Apparatus with a hydrogen storage alloy reservoir for operating a heat generating hydrogen consumer - Patent application

Abstract

To provide a fuel cell including an efficient cold starter that can be put into operation instantly and does not require a pressure tank.SOLUTION: A fuel cell includes at least one starting tank with a hydrogen storage alloy with cold start characteristics, and at least one operating tank or at least one reformer with at least one medium temperature hydride, and the starting tank is in fluid communication with an exothermic hydrogen consumer and the operating tank or the reformer, and a first starting tank includes a hydrogen storage alloy with equilibrium pressure for release at temperature of -40°C at least 100 kPa, and further includes a cooling device that allows hydrogen filling by the operating tank or the reformer while the fuel cell is being fed.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a cold start device comprising a hydrogen storage alloy reservoir for an exothermic hydrogen consumer, such as a fuel cell, and also to a method of operating such an exothermic hydrogen consumer. [Background technology]

[0002] In water electrolysis, water molecules are split into hydrogen (H2) and oxygen (O2) by an electric current. This process works in reverse in a fuel cell. The energy liberated by the electrochemical synthesis of hydrogen (H2) and oxygen (O2) into water can be converted to electricity with high efficiency.

[0003] The industrial implementation of the fuel cell principle has led to various approaches using different types of electrolytes and operating temperatures ranging from 10°C to 1000°C. Depending on their operating temperature, fuel cells are classified as low-temperature, intermediate-temperature and high-temperature fuel cells (see, for example, patent document 1). Low-temperature fuel cells operate at relatively moderate operating temperatures of 60°C to 120°C and, due to their moderate temperatures, are particularly suitable for mobile applications such as the operation of automobiles. In automobiles, low-temperature PEM type fuel cells are preferably used and operate in the temperature range of 60°C to 90°C.

[0004] The hydrogen required as fuel is usually supplied from pressure tanks, since hydrogen can be available over the entire operating temperature range when using such tanks. However, these pressure tanks are relatively large, so the range of mobile applications, such as during the operation of a car, is limited by the limited available storage space. It is known that hydrogen stores with a comparable capacity and taking up much less space can be made based on hydrogen storage alloys, these are known as hydrogen storage alloy stores. However, heat must be supplied to the hydrogen storage alloy stores to release the hydrogen, and for the storage of hydrogen the heat must be removed. Depending on the hydrogen storage alloy, temperatures in the range of -30 °C to 400 °C are required for hydrogen release. On the other hand, hydrogen pressures of less than 10 MPa are generally required, which is sufficient for the operation of a fuel cell, greatly simplifying the construction of these tanks compared to hydrogen pressure tanks.

[0005] Hydrogen storage alloys used as hydrogen reservoirs are also divided into various classifications as a function of release temperature. A summary of conventional hydrogen storage alloys and their properties can be found in "Hydrogen Storage Alloys" by John Wiley & Sons, Inc., 1999, Vol. 11, No. 1, pp. 1171-1175, 2002, which is incorporated herein by reference. Hydrogen is contained (stored) in the metal lattice and released (released) from the hydride according to the following equation: Metal + hydrogen ⇔ hydrogen storage alloy + heat The relationship between pressure, temperature and hydrogen concentration in a metal is represented as a concentration-pressure isotherm (CPI). As the pressure is increased, hydrogen is dissolved in the metal lattice at a given temperature. This process follows Sievert's law until a saturation concentration (α phase) is obtained. Then, the concentration in the metal increases without increasing the pressure and a hydride phase (β phase) is formed. This plateau region follows both van't Hoff's law and Gibbs' phase rule. At the end of the plateau, the pressure increases again quadratically and hydrogen is dissolved in the hydride phase according to Sievert's law. To compare different hydrides, it is customary to construct van't Hoff diagrams using equilibrium values ​​in the middle of the plateau. The reaction enthalpy (ΔH abs ) can be read off from the slope of the line.

[0006] For intermediate temperature hydrides, desorption at 10 kPa standard pressure begins in the range of 100°C to 200°C. Intermediate temperature hydrides have absolute reaction enthalpies (ΔH abs ) generally have a hydrogen storage density of about 2.5% to 5% by weight based on the parent metal. Intermediate temperature hydrides include, among others, alanines such as NaAlH4 and amides such as LiNH2, which have an H2 storage capacity of up to 4.5% by weight. The optimum hydrogen storage temperature is, for example, about 125°C for sodium alanine, and the hydrogen release temperature is 160-185°C. Intermediate temperature hydrides are promising candidates for mobile applications due to their relatively high hydrogen storage capacity and relatively low operating temperatures.

