EP1226617A2

EP1226617A2 - Fuel cell facility and operating method for the same

Info

Publication number: EP1226617A2
Application number: EP00978943A
Authority: EP
Inventors: Manfred Baldauf; Joachim Grosse; Günter Luft; Kurt Pantel; Walter Preidel; Manfred Waidhas; Ulrich Gebhardt; Rolf BRÜCK; Jörg-Roman KONIECZNY; Meike Reizig
Original assignee: Emitec Gesellschaft fuer Emissionstechnologie mbH; Siemens AG
Current assignee: Siemens AG; Vitesco Technologies Lohmar Verwaltungs GmbH
Priority date: 1999-09-23
Filing date: 2000-09-18
Publication date: 2002-07-31
Also published as: DE19945715A1; JP2003520392A; WO2001022512A2; WO2001022512A3; CN1421052A; CA2385632A1; US20020119352A1

Abstract

The invention relates to a fuel cell facility and an operating method for the same. The facility is operated at temperatures between 80 DEG C and 300 DEG C and guarantees optimum effectiveness because the waste heat from the fuel cell stack is used in at least another way.

Description

description

Fuel cell system and associated operating method

The invention relates to a fuel cell system and an operating method for such a fuel cell system. The invention is advantageously applied to a direct methanol fuel cell.

So-called DMFC fuel cells and so-called PEM fuel cells are currently being tested for use in motor vehicles. The concept of the direct methanol fuel cell (DMFC) differs from the hydrogen polymer electrolyte membrane (PEM = Proton Exchange Membrane or Polymer Electrolyte Membrane) fuel cell essentially in that the fuel methanol is direct , i.e. without an interposed reformer, is implemented at the anode. For this purpose, either pure methanol or a methanol / water mixture is introduced into the fuel cell as fuel, which is converted at the anode according to the equation CH ₃ 0H + H ₂ 0 -> C0 ₂ + 6 H ⁺ + 6 e ^" .

From DE 196 256 21 AI a direct methanol fuel cell system is known, which is operated with gaseous fuel. For this purpose, an evaporator is connected upstream of the cell and / or the stack. The system also provides a condenser downstream of the stack, in which the carbon dioxide formed is separated from the anode exhaust gas before it is returned to the evaporator. A disadvantage of the system is that the energy for the evaporator must be supplied externally.

The object of the invention is to improve the efficiency of known fuel line systems. The object is achieved by the features of claim 1. An associated operating method is specified in claim 11. Advantageous refinements of the invention result from the dependent claims.

The invention relates to a fuel cell system with at least one fuel cell stack, process medium supply lines, electrical lines and upstream evaporator, in which at least one line is provided through which the heat from at least part of the stack can be used in at least one other device. In the method according to the invention for operating a fuel cell system, the waste heat of at least part of the fuel stack is used in various ways.

The invention can be implemented in particular on a direct methanol fuel cell. The fuel is an alcohol, preferably methanol, which is directly in the Brerx. - Substance cell is implemented.

In the invention, the line is not only a pipe, a hose or some other objective connection between two elements of the system, but any other connection, that is to say a thermal contact, can also be so called. The "device" that is heated is primarily an element of the fuel cell system such as the evaporator, the condenser, the preheating for the fuel, the device for preheating the process medium, the gas cleaning system and / or the compressor. However, the heating of a device or room located outside the system and / or any further use of the first waste heat as well as the use of the second waste heat from the fuel cell stack, namely the waste heat of one of the aforementioned rates, also encompassed by the invention eg the use of waste heat from the evaporator to heat a living space or passenger depending on the application of the fuel cell system in the mobile or stationary area. The above-mentioned elements or devices are all heat exchangers and cool the introduced warm gases and / or liquids.

The use of the waste heat from a fuel cell stack, which in technical terminology is referred to briefly as a stack, is firstly via at least one exhaust gas and / or a heated cooling medium, which e.g. is passed from the stack into the evaporator and secondly via a thermal contact in which, for example, the evaporator is integrated in the stack.

According to one embodiment, the evaporator is arranged with the stack in a housing and / or is integrated in the end plates of the stack.

The integration of the evaporator in the stack also means, for example, that the process medium to be heated is carried out between the fuel cell units to cool them.

After carrying out the method, the fuel cell stack is operated at temperatures above 80 ° C. and below 300 ° C., preferably between 100 ° C. and 220 ° C. and in particular at a temperature of approx. 160 ° C. According to the high operating temperature, a DMFC system according to the invention can also be referred to as a high-temperature polymer electrolyte membrane fuel cell (HTM fuel cell).

The system is preferably operated in such a way that recyclable components of the anode and / or cathode exhaust gas, such as water and / or methanol, are recovered and / or circulated.

According to one embodiment, the system thus comprises a condenser through which the anode exhaust gas is passed. The mixture of methanol and water contained in the anode exhaust gas is condensed out and separated from the carbon dioxide. The fully J ÜJ dt HM

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According to a preferred embodiment, the gas cleaning is controlled with the aid of sensors, for example a sensor being attached to each gas outlet, which measures the temperature, composition and / or quantity of the gas released into the environment and passes it on to a control device.

