JP2014002921A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell system capable of sufficiently reducing the density of CO contained in a hydrogen-containing gas supplied to the fuel cell while preventing thermal runaway of a selective oxidation section.SOLUTION: The fuel cell system includes: a hydrogen generation device 1 having a reforming unit 14 that generates a hydrogen-containing gas by means of reforming reaction, a selective oxidation section 17 that reduces the density of carbon monoxide contained in the hydrogen-containing gas by means of selective oxidation reaction, and a selective oxidation temperature detection section 20; a fuel cell 2; a control section 12 that sets an upper limit value W of a power output from the fuel cell; and storage for storing actual power output Wr from the fuel cell when the control section issues an instruction to the fuel cell to output the power at a rated power output value Wmax. Defining difference ▵W as a value obtained by subtracting the actual power output Wr from the rated power output value Wmax, when the temperature of the selective oxidation section is equal to or smaller than a threshold value T, the control section sets the upper limit value W of the power output to Wmax; and when the temperature of the selective oxidation section exceeds the threshold value T, the control section sets the upper limit value W of the power output to a value W2 obtained by subtracting the difference ▵W from W1 which is a value smaller than Wmax.

Description

  The present invention relates to a fuel cell system.

  Development of a fuel cell system using a fuel cell stack (hereinafter simply referred to as “fuel cell”) that enables small-sized and highly efficient power generation as a distributed energy supply source is underway. A fuel cell system supplies a hydrogen-containing gas and an oxygen-containing gas to a fuel cell, which is the main body of a power generation unit, and proceeds with an electrochemical reaction between hydrogen and oxygen to generate chemical energy. This is a system that generates electricity by taking it out as natural energy.

  In general, hydrogen-containing gas is not supplied from the infrastructure. Therefore, the conventional fuel cell system uses a city gas supplied from an existing infrastructure or LPG as a raw material, and undergoes a reforming reaction with water vapor at a temperature of 600 to 700 ° C. using a Ru catalyst or a Ni catalyst. A hydrogen generation apparatus including a reforming unit is provided. Note that the hydrogen-containing gas obtained by the reforming reaction usually contains carbon monoxide derived from the raw material, and if the concentration is high, the power generation characteristics of the fuel cell are degraded.

  Therefore, in addition to the reforming unit, the hydrogen generator has a Cu—Zn-based catalyst or a noble metal that reduces carbon monoxide by advancing a transformation reaction between carbon monoxide and water vapor at a temperature of 200 ° C. to 350 ° C. A Ru catalyst or a Pt catalyst that adds a system catalyst and air as an oxidizing agent and selectively oxidizes carbon monoxide at a temperature of 100 ° C. to 200 ° C. to further reduce carbon monoxide. A reaction unit such as a selective oxidation unit is provided.

  The selective oxidation reaction is represented by the formula (1).

CO + 1 / 2O2 → CO2 (1)
The selective oxidation reaction is an exothermic reaction, and when the air (oxygen) flow rate is increased, the exothermic reaction proceeds and the temperature of the selective oxidation unit increases. On the other hand, when the air (oxygen) flow rate is lowered, the exothermic reaction is suppressed and the temperature of the selective oxidation unit is lowered.

  In order to reduce carbon monoxide derived from the raw material contained in the hydrogen-containing gas, generally, the air flow rate supplied to the selective oxidation unit is determined according to the raw material flow rate supplied to the reforming unit.

  By the way, in the long-term operation of the fuel cell system or the like, when the mixing of the air supplied to the selective oxidation unit and the hydrogen-containing gas becomes uneven, or the air supplied to the selective oxidation unit and the hydrogen-containing gas In the case where a mixed gas flow is unevenly distributed, a portion where the ratio of the air (oxygen) flow rate to the carbon monoxide flow rate is locally high in the selective oxidation unit, the carbon monoxide flow rate, and the air (oxygen) flow rate. In this part, the selective oxidation reaction (exothermic reaction) is accelerated, the temperature of a part of the selective oxidation part rises excessively, and is dragged by it. There was a fear of rising.

  Further, in the selective oxidation part, when the temperature of the selective oxidation part rises to around 190 ° C. to 200 ° C., in addition to the selective oxidation reaction, hydrogen and carbon monoxide contained in the hydrogen-containing gas, and methane by hydrogen and carbon dioxide Methanation begins to occur. The methanation reaction is represented by formulas (2) and (3).

CO + 3H2 → CH4 + H2O (2)
CO2 + 4H2 → CH4 + 2H2O (3)
The methanation reaction is an exothermic reaction similar to the selective oxidation reaction, and when the methanation reaction starts to occur, the exothermic reaction is accelerated, the temperature of the selective oxidation portion is increased, and the methanation reaction is further accelerated. As a result, the temperature of a part of the selective oxidation unit rises excessively, and the temperature of the entire selective oxidation unit is likely to be thermally runaway.

