JP6695263B2 - Fuel cell system, control device, and program - Google Patents

Description

  The present invention relates to a fuel cell system, a control device, and a program.

In recent years, a fuel cell system using a fuel cell such as a solid oxide fuel cell (SOFC) or a molten carbonate fuel cell (MCFC) has attracted attention. The fuel cell system includes a reformer and a stack. The reformer causes a fuel gas containing hydrocarbon to react with water vapor and oxygen in the air to be reformed to generate hydrogen (H ₂ ) and carbon monoxide (CO). The stack uses hydrogen and carbon monoxide produced in the reformer to generate electricity.

  In the reformer, the ratio of the amount of steam supplied to the amount of carbon in the fuel gas (S / C ratio: Steam / Carbon) and the ratio of the amount of oxygen supplied to the amount of carbon in the fuel gas (O / C ratio) : Oxygen / Carbon) may be increased to suppress carbon precipitation.

  Conventionally, the amount of carbon deposited in the reformer is reduced by supplying an oxidizer (air, steam) to the reformer and heating the reformer by a heating mechanism during partial load or when power generation is stopped. A technique has been proposed (see, for example, Patent Document 1).

  Further, a technique has been proposed in which oxygen is supplied to the reformer periodically for a certain period of time to increase the O / C ratio and reduce the amount of carbon deposited in the reformer (for example, patents). Reference 2).

  In addition, a technique has been proposed in which carbon dioxide in combustion exhaust gas is used for reforming instead of air and steam to improve power generation efficiency (see, for example, Patent Document 3).

JP, 2005-317402, A JP, 2002-134151, A JP, 2014-107056, A

  By the way, when the above S / C ratio is increased, a large amount of water vapor and nitrogen, which are resistance components for power generation of the fuel cell, are supplied to the stack, and the power generation efficiency of the fuel cell is reduced. Further, when the O / C ratio is increased, the fuel is consumed by the exothermic reaction between the fuel and oxygen, which lowers the power generation efficiency of the system.

  On the other hand, in the technique described in Patent Document 3, since carbon dioxide is used for reforming, it is possible to suppress a decrease in voltage due to water vapor, suppress fuel consumption, and obtain high power generation efficiency. However, on the other hand, when the temperature is lowered, the carbon deposition resistance is lower than that of steam and oxygen, and carbon deposition may not be sufficiently suppressed.

  On the other hand, in the technique described in Patent Document 2, since oxygen is constantly supplied when removing carbon, the hydrocarbon fuel, hydrogen and carbon monoxide that are desired to be used for power generation in the reformer are oxidized, and the power generation efficiency is reduced. there is a possibility. Further, in the technique described in Patent Document 1, since water vapor is supplied as an oxidant, there is a possibility that the power generation efficiency may be reduced as in the case of supplying oxygen. That is, with the techniques described in Patent Documents 1 to 3 described above, it is difficult to suppress carbon deposition while suppressing a decrease in power generation efficiency.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a fuel cell system, a control device, and a program that can suppress carbon deposition while suppressing a decrease in power generation efficiency. And

  In order to achieve the above object, the fuel cell system according to claim 1 includes a reformer to which a fuel gas containing hydrocarbon and a reforming agent of at least one of carbon dioxide and oxygen in the air are supplied. A fuel cell provided, a derivation unit for deriving an integrated carbon amount by integrating the amount of carbon deposited within a predetermined time by the reforming reaction of the reformer, and a carbon integration derived by the deriving unit. When the amount is greater than the first threshold value and is equal to or less than the second threshold value that is greater than the first threshold value, the carbon dioxide is supplied to the reformer in an amount greater than the oxygen, and the integrated carbon amount is the second threshold value. And a control unit that controls the supply of more oxygen to the reformer than the carbon dioxide.

  According to this fuel cell system, as compared with the case where carbon dioxide or oxygen in the air is always supplied in a larger amount than the other without considering the cumulative amount of carbon, the amount of carbon Precipitation can be suppressed.

  The fuel cell system according to claim 2 is the fuel cell system according to claim 1, wherein the control unit has the integrated carbon amount of more than the first threshold value and equal to or less than the second threshold value, and , The amount of carbon dioxide to be supplied to the reformer when the predicted demand for electric power is less than or equal to a predetermined amount, the carbon integrated amount is less than or equal to the first threshold, and the predicted When the demand for the amount of electric power to be supplied is greater than the predetermined amount, control is performed to increase the amount of carbon dioxide supplied to the reformer.

  The fuel cell system according to claim 3 is the fuel cell system according to claim 1, wherein the control unit has the integrated carbon amount of more than the first threshold value and equal to or less than the second threshold value, and , The amount of carbon dioxide to be supplied to the reformer when the predicted demand for heat amount is equal to or greater than a predetermined amount, the carbon integrated amount is equal to or less than the first threshold value, and the predicted When the demand for the amount of heat is smaller than the predetermined amount, control is performed to increase the amount of carbon dioxide supplied to the reformer.

  According to this fuel cell system, since the supply amounts of carbon dioxide and oxygen are controlled according to the demands of electric power and heat, it is possible to improve the economical efficiency without supplying the reforming agent in vain.

  The fuel cell system according to claim 4 is the fuel cell system according to any one of claims 1 to 3, wherein the derivation unit reduces the conversion rate of the hydrocarbons in the reformer. Each of the first threshold value and the second threshold value is further derived based on the ratio.

  According to this fuel cell system, since two threshold values are derived based on the rate at which the conversion rate of hydrocarbons decreases, it is possible to accurately determine the cumulative amount of carbon.

  Further, the fuel cell system according to claim 5 is the fuel cell system according to claim 4, wherein the first threshold value is deposited when the rate at which the conversion rate of the hydrocarbon decreases is the first rate. The second threshold value corresponds to the amount of carbon, and the second threshold value corresponds to the amount of carbon that is deposited when the rate of decrease in the conversion rate of the hydrocarbon is the second rate that is higher than the first rate.

  According to this fuel cell system, the amount of carbon deposited when the conversion rate of hydrocarbons is reduced at the first rate is the first threshold value, and is deposited when the second rate is higher than the first rate. Since the amount of carbon is set to the second threshold, it is possible to accurately determine the cumulative amount of carbon.

  Further, the fuel cell system according to claim 6 is the fuel cell system according to any one of claims 1 to 5, wherein the derivation part indicates the ease of carbon deposition in the reformer. The carbon integrated amount is derived by further deriving the carbon activity and temporally integrating the carbon deposition amount per unit time obtained by converting the derived carbon activity.

  According to this fuel cell system, since the carbon activity is derived and the carbon integrated quantity is derived from the carbon activity, the accurate carbon integrated quantity can be obtained by a relatively easy method.

