WO2022073054A1

WO2022073054A1 - Evaporator device for a fuel cell system

Info

Publication number: WO2022073054A1
Application number: PCT/AT2021/060366
Authority: WO
Inventors: David REICHHOLF; Franz KOBERG
Original assignee: Avl List Gmbh
Priority date: 2020-10-09
Filing date: 2021-10-08
Publication date: 2022-04-14
Also published as: AT524304A1; AT524304B1; DE112021003523A5

Abstract

The present invention relates to an evaporator device (10) for a fuel cell system (100), comprising: - a feed portion (20) for feeding water; - an evaporator portion (30) having a dividing device (40) for dividing the fed water from the feed portion (30) among a first evaporator line (50) having a cold heat exchanger side (KWT) of a first heat exchanger (52) and at least one second evaporator line (60) having a cold heat exchanger side (KWT) of a second heat exchanger (62); - a collecting container (70) connected, for fluid communication, to the first evaporator line (50) and to the at least one second evaporator line (60), for catching at least partially evaporated water; and - a discharge portion (80) for discharging water vapor from the collecting container (70); wherein the first heat exchanger (52) has a hot heat exchanger side (HWT) and the second heat exchanger (62) has a hot heat exchanger side (HWT) for conducting different hot process flows of the fuel cell system (100).

Description

Evaporator device for a fuel cell system

The present invention relates to an evaporator device for a fuel cell system, a fuel cell system with such an evaporator device, and a method for controlling an evaporation process using an evaporator device.

Fuel cell systems are known to provide the ability to recover energy in the system. This applies in particular to a fuel cell system in electrolysis mode, which generates heated process exhaust gases during electrolysis mode. In order to ensure heat recovery in the fuel cell system, heat exchangers are usually provided, which are able to return the waste heat in the process exhaust gases to the process. In particular, the process exhaust gases are used to preheat and/or vaporize feed gases in the fuel cell system.

A disadvantage of the known solutions is that the amount of heat required for the individual supply gases only rarely corresponds to the amount of heat contained in the exhaust gases. In some cases, the heat demand exceeds e.g. B. for evaporation of water in a feed gas, the amount of heat contained in a single process exhaust gas. As a result, even with maximum cooling of such an individual process exhaust gas, the transferred heat would not be sufficient to fully provide the required enthalpy of vaporization. In the case of known solutions, either additional post-heating is therefore necessary, or a process flow is used which is significantly hotter and/or has more heat content than is actually required. In the latter case, however, the hot process stream would be released into the environment with the corresponding residual heat, resulting in heat loss from the system.

It is the object of the present invention to at least partially eliminate the disadvantages described above. In particular, it is the object of the present invention, in a cost-effective and simple manner, to provide vaporization that saves as much energy as possible by heat recovery in a fuel cell system. The above object is achieved by an evaporator device having the features of claim 1, a fuel cell system having the features of claim 10 and a method having the features of claim 12. Further features and details of the invention result from the dependent claims, the description and the drawings . Features and details that are described in connection with the evaporator device according to the invention also apply, of course, in connection with a fuel cell system according to the invention and the method according to the invention and vice versa, so that the disclosure of the individual aspects of the invention is or can always be referred to alternately .

According to the invention, an evaporator device for a fuel cell system is provided. In order to carry out the evaporation, the evaporator device has a supply section for supplying water. Downstream of this feed section is an evaporator section with a dividing device for dividing the water supplied from the feed section to a first evaporator line with a cold heat exchanger side of a first heat exchanger and at least one second evaporator line with a cold heat exchanger side of a second heat exchanger. A collection container is also provided in fluid communication with the first evaporator branch and the at least one second evaporator branch for collecting at least partially evaporated water. Water vapor is discharged from the collection container via a discharge section. The first heat exchanger is equipped with a hot heat exchanger side and the second heat exchanger is also equipped with a hot heat exchanger side for conducting different, hot process streams of the fuel cell system. The first heat exchanger or the second heat exchanger or both heat exchangers are designed in particular as plate heat exchangers, although they can also be designed as tubular heat exchangers. Heat transfer works particularly well and efficiently with plate heat exchangers.

