Method for operating an electrolysis system and control unit

Abstract

The invention relates to a method for operating an electrolysis system (1), in particular a low-temperature electrolysis system (1), comprising an electrolysis stack (2) with an anode (2.1) and a cathode (2.2), wherein an electrolyte is supplied to the anode (2.1) and / or the cathode (2.2) via an electrolyte circuit (3) with an integrated pump (4). According to the invention, when the electrolysis system (1) is started, a power reserve of the pump (4) is activated and used to introduce heating power into the electrolyte of the electrolyte circuit (3). The invention further relates to a control unit for carrying out the method or individual method steps.

Description

The present invention relates to a method for operating an electrolysis system with the features of the preamble of claim 1. Furthermore, the invention relates to a control unit for carrying out the method or individual steps of the method. Preferred applications of the invention are low-temperature electrolysis systems for alkaline electrolysis (AEL), anion exchange membrane electrolysis (AEM) and / or polymer electrolyte membrane electrolysis (PEM). State of the art In low-temperature electrolysis, the electrolyte, usually potassium hydroxide in various concentrations (in AEL and AEM electrolysis) or water (in PEM electrolysis), is stored in a tank. It is drawn from the tank by a pump, which pumps the electrolyte through a stack comprising numerous electrolysis cells arranged in a stack. Electrolysis takes place in the electrolysis cells, splitting water into hydrogen and oxygen. When starting the electrolysis system, the stack must first be brought up to operating temperature, for example, by heating the tank in which the electrolyte is stored and / or the pipes that carry the electrolyte from the tank to the stack. Electric heating devices or heat exchangers through which a heating medium flows can be used to heat the tank and / or the pipes. In all these cases, the electrolyte is heated first, and then the stack is heated using the heated electrolyte. Heating the stack to operating temperature ensures that the required current density is achieved within the permissible cell or stack voltage range. Heating the stack is the determining factor for the start-up process. If the electrolysis system is also coupled to a fluctuating energy source, such as wind or solar power, the start-up process becomes even more crucial, as a rapid start is then necessary to ensure the required dynamic operation of the system. While heating the tank and / or the piping can accelerate the start-up process, this involves investment costs using an electric heating element or a heat exchanger. Furthermore, the heating element must be appropriately sized for a rapid start. However, it is typically only needed briefly during the start-up phase, thus negatively impacting the economic viability of the electrolysis system. The present invention addresses the problem of improving the rapid start-up capability of an electrolysis system while simultaneously saving installation space and costs. To achieve this problem, the method with the features of claim 1 is proposed. Advantageous embodiments of the invention are described in the dependent claims. Furthermore, a control unit for carrying out the method or individual steps of the method is specified. Disclosure of the invention A method for operating an electrolysis system, in particular a low-temperature electrolysis system, is proposed, comprising an electrolysis stack with an anode and a cathode, wherein an electrolyte is supplied to the anode and / or the cathode via an electrolyte circuit with an integrated pump. According to the invention, when the electrolysis system is started, a power reserve of the pump is activated and used to introduce heating power into the electrolyte of the electrolyte circuit. The proposed method utilizes the available pump capacity to heat the electrolyte in the electrolyte circuit. This allows the electrolysis system to reach full load more quickly. An electric heating element or heat exchanger can be eliminated or at least designed to be smaller, thus saving space and costs. The pump integrated into the electrolyte circuit circulates the electrolyte within the circuit, pumping it through the electrolysis stack. A desired flow rate is typically set. During startup, the electrolysis stack is not subjected to full current, and therefore the nominal gas production is not achieved. Consequently, the back pressure the pump must overcome is lower during startup than at full load. This means the pump has power reserves. These reserves are used to introduce heat in the proposed process. Preferably, to activate the pump's power reserve during startup, the pump is operated at an increased power output. This means that the pump is operated at a power level higher than that required for the desired flow rate. Operating the pump at an increased power output results in a higher flow rate, which is generally undesirable. To operate the electrolysis stack with the desired electrolyte flow rate despite increased pump power, a further development of the invention proposes throttling the electrolyte flow through the electrolysis stack during startup. As a result, the pressure in the electrolyte circuit increases downstream of the pump and upstream of a throttling device integrated into the electrolyte circuit. This leads to additional energy consumption by the pump, which—taking the pump efficiency into account—is introduced into the electrolyte as heat energy. This heat is generated by friction losses within the pump, the piping, and the fittings. To throttle the electrolyte flow through the electrolysis stack, a throttling device is preferably used, which is integrated into the electrolyte circuit between the pump and the electrolysis stack. The throttling device can be, in particular, a throttle valve or a throttle valve. This can already be present, so that no additional component is required. Alternatively or additionally, it is proposed that a bypass valve in a pump bypass path be opened during startup, allowing at least a portion of the