DE102012011326A1 - Fuel cell system for producing electrical drive power in e.g. passenger car, has duct element connecting exhaust air outlet of humidifier with environment, and valve devices adjusting duct elements as flow path for exhaust air from chamber - Google Patents

Abstract

The system (1) has a first duct element (19) connecting an exhaust air outlet of a cathode chamber (5) of a fuel cell (3) with an exhaust air inlet of an intercooler (13). A second duct element (21) connects an exhaust air outlet of the intercooler with an exhaust air inlet of a humidifier (14). Supply air and exhaust air pass through the intercooler and the humidifier. A third duct element (23) indirectly connects an exhaust air outlet of the humidifier with environment. Valve devices (20, 22, 24) selectively adjust the duct elements as a flow path for the exhaust air from the chamber. The valve devices are 3/2 directional valves. The humidifier is a membrane humidifier. The fuel cell is a proton exchange membrane fuel cell. An independent claim is also included for a method for operating a fuel cell system.

Description

The invention further relates to a fuel cell system having at least one fuel cell according to the further defined in the preamble of claim 1. The invention also relates to a method for operating a fuel cell system according to the closer defined in the preamble of claim 7. Art Finally, the invention relates to the use of such Fuel cell system and / or the method.

Fuel cell systems are known from the general state of the art. They can be used, for example, for generating electrical power, preferably electrical drive power, in vehicles. Such fuel cell systems often use so-called PEM fuel cells as fuel cells, in which the anode and the cathode are separated from one another by a proton exchange membrane as "electrolyte". The fuel cells themselves are generally stacked from a plurality of single cells and are referred to as a fuel cell stack or fuel cell stack.

For operation of the fuel cell, this anode side is typically supplied with hydrogen or a hydrogen-containing gas. On the cathode side, the supply of air as an oxygen supplier is well known and commonplace. In order to achieve a sufficient power density of the fuel cell, the air is supplied to the so-called cathode space of the fuel cell with an overpressure relative to the ambient pressure. The compressed by the air conveyor to a higher pressure level air is heated in the compression. The air is thus available after the compressor as a comparatively hot and dry supply air. However, it is now the case that the proton exchange membrane in the fuel cell is comparatively sensitive to excessively high temperatures and to dry operating media. From the DE 10 2007 003 144 A2 It is therefore known to cool the hot air supply to the air conveyor via a supply of air on one side and exhaust air on the other side through the charge air cooler through the exhaust air and then via a humidifier, which may be formed, for example, as a hollow fiber or Plattenmembranbefeuchter accordingly moisturize. The humidifier is designed as a gas / gas humidifier. On one side of its membranes flows cooled after the intercooler but still dry supply air, on the other side, the exhaust air flows from the fuel cell, which is loaded with the resulting product water in the fuel cell in the form of water vapor and possibly liquid droplets. Due to the moisture vapor permeable membranes of the gas / gas humidifier, the moisture in the exhaust air humidifies the dry supply air so that it can be cooled and moistened after charge air cooler and humidifier fed to the cathode compartment of the fuel cell.

This structure of the fuel cell system works well in conventional operation at the usual operating temperatures of a PEM fuel cell of about 70 to 90 ° C. At lower operating temperatures, and in particular at low ambient temperatures, such as occur after the start of a fuel cell system at low outdoor temperatures, especially at outdoor temperatures below freezing, occurring, however, the described structure of the fuel cell system now leads to significant problems. A low temperature in the area of the humidifier, in particular due to a still very low temperature of the exhaust air flowing out of the cathode compartment into the humidifier, leads to a strong entry of moisture into the supply air, which condenses there due to the comparatively low temperatures and at temperatures below freezing point freeze and block parts of the humidifier. The same applies to the further-flowing air laden with moisture and, in particular, liquid water, which can block and / or flood gas-carrying channels in the fuel cell. If individual areas and / or cells are blocked by water and are no longer reached by oxygen, this leads to considerable electrical problems in the area of the fuel cell and severely worsens their start-up performance.

It is the object of the present invention to provide a fuel cell system, which avoids these disadvantages, and which ensures a simple efficient and reliable start with a high efficiency of gas humidification, without the risk of strong condensation of water in the humidifier and / or Cathode space of the fuel cell consists.

