JPH0514457Y2 - - Google Patents

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention relates to a cooling structure for a high voltage fuel cell stack, particularly a liquid-cooled fuel cell.

[Prior art and its problems]

For example, in the case of a phosphoric acid fuel cell, a fuel cell and a cell stack are composed of a matrix supporting a phosphoric acid electrolyte, a positive electrode and a negative electrode having gas diffusivity arranged closely on both sides of this matrix, and a fuel cell at each of the positive and negative electrodes. A structure in which a large number of cells consisting of gas and separation plates with grooves for supplying gas and oxidizing gas are stacked, and a predetermined tightening load is applied to the stacked surfaces to enhance electrical contact between the stacked surfaces, thereby connecting the cells in cascade. DC power is generated by an electrochemical reaction by flowing a reactive gas through the cell stack. At this time, waste heat is generated as a byproduct of the electrochemical reaction, so it is necessary to provide a cooler in the cell stack to remove the waste heat and maintain the cell stack at a temperature suitable for the chemical reaction.

FIG. 4 is a schematic diagram showing the cooling structure of a conventional liquid-cooled fuel cell stack. In the figure,
Reference numeral 1 denotes a cell stack consisting of a stack of a large number of single cells 2. Each time a predetermined number of single cells are stacked, a conductive cooling plate 3 made of graphite or carbon plate is interposed between the single cells. Cooling pipes 4 are inserted into each of the plurality of grooves or holes formed in the cooling plate 3,
A plurality of cooling pipes 4 serve as supply side liquid guiding means 5 for guiding the cooling liquid.
and the collecting side liquid guiding means 6 via a pipe joint (not shown). Also, the liquid guiding means 5 and 6
are both made of metal tubes, one end of which is 5A.
and 6A are connected to a cooling liquid circulation and cooling device (not shown) to supply the cooling liquid 9 to each cooling pipe 4, and the liquid guiding means is grounded and held at ground potential. Further, both terminals 7A and 7B of the cell stack 1 are connected to the output circuit 10, and the low voltage side terminal 7B is grounded.

In the liquid-cooled fuel cell stack configured as described above, since the cooling pipe 4, the liquid guide means, and one terminal 7B of the cell stack are both grounded, the cooling plate 3 interposed between the cells A potential difference is generated between the cooling pipe 4 and the high-voltage side terminal 7A, and the potential difference increases as it approaches the high-voltage side terminal 7A, and in a high-voltage, large-capacity cell stack, the maximum potential difference may reach several thousand volts. In the case of FIG. 4, the insulation that maintains this potential difference relies on the insulation coating 8 deposited on the surface of each cooling pipe 4, and naturally the cooling pipe located closer to the high voltage terminal 7A is thicker. Requires insulation coating, e.g. output voltage 4000V
In the case of the cell stack, the thickness of the insulation coating 8 is 0.5 mm.
It also becomes before and after. Therefore, the cooling performance decreases because the thick insulation coating 8 with low thermal conductivity is interposed between the cooling plate 3 made of a good thermal conductor and the cooling pipe 4, and if the insulation coating thickness is adjusted to match the potential difference, A problem arises in that the cooling performance differs depending on the position, which affects the conversion efficiency of the fuel cell. Furthermore, if dielectric breakdown occurs at even one point between the insulation coating and the cooling plate, a portion of the cell stack will become short-circuited. For example, Japanese Patent Publication No. 58-33670 is known as a device that has improved the above-mentioned problems.

