Method for operating an electrolyte circuit and electrolyte circuit

Abstract

The invention relates to a method for operating an electrolyte circuit (1) via which, during normal operation, an electrolyte is supplied from a tank (4) to at least one electrolyser stack (2) of an electrolysis system (10) with the aid of a pump (3). According to the invention, at start-up, the quantity of electrolyte circulated via the electrolyte circuit (1) with the aid of the pump (3) is temporarily reduced. The invention also relates to an electrolyte circuit (1) and to an electrolysis system (10).

Description

[0001] Description

[0002] title

[0003] Method for operating an electrolyte circuit and electrolyte circuit

[0004] The present invention relates to a method for operating an electrolyte circuit with the features of the preamble of claim 1. Furthermore, the invention relates to an electrolyte circuit for an electrolysis system that is suitable for carrying out the method according to the invention or that can be operated according to the method.

[0005] The preferred application area of ​​the invention is electrolysis systems, in particular low-temperature electrolysis systems. Therefore, an electrolysis system with an electrolysis circuit according to the invention is further proposed.

[0006] State of the art

[0007] In low-temperature electrolysis, the electrolyte required for electrolysis is stored in a tank and fed to an electrolysis stack using a pump. In alkaline electrolysis (AEL) and anion-exchange membrane electrolysis (AEM), the electrolyte is typically potassium hydroxide in various concentrations. In polymer electrolyte membrane electrolysis (PEM), water is used as the electrolyte.

[0008] During the start-up process of a low-temperature electrolysis system, it must first be heated to the desired temperature to achieve the required current density within the permissible cell or stack voltage range. However, the heating process delays the start-up. To enable dynamic system operation, a rapid start-up is desirable. Heating during system start-up can be achieved using waste heat from the electrolysis process and / or external heating. External heating can be implemented using direct electric heating or a heat transfer medium, such as steam. Therefore, an electric heater and / or heat exchanger are required for external heating. Consequently, investment and operating costs increase with external heating, including the costs for energy consumption and / or maintenance.Since the heating system needs to be very large for a quick start, but its use is only required during startup, external heating is uneconomical.

[0009] The present invention is concerned with the objective of increasing the quick start capability of an electrolysis system, so that the heating process can be shortened in the event of start-up.

[0010] To solve the problem, the method with the features of claim 1 and the electrolyte circuit with the features of claim 5 are proposed. Advantageous embodiments of the invention can be found in the respective dependent claims. Furthermore, an electrolysis system with an electrolyte circuit according to the invention is described.

[0011] Disclosure of the invention

[0012] A method is proposed for operating an electrolyte circuit, through which, during normal operation, at least one electrolysis stack of an electrolysis system is supplied with electrolyte from a tank by means of a pump. According to the invention, the amount of electrolyte circulated via the electrolyte circuit by means of the pump is temporarily reduced during startup.

[0013] The electrolyte contributes significantly to the system's heat capacity. Reducing the amount of electrolyte, and thus the system's heat capacity, during the start-up process reduces the amount of thermal energy required to reach the necessary operating temperature. Therefore, the proposed method can significantly accelerate the start-up process. Simultaneously, the required heating energy is reduced, allowing for a smaller heating element or even its complete elimination. Instead, the waste heat from the ongoing electrolysis process can be utilized.

[0014] Preferably, to temporarily reduce the electrolyte quantity, a partial quantity of electrolyte is introduced from the tank or the electrolyte circuit into a buffer tank and temporarily stored there during the start-up process. The partial quantity of electrolyte stored in the buffer tank lowers the fill level in the electrolyte circuit tank, thus reducing the amount of electrolyte that needs to be heated and consequently lowering the heating load.

[0015] In an initial step during the start-up process, the buffer tank is filled with electrolyte. Following the start-up, the buffer tank can then be emptied, with the electrolyte being returned to the main tank or the electrolyte circuit. This reverses the temporary reduction in the electrolyte level. To heat the electrolyte transferred from the buffer tank to the main tank or the electrolyte circuit, the heat dissipation from at least one electrolysis stack can be utilized. Alternatively or additionally, an electric heating element or a heat exchanger can be used. Once the buffer tank is completely empty, meaning no electrolyte remains in the buffer tank, the system can be operated as usual.

[0016] According to a preferred embodiment of the invention, the electrolyte circuit pump or an additional pump is used to fill and / or empty the buffer tank. Using the electrolyte circuit pump eliminates the need for an additional pump, thus saving space and costs. For this purpose, the buffer tank is connected to the electrolyte circuit on the pressure side of the pump at its inlet. To prevent the buffer tank from filling with electrolyte during normal operation, the connection is preferably made via a valve that is kept closed during normal operation and opened during startup. If an additional pump is used to fill and / or empty the buffer tank, it can be connected to the electrolyte circuit or to the electrolyte circuit's tank, thus expanding the connection options. Preferably, the buffer tank is also connected via at least one valve in this case.