  Therefore, for example, Patent Document 1 discloses that when the temperature of the catalyst layer of the selective oxidation unit exceeds the upper limit temperature for the purpose of preventing the temperature of the selective oxidation unit from excessively rising, A technique for reducing the supply amount per unit time (corresponding to the air flow rate of the present invention) is disclosed.

JP 2010-262747 A

  However, in the conventional technique, there is no mention of durability deterioration due to long-time operation, and there is a problem that the carbon monoxide concentration (hereinafter referred to as “CO”) cannot be sufficiently reduced in the selective oxidation portion of the fuel cell system. there were. When the concentration of CO contained in the hydrogen-containing gas supplied to the fuel cell increases, there is a risk that the power generation output decreases due to CO poisoning of the fuel cell, or the life of the fuel cell decreases.

  The present invention solves the above-described conventional problem, and can sufficiently reduce the CO concentration of the hydrogen-containing gas supplied to the fuel cell while sufficiently suppressing thermal runaway of the temperature of the selective oxidation unit. An object is to provide a battery system.

  As a result of intensive studies, the present inventors have found that there is still room for improvement after durability deterioration due to long-time operation from the viewpoint of sufficiently reducing the CO concentration of the hydrogen-containing gas supplied to the fuel cell. It was.

  That is, in the above conventional technique, in order to sufficiently lower the temperature of the selective oxidation unit, if the flow rate of air supplied to the selective oxidation unit is reduced, it may be necessary to excessively reduce the air flow rate. In this case, it has been found that there is a problem that the air flow rate necessary for oxidizing the CO in the selective oxidation unit is insufficient, and the CO concentration cannot be sufficiently reduced in the selective oxidation unit. If the CO concentration cannot be sufficiently reduced in the selective oxidation part, the noble metal catalyst of the fuel cell may be poisoned and the catalytic activity may be lowered.

  Hereinafter, the problems of the conventional technique found by the present inventors will be described in more detail.

  FIG. 4 is a graph showing an example of the relationship between the CO concentration contained in the hydrogen-containing gas and the temperature of the selective oxidation unit. When the air flow rate command value is lowered from the reference value (for example, the air flow rate command value corresponding to O2 / CO = 2.0 is reduced to the air flow rate command value corresponding to O2 / CO = 1.7), the selective oxidation temperature is reduced. There was a tendency for the CO concentration to increase.

  For example, when the allowable CO concentration for preventing CO poisoning of the fuel cell is set to 20 ppm, in order to make the CO concentration less than 20 ppm, the air flow rate command value based on O2 / CO = 2.0 is used. In this case, an air flow rate command value equivalent to O2 / CO = 1.8 or more is required.

  However, with the air flow rate command value corresponding to O2 / CO = 1.8, the temperature of the selective oxidation unit can be lowered only to the lower limit of the temperature range in which the temperature of the selective oxidation unit reaches thermal runaway. There was a fear that it was not possible to sufficiently prevent the temperature of the battery from reaching a thermal runaway. In order to lower the temperature of the selective oxidation section to the upper limit of the temperature range suitable for the selective oxidation reaction, it is necessary to lower the air flow rate command value from O2 / CO = 2.0 equivalent to 1.6 equivalent.

  That is, when the air flow rate command value is lowered from the reference value, if the air flow rate is lowered excessively, the CO concentration contained in the hydrogen-containing gas may increase. On the other hand, if the CO concentration is to be sufficiently reduced, the temperature of the selective oxidation portion cannot be sufficiently reduced, and thermal runaway may not be sufficiently suppressed.

  Further, as shown in FIG. 2, the power generation output of the fuel cell is lower than the power generation output command value due to durability deterioration due to long-time operation.

  That is, at the start of operation, the rated power output command value matches the actual power output, but as the operation time elapses, the fuel cell power output decreases and the rated power output command value and the actual power output There will be a difference. Therefore, when the power generation output starts to decrease, it is necessary to prevent thermal runaway of the temperature of the selective oxidation unit based on the actual power generation output from the rated power generation output.

  In order to solve the problems of the conventional technique, the fuel cell system of the present invention uses a difference ΔW as a value obtained by subtracting the actual power generation output Wr from the rated power generation output Wmax, and the temperature of the selective oxidation unit is equal to or lower than the threshold T. In some cases, the upper limit value W of the power generation output is set to the rated power generation output Wmax, and when the temperature of the selective oxidation unit exceeds the threshold T, the upper limit value W of the power generation output is a value lower than the rated power generation output Wmax. (For example, when the air flow rate command value is equivalent to O2 / CO = 2.0, the temperature of the selective oxidation unit is the power generation output at which thermal runaway does not occur, or the upper limit thereof), and is set to a value W2 obtained by subtracting the difference ΔW. .

