FUEL CELL SYSTEM AND METHOD FOR RECIRCULATION OF EXHAUST GAS IN A FUEL CELL SYSTEM

Abstract

The present invention relates to a fuel cell system (100) comprising at least one fuel cell stack (1) having at least one cathode section (K) and at least one anode section (A), an air supply section (2) for supplying air (2) to the anode section (A) of the fuel cell stack (1), an exhaust air section (4) for discharging exhaust air (5) from the anode section (A) of the fuel cell stack (1), as well as a supply section (7) for supplying at least one main medium (6) to the cathode section (K) of the fuel cell stack (1), an exhaust gas discharge section (9) for discharging exhaust gas (8) from the cathode section (K) of the fuel cell stack (1), as well as a pump (12) for delivering the at least one main medium (6), the exhaust gas discharge section (9) being fluidically connected via a recirculation section (14) to the supply section (7) downstream of the pump (12) in order to recirculate exhaust gas (8), the recirculation section (14) being connected via a jet pump (16) to the supply section (7) in order to introduce recirculated exhaust gas (8) as the secondary flow (20) of the jet pump (16) into the at least one gaseous main medium (6) as the primary flow (18) of the jet pump (16). The invention also relates to a method for recirculating exhaust gas (8) in a fuel cell system (100).

Claims

1. Fuel cell system (100), comprising at least one fuel cell stack (1) having at least one cathode section (K) and at least one anode section (A), an air supply section (2) for supplying air (2) to the anode section (A) of the fuel cell stack (1), an exhaust air section (4) for discharging exhaust air (5) from the anode section (A) of the fuel cell stack (1), as well as a supply section (7) for supplying at least one main medium (6) to the cathode section (K) of the fuel cell stack (1), an exhaust gas discharge section (9) for discharging exhaust gas (8) from the cathode section (K) of the fuel cell stack (1), as well as a pump (12) for delivering the at least one main medium (6), characterised in that the exhaust gas discharge section (9) is fluidically connected via a recirculation section (14) to the supply section (7) downstream of the pump (12) in order to recirculate exhaust gas (8), the recirculation section (14) being connected via a jet pump (16) to the supply section (7) in order to introduce recirculated exhaust gas (8) as the secondary flow (20) of the jet pump (16) into the at least one gaseous main medium (6) as the primary flow (18) of the jet pump (16).

2. Fuel cell system (100) according to claim 1, characterised in that an evaporator unit (11) for generating at least one gaseous main medium (6) from at least one liquid main medium (6) is arranged between the pump (11) and the jet pump (16).

3. Fuel cell system (100) according to claim 2, characterised in that the evaporator unit (11) is designed as a multi-stage, in particular two-stage, evaporator unit (11).

4. Fuel cell system (100) according to claim 2 or 3, characterised in that the evaporator unit (11) is an electric evaporator unit or a heat-exchange evaporator unit, the heat-exchange evaporator unit being heated in particular by the exhaust gas (8) and/or the exhaust air (5) of the fuel cell system (100).

5. Fuel cell system (100) according to claim 1, characterised in that a first heat exchanger (21) for heating at least one liquid main medium (6) is arranged between the pump (11) and the jet pump (16), the at least one heated main medium (6) being heated by means of the first heat exchanger (21) such that the heated main medium (6) evaporates on account of the pressure drop in the jet pump (16).

6. Fuel cell system (100) according to claim 1, characterised in that at least one second heat exchanger (22), in particular comprising a catalyst, for heating the main medium (6) is arranged between the jet pump (16) and the supply section (7) of the fuel cell stack (1).

7. Fuel cell system (100) according to claim 1, characterised in that at least one first valve (24) is arranged on the recirculation section (14), in particular at the transition from the recirculation section (14) to the jet pump (16), in order to adjust a recirculation rate (RR) of the exhaust gas (8).

8. Fuel cell system (100) according to claim 1, characterised in that the jet pump (16) comprises at least one second valve (26) for adjusting the primary flow (18) and/or the secondary flow (20).

