HEAT EXCHANGER SYSTEM FOR OPERATING A FUEL CELL STACK

Description

State of the art

[0001] Hydrogen-based fuel cells are considered the basis for a future mobility concept because they emit only water and enable fast refueling times. For example, PEM (proton-exchange membrane) fuel cells can be operated in an electrocatalytic electrode process using air supplied to the fuel cell cathode with oxygen as the oxidant and hydrogen supplied to the fuel cell anode as the fuel, providing electrical energy with high efficiency.

[0002] The compressed cathode gas can reach temperatures of up to 200°C. To protect downstream components, such as a cathode gas humidifier or the fuel cell stack itself, the cathode gas must be cooled to <120°C by a heat exchanger, such as a charge air cooler. Patent publications DE 10 2018 202 906 A1 and DE 10 2010 008 210 A1 each disclose a heat exchanger system for fuel cell systems that have multiple heat exchangers. Disclosure of the invention

[0003] With a plurality of heat exchangers in the supplied or discharged cathode gas, a main cooling circuit of the fuel cell stack can be relieved, the efficiency of exhaust gas enthalpy recovery using a turbine can be increased, the efficiency of a second compressor stage can be improved using intercooling, and the fuel cell stack can be protected from excessively high air inlet temperatures. The extent of these effects must be optimized for the specific operating state of the fuel cell stack.

[0004] According to aspects of the invention, a heat exchanger system for operating a fuel cell stack, a method for controlling the heat exchanger system, a use of the heat exchanger system, a computer program, and a machine-readable storage medium are proposed according to the features of the independent claims, which at least partially achieve the described objects. Advantageous embodiments are the subject of the dependent claims and the following description.

[0005] The invention is based on the finding that by means of a suitable thermally variable coupling between the heat exchangers of the heat exchanger system, the temperatures of the supplied and / or discharged cathode gas can be optimized for different operating conditions of the fuel cell stack.

[0006] According to one aspect, a heat exchanger system for operating a fuel cell stack is proposed, comprising a first compressor and a second compressor for the cathode gas supplied to the fuel cell stack, wherein the second compressor is arranged fluidly downstream of the first compressor. Furthermore, the heat exchanger system comprises a turbine that is mechanically coupled to the second compressor and is subjected to flow by the discharged cathode gas from the fuel cell stack.Furthermore, the heat exchanger system comprises a first heat exchanger which is thermally coupled to the supplied cathode gas between the first compressor and the second compressor and further comprises a second heat exchanger which is thermally coupled to the supplied cathode gas downstream of the second compressor and further comprises a fourth heat exchanger which is thermally coupled to the discharged cathode gas downstream of the turbine, wherein the fourth heat exchanger is thermally variably coupled to the first heat exchanger and the second heat exchanger in order to control a heat exchange for cooling the first heat exchanger and the second heat exchanger.

[0007] Such variable thermal coupling can be achieved through gas-to-coolant heat exchangers, through the exchange of coolant between the heat exchangers, through gas-to-gas heat exchangers, through the exchange of gas flows between the heat exchangers, or other thermal couplings between the heat exchangers, such as through different heat-conducting materials or variable contact surfaces for heat exchange between the heat exchangers. Variable thermal coupling can be understood in particular as a thermal coupling that can be changed during operation, but also as a thermal coupling that allows for variable thermal coupling within the heat exchanger system to be structurally adjusted. The latter is particularly possible through the use of throttles in fluid flows, contact surfaces between heat exchangers, etc.

[0008] Directional information refers to a direction of the affected fluids.

[0009] With such a heat exchanger system, in particular, the temperature of cathode gas streams within the heat exchanger system can be optimized.

[0010] In particular, the temperature of the cathode gas between the first compressor and the second compressor can be brought to the lowest possible temperature level through variable thermal coupling, thus achieving better efficiency of the second compressor, which also results in a reduction in the load on the electric compression. Because less energy is required for compression, the power of the fuel cell stack can be reduced, resulting in lower costs.

