JP2017079110A - Fuel cell system - Google Patents

Abstract

An object of the present invention is to suppress the oxidation of a fuel electrode due to the backflow of mixed exhaust gas in an auxiliary part to a fuel chamber after the control of a control part is stopped. In the fuel cell system, when the power supply is stopped when the oxidant gas supply pipe is provided, the flow path in the oxidant gas supply pipe is closed, and when the power supply is performed, the fuel cell system is closed. A first open / close portion that switches from an open state to open the flow path in the oxidant gas supply pipe and a first check valve provided in the fuel gas supply pipe. [Selection] Figure 1

Description

  The technology disclosed in this specification relates to a fuel cell system.

  The fuel cell system includes a fuel cell stack including a plurality of single cells, an oxidant gas supply source, an oxidant gas supply pipe, a fuel gas supply source, a fuel gas supply pipe, an auxiliary unit, and a control unit. Prepare. The fuel cell stack is formed with an oxidant gas flow path communicating with the air chamber facing the air electrode of each single cell and a fuel gas flow path communicating with the fuel chamber facing the fuel electrode of each single cell. Yes. The oxidant gas supply source is connected to the oxidant gas flow path of the fuel cell stack via the oxidant gas supply pipe, and supplies the oxidant gas to the air chamber. The fuel gas supply source is connected to the fuel gas flow path of the fuel cell stack via the fuel gas supply pipe, and supplies the fuel gas to the fuel chamber. The auxiliary portion is formed with a merge space in which the oxidant off-gas discharged from the fuel cell stack and the fuel off-gas merge. The control unit controls the supply amount of the oxidant gas from the oxidant gas supply source and the supply amount of the fuel gas from the fuel gas supply source.

  In such a fuel cell system, when the power generation operation of the fuel cell stack is stopped, a mixed gas of an oxidant off-gas and a fuel off-gas (hereinafter referred to as a mixed exhaust gas) present in the merging space of the auxiliary unit is the fuel of the fuel cell stack. There is a risk that the fuel electrode may oxidize due to oxygen flowing back into the room and oxygen contained in the mixed exhaust gas. Therefore, when the power generation operation of the fuel cell stack is stopped, the supply amounts of the oxidant gas supply source and the fuel gas supply source are controlled by the control unit so that the mixed exhaust gas does not flow backward from the auxiliary unit into the fuel chamber of each single cell. The technique to make is proposed (refer patent document 1).

JP 2013-225484 A

  In the above conventional fuel cell system, since the oxidation of the fuel electrode is suppressed by the control of the control unit, for example, when the control unit becomes unable to control the oxidant gas supply source and the fuel gas supply source normally due to a power failure or the like, When the control unit stops controlling the oxidant gas supply source and the fuel gas supply source due to error detection, there is a possibility that the oxidation of the fuel electrode cannot be suppressed.

  The present specification discloses a technique capable of solving at least a part of the problems described above.

  The technology disclosed in this specification can be implemented as the following forms.

(1) A fuel cell system disclosed in this specification is a fuel including a plurality of unit cells each including an electrolyte layer containing a solid oxide or a carbonate, and an air electrode and a fuel electrode facing each other with the electrolyte layer interposed therebetween. A fuel cell stack having a oxidant gas flow path communicating with the air chamber facing the air electrode and a fuel gas flow path communicating with the fuel chamber facing the fuel electrode; An oxidant gas supply source for sending an oxidant gas; an oxidant gas supply pipe having one end connected to the oxidant gas supply source and the other end connected to the oxidant gas flow path; and a fuel for sending fuel gas A gas supply source; a fuel gas supply pipe having one end connected to the fuel gas supply source and the other end connected to the fuel gas flow path; and an oxidant including the oxidant gas discharged from the fuel cell stack Including off-gas and fuel gas Provided in the oxidant gas supply pipe in a fuel cell system, comprising: an auxiliary part in which a merge space where the fuel off-gas merges is formed; and a control part that controls the oxidant gas supply source and the fuel gas supply source. When the power supply is stopped, the flow path in the oxidant gas supply pipe is closed, and when the power is supplied, the flow path in the oxidant gas supply pipe is opened from the closed state. A first opening / closing portion that switches to an open state and a first check valve provided in the fuel gas supply pipe are provided. According to this fuel cell system, when the control of the control unit is stopped for some reason, the power supply to the first opening / closing unit is stopped, so that the first opening / closing unit is closed and the oxidant gas supply source The supply of the oxidant gas is cut off. Further, since the first check valve is provided in the fuel gas supply pipe, the fuel gas is prevented from flowing back from the fuel cell stack side to the fuel gas supply source side. In other words, the pressure and flow rate of the gas in the oxidant gas flow path in the fuel cell system are quickly reduced, and the pressure and flow rate of the gas in the fuel gas flow path are set to be larger than the pressure and flow rate of the gas in the oxidant gas flow path. produce. Thereby, after the control of the control unit is stopped, the amount of the oxidant off-gas discharged from the fuel cell stack flows into the auxiliary unit while the fuel off-gas discharged from the fuel cell stack is supplied into the auxiliary unit. The oxygen concentration of the mixed exhaust gas in the auxiliary part can be lowered. For this reason, even if the mixed exhaust gas flows backward into the fuel chamber, the oxidation of the fuel electrode can be suppressed.

(2) In the fuel cell system, the first opening / closing part may be provided closer to the fuel cell stack than an intermediate point in the oxidant gas supply pipe. According to this fuel cell system, the first opening / closing part is in a closed state as compared with the case where the first opening / closing part is provided closer to the oxidant gas supply source than the intermediate point in the oxidant gas supply pipe. Therefore, it is possible to prevent the gas pressure and flow rate in the oxidant gas flow path from increasing due to the small amount of oxidant gas remaining between the first opening / closing part and the fuel cell stack. As a result, the amount of the oxidant off-gas flowing into the auxiliary unit after the control unit is stopped is reduced, so that the oxygen concentration of the mixed exhaust gas in the auxiliary unit is further reduced, and the oxidation of the fuel electrode is more reliably suppressed. be able to.