9. Fuel cell system (100) according to claim 1, characterised in that the air supply section (3) comprises an air supply fan (28) for adjusting an amount of air (2) conveyed in the air supply section (3).

10. Fuel cell system (100) according to claim 1, characterised in that a useful gas supply section (30) of the fuel cell system (100) supplies the primary flow (18) and/or secondary flow (20) of the jet pump (16) with at least one additional gas or gas mixture, in particular from a storage volume (32), and/or recirculated exhaust air (5), in particular via an additional recirculation section (14), from the exhaust air section (4).

11. Fuel cell system (100) according to claim 1, characterised in that a recirculation fan (34) is arranged in the recirculation section (14) in order to adjust an amount of the exhaust gas (8) of the fuel cell stack (1) recirculated in the recirculation section (14).

12. Method for recirculating exhaust gas (8) in a fuel cell system (100) according to claim 1, comprising the following steps: delivering the main medium (6) by means of the pump (12), supplying air (2) via the air supply section (3) to the anode section (A) of the fuel cell stack (1), supplying the main medium (6) via the supply section (7) to the cathode section (K) of the fuel cell stack (1), recirculating the exhaust gas (8) from the exhaust gas discharge section (9) of the cathode section (K) via a recirculation section (14) to the supply section (7) of the cathode section (K), mixing the recirculated exhaust gas (8) as the secondary flow (20) with the main medium (6) as the primary flow (18) in the jet pump (16), supplying the mixed primary flow (18) and secondary flow (20) via the supply section (7) to the cathode section (K) of the fuel cell stack (1).

13. Method according to claim 12, characterised in that the recirculation rate (RR) of the fuel cell system (100) is controlled by means of a control unit (36).

Description

[0026] Other measures that improve the invention can be deduced from the following description of various exemplary embodiments of the invention, which are represented schematically in the figures, in which:

[0027] FIG. 1 is a circuit diagram of a fuel cell system comprising a jet pump, a recirculation section and an evaporator unit,

[0028] FIG. 2 is a circuit diagram of a fuel cell system comprising a jet pump, a recirculation section, an evaporator unit, a second heat exchanger and an additional recirculation section,

[0029] FIG. 3 is a circuit diagram of a fuel cell system comprising a jet pump, a recirculation section, an air supply fan, a first heat exchanger, a second heat exchanger and a recirculation fan, and

[0030] FIG. 4 is a circuit diagram of a fuel cell system comprising a jet pump, a recirculation section, a first heat exchanger, a second heat exchanger, a first valve, a storage volume and an additional recirculation section.

[0031] Elements having the same function and mode of operation are in each case denoted by the same reference signs in FIGS. 1 to 4.

[0032] FIG. 1 is a schematic circuit diagram of a fuel cell system 100 according to the invention comprising a jet pump 16, a recirculation section 14 and an evaporator unit 11. The main medium 6 is conveyed from the pump 12 to the evaporator unit 11 and pressurised. The gaseous main medium 6 enters the jet pump 16 as the primary flow 18 downstream of the evaporator unit 11. The exhaust gas 8 recirculated via the recirculation section 14 enters the jet pump 16 as the secondary flow 20. The primary flow 18 experiences a pressure drop and is accelerated in the jet pump 16. The secondary flow 20 is accelerated by the primary flow 18 in the jet pump 16 and both flows 18, 20 exit the jet pump 16 mixed together. The mixed flows 18, 20 enter the cathode section K of the regeneratively operated fuel cell stack 1 via the supply section 7 downstream of the jet pump 16. Air 2 is delivered to the anode section A via the air supply section 3. Exhaust gas 8 exits the exhaust gas discharge section 9. If water is used as the main medium 6, hydrogen-rich exhaust gas 8, for example, exits the exhaust gas discharge section 9. Some of the exhaust gas 8 is recirculated via the recirculation section 14. Exhaust air 5 enriched with oxygen exits the exhaust air section 4. A fuel cell system 100 designed in this manner allows for an advantageous reducing atmosphere in the supply section 7 of the fuel cell stack 1 from within the fuel cell system 100 itself and, at the same time, a high temperature tolerance and a high functional reliability of the components can be ensured.