Gas cleaning can e.g. can also be combined with the condenser and / or a device for preheating the process medium to form a catalytically coated heat exchanger into which the exhaust gas containing methanol is introduced. In this variant, electrical heating is advantageous for the cold start in order to ensure that the working temperature of the catalytic coating is reached quickly. In addition, the waste heat from gas cleaning e.g. be made usable via another heat exchanger.

According to a preferred embodiment, the cooling capacity of the evaporator is used to condense the exhaust gas, so that the evaporator and the condenser form an aggregate or a heat exchanger.

In the event of a cold start, protection against freezing of the stack and / or maintenance of the operating temperature in at least part of a stack of the system is advantageous in order to achieve a better start-up behavior. For this purpose, insulation of at least part of a stack may be preferred over maintaining the operating temperature through part-load operation. This insulation is realized, for example, by means of a double-walled housing, which may be filled with latent heat storage materials. At the Isola w 10 to t HH in o cn o in O in

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The system is started up with a liquid fuel during a cold start according to one embodiment of the method, the minimum stacking temperature for starting being predetermined by the freezing point of the electrolyte.

According to one embodiment, hydrogen is fed into the stack to start up the DMFC system because starting the stack with hydrogen is possible at much lower temperatures than when using the methanol / water mixture.

In this embodiment, a corresponding hydrogen store, such as a palladium sponge, a pressure vessel and / or a hydride store, is carried along.

According to one embodiment, the hydrogen storage is refilled electrolytically from the water and / or water-methanol tank, for example during operation of the system. The electrolysis is carried out with an extra electrolysis device and / or a stack or part of a stack is used for the electrolysis.

In this embodiment, the energy required for the electrolysis can be made available directly from a partial stack of the system and / or from an energy store such as a battery or a capacitor.

The hydrogen that is still unused after the system has been started can be used to heat a device such as the evaporator or can simply be introduced into the gas cleaning system. ⁾ to t HH in O in o in O in

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Actual values are reached with the target values. The control unit is generally used to optimize the efficiency and / or to optimally adapt to the power required by the system (for example via the accelerator pedal pressure). In particular, a stack voltage-dependent power control (driving the system with optimal load utilization), water management, which e.g. together with a starter cartridge, which eliminates the need to carry a water tank and the optimal use of energy by the control unit.

The control and construction of the system is carried out in such a way that heating and cooling of the individual components such as evaporators, preheaters, compressors and / or preheating units, on the one hand, which all require heat and stack, condenser, any cooling system and / or water separator, on the other hand, all are cooled , combined with optimal use of energy.

The invention is explained in more detail below on the basis of two preferred exemplary embodiments, which are shown in block diagrams.

Figures 1 and 2 each show the block diagrams of a direct methanol fuel cell system. The reference numbers of both block diagrams are identical for the same elements, lines are named in such a way that the reference number of the upstream element is placed in front of the reference number of the downstream element (e.g. line 1311 is the line in which the fluid flows from element 13 to element 11) ):

In FIG. 1, stack 1 can be seen, which is connected to the evaporator 2 once via the process medium supply line 21 and on the other hand via the process medium discharge line 12. For reasons of clarity, only one stack 1 of the direct methanol fuel cell system is shown, although one system with several stacks, among other things with low-voltage units for on-board power supply, may be advantageous.

A process medium supply line 31 leads from the compressor 3 to the stack 1. The compressor 3, which is regulated in a load-dependent manner via the control unit 6, is preceded by a heat exchanger or condenser 4, which in turn is connected to the stack 1 via the process medium discharge line 14 in such a way that the waste heat from the anode compartment of the stack 1 is used to preheat the oxidant air, because the spent fuel is introduced into the heat exchanger 4 through the line 14 at a temperature of approximately 160 ° C. In the heat exchanger 4, water and / or unused methanol is separated from the carbon dioxide and other gaseous impurities by condensation. The liquid phase obtained in the heat exchanger 4 is fed into the mixer 5 via the line 45. Direct feeding into the methanol tank 8 (via a line 48, not shown) is also possible, in which case a sensor in line 48 is advantageous for analyzing the composition. The line 45 has a sensor 46 which supplies information about the amount, pressure, temperature and / or composition of the mixture carried in the line 45 to the control device 6. For reasons of clarity, further sensors, depending on the embodiment, are not shown, which are attached in the lines 12 and / or 14 and which provide the control device with information about the quantity, pressure, temperature and / or composition of the mixture carried in the line. The separated gas phase of the anode exhaust gas is introduced via line 411 into the gas cleaning system 11, where it is freed of undesirable emissions before it leaves the system as exhaust gas containing carbon dioxide.

The mixer 5 is connected via lines 85 and 95 to the two fuel tanks, the methanol tank 8 and the water tank 9. Lines 85 and 95 each have a metering valve that is controlled by control unit 6. So only a load-dependent passes through the lines 85 and 95 IO ι to to H -> in o in o in O in

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For clarity, the fuel lines are shown with a short dash and the oxide lines are shown with a long dash.

