JP5274003B2 - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To positively reduce carbon monoxide concentration in starting in a fuel cell system. <P>SOLUTION: In a fuel cell system, when a prescribed range out of the total catalyst regions of a carbon monoxide shift reaction part becomes a prescribed temperature in starting of the fuel cell system (step 106), a fuel gas is supplied to the fuel cell and power generation is started even if the catalyst regions other than the prescribed range do not reach a prescribed temperature (step 108; power generation starting means). During the time from a point when the fuel cell generates power with a minimum capacity to a point when it generates power with a maximum capacity, the fuel cell is operated to generate power, as an upper limit of power generation, by the power generation upper limit value established based on the temperature of a plurality of places located separated along the flow of the fuel gas from the entrance to the exit, out of the total catalyst regions of the carbon monoxide shift reaction part (steps 110-118). <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a fuel cell system.

  As one type of fuel cell system, one shown in Patent Document 1 is known. As shown in FIG. 1 of Patent Document 1, the fuel cell system includes a fuel cell 30 that generates power using the fuel gas supplied to the fuel electrode 36 and the oxidant gas supplied to the oxidant electrode 32, and the modified fuel cell system. A reforming unit 14 that supplies fuel for quality and reforming water to generate fuel gas, and a catalyst is filled inside, and the concentration of carbon monoxide in the fuel gas from the reforming unit is reduced to reduce the fuel for the fuel cell. And a carbon monoxide shift reaction section 16 that supplies the electrode.

In the fuel cell system configured as described above, when starting the fuel cell system (S11), a carbon monoxide supply step for supplying a fuel gas containing a large amount of carbon monoxide to the fuel cell and a normal power generation temperature of the fuel cell. A power generation start step of starting power generation of the fuel cell from a lower first temperature (S15). Thereby, when starting the fuel cell system, the reformer 10 is not completely (stably) started up, and the power generation of the fuel cell 30 can be started from a state where the carbon monoxide concentration is high. According to this activation method, the time required for activation of the fuel cell power generation system can be shortened.
JP 2007-95561 A

  By the way, in the carbon monoxide shift reaction section, generally, as shown in the following chemical formula 1, carbon monoxide and water vapor react with a catalyst to generate a so-called shift reaction in which they are converted into hydrogen gas and carbon dioxide gas. ing. This shift reaction is an exothermic reaction. Since this shift reaction involves a catalyst, it is necessary to keep the carbon monoxide reducing portion within an appropriate temperature range (the active temperature range of the catalyst) in order to appropriately perform the shift reaction. In other words, the shift reaction occurs in the catalyst in the active temperature range, and the shift reaction hardly occurs in the catalyst not in the active temperature range. Further, the amount of catalyst in the carbon monoxide shift reaction unit is set in accordance with the amount of reforming fuel that is input to the reforming unit corresponding to the maximum rated load of the fuel cell.

(Chemical formula 1)
CO + H ₂ O → CO ₂ + H ₂

  Therefore, in the fuel cell system described in Patent Document 1 described above, the case where the reformer 10 is not completely (stably) started up at the time of start-up means that the entire catalyst region of the carbon monoxide shift reaction unit is at the active temperature. This is the case. That is, the amount of fuel for reforming that is input to the reforming unit corresponding to the required load (required power consumption) of the fuel cell with respect to the range in the active temperature range of the total catalyst region of the carbon monoxide shift reaction unit. In many cases, not all of the carbon monoxide in the gas derived from the reforming section appropriately causes a shift reaction, but only an amount that can be treated with a catalyst in the active temperature range causes a shift reaction appropriately. As a result, a high concentration of carbon monoxide is supplied to the fuel cell.

  However, when carbon monoxide having such a high concentration is supplied to the fuel cell, the catalyst of the fuel cell may be deteriorated by carbon monoxide, and reduction of carbon monoxide is desired.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to reliably reduce the carbon monoxide concentration at the time of startup in a fuel cell system.

In order to solve the above-mentioned problem, the structural feature of the invention according to claim 1 is that a fuel cell that generates power by using a fuel gas supplied to the fuel electrode and an oxidant gas supplied to the oxidant electrode, and reforming A reformer that supplies fuel and reforming water to generate fuel gas, and a catalyst is filled inside, and the carbon monoxide concentration in the fuel gas from the reformer is reduced to the fuel electrode of the fuel cell. In the fuel cell system including the carbon monoxide shift reaction unit to be supplied, when the predetermined range in the entire catalyst region of the carbon monoxide shift reaction unit becomes equal to or higher than the predetermined temperature at the start of the fuel cell system, the predetermined range Even when the catalyst region other than the above does not reach the predetermined temperature, in a state where the reforming fuel to be input to the reforming unit is limited to an amount that can be processed in the catalyst range of the carbon monoxide shift reaction unit that is equal to or higher than the predetermined temperature, the fuel gas is supplied to the fuel cell, fuel It is that having a power generation start means for starting the power generation of the fuel cell at a low power generation operation lower power generation amount from the rated operation of the battery.

The structural feature of the invention according to claim 2, heated in claim 1, the anode off-gas from the fuel electrode is supplied to burn the anode off-gas in the combustion oxidizing gas reformer by the combustion gas The fuel cell further includes a combustion unit, and the power generation start means is to start power generation of the fuel cell in a low hydrogen utilization operation lower than a hydrogen utilization rate at a predetermined power generation amount in a steady state of the fuel cell system.

The structural feature of the invention according to claim 3, heated in claim 1, the anode off-gas from the fuel electrode is supplied to burn the anode off-gas in the combustion oxidizing gas reformer by the combustion gas In addition, when the combustion heat is insufficient with only the anode off gas, a combustion fuel is additionally supplied, the combustion fuel is burned with the combustion oxidant gas, and the combustion portion is also heated with the combustion gas. Furthermore, the power generation start means is to start the power generation of the fuel cell by introducing more fuel for combustion than the provision for additional supply.

According to a fourth aspect of the present invention, in the third aspect of the present invention, the power generation start means inputs more fuel for combustion than specified in the additional supply, and at a predetermined power generation amount in a steady state of the fuel cell system. It is to start the power generation of the fuel cell with low hydrogen utilization operation lower than the hydrogen utilization rate.

Further, the structural feature of the invention according to claim 5 is that, in any one of claims 1 to 4, when the fuel cell can generate power with the maximum capacity from when it can generate power with the minimum capacity. Power generation upper limit value set based on the temperature of multiple locations located along the fuel gas flow from the inlet to the outlet in the entire catalyst region of the carbon monoxide shift reaction unit The power generation control means for generating power from the fuel cell is provided as the upper limit of the amount.

Further, the structural feature of the invention according to claim 6 is that, in claim 5 , the power generation control means is configured to generate power when the temperature at the most inlet side among the temperatures at a plurality of locations is equal to or higher than a predetermined temperature. When the temperature of the first limit setting means for setting the upper limit value to the first upper limit value and the location closest to the outlet side from the location on the inlet side is equal to or higher than the predetermined temperature, the power generation upper limit value is set to the first upper limit value. Second limit setting means for setting a larger second upper limit value.

Further, the structural feature of the invention according to claim 7 is that, in claim 5 , the temperature of the first place closest to the entrance among the temperatures of the plurality of places is detected by the first temperature sensor, The temperature of the first place is not less than a predetermined temperature, and the carbon monoxide concentration in the fuel gas in an amount corresponding to the first power generation amount lower than the rated power generation amount of the fuel cell is disposed at a catalyst amount position where the carbon gas concentration can be reduced below the predetermined concentration. It has been done.

Further, the structural feature of the invention according to claim 8 is that in claim 7 , the temperature of the second place on the outlet side from the first place is detected by the second temperature sensor, and the second temperature sensor is The temperature is equal to or higher than the predetermined temperature, and the carbon monoxide concentration in the fuel gas in an amount corresponding to the second power generation amount larger than the first power generation amount is arranged at a catalyst amount position where the carbon gas concentration can be reduced to a predetermined concentration or less. .

