Fuel cell device

Abstract

The invention is based on a fuel cell device for at least one fuel cell stack (14a, 16a, 18a, 20a; 14b; 14c, 16c) which has at least one reformer (22a; 22b; 22c) for reforming, in particular for steam reforming, a process gas, with a water supply module (24a; 24b; 24c) for supplying the reformer (22a; 22b; 22c) with process water under operating pressure. It is proposed that the water supply module (24a; 24b; 24c) comprises a pressure generation module (26a; 26b; 26c) which is provided for subjecting the process water to an operating pressure, and at least one water dosing module (28a, 30a, 32a, 34a; 28b; 28c, 30c) which is designed separately from the pressure generation module (26a; 26b; 26c) and which is provided for adjusting a mass flow of the process water under operating pressure which is fed to the reformer (22a; 22b; 22c).

Description

State of the art

[0001] A fuel cell device for at least one fuel cell stack, which has at least one reformer for reforming, in particular for steam reforming, a process gas, with a water supply module for supplying the reformer with process water under operating pressure, has already been proposed. Disclosure of the invention

[0002] The invention is based on a fuel cell device for at least one fuel cell stack, which has at least one reformer for reforming, in particular for steam reforming, a process gas, with a water supply module for supplying the reformer with process water under operating pressure.

[0003] It is proposed that the water supply module comprises a pressure generation module which is provided for subjecting the process water to an operating pressure, and at least one water dosing module which is designed separately from the pressure generation module and which is provided for adjusting a mass flow of the process water under operating pressure which is supplied to the reformer.

[0004] A "fuel cell device" is to be understood in particular as at least one part, in particular a subassembly, of a fuel cell system, in particular a solid oxide fuel cell system. A "fuel cell system" is preferably to be understood as a system that has at least one fuel cell stack consisting of a plurality of fuel cells / electrolysis cells and is intended for the stationary and / or mobile generation of electrical and / or thermal energy. A "fuel cell stack" is to be understood as a combination of a plurality of interconnected fuel cells / electrolysis cells, each of which is intended for the electrochemical conversion of fuel, in particular fuel gas, to generate electrical energy. A fuel cell stack is preferably designed as an SOFC fuel cell stack.The fuel cell / electrolysis cell of a fuel cell stack is designed, for example, as a solid oxide fuel cell (SOFC) / electrolysis cell (SOEC), a molten carbonate fuel cell / electrolysis cell, a direct methanol fuel cell / electrolysis cell, a polymer electrolyte fuel cell / electrolysis cell, or the like. A fuel cell stack is provided, for example, for converting a preferably hydrogen-containing, methane-containing, and / or ammonia-containing fuel, in particular natural gas or biogas, and an oxygen-containing fluid, in particular air, as reactants to generate electrical power. The fuel cell device can be at least partially integrated into the at least one fuel cell stack of the fuel cell system. Preferably, at least one water dosing module of the fuel cell module can be at least partially integrated into a fuel cell stack.In principle, however, it is conceivable for the entire fuel cell module to be designed separately from the fuel cell stack and to be connected to the at least one fuel cell stack during assembly of the fuel cell system. A “reformer” should preferably be understood as a chemical-technical device which is provided for at least one treatment of at least one hydrocarbon-containing process gas, in particular by steam reforming, by partial oxidation, by autothermal reforming and / or by a combination of steam reforming with CO2 dry reforming, in particular for obtaining the at least one fuel gas, in particular hydrogen. The reformer unit is preferably designed as a steam reformer unit. A “process gas” should preferably be understood as a fuel supplied from outside via the fuel cell device, in particular to the fuel cell system.The process gas is preferably in the form of natural gas. "Process water" is preferably understood to mean water that is supplied to the reformer for reforming the process gas. A "water supply module" is preferably understood to mean a module that is intended to supply the reformer of at least one fuel cell stack with process water for reforming. The water supply module is preferably connected to an external water supply. The water supply module is designed as a module that pressurizes externally supplied water and supplies it to the reformer of the at least one fuel cell stack as process water at a predetermined mass flow rate. Preferably, at least part of the water supply module is formed integrally with the fuel cell stack.The water supply module is preferably intended to supply several fuel cell stacks of a fuel cell system with process water for their reformers. A "pressure generation module" should preferably be understood as a sub-module of the water supply module, which is preferably intended solely for pressurizing the process water to an operating pressure. An "operating pressure" should preferably be understood as a pressure to which the process water is placed in a pressure line of the pressure generation module in order to be able to be introduced into the reformer with sufficient pressure through the water dosing module. The process water loses pressure as it flows through the water dosing module, which is why the pressure at which the process water leaves the water dosing module is lower than the operating pressure in the pressure line.A "water dosing module" is preferably understood to mean a sub-module of the water supply module that is provided solely for dosing, i.e., for adjusting a mass flow, of the process gas under operating pressure supplied to the reformer of at least one fuel cell stack. The water supply module preferably has a separate water dosing module for each fuel cell stack to be supplied with process water. The water dosing module can preferably be formed integrally with the fuel cell stack. "Formed separately from the pressure generation module" is understood to mean that the water dosing module is functionally separate from the pressure generation module. The pressure generation module is functionally separate from the water dosing module.The functions of pressure generation and dosing of process water by the water supply module are separated from each other by the separate design of the pressure generation module and the water dosing module. Pressurization of the process water occurs only in the pressure generation module, separate from the dosing of the process water in the water dosing module.

[0005] The process gas flow to the fuel cell stack required for the operation of the fuel cell stack depends on the requested electrical current. The process water flow required for reforming is a function of the process gas flow and a desired oxygen-to-carbon ratio in the reformer. In order to minimize deviations of the oxygen-to-carbon ratio from a target value, it must be possible to adjust the mass flow of process water supplied to the reformer with high precision. The inventive design of the fuel cell device makes it possible to provide a particularly cost-effective and variable fuel cell device for supplying one, preferably several, fuel cell stacks with process water for the respective reformer, which can adjust the mass flow of process water particularly easily and precisely.By separating the functions of pressure generation (by the pressure generation module) from the dosing of process water (by the water dosing modules), cost-effective components can be used. Advantageously, a fuel cell system can be easily expanded and connected to one pressure generation module via a water dosing module.

