JP2020053365A - Fuel cell system and reforming water flow control program - Google Patents

Abstract

To prevent the occurrence of cracks in a cell stack due to thermal stress of internal temperature of the cell stack immediately after the end of a startup operation.SOLUTION: In a fuel cell system, even if temperature of a cell stack 16 exceeds a certain level (threshold value Tcs), reforming water is not immediately supplied at a predetermined flow rate, but is supplied, over a predetermined period of time, such that the flow rate is gradually increased (gradient θ). Thus, as compared with a change rate in the case where a predetermined amount of reforming water is supplied at once, a change rate can be reduced, so that such a problem that combustion in the cell stack 16 causes a rapid temperature information change rate (gradient) to generate cracks due to thermal stress can be prevented.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a fuel cell system and a reforming water flow control program.

  In a fuel cell system, for example, a solid oxide fuel cell system (SOFC), a raw material gas and water are supplied to a reformer to be steam-reformed to generate a reformed gas containing hydrogen gas. The reformed gas is supplied to the anode of the cell stack, and the oxidizing gas (air) is supplied to the cathode of the fuel cell stack, so that the cell stack generates power.

  In a fuel cell system, a start-up operation is required as a preparation stage for power generation (normal operation). In the start-up operation, when the internal temperature of the cell stack reaches a predetermined temperature, a reformed gas is generated in the reformer by the flow rate of the raw material gas and the reformed water set as the normal operation, and the reformed gas is generated by the anode of the cell stack. Supplied.

  That is, the reformed gas supplied to the anode of the cell stack depends on the amounts of the raw material gas and the reformed water. In particular, when the reforming water that is not supplied in the start-up operation is supplied at once at a time when the internal temperature of the cell stack reaches a predetermined temperature, cracks caused by thermal stress due to combustion occur in the cell stack. May occur.

  As a reference, Patent Document 1 discloses that when fuel offgas not used for power generation is burned in a cell stack to process unused fuel, a large amount of fuel offgas is rapidly burned, resulting in thermal shock and local impact. It is described that a crack is generated due to excessive thermal stress, and that a reinforcing layer is provided on a part of an insulating base which physically forms a cell stack.

JP 2011-76809 A

  However, there is a limit to the improvement in physical strength, and in particular, no measures have been taken against thermal stress caused by the reformed gas supplied at once after the start-up operation.

  In consideration of the above facts, the present invention provides a fuel cell system and a reformed water amount control program which can prevent the occurrence of cracks in the cell stack due to thermal stress at the internal temperature of the cell stack immediately after the start operation. Is the purpose.

  The present invention provides a reformer that generates a reformed gas by supplying a source gas and water, the reformed gas is supplied to a fuel electrode, and an oxidizing gas is supplied to an air electrode. A fuel cell system comprising: a cell stack configured to generate power between the fuel electrode and the air electrode; a reforming water supply unit configured to supply reforming water to the reformer; and the cell stack. Cell stack temperature detecting means for detecting the internal temperature of the fuel cell, and controlling the combustion of the heating means using the raw material gas and the oxidizing gas to thereby control the entirety of the inside of the housing accommodating the reformer and the cell stack. Heating the internal temperature of the cell stack to a temperature at which power can be generated, and controlling the reforming water supply means based on the progress of the starting operation by the starting operation control means. To control the flow rate of reforming water It has a water flow control means.

  According to the present invention, in order for the fuel cell system to perform a normal operation, that is, a power generation operation, a startup operation for raising the internal temperature of the cell stack to a temperature at which power can be generated is required.

  In the start-up operation control means, the entire inside of the housing containing the reformer and the cell stack can be heated by the heat generated by the combustion using the raw material gas and the oxidizing gas to generate the internal temperature of the cell stack. Raise the temperature.

  Here, when the internal temperature of the cell stack reaches the temperature at which power can be generated, the reforming water is supplied to the reformer and the reformed gas is sent out to the cell stack. The flow of the reforming water is controlled by controlling the reforming water supply unit based on the progress of the starting operation by the starting operation control unit without switching from the operation to the normal operation at once. By controlling the flow rate of the reforming water, it is possible to suppress the occurrence of cracks and the like due to a rapid change in the internal temperature of the cell stack.

  Note that “based on the progress of the start-up operation” indicates that the flow rate control of the reforming water may be started at any time from the start to the end of the start-up operation. For example, the flow rate of the reforming water may be gradually controlled after the start operation, or the flow rate of the reformed water may be gradually controlled immediately after the start operation.

  In the present invention, the reforming water flow rate control means gradually increases the flow rate of the reforming water between a time when the internal temperature of the cell stack reaches a temperature at which power can be generated and a time after a predetermined time. Therefore, the flow rate during normal operation is characterized.

  As an embodiment of the control of the reforming water flow rate, the flow rate of the reforming water is gradually increased at a constant slope, for example, from a point in time when the internal temperature of the cell stack has reached the power generation enabling temperature to a time after a predetermined time. Or gradually increased stepwise to obtain a flow rate during normal operation. As a result, a rapid increase in the internal temperature of the cell stack can be suppressed.

