Fuel cell system

Abstract

The present invention provides a fuel cell system capable of improving the power generation efficiency between multiple fuel cell stacks. The fuel cell system comprises: a first fuel cell stack and a second fuel cell stack; a supply pipe having a branch portion; a discharge pipe having a confluence portion; a first branch pipe and a second branch pipe; a first confluence pipe; and a second confluence pipe. The cross-sections of the flows of the pipes are the same in size. The length of the first branch pipe connected to the branch portion and the first fuel cell stack is less than the length of the second branch pipe connected to the branch portion and the second fuel cell stack. The length of the first confluence pipe connected to the confluence portion and the first fuel cell stack is greater than the length of the second confluence pipe connected to the confluence portion and the second fuel cell stack.

Description

[0001] This application claims priority based on Japanese Patent Application No. 2021-050559 filed on March 24, 2021, and the contents are incorporated herein by reference. Technical Field

[0002] The present invention relates to a fuel cell system. Background Art

[0003] In the past, for example, there is known a fuel cell system comprising: two stacks having a plurality of stacked monomers and arranged in a direction orthogonal to the stacking direction of the plurality of monomers; and an oxidant gas supply pipe, a fuel gas supply pipe and a cooling medium supply pipe, which are arranged in the two stacks in a symmetrical manner on one side of the stacking direction of each stack (for example, refer to Japanese Patent Publication No. 2005-5196). Summary of the invention

[0004] Furthermore, in the above-mentioned fuel cell system, since the pipes are provided in two stacks in a corresponding manner, there arises a problem that the layout of the fuel cell system is limited and the versatility cannot be improved.

[0005] In addition, for example, when three or more stacks are arranged in a direction orthogonal to the stacking direction of the multiple monomers, it is difficult to set the various pipes in the multiple stacks in a corresponding manner, and the distribution of gas and refrigerant between the multiple stacks becomes uneven, resulting in a problem of reduced power generation efficiency of the entire system.

[0006] An aspect of the present invention provides a fuel cell system capable of improving power generation efficiency among a plurality of fuel cell stacks.

[0007] In order to solve the above problems and achieve the above objects, the present invention adopts the following means.

[0008] (1) A fuel cell system according to one embodiment of the present invention comprises: a plurality of fuel cell stacks, which include at least a first fuel cell stack and a second fuel cell stack; a supply pipe, which provides a branch portion for the flow of fluid supplied to the plurality of fuel cell stacks; a discharge pipe, which provides a confluence portion for the flow of fluid discharged from the plurality of fuel cell stacks; a first branch pipe connected to the branch portion and the first fuel cell stack; a second branch pipe connected to the branch portion and the second fuel cell stack; a first confluence pipe connected to the confluence portion and the first fuel cell stack; and a second confluence pipe connected to the confluence portion and the second fuel cell stack, wherein when the sizes of the flow cross-sections in the first branch pipe, the second branch pipe, the first confluence pipe and the second confluence pipe are the same, the length of the first branch pipe is smaller than the length of the second branch pipe, and the length of the first confluence pipe is larger than the length of the second confluence pipe.

[0009] (2) A fuel cell system according to one embodiment of the present invention comprises: a plurality of fuel cell stacks, which include at least a first fuel cell stack and a second fuel cell stack; a supply piping, which provides a branch portion for the flow of fluid supplied to the plurality of fuel cell stacks; a discharge piping, which provides a confluence portion for the flow of fluid discharged from the plurality of fuel cell stacks; a first branch piping connected to the branch portion and the first fuel cell stack; a second branch piping connected to the branch portion and the second fuel cell stack; a first confluence piping connected to the confluence portion and the first fuel cell stack; and a second confluence piping connected to the confluence portion and the second fuel cell stack, wherein the length of the first branch piping is smaller than the length of the second branch piping, and the flow cross-section of the first branch piping is smaller than the flow cross-section of the second branch piping, and the length of the first confluence piping is larger than the length of the second confluence piping, and the flow cross-section of the first confluence piping is larger than the flow cross-section of the second confluence piping.

[0010] (3) A fuel cell system according to one embodiment of the present invention comprises: a plurality of fuel cell stacks, each of which constitutes a plurality of stacks having at least a first stack group and a second stack group; a supply piping, which is provided for the circulation of a fluid supplied to the plurality of stack groups and has a branch portion; a discharge piping, which is provided for the circulation of the fluid discharged from the plurality of stack groups and has a confluence portion; a first branch pipe, which is connected to the branch portion and the first stack group; a second branch pipe, which is connected to the branch portion and the second stack group; a first confluence pipe, which is connected to the confluence portion and the first stack group; and a second confluence pipe, which is connected to the confluence portion and the second stack group, and when the sizes of the flow cross-sections in the first branch pipe, the second branch pipe, the first confluence pipe and the second confluence pipe are the same, the length of the first branch pipe is smaller than the length of the second branch pipe, and the length of the first confluence pipe is larger than the length of the second confluence pipe.