The fuel cell system is designed in particular as a reversibly operable fuel cell system. i.e. this can be operated both in fuel cell operation and in electrolysis operation.

According to the invention, the problem should also be solved that the highest possible proportion of waste heat from the fuel cell system in a supply medium, in in this case water vapour. Liquid water is fed to a fuel cell system in electrolysis mode and evaporates. In vaporized form, the water vapor is fed to the fuel cell stack, where it is split into hydrogen and oxygen while introducing electrical energy. This generates hydrogen and oxygen as well as heat, so that hydrogen-rich gas and oxygen-rich gas leave the fuel cell stack in a heated state. These are the two main exhaust gases of such a fuel cell system, which can also be referred to as process gases in the form of process exhaust gases or process streams. In order to use this waste heat in the process waste gases, it is fed back into the hot heat exchanger sides of the two evaporator strands of an evaporator device according to the invention.

Based on the above explanation, it can be seen that for each process stream there is at least one dedicated and separate hot heat exchanger side in a dedicated and separate heat exchanger. This makes it possible to adjust each heat exchanger in each evaporator line individually and specifically to the amount of heat present in the associated specific process stream. In other words, it is possible for the evaporation process to divide the water supplied in liquid form between the two evaporator strands via the dividing device. In this case, this division can be both fixed and variable, depending on the configuration of the evaporator device.

Depending on how it is divided, this leads to a first part of the liquid water getting into the first evaporator line and there into the cold heat exchanger side of the first heat exchanger. A second quantity of the liquid water is introduced into the cold heat exchanger side of the second heat exchanger in the second evaporator leg. In order to make the desired evaporation function available, waste heat is transferred in the respective heat exchanger by means of heat transfer from a respectively existing hot process stream of the fuel cell system. In this way, the water is heated in the respective evaporator branch and, in particular, exceeds its boiling temperature, so that the water leaves the respective heat exchanger at least partially in vapor form. The at least partially evaporated water is brought together in a common collection container and can be passed on from there via the discharge section to the fuel cell stack in gaseous form. The collection container can be connected directly to each individual evaporator line, but also are in fluid-communicating connection with a connecting section downstream of the two evaporator strands. In the simplest configuration, the collection container is a pipe section which brings the two evaporator strands together again.

As can be seen from the explanation above, a heat transfer strategy specifically optimized for this operating situation can now be made available for each evaporator branch and the specific hot process gas. If, for example, the hot process flow for the first evaporator branch is equipped with relatively less heat and the second hot process flow for the second evaporator branch is relatively hot, z. B. The amount of water in the second evaporator line can be selected to be greater than in the first evaporator line by controlled splitting. In particular, this division is carried out quantitatively, so that depending on the amount of heat present in the respective hot process stream, amounts of liquid water adapted to this amount of heat available are introduced into the respective evaporator branch.

Various advantages can thus be achieved. On the one hand, it is possible to use the amount of heat in each hot process exhaust gas as much as possible and to transfer it to the liquid water for evaporation. On the other hand, it ensures that maximum evaporation capacity is made available, ie the generation of superheated steam while liquid water remains is prevented and avoided. In particular, by controlled splitting, e.g. B. With the help of a valve device, it is therefore possible to supply the two parallel evaporator lines with water in an intelligent and adapted manner and in this way to combine and optimize the cooling strategy for the hot process exhaust gases and the evaporation strategy for evaporating the liquid water. In principle, superheated steam should be made available, but liquid water should be avoided at all costs.

Even with maximum utilization of the waste heat in the hot process gases, it can happen that this is not sufficient to evaporate the necessary amount of water for a current operating point. It is therefore possible for phase separation to take place in the collection container in order to prevent liquid water from continuing into the fuel cell stack. This remaining liquid water can either be drained or re-evaporated. Such a post-evaporation is e.g. B. possible by the liquid water is recirculated in the flow of at least one of the two heat exchangers. However, electrical post-evaporation with an additional heating device, as will be explained later, is also possible within the meaning of the present invention. In particular, forcibly guided currents can be provided, so that z. B. pumping devices and / or control devices that can be set according to run amounts of liquid or gas. An evaporator device according to the invention is used in particular in the so-called SOEC system.