FIG. 5 is a conceptual diagram of the cooling structure of a liquid-cooled fuel cell stack disclosed in Japanese Patent Publication No. 58-33670. In the figure, the cell stack is divided into a plurality of stacked bodies 1A, 1B, 1C, etc., and each stacked body has a separating plate 13A, which has a plurality of cooling pipe insertion grooves,
13B, 13C, a cooler 14 in which a plurality of cooling tubes each having an insulating coating inserted into each insertion groove are interconnected at both ends, and a plurality of coolers 14A,
14B and 14C are provided with an inlet space 15 and an outlet space 16 that communicate with each other via a dielectric wall 18, and the spaces 15 and 16 have a potential at one end of each laminate, for example, the high voltage end 7A for the laminate 1A. The potential of feed line 1
9. The inlet space 15 and the outlet space 16 are connected to a cooling water supply line 25 and a collection line 26, respectively, which are at ground potential via a dielectric partition wall 28, and are configured to circulate cooling water to the cooler 14. . In this way, by applying the potential at one end of the stacked body to the spaces 15 and 16 and providing the insulating partition wall 18 between each cooler, the coolers 14A and 14B in each stacked body 1A, 1B, and 1C are , 14C is maintained mainly by the dielectric partition wall 18, so that the potential difference between the cooling plate 13 and the cooler 14 can be made sufficiently small. Therefore, the insulation coating of the cooling tube can be made extremely thin to the extent that electrochemical corrosion of the cooling tube is prevented, and exhaust heat from the fuel cell can be efficiently removed. however,
In such a configuration, each laminate 1A, 1B, 1C
The inlet and outlet spaces 15, 1 are provided with a potential at one end of each stack due to the supply and collection lines 25 and 26 that circulate the cooling liquid being grounded.
6 is borne by the dielectric partition wall 28 and the coolant inside it, and in a high voltage fuel cell, a potential difference of several thousand volts is borne by the dielectric partition wall 28
8 will be applied. This potential difference generally reaches several to ten times the potential difference borne by the dielectric barrier ribs 18. Furthermore, since the inner diameter of the dielectric partition wall 28 is larger than the inner diameter of the dielectric partition wall 18, the magnitude of the current leaking to the ground via the cooling liquid in the dielectric partition wall 28 reaches a size that cannot be ignored, and the insulation of this part There is a problem that the reliability of moreover,
In the device configured as shown in FIG. 5, there are many dielectric partitions 18, 28, so if we assume that an insulated hose is used as the dielectric partition, cooling at the connection between the insulated hose and the metal pipe is There are problems in that special care is required to prevent liquid leakage, and the amount of leakage inspection and maintenance work increases.

[Purpose of invention]

This idea was created in view of the above-mentioned situation.
It is an object of the present invention to provide a liquid-cooled fuel cell stack having a small potential difference between a cooling plate and a cooling pipe and a potential difference applied to an insulating hose, high insulation reliability, and leakage current prevention performance.

[Key points of the idea]

In order to achieve the above object, the present invention includes a conductive cooling plate which is composed of a stack of a plurality of unit cells and has a plurality of cooling pipe insertion portions interposed between the unit cells for each predetermined number of unit cells; A cooler formed by connecting a plurality of cooling pipes with insulating coatings inserted into the insertion portion in parallel with each other at both ends, and a supply side and a collection side liquid conduit that communicate with this cooler and an external coolant circulation device. A cell stack comprising means 50 and 51, a cooler set 34 divided into a plurality of sets in the stacking direction of the cell stack, and a cooler set 34 arranged in parallel on the inlet side and outlet side of each cooler in each cooler set, respectively. A pair of intra-group liquid conduit pipe parts 35 and 36, connecting pipes 41 and 42, and inter-group liquid conduit pipe parts 45 and 4 are connected to each other.
The cooling unit 30 includes a plurality of cooling units 30 consisting of
The inter-assembly liquid guide pipe sections 45 and 46 communicate with each other in the stacking direction of the cell stacks, and are connected to the connecting pipes 4 and 46 respectively to the intra-assembly liquid guide pipe sections 35 and 36 of each cooling unit.
1 and 42, the cooling unit 30
The supply side and collection side liquid guide means 50 and 51 are connected in cascade between each of the inter-set liquid guide pipe sections 45 and 46 and between the inter-set liquid guide pipe sections 45C and 46C of the lowermost cooling unit of the cell stack on the low voltage side. It has a connecting insulating tube 48 and a cooling tube conductively connected to one of the cooling plates 33B located approximately in the middle of the unit cell stack in the portion where each of the cooling units is disposed. do.

That is, in the liquid-cooled fuel cell stack of the present invention, the plurality of cooling plates and coolers interposed between the cells are divided into N groups in the stacking direction of the cells, and by having the above structure, the same group can be separated. The potential difference between the cooling plate and the cooler in the cell stack is set to 1/1 of the output voltage of the cell stack.
The potential difference shared by each insulating hose is reduced to 1/N or less of the output voltage of the cell stack.

[Example of idea]

The present invention will be explained below based on one embodiment.

