WO2014012615A1

WO2014012615A1 - Fuel cell system

Info

Publication number: WO2014012615A1
Application number: PCT/EP2013/001778
Authority: WO
Inventors: Gert Hinsenkamp; Gerhard Konrad; Benjamin Steinhauser
Original assignee: Daimler Ag
Priority date: 2012-07-17
Filing date: 2013-06-15
Publication date: 2014-01-23
Also published as: DE102012014110A1

Abstract

The invention relates to a fuel cell system (1) having an air conveying device (12) for compressing feed air for a fuel cell (3), having a charge air cooler (13) which is in the form of an air/liquid heat exchanger and through one side of which the compressed feed air flows and through the other side of which a liquid cooling medium of a cooling circuit flows. The invention is characterized in that a further air/liquid heat exchanger (15) is provided in the region of the discharge air from the fuel cell (3), the discharge air flowing through one side and the cooling medium flowing through the other side of said further air/liquid heat exchanger.

Description

The fuel cell system

The invention relates to a fuel cell system with an air conveyor for compressing supply air for a fuel cell according to the closer defined in the preamble of claim 1.

Fuel cell systems are known from the general state of the art. They typically include a fuel cell, which is designed as a stack of individual cells, as a so-called fuel cell stack or fuel cell stack. This fuel cell is usually supplied with hydrogen or a hydrogen-containing gas on the anode side as fuel and air as an oxygen supplier on the cathode side. It is then the case that the air supplied to the fuel cell is typically compressed, for example via a flow compressor, a piston compressor, a Roots blower or the like. The compressed supply air is then heated after the compressor in most operating situations by the compression and has a relatively high temperature. At least when using PEM fuel cells, this represents a serious disadvantage, since the membranes present in the fuel cell are dried out and damaged by the hot supply air. Similarly disadvantageous is the comparatively high temperature of the compressed air affecting further components of the fuel cell system which are arranged in the air-conveying line between the compressor outlet and the stack inlet, such as e.g.

Humidifier, valves or flaps. Here are the possible disadvantages, especially in the form of kosteninstensive expenses in construction and materials for

Mastery of comparatively high temperatures.

From the general state of the art it is therefore known to provide a charge air cooler in order to cool the supply air to the fuel cell accordingly. Now it's like this, that a charge air cooler, as is known, for example, from DE 10 2009 014 743 A1, uses the cooling medium of a cooling circuit for cooling the supply air, in particular the cooling circuit, in which the fuel cell is arranged to dissipate waste heat. The problem with the construction described therein is that the cooling system is loaded accordingly and, in particular when used in a vehicle, correspondingly large areas of cooling heat exchangers are necessary for removing the heat from the cooling system to the environment.

To counteract this problem are also known from the prior art gas / gas heat exchanger instead of the gas / liquid heat exchanger, as has been used above as a charge air cooler known. Such a gas / gas heat exchanger as intercooler is described for example in DE 10 2009 043 569 A1. The construction shown there relieves the cooling system of the fuel cell system and thus a possible equipped with the fuel cell system vehicle considerably.

In addition, when using a turbine in the flow direction of the exhaust air to the intercooler, it allows the recovery of a part of the heat through the turbine in the form of mechanical energy.

In practice, however, the use of a gas / gas heat exchanger as a charge air cooler in some operating conditions serious problems, as it

unwanted condensation effects and thus possibly a freeze at a start at temperatures below freezing point can come. With very cold supply air, it can also be an undesirable and very unfavorable

Reverse direction come in the gas / gas heat exchanger. In this case, there is a heat flow from the warm exhaust air into the colder supply air in this operating situation. As a result, the membranes of the fuel cell are heated unnecessarily and thereby burdened.

Another problem with the gas / gas heat exchanger as intercooler is that it must be constructed comparatively large in order to ensure the required cooling capacity for the compressed supply air in all operating situations, especially under full load operation. The structure thus requires a lot of space.

