FUEL CELL SYSTEM, AND METHOD OF ITS OPERATION

Abstract

A fuel cell system having a fuel cell cooling circuit coupled to a battery cooling circuit through a coolant/coolant heat exchanger for removing heat from the fuel cell cooling circuit through the battery cooling circuit during normal steady state operation of the fuel cell system.

Claims

1.-22. (canceled)

23. A method for operating a fuel cell system, the fuel cell system comprising a fuel cell, the fuel cell having a steady state temperature TFC during steady state normal operation after startup; a fuel cell cooling circuit with fuel cell coolant for cooling the fuel cell, the fuel cell cooling circuit being configured for maintaining the steady state temperature TFC of the fuel cell during the steady state normal operation after startup; a battery, the battery having a steady state temperature TBat during the steady state normal operation after startup; wherein TBat is lower than TFC; a battery cooling circuit with battery coolant for cooling the battery, wherein the battery cooling circuit comprises a thermal-energy-remover for removing thermal energy from the battery coolant for maintaining the steady state temperature TBat of the battery during steady state normal operation after startup; wherein the battery cooling circuit and the battery coolant are separate from the fuel cell cooling circuit and the fuel cell coolant; a coolant/coolant heat exchanger thermally coupling the fuel cell cooling circuit with the battery cooling circuit for heat transfer from the fuel cell coolant to the battery coolant, the coolant/coolant heat exchanger comprising a first flow area and a second flow area with a heat conducting separation wall in between, wherein the first flow area is flow-connected to the fuel cell cooling circuit for flow of coolant there through, and wherein the second flow area is flow-connected to the battery cooling circuit for flow of battery coolant there through; characterized in that the method comprises maintaining the steady state temperature TFC of the fuel cell by removing thermal energy from the fuel cell by transfer of thermal energy from the fuel cell coolant to the battery coolant through the coolant/coolant heat exchanger continuously during normal operation after startup and removing the thermal energy from the battery coolant by the thermal-energy-remover for maintaining TBat in the battery.

24. The method according to claim 23, wherein the thermal-energy-remover is located in the battery cooling circuit downstream of the coolant/coolant heat exchanger and upstream of the battery and in flow direction between the coolant/coolant heat exchanger and the battery for cooling down the battery coolant down-stream of the coolant/coolant heat exchanger by the thermal-energy-remover before the battery coolant enters the battery when in operation, wherein the method comprises, during steady state operation of the fuel cell system, during a cooling cycle of the battery coolant in the battery cooling circuit, transferring thermal energy from the battery to the battery coolant for maintaining the steady state temperature TBat in the battery, subsequently transferring further thermal energy from the fuel cell coolant to the battery coolant in the coolant/coolant heat exchanger, and then removing the thermal energy that has been taken up by the battery coolant from the battery and from the fuel cell coolant by using the thermal-energy-remover to reach a cooling temperature Tcool of the battery coolant before the battery coolant with the cooling temperature Tcool enters the battery again, wherein the cooling temperature Tcool is lower than TBat in order for the coolant to take up thermal energy from the battery.

25. The method according to claim 24, wherein Tcool is at least 5 degrees lower than TBat.

26. The method according to claim 24, wherein the thermal-energy-remover comprises or consists of a radiator heat exchanger for removal of thermal energy from the battery coolant by the radiator heat exchanger with ambient air flow through the radiator heat exchanger; wherein the method comprises maintaining the steady state temperature TFC of the fuel cell by removing sufficient thermal energy from the fuel cell cooling circuit to the battery cooling circuit and by release of thermal energy from the battery cooling circuit through the radiator heat exchanger of the battery cooling circuit.

27. The method according to claim 26, wherein only the battery cooling circuit but not the fuel cell cooling circuit comprises a radiator heat exchanger for removal of thermal energy from the battery coolant by the radiator heat exchanger with ambient air.

28. The method according to claim 23, wherein TFC is in the range of 120° C. to 200° C., for example in the range of 160 to 185° C., and TBat is in the range of 25° C.-60° C.

29. The method according to claim 23, wherein the fuel cell cooling circuit comprises a fuel cell coolant pump for pumping the fuel cell coolant through the fuel cell cooling circuit; wherein the fuel cell cooling circuit comprises a main circuit (2A) and a side branch (2B), wherein the main circuit comprises serial flow in the following order: from the fuel cell coolant pump to a split point, from the split point to the fuel cell, from the fuel cell to a merge point, from the merge point to the fuel cell coolant pump; wherein the side branch (2B) comprises flow in series in the following order: from the split point to the coolant/coolant heat exchanger and from the coolant/coolant heat exchanger to the merge point; wherein the method comprises splitting the fuel cell coolant into two portions at the split point with a first portion through the fuel cell and second portion through the coolant/coolant heat exchanger.

