Heat exchanger system for operating a fuel cell stack

Abstract

A heat exchanger system for operating a fuel cell stack is proposed, comprising: a first compressor and a second compressor for supplying cathode gas to the fuel cell stack, wherein the second compressor is fluidly arranged after the first compressor; a turbine mechanically coupled to the second compressor to which the discharged cathode gas from the fuel cell stack flows; a first heat exchanger thermally coupled to the cathode gas supplied between the first and second compressors; a second heat exchanger thermally coupled to the cathode gas supplied downstream of the second compressor; and a fourth heat exchanger thermally coupled to the discharged cathode gas downstream of the turbine; wherein the fourth heat exchanger is thermally variably coupled to the first and second heat exchangers to control the heat exchange for cooling the first and second heat exchangers.

Description

Background Technology

[0001] Hydrogen-based fuel cells are considered fundamental to future mobility concepts because they essentially emit only water and allow for rapid refueling. For example, a PEM fuel cell (PEM, "proton-exchange-membrane"; German: Protonen-Austausch-Membran, proton exchange membrane) can operate in an electrocatalytic electrode process using air supplied to the cathode of the fuel cell with oxygen as the oxidant and hydrogen supplied to the anode of the fuel cell as fuel, in order to deliver electrical energy with high efficiency.

[0002] Compressed cathode gas can reach temperatures up to 200°C. To protect downstream components, such as cathode gas humidifiers or the fuel cell stack itself, the cathode gas must be cooled to <120°C via a heat exchanger, such as a so-called intercooler. Summary of the Invention

[0003] By utilizing heat exchangers in multiple conveyed or discharged cathode gases, the load on the main cooling loop of the fuel cell stack can be reduced, the efficiency of exhaust gas enthalpy recovery can be improved by using turbines, the efficiency of the second compressor stage can be improved by using intercooling, and the fuel cell stack can be protected from excessively high inlet temperatures. Here, the degree of these effects must be optimized for the corresponding operating conditions of the fuel cell stack.

[0004] Corresponding to aspects of the invention, a heat exchanger system for operating a fuel cell stack is proposed, a method for controlling the heat exchanger system, an application to the heat exchanger system, a computer program, and a machine-readable storage medium corresponding to the features of the independent claim are provided. Advantageous configurations are the subject of the dependent claims and the following description.

[0005] This invention is based on the understanding that by using appropriate thermally variable coupling between heat exchangers in a heat exchanger system, the temperature of the delivered 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, the system having a first compressor and a second compressor for supplying cathode gas to the fuel cell stack, wherein the second compressor is fluidly arranged after the first compressor. Furthermore, the heat exchanger system has a turbine mechanically coupled to the second compressor, to which the discharged cathode gas from the fuel cell stack flows. Additionally, the heat exchanger system has a first heat exchanger thermally coupled to the cathode gas supplied between the first and second compressors, and further has a second heat exchanger thermally coupled to the cathode gas supplied downstream of the second compressor, and further has a fourth heat exchanger thermally coupled to the discharged cathode gas downstream of the turbine, wherein the fourth heat exchanger is thermally variably coupled to the first and second heat exchangers to control the heat exchange for cooling the first and second heat exchangers.

[0007] This variable thermal coupling can be achieved through gas-coolant heat exchangers via coolant exchange between heat exchangers, through gas-gas heat exchangers via airflow exchange between heat exchangers, or through other thermal couplings between heat exchangers for heat exchange between these heat exchangers, such as through different thermally conductive materials or variable contact surfaces. Variable thermal coupling can be understood in particular as thermal coupling that can be altered during continuous operation, but it can also be understood as thermal coupling within the heat exchanger system that can be structurally adjusted. The latter is particularly achieved through the use of throttling elements in the fluid flow, at the contact surfaces between heat exchangers, etc.

[0008] Here, the direction refers to the direction of the fluid involved.

[0009] This heat exchanger system is particularly effective in optimizing the temperature of the cathode gas flow within the system.

[0010] In particular, variable thermal coupling can be used to keep the temperature of the cathode gas between the first and second compressors as low as possible, thereby improving the efficiency of the second compressor and reducing the burden on the electric compressor. Since 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 enables the cooling of the cathode gas downstream of the second compressor to reach the lowest possible temperature level, thereby providing particularly good protection of the fuel cell stack against thermal degradation and thus enabling an increase in service life. Furthermore, it advantageously reduces the load on the main cooling circuit, since a portion of the cooling power is achieved via cathode air.

