JP5401781B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system.

As a type of a hydrogen generator that can be used in a fuel cell system, one disclosed in Patent Document 1 is known. As shown in FIG. 1 of Patent Document 1, the hydrogen generator includes an outlet 20 for discharging the reformed gas to the outside, a temperature detecting means 7 provided at the outlet 20, and a temperature detecting means. And a control unit 8 that controls the heating temperature of the heating means 2 based on the detected value of 7.
Japanese Patent No. 3408521

  In the hydrogen generator described in Patent Document 1 described above, since the combustion of the heating means 2 is controlled by the temperature of the reforming section outlet, the responsiveness of the combustion control is slow, and the combustion exhaust gas is suppressed to low emission. There was a case that could not be done.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to improve the responsiveness of combustion control in a fuel cell system and reliably suppress combustion exhaust gas to low emissions.

In order to solve the above-described problems, the structural feature of the invention according to claim 1 is that a fuel cell that generates power using a fuel gas supplied to the fuel electrode and an oxidant gas supplied to the oxidant electrode, and a reforming A reforming unit that generates a fuel gas containing hydrogen by reforming the fuel, and during steady operation, only the anode off-gas from the fuel electrode of the fuel cell is supplied, and the anode off-gas is burned with combustion oxidant gas A combustion section that heats the reforming section with the combustion gas, a reforming fuel supply means that supplies reforming fuel to the reforming section, and a combustion oxidant gas that supplies combustion oxidant gas to the combustion section. A combustion section temperature control means for controlling the temperature of the combustion section by controlling the supply amount of the combustion oxidant gas by the combustion oxidant gas supply means. Reform by quality fuel supply means Reforming part temperature control means for controlling the temperature of the reforming part by controlling the supply amount of fuel, and the reforming part temperature control means has the temperature of the reforming part within a target temperature or a target temperature range. The target temperature or the target temperature range of the reforming unit temperature is a ratio of the heat amount of hydrogen consumed in the fuel cell to the heat amount of the reforming fuel supplied to the reforming unit. It is set by the process efficiency for each power generation load of the fuel cell and the temperature characteristic of the reforming section so as to be maximized, and the combustion section temperature control means performs control so that the temperature of the combustion section becomes the target temperature or the target temperature range. The target temperature or target temperature range of the temperature of the combustion section is such that the air ratio, which is the ratio of the actual combustion oxidant gas input amount and the ideal combustion oxidant gas input amount, is the combustion exhaust gas from the combustion portion. Is within the range of low emissions In addition, the optimal temperature set from the target temperature or target temperature range of the reforming section temperature set to maximize the process efficiency and the conversion rate-reforming section temperature characteristics for each power generation load of the fuel cell. It is set by the air ratio for each power generation load of the fuel cell-combustion part temperature characteristic in the conversion rate .

  The structural feature of the invention according to claim 2 is that, in claim 1, the reforming section temperature control means controls the fuel gas outlet temperature of the reforming section.

A structural feature of the invention according to claim 3 is that, in claim 1 or claim 2 , the combustion part temperature control means controls the radiation temperature of the flame generated in the combustion space of the combustion part.

According to a fourth aspect of the present invention, there is provided a structural feature of the third aspect , further comprising a temperature sensor for detecting a radiation temperature of a flame generated in the combustion space of the combustion section, wherein the temperature sensor is input to the combustion section. That is, the combustion oxidant gas is introduced into the combustion space from the side where the oxidant gas injection portion is provided and is fixed to the combustion portion.

The structural feature of the invention according to claim 5 is that, in claim 4 , the temperature sensor is a thermocouple or a thermistor.

The structural feature of the invention according to claim 6 is that, in claim 1 , the target temperature or target temperature range of the temperature of the combustion section is determined based on the temperature of the reforming section.

In the invention according to claim 1 configured as described above, the combustion section temperature control means controls the temperature of the combustion section by controlling the amount of combustion oxidant gas supplied by the combustion oxidant gas supply means. The reforming section temperature control means controls the reforming section temperature by controlling the amount of reforming fuel supplied by the reforming fuel supply section. Accordingly, the combustion in the combustion part can be controlled based on the temperature of the combustion part, not the combustion in the combustion part based on the temperature of the part other than the combustion part. The combustion exhaust gas from the combustion section can be reliably suppressed to low emission. Furthermore, since the reforming section temperature can be controlled to a desired temperature by adjusting the supply amount of the reforming fuel, the conversion ratio of the reforming fuel having a strong correlation with the reforming section temperature is set to a desired value. Control becomes possible.
Further, the combustion section temperature control means performs control so that the temperature of the combustion section becomes a target temperature or a target temperature range, and the reforming section temperature control means has a temperature of the reforming section that becomes a target temperature or a target temperature range. Thus, the combustion section temperature and the reforming section temperature can be appropriately and stably controlled.
Furthermore, since the target temperature or target temperature range of the temperature of the combustion section and the reforming section is determined according to the power generation load of the fuel cell, the operation can be performed with the optimal combustion state and the optimal conversion rate according to the fuel cell load. It becomes possible.

  In the invention according to claim 2 configured as described above, in the invention according to claim 1, the reforming section temperature control means controls the fuel gas outlet temperature of the reforming section. By controlling the optimal temperature, the reaction in the reforming section can be optimally controlled. Further, the fuel gas outlet temperature of the reforming section better reflects the reforming reaction of the reforming section.

In the invention according to claim 3 configured as described above, in the invention according to claim 1 or claim 2 , the combustion part temperature control means controls the radiation temperature of the flame generated in the combustion space of the combustion part. Therefore, since the temperature sensor can be installed at a relatively low temperature without detecting the temperature of the flame itself, the durability of the temperature sensor can be improved.

In the invention according to claim 4 configured as described above, the invention according to claim 3 further includes a temperature sensor that detects a radiation temperature of a flame generated in the combustion space of the combustion section, and the temperature sensor includes the combustion section. Since it has a structure that penetrates the combustion space and is fixed to the combustion portion from the side where the injection portion for the combustion oxidant gas that is input to is provided, the combustion oxidant gas that is input to the combustion portion The temperature sensor is cooled, and the durability of the temperature sensor can be further improved.

In the invention according to claim 5 configured as described above, in the invention according to claim 4 , since the temperature sensor is a thermocouple or a thermistor, the temperature of the combustion section is generally detected by an inexpensive temperature sensor. Can do.