  In the present invention, a raw material gas supply unit for supplying the raw material gas, a reformer temperature detection unit for detecting an internal temperature of the reformer, and activation of a cell stack internal temperature detected by the cell stack temperature detection unit First calculating means for calculating a rate of change from the start, wherein the start-up operation control means determines that the temperature detected by the reformer temperature detecting means is a critical value at which carbon deposition occurs in the reformer. At a point in time when a threshold value lower than the temperature is exceeded, the flow rate of the source gas is switched to a relatively small flow rate, and when the rate of change currently calculated by the first calculating means falls below the rate of change previously calculated, The flow rate of the source gas is switched to a relatively high flow rate.

  In the switching control of the raw material gas by the starting operation control means, when the temperature detected by the reformer temperature detection means exceeds a predetermined threshold value lower than the critical temperature at which carbon deposition occurs in the reformer. Then, the flow rate of the source gas is switched to a relatively small value.

  On the other hand, when the change rate calculated this time by the first calculation means is lower than the change rate calculated last time, the flow rate of the source gas is switched to a relatively large value.

  Thereby, heating can be continued with the internal temperature of the cell stack rising.

  The present invention is characterized in that the reforming water flow control means starts the supply of the reforming water before the internal temperature of the cell stack reaches a temperature at which power can be generated.

  By starting the supply of water for reforming before the internal temperature of the cell stack reaches the temperature at which power can be generated, for example, it is possible to reduce an increase in the internal temperature of the reformer and prevent carbon deposition in the reformer. can do.

  In the present invention, a raw material gas supply means for supplying the raw material gas, a reformer temperature detecting means for detecting an internal temperature of the reformer, an internal temperature of the cell stack, a flow rate of the raw material gas, and Second calculating means for calculating the relative humidity of the reformed gas supplied to the cell stack at regular intervals based on the internal temperature of the reformer, wherein the reforming water flow rate controlling means is provided. The flow rate of the reforming water is adjusted based on the calculation result of the second calculation means.

  When the supply of the reforming water is started before the internal temperature of the cell stack reaches the temperature at which power can be generated, it is necessary to consider the humidity of the reformed gas.

  Therefore, the second calculating means changes the relative humidity of the reformed gas supplied to the cell stack at regular intervals based on the internal temperature of the cell stack, the flow rate of the raw material gas, and the internal temperature of the reformer. calculate. The reforming water flow rate controlling means adjusts the flow rate of the reforming water based on the calculation result of the second calculating means. Thereby, the humidity of the reformed gas can be controlled.

  The present invention is a reformed water flow control program for operating a computer as the reformed water flow control means.

  As described above, the present invention has an effect that it is possible to prevent the occurrence of cracks in the cell stack due to the thermal stress at the internal temperature of the cell stack immediately after the start operation.

FIG. 1 is a schematic configuration diagram of a fuel cell system according to a first embodiment. (A) is a flowchart showing an interrupt routine for calculating the temperature gradient of the cell stack, which is executed at regular intervals after the fuel cell system according to the first embodiment is started, and (B) is a flowchart showing the first routine. 7 is a flowchart showing a start-up operation control routine executed when the fuel cell system according to the embodiment is started. 5 is a timing chart of startup operation control executed when the fuel cell system according to the first embodiment is started. FIG. 4 is a schematic configuration diagram of a fuel cell system according to a first modification of the first embodiment. 3 is a flowchart illustrating a reforming water flow rate control routine that is started when an instruction is received in step 122 of FIG. 2. 9 is a timing chart of startup operation control executed when the fuel cell system according to the second embodiment is started.

  (First Embodiment)

  FIG. 1 schematically shows a fuel cell system 10 according to the first embodiment. The fuel cell system 10 according to the first embodiment includes a control device 26. The control device 26 mainly includes a microcomputer 27 including a CPU 27A, a RAM 27B, and a ROM 27C, and obtains information from each unit to be controlled and controls the operation of each unit. Further, the control device 26 includes a threshold storage unit 26M.

  The main components to be controlled by the control device 26 are the vaporizer 12, the reformer 14, the cell stack 16, the air preheater 30, and the combustor 40.

  The fuel cell system 10 includes a high temperature section 18 in which a combustor 40, a cell stack 16, and a reformer 14 are housed. The high temperature section 18 may be called a hot box 18. The vaporizer 12, the air preheater 30, and the high-temperature section 18 are housed in the housing 11.

  The housing 11 is formed of a member having at least one of heat insulation and heat shielding, and is formed of, for example, a heat insulating material.

  The high temperature section 18 is provided in the housing 11 and is formed of a member having at least one of heat insulation and heat insulation, for example, a metal. During operation of the fuel cell system 10, the inside of the high-temperature section 18 has a higher temperature inside the housing 11 than the outside of the high-temperature section 18.