(3) In the fuel cell system, an opening area in a cross section perpendicular to the flow path of the fuel gas supply pipe is provided between the first check valve and the fuel cell stack in the fuel gas supply pipe. However, there may be provided a gas storage part in which an accommodation space larger than the fuel gas supply pipe is formed. According to this fuel cell system, even when the temperature of the fuel cell stack decreases after the power generation operation of the fuel cell stack stops and the pressure in the fuel cell stack decreases, the fuel gas stored in the gas storage section is Since the gas is continuously supplied into the chamber, it is possible to suppress an extreme decrease in the pressure and flow rate of the gas in the fuel gas flow path, to prevent the mixed exhaust gas from flowing back into the fuel chamber, and to suppress oxidation of the fuel electrode.

(4) In the fuel cell system, further, one end is connected to the joining space formed in the auxiliary portion, and the other end is provided in the discharge pipe drawn out of the auxiliary portion and the discharge pipe. A second check valve. According to this fuel cell system, since the second check valve is provided in the discharge pipe, it may be configured such that outside air is prevented from flowing into the merge space formed in the auxiliary portion. Thereby, it can suppress that the oxygen concentration of mixed exhaust gas becomes high resulting from external air flowing in into an auxiliary | assistant part via a discharge pipe, and can suppress the oxidation of a fuel electrode.

(5) In the fuel cell system, in the fuel gas supply pipe, a reforming unit provided between the first check valve and the fuel cell stack, a water supply source for sending water A water supply pipe having one end connected to the water supply source and the other end connected to the reforming unit, and a filter provided in the water supply pipe, and the control unit includes the water supply source Is provided between the filter and the reforming unit in the water supply pipe, and when the power supply is stopped, the flow path in the water supply pipe is closed, and the power supply A second opening / closing part that switches from the closed state to an open state that opens the flow path in the water supply pipe. According to this fuel cell system, when the control of the control unit stops for some reason, the power supply to the second opening / closing unit is stopped, so the second opening / closing unit is closed, and the filter is changed from the filter to the reforming unit. The water supply may be blocked. As a result, it is possible to suppress the fuel electrode from being oxidized due to the water in the filter being supplied to the reforming unit and the vapor-rich gas flowing from the reforming unit into the fuel chamber.

(6) In the fuel cell system, the second opening / closing part may be provided closer to the reforming part than an intermediate point in the water supply pipe. According to this fuel cell system, when the second opening / closing part is in a closed state, the second opening / closing part is closer to the water supply source than the intermediate point in the water supply pipe. The amount of water remaining between the open / close unit 2 and the reforming unit 2 can be more reliably suppressed from flowing into the fuel electrode by the water vapor-rich gas after the control of the control unit is stopped.

Explanatory drawing which shows the structure of the fuel cell system 1 roughly The block diagram which shows the structure of the control part 700 Explanatory drawing which shows transition of the temperature of the fuel cell stack 100, and the pressure and flow volume of the gas introduce | transduced in the fuel cell stack 100 about the comparison structure A Explanatory drawing which shows transition of the temperature of the fuel cell stack 100, and the pressure and flow rate of the gas introduced into the fuel cell stack 100 in the fuel cell system 1 of the present embodiment.

A. First embodiment:
A-1. Constitution:
(Configuration of fuel cell system 1)
FIG. 1 is an explanatory diagram schematically showing the configuration of the fuel cell system 1. FIG. 1 shows a cross-sectional configuration of a fuel cell stack 100 described later. In this specification, for the sake of convenience, the upward direction on the paper (the direction from an off-gas combustion unit 230 described later toward the fuel cell stack 100) is referred to as the upward direction, and the downward direction on the paper surface is referred to as the downward direction. 100 may actually be installed in an orientation different from such orientation. The fuel cell system 1 includes a fuel cell stack 100, a configuration on the supply side of the oxidant gas OG, a configuration on the supply side of the raw fuel gas RFG, a configuration on the discharge side of the offgas OOG and FOG, and a control unit 700 (FIG. 2) and a heat insulating container 800.

(Configuration of fuel cell stack 100)
The fuel cell stack 100 includes a plurality of (two in this embodiment) power generation units 102 and a pair of end plates 104 and 106. The two power generation units 102 are arranged side by side in a predetermined arrangement direction (vertical direction in the present embodiment). The pair of end plates 104 and 106 are arranged so as to sandwich the two power generation units 102 from above and below. The fuel cell stack 100 is fastened by a plurality of bolts (not shown) extending in the vertical direction.

  A plurality of holes penetrating in the vertical direction are formed in the peripheral portions of the respective layers (power generation unit 102, end plates 104, 106) constituting the fuel cell stack 100 in the vertical direction, and are formed in the respective layers and correspond to each other. The holes communicate with each other in the vertical direction to form an oxidant gas introduction manifold 161, an oxidant gas discharge manifold 162, a fuel gas introduction manifold 171, and a fuel gas discharge manifold 172.

  The oxidant gas introduction manifold 161 is a gas passage through which the oxidant gas OG is introduced from the outside of the fuel cell stack 100 and supplies the oxidant gas OG to each power generation unit 102, and penetrates one end plate 104. , Extending toward the other end plate 106. The oxidant gas discharge manifold 162 is a gas flow path for discharging the oxidant off-gas OOG discharged from each power generation unit 102 to the outside of the fuel cell stack 100, and from the lower surface of one end plate 104 to the other end plate. It extends toward 106 and penetrates through the other end plate 106. In the present embodiment, air is used as the oxidant gas OG.

  The fuel gas introduction manifold 171 is a gas flow path for supplying a fuel gas FG, which will be described later, from the outside of the fuel cell stack 100 and supplying the fuel gas FG to each power generation unit 102, and penetrates the other end plate 106. It extends toward one end plate 104. The fuel gas discharge manifold 172 is a gas flow path for discharging the fuel off-gas FOG discharged from each power generation unit 102 to the outside of the fuel cell stack 100, passes through the other end plate 106, and passes through the other end plate 104. It extends towards. The oxidant gas introduction manifold 161 is an example of an oxidant gas flow path, and the fuel gas introduction manifold 171 is an example of a fuel gas flow path.

  The pair of end plates 104 and 106 are rectangular flat plate-shaped conductive members, and are made of, for example, stainless steel. One end plate 104 is disposed on the upper side of the power generation unit 102 located on the uppermost side, and the other end plate 106 is disposed on the lower side of the power generation unit 102 located on the lowermost side. A plurality of power generation units 102 are held in a pressed state by a pair of end plates 104 and 106. The upper end plate 104 functions as a positive output terminal of the fuel cell stack 100, and the lower end plate 106 functions as a negative output terminal of the fuel cell stack 100.

  The power generation unit 102 includes a single cell 110, a separator 120, an air electrode side frame 130, an air electrode side current collector (not shown), a fuel electrode side frame 140, a fuel electrode side current collector (not shown), and a power generation unit. 102 and a pair of interconnectors 150 constituting the uppermost layer and the lowermost layer.

  The interconnector 150 is a rectangular flat plate-shaped conductive member, and is formed of, for example, ferritic stainless steel. The interconnector 150 ensures electrical continuity between the power generation units 102 and prevents reaction gas from being mixed between the power generation units 102. In the present embodiment, when two power generation units 102 are arranged adjacent to each other, one interconnector 150 is shared by two adjacent power generation units 102. That is, the upper interconnector 150 in a power generation unit 102 is the same member as the lower interconnector 150 in another power generation unit 102 adjacent to the upper side of the power generation unit 102. Further, since the fuel cell stack 100 includes the pair of end plates 104 and 106, the power generation unit 102 located at the top in the fuel cell stack 100 does not include the upper interconnector 150 and is located at the bottom. The power generation unit 102 does not include the lower interconnector 150. In FIG. 1, the end plate 104 is provided in the power generation unit 102 at the upper end, and the uppermost interconnector 150 in the power generation unit 102 is omitted. The lower end power generation unit 102 is provided with an end plate 106, and the lowermost interconnector 150 in the power generation unit 102 is omitted. Accordingly, only one interconnector 150 is shown.

  The unit cell 110 includes an electrolyte layer 112 and an air electrode (cathode) 114 and a fuel electrode (anode) 116 that face each other in the vertical direction (the arrangement direction in which the power generation units 102 are arranged) with the electrolyte layer 112 interposed therebetween. The single cell 110 of the present embodiment is a fuel electrode-supported single cell that supports the electrolyte layer 112 and the air electrode 114 with the fuel electrode 116.

  The electrolyte layer 112 is a rectangular flat plate-shaped member. For example, YSZ (yttria stabilized zirconia), ScSZ (scandia stabilized zirconia), SDC (samarium doped ceria), GDC (gadolinium doped ceria), perovskite oxide, etc. The solid oxide is formed. The air electrode 114 is a rectangular flat plate-shaped member, and is formed of, for example, a perovskite oxide (for example, LSCF (lanthanum strontium cobalt iron oxide), LSM (lanthanum strontium manganese oxide), LNF (lanthanum nickel iron)). ing. The fuel electrode 116 is a rectangular flat plate-shaped member, and is formed of, for example, Ni (nickel), cermet made of Ni and ceramic particles, Ni-based alloy, or the like. Thus, the single cell 110 (power generation unit 102) of the present embodiment is a solid oxide fuel cell (SOFC) that uses a solid oxide as an electrolyte.

  The separator 120 is a frame-like member in which a square hole 121 penetrating in the vertical direction is formed near the center, and is made of, for example, metal. The peripheral part of the hole 121 in the separator 120 is opposed to the peripheral part of the surface of the electrolyte layer 112 on the air electrode 114 side. The separator 120 is joined to the electrolyte layer 112 (single cell 110) by a joint portion (not shown) formed of a brazing material (for example, Ag brazing) disposed in the facing portion. The separator 120 suppresses gas leakage from the one electrode side to the other electrode side in the peripheral portion of the single cell 110. The single cell 110 to which the separator 120 is bonded is also referred to as a single cell with a separator.

  The air electrode side frame 130 is a frame-like member in which a rectangular hole 131 penetrating in the vertical direction is formed near the center, and is formed of an insulator such as mica, for example. The air electrode side frame 130 is in contact with the peripheral edge portion of the surface of the separator 120 opposite to the side facing the electrolyte layer 112 and the peripheral edge portion of the surface of the interconnector 150 facing the air electrode 114. . The air electrode side frame 130 secures an air chamber 166 between the air electrode 114 and the interconnector 150, and electrically isolates the pair of interconnectors 150 included in the power generation unit 102. The air electrode side frame 130 has an oxidant gas supply communication hole 132 communicating the oxidant gas introduction manifold 161 and the air chamber 166, and an oxidant gas communicating the air chamber 166 and the oxidant gas discharge manifold 162. A discharge communication hole 133 is formed.

  The fuel electrode side frame 140 is a frame-like member in which a rectangular hole 141 penetrating in the vertical direction is formed near the center, and is formed of, for example, metal. The fuel electrode side frame 140 is in contact with the peripheral portion of the surface of the separator 120 facing the electrolyte layer 112 and the peripheral portion of the surface of the interconnector 150 facing the fuel electrode 116. A fuel chamber 176 is secured between the fuel electrode 116 and the interconnector 150 by the fuel electrode side frame 140. Further, the fuel electrode side frame 140 has a fuel gas supply communication hole 142 that connects the fuel gas introduction manifold 171 and the fuel chamber 176, and a fuel gas discharge communication hole 143 that connects the fuel chamber 176 and the fuel gas discharge manifold 172. And are formed.

  The air electrode side current collector is in contact with the surface of the air electrode 114 opposite to the side facing the electrolyte layer 112 and the surface of the interconnector 150 facing the air electrode 114, whereby the air electrode 114. And the interconnector 150 are electrically connected. The fuel electrode side current collector electrically connects the fuel electrode 116 and the interconnector 150.

(Configuration of supply side of oxidant gas OG)
The configuration on the supply side of the oxidant gas OG includes an oxidant gas supply source 300, a first opening / closing part 310, and an oxidant gas supply pipe 320. The oxidant gas supply source 300 includes, for example, a compressor and a pump, and sends out the oxidant gas OG. Further, the oxidant gas supply source 300 can change the delivery amount of the oxidant gas OG under the control of the control unit 700. The first opening / closing part 310 is a so-called normally closed type opening / closing part that is in an open state on condition that power is supplied, and is in a closed state when power supply is stopped. It is a solenoid valve or valve.

  The oxidant gas supply pipe 320 includes a first oxidant gas supply pipe 321 and a second oxidant gas supply pipe 322. One end of the first oxidant gas supply pipe 321 is connected to the outlet of the oxidant gas supply source 300, and the other end of the first oxidant gas supply pipe 321 is connected to the input port of the first opening / closing part 310. It is connected. One end of the second oxidant gas supply pipe 322 is connected to the output port of the first opening / closing part 310, and the other end of the second oxidant gas supply pipe 322 is the oxidant gas introduction manifold of the fuel cell stack 100. 161 is connected to the inlet. Further, the first opening / closing part 310 is provided closer to the fuel cell stack 100 than the middle point in the oxidant gas supply pipe 320.