[0017] Advantageously, gravity is used to fill and / or empty the buffer tank with the electrolyte, so that filling and / or emptying is carried out solely by gravity or at least with the assistance of gravity. This requires that the buffer tank be located either geodesically below or geodesically above the electrolyte circuit tank or the main tank. If the buffer tank is located geodesically below the main tank, gravity can be used to fill the buffer tank. If the buffer tank is located geodesically above the main tank, gravity can be used to empty the buffer tank.

[0018] To ensure that the gas present in the buffer tank is displaced by the incoming electrolyte during filling, a gas outlet is preferably provided on the buffer tank. The gas can then escape through this outlet. A valve can be integrated into the gas outlet. When the buffer tank is subsequently emptied, air can flow into the buffer tank through the gas outlet, thus refilling it with air.

[0019] Furthermore, an electrolyte circuit for an electrolysis system with at least one electrolysis stack is proposed. An electrolyte can be supplied to the at least one electrolysis stack via the electrolyte circuit. The electrolyte circuit comprises: a tank for storing the electrolyte, a pump for circulating the electrolyte through the electrolyte circuit, and a buffer tank that can be switched on and off via at least one valve.

[0020] The electrolyte circuit is particularly suitable for carrying out the previously described process according to the invention, so that the same advantages can be achieved. In particular, the rapid start-up capability of the electrolysis system incorporating the electrolyte circuit can be increased. This is because, during start-up, a partial quantity of electrolyte can be introduced into the buffer tank by activating it and temporarily stored, thus reducing the amount of electrolyte that needs to be heated. At the same time, less energy is required for heating.

[0021] According to a preferred embodiment of the invention, the buffer tank has a gas outlet. During the filling of the buffer tank with the electrolyte, the gas present in the buffer tank can be displaced via the gas outlet.

[0022] The electrolyte circuit pump or an additional pump can be used to fill and / or empty the buffer tank. The additional pump expands the options for connecting the buffer tank to the electrolyte circuit. For example, the connection can then also be made indirectly via the electrolyte circuit tank. Using the existing electrolyte circuit pump reduces the required installation space and costs.

[0023] Advantageously, the buffer tank is arranged geodetically below the main tank, so that gravity can be used to fill the buffer tank with the electrolyte. In this case, filling the buffer tank is gravity-driven or at least assisted by gravity.

[0024] Alternatively, it is proposed that the buffer tank be arranged geodesically above the main tank, so that gravity can be used to empty the buffer tank. In this case, emptying the buffer tank is gravity-driven or at least gravity-assisted.

[0025] The buffer tank can also be structurally integrated into the electrolyte circuit tank. This measure further reduces the required installation space. Furthermore, pipe lengths can be reduced.

[0026] Furthermore, an electrolysis system with an electrolyte circuit according to the invention is proposed, into which at least one electrolysis stack is integrated. The at least one electrolysis stack can be supplied with an electrolyte via the electrolyte circuit, which can be, in particular, a potassium hydroxide solution or water. By way of example, the electrolyte is supplied to an anode of the at least one electrolysis stack via the electrolyte circuit. However, the proposed concept can also be transferred to a cathode-side circuit.

[0027] Preferred embodiments of the invention are explained in more detail below with reference to the accompanying drawings. These show:

[0028] Fig. 1 shows a schematic representation of an electrolysis system with a first electrolyte circuit according to the invention,

[0029] Fig. 2 shows a schematic representation of an electrolysis system with a second electrolyte circuit according to the invention and

[0030] Fig. 3 shows a schematic representation of an electrolysis system with a third electrolyte circuit according to the invention.

[0031] Detailed description of the drawings

[0032] Figure 1 shows an electrolysis system 10 with an electrolysis stack 2. The electrolysis stack 2 has an anode “A” and a cathode “C”. During operation, an electrolyte is supplied to the anode via an electrolyte circuit 1. In the case of a PEM electrolysis system, the electrolyte is water, in particular deionized water or DL ​​water.

[0033] A tank 4 for storing the electrolyte is integrated into the electrolyte circuit 1 of Figure 1. The tank 4 can be filled with electrolyte via a line 13. A pump 3 is arranged between the tank 4 and the electrolysis stack 2, which circulates the electrolyte through the electrolyte circuit 1. A heat exchanger 11 is also integrated into the electrolyte circuit 1 downstream of the pump 3. During operation, the temperature is regulated via this heat exchanger, and in particular, excess heat is dissipated. At startup, the system does not need to be cooled, but rather heated. This heating can be achieved, for example, by means of an electric heating element 12 housed in the tank 4. To relieve the heating element 12, a buffer tank 5 is integrated into the electrolyte circuit 1, which can be switched on and off via valves 7 and 8.At startup, valve 7 opens and pump 6 is activated, allowing electrolyte to flow from tank 4 into buffer tank 5 and lowering the electrolyte level in tank 4. This also reduces the amount of electrolyte to be heated, which is then supplied to the electrolysis stack 2 via electrolyte circuit 1 by pump 3. This shortens the heating time and thus the startup process.