Further, the structural feature of the invention according to claim 9 is that in claim 8 , the temperature of the third place on the outlet side from the second place is detected by the third temperature sensor, and the third temperature sensor is The temperature is equal to or higher than the predetermined temperature and the carbon monoxide concentration in the fuel gas in an amount corresponding to the third power generation amount larger than the second power generation amount is disposed at a catalyst amount position where the carbon gas concentration can be reduced to a predetermined concentration or less. .

Further, the structural feature of the invention according to claim 10 is that, in claim 5 , the temperature at a plurality of locations rises to a predetermined temperature or higher in the order of the temperature on the inlet side to the temperature on the outlet side of the carbon monoxide shift reaction section. Therefore, it is to increase the power generation upper limit value.

In the invention according to claim 1 configured as described above, the power generation start means is included in the entire catalyst region of the carbon monoxide shift reaction section (hereinafter referred to as the CO shift section) when the fuel cell system is started. When the predetermined range is equal to or higher than the predetermined temperature, even if the catalyst region other than the predetermined range has not reached the predetermined temperature, the fuel gas is supplied to the fuel cell to start power generation. As a result, the amount of gas from the reforming unit to the CO shift unit and the amount of reforming fuel to be fed into the reforming unit can be processed in the catalyst range that is equal to or higher than the predetermined temperature (the catalyst active temperature range). It is possible to limit the carbon monoxide to an appropriate concentration in the CO shift unit at the time of startup. The time of starting means from the start of starting until it becomes possible to start power generation with the maximum capacity, and includes the start of power generation smaller than the maximum capacity. The start-up is when the fuel cell system starts or when the reformer starts operation. Therefore, compared with the case where power generation is started only when the entire catalyst region of the CO shift unit becomes equal to or higher than the activation temperature range, the startup time (time from the start of startup to the start of power generation) and startup energy can be reduced. In this way, the start-up time and start-up energy can be reduced while reliably reducing the carbon monoxide concentration.
Furthermore, since the power generation start means starts the power generation of the fuel cell with a low power generation amount lower than the rated operation of the fuel cell, the amount of fuel input to the reforming section corresponding to the low power generation amount operation can be suppressed to a low level. As a result, the amount of gas from the reforming section to the CO shift section can be reduced. As a result, the catalyst range that is equal to or higher than the predetermined temperature can be small, so that the start-up time and start-up energy can be reduced while reliably reducing the carbon monoxide concentration.

In the invention according to Claim 2 as constructed above, in the invention according to claim 1, the anode off-gas from the fuel electrode is supplied to burn the anode off-gas in the combustion oxidizing gas reforming by the combustion gas The fuel cell further includes a combustion unit that heats the unit, and the power generation start unit starts power generation of the fuel cell in a low hydrogen utilization operation lower than a hydrogen utilization rate in a predetermined power generation amount in a steady state of the fuel cell system. Thus, when the reforming section is heated using anode off gas (unused gas) from the fuel electrode of the fuel cell (for example, when anode off gas is burned in the combustion section that heats the reforming section), at the start of power generation Since the amount of hydrogen used is small and the amount of hydrogen in the anode off-gas is relatively large, the amount of heat of combustion increases. The increased heat quantity increases the warming power of the reforming section and hence the CO shift section. As a result, the warm-up time of the CO shift unit can be shortened.

In the invention according to claim 3 configured as described above, in the invention according to claim 1 , the anode off-gas from the fuel electrode is supplied, the anode off-gas is burned with the combustion oxidant gas, and reformed by the combustion gas. In addition to heating the part, when the combustion heat is insufficient with only the anode off-gas, additional combustion fuel is supplied, the combustion fuel is burned with the combustion oxidant gas, and the reforming part is also heated with the combustion gas. And a power generation start means starts to generate power from the fuel cell by adding more fuel for combustion than the provision for additional supply. In this way, a system that supplements not only the anode off-gas but also the shortage of heat with combustion fuel in the combustion section is called a reheating system. In this reheating system, the amount of combustion heat increases because more fuel for combustion is supplied than the provision for additional supply at the start of power generation. The increased heat quantity increases the warming power of the reforming section and hence the CO shift section. As a result, the warm-up time of the CO shift unit can be shortened.

In the invention according to claim 4 configured as described above, in the invention according to claim 3 , the power generation start means inputs more fuel for combustion than the provision for additional supply, and the predetermined state of the steady state of the fuel cell system is determined. The power generation of the fuel cell is started with the low hydrogen utilization operation lower than the hydrogen utilization rate in the power generation amount. In the reheating system, not only the amount of fuel for combustion is supplied more than the provision of additional supply but also the anode off-gas containing a relatively large amount of hydrogen is supplied at the start of power generation, so that the amount of heat of combustion increases. Due to the increased heat quantity, the warming power of the reforming part and thus the CO shift part is further increased. As a result, the warm-up time of the CO shift unit can be further shortened.

In the invention according to claim 5 configured as described above, in the invention according to any one of claims 1 to 4, the power generation control means starts from the time when the fuel cell can generate power with the minimum capacity. Based on the temperature of multiple locations located along the flow of fuel gas from the inlet to the outlet in the entire catalyst region of the carbon monoxide shift reaction unit up to the point where power generation is possible at the maximum capacity The fuel cell is caused to generate power with the power generation upper limit value set as the upper limit of the power generation amount. As a result, the catalyst range that is equal to or higher than the predetermined temperature (that is, the active temperature range of the catalyst) can be detected based on the temperature at a plurality of locations, and the CO shift from the reforming unit to an amount that can be processed in the detected catalyst range. It is possible to limit the amount of gas to the part and hence the amount of reforming fuel to be fed to the reforming part, and the carbon monoxide can be reliably reduced to an appropriate concentration at the CO shift part at the time of startup.

In the invention according to claim 6 configured as described above, in the invention according to claim 5 , the first limit setting means is configured such that the temperature at the most inlet side among the temperatures at a plurality of locations is equal to or higher than a predetermined temperature. In the case where the power generation upper limit value is set to the first upper limit value, the second limit setting means causes the power The upper limit value is set to a second upper limit value that is greater than the first upper limit value. During startup, when the catalyst of the CO shift unit is warmed up from the inlet side, first, when the predetermined range from the inlet reaches a predetermined temperature or higher, the power generation output is controlled according to the power generation amount with the first upper limit as the upper limit. When the range including the place located on the outlet side from the place closest to the inlet side becomes a predetermined temperature or higher, the power generation output is controlled in accordance with the power generation amount with the second upper limit value larger than the first upper limit as the upper limit. Can do.

In the invention according to claim 7 configured as described above, in the invention according to claim 5 , the temperature of the first place closest to the inlet among the temperatures of the plurality of places is detected by the first temperature sensor. The temperature sensor has a catalyst amount that can reduce the carbon monoxide concentration in the fuel gas in an amount corresponding to the first power generation amount that is equal to or higher than the predetermined temperature and lower than the rated power generation amount of the fuel cell to a predetermined concentration or less. Arranged in position. As a result, the catalyst range that is equal to or higher than the predetermined temperature can be detected with certainty, and the power generation amount appropriate for the catalyst range can be reliably limited.

In the invention according to claim 8 configured as described above, in the invention according to claim 7 , the temperature of the second place on the outlet side from the first place is detected by the second temperature sensor, and the second temperature sensor is The temperature of the second place is not less than a predetermined temperature, and the carbon monoxide concentration in the fuel gas in an amount corresponding to the second power generation amount larger than the first power generation amount is disposed at a catalyst amount position where the carbon gas concentration can be reduced below the predetermined concentration. Yes. As a result, the catalyst range that is equal to or higher than the predetermined temperature can be detected with certainty, and the power generation amount appropriate for the catalyst range can be reliably limited.

In the invention according to claim 9 configured as described above, in the invention according to claim 8 , the temperature of the third place on the outlet side from the second place is detected by the third temperature sensor, and the third temperature sensor is The temperature of the third place is equal to or higher than the predetermined temperature, and the carbon monoxide concentration in the fuel gas in an amount corresponding to the third power generation amount larger than the second power generation amount is disposed at a catalyst amount position where the carbon gas concentration can be reduced below the predetermined concentration. Yes. As a result, the catalyst range that is equal to or higher than the predetermined temperature can be detected with certainty, and the power generation amount appropriate for the catalyst range can be reliably limited.