The fuel cell system according to claim 7 is the fuel cell system according to claim 6, wherein the reformer uses hydrogen and carbon monoxide by a first reforming reaction between the hydrocarbon and the carbon dioxide. To produce hydrogen and carbon monoxide by a second reforming reaction of the hydrocarbon and the oxygen,
Partial pressures p (CH ₄ ), p (CO), p (CO ₂ ), p (H ₂ ) in equilibrium of the hydrocarbon, the carbon monoxide, the carbon dioxide, the hydrogen, and the oxygen. , And p (O ₂ ) are the reaction ratio in the first reforming reaction, w, the reaction ratio in the second reforming reaction, v, the supply amount of the fuel gas per unit time, and the carbon dioxide. When the supply amount per unit time is α and the supply amount of the oxygen per unit time is β,
p (CH ₄ ) = A × (1-w−v) / (A × (1−w−v)) + (A × (2w + v)) + (α− (A × w)) + (A × ( 2w + 2v)) + (β- (A × 0.5v))
p (CO) = A × (2w + v) / (A × (1-w−v)) + (A × (2w + v)) + (α− (A × w)) + (A × (2w + 2v)) + ( β- (A × 0.5v))
p (CO ₂ ) = α− (A × w) / (A × (1-w−v)) + (A × (2w + v)) + (α− (A × w)) + (A × (2w + 2v) ) + (β- (A × 0.5v))
p (H ₂ ) = A × (2w + 2v) / (A × (1-w−v)) + (A × (2w + v)) + (α− (A × w)) + (A × (2w + 2v)) + (β- (A × 0.5v))
p (O ₂ ) = β− (A × 0.5v) / (A × (1-w−v)) + (A × (2w + v)) + (α− (A × w)) + (A × ( 2w + 2v)) + (β- (A × 0.5v))
Is represented by
The equilibrium constants K1 and K2 in each of the first reforming reaction and the second reforming reaction are
K1 = p (H ₂ ) ² × p (CO) ² / p (CH ₄ ) / p (CO ₂ ).
K2 = p (H ₂ ) ² × p (CO) / p (CH ₄ ) / p (O ₂ ) ^0.5
Is represented by
When the carbon activity is Ac and the equilibrium constant in the carbon deposition reaction of the fuel cell is K3,
Ac = K3 × p (CO) ² / p (CO ₂ ).
Is represented by
The reaction ratio w derived by the derivation unit according to the supply amount A of the fuel gas per unit time, the supply amount α of the carbon dioxide per unit time, and the supply amount β of the oxygen per unit time. , V, the respective values of the partial pressures p (CO) and p (CO ₂ ) are derived, and the carbon activity Ac is derived from the derived respective values.

  According to this fuel cell system, the carbon activity is derived from the partial pressure and the equilibrium constant of each component in the reforming reaction and the carbon deposition reaction in the equilibrium state, and further, the integrated carbon amount is derived from the carbon activity. Therefore, an accurate carbon integrated amount can be obtained by a relatively easy method.

  On the other hand, in order to achieve the above object, the control device according to claim 8 is a reformer to which a fuel gas containing hydrocarbon and a reforming agent of at least one of carbon dioxide and oxygen in the air are supplied. A control unit for controlling the operation of the fuel cell comprising: a deriving unit for deriving a carbon integrated amount by integrating the amount of carbon deposited within a predetermined time by the reforming reaction of the reformer. When the integrated carbon amount derived by the deriving unit is larger than a first threshold value and is equal to or smaller than a second threshold value larger than the first threshold value, the carbon dioxide is supplied to the reformer more than the oxygen. And a control unit that controls the supply of the oxygen to the reformer in an amount greater than that of the carbon dioxide when the integrated carbon amount is greater than the second threshold value.

  Furthermore, in order to achieve the above object, the program according to claim 9 causes a computer to function as a derivation unit and a control unit included in the fuel cell system according to any one of claims 1 to 7. is there.

  According to each of the above control device and program, compared with the case where one of carbon dioxide and oxygen in the air is always supplied more than the other without considering the cumulative amount of carbon, the decrease in power generation efficiency is suppressed. However, the precipitation of carbon can be suppressed.

  As described in detail above, according to the present invention, it is possible to suppress the precipitation of carbon while suppressing the decrease in power generation efficiency.

It is a block diagram showing an example of the whole composition of the fuel cell system concerning an embodiment. It is a graph which shows an example of the relationship between the measured value of the amount of carbon deposition which concerns on embodiment, and the conversion rate of methane. It is a graph which shows an example of the relationship between the carbon activity and the amount of carbon deposition per unit time according to the embodiment. It is a graph which shows an example of conversion from the carbon activity concerning an embodiment to the amount of carbon deposition per unit time. It is a graph which shows an example of the relationship between the cumulative amount of carbon deposition and time concerning an embodiment. 6 is a flowchart showing an example of the flow of processing by a program according to the embodiment. FIG. 7 is a schematic diagram for explaining an example of processing contents by a deriving unit according to the embodiment.

  Hereinafter, an example of a mode for carrying out the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing an example of the overall configuration of a fuel cell system 10 according to this embodiment.
The fuel cell system 10 according to the present embodiment includes a fuel cell 20 and a control device 30. The fuel cell 20 includes a reformer 22, a stack (fuel cell main body) 24, and a combustor 26. The reformer 22, stack 24, and combustor 26 are housed in a hot box.

The reformer 22 is arranged in the preceding stage of the stack 24. City gas Gf is supplied to the reformer 22. City gas Gf is an example of fuel gas containing hydrocarbons. The fuel gas may be other than city gas, biogas, a mixed gas of city gas and biogas, or the like. Regarding the composition of the city gas Gf, approximately 90% is methane (CH ₄ ) in the case of 13A gas. Methane is an example of hydrocarbons. The biogas referred to here means a flammable gas generated by methane-fermenting an organic waste derived from plants and animals. A typical composition of biogas is about 60% methane and about 40% carbon dioxide (CO ₂ ), although the composition may vary.

The reformer 22 is supplied with at least one of carbon dioxide and oxygen (O ₂ ) in the air. That is, the reformer 22 is a carbon dioxide reformer that supplies carbon dioxide CO ₂ to the city gas Gf for reforming, and partial oxidation that supplies oxygen O ₂ in the air to the city gas Gf to reform. And a reformer.

The reformer 22 has a catalyst for reforming. A catalyst having high activity and high carbon deposition resistance is used as the reforming catalyst. The carrier oxide to be supported is preferably basic. As the carrier, for example, alkaline earth metals such as magnesium oxide (MgO), calcium oxide (CaO), strontium oxide (SrO), and barium oxide (BaO) are used. By using the basic carrier, the carbon dioxide CO ₂ chemically adsorbed on the catalyst surface is stabilized, and the reaction between the carbon produced by the decomposition of methane and the carbon dioxide CO ₂ chemisorbed is promoted. Examples of the reforming catalyst include Ru / MgO, Rh / BaO, Ni / SrTiO _{3 and the} like. The reforming reaction by the carbon dioxide CO _{2 in the} reformer 22 is as shown in the following formula (1). In addition, Formula (1) shows an example of a 1st reforming reaction.

