JP2005259663A - Fuel cell power generation method and fuel cell power generation system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a long-time operation including starts and stops and high durability in an operation pattern including a lot of starts and stops by providing a fuel cell power generation method capable of preventing deterioration due to the corrosion of an electrode in starting a fuel cell without damaging the fuel cell. <P>SOLUTION: This fuel cell power generation method comprises: a production process for producing a hydrogen-rich reformed gas 42 from a hydrocarbon-based fuel 40; a power generation process for generating power by a fuel cell stack by introducing the reformed gas to the side of a fuel electrode of the fuel cell stack 6 and by introducing an oxidizer gas 32 to the side of an oxidizer electrode of the fuel cell stack; a stopping process for stopping the power generation; and a sealing process for sealing the hydrocarbon-based fuel or the produced reformed gas in the fuel electrode side after the stopping process. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a power generation method for a polymer electrolyte fuel cell, particularly a power generation method for a polymer electrolyte fuel cell that copes with frequent start / stop, and a polymer electrolyte fuel cell power generation system, particularly a solid that copes with frequent start / stop. The present invention relates to a polymer fuel cell power generation system.

  Solid polymer fuel cells have a low operating temperature of 100 ° C or less, so the start-up time can be shortened and handling is easy, so a wide range of demand is expected for automobiles and households (cogeneration and cogeneration). ing.

  A polymer electrolyte fuel cell introduces a fuel such as hydrogen or methanol to the fuel electrode side sandwiched between solid polymer membranes, and an oxidant gas such as air or oxygen to the other oxidant electrode side. Is introduced to generate an electromotive force between the solid polymer films, and an electric power is generated by taking out electrons to an external circuit. At that time, heat is generated. A set of fuel electrode-solid polymer film-oxidant electrode is called a cell, and a stack of a plurality of cells is called a stack.

In a polymer electrolyte fuel cell cogeneration system that includes a polymer electrolyte fuel cell, the power output is extracted from the fuel cell stack and the exhaust heat from the fuel cell stack is recovered and used as the heat output. To do. The cogeneration system has an overall thermal efficiency of 80 to 90% (LHV) that combines power output and heat output, can provide high energy savings, reduce energy costs, and reduce CO ₂ emissions. It is expected as a distributed power source that can greatly contribute to the surface.

  For example, a small polymer electrolyte fuel cell cogeneration system with an output of about 0.5 to 2 kW is assumed to be a market for ordinary households, but the power demand in ordinary households varies greatly depending on time zones. At the present time, no reverse power flow to the grid has been observed. Therefore, at night when the demand for electric power is low at home, it is necessary to stop the power and heat unless it is processed internally by providing a radiator for heat dissipation in the fuel cell unit. The

  On the other hand, the assumed life of a household fuel cell stack is said to be 40,000 hours on a DSS basis (start and stop once a day) and 3000 times or more of start and stop, and a high level of durability is required. In particular, at the time of start-up, the fuel-cell side electrode or the oxidant electrode-side electrode is likely to deteriorate due to corrosion due to the following factors, etc. It is a problem to be solved.

  That is, when the fuel cell stack is started, if the oxidant gas is introduced into the oxidant electrode and then the fuel is introduced into the fuel electrode, the potential of the oxidant electrode rises instantaneously and causes deterioration due to corrosion of the oxidant electrode. . Similarly, when the fuel cell stack is started up and fuel is introduced in a state where oxygen is in the fuel electrode, a partial cell is temporarily formed on the fuel electrode side, causing deterioration due to corrosion of the fuel electrode.

  The present invention provides a fuel cell power generation method and a fuel cell power generation system that avoids deterioration due to corrosion of the electrode of the fuel electrode and the electrode of the oxidant electrode at the time of starting the fuel cell stack and does not damage the fuel cell. Therefore, it is an object of the present invention to realize high durability in a long-time operation including start-stop and an operation pattern including many start-stops.

  In order to achieve the above object, a fuel cell power generation method according to the first aspect of the present invention includes a generation step of generating a hydrogen-rich reformed gas from a hydrocarbon-based fuel; A power generation step of introducing an oxidant gas into the oxidant electrode side of the fuel cell stack and generating power by the fuel cell stack; a stop step of stopping the power generation; and after the stop step, the hydrocarbon And a sealing step of sealing the generated fuel or the generated reformed gas to the fuel electrode side.

  According to this structure, after the stop step of stopping the power generation by the fuel cell stack, a sealing step of sealing the hydrocarbon fuel or the generated reformed gas to the fuel electrode side is provided. When the fuel cell stack is started up the next time, when the reformed gas is introduced to the fuel electrode side, oxygen and hydrogen on the fuel electrode side are used. Partial cell formation can be prevented, and deterioration of the fuel electrode due to corrosion can be prevented. In addition, since the hydrocarbon-based fuel or the generated reformed gas is sealed on the fuel electrode side after the power generation of the fuel cell stack is stopped, there is no air on the fuel electrode side. Air can be prevented from passing through the solid polymer membrane to the pole side, and when the fuel cell stack is started next time, the oxidant pole side can be prevented from instantaneously becoming a high potential. Deterioration due to corrosion can be prevented. As a result, it is possible to achieve high durability in a long-time operation including start-stop and an operation pattern including many start-stops.

  It is desirable to maintain the sealing step until the fuel cell stack is started next time after the fuel cell stack is stopped. In this way, when the fuel cell stack is started next time, it is possible to ensure that the fuel electrode side is in a hydrocarbon-based fuel atmosphere or a reformed gas atmosphere so that no air is present.

  A fuel cell power generation method according to a second aspect of the present invention is the fuel cell power generation method according to the first aspect, further comprising a power output step of outputting the generated power; and after the power output step, the oxidant electrode A holding step of keeping the side in a low atmosphere with an oxygen concentration of 10% by volume or less.

  If comprised in this way, since the said holding process and the said sealing process are provided, after completion | finish of the said electric power output process, the oxygen concentration electrode side is maintained in the low atmosphere whose oxygen concentration is 10 volume% or less, and after the said stop process The hydrocarbon-based fuel or the generated reformed gas can be sealed on the fuel electrode side, and a solid polymer film from the fuel electrode side to the oxidant electrode side can be formed while the fuel cell stack is stopped. Air diffusion can be prevented, and the oxidant electrode side can be reliably kept in a low oxygen concentration state. Therefore, when the reformed gas is introduced when the fuel cell stack is started next time, it is possible to reliably prevent electrode deterioration due to the oxidant electrode being instantaneously at a high potential.

  The holding step is preferably maintained until the fuel cell stack after the fuel cell stack is stopped is started next time. In this way, when the fuel cell stack is started next time, the oxidant electrode side can be surely in a state where the oxygen concentration is low.

  A fuel cell power generation method according to a third aspect of the invention is the fuel cell power generation method according to the first or second aspect, further comprising an introduction step of introducing an oxidant gas to the fuel electrode side after the stop step; The introduction step is performed when the accumulated operation time of the power generation step is a predetermined time or more, or when the power generation voltage falls below a predetermined reference value determined by a stack current value during the immediately preceding power generation step; The stopping step is performed at least after the introduction step.

  If comprised in this way, since the introduction process which introduce | transduces oxidant gas to the fuel electrode side is provided after the said stop process, when the accumulated operation time of the said electric power generation process is more than predetermined time, or during the said electric power generation process immediately before If the generated voltage falls below a predetermined reference value determined by the stack current value, impurities such as hydrocarbons and carbon monoxide adsorbed on the fuel electrode side catalyst during power generation may reach an allowable amount. By oxidizing the introduced hydrocarbon, carbon monoxide, and other impurities with the introduced oxidant gas, it is possible to prevent deterioration of the power generation performance of the fuel cell stack for a long time. Further, since the sealing step is performed at least after the introduction step, the hydrocarbon fuel or the generated reformed gas is sealed on the fuel electrode side, and the fuel cell stack is started next time, the fuel electrode When the reformed gas is introduced to the side, since no air exists on the fuel electrode side, partial cell formation by oxygen and hydrogen on the fuel electrode side can be reliably prevented.

  In order to achieve the above object, the fuel cell power generation system 101 according to the invention according to claim 4 introduces a hydrocarbon-based fuel 40 to generate a reformed gas rich in hydrogen as shown in FIG. A fuel cell stack that introduces the reformed gas 42 to the fuel electrode side, introduces the oxidant gas 32 to the oxidant electrode side, and generates power using the reformed gas 42 and the oxidant gas 32; 6; a replenishment flow path 146 for replenishing the hydrocarbon-based fuel 46 directly to the fuel electrode side; and sealing means 21, 23a, 27, 27a for sealing the replenished hydrocarbon-based fuel 46 to the fuel electrode side. , 28, 37, 38.