[0011] The variable thermal coupling advantageously allows the cooling of the cathode gas downstream of the second compressor to be brought to the lowest possible temperature level, enabling particularly good protection of the fuel cell stack against thermal degradation and thus increasing its service life. Furthermore, the load on the main cooling circuit is reduced, as part of the cooling capacity is achieved with the cathode air.

[0012] Advantageously, the fourth heat exchanger causes the discharged cathode gas to be heated to a higher temperature level before an exhaust in order to reduce water droplets from the exhaust.

[0013] According to one aspect, it is proposed that the heat exchanger system comprises a third heat exchanger which is thermally coupled to the discharged cathode gas in the fluid direction upstream of the turbine, and wherein the first heat exchanger and the second heat exchanger are thermally variably coupled to the third heat exchanger in order to control a heat exchange for heating the third heat exchanger.

[0014] With thermally variable coupling, heating of the discharged cathode gas upstream of the turbine can be optimized to the highest possible temperature level, improving turbine efficiency and thus reducing the load on the electrical compression. Here, too, the reduced electrical power required for compressing the cathode gas makes it possible to reduce the power of the fuel cell stack, which can also lead to a reduction in costs.

[0015] The fourth heat exchanger is thermally variably coupled to both the first heat exchanger and the second heat exchanger by means of a coolant and a first three-way valve to cool the cathode gas before and after the second compressor, respectively.

[0016] The coolant cooled by the first heat exchanger can be divided by the three-way valve so that both the cathode gas after the first heat exchanger and after the second heat exchanger are cooled to approximately 70°C.

[0017] According to one aspect, it is proposed that the first heat exchanger and the second heat exchanger are thermally variably coupled to the third heat exchanger by means of a coolant and a second three-way valve in order to supply heat to the discharged cathode gas upstream of the turbine.

[0018] A second three-way valve allows the coolant flows from the first and second heat exchangers to be optimally mixed together so that the third heat exchanger can bring the cathode gas discharged from the fuel cell stack to a high temperature level.

[0019] According to one aspect, it is proposed that the second heat exchanger is thermally coupled to the third heat exchanger by means of a coolant in order to supply heat to the discharged cathode gas upstream of the turbine.

[0020] In other words, the direct fluidic coupling of the coolant between the second and the third heat exchanger achieves a particularly direct thermal coupling, which can be adjusted, for example, by means of an adjustable throttle in the fluidic connection or a diameter of the fluidic connection between the two heat exchangers.

[0021] This allows the temperature in front of the turbine to be increased in order to improve the efficiency of the turbine.

[0022] According to one aspect, it is proposed that the heat exchanger system comprises a coolant pump, and the thermal coupling by means of the coolant is configured to effect a flow of the coolant between the first to fourth heat exchangers by means of the coolant pump.

[0023] According to one aspect, it is proposed that the heat exchanger system comprise a fifth heat exchanger that is thermally coupled to the discharged cathode gas upstream of the third heat exchanger in the fluid direction and is thermally coupled to the first heat exchanger to absorb heat. In particular, the coupling between the first heat exchanger and the fifth heat exchanger can be configured to be thermally variable.

[0024] According to one aspect, it is proposed that the fifth heat exchanger is thermally coupled to the first heat exchanger by means of the coolant.

[0025] According to one aspect, it is proposed that a thermal coupling with a cooling unit is inserted between the thermal coupling of the fourth heat exchanger with the first and the second heat exchanger.

[0026] This ensures that other units are also cooled in an optimized manner.

[0027] According to one aspect, it is proposed that the cooling unit comprises a power electronics cooler and / or an inverter cooler and / or an engine cooler and / or a converter cooler.

[0028] The rotor-shaft units as an example of an engine cooler, which can be either electric motor driven or turbine driven, must be cooled due to losses or friction in the rotor-shaft system, e.g. bearing losses due to the high speeds.

[0029] The coolers listed here can be thermally coupled in series, parallel, or mixed series and parallel.

[0030] Since the power electronics in particular, but also the rotor-shaft units, require a low temperature level, the lowest temperature level of the heat exchanger system can be used to cool the power electronics first and then the rotor-shaft units. This means that both sequential and parallel thermal coupling are possible.