CH ₄ + CO ₂ → 2H ₂ + 2CO (1)

The reforming reaction by the oxygen O ₂ in the air in the reformer 22 is as shown in the following formula (2). Formula (2) shows an example of the second reforming reaction.

CH ₄ + 0.5O ₂ → 2H ₂ + CO (2)

  For example, a solid oxide fuel cell is applied to the stack 24. The stack 24 has a plurality of stacked cells. Each cell has a fuel electrode, an electrolyte layer, and an air electrode. The reformed gas generated by the reformer 22 is supplied to the fuel electrode of each cell, and air is supplied to the air electrode of each cell as an oxidant gas.

  At the air electrode, oxygen ions in the air react with electrons to generate oxygen ions, as shown in the following formula (3). The oxygen ions reach the fuel electrode through the electrolyte layer.

(Air electrode reaction)
1 / 2O ₂ + 2e ⁻ → O ^{2 −} (3)

  On the other hand, in the fuel electrode, as shown by the following formulas (4) and (5), oxygen ions that have passed through the electrolyte layer react with hydrogen and carbon monoxide in the reformed gas to generate water vapor, carbon dioxide, And electrons are generated. The electrons generated at the fuel electrode reach the air electrode through the external circuit. Then, as the electrons move from the fuel electrode to the air electrode in this manner, power is generated in each cell. Further, in each cell, Joule heat is generated due to the above electrochemical reaction during power generation.

(Fuel electrode reaction)
^{_{H 2 + O 2- → H 2}} O + 2e - ... (4)
CO + O ²⁻ → CO ₂ + 2e ⁻ (5)

  The gas generated at the fuel electrode (hereinafter referred to as the anode off gas) includes not only water vapor and carbon dioxide generated in the fuel electrode reaction but also unreacted in the fuel electrode of the stack 24 generated in the reformer 22. Hydrogen and carbon monoxide. The temperature of the anode off gas flowing in the fuel cell 20 is, for example, 200 ° C. or higher and 800 ° C. or lower.

  The combustor 26 is arranged in the latter stage of the stack 24. The combustor 26 is supplied with the gas discharged from the air electrode of the stack 24 (hereinafter, referred to as cathode off gas) and the anode off gas discharged from the fuel electrode of the stack 24. As described above, the anode offgas contains unreacted hydrogen and carbon monoxide at the fuel electrode of the stack 24, and the combustor 26 burns the anode offgas using the cathode offgas containing oxygen. The combustion exhaust gas generated by the combustion of the combustor 26 is discharged to the outside of the fuel cell 20.

On the other hand, the control device 30 controls the operation of the fuel cell 20. The control device 30 is configured to include a calculation unit 32 and a storage unit 34. The storage unit 34 controls the supply amount of each of carbon dioxide CO ₂ and oxygen O ₂ based on the cumulative carbon amount (hereinafter, referred to as the cumulative carbon deposition amount Ca) to control the operation of the fuel cell 20. The program 34A is stored in advance. The program 34A may be pre-installed in the control device 30, for example. The program 34A may be realized by being stored in a non-volatile storage medium or distributed via a network and appropriately installed in the control device 30. Examples of the non-volatile storage medium include a CD-ROM (Compact Disc Read Only Memory), a magneto-optical disk, an HDD (Hard Disk Drive), a DVD-ROM (Digital Versatile Disc Read Only Memory), a flash memory, and a memory. Examples include cards.

  The calculation unit 32 includes a CPU (Central Processing Unit), and reads and executes the program 34A stored in the storage unit 34 to thereby derive the derivation unit 32A, the demand prediction unit 32B, the determination unit 32C, and the operation control unit 32D. Function as.

  By the way, when carbon dioxide is used for reforming, it is possible to suppress a decrease in voltage when steam is used and obtain high power generation efficiency. However, on the other hand, when the temperature is lowered, the carbon deposition resistance is lower than that of steam or oxygen, and the deposited carbon may not be sufficiently suppressed.

  On the other hand, when reforming is performed by partial oxidation using oxygen in the air, hydrogen and carbon monoxide that are desired to be used for power generation may be oxidized in the reformer, which may reduce power generation efficiency. However, reforming with oxygen has higher carbon deposition resistance than carbon dioxide, and is effective for suppressing carbon deposition in a short time.

  Further, the reforming reaction with carbon dioxide represented by the above formula (1) is an endothermic reaction. On the other hand, the oxygen-based reforming reaction represented by the above formula (2) is an exothermic reaction, and energy loss occurs due to heat generation. Therefore, it is considered that by appropriately mixing carbon dioxide and oxygen, it is possible to suppress heat generation and suppress a decrease in power generation efficiency.

  In consideration of the above matters, when performing reforming using carbon dioxide and oxygen in the air, it is desired to suppress carbon precipitation while suppressing a decrease in power generation efficiency.

  Therefore, the derivation unit 32A according to the present embodiment integrates the amount of carbon deposited within a predetermined time by the reforming reaction of the reformer 22 to derive an integrated carbon deposition amount Ca, and derives the derived integrated carbon. The precipitation amount Ca is output to the determination unit 32C. Further, the derivation unit 32A derives the first threshold value TH1 and the second threshold value TH2 used for the determination of the integrated carbon deposition amount Ca, and outputs the derived first threshold value TH1 and the second threshold value TH2 to the determination unit 32C. The second threshold TH2 is larger than the first threshold, and shows the maximum allowable value as an example. There is a relation of first threshold TH1 <second threshold TH2. A method of deriving the cumulative amount of deposited carbon Ca, the first threshold value TH1, and the second threshold value TH2 by the derivation unit 32A will be described later.

  The demand prediction unit 32B predicts the demand for the required amount of power and outputs the predicted demand for the amount of power (hereinafter, simply referred to as power demand Wa) to the determination unit 32C. The method of predicting the demand for the amount of electric power is not particularly limited, but may be predicted based on the actual value of the amount of electric power generated by the fuel cell 20 in the past, for example.

  The heat demand may be predicted instead of the power demand. In this case, the demand prediction unit 32B predicts the demand for the required amount of heat and outputs the predicted demand for the amount of heat to the determination unit 32C. In addition, as a method of predicting the demand for the amount of heat, for example, the demand for the amount of heat may be predicted based on the actual value of the amount of heat supplied in the past in the fuel cell 20.

  The determination unit 32C determines whether the integrated carbon deposition amount Ca derived by the derivation unit 32A is larger than the first threshold TH1 and equal to or smaller than the second threshold TH2. Further, the determination unit 32C determines whether or not the cumulative carbon deposition amount Ca is larger than the second threshold value TH2. In addition, the determination unit 32C determines whether or not the power demand Wa is equal to or less than a predetermined amount. Then, the determination unit 32C outputs these determination results to the operation control unit 32D.