The object of the present invention is now a

Specify fuel cell system with the features in the preamble of claim 1, which counteracts these problems and a simple, safe and secure

Ensures reliable construction, which relieves the cooling system and also prevents critical and adverse operating situations. The structure should also be simple and compact feasible.

This object is achieved by a fuel cell system with the

Characteristics in the characterizing part of claim 1 solved. advantageous

Further developments of the fuel cell system according to the invention will become apparent from the remaining dependent claims. A particularly preferred use of such a fuel cell system is specified in claim 10.

The fuel cell system according to the invention uses comparable to the aforementioned prior art, an air / liquid heat exchanger as Ladeiuftkühler, which of the compressed supply air and of a liquid cooling medium of a

Cooling circuit is flowed through. In addition, the invention uses

Fuel cell system, an air / liquid heat exchanger in the exhaust air from the fuel cell, which is traversed by the exhaust air and the cooling medium. As a result, a simple and compact realization of the actual charge air cooler is made possible as an air / liquid heat exchanger. The structure can be made very compact and guarantees an efficient, safe and reliable cooling of the compressed supply air after the air conveyor. In addition, the cooling medium then flows through a heat exchanger, which is flowed through by the cooling medium on the one hand and by the exhaust air on the other hand. The exhaust air can absorb heat from the cooling medium and, for example, with the exhaust air directly to the environment, whereby the cooling medium is cooled again. Also, this structure can be realized according to simple and compact.

In a preferred embodiment, for further cost reduction at least largely identical air / liquid heat exchanger on the

Supply side and the exhaust side are used.

In a very favorable development of the fuel cell system according to the invention, it is provided that a turbine is arranged downstream of the air / liquid heat exchanger in the flow direction of the exhaust air. About such a turbine, which in particular may be part of an electric turbocharger, so as to the turbine To provide accumulating power directly the air conveyor available, allows recovery of pressure and heat energy from the exhaust air of the fuel cell. Is in the flow direction of the exhaust air in front of the turbine on the

Cooling medium and the air / liquid heat exchanger of the structure according to the invention added additional heat into the exhaust air, the yield of mechanical power can be increased accordingly, resulting in an improvement of

Total efficiency of the fuel cell system by an increased

Energy recovery results. Furthermore, due to the inventive increase in the exhaust air temperature, the proportion of liquid water discharged from the fuel cell system is reduced.

According to a particularly favorable development of the invention

Fuel cell system, it may also be provided that the cooling circuit is designed as a standalone cooling circuit between the charge air cooler and the heat exchanger, which has a coolant conveyor. Such a structure uses its own cooling circuit, which is formed only between the two mentioned heat exchangers, ie the charge air cooler and the heat exchanger, which emits the heat absorbed into the exhaust air of the fuel cell system. A burden on the cooling system for cooling the fuel cell is thereby completely avoided and the fuel cell system in this embodiment can continue to build very compact. About a coolant conveyor, the cooling medium is circulated in the cooling circuit between the intercooler and the heat exchanger according to, for example, by a speed of the

Coolant conveyor adjustable volume flow of the cooling medium cooling can be controlled specifically. Thus, it is also possible in the operating situations in which no heat transfer is desired, this by turning off the

Coolant conveyor accordingly to prevent, whereby a very safe and reliable operation is ensured, which has a good functionality of the

Ensures fuel cell system in all operating situations.

In an alternative embodiment of the fuel cell system according to the invention, however, it may be provided that the cooling circuit is part of a cooling system, the cooling medium flows through the fuel cell in addition to the charge air cooler, and which has a coolant conveyor and a cooling heat exchanger for cooling the cooling medium. Such a construction in which both the intercooler and Also, the heat exchanger between the cooling medium and the exhaust air are integrated into the actual cooling circuit, still allows relief of the

Cooling circuit by a heat transfer to the exhaust air and yet ensures a simple and efficient structure, since a single coolant delivery device is sufficient in this case.