The evaporator device according to the invention makes it possible, in particular, to reuse all waste heat in the system itself. This is essential for system efficiency and is beneficial, especially when there is not enough heat available to meet demand. The better the system-internal utilization of the heat, the lower the additional heat supply from the outside and thus the better the efficiency. This is achieved in particular by the invention.

There can be advantages if the dividing device in an evaporator device according to the invention has at least one control device, in particular in the form of at least one valve means, for qualitative and/or quantitative control of a distribution ratio of the water to the evaporator branches. As has already been explained in the introduction, the possibility of dividing the individual evaporator branches into specific amounts of heat according to the invention makes it possible to achieve an optimization strategy for evaporation. If a control device is provided, this can be done both qualitatively and quantitatively, so that in particular it is even possible to completely shut off an individual evaporator branch. Valve devices are preferably provided which allow quantitative control of this splitting ratio. Individual valve means directly in front of the heat exchangers are just as conceivable as multi-way valves in the dividing device. The adjustment of the required amounts of heat in the individual evaporator strands to the amounts of heat contained in the individual specific process streams in the exhaust gas brings with it the optimization option described. It should also be pointed out that the steam requirement of a fuel cell system naturally depends on its operating point. The operating point of a fuel cell system in electrolysis mode is therefore still particularly dependent on the available electrical power, which z. B. strong when connected to a regenerative energy system can vary. Thus, not only the evaporator performance but also the possibility of regulation in the case of fluctuating operating points is significantly improved by an evaporator device according to the invention in a fuel cell system.

It is also advantageous if, in an evaporator device according to the invention, the collection container has at least one additional heating device for evaporating liquid residual water in the collection container. As has also already been explained, it can happen that the total amount of heat from all the hot process streams is not sufficient to provide the required amount of steam in the gaseous phase. In such a case, liquid residual water gets into the collection container. In order to also convert this into steam and make it available to the fuel cell stack for the electrolysis, an additional heating device can be provided here, preferably directly in the collection container. This additional heating device can be switched on and can be switched on either qualitatively and/or quantitatively as required. For example, the auxiliary heating device can be an electrical auxiliary heating device. However, in principle, additional heat exchangers are also conceivable, which provide the desired evaporation function as an additional heating device via other heat sources. Furthermore, it is also possible to ensure an additional evaporation function for the residual water by water drainage and recirculation in the feed section.

There are further advantages if, in an evaporator device according to the invention, the first heat exchanger and/or the second heat exchanger are designed for countercurrent operation between the respective cold heat exchanger side and the respective hot heat exchanger side. All heat exchangers are preferably designed in countercurrent operation. The countercurrent operation allows a higher efficiency in the heat transfer, so that the advantages according to the invention can be achieved with higher efficiency. For a particularly compact design, the heat exchangers are preferably designed as plate heat exchangers. It is also advantageous if, in an evaporator device according to the invention, the feed section and/or the evaporator section are aligned with their flow direction opposite or substantially opposite to the direction of gravity. In other words, liquid water flows upwards from the feed section through the evaporator strands. This orientation does not necessarily have to be vertical, but it is sufficient if the direction of gravity is oriented at an angle, in particular at an acute angle, to the conveying direction. This leads to, that a phase separation preferably takes place automatically in the evaporator section, and correspondingly liquid water remains in the evaporator strands until it has either been conducted into the collection container by the corresponding pumping action or has been evaporated by introducing the heat from the hot process exhaust gases.

Further advantages can result if, in an evaporator device according to the invention, the first heat exchanger and the second heat exchanger are thermally separated from one another, in particular thermally insulated. Avoiding cross-transfer of heat between the heat exchangers makes it possible to reduce the need for regulation or control, so that an optimized evaporation strategy can be influenced in a simplified manner. Because undesired cross-flows of heat are avoided, simplified control is possible through completely thermally separated temperature management of the evaporator strands.