  First, when the selective oxidation temperature is equal to or lower than a threshold value (for example, the temperature at which the selective oxidation unit does not cause thermal runaway or the upper limit thereof), the temperature of the selective oxidation unit is not likely to cause thermal runaway. Let W be set to Wmax.

  When the selective oxidation temperature exceeds a threshold value (for example, the temperature at which the selective oxidation unit does not cause thermal runaway or the upper limit thereof), the temperature of the selective oxidation unit may cause thermal runaway. A difference ΔW from W1 which is a value lower than Wmax (for example, when the air flow rate command value is equivalent to O2 / CO = 2.0, the temperature of the selective oxidation unit does not cause thermal runaway or its upper limit) Is set to a value W2 obtained by subtracting. As a result, the temperature of the selective oxidation section is lowered to a temperature range suitable for the selective oxidation reaction without significantly reducing O2 / CO. Moreover, the CO concentration contained in the hydrogen-containing gas is less than 20 ppm.

  Further, the fuel cell system of the present invention sets the upper limit value I of the current to be extracted from the fuel cell, and sets the upper limit value I of the current to Imax when the temperature of the selective oxidation unit is equal to or lower than the threshold value T. The upper limit value I of the current is set to I1, which is a value lower than Imax, so that the upper limit value W of the power generation output becomes W2 when the temperature of the section exceeds the threshold value T.

  In the fuel cell system of the present invention, when the selective oxidation temperature exceeds the threshold value T and then becomes the threshold value T or less, the upper limit value W of the power generation output is set to Wmax.

  Further, in the fuel cell system of the present invention, when the selective oxidation temperature exceeds the threshold value T and then becomes the threshold value T or less, the upper limit value I of the current is set to Imax.

  In the fuel cell system of the present invention, the power generation output decreases due to durability deterioration due to long-term operation, and there is a difference between the rated power generation output command value and the actual power generation output, but the selective oxidation unit is based on the actual power generation output. By suppressing the thermal runaway at the temperature, the CO concentration of the hydrogen-containing gas supplied to the fuel cell can be sufficiently reduced even when the fuel cell is operated for a long time, and the life reduction due to CO poisoning can be prevented.

1 is a schematic configuration diagram of a fuel cell system according to Embodiment 1 of the present invention. The graph which shows typically the relationship between the electric power generation output of the fuel cell system in Embodiment 1 of this invention, and time. The flowchart which shows typically 1 cycle of characteristic operation | movement of the fuel cell system in Embodiment 1 of this invention. The flowchart which shows typically 1 cycle of characteristic operation | movement of the fuel cell system in Embodiment 1 of this invention. The flowchart which shows typically 1 cycle of the characteristic operation | movement of the fuel cell system in Embodiment 2 of this invention. The flowchart which shows typically 1 cycle of the characteristic operation | movement of the fuel cell system in Embodiment 2 of this invention. Graph showing the selective oxidation temperature behavior when the selective oxidation part reaches thermal runaway as a conventional example The graph which shows typically the selective oxidation temperature behavior by operation | movement of step S1, S4, S5 of the fuel cell system in Embodiment 1 of this invention. The graph which shows typically the selective oxidation temperature behavior by operation | movement of step S6, S9, S10 of the fuel cell system in Embodiment 1 of this invention. The graph which shows typically the selective oxidation temperature behavior by operation | movement of step S11, S14, S15 of the fuel cell system in Embodiment 1 of this invention. The graph which shows typically the selective oxidation temperature behavior by operation | movement of step S16, S19, S20 of the fuel cell system in Embodiment 1 of this invention. A graph schematically showing the relationship of CO concentration to selective oxidation temperature

  In a first aspect of the present invention, a reforming section that supplies a raw material and water to generate a hydrogen-containing gas by a reforming reaction, and a hydrogen-containing gas that is supplied by selective oxidation air and that is generated by the reforming section by a selective oxidation reaction. A hydrogen generator comprising a selective oxidation unit that further reduces the carbon monoxide concentration and a selective oxidation temperature detection unit that detects a temperature of the selective oxidation unit, and a hydrogen content in which the carbon monoxide concentration is reduced in the selective oxidation unit A fuel cell that generates power by supplying gas and an oxygen-containing gas, a control unit that sets an upper limit value W of the power generation output of the fuel cell, and a control unit that instructs the fuel cell to output at the rated power generation output value Wmax And a storage unit for storing the actual power generation output Wr of the fuel cell, a value obtained by subtracting the actual power generation output Wr from the rated power generation output Wmax is defined as a difference ΔW, and the temperature of the selective oxidation unit is equal to or lower than a threshold T If there is power generation When the upper limit value W of the force is set to Wmax and the temperature of the selective oxidation unit exceeds the threshold value T, the upper limit value W of the power generation output is set to a value W2 obtained by subtracting the difference ΔW from the value W1 that is lower than Wmax. To do.

