JP5064861B2 - FUEL CELL SYSTEM AND METHOD FOR OPERATING FUEL CELL SYSTEM - Google Patents

Description

  The present invention relates to a fuel cell system using a fuel cell that operates at a high temperature, such as a solid oxide fuel cell, and a method for operating the fuel cell system.

  Conventionally, fuel cells have attracted attention as a clean power generation system that does not generate harmful substances. Among them, the solid oxide fuel cell operates at a higher temperature than the polymer electrolyte fuel cell, and is therefore energy efficient in terms of both power generation and utilization of high temperature energy.

A solid oxide fuel cell (hereinafter referred to as SOFC) has a laminated structure called a single cell in which a solid electrolyte layer made of an oxide ion conductor is sandwiched between an air electrode layer and a fuel electrode layer from both sides. An oxidant gas (oxygen) is supplied to the electrode layer side, and a fuel gas (H ₂ , CO, CH _4, etc.) is supplied to the fuel electrode layer side. The oxidant gas supplied to the air electrode layer side passes through the pores in the air electrode layer and reaches the vicinity of the interface with the solid electrolyte layer, and receives electrons from the air electrode layer at this portion and receives oxide ions (O ^2- ) is ionized. The oxide ions diffuse and move in the solid electrolyte layer toward the fuel electrode layer. Oxide ions that have reached the vicinity of the interface with the fuel electrode layer react with the fuel gas at this portion to generate reaction products (H ₂ O, CO _2, etc.), and discharge electrons to the fuel electrode layer. A structure in which a large number of single cells are stacked is called a stack, and fuel gas is supplied in units of cells or in units of stacks to generate (generate power) power to a load.

  The steady power generation temperature of the SOFC is 950 ° C., for example. When starting the SOFC, it is necessary to raise the SOFC in the normal temperature state to the steady power generation temperature. For this purpose, methods such as heating the entire SOFC with an electric heater, or providing an electric heater in the oxidant gas supply line, and supplying the heated oxidant gas to a high temperature by heating to the air electrode are adopted ( For example, see Patent Document 1).

  Hydrogen gas is most preferably used as the fuel gas, but it is often the case that a hydrocarbon-based fuel such as natural gas or propane gas is reformed into a hydrogen-rich fuel gas and introduced into the fuel electrode. As the oxidant gas, it is most preferable to use oxygen gas, but air is generally used because of the problem of availability.

  Also, when an electric heater is provided in the oxidant gas supply line, the combustion gas is generated by the burner using the starting fuel gas and air, and is supplied to the fuel electrode side of the fuel cell, and the oxidant gas is supplied. In some cases, the temperature of the fuel cell is increased and started while the temperature difference between the fuel cell and the air electrode is reduced. In this case, the combustion of the starting fuel gas is set to incomplete combustion, the combustion gas is made reducible, and the incomplete combustion gas (reducing gas) is supplied into the fuel electrode at the time of starting to maintain the reducibility of the fuel electrode. Has also been proposed (see, for example, Patent Document 2).

  FIG. 10 shows an outline of a fuel cell system using a conventional SOFC. In the figure, 1 is a power generation room using a fuel cell stack (SOFC) that generates power by supplying fuel gas and oxidant gas, and 2 is a fuel gas (reformed gas) that is changed from hydrogen (city gas) to hydrogen-rich fuel gas (reformed gas). The reforming heat exchanger for quality improvement, 3 is an air preheater (electric heater) for preheating oxidant gas (air), and 4 is a combustion chamber for burning gas (fuel gas + oxidant gas) discharged from the power generation chamber 1. Reference numeral 5 denotes an air distributor, and reference numeral 6 denotes a reducing combustion burner that generates reducing gas (incomplete combustion gas).

  The reforming heat exchanger 2 includes an evaporator 2-1, a fuel preheater 2-2, and a reformer 2-3, and the evaporator 2-1 uses pure water as a steam to produce a fuel preheater 2-2. Included in the fuel. The fuel containing the steam is preheated in the fuel preheater 2-2, led to the reformer 2-3, and reformed into hydrogen-rich fuel gas. In the reforming heat exchanger 2, heat is required for generating steam in the evaporator 2-1, preheating the fuel in the fuel preheater 2-2, and reforming the fuel in the reformer 2-3. A combustion gas discharge passage L1 from the combustion chamber 4 is provided as a passage for receiving the supply of heat.

  In this fuel cell system, the operation mode is divided into three modes: a start mode, a steady mode, and a stop mode. When the start of operation is instructed, the fuel cell system enters an activation mode. At the start of the start-up mode, the air preheater 3 is turned on while the fuel supply to the reforming heat exchanger 2 is shut off, and the high-temperature oxidant gas preheated by the air preheater 3 is supplied to the air distributor 5. To the air electrode side of the SOFC in the power generation chamber 1. Further, incomplete combustion of the fuel is started in the reduction combustion burner B 2, and a high-temperature reducing gas is supplied to the SOFC fuel electrode side in the power generation chamber 1. As a result, the temperature of the power generation chamber 1 rises while reducing the temperature difference between the fuel electrode side and the air electrode side of the SOFC in the power generation chamber 1.