There are also advantages if at least one sensor device is arranged in an evaporator device according to the invention in the feed section, in the evaporator section, in the collection container and/or in the discharge section, in particular with sensor means for determining at least one of the following parameters:

- temperature

- Print

- flow rate

- Liquid level in the collection tank

The above list is a non-exhaustive list. It is now possible to monitor the individual parameters in the individual lines with the sensor means, so that in particular the supplied water, the supplied amount of steam, but also the hot process streams can be monitored. The parameters recorded with the help of the sensor means serve to provide an optimized control, either in a regulating or in a controlling manner. It is also advantageous if, in an evaporator device according to the invention, the heat exchangers are of identical or essentially identical design. In addition to a significant cost reduction and a reduction in the complexity of the evaporator device, a simplified control option is provided in this way. As has also already been explained, the heat exchangers are preferably plate heat exchangers. An identical or substantially identical design is to be understood in particular as a thermally identical design, in particular with regard to the heat that can be transmitted and/or the heat that can be transmitted per unit of time and/or per unit of area.

Further advantages can result if, in an evaporator device according to the invention, the discharge section is arranged at the top of the collection container with respect to the direction of gravity. In particular, this arrangement is provided above a maximum liquid level in the collection container. In this way, the collection container can also be designed as a phase separation device, so to speak, since liquid water runs through the gravity device in the direction of the bottom of the collection container and essentially only evaporated water is carried on via the discharge section in the direction of the fuel cell stack.

The subject of the present invention is also a fuel cell system comprising

- at least one fuel cell stack with a gas section and an air section,

- a gas supply section for supplying gas section supply gas to the gas section,

- an air supply section for supplying air section supply gas to the air section,

- a gas discharge section for discharging gas section exhaust gas,

- an air discharge section for discharging air section exhaust gas.

In this case, an evaporator device according to the present invention is arranged in the air supply section. In this way, a fuel cell system according to the invention brings with it the same advantages as described in detail with reference to an inventive evaporator device have been explained. Air is fed in the air section feed gas. Depending on whether it is operated as a fuel cell system or as an electrolysis system, either nitrogen in particular (fuel cell system operation) or water in particular in liquid form or in the gas section in vaporized form (electrolysis system operation) is used in the gas section. In the electrolysis operation, water vapor is thus conducted to the gas section. Hydrogen and/or hydrogen-rich gas (electrolysis operation) is available as the gas section exhaust gas and oxygen and/or oxygen-rich gas (also electrolysis operation) is available as the air section exhaust gas.

It should also be pointed out that the gas feed gas, if it contains its own quantity of heat, can of course also be used as a hot process stream in order to provide a further heat source.

In a fuel cell system according to the invention, it can be advantageous if a second control device for controlling the volume flow to a hot heat exchanger side of the first heat exchanger and/or the second heat exchanger is arranged in the gas discharge section, in the air discharge section and/or in the gas feed section. This makes it possible to adjust the amount of heat that is supplied to the respective hot heat exchanger side. If there is too much heat in the respective process stream, e.g. B. a bypass can be provided past the respective heat exchanger in order to avoid overheating of the same.

The subject of the present invention is also a method for controlling an evaporation process using an evaporator device according to the invention, having the following steps:

- monitoring a steam requirement of a fuel cell system,

- supplying liquid water by means of the supply section,

- Distribution of the supplied water to the evaporator strands,

- evaporation of the divided water by means of heat exchangers,

Collecting the at least partially evaporated water in the collection container and removing water vapor by means of the removal section. A method according to the invention thus brings with it the same advantages as have been explained in detail with reference to an evaporator device according to the invention. The aim is to produce evaporated water.

It is advantageous if, in a method according to the invention, the amount of heat available on the respective hot heat exchanger side of the respective heat exchanger is taken into account in the quantitative division of the water supplied. In this way, the amount of water supplied can be adjusted to the maximum evaporation capacity of the respective hot process stream, so that the evaporation strategy is optimized.

It is also advantageous if, in a method according to the invention, additional heating is carried out in the collection container for an insufficient amount of heat on the hot heat exchanger sides of the heat exchanger. In this way, in addition to a high liquid level in the collection tank, the desired additional heating can be switched on proactively. The aim here is to convert the complete or substantially complete amount of water supplied into the vaporous state.