The operation control unit 32D controls the operation of the fuel cell 20. Here, the operation control unit 32D according to the present embodiment controls the supply amounts of carbon dioxide CO ₂ and oxygen O ₂ supplied to the reformer 22 based on the determination result of the determination unit 32C. The operation control unit 32D also controls the supply amount of the city gas Gf. The operation control unit 32D is an example of a control unit.

The city gas Gf supply path 50 is provided with a first valve 41. In the supply path 50, a flow meter Fm1 is provided between the first valve 41 and the fuel cell 20. The flow meter Fm1 measures the supply amount of the city gas Gf. A second valve 42 is provided in the carbon dioxide CO ₂ supply path 52. In the supply path 52, a flow meter Fm2 is provided between the second valve 42 and the fuel cell 20. The flow meter Fm2 measures the supply amount of carbon dioxide CO ₂ . A third valve 43 is provided in the oxygen O ₂ supply path 54. A flow meter Fm3 is provided in the supply path 54 between the third valve 43 and the fuel cell 20. The flow meter Fm3 measures the supply amount of oxygen O ₂ . Each of the flow meters Fm1 to Fm3 is connected to the derivation unit 32A.

The opening degree of each of the first valve 41, the second valve 42, and the third valve 43 is controlled by the operation control unit 32D. That is, the supply amount of the city gas Gf is adjusted by the operation control unit 32D controlling the opening degree of the first valve 41. Similarly, the supply amount of carbon dioxide CO ₂ is adjusted by the operation control unit 32D controlling the opening degree of the second valve 42. The supply amount of oxygen O ₂ is adjusted by the operation control unit 32D controlling the opening degree of the third valve 43.

Operation control unit 32D, when the integrated amount of deposited carbon Ca by the determination unit 32C is determined to be the second threshold value TH2 or less more than the threshold value TH1, the carbon dioxide CO ₂ in many reformer 22 than the oxygen _{O 2} Control the supply. When the determination unit 32C determines that the cumulative carbon deposition amount Ca is larger than the second threshold value TH2, the operation control unit 32D performs control to supply oxygen O ₂ in a larger amount than carbon dioxide CO ₂ .

That is, a range in which the cumulative amount Ca of deposited carbon is larger than the first threshold TH1 and is equal to or smaller than the second threshold TH2 indicates a range in which the amount of deposited carbon is relatively large. Therefore, by controlling the supply of carbon dioxide CO ₂ in a larger amount than that of oxygen O ₂ , it is possible to suppress the precipitation of carbon while suppressing the decrease in power generation efficiency. On the other hand, a range in which the cumulative amount of deposited carbon Ca is larger than the second threshold TH2 indicates a range in which the amount of deposited carbon is considerably large. Therefore, by controlling the supply of oxygen O ₂ in a larger amount than that of carbon dioxide CO ₂ , the precipitation of carbon can be suppressed in a short time. In addition, in the range where the cumulative carbon deposition amount Ca is equal to or less than the first threshold value TH1, the carbon deposition amount is relatively small, and the supply amounts of carbon dioxide CO ₂ and oxygen O ₂ are not particularly limited. As an example, the supply amount of carbon dioxide CO ₂ may be substantially equal to the supply amount of oxygen O ₂ , or may be slightly larger than the supply amount of oxygen O ₂ .

Here, the power demand Wa may be taken into consideration. For example, carbon dioxide CO ₂ supplied to the reformer 22 when the cumulative amount of carbon deposition Ca is larger than the first threshold TH1 and is equal to or smaller than the second threshold TH2 and the power demand Wa is equal to or smaller than a predetermined amount. Be L1. Further, the amount of carbon dioxide CO ₂ supplied to the reformer 22 is L2 when the cumulative amount of carbon deposition Ca is equal to or less than the first threshold value TH1 and the power demand Wa is greater than a predetermined amount. In this case, the operation control unit 32D performs control to increase the supply amount of carbon dioxide CO ₂ so that L1> L2.

More specifically, when the cumulative amount of deposited carbon Ca is relatively small and the predicted power demand Wa is relatively large, the supply amount of carbon dioxide CO ₂ is set to L2 and the rated operation is performed. The rated operation referred to here indicates a state in which the fuel cell 20 is operating at the rated output. Then, when the cumulative amount of deposited carbon Ca increases to some extent and the predicted power demand Wa is relatively small, the supply amount of carbon dioxide CO ₂ is set to L1 (> L2) to suppress the decrease in power generation efficiency, and It is possible to suppress the precipitation of. Here, the carbon deposition reaction in the fuel cell 20 is represented by the following formula (6) as an example.

2CO → C + CO ₂ (6)

In addition, you may consider heat demand instead of electric power demand Wa. In this case, for example, carbon dioxide supplied to the reformer 22 when the cumulative carbon deposition amount Ca is more than the first threshold TH1 and less than or equal to the second threshold TH2 and the heat demand is not less than a predetermined amount. Let the amount of CO _{2 be} L1. Further, the amount of carbon dioxide CO ₂ supplied to the reformer 22 when the cumulative amount of carbon deposition Ca is less than or equal to the first threshold value TH1 and the heat demand is less than a predetermined amount is L2. In this case, the operation control unit 32D performs control to increase the supply amount of carbon dioxide CO ₂ so that L1> L2.

When the fuel cell 20 is started, the temperature of the reformer 22 is low, so carbon may be deposited in the reforming with carbon dioxide CO ₂ . Therefore, in order to suppress the precipitation of carbon, it is desirable to supply oxygen O ₂ in a larger amount than carbon dioxide CO ₂ . In this case, the case where the supply amount of carbon dioxide CO ₂ is set to 0 (zero) and only oxygen O ₂ is supplied is included. On the other hand, when the fuel cell 20 is rated operation, in order to suppress a decrease in power generation efficiency, better to carbon dioxide CO ₂ more supply than oxygen O ₂ is preferred.

  Next, a method of deriving the first threshold TH1 and the second threshold TH2 by the deriving unit 32A will be described.

  The fuel cell 20 according to the present embodiment is subjected to a test operation according to a predetermined operation condition, and the first threshold value TH1 and the second threshold value TH2 are derived in advance.

(S1) First, as operating conditions, the supply amount (supply ratio) of each gas of city gas (methane) Gf, carbon dioxide CO ₂ , and oxygen O ₂ and the operating temperature of the reformer 22 are set. As operating conditions, for example, the supply amount of city gas (methane) Gf per unit time is A [mol / h], the supply amount of carbon dioxide CO ₂ is α [mol / h], and oxygen O ₂ is The supply amount per unit time is set to β [mol / h], and the operating temperature of the reformer 22 is set to T [K] (as an example, 923 K (= 650 ° C.)). The supply amount A of the city gas Gf, the supply amount α of carbon dioxide CO ₂ , and the supply amount β of oxygen O ₂ are represented by a ratio (for example, A: α: β = 1: x: y). Good. Further, although H ₂ O is not supplied in the present embodiment, it may be contained as saturated steam, and therefore may be considered.