  The oxidant gas and the reducing gas that have contributed to the temperature rise in the power generation chamber 1 pass through the combustion chamber 4 and the air distributor 5 and are discharged as exhaust gas through the discharge passage L1. Here, the evaporator 2-1 of the reforming heat exchanger 2, the fuel preheater 2-2, and the reformer 2-3 receive the supply of heat from the oxidant gas and the reducing gas passing through the discharge passage L1. When the temperature of the reformer 2-3 reaches, for example, 500 ° C. in response to the supply of this heat amount, the supply of fuel to the reforming heat exchanger 2 is started, and the steam from the evaporator 2-1 is included. The fuel is guided to the reformer 2-3 via the fuel preheater 2-2, reformed into a hydrogen-rich fuel gas, and supplied to the power generation chamber 1.

  In response to the supply of the fuel gas, power generation in the power generation chamber 1 is started, and the fuel gas and the oxidant gas discharged from the power generation chamber 1 are mixed and burned in the combustion chamber 4. Combustion gas from the chamber 4 passes through the air distributor 5, passes through the discharge passage L1, and is discharged as exhaust gas. Thus, regardless of the preheating of the oxidant gas in the air preheater 3 and the high temperature reducing gas from the reducing combustion burner B2, the supply of the calorific value of the combustion gas from the combustion chamber 4 is received. The reforming of the fuel gas in the reforming heat exchanger 2 can be continued. Normally, at this time, the air preheater 3 and the reduction combustion burner B2 are turned off.

  When the temperature of the power generation chamber 1 rises and reaches the steady power generation temperature, it shifts to the steady mode. In this steady mode, the temperature of the power generation chamber 1 is maintained at the steady power generation temperature by turning on / off the air preheater 3 or adjusting the flow rate of the combustion gas passing through the discharge passage L1. In addition, the exhaust gas discharged | emitted from the discharge channel | path L1 is sent to exhaust heat utilization apparatuses, such as a turbine system and a steam generator, and is utilized effectively.

JP 2006-261025 A JP2003-109641

  However, according to the above-described conventional fuel cell system, the high-temperature reducing gas from the reduction combustion burner B2 works effectively at the time of starting to raise the temperature of the power generation chamber 1, but lowers the temperature of the power generation chamber 1. It does not work effectively when stopping to go. That is, when stopping, the air preheater 3 is turned off and the oxidant gas is supplied as a coolant to the air electrode side of the SOFC in the power generation chamber 1. However, since the temperature of the reducing gas from the reduction combustion burner B2 is high, the power generation chamber The temperature on the fuel electrode side of the SOFC in 1 cannot be lowered, and the temperature difference between the fuel electrode side and the air electrode side of the SOFC in the power generation chamber 1 cannot be kept small.

  The present invention has been made to solve such a problem, and the object of the present invention is to use a fuel cell fuel cell by using an oxidant gas and a reducing gas not only at the time of starting but also at the time of stopping. An object of the present invention is to provide a fuel cell system and a method for operating the fuel cell system that can keep a temperature difference between the electrode side and the air electrode side small.

  In order to achieve such an object, the present invention provides a power generation unit using a fuel cell that generates power by supplying fuel gas to the fuel electrode and supplying oxidant gas to the air electrode, and gas discharged from the power generation unit. In a fuel cell system comprising a combustion section that burns fuel and a fuel reforming section that reforms the fuel using the amount of heat of the combustion gas generated in the combustion section to produce fuel gas for the power generation section. A reducing gas generating unit that generates gas, a first passage that directly leads the reducing gas from the reducing gas generating unit to the fuel electrode side of the fuel cell, and a fuel for the fuel cell through the cooling unit through the reducing gas from the reducing gas generating unit The second passage leading to the pole side and the generation of the reducing gas in the reducing gas generator are started, and one of the first and second passages is selected, and the selected passage is connected to the selected passage from the reducing gas generator. With a control unit to guide the reducing gas That.

In the present invention, the control unit starts generation of the reducing gas in the reducing gas generation unit, selects one of the first and second passages, and supplies the reducing gas from the reduction gas generation unit to the selected passage. Lead. For example, when the fuel cell system is started, generation of reducing gas in the reducing gas generator is started and the first passage is selected. When the fuel cell system is stopped, generation of the reducing gas in the reducing gas generator is started and the second passage is selected.
If it does in this way, at the time of starting of a fuel cell system, high temperature reducing gas from a reducing gas generation part will be directly supplied to the fuel electrode side of a fuel cell. In this case, if the preheated oxidant gas is supplied to the air electrode side of the fuel cell, the temperature of the power generation unit rises while keeping the temperature difference between the fuel electrode side and the air electrode side of the fuel cell small. Go.
When the fuel cell system is stopped, the high-temperature reducing gas from the reducing gas generation unit is cooled through the cooling unit and supplied to the fuel electrode side of the fuel cell. In this case, if the oxidant gas is supplied to the air electrode side of the fuel cell without preheating, the temperature of the power generation unit decreases while keeping the temperature difference between the fuel electrode side and the air electrode side of the fuel cell small. Go.

