METHOD FOR HEATING A FUEL CELL SYSTEM AND FUEL CELL SYSTEM

Abstract

The present invention relates to a method for heating a fuel cell system (1a; 1b; 1c; 1d) comprising at least one fuel cell stack (2) with an anode portion (3) and a cathode portion (4), and a reformer (5) upstream of the anode portion (3) for steam reforming using a fuel, the reformer (5) comprising a nickel-based catalyst, said method having the following steps: starting a heating process for heating the fuel cell system (1a; 1b; 1c; 1d) with a heating device (6) and conducting a carbon-containing fluid and conducting steam through the nickel-based catalyst of the reformer (5) during the heating process. The invention also relates to a fuel cell system (1a; 1b; 1c; 1d) which is designed to carry out a method according to the invention.

Claims

1. Method for heating a fuel cell system (1a; 1b; 1c; 1d) comprising at least one fuel cell stack (2) with an anode portion (3) and a cathode portion (4) as well as a reformer (5) upstream of the anode portion (3) for steam reforming using a fuel, the reformer (5) comprising a nickel-based catalyst, said method having the steps: starting a heating process for heating the fuel cell system (1a; 1b; 1c; 1d) with a heating device (6) and conducting a carbon-containing fluid and conducting steam through the nickel-based catalyst of the reformer (5) during the heating process.

2. Method according to claim 1, characterised in that the steam is conducted through the nickel-based catalyst from a predefinable threshold temperature in the fuel cell system (1a; 1b; 1c; 1d).

3. Method according to claim 1, characterised in that the fuel, in particular methane, natural gas or LPG, is used as carbon-containing fluid.

4. Method according to claim 1, characterised in that the fuel is used as carbon-containing fluid during the heating process in a fuel quantity of between 5% and 20% of the fuel quantity used during steam reforming in normal operation of the fuel cell system (1a; 1b; 1c; 1d).

5. Method according to claim 1, characterised in that the heating device (6) has a heat exchanger on the reformer (5) and an afterburner (7) for combusting cathode exhaust gas and/or anode exhaust gas from the at least one fuel cell stack (2), wherein afterburner exhaust gas is fed to a hot side of the heat exchanger downstream of the afterburner (7) in order to heat up the reformer (5) during the heating process.

6. Method according to claim 1, characterised in that the steam and the carbon-containing fluid in the form of fuel are conducted to the reformer (5), as a fuel/steam mixture, via an anode gas supply line (8) upstream of the reformer (5).

7. Method according to claim 6, characterised in that a fluid delivery device (9) for delivering the fuel to the reformer (5) is arranged upstream of the reformer (5) in the anode gas supply line (8) and a steam supply line (10) for feeding steam into the anode gas supply line (8) is arranged next to the anode gas supply line (8), wherein the steam is, during the heating process, conducted through the steam supply line (10) and fed into the anode gas supply line (8) downstream of the fluid delivery device (9) and mixed with the fuel.

8. Method according to claim 6, characterised in that a fluid delivery device (9) for delivering the fuel to the reformer (5) is arranged upstream of the reformer (5) in the anode gas supply line (8) and a steam supply line (10) for feeding steam into the anode gas supply line (8) is arranged next to the anode gas supply line (8), wherein the steam is, during the heating process, conducted through the steam supply line (10) and fed into the anode gas supply line (8) upstream of the fluid delivery device (9) and mixed with the fuel.

9. Method according to claim 6, characterised in that a fluid delivery device (9) for delivering the fuel to the reformer (5) is arranged upstream of the reformer (5) in the anode gas supply line (8) and a steam supply line (10) for feeding steam into the anode gas supply line (8) is arranged next to the anode gas supply line (8), wherein a hot side of an exhaust gas heat exchanger (11) is arranged in the steam supply line (10) and the steam is, during the heating process, conducted through the steam supply line (10) and the hot side of the exhaust gas heat exchanger (11), fed into the anode gas supply line (8) downstream or upstream of the fluid delivery device (9) and mixed with the fuel.

10. Fuel cell system (1a; 1b; 1c; 1d) which is designed to carry out a method according to claim 1, comprising at least one fuel cell stack (2) with an anode portion (3) and a cathode portion (4) as well as a reformer (5) upstream of the anode portion (3) for steam reforming a fuel, the reformer (5) comprising a nickel-based catalyst.

Description

[0027] In each case schematically:

[0028] FIG. 1 shows a block diagram explaining a fuel cell system according to a first embodiment of the present invention,

[0029] FIG. 2 shows a block diagram explaining a fuel cell system according to a second embodiment of the present invention,

[0030] FIG. 3 shows a block diagram explaining a fuel cell system according to a third embodiment of the present invention,

[0031] FIG. 4 shows a block diagram explaining a fuel cell system according to a fourth embodiment of the present invention and

[0032] FIG. 5 shows a curve diagram explaining a method for heating a fuel cell system according to the invention.

[0033] Elements with the same function and mode of action are given the same reference signs in FIGS. 1 to 4.

[0034] A fuel cell system 1a according to a first embodiment is shown schematically in FIG. 1. The fuel cell system 1a comprises a fuel cell stack 2 with an anode portion 3 and a cathode portion 4 as well as a reformer 5 upstream of the anode portion 3 for steam reforming a fuel. The reformer 5 comprises a nickel-based catalyst. A heating device 6 is provided to control the temperature of the fuel cell system 1a. The heating device 6 comprises a heat exchanger on the reformer 5, an afterburner 7 for combusting cathode exhaust gas and/or anode exhaust gas from the fuel cell stack 2 as well as a cathode gas heat exchanger 12 in a cathode gas supply line 13. In addition, the heating device 6 can be assigned further heating elements and functional components, which are not however described further here.

