Method for operating a submarine with a fuel cell and a hydrogen storage system

Description

[0001] The invention relates to a method for increasing the submerged range of a submarine which operates with a fuel cell and a hydrogen storage system.

[0002] The use of fuel cells in a submarine is different from virtually every other use of fuel cells. Because the fuel cell is used to generate power while submerged, there is no air from which oxygen can be extracted, no ambient air into which residual gases can be easily released, the ambient pressure in a submarine fluctuates, and range is important—the distance the submarine can travel submerged on one tank of fuel.

[0003] EP 2 840 636 A1 discloses a fuel cell with circulation operation in which inert gas disposal takes place.

[0004] WO 2010 / 056829 A2 discloses a process for separating components from a gas stream.

[0005] EP 2 687 282 A1 discloses a process for separating hydrogen from a hydrogen-containing gas mixture in a membrane with high purge gas pressure.

[0006] A fuel cell module with a water separator is known from US 2007 / 0065711 A1.

[0007] From DE 696 02 805 T2 a fuel cell with a gas-liquid mixing unit and a gas-liquid separation device is known.

[0008] From DE 43 18 818 C2 a device for providing process air for the operation of air-breathing fuel cell systems is known.

[0009] DE 603 13 309 T2 discloses a fuel cell system with a humidifier and a gas-liquid separator.

[0010] A fuel cell system with a recirculation device is known from AT 501 963 A1.

[0011] A fuel cell with a recirculation circuit is known from WO 2005 / 064730 A2.

[0012] A fuel cell system with water injection and humidifiers is known from JP 2000-58092 A.

[0013] A quick coupling device is known from CN 102 569 851 A1.

[0014] A fuel cell system with modules is known from US 2004 / 0043724 A1.

[0015] A modular fuel cell system is known from US 2013 / 0280635 A1.

[0016] A fuel cell with means for removing product water is known from US 4,976,162.

[0017] A fuel cell with a distribution pipe is known from US 2012 / 0135326 A1.

[0018] A submarine fuel cell device with a modular design is known from DE 10 2004 004624 B3.

[0019] A fuel cell stack is known from DE 10 2014 219164 A1.

[0020] DE 198 22 697 C1 discloses a fuel cell system with connections for a gas source and electrical connections.

[0021] From DE 10 2007 051311 A1 a fuel tank with at least one interface for a fuel cell module is known, wherein the interface enables a detachable coupling.

[0022] DE 102011 100 534 A1 discloses a method for operating a reformer fuel cell system.

[0023] EP 2 521 210 A2 discloses a method for operating a reformer fuel cell system.

[0024] From DE 10 2099 036 435 A1 a supply arrangement for a fuel cell pack, a fuel cell module and a method for operating the fuel cell module are known.

[0025] The operation of a gas system for an underwater vehicle is known from US 2015 / 0204486 A1.

[0026] WO 00 / 63993 A1 discloses a network-independent, pollutant-emission-free portable power supply device and a method for generating electricity by means of this device.

[0027] A hypergolic hydrogen generator system for fuel cell power plants is known from US 2005 / 0031918 A1.

[0028] The object of the invention is to maximize the range with a given amount of hydrogen for a submarine with a fuel cell.

[0029] This object is achieved by the method having the features specified in claim 1. Advantageous further developments emerge from the subclaims, the following description, and the drawings.

[0030] The method according to the invention is used to operate a submarine with a fuel cell and a hydrogen storage unit, as well as a pressure regulator between the hydrogen storage unit and the fuel cell. The method comprises the following steps: Specifying a first pressure for the anode side of the fuel cell, wherein the first pressure is designed as an ideal value for control operation, specifying a second pressure for the anode side of the fuel cell, wherein the second pressure is the minimum pressure, detecting a storage pressure at which hydrogen is supplied from the hydrogen storage to the pressure regulator, selecting a working pressure depending on the storage pressure, which is supplied to the anode side of the fuel cell and is adjusted by the pressure regulator.

[0031] The working pressure is selected depending on the storage pressure as well as the first pressure and the second pressure.

[0032] The ideal value is a preset value that should be set for optimal steady-state operation without external restrictions. This ideal value results, for example, from optimization with regard to durability, the amount of electrical energy generated, and efficiency. The goal would therefore be to operate the fuel cell at a pressure corresponding to the ideal value during normal operation.

[0033] The minimum pressure is the pressure below which the fuel cell shuts down. If the pressure provided by the hydrogen storage tank is insufficient to reach the minimum pressure in the fuel cell, the fuel cell shuts down. In this case, the submarine must first be refueled with hydrogen before the fuel cell can be restarted.