(S2) The reformer 22 is operated under the above operating conditions, and the reformed gas discharged from the reformer 22 is analyzed by a gas analyzer (gas chromatography or the like) to obtain methane, hydrogen, carbon monoxide, and dioxide. Obtain each concentration of carbon. From the obtained concentration, the conversion rate Conv of methane is derived using the following equation (7). Conv represents the conversion rate of methane [%], F _CH4 represents the concentration of methane, F _CO represents the concentration of carbon monoxide, and F _CO2 represents the concentration of carbon dioxide.

Conv = {1-F _CH4 / (F _CH4 + F _CO + F _CO2 )} × 100 (7)

  (S3) The reformer 22 is continuously operated under the above operating conditions, and the conversion rate Conv of methane at the time when a fixed time (for example, 170 hours (about 1 week)) has elapsed is calculated by the above equation (7). It derives using. Then, when the methane conversion rate Conv shows a remarkable decrease and falls below the methane conversion rate allowable value of the stack 24 (60% as an example), the test operation is terminated.

  (S4) The catalyst inside the reformer 22 is taken out, and the amount of carbon deposited on the catalyst is measured using an infrared absorption method or the like to obtain a measured value. As the carbon deposition amount in the catalyst, for example, 10 wt% (mass percent concentration) is obtained.

  By repeating the processes of (S1) to (S4), as shown in FIG. 2, the relationship between the measured value Cm of the carbon deposition amount and the conversion rate Conv of methane at a certain time is obtained. In the above (S1), since the above operating condition is not one, the supply amount of each gas and some operating temperatures of the reformer 22 are set, and the measured value Cm of the carbon deposition amount and the It is desirable to increase the plot with the conversion rate Conv.

FIG. 2 is a graph showing an example of the relationship between the measured carbon deposition amount Cm and the methane conversion Conv according to the present embodiment.
In FIG. 2, the horizontal axis represents the measured carbon deposition amount Cm, and the vertical axis represents the methane conversion rate Conv.

  Data showing the relationship between the measured value Cm of the amount of deposited carbon shown in FIG. 2 and the conversion rate Conv of methane is input to the derivation unit 32A. Then, the derivation unit 32A derives each of the first threshold value TH1 and the second threshold value TH2 based on the rate at which the conversion rate Conv of methane decreases. The first threshold value TH1 corresponds to the measured value Cm of the carbon deposition amount when the rate at which the methane conversion rate Conv shown in FIG. 2 decreases is the first rate. The first ratio is 1% as an example. The first ratio may be, for example, a range of 1% or more and less than 5%. The second threshold TH2 corresponds to the measured carbon deposition amount Cm when the methane conversion rate Conv shown in FIG. 2 decreases at the second rate. The second ratio is higher than the first ratio, and is 5% as an example. The second ratio may be in the range of 5% or more and less than 10%, for example.

  It should be noted that Ni-YSZ (yttria-stabilized zirconia) is generally used for the anode of the stack 24, and even if methane remains in the reformed gas discharged from the reformer 22, the stack 24 is not affected. Internal modification is possible. However, when a large amount of methane remains, carbon may be deposited in the stack 24 and the performance may be deteriorated.

  Since the above YSZ is not particularly basic and does not have a structure in which resistance to carbon deposition is enhanced, carbon is generally more likely to deposit as compared with a carbon dioxide reforming catalyst. Therefore, as in the case of the reformer 22, the following processes (S11) to (S14) may be repeated to derive the methane conversion rate allowable value of the stack 24 described above.

(S11) First, as operating conditions, for example, the supply amount of city gas Gf is A [mol / h], the supply amount of carbon dioxide CO ₂ is α [mol / h], and the supply amount of oxygen O ₂ is β [mol. / H], and the operating temperature of the stack 24 is set to T [K] (923K (= 650 ° C.) as an example). The supply amount A of the city gas Gf, the supply amount α of carbon dioxide CO ₂ , and the supply amount β of oxygen O ₂ are represented by a ratio (for example, A: α: β = 1: x: y). Good. Further, although H ₂ O is not supplied in the present embodiment, it may be contained as saturated steam, and therefore may be considered.

  (S12) The stack 24 is operated under the above operating conditions, the reformed gas coming out of the stack 24 is analyzed by a gas analyzer (gas chromatography, etc.), and each of methane, hydrogen, carbon monoxide, and carbon dioxide is analyzed. Get the concentration. From the obtained concentration, the conversion rate of methane is derived using the above equation (7). At this time, the operating voltage of the stack 24 is measured.

  (S13) The stack 24 is continuously operated under the above operating conditions, and the conversion rate Conv of methane at the time when a certain time (for example, 170 hours (about one week)) has elapsed is calculated using the above equation (7). Derive. Then, when the conversion rate of methane shows a remarkable decrease, or when it falls below the performance allowable value of the stack 24, the test operation is ended.

  (S14) The internal material of the stack 24 is taken out, and the amount of carbon deposited in the taken out internal material is measured using an infrared absorption method or the like to obtain a measured value. For example, 10 wt% (mass percent concentration) is obtained.

  By repeating the processes of (S11) to (S14), the relationship between the measured value of the carbon deposition amount for a certain period of time, the operating voltage of the stack 24, and the conversion rate of methane is obtained. From this relationship, the allowable methane conversion rate of the stack 24 is derived.

  Next, a method of deriving the cumulative carbon deposition amount Ca by the deriving unit 32A will be described with reference to FIGS.

FIG. 3 is a graph showing an example of the relationship between the carbon activity Ac and the carbon deposition amount Ct per unit time according to the present embodiment.
In FIG. 3, the horizontal axis represents the carbon activity Ac and the vertical axis represents the carbon deposition amount Ct per unit time. The carbon activity Ac is an example of an index indicating the ease of carbon deposition in the reformer 22. It is considered that the larger the value of the carbon activity Ac is, the more easily carbon is deposited.

The derivation unit 32A has the same operating conditions as in the case of the test operation in the above (S1) to (S4), and the supply amount A of the city gas Gf, the supply amount α of carbon dioxide CO ₂ , and the supply of oxygen O ₂ are set. The quantity β is entered. Further, the gas constant R (unit: J / mol · K), the operating temperature T of the reformer 22 (unit: K), and the Faraday constant F (unit: C / mol) are input to the derivation unit 32A. .. The value g1 [J / mol] of the Gibbs free energy ΔG1 determined by the above equation (1) and the value g2 of the Gibbs free energy ΔG2 determined by the above equation (2) are input to the derivation unit 32A. Further, the derivation unit 32A receives the value g3 of the Gibbs free energy ΔG3 determined by the above equation (6).