  If comprised in this way, the supply flow path 146 which supplies the hydrocarbon fuel 46 directly to the said fuel electrode side, and the sealing means 21, 23a, 27 which seal the supplied hydrocarbon fuel 46 to the fuel electrode side. 27a, 28, 37, and 38, the hydrocarbon fuel 46 introduced from the replenishment flow path 146 to the fuel electrode side after the end of power generation of the fuel cell stack 6 is sealed with the sealing means 21, 23a, 27, 27a, 28, 37, and 38 can be sealed to the fuel electrode side. Therefore, when the fuel cell stack 6 is started next time, when the reformed gas 42 is introduced to the fuel electrode side, partial cell formation due to oxygen and hydrogen on the fuel electrode side can be prevented. Deterioration can be prevented. Accordingly, it is possible to realize high durability of the fuel cell power generation system 101 in a long-time operation including start / stop and an operation pattern including many start / stops. The term “directly” means that the reformed gas generator 18 is not passed (bypassed). Therefore, the replenishment flow path 146 replenishes the hydrocarbon fuel 46 to the fuel electrode side without passing through the reformed gas generator 18.

  A fuel cell power generation system 101 according to a fifth aspect of the present invention is the fuel cell power generation system according to the fourth aspect, wherein the desulfurization means 17 for desulfurizing the hydrocarbon-based fuel 40 and the desulfurized hydrocarbon-based fuel 40 are modified. A fuel supply means 39 for supplying to the gas generating section 18; the hydrocarbon fuel 46 supplied by the supply flow path 146 is desulfurized by the desulfurization means 17 and supplied by bypassing the fuel supply means 39.

  With this configuration, the hydrocarbon fuel 46 desulfurized by the desulfurization means 17 can be supplied to the fuel electrode side without starting the fuel supply means 39.

  The fuel cell power generation system 101 according to the invention of claim 6 includes a reformed gas generation unit 18 that introduces a hydrocarbon-based fuel 40 and generates a hydrogen-rich reformed gas 42 as shown in FIG. A fuel cell stack 6 that introduces a gas 42 to the fuel electrode side, introduces an oxidant gas 32 to the oxidant electrode side, and generates power using the reformed gas 42 and the oxidant gas 32; Sealing means 21, 23 a, 27, 27 a, 28, 37, 38 for sealing the reformed gas 42 generated after stopping the power generation to the fuel electrode side; and pressure detection means 29 for detecting the pressure on the fuel electrode side And pressure control means 39, 28, 4 for sealing the generated reformed gas 42 on the fuel electrode side and controlling the pressure on the fuel electrode side at the time of sealing in a certain range based on the detected pressure. Is provided.

  If comprised in this way, since the pressure detection means 29 and the pressure control means 39, 28, 4 are provided, the produced | generated reformed gas 42 is enclosed with the said fuel electrode side which sealed the produced | generated reformed gas 42, The pressure on the fuel electrode side at the time of sealing can be controlled within a certain range based on the detected pressure, and the temperature in the fuel cell power generation system 101 decreases after power generation is stopped, and the pressure on the fuel electrode side Even if it falls, the fuel electrode side can be surely made into the reformed gas atmosphere.

  Since the present invention includes a sealing step for sealing hydrocarbon fuel or generated reformed gas to the fuel electrode side after the stopping step for stopping power generation by the fuel cell stack, the fuel electrode side is provided with a hydrocarbon-based fuel atmosphere. Alternatively, when the reformed gas atmosphere is set so that air does not exist and the fuel cell stack is started next time, when the reformed gas is introduced to the fuel electrode side, partial cells are formed by oxygen and hydrogen on the fuel electrode side. And the deterioration of the fuel electrode can be prevented. In addition, since the hydrocarbon-based fuel or the generated reformed gas is sealed on the fuel electrode side after the power generation of the fuel cell stack is stopped, there is no air on the fuel electrode side. When air permeates to the electrode side and the fuel cell stack is started next time, the oxidant electrode side can be prevented from instantaneously becoming a high potential, and deterioration due to corrosion of the oxidant electrode can be prevented. Thereby, it is possible to realize high durability in a long-time operation including start-stop and an operation pattern including many start-stops without using an inert gas.

  Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the mutually same or equivalent member, and the overlapping description is abbreviate | omitted.

  FIG. 1 is a block diagram showing a configuration of a fuel cell cogeneration system 101 according to the first embodiment.

  A fuel cell cogeneration system 101 as a fuel cell power generation system includes a fuel processing device 1, a fuel cell stack 6, a power conditioner 7, a desulfurizer 17 as a desulfurization means, a reforming raw material blower 39, and process water. Pump 3, recovered water tank 5, humidified water pump 13, stack air blower 15, selective oxidation air blower 51, combustion air blower 52, humidifier 16, and first heat exchange section 8, a second heat exchange unit 9, a third heat exchange unit 14, a stack cooling water pump 12, a steam / water separator 11, and a control unit 4. The fuel processing apparatus 1 includes a reforming unit 18 having a reforming catalyst (not shown), a conversion unit 19 having a CO conversion catalyst (not shown), a selective oxidation unit 20 having a selective oxidation catalyst (not shown), It has a steam generation part 36 and a combustion part 10. The control unit 4 controls the start operation, steady operation, and stop operation of the fuel cell cogeneration system 101.

  The fuel cell cogeneration system 101 further includes a fuel supply line 140, a raw material supply branch line 146 as a supplementary flow path, a selective oxidation air supply line 130a, a process water supply line 141, a water vapor supply line 141a, a combustion Air supply line 130, combustion fuel supply line 131, stack air supply line 132, purge air supply line 130b, reformed gas transfer line 142, fuel electrode off-gas transfer line 143, and switching line 142a A stack cooling water circulation line 160, a combustion exhaust gas discharge line 150, an oxidant electrode off-gas discharge line 133, a humidified water supply line 144, a heat recovery water circulation line 161, a drain water line 164, an excess water line 165, Is provided.

  A reforming raw material blower 39 as a fuel supply means is connected to a reforming raw material blower 39 as a hydrocarbon-based fuel (for example, ethane) via a fuel supply line 140 that connects the reforming raw material blower 39 and the reforming unit 18. , Methane, propane, butane, etc. as a main component, city gas 13A) is supplied to the reforming section 18. A desulfurizer 17 and a two-way valve 28 are installed on the fuel supply line 140. Since the desulfurizer 17 desulfurizes the reforming material 40 before the reforming material 40 is supplied to the reforming unit 18, the desulfurized reforming material 40 is supplied to the reforming unit 18. The two-way valve 28 is a control valve that controls the flow rate of the reforming raw material 40 supplied to the reforming unit 18 by a control signal (not shown) from the control unit 4. When the two-way valve 28 is closed, the fluid flow through the two-way valve 28 is blocked. Therefore, in this case, the fluid in the reforming unit 18 does not leak through the two-way valve 28.

  The reforming unit 18 reforms the supplied reforming raw material 40 to form a reformed gas 42 containing hydrogen as a main component (for example, about 70 to 75% in terms of hydrogen component). Is done. The reforming unit 18 includes a temperature detection device 75 that detects the temperature of the reforming unit 18, and the detected temperature is sent to the control unit 4 as a temperature signal i 75. In the shift unit 19, a CO shift reaction of the reformed gas 42 generated in the reforming unit 18 is performed. The transformation unit 19 includes a temperature detection device 76 that detects the temperature of the transformation unit 19, and the detected temperature is sent to the control unit 4 as a temperature signal i 76.

  The selective oxidation air supply line 130 a supplies the selective oxidation air 30 a supplied from the selective oxidation air blower 51 to the selective oxidation unit 20. In the selective oxidation unit 20, the carbon monoxide gas remaining in the reformed gas 42 subjected to the CO shift reaction is selectively oxidized. The selective oxidation unit 20 includes a temperature detection device 77 that detects the temperature of the selective oxidation unit 20, and the detected temperature is sent to the control unit 4 as a temperature signal i 77. A two-way valve 37 is installed on the selective oxidation air supply line 130a. The two-way valve 37 is set to open (fully open) or closed (fully closed) by an open / close signal (not shown) from the control unit 4. Is done. When the two-way valve 37 is opened, the selective oxidation air 30 a can be supplied to the selective oxidation unit 20. When the two-way valve 37 is closed, the fluid flow through the two-way valve 37 is blocked. Therefore, in this case, the fluid in the selective oxidation unit 20 does not leak through the two-way valve 37.

  The process water supply line 141 supplies process water 41 to the water vapor generation unit 36. In the water vapor generation part 36, the process water 41 is evaporated and the water vapor 41a is generated. The process water supply line 141 is connected to the recovered water tank 5, and the process water pump 3 and the two-way valve 38 are installed on the process water supply line 141. The process water pump 3 supplies the recovered water in the recovered water tank 5 as process water 41 to the steam generation unit 36. A water level detection device 71 is attached to the recovered water tank 5, and the water level detection device 71 sends the detected water level to the control unit 4 as a water level signal i71. The two-way valve 38 is set to open (fully open) or closed (fully closed) by an open / close signal (not shown) from the control unit 4. When the two-way valve 38 is opened, the process water 41 can be supplied to the water vapor generation unit 36. When the two-way valve 38 is closed, the fluid flow through the two-way valve 38 is blocked. Therefore, in this case, the fluid in the water vapor generation part 36 does not leak through the two-way valve 38.