[0031] Advantageously, the integration of additional heat sources into the overall concept of the heat exchanger system with a holistic

[0032] Optimization possible.

[0033] In addition, structural integration into an air module is possible, which contains the air compression components as well as the heat exchanger components of the heat exchanger system in a compact and integrated manner.

[0034] Furthermore, there may be advantages in terms of the required installation space, since no separate connections to another cooling system are required for cooling the power electronics or the rotor shaft unit, ie the motor cooling.

[0035] A method for controlling a heat exchanger system described above is proposed, wherein the heat exchanger system comprises a first temperature sensor and a second temperature sensor, and the first temperature sensor is arranged to measure a temperature of the supplied cathode gas upstream of the second compressor, and the second temperature sensor is arranged to measure a temperature of the discharged cathode gas upstream of the turbine. The first and / or second three-way valve is controlled such that the temperature of the second temperature sensor is maximized and / or the temperature of the first temperature sensor is minimized.

[0036] The use of a heat exchanger system described above to supply a mobile platform with electrical energy is proposed.

[0037] A mobile platform can be an at least partially automated system that is mobile and / or a driver assistance system. An example can be an at least partially automated vehicle or a vehicle with a driver assistance system. That is, in this context, an at least partially automated system includes a mobile platform with respect to at least partially automated functionality, but a mobile platform also includes vehicles and other mobile machines, including driver assistance systems. Other examples of mobile platforms can be driver assistance systems with multiple sensors, mobile multi-sensor robots such as robot vacuum cleaners or lawn mowers, a multi-sensor monitoring system, a manufacturing machine, a personal assistant, or an access control system. Each of these systems can be a fully or partially autonomous system.

[0038] Since the effective use of electrical energy is particularly relevant for the operation of a fuel cell system in mobile platforms, the advantages of such a system are particularly evident in the electrical supply of a mobile platform.

[0039] The described heat exchanger system for operating a fuel cell stack can also be used for stationary applications.

[0040] A computer program is proposed that includes instructions that, when executed by a computer, cause the computer to perform one of the methods described above. Such a computer program enables simple use of the described method in different systems.

[0041] A machine-readable storage medium is specified on which the computer program described above is stored.

[0042] In the following, embodiments of the invention are described with reference to Figures 1 to 7 explained in more detail. Here the: Figure 1 shows a heat exchanger system for operating a fuel cell stack; Figure 2 shows a modification of the heat exchanger system for operating a fuel cell stack; Figure 3 shows a further modification of the heat exchanger system for operating a fuel cell stack; Figure 4 shows a further modification of the heat exchanger system for operating a fuel cell stack; Figure 5 shows a further modification of the heat exchanger system for operating a fuel cell stack; Figure 6 shows a further modification of the heat exchanger system for operating a fuel cell stack; and Figure 7 shows a further modification of the heat exchanger system for operating a fuel cell stack.

[0043] The Figure 1outlines a heat exchanger system 100 for operating a fuel cell stack with a cathode side 195 of the fuel cell stack 190, a first compressor 142 and a second compressor 150 which is mechanically coupled to a turbine 155.

[0044] In a cathode path, a cathode gas is supplied to the upstream cathode side 195 of the fuel cell stack 190 and is discharged into the environment downstream of the cathode side 195.

[0045] Upstream, to supply the cathode side 195 of the fuel cell stack 190, air is drawn as cathode gas from the environment 191 through an air filter 145 to filter harmful particles and, in particular, harmful chemical compounds from the air. By means of a first compressor 142, driven by a motor M, a cathode gas stream of the filtered air is fed to a first heat exchanger 110, which is thermally coupled to the cathode gas stream. The first heat exchanger 110 absorbs heat from the compressed cathode gas stream to cool the cathode gas heated by the first compressor 142 before the second compression by a second compressor 150, in order to increase the efficiency of the compression process of the cathode gas stream. The first heat exchanger 110 couples this heat to a coolant that is thermally coupled to the first heat exchanger 110.The cooled cathode gas stream is fed to the second compressor 150 for further compression.