  The derivation unit 32A calculates the equilibrium constant K1 corresponding to the above equation (1), the equilibrium constant K2 corresponding to the above equation (2), and the equilibrium constant K3 corresponding to the above equation (6) from the following equations (8) to Each is derived by (10). However, g1 to g3 are values of Gibbs free energy ΔG1 to ΔG3 [J / mol], R is a gas constant, and T is an operating temperature.

K1 = Exp (-ΔG1 / RT) = Exp (-g1 / RT) (8)
K2 = Exp (-ΔG2 / RT) = Exp (-g2 / RT) (9)
K3 = Exp (-ΔG3 / RT) = Exp (-g3 / RT) (10)

On the other hand, partial pressures p (CH ₄ ), p (CO), p (CO ₂ ), p (H ₂ ), and p (in the equilibrium state of methane, carbon monoxide, carbon dioxide, hydrogen, and oxygen, respectively. O ₂ ) is represented by the following formulas (11) to (15). Here, w is the reaction ratio in the above formula (1), v is the reaction ratio in the above formula (2), α is the supply amount [mol / h] of carbon dioxide CO ₂ per unit time, and β is the unit of oxygen O ₂ . The supply amount [mol / h] per hour, A is the supply amount [mol / h] per unit time of the city gas Gf.

p (CH ₄ ) = A × (1-w−v) / (A × (1−w−v)) + (A × (2w + v)) + (α− (A × w)) + (A × ( 2w + 2v)) + (β− (A × 0.5v)) (11)
p (CO) = A × (2w + v) / (A × (1-w−v)) + (A × (2w + v)) + (α− (A × w)) + (A × (2w + 2v)) + ( β- (A × 0.5v)) (12)
p (CO ₂ ) = α− (A × w) / (A × (1-w−v)) + (A × (2w + v)) + (α− (A × w)) + (A × (2w + 2v) ) + (β− (A × 0.5v)) (13)
p (H ₂ ) = A × (2w + 2v) / (A × (1-w−v)) + (A × (2w + v)) + (α− (A × w)) + (A × (2w + 2v)) + (β- (A × 0.5v)) (14)
p (O ₂ ) = β− (A × 0.5v) / (A × (1-w−v)) + (A × (2w + v)) + (α− (A × w)) + (A × ( 2w + 2v)) + (β− (A × 0.5v)) (15)

  Further, the equilibrium constant K1 in the above equation (1) is represented by the following equation (16), and the equilibrium constant K2 in the above equation (2) is represented by the following equation (17).

K1 = p (H ₂ ) ² × p (CO) ² / p (CH ₄ ) / p (CO ₂ ) ... (16)
K2 = p (H ₂ ) ² × p (CO) / p (CH ₄ ) / p (O ₂ ) ^0.5 (17)

  Further, the carbon activity Ac is represented by the following formula (18). However, K3 is an equilibrium constant corresponding to the above equation (6) and is derived from the above equation (10).

Ac = K3 × p (CO) ² / p (CO ₂ ) ... (18)

  In the above, the equilibrium constants K1 and K2 are known values under a certain operating temperature T. From the relationships of the above equations (11) to (17), two simultaneous equations with the reaction ratios w and v as unknowns are established. When these two simultaneous equations are solved, the values of the reaction ratios w and v are obtained, and the above partial pressures p are determined. Since the equilibrium constant K3 is also a known value under a certain operating temperature T, the carbon activity Ac is derived from the above equation (18).

  That is, in the graph shown in FIG. 3, the carbon activity Ac derived as described above is associated with the carbon deposition amount Ct per unit time. The carbon deposition amount Ct per unit time is obtained by converting the measured value Cm of the carbon deposition amount in a constant time shown in FIG. 2 into the carbon deposition amount per unit time. Thereby, the relationship between the carbon deposition amount Ct per unit time and the carbon activity amount Ac is obtained.

FIG. 4 is a graph showing an example of conversion from the carbon activity Ac according to the present embodiment to the carbon deposition amount Ct per unit time.
In the left diagram of FIG. 4, the horizontal axis represents time and the vertical axis represents carbon activity Ac. In the right diagram of FIG. 4, the horizontal axis represents time and the vertical axis represents carbon deposition amount Ct per unit time.

The operating conditions (the amount of gas supplied to the reformer 22 and the operating temperature of the reformer 22) when the fuel cell 20 is actually operated may be different from the operating conditions of the fuel cell 20 in the test operation. .. The derivation unit 32A supplies the city gas Gf supply amount A, the carbon dioxide CO ₂ supply amount α, and the oxygen O ₂ supply amount β, which are measured by the flow meters Fm1 to Fm3 during the actual operation, and further, the reformer 22. Based on the operating temperature T of, the carbon activity Ac is derived using the above equations (8) to (18). The derived carbon activity Ac is shown in the left diagram of FIG. Then, the derivation unit 32A uses the relationship between the carbon deposition amount Ct per unit time and the carbon activity Ac shown in FIG. 3 described above to calculate the carbon activity Ac shown in the left diagram of FIG. 4 to the right of FIG. The carbon deposition amount Ct per unit time shown in the figure is converted.

FIG. 5 is a graph showing an example of the relationship between the cumulative carbon deposition amount Ca and time according to this embodiment.
In FIG. 5, the horizontal axis represents time and the vertical axis represents cumulative carbon deposition amount Ca.

  As shown in FIG. 5, the derivation unit 32A derives an integrated carbon deposition amount Ca by further temporally integrating the carbon deposition amount Ct per unit time shown in the right diagram of FIG. Specifically, the cumulative carbon deposition amount Ca is derived by the following formula (19). It should be noted that Ca represents the cumulative carbon deposition amount, and Ct (= Ct1 + Ct2 + Ct3 + ...) Shows the carbon deposition amount per unit time.

  Ca = ΣCt = Ct1 + Ct2 + Ct3 + ... (19)

Next, the operation of the control device 30 according to the first embodiment will be described with reference to FIG. 6. Note that FIG. 6 is a flowchart showing an example of the flow of processing by the program 34A according to the first embodiment.
The arithmetic unit 32 reads out and executes the program 34A stored in the storage unit 34 when the operation start of the fuel cell 20 is instructed.

First, in step 100 of FIG. 6, the operation control unit 32D performs a startup process of the fuel cell 20. In this case, the operation control unit 32D adjusts the opening of each of the first valve 41, the second valve 42, and the third valve 43 to supply the city gas Gf with the supply amount A and the carbon dioxide CO ₂ supply amount α, And the supply amount β of oxygen O ₂ is controlled to be a predetermined ratio. In the activated state of the fuel cell 20, since the operating temperature is low, the supply amount β of oxygen O ₂ is made larger than the supply amount α of carbon dioxide CO ₂ , and the fuel cell 20 is activated while suppressing the precipitation of carbon. In this case, the supply amount α of carbon dioxide CO ₂ may be set to 0 (zero) and only oxygen O ₂ may be supplied.