[0006] It is further proposed that the pressure generation module have a circulation circuit for the process water. A "circulation circuit for the process water" is preferably understood to mean a flow circuit in which the process water can flow continuously. The process water is taken from the circulation circuit, in particular from a section of a pressure line, and fed to the at least one water dosing module. This allows for a simple, constant pressurization of the process water.

[0007] It is further proposed that the pressure generation module comprise a circulation circuit for the process water, a storage tank integrated into the circulation circuit, and a circulation pump integrated into the circulation circuit. A "storage tank" is preferably understood to mean a storage volume in which process water can be stored. The storage tank serves as a buffer in the circulation circuit, in which process water flowing in the circulation circuit can be temporarily stored when it has not been supplied to the water dosing modules.

[0008] A "circulation pump" is preferably understood to mean a simple fluid pump designed to pump the process water in the fluid circuit. The circulation pump is preferably designed as a simple, controllable pump comprising an electric motor and a paddle wheel connected to the electric motor, which pumps the process water in the circulation circuit. "Integrated" is preferably understood to mean fluidically integrated. This makes it possible to provide a particularly simple circulation circuit in which the process water can be easily pressurized and which can easily compensate for pressure fluctuations and varying process water requirements.

[0009] It is further proposed that the pressure generation module have a cleaning element which is connected downstream of the circulation pump. A “cleaning element” should preferably be understood to mean an element which is intended to clean a fluid, in particular process water. The cleaning element is preferably intended to free the fluid, in particular the process water, from particles and / or other contaminants, such as in particular biocontamination. Preferably, the cleaning element is designed as a filter element. The cleaning element designed as a filter element is intended to filter a fluid, in particular the process water. In principle, it is also conceivable for the cleaning element to be designed as another cleaning element and to be intended, for example, to clean the process water by UV irradiation, in particular to reduce organic components in the process water."Downstream" should preferably be understood as being arranged downstream in the direction of flow. This allows the process water to be advantageously cleaned, in particular freed of small particles, thus protecting the downstream components of the pressure generation module and the at least one water dosing module.

[0010] Furthermore, it is proposed that the pressure generation module comprise a pressure control valve arranged between a pressure line and a return line of a circulation circuit of the pressure generation module. A "pressure control valve" is preferably understood to mean a valve that is switched based on an applied pressure and is intended to regulate a pressure, in particular a pressure in the pressure line. The pressure control valve can be used to adjust the pressure level on the inlet side of the pressure control valve, i.e., in the pressure line. The pressure control valve preferably comprises a spring-loaded valve element. The spring-loaded valve element is adjustable between a closed position and an open position.The spring-loaded valve element is designed to be moved towards its open position against a spring force by the pressure in the pressure line present on an inlet side of the pressure control valve. By adjusting the spring-loaded valve element, a pressure drop across the pressure control valve is set. The pressure upstream of the pressure control valve, i.e. in the pressure line, results from the pressure drop across the pressure control valve. The spring force against which the spring-loaded valve element can be deflected is preferably adjustable. By adjusting the spring force, the pressure in the pressure line that can be set by the pressure control valve can be varied. This makes it particularly easy to set a pressure on its inlet side, i.e. in the pressure line, using the pressure control valve.A "return line" is a line that is fluidically connected to the storage tank and through which process water can flow back into the storage tank. This allows the process water in the pressure line to be brought up to operating pressure and maintained at this pressure particularly easily and cost-effectively.

[0011] It is further proposed that the pressure generation module comprise a circulation circuit for the process water, which forms a pressure line to which the at least one water dosing module is fluidically connected. A "pressure line" is preferably understood to mean a line of the pressure generation module in which the process water is maintained at an operating pressure during normal operation. This makes it particularly easy to supply the at least one water dosing module with process water at operating pressure.

[0012] It is also proposed that the at least one water dosing module has a switching valve, preferably a solenoid valve, which is intended to control or regulate a mass flow of the process water flowing through the water dosing module. A “switching valve” should preferably be understood to mean a valve that can be switched back and forth between an open position and a closed position. In an open position, the switching valve releases a flow cross-section and a fluid, in particular process water, can flow through the switching valve. In a closed position, the switching valve is blocked and does not release a flow cross-section for a fluid, in particular the process water. By varying the opening and closing of the switching valve during operation, a mass flow of process water flowing through the switching valve can be adjusted.By varying the opening duration of the switching valve, the mass flow of process water flowing through the switching valve can be varied. A maximum mass flow is achieved when the switching valve is continuously open. A solenoid valve is preferably understood to be a switching valve that can be switched back and forth between its open and closed positions by means of an electrically or electronically controlled electromagnet. A switching valve designed as a solenoid valve can be switched back and forth between the closed and open positions particularly quickly. This allows the mass flow of process water in the water dosing module to be adjusted particularly easily and precisely.

[0013] It is further proposed that the at least one water dosing module has a control throttle connected downstream of the solenoid valve. A "control throttle" is preferably understood to mean a fluidic component that is intended to limit a flow rate, i.e. a mass flow of a flowing fluid, to a defined maximum. A control throttle is preferably understood to mean a control valve that is intended to regulate a volume flow. The control throttle preferably has a constriction of a line cross-section, across which the control throttle determines a maximum flow rate. The control throttle forms a local flow resistance. The control throttle preferably forms a maximum flow resistance in the water dosing module.Preferably, the control throttle defines a maximum mass flow of process water that can be fed to the reformer via the water dosing module. This advantageously allows for a simple and precise adjustment of the maximum mass flow of process water that can be fed to the reformer via the water supply module.

[0014] It is also proposed that the control throttle be designed such that a pressure loss across the control throttle is greater than the combined pressure loss of all elements of the water dosing module upstream of the control throttle. A "pressure loss across the control throttle" should preferably be understood as a difference between the pressure immediately upstream of the control throttle and the pressure immediately downstream of the control throttle. The pressure loss across the control throttle indicates the pressure difference experienced by the process water as it flows through the control throttle. This allows the mass flow of process water to be adjusted particularly precisely, and pressure fluctuations in the pressure line of the pressure generation module to be compensated for particularly easily.