[0034] The goal is to bring together various conflicting optimizations. On the one hand, it is desirable to operate at high pressure, as the efficiency of the fuel cell is particularly high at high partial pressures on the anode and cathode sides. On the other hand, the low to no pressure difference reduces the mechanical stress on the membrane. Furthermore, it is desirable to operate the fuel cell at very low pressure, as this allows the hydrogen reservoir to be emptied as far as possible, thus making more hydrogen available for energy generation and thus increasing the range. Furthermore, it must be considered that constant conditions are preferred for the operation of the fuel cell, including its service life.

[0035] It has therefore been shown that selecting the first pressure and the second pressure and regulating the working pressure as a function of the accumulator pressure between the first pressure and the second pressure leads to the maximum range of a submarine. In control operation, the working pressure is maintained at the first pressure, for example by the pressure regulator or a control device controlling the pressure regulator, as long as the accumulator pressure is high enough to keep the working pressure at the first pressure. Due to the pressure loss that occurs in a pressure regulator, the accumulator pressure must be correspondingly higher than the first pressure. When the accumulator is emptied to the point that the accumulator pressure drops below the first pressure but is still above the second pressure, the working pressure is reduced to a range between the first pressure and the second pressure.The reduction can occur continuously, for example, following the drop in the storage pressure. Alternatively, the operating pressure can also be reduced gradually or, in a further alternative, in one step to a pressure just above the second pressure. It is important that this allows the fuel cell to operate at an optimal pressure for as long as possible and then continue operating at a lower pressure to allow the hydrogen storage to be emptied as far as possible, thus achieving the maximum range by combining these two operating ranges.

[0036] It is important to note that the pressure delivered by a hydrogen storage device usually depends on the fill level. For pressure storage devices, the relationship is almost linear, but with metal hydride storage devices, a different dependency can be observed. This distinguishes a hydrogen storage device from a hydrogen generator, such as a reformer. The latter provides a more or less constant pressure for generating hydrogen, practically independent of the fill level of the reactant supply, but has at least a predetermined minimum pressure for operation due to operational reasons. This also applies if, for example, an intermediate storage device is connected downstream of the reformer. Such an intermediate storage device must be distinguished from a hydrogen storage device according to the invention.

[0037] To optimize range and keep the acoustic signature as low as possible, a compressor is omitted. This means that the working pressure cannot exceed the storage pressure. With a compressor, the working pressure could, of course, be selected completely independently of the storage pressure. The storage tank is also not filled by a reformer or other hydrogen generator while the submarine is underway, so the storage pressure drops over the operating time. The storage tank is refilled by refueling from the outside.

[0038] According to the invention, the pressure between the hydrogen storage unit and the fuel cell is not increased. Therefore, no compressor or similar device is used to avoid noise emissions.

[0039] According to the invention, the hydrogen is extracted exclusively from the hydrogen storage unit and not generated by a reformer. Especially in small submarines, it is advantageous to forgo a reformer arranged inside the pressure hull and to store the hydrogen exclusively in storage units outside the pressure hull. These can be, in particular, metal hydride storage units, compressed air storage units, or storage units for liquid hydrogen. Metal hydride storage units have proven to be particularly suitable. A reformer differs fundamentally from a hydrogen storage unit with regard to the hydrogen pressure provided. As long as the starting material for the reformer, for example methanol, is available, the reformer provides the hydrogen at a practically constant pressure. This eliminates any pressure dependence as a function of the remaining amount of available hydrogen.

[0040] A hydrogen storage device within the meaning of the invention can therefore only be filled by a refueling process.

[0041] In a further embodiment, the hydrogen storage device is a metal hydride storage device.

[0042] In a further embodiment of the invention, the working pressure is selected to be equal to the first pressure or, if this is not possible, as close to the first pressure as is possible due to the storage pressure.

[0043] In a further embodiment of the invention, a difference of at least 5 kPa, preferably at least 10 kPa, and particularly preferably at least 20 kPa, is maintained between the storage pressure and the working pressure. This pressure difference ensures that the somewhat lower working pressure can be easily adjusted and maintained. Pressure fluctuations in the storage tank thus do not directly affect the fuel cell.

[0044] The pressure at the inlet of the pressure regulator can be used as the value for the accumulator pressure. Since the variables are proportionally coupled due to the pressure loss across the supply line, the pressure at the inlet of the pressure regulator is a measure of the accumulator pressure.

[0045] In a further embodiment of the invention, the first pressure is selected between 250 kPa and 400 kPa. This pressure range has proven ideal for operation on board a submarine.

[0046] In a further embodiment of the invention, the second pressure is selected between 200 kPa and 50 kPa, preferably between 170 kPa and 120 kPa. This limit has proven to be the optimum between maximizing range and energy yield (due to insufficient mass conversion at too low a pressure).

[0047] In a further embodiment of the invention, an operating state is taken into account as further information in the method step of selecting a working pressure, wherein the operating state is selected from the list comprising purging, start-up, control operation and shutdown.