30. The method according to claim 29, wherein the fuel cell system comprises a controller for controlling the operation of the fuel cell system, including the temperature of the fuel cell, wherein the side branch (2B) comprises an adjustment valve that is functionally connected to the controller, wherein the adjustment valve is without shutoff capability and only adjustable between a maximum flow level and a minimum flow level through the adjustment valve and through the side branch (2B), wherein the minimum flow level is only larger than zero, and wherein the method comprises adjusting the flow between the minimum and maximum flow level automatically by the adjustment valve under control by the controller as a measure for controlling the temperature Tmain of the fuel cell coolant in the main circuit (2A) and the steady state fuel cell temperature TFC.

31. The method according to claim 30, wherein Tmain is in the range of 10-20 degrees lower than TFC.

32. The method according to claim 29, wherein the first portion is less than 50% of the second portion.

33. The method according to claim 23, wherein the fuel cell system comprises a fuel evaporator for evaporating fuel, wherein the fuel evaporator is thermally coupled to the fuel cell cooling circuit at a location in the fuel cell cooling circuit downstream of the fuel cell but upstream of the coolant/coolant heat exchanger for utilizing the region in the fuel cell cooling circuit with the highest temperature region; and wherein the method comprises reducing the temperature of the fuel cell coolant flowing from the fuel cell by flow through the evaporator first and subsequently reducing the temperature further by subsequent flow through in the coolant/coolant heat exchanger.

34. The method according to claim 29, wherein the fuel cell system comprises a fuel evaporator for evaporating fuel, wherein the fuel evaporator is thermally coupled to the fuel cell cooling circuit at a location in the fuel cell cooling circuit downstream of the fuel cell but upstream of the coolant/coolant heat exchanger for utilizing the region in the fuel cell cooling circuit with the highest temperature region; and wherein the method comprises reducing the temperature of the fuel cell coolant flowing from the fuel cell by flow through the evaporator first and subsequently reducing the temperature further by subsequent flow through in the coolant/coolant heat exchanger; wherein the fuel evaporator is thermally coupled to the fuel cell cooling circuit at a location in the fuel cell cooling circuit between the fuel cell and the merge point, downstream of the fuel cell but upstream of the merge point; wherein the method comprises, reducing the temperature of the fuel cell coolant downstream of the fuel cell by heat ex-change with the evaporator prior to mixing the coolant from the fuel cell with the coolant from the coolant/coolant heat exchanger at the merge point.

35. A fuel cell system comprising a fuel cell; a fuel cell cooling circuit with fuel cell coolant for cooling the fuel cell; a battery; a battery cooling circuit with battery coolant for cooling the battery, wherein the battery cooling circuit comprises a thermal-energy-remover for removing thermal energy from the battery coolant; wherein the battery cooling circuit and the battery coolant are separate from the fuel cell cooling circuit and the fuel cell coolant; a coolant/coolant heat exchanger thermally coupling the fuel cell cooling circuit with the battery cooling circuit for heat transfer from the fuel cell coolant to the battery coolant, the coolant/coolant heat exchanger comprising a first flow area and a second flow area with a heat conducting separation wall in between, wherein the first flow area is flow-connected to the fuel cell cooling circuit for flow of coolant there through, and wherein the second flow area is flow-connected to the battery cooling circuit for flow of battery coolant there through; characterized in that the thermal-energy-remover comprises or consists of a radiator heat exchanger for removal of thermal energy from the battery coolant by heat exchange with ambient air flow through the radiator heat exchanger, wherein the fuel cell system is configured for maintaining the steady state temperature TFC of the fuel cell by removing sufficient thermal energy from the fuel cell cooling circuit to the battery cooling circuit and by releasing thermal energy from the battery cooling circuit through the radiator heat exchanger of the battery cooling circuit, wherein only the battery cooling circuit but not the fuel cell cooling circuit comprises a radiator heat exchanger for removal of thermal energy from the battery coolant by heat exchange with ambient air.