  A double pipe 20 is connected to the vaporizer 12. In the double pipe 20, an inner flow path 22 and an outer flow path 24 are formed.

  A gas source (not shown) is connected to the outer flow passage 24, and methane as a raw material gas flows through the blower B1. A water source (not shown) is connected to the inner flow path 22, and water (liquid phase) flows in by the pump P. Methane and water are introduced into the double pipe 20 so as to flow in parallel (in the same direction). The double pipe 20 is connected to the vaporizer 12. Methane and water are supplied to vaporizer 12. In the vaporizer 12, the water is vaporized. The heat of the combustion exhaust gas G1 discharged from the combustor 40 described later is used for vaporization.

  In the first embodiment, methane is used as a raw material gas. However, the gas is not particularly limited as long as it can be reformed, and a hydrocarbon fuel can be used. Examples of the hydrocarbon fuel include natural gas, LP gas (liquefied petroleum gas), coal reformed gas, and lower hydrocarbon gas. Examples of the lower hydrocarbon gas include lower hydrocarbons having 4 or less carbon atoms, such as methane, ethane, ethylene, propane, and butane. Methane used in the first embodiment is preferable. The hydrocarbon fuel may be a mixture of the above-mentioned lower hydrocarbon gas.

  Methane and steam are sent from the vaporizer 12 to the reformer 14 via the pipe 70. The reformer 14 reforms methane to generate a fuel gas G2 containing hydrogen and having a temperature of about 600 ° C. One end of a fuel gas pipe 72 is connected to the reformer 14. The other end of the fuel gas pipe 72 is connected to an anode (fuel electrode) 16A of the cell stack 16. The fuel gas G2 generated in the reformer 14 is supplied to the anode 16A via the fuel gas pipe 72.

  The cell stack 16 is a solid oxide cell stack (SOFC: Solid Oxide Fuel Cell), and has a plurality of stacked fuel cells. The operating temperature of the cell stack 16 is set to about 650 ° C.

  Each fuel cell (not shown) of the cell stack 16 has an electrolyte membrane, an anode (fuel electrode) 16A and a cathode (air electrode) 16B which are respectively laminated on the front and back surfaces of the electrolyte membrane. I have.

  One end of an air pipe 74 is connected to the cathode 16B of the cell stack 16, and a blower B2 is connected to the other end of the air pipe 74. The air (oxidizing gas) G3 sent from the blower B2 is supplied to the cathode 16B via the air preheater 30 by the air pipe 74.

  At the cathode 16B, as shown in the following equation (1), oxygen in the air reacts with the electrons to generate oxygen ions. The generated oxygen ions reach the anode 16A of the cell stack 16 through the electrolyte membrane.

  (Air cathode reaction)

1 / 2O ₂ + 2e ⁻ → O ² -... (1)

Cathode off-gas is discharged from the cathode 16B.

  On the other hand, at the anode 16A of the cell stack 16, as shown in the following equations (2) and (3), oxygen ions that have passed through the electrolyte membrane react with hydrogen and carbon monoxide in the fuel gas to form water (steam). ) And carbon dioxide and electrons are produced. Electrons generated at the anode 16A move from the anode 16A to the cathode 16B through an external circuit, thereby generating power in each cell stack. Each cell stack generates heat during power generation.

  (Fuel electrode reaction)

H ₂ + O ²⁻ → H ₂ O + 2e ⁻ (2)

CO + O ²⁻ → CO ₂ + 2e ⁻ (3)

  One end of an anode off-gas pipe 76 is connected to the anode 16A. The anode off gas G4 is discharged from the anode 16A to the anode off gas pipe 76. The anode off-gas G4 contains unreacted hydrogen, unreacted carbon monoxide, carbon dioxide, water vapor, and the like.

  The other end of the anode offgas pipe 76 is connected to the combustor 40, and the anode offgas G4 is sent to the combustor 40.

  One end of a cathode off-gas tube 78 is connected to the cathode 16B. The other end of the cathode offgas pipe 78 is connected to the combustor 40, and the cathode offgas G5 is delivered to the combustor 40.

  In the combustor 40, the anode off-gas G4 discharged from the anode 16A of the cell stack 16 is burned. One end of a flue gas pipe 80 is connected to the outlet side of the combustor 40. The combustion exhaust gas G1 is introduced into the vaporizer 12 which also functions as a heat exchange unit via the air preheater 30, and is discharged to the outside after the heat exchange.

  The flue gas G1 exchanges heat with the normal temperature air G3 in the air preheater 30. Then, it is sent to the vaporizer 12, where heat exchange with water and methane is performed. The combustion exhaust gas G1 is discharged outside after heat exchange is performed in the vaporizer 12.

  (Start operation)

  First, the starting operation of the fuel cell system 10 according to the first embodiment will be described.

  When starting the fuel cell system 10, the high temperature section 18 is heated by the combustion of the raw material gas and the oxidizing gas, and the cell stack 16 is heated. Water (steam) for reforming is supplied to the reformer 14 in a state where the temperature of the cell stack 16 is equal to or higher than a certain value (threshold value Tcs).