pumped electrolyte to flow back from the pressure side to the suction side of the pump. This increases the pump's delivery volume while decreasing the amount of electrolyte supplied to the electrolysis stack and thus the flow rate through the stack. The bypass valve in the pump bypass path can therefore also be used to regulate the flow rate through the electrolysis stack. Furthermore, it is proposed that the pump be operated via speed control during normal operation of the electrolysis system. Speed ​​control allows the desired flow rate through the electrolysis stack to be set so that no losses occur. When starting the electrolysis system, a temporary, lossy throttling or bypass control of the pump is desirable, as this shortens the start-up process or eliminates the need for an electric heating element while maintaining the same start-up time. Furthermore, a control unit is proposed that is configured to execute steps of a method according to the invention. With the aid of the control unit, the pump integrated into the electrolyte circuit can be controlled, in particular, when the electrolysis system is started. Furthermore, the throttling device integrated into the electrolyte circuit can be adjusted with the aid of the control unit so that the desired flow rate through the electrolysis stack is achieved despite an increase in pump power. Alternatively or additionally, the bypass valve integrated into the pump bypass path can be opened with the aid of the control unit to increase the pump's delivery rate. The invention and its advantages are described in more detail below with reference to the accompanying drawings. These show: Fig. 1 a schematic representation of a first electrolysis system suitable for carrying out the process according to the invention or operable according to a process according to the invention, and Fig. 2 a schematic representation of a second electrolysis system suitable for carrying out the process according to the invention or operable according to a process according to the invention. Detailed description of the drawings Fig. 1 shows an electrolysis system 1 comprising an electrolysis stack 2 with an anode 2.1 and a cathode 2.2. The anode 2.1 is supplied with an electrolyte, for example potassium hydroxide or water, via an electrolyte circuit 3, into which a pump 4 is integrated. The electrolyte is stored in a tank 8. Electrolyte exiting the electrolysis stack 2 is recirculated via the electrolyte circuit 3 and, if necessary, mixed with freshly added electrolyte, in particular deionized water, which enters the tank 8 via an electrolyte inlet 9. Gas contained in the recirculated electrolyte is removed from the tank 8 via a gas outlet 10. In this case, an electric heater 11 is integrated into tank 8. The electric heater 11 can heat tank 8 and thus warm the electrolyte, which is particularly advantageous when starting the electrolysis system 1, as the heated electrolyte allows the electrolysis stack 2 to reach operating temperature more quickly. However, this requires that the electric heater is sufficiently large. To reduce the size of the electric heater 11 or eliminate it entirely, the electrolysis system 1 shown in Fig. 1 can be operated according to a method according to the invention during startup. For this purpose, the power of the pump 4 is increased during startup, and simultaneously a throttling device 5 integrated downstream of the pump 4 into the electrolyte circuit 3 is actuated, so that the power of the pump 4 increases, but the flow rate through the electrolysis stack 2 does not. In this way, heating power is introduced into the electrolyte circuit 3, which causes the electrolyte and the electrolysis stack 2 to heat up. Figure 2 shows another electrolysis system 1 that can be operated according to a method according to the invention. The electrolysis system 1 of Figure 2 also has an electrolysis stack 2 with an anode 2.1 and a cathode 2.2, wherein the anode 2.1 can be supplied with electrolyte from a tank 8 via an electrolyte circuit 3, into which a pump 4 is integrated. An electric heater 11 is also integrated into the tank 8. To allow for a smaller electric heater 11 or to eliminate it entirely, pump 4 has a pump bypass path 7 with an integrated bypass valve 6. The pumped electrolyte returns from the pressure side to the suction side of pump 4 via the pump bypass path 7, thus increasing the pump's delivery rate without increasing the flow rate through the electrolysis stack 2. This method also utilizes a power reserve of pump 4 to introduce heating power into the electrolyte circuit 3, thereby accelerating the start-up process.

Claims

Method for operating an electrolysis system (1), in particular a low-temperature electrolysis system (1), comprising an electrolysis stack (2) with an anode (2.1) and a cathode (2.2), wherein an electrolyte is supplied to the anode (2.1) and / or the cathode (2.2) via an electrolyte circuit (3) with an integrated pump (4), characterized in that when the electrolysis system (1) is started, a power reserve of the pump (4) is activated and used to introduce heating power into the electrolyte of the electrolyte circuit (3). Method according to claim 1, characterized in that, in order to activate the power reserve of the pump (4) during start-up, the pump (4) is operated at increased power. Method according to claim 1 or 2, characterized in that the electrolyte flow through the electrolysis stack (2) is throttled when starting, preferably using a throttling device (5) integrated into the electrolyte circuit (3) between the pump (4) and the electrolysis stack (2). Method according to one of the preceding claims, characterized in that, upon starting, a bypass valve (6) in a pump bypass path (7) is opened, so that at least a partial amount of the pumped electrolyte is returned from the pressure side to the suction side of the pump (4). Method according to one of the preceding claims, characterized in that in normal operation of the electrolysis system (1) the pump (4) is operated via a speed control. Control unit configured to perform steps of a method according to any of the preceding claims.

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