In the invention according to claim 10 configured as described above, in the invention according to claim 5 , the temperature of the plurality of locations is a predetermined temperature in the order of the temperature on the inlet side to the temperature on the outlet side of the carbon monoxide shift reaction unit. The power generation upper limit is increased as it rises above. By the way, a high temperature reformed gas is supplied from the reforming section to the carbon monoxide shift reaction section. The temperature is raised in order from the upstream side of the carbon monoxide shift reaction section depending on the temperature of the supplied reformed gas. When the heated upstream part reaches the activation temperature of the carbon monoxide shift reaction part, the temperature rises due to the exothermic heat of the catalytic reaction. As a result, the carbon monoxide shift reaction part is heated in order from the upstream at the time of start-up. The region above the temperature spreads from upstream to downstream. In this way, the power generation upper limit value is increased as the temperature at a plurality of locations rises above a predetermined temperature in the order of the temperature on the inlet side to the temperature on the outlet side of the carbon monoxide shift reaction unit. It is possible to reliably limit the amount of power generation appropriate for the range.

  Hereinafter, an embodiment of a fuel cell system according to the present invention will be described. FIG. 1 is a schematic diagram showing an outline of this fuel cell system. This fuel cell system includes a fuel cell 10 and a reformer 20 that generates fuel gas (reformed gas) containing hydrogen gas necessary for the fuel cell 10.

  The fuel cell 10 includes a fuel electrode 11, an air electrode 12 that is an oxidant electrode, and an electrolyte 13 interposed between the electrodes 11 and 12, and supplies the reformed gas supplied to the fuel electrode 11 and the air electrode 12. Electric power is generated using air (cathode air), which is the oxidant gas.

  The reformer 20 steam reforms the reforming fuel and supplies a hydrogen-rich reformed gas to the fuel cell 10. The reformer 20 includes a reforming unit 21, a cooling unit 22, a carbon monoxide shift reaction unit (hereinafter referred to as a “carbon monoxide shift reaction unit”). , A CO shift unit) 23, a carbon monoxide selective oxidation reaction unit (hereinafter referred to as a CO selective oxidation unit) 24, a combustion unit 25, and an evaporation unit 26. Examples of the reforming fuel include natural gas, gas fuel for reforming such as LPG, and liquid fuel for reforming such as kerosene, gasoline, and methanol. In this embodiment, natural gas will be described.

  The reforming unit 21 generates and derives a reformed gas from a mixed gas that is a reforming raw material in which reforming water is mixed with the reforming fuel. The reforming portion 21 is formed in a bottomed cylindrical shape, and includes an annular folded channel 21a extending along the axis in the annular cylindrical portion.

  The return channel 21 a of the reforming unit 21 is filled with a catalyst 21 b (for example, a Ru or Ni-based catalyst) and introduced from the reforming fuel introduced from the cooling unit 22 and the steam supply pipe 51. The gas mixture with the steam reacts and is reformed by the catalyst 21b to generate hydrogen gas and carbon monoxide gas (so-called steam reforming reaction). At the same time, a so-called carbon monoxide shift reaction occurs in which carbon monoxide generated in the steam reforming reaction reacts with steam to transform into hydrogen gas and carbon dioxide. These generated gases (so-called reformed gas) are led to a cooling unit (heat exchange unit) 22. The steam reforming reaction is an endothermic reaction, and the carbon monoxide shift reaction is an exothermic reaction. The activation temperature range of the catalyst 21b of the reforming unit 21 is 400 ° C to 800 ° C.

  Further, a temperature sensor 21 c that measures the temperature in the reforming unit 21, for example, the temperature in the vicinity of the wall between the reforming unit 21 is provided in the reforming unit 21. The detection result of the temperature sensor 21 c is transmitted to the control device 30.

  The cooling unit 22 is a heat exchanger (heat exchange unit) in which heat exchange is performed between the reformed gas derived from the reforming unit 21 and a mixed gas of reforming fuel and reformed water (steam). The temperature of the reformed gas having a high temperature is lowered by the mixed gas having a low temperature and led to the CO shift unit 23, and the temperature of the mixed gas is raised by the reformed gas and led to the reforming unit 21. Yes.

  Specifically, a reforming fuel supply pipe 41 connected to a fuel supply source (not shown) (for example, a city gas pipe) is connected to the cooling unit 22. The reforming fuel supply pipe 41 is provided with a fuel pump 42, a desulfurizer 46, and a reforming fuel valve 43 in order from the upstream. The reforming fuel valve 43 opens and closes the reforming fuel supply pipe 41. The fuel pump 42 supplies reforming fuel (and / or combustion fuel) and adjusts the supply amount. The desulfurizer 46 removes sulfur (for example, sulfur compounds) in the fuel. The fuel that is supplied to the reforming unit 21 and reformed is called reforming fuel, and the fuel that is supplied to the combustion unit 25 and burned is called combustion fuel.

  A combustion fuel supply pipe 44 connected to a combustion air supply pipe 64 connected to the combustion section 25 is connected between the desulfurizer 46 and the reforming fuel valve 43 of the reforming fuel supply pipe 41. Has been. A combustion fuel valve 45 is provided in the combustion fuel supply pipe 44. The combustion fuel valve 45 opens and closes the combustion fuel supply pipe 44. When the fuel pump 42 is driven and the reforming fuel valve 43 is closed and the combustion fuel valve 45 is opened, the combustion fuel is supplied to the combustion unit 25, and the fuel pump 42 is driven and the reforming fuel. When the valve 43 is opened and the combustion fuel valve 45 is closed, the reforming fuel is supplied to the reforming unit 21.

  Further, a steam supply pipe 51 connected to the evaporation section 26 is connected between the reforming fuel valve 43 and the cooling section 22 of the reforming fuel supply pipe 41. The steam supplied from the evaporation unit 26 is mixed with the reforming fuel, and the mixed gas is supplied to the reforming unit 21 through the cooling unit 22.

  The CO shift unit 23 is a unit that reduces carbon monoxide in the reformed gas supplied from the reforming unit 21 through the cooling unit 22, that is, a carbon monoxide reducing unit. The CO shift unit 23 includes a folded channel 23a extending along the vertical direction. The return channel 23a is filled with a catalyst 23b (for example, a Cu—Zn-based catalyst). In the CO shift unit 23, a so-called carbon monoxide shift reaction in which carbon monoxide and water vapor contained in the reformed gas introduced from the cooling unit 22 react with the catalyst 23b to be converted into hydrogen gas and carbon dioxide gas. Has occurred. This carbon monoxide shift reaction is an exothermic reaction.

  In the CO shift unit 23, a plurality of (three in this embodiment) temperature sensors 23c to 23e for measuring the temperature of the catalyst 23b of the CO shift unit 23 are provided. The detection results of the temperature sensors 23c to 23e are transmitted to the control device 30. These temperature sensors 23c to 23e are arranged apart along the flow of the reformed gas from the inlet to the outlet in the entire catalyst region of the CO shift unit 23.

  The temperature sensor (first temperature sensor) 23c detects the temperature S1 of the first place P1 closest to the inlet of the CO shift unit 23. This temperature sensor 23c has a predetermined concentration of carbon monoxide in the reformed gas in an amount corresponding to the first power generation amount W1 that is equal to or higher than the predetermined temperature S1a and the temperature of the first place P1 is lower than the rated power generation amount of the fuel cell 10. (For example, 5000 ppm) It is arrange | positioned in the position of the catalyst amount which can be reduced below.

  The temperature sensor (second temperature sensor) 23d detects the temperature S2 of the second location P2 on the outlet side from the first location P1. The temperature sensor 23d sets the carbon monoxide concentration in the reformed gas in an amount corresponding to the second power generation amount W2 that is equal to or higher than the first temperature S2a and the temperature of the second place P2 is equal to or higher than the predetermined temperature S2a (for example, It is disposed at a position where the catalyst amount can be reduced to 5000 ppm) or less.