[0012] The fourth heat exchanger advantageously heats the discharged cathode gas to a higher temperature level before the exhaust pipe, thereby reducing water droplets from the exhaust pipe.

[0013] According to one aspect, a heat exchanger system has a third heat exchanger that is thermally coupled to discharged cathode gas located in front of a turbine along the fluid direction, and wherein the first and second heat exchangers are thermally variably coupled to the third heat exchanger in order to control the heat exchange used to heat the third heat exchanger.

[0014] This thermally variable coupling allows for optimization of the heating of the cathode gas to be discharged before the turbine to the highest possible temperature level, thereby achieving better turbine efficiency and reducing the burden on the electric compressor. Furthermore, by reducing the electrical power required to compress the cathode gas, the power output of the fuel cell stack can be reduced, leading to cost reduction.

[0015] According to one perspective, the fourth heat exchanger is thermally variably coupled not only to the first heat exchanger but also to the second heat exchanger via a coolant and a first three-way valve, in order to cool the cathode gas before or after the second compressor.

[0016] The coolant cooled by the first heat exchanger can be divided by a three-way valve in such a way that not only the cathode gas after the first heat exchanger but also the cathode gas after the second heat exchanger is cooled by about 70°C.

[0017] According to one approach, the first and second heat exchangers are thermally variably coupled to the third heat exchanger via a coolant and a second three-way valve to transfer heat to the discharged cathode gas before the turbine.

[0018] The second three-way valve enables optimized mixing of coolant streams from the first and second heat exchangers, allowing the third heat exchanger to bring the cathode gas discharged from the fuel cell stack to a high temperature level.

[0019] According to one proposal, the second heat exchanger is thermally coupled to the third heat exchanger by means of a coolant in order to transfer heat to the discharged cathode gas before the turbine.

[0020] In other words, a particularly direct thermal coupling is achieved through the direct fluid coupling of the coolant between the second and third heat exchangers, which can be adjusted, for example, by means of an adjustable throttling section in the fluid connection or by means of the diameter of the fluid connection between the two heat exchangers.

[0021] This increases the temperature before the turbine, thereby improving the turbine's efficiency.

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

[0023] According to one aspect, the heat exchanger system has a fifth heat exchanger that is thermally coupled to the discharged cathode gas located upstream of the third heat exchanger along the fluid direction, and also thermally coupled to the first heat exchanger, in order to absorb heat. Here, the coupling between the first and fifth heat exchangers can be configured to be thermally variable.

[0024] According to one perspective, the fifth heat exchanger is thermally coupled to the first heat exchanger via a coolant.

[0025] One approach proposes inserting a thermal coupling with a cooler device between the thermal couplings of the fourth heat exchanger and the first and second heat exchangers.

[0026] Therefore, it is possible to optimize the cooling of other equipment as well.

[0027] According to one aspect, the cooler device has a power electronic device cooler and / or an inverter cooler and / or a motor cooler and / or a converter cooler.

[0028] Rotor-well units, as examples of motor coolers, can be driven by both electric motors and turbines. Due to losses or friction in the rotor-well system, such as bearing losses caused by high speeds, the rotor-well unit must be cooled.

[0029] The coolers listed here can be thermally coupled not only in series but also in parallel and in a hybrid series-parallel configuration.

[0030] Because both power electronics and rotor-shaft units require low temperature levels, the lowest temperature level of the heat exchanger system can be used to cool the power electronics first and then the rotor-shaft units. That is, it enables both thermally coupled series connections and thermally coupled parallel connections.

[0031] Therefore, it is possible to achieve a fully optimized overall solution for integrating additional heat sources into the heat exchanger system in an advantageous manner.

[0032] Furthermore, it is possible to structurally integrate it into an air module that is not only compact but also integrates the air compression components and heat transfer components of the heat exchanger system.

[0033] Furthermore, it offers advantages in terms of required installation space, as cooling of power electronics or rotor-shaft units, i.e., motor cooling, does not require separate connections to an additional cooling system.

[0034] A method is proposed for controlling the heat exchanger system described above, wherein the heat exchanger system has a first temperature sensor and a second temperature sensor, the first temperature sensor being arranged to measure the temperature of cathode gas supplied before a second compressor, and the second temperature sensor being arranged to measure the temperature of cathode gas discharged before a turbine. Here, a first three-way valve and / or a second three-way valve are controlled such that the temperature of the second temperature sensor is maximized and / or the temperature of the first temperature sensor is minimized.

[0035] An application of the heat exchanger system described above is proposed for supplying electrical power to a mobile platform.