  The steam supply line 141 a supplies the steam 41 a generated by the steam generating unit 36 to the reforming unit 18. The steam 41 a is used in the reforming reaction of the reforming raw material 40 in the reforming unit 18.

  The fuel cell stack 6 has a multiple structure in which solid polymer membranes (not shown) and separators (not shown) are alternately stacked. The reformed gas 42 is supplied to the fuel electrode side and oxidized to the oxidant electrode side. The stack air 32 as the oxidant gas is supplied, and electric power is generated by an electrochemical reaction. The fuel electrode off-gas 43 (reformed gas left behind) from the fuel electrode side, and the oxidant electrode off-gas 33 from the oxidant electrode side. Discharge.

  The fuel electrode off-gas transport line 143 supplies the fuel electrode off-gas 43 from the fuel electrode side of the fuel cell stack 6 to the combustion unit 10. A two-way valve 23 a is installed in the fuel electrode off-gas transfer line 143. The two-way valve 23a is set to open (fully open) or closed (fully closed) by an open / close signal (not shown) from the control unit 4. When the two-way valve 23a is opened, the fuel electrode off-gas 43 can flow from the fuel electrode side to the combustion unit 10 through the two-way valve 23a. When the two-way valve 23a is closed, the fluid flow through the two-way valve 23a is interrupted. Therefore, in this case, the fluid does not flow to the fuel electrode side through the two-way valve 23a, and the fluid on the fuel electrode side does not leak through the two-way valve 23a. The combustion air supply line 130 supplies the combustion air 30 supplied from the combustion air blower 52 to the combustion unit 10, and the combustion fuel supply line 131 supplies the combustion fuel 31 to the combustion unit 10. The combustion air 30 is used for combustion of the fuel electrode off gas 43 in the combustion unit 10 and combustion of the combustion fuel 31.

  The reformed gas transport line 142 connects the selective oxidation unit 20 of the fuel processing apparatus 1 and the fuel electrode side of the fuel cell stack 6 and transports the reformed gas 42 from the selective oxidation unit 20 to the fuel electrode side. The reformed gas transfer line 142 is provided with a three-way switching valve 21 and a pressure detection device 29 as pressure detection means. A switching signal i21 for switching the three-way switching valve 21 is sent from the control unit 4 to the three-way switching valve 21. The pressure detection device 29 is installed on the downstream side of the three-way switching valve 21, detects the pressure on the fuel electrode side, and the detected pressure is sent to the control unit 4 as a pressure signal i29. One end of a switching line 142 a is connected to the three-way switching valve 21, and the other end of the switching line 142 a is connected to a fuel electrode off-gas transfer line 143.

  When the three-way switching valve 21 is set to the a side by the switching signal i21, the reformed gas 42 passes through the reformed gas transport line 142, the three-way switch valve 21, and the reformed gas transport line 142 from the selective oxidation unit 20. It is transported to the fuel electrode side. On the other hand, when the three-way switching valve 21 is set to the b side by the switching signal i21, the reformed gas 42 is supplied from the selective oxidation unit 20 to the reformed gas transfer line 142, the three-way switching valve 21, the switching line 142a, the fuel electrode off-gas. It is conveyed to the combustion unit 10 through the conveyance line 143.

  When the three-way switching valve 21 is set to the a side and the reformed gas 42 is supplied from the selective oxidation unit 20 to the fuel electrode side for power generation of the fuel cell stack 6, the two-way valve 23a is set to open, The fuel electrode off-gas 43 can be transported from the fuel electrode side to the combustion unit 10 through the fuel electrode off-gas transport line 143. When the three-way switching valve 21 is set to the b side, the two-way valve 23a is set to be closed, and the reformed gas 42 that has reached the fuel electrode off-gas transfer line 143 does not flow back to the fuel electrode side.

  The stack air blower 15 causes the stack air 32 as an oxidant gas to be supplied to the oxidant electrode side via a stack air supply line 132 that connects the stack air blower 15 and the oxidant electrode side of the fuel cell stack 6. Supply. The humidifier 16 is installed on the stack air supply line 132. The humidifier 16 is supplied with humidified water 44 via the humidified water supply line 144, and the humidifier 16 humidifies the stack air 32 using the supplied humidified water 44. The surplus water 65 from the humidifier 16 is sent to the recovered water tank 5 via the surplus water line 165 and recovered as recovered water.

  A purge air supply line 130b is connected downstream of the three-way switching valve 21 in the reformed gas transfer line 142 and upstream of the pressure detection device 29. The purge air supply line 130b branches from the selective oxidation air supply line 130a, and supplies the selective oxidation air to the fuel electrode side as purge air 30b. A two-way valve 27a is installed in the purge air supply line 130b, and the purge air supply line 130b branches from the selective oxidation air supply line 130a upstream of the two-way valve 37. The two-way valve 27a is set to open (fully open) or closed (fully closed) by an open / close signal (not shown) from the control unit 4. When the two-way valve 27a is opened, the purge air 30b passes from the selective oxidation air blower 51 through the purge air supply line 130b and the reformed gas transfer line 142 to the fuel electrode side of the fuel cell stack 6. It becomes possible to flow in. When the two-way valve 27a is closed, the flow of fluid through the two-way valve 27a is interrupted. Therefore, in this case, the fluid in the reformed gas transfer line 142 and the fluid on the fuel electrode side do not leak through the two-way valve 27a.

  The raw material supply branch line 146 branches from the fuel supply line 140 on the downstream side of the reforming raw material blower 39 and the desulfurizer 17 and on the upstream side of the two-way valve 28, and the two-way valve 23 a is connected to the fuel electrode off-gas transfer line 143. The raw material 46 as a desulfurized hydrocarbon fuel is connected to the upstream side of the fuel, bypassing the fuel processing device 1 to the fuel electrode side, that is, bypassing the reforming unit 18, the shift unit 19, and the selective oxidation unit 20 to be supplied. . A two-way valve 27 is installed in the fuel supply branch line 146, and the two-way valve 27 is set to open (fully open) or closed (fully closed) by an open / close signal (not shown) from the control unit 4. When the two-way valve 27 is opened, the desulfurized raw material 46 can flow to the fuel electrode side through the fuel electrode off-gas transfer line 143. When the two-way valve 27 is closed, the fluid flow through the two-way valve 27 is blocked. Therefore, in this case, the fluid in the fuel electrode off-gas transfer line 143 does not leak through the two-way valve 27. When the two-way valve 27 is open, the two-way valve 23a is set to be closed. In the first embodiment, the reforming raw material 40 and the raw material 46 are gases (the same applies to the second embodiment described later).

  The combustion exhaust gas discharge line 150 discharges the combustion exhaust gas 50 generated in the combustion unit 10. The oxidant electrode off gas discharge line 133 discharges the oxidant electrode off gas 33 generated on the oxidant electrode side. The oxidant electrode off-gas discharge line 133 is connected to the combustion exhaust gas discharge line 150, and the oxidant electrode off-gas 33 that has passed through the oxidant electrode off-gas discharge line 133 is further discharged through the combustion exhaust gas discharge line 150. A check valve 25 is installed on the oxidant electrode off-gas discharge line 133. The check valve 25 allows the oxidant electrode off gas 33 to flow from the oxidant electrode side toward the combustion exhaust gas discharge line 150, and fluids such as the oxidant electrode off gas 33 and the combustion exhaust gas 50 move toward the oxidant electrode side. To block backflow.

  The stack cooling water pump 12 circulates the stack cooling water 60 through the stack cooling water circulation line 160.

  The first heat exchange unit 8 is connected to a heat recovery water circulation line 161 and a combustion exhaust gas discharge line 150, and heat exchange is performed between the combustion exhaust gas 50 (high temperature side) and the heat recovery water 61 (low temperature side). . A stack cooling water circulation line 160 and a hot heat recovery water circulation line 161 are connected to the second heat exchanging section 9, and heat exchange is performed between the stack cooling water 60 (high temperature side) and the hot heat recovery water 61 (low temperature side). Is called. A combustion exhaust gas discharge line 150 and a humidified water supply line 144 are connected to the third heat exchange unit 14, and heat exchange is performed between the combustion exhaust gas 50 (high temperature side) and the humidified water 44 (low temperature side). On the combustion exhaust gas discharge line 150, the third heat exchange unit 14 is disposed on the upstream side of the first heat exchange unit 8. The steam separator 11 is installed on the combustion exhaust gas discharge line 150 on the downstream side of the first heat exchange unit 8. On the warm heat recovery water circulation line 161, the first heat exchange unit 8 is disposed on the upstream side of the second heat exchange unit 9.

  The drain water line 164 connects the bottom of the steam / water separator 11 and the ceiling of the recovered water tank 5, and allows the drain water 64 recovered by the steam / water separator 11 to flow from the steam / water separator 11 to the recovered water tank 5. . The surplus water line 165 connects the bottom of the humidifier 16 and the ceiling of the recovered water tank 5, and the surplus water 65 that has not been used in the humidifier 16 is supplied from the humidifier 16 to the recovered water tank. Flow to 5.