[0033] FIG. 2 is a schematic circuit diagram of a fuel cell system 100 according to the invention comprising a jet pump 16, a recirculation section 14, an evaporator unit 11, a second heat exchanger 22 and an additional recirculation section 14 for recirculating exhaust air 5. Building on the description of FIG. 1, FIG. 2 shows exhaust air 5 being introduced into the jet pump 16 via an additional recirculation section 14 as a second secondary flow 20. This secondary flow 20 is, like the first secondary flow 20, also accelerated by the primary flow 18 in the jet pump 16 and exits the jet pump 16 mixed together with the primary flow 18. The embodiment of the fuel cell system 100 from FIG. 2 also shows a second heat exchanger 22 for heating the gaseous main medium 6 upstream of the supply section 7 of the cathode section K of the regeneratively operated fuel cell stack 1. By virtue of a second heat exchanger 22 arranged in this manner, the gas mixture consisting of the primary 18 and secondary flow 20 from the jet pump 16 can be heated to an optimal temperature for the fuel cell stack 1 and the efficiency of the fuel cell system 100 can advantageously be increased.

[0034] FIG. 3 is a circuit diagram of a fuel cell system 100 according to the invention comprising a jet pump 16, a recirculation section 14, an air supply fan 28, a first heat exchanger 21, a second heat exchanger 22 and a recirculation fan 34. As an alternative to the fuel cell systems 100 in FIGS. 1 and 2, according to this embodiment of the invention, the liquid main medium 6 is not evaporated by means of an evaporator unit 11, but rather by means of a first heat exchanger 21. The liquid main medium 6 is then heated to a temperature just below the evaporation temperature such that main medium 6 evaporates on account of the pressure drop upon entry into the jet pump 16, which decreases the evaporation temperature of the main medium 6. As a result, the costs and effort for an evaporator unit 11 can be reduced to the lower costs and effort for a first heat exchanger 21. An air supply fan 28 is advantageously provided in order to control the amount of air 2 in the air supply section 3 and/or the amount of exhaust air 5 in the exhaust air section 4 and to optimise the fuel cell system 100. A recirculation fan 34 may be integrated in the fuel cell system 100 as an additional solution in order to provide an additional boost.

[0035] FIG. 4 is a circuit diagram of a fuel cell system 100 according to the invention comprising a jet pump 16, a recirculation section 14, a first heat exchanger 21, a second heat exchanger 22, a first valve 24, a storage volume 32 and an additional recirculation section 14 for recirculating exhaust air 5. In addition to the design features of the jet pump 16, the recirculation rate RR of the exhaust gas 8 can also be regulated by means of a first valve 24. At least one additional gas or gas mixture may be supplied from a storage volume 32 to the primary flow 18 and/or the secondary flow 20 of the jet pump 16. FIG. 4 shows a gas being supplied from a storage volume 32 to the secondary flow 20 of the recirculated exhaust air 5.

[0036] The invention allows other design principles in addition to the embodiments set out above. In other words, the invention should not be considered limited to the exemplary embodiments explained with reference to the figures.

LIST OF REFERENCE SIGNS

[0037] 1 Fuel cell stack [0038] 2 Air [0039] 3 Air supply section [0040] 4 Exhaust air section [0041] 5 Exhaust air [0042] 6 Main medium [0043] 7 Supply section [0044] 8 Exhaust gas [0045] 9 Exhaust gas discharge section [0046] 11 Evaporator unit [0047] 12 Pump [0048] 14 Recirculation section [0049] 16 Jet pump [0050] 18 Primary flow [0051] 20 Secondary flow [0052] 21 First heat exchanger [0053] 22 Second heat exchanger [0054] 24 First valves [0055] 26 Second valve [0056] 28 Air supply fan [0057] 30 Useful gas supply section [0058] 32 Storage volume [0059] 34 Recirculation fan [0060] 36 Control unit [0061] 100 Fuel cell system [0062] A Anode section [0063] K Cathode section [0064] RR Recirculation rate