  (Normal operation)

  Next, a normal operation of the fuel cell system 10 according to the first embodiment will be described.

  The air G3 sent out by the blower B2 at a predetermined air discharge amount is supplied to the cathode 16B via the air preheater 30, is supplied to the power generation, and is then sent out to the combustor 40 via the cathode offgas pipe 78. On the other hand, the methane delivered at a predetermined discharge amount by the blower B1 is supplied to the vaporizer 12 through the outer flow path 24 of the double pipe 20. Further, the water (liquid phase) delivered at a predetermined discharge rate by the pump P is supplied to the vaporizer 12 via the inner flow path 22 of the double pipe 20. The water and methane supplied to the vaporizer 12 are heated by heat exchange with the combustion exhaust gas. Thereby, the water is vaporized, and the heated methane and steam are sent to the reformer 14. Then, the fuel gas G2 is reformed by the reformer 14 and supplied to the anode 16A for power generation. From the anode 16A, an anode off-gas G4 containing a fuel such as unreacted hydrogen is discharged and sent to the combustor 40 through an anode off-gas pipe 76. Further, the cathode offgas G5 is sent out to the combustor 40 via the cathode offgas pipe 78.

  In the combustor 40, the anode off-gas G4 is subjected to combustion, and the reformer 14 is heated by heat from the combustion. The combustion exhaust gas G1 is sent from the combustor 40 to the combustion exhaust gas pipe 80, and the air preheater 30 exchanges heat with the air G3. The combustion exhaust gas G1 is further sent to the vaporizer 12, where heat exchange is performed between methane and water, cooled, and then discharged to the outside. The carburetor 12 is a heat exchange unit immediately before the combustion exhaust gas G1 is discharged out of the fuel cell system 10. That is, the vaporizer 12 is the final heat exchange unit, and the combustion exhaust gas G1 is discharged to the outside of the fuel cell system 10 without actively performing heat exchange downstream of the vaporizer 12.

  (Carbon deposition temperature monitoring)

  In the start-up operation, the internal temperature of the reformer 14 needs to be maintained below the carbon deposition temperature (threshold value Tref1).

  As a comparative example of the means for maintaining the temperature lower than the carbon deposition temperature (threshold value Tref1), the flow rate of the raw material gas is adjusted (thinned) to suppress the rising gradient of the internal temperature of the reformer 14. . In this case, the rate of change in temperature rise (gradient) of the cell stack 16 due to combustion is reduced as compared with the case where the flow rate of the raw material gas is not reduced.

  Therefore, in the first embodiment, by supplying the raw material gas at the maximum flow rate, the temperature rise change rate (gradient) of the cell stack 16 is improved, and the temperature is maintained below the carbon deposition temperature (threshold value Tref1). The control form was established.

  In FIG. 1, a signal line for controlling the operation of the entire fuel cell system 10 is comprehensively represented by an arrow S, and a control signal (details will be described later) used for the start-up operation of the first embodiment is specialized. Lines are individually marked with arrows. That is, each individual arrow is a part of the signal line indicated by the arrow S.

  As shown in FIG. 1, a reformer temperature sensor 50 for detecting the temperature inside the reformer 14 is attached to the reformer 14. The temperature information detected by the reformer temperature sensor 50 is sent to the control device 26 via the signal line 52.

  A cell stack temperature sensor 54 for detecting the temperature inside the cell stack 16 is attached to the cell stack 16. The temperature information detected by the cell stack temperature sensor 54 is sent to the control device 26 via a signal line 56.

  In the control device 26, the driving of the blower B1 for supplying the raw material gas to the vaporizer 12 is controlled by a signal line 58, the driving of the blower B2 for supplying the oxidizing gas to the vaporizer 12 is controlled by a signal line 60, and The drive of the pump P for supplying water to the vaporizer is controlled by the signal line 62 to control the respective flow rates.

  Further, the control device 26 is provided with a threshold value storage unit 26M. The threshold storage unit 26M stores at least a critical internal temperature threshold Tref1 at which carbon deposition occurs inside the reformer 14 and a critical internal temperature at which water vapor condensation occurs inside the cell stack 16. And the threshold value Tcs are stored.

  The reformer temperature sensor 50, the cell stack temperature sensor 54, the blower B1, the blower B2, and the pump P correspond to a control device used for the above-described starting operation.

  In the start-up operation in the fuel cell system 10 according to the first embodiment, the flame is not completely misfired during the combustion in the combustor 40 without reducing the flow rate of the raw material gas as in the comparative example described above. In addition, the fuel cell is supplied at a flow rate equal to or higher than the minimum flow rate at which combustion can be maintained (for example, the maximum output of the blower B1), and the temperature of the cell stack 16 is raised to a temperature Tcs at which condensation of steam occurs.