[0046] By means of the second compressor 150, which is driven, for example, without a motor, the further compressed cathode gas stream is fed to a second heat exchanger 120, which is thermally coupled to the further compressed cathode gas stream.

[0047] The second heat exchanger 120 absorbs heat from the further compressed cathode gas stream to cool the cathode gas heated by the second compressor 150 to control the inlet temperature of the cathode gas stream into the cathode side 195 of the fuel cell stack 190. The second heat exchanger 120 couples this heat to the coolant, which is thermally coupled to the second heat exchanger 120. This in turn cooled cathode gas stream is directed to an inlet port of the cathode side 195 of the fuel cell stack 190.

[0048] Downstream of the fuel cell stack 190, the cathode gas stream is fed via an outlet connection 192 of the cathode side 195 of the fuel cell stack 190 to a third heat exchanger 130 which is thermally coupled to the cathode gas stream discharged from the cathode gas side 195 of the fuel cell stack 190.

[0049] The third heat exchanger 130 transfers heat to the exhausted cathode gas stream to heat the exhausted cathode gas stream, thereby increasing the temperature of the exhausted cathode gas stream for efficient operation of the downstream turbine. The third heat exchanger 130 extracts this heat from the coolant, which is thermally coupled to the third heat exchanger 130. This heated exhausted cathode gas stream is fed to the turbine 155 for operation of the turbine 155 to recover energy from the exhausted cathode gas stream.

[0050] From the turbine 155, the expanded cathode gas stream is fed to a fourth heat exchanger 140, which is thermally coupled to the expanded cathode gas stream.

[0051] The fourth heat exchanger 140 is thermally coupled to the coolant and transfers heat from the coolant to the expanded cathode gas stream to lower the temperature of the coolant.

[0052] The cathode gas stream heated in this way, flowing downstream of the cathode side 195 of the fuel cell stack 190 and exiting the fourth heat exchanger 140, is then released into the environment of the fuel cell stack 190.

[0053] The cooled coolant exiting the fourth heat exchanger 140 is supplied to both the first heat exchanger 110 and the second heat exchanger 120 via a first three-way valve 161 and can provide a thermally variable coupling of the fourth heat exchanger 140 to the first heat exchanger 110 and the second heat exchanger 120 through the controllable three-way valve 161.

[0054] The heated coolant exiting the first heat exchanger 110 and the second heat exchanger 120 is supplied to the third heat exchanger 130 via a second controllable three-way valve 162 and can thereby provide a thermally variable coupling of the first heat exchanger 110 and the second heat exchanger 120 to the third heat exchanger 130. Thus, by controlling the first three-way valve 161 and the second three-way valve 162, the heat exchange between the heat exchangers can be controlled such that the heat exchange can be optimized for different operating conditions of the fuel cell stack.

[0055] By means of a coolant pump 165, which fluidly connects the coolant outlet of the third heat exchanger 130 with the coolant inlet of the fourth heat exchanger 140, the coolant can be pumped around and thus exchanged in the described coolant circuit. This closes the cooling circuit. The coolant pump 165 can also be installed in a different position, e.g., between the heat exchanger 140 and the three-way valve 161.

[0056] All heat exchangers 110, 120, 130, 140 can be operated with the coolant in countercurrent with respect to the cathode gas flow.

[0057] The Figure 21 depicts a heat exchanger system 200 as a modification of the previously described heat exchanger system 100, in which the coolant outlet of the second heat exchanger 120 is directly connected to the coolant inlet of the third heat exchanger via a fluid connection 167. Since this modified heat exchanger system 200 has only a first three-way valve 161, the coolant outlet of the first heat exchanger 110 is directly coupled to the coolant inlet of the fourth heat exchanger 140. Thus, in the heat exchanger system 200, the first three-way valve 161 can be used to provide the variable thermal coupling between the fourth heat exchanger 140 and the first heat exchanger 110, as well as the second heat exchanger 120.