  With this configuration, the temperature of the selective oxidation unit is lowered to a temperature range suitable for the selective oxidation reaction, and thermal runaway of the temperature of the selective oxidation unit can be sufficiently prevented. In addition, the CO concentration contained in the hydrogen-containing gas is less than 20 ppm, and it is possible to prevent a decrease in power generation output due to CO poisoning of the fuel cell or a decrease in the life of the fuel cell.

The second invention sets an upper limit value I of the current to be extracted from the fuel cell. When the temperature of the selective oxidation unit is equal to or lower than the threshold T, the upper limit value I of the current is set to Imax, and the temperature of the selective oxidation unit is When the threshold value T is exceeded, the current upper limit value I is set to I1 which is lower than Imax so that the power generation output upper limit value W becomes W2.

  With this configuration, the temperature of the selective oxidation unit is lowered to a temperature range suitable for the selective oxidation reaction, and thermal runaway of the temperature of the selective oxidation unit can be sufficiently prevented.

  In the third invention, the control unit sets the upper limit value W of the power generation output to Wmax when the selective oxidation temperature exceeds the threshold value T and then becomes the threshold value T or less.

  With this configuration, the temperature of the selective oxidation unit is lowered to a temperature range suitable for the selective oxidation reaction, and thermal runaway of the temperature of the selective oxidation unit can be sufficiently prevented. In addition, the CO concentration contained in the hydrogen-containing gas is less than 20 ppm, and it is possible to prevent a decrease in power generation output due to CO poisoning of the fuel cell or a decrease in the life of the fuel cell.

  According to a fourth aspect of the present invention, when the selective oxidation temperature exceeds the threshold value T and then becomes equal to or lower than the threshold value T, the control unit sets the upper limit value I of the current to Imax.

  With this configuration, the temperature of the selective oxidation unit is lowered to a temperature range suitable for the selective oxidation reaction, and thermal runaway of the temperature of the selective oxidation unit can be sufficiently prevented.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
(Configuration of fuel cell system)
FIG. 1 is a schematic configuration diagram of a fuel cell system 100 using a hydrogen generator 1 and a fuel cell 2 according to Embodiment 1 of the present invention.

  The fuel cell system 100 includes a hydrogen generator 1 that generates a hydrogen-containing gas, a fuel cell 2 that generates power using the hydrogen-containing gas supplied from the hydrogen generator 1, and a switch from the hydrogen generator 1 to the fuel cell 2. A hydrogen gas supply path 4 for supplying hydrogen gas via the valve 3a, and a fuel supply path 6 for supplying the fuel discharged from the fuel cell 2 to the burner unit 5 of the hydrogen generator 1 via the switching valve 3b. A fuel cell bypass path 7 that connects the valve 3a and the switching valve 3b, and a control unit 12 that controls the operation of the hydrogen generator 1 and the fuel cell 2 in accordance with a load 26 used in a general household, etc. It has. In addition, since it is a structure equivalent to the general polymer electrolyte fuel cell system 100, detailed description of another structure is abbreviate | omitted.

  The hydrogen generator 1 includes a water supply unit 8 that supplies water to the hydrogen generator 1 and a desulfurization unit 9 that allows a hydrocarbon-based raw material containing a sulfur component to pass therethrough and adsorbs and removes the sulfur component contained in the raw material. And a reformer 10 that generates a hydrogen-containing gas using the raw material after passing through the desulfurization unit 9 and the water supplied from the water supply unit 8, and the flow rate of the raw material supplied to the desulfurization unit 9 is controlled. And a raw material supply unit 11.

The reformer 10 evaporates the water supplied from the water supply unit 8 and preheats the mixed gas of the raw material and water vapor, and the reforming unit 14 advances the reforming reaction between the raw material and water vapor. The reforming unit 15 includes a modification unit 15 that performs a modification reaction of CO and water vapor in the hydrogen-containing gas generated in the reforming unit 14 to reduce the CO concentration of the hydrogen-containing gas. Further, CO remaining in the hydrogen-containing gas after passing through the shift unit 15 is mainly oxidized using air supplied from the air supply unit 16 to the hydrogen-containing gas after passing through the shift unit 15. And a selective oxidation portion 17 to be removed.
The reforming section 14 is provided with a Ru-based reforming catalyst, the shift section 15 is provided with a Cu—Zn-based shift catalyst, and the selective oxidation section 17 is provided with a Ru-based selective oxidation catalyst.

  Further, the reforming unit 14, the conversion unit 15, and the selective oxidation unit 17 are provided with a reforming temperature detection unit 18, a conversion temperature detection unit 19, and a selective oxidation temperature detection unit 20 that detect respective temperatures.

  The reformer 10 includes a burner unit 5 for supplying heat necessary for each reaction in the reforming unit 14, the shift unit 15, and the selective oxidation unit 17. The burner unit 5 is provided with a fuel supply path 6 for supplying fuel and a combustion fan 21 for supplying air. The fuel is supplied from the hydrogen gas supply path 4 to the burner unit 5 via the fuel cell bypass path 7 or from the fuel supply path 6 via the fuel cell 2.