  The temperature sensor (third temperature sensor) 23e detects the temperature S3 of the second location P3 on the outlet side from the second location P2. The temperature sensor 23e sets the concentration of carbon monoxide in the reformed gas in an amount corresponding to the third power generation amount W3 that is equal to or higher than the second power generation amount W2 and the temperature of the third location P3 is equal to or higher than the predetermined temperature S3a (for example, It is disposed at a position where the catalyst amount can be reduced to 5000 ppm) or less.

  For example, the first position P1 is an inlet portion in the catalyst region, and is a position corresponding to the first power generation amount W1 that is the minimum power generation amount (200 W). The second position P2 is an intermediate portion of the catalyst region, and is a position corresponding to the second power generation amount W2 that is the intermediate power generation amount (500 W). The 3rd position P3 is an exit part among catalyst fields, and is a position corresponding to the 3rd power generation amount W3 which is the maximum power generation amount (1000W).

  The predetermined temperature is set to different values S1a, S2a, and S3a for each temperature sensor, but may be set to the same value. In any case, the predetermined temperature is set to a value in the active temperature range (for example, 180 to 300 ° C.) of the catalyst 23b.

  The CO selective oxidation unit 24 further reduces the carbon monoxide in the reformed gas supplied from the CO shift unit 23 and supplies it to the fuel cell 10, that is, a carbon monoxide reduction unit. The CO selective oxidation unit 24 is formed in a cylindrical shape, and is provided so as to cover the outer peripheral wall of the evaporation unit 26. The CO selective oxidation unit 24 is filled with a catalyst 24a (for example, a Ru or Pt catalyst).

  In the CO selective oxidation unit 24, a temperature sensor 24b for measuring the temperature in the CO selective oxidation unit 24 is provided. The detection result of the temperature sensor 24 b is transmitted to the control device 30.

  A connecting pipe 89 connected to the CO shift section 23 and a reformed gas supply pipe 71 connected to the fuel electrode 11 of the fuel cell 10 are connected to the lower and upper side walls of the CO selective oxidation section 24, respectively. ing. An oxidation air supply pipe 61 is connected to the connection pipe 89. As a result, the reformed gas from the CO shift unit 23 and the oxidizing air from the atmosphere are introduced into the CO selective oxidation unit 24. The oxidizing air supply pipe 61 is provided with an oxidizing air pump 62 and an oxidizing air valve 63 in order from the upstream. The oxidizing air pump 62 supplies oxidizing air and adjusts the supply amount. The oxidation air valve 63 opens and closes the oxidation air supply pipe 61.

  Therefore, carbon monoxide in the reformed gas introduced into the CO selective oxidation unit 24 reacts (oxidizes) with oxygen in the oxidizing air to become carbon dioxide. This reaction is an exothermic reaction and is promoted by the catalyst 24a. Thereby, the reformed gas is derived by further reducing the carbon monoxide concentration (10 ppm or less) by the oxidation reaction, and is supplied to the fuel electrode 11 of the fuel cell 10.

  A CO selective oxidation unit 24 is connected to the inlet of the fuel electrode 11 of the fuel cell 10 via a reformed gas supply pipe 71, and the combustion unit 25 is connected to the outlet of the fuel electrode 11 via an offgas supply pipe 72. Is connected. The bypass pipe 73 bypasses the fuel cell 10 and directly connects the reformed gas supply pipe 71 and the offgas supply pipe 72. An anode gas valve 74 is provided in the reformed gas supply pipe 71 between the branch point of the bypass pipe 73 and the fuel cell 10. The off gas supply pipe 72 is provided with an anode off gas valve 75 between the junction with the bypass pipe 73 and the fuel cell 10. A bypass valve 76 is provided in the bypass pipe 73.

  From the start of the fuel cell system to the start of power generation, the anode gas valve 74 and the anode off-gas valve 75 are closed and bypassed to avoid supplying reformed gas with a high carbon monoxide concentration from the reformer 20 to the fuel cell 10. In order to supply the reformed gas from the reformer 20 to the fuel cell 10 during the power generation operation, the anode gas valve 74 and the anode offgas valve 75 are opened and the bypass valve 76 is closed.

  A cathode air supply pipe 67 is connected to the inlet of the air electrode 12 of the fuel cell 10, and an exhaust pipe 82 is connected to the outlet of the air electrode 12. Air is supplied to the air electrode 12, and off-gas is exhausted. The cathode air supply pipe 67 is provided with a cathode air pump 68 and a cathode air valve 69 in order from the upstream. The cathode air pump 68 supplies cathode air and adjusts the supply amount. The cathode air valve 69 opens and closes the cathode air supply pipe 67.

  The combustion unit 25 uses at least one of combustion fuel supplied through the combustion fuel supply pipe 44, reformed gas supplied from the reforming unit 21, and anode off-gas from the fuel cell 10 for combustion. It burns with the combustion air supplied by the air pump 65, and heats the reforming part 21 with the combustion gas. The combustion unit 25 generates combustion gas for heating the reforming unit 21 and supplying heat necessary for the steam reforming reaction, and a lower end portion is inserted into the inner peripheral wall of the reforming unit 21. It is arranged with a space.

  A combustion fuel supply pipe 44 connected to a fuel supply source (not shown) (for example, a city gas pipe) is connected to the combustion section 25 via a combustion air supply pipe 64 and is connected to the outlet of the fuel electrode 11 at one end. Is connected to the other end of the off-gas supply pipe 72. Basically, when the fuel cell 10 is started, combustion fuel is supplied to the combustion unit 25, and when the temperature S1 of the CO shift unit 23 is lower than the predetermined temperature S1a during the startup of the fuel cell 10, CO selective oxidation is performed. When the reformed gas from the unit 24 is supplied to the combustion unit 25 without passing through the fuel cell 10 and the power generation of the fuel cell 10 is started, the anode off-gas discharged from the fuel cell 10 (unused in the fuel electrode 11) Thus, a reformed gas containing reforming fuel and the like that are not reformed in the reforming section is supplied to the combustion section 25.

  In addition, during the power generation operation, if the amount of combustion heat by the reformed gas or anode off gas is not sufficient for heating the reforming section to a predetermined temperature, the amount of combustion corresponding to the shortage of combustion heat amount The fuel is supplemented by supplying additional fuel. In this way, a system that supplements not only the anode off-gas but also the insufficient heat quantity with the combustion fuel in the combustion section 25 is called a reheating system. In addition to this reheating system, the fuel cell system supplies only the anode off-gas to the combustion unit 25 during power generation operation, and does not supply additional combustible gas such as combustion fuel as in the reheating system. There is a less system. The present invention is applicable not only to a rebirth system but also to a rebirthless system.

  Further, a combustion air supply pipe 64 is connected to the combustion unit 25, and combustion air for burning (oxidizing) a combustible gas such as a combustion fuel, anode off gas, and reformed gas is supplied from the atmosphere. It has become so. The combustion air supply pipe 64 is provided with a combustion air pump 65 and a combustion air valve 66 in order from the upstream. The combustion air pump 65 is combustion oxidant gas supply means for supplying combustion air as combustion oxidant gas and adjusting the supply amount. The combustion air valve 66 opens and closes the combustion air supply pipe 64.

  When the combustion unit 25 configured as described above is ignited, the supplied combustion fuel, reformed gas or anode off-gas is combusted by the combustion air to generate high-temperature combustion gas. The combustion gas flows through the combustion gas passage 27 and is exhausted as combustion exhaust gas through the exhaust pipe 81. Thus, the combustion gas heats the reforming unit 21 and the evaporation unit 26 in this order. The combustion gas flow path 27 is disposed in contact with the inner peripheral wall of the reforming section 21 and is folded and disposed between the outer peripheral wall of the reforming section 21 and the heat insulating section 28 and folded. In other words, the flow path is disposed in contact between the heat insulating portion 28 and the evaporation portion 26.

  The evaporation unit 26 boils (evaporates) the reformed water to generate water vapor, and supplies the water vapor to the reformer 21 via the cooling unit 22. The evaporator 26 is formed in a cylindrical shape so as to cover and contact the outer peripheral wall of the combustion gas passage 27.