Further advantages, features and details of the invention result from the following description, in which exemplary embodiments are described in detail with reference to the drawings. The features mentioned in the claims and in the description can each be essential to the invention individually or in any combination. They show schematically:

1 shows an embodiment of an evaporator device according to the invention,

2 shows a further embodiment of an evaporator device according to the invention,

3 shows a further embodiment of an evaporator device according to the invention,

4 shows a further embodiment of an evaporator device according to the invention, 5 shows a further embodiment of an evaporator device according to the invention,

FIG. 6 shows the embodiment of FIG. 5 in a side view, and

7 shows an embodiment of a fuel cell system according to the invention.

FIG. 1 schematically shows a particularly simple embodiment of an evaporator device 10. This is equipped here with two parallel evaporator branches 50 and 60, which together form the evaporator section 30. Liquid water is supplied via a supply section 20 and divided between the two evaporator strands 50 and 60 via a dividing device 40 . A control device 42 with valve means 44 is arranged in the two evaporator strands 50 and 60 in order to qualitatively and/or quantitatively regulate the amount of liquid water divided. Valve means 44 are located in front of the respective heat exchangers 52 and 62.

As can further be seen from FIG. In countercurrent operation in particular, heat from hot process waste gases is now transferred from the hot heat exchanger side HWT in the first heat exchanger 52 and in the second heat exchanger 62 to the liquid water, and this is at least partially evaporated. The evaporated parts of the supplied water are discharged here via a discharge section 80 . A common pipe section of the discharge section 80 is provided here as a collecting tank 70 for collecting the at least partially evaporated water.

FIG. 2 schematically shows an addition in which an additional heating device 72 is arranged in the discharge section 80 . Functionality is given here in the same way as has been explained with reference to FIG. Likewise as in FIG. 1, the conveying direction of the liquid water is oriented counter to a direction of gravity SR.

FIG. 3 shows that downstream of the evaporator section 30, a collecting container 70 with enlarged dimensions can also be provided, which rather it is integrated into the discharge section 80, so to speak. In such a case, in addition to bringing together the evaporated amounts of water, the collection container forms a collection option for remaining liquid water.

According to FIG. 4, an additional heating device 72, e.g. B. integrated as an additional electric heater. FIG. 4 also shows how sensor devices 90 can detect the process streams in order to determine the corresponding amount of heat for optimizing the evaporation strategy. In particular, the temperatures and/or the volume flows of the respective process flows are recorded here.

FIGS. 5 and 6 schematically show a design of such an evaporator device 10. Two parallel heat exchangers 52 and 62 are provided here, which form the first evaporator branch 50 and the second evaporator branch 60 in the evaporator section 30. The liquid water is guided against the direction of gravity SR from bottom to top, finally into a collection container 70 . In this there is an additional heating device 72 so that a post-evaporation of liquid residual water can take place in order to ensure that only or essentially only evaporated water is present at the discharge section 80 . Here, too, a control device 42 with the already explained valve means 44 is provided downstream in the feed section 20 .

FIG. 6 shows the embodiment of FIG. 5 in a lateral cross section, in which the counterflow operation from top left to bottom right for the hot process waste gases can again be clearly seen. Here, too, the reference is shown counter to the direction of gravity SR for the water to be evaporated.

FIG. 7 shows schematically how an evaporator device 10 according to the invention can be integrated into a fuel cell system 100. Here, the evaporator device 10 forms part of the air supply portion 140 . The exhaust gases of the fuel cell stack 110 and here in particular from the gas discharge section 122 and the air discharge section 142 are provided as hot process streams. The above explanations of the embodiments describe the present invention exclusively in the context of examples. It goes without saying that individual features of the embodiments can be freely combined with one another, insofar as this makes technical sense, without departing from the scope of the present invention.