By the way, the refueling-less system burns only the anode offgas in the fuel cell system in which the combustion fuel is not mixed with the anode offgas during the steady operation in which the anode offgas is burned in the combustion portion, that is, in the steady operation. This is a fuel cell system. In this refueling-less system, only the anode off gas is supplied to the combustion section and burned, so the combustion section temperature changes according to the composition of the anode off gas, that is, the conversion rate. The conversion rate varies depending on the reforming section temperature. The conversion rate can be substituted by the reforming section temperature, and the combustion section temperature can be determined according to the reforming section temperature. That is, in the invention according to claim 6 configured as described above, in the invention according to claim 1 , the target temperature or the target temperature range of the temperature of the combustion section is determined based on the temperature of the reforming section. It becomes possible to operate in an optimal combustion state for each conversion rate.

  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. The fuel cell system includes a fuel cell 10 and a reformer 20 that generates a reformed gas (fuel 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. Note that air-enriched gas may be supplied instead of air.

  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 reforming unit 21 is provided with a temperature sensor 21c that detects (measures) the temperature of the reforming unit 21 (reforming unit temperature: T1). The detection result of the temperature sensor 21 c is transmitted to the control device 30. The reforming section temperature may be the temperature of the catalyst 21b in the reforming section 21 or the temperature of the fluid flowing through the filling section of the catalyst 21b having a good correlation with the temperature of the catalyst 21b. The temperature of the packed portion of the catalyst 21b is preferably the temperature of the lower half region of the packed portion of the catalyst 21b in the flow direction. The temperature of the fluid flowing through the filling portion of the catalyst 21b may be the temperature of the fluid flowing in the filling portion of the catalyst 21b, or the temperature of the fluid flowing out of the filling portion of the catalyst 21b and almost equal to the temperature of the filling portion of the catalyst 21b ( Or the temperature of the fluid flowing through the outlet of the reforming unit 21). In the present embodiment, the temperature sensor 21 c is provided at the outlet of the reforming unit 21 and detects the outlet temperature of the reforming unit 21. Specifically, the temperature sensor 21c is provided at a position about 8 mm away in the gas flow direction from the outlet of the filling portion of the catalyst 21b (the outlet of the reforming portion 21). The temperature of the temperature sensor 21 c is equal to the fluid temperature at the outlet of the reforming unit 21.

  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 is reforming fuel supply means for supplying reforming fuel and adjusting 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 directly supplied to the combustion unit 25 and combusted is called combustion fuel.

  A steam supply pipe 51 connected to the evaporation section 26 is connected between the reforming fuel valve 43 of the reforming fuel supply pipe 41 and the cooling section 22. 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 evaporation unit 26 evaporates the reformed water to generate water vapor, and supplies the water vapor to the reforming unit 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 and adjusts the reforming water supply amount. The reforming water valve 54 opens and closes the water supply pipe 52.

  The evaporation unit 26 is provided with a temperature sensor 26 a that detects the temperature of water vapor in the evaporation unit 26. The detection result of the temperature sensor 26 a is transmitted to the control device 30. If the temperature of the water vapor can be detected, for example, the temperature sensor 26 a may be provided in the vicinity of the inlet of the cooling unit 22 or in the water vapor supply pipe 51 between the evaporation unit 26 and the cooling unit 22. The temperature of the water vapor is the temperature of the reforming water supplied to the reforming unit 21.

  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 temperature sensor 23c that measures the temperature in the CO shift unit 23 is provided. The detection result of the temperature sensor 23 c is transmitted to the control device 30.

  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. The reformed gas supply pipe 71 is provided with a first reformed gas valve 74 between the branch point of the bypass pipe 73 and the fuel cell 10. The off gas supply pipe 72 is provided with an off gas valve 75 between the junction with the bypass pipe 73 and the fuel cell 10. A second reformed gas valve 76 is provided in the bypass pipe 73.

  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 part 25 generates combustion gas for heating the reforming part 21 and supplying heat necessary for the steam reforming reaction. The lower end part is inserted into the inner peripheral wall of the reforming part 21. It is arranged with a space. As shown in FIG. 2, the combustion section 25 includes a base 25a, a cylindrical combustion cylinder 25b provided on the base 25a and communicating with the base 25a, an off-gas nozzle 25c, and a temperature sensor 25e. . The combustion unit 25 is ignited by an ignition electrode (not shown) according to a command from the control device 30.

  A combustion air supply pipe 64 is connected to the base portion 25a, and combustion air is introduced into the space 25a1 in the base portion 25a. The upper end (one end) of the combustion cylinder 25b is connected to the base portion 25a, and the lower side (the other end) is opened. A disc-shaped partition plate 25b1 is provided in the middle of the longitudinal direction of the combustion cylinder 25b, and partitions the combustion cylinder 25b in the longitudinal direction.

  The off-gas nozzle 25c passes through the base 25a, passes through the center of the partition plate 25b1, and extends to the combustion space 25d. The tip portion of the off-gas nozzle 25c is closed, and a first injection port 25c1 is provided on a side surface portion slightly away from the tip. The first injection port 25c1 has a substantially circular cross section, and a plurality of the first injection ports 25c1 are provided.

  The temperature sensor 25e detects the radiation temperature of the flame 25f generated in the combustion space 25d of the combustion unit 25 and transmits the detection result to the control device 30 (for example, a radiation thermometer). The temperature sensor 25e penetrates the combustion space 25d from the side (partition plate 25b1 side) provided with the second injection port 25b2 that is a charging portion for the combustion oxidant gas to be charged into the combustion portion 25, and burns into the combustion portion 25. It is structured to be fixed to.

  That is, the temperature sensor 25e is a sheath thermocouple, and is inserted into the combustion space 25d through the base 25a and through the partition plate 25b1. The tip portion (slightly behind the tip 25e1) is a temperature measurement unit. The tip 25e1 of the temperature sensor 25e is provided so as to be closer to the partition plate 25b1 than the end 25c2 of the first injection port 25c1 on the partition plate 25b1 side, but is not limited thereto. Any position where the temperature measuring unit of the temperature sensor 25e can measure the radiation temperature of the flame 25f may be used. Specifically, it suffices if it is outside the flame surface 25f1 of the flame 25f inside the combustion space 25d. Here, the flame surface refers to a boundary surface between a portion where a combustion reaction (oxidation reaction) of fuel gas (for example, anode off gas) occurs and a portion other than that. The combustion space 25d is a portion provided for burning the fuel gas, and is a space on the side where the tip of the off-gas nozzle 25c of the partition plate 25b1 protrudes in the combustion cylinder 25b.