[0011] (4) A fuel cell system according to one embodiment of the present invention comprises: a plurality of fuel cell stacks, each of which constitutes a plurality of stacks having at least a first stack group and a second stack group; a supply piping, which provides for the circulation of a fluid supplied to the plurality of stack groups and has a branch portion; a discharge piping, which provides for the circulation of the fluid discharged from the plurality of stack groups and has a confluence portion; a first branch piping connected to the branch portion and the first stack group; a second branch piping connected to the branch portion and the second stack group; a first confluence piping connected to the confluence portion and the first stack group; and a second confluence piping connected to the confluence portion and the second stack group, the length of the first branch piping being smaller than the length of the second branch piping, the flow cross-section of the first branch piping being smaller than the flow cross-section of the second branch piping, the length of the first confluence piping being larger than the length of the second confluence piping, and the flow cross-section of the first confluence piping being larger than the flow cross-section of the second confluence piping.

[0012] According to the above aspect (1), the pressure loss at the first branch pipe and the first merging pipe can be made nearly equal to the pressure loss at the second branch pipe and the second merging pipe, so that the fluid can be uniformly supplied to the first fuel cell stack and the second fuel cell stack.

[0013] According to the scheme (2) above, the pressure loss at the first branch pipe can be made nearly equal to the pressure loss at the second branch pipe, and the pressure loss at the first confluent pipe can be made nearly equal to the pressure loss at the second confluent pipe. The pressures of the first fuel cell stack and the second fuel cell stack can be made equal, and fluctuations in performance and durability can be suppressed.

[0014] According to the above aspect (3), the pressure loss in the first branch pipe and the first merging pipe and the pressure loss in the second branch pipe and the second merging pipe can be made nearly equal, and the fluid can be uniformly supplied to the first stack and the second stack.

[0015] According to the scheme (4) above, the pressure loss at the first branch pipe can be made nearly equal to the pressure loss at the second branch pipe, and the pressure loss at the first confluent pipe can be made nearly equal to the pressure loss at the second confluent pipe. The pressure of the first stack and the second stack can be made equal, and fluctuations in performance and durability can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a diagram schematically showing the structure of a fuel cell system in an embodiment of the present invention.

[0017] Figure 2 This is a diagram showing an example of the pressure of a predetermined fluid at each fuel cell stack of the fuel cell system in the embodiment of the present invention.

[0018] Figure 3 It is a diagram schematically showing the configuration of a fuel cell system in a first modified example of the embodiment of the present invention.

[0019] Figure 4 This is a diagram showing an example of the pressure of a predetermined fluid at each fuel cell stack of a fuel cell system in a first modified example of the embodiment of the present invention.

[0020] Figure 5 This is a diagram showing the correspondence relationship between the flow rate of a predetermined fluid and the flow rate difference at each fuel cell stack of the fuel cell system in the first modified example of the embodiment of the present invention.

[0021] Figure 6 It is a diagram schematically showing the configuration of a fuel cell system in a second modified example of the embodiment of the present invention.

[0022] Figure 7 This is a diagram showing an example of the pressure of a predetermined fluid at each fuel cell stack of a fuel cell system in a second modified example of the embodiment of the present invention.

[0023] Figure 8 FIG. 1 is a diagram schematically showing a configuration of a fuel cell system in a third modified example of the embodiment of the present invention.

[0024] Fig. 9 This is a diagram showing an example of the pressure of a predetermined fluid at each fuel cell stack of a fuel cell system in a third modified example of the embodiment of the present invention. DETAILED DESCRIPTION

[0025] Hereinafter, a fuel cell system 10 according to an embodiment of the present invention will be described with reference to the drawings.

[0026] Figure 1 1 is a diagram schematically showing the structure of a fuel cell system 10 in an embodiment.

[0027] like Figure 1 As shown, the fuel cell system 10 of the embodiment includes a plurality of fuel cell stacks 11 , a supply pipe 13 , a plurality of branch pipes 15 , a discharge pipe 17 , and a plurality of merging pipes 19 .

[0028] The plurality of fuel cell stacks 11 include, for example, a first fuel cell stack 21 and a second fuel cell stack 23 .

[0029] Each fuel cell stack 11 is, for example, a polymer electrolyte fuel cell and includes a plurality of stacked fuel cells 11a and a pair of end plates (a first end plate 11b and a second end plate 11c) sandwiching the stack of the plurality of fuel cells from both sides in the stacking direction.

[0030] The fuel cell monomer 11a includes an electrolyte electrode structure and a pair of separators sandwiching the electrolyte electrode structure. The electrolyte electrode structure includes a solid polymer electrolyte membrane and a fuel electrode and an oxygen electrode sandwiching the solid polymer electrolyte membrane. The solid polymer electrolyte membrane includes a cation exchange membrane, etc. The fuel electrode (anode) includes an anode catalyst and a gas diffusion layer, etc. The oxygen electrode (cathode) includes a cathode catalyst and a gas diffusion layer, etc.

[0031] Each fuel cell stack 11 generates electricity through a catalytic reaction between a fuel gas containing hydrogen supplied to an anode and an oxidant gas such as air containing oxygen supplied to a cathode.

[0032] The plurality of fuel cell stacks 11 including the first fuel cell stack 21 and the second fuel cell stack 23 are arranged in sequence in a direction orthogonal to the stacking directions, for example, so that the stacking directions of the plurality of fuel cell units 11 a are parallel to each other.

[0033] Each fuel cell stack 11 includes a supply flow path 31 through which a predetermined fluid supplied to each of the plurality of fuel cells 11 a flows, and a discharge flow path 33 through which a predetermined fluid discharged from each of the plurality of fuel cells 11 a flows.