  The stack cooling water circulation line 160 connects the stack cooling water pump 12, the second heat exchanging unit 9, and the fuel cell stack 6, and the stack cooling water 60 includes the stack cooling water pump 12, the second heat exchanging unit 9, and the fuel cell. The stack 6 is circulated in this order.

  The power conditioner 7 includes a DC / DC converter and a DC / AC inverter (not shown), adjusts the voltage of DC power (stack voltage) generated by the fuel cell stack 6, and further converts DC to AC. Moreover, the power conditioner 7 receives the control signal i74 from the control part 4, and outputs the alternating current power of the electric power value which the control signal i74 requires to an external load (not shown). In the wiring connecting the fuel cell stack 6 and the power conditioner 7, a voltage detection device 68 for detecting the stack voltage, a current detection device 69 for detecting the stack current, and the relay 34 are installed. The voltage detection device 68 sends a voltage signal i68 representing the detected stack voltage to the control unit 4, and the current detection device 69 sends a current signal i69 representing the detected stack current to the control unit 4. The relay 34 opens and closes the relay 34 by an open / close signal i34 sent from the control unit 4, and when the relay 34 is closed, the power required by the control signal i74 is output to an external load (not shown). 6 outputs electric power, and the relay 34 is opened, whereby the output of electric power from the fuel cell stack 6 is stopped.

  The stack air blower 15, the reforming raw material blower 39, the selective oxidation air blower 51, the combustion air blower 52, the process water pump 3, the humidifying water pump 13, and the stack cooling water pump 12 are respectively used as prime movers. It is driven by an electric motor (not shown). Each electric motor except the electric motor that drives the reforming raw material blower 39 is controlled in rotation speed by a control signal (not shown) from the control unit 4, and the stack air 32, the selective oxidation air 30a, and the combustion air 30, the flow rates of the process water 41, the humidified water 44, and the stack cooling water 60 are controlled. Whether or not the electric motor that drives the reforming material blower 39 at a constant rotational speed is controlled by a control signal (not shown) from the control unit 4 is controlled. Each electric motor stops when each control signal (not shown) is not sent from the control unit 4.

Next, the operation of the fuel cell cogeneration system 101 according to the first embodiment during power generation (rated power output state) will be described.
The reforming raw material 40 is supplied from the reforming raw material blower 39 to the desulfurizer 17, and the deodorizing agent containing the sulfur content in the reforming raw material 40 is removed and desulfurized. The desulfurized reforming raw material 40 is supplied to the reforming unit 18 of the fuel processing apparatus 1. At this time, the two-way valve 28 is in the open position, and the flow control of the reforming raw material 40 is performed by the two-way valve 28. At this time, the two-way valve 27 is in the closed position, and the raw material 46 is not supplied to the fuel electrode side. The process water 41 is supplied from the recovered water tank 5 to the water vapor generating unit 36 of the fuel processing apparatus 1 by the process water pump 3. At this time, the two-way valve 38 is in the open position, and the electric motor (not shown) that drives the process water pump 3 is controlled in rotational speed, and the flow rate of the process water 41 is controlled. Water vapor 41a is generated in the water vapor generating unit 36, and the generated water vapor 41a is supplied to the reforming unit 18 and used as reforming water vapor. That is, in the reforming unit 18, when the reforming raw material 40 is, for example, methane, a reforming catalyst (not shown) performs a steam reforming reaction that can be expressed as CH ₄ + H ₂ O → CO + 3H _2. Produces.

The reformed gas 42 is supplied from the reformer 18 to the shifter 19, and the shifter 19 undergoes a shift reaction represented by CO + H ₂ O → CO ₂ + H ₂ by a CO shift catalyst (not shown). CO in the gas 42 is removed. Further, the reformed gas 42 is sent from the shift unit 19 to the selective oxidation unit 20. The selective oxidation air 30 a is supplied from the selective oxidation air blower 51 to the selective oxidation unit 20. At this time, the two-way valve 37 is in the open position, an electric motor (not shown) that drives the selective oxidation air blower 51 is controlled in rotational speed, and the flow rate of the selective oxidation air 30a is controlled. The CO gas remaining in the reformed gas 42 is selectively oxidized by the selective oxidation unit 30 by the selective oxidation air 30a, and a selective oxidation reaction represented by CO + (1/2) O ₂ → CO ₂ is performed. . At this time, the two-way valve 27a is in the closed position, and the purge air 30b branched from the selective oxidation air 30a is not supplied.

  The reformed gas 42 from which the CO gas has been removed by the selective oxidation unit 20 is supplied to the fuel electrode side of the fuel cell stack 6. At this time, the three-way switching valve 21 is at the position a. The stack air 32 is supplied from the stack air blower 15 to the humidifier 16, humidified by the humidifier 16, and supplied to the oxidant electrode side of the fuel cell stack 6. At this time, an electric motor (not shown) that drives the stack air blower 15 is controlled in rotational speed, and the flow rate of the stack air 32 is controlled. An electric motor (not shown) that drives the humidifying water pump 13 is controlled in rotational speed, and the flow rate of the humidifying water 44 is controlled. The humidified stack air 32 is supplied to the oxidizer electrode side in order to maintain durability and realize high power generation efficiency in terms of the characteristics of the solid polymer type fuel cell stack 6. This is because (not shown) needs to be in a sufficiently humidified state.

  In the fuel cell stack 6, the reformed gas 42 is supplied to the fuel electrode side, the stack air 32 is supplied to the oxidant electrode side, and direct current is generated by an electrochemical reaction using the reformed gas 42 and the stack air 32. Electric power is generated, voltage conversion and DC / AC conversion are performed by the power conditioner 7, and AC power is output to an external load (not shown). The fuel electrode off-gas 43 is discharged from the fuel electrode side, and the oxidant electrode off-gas 33 is discharged from the oxidant electrode side. At this time, since the two-way valve 23a is in the open position, the fuel electrode off-gas 43 can be discharged.

  The fuel electrode off-gas 43 is supplied to the combustion unit 10 of the fuel processing apparatus 1 and is combusted in the combustion unit 10. The combustion exhaust gas 50 is generated by this combustion, and the combustion exhaust gas 50 is discharged from the combustion unit 10. The oxidant electrode off-gas 33 joins the combustion exhaust gas 50 and is discharged.

  That is, the combustion exhaust gas 50 is discharged from the combustion unit 10 and mixed with the oxidant electrode off gas 33, and the humidified water 44 is heated from 40 ° C. to 65 ° C., for example, at the third heat exchange unit 14. The heat recovery water 61 is cooled to, for example, 20 ° C. to 28 ° C. and is cooled to, for example, 55 ° C. to 22 ° C. by the heat recovery water 61. Further, the steam is separated and exhausted by the steam separator 11. The water, that is, the drain water 64 separated by the steam separator 11 is sent to the recovered water tank 5 and recovered as recovered water.

  The humidified water 44 supplied to the humidifier 16 raises the stack air to, for example, 55 ° C. in the humidifier 16 and humidifies it to RH 95% or more. The hot heat recovery water 61 is heated from 28 ° C. to 64 ° C., for example, by the stack cooling water 60 in the second heat exchange unit 9 and returned to the hot water tank (not shown), and the amount of heat is stored in the hot water tank.

  The stack cooling water 60 supplied to the fuel cell stack 6 cools the fuel cell stack 6, and the stack cooling water 60 itself is heated from 55 ° C. to 65 ° C. by the fuel cell stack 6 and exits the fuel cell stack 6. After passing through the cooling water pump 12, the second heat exchanging unit 9 cools the heated heat recovery water 61 from 65 ° C. to 55 ° C., and supplies the fuel cell stack 6 again to circulate. An electric motor (not shown) that drives the stack cooling water pump 12 is controlled in rotational speed, and the flow rate of the stack cooling water 60 is controlled. The power generation efficiency of the fuel cell stack 6 is normally 50 to 70% (LHV), and the loss is consumed as heat generated by the fuel cell stack 6, and this heat generated is removed by the stack cooling water 60.

  The control unit 4 sends an open / close signal (not shown) for opening or closing the opening position to the two-way valves 23a, 27, 27a, 37, 38, and a control signal (not shown) for controlling the flow rate. 28 and further to each electric motor (not shown) other than the electric motor (not shown) for driving the reforming material blower 39. Further, the control unit 4 sends a switching signal i21 for switching the three-way switching valve 21 to the a side before the power generation is started, and controls the power conditioner 7 to output power to an external load (not shown) when the power generation is started. Send control signal i74. The control unit 4 sends an open / close signal to the relay 34 to close the relay 34 at the start of power output from the fuel cell stack 6. Further, the control unit 4 includes a pressure signal i29 from the pressure detection device 29, a voltage signal i68 from the voltage detection device 68, a current signal i69 from the current detection device 69, a water level signal i71 from the water level detection device 71, and a temperature detection. A temperature signal i75 from the device 75, a temperature signal i76 from the temperature detection device 76, and a temperature signal i77 from the temperature detection device 77 are sent.