[0058] The Figure 3 outlines a heat exchanger system 300 which is a modification of the one in the Figure 2described system 200, has a fifth heat exchanger 170, which is thermally coupled to the discharged cathode gas in the fluid direction upstream of the third heat exchanger and is thermally coupled to the first heat exchanger in order to absorb heat. This thermal coupling is realized by a fluid connection of the coolant outlet of the first heat exchanger 110 to a coolant inlet of the fifth heat exchanger 170, and the coolant outlet is coupled via a fluid connection 169 to both the coolant outlet 166 of the third heat exchanger 130 and to an inlet of the coolant pump 165. This results in both the coolant flow from the third heat exchanger 130 and the fifth heat exchanger 170 flowing together into the inlet of the coolant pump 165.

[0059] The Figure 4 outlines a heat exchanger system 400 which is a modification of the one in the Figure 1described system 100, in which a thermal coupling with a cooling unit is inserted between the thermal coupling of the fourth heat exchanger 140 with the first heat exchanger 110 and the second heat exchanger 120. The cooling unit has a power electronics cooler and an engine cooler. This thermal coupling is realized in the heat exchanger system 400 in that the coolant outlet of the fourth heat exchanger 140 is first fluidly coupled to the power electronics cooler 410 in order to cool power electronics and subsequently fluidly coupled to the engine cooler 420 in order to cool the engine. A coolant outlet of the engine cooler 420 is then fluidly coupled to the first three-way valve 161.

[0060] The Figure 5 outlines a heat exchanger system 500 which is a modification of the one in the Figure 4described system 400, the coolant outlet of the fourth heat exchanger 140 is coupled in parallel to the power electronics cooler and to the engine cooler 420. The fluid coupling 531 of the power electronics cooler 410 to the fourth heat exchanger 140 has a throttle 510 to adjust the thermal coupling between the power electronics cooler 410 and the engine cooler 420. The two coolant outlets of the power electronics cooler 410 and the engine cooler 420 are fluidically combined and fed to the first three-way valve 161. The difference from the heat exchanger system 400 is therefore the parallel routing of the coolant through the two coolers 410 and 420.

[0061] The Figure 6 outlines a heat exchanger system 600 which is a modification of the one in the Figure 4described system 400, an engine cooler 610 for the second compressor 150, which is fluidly and thermally coupled in series between the fourth heat exchanger 140 and the first three-way valve 161. That is, the coolant outlet of the engine cooler 420 is fluidly coupled to a coolant inlet of the engine cooler 610, and a coolant outlet of the engine cooler 610 is fluidly coupled to the first three-way valve 161.

[0062] The Figure 7 outlines a heat exchanger system 700 which is a modification of the one shown in the Figure 5described system 500, a fluidically and thermally parallel coupling of the fourth heat exchanger 140 with, on the one hand, the power electronics cooler 410 and the engine cooler 420 and, on the other hand, with the engine cooler 610 of the second compressor 150. This means that the coolant flow emerging from the coolant outlet of the fourth heat exchanger is, on the one hand, guided into the fluidically parallel coupling of the power electronics cooler 410 and the engine cooler 420 and, on the other hand, is guided in fluidically parallel fashion through the engine cooler 610 of the second compressor 150, and the respective parallel coolant branches are brought together at the first three-way valve 161.In this case, the coolant flow between the parallel coolant branches can be divided by means of a first throttle 710, which is arranged in a coolant supply to the engine cooling 420, and a second throttle 720, which is arranged in a coolant supply from the fourth heat exchanger 140 and the engine cooler 610 of the second compressor 150, and thus the thermal coupling in the two coolant branches can be adjusted.

[0063] Those skilled in the art will recognize that, in addition to the topologies of the heat exchanger system for operating a fuel cell stack presented here, the inventive teaching can also be implemented with other topologies. Such as, for example, an air system with multiple compression or a different configuration of pumps and valves.

