Fuel cell system and shut-down method

Abstract

The invention relates to a fuel cell system (1) comprising a fuel cell stack (2) and a plurality of valves (6, 7, 8, 9) provided for the passage of operating media and reaction products of the fuel cell stack (2), at least one of these valves (6, 7, 8, 9) being in the form of a normally closed valve both on the anode side and on the cathode side.

Description

[0001] Fuel cell system and shutdown procedure

[0002] The invention relates to a fuel cell system designed according to the preamble of claim 1. Furthermore, the invention relates to a shutdown method, i.e., an emergency shutdown method, designed for use in a fuel cell system.

[0003] A fuel cell system of this type is known, for example, from JP 05275102 A. The known fuel cell system comprises several pressure vessels in which nitrogen is stored. A normally closed valve is connected to one of these pressure vessels, from which gas can be extracted for an emergency shutdown.

[0004] Another fuel cell system having the features according to the preamble of claim 1 is disclosed in JP 2006155917 A. This fuel cell system uses both a normally closed valve and a normally open valve.

[0005] EP 3 190 650 B1 relates to a method for supplying and purging a fuel cell. This method utilizes, among other things, a purge line and a connected shutdown line.

[0006] During an emergency shutdown of a fuel cell system, it is generally possible to immediately close a hydrogen tank valve and simultaneously open an electrical switch. This eliminates the possibility of controlled bleeding. An undefined state can arise in the fuel cell system, particularly in the fuel cell stack, which tends to shorten the service life of the fuel cell system. If air is present in the cell stack when the current flow is interrupted, this can lead to increased electrode potentials, which can have a damaging effect, particularly on catalyst materials. Liquid water in the fuel cell stack can represent a local hydrogen deficiency, which can also have adverse effects on a catalyst. Furthermore, liquid water in the cell stack can lead to hot spots, which can have a damaging effect on both the catalyst and membranes.

[0007] The invention is based on the object of achieving progress in the emergency shutdown of fuel cell systems compared to the cited prior art, whereby in particular the risk of damage to the fuel cell components is to be minimized.

[0008] This object is achieved according to the invention by a fuel cell system having the features of claim 1. The object is also achieved by a method for emergency shutdown of a fuel cell system, i.e., a shutdown method, designed according to claim 6. The embodiments and advantages of the invention explained below in connection with the method also apply mutatis mutandis to the device, i.e., the fuel cell system, and vice versa.

[0009] The fuel cell system, in a known basic concept, comprises a fuel cell stack and a plurality of valves provided for the passage of operating media and reaction products of the fuel cell stack, at least one of which is designed as a normally closed valve. According to claim 1, at least one normally closed valve is arranged on both the anode side and the cathode side.

[0010] In particular, there are at least two normally closed valves on both the anode and cathode sides. In each case, the behavior of the fuel cell stack during shutdown, i.e., emergency shutdown, can be specifically influenced by appropriate selection and control of the normally closed valves. According to one possible design, a normally closed valve located on the anode side differs in its closing behavior during a power failure from the closing behavior of a normally closed valve on the cathode side in the same situation.

[0011] To achieve the different closing behaviors of the valves, at least one of the normally closed valves can be designed as a damped valve. Due to the damping, this valve closes more slowly than a valve of the same design that operates without damping.

[0012] The normally closed valves can, for example, be designed as spring-loaded valves. In principle, weight loading of the normally closed valves is also possible.

[0013] The method according to the application for the emergency shutdown of a fuel cell system, which comprises a plurality of fuel cells, generally provides that, as a measure for the emergency shutdown, valves designed as normally closed valves on the anode and cathode sides of the fuel cells, which are provided for the passage of operating media during regular operation of the fuel cell system, are closed.

[0014] In one possible process variant, at least one of the normally closed valves is triggered with a delay. The normally closed valve with a delay can have a higher closing speed than the at least one other normally closed valve that triggers without a delay. This opens up the possibility for the various normally closed valves, some of which respond immediately upon detection of a condition of the fuel cell system that triggers the emergency shutdown, and some of which respond with a delay, to complete the closing process at least approximately at the same time. This and other process variants create the possibility, in particular, of supplying the cells of the fuel cell system with more hydrogen than atmospheric oxygen during the emergency shutdown, compared to stoichiometrically ideal conditions.The high hydrogen volume creates the conditions for the remaining oxygen in the fuel cell stack to completely react, forming a virtually pure H2 / N2 / H2O atmosphere. The formation of liquid water is minimized by minimizing the air flow.

[0015] An embodiment of the invention is explained in more detail below with reference to a drawing. In the drawings:

[0016] Fig. 1 shows a roughly schematic view of a fuel cell system including a fuel cell stack,

[0017] Fig. 2 shows a flow chart of an operating procedure designed for the fuel cell system according to Fig. 1, including a shutdown procedure, i.e. an emergency shutdown.

[0018] A fuel cell system, designated overall by reference numeral 1, comprises a fuel cell stack 2, which is also referred to as a stack for short, and represents the core component of the fuel cell system 1. Regarding the basic function of the fuel cell system 1, reference is made to the prior art cited at the beginning.

[0019] Fuel cells 3, i.e., the electrochemical cells from which stack 2 is constructed, are not shown in detail. The same applies to end plates, between which the cells of stack 2 are arranged under mechanical prestress. The media required for the operation of the fuel cell system are supplied to stack 2 via distributor assemblies 4, 5, namely a cathode-side distributor assemblies 4 and an anode-side distributor assemblies 5. In a manner not shown in detail but known per se, the distributor assemblies 4, 5 are also designed to drain media from stack 2.

