DE102009006159A1 - Control / regulation of a temperature of a fuel cell - Google Patents

Abstract

A method for providing electrical energy by means of a fuel cell (12) comprises the following steps: - charging an anode (8) of the fuel cell (12) with a fuel gas stream (60); Pressurizing a cathode (4) of the fuel cell (12) with an oxidant stream (50; producing a burner exhaust stream (58) by means of a burner (22); and pressurizing the cathode with the burner exhaust stream (58) Provision of electrical energy comprises a fuel cell (12) having an anode (8) and a cathode (4) The plant (10) further comprises a burner (22) for generating a burner exhaust stream (58) and allows the cathode to be charged with the burner exhaust stream (58).

Description

The The invention relates to a method for providing electrical Energy by means of a fuel cell, with the following steps: Pressurizing an anode of the fuel cell with a fuel gas stream and charging a cathode of the fuel cell with an oxidizing gas stream. The The invention further relates to a system for providing electrical Energy, with a fuel cell, an anode and a cathode having.

A Fuel cell usually has a certain operating temperature. If the temperature of the fuel cell is below the operating temperature, so is either no power generation or only a limited Power generation possible, or the efficiency of the fuel cell is not optimal. The operating temperature of a solid oxide fuel cell (SOFC, Solid Oxide Fuel Cell), for example, at about 850 ° C. lie. To reach the operating temperature, it is common the fuel cell or the entire system in which the fuel cell is embedded, heat up. The fuel cell can, for example embedded in a fuel cell stack. Is the operating temperature achieved, so the fuel cell generated by the reaction of Oxidizer (typically air) and fuel gas in addition to electrical energy in general also enough thermal energy to their Temperature above the operating temperature.

From the DE 10 2007 019 359 A1 a method for starting a fuel cell system is known in which a fuel cell cathode gas is supplied, which is preheated before entering the fuel cell by burner exhaust gas of a residual gas burner.

It The object of the invention is an energy-saving and / or fast Method for heating a fuel cell, in particular a Solid oxide fuel cell, to be specified. It is still the task of Invention to provide a system for implementing the method. These The object is achieved by the features of the independent claims solved. Developments and advantageous embodiments result from the dependent claims.

• – Erzeugen eines Brennerabgasstroms mittels eines Brenners; und
• – Beaufschlagen der Kathode mit dem Brennerabgasstrom.

The method according to the invention builds on the generic state of the art in that it further comprises the following steps:

• - generating a burner exhaust stream by means of a burner; and
• - Applying the cathode with the burner exhaust gas stream.

The Burner exhaust produced by the burner thus enters direct physical Contact with the cathode of the fuel cell. A heat exchanger between the cathode and the burner exhaust stream is not necessarily provided. The cathode can thus be heated faster, and it is too expect their temperature to change faster the temperature or a flow rate of the burner exhaust gas flow than in the case where the cathode is only indirectly, viz a heat exchanger, with the burner exhaust gas in thermal contact stands. It is not excluded that while applying the cathode with the burner exhaust stream at the same time with the cathode other gases is applied, or that the burner exhaust gas stream contained in a larger stream. Especially it is possible that the burner exhaust stream with the oxidizer stream is mixed upstream of the cathode.

It can be provided that a first Oxidatorstrom in a second Oxidator and a third Oxidatorstrom is divided, wherein the second Oxidatorstrom the cathode is supplied and the third oxidizer stream is fed to the burner. A regulation or controlling a heating or cooling of the fuel cell can thus via a regulation or control of the flow rate between the second oxidant stream and the third oxidizer stream respectively. It may be advantageous that a throughput of the first oxidizer current remains constant. A supply to the cathode with the oxidizer thus correlates with a supply of the burner with the oxidizer.

In particular, it can be provided that, during a first operating phase, a throughput of the third oxidizer flow is greater than a flow rate of the second oxidizer flow, and in a later second operating phase the flow rate of the second oxidizer flow is greater than the flow rate of the third oxidizer flow. The sum of the flow rate of the second oxidizer stream and the flow rate of the third oxidizer stream can remain constant. In the first operating phase, a heating of the fuel cell can take place. During the heating phase, and in particular at the beginning of the heating phase, when a temperature of the fuel cell is below the operating temperature, a large heating power can thus be made available, while at the same time avoiding supplying the cathode with the oxidizer not yet needed. The second operating phase may be a stationary operating phase. The stationary operating phase is characterized in that a temperature of the fuel cell is equal to the operating temperature or above the operating temperature. If the heat development of the fuel cell is sufficient to maintain the operating temperature, then the flow rate of the third oxidizer stream can be zero. On the other hand, if it is insufficient, the fuel cell must also be heated during stationary operation of the fuel cell. However, it is also in In this case, it is to be expected that the throughput of the third oxidizer flow necessary for providing the required heating power is significantly lower than the throughput of the second oxidator flow suitable for stationary operation of the fuel cell.