(Configuration on the supply side of the raw fuel gas RFG)
The configuration on the supply side of the raw fuel gas RFG includes a fuel gas supply source 400, a desulfurization unit 410, a first check valve 420, a gas storage unit 430, a fuel gas supply pipe 440, and a vaporization unit 210. The reforming unit 220, the water supply source 500, the filter 510, the second opening / closing unit 520, and the water supply pipe 530 are included.

  The fuel gas supply source 400 includes, for example, a compressor and a pump, and sends out the raw fuel gas RFG. Further, the fuel gas supply source 400 can change the delivery amount of the raw fuel gas RFG under the control of the control unit 700. The desulfurization unit 410 removes sulfur from the raw fuel gas RFG sent out by the fuel gas supply source 400.

  The first check valve 420 allows the raw fuel gas RFG output from the desulfurization unit 410 to flow into the fuel cell stack 100 side, while the raw fuel gas RFG from the fuel cell stack 100 side to the desulfurization unit 410 side. To prevent backflow. The gas storage unit 430 is a member having an input port and an output port, and an accommodation space 431 is formed therein. The outer shape of the gas storage unit 430 is, for example, a columnar shape. Regarding the accommodation space 431, the opening area in a cross section orthogonal to the flow path of the fuel gas supply pipe 440 is larger than that of the fuel gas supply pipe 440. The gas reservoir 430 is formed of, for example, a metal material or a resin material (particularly rubber), and is preferably formed of a material that is deformed by a pressure change.

  The fuel gas supply pipe 440 includes a first fuel gas supply pipe 441, a second fuel gas supply pipe 442, a third fuel gas supply pipe 443, a fourth fuel gas supply pipe 444, and a fifth fuel gas supply pipe 440. A fuel gas supply pipe 445 and a sixth fuel gas supply pipe 446 are included. One end of the first fuel gas supply pipe 441 is connected to the outlet of the fuel gas supply source 400, and the other end of the first fuel gas supply pipe 441 is connected to the input port of the desulfurization unit 410. One end of the second fuel gas supply pipe 442 is connected to the output port of the desulfurization unit 410, and the other end of the second fuel gas supply pipe 442 is connected to the input port of the first check valve 420. .

  One end of the third fuel gas supply pipe 443 is connected to the output port of the first check valve 420, and the other end of the third fuel gas supply pipe 443 is connected to the input port of the gas storage unit 430. Yes. One end of the fourth fuel gas supply pipe 444 is connected to the output port of the gas storage unit 430, and the other end of the fourth fuel gas supply pipe 444 is connected to the input port of the vaporization unit 210. One end of the fifth fuel gas supply pipe 445 is connected to the output port of the vaporization unit 210, and the other end of the fifth fuel gas supply pipe 445 is connected to the input port of the reforming unit 220. One end of the sixth fuel gas supply pipe 446 is connected to the output port of the reforming unit 220, and the other end of the sixth fuel gas supply pipe 446 is connected to the introduction port of the fuel gas introduction manifold 171.

  The water supply source 500 includes, for example, a compressor and a pump, and sends out water RW. Further, the water supply source 500 can change the amount of water RW delivered under the control of the control unit 700. The filter 510 has an accommodation space 511 in which water can be accommodated, and the filter 510 purifies the water RW sent from the water supply source 500 into pure water. The second opening / closing part 520 is a so-called normally-closed opening / closing part that is in an open state on the condition that power is supplied and is in a closed state when the power supply is stopped. It is a solenoid valve or valve. Further, the second opening / closing part 520 is provided on the fuel cell stack 100 side of the water supply pipe 530 with respect to the intermediate point between the filter 510 and the fuel cell stack 100.

  The water supply pipe 530 includes a first water supply pipe 531, a second water supply pipe 532, and a third water supply pipe 533. The first water supply pipe 531 is connected to the outlet of the water supply source 500, and the other end of the first water supply pipe 531 is connected to the input port of the filter 510. One end of the second water supply pipe 532 is connected to the output port of the filter 510, and the other end of the second water supply pipe 532 is connected to the input port of the second opening / closing part 520. One end of the third water supply pipe 533 is connected to the output port of the second opening / closing part 520, and the other end of the third water supply pipe 533 is connected to the input port of the vaporization part 210.

  In the vaporization section 210, an internal space 211 including a water introduction chamber and a mixing chamber communicating with the water introduction chamber is formed. The water RW that has flowed into the water introduction chamber via the second opening / closing part 520 is heated and vaporized by a heating source (not shown) to become water vapor. The steam flows into the mixing chamber and mixes with the raw fuel gas RFG that flows into the mixing chamber via the gas reservoir 430, and as a result, a mixed gas is generated. The reforming unit 220 has a reforming chamber 221 formed therein. The mixed gas generated in the vaporization unit 210 is heated by a heating source (not shown), and is supplied to the reforming reaction in the reforming chamber 221. As a result, the hydrogen-rich fuel gas FG is supplied to the fuel gas introduction manifold 171. Is done.

(Exhaust gas OOG, FOG discharge side configuration)
The configuration on the exhaust side of the oxidant off-gas OOG and the fuel off-gas FOG includes an off-gas combustion unit 230, a second check valve 600, and an exhaust pipe 610. A merge space 231 communicating with the oxidant gas discharge manifold 162 and the fuel gas discharge manifold 172 is formed inside the off-gas combustion unit 230. The oxidant off-gas OOG discharged from the oxidant gas discharge manifold 162 and the fuel off-gas FOG discharged from the fuel gas discharge manifold 172 merge in the merge space 231 and mix and burn. Note that a catalyst that promotes combustion of the oxidant off-gas OOG and the fuel off-gas FOG is disposed in the merge space 231. The off-gas combustion unit 230 is an example of an auxiliary unit.

  The second check valve 600 allows the oxidant off-gas OOG and the fuel off-gas FOG discharged from the off-gas combustion unit 230 to flow out of the fuel cell stack 100, while external air is on the off-gas combustion unit 230 side. To prevent backflow. The discharge pipe 610 includes a first discharge pipe 611 and a second discharge pipe 612. One end of the first exhaust pipe 611 is connected to the exhaust port of the off-gas combustion unit 230, and the other end of the first exhaust pipe 611 is connected to the input port of the second check valve 600. One end of the second discharge pipe 612 is connected to the output port of the second check valve 600, and the other end of the second discharge pipe 612 is drawn out of the fuel cell system 1.

  The heat insulating container 800 has a configuration in which a heat insulating material is disposed on the inner side surface of a housing formed of, for example, stainless steel. The above-described fuel cell stack 100, the vaporization unit 210, the reforming unit 220, and the off-gas combustion unit 230 constitute a power generation module. By accommodating the power generation module in the heat insulating container 800, the power generation module is maintained at a high temperature when generating power. In the present embodiment, among the components of the fuel cell system 1 described above, a power generation module, a part of the oxidant gas supply pipe 320, a part of the fuel gas supply pipe 440, and a part of the water supply pipe 530 , A part of the discharge pipe 610 is accommodated in the heat insulating container 800, and the oxidizing gas supply source 300, the first opening / closing part 310, the fuel gas supply source 400, the desulfurization part 410, and the first The check valve 420, the gas storage unit 430, the water supply source 500, the filter 510, the second opening / closing unit 520, and the second check valve 600 are disposed outside the heat insulating container 800.

(Configuration of control unit)
The control unit 700 includes a CPU 710 and a memory 720, and is operable when supplied with power from an external power source W. The memory 720 stores a control program for controlling the fuel cell system 1, various settings, and the like. The CPU 710 controls each component of the fuel cell system 1 according to a program read from the memory 720 and the like.

  More specifically, the CPU 710 controls on / off of the delivery operation of the oxidant gas supply source 300. Further, the CPU 710 changes the delivery pressure and delivery amount of the oxidant gas OG by the oxidant gas supply source 300 based on detection results of a pressure sensor and a flow rate sensor (not shown) provided in the oxidant gas supply pipe 320. Thus, the pressure and flow rate of the oxidant gas OG introduced into the fuel cell stack 100 (oxidant gas introduction manifold 161) (hereinafter referred to as oxidant gas OG introduction pressure and introduction flow rate) are adjusted to predetermined target values. Further, the CPU 710 controls on / off of the delivery operation of the fuel gas supply source 400. Further, the CPU 710 changes the delivery pressure and the delivery amount of the raw fuel gas RFG by the fuel gas supply source 400 based on the detection results of a pressure sensor and a flow rate sensor (not shown) provided in the fuel gas supply pipe 440. Pressure and flow rate (hereinafter referred to as fuel gas FG introduction pressure and introduction flow rate) of the fuel gas FG reformed by the reforming unit 220 into the fuel cell stack 100 (fuel gas introduction manifold 171) Adjust to a predetermined target value. In addition, the CPU 710 controls on / off of the delivery operation of the water supply source 500. Further, the CPU 710 changes the flow rate of the water RW introduced into the vaporization unit 210 by changing the amount of water RW delivered by the water supply source 500 based on the detection result of a flow rate sensor (not shown) provided in the water supply pipe 530. Is adjusted to a predetermined target value.

  In the present embodiment, on / off of power supply to the first opening / closing unit 310 and the second opening / closing unit 520 is performed based on control by the control unit 700. Therefore, when power supply from the power source W to the control unit 700 is stopped, the first opening / closing unit 310 and the second opening / closing unit 520 are closed.

A-2. Operation when control unit 700 cannot control or stops control:
For example, when a power failure, disconnection of a power supply line between the control unit 700 and the power supply W, damage to the control unit 700 itself, or the like occurs, the control unit 700 cannot control the fuel cell system 1 normally. It becomes impossible. Further, when an abnormal state of the fuel cell system 1 is detected, for example, the delivery pressure by the oxidant gas supply source 300 or the fuel gas supply source 400 reaches an abnormal value based on the detection result of the pressure sensor, the fuel cell system 1 The control operation is forcibly terminated (shut down), and a control stop state in which the power supply from the power source W is cut off is entered.

  Here, as will be described later, when the control unit 700 enters an uncontrollable state or a control stop state, and the power generation operation of the fuel cell stack 100 stops, the inside of the merge space 231 of the offgas combustion unit 230 (hereinafter simply referred to as the offgas combustion unit). 230) (which may be referred to as “230”), the mixed gas of the oxidant off-gas OOG and the fuel off-gas FOG (hereinafter referred to as “mixed exhaust gas”) flows back into the fuel chamber 176 of each power generation unit 102, The fuel electrode 116 may be oxidized. In the fuel cell system 1 of the present embodiment, the oxidation of the fuel electrode 116 can be suppressed without requiring control by the control unit 700 even when the control unit 700 is in an uncontrollable state or the like. Hereinafter, among the components of the fuel cell system 1, a first opening / closing part 310, a first check valve 420, a gas storage part 430, a second check valve 600, and a second opening / closing part 520 are provided. The configuration without this will be referred to as comparative configuration A, and the effects of the fuel cell system 1 of the present embodiment will be described in comparison with comparative configuration A.

(Suppression of oxidation of fuel electrode 116 by first opening / closing part 310, first check valve 420, and gas storage part 430)
When the control unit 700 becomes uncontrollable, the power supply to the oxidant gas supply source 300, the fuel gas supply source 400, and the water supply source 500 is stopped. However, the oxidant gas OG, the raw fuel gas RFG, and the water RW are inertial due to the inertial operation of the oxidant gas supply source 300, the fuel gas supply source 400, and the water supply source 500 and the residual pressure in the pipes 320, 440, and 530. May continue to be supplied for minutes.

  FIG. 3 is an explanatory diagram showing the transition of the temperature of the fuel cell stack 100 and the pressure and flow rate of the gas introduced into the fuel cell stack 100 after the control unit 700 stops controlling, for the comparative configuration A. FIG. 4 is an explanatory diagram showing the transition of the temperature of the fuel cell stack 100 and the pressure and flow rate of the gas introduced into the fuel cell stack 100 after the control unit 700 stops controlling the present embodiment. In each figure, the PC graph shows the change in the introduction pressure of the oxidant gas OG into the air chamber 166, the PA graph shows the change in the introduction pressure of the fuel gas FG into the fuel chamber 176, and the PS graph. Indicates a change in pressure in the off-gas combustion unit 230. The FC graph shows a change in the flow rate of the oxidant gas OG introduced into the air chamber 166, and the FA graph shows a change in the flow rate of the fuel gas FG introduced into the fuel chamber 176. In the graph of FA and FC shown in FIG. 3, that the introduction flow rate of the oxidant gas OG and the introduction flow rate of the fuel gas FG are in the minus range, the mixed exhaust gas in the off-gas combustion unit 230 is the fuel cell stack 100. This means that the air is flowing backward (in the fuel chamber 176 etc.). Further, in the graphs of FA and FC shown in FIG. 4, the introduction flow rate of the oxidant gas OG and the introduction flow rate of the fuel gas FG are 0 (zero), indicating that the oxidant gas OG and the fuel gas FG are in the fuel cell stack 100. This means that the mixed exhaust gas in the off-gas combustion unit 230 does not flow back into the fuel cell stack 100 (such as the fuel chamber 176).