[0034] The supply flow path 31 is connected to the branch pipe 15 and the supply pipe 13 described later. For example, the supply flow path 31 is connected to the branch pipe 15 at the first end plate 11b of the fuel cell stack 11.

[0035] The exhaust flow path 33 is connected to the merging pipe 19 and the exhaust pipe 17 described later. For example, the exhaust flow path 33 is connected to the merging pipe 19 at the first end plate 11 b of the fuel cell stack 11 .

[0036] The supply flow path 31 and the exhaust flow path 33 are respectively arranged along the stacking direction of the plurality of fuel cell monomers 11a. The flow direction of the prescribed fluid in the supply flow path 31 and the flow direction of the prescribed fluid in the exhaust flow path 33 are opposite directions in the stacking direction. For example, the flow direction of the prescribed fluid in the supply flow path 31 is from the first end plate 11b side toward the second end plate 11c side, and the flow direction of the prescribed fluid in the exhaust flow path 33 is from the second end plate 11c side toward the first end plate 11b side.

[0037] The supply flow path 31 includes a fuel supply flow path through which the fuel gas flows, an oxidant supply flow path through which the oxidant gas flows, and a coolant supply flow path through which a cooling medium supplied to cool the plurality of fuel cell cells 11 a flows.

[0038] The discharge flow path 33 includes a fuel discharge flow path through which the fuel gas flows, an oxidant discharge flow path through which the oxidant gas flows, and a coolant discharge flow path through which the cooling medium discharged after cooling the plurality of fuel cell cells 11 a flows.

[0039] The supply pipe 13 includes a branch portion 13a connected to a plurality of branch pipes 15. A predetermined fluid supplied to the plurality of fuel cell stacks 11 flows through the supply pipe 13 and the plurality of branch pipes 15. The number of the plurality of branch pipes 15 is the same as the number of the plurality of fuel cell stacks 11. The plurality of branch pipes 15 include, for example, a first branch pipe 41 and a second branch pipe 43. The first branch pipe 41 is connected to the supply flow path 31 of the first fuel cell stack 21. The second branch pipe 43 is connected to the supply flow path 31 of the second fuel cell stack 23.

[0040] The supply pipe 13 and the branch pipe 15 include a fuel supply pipe and a fuel branch pipe through which fuel gas flows, an oxidant supply pipe and an oxidant branch pipe through which oxidant gas flows, and a refrigerant supply pipe and a refrigerant branch pipe through which cooling medium flows.

[0041] The exhaust pipe 17 includes a confluence portion 17a connected to a plurality of confluence pipes 19. A predetermined fluid discharged from the plurality of fuel cell stacks 11 flows through the exhaust pipe 17 and the plurality of confluence pipes 19. The number of the plurality of confluence pipes 19 is the same as the number of the plurality of fuel cell stacks 11. The plurality of confluence pipes 19 include, for example, a first confluence pipe 45 and a second confluence pipe 47. The first confluence pipe 45 is connected to the exhaust flow path 33 of the first fuel cell stack 21. The second confluence pipe 47 is connected to the exhaust flow path 33 of the second fuel cell stack 23.

[0042] The discharge pipe 17 and the merging pipe 19 include a fuel discharge pipe and a fuel merging pipe through which fuel gas flows, an oxidant discharge pipe and an oxidant merging pipe through which oxidant gas flows, and a refrigerant discharge pipe and a refrigerant merging pipe through which cooling medium flows.

[0043] In the embodiment, the size of the cross section for the flow of the predetermined fluid is the same in each of the plurality of branch pipes 15 and the plurality of converging pipes 19. The size of the cross section is, for example, the diameter in a circular pipe or the hydraulic equivalent diameter (equivalent diameter: equivalent circular pipe diameter) in a pipe having a cross-sectional shape other than a circular pipe.

[0044] The length Lin1 of the first branch pipe 41 connected between the branch portion 13a of the supply pipe 13 and the supply flow path 31 of the first fuel cell stack 21 is relatively smaller than the length Lin2 of the second branch pipe 43 connected between the branch portion 13a of the supply pipe 13 and the supply flow path 31 of the second fuel cell stack 23 (Lin1<Lin2).

[0045] The length Lout1 of the first confluence pipe 45 connected between the confluence 17a of the exhaust pipe 17 and the exhaust flow path 33 of the first fuel cell stack 21 is relatively larger than the length Lout2 of the second confluence pipe 47 connected between the confluence 17a of the exhaust pipe 17 and the exhaust flow path 33 of the second fuel cell stack 23 (Lout1>Lout2).

[0046] Figure 2 1 is a diagram showing an example of the pressure of a predetermined fluid at each fuel cell stack 11 of the fuel cell system 10 in the embodiment.

[0047] exist Figure 2 In the example shown, as shown in the following mathematical formula (1), the sum of the length Lin1 of the first branch pipe 41 and the length Lout1 of the first converging pipe 45 (Lin1+Lout1) is the same as the sum of the length Lin2 of the second branch pipe 43 and the length Lout2 of the second converging pipe 47 (Lin2+Lout2).

