydrogen in bound form can be higher than in gaseous or liquid form. This allows for more compact and efficient storage of hydrogen, which can be beneficial for energy storage and transportation. While gaseous hydrogen must be stored at high pressure and liquid hydrogen at very low temperatures, bound hydrogen can often be stored at ambient temperature and pressure. This reduces the requirements for storage infrastructure and the associated costs.

[0016] Furthermore, bound hydrogen can be stored for longer periods without significant losses, whereas gaseous or liquid hydrogen may be more susceptible to losses due to diffusion or evaporation.

[0017] In one embodiment of the invention, the second fuel cell is connected to the first oxygen storage device via the second oxygen line. This has the advantage that by sharing an oxygen storage device for both fuel cells, the system uses resources more efficiently. This can help reduce the size and weight of the system, which can be particularly advantageous in mobile applications or in situations where available space is limited. Furthermore, a shared oxygen storage device for both fuel cells can help reduce the cost of the system because fewer components are required. This can impact both the initial cost and the maintenance cost. In addition, using a shared oxygen storage device for both fuel cells simplifies the system design because fewer components and connections are required.This can help reduce sources of error and increase the maintainability of the system.

[0018] In an alternative embodiment of the invention, the second fuel cell is connected to a second oxygen reservoir via the second oxygen line. When multiple fuel cells must operate under different operating conditions, the use of separate oxygen reservoirs can allow for better control over the individual requirements of each cell. This can help optimize the efficiency and performance of each fuel cell while allowing precise control of the oxygen flow in different operating conditions. Separate Oxygen storage systems can increase resilience and redundancy in critical applications. If an oxygen storage system fails or becomes damaged, it can only affect a single fuel cell rather than impacting the entire system. In such cases, the failure of one fuel cell can be compensated for by other fuel cells increasing their output to meet the overall energy demand. In some applications, it may be necessary to install fuel cells physically separated from each other, e.g., due to space or thermal constraints. In such cases, the use of separate oxygen storage systems can facilitate fuel cell installation and operation by simplifying the connections between the cells and their respective oxygen storage systems.

[0019] It is advantageous if the system includes a control unit for controlling the mass flows of oxygen or oxygen-containing gas, hydrogen, and water in the system as a function of the amount of electrical energy to be generated. This is crucial for the efficient operation of the system. A control unit enables precise adjustment of the mass flows of oxygen and hydrogen in the fuel cells to generate the desired amount of electrical energy. This can help maximize system efficiency and optimize power output. A control unit can dynamically adjust the mass flows of oxygen, hydrogen, and water based on current power requirements and operating conditions. This enables rapid response to fluctuations in power demand and ensures that the system operates efficiently at all times.The control unit can monitor and control the consumption of hydrogen and oxygen to ensure that resources are used optimally. This can help to minimize hydrogen and oxygen consumption and reduce the operating costs of the system. By precisely controlling the mass flows, the control unit can help to extend the service life of the fuel cells. A consistent and optimal supply of oxygen and hydrogen to the cells can reduce fuel cell degradation and increase their service life. The control unit can also help to increase the safety of the system by controlling the mass flows of. Oxygen, hydrogen, and water are continuously monitored and adjusted to avoid potential hazards such as leaks, overpressure, or uncontrolled reactions. A control unit enables easy integration of fuel cell systems into other electrical systems, such as the power grid or hybrid drives in vehicles. The control unit can adjust electrical energy production based on the requirements of these systems, thus ensuring seamless cooperation.

[0020] It is advisable for the control unit to be connected to controllable valves for controlling the mass flows of oxygen or oxygen-containing gas and hydrogen. This allows the oxygen supply and hydrogen supply to be flexibly adapted to different operating conditions and performance requirements. This allows system performance to be optimized under changing loads or environmental conditions.

[0021] Furthermore, it is advantageous if the control unit is connected to a controllable pump for controlling the mass flow of water. When hydrogen is supplied from the second hydrogen storage unit, which is a hydrolysis-based hydrogen storage system (i.e., the stored hydrogen is chemically bound to a carrier material and can only be released by adding water (or steam), the amount of water supplied automatically regulates the desorption of hydrogen.

[0022] A controllable pump for controlling a mass flow of water for the desorption of hydrogen is usefully supplemented by upstream water storage. Specifically, this means that the first water outlet of the first fuel cell flows into a first water storage tank, and that the second water outlet of the second fuel cell flows into the first water storage tank or a second water storage tank. These measures can lead to more efficient use of the carrier material in the second hydrogen storage tank, because the controlled addition of water from the buffer tanks allows the carrier material to be evenly supplied with water. This can lead to more efficient use of the carrier material and a higher hydrogen yield. Furthermore, a water storage tank enables hydrogen production to be controlled at the respective This allows for adjustment of demand over a much wider range than is possible with valves in the water pipes alone. This means that not only can the water supply be reduced when hydrogen demand is lower, thereby slowing hydrogen release, but the water supply can also be increased further when demand is higher, achieving faster hydrogen production.