  During the control operation of the control unit 700, the introduction pressure of the oxidant gas OG is higher than the introduction pressure of the fuel gas FG, and the introduction flow rate of the oxidant gas OG is larger than the introduction flow rate of the fuel gas FG. Therefore, in the comparative configuration A, when the control by the control unit 700 is stopped (see time T0 in FIG. 3), the oxidant is maintained while the introduction pressure of the oxidant gas OG is higher than the introduction pressure of the fuel gas FG. The introduction pressure of the gas OG and the introduction pressure of the fuel gas FG decrease. Further, while maintaining the state where the introduction flow rate of the oxidant gas OG is higher than the introduction flow rate of the fuel gas FG, the introduction flow rate of the oxidant gas OG and the introduction flow rate of the fuel gas FG decrease (time T0 in FIG. 3). And the period of time T2). Further, when the control by the control unit 700 is stopped, the power generation operation of the fuel cell stack 100 is stopped and the power generation reaction in each single cell 110 is stopped, so that the temperature of the fuel cell stack 100 is lowered.

  Thereafter, the introduction pressure of the fuel gas FG becomes equal to the pressure in the off-gas combustion unit 230 before the introduction pressure of the oxidant gas OG (see time T2 in FIG. 3), whereby the off-gas combustion unit 230 of the fuel off-gas FOG. The inflow amount to the inside becomes close to zero earlier than the inflow amount of the oxidant offgas OOG into the offgas combustion unit 230. That is, in the comparative configuration A, since the oxidant offgas OOG flows more into the offgas combustion unit 230 than the fuel offgas FOG after the control by the control unit 700 is stopped, oxygen in the mixed exhaust gas in the offgas combustion unit 230 The concentration is relatively high.

  Thereafter, the introduction pressure of the oxidant gas OG becomes equal to the pressure in the off-gas combustion unit 230 (see time T3 in FIG. 3). Further, as described above, when the temperature of the fuel cell stack 100 decreases due to the stop of the power generation reaction in each single cell 110, the internal space (the air chamber 166 and the fuel chamber 176) of the fuel cell stack 100 is accordingly accompanied. ) The volume of gas inside shrinks. Note that the volume of the internal space of the fuel cell stack 100 can also contract as the temperature of the fuel cell stack 100 decreases, but the contraction rate is smaller than the contraction rate of the volume of gas in the internal space. For this reason, the pressure in the fuel cell stack 100 is further lower than the atmospheric pressure outside the fuel cell stack 100 and the off-gas combustion unit 230 (hereinafter referred to as the external atmospheric pressure). The exhaust pipe 610 may flow backward. When the external air flows backward, the mixed exhaust gas remaining in the off-gas combustion unit 230 flows back into the fuel chamber 176 accordingly. When the mixed exhaust gas flows back into the fuel chamber 176, the mixed oxygen exhaust gas having a high oxygen concentration in the off-gas combustion unit 230 flows back into the fuel chamber 176, so that the oxidation of the fuel electrode 116 may progress greatly. Note that when the temperature of the fuel cell stack 100 is approximately 400 degrees or less, the oxidation reaction does not occur at the fuel electrode 116 even if the mixed exhaust gas flows backward into the fuel chamber 176.

  On the other hand, in the fuel cell system 1 of the present embodiment, the first opening / closing part 310 is provided in the oxidant gas supply pipe 320 between the oxidant gas supply source 300 and the fuel cell stack 100. Yes. When the control of the control unit 700 is stopped, the first opening / closing unit 310 is closed, so that the introduction of the oxidant gas OG due to the inertia operation of the oxidant gas supply source 300 is blocked. For this reason, when the introduction pressure of the oxidant gas OG becomes equal to the pressure in the offgas combustion unit 230 before the introduction pressure of the fuel gas FG (see time T1 in FIG. 4), the offgas combustion of the oxidant offgas OOG. The amount of inflow into the portion 230 becomes close to zero earlier than the amount of inflow of the fuel offgas FOG into the offgas combustion portion 230. That is, in the fuel cell system 1 of the present embodiment, after the control by the control unit 700 is stopped, the fuel offgas FOG flows more into the offgas combustion unit 230 than the oxidant offgas OOG. The oxygen concentration of the mixed exhaust gas at becomes relatively low. Thereby, in the fuel cell system 1 of the present embodiment, even if the mixed exhaust gas in the off-gas combustion unit 230 flows back into the fuel chamber 176, the oxygen concentration of the mixed exhaust gas is lower than that in the comparative configuration A. Oxidation of the fuel electrode 116 can be suppressed.

  In the fuel cell system 1, a first check valve 420 is provided in the fuel gas supply pipe 440 between the desulfurization unit 410 and the fuel cell stack 100. The first check valve 420 allows the supply of the raw fuel gas RFG due to the inertial operation or the like of the fuel gas supply source 400 while preventing the back flow of the raw fuel gas RFG. It can suppress that the pressure of a downstream side falls. Thereby, since the pressure drop in the fuel cell stack 100 and the off-gas combustion unit 230 is suppressed as compared with the comparative configuration A, the mixed exhaust gas in the off-gas combustion unit 230 becomes the fuel chamber 176 after the control of the control unit 700 is stopped. It is possible to suppress backflow into the inside. Specifically, as compared with the comparative configuration A, the timing at which the mixed exhaust gas flows backward is delayed (see time T3 in FIG. 3 and time T4 in FIG. 4).