[0048] [Mathematical formula 1]

[0049] Lin1+Lout1=Lin2+Lout2···(1)

[0050] exist Figure 2 It is shown in the figure: when the pressure at the branch portion 13a of the supply pipe 13 is set to a specified pressure P and the pressure at the confluence 17a of the exhaust pipe 17 is set to zero, there is a correspondence between the pressure loss Pin1 at the first branch pipe 41, the pressure loss Pstk1 at the first fuel cell stack 21 and the pressure loss Pout1 at the first confluence pipe 45 and the pressure loss Pin2 at the second branch pipe 43, the pressure loss Pstk2 at the second fuel cell stack 23 and the pressure loss Pout2 at the second confluence pipe 47.

[0051] like Figure 2 As shown, by making the length Lin1 of the first branch pipe 41 relatively smaller than the length Lin2 of the second branch pipe 43, the pressure loss Pin1 at the first branch pipe 41 is relatively smaller than the pressure loss Pin2 at the second branch pipe 43. In addition, by making the length Lout1 of the first confluent pipe 45 relatively larger than the length Lout2 of the second confluent pipe 47, the pressure loss Pout1 at the first confluent pipe 45 is relatively larger than the pressure loss Pout2 at the second confluent pipe 47. When the pressure loss Pstk1 at the first fuel cell stack 21 and the pressure loss Pstk2 at the second fuel cell stack 23 are the same, by satisfying the above mathematical formula (1), the pressure loss from the branch portion 13a of the supply pipe 13 to the confluent portion 17a of the exhaust pipe 17 is the same for each fuel cell stack 21, 23.

[0052] As described above, the fuel cell system 10 of the embodiment is set to (Lin1 < Lin2) and (Lout1 > Lout2), so that the pressure loss at the first branch pipe 41 and the first merging pipe 45 and the pressure loss at the second branch pipe 43 and the second merging pipe 47 can be nearly equal. As a result, the first fuel cell stack 21 and the second fuel cell stack 23 can be uniformly supplied with fluid.

[0053] By satisfying the above-mentioned mathematical formula (1), the pressure loss from the branch portion 13 a of the supply pipe 13 to the junction portion 17 a of the discharge pipe 17 can be made the same for each of the fuel cell stacks 21 , 23 .

[0054] (Variation Example)

[0055] Hereinafter, a modification of the embodiment will be described. It should be noted that the same reference numerals are given to the same parts as those of the above-mentioned embodiment, and the description thereof will be omitted or simplified.

[0056] In the above-described embodiment, the sizes of the cross sections for the flow of the predetermined fluid in each of the plurality of branch pipes 15 and the plurality of merging pipes 19 are set to be the same, but the present invention is not limited thereto.

[0057] Figure 3 1 is a diagram schematically showing the structure of a fuel cell system 10A in a first modified example of the embodiment.

[0058] like Figure 3 As shown, in the fuel cell system 10A of the first variant, the size of the cross-section of the flow of the first branch pipe 41 is relatively small compared with the size of the cross-section of the flow of the second branch pipe 43, and the size of the cross-section of the flow of the first confluence pipe 45 is relatively small compared with the size of the cross-section of the flow of the second confluence pipe 47.

[0059] For example, the hydraulic equivalent diameter Din1 of the first branch pipe 41 is relatively smaller than the hydraulic equivalent diameter Din2 of the second branch pipe 43 (Din1<Din2), and the hydraulic equivalent diameter Dout1 of the first confluent pipe 45 is relatively larger than the hydraulic equivalent diameter Dout2 of the second confluent pipe 47 (Dout1>Dout2).

[0060] Figure 4 1 is a diagram showing an example of the pressure of a predetermined fluid at each fuel cell stack 11 of the fuel cell system 10A in the first modification.

[0061] exist Figure 4 In the example shown, as shown in the following mathematical formula (2), in each fuel cell stack 21, 23, the ratio of the length of each pipe 41, 43 on the branch portion 13a side to the fourth power of the hydraulic equivalent diameter is the same as the ratio of the length of each pipe 45, 47 on the confluence portion 17a side to the fourth power of the hydraulic equivalent diameter.

[0062] [Mathematical formula 2]

[0063]

[0064] The ratio (L / D) of the length (L) of each pipe 41, 43, 45, 47 to the fourth power of the hydraulic equivalent diameter (D) in the above mathematical formula (2) is: 4 ) is a parameter proportional to the pressure loss of a predetermined fluid flowing through each of the pipes 41, 43, 45, 47. That is, the pressure loss is proportional to the length (L) and inversely proportional to the fourth power of the hydraulic equivalent diameter (D).

[0065] Figure 4It is shown that: when the pressure at the branch portion 13a of the supply pipe 13 is set to a specified pressure P and the pressure at the confluence 17a of the exhaust pipe 17 is set to zero, there is a correspondence between the pressure loss Pin1 at the first branch pipe 41, the pressure loss Pstk1 at the first fuel cell stack 21, and the pressure loss Pout1 at the first confluence pipe 45, and the pressure loss Pin2 at the second branch pipe 43, the pressure loss Pstk2 at the second fuel cell stack 23, and the pressure loss Pout2 at the second confluence pipe 47.

[0066] exist Figure 4 In the embodiment, by making the length Lin1 of the first branch pipe 41 relatively smaller than the length Lin2 of the second branch pipe 43, and correspondingly making the hydraulic equivalent diameter Din1 of the first branch pipe 41 relatively smaller than the hydraulic equivalent diameter Din2 of the second branch pipe 43, the pressure loss Pin1 at the first branch pipe 41 is the same as the pressure loss Pin2 at the second branch pipe 43.