For the sake of clarity, the integration of the cooling circuit in the use of the stack waste heat has been omitted in the two embodiments shown. The cooling circuit, if present, is preferably also passed through the evaporator or a device for preheating the process media.

A "fuel cell system" is a system that has at least one stack with at least one fuel cell unit, the corresponding process medium supply and discharge channels, electrical lines and end plates, possibly a cooling system with cooling medium and the entire fuel cell stack periphery (reformer, compressor, preheater , Blower, heating for process medium preheating, etc.).

A stack is a stack with at least one fuel cell unit with the associated lines and, if available, at least part of the cooling system.

An antifreeze that is not electrically conductive can be contained in the cooling system. Other units are either isolated by the insulation methods (So) and / or local heating devices at temperatures above freezing, which may vary depending on the unit concerned (e.g. if a water pipe is affected, the freezing point is different from that of a water / Methanol mixture line) is held.

The invention discloses a DMFC system which, at high operating temperatures (HTM fuel cell), optimizes the energy and fuel-related efficiency by utilizing the waste heat from the stack.

Claims

claims

1. Fuel cell system with at least one fuel cell stack, process medium supply lines, electrical lines and upstream evaporator, in which at least one line is provided through which the heat from at least part of the fuel cell stack can be used in at least one other device.

2. The fuel cell system according to claim 1, wherein the evaporator is integrated in the fuel cell stack and / or is accommodated with the fuel cell stack in a housing.

3. Fuel cell system according to one of the preceding claims, which comprises a heat exchanger through which at least the anode and / or the cathode exhaust gas is passed.

4. Fuel cell system according to one of the preceding claims, in which the evaporator and a condenser are one device.

5. Fuel cell system according to one of the preceding claims, in which a gas cleaning system is provided.

6. Fuel cell system according to one of the preceding claims, in which at least part of a module, a tank and / or a line has an insulation and / or a local heating element.

7. Fuel cell system according to one of the preceding claims, in which at least one supply opening of a process medium and / or coolant supply line can be closed.

8. Fuel cell system according to one of the preceding claims, in which a filter is connected upstream of the fuel cell stack.

9. Fuel cell system according to one of the preceding claims, in which a control device and at least one analysis device is provided in the system, into which information about current measured values is fed and which controls the control devices of the system on the basis of a comparison of the predetermined and / or calculated target values measured actual values are brought into agreement with the target values.

10. Fuel cell system in which a starter cartridge is provided to start the system, in which the methanol / water mixture suitable for implementation at the anode is ready.

11. Fuel cell system that has a hydrogen storage.

12. Method for operating a fuel cell system, in which waste heat from at least part of a fuel cell stack is used.

13. The method according to claim 12, wherein the waste heat is used in a device of the fuel cell system to be heated.

14. The method according to any one of claims 12 or 13, in which recyclable components of the fuel cell stack exhaust gas are recovered and / or recycled.

15. The method according to any one of claims 12 to 14, in which water and / or methanol is recovered from the exhaust gas of a direct methanol fuel cell by introducing it into a heat exchanger, such as an evaporator, a device for preheating the process media and / or a condenser ,

16. The method according to any one of claims 12 to 15, wherein the exhaust gas of the system is passed through a gas cleaning system.

17. The method according to any one of claims 12 to 16, wherein the fuel cell stack is operated at an operating temperature between 80 ° C and 300 ° C.

18. The method according to any one of claims 12 to 17, in which at least part of a module, a tank and / or a line of the system is isolated and / or heated during the rest phase of the system.

19. Method for operating a direct methanol fuel cell system in which the operating temperature of the evaporator is lower than the temperature of the fuel cell stack exhaust gas.

20. The method according to any one of claims 12 to 19, in which hydrogen is introduced into the fuel cell stack as a fuel during cold starting.

21. The method according to claim 20, in which hydrogen from the fuel cell stack exhaust gas is further used during cold starting and / or is introduced into the gas cleaning system.

22. The method according to any one of claims 12 to 21, wherein the cooling medium is guided in direct current during the cold start of the system.

23. The method according to claim 22, in which a temperature profile which is as uniform as possible is obtained after a cold start by switching the cooling medium to counterflow.

24. The method according to any one of claims 12 to 23, wherein the process medium and / or the cooling medium is filtered before being introduced into the fuel cell stack.

25. The method according to any one of claims 12 to 24, in which a control device is used which is used to optimize the efficiency. efficiency of the system records at least one measured actual value of at least one analysis device of the system, compares it with a predetermined or calculated target value and controls at least one connected control device in such a way that the actual value matches the target value.

26. The method according to claim 15, in which a hydrogen storage is replenished by electrolysis of water and / or a water-methanol mixture.

27. The method according to any one of the preceding claims, in which the second waste heat is used.

28. The method according to any one of the preceding claims, in which the fuel is supplied to the fuel cell stack in liquid form and / or from a starter cartridge during cold starting.