  A plurality of second injection ports 25b2 (20 in the embodiment) are provided around the off-gas nozzle 25c of the partition plate 25b1. The off-gas nozzle 25c is connected to the off-gas supply pipe 72, and the anode off-gas is supplied from the off-gas supply pipe 72 to the off-gas nozzle 25c and is introduced into the combustion space 25d from the first injection port 25c1. Combustion air is supplied from the combustion air supply pipe 64 to the space 25a1 in the base portion 25a, and is introduced into the combustion space 25d from the second injection port 25b2. The anode off gas charged into the combustion space 25d is burned by the combustion air to form a flame 25f.

  In the present embodiment, a thermocouple is used as the temperature sensor 25e, but a thermistor may be used. The off-gas nozzle 25c is used not only for off-gas but also for reformed gas that bypasses the fuel cell 10. On the other hand, the combustion fuel is premixed with air and supplied from the combustion air supply pipe 64.

  Further, the temperature sensor 25e may be inserted into the combustion space 25d through one of the second injection ports 25b2. Since the tip portion of the temperature sensor 25e is cooled by the air ejected from the second injection port 25b2 into the combustion space 25d, the durability of the temperature sensor 25e can be further improved.

  According to the combustion section 25 having such a configuration, diffusion combustion is performed in which the anode off-gas or the reformed gas input from the first injection port 25a1 is burned with the combustion air input from the second injection port 25a2. it can. Further, it is possible to perform premixed combustion in which combustion fuel is mixed with combustion air in advance and injected from the second injection port 25a2 for combustion.

  The combustion air supply pipe 64 is provided with a combustion air pump (combustion oxidant gas supply means) 65 and a combustion air valve 66. The combustion air pump 65 sucks combustion air from the atmosphere and discharges it to the combustion unit 25, and adjusts the amount of combustion air supplied to the combustion unit 25 in accordance with a command from the control device 30. The combustion air valve 66 opens and closes the combustion air supply pipe 64 in accordance with a command from the control device 30.

  Furthermore, between the desulfurizer 46 and the reforming fuel valve 43 of the reforming fuel supply pipe 41, one end is connected between the fuel cell 10 of the reforming gas supply pipe 71 and the first reformed gas valve 74. The other end of the combustion fuel supply pipe 44 is connected. 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. One end is connected between the fuel cell 10 of the offgas supply pipe 72 and the offgas valve 75 and the other end is connected between the combustion air valve 66 of the combustion air supply pipe 64 and the combustion unit 25. A combustion fuel supply pipe 47 is provided. A combustion fuel valve 48 is provided in the combustion fuel supply pipe 47. The combustion fuel valve 48 opens and closes the combustion fuel supply pipe 47.

  From the time when the system is started to the time when the supply of the reforming fuel to the reforming unit 21 is started, the reforming fuel valve 43, the first reformed gas valve 74, and the offgas valve 75 are closed, and the combustion fuel. The valve 45 and the combustion fuel valve 48 are opened, and the fuel pump 42 is driven. As a result, the combustion fuel is directly supplied to the combustion section 25 through the combustion fuel supply pipe 44, the fuel cell 10 and the combustion fuel supply pipe 47 without passing through the reforming section 21.

  In addition, the reforming fuel valve 43 and the second reformed gas valve 76 are opened from the start of supply of the reforming fuel to the reforming unit 21 to the start of steady operation (power generation), and the combustion fuel valve 45 is opened. And the combustion fuel valve 48 is closed, and the fuel pump 42 is driven. The first reformed gas valve 74 and the offgas valve 75 remain closed. Thus, in order to avoid supplying reformed gas having a high carbon monoxide concentration from the CO selective oxidation unit 24 to the fuel cell 10, the reformed gas from the CO selective oxidation unit 24 is supplied to the fuel cell 10 in the combustion unit 25. Supplied directly without going through.

  During steady operation (power generation), the reforming fuel valve 43, the first reformed gas valve 74, and the offgas valve 75 are opened, and the combustion fuel valve 45, the combustion fuel valve 48, and the second reformed gas valve 76 are opened. Is closed and the fuel pump 42 is driven. As a result, the combustion portion 25 contains the anode off-gas from the fuel electrode 11 of the fuel cell 10 (hydrogen that has been supplied to the fuel electrode 11 of the fuel cell 10 and discharged without being consumed, or unreformed reforming fuel). Only the reformed gas is supplied. At this time, the combustion unit 25 does not recharge the combustion by separately adding a combustible gas such as a combustion fuel. This is a so-called reboundless system.

  As described above, in the combustion unit 25, the combustion fuel, reformed gas, or anode off gas (these are combustible gases) supplied to the combustion unit 25 are combusted by the combustion air supplied to the combustion unit 25. Hot combustion gas is generated. This combustion gas is formed between the reforming section 21 and the heat insulating section 28 and between the heat insulating section 28 and the evaporation section 26 and disposed so as to heat the reforming section 21 and the evaporation section 26. It flows through the flow path 27, passes through the exhaust pipe 81, and is discharged outside as combustion exhaust gas. The combustion gas heats the reforming catalyst 21a of the reforming unit 21 so as to be in the activation temperature range, and heats the evaporation unit 22 to generate water vapor.

  The fuel cell system also includes a control device 30, which includes the temperature sensors 21 c, 23 c, 24 b, 25 e, 26 a, the pumps 42, 53, 62, 65, 68, and the valves 43. , 45, 48, 54, 63, 66, 69, 74, 75, 76 and the combustion section 25 (ignition electrode) are connected (see FIG. 3). 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 is operating the fuel cell system. The RAM temporarily stores variables necessary for executing the program, and the ROM stores the program.