[0067] In addition, by making the length Lout1 of the first confluence pipe 45 relatively larger than the length Lout2 of the second confluence pipe 47, and accordingly making the hydraulic equivalent diameter Dout1 of the first confluence pipe 45 relatively larger than the hydraulic equivalent diameter Dout2 of the second confluence pipe 47, the pressure loss Pout1 at the first confluence pipe 45 is equal to the pressure loss Pout2 at the second confluence pipe 47. When the pressure loss Pstk1 at the first fuel cell stack 21 and the pressure loss Pstk2 at the second fuel cell stack 23 are equal, the pressure loss from the branch portion 13a of the supply pipe 13 to the confluence portion 17a of the exhaust pipe 17 is equal to each fuel cell stack 21, 23 by satisfying the above-mentioned mathematical formula (2).

[0068] In the first modification, the length (L) and the hydraulic equivalent diameter (D) of each pipe 41 , 43 , 45 , 47 may be set to satisfy the following mathematical formula (3), for example.

[0069] The following mathematical formula (3) is expressed by the length Lin1 and the hydraulic equivalent diameter Din1 of the first branch pipe 41, the length Lout1 and the hydraulic equivalent diameter Dout1 of the first confluent pipe 45, the length Lin2 and the hydraulic equivalent diameter Din2 of the second branch pipe 43, the length Lout2 and the hydraulic equivalent diameter Dout2 of the second confluent pipe 47, the fluid flow Qin of each fuel cell stack 11 in each fuel cell stack 11 supplied at rated output, the pressure loss ΔPstk at each fuel cell stack 11 when a specified fluid with a fluid flow Qin is supplied to each fuel cell stack 11, the viscosity coefficient μ of the specified fluid, the specified threshold α, the flow difference β of the specified fluid between the first fuel cell stack 21 and the second fuel cell stack 23, and the specified coefficient b.

[0070] [Mathematical formula 3]

[0071]

[0072] The predetermined threshold value α in the above mathematical formula (3) represents the tolerance for fluctuations in the flow rate of the predetermined fluid between the first fuel cell stack 21 and the second fuel cell stack 23. For example, when α=0.2, a 20% fluctuation in the flow rate is allowed. The predetermined threshold value α is set, for example, within the range of the flow rate required to ensure the desired power generation.

[0073] Figure 5 1 is a diagram showing the correspondence relationship between the flow rates Q1 and Q2 of a predetermined fluid and the flow rate difference β at each fuel cell stack 11 of the fuel cell system 10A in the first modification.

[0074] like Figure 5 As shown, by using the specified threshold α to specify the flow difference β, the increase in the difference between the flow rate Q1 of the specified fluid at the first fuel cell stack 21 and the flow rate Q2 of the specified fluid at the second fuel cell stack 23 is suppressed, and the same fluid flow rate Qin is supplied to each fuel cell stack 21, 23.

[0075] According to the first modification, by setting (Lin1<Lin2) and (Lout1>Lout2) and (Din1<Din2) and (Dout1>Dout2), the pressure loss at the first branch pipe 41 and the pressure loss at the second branch pipe 43 can be made nearly equal, and the pressure loss at the first confluent pipe 45 and the pressure loss at the second confluent pipe 47 can be made nearly equal. Thus, the pressure of each fuel cell stack 21, 23 can be made equal, and fluctuations in performance and durability can be suppressed.

[0076] By satisfying the above-mentioned mathematical formula (3), the pressure loss from the branch portion 13 a of the supply pipe 13 to the junction portion 17 a of the discharge pipe 17 can be made the same for each of the fuel cell stacks 21 , 23 .

[0077] The plurality of fuel cell stacks 11 of the fuel cell system 10 of the above-described embodiment include the first fuel cell stack 21 and the second fuel cell stack 23 , but the present invention is not limited thereto.

[0078] Figure 6 1 is a diagram schematically showing the structure of a fuel cell system 10B in a second modified example of the embodiment.

[0079] like Figure 6 As shown, the fuel cell system 10B of the second modification includes a plurality of stacks 51 , supply pipes 53 , a plurality of branch pipes 55 , a discharge pipe 57 , and a plurality of merging pipes 59 .

[0080] The plurality of stack groups 51 include, for example, a first stack group 61 and a second stack group 63 .

[0081] Each stack 51 includes, for example, the first fuel cell stack 21 and the second fuel cell stack 23 in the above-described embodiment, the first branch pipe 41 and the second branch pipe 43, and the first converging pipe 45 and the second converging pipe 47. The first branch pipe 41 and the second branch pipe 43 of each stack 51 are connected to a supply portion (for example, the first supply portion 61a of the first stack 61 and the second supply portion 63a of the second stack 63) corresponding to the branch portion 13a of the supply pipe 13 in the above-described embodiment. The first converging pipe 45 and the second converging pipe 47 of each stack 51 are connected to a discharge portion (for example, the first discharge portion 61b of the first stack 61 and the second discharge portion 63b of the second stack 63) corresponding to the converging portion 17a of the discharge pipe 17 in the above-described embodiment.