36. The fuel cell system according to claim 35, wherein the thermal-energy-remover is located in the battery cooling circuit downstream of the coolant/coolant heat exchanger and upstream of the battery and in flow direction between the coolant/coolant heat exchanger and the battery for cooling down the battery coolant downstream of the coolant/coolant heat exchanger by the thermal-energy-remover before the battery coolant enters the battery when in operation, wherein the fuel cell system is configured for, during steady state operation of the fuel cell system, during a cooling cycle of the battery coolant in the battery cooling circuit, transferring thermal energy from the battery to the battery coolant for maintaining the steady state temperature TBat in the battery, subsequently transfer-ring further thermal energy from the fuel cell coolant to the battery coolant in the coolant/coolant heat exchanger, and then removing the thermal energy that has been taken up by the battery coolant from the battery and from the fuel cell coolant by using the thermal-energy-remover to reach a cooling temperature Tcool of the battery coolant before the battery coolant with the cooling temperature Tcool enters the battery again, wherein the cooling temperature Tcool is lower than TBat in order for the coolant to take up thermal energy from the battery.

37. The fuel cell system according to claim 35, wherein the fuel cell cooling circuit comprises a fuel cell coolant pump for pumping the fuel cell coolant through the fuel cell cooling circuit; wherein the fuel cell cooling circuit comprises a main circuit (2A) and a side branch (2B); wherein the main circuit (2A) comprises serial flow during operation in the following order: from the fuel cell coolant pump to a split point, from the split point to the fuel cell, from the fuel cell to a merge point, from the merge point to the fuel cell coolant pump; wherein the side branch (2B) comprises flow during operation in series in the following order: from the split point to the coolant/coolant heat exchanger and from the coolant/coolant heat exchanger to the merge point; wherein the fuel cell system is configured for splitting the fuel cell coolant into two portions at the split point with a first portion through the fuel cell and second portion through the coolant/coolant heat exchanger, wherein the first portion is less than 50% of the second portion.

38. The fuel cell system according to claim 37, wherein the fuel cell system comprises a controller for controlling the operation of the fuel cell system, including the temperature of the fuel cell, wherein the side branch (2B) comprises an adjustment valve that is functionally connected to the controller, wherein the adjustment valve is without shutoff capability and only adjustable between a maximum flow level and a minimum flow level through the adjustment valve and through the side branch (2B), wherein the minimum flow level is only larger than zero, and wherein the system is configured for adjusting the flow between the minimum and maximum flow level automatically by the adjustment valve under control by the controller as a measure for controlling the temperature Tmain of the fuel cell coolant in the main circuit (2A) and the steady state fuel cell temperature TFC.

39. The fuel cell system according to 35, wherein the fuel cell system comprises a fuel evaporator for evaporating fuel, wherein the fuel evaporator is thermally coupled to the fuel cell cooling circuit at a location in the fuel cell cooling circuit downstream of the fuel cell but upstream of the coolant/coolant heat exchanger for utilizing the region in the fuel cell cooling circuit with the highest temperature region and for flow of the fuel cell coolant through the evaporator first and subsequently flow through the coolant/coolant heat exchanger and transfer of thermal energy from the fuel cell coolant to the battery coolant.

40. The fuel cell system according to claim 38, wherein the fuel cell system comprises a fuel evaporator for evaporating fuel, wherein the fuel evaporator is thermally coupled to the fuel cell cooling circuit at a location in the fuel cell cooling circuit downstream of the fuel cell but upstream of the coolant/coolant heat exchanger for utilizing the region in the fuel cell cooling circuit with the highest temperature region and for flow of the fuel cell coolant through the evaporator first and subsequently flow through the coolant/coolant heat exchanger and transfer of thermal energy from the fuel cell coolant to the battery coolant; wherein the fuel evaporator is thermally coupled to the fuel cell cooling circuit at a location in the fuel cell cooling circuit between the fuel cell and the merge point, downstream of the fuel cell but upstream of the merge point for reducing the temperature of the fuel cell coolant flowing from the fuel cell by flow through the evaporator first and subsequently reducing the temperature further by subsequent flow through the coolant/coolant heat exchanger at the merge point.

41. The fuel cell system according to claim 35, wherein the system comprises at least one further components in the battery cooling circuit for cooling the component by the battery coolant, the further components including at least one of an air compressor for compressing air as oxygen supply for the fuel cell, and an electrical converter for converting electrical direct current from the fuel cell to an alternating current or to a direct current with a different voltage.

Description

SHORT DESCRIPTION OF THE DRAWINGS

[0037] The invention will be explained in more detail with reference to the drawing, where

[0038] FIG. 1 illustrates an embodiment of a cooling circuit principle

[0039] FIG. 2 illustrates an alternative cooling circuit arrangement.