One Ratio of a flow rate of the second Oxidatorstroms for example, to a flow rate of the third Oxidatorstroms be controlled or regulated by means of a three-way valve. It understands itself, that in this case the three-way valve the first Oxidatorstrom into the second oxidizer stream and the third oxidizer stream.

Of the second oxidant stream and leaving the cathode exhaust stream can be passed through a common heat exchanger become. The second oxidizer stream can thus pass through the cathode leaving the exhaust stream to be preheated. The the cathode exiting exhaust stream, for example, does not flow past the cathode burned oxidizer gas and possibly from the cathode contained gas.

• – Vorgeben einer Mindesttemperatur T_min;
• – Messen einer Ist-Temperatur T_ist des zweiten Oxidatorstroms stromabwärts des Wärmetauschers; wenn die gemessene Ist-Temperatur T_ist niedriger als die Mindesttemperatur T_min ist, Erhöhen eines Durchsatzes des dritten Oxidatorstroms.

The method may further include the following steps:

• - Specifying a minimum temperature T _min ;
• - measuring an actual temperature T _is of the second oxidant stream downstream of the heat exchanger; if the measured actual temperature T _{ist is} lower than the minimum temperature T _min , increasing a flow rate of the third oxidant stream.

The minimum temperature can be below or above the operating temperature. Advantageously, the minimum temperature is below the operating temperature of the fuel cell when the fuel cell generates more heat than needed to maintain the operating temperature. Advantageously, the minimum temperature is above the operating temperature if the fuel cell produces less heat than would be needed to maintain the operating temperature. The actual temperature T _ist can be measured in the second oxidizer stream immediately downstream of the heat exchanger. Alternatively, however, it can also be measured directly in front of an inlet of the cathode, through which the second oxidizer stream alone or possibly mixed with another stream enters the cathode.

It may be advantageous, the second Oxidatorstrom downstream of the heat exchanger to merge with the burner exhaust gas stream. The resulting combined stream can then directly the cathode be supplied.

It can be provided that a temperature T _{burner exhaust gas of} the burner exhaust gas flow and / or a _{burner exhaust gas} flow rate I of the _burner exhaust gas flow are controlled or regulated such that an absolute value | dT _BSZ / dt | a time rate of change dT _BSZ / dt a temperature T _{BSZ of} the fuel cell does not exceed a predetermined first maximum value. Too rapid changes in the temperature of the fuel cell, whether during heating or cooling, can thus be avoided.

It is also possible that a flow rate I _{52 of} the third oxidizer flow is controlled or regulated such that an absolute value | dT _burner exhaust _gas / dt | a temporal rate of change of the temperature T _burner exhaust gas burner exhaust gas flow does not exceed a predetermined second maximum value. As a result, too rapid changes in the temperature of the fuel cell can be avoided.

It can further be provided that a fuel flow is supplied to the burner and a flow rate I _{54 of} the fuel flow is controlled or controlled in dependence on a flow rate I _{52 of} the third oxidizer flow. A supply of fuel to the burner can thus be adapted to the amount of oxidizer available to the burner per unit of time. Advantageously, the fuel used is such a fuel, during the combustion of which no or only a few soot particles are formed. For example, methane or natural gas can be used as the fuel. Depending on the embodiment, it is not absolutely necessary to measure the flow rate I _{52 of} the third oxidizer stream. For example, the flow rate I _{54 of} the fuel flow may also be regulated in response to a flow rate I _{48 of} the first oxidizer flow and / or a corresponding speed of a blower for generating the first oxidizer flow and / or a position of the flow divider (that is, the flow split ratio of the flow divider). to be controlled. For this purpose it can be provided that a control unit, for example an electronic control unit, can access a look-up table (LUT). For example, the LUT may indicate the flow rate I _{52 of} the third oxidizer flow as a function of the speed of the fan and / or the position of the flow divider.

The inventive system is based on the generic State of the art in that the system is a burner for Producing a burner exhaust gas stream and for a Charging the cathode with the burner exhaust gas flow suitable or is provided. A heat exchanger for transmission Heat from the burner exhaust gas to the cathode can thus be saved.