According to a particularly favorable development, it may be provided that the flow through the charge air cooler and the heat exchanger by a

Valve device is controllable. In this way it is further ensured that in the operating situations in which a cooling is not desirable or there is a risk of reversal of the effective direction, to a flow through the corresponding

Heat exchanger is omitted. In a particularly favorable development, the valve device can be designed as a thermostatic valve, so that automatically takes place as a function of the temperature of the cooling medium, a flow through the charge air cooler and the cooling heat exchanger or not.

The fuel cell system according to the invention can be constructed correspondingly compact and enables safe and reliable operation in all

Operating situations, especially at the start of the fuel cell system at temperatures below freezing. Together with the fact that the cooling system is largely relieved even in the fuel cell system according to the invention by the structure of the registered via the intercooler heat, this results in the particular suitability for use in one

Fuel cell system in a vehicle. Here are on the one hand difficult

Operating conditions, such as a start under difficult

Environmental conditions - eg. As temperatures below freezing - often encountered, so that an adjustment of the fuel cell system to such difficult operating conditions is crucial. Furthermore, the structure must be implemented in accordance compact, since in a vehicle typically only very little space is available. Ultimately, it is most of all

Vehicle systems also crucial that the cooling system of the vehicle

is relieved accordingly, since the available radiator surface at

Vehicle applications of fuel cell systems in general already a critical issue in the design of the fuel cell system, since the

Temperature difference between the fuel cell and the environment typically is much lower than between an internal combustion engine and the environment and the available area of the cooling heat exchanger thus has a limiting effect on the performance of the fuel cell system.

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

Showing:

1 shows a vehicle with a fuel cell system according to the invention.

Fig. 2 shows an alternative embodiment of a fuel cell system according to the

Invention; and

3 shows a further alternative embodiment of the fuel cell system according to the invention.

In the representation of Figure 1, a fuel cell system 1 can be seen, which is arranged in an indicated vehicle 2, and which is to serve in this vehicle 2 for providing electrical drive power. The vehicle 2 may preferably be a motor vehicle, for example a rail-bound or trackless land vehicle, a logistics transporter, a watercraft or the like.

Core of the fuel cell system 1 is a fuel cell 3 and a

Fuel cell stack 3, which is constructed as a stack of single cells in PEM technology. The individual cells are not visible in the representation of the figure. Each of the individual cells has a cathode space and an anode space, wherein a common anode space 4 and a common cathode space 5 are shown symbolically in the representation of FIG. Between the anode compartment 4 and the cathode compartment 5, a heat exchanger 6 for removing waste heat from the fuel cell 3 via a liquid cooling medium is indicated. This liquid cooling medium flows from a coolant conveyor 7 promoted in the circuit between the fuel cell 3 and the heat exchanger 6 of the fuel cell 3 and a

Cooling heat exchanger 8 for dissipating the waste heat to the environment of the vehicle 2. The cooling power, for example, by influencing the speed of the Coolant conveyor 7 can be adjusted or can be adjusted via a bypass, not shown here parallel to the cooling heat exchanger 8 with a suitable valve.

Hydrogen is supplied from a compressed gas reservoir 9 via a pressure regulating and metering valve 10 to the anode compartment 4 of the fuel cell 3. Unconsumed hydrogen passes from the fuel cell via an exhaust pipe 11, for example, to the

Environment or in the area of a burner in which the residual hydrogen

is burned. Alternative constructions with an anode recirculation for recycling the unused hydrogen or the like are conceivable here and known from the general state of the art. For the invention, the anode side is not relevant, so that this generally known structure is not discussed here.

