GB2407432A

GB2407432A - Fuel cell having a heating and /or cooling circuit

Info

Publication number: GB2407432A
Application number: GB0423601A
Authority: GB
Inventors: Gesine Arends; Peter Riegger
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2003-10-24
Filing date: 2004-10-22
Publication date: 2005-04-27
Anticipated expiration: 2024-10-22
Also published as: JP2005129537A; GB0423601D0; GB2407432B; DE10349630A1

Abstract

The present invention relates to a fuel cell having an internal heating and/or cooling circuit that is coupled thermally to an external heating and/or cooling circuit, characterized in that, to regulate the internal heating-medium and/or coolant flow flowing through the fuel cell (1), a bypass valve (5) is fitted in order, optionally, to activate a bypass line (27) that extends in parallel to the internal coolant flow for at least a portion of the coolant flow.

Description

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"Fuel cell having a heating and/or cooling circuit" The invention relates to a fuel cell having a heating and/or cooling circuit according to the preamble of the independent Claim 1.

Prior art:

Fuel cells or, alternatively, fuel-cell modules are used, inter alla, for power-heat coupling systems (PHC systems).

In regard to the fuel cell or the fuel-cell module, no distinction is made below between whether reference is to a single fuel cell or to a fuel-cell module, in which one or more fuel cells are interconnected that are wired together in any desired way. The term 'fuel cell' will be used quite generally below.

Power-heat coupling systems are designed in such a way that they inject both the electrical energy and the heat produced in the generation of the electrical energy into a respective system. An attempt is made to operate the fuel cell with an electrical efficiency that is as good as possible and to inject the waste heat accumulating under these conditions into the system.

To achieve as good as possible an efficiency for the fuel cell, the latter must be operated at a certain operating temperature that is as constant as possible. The operating temperature depends on the type of fuel cell.

Polymer/electrolyte-membrane cells (PEN cells) are currently typically operated at 80 C to 90 C.

In this connection, the fuel cell or the fuel-cell module is preferably constructed in such a way that cooling devices through which a coolant flow can flow are fitted around one or more fuel cells and, optionally, also between them. In principle, the fuel cell can also be cooled with gaseous media, for example air, in order to take up the waste heat produced in the fuel cell and remove it from the fuel cell or the fuelcell module. Suitable connections for entry into the fuel cell and from the fuel cell are provided for this purpose.

According to the electrical power required from the fuel cell, which may be subject to fluctuations, it therefore produces more or less waste heat as a function thereof. As a result, it is necessary to provide suitable measures for regulating the operating temperature of the fuel cell. Such a measure for regulating the cooling circuit of a fuel cell is to be found, for example, in US 6,087,028. In this case, a cooler disposed in a cooling circuit for the fuel cell is cooled by a fan and the heat is removed to the outside. The fan is activated by means of an intelligent circuit.

Such a device can regulate a fuel cell to in a certain operating range. However, owing to fluctuating regulating parameters, deviations from the optimum operating temperature repeatedly occur in this connection. In particular, problems arise in regard to establishing an optimum operating temperature for the fuel cell if fluctuating external temperatures have additionally to be taken into account. Viewed over a seasonal pattern, for example, this may be from -20 C to +35 or +40 C or even more.

With such fluctuations in the external temperatures, the efficiency of the fuel cell suffers enormously and the cost efficiency of the fuel cell decreases accordingly.

Object of the invention The object of the present invention is therefore to describe a fuel cell with a heating and/or cooling circuit in which better control and/or regulation of the operating temperature of the fuel cell is possible.

This object is achieved by the technical teaching of Claim 1.

The measures mentioned in the subclaims make possible advantageous designs and developments of the invention.

Accordingly, the fuel cell according to the invention is outstanding in that it is equipped with a heating and/or cooling circuit that is coupled thermally to an external heating and/or cooling circuit and in that, to regulate the internal heating-medium and/or coolant flow flowing through the fuel cell, a bypass valve is fitted in order, optionally, to activate a bypass line that extends in parallel to the internal coolant flow for at least a portion of the coolant flow.

As accurate as possible a regulation of the temperature difference between the inlet and the outlet of the heating medium and/or coolant flow through the fuel cell can thereby be achieved. Consequently, the operating temperature of the fuel cell can be regulated in a range independent of the external heating/cooling circuit in such a way that as good as possible an efficiency can be ensured for it.

In a first embodiment, provision can now be made that a control and/or regulating unit is fitted that is dependent on the heating and/or cooling requirement of the fuel cell and that, to regulate the heating-medium and/or coolant flow passing through the cell, acts on the bypass valve.