[0035] The cathode gas supply line 12 is provided in order to feed cathode supply gas to the cathode portion 4. Cathode supply gas can in particular be understood to be air or another oxygen-containing fluid. An anode gas supply line 8 is arranged upstream of the anode portion 3. Anode gas or a process fluid for the anode portion can be conducted through the anode gas supply line in the direction of the reformer and/or the anode portion. In other words, not only gas, but also another process fluid for the anode portion can be conducted through the anode gas supply line.

[0036] The afterburner 7 is arranged downstream of the fuel cell stack 2 and upstream of a hot side of the cathode heat exchanger 12. A fluid delivery device 9 for delivering the fuel to the reformer 5 is arranged in the anode gas supply line 8 upstream of the reformer 5. The fuel cell system 1a also has a recirculation path 14 through which fuel cell exhaust gas, in particular anode exhaust gas from the anode portion 3, can be recycled downstream of the fuel cell stack 2 or fed back into the anode portion.

[0037] FIG. 2 shows a fuel cell system 1b according to a second embodiment. The fuel cell system 1b shown in FIG. 2 corresponds substantially to the fuel cell system 1a shown in FIG. 1, wherein a steam supply line 10 for feeding steam into the anode gas supply line 8 downstream of the fluid delivery device 9 is arranged next to the anode gas supply line 8.

[0038] FIG. 3 shows a fuel cell system 1c according to a third embodiment. The fuel cell system 1b.sup.1 shown in FIG. 3 corresponds substantially to the fuel cell system 1a shown in FIG. 1, wherein a steam supply line 10 for feeding steam into the anode gas supply line 8 upstream of the fluid delivery device 9 is arranged next to the anode gas supply line 8.

.sup.1 Should presumably be 1c

[0039] FIG. 4 shows a fuel cell system 1d according to a fourth embodiment. The fuel cell system 1b.sup.2 shown in FIG. 4 corresponds substantially to the fuel cell system 1a shown in FIG. 1, wherein a steam supply line 10 for feeding steam into the anode gas supply line 8 is arranged next to the anode gas supply line 8 and a hot side of an exhaust gas heat exchanger 11 is arranged in the steam supply line 10. This makes it possible, during the heating process, for the steam to be conducted through the steam supply line 10 and the hot side of the exhaust gas heat exchanger 11, then fed into the anode gas supply line 8 and mixed with the fuel.

.sup.2 Should presumably be 1d

[0040] A method for heating up a fuel cell system 1d as shown in FIG. 4 according to a preferred embodiment is now described with reference to FIG. 5. For this purpose, the heating process for heating up the fuel cell system 1d is first initiated by means of the heating device 6. From a temperature T1 of approx. 50° C., associated with a time Z1, methane is fed to the reformer 5 through the anode gas supply line 8 in a fuel quantity of approx. 10% of the fuel quantity used during steam reforming in normal operation of the fuel cell system 1d. As soon as a threshold temperature T2 of over 100° C. is reached in the fuel cell system, at a time Z2, steam is fed to the reformer 5 or the nickel-based catalyst located therein via the steam supply line 10, the hot side of the exhaust gas heat exchanger 11 and then the anode gas supply line 8. At 200° C., a carbon formation and a corresponding deposit could begin, which is however prevented by the supply of the steam. As soon as the fuel cell system 1d has reached an operating point P, at which a temperature of approx. 520° C. has been reached, the heating-up operation is terminated.

[0041] If no more power is to be generated through the fuel cell system 1d, the fuel cell system 1d is shut down. For this purpose, the electrical consumer (not shown) of the fuel cell system 1d is switched off, as a result of which the current drops close to zero. The fuel cell system 1d is then cooled with air. The fuel supply can for example be throttled to approx. 10% of the nominal rate. In addition, water can be introduced without carbon according to equilibrium conditions. The air is then regulated to as low as possible a temperature in the afterburner 7 at which a complete oxidation of a reformate gas is still possible. As a result, the fuel cell system 1d cools down. As soon as the temperature of the reformer reaches a target temperature of approx. 200′C, a recirculation of the fuel cell exhaust gas which is carried out during the shutdown process is stopped and the recirculation path 14 is purged with fuel gas to clear water and carbon monoxide from the fuel cell system and oxidise these. This also prevents or at least minimises the formation of nickel oxide as well as the condensation of steam in the reformer 5. The afterburner 7 is then deactivated and the fuel cell system 1d is completely actively cooled with air or cooled naturally. This can protect the reformer against damage and the necessary reduction of the catalyst can be omitted or shortened the next time the fuel cell system 1d is put into operation. Small amounts of carbon which may hereby form can be tolerated since they are regenerated the next time the fuel cell system 1d is put into operation.

[0042] In addition to the embodiments described, the invention allows further design principles. In other words, the invention should not be considered to be limited to the exemplary embodiments explained with reference to the drawings.

LIST OF REFERENCE SIGNS

[0043] 1a-1d fuel cell system [0044] 2 fuel cell stack [0045] 3 anode portion [0046] 4 cathode portion [0047] 5 reformer [0048] 6 heating device [0049] 7 afterburner [0050] 8 anode gas supply line [0051] 9 fluid delivery device [0052] 10 steam supply line [0053] 11 exhaust gas heat exchanger [0054] 12 cathode gas heat exchanger [0055] 13 cathode gas supply line [0056] 14 recirculation path