The cathode chamber 5 of the fuel cell 3, air via an air conveyor 12, a charge air cooler 13 and a humidifier 14 is supplied. Exhaust air from the

Cathode space 5 in turn passes through the humidifier 14 and an air / liquid heat exchanger 15 and a turbine 16 to the environment. The turbine 16 serves to use pressure energy and thermal energy in the exhaust air and converts them at least partially into mechanical energy. The turbine 16 is seated together with the air conveyor 12 on a common shaft 17, so that the energy recovered in the region of the turbine 16 can be used directly to drive the air conveyor 12. In the normal case, the power occurring in the region of the turbine 16 will not be sufficient for driving the air conveying device 12. Therefore, an electric machine 18 is provided, which provides the required power difference for driving the air conveyor 12. Should it be in individual

Operational situations happen that in the turbine 16 more power is obtained, as required by the air conveyor 12, then the structure can also be used so that the electric machine 18 is operated as a generator to recover electrical energy. This construction of air conveyor 12, turbine 16 and electric machine 12 is also referred to as ETC or electric turbocharger. In addition to the turbine 16, of course, the application of a different expander in this structure would be conceivable and possible. The supply air to the fuel cell 3 is correspondingly hot and dry after the air conveyor 12. This is arranged for those in the fuel cell 3

Proton exchange membranes are very unfavorable, as they dry out easily and can be damaged thereby. To counteract the problem,

The supply air heated by the compression in the air delivery device 12 therefore first flows through the charge air cooler 13, in the region of which the supply air is cooled, for which purpose a liquid cooling medium is used, which is circulated in a cooling circuit 19 by a coolant delivery device 20. The thus cooled but still dry supply air then enters the humidifier 14, which may be designed in particular as a gas / gas humidifier. A typical structure would be, for example, that arranged therein for water vapor-permeable membranes, which are overflowed on one side of the dry supply air to the cathode chamber 5. On the other hand, the membranes are overflowed by the exhaust air laden with the largest part of the product water produced in the fuel cell 3, so that water vapor passes through the membranes from the moist exhaust air into the dry supply air and moisturizes it. The then relatively dry exhaust air then flows through the heat exchanger 15 to the turbine 16. Der

Heat exchanger 15 is now formed so that it is also part of the cooling circuit 19 and thus suitable for heating the exhaust air by the recirculated in the cooling circuit 19 cooling medium. This cooling medium has absorbed heat from the heated supply air in the region of the intercooler 13 and thus now heats the exhaust air of the fuel cell 3. By a corresponding influence, for example, of the

Volumetric flow of the coolant conveyor 20, the heat transfer can be adjusted accordingly. Thus, in certain operating situations in which heat transfer is not desired, the coolant flow can be turned off or reduced accordingly, resulting in a very good controllability and a very good

Adaptability of the fuel cell system 1 to different operating situations arises. The waste heat introduced into the exhaust air can then at least partially be converted into mechanical power in the turbine 16 and be used to improve the exhaust gas

Efficiency of the entire fuel cell system 1 can be used.

In the illustration of Figure 2, a comparable structure of the fuel cell system 1 is shown again without the vehicle 2. This structure is particularly suitable for use in a vehicle 2. Unlike the construction shown in Figure 1, the cooling circuit 19 is not designed here as a separate cooling circuit with its own coolant conveyor 20, but the intercooler 13 and the heat exchanger 15 are part of the cooling system of the

Fuel cell system 1. The coming of the cooling heat exchanger 8 cooling medium flows in the illustrated embodiment in parallel through the heat exchanger 6 of the fuel cell 3 on the one hand and by the intercooler 13 and then by the heat exchanger 15 on the other. To influence the cooling of the compressed supply air while a valve device 21 is provided. About this valve device 21, for example, active in the operating situations in which no cooling of the supply air is desired, the flow of this branch can be prevented with cooling medium. These are in particular situations when starting the fuel cell system 1, especially when the ambient temperature is very low and the supply air after the

Air conveyor so that only minimally heated. In order to further minimize the control effort for the valve device 21, it may further be provided that this valve device 21 is designed as a thermostatic valve. It then opens automatically from a certain preset temperature of the cooling medium in the cooling system and allows so without active activation of the described functionality.