A suitable control and/or regulating unit makes it possible to regulate the bypass valve depending on the operating point of the fuel cell and the state of the external heating/cooling cirpit. That is to say, depending on how much electrical energy is drawn from the fuel cell, it heats up and the bypass valve can be adjusted by a control and/or regulating unit according to this increasing heating so that as optimum as possible a temperature difference can thereby be established between entry and exit of the heating-medium and/or coolant flow through the fuel cell.

In addition, provision is preferably made in a development that the control and/or regulating unit for the bypass valve for operating the fuel cell is constructed in such a way that an optimum temperature difference is produced between inlet and outlet of the heating-medium and/or coolant flow passing through said fuel cell in order to achieve a high efficiency.

In a further embodiment of the present invention, provision may be made that the control and/or regulating unit for the bypass valve for operating the fuel cell is constructed in such a way that a temperature difference that is independent of fluctuating external temperature conditions is produced between inlet and outlet of the heating-medium and/or coolant flow passing through the fuel cell.

An improvement can thereby additionally be achieved in the efficiency of the fuel cell, with the result that it can be operated in its optimum operating range regardless of the external heating/cooling circuit, for example, both in summer and in winter.

In addition, a pump can also preferably be provided for pumping the heating-medium and/or coolant flow in the heating and/or cooling circuit. The heating-medium and/or coolant flow can be circulated substantially better by said pump.

In a particular embodiment, provision can additionally be made that, by means of said pump or by means of a second pump, pumping of the heatingmedium or coolant flow is provided in the short-circuit mode of the fuel cell for the purpose of rapidly heating it to take the optimum temperature difference into account. This makes it possible, for example, for the waste heat accumulating during the generation of electrical energy in the start-up mode of the fuel cell to be used for the further preheating of the fuel cell itself, as uniform as possible a temperature distribution being effected in the fuel cell as a result of the circulation of the heating-medium and/or coolant flow. This again produces an optimum temperature difference between inlet and outlet of the heating-medium and/or coolant flow passing through the fuel cell.

In a further embodiment, provision can be made that a heat exchanger is provided in the heating and/or cooling circuit for coupling the heat flow out into the external heating and/or cooling circuit. In an embodiment improved with respect thereto, provision may be made that a heat exchanger is provided for coupling a heat flow in from the external heating and/or cooling circuit. This makes it possible, for example, to bring the fuel cell rapidly to its operating temperature in the start-up mode by externally supplied heat, with the result that the efficiency of the fuel cell or of the fuel-cell module is again thereby improved.

In addition, provision may, for example, be made that heat is drawn from an external heating system or that heat is drawn from a heat exchanger optionally externally present in order to bring the fuel cell to its optimum operating temperature as rapidly as possible. In addition, provision may be made that one or optionally even more pumps may again additionally be provided in the external heating and/or cooling circuit. Likewise, provision may also be made that a burner or an equivalent device for generating heat is provided in said external heating and/or cooling circuit.

Optionally, further heating and/or cooling bodies by means of which the waste heat delivered during the operation of the fuel cell can be expediently used may be disposed in said external heating and/or cooling circuit.

In an embodiment improved with respect thereto, provision may be made that a heat exchanger is provided for coupling a heat flow from a line for the anode residual gas of the fuel cell into its heating and/or cooling circuit. This additionally makes it possible to improve the efficiency of the entire system.

In a further embodiment, it is possible in turn that a heat exchanger is provided for coupling a heat flow from a line for the waste air of the fuel cell into its heating and/or cooling circuit. This may also improve the efficiency of the PHC system accordingly.

In order to achieve a still better efficiency of the PHC system, provision may be made in a further embodiment additionally improved with respect thereto that a heat exchanger is provided for coupling in a heat flow from a gas- or fuel-processing device in the heating and/or cooling circuit of the fuel cell. The residual heat produced in processing the gas or the fuel may thereby be utilized to improve the efficiency of the HPC system further.

In such an embodiment, provision may, for example, be made that a gas or fuel supply is provided from a gas- or fuel- processing device disposed upstream of the fuel cell. A compact fuel-cell device can thereby be achieved, for example, that has upstream gas or fuel processing and that additionally makes possible an improvement in the efficiency of the entire system by the utilization of its waste heat.

In relation to the arrangement of the bypass valve, it is stated at this point that it can be disposed both upstream and downstream of the fuel cell. The sole decisive factor is the conveyance of the heating-medium and/or coolant flow parallel to the heating-medium and/or coolant flow flowing through the fuel cell itself so that, depending on requirements, between 100% and 0% of the heating-medium and/or coolant flow through the fuel cell or, correspondingly, between 0% and 100% can be fed past it in parallel.