Reference List

10 evaporator device

20 feeding section

30 evaporator section

40 dividing device

42 control device

44 valve means

50 first evaporator line

52 first heat exchanger

60 second evaporator line

62 second heat exchanger

70 collection bins

72 Auxiliary heater

80 discharge section

90 sensor device

100 fuel cell system

110 fuel cell stack

112 gas section

114 air section

120 gas supply section

122 gas discharge section

140 air supply section

142 air discharge section

SR gravity direction

KWT cold heat exchanger side

HWT hot heat exchanger side

Claims

Evaporator device (10) for a fuel cell system (100), having a feed section (20) for the supply of water, an evaporator section (30) with a dividing device (40) for dividing the water supplied from the feed section (30) to a first evaporator branch (50) with a cold heat exchanger side (KWT) of a first heat exchanger (52) and at least one second evaporator line (60) with a cold heat exchanger side (KWT) of a second heat exchanger (62), further having a collecting tank (70) in fluid communication with the first evaporator line (50) and the at least one second evaporator line (60) for collecting at least partially evaporated water and a discharge section (80) for discharging water vapor from the collection container (70), the first heat exchanger (52) having a hot heat exchanger side (HWT ) and the second heat exchanger (62) have a hot heat exchanger side (HWT) for the Fü management of different, hot process streams of the fuel cell system (100). Evaporator device (10) according to Claim 1, characterized in that the dividing device (40) has at least one control device (42), in particular in the form of a valve means (44), for qualitative and/or quantitative control of a distribution ratio of the water to the evaporator branches (50, 60).

3. Evaporator device (10) according to one of the preceding claims, characterized in that the collecting container (70) has at least one additional heating device (72) for evaporating liquid residual water in the collecting container (70). Evaporator device (10) according to one of the preceding claims, characterized in that the first heat exchanger (52) and/or the second heat exchanger (62) are designed for countercurrent operation between the respective cold heat exchanger side (KWT) and the respective hot heat exchanger side (HWT). . Evaporator device (10) according to one of the preceding claims, characterized in that the feed section (20) and/or the evaporator section (30) are aligned with their flow direction counter to or essentially counter to the direction of gravity (SR). Evaporator device (10) according to one of the preceding claims, characterized in that the first heat exchanger (52) and the second heat exchanger (62) are thermally separated from one another, in particular thermally insulated. Evaporator device (10) according to one of the preceding claims, characterized in that at least one sensor device (90) is arranged in the feed section (20), in the evaporator section (30), in the collection container (70) and/or in the discharge section (80), in particular with Sensor means for determining at least one of the following parameters:

- temperature

- Print

- flow rate

- Liquid level in the collection container (70) evaporator device (10) according to any one of the preceding claims, characterized in that the heat exchangers (52, 62) are of identical or substantially identical design. Evaporator device (10) according to one of the preceding claims, characterized in that the discharge section (80) is arranged at the top of the collection container (70) with respect to the direction of gravity (SR). fuel cell system (100), comprising

- at least one fuel cell stack (110) with a gas section (112) and an air section (114), a gas supply section (120) for supplying gas section feed gas to the gas section (112), 17 an air supply section (140) for supplying air section supply gas to the air section (114),

- a gas discharge section (122) for discharging gas section exhaust gas,

- an air discharge section (142) for discharging air section exhaust gas, wherein an evaporator device (10) having the features of one of claims 1 to 9 is arranged in the air supply section. Fuel cell system (100) according to Claim 10, characterized in that in the gas discharge section (122), in the air discharge section (142) and/or in the gas supply section (120) there is a second control device for controlling the volume flow to a respective hot heat exchanger side (HWT) of the first heat exchanger (52) and/or the second heat exchanger (62) is arranged. Method for controlling an evaporation process by means of an evaporator device (10) having the features of one of claims 1 to 9, having the following steps:

- monitoring a steam requirement of a fuel cell system (100),

- supplying liquid water by means of the supply section (20),

- Dividing the supplied water to the evaporator strands (50, 60),

- evaporating the divided water by means of the heat exchangers (52, 62),

- Collecting the at least partially evaporated water in the collection container (70) and

- Draining of water vapor by means of the discharge section (80). Method according to Claim 12, characterized in that the amount of heat available on the respective hot heat exchanger side (HWT) of the respective heat exchanger (52, 62) is taken into account in the quantitative division of the water supplied. 18 The method according to any one of claims 12 or 13, characterized in that for an insufficient amount of heat on the hot heat exchanger sides (HWT) of the heat exchanger (52, 62) an additional heating in the collector (70) is carried out.