DETAILED DESCRIPTION / PREFERRED EMBODIMENT

[0040] FIG. 1 illustrates a diagram of a cooling circuit 2 for a fuel cell system 1 in which only some of the components of the fuel cell system 1 are illustrated for convenience and easy overview. The fuel cell cooling circuit 2 is thermally connected to a battery cooling circuit 3 through a coolant/coolant heat exchanger 4. The fuel cell cooling circuit 2 comprises a main circuit 2A, which is show by thick arrows and lines, where the fuel cell coolant flows from the fuel cell coolant pump 5 through the fuel cell 6 and then back to the fuel cell coolant pump 5. The fuel cell cooling circuit 2 also comprises a side branch 2B that divides off the main circuit 2A at a split point 7 downstream of the fuel cell coolant pump 5 at a flow location between the fuel cell coolant pump 5 and the coolant inlet 8 of the fuel cell 6. The fuel cell coolant in the side branch 2B flows through a flow adjustment valve 9, through the coolant/coolant heat exchanger 4 and back to a merging point 10 where the fuel cell coolant from the main circuit 2A and the fuel cell coolant from the side branch 2B merge. The merging point 8 is located upstream of the pump 5 and downstream of the fuel cell at a flow location between the fuel cell 6 and the fuel cell coolant pump 5.

[0041] Optionally, an evaporator 11 for evaporation of fuel, for example a mix of methanol and water, is located downstream of the fuel cell 6, between the fuel cell 6 and the merging point 10, which is in the region of the main circuit 2A where the temperature of the fuel cell coolant is highest and evaporation most efficient.

[0042] The thinner arrows in the side branch 2B illustrate the lower flow of coolant in the side branch 2B relatively to the main flow in the main circuit 2A. For example, at the split point 7, only a relative amount in the range of 5% to 30% of the flow is divided off the main circuit 2A.

[0043] In the battery cooling circuit 3, battery coolant flows through the coolant/coolant heat exchanger 4, advantageously in a counterflow direction relatively to the flow of the fuel cell coolant, as a counterflow configuration yields the highest efficacy for heat exchange. A battery coolant pump 12 pumps the battery coolant serially through the coolant/coolant heat exchanger 4, radiator heat exchanger 13, and the battery 14 before the battery coolant returns to the battery coolant pump 12. The radiator heat exchanger 13 is located upstream of the battery 14 at a location between the heat exchanger 4 and the battery 14 in order for removing heat from the battery coolant, after the battery coolant has taken up heat from both the battery 14 and form the fuel cell coolant in the coolant/coolant heat exchanger 4. The battery coolant pump 12 could be located elsewhere in the battery cooling circuit 3.

[0044] At the coolant exit of the fuel cell 6, the fuel cell coolant has the operation temperature T.sub.FC of the fuel cell, for example 175° C. It is pointed out that the temperature is an approximative value in the case of a fuel cell stack, as the temperature in a fuel cell stack may vary a few degrees from one end to the other due to the coolant being heated up gradually through the fuel cell stack.

[0045] If an evaporator 11 is included in the fuel cell cooling circuit 2, the temperature of the FC coolant is lowered respectively by the evaporator 11, which takes up thermal energy from the fuel cell coolant, resulting in a temperature T.sub.Main for the fuel cell coolant in the main circuit 2A upstream of the merge point 10. The side branch provides cooled fuel cell coolant from the heat exchanger 4 at a temperature T.sub.Hex, for example in the range of 50° C. to 80° C., optionally in the range of 50° C. to 70° C.

[0046] The fuel cell coolant flows from the side branch 2B and the main circuit 2A are mixed at the merge point 10, resulting in the fuel cell coolant having a temperature T.sub.Mix, which is between T.sub.Main and T.sub.Hex, for example in the range 150° C. to 170° C., such as around 160° C.

[0047] Examples of temperatures as indicated in FIG. 1 are as follows:

[0048] TFC: 120° C. to 200° C., for example in the range of 160 to 185° C.;

[0049] T.sub.Mix: Typically 10-20 degrees lower than T.sub.FC;

[0050] T.sub.Main: 120° C. to 200° C., for example in the range of 150 to 185° C., depending on whether an evaporator is located downstream of the FC, upstream of the merge point;

[0051] T.sub.Hex: Typically 10-40 degrees above T.sub.Bat, for example 50° C.-70° C.

[0052] T.sub.Bat: 25° C.-60° C.

[0053] T.sub.cool: 20° C.-50° C., depending on the air temperature and the necessary cooling temperature of the battery.