• – einen Stromteiler zum Teilen eines ersten Oxidatorstroms in einen zweiten Oxidatorstrom und einen dritten Oxidatorstrom;
• – eine zweite Oxidatorleitung zum Führen des zweiten Oxidatorstroms an die Kathode; und
• – eine dritte Oxidatorleitung zum Führen des dritten Oxidatorstroms an den Brenner.

The system can also have:

• A flow divider for dividing a first oxidizer stream into a second oxidizer stream and a third oxidizer stream;
• A second oxidizer line for guiding the second oxidant stream to the cathode; and
• A third oxidizer line for guiding the third oxidizer flow to the burner.

the Flow divider can be a conveyor unit, for example a blower, be upstream for sucking the first oxidizer.

advantageously, a current division ratio of the current divider is controllable. A flow rate ratio of the second oxidant stream to third Oxidatorstrom can thus be adjusted.

It can be further provided that the system has a heat exchanger for producing a thermal contact between an exhaust gas flow of Having cathode and the second Oxidatorstrom. The second oxidizer stream can thus be preheated by waste heat of the fuel cell become.

the Burner can use a soot filter to remove soot particles be downstream. This way may possibly be in the Burner exhaust gas soot particles from the burner exhaust gas be filtered out. A deposit of soot on the cathode can thus be avoided.

The The invention will now be described with reference to the accompanying drawings exemplified. In this case, denote or similar Reference signs the same or similar components. Such Components become at least partial to avoid repetition explained only once.

It demonstrate:

1 a schematic circuit diagram of a system according to the invention;

2 a flowchart of a method according to the invention.

In the 1 schematically illustrated attachment 10 includes a fuel cell 12 , a burner 22 , designed as a three-way valve flow divider 30 and a heat exchanger 38 , The fuel cell 12 may be a solid oxide fuel cell. It can be component of a fuel cell stack. The fuel cell 12 includes a cathode 4 , a membrane 6 and an anode 8th , which together form a membrane electrode assembly (MEA, Membrane Electrode Assembly). During operation of the fuel cell can between the cathode 4 and the anode 8th an electrical voltage can be tapped. The fuel cell 12 has a first entrance 14 on, over the cathode 4 an oxidizer, for example air or another oxygen-containing gas mixture, is supplied. The cathode 4 has an exit 16 on, over the unburned oxidizer and possibly discharged from the cathode gas is discharged. The anode 8th has an entrance 18 for receiving fuel gas 60 as well as an exit 20 for the delivery of anode exhaust gas 62 on. The anode exhaust gas 62 contains unburned fuel gas and any gas separated from the anode. The burner 22 has a first entrance 24 for receiving an oxidizer and a second input 26 for receiving a fuel. The burner 22 has an exit 28 for dispensing a burner exhaust gas. The burner exhaust gas is produced in the burner 22 when burning the burner 22 supplied fuel with the oxidizer. The oxidizer becomes the burner 22 in the form of an oxidizer stream 52 (Third Oxidatorstrom) supplied. The fuel becomes the burner 22 in the form of a fuel stream 54 fed. The burner exhaust gas is from the burner 22 in the form of an exhaust stream 58 in the direction of the fuel cell 12 continued.

The cathode 4 and the burner 22 are supplied with oxidizer as follows. A first oxidizer stream 48 is through the flow divider 30 in a second oxidizer stream 50 and the third oxidizer stream 52 divided. The third oxidizer stream 52 becomes immediately the entrance 24 of the burner 22 fed. The second oxidizer stream 50 becomes the entrance 14 the cathode 4 fed to a junction 56 with the burner exhaust stream 58 is merged. The from the second Oxidatorstrom 50 and the burner exhaust stream 58 existing combined electricity 66 meets a surface of the cathode 4 and is guided along this surface. From the surface of the cathode 4 unabsorbed gas and possibly from the surface of the cathode 4 separated gas leaves the fuel cell 12 over the exit 16 in the form of a cathode exhaust stream 64 , The cathode exhaust stream 64 enters through an entrance 40 of the heat exchanger 38 in the heat exchanger 38 and leaves him via an exit 42 , The heat exchanger transfers 38 Heat from the cathode exhaust stream 64 on the second Oxidatorstrom 50 , The second oxidizer stream 50 enters the heat exchanger 38 over an entrance 44 and leaves the heat exchanger 38 via an exit 46 , With regard to the flow direction of the second oxidizer stream 50 is the heat exchanger 38 upstream of the junction 56 at which the second Oxidatorstrom 50 and the burner exhaust stream 58 unite. The exit 28 of the burner 22 may be downstream of a soot filter, the burner exhaust gas flow 58 at least partially exempted from any soot particles present. The current division ratio of the current divider 30 that is, the ratio of the flow rate of the second oxidizer stream 50 to the flow rate of the third Oxida torstroms 52 , is adjustable. In particular, the current split ratio can be set so that the first oxidant stream 48 completely through the exit 34 of the flow divider 30 occurs. In this case, the third oxidizer current disappears 52 , and in the Brenner 22 then no combustion takes place. The current division ratio of the current divider 30 can also be adjusted so that the first Oxidatorstrom 48 completely through the second exit 36 of the flow divider 30 occurs. In this case, the second oxidizer current disappears 50 , For controlling the current dividing ratio of the current divider 30 an electronic control unit is provided (not shown).