  Further, a storage device 31 is connected to the control device 30 (see FIG. 3). As shown in FIG. 4, the storage device 31 is a map or an arithmetic expression indicating a correlation (T1a = f1 (Wx)) between the power generation load (required power generation amount) Wx of the fuel cell 10 and the reformer temperature target value T1a. , And a map or an arithmetic expression indicating the correlation (T2a = f2 (Wx)) between the power generation load Wx of the fuel cell 10 and the combustion part temperature target value T2a. The power generation load of the fuel cell 10 is the power generation amount of the fuel cell 10 determined based on the power consumption (total power consumption) of the power load (home appliance) connected to the fuel cell 10. In FIG. 4, the horizontal axis represents the power generation load (W) and the vertical axis represents the temperature (° C.).

  A calculation method of a map or an arithmetic expression indicating the correlation (T1a = f1 (Wx)) between the power generation load Wx of the fuel cell 10 and the reforming unit temperature target value T1a will be described with reference to FIG. In FIG. 5, the correlation between the reforming part temperature (reforming part outlet temperature) and the process efficiency (process efficiency-reforming part temperature characteristic), the reforming part temperature (reforming part outlet temperature) and the conversion rate (Conversion rate-reforming part temperature characteristics).

  The correlation between the reforming section temperature (the reforming section outlet temperature) and the process efficiency is created based on data measured using an actual machine. The process efficiency is represented by the ratio of the amount of heat of hydrogen consumed in the fuel cell 10 to the amount of heat of the reforming fuel supplied to the reforming unit 21. Specifically, the reforming fuel is introduced into the reforming unit 21 at a specified supply amount corresponding to a predetermined power generation load, and the combustion amount (off gas / simulated off gas) in the combustion unit 25 is varied, thereby reforming. The process efficiency is measured while changing the outlet temperature. Based on the result, the process efficiency-reforming part temperature characteristic is derived. This process efficiency-reforming portion temperature characteristic is derived for each reforming fuel supply amount (for each power generation load) by changing the amount of reforming fuel supplied to the reforming portion 21.

  For example, the process efficiency-reforming portion temperature characteristic g1-1 shown by the solid line in FIG. 5 is defined as the reforming fuel corresponding to the intermediate power generation output Wmid between the minimum power generation output and the maximum power generation output of the fuel cell 10. The case of supply amount is shown. The process efficiency-reforming portion temperature characteristic g1-2 shown by the broken line in FIG. 5 shows the case where the specified supply amount of reforming fuel corresponding to the minimum power generation output Wmin of the fuel cell 10 is shown. The process efficiency-reforming part temperature characteristic g1-3 indicated by the one-dot broken line in FIG. 5 shows the case of the specified supply amount of reforming fuel corresponding to the maximum power generation output Wmax of the fuel cell 10.

  As is clear from this, each process efficiency-reforming part temperature characteristic g1-1 to g1-3 is convex and has a maximum value, and therefore, the reforming part temperature having the highest process efficiency is determined as the reforming part temperature. The target value can be set. For example, in the case of an intermediate power generation output, f1 (Wmid) is set as the reforming unit temperature target value T1a. Further, when the amount of reforming fuel supplied increases, that is, when the power generation load increases, the process efficiency-reforming portion temperature characteristic moves obliquely upward to the right (for example, from characteristic g1-1 to characteristic g1-3). The reforming section temperature target value T1a is increased. Conversely, when the supply amount of reforming fuel decreases, that is, when the power generation load decreases, the process efficiency-reforming portion temperature characteristic moves obliquely downward to the left (for example, from characteristic g1-1 to characteristic g1-2). The reforming section temperature target value T1a becomes smaller. Thus, since the reforming unit temperature target value can be calculated for each process efficiency-reforming unit temperature characteristic (that is, for each power generation load or for each reforming fuel supply amount), the power generation load Wx of the fuel cell 10 can be calculated. It is possible to calculate a map or an arithmetic expression indicating the correlation (T1a = f1 (Wx)) between the reforming unit temperature target value T1a.

  In FIG. 5, when the power generation load is Wmin, the reformer temperature target value T1a is f1 (Wmin), and when the power generation load is Wmid, the reformer temperature target value T1a is f1 (Wmid). When the load is Wmax, the reformer temperature target value T1a is f1 (Wmax).

  Next, a calculation method of a map or an arithmetic expression indicating the correlation (T2a = f2 (Wx)) between the power generation load Wx of the fuel cell 10 and the reforming unit temperature target value T2a will be described with reference to FIG. FIG. 6 shows the correlation (air ratio-combustion part temperature characteristic) between the air ratio λ and the combustion part temperature T2 for each conversion rate.

  The correlation between the air ratio λ and the combustion part temperature T2 for each conversion rate is created based on data measured using an actual machine. The air ratio λ is expressed by (actual combustion air input amount / ideal combustion air input amount). In order to change the air ratio λ, the actual input amount (supply amount) of combustion air may be changed. Specifically, at a predetermined conversion rate, reforming fuel is introduced into the reforming unit 21 at a specified supply amount corresponding to a predetermined power generation load, and the combustion unit temperature T2 is measured while changing the air ratio λ. Based on the result, the air ratio-combustion part temperature characteristic is derived. This air ratio-combustion section temperature characteristic is derived for each reforming fuel supply amount (for each power generation load) by changing the amount of reforming fuel supplied to the reforming section 21.

  For example, the air ratio-combustion part temperature characteristics (h1 (Xa), h1 (Xb), h1 (Xc), h1 (Xd)) of each conversion rate (Xa, Xb, Xc, Xd) are shown by the solid line in FIG. As shown in the figure, a case of a specified supply amount of reforming fuel corresponding to an intermediate power generation output Wmid between the minimum power generation output and the maximum power generation output of the fuel cell 10 is shown. Air ratio-combustion part temperature characteristics (h2 (Xa), h2 (Xb), h2 (Xc), h2 (Xd)) of each conversion rate (Xa, Xb, Xc, Xd) shown by broken lines in FIG. Shows the case of the specified supply amount of reforming fuel corresponding to the minimum power generation output Wmin of the fuel cell 10. Air ratio-combustion part temperature characteristics (h3 (Xa), h3 (Xb), h3 (Xc), h3 (Xd)) of each conversion rate (Xa, Xb, Xc, Xd) shown by a dashed line in FIG. ) Shows the case of the specified supply amount of reforming fuel corresponding to the maximum power output Wmax of the fuel cell 10. The relationship between the conversion rates is Xa <Xb <Xc <Xd.