[0082] The supply pipe 53 of the second modified example includes a branch portion 53a connected to a plurality of branch pipes 55. A predetermined fluid supplied to the plurality of stacks 51 flows through the supply pipe 53 and the plurality of branch pipes 55. The number of the plurality of branch pipes 55 is the same as the number of the plurality of stacks 51. The plurality of branch pipes 55 includes, for example, a first branch pipe 71 and a second branch pipe 73. The first branch pipe 71 is connected to the first supply portion 61a of the first stack 61. The second branch pipe 73 is connected to the second supply portion 63a of the second stack 63.

[0083] The supply pipe 53 and the branch pipe 55 include a fuel supply pipe and a fuel branch pipe through which fuel gas flows, an oxidant supply pipe and an oxidant branch pipe through which oxidant gas flows, and a refrigerant supply pipe and a refrigerant branch pipe through which cooling medium flows.

[0084] The discharge pipe 57 of the second modified example includes a confluence portion 57a ​​connected to a plurality of confluence pipes 59. A predetermined fluid discharged from a plurality of stacks 51 flows through the discharge pipe 57 and the plurality of confluence pipes 59. The number of the plurality of confluence pipes 59 is the same as the number of the plurality of stacks 51. The plurality of confluence pipes 59 includes, for example, a first confluence pipe 75 and a second confluence pipe 77. The first confluence pipe 75 is connected to the first discharge portion 61b of the first stack 61. The second confluence pipe 77 is connected to the second discharge portion 63b of the second stack 63.

[0085] The discharge pipe 57 and the merging pipe 59 include: a fuel discharge pipe and a fuel merging pipe through which fuel gas flows; an oxidant discharge pipe and an oxidant merging pipe through which oxidant gas flows; and a refrigerant discharge pipe and a refrigerant merging pipe through which cooling medium flows.

[0086] In the second modification, the size of the cross section for the flow of the predetermined fluid is the same in each of the plurality of branch pipes 55 and the plurality of converging pipes 59. The size of the cross section is, for example, the diameter in a circular pipe or the hydraulic equivalent diameter (equivalent diameter: equivalent diameter of a circular pipe) in a pipe having a cross-sectional shape other than a circular pipe.

[0087] The length Lin11 of the first branch pipe 71 connected between the branch portion 53a of the supply pipe 53 and the first supply portion 61a of the first stack 61 is relatively smaller than the length Lin12 of the second branch pipe 73 connected between the branch portion 53a of the supply pipe 53 and the second supply portion 63a of the second stack 63 (Lin11<Lin12).

[0088] The length Lout11 of the first confluent pipe 75 connected between the confluence 57a of the discharge pipe 57 and the first discharge portion 61b of the first stack 61 is relatively larger than the length Lout12 of the second confluent pipe 77 connected between the confluence 57a of the discharge pipe 57 and the second discharge portion 63b of the second stack 63 (Lout11>Lout12).

[0089] Figure 7 It is a diagram showing an example of the pressure of a predetermined fluid in each fuel cell stack 11 of a fuel cell system 10B in a second modified example of the embodiment.

[0090] exist Figure 7In the example shown, as shown in the following mathematical formula (4), the sum of the length Lin11 of the first branch pipe 71 and the length Lout11 of the first converging pipe 75 (Lin11+Lout11) is the same as the sum of the length Lin12 of the second branch pipe 73 and the length Lout12 of the second converging pipe 77 (Lin12+Lout12).

[0091] [Formula 4]

[0092] Lin11+Lout11=Lin12+Lout12···(4)

[0093] Figure 7 It is shown that: when the pressure at the branch portion 53a of the supply piping 53 is set to a specified pressure P and the pressure at the confluence 57a of the discharge piping 57 is set to zero, there is a correspondence between the pressure loss Pin11 at the first branch pipe 71, the pressure losses Pin1, Pstk1, Pout1, Pin2, Pstk2, Pout2 at the first stack 61 and the pressure loss Pout11 at the first confluence pipe 75 and the pressure loss Pin12 at the second branch pipe 73, the pressure losses Pin1, Pstk1, Pout1, Pin2, Pstk2, Pout2 at the second stack 63 and the pressure loss Pout12 at the second confluence pipe 77.

[0094] like Figure 7 As shown, by making the length Lin11 of the first branch pipe 71 relatively smaller than the length Lin12 of the second branch pipe 73, the pressure loss Pin11 at the first branch pipe 71 is relatively smaller than the pressure loss Pin12 at the second branch pipe 73. In addition, by making the length Lout11 of the first converging pipe 75 relatively larger than the length Lout12 of the second converging pipe 77, the pressure loss Pout11 at the first converging pipe 75 is relatively larger than the pressure loss Pout12 at the second converging pipe 77. When the pressure loss at the first stack 61 and the pressure loss at the second stack 63 are the same, by satisfying the above-mentioned mathematical formula (4), the pressure loss from the branch portion 53a of the supply pipe 53 to the converging portion 57a ​​of the discharge pipe 57 is the same for each stack 61, 63.

[0095] According to the second modification, by setting (Lin11<Lin12) and (Lout11>Lout12), the pressure loss in the first branch pipe 71 and the first merging pipe 75 can be made nearly equal to the pressure loss in the second branch pipe 73 and the second merging pipe 77. Thus, the fluid can be uniformly supplied to the first stack 61 and the second stack 63.

