METHOD FOR OPERATING A SOLID OXIDE FUEL CELL DEVICE, THE SOLID OXIDE FUEL CELL DEVICE AND A MOTOR VEHICLE OUTFITTED WITH SUCH

Abstract

A method for operating a solid oxide fuel cell device is provided, which includes: using waste heat arising during the operation of the solid oxide fuel cell to produce cold by means of a refrigeration machine integrated in a refrigeration circuit for cooling of the exhaust gas at the anode side, condensing the water in the exhaust gas arising at the anode side with the aid of the refrigeration machine by a first water condenser, separating the water by a water separator, compressing the CO.sub.2 exhaust gas flow at the anode side, wherein the cooling power produced by the refrigeration machine is used for cooling of the CO.sub.2 exhaust gas flow, and storing the compressed CO.sub.2 in a CO.sub.2 storage.

A solid oxide fuel cell device and a motor vehicle having a solid oxide fuel cell device are also provided.

Claims

1. A method for operating a solid oxide fuel cell device, comprising: using waste heat arising during the operation of the solid oxide fuel cell to produce cold using a refrigeration machine integrated in a refrigeration circuit for cooling of the exhaust gas at the anode side; condensing water in the exhaust gas at the anode side using the refrigeration machine and a first water condenser; separating the water using a water separator; compressing the CO.sub.2 exhaust gas flow at the anode side, wherein a cooling power produced by the refrigeration machine is used for cooling the CO.sub.2 exhaust gas flow; and storing the compressed CO.sub.2 in a CO.sub.2 storage.

2. The method according to claim 1, wherein the water in the exhaust gas at the anode side is fully condensed by a first temperature level of a first stage of the refrigeration circuit, and the CO.sub.2 in the exhaust gas at the anode side is liquefied and thus further compressed after a first and/or a second compressor stage in a second stage of the refrigeration circuit by a second temperature level, which is lower than that of the first stage.

3. The method according to claim 1, wherein at least one valve is arranged in the refrigeration circuit to supply at least one gas cooler, and the power is adjusted by the at least one valve.

4. A solid oxide fuel cell device, comprising: a fuel cell stack with at least one fuel cell; a methane tank; a CO.sub.2 storage; a water separator; at least one compressor; and a refrigeration machine integrated in a refrigeration circuit for cooling an exhaust gas on an anode side.

5. The solid oxide fuel cell device according to claim 4, wherein the refrigeration machine is formed by an absorption refrigeration system to produce cold from the waste heat on the cathode side in the refrigeration circuit.

6. The solid oxide fuel cell device according to claim 4, wherein the refrigeration machine is formed by a thermocompressor having at least one jet pump to produce cold from the waste heat on the cathode side in the refrigeration circuit.

7. The solid oxide fuel cell device according to claim 6, wherein a first water condenser and second water condenser are arranged in the refrigeration circuit.

8. The solid oxide fuel cell device according to claim 7, wherein the two water condensers are combined in one structural component.

9. The solid oxide fuel cell device according to claim 4, wherein at least one compressor is situated downstream from the water separator and a gas cooler is situated downstream from the at least one compressor, the at least one gas cooler being connected to the refrigeration circuit.

10. A motor vehicle having a solid oxide fuel cell device according to claim 4.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0016] Further benefits, features and details will emerge from the claims, the following description of embodiments, and the drawings.

[0017] FIG. 1 shows a schematic representation of a solid oxide fuel cell device with gas coolers connected to a refrigeration machine.

[0018] FIG. 2 shows a schematic representation of a solid oxide fuel cell device with a two-stage refrigeration circuit.