[0007] For high-temperature hydrides, desorption at 10 kPa standard pressure begins above 200 °C. They have an absolute reaction enthalpy ΔH for the hydrogen storage reaction higher than 65 kJ / mol H2. abs They generally have a higher hydrogen storage density of about 7% to 15% by weight based on the parent metal. They are often formed with light metals (magnesium, aluminum) and / or non-metals (nitrogen, bromine), and therefore their high capacity would likely make them suitable for use in fuel cells and H2 internal combustion engines, but their high temperatures make their use as reservoirs for fuel cells problematic. Thus, high temperature hydrides are not currently used in fuel cells and H2 internal combustion engines.

[0008] Low-temperature hydrides, with release temperatures at 10 kPa standard pressure in the range of -40°C to 100°C or less, are only used in very special cases of mobile applications, especially forklift and two-wheeler prototypes, where low storage capacities can be tolerated due to their relatively low gravimetric storage capacity for less than 2 wt.% hydrogen. They have absolute reaction enthalpies ΔH for the hydrogen absorption reaction of H2 of less than 30 kJ / mol. abs is defined as follows:

[0009] For general use of hydrogen storage alloys, it is therefore necessary to have an external heating system that heats the hydrogen storage alloys to its discharge temperature. The energy required for heating the hydrogen storage alloys has hitherto generally been taken from a fuel cell or other heat source. However, it is not possible to take the energy required for discharging the hydrogen storage alloys during the first minutes of operation when starting the fuel cell and when it has not yet provided enough heat to heat the hydrogen storage alloys. Furthermore, in practice known fuel cells can only generate power for external use above a certain starting temperature. Therefore, in the case of a cold start or a quick start, the fuel cell must first be heated to a temperature above the starting temperature. Due to the large thermal mass of the fuel cell, a considerable heating power is required for this purpose, especially when a cold start is also to occur in a short time, as in the case of conventional internal combustion engines.

[0010] The same applies to supplying the fuel cell with hydrogen from a reformer using fuels such as methanol, ammonia, formic acid or LOHC (Liquid Organic Hydrogen Carrier). Energy is now also needed, not yet available in the system, to start the fuel cell via the reformer.

[0011] A fuel cell for mobile applications with a cold start device is known from US Pat. No. 5,399,633, which comprises a hydrogen pressure tank as hydrogen storage and a device for heating the hydrogen storage alloy. Hydrogen from the pressure tank is circulated through the storage of released hydrogen storage alloy. This improves the performance of the fuel cell system, since the temperature rise is accompanied by the formation of a corresponding hydrogen storage alloy. However, in the case of the cold start device known from US Pat. No. 5,399,633, the number of cold and instant start processes is limited by the size of the pressure storage, since the pressure storage is gradually discharged and is not automatically recharged at each cold start and instant start. Therefore, this system only offers an improved function of the storage by the pressure tank, which allows cold and instant starts even without the device.

[0012] Non-Patent Document 2 discloses the synthesis of complex hydrides and room temperature hydrides in a tank, which improves cold start characteristics with a high loading capacity of the complex hydride (CxH) and a high reaction rate of the room temperature hydride (MeH). The room temperature hydride is filled with hydrogen during cold start and heats up as a result of an exothermic reaction. The complex hydride also heats up as a result, so it gradually reaches the operating temperature and gradually releases hydrogen, thereby supplying hydrogen to the fuel cell. Due to this reaction cascade of the room temperature hydride and the complex hydride and the slow heating up of the complex hydride, the system is relatively slow. Furthermore, the document does not describe how the loading of the room temperature hydride should be performed.