[0096] By satisfying the above-mentioned mathematical formula (4), the pressure loss from the branch portion 13 a of the supply pipe 13 to the junction portion 17 a of the discharge pipe 17 can be made the same for each of the fuel cell stacks 21 , 23 .

[0097] In the above-described second modification, the sizes of the cross sections for the flow of the predetermined fluid in each of the plurality of branch pipes 55 and the plurality of merging pipes 59 are set to be the same, but the present invention is not limited to this.

[0098] Figure 8 1 is a diagram schematically showing a configuration of a fuel cell system 10C in a third modified example of the embodiment.

[0099] like Figure 8 As shown, in the fuel cell system 10C of the third variant, the size of the cross-section of the flow of the first branch pipe 71 is relatively smaller than the size of the cross-section of the flow of the second branch pipe 73, and the size of the cross-section of the flow of the first confluence pipe 75 is relatively larger than the size of the cross-section of the flow of the second confluence pipe 77.

[0100] For example, the hydraulic equivalent diameter Din11 of the first branch pipe 71 is relatively smaller than the hydraulic equivalent diameter Din12 of the second branch pipe 73 (Din11<Din12), and the hydraulic equivalent diameter Dout11 of the first confluent pipe 75 is relatively larger than the hydraulic equivalent diameter Dout12 of the second confluent pipe 77 (Dout11>Dout12).

[0101] Fig. 9 1 is a diagram showing an example of the pressure of a predetermined fluid at each fuel cell stack 11 of a fuel cell system 10C in the third modification.

[0102] exist Fig. 9 In the example shown, as shown in the following mathematical formula (5), in each stack 61, 63, the ratio of the length of each pipe 71, 73 on the branch portion 53a side to the fourth power of the hydraulic equivalent diameter is the same as the ratio of the length of each pipe 75, 77 on the confluence portion 57a ​​side to the fourth power of the hydraulic equivalent diameter.

[0103] [Formula 5]

[0104]

[0105] The ratio (L / D) of the length (L) of each pipe 71, 73, 75, 77 to the fourth power of the hydraulic equivalent diameter (D) in the above equation (5) is: 4 ) is a parameter proportional to the pressure loss of a predetermined fluid flowing through each of the pipes 71, 73, 75, 77. That is, the pressure loss is proportional to the length (L) and inversely proportional to the fourth power of the hydraulic equivalent diameter (D).

[0106] In addition, in the fuel cell system 10C of the third variant, similar to the fuel cell system 10A of the first variant, as shown in the above mathematical formula (2), in each fuel cell stack 21, 23, the ratio of the length of each pipe 41, 43 on the second supply part 63a side to the fourth power of the hydraulic equivalent diameter is the same as the ratio of the length of each pipe 45, 47 on the second discharge part 63b side to the fourth power of the hydraulic equivalent diameter.

[0107] Fig. 9 It is shown that: when the pressure at the branch portion 53a of the supply piping 53 is set to a specified pressure P and the pressure at the confluence 57a of the discharge piping 57 is set to zero, there is a correspondence between the pressure loss Pin11 at the first branch pipe 71, the pressure losses Pin1, Pstk1, Pout1, Pin2, Pstk2, Pout2 at the first stack 61 and the pressure loss Pout11 at the first confluence pipe 75 and the pressure loss Pin12 at the second branch pipe 73, the pressure losses Pin1, Pstk1, Pout1, Pin2, Pstk2, Pout2 at the second stack 63 and the pressure loss Pout12 at the second confluence pipe 77.

[0108] exist Fig. 9 In the embodiment, by making the length Lin11 of the first branch pipe 71 relatively smaller than the length Lin12 of the second branch pipe 73, and correspondingly making the hydraulic equivalent diameter Din11 of the first branch pipe 71 relatively smaller than the hydraulic equivalent diameter Din12 of the second branch pipe 73, the pressure loss Pin11 at the first branch pipe 71 is the same as the pressure loss Pin12 at the second branch pipe 73.

[0109] In addition, by making the length Lout11 of the first confluence pipe 75 relatively larger than the length Lout12 of the second confluence pipe 77, and correspondingly making the hydraulic equivalent diameter Dout11 of the first confluence pipe 75 relatively larger than the hydraulic equivalent diameter Dout12 of the second confluence pipe 77, the pressure loss Pout11 at the first confluence pipe 75 is the same as the pressure loss Pout12 at the second confluence pipe 77.

[0110] When the pressure loss at the first stack 61 and the pressure loss at the second stack 63 are the same, by satisfying the above mathematical formula (5), the pressure loss from the branch portion 53a of the supply piping 53 to the confluence portion 57a ​​of the discharge piping 57 is the same for each stack 61, 63.

[0111] In the third modification, the length (L) and the hydraulic equivalent diameter (D) of each pipe 71 , 73 , 75 , 77 may be set to satisfy the following mathematical formula (6), for example.

[0112] The following mathematical formula (6) is expressed by the length Lin11 and the hydraulic equivalent diameter Din11 of the first branch pipe 71, the length Lout11 and the hydraulic equivalent diameter Dout11 of the first confluent pipe 75, the length Lin12 and the hydraulic equivalent diameter Din12 of the second branch pipe 73, the length Lout12 and the hydraulic equivalent diameter Dout12 of the second confluent pipe 77, the fluid flow Qin of each fuel cell stack 11 in each fuel cell stack 11 supplied at rated output, the pressure loss ΔPstk at each fuel cell stack 11 when a specified fluid with a fluid flow Qin is supplied to each fuel cell stack 11, the viscosity coefficient μ of the specified fluid, the specified threshold α, the flow difference β of the specified fluid between the first stack group 61 and the second stack group 63, and the specified coefficient b.