[0034] When buffer tank 5 is filled, the inflowing electrolyte displaces the gas already present in buffer tank 5. This gas exits buffer tank 5 via a gas outlet 9. As shown in Figure 1, the gas outlet 9 can lead into a line 14, through which the product gas is discharged from tank 4. Alternatively, the gas outlet 9 can be connected to another route, provided that the different pressure levels of tank 4 and buffer tank 5 do not prevent buffer tank 5 from emptying during electrolysis.

[0035] To empty buffer tank 5, valve 7 is closed and valve 8 is opened, allowing the electrolyte discharged from buffer tank 5 to flow back into tank 4. Emptying can be accomplished by gravity. However, this requires that buffer tank 5 is geodetically positioned above tank 4.

[0036] Another preferred embodiment of an electrolyte circuit 1 according to the invention can be seen in Figure 2. Here, the buffer tank 5 is connected to the electrolyte circuit 1 via the valve 7 on the inlet side, downstream of the pump 3. This arrangement has the advantage that an additional pump 6 (see Figure 1) is unnecessary. To fill the buffer tank 5 with the electrolyte, only the valve 7 needs to be opened and the pump 3 operated. The buffer tank 5 is emptied directly into the tank 4 via the valve 8. Ideally, the buffer tank 5 is arranged geodesically above the tank 4, so that gravity can be used for emptying when the valve 8 is open.

[0037] Another variant of an electrolyte circuit 1 according to the invention is shown in Figure 3. The basic principle is the same as that shown in Figure 2, so that an additional pump 6 is also unnecessary here. However, in this case, the buffer tank 5 is arranged geodesically below the tank 4, so that when valve 7 is opened, it fills with electrolyte due to the difference in height, i.e., by gravity. The necessary pressure equalization takes place via the gas outlet 9. Since a valve 8' is integrated into the gas outlet 9, this must be opened beforehand. Closing both valves 7 and 8 stops the filling process. To empty the buffer tank 5, valve 7 is opened, so that the return flow exiting the electrolysis stack 2 is fed into the buffer tank 5.The oxygen carried by the return flow displaces the electrolyte present in buffer tank 5, causing it to return to electrolyte circuit 1. It is important to note that the return line of the electrolyte circuit is located geodetically below buffer tank 5 and that buffer tank 5 is connected via a continuously rising pipe. This ensures that when valve 7 is opened, the oxygen rises into buffer tank 5 and displaces the electrolyte in the opposite direction of flow into electrolyte circuit 1. The emptying rate can be regulated by adjusting the position of valve 7. Once buffer tank 5 is empty, valve 7 is closed again.

[0038] In contrast to the embodiments shown in Figures 1 to 3, a buffer tank 5 can supply the electrolyte circuit 1 of several electrolysis stacks 2. Furthermore, the buffer tank 5 can be structurally integrated into the tank 4.

Claims

Claims 1. Method for operating an electrolyte circuit (1) via which, in normal operation, an electrolyte from a tank (4) is supplied to at least one electrolysis stack (2) of an electrolysis system (10) by means of a pump (3), characterized in that, in the start-up case, the amount of electrolyte circulated via the electrolyte circuit (1) by means of the pump (3) is temporarily reduced.

2. Method according to claim 1, characterized in that, for the temporary reduction of the electrolyte quantity, a partial quantity of electrolyte is introduced from the tank (4) or from the electrolyte circuit (1) into a buffer tank (5) and temporarily stored in the buffer tank (5) during the start-up process.

3. Method according to claim 2, characterized in that the pump (3) or an additional pump (6) is used to fill and / or empty the buffer tank (5).

4. Method according to claim 2 or 3, characterized in that gravity is used to fill and / or empty the buffer tank (5) with the electrolyte.

5. Electrolyte circuit (1) for an electrolysis system (10) with at least one electrolysis stack (2) to which an electrolyte can be supplied via the electrolyte circuit (1), comprising a tank (4) for storing the electrolyte, a pump (3) for circulating the electrolyte via the electrolyte circuit (1), a buffer tank (5) which can be switched on and off via at least one valve (7, 8).

6. Electrolyte circuit (1) according to claim 5, characterized in that the buffer tank (5) has a gas outlet (9).

7. Electrolyte circuit (1) according to claim 5 or 6, characterized in that the buffer tank (5) is arranged geodetically below the tank (4) so ​​that gravity can be used to fill the buffer tank (5) with the electrolyte.

8. Electrolyte circuit (1) according to claim 5 or 6, characterized in that the buffer tank (5) is arranged geodetically above the tank (4) so ​​that gravity can be used to empty the buffer tank (5).

9. Electrolyte circuit (1) according to one of claims 5 to 8, characterized in that the buffer tank (5) is structurally integrated into the tank (4).

10. Electrolysis system (10) with an electrolyte circuit (1) according to one of claims 5 to 9, in which at least one electrolysis stack (2) is integrated.

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