[0013] Non-Patent Document 3 describes LaNi as a hydrogen storage alloy for heat generation. 4.85 Al 0.15 and HYDRALLOY C5 (registered trademark) (Ti) as a hydrogen storage alloy for hydride supply below 0°C. 0.95 Zr 0.05 Mn 1.46 V 0.45 Fe 0.09 We will tackle the charging and discharging of a closed system consisting of

[0014] All the above mentioned systems are based on the fuel cell being supplied by a hydrogen storage alloy which is heated by another heat source before starting. Only after the hydrogen storage alloy is heated, the fuel cell is operational. It is the object of the present invention to provide an efficient cold start device for an exothermic hydrogen consumer such as a fuel cell, which can be put into operation immediately and does not require a pressure tank or an external hydrogen source, which is a disadvantage due to the limited space available in, for example, a passenger car. Furthermore, the cold start device should be available for a large number of starting operations, independent of its storage capacity. [Prior art documents] [Patent documents]

[0015] [Patent Document 1] DE 19836352 A1 [Patent Document 2] German Patent No. 10317123 [Non-patent literature]

[0016] [Non-Patent Document 1] B. Sakintuna et al., “Metal hydride materials for solid hydrogen storage: A review”, International Journal of Hydrogen Energy, vol. 32 (2007), 1121-1140 [Non-Patent Document 2] I. Burger et al., "Advanced reactor concept for complex hydrides: Hydrogen absorption from room temperature," International Journal of Hydrogen Energy, vol. 39 (2014), pp. 7030-7041 [Non-Patent Document 3] M. Kolbig et al., "Characterization of metal hydrides for thermal applications in vehicles below 0°C," International Journal of Hydrogen Energy, vol. 44 (2019), pp. 4878-4888 Summary of the Invention

[0017] According to the invention, this object is achieved by a method for operating an exothermic hydrogen consumer, such as a fuel cell, having the features set forth in claim 1. Preferred embodiments of the invention are set forth in the dependent claims. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] A first embodiment of the present invention provides an apparatus for operating an exothermic hydrogen consumer, such as a fuel cell, comprising: an exothermic hydrogen consumer; at least one start-up tank comprising a first hydrogen storage alloy having cold start characteristics; and an absolute reaction enthalpy (ΔH) for the hydrogen storage reaction in the range of less than 80 kJ / mol H2, preferably 20 kJ / mol H2 to less than 65 kJ / mol H2. abs and at least one operating tank or at least one reformer, the at least one second hydrogen storage alloy having a cold start characteristic, the at least one second hydrogen storage alloy having an equilibrium pressure for release of hydrogen at a temperature of -40°C of less than 100 kPa, the start-up tank being in fluid communication with the exothermic hydrogen consumer and the operating tank or reformer, the first hydrogen storage alloy having cold start characteristics having an equilibrium pressure for release of hydrogen at a temperature of -40°C of at least 100 kPa, and the start-up tank further comprising a cooling device to enable it to be filled with hydrogen from the operating tank or reformer while the exothermic hydrogen consumer is being supplied.

[0019] The exothermic hydrogen consumer is preferably a fuel cell comprising at least one cathode and at least one anode with an electrolyte disposed therebetween. The exothermic hydrogen consumer is most preferably a PEM fuel cell, for example a low temperature PEM fuel cell.

[0020] The start-up tank is preferably spherical or cylindrical in shape. In one embodiment of the invention, the hydrogen storage alloy of the start-up tank is of the titanium-chromium-manganese alloy series.

[0021] A second embodiment of the present invention provides a method of operating an exothermic hydrogen consumer, such as a fuel cell, in which the exothermic hydrogen consumer is first supplied with hydrogen from at least one start-up tank comprising a first hydrogen storage alloy having an equilibrium pressure for release at a temperature of -40°C of at least 100 kPa, and after reaching the operating temperature of the exothermic hydrogen consumer, an absolute reaction enthalpy (ΔH) for the hydrogen storage reaction in the range of less than 80 kJ / mol H2, preferably 20 kJ / mol H2 to less than 65 kJ / mol H2. abs) having an equilibrium pressure for hydrogen release at a temperature of -40°C less than 100 kPa, and the hydrogen storage alloy of the start-up tank is cooled to be filled with hydrogen from the second operating tank or reformer while the hydrogen consumer is simultaneously being supplied by the second operating tank or reformer.

[0022] As mentioned above, the hydrogen consumer is initially supplied with hydrogen from a start-up tank, which preferably comprises at least one hydrogen storage alloy having an equilibrium pressure for release at a temperature of -40°C of at least 300 kPa, more preferably at least 1000 kPa, in particular at least 1300 kPa, which is particularly advantageous for fuel cells operating in recirculation mode.