  In the present invention, the means for preheating the oxidant gas may be an electric heater, but an oxidant preheating part for preheating the oxidant gas to the power generation part is provided by using the amount of heat of the combustion gas generated in the combustion part. This will save energy. In this case, a third passage is provided to guide the reducing gas from the reducing gas generation unit to the combustion gas discharge unit from the fuel reforming unit, and the generation of the reducing gas in the reducing gas generation unit is started. It is conceivable to select one of the second and third passages and perform control so as to guide the reducing gas from the reducing gas generator to the selected passage. For example, the generation of the reducing gas in the reducing gas generator is started, and the third passage is selected for a predetermined period immediately after the start of the generation of the reducing gas, so that the reducing gas from the reducing gas generator is When the control is performed so as to lead to the discharge part, soot immediately after the generation of the reducing gas is discharged through the discharge part of the combustion gas, the first passage and the second passage are selected, and the fuel cell It becomes possible to start supply of the reducing gas to the fuel electrode side.

  In addition, when an oxidant gas preheating part that preheats the oxidant gas to the power generation part is provided using the calorie of the combustion gas generated in the combustion part, combustion from the combustion part to the oxidant gas preheating part is performed. It is conceivable to provide heated gas supply means for adding heated gas to the gas supply path. In this way, by adjusting the amount of heat of the heated gas from the heated gas supply means, that is, by adjusting the capacity of the heated gas supply means, the temperature of the air electrode of the fuel cell to which the oxidant gas is introduced is adjusted. It becomes possible to adjust.

  According to the present invention, a reducing gas generator that generates high-temperature reducing gas, a first passage that directly leads the reducing gas from the reducing gas generator to the fuel electrode side of the fuel cell, and a reduction from the reducing gas generator The second passage for guiding the gas to the fuel electrode side of the fuel cell through the cooling section and the generation of the reducing gas in the reducing gas generation section are started, and one of the first and second passages is selected and selected And a control unit that guides the reducing gas from the reducing gas generation unit to the passage, for example, when starting the fuel cell system, the generation of the reducing gas in the reducing gas generation unit is started and the first passage is selected. Thus, when the fuel cell system is stopped, the generation of the reducing gas in the reducing gas generator is started and the second passage is selected so that the oxidant gas can be used not only at the start but also at the stop. Using reducing gas , It is possible to keep small the temperature difference between the fuel electrode side and the air electrode side of the fuel cell.

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a system configuration diagram showing an outline of an embodiment of a fuel cell system according to the present invention. 10, the same reference numerals as those in FIG. 10 denote the same or equivalent components as those described with reference to FIG. 10, and the description thereof is omitted.

  In this embodiment, the combustion gas discharge passage L1 from the combustion chamber 4 to the reforming heat exchanger 2 is used as a first discharge passage, and the second discharge passage L2 is provided in parallel with the first discharge passage L1. And the combustion gas from the combustion chamber 4 is guided to the air preheater 6 through the second discharge passage L2. That is, instead of the air preheater 3 (FIG. 10) that has conventionally been an electric heater, an air preheater 6 using the amount of heat of the combustion gas passing through the discharge passage L2 as an energy source is provided. The oxidant gas is preheated.

  Further, a combustion gas discharge passage (third flow path) that bypasses the discharge passages L1 and L2 with respect to the first discharge passage L1 to the reforming heat exchanger 2 and the second discharge passage L2 to the air preheater 6. A discharge passage L3, a valve V1 is provided in the first discharge passage L1, a valve V2 is provided in the second discharge passage L2, and a valve V3 is provided in the third discharge passage L3.

  In this embodiment, the confluence point P1 on the inlet side of the discharge passages L1, L2, and L3 is also called an inflow port (combustion gas inflow port), and the confluence point P2 on the outlet side of the discharge passages L1, L2, and L3 is defined as the inflow point P2. Also called exhaust port (combustion gas exhaust port). Further, the line EX on the outlet side of the discharge passages L1, L2, L3 reaching the discharge port P2 is referred to as a combustion gas discharge unit. The combustion gas discharged from the discharge port P2 is sent as exhaust gas to exhaust heat utilization equipment such as a turbine system and a steam generator for effective use.

  The reforming heat exchanger 2 is provided with a fuel supply passage L5 to the reforming heat exchanger 2 and a hydrogen gas supply passage L7 used in a start mode and a stop mode, which will be described later. The supply passage L5 is provided with a valve V5, and the hydrogen gas supply passage L7 is provided with a valve V7. Further, a complete combustion burner B1 is provided as a heating gas supply means for adding heated gas to the inlet P1 (passage to the combustion gas discharge passages L1, L2, and L3 from the combustion chamber 4). A valve V4 is provided in the fuel supply passage L4 to the complete combustion burner B1.

  Further, a valve V6 is provided in the supply path L6 for the oxidant gas to the air preheater 6, and a temperature sensor 7 for detecting the temperature in the power generation chamber 1 as the power generation chamber temperature T1 is provided for the power generation chamber 1. The reforming heat exchanger 2 is provided with a temperature sensor 8 for detecting the temperature in the reformer 2-3 as the reformer temperature T2, and the reducing combustion burner B2 is provided with the reducing combustion burner. A temperature sensor 9 is provided for detecting the temperature of the reducing gas from B2 as the reducing gas temperature T3.