[0036] A mobile platform can be a system that is at least partially automated, and is mobile and / or has a driver assistance system. An example could be a vehicle that is at least partially automated, or a vehicle with a driver assistance system. That is, in this respect, a system that is at least partially automated includes a mobile platform associated with at least partial automation functionality, but a mobile platform also includes vehicles and other mobile machines that include driver assistance systems. Further examples of mobile platforms could be driver assistance systems with multiple sensors, mobile multi-sensor robots—such as robotic vacuum cleaners or lawnmowers—multi-sensor monitoring systems, manufacturing machines, personal assistants, or access control systems. Each of these systems can be fully or partially autonomous.

[0037] Because the efficient use of electrical energy is important for the operation of fuel cell systems, especially on mobile platforms, the advantages of such systems are particularly evident in the power supply for mobile platforms.

[0038] The heat exchanger system described for operating fuel cell stacks can also be used for static applications.

[0039] A computer program is proposed, comprising instructions that, when executed by a computer, cause the computer to perform any of the methods described above. This computer program enables the simple use of the described methods in various systems.

[0040] This describes a machine-readable storage medium on which the computer program described above is stored. Attached Figure Description

[0041] The following is for reference only. Figures 1 to 7Embodiments of the invention will now be described in more detail. The accompanying drawings are shown herein:

[0042] Figure 1 Heat exchanger systems used to operate fuel cell stacks;

[0043] Figure 2 A variant of a heat exchanger system for operating fuel cell stacks;

[0044] Figure 3 Another variant of the heat exchanger system for operating fuel cell stacks;

[0045] Figure 4 Another variant of the heat exchanger system for operating fuel cell stacks;

[0046] Figure 5 Another variant of the heat exchanger system for operating fuel cell stacks;

[0047] Figure 6 Another variant of the heat exchanger system for operating fuel cell stacks; and

[0048] Figure 7 Another variant of the heat exchanger system for operating fuel cell stacks. Detailed Implementation

[0049] Figure 1 A heat exchanger system 100 for operating a fuel cell stack is shown, the heat exchanger system having a cathode side 195 of a fuel cell stack 190, a first compressor 142 and a second compressor 150 mechanically coupled to a turbine 155.

[0050] In the cathode path, cathode gas is delivered to the upstream cathode side 195 of the fuel cell stack 190 and introduced into the surrounding environment downstream of the cathode side 195.

[0051] Upstream, air is drawn from the surrounding environment 191 via an air filter 145 as cathode gas to supply the cathode side 195 of the fuel cell stack 190, filtering out harmful particles and, in particular, harmful compounds from the air. The filtered air cathode gas stream is delivered to a first heat exchanger 110, thermally coupled to the cathode gas stream, via a first compressor 142 driven by a motor M. 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 a second compression by a second compressor 150, thereby improving the efficiency of the compression process of the cathode gas stream. The first heat exchanger 110 couples this heat to a coolant thermally coupled to it. The cooled cathode gas stream is then delivered to the second compressor 150 for further compression.

[0052] The further compressed cathode gas flow is delivered to a second heat exchanger 120 by means of, for example, a second compressor 150 driven without a motor, which is thermally coupled to the further compressed cathode gas flow.

[0053] The second heat exchanger 120 absorbs heat from the further compressed cathode gas flow to cool the cathode gas heated by the second compressor 150, thereby controlling the inlet temperature of the cathode gas flow entering the cathode side 195 of the fuel cell stack 190. The second heat exchanger 120 couples this heat to a coolant thermally coupled to it. This re-cooled cathode gas flow is then introduced into the inlet connector of the cathode side 195 of the fuel cell stack 190.

[0054] Downstream of the fuel cell stack 190, cathode gas flows through the output connector 192 of the cathode side 195 of the fuel cell stack 190 and is delivered to a third heat exchanger 130, which is thermally coupled to the cathode gas flow discharged from the cathode gas side 195 of the fuel cell stack 190.

[0055] The third heat exchanger 130 outputs heat to the discharged cathode gas flow to heat it, thereby increasing its temperature for efficient operation of the downstream turbine. This heat is coupled from a coolant thermally coupled to the third heat exchanger 130. The heated discharged cathode gas flow is directed to the turbine 155 for operation, recovering energy from the discharged cathode gas flow. The depressurized cathode gas flow is then delivered from the turbine 155 to a fourth heat exchanger 140 thermally coupled to it.

[0056] The fourth heat exchanger 140 is thermally coupled to the coolant and outputs heat from the coolant to the depressurized cathode gas flow in order to reduce the temperature of the coolant.