  A water supply pipe 52 connected to a reforming water tank (not shown) is connected to a lower portion (for example, a lower portion of the side wall surface and a bottom surface) of the evaporation section 26. A water vapor supply pipe 51 is connected to the upper part (for example, the upper part of the side wall surface) of the evaporation unit 26. The reformed water introduced from the reformed water tank is heated by the heat from the combustion gas and the heat from the CO selective oxidation unit 24 in the course of flowing through the evaporation unit 26 to become water vapor and the water vapor supply pipe 51. And it leads to the reforming part 21 through the cooling part 22. The water supply pipe 52 is provided with a reforming water pump 53 and a reforming water valve 54 in order from the upstream. The reforming water pump 53 supplies reforming water to the evaporation unit 26. The reforming water valve 54 is reforming water adjusting means for opening and closing the water supply pipe 52 and adjusting the amount of reforming water supply. The supply amount of the reforming water may be adjusted by the reforming water pump 53.

  In addition, the evaporation unit 26 is provided with a temperature sensor 26 a that detects the temperature in the evaporation unit 26. The temperature sensor 26a is preferably provided in the upstream part (inlet side) in the evaporation part 26. The detection result of the temperature sensor 26 a is transmitted to the control device 30.

  In addition, the fuel cell system includes a control device 30. The control device 30 includes the temperature sensors 21c, 23c, 23d, 23e, 24b, 26a, the pumps 42, 53, 62, 65, 68, and the like. The valves 43, 45, 54, 63, 66, 69, 74, 75, and 76 and the combustion unit 25 (ignition device) are connected (see FIG. 2). The control device 30 includes a microcomputer (not shown), and the microcomputer includes an input / output interface, a CPU, a RAM, and a ROM (all not shown) connected through a bus. The CPU, based on the temperature from the temperature sensors 21c, 23c, 24b, 26a, each pump 42, 53, 62, 65, 68, each valve 43, 45, 54, 63, 66, 69, 74, 75, 76. And, the operation of the fuel cell system is controlled by controlling the combustion unit 25 (ignition device). The RAM temporarily stores variables necessary for executing the program, and the ROM stores the program.

  Next, an example of the operation of the above-described fuel cell system will be described. When main power (not shown) is turned on, control device 30 starts the program at step 100 and advances the program to step 102. In step 102, the control device 30 determines whether or not to start operation. When the start switch (not shown) is pressed and the operation is started according to the operation plan, the control device 30 determines “YES” in step 102 and warms up the reformer 20. (Step 104). Otherwise, the determination of “NO” is repeatedly executed at step 102.

  When the start-up operation is started, the control device 30 opens the combustion air valve 66 and drives the combustion air pump 65 in step 104 to supply the combustion air to the combustion unit 25. Further, the control device 30 energizes the ignition electrode of the combustion unit 25. Further, the control device 30 opens the combustion fuel valve 45 and drives the fuel pump 42 to supply the combustion fuel to the combustion unit 25. As a result, the combustion fuel is burned in the combustion section 25, and the reforming section 21 and the evaporation section 26 are heated by the combustion gas. At this time, the reforming fuel valve 43, the reforming water valve 54, the oxidizing air valve 63, the anode gas valve 74, the bypass valve 76, and the anode off-gas valve 75 are closed.

  Then, the control device 30 controls the reforming water valve 54 and the reforming water pump 53 to supply a predetermined amount of water to the evaporation unit 26 and temporarily stops the supply of water. Thereafter, the control device 30 determines that water vapor has been generated when the temperature sensor 26a becomes equal to or higher than a predetermined value (for example, 100 ° C.). Then, after confirming the generation of water vapor, the control device 30 opens the reforming water valve 54 and drives the reforming water pump 53 to start supplying a predetermined flow rate of water to the evaporation unit 26.

  Thereafter, the control device 30 opens the reforming fuel valve 43 and drives the fuel pump 42 to supply the reforming fuel to the reforming unit 21. Further, the control device 30 opens the oxidation air valve 63 and drives the oxidation air pump 62 to supply the oxidation air to the CO selective oxidation unit 24 by a predetermined flow rate (predetermined supply amount). Thus, the reformed fuel and steam mixed gas are supplied to the reforming unit 21, and the reforming unit 21 generates the reformed gas by causing the steam reforming reaction and the carbon monoxide shift reaction described above. Then, the reformed gas derived from the reforming unit 21 warms up the CO shift unit 23 (and the CO selective oxidation unit 24), is derived from the CO selective oxidation unit 24, does not pass through the fuel cell 10, and is bypassed. The fuel is supplied directly to the combustion unit 25 through 73 and burned. At this time, when the amount of heat for reforming is insufficient in the reforming unit 21, the combustion fuel valve 45 is opened and the fuel for combustion is supplied to the combustion unit 25, thereby supplementing the insufficient amount of heat. .

  During the generation of such reformed gas, the high-temperature reformed gas is supplied from the reforming unit 21 to the CO shift unit 23. The temperature is raised sequentially from the upstream side of the CO shift unit 23 according to the temperature of the supplied reformed gas. When the heated upstream portion reaches the activation temperature of the CO shift unit 23, a temperature rise due to heat generation of the catalytic reaction is also added. As a result, the CO shift unit 23 is heated in order from the upstream at the start, It spreads from upstream to downstream. Note that a heater for warming up the reformed gas may be provided on the inlet side of the CO shift unit 23 to accelerate the warm-up, and similar control is possible.

  In addition, during the generation of such reformed gas, the control device 30 detects the temperature S1 of the first location P1 of the catalyst of the CO shift unit 23 with the temperature sensor 23c in step 106, and the detected temperature S1 is It is determined whether or not the temperature is equal to or higher than a predetermined temperature S1a. When the temperature S1 is lower than the predetermined temperature S1a, the controller 30 determines that the carbon monoxide concentration in the reformed gas is higher than the predetermined concentration, that is, the warm-up is not completed, and the control device 30 performs the process of step 106. repeat.

  On the other hand, if the temperature S1 is equal to or higher than the predetermined temperature S1a (time Tm1 in FIG. 4), the controller 30 determines that the carbon monoxide concentration in the reformed gas is equal to or lower than the predetermined concentration. The gas valve 75 is opened and the bypass valve 76 is closed, so that the CO selective oxidation unit 24 is connected to the inlet of the fuel electrode 11 of the fuel cell 10 and the outlet of the fuel electrode 11 is connected to the combustion unit 25 (step 108). And the control apparatus 30 starts the electric power generation of the fuel cell 10 by the low electric power generation operation which generate | occur | produces with the 1st electric power generation amount W1 (for example, 300W) whose electric power generation amount is lower than rated operation (electric power generation start means). At this time, the control device 30 starts power generation of the fuel cell 10 at a low hydrogen usage rate Uf1 lower than the hydrogen usage rate Uf3 at a predetermined power generation amount W3 in a steady state of the fuel cell system.

  The steady state is an operation state when the rated operation becomes possible (after time Tm3). The hydrogen utilization rate during startup is controlled to be lower than the hydrogen utilization rate of a predetermined power generation amount in a steady state. The rated operation is to operate the fuel cell 10 with the maximum power generation amount. The amount of power generation during rated operation is called the rated power generation amount. The start-up operation (at the time of start-up) is an operation for warming up the reformer 20 until the fuel cell 10 can be rated-operated, and is a state where the temperature S3 of the CO shift unit 23 is lower than the predetermined temperature S3a ( (Between times Tm0 and Tm3). Even during the start-up operation, if the temperature S1 of the CO shift unit 23 is equal to or higher than the predetermined temperature S1a (after time Tm1), power generation is possible (during power generation operation) under output restriction.

  In the catalyst region from the inlet where the temperature is equal to or higher than the predetermined temperature S1a to the first location P1, the carbon monoxide concentration in the reformed gas can be reduced to a predetermined concentration or lower. However, the carbon monoxide concentration can be reduced to a predetermined concentration in the catalyst region only by the gas flow rate corresponding to the lowest power generation output (first power generation amount). That is, when a flow rate higher than the gas flow rate is exceeded, the treatment capacity of the catalyst region is exceeded, and the carbon monoxide concentration becomes a value larger than a predetermined concentration.