  As is apparent from this, even with the same air ratio λ, the greater the conversion rate, the higher the combustor temperature T2. This is because the position and shape of the flame differ as the composition (methane concentration) in the anode off-gas changes. Therefore, in order to perform stable combustion, it is necessary to burn at an optimum conversion rate and to burn at a low emission range at the optimum conversion rate. That is, the combustion part temperature T2 corresponding to the air ratio λ of the intermediate value in the low emission range with respect to the optimum conversion rate may be set as the combustion part temperature target value.

  Further, when the supply amount of reforming fuel increases, that is, when the power generation load increases, the air ratio-combustion section temperature characteristic moves downward, and the combustion section temperature target value T2a decreases. On the other hand, when the supply amount of reforming fuel decreases, that is, when the power generation load decreases, the air ratio-combustion section temperature characteristic moves upward, and the combustion section temperature target value T2a decreases. That is, when compared with the same air ratio λ, when the power generation load is small, a small flame is formed near the injection port, so the combustion part temperature T2 becomes high. Conversely, when the power generation load is large, the flow rate is fast, and the flame is formed at a location far from the injection port, so the combustion section temperature T2 is lowered. Thus, since the combustion part temperature target value can be calculated for each air ratio-combustion part temperature characteristic of each conversion rate (that is, for each power generation load or each reforming fuel supply amount), the power generation load of the fuel cell 10 can be calculated. It is possible to calculate a map or an arithmetic expression indicating the correlation (T2a = f2 (Wx)) between Wx and the combustion part temperature target value T2a.

  In FIG. 6, the combustion portion temperature target value T2a at the optimum conversion rate Xc is taken as an example. The combustion part temperature target value T2a is f2 (Wmin) when the power generation load is Wmin, the combustion part temperature target value T2a is f2 (Wmid) when the power generation load is Wmid, and the combustion part temperature target when the power generation load is Wmax. The value T2a is f2 (Wmax).

  Incidentally, as shown in FIG. 5, the reforming section temperature (reforming section outlet temperature) and the conversion rate have a high correlation. This correlation is created based on data measured using a real machine. The conversion rate is the ratio of the reformed fuel supplied to the reforming unit 21 that has been reformed to hydrogen among the reformed fuel supplied to the reforming unit 21. Specifically, the reforming fuel is introduced into the reforming unit 21 at a specified supply amount corresponding to a predetermined power generation load, and the combustion amount (off gas / simulated off gas) in the combustion unit 25 is varied, thereby reforming. The conversion rate of the reformed gas flowing out (derived) from the reforming section 21 is derived while changing the section outlet temperature. Based on the result, the conversion rate-reforming part temperature characteristic is derived. The conversion rate-reforming portion temperature characteristic is such that the conversion rate increases as the reforming portion temperature increases. This conversion rate-reforming portion temperature characteristic is derived for each reforming fuel supply amount (for each power generation load) by changing the amount of reforming fuel supplied to the reforming portion 21.

  For example, the reforming fuel whose conversion rate-reforming portion temperature characteristic g2-1 shown by the solid line in FIG. 5 corresponds to a power generation output Wmid intermediate between the minimum power generation output Wmin and the maximum power generation output Wmax of the fuel cell 10 is shown. This shows the case of the specified supply amount. The conversion rate-reforming part temperature characteristic g2-2 shown by the broken line in FIG. 5 shows the case of a specified supply amount of reforming fuel corresponding to the minimum power generation output Wmin of the fuel cell 10. The conversion rate-reforming portion temperature characteristic g2-3 shown by the one-dot broken line in FIG. 5 shows the case of the specified supply amount of reforming fuel corresponding to the maximum power generation output Wmax of the fuel cell 10.

  As is clear from this, when the supply amount of reforming fuel increases, that is, when the power generation load increases, the conversion rate-reforming portion temperature characteristic moves downward (for example, from characteristic g2-1 to characteristic g2-3). Move). On the other hand, when the supply amount of reforming fuel decreases, that is, when the power generation load decreases, the conversion rate-reforming portion temperature characteristic moves upward (for example, moves from characteristic g2-1 toward characteristic g2-2). .

  Further, as described above, it is preferable to set the reforming section temperature having the highest process efficiency as the reforming section temperature target value. When the power generation load is Wmid, the reforming section temperature target value T1a is f1 (Wmid). . When the reforming section temperature is f1 (Wmid), the optimum conversion ratio is Xc from the conversion ratio-reforming section temperature characteristic. That is, the conversion rate of the reforming unit 21 is set to the optimum conversion rate Xc by adjusting the supply amount of the reforming fuel so that the reforming unit temperature becomes the reforming unit temperature target value T1a (= f1 (Wmid)). Can be adjusted. Specifically, when the reforming section temperature is higher than the reforming section temperature target value T1a, the anode off-gas heat quantity is decreased by decreasing the reforming fuel supply amount, thereby lowering the reforming section temperature. On the contrary, when the reforming section temperature is lower than the reforming section temperature target value T1a, the anode off-gas heat quantity is increased by increasing the reforming fuel supply amount, and the reforming section temperature is raised.

  It is preferable to set the reforming section temperature having the highest process efficiency as the target value. In addition to the process efficiency, the target value is determined based on the conditions under which the fuel cell system (fuel cell, reformer, etc.) can be stably operated. Specifically, if the conversion rate is too low, the rate of change of the conversion rate (hydrogen generation amount) with respect to the reformed gas temperature (reforming unit outlet temperature) increases. Therefore, the lower limit of the conversion rate is set, and the target value is set within a range not lower than this.

  Furthermore, even at the same air ratio λ, the greater the conversion rate, the higher the combustion section temperature T2. This is because the position and shape of the flame differ as the composition (methane concentration) in the anode off-gas changes. Therefore, in order to perform stable combustion, it is necessary to burn at the optimum conversion rate Xc and to burn in the low emission range at the optimum conversion rate Xc. That is, it is necessary to adjust the supply amount of the combustion air so that the combustion section temperature T2 corresponding to the intermediate air ratio λ in the low emission range with respect to the optimum conversion rate becomes the combustion section temperature target value T2a. Specifically, when the combustion air is increased (high λ) in a prescribed combustible gas, the flame moves away from the injection port, and when the combustion air is decreased (low λ), the flame moves closer to the injection port. . That is, if the temperature is low λ, the combustion zone temperature T2 is high, and if it is high λ, the combustion zone temperature T2 is low. Therefore, the combustion zone temperature is such that the CO and NOx concentration in the flue gas is below the specified concentration. The supply amount of combustion air is adjusted so as to be T2.

  Thus, by controlling the conversion rate of the reforming section 21 optimally at the reforming section temperature and optimally controlling the combustion of the combustion section 25 at the combustion section temperature, high efficiency operation and low emission can be obtained. Combustion control becomes possible.

  Further, the temperature of the combustor varies depending on the composition of the anode off gas, that is, the conversion rate. The conversion rate varies depending on the reforming section temperature. The conversion rate can be substituted by the reforming section temperature, and the combustion section temperature can be determined according to the reforming section temperature. That is, since the target temperature or target temperature range of the temperature of the combustion section is determined based on the temperature of the reforming section, it is possible to operate in an optimal combustion state for each conversion rate. At this time, as shown in FIG. 7, a map indicating the combustion part temperature target value with respect to the reforming part temperature may be used. This map can be easily derived by using the maps shown in FIGS. This map is stored in the storage device 31.

  The operation of the fuel cell system described above will be described. When a start switch (not shown) is turned on at time t0, control device 30 starts the start-up operation of the fuel cell system. That is, the fuel cell system enters the warm-up mode. The control device 30 opens the combustion air valve 66 and drives the combustion air pump 65 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 closes the reforming fuel valve 43, the first reformed gas valve 74, and the offgas valve 75, opens the combustion fuel valves 45 and 48, drives the fuel pump 42, and supplies the combustion fuel. The fuel is supplied directly to the combustion unit 25 via the fuel cell 10. 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.

  When activated, the control device 30 supplies a predetermined amount of water to the evaporation unit 26 (if the system is in negative pressure, the water is supplied after the negative pressure is eliminated), and the supply of water is temporarily stopped. To do. 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.). The control device 30 starts supplying water at a predetermined flow rate to the evaporation unit 26 after confirming the generation of water vapor.

  Thereafter, the control device 30 opens the reforming fuel valve 43, closes the combustion fuel valves 45 and 48, the first reformed gas valve 74 and the offgas valve 75, drives the fuel pump 42, and reforms the fuel. Is supplied 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. The reformed gas derived from the reforming unit 21 is reduced in carbon monoxide gas by the CO shift unit 23 and the CO selective oxidation unit 24 and is derived from the CO selective oxidation unit 24 without passing through the fuel cell 10. The fuel is directly supplied to the combustion unit 25 through the bypass pipe 73 and burned.

  Although there is no reformed output gas temperature control (reformer outlet temperature control) for the combustion mode and the start-up mode during combustion of the reformed gas bypassing the fuel cell 10, the air ratio λ-combustor temperature in each mode Combustion control is performed using the T2 temperature map (FIG. 6).

  During the generation of the reformed gas, the control device 30 uses the temperature sensor 24b (and / or the temperature sensor 23c) to control the temperature of the catalyst 24a of the CO selective oxidation unit 24 (and / or the catalyst 23b of the CO shift unit 23). If the detected temperature is equal to or higher than the predetermined temperature, the first reformed gas valve 74 and the offgas valve 75 are opened assuming that the carbon monoxide concentration in the reformed gas is equal to or lower than the predetermined low concentration. The second reformed gas valve 76 is closed to connect the CO selective oxidation unit 24 to the inlet of the fuel electrode 11 of the fuel cell 10 and to the outlet of the fuel electrode 11 to the combustion unit 25. Thereby, the start-up operation for warming up the fuel cell system is completed, and then the steady operation is started. That is, the fuel cell system enters the power generation mode.

  In the power generation mode, the control device 30 supplies the reforming fuel, the combustion air, the oxidizing air, the cathode air, and the reforming water so as to obtain a desired output power (current / power consumed by the load device). It comes to supply. That is, the control device 30 calculates the supply amount of the reforming fuel at the start of power generation or when the power generation load is changed, and drives the fuel pump 42 so as to be the supply amount.

  Specifically, when starting the steady operation, the control device 30 executes the program shown in FIG. 8A every predetermined short time Ta. The control device 30 acquires the required power generation amount (power generation load) for the fuel cell 10 in step 102, and determines in step 104 whether or not the power generation load has changed. At the start of power generation, it is determined whether power generation has started.

  The control device 30 determines “YES” in step 104 when power generation is started or when the power generation load is changed, and the reforming fuel is supplied based on the required power generation amount (power generation load) for the fuel cell 10 acquired previously. An amount (required fuel supply amount) is determined (step 106), and the fuel pump 42 is driven with the determined supply amount (step 108). Further, the control device 30 is a map or an arithmetic expression indicating the correlation (T2a = f2 (Wx)) between the power generation load previously acquired in step 102 and the power generation load Wx of the fuel cell 10 and the combustion part temperature target value T2a. (See FIG. 4), the combustion part temperature target value T2a is derived (step 110). For example, when the power generation load is Wa, the combustion part temperature target value T2a is f2 (Wa).

  The control device 30 is a map or an arithmetic expression (T1a = f1 (Wx)) indicating the correlation (T1a = f1 (Wx)) between the power generation load previously acquired in step 102 and the power generation load Wx of the fuel cell 10 and the reforming unit temperature target value T1a The reforming part temperature target value T1a is derived from (see FIG. 4) (step 112). For example, when the power generation load is Wa, the reforming unit temperature target value T1a is f1 (Wa).

  On the other hand, when the power generation load is not changed at the start of power generation, the control device 30 does not execute the processes of steps 106 to 112 while the power generation load is not changed after the start of power generation.

  Thus, after the reforming fuel supply amount is determined at the start of power generation or when the power generation load is changed and the fuel pump 42 is driven by the supply amount, the control device 30 controls the combustion air supply amount at a predetermined short cycle. In parallel with this, the reforming fuel supply amount is controlled in a predetermined long cycle. This is due to the following reason. The combustor temperature T2 is fast in response and needs to be controlled in a short cycle. On the other hand, the reformer outlet temperature T1 is slow in responsiveness, and as a swell factor from the specified value (width), the reforming fuel flow rate (supply amount) is mainly shifted from the indicated value. This is because it can be considered.