Next, the operation at the time of starting the fuel cell cogeneration system 101 according to the first embodiment will be described.
Since the three-way switching valve 21 is finally set to the b-side position and the two-way valves 23a, 27, 27a, 28, 37, and 38 are set to the closed positions during the previous stop operation, The three-way switching valve 21 is in the position on the b side, and the two-way valves 23a, 27, 27a, 28, 37, and 38 are in the closed position. First, the combustion air 30 is supplied to the combustion unit 10 for purging of a burner (not shown), and simultaneously with the start of the supply of the combustion fuel 31, the burner is ignited and combustion in the combustion unit 10 is started. Combustion exhaust gas 50 is discharged. Next, the reforming raw material blower 39 is started and the two-way valve 28 is opened at the same time. The reforming raw material 40 is desulfurized by passing through the desulfurizer 17 and then supplied to the reforming unit 18. At the same time, the humidifying water pump 13 is activated to supply the humidifying water 44 to the humidifier 16. At this time, the stack air 32 is not supplied, and the humidified water 44 supplied to the humidifier 16 is sent to the recovered water tank 5 via the surplus water line 165 and circulates. When the humidifying water pump 13 is activated, the humidifying water 44 can be heated by the combustion exhaust gas 50 in the third heat exchanging section 14, and the temperature of the humidifying water 44 is sufficiently increased by the start of power generation, so that the stack air 32 The lack of humidification can be avoided.

  At the initial stage of start-up, the temperature of the reforming unit 18 does not reach the temperature at which the reforming reaction occurs, so that the reforming reaction in the reforming unit 18 does not occur. The reforming material 40 is sent to the combustion unit 10 through the reforming unit 18, the shift unit 19, and the selective oxidation unit 20, and combustion of the reforming material 40 in the combustion unit 10 is started. Due to the combustion in the combustion unit 10, the temperatures of the reforming unit 18, the shift unit 19 and the selective oxidation unit 20 rise.

  When the temperature of the reforming unit 18, the temperature of the transformation unit 19, and the temperature of the selective oxidation unit 20 all exceed 100 ° C., the process water pump 3 is started and the process water 41 is supplied to the steam generation unit 36. Steam 41a is supplied to the reforming unit 18. The flow rate of the process water 41 is determined based on a predetermined S (water vapor 41a) / C (carbon in reforming raw material) ratio (molar ratio).

  After elapse of a predetermined time (for example, 10 minutes) after the supply of the process water 41 is started, the selective oxidation air 30a is supplied to the selective oxidation unit 20 based on a predetermined molar ratio with the reforming raw material 40. When the catalyst temperature in the fuel processor 1 reaches a predetermined temperature (when the temperature of the reforming section is 670 ° C., the temperature of the shift section 19 is 250 ° C., and the temperature of the selective oxidation section 20 is 120 ° C.) The three-way switching valve 21 is switched to the position on the a side, and at the same time, the two-way valve 23a is opened to supply the reformed gas 42 rich in hydrogen and containing about 10 ppm or less of carbon monoxide to the fuel electrode side. At this time, the stack voltage remains zero because the oxidizer electrode side has a nitrogen atmosphere with almost no oxygen.

  After a predetermined time (for example, 2 minutes) has elapsed from the start of supply of the reformed gas 42, the stack air blower 15 is started, the stack air 32 is supplied to the oxidizer electrode, and the fuel cell stack 6 starts generating power. To do. At this time, the stack voltage of the fuel cell stack 6 becomes an open circuit voltage. However, since the hydrogen-rich reformed gas 42 is supplied to the fuel electrode side first, this causes an instantaneous potential increase on the oxidant electrode side. It is possible to start without damaging the fuel cell stack 6 without causing deterioration due to electrode corrosion. Therefore, high durability of the fuel cell stack 6 can be realized.

  The internal auxiliary machine power (partially not shown) of the fuel cell cogeneration system 101 is switched from the system side (not shown) to the fuel cell stack 6 side so that it can be operated independently. Next, the relay 34 is changed from open to closed, the power conditioner 7 is activated, and output of electric power to an external load (not shown) is started. The internal auxiliary machine of the system refers to a rotary auxiliary machine such as a blower and a pump, sensors such as a thermocouple and a pressure gauge, and the control unit 4. The power output of the power conditioner 7 is increased, and at the same time, the flow rates of the reforming raw material 40, the selective oxidation air 30a, the stack air 32, the process water 41, and the combustion air 30 are increased, and the power is output to the target output (rated output). Increase output.

  At this time, the fuel cell stack 6 discharges the fuel electrode off-gas 43 containing about 50% (mol%) of hydrogen (dry base) and the oxidant electrode off-gas 33 containing about 10% (mol%) of oxygen (dry base). . The fuel electrode off gas 43 is combusted in the combustion unit 10 and heats the reforming unit 18 and the like in the fuel processing apparatus 1. The oxidant electrode off-gas 33 merges with the combustion exhaust gas 50 from the combustion unit 10 and heats the humidified water 44 in the third heat exchange unit 14.

Next, a power generation stop operation method of the fuel cell cogeneration system 101 according to the first embodiment will be described with reference to FIG. The following operation is performed under the control of the control unit 4.
In the figure, the horizontal axis represents time, and the vertical axis represents operating parameters, that is, fuel cell power generation output% that is power generated by the fuel cell stack 6, flow rate% of the reforming raw material 40, flow rate% of the raw material 46, process water. 41, flow rate% of the selective oxidation air 30a, flow rate% of the stack air 32, and temperature% of the reforming unit 18. Except for the raw material 46, the value at the rated operation is 100%. The raw material 46 has a value equal to the flow rate at the rated operation of the reforming raw material 40 as 100%. The value of 100% indicates that the fuel cell power generation output is 1.3 kW, the reforming raw material 40 is 11 mol / h, the process water 41 is 37 mol / h, the selective oxidation air 30a is 4 mol / h, and the stacking air 32 is 161 mol / h. h, the temperature of the reforming section 18 is 700 ° C.

  First, it is assumed that the fuel cell cogeneration system 101 is in a rated power output state. At this time, the value of the operating parameter other than the raw material 46 is 100%, and the value of the raw material 46 is 0%. At this time, the two-way valves 23a, 37 and 38 are in the open position, the three-way switching valve 21 is in the position a, and the two-way valves 27 and 27a are in the closed position. The two-way valve 28 controls the flow rate of the reforming raw material 40.

  At time t1, reduction of the power output of the power conditioner 7 is started so that the fuel cell power generation output from the fuel cell stack 6 becomes 8%. At the same time, the flow rate of the reforming raw material 40, the process water 41, the selective oxidation air 30a, and the stacking air 32 are reduced so that the flow rates become 15%, 18%, 18%, and 20%, respectively. . The flow rate of the raw material 46 is maintained at 0%. These values, excluding the raw material 46, are the minimum flow rate, and the flow rate is reduced only to these values. This is for maintaining the supply of the fuel electrode off gas 43 from the fuel electrode to the combustion unit 10 and maintaining the combustion of the fuel electrode off gas 43 in the combustion unit 10. The flow rate is decreased from the control unit 4 by an electric motor for driving a stack air blower (not shown), a two-way valve 28, an electric motor for driving a selective oxidation air blower (not shown), and an electric motor for driving a process water pump (not shown). Each control signal (not shown) sent to (not shown) is changed. The fuel cell power generation output is decreased by changing a control signal i74 from the control unit 4 to the power conditioner 7. After time t1, the temperature of the reforming unit 18 gradually decreases.

  At time t1 '(for example, 5 minutes have elapsed from time t1), the power output of the power conditioner 7 becomes 0, the fuel cell power generation output from the fuel cell stack 6 becomes 8%, the reforming raw material 40, process water 41, and selection The flow rates of the oxidizing air 30a and the stacking air 32 are 15%, 18%, 18%, and 20%, respectively. The power output process ends at time t1 '. That is, at this time, the power output from the power conditioner 7 to the external load (not shown) is zero. The fuel cell power generation output from the fuel cell stack 6 is consumed as standby power of the power conditioner 7 and power of an internal auxiliary machine (not shown).

  At time t2 (e.g., one minute has elapsed from time t1 '), the power of the internal auxiliary equipment (not shown) of the system is switched from the fuel cell stack 6 side to the system side (not shown) so that the fuel cell power generation output becomes 3%. The power generation output from the fuel cell stack 6 is reduced. The fuel cell power generation output is consumed as standby power for the power conditioner 7.

  At this time, the cell average voltage (stack voltage / number of cells) of the fuel cell stack 6 is about 0.9 V, which is a high potential. Therefore, the cells of the fuel cell stack 6 are likely to deteriorate. Therefore, it is not desirable to keep the potential high for a long time.

  At time t3 (for example, 10 seconds have elapsed from time t2), the supply of the stacking air 32 is stopped, the operation of the humidifying water pump 13 is stopped, and the supply of the humidifying water 44 to the humidifier 16 is stopped. Note that the position of the three-way switching valve 21 remains a, and the supply of the reformed gas 42 to the fuel cell stack 6 is continued.