DETAILED DESCRIPTION

[0019] FIG. 1 shows a schematic representation of a solid oxide fuel cell device 1 with an integrated refrigeration machine. Via a methane tank 2, methane as the fuel is taken by means of a fuel line 3 to the fuel cell stack 29. During the chemical fuel cell reaction, oxygen is produced at the cathode side, while water and carbon dioxide are prevalent as exhaust gas on the anode side. Unreacted fuel is recirculated through a recirculation line. The remaining anode exhaust gas is taken by an anode exhaust gas line 5 to a first heat exchanger 7, which further heats the compressed and heated air provided by a compressor 18 on the cathode side. The cathode exhaust gas is taken by a cathode exhaust gas line 6 to a second heat exchanger 8, which further heats the air upstream from the fuel cell stack 29, i.e., it uses the waste heat on the cathode side to control the temperature of the fresh air. The temperature of the cathode exhaust gas after going through the second heat exchanger 8 is still over 300° C. and it is used as the heat source 22 for the refrigeration machine. The refrigeration machine can be formed by either an absorption refrigeration system or a thermocompressor (FIG. 1). In the thermocompressor, the refrigerant 27 is condensed in a condenser 10, after which a portion of the refrigerant 27 is cooled down by throttling by means of a valve 13. In an evaporator 30, the refrigerant 27 is evaporated, thereby providing the cooling power. Next, the refrigerant is again compressed in the jet pump 11. The other portion of the liquid refrigerant 27 is compressed by means of a pump 9 downstream from the condenser 10 and then heated by the waste heat of the fuel cell stack 29. The refrigerant 27 is then expanded in the jet nozzle of the jet pump 11 and serves as the driving energy for the intake mass flow.

[0020] With such a solid oxide fuel cell device 1 it is possible to carry out the method described herein for the operation of the solid oxide fuel cell device 1, involving the following steps: [0021] using the waste heat arising during the operation of the solid oxide fuel cell, especially on the cathode side, to produce cold by means of a refrigeration machine integrated in a refrigeration circuit for cooling of the exhaust gas at the anode side, and this until it falls below ambient temperature, [0022] condensation of the water in the exhaust gas arising at the anode side with the aid of the refrigeration machine by a first water condenser 14, [0023] separating the water by a water separator 16, [0024] compressing the CO.sub.2 exhaust gas flow at the anode side, wherein the cooling power produced by the refrigeration machine is used for cooling of the CO.sub.2 exhaust gas flow, [0025] storing of the compressed CO.sub.2 in a CO.sub.2 storage 19.

[0026] It is evident from FIG. 1 that a further valve 13 is situated downstream from the condenser 10 in order to supply a least one gas cooler 17 with the refrigerant 27. By installing at least one of these valves 13, it is possible to control the refrigerating power for the cooling of the CO.sub.2 flow. By using a second water condenser 15, which can also be combined with the first water condenser 14 to form a structural component, the anode exhaust gas can be cooled down in a first step by the first water condenser 14 and the coolant 28 to ambient temperature. In a second step, the anode exhaust gas is further cooled down by the refrigerant 27 in the second water condenser 15, so that the residual water is also still condensed. After the separating of the water from the anode exhaust gas, the remaining CO.sub.2 gas flow is compressed by multiple compressor stages 25, 26. Between the compressor stages 25, 26, the CO.sub.2 gas flow is cooled by gas coolers 17, which are connected to the refrigeration circuit of the refrigeration machine, so that the compression ratio is increased, and thus the compressor work of the individual compressor stages 25, 26 and/or the number of the compressor stages 25, 26 can be reduced.

[0027] FIG. 2 shows a schematic representation of a solid oxide fuel cell device 1 having a two-stage refrigeration circuit. Thanks to this two-stage refrigeration circuit it is possible for the water in the exhaust gas produced on the anode side to be fully condensed by means of a first temperature level of a first stage of the refrigeration circuit, and for the CO.sub.2 in the exhaust gas produced on the anode side to be liquefied and thus further condensed in a second stage of the refrigeration circuit by means of a second temperature level, which is less than that of the first stage, after a first and/or a second compressor stage 25, 26. In this way, larger compression ratios are achieved at lower compressor power, so that compressor stages 25, 26 can be economized if necessary. Two jet pumps 11, 12 are required for the two-stage refrigeration circuit. The first jet pump 11 compresses the refrigerant 27 from the lower evaporation temperature level to the pressure level of the second water condenser 15. After this, the refrigerant 27 is cooled in a heat exchanger 7 and then further compressed in the second jet pump 12.

[0028] Aspects of the various embodiments described above can be combined to provide further embodiments. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled.