Solid oxide fuel cell system

Abstract

To provide a solid oxide fuel cell system capable of suppressing temperature rise in a cell stack and obtaining a predetermined power generation output over a long period of time.SOLUTION: A solid oxide fuel cell system includes a solid oxide cell stack (2), an anode gas supply channel (4) that supplies anode gas to an anode chamber of the cell stack (2), anode gas supply means (12) for supplying anode gas, a cathode gas supply channel (6) that supplies cathode gas to the cathode chamber of the cell stack (2), and cathode gas supply means (24) for supplying cathode gas, and the cell stack (2) is housed in a high temperature module (38). A cathode gas branch channel (72) is provided that branches from the cathode gas supply channel (6) and extends into the high temperature module (38), and a portion of the cathode gas flowing through the cathode gas supply channel (6) is fed into the high temperature module (38) through the cathode gas branch channel (72).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a solid oxide fuel cell system in which a cell stack is housed in a high-temperature module.

Background Art

[0002] As a fuel cell system, one equipped with a solid oxide cell stack formed by laminating flat battery cells has been proposed (see, for example, Patent Document 1). The battery cells of this cell stack include a solid oxide electrolyte layer, an anode (fuel electrode) disposed on one side of this electrolyte layer, and a cathode (oxygen electrode) disposed on the other side. An anode chamber is defined facing the anode, and a cathode chamber is defined facing the cathode. An anode gas is supplied to the anode chamber of this cell stack, a cathode gas is supplied to its cathode chamber, and power generation is performed by an electrochemical reaction (fuel cell reaction) between the anode gas and the cathode gas in the battery cell.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In such a solid oxide fuel cell system, when the operating time becomes long, the cell stack deteriorates over time, and the temperature of the cell stack tends to rise due to the deterioration over time. Since an increase in the temperature of the cell stack has an adverse effect on durability, it is desirable to suppress the operating temperature of the cell stack to a certain temperature. As methods for suppressing this temperature, there are a method of cooling the cell stack by increasing the supply flow rate of the cathode gas and a method of reducing the power generation output of the cell stack.

[0005] However, while increasing the cathode gas supply flow rate allows for a certain degree of increase, it cannot be increased indefinitely. After increasing the supply flow rate to a certain point, the power output of the cell stack is reduced. Similarly, reducing the power output of the cell stack is reduced from a point in the fuel cell system's operation after installation, but only after it has not been running for very long. Regardless of which method is adopted, the power output of the cell stack is reduced, and such power output reduction control prevents users of the fuel cell system from fully enjoying the benefits of installing it.

[0006] For this reason, in the fuel cell system described in Patent Document 1, a cooling gas passage is provided between adjacent battery cells, and the cell stack is cooled by the cooling gas (for example, air) flowing through this cooling gas passage.

[0007] However, such fuel cell systems require cooling gas passages between adjacent battery cells, which increases the number of components in the cell stack, leading to higher costs and a larger overall size of the cell stack.

[0008] The objective of the present invention is to provide a solid oxide fuel cell system that can suppress the temperature rise of the cell stack and obtain a predetermined power output over a long period of time. [Means for solving the problem]

[0009] The solid oxide fuel cell system according to claim 1 of the present invention is a solid oxide cell stack comprising a plurality of battery cells having an electrolyte layer that conducts ions, an anode disposed on one side of the electrolyte layer, and a cathode disposed on the other side of the electrolyte layer; an anode gas supply channel for supplying anode gas to the anode chamber of the cell stack; anode gas supply means for supplying anode gas through the anode gas supply channel; a cathode gas supply channel for supplying cathode gas to the cathode chamber of the cell stack; and cathode gas supply means for supplying cathode gas through the cathode gas supply channel, wherein the cell stack is housed in a high-temperature module that defines a high-temperature space. A cathode gas branch channel is provided that branches off from the cathode gas supply channel and extends into the high-temperature module. The cathode gas branching channel is provided with a cooling cathode gas flow rate adjustment means for adjusting the supply flow rate of cathode gas supplied into the high-temperature module, and the cooling cathode gas flow rate adjustment means includes a first throttling member that limits the flow rate of cathode gas, a cathode gas bypass channel provided to bypass the first throttling member, and a bypass gas flow rate adjustment means provided in the cathode gas bypass channel. A portion of the cathode gas flowing through the cathode gas supply channel is supplied to the high-temperature module through the cathode gas branch channel.

[0010] Furthermore, the solid oxide fuel cell system according to claim 2 of the present invention The solid oxide fuel cell system comprises a solid oxide cell stack having a plurality of battery cells, each having an electrolyte layer that conducts ions, an anode disposed on one side of the electrolyte layer, and a cathode disposed on the other side of the electrolyte layer; an anode gas supply channel for supplying anode gas to the anode chamber of the cell stack; anode gas supply means for supplying anode gas through the anode gas supply channel; a cathode gas supply channel for supplying cathode gas to the cathode chamber of the cell stack; and cathode gas supply means for supplying cathode gas through the cathode gas supply channel, wherein the cell stack is housed in a high-temperature module that defines a high-temperature space. A cathode gas branch channel is provided that branches off from the cathode gas supply channel and extends into the high-temperature module. The cathode gas branch channel is equipped with a cooling cathode gas flow rate adjustment means for adjusting the flow rate of cathode gas supplied into the high-temperature module. The cooling cathode gas flow rate adjustment means includes a first flow control valve for adjusting the flow rate of cathode gas, a cathode gas bypass channel provided to bypass the first flow control valve, and a bypass gas flow rate adjustment means provided in the cathode gas bypass channel. A portion of the cathode gas flowing through the cathode gas supply channel is supplied into the high-temperature module through the cathode gas branch channel.

[0013] Furthermore, the claims of the present invention 3 The solid oxide fuel cell system described herein is characterized in that the bypass gas flow rate adjustment means includes a second throttling member for limiting the flow rate of cathode gas, and an on / off valve for opening and closing the cathode gas bypass passage or a second flow rate adjustment valve for adjusting the flow rate of cathode gas.

[0014] Furthermore, the claims of the present invention 4In the solid oxide fuel cell system described above, a cathode gas preheater is provided in the high-temperature module to exchange heat between the combustion exhaust gas obtained by burning the anode off gas from the cell stack and the cathode gas flowing through the cathode gas supply channel, and the cathode gas flowing through the cathode gas branch channel is supplied to the high-temperature module after heat exchange has been performed with the combustion exhaust gas obtained by burning the anode off gas in the cathode gas preheater. [Effects of the Invention]

[0016] The solid oxide fuel cell system according to claim 1 of the present invention comprises a solid oxide cell stack having a plurality of battery cells, an anode gas supply means for supplying anode gas through an anode gas supply channel, and a cathode gas supply means for cooling for supplying cathode gas through a cathode gas supply channel. The cell stack is housed in a high-temperature module that defines a high-temperature space, and a cathode gas branch channel is provided that branches off from the cathode gas supply channel and extends into the high-temperature module. As a result, a portion of the cathode gas flowing through the cathode gas supply channel is supplied into the high-temperature module through the cathode gas branch channel, and this cathode gas can suppress the temperature rise of the cell stack housed in the high-temperature module, thereby enabling the acquisition of a predetermined power output over a long period of time. Furthermore, since a cooling cathode gas flow rate adjustment means is provided in the cathode gas branching channel to adjust the supply flow rate of cathode gas, this cooling cathode gas flow rate adjustment means can adjust the supply flow rate of cathode gas supplied into the high-temperature module, thereby suppressing the temperature rise of the cell stack housed in this high-temperature module. Moreover, by using a first throttling member as the cooling cathode gas flow rate adjustment means, the flow rate of cathode gas supplied through the cathode gas branching channel can be restricted. Furthermore, since the cooling cathode gas flow rate adjustment means includes a cathode gas bypass channel that bypasses the first throttling member and a bypass gas flow rate adjustment means provided in this cathode gas bypass channel, the supply flow rate of cathode gas supplied into the high-temperature module can be adjusted by the first throttling member in the cathode gas branching channel and the bypass gas flow rate adjustment means in the bypass channel, and this supply flow rate adjustment can be performed in two stages.

[0017] Furthermore, according to the solid oxide fuel cell system described in claim 2 of the present invention, Since its basic configuration is the same as that of the invention described in claim 1, it produces the same effects as described above. Furthermore, by using a first flow control valve as a means for adjusting the flow rate of the cooling cathode gas, the flow rate of the cathode gas supplied through the cathode gas branch passage can be adjusted. Moreover, since the cooling cathode gas flow rate adjustment means includes a cathode gas bypass passage that bypasses the first flow control valve and a bypass gas flow rate adjustment means disposed in this cathode gas bypass passage, the supply flow rate of the cathode gas supplied into the high-temperature module can be adjusted by the first flow control valve in the cathode gas branch passage and the bypass gas flow rate adjustment means in the bypass passage, and this supply flow rate adjustment can be performed in two stages.

[0020] Furthermore, the claims of the present invention 3 According to the solid oxide fuel cell system described above, the supply flow rate of cathode gas supplied through the cathode bypass channel can be adjusted by using a combination of a second throttling member and an on / off valve (or a second flow control valve) as a bypass gas flow rate adjustment means.

[0021] Furthermore, the claims of the present invention 4According to the solid oxide fuel cell system described in [reference], the cathode gas flowing through the cathode gas branch flow path is heat-exchanged with the combustion exhaust gas obtained by burning the anode off-gas in the cathode gas waste heat recovery device, and then fed into the high-temperature module. Therefore, the cathode gas fed into the high-temperature module is fed after being heated, and it is possible to prevent the inside of this high-temperature module from being rapidly cooled by the cold cathode gas.

Brief Description of Drawings

[0023] [Figure 1] Overall view schematically showing a first embodiment of a solid oxide fuel cell system according to the present invention. [Figure 2] Schematic cross-sectional view schematically showing a cell stack of the solid oxide fuel cell system of FIG. 1 after being cut. [Figure 3] Schematic view schematically showing a cooling cathode gas flow rate adjusting means and related configurations in the solid oxide fuel cell system of FIG. 1. [Figure 4] Graph showing the relationship between the cathode gas supply flow rate, the temperature of the cell stack, and its power generation output in the solid oxide fuel cell system of FIG. 1. [Figure 5] Schematic view schematically showing a modified form of the cooling cathode gas flow rate adjusting means. [Figure 6] Graph showing the relationship between the cathode gas supply flow rate, the temperature of the cell stack, and its power generation output when using the modified form of the cooling cathode gas flow rate adjusting means. [Figure 7] Schematic view schematically showing a part of a second embodiment of a solid oxide fuel cell system according to the present invention. [Figure 8] FIG. 8(a) is a graph showing the relationship between the power generation output of the cell stack and its temperature when the supply flow rate of the cathode gas is kept constant in the solid oxide fuel cell system, and FIG. 8(b) is a graph showing the relationship between the supply flow rate of the cathode gas and the power generation output of the cell stack when the temperature of the cell stack is kept constant.

Embodiments for Carrying Out the Invention

[0024] Hereinafter, embodiments of the fuel cell system according to the present invention will be described with reference to the attached drawings. First, a first embodiment of the solid oxide fuel cell system according to the present invention will be described with reference to Figures 1 to 3.

[0025] In Figures 1 and 2, the solid oxide fuel cell system of the first embodiment includes a cell stack 2 that generates electricity through an electrochemical reaction between anode gas (reformed gas obtained by steam reforming of city gas) and cathode gas (oxidizing gas such as air). An anode gas supply channel 4 for supplying anode gas (raw fuel gas such as city gas) and a cathode gas supply channel 6 for supplying cathode gas (oxidizing gas) are provided on the inlet side of the cell stack 2. Furthermore, an anode off-gas discharge channel 8 for discharging anode off-gas and a cathode off-gas discharge channel 10 for discharging cathode off-gas are provided on the discharge side of the cell stack 2.

[0026] A fuel blower 12, which constitutes the anode gas supply means, is installed in this anode gas supply channel 4. Through the action of this fuel blower 12, anode gas (raw fuel gas) from an anode gas supply source 14 (which consists of, for example, buried pipes supplying city gas, fuel gas tanks, etc.) is supplied through the anode gas supply channel 4. A desulfurizer 16 is further provided in this anode gas supply channel 4, and the sulfur components contained in the anode gas (raw fuel gas) are removed by this desulfurizer 16, and the anode gas from which the sulfur components have been removed is supplied to the reforming unit 18.

[0027] The illustrated reforming unit 18 comprises a reforming section 20 for reforming the anode gas (raw fuel gas) and a combustion section 22 for burning the anode-off gas and cathode-off gas from the cell stack 2. The reforming section 20 is filled with a reforming catalyst for reforming the anode gas. The anode gas (e.g., city gas) and reformed water (pure water) used for steam reforming are supplied to the reforming section 20 through the anode gas supply channel 4, and steam reforming of the anode gas is performed in the reforming section 20 using the combustion heat of the fuel section 22. In this configuration, the reforming section 20 and the combustion section 22 are integrally configured as the reforming unit 18, but the reforming section 20 may be configured separately as a reformer, and the combustion section 22 as a combustor.

[0028] The reformed gas (anode gas) that has been steam reformed in the reforming unit 18 is supplied to the cell stack 2 downstream. In addition, a cathode gas supply means, such as an air blower 24, is installed in the cathode gas supply channel 6, and this air blower 24 supplies cathode gas to the cell stack 2 through the cathode gas supply channel 6.

[0029] The cell stack 2 will be described primarily with reference to Figure 2. The illustrated cell stack 2 consists of a plurality of battery cells 26 stacked vertically in Figure 2, and each battery cell 26 is composed of substantially the same shape of flat cell. Each battery cell 26 comprises a solid oxide electrolyte layer 28 that conducts ions, an anode 30 (fuel electrode) disposed on one side of the electrolyte layer 28 (the lower side in Figure 2), and a cathode 32 (oxygen electrode) disposed on the other side of the electrolyte layer 28 (the upper side in Figure 2). An interconnector 34 is disposed between each battery cell 26, and the battery cells 26 are electrically connected via this interconnector 34. In this example, as shown in Figure 2, the electrolyte layer 28 is provided on the surface side of the anode 30 of each battery cell 26, the cathode 32 is provided on the surface side of the electrolyte layer 28, an anode chamber 35 is defined on the anode 30 side of the electrolyte layer 28, and a cathode chamber 36 is defined on the cathode side of the electrolyte layer 28.

[0030] With this configuration, the anode gas (reformed gas) from the anode gas supply channel 4 (see Figure 1) is distributed by the inlet manifold (not shown) as shown by the solid arrows in Figure 2, and then supplied to the anode chamber 35 of each battery cell 26. The anode off gas discharged from the anode chamber 35 of each battery cell 26 flows to the outlet manifold (not shown) and then is supplied to the combustion section 22 of the reforming unit 18 (see Figure 1) through the anode off gas discharge channel 8.

[0031] Furthermore, the cathode gas from the cathode gas supply channel 6 is distributed by an inlet manifold (not shown), as indicated by the dashed arrows in Figure 2, and then supplied to the cathode chamber 36 of each battery cell 26. The cathode-off gas from the cathode chamber 36 of each battery cell 26 flows to an outlet manifold (not shown) and then is supplied to the combustion section 22 of the reforming unit 18 through the cathode-off gas discharge channel 10.

[0032] Returning to Figure 1, in this fuel cell system, the cell stack 2 and the reforming unit 18 are housed in a high-temperature space 40 defined by a high-temperature module 38 whose outer surface is covered with insulating material. The anode off-gas from the anode chamber 35 (see Figure 2) and the cathode off-gas from the cathode chamber 36 (see Figure 2) of the cell stack 2 are supplied to the combustion section 22 of the reforming unit 18, where the anode off-gas is burned. The heat of this combustion heats the reforming section 20 and maintains a high temperature inside the high-temperature module 38.

[0033] In this solid oxide fuel cell system, the waste heat from the combustion exhaust gas discharged from the combustion section 22 of the reforming unit 18 is recovered as hot water. Referring further to Figure 1, a hot water storage device 42 is provided for storing the waste heat as hot water. This hot water storage device 42 includes a hot water storage tank 44 for storing hot water, a circulation channel 48 for circulating the water in the hot water storage tank 44 through a heat exchanger 46 for waste heat recovery, and a circulation pump 50 for flowing the water from the hot water storage tank 44 through the circulation channel 48.

[0034] With this configuration, when the circulation pump 50 operates, the hot water in the hot water storage tank 44 is supplied to the heat recovery heat exchanger 46 through the circulation channel 48. In this heat recovery heat exchanger 46, heat is exchanged between the combustion exhaust gas flowing from the combustion section 22 of the reforming unit 18 through the combustion exhaust gas discharge channel 52 and the water flowing through the circulation channel 48. The water heated by the heat exchange (hot water) is then stored in the hot water storage tank 44. The combustion exhaust gas from the combustion exhaust gas discharge channel 52 is discharged to the outside through the combustion exhaust gas exhaust channel 54.

[0035] Furthermore, when the combustion exhaust gas is cooled by heat exchange in the heat recovery heat exchanger 46, the water contained in the combustion exhaust gas condenses, and this condensed water is purified into pure water by the water purifier 56 and then collected in the water tank 58. This condensed water (pure water) collected in the water tank 58 is used for steam reforming in the reforming unit 18.

[0036] In this embodiment, the pure water tank 44 and the reforming section 20 of the reforming unit 18 are connected by a water supply channel 60, and a water pump 62 is provided in this water supply channel 60 as a means of supplying water. With this configuration, when the water pump 62 is operated, the condensed water (pure water) in the water tank 58 is supplied to the reforming section 20 of the reforming unit 18 through the water supply channel 60.

[0037] In this embodiment, a cathode gas preheater 64 is further provided within the high-temperature module 38. This cathode gas preheater 64 performs heat exchange between the cathode gas flowing through the cathode gas supply channel 6 and the combustion exhaust gas flowing through the combustion exhaust gas discharge channel 52. The cathode gas heated by this heat exchange is supplied to the cathode chamber 36 (see Figure 2) of the cell stack 2, and the combustion exhaust gas cooled by the heat exchange flows to the heat recovery heat exchanger 46.

[0038] In this solid oxide fuel cell system, as shown in Figure 2, anode gas (reformed gas) from the anode gas supply channel 4 is supplied to the anode chamber 35 of the battery cell 26 in the cell stack 2, and cathode gas from the cathode supply channel 6 is supplied to the cathode chamber 36 of the battery cell 26 in the cell stack 2. Electricity is generated by the electrochemical reaction between the anode gas in the anode chamber 35 and the cathode gas in the cathode chamber 36. The generated power in each battery cell 26 is collected via the interconnector 20, and the collected generated power is converted from DC current to AC current before being supplied to a power load (not shown), such as a lighting device or home appliance.

[0039] In such solid oxide fuel cell systems, if the operation is controlled to keep the power output of the cell stack 2 constant, as shown in Figure 8(a), the operating temperature of the cell stack 2 tends to rise due to degradation over time as the operating time increases. A temperature rise exceeding a predetermined temperature of the cell stack 2 will adversely affect the durability of the cell stack 2.

[0040] Therefore, in order to suppress this temperature rise of the cell stack 2, the operation is controlled as shown in Figure 8(b). Specifically, in order to maintain the operating temperature of the cell stack at a constant temperature, the supply flow rate of cathode gas is increased as the operating time increases to enhance the cooling effect of the cathode gas on the cell stack 2. When cooling by increasing the supply flow rate becomes difficult, the power output of the cell stack 2 is reduced to suppress the rise in its operating temperature.

[0041] However, such control that suppresses the power generation of cell stack 2 prevents the full enjoyment of the benefits of installing a fuel cell system, and it is desirable to minimize the operating time of the control that suppresses power generation output.

[0042] For this reason, in this embodiment, a cathode gas branch channel 72 is provided branching off from the cathode gas supply channel 6, and a cooling cathode gas flow rate adjustment means 74 is provided in this cathode gas branch channel 72. This cathode gas branch channel 72 is led into the high-temperature module 38 and extends through the cathode gas preheater 64 to the vicinity of the reforming unit 18 at the upper end of the high-temperature space 40.

[0043] With this configuration, a portion of the cathode gas supplied through the cathode gas supply channel 6 is sent to the cathode gas preheater 64 through the cathode gas branch channel 72. In the cathode gas preheater 64, heat exchange takes place between the cathode gas flowing through the cathode gas branch channel 72 and the combustion exhaust gas flowing through the combustion exhaust gas discharge channel 52. The cathode gas heated by this heat exchange is then sent to the vicinity of the reforming unit 18 in the high-temperature module 38. The supplied cathode gas then flows from top to bottom within the high-temperature module 38 and is discharged to the outside through the exhaust port 76. As it flows around the cell stack 2, it cools the cell stack 2, suppressing its temperature rise.

[0044] In relation to this exhaust port 76, for example, it can be configured as follows: Combustion exhaust gas from the combustion exhaust gas discharge channel 52 is discharged from the exhaust port 76 of the high-temperature module 38 through the high-temperature space 40, and cathode gas supplied into the high-temperature module 38 as cooling cathode gas (cathode gas supplied through the cathode gas branch channel 72) is discharged together with the combustion exhaust gas discharged from this exhaust port 76. In this case, it is desirable to place a combustion catalyst 78 at the exhaust port 76 of the high-temperature module 38 and burn any unburned gas contained in the combustion exhaust gas with this fuel catalyst 78. When configured in this way, the combustion exhaust gas discharged from this exhaust port 76 (including the cathode gas supplied for cooling) is supplied to the heat recovery heat exchanger 46 and used for heat exchange with water from the hot water storage tank 44, and the combustion exhaust gas treated by the combustion catalyst 78 is discharged to the outside through the combustion exhaust gas exhaust channel 54.

[0045] In this embodiment, the cathode gas flowing through the cathode gas branch channel 72 is guided into the high-temperature module 38 through the cathode gas preheater 64. However, it is also possible to guide the cathode gas directly to the vicinity of the reforming unit 18 without passing through the cathode gas preheater 64.

[0046] The cooling cathode gas flow rate adjustment means 74 provided in the cathode gas branching passage 72 can be configured as shown in Figure 3. In Figure 3, in this embodiment, the cooling cathode gas flow rate adjustment means 74 includes a first throttling member 80 disposed in the cathode gas branching passage 72, a cathode gas bypass passage 82 that bypasses the first throttling member 80, and an on-off valve 84 and a second throttling member 86 disposed in the cathode gas bypass passage 82, wherein the on-off valve 84 and the second throttling member 86 constitute a bypass gas flow rate adjustment means that adjusts the flow rate of the cathode gas bypass passage 82.

[0047] The first throttling member 80 restricts the flow rate of cathode gas through the cathode gas branch passage 72, and the second throttling member 86 restricts the flow rate of cathode gas through the cathode gas bypass passage 82. In this case, the second throttling member 86 is set to supply a greater flow rate of cathode gas than the first throttling member 80. The on / off valve 84 controls the opening and closing of the cathode gas bypass passage 82.

[0048] When using the cooling cathode gas flow rate adjustment means 74 configured as described above, at the time of initial installation of the fuel cell system, the on-off valve 84 is kept closed, and a portion of the cathode gas flowing through the cathode gas supply channel 6 is supplied into the high-temperature module 38 through the cathode gas branch channel 72. The supply flow rate is limited by the first throttling member 80, and a small amount of cathode gas is supplied into the high-temperature module 38.

[0049] As the fuel system continues to operate for an extended period, the cell stack 2 deteriorates over time, causing the on-off valve 84 to be switched to the open state. In this way, a portion of the cathode gas flowing through the cathode gas supply passage 6 is supplied through the cathode gas branch passage 72 (its supply flow rate is limited by the first throttling member 80), and a portion of the remaining cathode gas is supplied through the cathode gas bypass passage 82 (its supply flow rate is limited by the second throttling member 86). Thus, the supply flow rate of cathode gas supplied into the high-temperature module 38 through the cathode gas branch passage 72 increases, enhancing the cooling effect of the cathode gas and further suppressing the temperature rise of the cell stack 2.

[0050] When the above-mentioned cooling cathode gas flow rate adjustment means 74 is used, the changes in the cathode gas flow are as shown in Figure 4. That is, when attempting to control the power output of the cell stack 2 to remain constant, the operating temperature of the cell stack 2 tends to rise as the operating time increases. This temperature rise is suppressed by increasing the supply flow rate of cathode gas supplied to the cell stack 2 through the cathode gas supply channel 6. At this time, a portion of the cathode gas flowing through the cathode gas supply channel 6 is also supplied to the high-temperature module 38 through the cathode branch channel 72, and the temperature rise of the cell stack 2 is also suppressed by the cathode gas supplied to the high-temperature module 38.

[0051] Then, when it becomes difficult to suppress the temperature rise of the cell stack 2 with the cathode gas supplied to the cathode chamber 36 (see Figure 3) of the cell stack 2 through the cathode gas supply channel 6, the on / off valve 84 is switched to the open state. In this way, the amount of cathode gas supplied into the high-temperature module 38 increases in steps, enhancing the cooling effect and continuously suppressing the temperature rise of the cell stack 2. As a result, it becomes possible to continue operating the cell stack 2 without reducing its power output.

[0052] In this embodiment, a combination of an on-off valve 84 and a second throttling member 86 is used as a bypass gas flow rate adjustment means. However, instead of this configuration, the system may be configured with a combination of the second throttling member 86 and a flow control valve (not shown) (which constitutes the second flow control valve) that controls the flow rate of cathode gas flowing through the cathode gas bypass passage 82, or the second throttling member 86 may be omitted and the system may simply consist of a flow control valve.

[0053] Furthermore, in the embodiment described above, a cathode gas bypass passage 82 that bypasses a portion of the cathode gas branch passage 72 and bypass gas flow rate adjustment means (on-off valve 84 and second throttling member 86) are provided. However, as shown in Figure 5, these cathode gas bypass passage 82 and bypass gas flow rate adjustment means may be omitted.

[0054] In Figure 5, in this modified form, the cathode gas branching channel 72A is provided Cooling cathode gas The flow rate adjustment means 74A consists of, for example, a flow rate control valve 92 (which constitutes the first flow rate control valve) that adjusts the flow rate of cathode gas flowing through the cathode gas branch passage 72A. This flow rate control valve 92 adjusts the supply flow rate of cathode gas that is supplied from the cathode gas supply passage 6 to the high-temperature module 38 through the cathode gas branch passage 72A.

[0055] When this modified form of the cooling cathode gas flow rate adjustment means 74A is used, the changes in the cathode gas flow are as shown in Figure 6. That is, when attempting to control the power output of the cell stack to be kept constant, the operating temperature of the cell stack tends to rise as the operating time increases. This temperature rise is suppressed by increasing the supply flow rate of cathode gas supplied to the cell stack through the cathode gas supply channel 6. At this time, a portion of the cathode gas flowing through the cathode gas supply channel 6 is sent into the high-temperature module 38 through the cathode gas branch channel 72A, and the temperature rise of the cell stack 2 is also suppressed by the cathode gas sent into the high-temperature module 38. The supply flow rate of cathode gas supplied through this cathode branch channel 72A is adjusted, for example, by controlling the flow control valve 92, so that it gradually increases somewhat with the passage of operating time.

[0056] Furthermore, due to design constraints on the cell stack caused by the pressure difference between the anode gas and cathode gas, when it becomes difficult to suppress the temperature rise by supplying cathode gas to the cell stack through the cathode gas supply channel 6, the flow control valve 92 is controlled to fluctuate more significantly. In this way, the amount of change in the supply flow rate of cathode gas delivered into the high-temperature module 38 increases, enhancing the cooling effect, and even with this configuration, the temperature rise of the cell stack can be continuously suppressed.

[0057] In this modified configuration, a combination of an on-off valve and a throttling member (not shown) may be used instead of the flow control valve 92. In this case, when the temperature rise of the cell stack 2 can be suppressed by the cathode gas supplied to the cell stack through the cathode gas supply passage 6, the cell stack may be cooled by the cathode gas supplied to the cell stack, and the on-off valve may be opened when cooling by this cathode gas becomes difficult. When the on-off valve is opened, a portion of the cathode gas flowing through the cathode gas supply passage 6 is sent into the high-temperature module 38 through the cathode gas branch passage 72A, and the temperature rise of the cell stack in the high-temperature module 38 can be suppressed by the cathode gas sent in this way, and the same effect as described above can be obtained even with this configuration. Note that a flow control valve may be used instead of this throttling member.

[0058] Next, with reference to Figure 7, a second embodiment of the solid oxide fuel cell system according to the present invention will be described. In this second embodiment, only the parts that differ from the first embodiment described above are shown in the drawings. Other components not shown are substantially the same as those in the first embodiment described above. In this second embodiment, components that are substantially the same as those in the first embodiment described above are given the same reference numerals, and their descriptions are omitted.

[0059] In Figure 7, the solid oxide fuel cell system of this second embodiment is provided with an independent cooling gas supply channel 102 that guides the cooling gas into the high-temperature module 38, and a cooling gas blower 104 is provided in this cooling gas supply channel 102 as a means for supplying cooling gas.

[0060] In this embodiment, air (outside air) is used as the cooling gas, and an air blower is used as the cooling gas blower 104. The cooling gas (air) from the cooling gas blower 104 (air blower) is guided into the high-temperature module 38 through the cooling gas supply channel 102, preheated in the cathode gas preheater 46 as described above, and then supplied into the high-temperature module 38. The supply flow rate of the cooling gas supplied through the cooling gas supply channel 102 can be adjusted, for example, by controlling the rotation speed of the cooling gas blower 104. By increasing the rotation speed, the supply flow rate of the cooling gas can be increased.

[0061] Even with this configuration, the cooling gas (air) supplied through the cooling gas supply channel 102 can suppress the temperature rise of the cell stack (not shown), thereby enabling the cell stack to operate for a long period of time while maintaining a constant power output. The cathode gas (air) from the air blower 24 (cathode gas supply means) is supplied to the cathode chamber (not shown) of the cell stack through the cathode gas supply channel 6.