[0057] Then, the cathode gas flow, heated in this way and flowing downstream of the cathode side 195 of the fuel cell stack 190, exiting from the fourth heat exchanger 140, is output to the surrounding environment of the fuel cell stack 190.

[0058] Through the first three-way valve 161, the cooled coolant from the fourth heat exchanger 140 is delivered not only to the first heat exchanger 110 but also to the second heat exchanger 120, and the controllable three-way valve 161 can provide thermally variable coupling between the fourth heat exchanger 140 and the first heat exchanger 110 and the second heat exchanger 120.

[0059] Heated coolant from the first heat exchanger 110 and the second heat exchanger 120 is delivered to the third heat exchanger 130 via a controllable second three-way valve 162, thereby providing a thermally variable coupling between the first heat exchanger 110, the second heat exchanger 120, and the third heat exchanger 130. Therefore, heat exchange between these heat exchangers can be controlled by controlling the first three-way valve 161 and the second three-way valve 162, allowing the heat exchange to be optimized for different operating conditions of the fuel cell stack.

[0060] By means of a coolant pump 165 that fluidly connects the coolant outlet of the third heat exchanger 130 to the coolant inlet of the fourth heat exchanger 140, coolant can be pumped and thus exchanged in the coolant circuit. The coolant circuit is thus closed. The coolant pump 165 can also be installed in other locations, such as between the heat exchanger 140 and the three-way valve 161.

[0061] Here, all heat exchangers 110, 120, 130, and 140 can operate on a counter-current principle relative to the cathode airflow using the coolant.

[0062] Figure 2 A heat exchanger system 200 is illustrated as a variant of the aforementioned 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. Because this variant heat exchanger system 200 only has 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 in the illustration. Therefore, variable thermal coupling between the fourth heat exchanger 140 and the first heat exchanger 110 and the second heat exchanger 120 can be provided in the heat exchanger system 200 by means of the first three-way valve 161.

[0063] Figure 3 Draw as relative to Figure 2 A variant of the system 200 described herein, a heat exchanger system 300, has a fifth heat exchanger 170 that is thermally coupled to the discharged cathode gas located upstream of the third heat exchanger along the fluid direction and to the first heat exchanger to absorb heat. This thermal coupling is achieved via a fluid-related connection between the coolant outlet of the first heat exchanger 110 and the coolant inlet of the fifth heat exchanger 170, and the coolant outlet is coupled not only to the coolant outlet 166 of the third heat exchanger 130 but also to the inlet of the coolant pump 165 via a fluid-related connection 169. This results in both coolant flows from the third heat exchanger 130 and the fifth heat exchanger 170 flowing together into the inlet of the coolant pump 165.

[0064] Figure 4 Draw as relative to Figure 1 A variant of the system 100 described herein is a heat exchanger system 400 in which a thermal coupling with a cooler device is inserted between the thermal couplings of the fourth heat exchanger 140 and the first heat exchanger 110 and the second heat exchanger 120. Here, the cooler device includes a power electronics cooler and a motor cooler. This thermal coupling is achieved in the heat exchanger system 400 such that the coolant outlet of the fourth heat exchanger 140 is first fluid-coupled to the power electronics cooler 410 to cool the power electronics, and then fluid-coupled to the motor cooler 420 to cool the motor. The coolant outlet of the motor cooler 420 is then fluid-coupled to a first three-way valve 161.

[0065] Figure 5 Draw as relative to Figure 4 A variant of system 400 described herein is a heat exchanger system 500 that couples the coolant outlet of a fourth heat exchanger 140 in parallel with a power electronics cooler and a motor cooler 420. Here, the fluid coupling 531 between the power electronics cooler 410 and the fourth heat exchanger 140 has a throttling section 510 to adjust the thermal coupling between the power electronics cooler 410 and the motor cooler 420. The two coolant outlets of the power electronics cooler 410 and the motor cooler 420 are fluidly merged and supplied to a first three-way valve 161. The difference from heat exchanger system 400 is that the coolant is guided in parallel through the two coolers 410 and 420.

[0066] Figure 6 Draw as relative to Figure 4 A variant of the system 400 described herein is a heat exchanger system 600, which has a motor cooler 610 for a second compressor 150, which is fluidly and in series thermally coupled between a fourth heat exchanger 140 and a first three-way valve 161. Specifically, the coolant outlet of the motor cooler 420 is fluidly coupled to the coolant inlet of the motor cooler 610, and the coolant outlet of the motor cooler 610 is fluidly coupled to the first three-way valve 161.