[0015] It is further proposed that the at least one water dosing module has a backflow preventer, in particular a check valve, which is connected downstream of a switching valve, in particular a solenoid valve of the water dosing module. A "backflow preventer" should preferably be understood as a device that prevents a fluid from flowing back against the predetermined flow direction. The backflow preventer, in particular the check valve, is provided to prevent a fluid, in particular a process gas or process water, from flowing back from the reformer into the water dosing module. This allows the water dosing module to be protected against a process gas backflow in a particularly simple and cost-effective manner.

[0016] It is further proposed that the at least one water dosing module comprise a cleaning element, which is arranged upstream of a switching valve, in particular a solenoid valve of the water dosing module. The cleaning element is preferably designed as a filter element for filtering the process water. In principle, it would also be conceivable for the cleaning element to be designed as another cleaning element for cleaning a fluid, in particular the process water. "Upstream" should preferably be understood to mean arranged upstream in the direction of flow. This allows the switching valve and the control throttle to be particularly advantageously protected from contamination, thus ensuring the functional reliability of the water dosing module particularly easily.

[0017] It is further proposed that the water supply module comprise at least one further water dosing module for supplying a reformer of another fuel cell stack with process water at operating pressure, which is fluidically connected to the pressure generation module. This allows the water supply module to be used particularly easily to supply multiple fuel cell stacks of a fuel cell system. This allows for a particularly efficient water supply module to be provided, since only a simple circulation pump is sufficient to generate the operating pressure for several fuel cell stacks. The water supply module is therefore particularly easy and cost-effective to scale for fuel cell systems with multiple fuel cell stacks.

[0018] Furthermore, a method for operating the fuel cell device with the water supply module for supplying the reformer of the at least one fuel cell stack with pressurized process water is proposed. In a first method step, the process water is compressed to an operating pressure in a pressure generation module of the water supply module, and in a further, separate method step, a mass flow of process water, which is supplied to the reformer, is adjusted in a water metering module. Although the first method step for generating the operating pressure and the second method step for metering the mass flow of process water are functionally separate from one another, they occur at least substantially simultaneously during operation.This provides a particularly simple, cost-effective and accurate method for adjusting the mass flow of process water that must be fed to the reformer for reforming.

[0019] It is further proposed that a switching valve, in particular a solenoid valve of the water dosing module, be controlled by means of a pulse-width modulated (PWM) signal to adjust the mass flow of process water. A “pulse-width modulated (PWM) signal” should preferably be understood to mean a digital signal that can be changed using a digital modulation type in which a technical variable, in particular an electrical voltage, alternates between two values. A rectangular pulse, the length of which varies, is generated, preferably at a constant frequency. The ratio between the pulse and the period (sum of the pulse and pause durations) is referred to as the duty cycle. This allows the mass flow of process water to be adjusted particularly easily and precisely by the water dosing module.

[0020] Furthermore, a fuel cell system is proposed comprising a plurality of fuel cell stacks, each of which preferably has a reformer, and a fuel cell device comprising a water supply module, a pressure generation module, and a water dosing module for each reformer to supply the respective reformer with process water at operating pressure. As a result, the pressure generation module of the water supply module can be advantageously used by a plurality of fuel cell stacks, increasing efficiency compared to separate pressure generation modules for each fuel cell stack.

[0021] The fuel cell system according to the invention is not intended to be limited to the application and embodiment described above. In particular, the fuel cell system according to the invention may have a number of individual elements, components, units, and method steps that differs from the number stated herein to fulfill a functionality described herein. Furthermore, in the value ranges specified in this disclosure, values within the stated limits are also to be considered disclosed and can be used arbitrarily. drawing

[0022] Further advantages will become apparent from the following description of the drawings. The drawings illustrate three exemplary embodiments of the invention. The drawings, the description, and the claims contain numerous features in combination. Those skilled in the art will also expediently consider the features individually and combine them into useful further combinations.

[0023] They show: Fig. 1 a schematic structural diagram of a fuel cell system according to the invention in a first exemplary embodiment with several fuel cell stacks and a fuel cell device according to the invention with a water supply module which has a pressure generation module and several water dosing modules, Fig. 2 a schematic structural diagram of a fuel cell system according to the invention in a second embodiment with a fuel cell stack and a water supply module integrated into the fuel cell stack and Fig. 3 a schematic structural diagram of a fuel cell system according to the invention in a third embodiment. Description of the embodiments

[0024] The Fig. 1 shows a fuel cell device 12a according to the invention in a first embodiment. Fig. 1 shows a fuel cell system 10a according to the invention with the fuel cell device 12a. The fuel cell system 10a is provided for generating electrical energy and thermal energy. The fuel cell system 10a is provided for generating electrical energy and / or thermal energy for use by converting a fuel gas. The fuel cell system is preferably designed as a stationary system. In principle, it would also be conceivable for the fuel cell system 10a to be designed as a mobile system. The fuel cell system 10a comprises a first fuel cell stack 14a. The fuel cell system 10a comprises further fuel cell stacks 16a, 18a, 20a. In the exemplary embodiment, the fuel cell system 10a has a total of four fuel cell stacks 14a, 16a, 18a, 20a.In principle, it is also conceivable for a fuel cell system 10a according to the invention to have a different number of fuel cell stacks 14a, 16a, 18a, 20a. For example, a fuel cell system 10a with only one fuel cell stack 14a, two fuel cell stacks, or more than four, or more than ten fuel cell stacks 14a, 16a, 18a, 20a is conceivable. The fuel cell device 12a according to the invention is easily scalable for fuel cell systems 10a with different numbers of fuel cell stacks 14a, 16a, 18a, 20a.