According to the invention this object is achieved by the features in the characterizing part of claim 1. In addition, a method with the features in the characterizing part of claim 7 solves this problem. In claim 10, a preferred use is also given. Advantageous developments and refinements of the fuel cell system and the method emerge from the dependent subclaims.

In the fuel cell system according to the invention, it is provided that on the exhaust air side, in addition to the usual wiring with a first line element which connects the exhaust air outlet of the cathode chamber with the exhaust air inlet of the humidifier and a second conduit element, which connects the exhaust air outlet of the humidifier with the exhaust air inlet of the charge air cooler, and a third conduit element which connects the exhaust air outlet of the charge air cooler at least indirectly with the environment, an alternative possibility for flow guidance is provided. This consists essentially of a fourth line element which connects the exhaust air outlet of the cathode chamber with the exhaust air inlet of the charge air cooler, a fifth line element which connects the exhaust air outlet of the charge air cooler with the exhaust air inlet of the humidifier, and a sixth line element which the exhaust air outlet of the humidifier at least indirectly with the Environment connects. Valve means are also provided in the fuel cell system according to the invention, by means of which either the first line element, the second line element and the third line element or the fourth line element, the fifth line element and the sixth line element can be adjusted as a flow path for exhaust air from the cathode space of the fuel cell.

The fuel cell system according to the invention thus provides a first flow path for the exhaust air, which corresponds to the flow path known from the prior art. Via further line elements and valve devices, a second flow path can be selected, which first sends the exhaust air from the cathode compartment of the fuel cell through the charge air cooler, in the area of which the exhaust air is significantly heated and thereby cools the supply air on the other side of the charge air cooler. The thus preheated exhaust air then enters the humidifier and, unlike the structure according to the prior art, preferably in situations with low operating temperature of the fuel cell system, ie in particular in starting situations of the fuel cell system, a significantly warmer exhaust air in the humidifier available. As a result, the risk of condensation of water is significantly reduced and the risk of any formation of ice in the humidifier and thus also the cathode compartment of the fuel cell is significantly reduced. Thus, especially during a cold start under freezing conditions less liquid water and ice is formed in the humidifier. As a result, no gas-carrying sections are clogged in the humidifier and / or the cathode compartment of the fuel cell. The pressure loss compared to conventional structures in the same operating situation is thus significantly reduced. In addition, the efficiency of the humidifier is improved by a higher temperature, since this efficiency depends approximately linearly on the inlet temperature of the moisture-supplying medium. The humidification is thus improved and a longer life of the proton exchange membranes in the fuel cell can be achieved.

Overall, the fuel cell system can therefore start more efficiently and faster at low ambient temperatures. The acceptance of the system by a user, in particular when using the fuel cell system in a vehicle, can thereby be increased compared to systems which require a longer time for a cold start.

When the fuel cell system then reaches its intended operating temperature, a high temperature at the humidifier exhaust port is no longer necessarily desirable, as this causes high stress on the diaphragms of the gas / gas humidifier, typically designed as a membrane humidifier. In these situations, then can be switched back to the conventional structure and the fuel cell system can be operated efficiently and reliably during normal operation in a conventional manner.

The inventive method for operating a fuel cell system, it now provides that a fuel cell system in a structure, as already described above, is now operated so that when starting the fuel cell system until reaching a predetermined limit temperature, which is typically of the order of 20 to 50 ° C, an operation takes place in the manner that the exhaust air from the cathode compartment first flows through the intercooler and then the humidifier, and that after exceeding the limit temperature first of the humidifier and then the intercooler are flowed through by the exhaust air. With the method according to the invention, the corresponding advantages can be achieved analogously to the above description of the fuel cell system.

Both the structure according to the invention of the fuel cell system and the method for operating such a fuel cell system have their particular advantages when the fuel cell system has to be started frequently. This is especially true when the temperatures are often very low, for example, at or below freezing. Such a purpose is especially in fuel cell systems in vehicles, since a frequent starting and restarting the fuel cell system is necessary in normal operation. In addition, vehicles are traveling in many parts of the world and, depending on the season, often have to be started quickly and reliably even in very cold ambient temperatures. The particularly preferred use of the fuel cell system and the method for operating such a fuel cell system is therefore in a fuel cell vehicle. Such Fuel cell vehicle may be, for example, a passenger car or a commercial vehicle. Likewise, it is conceivable that the fuel cell vehicle in the sense of the invention is a driverless transport system, a logistics vehicle, a watercraft or an aircraft.