That is to say, during the warm-up mode of the fuel cell, the entire heating-medium and/or coolant flow is preferably passed through the fuel cell in order to bring it as quickly and uniformly as possible to its operating temperature. If heat is now additionally introduced from further, above-cited heat sources, for example a heat exchanger that introduces a heat flow from a gas- or fuel- processing device connected upstream of the fuel cell into the heating and/or cooling circuit, a portion of the heating-medium and/or coolant flow can be fed in parallel past the fuel cell, with the result that the latter continues to have a temperature difference, suitable for its optimum operating temperature, between inlet and outlet for the heating- medium and/or coolant flow fed through the fuel cell.

In addition, provision may also be made, for example, that delivery of at least one of the pumps can be regulated. The volumetric flow through the fuel cell or, alternatively, past it per unit time can consequently be modified.

In general, all the possible heat sources that are suitable for improving the efficiency of the PHC system may be used for coupling-in. The bypass valve and, optionally, the volumetric flow of the heating-medium and/or coolant flow is then to be adjusted in accordance with the supply of additional heat from such additional heat sources in order to achieve an optimum temperature difference for the fuel cell.

In regard to the control and/or regulating unit, provision may, for example, be made that a characteristic diagram control dependent on the temperature and/or on the state of the external heating/cooling circuit and/or on temperature parameters of additional heat sources control the flow of the heating-medium and/or coolant flow through the heating and/or cooling circuit and/or through the cooling device of the fuel cell.

Furthermore, the operating temperature of the fuel cell itself, the inlet and the outlet temperature of the fuel cell and also, optionally, the volumetric flow of the heating-medium and/or coolant flow may, for example, be taken into account. Such a case may then involve regulation of the heating-medium and/or coolant flow. It goes without saying that the valve position of the bypass valve may also be taken into account for the regulation of the heating- medium and/or coolant flow through the fuel cell. In addition, a thermostat-controlled bypass valve, for example, may also be used.

Exemplary embodiment: An exemplary embodiment of the invention is shown in the drawing and is explained in greater detail below by reference to the figure shown.

The accompanying figure shows an exemplary structure of a fuel cell with a heating and/or cooling circuit.

The accompanying figure shows a fuel cell 1 having a heating and/or cooling circuit 2 that is thermally coupled to an external heating and/or cooling circuit 4 by means of a heat exchanger 3. Provided in parallel with the heating medium and/or coolant flow flowing through the fuel cell 1 is a line 27 that determines the proportion of the heating- medium and/or coolant flow flowing through the fuel cell 1 by means of a bypass valve 5.

Depending on the adjustment of the bypass valve 5, between 0% and 100% of the heating-medium and/or coolant flow may flow through the fuel cell 1 or, in the converse case, between 100% and 0% may flow through the line 27 routed in parallel to the fuel cell 1.

To deliver the waste heat produced during the generation of electrical energy to the external heating and/or cooling circuit 4, the heat exchanger 4 is situated in the heating and/or cooling circuit 2. Further heat exchangers 8, 29, 30 may now be introduced into said heating and/or cooling circuit 2. These three heat exchangers are shown in a broken-line representation, i.e. they are fitted optionally.

In this connection, the heat exchanger 8 is coupled to a gas- or fuelprocessing device 9 provided in a preferred design. The waste heat produced therein may be coupled into the heating and/or cooling circuit 2 via the heat exchanger 8. Said heat can be fed past the fuel cell 1 by means of the bypass valve 5 if the fuel cell 1 were to exceed its optimum operating temperature with the supply of this amount of heat. Equally, increasing the volumetric flow per unit time by increasing the delivery of the pump 6 would be possible in order to pass more heat through the heating and/or cooling circuit 2.

The lines 24, 25 and 26 describe the heating and/or cooling circuit 2 for the fuel cell 1. Provided in parallel with the fuel cell 1 is now a line 27 that branches off at the node 23 and is routed to the bypass valve 5 so that the heating-medium and/or coolant flow flowing through said line can be fed past the fuel cell 1.

In a particular embodiment, provision can now be made that a further line 34 that is routed from the node 32 in the line 26 to the node 33 in line 25 is provided in addition to said line 27 and, consequently, also to the coolant flow flowing through the fuel cell 1. Incorporated in said line 34 is then a pump 31 that, in the start-up mode for the fuel cell 1, effects a short circuit for the heating- medium and/or coolant flow of the fuel cell in order to make possible as rapid and uniform as possible a warm-up of the fuel cell 1.

The optionally fitted gas- or fuel-processing device 9 is equipped with a gas or fuel supply line 18, an air or oxygen supply line 19 and optionally a water supply line 20. Via the gas or fuel supply line 21, gas or fuel can be fed to the connection 10 and the line, connected thereto, for the gas or fuel supply 13 of the fuel cell 1.

Air or oxygen for the fuel cell 1 can be fed to the line 12 via the connection 22.