  Specifically, the control device 30 executes the program shown in FIG. 8B every predetermined short time Tb (with a predetermined short cycle). The short time Tb is the same time as the short time Ta. In step 202, the control device 30 acquires the combustion section temperature T2 by the temperature sensor 25e, and the combustion section temperature T2 is used for combustion so that the acquired combustion section temperature T2 becomes the combustion section temperature target value T2a previously derived in step 110. The combustion air supply amount is controlled by the combustion air pump 65 which is an air supply means (combustion part temperature control means).

  Further, the control device 30 executes the program shown in FIG. 8C every predetermined long time (with a predetermined long cycle). This long time Tc is longer than the short time Tb. In step 302, the control device 30 acquires reforming unit temperature T1 by the temperature sensor 21c, and is a reforming fuel supply means so that the acquired reforming unit temperature T1 becomes the reforming unit temperature target value T1a. The fuel supply amount for reforming is controlled by the fuel pump 42 (reforming section temperature control means).

  Further, the control device 30 calculates the supply amount of reforming water based on the supply amount of reforming fuel and the S / C (steam carbon ratio), and drives the reforming water pump 53 so as to obtain the supply amount. ing. The control device 30 calculates the supply amount of the oxidation air so that the amount of carbon monoxide is not more than a predetermined amount, and drives the oxidation air pump 62 so as to obtain the supply amount. Then, the control device 30 calculates the supply amount of cathode air sufficient to react with the reformed gas supplied from the reformer 20, and drives the cathode air pump 68 so as to obtain the supply amount. . When the stop switch is pushed, the fuel cell system performs a stop operation and stops.

  As is apparent from the above description, in this embodiment, the combustion section temperature control means (step 202) is operated by the combustion oxidant gas supply means (combustion air pump 65) for the combustion oxidant gas (combustion oxidant gas). The temperature of the combustion unit 25 is controlled by controlling the supply amount of air), and the reforming unit temperature control means (step 302) supplies the reforming fuel supply amount by the reforming fuel supply means (fuel pump 42). To control the temperature of the reforming section 21. Thereby, the combustion in the combustion unit 25 can be controlled based on the temperature of the combustion unit (combustion space temperature), instead of controlling the combustion in the combustion unit 25 based on the temperature of the part other than the combustion unit 25. Therefore, the responsiveness of the combustion control can be improved and the combustion exhaust gas from the combustion unit 25 can be reliably suppressed to low emission. Furthermore, since the reforming section temperature can be controlled to a desired temperature by adjusting the supply amount of the reforming fuel, the conversion ratio of the reforming fuel having a strong correlation with the reforming section temperature is set to a desired value. Control becomes possible.

  The control of the combustion air supply amount and the control of the reforming fuel supply amount are performed in parallel. As a result, it is possible to suppress and appropriately control the divergence of the combustion section temperature regardless of which of the combustion air supply amount and the reforming fuel supply amount is changed.

  Further, since the reforming unit temperature control means controls the fuel gas outlet temperature of the reforming unit 21, the reaction in the reforming unit 21 is optimally controlled by controlling the optimum temperature as the reforming unit temperature. can do. That is, the fuel gas outlet temperature of the reforming unit 21 better reflects the reforming reaction of the reforming unit 21, and the fuel gas outlet temperature of the reforming unit 21 is controlled to an optimum temperature so that the reforming unit 21 The reaction at 21 can be optimally controlled.

  Further, the combustion section temperature control means performs control so that the temperature of the combustion section 25 becomes the target temperature or the target temperature range, and the reforming section temperature control means controls the temperature of the reforming section to be the target temperature or the target temperature range. Therefore, the combustion section temperature and the reforming section temperature can be appropriately and stably controlled.

  Further, since the combustion part temperature control means controls the radiation temperature of the flame generated in the combustion space of the combustion part 25, the temperature sensor 25e can be installed in a relatively low temperature place without detecting the temperature of the flame itself. Therefore, the durability of the temperature sensor 25e can be improved.

  The temperature sensor 25e further includes a temperature sensor 25e (for example, a thermocouple or a thermistor) that detects the radiation temperature of the flame generated in the combustion space of the combustion unit 25, and the temperature sensor 25e contains the oxidant gas for combustion input to the combustion unit 25. The temperature sensor 25e is cooled by the oxidant gas for combustion introduced into the combustion section 25 because the structure penetrates the combustion space from the side where the introduction section is provided and is fixed to the combustion section 25. The durability of the sensor 25e can be further improved. Depending on the position of the temperature sensor 25e, it is also cooled by the anode off gas.

  Moreover, since the temperature sensor 25e is a thermocouple, the temperature of the combustion part can be detected by a generally inexpensive temperature sensor.

  By the way, the refueling-less system is a fuel cell system in which combustion fuel is not mixed with the anode off gas during the steady operation in which the anode off gas is burned in the combustion unit 25, that is, only the anode off gas in the combustion unit 25 during the steady operation. It is a fuel cell system that burns. In this refueling-less system, only the anode off gas is supplied to the combustion section 25 and burned, so that the combustion section temperature changes according to the composition of the anode off gas, that is, the conversion rate. The conversion rate varies depending on the reforming section temperature. The conversion rate can be substituted by the reforming section temperature, and the combustion section temperature can be determined according to the reforming section temperature. That is, since the target temperature or target temperature range of the temperature of the combustion unit 25 is determined based on the temperature of the reforming unit 21, operation can be performed in an optimal combustion state for each conversion rate.

  Further, since the target temperature or the target temperature range of the temperature of the combustion section 25 and the reforming section 21 is determined according to the power generation load of the fuel cell 10, the optimal combustion state and the optimal conversion are determined according to the load of the fuel cell 10. Driving at a rate is possible.

  Further, the target temperature or the target temperature range of each temperature of the combustion unit 25 and the reforming unit 21 is each map or each showing the relationship between the power generation load of the fuel cell 10 and the temperature of the combustion unit 25 and the temperature of the reforming unit 21. Since it is determined using the function, the combustion section temperature and the reforming section temperature can be easily controlled.