[0062] Although various embodiments of the solid oxide fuel cell system according to the present invention have been described above, the present invention is not limited to these embodiments, and various changes and modifications are possible without departing from the scope of the present invention. [Explanation of Symbols]

[0063] 2-cell stack 4 Anode gas supply channel 6. Cathode gas supply channel 12. Fuel blower (anode gas supply means) 18 Modification Unit 24. Air blower (cathode gas supply means) 26 battery cells 28 Solid oxide electrolyte layer 30 Anode (Fuel electrode) 32 Cathode (oxygen electrode) 35 Anode Room 36 Cathode Chamber 38 High-temperature module 40 High-temperature space 72,72A Cathode Gas Branch Channel 74,74A Cooling cathode gas flow rate adjustment means 80 First diaphragm member 82 Cathode Gas Bypass Channel 84 Shut-off valves 86 Second throttling member 92 Flow control valve 102 Cooling gas supply channel 104 Cooling gas supply means

Claims

1. A solid oxide fuel cell system comprising: a solid oxide cell stack having an electrolyte layer that conducts ions, a plurality of battery cells having an anode disposed on one side of the electrolyte layer and a cathode disposed on the other side of the electrolyte layer; an anode gas supply channel for supplying anode gas to the anode chamber of the cell stack; anode gas supply means for supplying anode gas through the anode gas supply channel; a cathode gas supply channel for supplying cathode gas to the cathode chamber of the cell stack; and cathode gas supply means for supplying cathode gas through the cathode gas supply channel, wherein the cell stack is housed in a high-temperature module that defines a high-temperature space, A solid oxide fuel cell system is provided, characterized in that a cathode gas branch channel is provided that branches off from the cathode gas supply channel and extends into the high-temperature module, the cathode gas branch channel is provided with cooling cathode gas flow rate adjustment means for adjusting the supply flow rate of cathode gas supplied into the high-temperature module, the cooling cathode gas flow rate adjustment means includes a first throttling member for limiting the flow rate of cathode gas, a cathode gas bypass channel provided to bypass the first throttling member, and a bypass gas flow rate adjustment means provided in the cathode gas bypass channel, and a portion of the cathode gas flowing through the cathode gas supply channel is supplied into the high-temperature module through the cathode gas branch channel.

2. A solid oxide type fuel cell system comprising: a solid oxide type cell stack having an electrolyte layer that conducts ions, an anode disposed on one side of the electrolyte layer, and a cathode disposed on the other side of the electrolyte layer, a plurality of battery cells, an anode gas supply channel for supplying anode gas to the anode chamber of the cell stack, anode gas supply means for supplying anode gas through the anode gas supply channel, a cathode gas supply channel for supplying cathode gas to the cathode chamber of the cell stack, and cathode gas supply means for supplying cathode gas through the cathode gas supply channel, wherein the cell stack is housed in a high-temperature module that defines a high-temperature space, A solid oxide fuel cell system is provided, characterized in that a cathode gas branch channel is provided that branches off from the cathode gas supply channel and extends into the high-temperature module, a cooling cathode gas flow rate adjustment means is provided in the cathode gas branch channel for adjusting the supply flow rate of cathode gas supplied into the high-temperature module, the cooling cathode gas flow rate adjustment means includes a first flow control valve for adjusting the flow rate of cathode gas, a cathode gas bypass channel provided to bypass the first flow control valve, and a bypass gas flow rate adjustment means provided in the cathode gas bypass channel, and a portion of the cathode gas flowing in the cathode gas supply channel is supplied into the high-temperature module through the cathode gas branch channel.

3. The solid oxide fuel cell system according to claim 1 or 2, characterized in that the bypass gas flow rate adjustment means includes a second throttling member for limiting the flow rate of cathode gas, and an on / off valve for opening and closing the cathode gas bypass passage or a second flow rate adjustment valve for adjusting the flow rate of cathode gas.

4. The solid oxide fuel cell system according to claim 1 or 2, wherein the high-temperature module is provided with a cathode gas preheater that exchanges heat between combustion exhaust gas obtained by burning anode off gas from the cell stack and cathode gas flowing through the cathode gas supply channel, and the cathode gas flowing through the cathode gas branch channel is supplied to the high-temperature module after heat exchange has been performed with the combustion exhaust gas obtained by burning anode off gas in the cathode gas preheater.

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