FIG. 1 is a block diagram of a cooling system for a liquid-cooled fuel cell stack showing an embodiment of the present invention. In the figure, 1A, 1B, and 1C indicate the range of the cell stack cooled by the cooling units divided into N groups, and the ranges 1A, 1B, and 1C each include a plurality of cooling plates 33A, 33B, 33C, etc. A cooling plate 33, a plurality of coolers 34 such as 34A, 34B, and 34C, and coolers 34A, 34B, and 34C.
The internal liquid guide pipe portions 35 and 36 communicate with the ends of the
The cooling unit 30 includes an inter-assembly liquid conduit pipe section 45A on the supply side and an inter-assembly liquid conduit tube section 46A on the collection side, which communicate with the intra-assembly liquid conduit tube sections 35 and 36 via connection pipes 41 and 42. It is arranged. Each part of the cooling unit 30 is formed of a metal pipe with good thermal conductivity and corrosion resistance, and is connected to each other by welding or a pipe joint (not shown), and is connected to a position near the intermediate potential among the cooling plates 33A, 33B, and 33C. By bringing the cooling plate 33B and cooler 34B into conductive contact, the potential of the entire cooling unit is maintained at approximately the midpoint potential of the divided cell stacks 1A. Sectioned cell stack 1B,
The same applies to 1C etc., and the inter-assembly liquid conduit section 45B,
46B has the intermediate potential of the cell stack 1B part,
Cell stack 1 is installed in the inter-assembly liquid guide pipe portions 45C and 46C.
An intermediate potential of the C portion is given. Reference numeral 48 indicates between the liquid guide pipe parts between adjacent sets, the grounded liquid guide pipe parts 50 and 51 of the external coolant circulation device as supply side and collection side liquid guide means, and the lowest part of the cell stack which is the low voltage side. An insulated pipe connecting between the interassembly liquid guiding pipe parts 45C and 46C of the cooling unit,
For example, an insulated hose made of polytetrafluoroethylene or the like, which has good heat resistance, water resistance, internal pressure resistance, and flexibility, is used. Also cooler 34B
A conductive film 58 that can withstand the electrolyte and operating temperature of the cell is deposited on the cooling pipe portion of the cooling plate 3.
In addition to maintaining electrical contact with 3B, other cooling pipes such as 34A and 34C are coated with an electrolyte and an insulating coating that can withstand high temperatures, such as perfluoroethyl ether-polytetrafluoroethylene copolymer (referred to as PFA) film, etc. An insulating coating 38 consisting of the cooling plates 33A, 33C, etc. is provided to maintain insulation between the cooling plates 33A, 33C, etc.

FIG. 2 is a perspective view of essential parts showing the structure of the cell stack in the above-described embodiment, and shows a ribbed electrode type phosphoric acid fuel cell as an example. In the figure, 62 is a matrix supporting an electrolyte, 63 is an air electrode, 64 is a hydrogen electrode, 65 is an air electrode side electrode substrate having ribs for air supply, 6
Reference numeral 6 denotes a hydrogen electrode side electrode substrate having ribs for supplying hydrogen, and the unit cells thus formed are stacked in multiple layers with a separator 67 in between to form a cell stack, and each unit cell is stacked in multiple layers with a separator 67 in between. A cooling plate 33 is interposed therein. The cooling plate 33 is a carbon-based or graphite-based plate-like body having the same quality as the separator, and a plurality of insertion portions (grooves) 68 into which cooling pipes are inserted are provided at intervals on one surface of the cooling plate 33. It is being By separating the cooling plate 33 and the separator 67 in this way, there is an advantage that there is no restriction on the number of cooling pipe insertion portions, and the cooling plate can be manufactured easily. Further, the cooling plate 33 may be configured to also serve as a separator, and in this case, the separator can be partially omitted.

FIG. 3 is a perspective view of the cooler section in the above-described embodiment, showing a plurality of cooling pipes 71 each having an insulating coating 38.
The cooler 34 is formed by connecting both ends in parallel to each other by a connecting pipe 72, and is housed in the cooling pipe insertion part 68 of the cooling plate 33, and the both ends are connected to the internal liquid guide pipe parts 35 and 36. connected to. In the case of FIG. 3, the cooling pipes 71 are each bent into a U-shape, and the connecting pipe 72 and the internal liquid guiding pipe portions 35, 36 are bent.
Although an example has been shown in which the cooling pipes 71 are arranged on one side of the cell stack, it is also possible to arrange the cooling pipes 71 in a straight line and the internal liquid guide pipe sections 35 and 36 on both sides of the cell stack.