  The supply of the stack air 32 to the oxidant electrode side is stopped by stopping the stack air blower 15. The power conditioner 7 connected to the fuel cell stack 6 consumes standby power and serves as an electric load for the fuel cell stack 6, and the reformed gas 42 and the oxidant supplied to the fuel electrode side of the fuel cell stack 6. Since oxygen present on the pole side is consumed, the oxygen side becomes deficient on the oxidant pole side, and the oxidant pole side becomes an atmosphere having a low oxygen concentration. Along with this, the cell average voltage of the fuel cell stack 6 decreases. Since the stack air blower 15 is maintained in the stopped state thereafter, the oxidant electrode is maintained in a state where the oxygen concentration is low. This state is not only immediately after the power generation stop of the fuel cell stack 6 described later but also the next fuel cell. It is maintained until the stack 6 is activated (holding step). Since the reformed gas 42 is continuously supplied to the fuel electrode side, there is no shortage of fuel on the fuel electrode side.

At this time, if the stack current value is 0.01 A / cm ² or less, it is possible to reduce the overall voltage while suppressing variations in the cell average voltage, and cells that are damaged by the high cell voltage (stack voltage) can be obtained. Disappear. This shortens the time during which the cells of the fuel cell stack 6 are maintained at a high potential, so that deterioration due to the high potential can be avoided.

  In addition, this makes it possible to reduce the cell average voltage in a state where the fuel electrode does not run out of fuel, and to prevent corrosion of the oxidant electrode. Therefore, the stop operation can be performed without damaging the fuel cell stack 6, and deterioration can be prevented.

  Insufficient oxygen concentration on the oxidant electrode side means that the oxygen concentration on the oxidant electrode side is 10% by volume or less, preferably 3% by volume or less.

  As described above, since the oxidizer electrode is kept in a low oxygen concentration state, that is, in an oxygen-deficient state, when the reformed gas 42 is introduced to the fuel electrode side when the fuel cell stack 6 is started next time, The oxidant electrode does not instantaneously become a high potential, and electrode deterioration due to the oxidant electrode becoming a high potential can be prevented.

  When the relay 34 is opened and the power load of the fuel cell stack 6 is cut off at time t4 (e.g., 8 minutes elapses from the time t3), the fuel cell power output from the fuel cell stack 6 becomes zero. At this point, the power generation process ends.

  After the two-way valve 23a is closed at time t5 (for example, 10 seconds have elapsed from the time t4), the two-way valve 28 is closed and the reforming material blower 39 is stopped at the same time, thereby reforming the reforming material 40. The supply to the unit 18 is stopped, the two-way valve 38 is closed, the supply of the process water 41 to the water vapor generating unit 36 is stopped, and the two-way valve 37 is closed to the selective oxidation unit 20 of the selective oxidation air 30a. Stop supplying. Next, the two-way valve 23a is closed. As a result, the fuel electrode side of the fuel processing device 1 and the fuel cell stack 6 can be partitioned by the three-way switching valve 21 (position on the a side) and the two-way valves 23a, 27, 27a, 28, 37, 38, and the reformed gas 42 can be sealed in the reformed gas sealing region. If the reformed gas 42 is sealed in the reformed gas sealing region, the reformed gas 42 is sealed on the fuel electrode side. The three-way switching valve 21 and the two-way valves 23a, 27, 27a, 28, 37, and 38 are sealing means of the present invention.

  After stopping the power generation of the fuel cell stack 6, the pressure measuring device 29 monitors the reformed gas sealing area where the reformed gas 42 is sealed. When the fuel cell stack 6 stops generating power, the stop process of stopping power generation ends. The reformed gas sealing region includes the reforming unit 18, the shift unit 19, the selective oxidation unit 20, the downstream side of the two-way valve 28 of the fuel supply line 140, and the selective oxidation air supply line 130 a. The downstream side of the valve 37, the downstream side of the two-way valve 27a of the purge air supply line 130b, the downstream side of the two-way valve 38 of the steam generator 36 and the process water supply line 141, the steam supply line 141a, and the fuel cell stack 6 The fuel electrode side, the reformed gas transfer line 142 and the fuel electrode off gas transfer line 143 are configured to include the upstream side of the two-way valve 23a and the downstream side of the raw material supply branch line 146 of the two-way valve 27.

  When the pressure in the reformed gas sealing area detected by the pressure detector 29 falls below 1 kPaG at time t6 (for example, 60 minutes have elapsed from time t5), the reformed gas sealing area of air in the atmosphere In order to avoid contamination, the reforming raw material blower 39 is started, the two-way valve 27 is opened at the same time, the supply of the raw material 46 to the desulfurizer 17 is started, and the desulfurized raw material 46 having a flow rate of 30% is modified. The material gas sealing region is replenished, that is, sealed, and sealed (sealing process) so that the pressure in the reformed gas sealing region does not become negative. The sealing time is, for example, 1 minute. The reforming material blower 39 stops after the completion of the sealing. Further, the two-way valve 27 is also closed after the completion of the encapsulation. Since the raw material 46 has been desulfurized, the catalyst (not shown) of the fuel processing device 1 and the fuel cell stack 6 is not poisoned by sulfur. In addition, since the reformed gas sealing region does not become negative pressure, it is possible to reliably prevent air from being mixed, and when the reformed gas 42 is supplied to the fuel electrode side at the start of power generation of the fuel cell stack 6, the mixed gas was mixed. It is possible to prevent electrode deterioration due to formation of a partial cell on the fuel electrode side due to air, and high durability can be realized.

  If the inventors of the present invention replenish the raw material 46 from a line connected to the outlet of the reformed gas 42 of the fuel processing apparatus 1 by a test (for example, reforming between the reformed gas outlet and the three-way switching valve 21). The gas transport line 142 is replenished with the raw material 46), and the knowledge that the replenished raw material 46 does not reach the reforming section 18 having a high temperature (for example, 400 ° C. or higher) in the fuel processing apparatus 1 has been obtained. It was. According to the fuel processing apparatus 1 according to the first embodiment of the present invention, even when the temperature of the reforming unit 18 is high (for example, 400 ° C. or higher), it is far from the outlet of the reformed gas 42 of the fuel processing apparatus 1. If the raw material 46 is replenished from the outlet of the fuel electrode off-gas 43 on the fuel electrode side of the fuel cell stack 6 that is disposed, the raw material 46 does not reach the reforming unit 18, and the raw material 46 is carbonized in the reforming unit 18. And the deterioration of the reforming catalyst (not shown) of the reforming unit 18 is not caused.

  At time t7 (for example, 120 minutes have elapsed from time t6), that is, when the reforming section 18 falls below the upper limit temperature (for example, 59% (400 ° C.)) at which coking due to carbonization of the reforming raw material 40 does not occur. The raw material blower 39 is started and the two-way valves 23a and 28 are simultaneously opened, and the gas remaining in the reformed gas sealing region is purged by the reforming raw material 40. The time for purging is a time sufficient for purging, for example, 5 minutes. This purging is performed by lowering the temperature of the reformed gas sealing region and condensing the water vapor remaining in the reformed gas 42 to the catalyst (reformed catalyst, shift catalyst, selective oxidation catalyst) in the fuel processing apparatus 1. This is to avoid that. When moisture condenses on the catalyst, the moisture penetrates into the pores on the catalyst surface and the water may boil at the next start, which may damage the catalyst pore structure. The reforming material blower 39 stops after the purging and sealing by the reforming material 40 are completed.

  At time t8 (e.g., 5 minutes elapses from time t7), the two-way valve 23a is closed and sealing with the reforming raw material 40 is started. The sealing time is a time sufficient for sealing, for example, 10 seconds. The sealing with the reforming raw material 40 may be performed until the pressure indication value of the pressure detection device 29 is monitored and the value rises to a sealing pressure reference value (for example, 20 kPaG). The flow rate of the reforming raw material 40 at the time of sealing is controlled by the two-way valve 28, and the flow rate of the reforming raw material 40 at this time is equivalent to, for example, 12% during rated operation. After the completion of the sealing, the two-way valve 28 is closed, and the raw material sealing region (same as the reformed gas sealing region) including the fuel electrode side of the fuel processing device 1 and the fuel cell stack 6 is set to the three-way switching valve 21 (the a-side switching valve 21). Position), the two-way valves 23a, 27, 27a, 28, 37, 38 can be partitioned to seal the reforming raw material 40 in the raw material sealing region (sealing step). Thereby, the raw material sealing region including the fuel electrode side can be made a raw material atmosphere (hydrocarbon fuel atmosphere). When the raw material sealing region including the fuel electrode is used as the raw material atmosphere in a place where the oxygen concentration of the oxidant electrode is already low, the oxidant electrode is viewed from the fuel electrode side while the fuel cell stack 6 is stopped. Air diffusion through a solid polymer film (not shown) to the side can be prevented, and the oxidant electrode side can be reliably kept in a low oxygen concentration state.