  Next, in step 102, the operation control unit 32D determines whether or not the operating temperature of the fuel cell 20 has reached a predetermined temperature and the rated operation has been performed at the rated output. When it is determined that the rated operation has been performed (in the case of affirmative determination), the processing proceeds to step 104, and when it is determined that the rated operation has not been performed (in the case of negative determination), the process goes to standby in step 102.

In step 104, the operation control unit 32D controls the fuel cell 20 to perform the rated operation at the rated output. In the state of the rated operation, the supply amount α of carbon dioxide CO ₂ is made larger than the supply amount β of oxygen O ₂ , so that the precipitation of carbon is suppressed while suppressing the decrease in power generation efficiency.

  In step 106, the operation control unit 32D determines whether or not a predetermined time has elapsed from the start of the rated operation. When it is determined that the predetermined time has elapsed from the start of the rated operation (in the case of positive determination), the process proceeds to step 108, and when it is determined that the predetermined time has not elapsed from the start of the rated operation (in the case of negative determination), step 106. And wait.

In step 108, the derivation unit 32A derives the carbon activity Ac according to the measured values of the supply amount A of city gas Gf, the supply amount α of carbon dioxide CO ₂ , and the supply amount β of oxygen O _2. Then, the derived carbon activity Ac is converted into a carbon deposition amount Ct per unit time. Further, the carbon deposition amount Ct per unit time is integrated over time to derive the integrated carbon deposition amount Ca. The carbon activity Ac is derived by using the above equations (8) to (18). Further, the cumulative carbon deposition amount Ca is derived using the above equation (19).

  In step 110, the determination unit 32C determines whether the integrated carbon deposition amount Ca derived by the derivation unit 32A is larger than the first threshold value TH1. When it is determined that the cumulative carbon deposition amount Ca is larger than the first threshold TH1 (in the case of affirmative determination), the process proceeds to step 112, and when it is determined that the cumulative carbon deposition amount Ca is equal to or less than the first threshold TH1 (negative determination In the case of), the process returns to step 104.

  In step 112, the determination unit 32C determines whether the integrated carbon deposition amount Ca derived by the derivation unit 32A is larger than the second threshold value TH2 (> TH1). When it is determined that the cumulative carbon deposition amount Ca is larger than the second threshold value TH2 (in the case of affirmative determination), the process proceeds to step 114, and when it is determined that the cumulative carbon deposition amount Ca is equal to or less than the second threshold value TH2 (negative determination) In the case of), the process proceeds to step 116.

In step 114, the operation control unit 32D controls the supply amount β of oxygen O ₂ to be larger than the supply amount α of carbon dioxide CO ₂ for a certain period of time according to the determination result of the determination unit 32C. Then, the process proceeds to step 120.

  On the other hand, in step 116, the determination unit 32C determines whether or not the power demand Wa predicted by the demand prediction unit 32B is less than or equal to a certain amount. If it is determined that the power demand Wa is less than or equal to the certain amount (in the case of affirmative determination), the process proceeds to step 118, and if it is determined that the power demand Wa is greater than the certain amount (in the case of negative determination), the process returns to step 104. The heat demand may be used for the determination instead of the power demand Wa. That is, the determination unit 32C determines whether or not the heat demand predicted by the demand prediction unit 32B is a certain amount or more. When it is determined that the heat demand is equal to or more than the certain amount (in the case of positive determination), the process proceeds to step 118, and when it is determined that the heat demand is less than the certain amount (in the case of negative determination), the process returns to step 104.

In step 118, the operation control unit 32D determines the supply amount α of carbon dioxide CO ₂ for a certain period of time according to the determination result of the determination unit 32C, the integrated carbon deposition amount Ca is the first threshold value TH1 or less, and the power demand Wa is The control is performed to increase the supply amount of carbon dioxide CO ₂ to be supplied when the amount is larger than a certain amount. That is, the supply amount α of carbon dioxide CO ₂ in step 118 is larger than the supply amount of carbon dioxide CO _{2 in} step 104. In this case, the supply amount β of oxygen O ₂ may be set to 0 (zero) and only carbon dioxide CO ₂ may be supplied. Then, the process proceeds to step 120.

  In step 120, the operation control unit 32D determines whether or not there is an instruction to end the operation of the fuel cell 20. If it is determined that there is an instruction to end the operation of the fuel cell 20 (in the case of a positive determination), the process proceeds to step 122, and if it is determined that there is no instruction to end the operation of the fuel cell 20 (in the case of a negative determination), the step Return to 104. Note that, as an example, it may be determined that the operation of the fuel cell 20 is ended when the operation end instruction from the operator is received.

In step 122, the operation control unit 32D fully closes the first valve 41, the second valve 42, and the third valve 43, and stops the supply of the city gas Gf, carbon dioxide CO ₂ , and oxygen O ₂ . The operation control unit 32D performs control for ending the operation of the fuel cell 20 and ends the series of processes.

  FIG. 7 is a schematic diagram for explaining an example of processing contents by the derivation unit 32A according to the present embodiment.

As shown in FIG. 7, the input value group 1 to the input value group 3 are input to the derivation unit 32A. The input value group 1 includes a gas constant R [J / mol · K], an operating temperature T [K] of the reformer 22, and a Faraday constant F [C / mol]. The input value group 2 includes values g1 to g3 [J / mol] of Gibbs free energy ΔG1 to ΔG3. The input value group 3 includes a supply amount A [mol / h] of city gas Gf, a supply amount α [mol / h] of carbon dioxide CO ₂ , and a supply amount β [mol / h] of oxygen O ₂ . Is included.

  Then, the derivation unit 32A derives the cumulative carbon deposition amount Ca using each parameter included in the input value group 1 to the input value group 3. The cumulative carbon deposition amount Ca is obtained by converting the carbon activity Ac derived by the above formulas (8) to (18) into a carbon deposition amount Ct per unit time, and converting the converted carbon deposition amount Ct per unit time into time. It is derived by cumulatively integrating.

According to this embodiment, when the integrated amount of deposited carbon Ca is the second threshold TH2 or less more than the threshold value TH1, do a lot supplies control than carbon dioxide CO ₂ oxygen O _2. On the other hand, if the integrated amount of deposited carbon Ca exceeds a second threshold value TH2, the oxygen _{O 2} do more supplies control than carbon dioxide CO _2. By this control, it is possible to effectively suppress the deposition of carbon while suppressing the decrease in power generation efficiency.
Moreover, since the supply amounts of carbon dioxide CO ₂ and oxygen O ₂ are controlled according to the power demand Wa, it is possible to improve the economical efficiency without wastefully supplying the modifier.