  Here, control of the hydrogen utilization rate will be described. Hydrogen utilization rate = (amount of hydrogen used for power generation (hydrogen flow rate) / amount of hydrogen supplied to the fuel cell (hydrogen flow rate)). The power generation amount of the fuel cell 10 can be controlled by the control device 30. In the present embodiment, control is performed by an inverter (not shown) connected to the control device 30. The flow rate of hydrogen supplied to the fuel cell 10 is substantially proportional to the flow rate of fuel gas (reformed gas) supplied to the fuel cell 10. The fuel gas flow rate is determined by the reforming fuel flow rate supplied to the reforming unit 21. The hydrogen utilization rate is controlled by the reforming fuel flow rate (the hydrogen utilization rate decreases as the flow rate increases) or is controlled by the power generation amount (the hydrogen utilization rate decreases as the power generation amount decreases).

  In the present embodiment, the control is performed by the reforming fuel flow rate. That is, the amount of power generation corresponding to each stage at the time of startup (varied according to the user load with each power generation upper limit value as an upper limit) is determined in advance. Moreover, the target hydrogen utilization rate corresponding to each stage is determined in advance at the time of startup (however, the target hydrogen utilization rate may be changed depending on the amount of power generation). The reforming fuel flow rate obtained by calculation from the power generation amount and the target hydrogen utilization rate is supplied to the reforming unit 21. Of course, it is also possible to control the power generation amount by determining the reforming fuel flow rate and the target hydrogen utilization rate. The target hydrogen utilization rate is not a predetermined value, but may be determined and controlled to an optimal value based on the temperature of the CO shift unit 23, the amount of power generation, and the like.

  In step 110, the control device 30 limits the maximum output of the fuel cell 10 to W1 to generate power and sets the hydrogen utilization rate to the low hydrogen utilization rate Uf1.

  Further, the CO shift unit 23 is warmed up by the reformed gas supplied from the reforming unit 21 or self-heating, and the temperature on the downstream side from the first location P1 rises. In step 112, the controller 30 detects the temperature S2 of the second location P2 of the catalyst of the CO shift unit 23 with the temperature sensor 23d, and determines whether or not the detected temperature S2 is equal to or higher than the predetermined temperature S2a. When the temperature S2 is lower than the predetermined temperature S2a, the control device 30 repeats the process of step 112. On the other hand, if the temperature S2 is equal to or higher than the predetermined temperature S2a (time Tm2 in FIG. 4), the control device 30 changes the maximum output of the fuel cell 10 from W1 to W2 and sets it to W2 in step 114 to generate power. The hydrogen utilization rate is changed from Uf1 to Uf2 and set to Uf2 to generate electricity. Uf2 is a value larger than the low hydrogen utilization rate Uf1 and smaller than the hydrogen utilization rate Uf3 in a steady state in which the power generation operation can be performed with the rated power generation amount.

  Further, while the CO shift unit 23 is warmed up, the control device 30 detects the temperature S3 of the third place P3 of the catalyst of the CO shift unit 23 with the temperature sensor 23e in step 116, and this detected temperature S3. Is determined to be equal to or higher than a predetermined temperature S3a. When the temperature S3 is lower than the predetermined temperature S3a, the control device 30 repeats the process of step 116. On the other hand, if the temperature S3 is equal to or higher than the predetermined temperature S3a (time Tm3 in FIG. 4), the control device 30 changes the maximum output of the fuel cell 10 from W2 to W3 and restricts to W3 to generate power in step 118. The hydrogen utilization rate is changed from Uf2 to Uf3 and set to Uf3 to generate power. Thereby, a steady state is started.

  As described above, the control device 30 controls the maximum output W1 when the temperature S1 is equal to or higher than the predetermined temperature S1a, the maximum output W2 when the temperature S2 is equal to or higher than the predetermined temperature S2a, and the maximum output W3 when the temperature S3 is equal to or higher than the predetermined temperature S3a. The power is generated in such a way that it follows the user load within the range below the maximum output.

  During the power generation operation, the control device 30 determines in step 120 whether to stop the operation. If the stop switch (not shown) is pressed and the operation is stopped according to the operation plan, the control device 30 determines “YES” in step 120 and stops the fuel cell system. (Step 122). Otherwise, the determination of “NO” is repeatedly executed at step 120.

  In step 122, the control device 30 stops driving the fuel pump 42, stops the supply of reforming fuel, and closes the reforming fuel valve 43. The control device 30 stops the driving of the reforming water pump 53, stops the supply of the reforming water, and closes the reforming water valve 54. The control device 30 stops the driving of the oxidizing air pump 62, stops the supply of the oxidizing air, and closes the oxidizing air valve 63. The control device 30 stops driving the fuel pump 42, stops the supply of combustion fuel, and closes the combustion fuel valve 45. The control device 30 stops driving the combustion air pump 65, stops the supply of combustion air, and closes the combustion air valve 66. Then, the control device 30 closes the anode gas valve 74, the anode off gas valve 75, and the bypass valve 76. Thereby, the power generation of the fuel cell 10 is stopped. Thereafter, the program is advanced to step 124 and this program is terminated.

  Further, the operation of the above-described fuel cell system will be described with reference to the time charts of FIGS. FIG. 4 shows the temperatures of the respective locations P1 to P3 of the CO shift unit 23 in the upper stage, the user load (shown by a broken line) and the limit value (shown by a dashed line) in the middle stage, and the power generation amount (solid line) and the limit value (middle stage in the lower stage). The power generation amount determined by (1) and (indicated by a one-dot broken line) is shown. FIG. 5 shows the temperature of each location P1 to P3 of the CO shift unit 23 in the upper stage, and the hydrogen utilization rate in the lower stage.

  As shown in FIGS. 4 and 5, the start-up is started at time Tm0. Thereafter, when the temperature S1 of the first location P1 of the CO shift unit 23 becomes equal to or higher than the predetermined temperature S1a at time Tm1, power generation is started. From time Tm1 to time Tm2 (until the temperature S2 of the second location P2 of the CO shift unit 23 becomes equal to or higher than the predetermined temperature S2a), the upper limit value of the power generation amount is limited to W1. Therefore, as shown in FIG. 4, even if the user load (shown by a broken line) exceeds W1, the power generation of the fuel cell 10 is maintained at W1. At this time, the hydrogen utilization rate is limited to Uf1. As a result, the amount of heat of the anode off gas led out from the fuel cell 10 to the combustion unit 25 is large, and the CO shift unit 23 can be warmed up early.

  When the temperature S2 of the second location P2 of the CO shift unit 23 becomes equal to or higher than the predetermined temperature S2a at time Tm2, the upper limit value of the power generation amount is increased from W1 to W2. From time Tm2 to time Tm3 (until the temperature S3 of the third place P3 of the CO shift unit 23 becomes equal to or higher than the predetermined temperature S3a), the upper limit value of the power generation amount is limited to W2. Therefore, as shown in FIG. 4, when the user load does not exceed W2, power generation is performed following the user load. When the user load exceeds W2, the power generation of the fuel cell 10 is maintained at W2. At this time, the hydrogen utilization rate is increased from Uf1 to Uf2 and limited to Uf2. As a result, the amount of heat of the anode off gas led out from the fuel cell 10 to the combustion unit 25 is large, and the CO shift unit 23 can be warmed up early.

  When the temperature S3 of the third place P3 of the CO shift unit 23 becomes equal to or higher than the predetermined temperature S3a at time Tm3, the upper limit value of the power generation amount is increased from W2 to W3. After time Tm3 (start of steady state), the upper limit value of the power generation amount is limited to W3. Therefore, as shown in FIG. 4, when the user load does not exceed W3, power generation is performed following the user load, and when the user load exceeds W3, the power generation of the fuel cell 10 is maintained at W3. At this time, the hydrogen utilization rate is increased from Uf2 to Uf3 and limited to Uf3. 4 and 5 are schematic views, and in particular, the temperature after the temperature of the CO shift portion becomes equal to or higher than a predetermined value is not constant, but fluctuates in a temperature range higher than the predetermined value.