  When the pressure in the raw material sealing area detected by the pressure detection device 29 falls below 1 kPaG at time t9, the reforming raw material blower is again used to avoid mixing air in the raw material sealing area. 39 is started and the two-way valve 28 is opened at the same time, and the desulfurized reforming raw material 40 is replenished and sealed in the raw material sealing region, and the pressure in the raw material sealing region is increased to the sealed pressure reference value and sealed. The possibility of a pressure below 1 kPaG is virtually eliminated. In this way, the raw material sealing region including the fuel electrode side can be maintained in the raw material atmosphere. Since the reforming raw material 40 to be enclosed has been desulfurized, the catalyst of the fuel processing device 1 and the fuel cell stack 6 is not poisoned with sulfur. The reforming material blower 39 stops after the completion of the sealing. The two-way valve 28 is also closed after the completion of the encapsulation.

FIG. 3 shows the relationship between the stack current detected by the current detection device 69 and the stack voltage detected by the voltage detection device 68. Curve 1 shows the relationship between the stack current and the stack voltage initial value (the value at the initial operation or the value immediately after purging with purge air 30b described later). Curve 2 shows the relationship between the stack current and the stack voltage reference value. The stack voltage reference value is the stack voltage at which impurities such as hydrocarbons and carbon monoxide are adsorbed on the fuel electrode side catalyst during power generation and gradually accumulate to reduce the stack voltage value, which requires removal of impurities. Value. In the figure, when the stack current is 35 A, the initial stack voltage value is 38 V in curve 1, the reference stack voltage value is 36 V in curve 2, and when the stack current is 15 A, the initial stack voltage value is 41 V in curve 1. In 2, the stack voltage reference value is 38V.
When the cumulative power generation time of the fuel cell stack 6 has reached a predetermined value (for example, 500 hours), or when the stack voltage falls below the reference value obtained from the curve 2 based on the measured stack current during power generation Purges the fuel electrode side with the purge air 30b as follows, removes impurities (hydrocarbon, CO, etc.) by oxidation treatment, recovers stack voltage, and prevents deterioration of power generation performance of the fuel cell stack 6 To do.

  This case will be described with reference to FIG. In the figure, the vertical axis also represents the flow rate% of the purge air 30b, the 100% flow rate of the purge air 30b is 5 mol / h, and the purge with purge air is performed between time t8 and time t9. It is the same as FIG. 2 except that it is performed. As shown in the figure, after the sealing of the reforming raw material 40 started at time t8 to the reforming unit 18 is completed, the sealing of the raw material 40 into the raw material sealing region started at time t9 and Before sealing, the two-way valve 27a in the purge air supply line 130b is opened, the two-way valve 23a in the fuel electrode off-gas transfer line 143 is opened, and the purge air on the fuel electrode side of the fuel cell stack 6 is opened. Air purge is performed by 30b (introduction step) (flow rate 100%). The air purge with the purge air 30b is performed for a time sufficient for the air purge, for example, 60 seconds.

FIG. 5 is a block diagram showing a configuration of a fuel cell cogeneration system 201 according to the second embodiment of the present invention.
A difference in configuration of the fuel cell cogeneration system 201 as the fuel cell power generation system from the fuel cell cogeneration system 101 (FIG. 1) will be described. The fuel cell cogeneration system 201 does not include the raw material supply branch line 146 and the two-way valve 27. However, the other configuration is the same as the configuration of the fuel cell cogeneration system 101 described above.

  Regarding the operation of the fuel cell cogeneration system 201 during power generation (rated power output state), except that the description regarding the two-way valve 27 should be deleted, the fuel cell cogeneration system 101 (FIG. 1) during power generation ( This applies to the description of the action of (rated power output state).

  Regarding the operation at the time of starting the fuel cell cogeneration system 201, the description regarding the operation at the time of starting the fuel cell cogeneration system 101 (FIG. 1) is applicable except that the description regarding the two-way valve 27 should be deleted. .

  FIG. 6 shows a power generation stop operation method of the fuel cell cogeneration system 201 according to the second embodiment. The times t11, t11 ', t12, t13, and t14 correspond to the times t1, t1', t2, t3, and t4 in FIG. Hereinafter, the time after the time t15 will be described with reference to FIG.

  After the two-way valve 23a is closed at time t15 (e.g., 10 seconds have elapsed from time t14), the fuel processing device 1 and the fuel cell stack 6 detected by the pressure detection device 29 while the two-way valve 28 remains open. The reforming raw material 40 is continuously sealed in the reforming section 18 until the pressure in the reformed gas sealing region including the fuel electrode side reaches a predetermined range (for example, 40 to 50 kPaG). At this time, the supply of the process water 41 and the selective oxidation air 30a is continued in the same manner. The process water 41 is supplied to prevent carbonization of the reforming raw material 40 in the reforming catalyst, and the selective oxidation air 30a is supplied to prevent CO poisoning of the fuel electrode catalyst (not shown) of the fuel cell stack 6. To do. As a result, the reformed gas 42 reaches the reformed gas sealing region via the reformed gas transfer line 142. Encapsulation of the reformed gas 42 in the reforming unit 18 starts the reforming material blower 39 and opens the opening of the two-way valve 28 so that the pressure in the reformed gas sealing region reaches the above-described certain range. And the flow rate of the reforming raw material 40 is controlled. Here, the certain range means that the temperature of the reforming unit 18 decreases even if the temperature in the fuel cell power generation system 101 decreases while the fuel cell power generation system 101 is stopped and the pressure on the fuel electrode side decreases. In the reforming catalyst, the range of the pressure at which the fuel electrode side can be surely put into the reformed gas atmosphere practically until the reforming material 40 can be purged and sealed without being carbonized. Say.

  The controller 4 receives the pressure signal i29 sent from the pressure detecting device 29 at time t16 and receives the pressure signal i29 sent from the pressure detecting device 29, and sends a control signal (not shown) to the two-way valves 28 and 30a. The feed two-way valves 28 and 30a are closed, and at the same time, an electric motor (not shown) for driving the reforming material blower 39 and an electric motor (not shown) for driving the selective oxidation air blower 51 are stopped. Five seconds after the two-way valves 28 and 30a are closed (t17), the two-way valve 38 is closed, and at the same time, an electric motor (not shown) that drives the process water pump 3 is stopped. In this way, the reformed gas sealing region including the fuel electrode side of the fuel processing device 1 and the fuel cell stack 6 is partitioned by the three-way switching valve 21 and the two-way valves 23a, 27a, 28, 37, 38, The reformed gas 42 can be sealed in the reformed gas sealing region. Therefore, the reformed gas sealing region including the fuel electrode side can be reliably made the reformed gas atmosphere, and the reformed gas sealed region can be held in the reformed gas atmosphere. The reforming material blower 39, the electric motor (not shown) for driving the reforming material blower 39, the two-way valve 28, and the control unit 4 are the pressure control means of the present invention.

  Even after the reformed gas 42 is sealed, even if the temperature of the reformed gas sealing region decreases and the sealing pressure in the reformed gas sealing region detected by the pressure detection device 29 decreases, the reformed gas sealing is performed. It is desirable to prevent the area from becoming negative pressure. For this purpose, when the reformed gas 42 is sealed, the sealing pressure within a certain range is determined so as not to become a negative pressure in consideration of the pressure drop due to the temperature drop. As a result, air in the atmosphere can be prevented from being mixed, electrode deterioration due to partial cell formation on the fuel electrode side of the fuel cell stack 6 due to air mixing can be prevented, and high durability can be realized. Can do.

  At time t18 (for example, 120 minutes have elapsed from time t17), that is, when the reforming section 18 has fallen below the upper limit temperature (for example, 59% (400 ° C.)) at which coking due to carbonization of the reforming raw material 40 does not occur. The raw material blower 39 is started and the two-way valves 23a and 28 are simultaneously opened, and the gas remaining in the reformed gas sealing region is purged by the s reforming raw material 40. The time for purging is a time sufficient for purging, for example, 5 minutes. In this way, it is possible to avoid the water vapor remaining in the reformed gas 42 from condensing on the catalyst (the reforming catalyst, the shift catalyst, the selective oxidation catalyst) in the fuel processing apparatus 1. Durability can be realized.

  At time t19 (e.g., 5 minutes have elapsed from time t18), the two-way valve 23a is closed and sealing with the reforming raw material 40 is started. The flow rate of the reforming raw material 40 at the time of sealing is controlled by the two-way valve 28, and the flow rate of the reforming raw material 40 at this time is equivalent to, for example, 12% during rated operation. After completion of the sealing, the reforming material blower 39 is stopped and the two-way valve 28 is closed at the same time, and the material sealing area including the fuel electrode side of the fuel processing device 1 and the fuel cell stack 6 (same as the reforming gas sealing area). ) Can be sealed with the reforming raw material 40 (sealing step). Thereby, the raw material sealing region including the fuel electrode side can be made a raw material atmosphere (hydrocarbon fuel atmosphere).

