HUMIDIFIER MODULE, HUMIDIFIER, FUEL CELL SYSTEM HAVING SUCH, AND METHOD FOR HUMIDIFYING A GAS

Abstract

A humidifier module for a humidifier in a fuel cell system is provided having a gas-permeable membrane, on one side of which there is arranged a flow field core defining a flow field, wherein the flow field core comprises at least two separating webs, between which a channel is formed. The separating webs are formed from a hygroscopic, not water-soluble material, such that a liquid flowing in the at least one channel can be stored temporarily in the hygroscopic separating webs. Furthermore, the invention relates to a humidifier having humidifier modules, a fuel cell system having a humidifier, and a method for humidifying a gas are also provided.

Claims

1. A humidifier module for a humidifier in a fuel cell system, comprising: a gas-permeable membrane, on one side of which there is arranged a flow field core defining a flow field, wherein the flow field core includes at least two separating webs and a channel formed between the separating webs, and wherein the separating webs are formed from a hygroscopic material that is not water-soluble, such that a liquid flowing in the channel can be stored temporarily in the hygroscopic separating webs.

2. The humidifier module according to claim 1, wherein the flow field core is encased in a hydrophobic frame or the flow field core is received in a hydrophobic carrier plate.

3. The humidifier module according to claim 1, wherein a plurality of channels are present, separated from each other by hygroscopic separating webs, and the channels extend in a straight line and parallel to each other.

4. The humidifier module according to claim 1, wherein a plurality of channels are present, separated from each other by hygroscopic separating webs, and the separating webs have at least one deflection.

5. The humidifier module according to claim 4, wherein the hygroscopic separating webs have deflections at regular spacing from each other along their longitudinal direction of extension.

6. A humidifier for humidifying a gas for a fuel cell system, comprising: two end plates, on which there are formed an inlet for dry gas, an outlet for moistened gas, an additional inlet for humid gas and an additional outlet for dehumidified gas; and a plurality of humidifier modules arranged between the end plates, each of the humidifier modules including a gas-permeable membrane, on one side of which there is arranged a flow field core defining a flow field, wherein the flow field core includes at least two separating webs and a channel formed between the separating webs, and wherein the separating webs are formed from a hygroscopic material that is not water-soluble, such that a liquid flowing in the channel can be stored temporarily in the hygroscopic separating webs.

7. A fuel cell system having a fuel cell stack, to which cathode gas can be supplied on the cathode side and fuel can be supplied on the anode side, and having a humidifier according to claim 6 connected upstream from the fuel cell stack on the cathode side.

8. The fuel cell system according to claim 7, wherein a separator is present at the anode outlet side, a drain of the separator is fluid-mechanically connected to the humidifier, and/or a cathode vent gas line is fluid-mechanically connected to the humidifier at the cathode outlet side.

9. A method for humidifying a gas in a fuel cell system having a fuel cell stack, which is fluidically connected to a humidifier including two end plates, on which there are formed an inlet for dry gas, an outlet for moistened gas, an additional inlet for humid gas and an additional outlet for dehumidified gas, and a plurality of humidifier modules arranged between the end plates, wherein each of the humidifier modules includes a gas-permeable membrane, on one side of which there is arranged a flow field core defining a flow field, wherein the flow field core includes at least two separating webs and a channel formed between the separating webs, wherein the separating webs are formed from a hygroscopic material that is not water-soluble, such that a liquid flowing in the channel can be stored temporarily in the hygroscopic separating webs, the method comprising: removing liquid water from the fuel cell stack and supplying the liquid water to the humidifier; taking up at least a portion of the liquid water in the hygroscopic separating webs and temporarily storing this portion of the liquid water; and at least partially emptying the hygroscopic separating webs by evaporating the liquid water and thereby humidifying the gas being supplied to the fuel cell stack.

10. The method according to claim 9, wherein the liquid water from the fuel cell stack is removed at the an anode side and/or at a cathode side of the fuel cell stack.

Description

DETAILED DESCRIPTION

[0027] FIG. 1a and FIG. 1b show a humidifier module 1 for a humidifier 15 having a gas-permeable membrane 3, on one side of which there is arranged a flow field core 4 defining a flow field. The flow field core 4 comprises a plurality of separating webs 5, between each of which there is formed a channel 6. The separating webs 5 are formed from a hygroscopic, not water-soluble material, especially calcium silicate, such that liquid water flowing in the channels 6 can be removed, taken up in the hygroscopic separating webs 5, temporarily stored there, and given off as needed by means of evaporation from the separating webs 5.

[0028] FIG. 1b illustrates how the flow field core 4 is surrounded by a hydrophobic frame 7. In the present instance, the flow field core 4 is press-fitted into a hydrophobic carrier plate. The hydrophobic frame 7 of the flow field core 4 hinders the escape of the liquid water from the flow field core 4 to the outside and thus seals off the flow field core 4.

[0029] The straight extension of the channels 6, formed parallel to each other, enables a guiding of the fluid moving therein, with little pressure loss. The separating webs 5 serve in addition as a support for the membrane 3 of the humidifier module 1 or the humidifier 15 and stabilize the humidifier module 1 or also the humidifier 15.