Claims

1. Heat exchanger system (100, 200, 300, 400, 500, 600, 700) for operating a fuel cell stack (190), having: a first compressor (142) and a second compressor (150) for the cathode gas fed to the fuel cell stack (190), wherein the second compressor (150) is arranged fluidically downstream of the first compressor (142); a turbine (155) which is mechanically coupled to the second compressor (150) and against which cathode gas discharged from the fuel cell stack (190) flows; a first heat exchanger (110) which is thermally coupled to the supplied cathode gas between the first compressor (142) and the second compressor (150); a second heat exchanger (120) which is thermally coupled to the supplied cathode gas downstream of the second compressor (150); a fourth heat exchanger (140) which is thermally coupled to the discharged cathode gas downstream of the turbine (155); wherein the fourth heat exchanger (140) is thermally variably coupled to the first heat exchanger (110) and to the second heat exchanger (120) in order to control a heat exchange for cooling the first heat exchanger (110) and the second heat exchanger (120), characterized in that the fourth heat exchanger (140) is thermally variably coupled to both the first heat exchanger (110) and the second heat exchanger (120) by means of a coolant and a first three-way valve (161) in order to cool the cathode gas upstream and downstream of the second compressor (150).

2. Heat exchanger system (100, 200, 300, 400, 500, 600, 700) according to Claim 1, which has a third heat exchanger (130) which is thermally coupled to the discharged cathode gas in the fluid direction upstream of the turbine (155), and wherein the first heat exchanger (110) and the second heat exchanger (120) are thermally variably coupled to the third heat exchanger (130) in order to control a heat exchange for heating the third heat exchanger (130).

3. Heat exchanger system (100, 200, 400, 500, 600, 700) according to Claim 1 or 2, wherein the first heat exchanger (110) and the second heat exchanger (120) are thermally variably coupled to the third heat exchanger (130) by means of a coolant and a second three-way valve (162) in order to supply heat to the discharged cathode gas upstream of the turbine (155).

4. Heat exchanger system (100, 200, 300, 400, 500, 600, 700) according to Claim 1 or 2, wherein the second heat exchanger (120) is thermally coupled to the third heat exchanger (130) by means of a coolant in order to supply heat to the discharged cathode gas upstream of the turbine (155).

5. Heat exchanger system (100, 200, 300, 400, 500, 600, 700) according to one of the preceding claims, which has a coolant pump (165), and the thermal coupling by means of the coolant is configured to bring about a flow of the coolant between the first to fourth heat exchangers (110, 120, 130, 140) by means of the coolant pump (165).

6. Heat exchanger system (300) according to Claim 4, having a fifth heat exchanger (170), which is thermally coupled to the discharged cathode gas in the fluid direction upstream of the third heat exchanger (130) and is thermally coupled to the first heat exchanger (110) in order to absorb heat.

7. Heat exchanger system (300) according to Claim 6, wherein the fifth heat exchanger (170) is thermally coupled to the first heat exchanger (110) by means of the coolant.

8. Heat exchanger system (400, 500, 600, 700) according to one of the preceding claims, wherein a thermal coupling to a cooler assembly is inserted between the thermal coupling of the fourth heat exchanger (140) to the first (110) and the second heat exchanger (120).

9. Heat exchanger system (400, 500, 600, 700) according to Claim 8, wherein the cooler assembly has a power electronics cooler (410) and / or an inverter cooler and / or a motor cooler (420) and / or a converter cooler.

10. Method for controlling a heat exchanger system (100, 200, 300, 400, 500, 600, 700) according to one of the preceding claims, wherein the heat exchanger system (100, 200, 300, 400, 500, 600, 700) has a first temperature sensor and a second temperature sensor, and the first temperature sensor is arranged to measure a temperature of the supplied cathode gas upstream of the second compressor (150), and the second temperature sensor is arranged to measure a temperature of the discharged cathode gas upstream of the turbine (155), and the first (161) and / or second three-way valve (162) are / is controlled in such a way that the temperature of the second temperature sensor becomes maximum and / or the temperature of the first temperature sensor becomes minimum.

11. Use of a heat exchanger system (100, 200, 300, 400, 500, 600, 700) according to Claims 1 to 9 for supplying a mobile platform with electrical energy.

12. Computer program comprising instructions which, when the computer program is executed by a computer, cause the latter to perform the method according to Claim 10.

13. Machine-readable storage medium on which the computer program product according to Claim 12 is stored.