During a start phase (first operating phase), the fuel cell is initially "cold", ie its temperature is below its operating temperature. By controlling the flow rate of the first oxidant stream 48 and the current dividing ratio of the current divider 30 , possibly in combination with fuel flow rate control 54 , the flow rate and the temperature of the burner exhaust gas flow 58 controlled. To make sure the fuel cell 12 is not damaged by excessive temperature changes, the control / control of the first Oxidatorstroms takes place 48 and the current dividing ratio of the current divider 30 such that the time rate of change of a temperature (the temperature increase per unit time) of the burner exhaust stream 58 does not exceed a predetermined maximum value. It may be particularly advantageous that the temperature of the burner exhaust stream 58 increases linearly. For measuring the temperature of the burner exhaust gas flow 58 can within the burner exhaust stream 58 a temperature sensor may be arranged. The startup phase is completed as soon as the temperature of the second oxidant stream 50 between the exit 46 of the heat exchanger 38 and the Association Office 56 exceeds a predetermined minimum value. Alternatively, the starting phase may also be defined as being completed when a temperature of the cathode exhaust gas flow 64 exceeds a predetermined minimum value. The respective predetermined minimum value can, depending on the embodiment of the system 10 and in particular the fuel cell 12 above or below the operating temperature of the fuel cell 12 lie.

In summary, it can be stated that the temperature of the fuel cell 12 can regulate / control by specifying a target temperature or a permitted temperature interval for a temperature of the cathode exhaust stream 64 between the exit 16 and the entrance 40 , and / or by presetting a desired temperature or an allowed temperature interval for a temperature of the second oxidant stream 50 between the exit 46 and the entrance 14 , During steady state operation, the fuel flow may 54 be turned off. Even then, by controlling the flow rate of the third oxidant stream 52 a temperature of the cathode 4 be controlled / controlled.

The flowchart in 2 FIG. 12 illustrates a method for controlling a temperature of the fuel cell explained with reference to FIG 12 , In a first step S1, an actual temperature T _ist of the cathode 4 supplied united stream 66 certainly. In the following step S2, it is determined whether the thus determined actual temperature falls below a predetermined minimum temperature T _min . If this is the case, then the current division ratio of the current divider 30 in favor of the third oxidizer stream 52 and at the expense of the second oxidizer stream 50 changed, that is, the flow rate of the third Oxidatorstroms 42 is increased while the flow rate of the second oxidizer stream 50 is reduced by the corresponding amount. The power of the burner 22 is increased (step S3). After step S3, the process returns to S1. However, if it was determined in step S2 that the measured temperature T _ist does not fall below the minimum temperature T _min , it is examined in step S 4 whether the actual temperature T _ist exceeds a predefined maximum temperature T _max . If this is the case, then in step S5, the current division ratio of the current divider 30 in favor of the second oxidizer stream 50 and at the expense of the third oxidizer stream 52 changed. The process then returns to step 51 back. Will in step 54 when the detected temperature T _ist does not exceed the predetermined temperature T _max , the process returns directly to step S1.

The in the above description, in the drawings and in the Claims disclosed features of the invention can both individually and in any combination for the To be essential to the realization of the invention.