[0054] As the fuel cell system 1 typically comprises a controller 15 for controlling the operation of the fuel cell system 1, including the temperature of the fuel cell 6, the adjustment valve 9 is advantageously functionally connected to the controller 15.

[0055] The illustrated configuration has some peculiarities: [0056] The temperature T.sub.Mix of the fuel cell coolant is the same at the inflow 8 to the fuel cell 6 and at the inflow to the coolant/coolant heat exchanger 4. [0057] The main circuit 2A and the side branch 2B are arranged in parallel, being split downstream of the pump 5 and merge again upstream of the pump 5. [0058] There is no radiator in the fuel cell cooling circuit 2 but only in the battery cooling circuit 3, implying that the heat is removed from the fuel cell cooling circuit 2 only by the battery cooling circuit 3.

[0059] During startup, the coolant/coolant heat exchanger 4 is used for heating up the battery, which is implicit, as the heat is transferred from the fuel cell cooling circuit 2 to the battery cooling circuit 3.

[0060] In some embodiments, in order to safeguard that there is always cooling performance present, the valve 9 may be configured for flow adjustment between a minimum value and a maximum value, where the minimum value is higher than zero. In other words, in this embodiment, the adjustment valve 9 cannot be fully closed. This implies that the adjustment valve 9 can be made relatively simple and light weight without the necessity of being tight with respect to flow through the adjustment valve 9. This reduces costs for the circuit. The fact that such valve would always be open implies no drawback, as a flow through the coolant/coolant heat exchanger 4 is desired not only during normal operation where the battery cooling circuit 3 is used to remove heat from the fuel cell cooling circuit 2, but also in upstart phases, where the heat from the fuel cell 6 is useful for heating the battery 14 quickly to the best operational temperature.

[0061] Although, the singular terms of fuel cell and battery and other components have been used in general, it also includes more than one thereof. For example, it is typical that more than one battery is used in such systems, and more than one fuel cell, namely rather a fuel cell stack.

[0062] FIG. 2 illustrates an alternative embodiment in which the battery cooling circuit 3 comprises further components. Exemplified as components are a compressor 19 used for pumping air into the system for the fuel cell and an electrical converter 16, for example a DC/DC converter for converting the DC power from the fuel cell 6 to the correct voltage for the power consuming components, for example the electrical motors of a vehicle for the propulsion, and/or a DC/AC converter for providing the correct electrical power for the compressor 19.

[0063] For example, the temperature of the battery coolant just downstream of the coolant/coolant heat exchanger 4 is around 60° C. This temperature increases by thermal energy transfer from the compressor to T.sub.comp, for example to a temperature T.sub.comp 10-30 degrees higher than the temperature of the battery coolant just downstream of the coolant/coolant heat exchanger 4, and is then cooled down by the radiator heat exchanger 13 to T.sub.Cool, for example in the range 20-50° C., however, depending on the outside temperature and the operational temperature T.sub.Bat of the battery. The battery heats the battery coolant to a higher temperature T.sub.Bat, depending on the optimum operation temperature of the battery 14. Prior to entering the coolant/coolant heat exchanger 4 again, some thermal energy is removed from the converter 16, which heats the battery coolant additionally.

[0064] Notice that the position of the pump 12 in the battery cooling circuit 3 is not necessarily as indicated, as the pump 12 can also be installed at other positions in the battery cooling circuit 3.

[0065] In order to adjust the battery temperature, a battery bypass 18 is optionally provided, typically with an adjustment valve 17 in the bypass in order to adjust the flow level of the battery coolant through the battery 14. This gives a further degree of freedom to adjust the temperature for the battery relatively to the other components in the battery coolant circuit 3, such as the converter 16 and the compressor 19.

REFERENCE NUMBERS

[0066] 1 fuel cell system

[0067] 2 fuel cell cooling circuit

[0068] 2A main circuit of the fuel cell cooling circuit 1

[0069] 2B side branch of the fuel cell cooling circuit 1

[0070] 3 battery cooling circuit

[0071] 4 coolant/coolant heat

[0072] 5 fuel cell coolant pump

[0073] 6 fuel cell

[0074] 7 split point

[0075] 8 coolant entrance of fuel cell 6

[0076] 9 flow adjustment valve

[0077] 10 merging point

[0078] 11 evaporator

[0079] 12 battery coolant pump

[0080] 13 radiator heat exchanger

[0081] 14 battery

[0082] 15 controller

[0083] 16 converter 17 adjustment valve

[0084] 18 battery bypass

[0085] 19 compressor