Further advantageous embodiments of the fuel cell system according to the invention and the method according to the invention will become apparent from the dependent subclaims and will be apparent from the embodiment, which will be described below with reference to the figures.

Showing:

1 a fuel cell system in a possible embodiment according to the invention in a first operating state;

2 the fuel cell system according to 1 in a second operating state.

In the presentation of the 1 is a fuel cell system 1 shown in principle with the essential elements of the invention. The fuel cell system 1 is located in a schematically indicated vehicle 2 and should be used there to generate electrical drive power. The core of the fuel cell system 1 forms a fuel cell 3 , which is designed as a stack of single cells in PEM technology. This fuel cell stack or fuel cell stack 3 has an anode compartment 4 and a cathode compartment 5 on. These are in a conventional manner by a proton-conducting membrane 6 separated from each other. This proton-conducting membrane serves as an "electrolyte" and is typically part of a so-called membrane electrode assembly (MEA) in each of the single cells of the fuel cell stack 3 , The anode compartment 4 the fuel cell stacks 3 becomes hydrogen from a compressed gas storage 7 via a principle indicated pressure regulating and metering valve 8th fed. The unused hydrogen passes through a pipe 9 from the anode compartment 4 of the fuel cell stack 3 , In principle, here is an afterburning of the residual hydrogen or a circulation of the hydrogen around the anode compartment 4 possible in a conventional manner. As the anode side of the fuel cell system 1 For the present invention of minor importance, however, has been omitted to a representation of such details.

The cathode compartment 5 of the fuel cell stack 3 air is supplied as an oxygen supplier. This is typically via an air filter, not shown here by an air conveyor 10 aspirated and to the cathode compartment 5 of the fuel cell stack 3 promoted. As an air conveyor, for example, a compressor, in particular a screw compressor, a Roots blower or the like can be used. The air conveyor 10 However, it may also be designed as a flow compressor. To drive the air conveyor 10 is used in the embodiment shown here, an electrical machine 11 , which together with the air conveyor 10 on a wave 12 is arranged. The supply air to the cathode compartment 5 of the fuel cell stack 3 flows first over a charge air cooler 13 , which is flowed through by supply air on one side and materially separated, but in thermally conductive contact thereto, by exhaust air on the other side. The intercooler 13 may be formed, for example, in the manner of a plate heat exchanger. After the after the air conveyor 10 compressed and thereby heated supply air in the intercooler 13 cooled down, it flows through a humidifier 14 , which serves as a gas / gas humidifier 14 is formed and also flows through on one side of supply air and on the other side of exhaust air. The supply air flow and the exhaust air flow are separated by membranes, which are not permeable to the air, but which transport water vapor from the exhaust side to the supply air side. The membranes may be formed, for example, flat. The humidifier 14 would then be comparable to a plate heat exchanger designed as a plate humidifier. It is also possible that the membranes are realized as hollow fiber membranes. The humidifier 14 would then be designed so that one gas stream flows through the hollow fibers and the other gas stream flows around the hollow fibers.

The supply air passes into the cathode compartment after it has cooled and moistened 5 of the fuel cell stack 3 , Here, the oxygen contained in the supply air is at least partially together with that in the anode compartment 4 present hydrogen converted into electrical power and product water. Due to the cooled and humidified supply air is always an ideal humidification of the proton exchange membranes 6 ensures that they are not overheated and dried out, which would adversely affect their lifespan.

The exhaust side of the fuel cell system 1 is now comparatively complex. In the presentation of the fuel cell system 1 in 1 is the regular operation of the exhaust side at the usual operating temperatures of the fuel cell stack 3 shown. These usual temperatures are typically 70 to 90 ° C. The in 1 illustrated operation should preferably be used at temperatures of more than 20 to 50 ° C limit temperature. The case coming to use line elements are in the representation of 1 shown drawn through, more not required for this purpose line elements are shown in dashed lines.