[0025] The fuel cell stacks 14a, 16a, 18a, 20a of the fuel cell system 10a are essentially identical. The fuel cell stacks 14a, 16a, 18a, 20a are designed as SOFC fuel cell stacks. The fuel cell stacks 14a, 16a, 18a, 20a each have fuel cells (not shown in detail), in particular SOFC fuel cells. Furthermore, the fuel cell stacks 14a, 16a, 18a, 20a each have a reformer 22a. The reformer 22a of a fuel cell stack 14a, 16a, 18a, 20a is provided for reforming a process gas into a fuel gas. The process gas is, for example, a natural gas or a biogas. The reformer 22a is preferably designed as a steam reformer. The fuel cell stacks 14a, 16a, 18a, 20a with their fuel cells, their reformers 22a and the other components, such as supply modules and heat exchangers, will not be described in detail here and correspond to the state of the art.

[0026] The fuel cell device 12a has a water supply module 24a. The water supply module 24a is provided for supplying the fuel cell stacks 14a, 16a, 18a, 20a with process water. The water supply module 24a is provided for supplying the reformers 22a of the fuel cell stacks 14a, 16a, 18a, 20a with process water at operating pressure. The water supply module 24a is provided for applying an operating pressure to the process water. The water supply module 24a is provided for metered distribution of the process water at operating pressure to the reformers 22a of the fuel cell stacks 14a, 16a, 18a, 20a. The water supply module 22a is intended to set a mass flow of process water under operating pressure to the reformers 22a of the fuel cell stacks 14a, 16a, 18a, 20a.

[0027] The water supply module 24a has a pressure generation module 26a. The pressure generation module 26a is designed to compress the process water to the operating pressure. In an operating state, the pressure generation module 26a is designed to apply the operating pressure to the process water. The water supply module 24a has a water dosing module 28a. The water supply module 24a has several water dosing modules 28a, 30a, 32a, 34a. The water supply module 24a has one water dosing module 28a, 30a, 32a, 34a for each fuel cell stack 14a, 16a, 18a, 20a. The water dosing modules 28a, 30a, 32a, 34a each separately and independently adjust a mass flow of process water under operating pressure, which is supplied to the respective fuel cell stack 14a, 16a, 18a, 20a. The water dosing modules 28a, 30a, 32a, 34a are each designed independently of one another.The water dosing modules 28a, 30a, 32a, 34a are designed separately. The water dosing modules 28a, 30a, 32a, 34a are each assigned to and coupled to exactly one fuel cell stack 14a, 16a, 18a, 20a, in particular its reformer 22a. The water dosing modules 28a, 30a, 32a, 34a allow a mass flow of process water under operating pressure to be individually adjusted to the reformer 22a of each fuel cell stack 14a, 16a, 18a, 20a.

[0028] The water supply module 24a is provided to functionally separate the application of the operating pressure to the process water and the adjustment of a mass flow delivered to the reformers 22a of the fuel cell stacks 14a, 16a, 18a, 20a. The pressure generation module 26a is designed separately from the at least one water dosing module 28a, 30a, 32a, 34a. The water dosing modules 28a, 30a, 32a, 34a are each designed functionally separately from the pressure generation module 26a. The pressure generation module 26a is essentially provided solely for applying the operating pressure to the process water. The pressure generation module 26a does not adjust the mass flow of process water delivered to the fuel cell stacks 14a, 16a, 18a, 20a. The water dosing modules 28a, 30a, 32a, 34a are each provided solely for adjusting a mass flow of process water to be supplied to the reformer 22a of the respective fuel cell stack 14a, 16a, 18a, 20a.The water dosing modules 28a, 30a, 32a, 34a are not intended to apply pressure to the process water.

[0029] The pressure generation module 26a has a circulation circuit 36a for the process water. In the circulation circuit 36a, the process water is pressurized to the operating pressure. The pressure generation module 26a has a storage tank 38a. The storage tank 38a forms a reservoir for the process water. The storage tank 38a preferably forms a starting point for the circulation circuit 36a. The circulation circuit 36a formed by the pressure generation module 26a starts in the storage tank 38a and is returned thereto. The circulation circuit 36a has a supply line 40a. The supply line 40a is directly fluidically connected to the storage tank 38a. The process water can flow from the storage tank 38a into the lines of the circulation circuit 36a through the supply line 40a. The water supply module 24a has a circulation pump 42a. The circulation pump 42a is integrated into the circulation circuit 36a.The circulation pump 42a is preferably connected directly to the supply line 40a of the circulation circuit 36a. The circulation pump 42a is preferably connected directly downstream of the storage tank 38a in terms of fluid technology. The circulation pump 42a is intended to pump the process water through the circulation circuit 36a. The circulation pump 42a is intended to apply the operating pressure to the process water. During operation, the circulation pump 42a applies the operating pressure to the process water and forwards it to the water dosing modules 28a, 30a, 32a, 34a of the water supply module 24a. The circulation pump 42a can preferably be designed as a simple and cost-effective circulation pump 42a that has low requirements for internal pump leakage. Preferably, the circulation pump 42a has an electric motor which has a pump wheel of the circulation pump 42a for conveying the process water.

[0030] The circulation circuit 36a has a pressure line 50a. The pressure line 50a is intended to convey the process water brought to operating pressure. The pressure line 50a is connected downstream of the circulation pump 42a. The process water compressed by the circulation pump 42a flows in the pressure line 50a. The pressure line 50a is intended to be fluidically connected to the water dosing modules 26a, 28a, 30, 34 of the water supply module 24a. The water dosing modules 26a, 28a, 30, 34 of the water supply module 24a are each fluidically connected to the pressure line 50a separately via their own coupling point.

[0031] The pressure generation module 26a preferably has a cleaning element 44a. The cleaning element 44a is designed as a filter element. The cleaning element 44a is arranged downstream of the circulation pump 42a, in particular directly. The cleaning element 44a is intended to filter out particles from the process water under operating pressure. The cleaning element 44a is provided for cleaning the process water in the circulation circuit 36a. The cleaning element 44a is arranged before, i.e., upstream of, a first coupling point 52a for connecting a water dosing module 26a, 28a, 30a, 32a, 34a. In principle, it would also be conceivable for no filter element 44a to be arranged in the circulation circuit 36a.In principle, it would also be conceivable that, in addition to the cleaning element 44a for filtering particles in the process water, further elements for filtering or combating biocontamination in the process water are arranged in the circulation circuit 36a.