Next, the functions of the cooling system configured as shown in FIGS. 1 to 3 will be explained. Assuming that the potential difference between the high and low voltage terminals 7A and 7B of the cell stack is 4000 V and the number N of cooling units 30 is 10, the stack portions divided by cooling units such as 1A, 1B, and 1C in FIG. The potential difference is 400V each. Furthermore, since the cooling units are each conductively connected to the intermediate potential point of the stack portion, the potential difference between the coolers in the cooling unit 30, for example, 34A, 34C and the cooling plates 33A, 33C, is kept below 1/2 of 400V, that is, the fourth The potential difference can be reduced to less than 1/20 of the conventional structure shown in the figure, making it possible to make the insulation coating of the cooling pipe extremely thin. On the other hand, the potential difference borne by each of the insulating tubes 48 that cascade connects the inter-assembly liquid guiding pipe sections of the cooling unit and the inter-assembling liquid guiding pipe section of the lowest cooling unit of the cell stack and the supply side and collection side liquid guiding means is 400V. For example, it is reduced to 1/10 of that of the conventional structure shown in FIG. Therefore, if the coolant 9 supplied to the cooling system is a coolant with a specific resistance of about 10 ⁵ Ω-cm at the operating temperature of the stack, there will be a leakage that flows to the ground via the coolant in the multiple insulated pipes. The current can be reduced to less than 1/10 of that in the conventional structure shown in FIG. 5, for example. Furthermore, since the insulating tubes 48 are interposed so as to cascade connect the inter-assembly liquid guide tubes arranged in series in parallel with the stacking direction of the cell stacks, even if the length of the insulating tubes 48 is increased, the installation space of the cell stacks can be saved. Since no influence is exerted, the leakage current can be further reduced and the reliability of the insulation of the insulating tube portion can be improved. Further, by reducing the leakage current, electrochemical corrosion of the inter-assembly liquid guide pipe at the joint with the insulating pipe is reduced, and the corrosion-protective structure of the liquid guide pipe can be simplified. Furthermore, since the cooling unit does not include insulating tubes corresponding to each cooler, and the inter-cooler insulating tube 48 is disposed at the outermost side of the cell stack, inspection and maintenance for liquid leaks can be facilitated. can.

[Effect of idea]

As described above, the present invention includes a conductive cooling plate that is made of a stack of a plurality of single cells and has a plurality of cooling pipe insertion parts interposed between the single cells for each predetermined number of single cells, and A cooler formed by connecting a plurality of cooling pipes having insulating coatings inserted in the cooling pipes in parallel to each other at both ends thereof, a supply side and a collection side liquid guiding means 50 communicating with the cooler and an external cooling liquid circulation device, and 51, the cell stack is equipped with a cooler set 34 divided into a plurality of sets in the stacking direction of the cell stack, and a cooler set 34 connected in parallel to the inlet side and the outlet side of each cooler in each cooler set, respectively. A pair of internal liquid guiding pipe parts 35 and 36 and connecting pipes 41 and 4
2 and inter-assembly liquid guide pipe sections 45 and 46, each of the inter-assembly liquid guide pipe sections 45 and 46 communicates in the stacking direction of the cell stacks and connects to the intra-assembly guide of each cooling unit. Liquid pipe section 35
and 36, respectively, the connecting pipes 41 and 42.
In a liquid-cooled fuel cell cell stack, the inter-assembly liquid conduit pipe sections 45 and 46 of the cooling unit 30 communicate with each other, and the inter-assembly liquid conduit tube section of the lowest cooling unit of the cell stack on the low voltage side. 45C and 46C and the supply side and collection side liquid guiding means 50 and 51 are connected in series, and an insulating pipe 48 and a cooling plate 33B located approximately in the middle of the unit cell stack in the portion where each of the cooling units is disposed.
cooling pipes each having a conductive connection to one of the cooling pipes. As a result, the potential difference between the cooler in the cooling unit and the cooling plate housing the cooler can be reduced to 1/2N of the output voltage of the cell stack, and the potential difference shared by each insulating tube can be reduced to 1/N. Compared to conventional technology, the reliability of the insulation between the cooling plate and the cooling tube and the reliability of the insulation of the insulation tube can be improved at the same time, and the thickness of the insulation coating of the cooling tube can be reduced, resulting in high cooling performance. In addition, it is possible to provide a liquid-cooled fuel cell stack in which the leakage current that flows through the insulated cylinder cooling water is small. In addition, insulating tubes were placed only in the parts where the inter-assembly liquid conduit tubes arranged parallel to the stacking direction of the cell stacks were concentrically cascaded. This eliminates the space needed to install insulating tubes in the conventional technology, which requires dielectric partitions (dielectric partitions), thereby reducing the installation space for cell stacks and improving insulation reliability by making the insulating tubes sufficiently long. It is possible to actively improve the performance and reduce leakage current. Furthermore, since the number of insulating tubes used is small and the insulating tubes can be arranged at easily visible positions on the sides of the cell stack, there is an advantage that inspection and equipment of the insulating tube joints can be facilitated.