  Further, a valve V11 is provided in the fuel supply passage L11 to the reduction combustion burner B2, and the supply passage of the reducing gas from the reduction combustion burner B2 to the power generation chamber 1 is the first supply passage L9 and the second supply passage. It is divided into L10. A valve V9 is provided in the first supply passage L9. A valve V10 and a cooling heat exchanger 10 are provided in the second supply passage L10. The cooling heat exchanger 10 is provided with a cold water supply passage L12 and a hot water discharge passage L13, and the cold water supply passage L12 is provided with a valve V12. Further, the reduction gas from the reduction combustion burner B2 is led to the fuel gas discharge section EX between the junction point on the inlet side of the reducing gas supply passages L9 and L10 to the power generation chamber 1 and the fuel gas discharge section EX. A gas discharge passage L8 is provided, and a valve V8 is provided in the reducing gas discharge passage L8.

  In addition, the fuel cell system receives the power generation chamber temperature T1 from the temperature sensor 7, the reformer temperature T2 from the temperature sensor 8, and the reducing gas temperature T3 from the temperature sensor 9, and inputs the valves V1 to V12 and complete combustion. A controller 11 is provided as a control device for controlling the operations of the burner B1 and the reduction combustion burner B2. The controller 11 is realized by hardware including a processor and a storage device, and a program that realizes various functions as a control device in cooperation with these hardware.

  In this embodiment, the power generation chamber 1 corresponds to the power generation section referred to in the present invention, the reforming heat exchanger 2 corresponds to the fuel reforming section, the combustion chamber 4 corresponds to the combustion section, and the air preheater. 6 corresponds to the oxidizing gas preheating section, the controller 11 corresponds to the control section, the valves V1 to V3 correspond to the heat quantity adjusting section, the complete combustion burner B1 corresponds to the heating gas supply means, and the reducing combustion burner B2 reduces. Corresponding to the gas generating part, the cooling heat exchanger 10 corresponds to the cooling part.

  Hereinafter, with reference to the time chart shown in FIG. 2, the control operation unique to the present embodiment executed by the controller 11 will be described. In addition, as a state before the start of operation to enter this control operation, all the valves V1 to V12 are assumed to be off (fully closed). Further, it is assumed that the combustion operation of the complete combustion burner B1 and the reduction combustion burner B2 is turned off (extinguishing).

[Startup mode]
When the controller 11 is instructed to start operation, this time is set as the start of the start mode, the valves V2, V4, V6, V7, V8, V11 are turned on (fully opened), and the complete combustion burner B1 and the reduction combustion burner are turned on. The combustion operation of B2 is turned on (ignition) (point t1 shown in FIG. 2). As a result, as shown in FIG. 3, the supply of fuel to the complete combustion burner B1 and the reduction combustion burner B2 is started. Further, the inflow of the oxidant gas to the air preheater 6 is started.

  The complete combustion burner B1 receives supply of fuel to generate complete combustion gas, and sends the generated complete combustion gas to the inlet P1. The complete combustion gas sent to the inflow port P1 flows only into the discharge passage L2, since only the valve V2 is turned on among the valves V1, V2, and V3. In response to the supply of the calorific value of the complete combustion gas flowing through the discharge passage L2, the oxidant gas flowing into the air preheater 6 is preheated, and the preheated oxidant gas passes through the air distributor 5 to generate the power generation chamber 1 (SOFC). To the air electrode side).

  The reduction combustion burner B <b> 2 receives the supply of fuel, generates high-temperature reducing gas, and tries to send the reducing gas to the power generation chamber 1. However, in this case, since the valves V9 and V10 are still on, the reducing gas is not supplied to the power generation chamber 1. In this case, since the valve V8 is turned on, the reducing gas from the reducing combustion burner B2 is guided to the fuel gas discharge part EX through the discharge passage L8 and discharged from the discharge port P2. At the start of the combustion of the reduction combustion burner B2, soot may be generated, so that it is discharged from the outlet P2 without being sent to the power generation chamber 1 for a while.

  When the reducing gas temperature T3 reaches 600 ° C. (point t2 shown in FIG. 2 (q)), the controller 11 turns off the valve V8 (fully closed) and turns on the valve V9 (fully opened). As a result, as shown in FIG. 4, the discharge of the reducing gas from the reducing combustion burner B2 through the combustion gas discharge section EX is stopped and supplied directly to the power generation chamber 1 (SOFC fuel electrode side) through the supply passage L9. Will be. Thereafter, the controller 11 adjusts the amount of heat of the reducing gas from the reducing combustion burner B2 so that the reducing gas temperature T3 is maintained at 600 ° C., for example.

  Note that hydrogen gas from the supply passage L7 is supplied to the SOFC fuel electrode side in the power generation chamber 1 through the reforming heat exchanger 2. The hydrogen gas, the oxidant gas and the reducing gas supplied to the power generation chamber 1 are discharged to the combustion chamber 4 and sent to the inlet P1 through the air distributor 5, where they merge with the complete combustion gas from the complete combustion burner B1. The combined gas passes through the discharge passage L2 to the discharge port P2, and is discharged as exhaust gas.

  The temperature in the power generation chamber 1 (power generation chamber temperature T1) is supplied with the preheated oxidant gas from the air preheater 6, that is, supplied with the oxidant gas heated to a high temperature by heat exchange with the complete combustion gas. In response to the supply of the reducing gas from the reducing combustion burner B2, that is, the high temperature reducing gas supplied directly from the reducing combustion burner B2, the temperatures of the fuel electrode side and the air electrode side of the SOFC It starts to rise while keeping the difference small. In this case, when the high-temperature gas flows only through the discharge passage L2 among the discharge passages L1 to L3, the oxidant gas to the power generation chamber 1 is intensively warmed by the air preheater 6, and the power generation chamber temperature T1 is increased. It rises efficiently and starts up smoothly.