[0113] [Mathematical formula 6]

[0114]

[0115] The predetermined threshold value α in the above mathematical formula (6) represents the tolerance for fluctuations in the flow rate of the predetermined fluid between the first stack 61 and the second stack 63. For example, when α=0.2, a 20% fluctuation in the flow rate is allowed. The predetermined threshold value α is set, for example, within the range of the flow rate required to ensure the desired power generation.

[0116] According to the third modification, by (Lin11<Lin12), (Lout11>Lout12), (Din11<Din12), and (Dout11>Dout12), the pressure loss at the first branch pipe 71 and the pressure loss at the second branch pipe 73 can be made nearly equal, and the pressure loss at the first merging pipe 75 and the pressure loss at the second merging pipe 77 can be made nearly equal. Thus, the pressure of each stack 61, 63 can be made equal, and fluctuations in performance and durability can be suppressed.

[0117] By satisfying the above-mentioned mathematical formula (6), the pressure loss from the branch portion 53 a of the supply pipe 53 to the junction portion 57 a of the discharge pipe 57 can be made the same for each stack 61 , 63 .

[0118] The embodiments of the present invention are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and changes can be made without departing from the scope of the main purpose of the invention. These embodiments and their variations are included in the scope and main purpose of the invention, and are also included in the invention recorded in the technical solution and its equivalent scope.

Claims

1. A fuel cell system, characterized in that: The fuel cell system comprises: A plurality of fuel cell stacks, including at least a first fuel cell stack and a second fuel cell stack; a supply pipe through which a fluid supplied to the plurality of fuel cell stacks flows and which has a branch portion; an exhaust pipe through which the fluid exhausted from the plurality of fuel cell stacks flows and which has a confluence portion; a first branch pipe connected to the branch portion and the first fuel cell stack; a second branch pipe connected to the branch portion and the second fuel cell stack; a first confluence pipe connected to the confluence portion and the first fuel cell stack; as well as a second confluence pipe connected to the confluence portion and the second fuel cell stack; When the sizes of the flow cross sections in the first branch pipe, the second branch pipe, the first merging pipe, and the second merging pipe are the same, The length of the first branch pipe is shorter than the length of the second branch pipe, The length of the first merging pipe is greater than the length of the second merging pipe.

2. A fuel cell system, characterized in that: The fuel cell system comprises: A plurality of fuel cell stacks, including at least a first fuel cell stack and a second fuel cell stack; a supply pipe through which a fluid supplied to the plurality of fuel cell stacks flows and which has a branch portion; an exhaust pipe through which the fluid exhausted from the plurality of fuel cell stacks flows and which has a confluence portion; a first branch pipe connected to the branch portion and the first fuel cell stack; a second branch pipe connected to the branch portion and the second fuel cell stack; a first confluence pipe connected to the confluence portion and the first fuel cell stack; as well as a second confluence pipe connected to the confluence portion and the second fuel cell stack; The length of the first branch pipe is smaller than the length of the second branch pipe, and the flow cross section of the first branch pipe is smaller than the flow cross section of the second branch pipe. The length of the first merging pipe is greater than the length of the second merging pipe, and a cross-sectional area of ​​a flow in the first merging pipe is greater than a cross-sectional area of ​​a flow in the second merging pipe.

3. A fuel cell system, characterized in that: The fuel cell system comprises: A plurality of fuel cell stacks, each of which is composed of a plurality of stack groups having at least a first stack group and a second stack group; a supply pipe through which fluid supplied to the plurality of stacks flows and which has a branch portion; a discharge pipe through which the fluid discharged from the plurality of stacks flows and which has a confluence portion; a first branch pipe connected to the branch portion and the first stack; a second branch pipe connected to the branch portion and the second stack; a first confluence pipe connected to the confluence portion and the first stack; as well as a second confluence pipe connected to the confluence portion and the second stack; When the sizes of the flow cross sections in the first branch pipe, the second branch pipe, the first merging pipe, and the second merging pipe are the same, The length of the first branch pipe is shorter than the length of the second branch pipe, The length of the first merging pipe is greater than the length of the second merging pipe.

4. A fuel cell system, characterized in that: The fuel cell system comprises: A plurality of fuel cell stacks, each of which is composed of a plurality of stack groups having at least a first stack group and a second stack group; a supply pipe through which fluid supplied to the plurality of stacks flows and which has a branch portion; a discharge pipe through which the fluid discharged from the plurality of stacks flows and which has a confluence portion; a first branch pipe connected to the branch portion and the first stack; a second branch pipe connected to the branch portion and the second stack; a first confluence pipe connected to the confluence portion and the first stack; as well as a second confluence pipe connected to the confluence portion and the second stack; The length of the first branch pipe is smaller than the length of the second branch pipe, and the flow cross section of the first branch pipe is smaller than the flow cross section of the second branch pipe. The length of the first merging pipe is greater than the length of the second merging pipe, and a cross-sectional area of ​​a flow in the first merging pipe is greater than a cross-sectional area of ​​a flow in the second merging pipe.

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