  At this time, paying attention to the fact that the rising gradient of the internal temperature of the reformer 14 changes depending on the flow rate of the raw material gas, a temperature Tref2 (for example, slightly lower than the temperature Tref1 at which carbon deposition occurs in the reformer 14). , Tref2 = Tref1−about 30 ° C.), the supply of the raw material gas is stopped (for example, the blower B1 is stopped), and the supply of the raw material gas is monitored while monitoring the rate of change in temperature rise (gradient) of the cell stack 16. Is determined (on / off control (intermittent control) of the supply of the raw material gas).

  (Control of reforming water flow rate)

  By the way, in the first embodiment, the reforming water is supplied to the reformer 14 in a state where the temperature of the cell stack 16 is equal to or higher than a certain value (threshold value Tcs). The normal operation is executed. At this time, if a predetermined amount is supplied at a stretch as the amount of the reforming water to be supplied to the reformer 14, the rapid temperature information change rate (gradient ), Which may cause cracks due to thermal stress.

  As a comparative example, a reinforced layer is provided on a part of the insulating substrate that physically forms the cell stack. However, the rate of change that temporarily occurs in the early stage of normal operation is large (for example, a slope of 45 ° to 60 °). ° or more) There is a case that it does not correspond to the temperature rise.

  Therefore, in the first embodiment, the supply of the reforming water after the temperature of the cell stack 16 becomes equal to or higher than a certain value (threshold value Tcs) is gradually increased to a predetermined amount over a certain period of time. The reforming water flow rate control was established. In other words, the reforming water flow rate control according to the first embodiment is a control that makes the changing rate smaller than the changing rate when a predetermined amount of the reforming water is supplied at once.

  This reforming water flow rate control is executed when it is determined in the above-described carbon deposition temperature monitoring control that the internal temperature Ts of the cell stack 16 has reached the threshold value Tcs (Ts ≧ Tcs). In this case, the reforming water is not supplied at a predetermined flow rate. In this case, it is not particularly necessary to determine whether the transition period from the time when the supply of the reforming water is started to the time when the flow rate reaches a predetermined flow rate is the start operation or the normal operation. In the embodiment, the start operation is performed until it is determined that the internal temperature Ts of the cell stack 16 has reached the threshold value Tcs and execution of the reforming water flow rate control is instructed (see Step 122 in FIG. 2 described later). Shall be defined.

  The operation of the first embodiment will be described below with reference to the flowchart of FIG. 2 and the timing chart of FIG.

  FIG. 2A shows an interrupt for calculating a temperature gradient of the cell stack 16 that is executed at regular intervals (every 1 to 5 minutes) after the fuel cell system according to the first embodiment is started. It is a flowchart which shows a routine.

  FIG. 2B is a flowchart illustrating a start-up control routine executed when the fuel cell system according to the first embodiment is started.

  In the first embodiment, the interruption time (interval) of the interruption routine of FIG. 2A is set to one minute. The setting of this interval depends on the combustion mode of the startup operation. For example, in the first embodiment, the combustor 40 of the cell stack 16 is applied, and the rate of change in temperature information (gradient) depending on the presence or absence of combustion is changed by the external heater 64 (see FIG. Set the interval shorter. On the other hand, when an external heater 64 (external combustor) used for the starting operation is provided separately from the combustor 40 for heating the cell stack 16 (in the case of the configuration of the first modification shown in FIG. 4), the heating is performed. Since the temperature information change rate (gradient) due to the presence or absence of (combustion) is less sensitive than applying the combustor 40, the interval is set longer (for example, 5 minutes). The setting may be corrected between 1 minute and 5 minutes depending on the specifications of the combustor 40 or the external heater 64.

  First, the flow of the temperature gradient calculation interrupt routine of the cell stack 16 will be described with reference to the flowchart of FIG.

  In step 100, the internal temperature Ts of the cell stack 16 is detected by the cell stack temperature sensor 54. The detected internal temperature Ts of the cell stack 16 is sequentially stored.

  In the next step 102, the history of the internal temperature Ts of the cell stack 16 is read, and then the process proceeds to step 104, where the rate of change of the internal temperature Ts of the cell stack 16 from the start of activation (if normal, the rising gradient). Is calculated, and the routine proceeds to step 106.

  In step 106, the result of comparison with the previous (previous) calculated value (average value), that is, the determination of whether the current value is higher or lower than the previous time is updated and stored, and this routine ends. That is, the determination to be updated and stored becomes the latest information every time the cell stack temperature gradient calculation interrupt routine is executed (in the first embodiment, every one minute).

  Next, the flow of a start-up operation control routine of the fuel cell system 10 will be described with reference to the flowchart of FIG.

  In step 110, a control temperature Tref2 is set by subtracting a constant value A from a preset threshold value Tref1 of the internal temperature Tk of the reformer 14. The threshold value Tref1 is a critical value of the temperature at which carbon deposition occurs inside the reformer 14, and it is important to control the temperature not to exceed the threshold value Tref1 during the start-up operation. Therefore, the control temperature Tref2 is set by subtracting the constant value A from the threshold value Tref1, and the internal temperature Tk of the reformer 14 is monitored using the control temperature Tref2 as an upper limit.