[0023] The object directed to a method is achieved by a method for generating electrical energy in which oxygen or oxygen-containing gas is electrochemically combined with hydrogen from a first hydrogen storage device for fluidic hydrogen, whereby electrical energy and water are produced, characterized in that the water is fed to a second hydrogen storage device for hydrogen bound to a hydrogen carrier and releasable by adding water, whereby hydrogen is produced, which in turn is electrochemically combined with oxygen or oxygen-containing gas and the water produced in this process is also fed to the second hydrogen storage device. Excess water does not have to be discarded, but can be stored and fed into the second hydrogen storage unit when needed. It is particularly advantageous if the process is started by electrochemically combining oxygen or oxygen-containing gas with hydrogen from the first hydrogen storage for fluidic hydrogen, whereby in addition to electrical energy and water, heat is also generated with which the second hydrogen storage is heated, and wherein the process is continued by stopping the hydrogen supply from the first hydrogen storage and continuing with hydrogen from the second hydrogen storage.

[0026] However, it may also be advantageous not to completely reduce the hydrogen supply from the first storage facility, but to compensate for the lack of water for the release of hydrogen from the second hydrogen storage facility by supplying a corresponding amount of hydrogen from the first Hydrogen is extracted from the hydrogen storage device and electrochemically combined with oxygen or oxygen-containing gas. By combining various hydrogen storage methods according to the invention, the energy density of the overall system can be improved, for example, by avoiding or minimizing additional water tanks. In addition, the use of heat generated in fuel cells using hydrogen from direct hydrogen storage can help accelerate the release of hydrogen from indirect hydrogen storage. [0G29] In addition, fuel cell systems with integrated liquid or gaseous hydrogen storage have shorter start-up times compared to hydrogen storage processes. SHORT DESCRIPTION OF THE SIGNS

[0030] FIG 1 shows a system for generating electrical energy according to the invention,

[0031] FIG 2 shows an alternative system for generating electrical energy according to the invention and

[0032] FIG 3 shows another system for generating electrical energy according to the invention. DESCRIPTION OF THE EMBODIMENTS

[0033] Figure 1 shows an embodiment of a system 1 for generating electrical energy 22 according to the invention. Furthermore, Figure 1 indicates that not only electrical energy 22 but also water (first water reservoir 20, second water reservoir 21) is generated, and that a certain amount of heat 23 is also generated.

[0034] The system 1 comprises a first oxygen storage 2 for oxygen or for an oxygen-containing gas and a first hydrogen storage 3 for fluidic hydrogen. The hydrogen storage 3 can be a compressed gas storage or be designed as a liquid gas storage device. The system 1 further comprises a first fuel cell 4, which is connected to the first oxygen storage device 2 via a first oxygen line 5 and to the first hydrogen storage device 3 via a first hydrogen line 6 and has a first water outlet 7. The system 1 further comprises a second hydrogen storage 8 for hydrogen bound to a hydrogen carrier and releasable by adding water, a second fuel cell 9 which can be supplied with oxygen via a second oxygen line 10, which is further connected to the second hydrogen storage 8 via a second hydrogen line 11 and has a second water outlet 12. According to the invention, the first and second water outlets 7, 12 are connected to a water inlet 15 of the second hydrogen storage 8 via first and second water lines 13, 14.

[0037] In the embodiment of Figure 1, the second fuel cell 9 is connected to a second oxygen storage 16.

[0038] Efficient operation of system 1 is ensured by a control unit 17 for controlling the mass flows of oxygen, hydrogen, and water as a function of the amount of electrical energy to be generated. For example, the oxygen quantities to be supplied to the first and second fuel cells 4, 9 are controlled by controllable valves 18 arranged in the first and second oxygen lines 5, 10. Analogously, controllable valves 18 are arranged in the first and second hydrogen lines 6, 11 to regulate the hydrogen supply to the fuel cells 4, 9. Additionally, pumps 19 with adjustable power are arranged in the first and second water lines 13, 14 to regulate the hydrogen supply to the second fuel cell 9 and are connected to the control unit 17.

[0040] For more flexibility in the operation of System 1, the first Water outlet 7 into a first water reservoir 20. The second water outlet 12 can flow into the first water reservoir 20 or, as shown in Figure 1, into the second water reservoir 21.

[0041] Figure 2 shows a greatly simplified variant of the system 1 for generating electrical energy according to the invention compared to the exemplary embodiment in Figure 1. The system 1 for generating electrical energy comprises only a first oxygen storage device 2 for oxygen or for an oxygen-containing gas and a first hydrogen storage device 3 for fluidic hydrogen, a first fuel cell 4, which is connected to the first oxygen storage device 2 via a first oxygen line 5 and, for supplying hydrogen, to the first hydrogen storage device 3 via a first hydrogen line 6, and has a first water outlet 7.According to the invention, the system 1 further comprises a second hydrogen storage 8 for hydrogen bound to a hydrogen carrier and releasable by adding water, the first water outlet 7 is connected via a first water line 13 to a water inlet 15 of the second hydrogen storage 8 and a second hydrogen line 11 branches off from the second hydrogen storage 8 and opens into the first fuel cell 4.