[0067] Figure 7 Draw as relative to Figure 5A variant of the system 500 described herein is a heat exchanger system 700, which has a fourth heat exchanger 140 that is fluidly coupled in parallel with the power electronics cooler 410 and the motor cooler 420 on one hand, and fluidly coupled in parallel with the motor cooler 610 of the second compressor 150 on the other hand. Specifically, the coolant flow from the coolant outlet of the fourth heat exchanger is directed, on the one hand, to the fluidly coupled parallel connection of the power electronics cooler 410 and the motor cooler 420, and on the other hand, fluidly coupled in parallel through the motor cooler 610 of the second compressor 150, and merges with the corresponding parallel-operating coolant branch at the first three-way valve 161. Here, the coolant flow between the parallel-operating coolant branches can be divided by means of the first throttling section 710 arranged in the coolant supply to the motor cooler 420 and the second throttling section 720 arranged in the coolant supply from the fourth heat exchanger 140 and the second compressor 150 motor cooler 610, so that the thermal coupling in the two coolant branches can be adjusted.

[0068] Those skilled in the art will recognize that, in addition to the topology of the heat exchanger system shown herein for operating a fuel cell stack, the teachings of this invention can also be implemented using other topologies, such as an air system with multiple compressors or other pump-valve pathways.

Claims

1. A heat exchanger system for operating a fuel cell stack (190), The heat exchanger system has: A first compressor (142) and a second compressor (150) are used to supply cathode gas to the fuel cell stack (190), wherein, The second compressor (150) is arranged after the first compressor (142) in terms of fluid flow; A turbine (155) is mechanically coupled to a second compressor (150) and the discharged cathode gas from the fuel cell stack (190) flows to the turbine; A first heat exchanger (110) is thermally coupled to the cathode gas being transported between the first compressor (142) and the second compressor (150); The second heat exchanger (120) is thermally coupled to the cathode gas being transported downstream of the second compressor (150); A fourth heat exchanger (140) 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 the second heat exchanger (120) to control the heat exchange used to cool the first heat exchanger (110) and the second heat exchanger (120). The fourth heat exchanger (140) is thermally variably coupled not only to the first heat exchanger (110) but also to the second heat exchanger (120) by means of a coolant and a first three-way valve (161) in order to cool the cathode gas before or after the second compressor (150).

2. The heat exchanger system according to claim 1, wherein the heat exchanger system has a third heat exchanger (130) thermally coupled to discharged cathode gas located in front of the turbine (155) along the fluid direction, 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 the heat exchange used to heat the third heat exchanger (130).

3. The heat exchanger system according to claim 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 transfer heat to the discharged cathode gas before the turbine (155).

4. The heat exchanger system according to claim 2, wherein, The second heat exchanger (120) is thermally coupled to the third heat exchanger (130) by means of a coolant in order to transfer heat to the discharged cathode gas before the turbine (155).

5. The heat exchanger system according to any one of claims 1 to 4, wherein the heat exchanger system has a coolant pump (165), and the thermal coupling by means of the coolant is configured to enable the flow of the coolant between the first heat exchanger to the fourth heat exchanger by means of the coolant pump (165).

6. The heat exchanger system according to claim 4, wherein the heat exchanger system has a fifth heat exchanger (170) thermally coupled to discharged cathode gas located ahead of the third heat exchanger (130) along the fluid direction, and thermally coupled to the first heat exchanger (110) to absorb heat.

7. The heat exchanger system 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. The heat exchanger system according to any one of claims 1 to 4, wherein, A thermal coupling with the cooler device is inserted between the thermal couplings of the fourth heat exchanger (140) and the first heat exchanger (110) and the second heat exchanger (120).

9. The heat exchanger system according to claim 8, wherein, The cooler device has a power electronic device cooler (410) and / or an inverter cooler and / or a motor cooler (420) and / or a converter cooler.

10. A method for controlling a heat exchanger system according to any one of claims 1 to 9, wherein, The heat exchanger system has a first temperature sensor and a second temperature sensor, wherein the first temperature sensor is arranged to measure the temperature of the cathode gas delivered before the second compressor (150), and the second temperature sensor is arranged to measure the temperature of the cathode gas discharged before the turbine (155), and controls the first three-way valve (161) and / or the second three-way valve (162) such that the temperature of the second temperature sensor is maximized and / or the temperature of the first temperature sensor is minimized.

11. An application of a heat exchanger system according to any one of claims 1 to 9 for supplying electrical energy to a mobile platform.

12. A computer program product comprising instructions that, when executed by a computer, cause the computer to perform the method according to claim 10.

13. A machine-readable storage medium on which a computer program product according to claim 12 is stored.

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