  In the above, the fuel cell system and its control device have been illustrated and described as the embodiments. The embodiment may be in the form of a program that causes a computer to execute the functions of the units included in the control device. The embodiment may be in the form of a computer-readable storage medium storing this program.

  In addition, the configuration of the control device described in the above embodiment is an example, and may be changed according to the situation without departing from the spirit of the invention.

  The flow of processing of the program described in the above embodiment is also an example, and unnecessary steps may be deleted, new steps may be added, or the processing order may be changed without departing from the spirit of the invention. Good.

  Further, in the above-described embodiment, the case where the process according to the embodiment is realized by the software configuration by using the computer by executing the program has been described, but the present invention is not limited to this. The embodiment may be realized by, for example, a hardware configuration or a combination of a hardware configuration and a software configuration.

10 Fuel cell system 20 Fuel cell (hot box)
22 reformer 24 stack (fuel cell body)
26 Combustor 30 Control device 32 Calculation part 32A Derivation part 32B Demand prediction part 32C Judgment part 32D Operation control part 34 Storage part 34A Program 41 1st valve 42 2nd valve 43 3rd valve 50, 52, 54 Supply path

Claims (9)

A fuel cell including a fuel gas containing a hydrocarbon, and a reformer to which a reforming agent for at least one of carbon dioxide and oxygen in the air is supplied,
A derivation unit for deriving an integrated carbon amount by integrating the amount of carbon deposited within a predetermined time by the reforming reaction of the reformer,
When the integrated carbon amount derived by the derivation unit is larger than a first threshold value and is equal to or less than a second threshold value larger than the first threshold value, the carbon dioxide is supplied to the reformer in an amount larger than the oxygen, When the integrated carbon amount is greater than the second threshold value, a control unit that controls the supply of the oxygen to the reformer in an amount greater than that of the carbon dioxide,
Fuel cell system equipped with.   The control unit controls the reformer when the integrated carbon amount is greater than the first threshold value and is equal to or less than the second threshold value, and the predicted demand for electric energy is equal to or less than a predetermined amount. The amount of the carbon dioxide to be supplied is supplied to the reformer when the integrated carbon amount is equal to or less than the first threshold value and the predicted demand for the amount of electric power is larger than the predetermined amount. The fuel cell system according to claim 1, wherein control is performed to increase the amount of carbon dioxide.   The control unit supplies the reformer when the integrated carbon amount is greater than the first threshold value and equal to or less than the second threshold value, and the predicted heat demand is equal to or greater than a predetermined amount. The amount of the carbon dioxide to be supplied to the reformer when the integrated carbon amount is less than or equal to the first threshold value and the demand for the predicted calorific value is less than the predetermined amount. The fuel cell system according to claim 1, wherein the fuel cell system is controlled such that the amount of carbon is increased.   The derivation unit further derives each of the first threshold value and the second threshold value based on a rate at which the conversion rate of the hydrocarbon in the reformer decreases. The fuel cell system described. The first threshold value corresponds to the amount of carbon deposited when the rate at which the conversion rate of the hydrocarbon decreases is the first rate,
The fuel cell system according to claim 4, wherein the second threshold value corresponds to the amount of carbon deposited when the rate of decrease in the conversion rate of the hydrocarbon is the second rate higher than the first rate.   The derivation unit further derives a carbon activity indicating the ease of carbon deposition in the reformer, and temporally integrates the carbon deposition amount per unit time obtained by converting the derived carbon activity. The fuel cell system according to claim 1, wherein the integrated carbon amount is derived by performing the operation. The reformer produces hydrogen and carbon monoxide by a first reforming reaction of the hydrocarbon and carbon dioxide, and produces hydrogen and carbon monoxide by a second reforming reaction of the hydrocarbon and oxygen. Generate,
Partial pressures p (CH ₄ ), p (CO), p (CO ₂ ), p (H ₂ ) in equilibrium of the hydrocarbon, the carbon monoxide, the carbon dioxide, the hydrogen, and the oxygen. , And p (O ₂ ) are the reaction ratio in the first reforming reaction, w, the reaction ratio in the second reforming reaction, v, the supply amount of the fuel gas per unit time, and the carbon dioxide. When the supply amount per unit time is α and the supply amount of the oxygen per unit time is β,
p (CH ₄ ) = A × (1-w−v) / (A × (1−w−v)) + (A × (2w + v)) + (α− (A × w)) + (A × ( 2w + 2v)) + (β- (A × 0.5v))
p (CO) = A × (2w + v) / (A × (1-w−v)) + (A × (2w + v)) + (α− (A × w)) + (A × (2w + 2v)) + ( β- (A × 0.5v))
p (CO ₂ ) = α− (A × w) / (A × (1-w−v)) + (A × (2w + v)) + (α− (A × w)) + (A × (2w + 2v) ) + (β- (A × 0.5v))
p (H ₂ ) = A × (2w + 2v) / (A × (1-w−v)) + (A × (2w + v)) + (α− (A × w)) + (A × (2w + 2v)) + (β- (A × 0.5v))
p (O ₂ ) = β− (A × 0.5v) / (A × (1-w−v)) + (A × (2w + v)) + (α− (A × w)) + (A × ( 2w + 2v)) + (β- (A × 0.5v))
Is represented by
The equilibrium constants K1 and K2 in each of the first reforming reaction and the second reforming reaction are
K1 = p (H ₂ ) ² × p (CO) ² / p (CH ₄ ) / p (CO ₂ ).
K2 = p (H ₂ ) ² × p (CO) / p (CH ₄ ) / p (O ₂ ) ^0.5
Is represented by
When the carbon activity is Ac and the equilibrium constant in the carbon deposition reaction of the fuel cell is K3,
Ac = K3 × p (CO) ² / p (CO ₂ ).
Is represented by
The deriving unit derives the reaction ratio w according to the supply amount A of the fuel gas per unit time, the supply amount α of the carbon dioxide per unit time, and the supply amount β of the oxygen per unit time. , V, the respective values of the partial pressures p (CO) and p (CO ₂ ) are derived, and the carbon activity Ac is derived from the derived respective values. .. A control device for controlling the operation of a fuel cell comprising a reformer to which a reforming agent of at least one of carbon dioxide and oxygen in the air is supplied.
A derivation unit for deriving an integrated carbon amount by integrating the amount of carbon deposited within a predetermined time by the reforming reaction of the reformer,
When the integrated carbon amount derived by the derivation unit is larger than a first threshold value and is equal to or less than a second threshold value larger than the first threshold value, the carbon dioxide is supplied to the reformer in an amount larger than the oxygen, When the cumulative amount of carbon is greater than the second threshold value, a control unit that controls to supply more oxygen to the reformer than carbon dioxide,
Control device equipped with.   A program that causes a computer to function as a derivation unit and a control unit included in the fuel cell system according to claim 1.