[Brief explanation of drawings]

Fig. 1 is a conceptual diagram of a cooling system for a liquid-cooled fuel cell stack showing an embodiment of the present invention, Fig. 2 is a configuration diagram of a cell stack showing an example of the arrangement of cooling plates in the embodiment of Fig. 1, and Fig. 3 1 is a perspective view of a cooler portion in the embodiment of FIG. 1, FIG. 4 is a structural diagram showing a conventional cooling system, and FIG. 5 is a structural diagram showing an improved conventional cooling system. 1...Cell stack, 2...Single battery, 3,1
3, 33... Cooling plate, 4, 14, 34... Cooler, 8, 38... Insulating coating of cooling pipe, 30... Cooling unit, 35, 36... Intra-assembly liquid guiding pipe section, 45
A, 45B, 45C... Supply side interassembly liquid conduit pipe section,
46A, 46B, 46C... Collection side interassembly liquid conduit pipe section, 41, 42... Connection pipe, 48... Insulation pipe, 5
8... Conductive coating, 9... Cooling liquid, 50, 51...
Supply side and collection side liquid guiding means, 62... matrix, 63, 64... electrode, 65, 66... ribbed separator, 18, 28... dielectric wall.

Claims (1)

[Scope of Claim for Utility Model Registration] 1) An electrically conductive cooling plate comprising a laminate of a plurality of unit cells and having a plurality of cooling pipe insertion portions interposed between the units for each predetermined number of units; a cooler formed by connecting a plurality of cooling tubes each having an insulating coating inserted into an insertion portion in parallel with each other at both ends;
This cell stack is equipped with supply side and collection side liquid guide means 50 and 51 communicating with this cooler and an external cooling liquid circulation device, and includes a cooler set 34 divided into a plurality of sets in the stacking direction of the cell stack. , a pair of intra-set liquid guide pipe sections 35 and 36, connecting pipes 41 and 42, and an inter-set liquid guide pipe section 45 and 36 connected in parallel to the inlet and outlet sides of each cooler in each cooler set, respectively. 46, each of the inter-assembly liquid guide pipe sections 45 and 46 communicates in the stacking direction of the cell stack and is connected to the intra-assembly liquid guide pipe sections 35 and 36 of each cooling unit, respectively. In a liquid-cooled fuel cell stack formed by communicating via pipes 41 and 42, the liquid guide pipe portions 45 and 46 between each set of the cooling unit 30 and between the lowermost cooling unit of the cell stack on the low voltage side. Liquid guide pipe parts 45C and 46C
and one of the cooling plates 33B located approximately in the middle of the unit cell stack in the portion where the respective cooling units are disposed. What is claimed is: 1. A liquid-cooled fuel cell stack comprising cooling pipes each electrically connected to a cooling pipe. 2) In the utility model registration claim described in claim 1, at least a portion of the cooling pipe of the cooler housed in the cooling plate that is conductively connected to the cooling unit is coated with a conductive coating. A liquid-cooled fuel cell stack characterized in that the cooling plate and the cooling pipe are electrically connected to each other through the cooling plate and the cooling pipe.