[0023] According to the method of the invention, an exothermic hydrogen consumer, such as a fuel cell, receives a sufficient supply of hydrogen from a start-up tank under cold start conditions so that the exothermic hydrogen consumer is started up and warmed up to the operating temperature. Then, the operating tank or reformer as the main hydrogen storage is likewise heated to its operating temperature by waste heat or electricity, if any, from the exothermic hydrogen consumer, e.g. a fuel cell, and takes over supplying hydrogen to the hydrogen consumer. If the hydrogen consumer is supplied by the operating tank or reformer, the start-up tank is refilled with hydrogen from the operating tank or reformer. For this purpose, the start-up tank needs to be cooled, for example by a Peltier element. The cooling reduces the equilibrium pressure of the first hydrogen storage alloy in the start-up tank, which can then be refilled with hydrogen from the main storage (operating tank or reformer), so that a new start-up operation can be performed after switching off the exothermic hydrogen consumer. For this purpose, the start-up tank needs to be connected between the hydrogen consumer and the operating tank, or the start-up tank, the hydrogen consumer and the operating tank need to be arranged so that hydrogen from the start-up tank can flow not only to the consumer but also (in a separate switching configuration) from the operating tank to the start-up tank.

[0024] The described method with refilling of the start-up tank during the operation of the exothermic hydrogen consumer allows for significantly more cold start operations that are not limited by the volume of the start-up tank compared to previous approaches, which is an advantageous effect of the present invention in addition to the simplified configuration of the device for the operation of, for example, a fuel cell. Furthermore, the approach provided by the present invention allows the use of very cheap storage means for the main hydrogen storage, without the need for cold and / or instant start characteristics per se. As a result, it becomes possible to use hydrogen storage alloys with higher efficiency etc., or other cheap hydrogen supply devices (for example reformers) that do not have the ability of cold and / or instant start. The device and the method of the present invention ensure the supply of hydrogen for the operation of exothermic hydrogen consumers, such as fuel cells for automotive applications, especially at low temperatures, without the delays of pressure tanks, but without their expensive configuration and with very small space requirements.

[0025] In a further embodiment of the invention, the start-up tank has a shell around the first hydrogen storage alloy present therein, which shell can withstand hydrogen pressure up to the maximum equilibrium pressure of the hydride at the operating temperature of the heat-generating hydrogen consumer, such as a fuel cell, or the maximum operating temperature of an external heating device, preferably a Peltier element cooling, which can in turn serve as a heating device. Super duplex stainless steels or fiber-reinforced composites are suitable for the shell of the reservoir of the first hydrogen storage alloy. The lower the equilibrium pressure at the operating temperature of the heat-generating hydrogen consumer and therefore the maximum possible temperature in the system, the thinner and lighter the shell of the reservoir of the first hydrogen storage alloy can be.

[0026] In a further embodiment of the invention, the device for operating an exothermic hydrogen consumer, such as a fuel cell, comprises a cooling system for cooling the operating tank or the start-up tank for refilling as soon as the reformer takes over the supply to the fuel cell. Peltier elements have the advantageous effect here of being very space-saving and allowing direct cooling of the shell by thermal conduction or cooling of the tank system by internal cooling channels in combination with a heat exchanger. Furthermore, systems based on Peltier elements do not require maintenance, since they do not contain moving parts. Finally, they are easily reversible (cooling can also be used for heating by reversing the electrical polarity). As an alternative, it is also possible to use conventional compressor-based cooling installations, preferably reversible (functioning as heating).

[0027] The hydrogen storage alloy of the start-up tank is preferably selected such that hydrogen is released under sub-zero start-up conditions such as -40°C or similar low temperatures. Even if a hydrogen storage alloy with a higher release temperature is selected, to still allow hydrogen release, for example at very low temperatures, heat transfer from the surroundings can be provided as needed, for example by a Peltier element acting as heating, by a conventional separate heating device, or by the cooling medium of an exothermic hydrogen consumer.

[0028] The beneficial effect is that heat transfer is retarded by the low supply pressure of the exothermic hydrogen consumer or by the high charge and operating pressure during operation, so that in either case additional heat is only required if the system is supplying this heat.

[0029] When the exothermic hydrogen consumer reaches its normal operating temperature (approximately 60°C-80°C for low-temperature PEM fuel cells) as a result of the operation enabled by the start-up tank, the operating tank or the reformer and any further consumers present in the vehicle, e.g., on-board heating, can be supplied with thermal energy from the fuel cell waste heat. A further portion of the power from the exothermic hydrogen consumer, typically electrical power (e.g., less than 5%), is utilized to cool the start-up tank via its dedicated cooling system after this operating state is reached.