[0032] The circulation circuit 36a has a return line 46a. The return line 46a is designed to return the process water to the storage tank 38a. The return line 46a is fluidically connected directly to the storage tank 38a. The return line 46a connects the pressure line 50a to the storage tank 38a. Via the return line 46a, process water can be returned from the pressure line 50a to the storage tank 38a. During operation, process water that has not been delivered to the water dosing modules 28a, 30a, 32a, 34a is returned to the storage tank 38a via the return line 46a.

[0033] The pressure generation module 26a has a pressure control valve 48a. The pressure control valve 48a is provided for adjusting the pressure level in the pressure line of the circulation circuit 36a. The pressure control valve 48a is provided for adjusting the operating pressure of the process water in the pressure line 50a. The pressure control valve 48a can be used to adjust the operating pressure of the process water in the pressure line 50a. The pressure control valve 48a is designed as an adjustable pressure switching valve. The pressure control valve 48a preferably has a spring-loaded valve element that can be adjusted by the pressure of the process water in the pressure line 50a. The pressure control valve 48 regulates the pressure drop across the pressure control valve 48a through the spring force acting on the spring-loaded valve element.The pressure drop across the pressure control valve 48a preferably determines the pressure on the inlet side of the pressure control valve 48a, i.e., the pressure of the process water in the pressure line 50a. By varying the spring force of the pressure control valve 48a, the operating pressure of the process water in the pressure line 50a can be adjusted. The pressure control valve 48a is arranged between the pressure line 50a and the return line 46a. The pressure control valve 48a preferably defines the transition between the pressure line 50a and the return line 46a. An inlet of the pressure control valve 48a is fluidly connected to one end of the pressure line 50a. An outlet of the pressure control valve 46a is connected to the beginning of the return line 46a.

[0034] During operation, the circulation pump 42a pumps process water from the storage tank 36a into the pressure line 50a. The process water flows through the cleaning element 44a and is thereby cleaned. The pressure control valve 48a at the end of the pressure line 50a regulates the pressure of the process water in the pressure line 50a to the operating pressure. The operating pressure in the pressure line 50a is determined by the pressure drop across the adjustable pressure control valve. Excess process water can drain away via the pressure control valve 48. The excess process water from the pressure line 50a flows through the pressure control valve 48a and the return line 46a back into the storage tank 38a. During operation, the circulation pump 42a continuously pumps process fluid from the storage tank 38a into the pressure line 50a.During operation, the circulation pump 42a continuously pumps process fluid from the storage tank 38a into the pressure line 50a and thereby into the water dosing modules 28a, 30a, 32a, 34a connected to the pressure line 50a. The pressure control valve 48a maintains the pressure of the process water in the pressure line 50a essentially at the operating pressure. During normal operation, the pressure of the process water in the pressure line 50a preferably fluctuates only minimally around the set operating pressure. The excess process water that is not supplied to the water dosing modules 28a, 30a, 32a, 34a is directed back into the storage tank 38a through the pressure control valve 48a and the return line 46a.

[0035] The pressure generation module 26a preferably has a pressure sensor 62a arranged in the pressure line 52a. The pressure sensor 52a is provided for monitoring the pressure of the process water in the pressure line 52a. By means of the pressure sensor 62a, it can preferably be monitored during operation whether the process water in the pressure line 52a is adjusted with sufficient accuracy to the operating pressure. The water supply module 24a has a computing unit 64a. The computing unit 64a is preferably provided at least for controlling or regulating the water supply module 24a. The computing unit 64a is provided for controlling or regulating the pressure generation module 26a. The computing unit 64a preferably detects the sensor signals of the pressure sensor 62a and evaluates them. The computing unit 64a is provided for controlling the circulation pump 42a. The computing unit 64a preferably controls the circulation pump 42a depending on a current load requirement.Preferably, the computing unit 64a for adjusting the operating pressure is provided to control the pressure control valve 48a. The computing unit 64a is provided to adjust a spring force of the pressure control valve 48a and thus the operating pressure of the process water in the pressure line 50a. In principle, it would be conceivable for the computing unit 64a to be designed as part of a higher-level computing unit of the fuel cell system 10a.

[0036] The water supply module 24a has a water inlet 66a. Water is supplied to the water supply module 24a via the water inlet 66a from an external source, for example, a water connection. The water inlet 66a is formed as part of the pressure generation module 26a. The water inlet 66a is preferably integrated into the pressure generation module 26a. The water inlet is preferably arranged in the storage tank 38a. Water preferably flows from an external source directly into the storage tank 38a via the water inlet 66a. In principle, it would also be conceivable for the water inlet to be integrated into the return line 46a or the supply line 40a.

[0037] The water dosing modules 28a, 30a, 32a, 34a are all fluidically connected to the pressure line 50a via a coupling point 52a. The water dosing modules 28a, 30a, 32a, 34a are all connected to the pressure line 50a between the circulation pump 42a and the pressure control valve 48a. The water dosing modules 28a, 30a, 32a, 34a are all designed identically. Therefore, only the first water dosing module 28a, which is assigned to the first fuel cell stack 14a and supplies its reformer 22a with process water, is described in more detail below. An explanation of the other water dosing modules 30a, 32a, 34a can be provided based on the following description of the first water dosing module 28a.

[0038] The water dosing module 28a is designed separately from the pressure generation module 26a. The water dosing module 28a is functionally designed differently from the pressure generation module 26a. The water dosing module 28a is designed to adjust a mass flow of the process water under operating pressure that is supplied to the reformer 22a. The water dosing module 28a is designed to adjust a quantity of pressurized process water that is supplied to the reformer for reforming the process gas. The water dosing module 28a is designed for a precise adjustment of a mass flow of the process water that is supplied to the reformer 22a. Only by precisely adjusting the mass flow of process water under operating pressure that is supplied to the reformer 22a can a ratio of process water to process gas in the reformer 22a be advantageously easily and precisely adjusted.By precisely adjusting the ratio of process water to process gas in the reformer 22a, an oxygen-to-carbon ratio can be adjusted particularly well. This advantageously prevents the oxygen-to-carbon ratio from falling below a minimum value, which could cause adverse operating conditions, particularly damage to the fuel cell stacks 14a, 16a, 18a, 20a.