The waste air from the fuel cell 1 can be collected via the line 14 and fed to the optionally fitted heat exchanger 30 for the purpose of utilizing the waste heat. The anode residual gas can be collected via the line 15 and fed to an optionally fitted heat exchanger 29, likewise for the purpose of injecting the residual heat present therein. The further conveyance of the anode residual gas and the waste air out of the heat exchanger is shown here only by an arrow direction. A coupling-in in the external heating circuit 4 is likewise expedient so that better utilization of the heat of condensation can be achieved.

To induce the heating-medium and/or coolant flow to flow in the heating or cooling circuit 2, a pump 6 is incorporated between the lines 24 and 25. Depending on the position of the bypass valve 5, said pump 6 pumps the heating-medium and/or coolant flow completely or only partly through the cooling device in the fuel cell 1 in order to cool it.

Given an appropriate setting of the bypass valve 5, however, it can also be fed in parallel past the fuel cell 1 into the heat exchanger 3 and from the latter conveyed into the line 26.

In a particular embodiment of the invention, provision is made in this connection that the delivery of the pump 6 can be regulated.

The electrical energy generated by the fuel cell 1 can be tapped off via the electrical connections 16 and 17.

In addition to the external heating and/or cooling circuit, the external heating and/or cooling device 7 is also shown.

The latter is connected to the heat exchanger 3 via the lines 28. In this connection, continuous lines show the flow direction of said heatingmedium and/or coolant flow.

The arrows shown in a broken-line representation show the reverse direction of said heating-medium and/or coolant flow, which reverse direction is provided for the case where external preheating of the fuel cell 1 is to take place. In the external heating and/or cooling device, symbols are also shown that indicate a pump, a reservoir, a burner, a valve and a heating body by way of example for further possible components of an external heating and/or cooling device.

Claims

Patent claims: 1. Fuel cell having an internal heating and/or cooling

circuit that is coupled thermally to an external heating and/or cooling circuit, characterized in that, to regulate the internal heating-medium and/or coolant flow flowing through the fuel cell (1), a bypass valve (5) is fitted in order, optionally, to activate a bypass line (27) that extends in parallel to the internal coolant flow for at least a portion of the coolant flow.
2. Fuel cell according to Claim 1, characterized in that a control and/or regulating unit is fitted that is dependent on the heating and/or cooling requirement of the fuel cell (1) and that, to regulate the heating medium and/or coolant flow passing through the cell, acts on the bypass valve (5) .
3. Fuel cell according to Claim 1 or 2, characterized in that the control and/or regulating unit for the bypass valve (5) for operating the fuel cell (1) is constructed in such a way that an optimum temperature difference is produced between inlet and outlet of the heating-medium and/or coolant flow passing through said fuel cell.
4. Fuel cell according to any one of Claims 1 to 3, characterized in that the control and/or regulating unit for the bypass valve (5) for operating the fuel cell (1) is constructed in such a way that a temperature difference that is independent of fluctuating external temperature conditions is produced between inlet and outlet of the heating medium and/or coolant flow passing through the fuel cell (1).
5. Fuel cell according to any one of Claims 1 to 4, characterized in that a pump (6) is provided for pumping the heating-medium and/or coolant flow in the heating and/or cooling circuit (2).
6. Fuel cell according to any one of Claims 1 to 5, characterized in that a pump (31) is provided for pumping the heating-medium and/or coolant flow in the short-circuit mode of the fuel cell (1) for the purpose of rapidly heating it to take the optimum temperature difference into account.
7. Fuel cell according to any one of Claims 1 to 6, characterized in that a heat exchanger (3) is provided in the heating and/or cooling circuit (2) for coupling the heat flow out into the external heating and/or cooling circuit (4).
8. Fuel cell according to any one of Claims 1 to 7, characterized in that a heat exchanger (3) is provided in the heating and/or cooling circuit (2) for coupling a heat flow in from the external heating and/or cooling circuit (4).
9. Fuel cell according to any one of Claims 1 to 8, characterized in that a heat exchanger (29) is provided for coupling a heat flow from a line (15) for the anode residual gas of the fuel cell (1) into its heating and/or cooling circuit (2).
10. Fuel cell according to any one of Claims 1 to 9, characterized in that a heat exchanger (30) is provided for coupling in a heat flow from a line (14) for the waste air of the fuel cell (1) into its heating and/or cooling circuit (2).
11. Fuel cell according to any one of Claims 1 to 10, characterized in that a heat exchanger (8) is provided for coupling in a heat flow from a gas- or fuel processing device (9) in the heating and/or cooling circuit (2) of the fuel cell (1).
12. Fuel cell according to any one of Claims 1 to 11, characterized in that a gas or fuel feed (21) is provided from a gas- or fuel-processing device (9) disposed upstream of the fuel cell (1).
13. A fuel cell substantially as herein described with reference to the accompanying drawing.