  The processes in steps 106 to 118 described above are power generation control means, the processes in steps 106 and 110 are first limit setting means, and the processes in steps 112 and 114 (or steps 116 and 118) are second limit setting. Means.

  As is apparent from the above description, in this embodiment, the power generation start means (steps 106 and 108) has a predetermined range within the entire catalyst region of the CO shift unit 23 when the fuel cell system is activated. When the temperature is higher than the temperature, even if the catalyst region other than the predetermined range does not reach the predetermined temperature, the fuel gas is supplied to the fuel cell to start power generation. As a result, the amount of gas from the reforming unit 21 to the CO shift unit 23 and the reforming to be input to the reforming unit 21 is increased to an amount that can be processed in the catalyst range that is equal to or higher than a predetermined temperature (that is, the active temperature range of the catalyst). It is possible to limit the amount of fuel used, and the CO shift unit 23 can reliably reduce the carbon monoxide to an appropriate concentration at the time of startup. The time of start-up means from the start of start-up (time Tm0) until it is possible to start power generation with the maximum capacity (time Tm3), and includes the start of power generation smaller than the maximum capacity (time Tm1).

  Moreover, compared with the case where power generation is started only when the entire catalyst region of the CO shift unit 23 becomes equal to or higher than the activation temperature range, the startup time (time from the start of startup to the start of power generation) and startup energy can be reduced. In this way, the start-up time and start-up energy can be reduced while reliably reducing the carbon monoxide concentration.

  In addition, the carbon monoxide concentration can be reliably reduced even in a transient state at the time of startup. Furthermore, stable operation is possible by supplying low concentration of carbon monoxide, and efficient operation is possible.

  Further, since the power generation start means starts the power generation of the fuel cell 10 with a low power generation amount operation that has a lower power generation amount than the rated operation of the fuel cell 10, the amount of fuel input to the reforming unit 21 corresponding to the low power generation amount operation is reduced. The amount of gas from the reforming unit 21 to the CO shift unit 23 can be suppressed to a small amount. As a result, the catalyst range that is equal to or higher than the predetermined temperature can be small, so that the start-up time and start-up energy can be reduced while reliably reducing the carbon monoxide concentration. In particular, when the low power generation amount operation continues by the user, the carbon monoxide concentration can be reduced and the energy can be reduced, and the efficiency can be improved.

  The combustion section 25 is supplied with anode off-gas from the fuel electrode 11, burns the anode off-gas with combustion oxidizing gas, and heats the reforming section 21 with the combustion gas. The power generation start means starts power generation of the fuel cell 10 in a low hydrogen usage operation lower than the hydrogen usage rate at a predetermined power generation amount in a steady state of the fuel cell system. When the reforming unit 21 is heated using unused gas (anode offgas) from the fuel electrode 11 of the fuel cell 10 (for example, when anode offgas is burned in the combustion unit that heats the reforming unit), Since the amount of hydrogen used is small and the amount of hydrogen in the anode off-gas is relatively large, the amount of heat of combustion increases. Due to the increased amount of heat, the warming function of the reforming section 21 and thus the CO shift section 23 increases. As a result, the warm-up time of the CO shift unit 23 can be shortened. In addition, since an excess amount of heat can be used to warm up the CO shift unit 23 at the time of startup, the balance between power generation and hot water supply is maintained even when there is little hot water supply such as in summer, and energy efficiency is unlikely to decrease.

  In addition, the power generation control means performs the entire catalyst of the CO shift unit 23 between the time point when the fuel cell 10 can generate power with the minimum capacity (time Tm1) and the time point when power generation with the maximum capacity becomes possible (time Tm3). The fuel cell is generated using the power generation upper limit value set based on the temperatures S1 to S3 at a plurality of locations P1 to P3 located apart from each other in the region along the flow of the fuel gas from the inlet to the outlet. Let As a result, the catalyst range that is equal to or higher than the predetermined temperature (that is, the active temperature range of the catalyst) can be detected based on the temperatures at a plurality of locations. It is possible to limit the amount of gas to the shift unit 23 and hence the amount of reforming fuel to be input to the reforming unit 21, and the CO shift unit 23 can reliably reduce carbon monoxide to an appropriate concentration at the time of startup. it can.

  In addition, the carbon monoxide concentration can be reliably reduced even when there is an influence of temperature disturbance at the time of startup or the like.

  The first limit setting means sets the power generation upper limit value to the first upper limit value W1 when the temperature S1 of the most inlet side location P1 in the carbon monoxide shift reaction unit 23 is equal to or higher than the predetermined temperature S1a. If the temperature S2 (or S3) of the place P2 (or P3) located closer to the outlet side than the place on the most inlet side is equal to or higher than the predetermined temperature S2a (or S3a), The upper limit value is set to a second upper limit value W2 (or W3) that is greater than the first upper limit value W1. When the catalyst of the CO shift unit 23 is warmed up from the inlet side at the start-up, first, when the predetermined range from the inlet reaches a predetermined temperature or higher, the power generation output is set according to the power generation amount with the first upper limit as the upper limit. When the range including the place located on the exit side from the place on the most entrance side becomes equal to or higher than the predetermined temperature, the power generation output is controlled in accordance with the power generation amount with the second upper limit value larger than the first upper limit as the upper limit. be able to.

  Further, the temperature of the first place P1 closest to the inlet in the carbon monoxide shift reaction unit 23 is detected by the first temperature sensor 23c, and the first temperature sensor 23c detects that the temperature S1 of the first place P1 is equal to or higher than the predetermined temperature S1a. The carbon monoxide concentration in the fuel gas in an amount corresponding to the first upper limit value W1, which is the first power generation amount lower than the rated power generation amount of the fuel cell, is disposed at a catalyst amount position where the carbon monoxide concentration can be reduced below a predetermined concentration. Yes. As a result, the catalyst range that is equal to or higher than the predetermined temperature can be detected with certainty, and the power generation amount appropriate for the catalyst range can be reliably limited.

  Further, the temperature S2 of the second location P2 on the outlet side from the first location P1 is detected by the second temperature sensor 23d, and the second temperature sensor 23d detects that the temperature S2 of the second location P2 is equal to or higher than the predetermined temperature S2a. The carbon monoxide concentration in the fuel gas in an amount corresponding to the second upper limit value W2 that is the second power generation amount larger than the power generation amount W1 is disposed at a catalyst amount position where the carbon monoxide concentration can be reduced below a predetermined concentration. As a result, the catalyst range that is equal to or higher than the predetermined temperature can be detected with certainty, and the power generation amount appropriate for the catalyst range can be reliably limited.

  In addition, the temperature S3 of the third place P3 on the exit side from the second place P2 is detected by the third temperature sensor 23e, and the third temperature sensor 23e detects that the temperature S3 of the third place P3 is equal to or higher than the predetermined temperature S3a. The carbon monoxide concentration in the fuel gas in an amount corresponding to the third upper limit value W3, which is the third power generation amount larger than the power generation amount, is disposed at a catalyst amount position where the carbon monoxide concentration can be reduced below a predetermined concentration. As a result, the catalyst range that is equal to or higher than the predetermined temperature can be detected with certainty, and the power generation amount appropriate for the catalyst range can be reliably limited.

  In the above-described embodiment, the temperatures at a plurality of locations (first to third locations P1 to P3 in this embodiment) are predetermined in the order of the temperature on the inlet side to the temperature on the outlet side of the CO shift unit 23. The power generation upper limit is increased as the temperature rises. According to this, the CO shift unit 23 increases the temperature sequentially from the upstream at the time of startup, and an appropriate power generation amount corresponding to the catalyst range that has reached the predetermined temperature while the region above the predetermined temperature spreads from the upstream to the downstream. Can be surely limited.