  In addition, a fuel cell 10 that generates power using the fuel gas and the oxidant gas respectively supplied to the fuel electrode 11 and the oxidant electrode 12, and a reforming unit that generates a fuel gas containing hydrogen by reforming the reforming fuel. 21 and a combustion section 25 that is supplied with a combustible gas, burns the combustible gas with a combustion oxidant gas, and heats the reforming section 21 with the combustion gas. 25 is further provided with a temperature sensor 25e which is disposed in the combustion space 25 and detects the radiation temperature of the flame generated in the combustion space. Thereby, the temperature of the combustion part 25 can be detected reliably and early without being affected by the reforming part 21 as much as possible. Therefore, instead of controlling the combustion in the combustion unit 25 based on the temperature of the portion other than the combustion unit 25, the combustion in the combustion unit 25 can be controlled based on the temperature of the combustion unit 25. Responsiveness can be improved, and combustion exhaust gas from the combustion section 25 can be reliably suppressed to low emission.

1 is a schematic diagram showing an outline of an embodiment of a fuel cell system according to the present invention. It is sectional drawing which shows the combustion part shown in FIG. It is a block diagram which shows the fuel cell system shown in FIG. The map showing the correlation between the power generation load of the fuel cell and the reforming unit temperature target value and the correlation between the power generation load of the fuel cell and the combustion unit temperature target value, which are stored in the storage device shown in FIG. It is a map to show. It is a figure which shows the conversion rate-reforming part temperature characteristic, and process efficiency-reforming part temperature characteristic. It is a figure which shows the air ratio-combustion part temperature characteristic for every conversion rate. It is a figure which shows the relationship between reforming part temperature and combustion part temperature. (A)-(c) is a flowchart of the control program performed with the control apparatus shown in FIG. 3, (a) is a fuel supply amount for reforming, combustion at the time of a power generation start, and a power generation load change. The part temperature target value and the reforming part temperature target value are derived, (b) is for controlling the combustion part temperature, and (c) is for controlling the reforming part temperature.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Fuel cell, 11 ... Fuel electrode, 12 ... Air electrode, 20 ... Reformer, 21 ... Reforming part, 21c ... Temperature sensor (reforming part temperature detection means), 22 ... Cooling part (heat exchange part), 23 ... Carbon monoxide shift reaction part (CO shift part), 24 ... Carbon monoxide selective oxidation reaction part (CO selective oxidation part), 25 ... Combustion part, 25a ... Base part, 25b ... Combustion cylinder, 25c ... Off-gas nozzle, 25e ... Temperature sensor (combustion part temperature detection means) 26 ... Evaporation part, 27 ... Combustion gas flow path, 28 ... Heat insulation part, 30 ... Control device (reforming part temperature control means, combustion part temperature control means), 41 ... Fuel supply Pipe, 42 ... Fuel pump (reforming fuel supply means), 43 ... Reforming fuel valve, 44, 47 ... Combustion fuel supply pipe, 45, 48 ... Combustion fuel valve, 46 ... Desulfurizer, 51 ... Steam Supply pipe 52 ... Water supply pipe 53 ... Reformed water pump 54 Reformed water valve, 61 ... oxidizing air supply pipe, 62 ... oxidizing air pump, 63 ... oxidizing air valve, 64 ... combustion air supplying pipe, 65 ... combustion air pump (combustion oxidant gas supply means) , 66 ... Combustion air valve, 67 ... Cathode air supply pipe, 68 ... Cathode air pump, 69 ... Cathode air valve, 71 ... Reformed gas supply pipe, 72 ... Off gas supply pipe, 73 ... Bypass pipe, 74 ... 1st reformed gas valve, 75 ... Off gas valve, 76 ... 2nd reformed gas valve, 81, 82 ... Exhaust pipe, 89 ... Connecting pipe.

Claims (6)

A fuel cell that generates electric power using the fuel gas supplied to the fuel electrode and the oxidant gas supplied to the oxidant electrode;
A reforming section for generating the fuel gas containing hydrogen by reforming the reforming fuel;
During steady operation, only the anode off gas from the fuel electrode of the fuel cell is supplied, the anode off gas is burned with a combustion oxidant gas, and the reforming unit is heated with the combustion gas;
Reforming fuel supply means for supplying reforming fuel to the reforming section;
A fuel cell system comprising a combustion oxidant gas supply means for supplying a combustion oxidant gas to the combustion section,
Combustion part temperature control means for controlling the temperature of the combustion part by controlling the supply amount of the combustion oxidant gas by the combustion oxidant gas supply means;
Reforming part temperature control means for controlling the temperature of the reforming part by controlling the supply amount of the reforming fuel by the reforming fuel supply means,
The reforming unit temperature control means performs control so that the temperature of the reforming unit becomes a target temperature or a target temperature range,
The target temperature or the target temperature range of the temperature of the reforming unit has the largest process efficiency, which is the ratio of the amount of heat of hydrogen consumed in the fuel cell to the amount of heat of the reforming fuel supplied to the reforming unit. So as to be set by the process efficiency-reforming part temperature characteristics for each power generation load of the fuel cell,
The combustion part temperature control means performs control so that the temperature of the combustion part becomes a target temperature or a target temperature range,
The target temperature or target temperature range of the temperature of the combustion section is such that an air ratio, which is a ratio of the actual input amount of the combustion oxidant gas and the ideal input amount of the combustion oxidant gas, is from the combustion portion. The target temperature or the target temperature range of the reforming part temperature set so that the process efficiency is maximized so that the combustion exhaust gas in the range of low emission is within the range where the emission is low, and for each power generation load of the fuel cell A fuel cell system, which is set by an air ratio for each power generation load of the fuel cell and a combustion part temperature characteristic at an optimum conversion ratio set from the conversion ratio-reforming part temperature characteristic .   2. The fuel cell system according to claim 1, wherein the reforming section temperature control means controls the fuel gas outlet temperature of the reforming section. 3. The fuel cell system according to claim 1 , wherein the combustion part temperature control means controls a radiation temperature of a flame generated in a combustion space of the combustion part. The temperature sensor according to claim 3 , further comprising a temperature sensor that detects a radiation temperature of a flame generated in the combustion space of the combustion section.
The temperature sensor has a structure that penetrates the combustion space and is fixed to the combustion part from the side where the injection part for the combustion oxidant gas supplied to the combustion part is provided. A fuel cell system. 5. The fuel cell system according to claim 4 , wherein the temperature sensor is a thermocouple or a thermistor. 2. The fuel cell system according to claim 1 , wherein a target temperature or a target temperature range of the temperature of the combustion section is determined based on a temperature of the reforming section.

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