[0048] The purging operating mode can be aimed at removing inert gas and / or water. To do this, the pressure inside the fuel cell is briefly increased and a suitable valve is briefly opened. The pressure can be increased to a value above the initial pressure. The fuel cell then returns to the normal pressure range. This can happen either by hydrogen and oxygen reacting, causing the pressure to drop, or by the valve being open until the pressure has dropped. The operating mode can then transition to regular operation. In this context, short-term means as short as possible. The increased pressure should place as little strain as possible on the fuel cell and, above all, the membrane. The period for this is therefore determined in particular by regulation and control parameters and should be kept as short as possible.

[0049] Startup and shutdown cycles are more frequent in a submarine, as multiple stacks, each with multiple fuel cells, are typically operated. The number of stacks in operation can depend on the submarine's energy requirements and is subject to significant fluctuations. Therefore, individual stacks are regularly commissioned (i.e., started up when energy demand increases) or decommissioned (i.e., shut down when energy demand decreases).

[0050] In a further embodiment of the invention, during the start-up operating state, the working pressure is initially selected to be below the second pressure, and then the working pressure is increased until the working pressure selected for normal operation is reached. Particularly preferably, the working pressure is briefly selected to be above the first pressure, resulting in a short-term increase in conversion and thus heating, so that the fuel cell reaches the steady state more quickly. Because the working pressure is initially selected to be below the second pressure, start-up is always possible in the same way, regardless of the fill level of the hydrogen storage tank and thus the storage pressure. In this context, "initially" means that this process begins with the appropriate parameters, in particular pressure, and that the parameters, in particular the pressure, are then changed during the course of the process, i.e. subsequently.

[0051] In a further embodiment of the invention, the operating pressure is selected below the second pressure during the shutdown operating state. However, the pressure is different from zero, so that a certain small amount of hydrogen is still available. As a result, the hydrogen supply is not immediately reduced to zero. For example, this operating pressure is maintained until the fuel cell has reached a predetermined minimum current value, for example, zero amperes. The fuel cell is then shut down. For example, the gas supply lines are closed.

[0052] In a further embodiment of the invention, a third pressure is selected as the working pressure in the flushing operating state, wherein the third pressure corresponds to 1.2 to 2.5 times the first pressure.

[0053] In a further embodiment of the invention, a submarine with a second hydrogen storage device is selected, wherein the second hydrogen storage device is a high-pressure hydrogen storage device. For example, the high-pressure hydrogen storage device is a compressed gas cylinder with a pressure of 10 MPa to 40 MPa. This can be a commercially available compressed gas cylinder. This requires only a small volume, since this hydrogen is preferably only used to ensure the increase in working pressure during purging, regardless of the fill level of the hydrogen storage device.

[0054] In a further embodiment of the invention, the cathode working pressure is selected to be equal to the working pressure of the anode side, with a tolerance of maximum ± 20 kPa, preferably maximum ± 10 kPa, particularly preferably ± 5 kPa, being specified.

[0055] Due to the low pressure difference, mechanical stress on the membrane is reduced or even completely avoided.

[0056] In a preferred embodiment of the invention, the hydrogen storage device is a metal hydride storage device. The hydrogen is securely bound in the metal hydride. In submarine applications, the weight disadvantage of this storage technology is less relevant due to the displacement of the storage device itself.

[0057] In a further embodiment of the invention, the fuel cell is switched off as soon as the storage pressure is no longer sufficient to adjust the pressure in the fuel cell to at least the second pressure.

[0058] According to the invention, the hydrogen storage tank and the fuel cell are connected via a pressure regulator. The method according to the invention serves to operate a submarine that carries hydrogen in a hydrogen storage tank, where the pressure is a function of the fill level. For submarines with a reformer for generating hydrogen, other methods are preferred. Therefore, a submarine for carrying out the method preferably does not have a reformer.

[0059] In a further aspect, the invention relates to a submarine with a hydrogen storage device, a pressure regulator and a fuel cell as well as a control device for carrying out the method according to the invention.

[0060] The method according to the invention is explained in more detail below using an embodiment shown in the drawings. Fig. 1 Scheme of the procedure Fig. 2 Boot-up scheme Fig. 3 Flushing scheme

[0061] In Fig. 1 The pressure relationship is shown schematically. A value correlated with the fill level F of the hydrogen storage tank is plotted on the abscissa. For example, this value is chosen so that the storage pressure p S is linearly correlated, as shown. The actual curve may be different, but this would only lead to a corresponding change in the graphical representation. The pressure is indicated on the ordinate.

[0062] A first pressure p 1 is specified, which represents the ideal value for control operation of the anode side of the fuel cell. Furthermore, a second pressure p 2 is specified, which represents a minimum pressure for operation of the anode side of the fuel cell. These two specified pressures are time-independent and exhibit no correlation, for example, with the fill level F. Therefore, they appear as horizontal lines. For example, let p 1 be 250 kPa and p 2 be 150 kPa.