[0039] The water dosing module 28a has a switching valve 54a. The switching valve 54a is designed to control or regulate the mass flow of the pressurized process water flowing through the water dosing module 28a. The switching valve 54a is designed as a controllable valve. The switching valve 54a has an open position and a closed position. In the open position, process water can flow through the switching valve 54a. In the closed position, the switching valve 54a is blocked and no process water can flow through the switching valve 54a. The switching valve 54a is designed as a solenoid valve. The switching valve 54a, designed as a solenoid valve, has an electromagnet that can quickly switch the switching valve 54a back and forth between its open position and its closed position. In principle, it would also be conceivable for the switching valve 54a to be designed as a valve that switches at different speeds.The switching valve 54a is intended to be controlled by the processing unit 64a of the water supply module 24a. In principle, it would also be conceivable for the switching valve 54a to be controlled by another processing unit, for example, an internal processing unit of the associated fuel cell stack 14a. By alternately opening and closing the switching valve 54a during operation, a mass flow of process water flowing through the switching valve 54a on average over time can be easily and precisely adjusted. Preferably, the switching valve 54a is intended to be controlled via a pulse width modulated (PWM) signal to adjust the mass flow of process water. The duty cycle, i.e., a ratio of the opening duration to the closing duration of the switching valve 54a, allows the mass flow of process water flowing through the switching valve 54a to be precisely controlled on average over time.

[0040] The water dosing module 28a preferably has a cleaning element 56a. The cleaning element 56a is designed as a filter element. The cleaning element 56a is preferably connected upstream of the switching valve 54a of the water dosing module 28a. The cleaning element 56a is provided for filtering the process water supplied to the switching valve 54a. Filtering can prevent contamination and thus a deterioration in the accuracy of the switching valve 54a.

[0041] The water dosing module 28a has a control throttle 58a. The control throttle 58a is connected downstream of the switching valve 54a. The control throttle 58a is designed to limit the flow of process water. The control throttle 58a is designed to limit the mass flow of process water flowing through the water dosing module 28a to a maximum value. The control throttle 58a defines a maximum possible flow of process water through the water dosing module 28a when the switching valve 54a is permanently open.

[0042] The control throttle 58a is designed such that a pressure loss across the control throttle 58a is greater than a combined pressure loss of all elements of the water dosing module 22a connected upstream of the control throttle 58a. The control throttle 58a forms by far the greatest flow resistance in the water dosing module 22a. The control throttle 58a is designed such that a pressure loss across the control throttle 58a is greater than a pressure loss across the cleaning element 56a and the switching valve 54a. The pressure loss across the control throttle 58a is significantly higher than the sum of the pressure losses across the cleaning element 56a and the switching valve 54a. The pressure loss across the control throttle 58a is preferably at least 10%, preferably at least 15%, particularly preferably at least 25% higher than the pressure loss across the cleaning element 56a and the switching valve 54a. This allows a mass flow to be precisely adjusted.Furthermore, the mass flow of process water can thereby be kept substantially constant in the event of pressure fluctuations in the pressure line 50a of the pressure generation module 26a.

[0043] The water dosing module 28a has a backflow prevention device. The backflow prevention device is formed by a check valve 60a. The check valve 60a is connected downstream of the switching valve 54a. The check valve 60a is also connected downstream of the control throttle 58a. The check valve 60a is preferably designed as the last fluidic component of the water dosing module 28a. Preferably, only one connection is connected downstream of the check valve 60a, via which the water dosing module 28a is connected to the reformer 22a of the fuel cell stack 14a. The check valve 60a is provided to prevent fluid from flowing back from the reformer into the water dosing module 28a. In particular, the check valve 60a is provided to allow a process gas to flow from the reformer 22a into the water dosing module 28a, particularly during load operation.

[0044] Preferably, it would be conceivable for the water dosing module 28a to have a nozzle 68a at its connection, which connects the water dosing module 28a to the reformer 22a of the fuel cell stack 14a. This nozzle is intended to atomize the process water flowing into the reformer 22a. By atomizing the pressurized process water upon entering the reformer 22a, evaporation of the process water for reforming the process gas can occur more quickly and in a more defined manner. Preferably, it would be conceivable for the check valve 60a to be integrated into the nozzle 68a.

[0045] In a method according to the invention for the fuel cell device 12a for supplying the reformers 22a of the fuel cell units 14a, 16a, 18a, 20a with a set mass flow of process water, the process water is compressed to an operating pressure in the pressure generation module 26a of the water supply module 24a in a first process step. In the first process step, the process water is pressurized to the operating pressure by the circulation pump 42a and the pressure control valve 28a in the pressure line 50a. In the first process step, excess process water flows back into the storage tank 38a via the pressure control valve 48a and the return line 46a. In a second, separate process step, a mass flow of process water, which is fed to the respective reformer 22a of the fuel cell stacks 14a, 16a, 18a, 20a, is set in the water dosing modules 28a, 30a, 32a, 34a.The switching valve 54a, designed as a solenoid valve, is controlled by a pulse-width modulated (PWM) signal to adjust the mass flow of process water. The first and second process steps run simultaneously during normal operation.

[0046] In the Fig. 2 and Fig. 3 shows two further embodiments of the invention. The following descriptions and the drawings are essentially limited to the differences between the embodiments, whereby with regard to components with the same designation, in particular with regard to components with the same reference numerals, reference is also made to the drawings and / or the description of the other embodiments, in particular to the Fig. 1. To distinguish the embodiments, the letter a is added to the reference numerals of the embodiment in the Fig. 1. In the examples of the Fig. 2 and Fig. 3, the letter a is replaced by the letters b and c.