  In the embodiment described above, the power generation start unit starts power generation of the fuel cell 10 in a low hydrogen utilization operation lower than the hydrogen utilization rate in a predetermined power generation amount in a steady state of the fuel cell system. In the reheating system, the power generation start means may start the power generation of the fuel cell by introducing more fuel for combustion than the provision for additional supply. According to this, in the reheating system, when the power generation is started, the combustion fuel is supplied more than the additional supply regulation, so that the amount of combustion heat increases. Due to the increased amount of heat, the warming function of the reforming section 21 and thus the CO shift section 23 increases. As a result, the warm-up time of the CO shift unit 23 can be shortened. The provision of additional supply is an additional supply amount that corresponds to the amount of heat that is normally supplemented in a steady state.

  The power generation start means starts power generation of the fuel cell 10 at a low hydrogen usage operation lower than the hydrogen usage rate at a predetermined power generation amount in a steady state of the fuel cell system, and additionally supplies combustion fuel together with this. You may make it throw more than regulation. According to this, in the reheating system, not only the combustion fuel is supplied more than the provision of additional supply at the start of power generation, but also the anode off gas containing a relatively large amount of hydrogen is supplied, so that the amount of heat of combustion increases. Due to the increased heat quantity, the warming power of the reforming part and thus the CO shift part is further increased. As a result, the warm-up time of the CO shift unit can be further shortened. It is also possible to adjust both as necessary.

1 is a schematic diagram showing an outline of an embodiment of a fuel cell system according to the present invention. It is a block diagram which shows the fuel cell system shown in FIG. 3 is a flowchart of a control program executed by the control device shown in FIG. It is a time chart which shows an example of the temperature of the CO shift part by the flowchart shown in FIG. 3, a user load, a power generation amount limit value, and a power generation amount. It is a time chart which shows an example of the temperature of a CO shift part by the flowchart shown in FIG. 3, and a hydrogen utilization factor.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Fuel cell, 11 ... Fuel electrode, 12 ... Air electrode, 20 ... Reformer, 21 ... Reformer, 21c ... Temperature sensor, 22 ... Cooling part (heat exchange part), 23 ... Carbon monoxide shift reaction part (CO shift part), 23c, 23d, 23e ... temperature sensor, 24 ... carbon monoxide selective oxidation reaction part (CO selective oxidation part), 24b ... temperature sensor, 25 ... combustion part, 26 ... evaporation part, 26a ... temperature sensor , 27 ... combustion gas flow path, 28 ... heat insulating part, 30 ... control device (power generation start means, power generation control means, first and second limit setting means), 41 ... reforming fuel supply pipe, 42 ... fuel pump, 43 ... Reforming fuel valve, 44 ... Combustion fuel supply pipe, 45 ... Combustion fuel valve, 46 ... Desulfurizer, 51 ... Steam supply pipe, 52 ... Feed water pipe, 53 ... Reforming water pump, 54 ... Reforming Water valve, 61 ... oxidation air supply pipe, 62 ... oxidation Air pump, 63 ... Oxidation air valve, 64 ... Combustion air supply pipe, 65 ... Combustion air pump, 66 ... Combustion air valve, 67 ... Cathode air supply pipe, 68 ... Cathode air pump, 69 ... Cathode Air valve, 71, 77 ... reformed gas supply pipe, 72 ... off gas supply pipe, 73 ... bypass pipe, 74 ... anode gas valve, 75 ... anode off gas valve, 76 ... bypass valve, 78 ... third reformed gas valve, 81 , 82 ... exhaust pipe, 89 ... connection pipe.

Claims (10)

A fuel cell that generates electric power from the fuel gas supplied to the fuel electrode and the oxidant gas supplied to the oxidant electrode;
A reforming section that is supplied with reforming fuel and reforming water to generate the fuel gas;
A carbon monoxide shift reaction section that is filled with a catalyst and that supplies the fuel electrode of the fuel cell with a reduced concentration of carbon monoxide in the fuel gas from the reforming section;
In a fuel cell system comprising:
When the fuel cell system is started up, when a predetermined range in the entire catalyst region of the carbon monoxide shift reaction unit is equal to or higher than a predetermined temperature, even when a catalyst region other than the predetermined range has not reached the predetermined temperature, The fuel gas is supplied to the fuel cell in a state where the reforming fuel to be fed into the reforming unit is limited to an amount that can be processed in the catalyst range of the carbon monoxide shift reaction unit that is equal to or higher than the predetermined temperature. A fuel cell system comprising power generation start means for starting power generation of the fuel cell with a low power generation amount operation that has a lower power generation amount than the rated operation of the fuel cell. The combustion part according to claim 1, further comprising a combustion part that is supplied with anode off-gas from the fuel electrode, burns the anode off-gas with combustion oxidant gas, and heats the reforming part with the combustion gas,
The fuel cell system is characterized in that the power generation start unit starts power generation of the fuel cell in a low hydrogen utilization operation lower than a hydrogen utilization rate at a predetermined power generation amount in a steady state of the fuel cell system. According to claim 1, in addition to the anode off-gas from the fuel electrode to heat the reforming section by the combustion gas burned in combustion oxidizing gas and the anode off-gas is supplied, only the anode off-gas combustion heat A combustion section that additionally supplies combustion fuel when the fuel is insufficient, burns the combustion fuel with the combustion oxidant gas, and heats the reforming section with the combustion gas;
The fuel cell system is characterized in that the power generation start means starts the power generation of the fuel cell by introducing more fuel for combustion than the provision for the additional supply. 4. The power generation start means according to claim 3 , wherein the combustion fuel is supplied at a low hydrogen utilization operation lower than a hydrogen utilization rate in a predetermined power generation amount in a steady state of the fuel cell system while supplying more fuel for combustion than the provision for the additional supply. A fuel cell system, wherein power generation of the fuel cell is started. In any one of claims 1 to 4, between the time that the fuel cell becomes possible power at the minimum capacity to the point where it became possible power at full capacity, the carbon monoxide shift reaction section Ru is generating the fuel cell power generation limit value set based on the temperature of a plurality of locations that are located away from the inlet along the flow of the fuel gas to the outlet of the total catalyst area as the upper limit of power generation amount fuel cell system comprising the power generation control unit. 6. The power generation control unit according to claim 5 , wherein the power generation control means sets the power generation upper limit value to the first upper limit value when the temperature at the most inlet side among the temperatures at the plurality of locations is equal to or higher than a predetermined temperature. When the temperature of one limit setting means and the location located on the outlet side from the most inlet side location is equal to or higher than a predetermined temperature, the power generation upper limit value is set to a second upper limit value that is greater than the first upper limit value. And a second restriction setting means. In Claim 5 , The temperature of the 1st place nearest to the entrance side among the temperature of these places is detected by the 1st temperature sensor, The temperature of the 1st place is more than predetermined temperature, A fuel cell, characterized in that it is disposed at a catalyst amount position that can reduce the concentration of carbon monoxide in the fuel gas in an amount corresponding to a first power generation amount lower than the rated power generation amount of the fuel cell to a predetermined concentration or less. system. The temperature of the second location on the outlet side from the first location is detected by a second temperature sensor according to claim 7 , and the second temperature sensor detects the first power generation when the temperature of the second location is equal to or higher than a predetermined temperature. A fuel cell system, wherein the fuel cell system is disposed at a catalyst amount position capable of reducing the carbon monoxide concentration in the fuel gas in an amount corresponding to the second power generation amount larger than the amount to the predetermined concentration or less. 9. The temperature of the third place on the outlet side from the second place is detected by a third temperature sensor according to claim 8 , and the third temperature sensor detects the second power generation when the temperature of the third place is equal to or higher than a predetermined temperature. A fuel cell system, wherein the fuel cell system is disposed at a catalyst amount position capable of reducing the carbon monoxide concentration in the fuel gas in an amount corresponding to the third power generation amount larger than the amount to the predetermined concentration or less. 6. The power generation upper limit value according to claim 5 , wherein the upper limit value of power generation is increased as the temperature at the plurality of places rises to a predetermined temperature or higher in order from the temperature at the inlet side of the carbon monoxide shift reaction unit to the temperature at the outlet side. Fuel cell system.

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