[0020] Various valves 6, 7, 8, 9 perform different functions within the fuel cell system 1, with all valves 6, 7, 8, 9 being designed as normally closed, spring-loaded valves. During the intended operation of the fuel cell system 1, which supplies electrical current, the normally closed valves 6, 7, 8, 9 are controlled by a control unit (not shown), which is also linked to other components of the fuel cell system 1.

[0021] The valves 6, 7 are arranged on the cathode side of the fuel cells 3 and are intended, in particular, for the passage of air and thus also atmospheric oxygen. In principle, it is also possible to operate the fuel cell system 1 with another gas containing oxygen, especially in a higher concentration than air, or with pure oxygen.

[0022] On the anode side of the stack 2, in the arrangement shown in Fig. 1 on its underside, the valves 8, 9 are arranged, which primarily conduct hydrogen. The orientation of the components 2, 3, 6, 7, 8, 9 of the fuel cell stack 2 according to Fig. 1 does not necessarily imply the actual spatial arrangement of the components 2, 3, 6, 7, 8, 9. The fuel cell system 1 is suitable for both mobile and stationary applications.

[0023] In the event of an emergency shutdown of the fuel cell system 1, all valves 6, 7, 8, and 9 are automatically closed. In this context, reference is made to the flowchart in Fig. 2. The first step S1 marks the beginning of the intended operation of the fuel cell system 1. In step S2, standard operating parameters of the fuel cell system 1 are recorded. The following step S3 represents a query in which it is checked whether the recorded parameters are within the specified target ranges. If this is the case, operation continues with step S2.

[0024] If, however, inadmissible deviations between the recorded values ​​and the target values ​​are detected, the shutdown of the fuel cell system 1 is initiated in step S4. In this context, the possibility of a hardware-triggered shutdown, for example, using an emergency stop switch or interlock switch, should be noted.

[0025] A further query is performed in step S5: If the setpoint ranges are moderately exceeded, essentially operating in the yellow zone, a shutdown process is initiated, referred to as step S6. However, if a serious deviation from the values ​​to be maintained during normal operation is detected, essentially operating in the red zone, an emergency shutdown is triggered in step S7.

[0026] The emergency shutdown is characterized by the fact that the various normally closed valves 6, 7, 8, 9 still allow the passage of media to varying degrees during the shutdown process. Specifically, the valves 6, 7, 8, 9 are designed and controlled in such a way that in the period from the beginning to the end of the shutdown process, the amount of hydrogen passed through is more than twice 21% of the air volume. If a gas with a higher oxygen content is used instead of air, a larger amount of hydrogen is required. If the oxygen content in the gas supplied on the cathode side is, for example, 30%, 60% of this amount of substance, i.e., the molar amount, is to be calculated as the reference value. The calculated reference value represents the lower limit of the amount to be exceeded that must be introduced into the fuel cell stack 2 in the form of hydrogen during the shutdown.Due to the large volume of hydrogen flowing into Stack 2 during shutdown, compared to oxygen, especially atmospheric oxygen, an atmosphere is created in Stack 2 that is almost exclusively composed of hydrogen, nitrogen and gaseous water.

[0027] List of reference symbols Fuel cell system Fuel cell stack, stack Fuel cell Distributor arrangement Distributor arrangement Valve Valve Valve Valve Process step

Claims

Patent claims 1. Fuel cell system (1), comprising a fuel cell stack (2) and a plurality of valves (6, 7, 8, 9) provided for the passage of operating media and reaction products of the fuel cell stack (2), at least one of which is designed as a normally closed valve, characterized in that at least one normally closed valve (6, 7, 8, 9) is arranged on both the anode side and the cathode side.

2. Fuel cell system (1) according to claim 1, characterized in that at least two normally closed valves (6, 7, 8, 9) are arranged on the anode side and on the cathode side of the fuel cells of the fuel cell stack.

3. Fuel cell system (1) according to claim 1 or 2, characterized in that the normally closed valves (6, 7, 8, 9) arranged on the anode and cathode sides respectively differ from one another with regard to their closing behavior in the event of a power failure.

4. Fuel cell system (1) according to claim 3, characterized in that at least one of the normally closed valves (6, 7, 8, 9) is designed as a damped valve which closes at a reduced speed compared to at least one further normally closed valve (6, 7, 8, 9).

5. Fuel cell system (1) according to one of claims 1 to 4, characterized in that the normally closed valves (6, 7, 8, 9) are spring-loaded.

6. Method for emergency shutdown of a fuel cell system (1) comprising a plurality of fuel cells (3), wherein as a measure for emergency shutdown on the anode and cathode sides of the fuel cells, valves (6, 7, 8, 9) designed as normally closed valves, which are provided for the passage of operating media during regular operation of the fuel cell system (1), are closed.

7. Method according to claim 6, characterized in that at least one of the normally closed valves (6, 7, 8, 9) is triggered with a delay.

8. The method according to claim 7, characterized in that the normally closed valve (6, 7, 8, 9) which is triggered with a delay has a higher closing speed than the at least one further normally closed valve (6, 7, 8, 9) which is triggered without a delay.

9. The method according to claim 8, characterized in that the various normally closed valves (6, 7, 8, 9), some of which respond immediately upon detection of a state of the fuel cell system (1) triggering the emergency shutdown, and some of which respond with a delay, complete the closing process at least approximately at the same time.

10. Method according to one of claims 6 to 9, characterized in that more hydrogen than atmospheric oxygen is supplied to the cells (3) of the fuel cell system (1) during the emergency shutdown, compared to stoichiometrically ideal conditions.

Images