  Moreover, the first opening / closing part 310 is provided closer to the fuel cell stack 100 than the middle point in the oxidant gas supply pipe 320. Accordingly, when the first opening / closing part 310 is in a closed state as compared with the case where the first opening / closing part 310 is provided closer to the oxidant gas supply source 300 than the intermediate point in the oxidant gas supply pipe 320. Inflow amount of the oxidant off-gas OOG into the off-gas combustion unit 230 after the control of the control unit 700 is stopped by the amount of the oxidant gas OG remaining between the first opening / closing unit 310 and the fuel cell stack 100. Therefore, it is possible to suppress an increase in the oxygen concentration of the mixed exhaust gas in the off-gas combustion unit 230. The first opening / closing part 310 may be provided in a portion within 1/4 of the oxidant gas supply pipe 320 from the fuel cell stack 100. In short, the closer the first opening / closing part 310 is to the fuel cell stack 100, the better.

  Furthermore, in the fuel cell system 1 of the present embodiment, the gas storage unit 430 is provided in the fuel gas supply pipe 440 between the first check valve 420 and the fuel cell stack 100. In addition, the pressure in the gas storage unit 430 is higher than the pressure in the off-gas combustion unit 230 by the first check valve 420 described above. For this reason, when the volume of gas in the fuel cell stack 100 contracts, the raw fuel gas RFG in the gas storage unit 430 flows into the fuel chamber 176 with priority over the mixed exhaust gas in the off-gas combustion unit 230.

  Further, the volume of the storage space 431 of the gas storage unit 430 includes the piping volume of the second oxidant gas supply pipe 322, the piping volume of the third water supply pipe 533, the internal volume of the fuel cell stack 100, and the off gas. It is not less than the total volume of the volume of the combustion unit 230 and the pipe volume of the discharge pipe 610. As a result, the fuel chamber 176 in the fuel cell stack 100 can be sufficiently filled with the raw fuel gas RFG in the gas storage unit 430, so that the mixed exhaust gas in the off-gas combustion unit 230 is fueled compared to the comparative configuration A. Back flow into the chamber 176 can be suppressed.

(Suppression of oxidation of fuel electrode 116 by second check valve 600)
As described above, when the external air flows back into the off-gas combustion unit 230, the oxygen concentration of the mixed exhaust gas in the off-gas combustion unit 230 may increase due to oxygen contained in the external air. Further, even if the pressure in the fuel cell stack 100 does not become lower than the external pressure, the external air rides on the airflow and flows backward through the exhaust pipe 610 and flows into the offgas combustion unit 230, whereby the offgas combustion unit 230. There is a possibility that the oxygen concentration of the mixed exhaust gas inside becomes high.

  On the other hand, in the fuel cell system 1 of the present embodiment, the second check valve 600 is provided in the discharge pipe 610. For this reason, it is suppressed that external air flows backward into the off-gas combustion unit 230. Thereby, it is possible to suppress the oxygen concentration of the mixed exhaust gas from being increased due to the external air flowing into the off-gas combustion unit 230, and to suppress the oxidation of the fuel electrode 116.

(Suppression of oxidation of fuel electrode 116 by second opening / closing part 520)
When the control unit 700 becomes uncontrollable, the power supply to the water supply source 500 is also stopped. However, due to the residual pressure or the like in the water supply pipe 530, the water RW in the accommodation space 511 of the filter 510 flows into the vaporization unit 210 and is vaporized to generate water vapor, and the water vapor flows into the fuel chamber 176, and the fuel chamber The fuel electrode 116 may be oxidized due to the 176 being in a water vapor rich state.

  On the other hand, in the fuel cell system 1 of the present embodiment, the second opening / closing part 520 is provided in the water supply pipe 530 between the filter 510 and the fuel cell stack 100. When the control of the control unit 700 is stopped, the second opening / closing unit 520 is closed, so that the inside of the accommodation space 511 of the filter 510 due to the inertia operation of the water supply source 500, the residual pressure in the water supply pipe 530, and the like. The supply of water RW is cut off. As a result, the fuel electrode 116 can be prevented from being oxidized due to the fuel chamber 176 being in a water vapor rich state.

  Moreover, the second opening / closing part 520 is provided closer to the fuel cell stack 100 than the middle point in the water supply pipe 530. Therefore, when the second opening / closing part 520 is in the closed state, the second opening / closing part 520 is closer to the water supply source 500 than the intermediate point in the water supply pipe 530. The amount of water RW remaining between the open / close unit 520 and the vaporization unit 210 is small, and the fuel electrode 116 is oxidized due to the flow of water vapor into the fuel chamber 176 after the control of the control unit 700 is stopped. It can suppress more reliably. The second opening / closing part 520 may be provided in a portion within 1/4 of the fuel cell stack 100 in the water supply pipe 530. In short, the closer the second opening / closing part 520 is to the fuel cell stack 100, the better.

(Volume in the confluence space 231 of the off-gas combustion unit 230)
The volume in the merge space 231 of the off-gas combustion unit 230 is 1/3 or more of the volume in the fuel chamber 176 of the fuel cell stack 100 (the total volume of the plurality of fuel chambers 176 when a plurality of fuel chambers 176 are provided). Preferably, it is 2/3 times or more. Assuming that the temperature during the power generation operation of the fuel cell stack 100 is 700 degrees and the temperature at which the fuel electrode 116 does not oxidize is 400 degrees, the temperature of the fuel cell stack 100 reaches 400 degrees due to the correlation between the volume and the temperature. When the fuel cell stack 176 is lowered, the volume of the gas in the fuel chamber 176 is reduced by about 30% as compared with the time when the fuel cell stack 100 is generating power. Therefore, if the volume in the merge space 231 is 1/3 or more of the volume of the fuel chamber 176, the decrease in the gas in the fuel chamber 176 can be supplemented by the mixed exhaust gas in the merge space 231. Even if the second check valve 600 is not provided, external air can be prevented from flowing into the merge space 231. Since the mixed exhaust gas in the merge space 231 also flows into the air chamber 166, it is assumed that the volumes of the air chamber 166 and the fuel chamber 176 are substantially the same, and the volume in the merge space 231 is the fuel chamber. It is more preferable that it is 2/3 or more of the volume in 176.

B. Modifications The technology disclosed in the present specification is not limited to the above-described embodiment, and can be modified into various forms without departing from the gist thereof. For example, the following modifications are also possible. .