In the illustration of Figure 3 is another possible embodiment of the

Fuel cell system 1 shown. In this embodiment of the

Fuel cell system 1 is completely dispensed with the turbine 16 and it is arranged in the flow direction after the heat exchanger 15, only a pressure-maintaining valve 22. Although energy recovery via the turbine can not be achieved in this way, by dissipating the heat via the exhaust air to the environment, a relief of the overall cooling system is achieved in any case. Furthermore, reduced by the inventive increase in the exhaust air temperature in this

Verschlatungsvariante discharged from the fuel cell system

Liquid water content.

A further detail can be seen in the embodiment of FIG. 3 in the region of the intercooler 13, the humidifier 14 and the heat exchanger 15. These are integrated to form a common unit. This can be of decisive advantage, since the gas flow for both the charge air cooler 13 and for the humidifier 14 as well as for the heat exchanger 15 to a correspondingly distributed

Flow cross-section, for example, must be divided by a plurality of hollow fiber membranes, channels or the like. Through the structural integration of the Intercooler 13 and the heat exchanger 15 in the humidifier 14 can thus reduce the pressure loss for the supply air and the exhaust air and it can be a total of a very compact design achieve, which is particularly crucial when used in the vehicle 2, as typically here anyway only little space is available.

The variants of the fuel cell system described and their embodiments can be combined with each other arbitrarily. So it is of course possible to dispense with a structure of the fuel cell system 1 analogous to that in Figure 1, for example, the turbine 16 and / or an integration of

Charge air cooler 13 and / or the heat exchanger 15 in the humidifier 14 make. The same applies to a combination of the fuel cell systems 1 from FIGS. 2 and 3. Numerous variants and configurations are thus possible within the scope of the present invention.

Claims

Daimler AG claims

1. A fuel cell system (1) with an air conveyor (12) for compressing supply air for a fuel cell (3), designed as an air / liquid heat exchanger intercooler (13), which of the compressed supply air on the one hand and a liquid cooling medium of a cooling circuit flows through the other hand,

characterized in that

a further air / liquid heat exchanger (15) in the region of the exhaust air from the fuel cell (3) is provided, which is flowed through by the exhaust air on one side and by the cooling medium on the other side.

2. Fuel cell system (1) according to claim 1,

characterized in that

a turbine (16) is arranged in the flow direction of the exhaust air after the air / liquid heat exchanger.

3. Fuel cell system (1) according to claim 1 or 2,

characterized in that

the cooling circuit is formed as an independent cooling circuit (19) between the charge air cooler (3) and the heat exchanger (15), which is a

Has coolant delivery device (20).

4. Fuel cell system (1) according to claim 1 or 2,

characterized in that

the cooling circuit is part of a cooling system whose cooling medium, in addition to the charge air cooler (13), also flows through the fuel cell (3), and which one Has coolant delivery device (7) and / a cooling heat exchanger (8) for cooling the cooling medium.

5. Fuel cell system (1) according to claim 4,

characterized in that

the intercooler (13) in the flow direction of the cooling medium before

Heat exchanger (15) is arranged.

6. Fuel cell system (10) according to claim 4 or 5,

characterized in that

the charge air cooler (13) and the heat exchanger (15) are flowed through in parallel to the fuel cell (3) of cooling medium.

7. Fuel cell system (1) according to claim 6,

characterized in that

the flow through charge air cooler (13) and heat exchanger (15) by a valve device (21) is controllable.

8. Fuel cell system (1) according to claim 7,

characterized in that

the valve device (21) is designed as a thermostatic valve.

9. Fuel cell system (1) according to one of claims 1 to 8,

characterized in that

the charge air cooler (13) and / or the heat exchanger (15) are integrated in a gas / gas humidifier (14).

10. Use of the fuel cell system (1) according to one of claims 1 to 9 for generating electrical drive power in a vehicle (2).