[0063] If the storage pressure p S is significantly greater than the first pressure p 1 , the working pressure p A can be selected and set to the ideal value p 1 . Only when the storage pressure p S approaches the first pressure p 1 does the working pressure p A need to be adjusted. For example, if we assume that a pressure difference Δp of 20 kPa to the storage pressure p S is necessary for a controlled and stable setting of the working pressure p A, the working pressure is reduced as soon as the storage pressure p S falls below 270 kPa in the case shown. The working pressure is then selected to be Δp = 20 kPa lower than the storage pressure until the working pressure reaches the limit of the second pressure p 2 of 150 kPa here. From this point on, the hydrogen is no longer sufficient and the fuel cell is switched off. In this example, the storage pressure is then 170 kPa.

[0064] In Fig. 2 The start-up operating state is shown as an example. The time t is plotted on the abscissa. The working pressure p A is initially selected at a level below the second pressure p 2 , for example, 50 kPa. Since the hydrogen storage tank is not operated at a pressure lower than p 2 , this pressure is reliably available. Provided the storage pressure p S is sufficiently high, the working pressure p A is increased quickly, even beyond the first pressure p 1 , for example to a maximum pressure of 350 kPa. This allows the fuel cell to be operated at higher loads, and thus faster heating of the fuel cell can be achieved. The working pressure p A is then reduced to the first pressure p 1 .

[0065] In Fig. 3The purging operating mode is shown as an example. The working pressure p A is briefly increased, for example, to 350 kPa. Opening an outlet valve, for example to discharge inert gas, causes the pressure to drop slightly. The pressure then continues to drop due to hydrogen conversion at the anode until it reaches the ideal value of the first pressure, 250 kPa in the example shown.

Claims

1. A method of operating a submarine having a fuel cell and a hydrogen storage tank and a pressure regulator between the hydrogen storage tank and the fuel cell, the method comprising the following steps: - Specification of a first pressure p1 for the anode side of the fuel cell, whereby the first pressure p1 is designed as the ideal value for control operation, - Specification of a second pressure p2 for the anode side of the fuel cell, whereby the second pressure p2 is the minimum pressure, - Detection of a storage pressure pS at which hydrogen is supplied from the hydrogen storage tank to the pressure regulator, - Selection of a working pressure pA depending on the storage pressure pS, which is applied to the anode side of the fuel cell and is set by the pressure regulator, wherein the working pressure pA is selected as a function of the storage pressure pS and the first pressure p1and the second pressure p2, characterised in that the pressure is not increased between the hydrogen storage tank and the fuel cell, wherein the hydrogen is taken from the hydrogen storage tank and is not produced by a reformer.

2. Method according to claim 1, characterised in that the working pressure pA is selected at the level of the first pressure p1 or, if this is not possible, as close to the first pressure p1 as is possible on the basis of the storage pressure pS.

3. Method according to one of the preceding claims, characterised in that a difference of at least 5 kPa, preferably of at least 10 kPa, particularly preferably of at least 20 kPa, is maintained between the storage pressure pS and the working pressure PA.

4. Method according to one of the preceding claims, characterised in that the first pressure p1 is selected between 250 kPa and 400 kPa.

5. Method according to one of the preceding claims, characterised in that the second pressure p2 is selected between 200 kPa and 50 kPa, preferably between 170 kPa and 120 kPa.

6. Method according to one of the preceding claims, characterised in that in the method step of selecting a working pressure pA, an operating state is taken into account as further information, the operating state being selected from the list comprising flushing, start-up, normal operation and shutdown.

7. Method according to claim 6, characterised in that in the start-up operating state, the working pressure pA is initially selected below the second pressure p2 and is then increased until the working pressure pA selected for normal operation is reached.

8. Method according to claim 7, characterised in that the operating pressure pA is briefly selected above the first pressure p1 during the start-up operating state .

9. Method according to one of claims 6 to 8, characterised in that the working pressure pA is selected below the second pressure p2 in the shutdown operating state.

10. Method according to one of claims 6 to 9, characterised in that a third pressure is selected as the working pressure pA in the flushing operating state, the third pressure corresponding to 1.2 times to 2.5 times the first pressure p(1).

11. Method according to claim 10, characterised in that a submarine with a second hydrogen storage system is selected, wherein the second hydrogen storage system is a high-pressure hydrogen storage system.

12. Method according to one of the preceding claims, characterised in that the cathode working pressure is selected to be equal to the working pressure pA of the anode side , wherein a tolerance of at most ± 20 kPa, preferably of at most ± 10 kPa, particularly preferably of ± 5 kPa, is specified.

13. Submarine with a hydrogen storage tank, a pressure regulator and a fuel cell as well as a control device for carrying out the method according to one of the preceding claims.