A first conduit element 15 connects the exhaust air outlet of the cathode compartment 5 with the exhaust air inlet of the humidifier 14 , A second conduit element 16 connects the exhaust air outlet of the humidifier 14 with the exhaust air inlet of the intercooler 13 , Finally, a third line element connects 17 the exhaust air outlet of the intercooler 13 with a turbine 18 , In the area of this turbine 18 Thermal energy and pressure energy, which is present in the exhaust air, at least partially recovered before the exhaust air is discharged to the environment. The turbine 18 is on the same wave 12 arranged as the electric machine 11 and the air conveyor 10 , These three components together form a so-called electric turbocharger, which is also referred to as ETC. About the turbine 18 In this case, part of the energy in the exhaust air can be recovered. This energy is the air conveyor 10 again provided. The typically required energy difference for driving the air conveyor 10 is by the electric machine 11 provided. In special operating situations it can also happen that in the area of the turbine 18 more energy is generated than in the area of the air conveyor 10 is needed. In this case, over the electric machine 11 generate electric power in generator operation.

In another embodiment of the invention, the fuel cell system according to the invention 1 no turbine on (not shown). In this case, the third line element connects 17 the exhaust air outlet of the intercooler 13 not with a turbine, but with the environment, so that the exhaust air flow after the intercooler 13 or the valve device 24 can be delivered to the environment. The sixth line element 23 may continue to flow in this case after the valve device 24 in the third conduit element 17 lead.

In the presentation of the 2 is the same fuel cell system without the indicated vehicle 2 , shown again. Analogous to the systematics in 1 Here, the other operating case is shown, which in turn is indicated by the solid line elements, while the in 1 solid line elements are shown here by dashed lines. The in 2 illustrated operation should be carried out in particular at operating temperatures below the above limit temperature, typically so when starting the fuel cell system 1 , Especially at a start at low ambient temperatures, for example, temperatures below the freezing point of water. The flow of the supply air corresponds to that already in 1 described flow of supply air. The exhaust air now flows through a fourth line element 19 from the exhaust air outlet of the cathode compartment 5 to the exhaust air inlet of the intercooler 13 , This is the case in the region of the first line element 15 and the fourth conduit element 19 a valve device 20 arranged. This is designed as a 3/2-way valve and thus allows either a flow through the first line element 15 or the fourth conduit element 19 , Alternatively to the use of a 3/2-way valve 20 Of course, this would also be the use of two separate switching valves in the first line element 15 and the second conduit element 19 analogous conceivable.

After the relatively humid and relatively cool in this operating situation exhaust air from the cathode compartment 5 of the fuel cell stack 3 the intercooler 13 has flowed through, this is heated and is connected via a fifth line element 21 from the exhaust air outlet of the intercooler 13 to the exhaust entrance of the humidifier 14 directed. Again, here is a valve device 22 between the third conduit element 17 and the fifth conduit element 21 intended. Also for this valve device 22 this applies to the valve device 20 already said analog. After the humidifier 14 is flowed through by the now heated exhaust air, this exhaust air from the exhaust outlet of the humidifier 14 via a sixth line element 23 either directly to the environment (not shown) or again via the turbine 18 with recovery of thermal energy and pressure energy to the environment. To switch between using the second conduit element 16 and the sixth conduit element 23 to be able to switch back and forth is again a valve device 24 provided, for which the same applies as for the valve devices 20 and 22 already executed.

With the described construction of the fuel cell system 1 is it possible to do this once in the interconnection 1 and once in the interconnection according to 2 to operate. In an interconnection according to 2 in the case of a low ambient temperature, and in particular for the cold start case of the fuel cell system 1 will be a high efficiency of the humidifier 14 achieved due to the additional heating of him supplied moist-supplying exhaust air. In addition, the amount of liquid water and in particular an icing of the humidifier can be 14 and thus optionally the cathode compartment 5 the fuel cell 3 avoid. This will result in a faster and more efficient start with better fuel cell stack operating conditions 3 and less pressure losses possible.

About the valve devices 20 . 22 . 24 can be switched between the two circuit variants. Such switching preferably takes place as a function of a temperature. This temperature is then the decisive for the temperature limit temperature. As temperature comes for this example, the temperature of the supply air at the entrance of the fuel cell stack 3 in question, or the temperature of the exhaust air at the output of the fuel cell stack 3 , It is also conceivable that a mean temperature of the air in the fuel cell stack 3 is used as the basis for the limit temperature. In addition or as an alternative to the temperature of the air, the temperature of the fuel, ie of the hydrogen or hydrogen-containing gas, and / or of the coolant at the respective input or output of the fuel cell stack may also be different 3 or a corresponding average temperature of the fuel and / or the coolant in the fuel cell stack 3 be used. Here, the temperature of the air, the fuel and / or the coolant at the respective input and / or output of the fuel cell stack 3 prefers. Furthermore, it is preferred if additional temperature sensors are not used for determining the limit temperature, but rather temperature sensors which are already present anyway for the regulation of the operation of the fuel cell system.