[0042] In the embodiment of Figure 2, a controller 17 with the associated controllable valves 18 and pump 19 is also provided for the efficient operation of the system 1. The embodiment of Figure 3 shows the system 1 for generating electrical energy according to the invention, comprising a first fuel cell 4 and a second fuel cell 9. In addition to the embodiment of Figure 1, the first fuel cell 4 is not only connected to the first hydrogen storage device 3, but can also be supplied with hydrogen from the second hydrogen storage device 8, as already shown in Figure 2. For reasons of clarity, Figure 3 does not show that such a hydrogen supply from both hydrogen storage devices 3, 8 is of course also sensible and possible for the second fuel cell 9. REFERENCE NUMBER LIST 1 system for generating electrical energy 2 first oxygen storage 3 first hydrogen storage (for fluid hydrogen) 4 first fuel cell 5 first oxygen line 6 first hydrogen pipeline 7 first water outlet 8 second hydrogen storage (with hydrogen carrier) 9 second fuel cell 10 second oxygen line 11 second hydrogen pipeline 12 second water outlet 13 first water pipe 14 second water pipe 15 Water inlet 16 second oxygen storage 17 Control unit 18 controllable valve 19 controllable pump 20 first water reservoir 21 second water reservoir 22 electrical energy 23 Heat

Claims

Claims What is claimed:

1. System (1) for generating electrical energy, comprising a first oxygen storage device (2) for oxygen or for an oxygen-containing gas and a first hydrogen storage device (3) for fluidic hydrogen, a first fuel cell (4) which is connected to the first oxygen storage device (2) via a first oxygen line (5) and, for supplying hydrogen, to the first hydrogen storage device (3) via a first hydrogen line (6), and which has a first water outlet (7), the system (1) further comprising a second hydrogen storage device (8) for hydrogen bound to a hydrogen carrier and which can be released again by adding water, characterized in that the first water outlet (7) is connected to a water inlet (15) of the second hydrogen storage device (8) via a first water line (13), and in that a second hydrogen line (11) branches off from the second hydrogen storage device (8) for supplying hydrogen in the system (1).

2. The system (1) according to claim 1, wherein the first hydrogen storage (3) is a compressed gas storage.

3. The system (1) according to claim 1, wherein the first hydrogen storage (3) is a liquid gas storage.

4. The system (1) according to one of the preceding claims, further comprising a second fuel cell (9) which can be supplied with oxygen or with oxygen-containing gas via a second oxygen line (10), which is further connected via the first hydrogen line (6) to the first hydrogen storage device (3) or via the second hydrogen line (11) to the second hydrogen storage device (8) or to both hydrogen storage devices (6, 11) and has a second water outlet (12) which is connected via a second water line (14) to the water inlet (15) of the second hydrogen storage device (8).

5. The system (1) according to claim 4, wherein the second fuel cell (9) is connected to the first oxygen storage (2) via the second oxygen line (10).

6. The system (1) according to claim 4, wherein the second fuel cell (9) is connected to a second oxygen storage (16) via the second oxygen line (10).

7. The system (1) according to any one of the preceding claims, further comprising a control unit (17) for controlling the mass flows of oxygen or oxygen-containing gas, hydrogen and water in the system (1) as a function of an amount of electrical energy to be generated.

8. The system (1) according to claim 7, wherein the control unit (17) is connected to controllable valves (18) for controlling the mass flows of oxygen or oxygen-containing gas and hydrogen.

9. The system (1) according to one of claims 7 or 8, wherein the control unit (17) is connected to a controllable pump (19) for controlling a mass flow of water.

10. The system (1) according to one of the preceding claims, wherein the first water outlet (7) opens into a first water reservoir (20).

11. The system (1) according to claims 4 and 10, wherein the second water outlet (12) opens into the first water reservoir (20) or a second water reservoir (21).

12. A method for generating electrical energy in which oxygen or oxygen-containing gas is electrochemically combined with hydrogen from a first hydrogen storage device (3) for fluidic hydrogen, whereby electrical energy and water are produced, characterized in that the water is fed to a second hydrogen storage device (8) for hydrogen bound to a hydrogen carrier and releasable by adding water, whereby hydrogen is produced, which in turn is electrochemically combined with oxygen or oxygen-containing gas and the water produced in this process is also fed to the second hydrogen storage device (8).

13. The method of claim 12, wherein excess water is stored.

14. The method according to one of claims 12 or 13, wherein the method is started by electrochemically combining oxygen or oxygen-containing gas with hydrogen from the first hydrogen storage device (3) for fluidic hydrogen, wherein, in addition to electrical energy and water, heat is also generated with which the second hydrogen storage device (8) is heated, and wherein the method is continued by stopping the hydrogen supply from the first hydrogen storage device (3) and continuing with hydrogen from the second hydrogen storage device (8).

15. The method according to one of claims 12 or 13, wherein missing quantities of water for the release of hydrogen from the second hydrogen storage (8) are compensated by taking a corresponding quantity of hydrogen from the first hydrogen storage (3) and electrochemically combining it with oxygen or with oxygen-containing gas.

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