  The reforming unit 14 and the evaporation unit 13 are configured to be supplied with heat from the combustion exhaust gas generated in the burner unit 5 through the wall surface of the inner cylinder 22. In the configuration of the reforming unit 14, the transformation unit 15, and the selective oxidation unit 17, illustration and detailed description of the same components as the general configuration are omitted.

  The hydrocarbon-based raw material supplied to the desulfurization section 9 may be a raw material containing an organic compound composed of at least carbon such as hydrocarbon and hydrogen element, for example, city gas mainly composed of methane, Natural gas, LPG, etc. Here, a city gas gas infrastructure line 23 is used as a raw material supply source, and the desulfurization section 9 is connected to the gas infrastructure line 23. The desulfurization part 9 has a shape that can be attached to and detached from the desulfurization connection part 24 arranged on the upstream side and the downstream side, and when the adsorption amount for the sulfur component of the desulfurization part 9 is saturated and the adsorption characteristics are reduced, The new desulfurization unit 9 can be replaced. The desulfurization section 9 is filled with a zeolite-based adsorption / removal agent that adsorbs sulfur compounds, which are odorous components in city gas. Moreover, the desulfurization connection part 24 also has a valve function which controls the distribution | circulation of a raw material, for example, an electromagnetic valve is provided in a structure. In addition, the desulfurization part 9 is good also as a structure using hydrodesulfurization.

  The water supply unit 8 has a pump having a flow rate adjusting function. The raw material supply unit 11 is disposed in a raw material supply path 25 that connects the desulfurization unit 9 and the reformer 10, and controls the flow rate of the raw material supplied to the reformer 10, thereby desulfurizing unit 9 from the gas infrastructure line 23. The flow rate of the raw material supplied to is controlled. In addition, the raw material supply part 11 should just be able to control the raw material flow volume supplied to the desulfurization part 9, and may be arrange | positioned in the downstream of the raw material supply part 11. FIG. The raw material supply unit 11 has a booster pump, and has a function of adjusting the flow rate of the raw material supplied to the desulfurization unit 9 by controlling, for example, input current pulses, input power, and the like.

  The control unit 12 stores the operation information such as the operation sequence of the reformer 10, the raw material integrated flow rate, and the like using a semiconductor memory, a CPU, and the like, calculates appropriate operation conditions according to the situation, and the fuel cell 2, The operating conditions necessary for operation, such as the water supply unit 8, the raw material supply unit 11, the air supply unit 16, and the switching valves 3a and 3b of the hydrogen generator 1, are commanded.

(Operation of fuel cell system)
The operation (starting, power generation, stopping) of the fuel cell system 100 configured as described above will be described below centering on the operation of the hydrogen generator 1.

First, when the hydrogen generator 1 is started from a stopped state, the raw material is supplied from the raw material supply unit 11 to the reformer 10 through the raw material supply path 25 according to a command from the control unit 12. The raw material that has passed through the evaporation unit 13, the reforming unit 14, the conversion unit 15, and the selective oxidation unit 17 is supplied from the fuel supply path 6 to the burner unit 5 via the hydrogen gas supply path 4 and the fuel cell bypass path 7, and is a combustion fan. The reformer 10 starts to be heated by being ignited by the burner unit 5 supplied with the combustion air by 21.

  After the heating by the burner unit 5 is started, the water supply unit 8 is operated to supply water to the reformer 10 to start the reforming reaction between water and the raw material. In the present embodiment, city gas (13A) containing methane as a main component is used as a raw material. The water supply flow rate from the water supply unit 8 is controlled so that water vapor is about 3 moles per mole of carbon atoms in the average molecular formula of the city gas (S / C = about 3).

  Further, the air supply unit 16 is operated to supply air to the reformer 10. The air supply flow rate from the air supply unit 16 is controlled such that the oxygen flow rate is twice the number of moles (O2 / CO = 2) of the CO flow rate contained in the hydrogen-containing gas. In the reformer 10, a steam reforming reaction is advanced in the reforming unit 14, a transformation reaction is performed in the transformation unit 15, and a selective oxidation reaction of CO is performed in the selective oxidation unit 17. At this time, the combustion of the burner unit 5 is controlled so that the reforming unit 14, the conversion unit 15, and the selective oxidation unit 17 have temperatures suitable for each reaction.

  After the CO concentration is reduced to a predetermined concentration (in this embodiment, less than 20 ppm on a dry gas basis), the switching valves 3a and 3b are operated to supply the hydrogen-containing gas to the fuel cell 2 through the hydrogen gas supply path 4. Thus, the power generation operation is performed in the fuel cell 2. Further, the fuel discharged from the fuel cell 2 passes through the fuel supply path 6 and is supplied to the burner unit 5.