[0047] The Fig. 2 shows a fuel cell device 12b according to the invention in a second embodiment. Fig. 2 shows a fuel cell system 10b according to the invention with the fuel cell device 12b. In contrast to the first exemplary embodiment, the fuel cell system 10b has only one fuel cell stack 14b. The fuel cell stack 14b has a reformer 22b. The fuel cell device 12b has a water supply module 24b. The water supply module 24b is provided for supplying the fuel cell stack 14b with process water. The water supply module 24b is provided for supplying the reformer 22b of the fuel cell stack 14b with process water under operating pressure. The water supply module 24b has a water inlet 66b. Water is supplied to the water supply module 24b via the water inlet 66b from an external source, for example, a water connection.

[0048] The water supply module 24b has a pressure generation module 26b. The pressure generation module 26b is designed to compress the process water to the operating pressure. The pressure generation module 26b has a circulation circuit 36b for the process water. The pressure generation module 26b has a storage tank 38b. The circulation circuit 36b has a supply line 40b. The water supply module 24b has a circulation pump 42b. The circulation pump 42b is integrated into the circulation circuit 36b. The circulation circuit 36b has a pressure line 50b. The pressure line 50b is designed to conduct the process water brought to operating pressure. The pressure generation module 26b preferably has a cleaning element 44b. The cleaning element 44b is designed as a filter element. The cleaning element 44b is connected downstream of the circulation pump 42b, in particular directly.

[0049] The circulation circuit 36b has a return line 46b. The pressure generation module 26b has a pressure control valve 48b. The pressure control valve 48b is provided for adjusting the pressure level in the pressure line 50b of the circulation circuit 36b. The pressure generation module 26b has the same components as in the first embodiment.

[0050] The water supply module 24b has a water dosing module 28b. The water supply module 24b is designed to functionally separate the application of the operating pressure to the process water and the setting of a mass flow delivered to the reformer 22b of the fuel cell stack 14b. The pressure generation module 24b is designed separately from the water dosing module 26b. The water dosing module 26b is fluidly connected to the pressure line 50b via a coupling point 52b. The water dosing module 28b has a switching valve 54b. The switching valve 54b is designed to control or regulate the mass flow of the pressurized process water flowing through the water dosing module 28b. The switching valve 54b is designed as a solenoid valve. The switching valve 54b is intended to be controlled by a computing unit 64b of the water supply module 24b.The water dosing module 28b preferably has a cleaning element 56b. The cleaning element 56b is designed as a filter element. The water dosing module 28b has a control throttle 58b. The water dosing module 28b has a backflow prevention device. The backflow prevention device is formed by a check valve 60b.

[0051] The water dosing module 28b is essentially the same as in the first embodiment.

[0052] The difference from the first embodiment is that the water supply module 24b has only one water dosing module 28b, and that the water supply module 24b is arranged in the assembly of the fuel cell stack 14b. The entire water supply module 24b, i.e., the pressure generation module 26b and the one water dosing module 28b, are arranged within a housing of the fuel cell stack 14b.

[0053] The Fig. 3 shows a fuel cell device 12c according to the invention in a third embodiment. Fig.3 shows a fuel cell system 10c according to the invention with the fuel cell device 12c. The fuel cell system 10b has, for example, two fuel cell stacks 14c, 16c. In principle, it would also be conceivable for the fuel cell system 10c to have a different number of fuel cell stacks 14c, 16c. The fuel cell stacks 14c, 16c each have a reformer 22c. The fuel cell device 12c has a water supply module 24c. The water supply module 24c is provided for supplying the fuel cell stacks 14c, 16c with process water. The water supply module 24c is provided for supplying the reformers 22c of the fuel cell stacks 14c, 16c with process water under operating pressure. The water supply module 24c has a water inlet 66c. Water is supplied from an external source, for example a water connection, to the water supply module 24c via the water inlet 66c.

[0054] The water supply module 24c has a pressure generation module 26c. The pressure generation module 26c is designed to compress the process water to the operating pressure. The pressure generation module 26c has a circulation circuit 36c for the process water. The pressure generation module 26c has a storage tank 38c. The circulation circuit 36c has a supply line 40c. The water supply module 24c has a circulation pump 42c. The circulation pump 42c is integrated into the circulation circuit 36c. The circulation circuit 36c has a pressure line 50c. The pressure line 50c is designed to conduct the process water brought to operating pressure. The pressure generation module 26c preferably has a cleaning element 44c. The cleaning element 44c is designed as a filter element. The cleaning element 44c is connected downstream of the circulation pump 42c, in particular directly.

[0055] The circulation circuit 36c has a return line 46c. The pressure generation module 26c has a pressure control valve 48c. The pressure control valve 48c is provided for adjusting the pressure level in the pressure line 50c of the circulation circuit 36c. The pressure generation module 26c has the same components as in the first embodiment.

[0056] The water supply module 24c has a water dosing module 28c, 30c for each fuel cell stack 14c, 16c. The water dosing modules 28c, 30c are designed identically, which is why only one water dosing module 28c will be described in more detail below. The water supply module 24c is intended to functionally separate the application of the operating pressure to the process water and the setting of a mass flow that is delivered to the reformer 22c of the fuel cell stack 14c. The pressure generation module 24c is designed separately from the water dosing module 26c. The water dosing module 26c is fluidically connected to the pressure line 50c via a coupling point 52c. The water dosing module 28c has a switching valve 54c. The switching valve 54c is intended to control or regulate the mass flow of the pressurized process water flowing through the water dosing module 28c.The switching valve 54c is designed as a solenoid valve. The switching valve 54c is intended to be controlled by a processing unit 64c of the water supply module 24c. The water dosing module 28c preferably has a cleaning element 56c. The cleaning element 56c is designed as a filter element. The water dosing module 28c has a control throttle 58c. The water dosing module 28c has a backflow prevention device. The backflow prevention device is formed by a check valve 60c. In contrast to the first exemplary embodiment, the positioning of the control throttle 58c and the check valve 60c is reversed. The check valve 60c is connected directly downstream of the switching valve 54c. The control throttle 58c is connected downstream of the check valve 60c. The control throttle is arranged directly at a connection to the reformer 22c. The control throttle 58c is preferably designed as a nozzle.The control throttle 58c, designed as a nozzle, is intended to atomize the process water flowing into the reformer 22c. By using the control throttle 58c required for the operation of the water dosing module 28c to atomize the process water upon entering the reformer 22c, additional components for atomizing the process water can be dispensed with.