[0030] The operating tank or reformer is preferably configured such that at its native operating temperature, which is not necessarily the same as the operating temperature of the exothermic hydrogen consumer, it produces a hydrogen pressure higher than the equilibrium pressure of the cold start tank, thereby allowing the start tank to be refilled from the operating tank.

[0031] The heat generated in the start-up tank during refilling is preferably removed in order to keep the equilibrium pressure in the start-up tank constant and to allow the start-up tank to be refilled. As soon as the start-up tank is completely filled, the cooling facility can be switched off.

Claims

1. 1. An apparatus for operating a heat generating hydrogen consumer, such as a fuel cell, comprising: said heat generating hydrogen consumer; at least one start-up tank comprising a first hydrogen storage alloy having cold start characteristics; and a hydrogen storage alloy having a hydrogen storage capacity of less than 80 kJ / mol. ２ Absolute reaction enthalpy (ΔH ａｂｓ and at least one operating tank or at least one reformer, the at least one second hydrogen storage alloy having a cold start characteristic, the at least one second hydrogen storage alloy having an equilibrium pressure for release of hydrogen at a temperature of -40°C of less than 100 kPa, the start-up tank being in fluid communication with the exothermic hydrogen consumer and the operating tank or the reformer, the first hydrogen storage alloy having cold start characteristics having an equilibrium pressure for release of hydrogen at a temperature of -40°C of at least 100 kPa, and the start-up tank further comprising a cooling device to allow the start-up tank to be filled with hydrogen from the operating tank or the reformer while the exothermic hydrogen consumer is being supplied by the operating tank or the reformer.

2. 10. The apparatus of claim 1, wherein the exothermic hydrogen consumer is a fuel cell comprising at least one cathode and at least one anode with an electrolyte disposed therebetween.

3. 3. The apparatus of claim 1 or claim 2, wherein the start-up tank comprises a hydrogen storage alloy having an equilibrium pressure for release at a temperature of -40°C of at least 300 kPa.

4. 4. The apparatus of claim 3, wherein the start-up tank comprises a hydrogen storage alloy having an equilibrium pressure for release at a temperature of -40°C of at least 1300 kPa.

5. 5. The apparatus according to claim 1, wherein the hydrogen storage alloy of the start-up tank is of the titanium-chromium-manganese alloy type.

6. 6. The device according to claim 1, wherein cooling of the store of the first hydrogen storage alloy is provided by a Peltier element or by compressor system cooling.

7. 1. A method for operating an exothermic hydrogen consumer, such as a fuel cell, comprising: first receiving a supply of hydrogen from at least one start-up tank comprising a first hydrogen storage alloy having an equilibrium pressure for release at a temperature of −40° C. of at least 100 kPa; and after reaching the operating temperature of the exothermic hydrogen consumer, producing less than 80 kJ / mol of H ２ Absolute reaction enthalpy (ΔH ａｂｓ ), the at least one second hydrogen storage alloy having an equilibrium pressure for release of hydrogen at a temperature of -40°C of less than 100 kPa, or a reformer, wherein the hydrogen storage alloy of the start-up tank is cooled for being filled with hydrogen from the operating tank or reformer while the heat-generating hydrogen consumer is simultaneously being supplied by the operating tank or reformer.

8. 8. The method of claim 7, wherein the exothermic hydrogen consumer is a fuel cell comprising at least one cathode and at least one anode with an electrolyte disposed therebetween.

9. 9. The method according to claim 7 or 8, wherein the start-up tank comprises a hydrogen storage alloy having an equilibrium pressure for release of hydrogen at a temperature of -40°C of at least 300 kPa.

10. 10. The method of claim 9, wherein the start-up tank comprises a hydrogen storage alloy having an equilibrium pressure for release of hydrogen at a temperature of -40°C of at least 1000 kPa.

11. 11. The method of claim 10, wherein the start-up tank comprises a hydrogen storage alloy having an equilibrium pressure for release of hydrogen at a temperature of -40°C of at least 1300 kPa.

12. 12. The method according to any one of claims 7 to 11, wherein the hydrogen storage alloy of the starter tank is of the titanium-chromium-manganese alloy type.

13. 13. The method according to any one of claims 7 to 12, wherein cooling of the store of first hydrogen storage alloy is provided by a Peltier element or by compressor system cooling.

14. 14. The method of claim 7, wherein waste heat from the exothermic hydrogen consumer is used to heat the operating tank or the reformer while the exothermic hydrogen consumer is being supplied by the operating tank or the reformer.