  When the power generation chamber temperature T1 reaches 600 ° C. (point t3 shown in FIG. 2 (o)), the controller 11 turns on the valve V1 (fully opened). As a result, as shown in FIG. 5, the combined gas of the complete combustion gas from the complete combustion burner B1 and the exhaust gas from the combustion chamber 4 from the power generation chamber 1 flows into the discharge passage L1, and flows. The temperature in the reformer 2-3 (reformer temperature T2) rises in response to the supply of heat of the combined gas.

  When the reformer temperature T2 reaches 500 ° C. (point t4 shown in FIG. 2 (p)), the controller 11 sets this time as the start of power generation using fuel gas, and sets the valves V2, V4, V7, V9, V11 is turned off and valve V5 is turned on. Further, the complete combustion burner B1 and the reduction combustion burner B2 are turned off.

  Thereby, as shown in FIG. 6, the supply of the complete combustion gas from the complete combustion burner B1 to the inlet P1 is cut off, and the supply of the reducing gas from the reduction combustion burner B2 to the power generation chamber 1 is cut off. Further, the flow of gas to the discharge passage L2 is stopped, and the flow to only the discharge passage L1. Further, the supply of hydrogen gas from the supply passage L7 to the power generation chamber 1 through the reforming heat exchanger 2 is cut off, and the supply of fuel to the reforming heat exchanger 2 from the supply passage L5 is started.

  When the supply of fuel from the supply passage L5 is started, the reforming heat exchanger 2 includes the vapor from the evaporator 2-1 in the fuel, and the reformer 2 passes through the fuel preheater 2-2. -3, reformed into hydrogen-rich fuel gas, and supplied to the power generation chamber 1. As a result, power generation using the fuel gas in the power generation chamber 1 is started, and the fuel gas and the oxidant gas discharged from the power generation chamber 1 are mixed and burned in the combustion chamber 4. Combustion gas from the chamber 4 passes through the air distributor 5, passes through the discharge passage L1, reaches the discharge port P2, and is discharged as exhaust gas.

  In this case, since the flow of gas to the exhaust passage L2 is stopped and only the exhaust passage L1 is flowed, the entire amount of combustion gas from the combustion chamber 4 flows through the exhaust passage L1, and the complete combustion burner B1 Even after the complete combustion gas from NO and the reducing gas from the reduction combustion burner B2 are shut off, the reforming of the fuel gas in the reforming heat exchanger 2 is continued. At the start of reforming of the fuel gas in the reforming heat exchanger 2, a larger amount of heat is required for the endothermic reaction, and this amount of heat is ensured by the total amount of combustion gas from the combustion chamber 4.

  In this case, since the gas flow to the discharge passage L2 is stopped, the oxidant gas is not preheated in the air preheater 6, and the oxidant gas to the power generation chamber 1 also serves as a coolant. It will be. Thereby, the temperature rise of the power generation chamber temperature T1 and the reformer temperature T2 is suppressed, and it is avoided that the power generation chamber temperature T1 and the reformer temperature T2 become excessive temperatures.

(Steady mode)
When the power generation chamber temperature T1 reaches 950 ° C. (point t5 shown in FIG. 2 (o)), the controller 11 sets the power generation chamber temperature T1 to 950 ° C. with this point in time as the start of the steady mode (at the end of the start-up mode). The opening control of the valves V1, V2, and V3 is started so as to maintain (steady temperature).

  That is, as shown in FIG. 7, the combustion supplied to the reforming heat exchanger 2 and the air preheater 6 by controlling the opening θ1 of the valve V1, the opening θ2 of the valve V2, and the opening θ3 of the valve V3. The amount of heat of the combustion gas from the chamber 4 is controlled.

  As a result, the power generation chamber temperature T1 is adjusted in the steady mode by using the amount of heat (exhaust heat) of the combustion gas from the combustion chamber 4 instead of turning on / off the electric heater. The amount of power used is reduced and energy saving is achieved.

  Further, since the combustion gas after the heat exchange in the reforming heat exchange 2 is discharged from the discharge passage L1, and the combustion gas after the heat exchange in the air preheater 6 is discharged from the discharge passage L2, the discharge passage L3 Even if the temperature of the combustion gas from is high, the high-temperature combustion gas is not directly sent to the exhaust heat utilization device in the subsequent stage, and it is possible to prevent deterioration of the members of the exhaust heat utilization device.

[Stop mode]
When the controller 11 is instructed to end the operation, this time is set to the end of the steady mode (at the start of the stop mode), the valves V1, V2, and V5 are turned off (fully closed), and the valves V3, V7, and V8 are set. , V11 is turned on (fully open), and the reduction combustion burner B2 is turned on (point t6 shown in FIG. 2).

  Thus, as shown in FIG. 8, the flow of gas from the combustion chamber 4 to the exhaust passages L1 and L2 is stopped, and the combustion gas from the combustion chamber 4 passes only through the exhaust passage L3 bypassing the exhaust passages L1 and L2. Will be discharged. In this case, since the oxidant gas is not preheated in the air preheater 6, the oxidant gas that has not been preheated is supplied to the power generation chamber 1 (SOFC fuel electrode side).