Below the abovementioned limit temperature, the process procedure according to the in 2 used interconnection, above the limit temperature, the interconnection according to 1 , which corresponds to the conventional interconnection of a fuel cell system.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102007003144 A2 [0003]

Claims (10)

Fuel cell system ( 1 ) with at least one fuel cell ( 3 ), which has a cathode space ( 5 ) and an anode compartment ( 4 ), with an air conveying device ( 10 ), with a charge air cooled by supply air and exhaust air ( 13 ) and a humidifier flowed through by supply air and exhaust air ( 14 ), with a first line element ( 15 ), which has an exhaust air exit of the cathode space ( 5 ) with an exhaust air inlet of the humidifier ( 14 ), with a second conduit element ( 16 ), which controls the exhaust air outlet of the humidifier ( 14 ) with the exhaust air inlet of the intercooler ( 13 ) and with a third line element ( 17 ), which controls the exhaust air outlet of the intercooler ( 13 ) at least indirectly connects to the environment, characterized in that a fourth line element ( 19 ) the exhaust air outlet of the cathode space ( 5 ) with the exhaust air inlet of the intercooler ( 13 ), a fifth line element ( 21 ) the exhaust air outlet of the intercooler ( 13 ) with the exhaust air inlet of the humidifier ( 14 ), a sixth line element ( 23 ) the exhaust air outlet of the humidifier ( 14 ) at least indirectly connects to the environment, and that valve means ( 20 . 22 . 24 ) are provided, through which optionally the first line element ( 15 ), the second conduit element ( 16 ) and the third conduit element ( 17 ) or the fourth line element ( 19 ), the fifth line element ( 21 ) and the sixth conduit element ( 23 ) as a flow path for the exhaust air from the cathode compartment ( 5 ) are adjustable. Fuel cell system ( 1 ) according to claim 1, characterized in that the valve devices ( 20 . 22 . 24 ) in the form of three 3/2-way valves, via which the exhaust air outlet of the cathode space ( 5 ) optionally with the first line element ( 15 ) or the fourth line element ( 19 ), the exhaust air outlet of the humidifier ( 14 ) optionally with the second line element ( 16 ) or the sixth line element ( 23 ) and the exhaust air outlet of the intercooler ( 13 ) optionally with the third line element ( 17 ) or the fifth line element ( 21 ) are connectable. Fuel cell system ( 1 ) according to claim 1 or 2, characterized in that the third conduit element ( 17 ) on the output side via a turbine ( 18 ) is connected to the environment. Fuel cell system ( 1 ) according to claim 1, 2 or 3, characterized in that the sixth conduit element ( 23 ) on the output side via a turbine ( 18 ) is connected to the environment. Fuel cell system ( 1 ) according to one of claims 3 or 4, characterized in that the turbine ( 18 ) and the air conveyor ( 10 ) together with an electric machine ( 11 ) form an electric turbocharger. Fuel cell system ( 1 ) according to one of claims 1 to 5, characterized in that the humidifier ( 14 ) is designed as a membrane humidifier, which for water vapor permeable membranes, in the form of hollow fiber membranes or flat membranes, having. Method for operating a fuel cell system ( 1 ) with at least one fuel cell ( 3 ) with a charge air cooler through which supply air and exhaust air flow ( 13 ) and a humidifier flowed through by supply air and exhaust air ( 14 ), characterized in that at temperatures of the fuel cell ( 3 ) above a predetermined limit temperature, the exhaust air from the fuel cell ( 3 ) first through the exhaust side of the humidifier ( 14 ) and then through the exhaust air side of the intercooler ( 13 ), and that at temperatures below the limit temperature, the exhaust air from the fuel cell ( 3 ) first through the exhaust air side of the intercooler and then through the exhaust side of the humidifier. A method according to claim 7, characterized in that the limit temperature is set at 20 to 50 ° C. A method according to claim 7 or 8, characterized in that at least during operation of the fuel cell system ( 1 ) above the predetermined limit temperature, a recovery of energy from the exhaust air flow by means of a turbine. Use of the fuel cell system ( 1 ) according to one of claims 1 to 6 and / or the method according to one of claims 7 to 9 in a fuel cell vehicle.

Images