  In the next step 112, supply of the oxidizing gas (air) is started at a constant flow rate (see arrow a in FIG. 3), and then in step 114, supply of the raw material gas is started at a constant flow rate (see arrow b in FIG. 3). ).

  The constant flow rate of the oxidizing gas is set to be equal to or less than the maximum flow rate at which the flame is not completely misfired and the combustion can be maintained when the combustor 40 burns.

  Further, the constant flow rate of the raw material gas is not less than the minimum flow rate at which the flame does not completely misfire and the combustion can be maintained when the combustor 40 burns.

  In the next step 116, the combustion control in the combustor 40 is started. In the combustor 40, the combustion is performed in a constant combustion state by the supplied fixed amount of the oxidizing gas and the fixed amount of the raw material gas, and the combustion is stopped while the supply of the raw material gas described later is stopped.

  In the next step 118, the internal temperature Ts of the cell stack 16 is detected by the cell stack temperature sensor 54, and the process proceeds to step 120.

  In step 120, the detected internal temperature Ts of the cell stack 16 is compared with a threshold value Tcs of a temperature at which a transition to normal operation is possible.

  If it is determined in step 120 that the internal temperature Ts of the cell stack 16 has reached the threshold value Tcs (Ts ≧ Tcs) (affirmative determination) (see arrow c in FIG. 3), it is determined that the start-up operation has been completed. Then, the process proceeds to step 122 to instruct execution of the reforming water flow rate control (see arrow d in FIG. 3), and then proceeds to step 124. The operation of the reforming water flow control routine (details described later) shown in FIG. 5 is started by the execution instruction of the reforming water flow control in step 122.

  In step 124, a transition to a normal operation is instructed. Thereby, reforming is performed in the reformer 14 and power generation is started in the cell stack 16. At this time, the supply flow rate of the raw material gas is controlled so that the internal temperature Tk of the reformer 14 becomes constant (see the arrow e in FIG. 3).

  On the other hand, when it is determined in step 120 that the internal temperature Ts of the cell stack 16 is lower than the threshold value Tcs (Ts <Tcs) (negative determination), the startup operation needs to be continued, and the startup operation end timing is determined. The process proceeds to step 126 for monitoring, detects the internal temperature Tk of the reformer 14, and proceeds to step 128.

  In step 128, the detected internal temperature Tk of the reformer 14 is compared with the control temperature Tref2.

  When it is determined in step 128 that the internal temperature Tk of the reformer 14 is lower than the control temperature Tref2 (Tk <Tref2) (negative determination), the process proceeds to step 130 to determine whether or not the supply of the source gas is stopped. to decide.

  If a negative determination is made in step 130, it is determined that the combustor 40 is burning, the internal temperature Tk of the reformer 14 is lower than the control temperature, and that combustion can be continued. repeat.

  If an affirmative determination is made in step 130, it is determined that the combustion in the combustor 40 is currently stopped, and the process proceeds to step 134.

  On the other hand, in step 128, when it is determined that the internal temperature Tk of the reformer 14 has reached the control temperature Tref2 (Tk ≧ Tref2) (affirmative determination) (see the arrow f in FIG. 3), the combustion is further stopped. When the combustion in the reformer 40 is continued, it is determined that the internal temperature of the reformer 14 may become equal to or higher than the threshold value Tref1, and the routine proceeds to step 132, where the drive of the blower B1 is controlled to Is stopped (see arrow g in FIG. 3), and the process proceeds to step 134. If the supply of the source gas is already stopped, the stopped state is maintained.

  The processing in step 134 is a state in which the supply of the source gas is always stopped. From the state in which the source gas supply is stopped, the latest average value updated and stored in step 106 of the interrupt routine of FIG. The result of the value comparison is read, and then the process proceeds to step 136.

  In step 136, it is determined whether or not the latest average value comparison result read in step 134 is a result of "below the previous calculated value".

  If a negative determination is made in step 136, it is determined that the calculated value is not smaller than the previously calculated value, and the process returns to step 118 and repeats the above steps.

  If the result of the determination in step 136 is affirmative, it is determined that the value is lower than the previously calculated value, and the process proceeds to step 138 to control the drive of the blower B1 and restart the supply of the source gas at a constant flow rate. (Refer to the arrow h in FIG. 3).

  FIG. 5 is a flowchart illustrating a reforming water flow control routine that is started when an instruction is received in step 122 of FIG. The routine of FIG. 5 is performed in parallel with the control of FIG.

  In step 150, the target flow rate Fr of the reforming water is read, and then the process proceeds to step 152, where the predicted time tp to reach the target flow rate Fr is set, and the process proceeds to step 154.

In step 154, an ascending gradient (slope θ) of the flow rate is calculated so that the target flow rate Fr is obtained after the time tp (θ = tan ⁻¹ (Fr / tp)).

  In the next step 156, the flow rate is controlled based on the gradient θ calculated in step 154, and the supply of the reforming water is started.