  In the above-described first embodiment (FIG. 1), the raw material supply branch line 146 is provided downstream from the reforming raw material blower 39 and the desulfurizer 17 and upstream of the two-way valve 28 from the fuel supply line 140. It was explained as branching. Hereinafter, a case where the arrangement of the desulfurizer 17 and the reforming raw material blower 39 and the branch point of the raw material supply branch line 146 from the fuel supply line 140 are changed will be described.

FIG. 7 is a block diagram showing a configuration of a fuel cell cogeneration system 301 according to the third embodiment of the present invention.
A difference in configuration of the fuel cell cogeneration system 301 as the fuel cell power generation system from the fuel cell cogeneration system 101 (FIG. 1) will be described.

  The fuel cell cogeneration system 301 arranges the desulfurizer 17, the reforming material blower 39, and the two-way valve 28 in this order on the fuel supply line 140 along the flow of the reforming material 40, and supplies the replenishment flow path. The raw material supply branch line 146 is branched from the fuel supply line 140 downstream of the desulfurizer 17 and upstream of the reforming raw material blower 39. The fact that the two-way valve 27 is installed in the raw material supply branch line 146 and that the raw material supply branch line 146 is connected to the fuel electrode off-gas transfer line 143 on the upstream side of the two-way valve 23a means that the fuel cell cogeneration system 101 ( The same as FIG.

  The reforming raw material blower 39 as a fuel supply means is a hydrocarbon-based fuel desulfurized by the desulfurizer 17 via a fuel supply line 140 that connects the desulfurizer 17, the reforming raw material blower 39 and the reforming unit 18. The reforming raw material 40 is supplied to the reforming section 18. In addition, the reforming raw material 40 desulfurized by the desulfurizer 17 bypasses the reforming raw material blower 39 and the fuel processing device 1, and passes through the raw material supply branch line 146 as the raw material 46 and the fuel electrode of the fuel cell stack 6. It is replenished to the side. FIG. 7 is the same as FIG. 1 except for the arrangement of the desulfurizer 17, the reforming raw material blower 39 and the two-way valve 28, the configuration of the fuel supply line 140, and the configuration of the raw material supply branch line 146. The raw material 46 desulfurized by the desulfurizer 17 can be supplied to the fuel electrode side by bypassing the reforming raw material blower 39 because the supply pressure of the reforming raw material 40 to the desulfurizer 17 is sufficiently higher than the atmospheric pressure. This is because it has a high value, for example, a value of about 1.5 to 2.5 kPaG.

  At the time of power generation (rated power output state) and startup of the fuel cell cogeneration system 301, the reforming raw material blower 39 supplies the reforming raw material 40 desulfurized by the desulfurizer 17 to the reforming unit 18 of the fuel processing apparatus 1. Supply. Except for this point, the fuel cell cogeneration system 301 according to the present embodiment operates at the time of power generation (rated power output state) and at the start of the fuel cell cogeneration system 101 according to the first embodiment described above. The operation is the same as that during power generation (rated power output state) and startup.

  The fuel cell cogeneration system 301 stops the power generation of the fuel cell stack, and does not start the reforming material blower 39, but reforms the reforming material 40 desulfurized by the desulfurizer 17 in the fuel processing device 1. The unit 18 may be supplied. In this respect, the power generation stop operation method of the fuel cell cogeneration system 301 of the present embodiment is different from the power generation stop operation method of the fuel cell cogeneration system 101 according to the first embodiment described above.

  Hereinafter, the difference between the power generation stop operation method of the fuel cell cogeneration system 301 of the present embodiment and the power generation stop operation method of the fuel cell cogeneration system 101 according to the first embodiment will be described in detail.

  At time t6 (similar to t6 described in the first embodiment), the sealing of the raw material 46 into the reformed gas sealing region via the raw material supply branch line 146 is detected by the pressure detection device 29. When the pressure in the reformed gas sealing region is lower than 0.5 kPaG, the two-way valve 27 is opened. At this time, the reforming material blower 39 is not started. Further, the amount of the raw material 46 enclosed is not controlled. The sealing of the raw material 46 is completed when the pressure in the reformed gas sealing area detected by the pressure detection device 29 reaches a predetermined pressure (for example, 1.5 kPaG). By doing in this way, it can avoid effectively that the air in air | atmosphere mixes in a reformed gas sealing area. Further, since the reforming material blower 39 is not started and the reforming material blower 39 is bypassed to enclose the material 46, the fuel electrode side is overpressurized due to malfunction of the reforming material blower 39 or the like. There is nothing. The two-way valve 27 is closed after completion of the sealing.

  When the pressure in the reformed gas sealing area falls below 0.5 kPaG, the material 46 starts to be sealed, and the pressure in the reformed gas sealing area reaches a predetermined pressure (for example, 1.5 kPaG). In this case, the sealing of the raw material 46 is stopped. However, if the pressure in the reformed gas sealing region is lower than 0.5 kPaG without starting this, the sealing of the raw material 46 is started. After 10 minutes have elapsed after the stop, the sealing is stopped, and then the sealing is started again, and after stopping for 1 minute, it is stopped again, and this sealing process is repeated 10 times (the number of times of sealing is 10 times). May be. By doing in this way, it can avoid effectively that the air in air | atmosphere mixes in a reformed gas sealing area.

1 is a block diagram showing a configuration of a fuel cell cogeneration system according to a first embodiment of the present invention. It is a chart explaining the electric power generation stop operation method of the fuel cell cogeneration system of Drawing 1 in order of passage of time. It is an IV curve which shows (1) an initial relationship of a stack current and a stack voltage, and (2) the relationship when an air purge is required. In the chart of FIG. 2, it is a chart in the case of performing an air purge between time t7 and time t8. It is a block diagram which shows the structure of the fuel cell cogeneration system which concerns on the 2nd Embodiment of this invention. 6 is a chart for explaining a power generation stop operation method of the fuel cell cogeneration system of FIG. 5 in order of time passage. It is a block diagram which shows the structure of the fuel cell cogeneration system which concerns on the 3rd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel processing apparatus 4 Control part 6 Fuel cell stack 17 Desulfurizer (desulfurization means)
18 Reformer (reformed gas generator)
21 Three-way switching valve (sealing means)
23a, 27, 27a, 28, 37, 38 Two-way valve (sealing means)
29 Pressure detector 30a Selective oxidation air 30b Purge air 32 Stack air (oxidant gas)
39 Raw material blower for reforming (fuel supply means)
40 Raw material for reforming (hydrocarbon fuel)
41 Process water 42 Reformed gas 46 Raw material (hydrocarbon fuel)
101, 201 Fuel cell cogeneration system (fuel cell power generation system)
146 Raw material supply branch line (replenishment flow path)

Claims (6)

A production process for producing a hydrogen-rich reformed gas from a hydrocarbon-based fuel;
A power generation step of introducing the reformed gas into the fuel electrode side of the fuel cell stack, introducing the oxidant gas into the oxidant electrode side of the fuel cell stack, and generating power with the fuel cell stack;
A stopping step of stopping the power generation;
A sealing step of sealing the hydrocarbon fuel or the generated reformed gas to the fuel electrode side after the stopping step;
Fuel cell power generation method. A power output step of outputting the generated power;
A holding step of maintaining the oxidant electrode side in an atmosphere having a low oxygen concentration of 10% by volume or less after the power output step is completed;
The fuel cell power generation method according to claim 1. An introduction step of introducing an oxidant gas to the fuel electrode side after the stop step;
The introduction step is performed when the accumulated operation time of the power generation step is a predetermined time or more, or when the power generation voltage falls below a predetermined reference value determined by a stack current value during the immediately preceding power generation step;
The sealing step is performed at least after the introduction step;
The fuel cell power generation method according to claim 1 or 2. A reformed gas generator that introduces a hydrocarbon-based fuel to generate a hydrogen-rich reformed gas;
A fuel cell stack that introduces the reformed gas into the fuel electrode, introduces an oxidant gas into the oxidant electrode, and generates power using the reformed gas and the oxidant gas;
A replenishment flow path for replenishing the hydrocarbon fuel directly to the fuel electrode side;
Sealing means for sealing the replenished hydrocarbon fuel on the fuel electrode side;
Fuel cell power generation system. A desulfurization means for desulfurizing the hydrocarbon fuel;
Fuel supply means for supplying the desulfurized hydrocarbon fuel to the reformed gas generator;
The hydrocarbon-based fuel supplied by the supply passage is desulfurized by the desulfurization means and supplied by bypassing the fuel supply means;
The fuel cell power generation system according to claim 4. A reformed gas generator that introduces a hydrocarbon-based fuel to generate a hydrogen-rich reformed gas;
A fuel cell stack that introduces the reformed gas into the fuel electrode, introduces an oxidant gas into the oxidant electrode, and generates power using the reformed gas and the oxidant gas;
Sealing means for sealing the generated reformed gas to the fuel electrode side after power generation of the fuel cell stack is stopped;
Pressure detecting means for detecting the pressure on the fuel electrode side;
Pressure control means for sealing the generated reformed gas on the fuel electrode side and controlling the pressure on the fuel electrode side at the time of sealing to a certain range based on the detected pressure;
Fuel cell power generation system.

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