4

cathode

6

membrane

8th

anode

10

investment

12

fuel cell

14

entrance

16

output

18

entrance

20

output

22

burner

24

entrance

26

entrance

28

output

30

current divider

32

entrance

34

output

36

output

38

heat exchangers

40

entrance

42

entrance

44

entrance

46

output

48

oxidant

50

oxidant

52

oxidant

54

fuel flow

56

association office

58

Burner exhaust stream

60

Fuel gas stream

62

Anode exhaust stream

64

Cathode exhaust stream

66

united electricity

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 102007019359 A1 [0003]

Claims (15)

Method for providing electrical energy by means of a fuel cell ( 12 ), comprising the following steps: - applying an anode ( 8th ) of the fuel cell ( 12 ) with a fuel gas stream ( 60 ); and - applying a cathode ( 4 ) of the fuel cell ( 12 ) with an oxidizer stream ( 50 ); characterized in that the method further comprises the steps of: - generating a burner exhaust gas stream ( 58 ) by means of a burner ( 22 ); and - charging the cathode ( 4 ) with the burner exhaust stream ( 58 ). Method according to claim 1, characterized in that a first oxidizer stream ( 48 ) into a second oxidizer stream ( 50 ) and a third oxidizer stream ( 52 ), the second oxidant stream ( 50 ) the cathode ( 4 ) and the third oxidizer stream ( 52 ) the burner ( 22 ) is supplied. A method according to claim 2, characterized in that during a first phase of operation, a flow rate of the third Oxidatorstroms ( 52 ) is greater than a flow rate of the second oxidizer stream ( 50 ) and that in a later second phase of operation, the flow rate of the second oxidizer stream ( 50 ) is greater than the flow rate of the third oxidizer stream ( 52 ). A method according to claim 2, characterized in that a ratio of a flow rate of the second Oxidatorstroms ( 50 ) to a flow rate of the third oxidizer stream ( 52 ) by means of a three-way valve ( 30 ) is controlled or regulated. Process according to claim 2, characterized in that the second oxidant stream ( 50 ) and a cathode ( 4 ) leaving exhaust stream ( 64 ) by a common heat exchanger ( 38 ). A method according to claim 5, characterized in that it further comprises the following steps: - Specifying a minimum temperature T _min ; Measuring an actual temperature T _is the second oxidizer current ( 50 ) downstream of the heat exchanger ( 38 ); If the measured actual temperature T _{ist is} lower than the minimum temperature T _min , increasing a flow rate of the third oxidant stream ( 52 ). Process according to claim 5, characterized in that the second oxidizer stream ( 50 ) downstream of the heat exchanger ( 38 ) with the burner exhaust stream ( 58 ) is merged. A method according to claim 1, characterized in that a temperature T _{burner exhaust gas of} the burner exhaust stream ( 58 ) and / or a flow rate I _{burner exhaust gas of} the burner exhaust gas flow ( 58 ) are controlled or regulated such that an absolute value | dT _BSZ / dt | a time rate of change dT _BSZ / dt a temperature T _{BSZ of} the fuel cell ( 12 ) does not exceed a predetermined first maximum value. Process according to claim 1, characterized in that a flow rate I _{52 of} the third oxidizer stream ( 52 ) is controlled or regulated such that an absolute value | dT _burner exhaust _gas / dt | a time rate of change of the temperature T _{burner exhaust gas of} the burner exhaust stream ( 58 ) does not exceed a predetermined second maximum value. Method according to claim 1, characterized in that the burner ( 22 ) a fuel stream ( 54 ) and a flow rate I _{54 of} the fuel stream ( 54 ) in response to a flow rate I _{52 of} the third oxidizer stream ( 52 ) is regulated or controlled. Investment ( 10 ) for providing electrical energy, with a fuel cell ( 12 ), which is an anode ( 8th ) and a cathode ( 4 ), characterized in that the plant ( 10 ) a burner ( 22 ) for generating a burner exhaust stream ( 58 ) and for applying the cathode ( 4 ) with the burner exhaust stream ( 58 ) is suitable or intended. Installation according to claim 11, characterized in that it further comprises: - a flow divider ( 30 ) for dividing a first oxidizer stream ( 48 ) into a second oxidizer stream ( 50 ) and a third oxidizer stream ( 52 ); A second oxidizer line for guiding the second oxidizer stream ( 50 ) to the cathode ( 4 ); and a third oxidizer line for guiding the third oxidant stream ( 52 ) to the burner ( 22 ). Plant according to claim 12, characterized in that a current sharing ratio of the current divider ( 30 ) is controllable. Plant according to claim 12, characterized in that it comprises a heat exchanger ( 38 ) for establishing a thermal contact between an exhaust gas flow ( 64 ) the cathode ( 4 ) and the second oxidizer stream ( 50 ) having. Plant according to claim 11, characterized in that the burner ( 22 ) is a soot filter for removing soot particles downstream.