Claims

[1] Fuel cell device for at least one fuel cell stack (14a, 16a, 18a, 20a; 14b; 14c, 16c) having at least one reformer (22a; 22b; 22c) for reforming, in particular for steam reforming, a process gas, with a water supply module (24a; 24b; 24c) for supplying the reformer (22a; 22b; 22c) with process water under operating pressure, characterized by in that the water supply module (24a; 24b; 24c) has a pressure generation module (26a; 26b; 26c) which is provided for subjecting the process water to an operating pressure, and at least one water dosing module (28a, 30a, 32a, 34a; 28b; 28c, 30c) which is designed separately from the pressure generation module (26a; 26b; 26c) and which is provided for adjusting a mass flow of the process water under operating pressure which is fed to the reformer (22a; 22b; 22c). [2] Fuel cell device according to claim 1, characterized bythat the pressure generation module (26a; 26b; 26c) has a circulation circuit (36a; 36b; 36c) for the process water. [3] Fuel cell device according to claim 1 or 2, characterized by that the pressure generation module (26a; 26b; 26c) has a circulation circuit (36a; 36b; 36c) for the process water, a storage tank (38a; 38b; 38c) integrated into the circulation circuit (36a; 36b; 36c) and a circulation pump (42a; 42b; 42c) integrated into the circulation circuit (36a; 36b; 36c). [4] Fuel cell device according to claim 3, characterized by that the pressure generation module (26a; 26b; 26c) has a cleaning element (44a; 44b; 44c) which is connected downstream of the circulation pump (42a; 42b; 42c). [5] Fuel cell device according to one of the preceding claims, characterized byin that the pressure generation module (26a; 26b; 26c) has a pressure control valve (48a; 48b; 48c) which is arranged between a pressure line (50a; 50b; 50c) and a return line (46a; 46b; 46c) of a circulation circuit (36a; 36b; 36c) of the pressure generation module (26a; 26b; 26c). [6] Fuel cell device according to one of the preceding claims, characterized by that the pressure generation module (26a; 26b; 26c) has a circulation circuit (36a; 36b; 36c) for the process water, which forms a pressure line (50a; 50b; 50c) to which the at least one water dosing module (28a, 30a, 32a, 34a; 28b; 28c, 30c) is fluidically connected. [7] Fuel cell device according to one of the preceding claims, characterized bythat the at least one water dosing module (28a, 30a, 32a, 34a; 28b; 28c, 30c) has a switching valve (54a; 54b; 54c), preferably a solenoid valve, which is intended to control or regulate a mass flow of the process water flowing through the water dosing module (28a, 30a, 32a, 34a; 28b; 28c, 30c). [8] Fuel cell device according to claim 7, characterized by that the at least one water dosing module (28a, 30a, 32a, 34a; 28b; 28c, 30c) has a control throttle (58a; 58b; 58c) which is connected downstream of the switching valve (54a; 54b; 54c). [9] Fuel cell device according to claim 8, characterized by that the control throttle (58a; 58b; 58c) is designed such that a pressure loss across the control throttle (58a; 58b; 58c) is greater than a combined pressure loss of all elements of the water dosing module (28a, 30a, 32a, 34a; 28b; 28c, 30c) upstream of the control throttle (58a; 58b; 58c). [10] Fuel cell device according to one of the preceding claims, characterized by that the at least one water dosing module (28a, 30a, 32a, 34a; 28b; 28c, 30c) has a backflow prevention device, in particular a check valve (60a; 60b; 60c), which is connected downstream of a switching valve (54a; 54b; 54c), in particular a solenoid valve of the water dosing module (28a, 30a, 32a, 34a; 28b; 28c, 30c). [11] Fuel cell device according to one of the preceding claims, characterized by that the at least one water dosing module (28a, 30a, 32a, 34a; 28b; 28c, 30c) has a cleaning element (56a; 56b; 56c) which is connected upstream of a switching valve (54a; 54b; 54c) of the water dosing module (28a, 30a, 32a, 34a; 28b; 28c, 30c). [12] Fuel cell device according to one of the preceding claims, characterized bythat the water supply module (24a; 24c) has at least one further water dosing module (28a, 30a, 32a, 34a; 28b; 28c, 30c) for supplying a reformer (22a; 22b; 22c) of a further fuel cell stack (14a, 16a, 18a, 20a; 14b; 14c, 16c) with process water under operating pressure, which is fluidically connected to the pressure generation module (26a; 26c). [13] Method for operating a fuel cell device, comprising a water supply module (24a; 24b; 24c) for supplying a reformer of a fuel cell stack (14a, 16a, 18a, 20a; 14b; 14c, 16c) with a pressurized process water according to one of claims 1-12, characterized byin that in a first process step in a pressure generation module (26a; 26b; 26c) of the water supply module (24a; 24b; 24c) the process water is compressed to an operating pressure and in that in a further, separate process step in a water dosing module (28a, 30a, 32a, 34a; 28b; 28c, 30c) a mass flow of process water which is fed to the reformer (22a; 22b; 22c) is set. [14] Method according to claim 13, characterized by that a solenoid valve of the water dosing module (28a, 30a, 32a, 34a; 28b; 28c, 30c) is controlled by means of a pulse width modulated (PWM) signal to adjust the mass flow of process water. [15] Fuel cell system (10a; 10b; 10c) with a plurality of fuel cell stacks (14a, 16a, 18a, 20a; 14b; 14c, 16c), each of which preferably has a reformer (22a; 22b; 22c), and with a fuel cell device (12a; 12b; 12c) according to one of claims 1 to 12, characterized byin that the fuel cell device (12a; 12b; 12c) has a water supply module (24a; 24b; 24c) which has a pressure generation module (26a; 26b; 26c) and a water dosing module (28a, 30a, 32a, 34a; 28b; 28c, 30c) for each reformer (22a; 22b; 22c) in order to supply the respective reformer (22a; 22b; 22c) with process water under operating pressure.

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