  In the above embodiment, as the fuel cell system, the desulfurization unit 410, the gas storage unit 430, the water supply source 500, the filter 510, the second opening / closing unit 520, the water supply pipe 530, the vaporization unit 210, The fuel cell system 1 provided with the component of the reforming part 220, the 2nd non-return valve 600, and the heat insulation container 800 was illustrated. However, the fuel cell system is not limited to this, and may be configured not to include at least one of these components excluding the heat insulating container 800. In addition, the fuel cell system may have a configuration in which, for example, the oxidant gas supply pipe 322 includes a heat exchange unit or a preheating unit that heats the oxidant gas OG.

  In the above embodiment, the power supply to the first opening / closing unit 310 and the second opening / closing unit 520 is illustrated based on the control performed by the control unit 700, but is not limited thereto. Even when the control unit 700 is activated, power supply to the first opening / closing unit 310 and the second opening / closing unit 520 is started from the power source W common to the control unit 700 independently of the control of the control unit 700. Good. Even in such a configuration, when the control unit 700 cannot be controlled normally due to a power failure or the like, the oxidation of the fuel electrode 116 can be suppressed by the first opening / closing unit 310 and the first check valve 420 described above. it can.

  In the above embodiment, the off-gas combustion unit 230 is exemplified as the auxiliary unit. However, the auxiliary unit is not limited to this, and may not burn the oxidant off-gas OOG and the fuel off-gas FOG. In short, the auxiliary portion only needs to have a confluence space where the oxidant offgas OOG and the fuel offgas FOG merge.

  In the above-described embodiment, the SOFC including the electrolyte layer including the solid oxide is illustrated as the single cell. However, the single cell is not limited to this, for example, a molten carbonate fuel including a charged layer including carbonate. A battery (MCFC) may be used. In short, any high-temperature fuel cell having a temperature during rated operation of approximately 600 degrees or more may be used.

  In the above embodiment, the number of power generation units 102 included in the fuel cell stack 100 is merely an example, and the number of power generation units 102 is appropriately determined according to the output voltage required for the fuel cell stack 100 or the like.

  In the above embodiment, when two power generation units 102 are arranged adjacent to each other, one interconnector 150 is shared by two adjacent power generation units 102. Two power generation units 102 may be provided with respective interconnectors 150. In the above embodiment, the upper interconnector 150 of the uppermost power generation unit 102 in the fuel cell stack 100 and the lower interconnector 150 of the lowermost power generation unit 102 are omitted. These interconnectors 150 may be provided without being omitted.

  In the above embodiment, the city gas is reformed to obtain a hydrogen-rich fuel gas. However, the fuel gas may be obtained from other raw materials such as LP gas, kerosene, methanol, gasoline, etc. Hydrogen may be used.

1: Fuel cell system 100: Fuel cell stack 102: Power generation unit 104, 106: End plate 110: Single cell 112: Electrolyte layer 114: Air electrode 116: Fuel electrode 142: Fuel gas supply communication hole 143: Fuel gas discharge communication hole 150: interconnector 161: oxidant gas introduction manifold 162: oxidant gas discharge manifold 166: air chamber 171: fuel gas introduction manifold 172: fuel gas discharge manifold 176: fuel chamber 210: vaporization section 211: internal space 220: reforming Unit 221: reforming chamber 230: off-gas combustion unit 231: merge space 300: oxidant gas supply source 310: first open / close unit 320: oxidant gas supply pipe 400: fuel gas supply source 410: desulfurization unit 420: first Check valve 430: gas reservoir 43 : Accommodation space 440: fuel gas supply pipe 500: water supply source 510: filter 511: accommodation space 520: second opening / closing part 530: water supply pipe 600: second check valve 610: discharge pipe 700: control part 710 : CPU 720: Memory FG: Fuel gas FOG: Fuel off gas OG: Oxidant gas OOG: Oxidant off gas RFG: Raw fuel gas RW: Water W: Power supply

Claims (6)

A fuel cell stack comprising a plurality of single cells each including an electrolyte layer containing a solid oxide or a carbonate, and an air electrode and a fuel electrode facing each other with the electrolyte layer interposed therebetween, in an air chamber facing the air electrode A fuel cell stack formed with a communicating oxidant gas flow path and a fuel gas flow path communicating with the fuel chamber facing the fuel electrode;
An oxidant gas supply source for delivering oxidant gas;
An oxidant gas supply pipe having one end connected to the oxidant gas supply source and the other end connected to the oxidant gas flow path;
A fuel gas supply source for delivering fuel gas;
A fuel gas supply pipe having one end connected to the fuel gas supply source and the other end connected to the fuel gas flow path;
An auxiliary portion formed with a merge space in which an oxidant off-gas containing the oxidant gas discharged from the fuel cell stack and a fuel off-gas containing the fuel gas merge;
A controller for controlling the oxidant gas supply source and the fuel gas supply source;
In a fuel cell system comprising:
When the oxidant gas supply pipe is provided and power supply is stopped, the flow path in the oxidant gas supply pipe is closed, and when power is supplied, the oxidant gas is released from the closed state. A first opening / closing part that switches to an open state that opens the flow path in the supply pipe;
A fuel cell system comprising: a first check valve provided in the fuel gas supply pipe. The fuel cell system according to claim 1, wherein
The fuel cell system, wherein the first opening / closing part is provided closer to the fuel cell stack than an intermediate point in the oxidant gas supply pipe. The fuel cell system according to claim 1 or 2,
Of the fuel gas supply pipe, between the first check valve and the fuel cell stack, an opening area in a cross section perpendicular to the flow path of the fuel gas supply pipe is larger than that of the fuel gas supply pipe. A fuel cell system, characterized in that a gas storage part in which an accommodation space is formed is provided. The fuel cell system according to any one of claims 1 to 3, further comprising:
A discharge pipe having one end connected to the merge space formed in the auxiliary portion and the other end drawn out of the auxiliary portion;
A fuel cell system comprising: a second check valve provided in the discharge pipe. The fuel cell system according to any one of claims 1 to 4, further comprising:
A reforming unit provided between the first check valve and the fuel cell stack in the fuel gas supply pipe;
A water supply source for delivering water;
A water supply pipe having one end connected to the water supply source and the other end connected to the reforming unit;
A filter provided in the water supply pipe,
The control unit controls the water supply source,
In the case where the water supply pipe is provided between the filter and the reforming unit and power supply is stopped, the flow path in the water supply pipe is closed, and power supply is performed. And a second open / close section that switches from the closed state to an open state that opens the flow path in the water supply pipe. The fuel cell system according to claim 5, wherein
The fuel cell system, wherein the second opening / closing part is provided closer to the reforming part than an intermediate point in the water supply pipe.

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