  In the next step 158, it is determined whether or not the flow rate of the reforming water has reached the target flow rate Fr. If a negative determination is made, the reforming water flow rate control is continued. Then, the supply of the reforming water is switched to the quantitative supply control, and this routine ends.

  (Function and effect by monitoring carbon deposition temperature)

  In the first embodiment, during the start-up operation, the raw material gas can be supplied at a constant flow rate during the combustion in the combustor 40 without considering the carbon deposition of the reformer 14, so that the internal temperature Ts of the cell stack 16 can be increased. Can be quickly raised to a temperature at which normal operation is possible as compared with the comparative example (flow rate control of the raw material gas in consideration of carbon deposition in the reformer 14).

  Further, at the internal temperature Tk of the reformer 14, a control temperature Tref2 which is lower by a predetermined temperature than a threshold value Tref1 at which carbon deposition occurs in the reformer 14 is set, and when the temperature reaches the control temperature Tref2, The supply of gas was stopped to prevent the internal temperature Tk of the reformer 14 from reaching the threshold value Tref1. That is, since the supply control of the source gas may be an ON (blower B1 maximum output) / OFF (blower B1 stop) control, the control is facilitated.

  (Function and effect by controlling the flow rate of reforming water)

  In the first embodiment, even if the temperature of the cell stack 16 becomes equal to or higher than a certain value (threshold value Tcs), the reforming water is not immediately supplied at a predetermined flow rate, and a predetermined time is required. The supply was performed while gradually increasing the amount (inclination θ, see step 154 in FIG. 5).

  For this reason, the rate of change can be made smaller than the rate of change when a predetermined amount of the reforming water is supplied at once, and the temperature information change rate (gradient) becomes sharp by the combustion in the cell stack 16, The generation of cracks due to thermal stress can be prevented.

  (Second embodiment)

  Hereinafter, a second embodiment of the present invention will be described. The same components as those of the first embodiment are denoted by the same reference numerals, and the description of the components will be omitted.

  The feature of the second embodiment is that, as shown in FIG. 6, the time tp until the flow rate of the reforming water reaches a predetermined flow rate is divided by n (n is a positive integer), and Then, the flow rate is increased (hereinafter, referred to as step control).

  The stepwise control of the reforming water flow rate according to the second embodiment is equivalent to macro control in which the flow rate is gradually increased at a constant gradient (slope θ). When changing the flow rate, it is easy to change the flow rate to increase in one step or to temporarily lower the flow rate, and it is easy to change the control pattern according to the environment (temperature, humidity, etc.) of the site. Become. It is to be noted that the time for the division may not be constant, and a time change control may be performed such as increasing the fixed amount supply time at the beginning of the flow rate supply and shortening the fixed amount supply time at the end of the flow supply.

  In the carbon deposition temperature monitoring control according to the first embodiment and the second embodiment, the internal temperature Ts of the cell stack 16 is detected at regular intervals (1 minute to 5 minutes), and the temperature from the start is determined. Depending on the state of the average value of the change rate (above or below the previous time), the source gas is controlled to be turned on (blower B1 maximum output) or turned off (blower B1 stopped). Accordingly, when the rate of change of the internal temperature of the cell stack 16 (temperature rise gradient) has already been grasped by an evaluation test or the like, the timing of the on / off control of the source gas may be set in advance by a sequence program. Good.

  (Modification 1)

  In the control at the time of the start-up operation in the first embodiment and the second embodiment, the start-up operation is performed by the combustion of the combustor 40 located inside the housing 11 of the fuel cell system 10. As shown in FIG. 4, the present invention is also applicable to a fuel cell system 10A having an external heater 64 (external combustor).

  In this case, as described above, since the sensitivity of the temperature information change rate (gradient) differs depending on the presence or absence of combustion, the interval (1 minute to 5 minutes) for executing the interrupt routine of FIG. Minutes). For reference, the correlation between the interval when the combustor 40 is used and the interval when the external heater 64 is used is not particularly limited, and may be the same interval or different intervals.

  (Modification 2)

  In the first embodiment and the second embodiment (including the first modification), when the temperature of the cell stack 16 becomes equal to or higher than a certain value (threshold value Tcs), the supply of the reforming water is performed. Although the control to start is performed, the reforming water may be gradually supplied (hereinafter, referred to as early reforming water supply) from the initial stage of the startup, for example, from the time when the supply of the raw material gas is first started.

  Thereby, the threshold value Tref1 at which carbon deposition occurs can be set higher than when the reforming water is not supplied, so that the control range of the flow rate of the raw material gas can be expanded. In other words, in the second modification, the on / off operation supply of the raw material gas (carbon deposition temperature monitoring control) is not essential. That is, conventional control may be used in which the internal temperature Ts of the cell stack 16 is increased while finely adjusting the flow rate of the raw material gas so that the internal temperature Ts of the reformer 14 does not reach the threshold value Tref1. .