  During the power generation operation, the control unit 12 outputs the rated power generation output value Wmax to the fuel cell 2 according to the power generation output W required by the fuel cell system 100 by the load 26 and the rated power generation to the hydrogen generator 1. A hydrogen-containing gas corresponding to the output value Wmax is generated, and the raw material flow rate and the reformed water corresponding to the raw material flow rate are set so that the reforming unit 14, the shift unit 15 and the selective oxidation unit 17 have a temperature suitable for each reaction. And the air flow rate and combustion of the burner unit 5 (λ (air ratio to fuel) = about 1.7) are controlled.

  When stopping the operation of the fuel cell system 100, the switching valve 3 a, 3 b is operated according to a command from the control unit 12, and the hydrogen-containing gas supplied to the fuel cell 2 is passed through the fuel cell bypass path 7 to the burner unit. 5 is supplied. Thereafter, the operations of the water supply unit 8, the raw material supply unit 11, and the air supply unit 16 are stopped, the supply of water, the raw material, and the air is stopped, and the operation of the hydrogen generator 1 is stopped.

  The hydrogen generator 1 is stopped when the switching valves 3a and 3b are operated to seal the reformer 10, and the amount of raw material corresponding to the amount of the reformer 10 that cools and decreases its volume. It is preferable to perform an operation for preventing the outside air from being mixed in the reformer 10 such as an operation for supplying the air.

  FIG. 2 shows that the power generation output value changes with time in the operation of the fuel cell system 100.

  When the operation time of the fuel cell system 100 elapses for a certain period of time, the rated power output value Wmax starts to decrease due to the decrease in the power generation capability of the fuel cell. For example, the rated power generation output value Wmax is reduced to the actual power generation output value Wr at an arbitrary time after deterioration.

  Next, characteristic operations of the fuel cell system 100 according to Embodiment 1 of the present invention will be described with reference to FIGS.

  FIG. 3 is a flowchart schematically showing one cycle of the characteristic operation of the fuel cell system 100 according to Embodiment 1 of the present invention. Actually, during the power generation operation of the fuel cell system 100, the operation of one cycle shown in FIG. 3 is continuously performed without being intermittent.

  The control unit 12 included in the fuel cell system 100 first selects the selective oxidation temperature Ta detected by the selective oxidation temperature detection unit 20, the upper limit value W of the power generation output, the rated power generation output value Wmax, and the actual power generation output Wr. Obtain (step S1).

  And the control part 12 determines whether the selective oxidation temperature Ta exceeds the selective oxidation temperature threshold value T1 preset in the memory | storage part of the control part 12 (step S2). Here, when the control unit 12 determines that the selective oxidation temperature Ta is equal to or lower than the selective oxidation temperature threshold T1 (YES in step S2), the upper limit value W of the power generation output is set to Wmax (step S3).

  Here, when the control unit 12 determines that the selective oxidation temperature Ta exceeds the selective oxidation temperature threshold T1 (YES in step S4), the control unit 12 sets the upper limit value W of the power generation output to W2 = (W1−ΔW). ). (Step S5). W1 is a value lower than the rated power generation output value Wmax. For example, when the air flow rate command value is equivalent to O2 / CO = 2.0, the temperature of the selective oxidation unit is the power generation output at which thermal runaway does not occur, or the upper limit thereof. ΔW is a value obtained by subtracting the actual power generation output Wr from the rated power generation output value Wmax.

  In other words, when the selective oxidation temperature exceeds the threshold value T1, the upper limit value W of the power generation output is lowered to W2 = (W1−ΔW), so that the flow rate of hydrogen-containing gas generated in the hydrogen generator 1 is reduced. The reference value of the command value of the air flow rate determined according to the raw material flow rate supplied to the unit 14 and the raw material flow rate supplied to the selective oxidation unit 17 can be lowered. Therefore, the temperature of the selective oxidation unit 17 can be lowered to a temperature range suitable for the selective oxidation reaction, and thermal runaway of the temperature of the selective oxidation unit 17 can be sufficiently prevented. Further, since the CO concentration contained in the hydrogen-containing gas is less than 20 ppm, it is possible to prevent a decrease in power generation output due to CO poisoning of the fuel cell 2 or a decrease in the life of the fuel cell 2.

  In FIG. 4, the control unit 12 included in the fuel cell system 100 first selects the selective oxidation temperature Ta detected by the selective oxidation temperature detection unit 20, the upper limit value I of the current extracted from the fuel cell, and the upper limit value of the power generation output. I1 which is a value lower than Imax is acquired as the upper limit value I of the current so that W becomes W2 (step S6).

  And the control part 12 determines whether the selective oxidation temperature Ta exceeds the selective oxidation temperature threshold value T1 preset in the memory | storage part of the control part 12 (step S7). Here, when the control unit 12 determines that the selective oxidation temperature Ta is equal to or lower than the selective oxidation temperature threshold T1 (YES in step S7), the upper limit value I of current is set to Imax (step S8).