  Further, the reducing combustion burner B <b> 2 generates reducing gas and tries to send the reducing gas to the power generation chamber 1. However, in this case, since the valves V9 and V10 are still on, the reducing gas is not supplied to the power generation chamber 1. In this case, since the valve V8 is turned on, the reducing gas from the reducing combustion burner B2 is guided to the fuel gas discharge part EX through the discharge passage L8 and discharged from the discharge port P2. At the start of the combustion of the reduction combustion burner B2, soot may be generated, so that it is discharged from the outlet P2 without being sent to the power generation chamber 1 for a while.

  When the reducing gas temperature T3 reaches 600 ° C. (point t7 shown in FIG. 2 (q)), the controller 11 turns off the valve V8 (fully closed) and turns on the valves V10 and V12 (fully opened). As a result, as shown in FIG. 9, the reduction gas from the reduction combustion burner B2 is stopped from being discharged through the combustion gas discharge section EX, and supplied to the power generation chamber 1 (SOFC fuel electrode side) through the supply passage L10. Will be. At this time, the cooling heat exchanger 10 cools the reducing gas passing through the supply passage L10. Thereby, not the high temperature reducing gas but the reducing gas cooled by the cooling heat exchanger 10 is supplied to the power generation chamber 1. Thereafter, the controller 11 adjusts the amount of heat of the reducing gas from the reducing combustion burner B2 so that the reducing gas temperature T3 is maintained at 600 ° C.

  The temperature in the power generation chamber 1 (power generation chamber temperature T1) is reduced by being supplied with the unpreheated oxidant gas from the air preheater 6 and cooled by the cooling heat exchanger 10 from the reduction combustion burner B2. Upon receiving the gas supply, the gas begins to descend while keeping the temperature difference between the fuel electrode side and the air electrode side of the SOFC small. In this case, the oxidant gas that has not been preheated from the air preheater 6 and the reducing gas that has passed through the cooling heat exchanger 10 from the reduction combustion burner B2 act as coolants, thereby speeding up the drop in the power generation chamber temperature T1.

  The supply of fuel to the reforming heat exchanger 2 is shut off by turning off the valve V5, and the supply of hydrogen gas to the power generation chamber 1 through the reforming heat exchanger 2 is started by turning on the valve V7. . Thereby, the power generation using the fuel gas in the power generation chamber 1 is stopped, and the power generation using the hydrogen gas is switched to. When the power generation chamber temperature T1 reaches 150 ° C. (point t8 shown in FIG. 2 (o)), the controller 11 turns off the valves V3, V6, V7, V10, V11, and V12 and reduces the combustion burner B2. Turn off. Thereby, the fuel cell system of this Embodiment is returned to the state before the driving | operation start shown by FIG.

  In the above-described embodiment, the complete combustion gas from the complete combustion burner B1 is added to the junction P1 on the inlet side of the discharge passages L1, L2, and L3, but it may be added to the combustion chamber 4. . When the complete combustion gas is added to the junction P1 on the inlet side of the discharge passages L1, L2, and L3, only a part of the gas from the combustion chamber 4 via the air distributor 5 is heated and the temperature does not become uniform. There are cases like this. On the other hand, when the complete combustion gas is added to the combustion chamber 4, the gas from the combustion chamber 4 can be uniformly warmed and discharged to the junction P1 on the inlet side of the discharge passages L1, L2, and L3. Become. Further, the oxidant gas from the air preheater 6 can be further preheated by the air distributor 5 to accelerate the temperature rise of the power generation chamber temperature T1.

  Further, a space (buffer) serving as a buffer is provided between the confluence point P1 on the inlet side of the discharge passages L1, L2, and L3 and the air distributor 5, and the complete combustion gas from the complete combustion burner B1 is added to the buffer. It may be. When such a buffer is provided, it becomes possible to have an agitation effect for stabilizing the airflow or for equalizing the temperature. For example, a configuration in which the buffer is made into a space having a rectifying action, a mixer member for stirring, or a member having a high thermal conductivity for heat equalization is arranged inside the buffer.

  In the above-described embodiment, the third discharge passage that bypasses the first discharge passage L1 and the second discharge passage L2 is provided. However, only the first discharge passage L1 and the second discharge passage L2 are provided. It is good also as a structure. When the exhaust passage L3 that bypasses the exhaust passages L1 and L2 is provided, the combustion gas supplied to the reforming heat exchanger 2 and the air preheater 6 by controlling the opening degree of the valve V3 provided in the exhaust passage L3. Since the amount of heat can be controlled, controllability is improved.

  Further, the discharge passages L1, L2, and L3 are not necessarily provided with valves. For example, only the first discharge passage L1 and the second discharge passage L2 are configured, and the valve V1 is provided only in the first discharge passage L1, or the valve V2 is provided only in the second discharge passage L2. Also good. In this case, the amount of heat of the combustion gas passing through the other exhaust passage can be adjusted using the correlation by adjusting the opening of the valve (the amount of heat of the combustion gas) passing through the one exhaust passage. is there.