  By the way, when the early supply of the reformed water is performed as in the second modification, the deterioration and breakage of the cell stack 16 due to the dew condensation of the moisture contained in the reformed gas becomes a problem.

  In order to prevent this problem, a path for supplying fuel to the cell stack 16 based on the internal temperature Ts of the cell stack 16, the flow rate Fg of the raw material gas, and the internal temperature Tk of the reformer 14, or the cell stack 16 , It is necessary to calculate the relative humidity Rk of the reformed gas at regular intervals (for example, every 30 seconds) and to control the flow rate of the reformed water.

  As an example, when the relative humidity Rk reaches 70%, which is less than 100%, the flow rate of the reforming water is suppressed.

  From the above, the on / off operation supply of the raw material gas (carbon deposition temperature monitoring control) and the supply of the reforming water having a gradient (reforming) performed in the first and second embodiments are described. The control of the flow rate of the raw material gas is the same as the conventional one, and the configuration in which only the supply of the reforming water having a slope is not denied (Table 1 below). "2").

  Table 1 below shows the respective evaluations of the starting operation control for each combination of the supply timing of the reforming water and the supply pattern of the raw material gas. In any combination, the problem of the present invention (the avoidance of the influence of the thermal stress of the cell stack 16) can be solved.

  Note that the combination of “1” in Table 1 corresponds to the first embodiment (constant slope increase control) and the second embodiment (stage control).

  Further, the combination of “2” in Table 1 does not execute the carbon deposition temperature monitoring control, and is specialized for preventing the cell stack 16 from cracking.

  Further, the combination of “3” and “4” in Table 1 corresponds to the second modification.

Reference Signs List 10 fuel cell system 12 vaporizer 14 reformer 16 cell stack 16A anode (fuel electrode)
16B cathode (air electrode)
18 High temperature part (hot box)
Reference Signs List 20 double pipe 22 inner flow path 24 outer flow path 26 controller (start-up operation control means, reforming water flow rate control means)
26M threshold storage unit 27 microcomputer 27A CPU
27B RAM
27C ROM
Reference Signs List 30 air preheater 40 combustor 50 reformer temperature sensor 52 signal line 54 cell stack temperature sensor (cell stack temperature detecting means)
56 signal line 58 signal line 60 signal line 62 signal line 70 pipe 72 fuel gas pipe 74 air pipe 76 anode off gas pipe 78 cathode off gas pipe 80 combustion exhaust gas pipe S signal line B1 blower (source gas supply means)
B2 blower P pump (reforming water supply means)
G1 Combustion exhaust gas G2 Fuel gas G3 Air G4 Anode off gas G5 Cathode off gas

Claims (6)

A reformer that generates a reformed gas by supplying a raw material gas and water, the reformed gas is supplied to a fuel electrode, and an oxidant gas is supplied to an air electrode, A cell stack that generates electric power between the air electrode and the air electrode,
Reforming water supply means for supplying reforming water to the reformer,
Cell stack temperature detection means for detecting the internal temperature of the cell stack,
By controlling the combustion of the heating means using the raw material gas and the oxidizing gas, the entire inside of the housing accommodating the reformer and the cell stack is heated to generate the internal temperature of the cell stack. Starting operation control means for increasing the temperature to a possible temperature;
Based on the progress of the start-up operation by the start-up operation control unit, the reforming water supply unit is controlled to control the flow rate of the reforming water,
A fuel cell system having: The reforming water flow control means,
The flow rate of the reforming water is gradually increased to a flow rate during normal operation between a time when the internal temperature of the cell stack reaches a temperature at which power can be generated and a time after a predetermined time. The fuel cell system as described. Source gas supply means for supplying the source gas,
Reformer temperature detection means for detecting the internal temperature of the reformer,
First calculating means for calculating a rate of change of the internal temperature of the cell stack detected by the cell stack temperature detecting means from the start of activation, and
The activation operation control means,
When the temperature detected by the reformer temperature detecting means exceeds a threshold lower than a critical temperature at which carbon deposition occurs in the reformer, the flow rate of the raw material gas is reduced to a relatively small flow rate. 3. The fuel cell according to claim 1, wherein the flow rate of the source gas is switched to a relatively high flow rate when the rate of change currently calculated by the first calculation means is lower than the rate of change calculated last time. system. The reforming water flow control means,
2. The fuel cell system according to claim 1, wherein the supply of the reforming water is started before the internal temperature of the cell stack reaches a temperature at which power can be generated. 3. Source gas supply means for supplying the source gas,
Reformer temperature detection means for detecting the internal temperature of the reformer,
A second calculation for calculating the relative humidity of the reformed gas supplied to the cell stack at regular intervals based on the internal temperature of the cell stack, the flow rate of the raw material gas, and the internal temperature of the reformer. Means, and
The fuel cell system according to claim 4, wherein the reforming water flow rate control means adjusts the flow rate of the reforming water based on the calculation result of the second calculation means. Computer
Operate as reforming water flow rate control means according to any one of claims 1 to 5,
Reforming water flow control program.