[0030] FIG. 2 shows an alternative embodiment, in which the channels 6 running between the hygroscopic separating webs 5 undergo several deflections 8. In the present instance, deflections 8 are formed at regular spacing from each other along the lengthwise extension of the separating webs 5, the individual separating webs 5 being arranged parallel to each other. The deflections 8 provide surfaces on which liquid droplets can be separated, so that liquid water can be removed from the fluid moving along the channels 6, taken up into the hygroscopic separating webs 5, and be stored temporarily therein.

[0031] FIG. 3 shows a fuel cell system 2 with a humidifier 15 for humidifying a gas. The humidifier 15 here has two not otherwise represented end plates, on which there are formed an inlet 14 for dry gas, an outlet 18 for moistened gas, an additional inlet 17 for humid gas and an additional outlet 13 for dehumidified gas. A plurality of the previously described humidifier modules 1 are arranged between the two end plates.

[0032] The fuel cell system 2 comprises, as its central component, a fuel cell stack 16, having a plurality of not otherwise represented fuel cells arranged in a stack. Each fuel cell is coordinated with an anode space as well as a cathode space, the anode and the cathode being separated from each other by an ionically conductive polymer electrolyte membrane.

[0033] Moreover, between every two such membrane electrode arrangements there is situated a not otherwise represented bipolar plate, which serves for the supplying of reactants to the anode and cathode spaces and also produces the electrical connection between the individual fuel cells.

[0034] In order to supply the fuel cell stack 2 with the reactants, i.e., the cathode gas and the fuel, the fuel cell stack 16 is connected at the anode side to an anode feed line 20 for supplying a hydrogen-containing anode gas from an anode reservoir 19. The anode operating pressure on the anode side of the fuel cell stack 16 can be adjusted by an actuator 28 in the anode feed line 20. At the anode outlet side there is an anode vent gas line 24, being connected fluid-mechanically to an anode recirculation line 21 for transporting away the unreacted anode gas, connected fluid-mechanically to the anode feed line 20. Furthermore, at the anode side, a separator 22 is present in the anode recirculation line 21, being in particular a water separator, whose drain is connected by means of a liquid feed line 23 upstream from the humidifier 15 to a cathode feed line 30. This allows the liquid water produced on the anode side to be supplied to the humidifier 15.

[0035] On the cathode side, the fuel cell stack 16 is connected to a cathode feed line 30 for supplying the oxygen-containing cathode gas. For the delivery and compression of the cathode gas, a compressor 26 is arranged in a part of the cathode feed line 30 configured as a dry feed line 11. In the embodiment shown, the compressor 26 is configured as a compressor 26 operated basically by an electric motor, being powered by a not otherwise represented electric motor designed with corresponding power electronics.

[0036] By the compressor 26, the cathode gas which is sucked in from the surroundings is taken to the humidifier 15 by means of the dry feed line 11. A second part of the cathode feed line 30 connects the humidifier 15 to the fuel cell stack 16 and carries moistened cathode gas to the cathode spaces of the fuel cell stack 16. Furthermore, liquid water and unreacted cathode gas is taken by the cathode vent gas line 31 back to the humidifier 15, or the unreacted cathode gas (especially the exhaust air) may be taken from the cathode spaces 18 of the fuel cell stack 16 to a not otherwise represented exhaust gas treatment. Finally, the humidifier 15 also has a humidifier drain line 32 for removal of dehumidified cathode exhaust gas.

[0037] The liquid feed line 23 can furthermore be connected fluid-mechanically to the cathode drain line 31 upstream from the humidifier 15. This likewise enables a supplying of liquid water to the humidifier 15, since the exhaust gas is additionally humidified before it enters the humidifier 15 and its humidifier module 1. Alternatively or additionally, a bypass line 12 may be present downstream from the compressor 26, being fluid-mechanically connected to the humidifier drain line 32.

[0038] The method for humidifying a gas in a fuel cell system 2 involves in particular the following steps. At first, liquid water is removed from the fuel cell stack 16 and supplied to the humidifier 15. The liquid water arises during the reaction of the fuel cell, which then leaves the fuel cell stack 16 in the form of vent gas and can be utilized in the humidifier 15. The supplying of liquid may also occur in addition on the anode side through the connected liquid feed line 23, which is fluid-mechanically connected to the dry feed line 11 and to the cathode drain line 31. The liquid water together with the cathode vent gas flows through the channels 6 of the humidifier module 1 of the humidifier 15 and is taken up and stored temporarily in the hygroscopic separating webs 5. The separating webs 5 can be at least partly emptied when necessary, especially when no further liquid water is being provided to the humidifier 15 or when the workload is heavy, by means of evaporation of the liquid water, so that the gas being supplied to the fuel cell stack 16 can be humidified.

[0039] The partial emptying can occur when the moisture of the membrane 3 falls below a given or predeterminable threshold value. This threshold value could be determined by means of an electrical conductivity of the humidifier 15. Alternatively, the liquid water can also be emptied automatically from the separating webs 5 at regular intervals. In another alternative embodiment, the separating webs 5 are emptied when no liquid water is being supplied or can be supplied from the fuel cell stack 16, or when the fuel cell system 2 is working in an operating mode with a higher water demand.

[0040] 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.