  In the above-described embodiment, the outlet sides of the discharge passages L1, L2, and L3 are merged. However, exhaust gas is drawn out from each discharge passage without joining the outlet sides of the discharge passages L1, L2, and L3. The exhaust heat utilization device provided for each exhaust passage may be guided. Alternatively, only the discharge passages L1 and L2 may be merged, and the exhaust gas discharged from the merge point may be guided to the exhaust heat utilization device arranged at the subsequent stage. Further, if a mechanism for changing the type of exhaust gas entering the exhaust heat utilization device is created, a very high temperature gas from the exhaust passage L3 is supplied to the exhaust heat utilization device as needed, or from the exhaust passages L1 and L2. A degree of freedom is born, such as supplying a relatively low temperature gas to exhaust heat utilization equipment.

  In the above-described embodiment, the reducing gas from the reducing combustion burner B2 has been described as the reducing gas discharge passage L8 that guides the reducing gas to the fuel gas discharging unit EX. However, the reducing gas is discharged only to the fuel gas discharging unit EX. Instead, it can be modified such that it is connected to an arbitrary exhaust gas outlet, and toxic components are appropriately removed and discharged.

  In the above-described embodiment, the complete combustion burner B1 is used only in the start mode, but the complete combustion burner B1 may be used even in the steady mode. For example, when the amount of heat is not sufficient as a whole, a situation where the total amount of heat is insufficient can be avoided by using the complete combustion burner B1. In this case, it is possible to discard the excess heat amount due to the use of the complete combustion burner B1 through the discharge passage L3. If the amount of heat of the complete combustion gas from the complete combustion burner B1 can be adjusted, heat can be supplied only when necessary, and an energy saving effect can be expected. Further, when the complete combustion burner B1 is used, the flow rate of the high-temperature gas supplied to the reforming heat exchanger 2 and the air preheater 6 can be increased, and heat is supplied from the complete combustion burner B1 at an appropriate temperature. Thus, the heat exchange efficiency can be increased.

  Further, the complete combustion gas from the complete combustion burner B1 may be directly added to the discharge passage L2 instead of the junction P1 on the inlet side of the discharge passages L1, L2, and L3. In this way, by adjusting the amount of heat of the complete combustion gas from the complete combustion burner B1, that is, by adjusting the capacity of the complete combustion burner B1, the SOFC air electrode in the power generation chamber 1 into which the oxidant gas is introduced. The temperature can be adjusted.

  In the above-described embodiment, the fuel cell in the power generation chamber 1 is the SOFC. However, a high-temperature fuel cell such as a molten carbonate fuel cell may be used. In the above-described embodiment, the complete combustion burner is used as the heating gas supply means. However, an electric heater is provided instead of the complete combustion burner, and the gas heated by the electric heater is added to the inlet P1. Good.

  Further, an exhaust heat utilization system may be connected to the hot water discharge passage L13 of the cooling heat exchanger 10. A system that uses the amount of heat of hot water for air conditioning, etc., and supplies the obtained cold water through the supply passage L12 to use the amount of heat of exhaust heat and does not require new energy for supplying cold water. Can be configured.

  Further, by adjusting the opening degree of the valves V8, V9 and V10 in the start mode and the stop mode, the flow rate balance between the high temperature reducing gas passing through the discharge passage L8 or the supply passage L9 and the low temperature reducing gas passing through the L10. Can be adjusted. In this way, the amount of heat of the reducing gas supplied to the fuel electrode can be adjusted, and the temperature of the fuel electrode can be adjusted independently of the temperature of the air electrode. As a result, it is possible to adjust to reduce the temperature difference between the air electrode temperature and the fuel electrode temperature in the start mode and the stop mode.

1 is a system configuration diagram showing an outline of an embodiment of a fuel cell system according to the present invention. It is a time chart for demonstrating the control action which the controller in this fuel cell system performs. FIG. 3 is a diagram for explaining a control operation at a time point t1 (at the start of an activation mode) in the time chart shown in FIG. FIG. 3 is a diagram illustrating a control operation at time t2 in the time chart shown in FIG. FIG. 3 is a diagram illustrating a control operation at time t3 in the time chart shown in FIG. FIG. 3 is a diagram for explaining a control operation at time t4 in the time chart shown in FIG. FIG. 3 is a diagram for explaining a control operation at time t5 (at the start of the steady mode (at the end of the start-up mode)) in the time chart shown in FIG. FIG. 3 is a diagram illustrating a control operation at time t6 (at the end of the steady mode (at the start of the stop mode)) in the time chart shown in FIG. FIG. 3 is a diagram illustrating a control operation at time t7 in the time chart illustrated in FIG. 2. It is a figure which shows the outline of the fuel cell system using the conventional SOFC.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Power generation chamber, 2 ... Reforming heat exchanger, 2-1 ... Evaporator, 2-2 ... Fuel preheater, 2-3 ... Reformer, 4 ... Combustion chamber, 5 ... Air distributor, 6 ... Air Preheater, 7, 8, 9 ... temperature sensor, 10 ... cooling heat exchanger, 11 ... controller, V1 to V12 ... valve, B1 ... complete combustion burner, B2 ... reduction combustion burner, L1 ... first exhaust passage, L2 ... second discharge passage, L3 ... third discharge passage, L4, L5, L11 ... fuel supply passage, L6 ... oxidant gas supply passage, L7 ... hydrogen gas supply passage, L8 ... reducing gas discharge passage L9, L10 ... reducing gas supply passage, L12 ... cold water supply passage, L13 ... hot water discharge passage, P1 ... inflow port (combustion gas inflow port), P2 ... discharge port (combustion gas discharge port), EX ... Combustion gas discharge part.