  Here, when the control unit 12 determines that the selective oxidation temperature Ta exceeds the selective oxidation temperature threshold T1 (YES in step S9), the control unit 12 sets the current so that the upper limit value W of the power generation output becomes W2. Is set to I1, which is a value lower than Imax (step S10).

(Embodiment 2)
<Configuration of the fuel cell system> and <Operation of the fuel cell system> are the same as those in the first embodiment, and are omitted.

  Next, characteristic operations of the fuel cell system 100 according to Embodiment 2 of the present invention will be described with reference to FIGS.

  The control unit 12 included in the fuel cell system 100 first selects the selective oxidation temperature Ta detected by the selective oxidation temperature detection unit 20, the upper limit value W of the power generation output, the rated power generation output value Wmax, and the actual power generation output Wr. Obtain (step S11).

  When the control unit 12 exceeds the selective oxidation temperature threshold T1 preset in the storage unit of the control unit 12 (step S12) and then determines that the selective oxidation temperature Ta is equal to or lower than the selective oxidation temperature threshold T1 (step S14). ), The upper limit W of the power generation output is set to Wmax (step S15).

  In FIG. 6, the control unit 12 included in the fuel cell system 100 first selects the selective oxidation temperature Ta detected by the selective oxidation temperature detection unit 20, the upper limit value I of the current extracted from the fuel cell, and the upper limit value of the power generation output. I1 which is a value lower than Imax is acquired as the upper limit value I of the current so that W becomes W2 (step S6).

  When the control unit 12 exceeds the selective oxidation temperature threshold T1 preset in the storage unit of the control unit 12 (step S17) and then determines that the selective oxidation temperature Ta is equal to or lower than the selective oxidation temperature threshold T1 (step S19). ), The upper limit value I of the current is set to Imax (step S20).

Example 1
Next, characteristic operations of the fuel cell system 100 and the hydrogen generator 1 according to Embodiment 1 of the present invention will be described with reference to FIGS. 3 and 8.

  First, in FIG. 7, the power generation output required by the fuel cell 2, the power generation output command value commanded to the fuel cell 2 to follow the power generation output required by the fuel cell 2, and the air supply unit 16 are commanded. The graph showing the time change between the air flow rate command value and the selective oxidation temperature detected by the selective oxidation temperature detection unit 20 shows the selective oxidation temperature behavior when the selective oxidation unit 17 reaches thermal runaway.

  When normal, the selective oxidation temperature is stable, whereas when abnormal, the selective oxidation temperature rises excessively, and in addition to the selective oxidation reaction, a methanation reaction starts, and the temperature of the selective oxidation unit 17 increases. Thermal runaway (rapid rise) has been reached.

  The cause of the abnormality is, for example, that the mixture of the air and the hydrogen-containing gas supplied to the selective oxidation unit 17 becomes non-uniform due to the long-term operation of the fuel cell system 100, or the supply to the selective oxidation unit 17 Some change occurs in the hydrogen generator 1 such as a drift in the flow of the mixed gas of the air and the hydrogen-containing gas to be generated, and in the selective oxidation unit 17 a portion where the ratio of the air flow rate to the CO flow rate is locally high or In addition, there is a portion where the absolute flow rate of the CO flow rate and the air flow rate is high, in which the selective oxidation reaction (exothermic reaction) is accelerated, and the temperature of a part of the selective oxidation unit 17 rises excessively. It is conceivable that the temperature of the selective oxidation unit 17 as a whole increases due to the drag.

  Next, FIG. 8 shows a selective oxidation temperature behavior by the operations of steps S1, S2, S4, and S5, which are characteristic operations of the present invention.

  First, at time t1, in step S1, the selective oxidation temperature Ta detected by the selective oxidation temperature detector 20, the upper limit value W of the current power generation output, the rated power generation output value Wmax, and the actual power generation output Wr are acquired. To do.

  Next, in step S <b> 4, the control unit 12 determines that the selective oxidation temperature exceeds the selective oxidation temperature threshold set in advance in the storage unit of the control unit 12. The selective oxidation temperature threshold was set as a temperature at which the selective oxidation unit 17 does not cause thermal runaway.

Next, in step S5, the control unit 12 lowers the upper limit value W of the power generation output to W2 = (W1−ΔW). That is, when the selective oxidation temperature exceeds the threshold value, the upper limit value W of the power generation output is set to W2 =
By reducing to (W1-ΔW), the flow rate of the hydrogen-containing gas produced in the hydrogen generator 1 is lowered, so that the raw material flow rate supplied to the reforming unit 14 and the raw material flow rate supplied to the selective oxidation unit 17 are reduced. The reference value of the command value of the air flow rate determined accordingly can be lowered. Therefore, the temperature of the selective oxidation unit 17 can be lowered to a temperature range suitable for the selective oxidation reaction without significantly reducing O2 / CO, and thermal runaway of the temperature of the selective oxidation unit 17 can be sufficiently prevented. . Further, since the CO concentration contained in the hydrogen-containing gas is less than 20 ppm, it is possible to prevent a decrease in power generation output due to CO poisoning of the fuel cell 2 or a decrease in the life of the fuel cell 2.