Claims (6)

A power generation unit using a fuel cell that generates power by supplying a fuel gas to the fuel electrode and an oxidant gas to the air electrode, a combustion unit for burning the gas discharged from the power generation unit, and generated in the combustion unit In a fuel cell system comprising a fuel reforming unit that reforms fuel using the amount of heat of combustion gas and uses it as fuel gas to the power generation unit,
A reducing gas generator that generates high temperature reducing gas;
A first passage for directly leading the reducing gas from the reducing gas generating section to the fuel electrode side of the fuel cell;
A second passage for guiding the reducing gas from the reducing gas generation unit to the fuel electrode side of the fuel cell through a cooling unit;
A control unit that starts generation of the reducing gas in the reducing gas generation unit, selects one of the first and second passages, and guides the reducing gas from the reduction gas generation unit to the selected passage; A fuel cell system comprising: The fuel cell system according to claim 1, wherein
A third passage for guiding the reducing gas from the reducing gas generation unit to the combustion gas discharge unit from the fuel reforming unit,
The control unit starts generation of reducing gas in the reducing gas generation unit, selects any one of the first, second, and third passages, and supplies the reducing gas generation unit to the selected passage. A fuel cell system that guides the reducing gas from the fuel cell. The fuel cell system according to claim 1, wherein
An oxidant gas preheating unit that preheats the oxidant gas to the power generation unit using the amount of heat of the combustion gas generated in the combustion unit;
A fuel cell system comprising heating gas supply means for adding a heated gas to a combustion gas supply path from the combustion section to the oxidant gas preheating section. A power generation unit using a fuel cell that generates power by supplying a fuel gas to the fuel electrode and an oxidant gas to the air electrode, a combustion unit for burning the gas discharged from the power generation unit, and generated in the combustion unit A fuel reforming unit that reforms fuel using the calorific value of the combustion gas to produce fuel gas for the power generation unit, a reducing gas generating unit that generates high-temperature reducing gas, and a reducing gas from the reducing gas generating unit A first passage that directly leads the fuel gas to the fuel electrode side of the fuel cell, and a second passage that guides the reducing gas from the reducing gas generator to the fuel electrode side of the fuel cell through a cooling portion A method of operating a fuel cell system applied to
At the start of the fuel cell system, the generation of the reducing gas in the reducing gas generation unit is started, and the first passage is selected to supply the reducing gas from the reducing gas generation unit to the fuel electrode of the fuel cell. Sending directly to the side and starting the temperature rise of the fuel electrode,
When the fuel cell system is stopped, generation of reducing gas in the reducing gas generation unit is started, and the second passage is selected, and the reducing gas from the reducing gas generation unit is passed through the cooling unit to the fuel. A method of operating the fuel cell system, comprising the step of sending to the fuel electrode side of the battery and starting cooling of the fuel electrode. A power generation unit using a fuel cell that generates power by supplying a fuel gas to the fuel electrode and an oxidant gas to the air electrode, a combustion unit for burning the gas discharged from the power generation unit, and generated in the combustion unit A fuel reforming unit that reforms fuel using the calorific value of the combustion gas to produce fuel gas for the power generation unit, a reducing gas generating unit that generates high-temperature reducing gas, and a reducing gas from the reducing gas generating unit A first passage that directly leads the fuel gas to the fuel electrode side of the fuel cell, a second passage that guides the reducing gas from the reducing gas generator to the fuel electrode side of the fuel cell through a cooling unit, and the reducing gas generator A fuel cell system that is applied to a fuel cell system comprising a third passage that guides the reducing gas from the fuel reforming unit to the combustion gas discharge unit,
The generation of the reducing gas in the reducing gas generator is started, and the third passage is selected for a predetermined period immediately after the generation of the reducing gas is started, and the reducing gas from the reducing gas generator is burned. A method for operating a fuel cell system, comprising the step of leading to a gas discharge unit. A power generation unit using a fuel cell that generates power by supplying a fuel gas to the fuel electrode and an oxidant gas to the air electrode, a combustion unit for burning the gas discharged from the power generation unit, and generated in the combustion unit A fuel reforming unit that reforms fuel using the calorific value of the combustion gas to produce fuel gas for the power generation unit, a reducing gas generating unit that generates high-temperature reducing gas, and a reducing gas from the reducing gas generating unit Generated in the combustion section, a first path for directly leading the fuel gas to the fuel electrode side of the fuel cell, a second path for guiding the reducing gas from the reducing gas generating section to the fuel electrode side of the fuel cell through a cooling section, and An oxidant gas preheating unit that preheats the oxidant gas to the power generation unit using the amount of heat of the combustion gas that is heated, and a gas heated in the combustion gas supply path from the combustion unit to the oxidant gas preheating unit Fuel cell system with heating gas supply means for adding A method of operating a fuel cell system applied to arm,
Adjusting the temperature of the air electrode of the fuel cell through which the oxidant gas is guided by adjusting the amount of heat of the heated gas from the heated gas supply means, .

Images