(Example 2)
Next, characteristic operations of the fuel cell system 100 and the hydrogen generator 1 according to Embodiment 1 of the present invention will be described with reference to FIGS. 5 and 10.

  Steps S11, S12, S14, and S15 in FIGS. 5 and 10 are selected when an operation for shifting from S4 to S2 is added after the operations in steps S1, S2, S4, and S5 described in FIGS. It represents the oxidation temperature behavior.

  First, at time t2, in step S14, the control unit 12 determines that the selective oxidation temperature is equal to or lower than the selective oxidation temperature threshold. Next, in step S15, the control unit 12 sets the upper limit value W of the power generation output to Wmax.

  That is, when the selective oxidation temperature becomes equal to or lower than the threshold value T2, the temperature of the selective oxidation unit 17 is not likely to cause thermal runaway, so the upper limit value W of the power generation output can be returned to Wmax. Therefore, the power generation output required by the fuel cell 2 can be generated. Further, since O2 / CO increases, the CO concentration contained in the hydrogen-containing gas is less than 20 ppm, and it is possible to prevent a decrease in power generation output due to CO poisoning of the fuel cell 2 or a decrease in the life of the fuel cell 2. .

  In addition, after the operation of steps S1, S2, S4, S14, and S15 shifts to END, the operation returns to START again and the operation is repeated.

  As described above, the fuel cell system according to the present invention can sufficiently prevent thermal runaway at the temperature of the selective oxidation unit. Furthermore, since it is possible to prevent a decrease in power generation output due to CO poisoning of the fuel cell, a stoppage of power generation, or a decrease in the life of the fuel cell, it is also applicable to applications that combine a solar power generation system, a storage battery, etc. it can.

DESCRIPTION OF SYMBOLS 1 Hydrogen generator 2 Fuel cell 3a Switching valve 3b Switching valve 4 Hydrogen gas supply path 5 Burner unit 6 Fuel supply path 7 Fuel cell bypass path 8 Water supply part 9 Desulfurization part 10 Reformer 11 Raw material supply part 12 Control part 13 Evaporation Unit 14 Reforming unit 15 Transformation unit 16 Air supply unit 17 Selective oxidation unit 18 Reforming temperature detection unit 19 Transformation temperature detection unit 20 Selective oxidation temperature detection unit 21 Combustion fan 22 Inner cylinder 23 Gas infrastructure line 24 Desulfurization connection unit 25 Raw material supply Path 26 Load 100 Fuel cell system

Claims (4)

A reforming unit that supplies a raw material and water to generate a hydrogen-containing gas by a reforming reaction, and carbon monoxide in the hydrogen-containing gas that is generated by the reforming unit by a selective oxidation reaction that is supplied with selective oxidation air A hydrogen generator comprising: a selective oxidation unit that further reduces the concentration; and a selective oxidation temperature detection unit that detects a temperature of the selective oxidation unit;
A fuel cell that generates power by being supplied with the hydrogen-containing gas and the oxygen-containing gas having a reduced carbon monoxide concentration in the selective oxidation unit;
A control unit for setting an upper limit value W of the power generation output of the fuel cell;
A storage unit that stores an actual power generation output Wr of the fuel cell when the control unit instructs the fuel cell to output at a rated power generation output value Wmax;
With
A value obtained by subtracting the actual power generation output Wr from the rated power generation output Wmax is defined as a difference ΔW.
The control unit sets an upper limit value W of the power generation output to Wmax when the temperature of the selective oxidation unit is equal to or lower than a threshold T, and when the temperature of the selective oxidation unit exceeds the threshold T, the power generation A fuel cell system in which an upper limit value W of output is set to a value W2 obtained by subtracting the difference ΔW from W1 which is a value lower than Wmax. The control unit sets an upper limit value I of a current to be extracted from the fuel cell,
When the temperature of the selective oxidation unit is equal to or lower than the threshold value T, the upper limit value I of the current is set to Imax, and when the temperature of the selective oxidation unit exceeds the threshold value T, the upper limit value W of the power generation output is The fuel cell system according to claim 1, wherein the upper limit value I of the current is set to I1 which is a value lower than Imax so as to be W2.   The control unit sets the upper limit value W of the power generation output of the fuel cell to Wmax when the temperature of the selective oxidation unit becomes equal to or lower than the threshold value T after exceeding the threshold value T. The fuel cell system described.   4. The fuel cell system according to claim 3, wherein the control unit sets the upper limit value I of the current to Imax when the temperature of the selective oxidation unit exceeds the threshold value T and then becomes equal to or lower than the threshold value T. 5.