JP6779093B2 - Fuel cell systems, controls, and programs - Google Patents

Description

The present invention relates to fuel cell systems, controls, and programs.

In recent years, with the introduction of the feed-in tariff (FIT), in which electric power companies purchase electricity generated using renewable energy at a fixed price, biogas-based power generation is drawing attention. The biogas referred to here means a flammable gas generated by methane fermentation of organic waste derived from animals and plants. The typical composition of biogas is about 60% for methane (CH ₄ ) and about 40% for carbon dioxide (CO ₂ ), but the composition is not constant.

Conventionally, a gas engine is mainly used for power generation using biogas as a fuel, but it is difficult for a gas engine to respond to a change in a fuel composition ratio. Therefore, it may be dealt with by co-firing biogas and city gas. In addition, the amount of biogas supplied is often unstable, and it may be difficult to generate electricity stably with biogas alone. In this case, stable power generation can be achieved by using city gas together.

As a power generation means other than the above gas engine, high temperature such as solid oxide fuel cell (SOFC: Solid Oxide Fuel Cell) and molten carbonate fuel cell (MCFC: Molten Carbonate Fuel Cell), which have higher power generation efficiency than gas engine. A technique using a type fuel cell has been proposed (see, for example, Patent Document 1).

Further, a technique has been proposed in which carbon dioxide, which is an impurity in biogas, is removed and stored in a gas holder to stably supply biogas and generate electricity with a fuel cell (see, for example, Patent Document 2).

Further, a technique has been proposed in which biogas is adsorbed and stored, carbon dioxide in the biogas is not removed, and carbon dioxide is used for reforming the biogas (see, for example, Patent Document 3).

Japanese Unexamined Patent Publication No. 2011-81989 Japanese Unexamined Patent Publication No. 2005-129304 Japanese Unexamined Patent Publication No. 2008-153149

When carbon dioxide in biogas is used for reforming, efficient operation is possible, but on the other hand, the composition ratio of methane in biogas is larger than the composition ratio of carbon dioxide, so carbon in equilibrium May deposit. In addition, when carbon dioxide in biogas is not taken into consideration and supplied to a general fuel cell system mainly composed of city gas fuel, excessive supply of an oxidant may cause a decrease in power generation efficiency.

The present invention has been made in view of the above circumstances, and provides a fuel cell system, a control device, and a program capable of effectively suppressing carbon precipitation while minimizing a decrease in efficiency. The purpose is.

In order to achieve the above object, the fuel cell system according to claim 1 is supplied with a first fuel gas containing a hydrocarbon and carbon dioxide, and a modifier for reforming the hydrocarbon. A fuel cell equipped with a device and a control device for controlling the operation of the fuel cell are provided, and the control device has a predetermined range of carbon activity indicating the ease of carbon dioxide precipitation in the fuel cell. When the reformer uses water as the modifier, the first reforming reaction between the hydrocarbon and carbon dioxide causes hydrogen to be contained in the reformer. Carbon monoxide is produced, hydrogen and carbon monoxide are produced by the second modification reaction between the hydrocarbon and the water, and carbon dioxide is further produced by the third modification reaction between the carbon monoxide and the water. Hydrogen is produced, and the partial pressures p (CH ₄ ), p (H ₂ O), p (CO) of the hydrocarbon, the water, the carbon monoxide, the carbon dioxide, and the hydrogen in each equilibrium state. , P (CO ₂ ), and p (H ₂ ) are w for the reaction ratio in the first modification reaction, y for the reaction ratio in the second modification reaction, and z for the reaction ratio in the third modification reaction. The flow rate of the first fuel gas supplied to the reformer per unit time is A, the concentration of hydrocarbon in the first fuel gas is c, the concentration of carbon dioxide in the first fuel gas is d, and the above. When the amount of water supplied is H,
p (CH ₄ ) = (c × A) × (1-wy)
p (H ₂ O) = H- (c × A) × (y + z)
p (CO) = (c × A) × (2w + yz)
p (CO ₂ ) = (d × A) − (c × A) × (wz)
p (H ₂ ) = (c × A) × (2w + 3y + z)
Represented by
The equilibrium constants K1, K2, and K3 in each of the first reforming reaction, the second reforming reaction, and the third reforming reaction are
K1 = p (H ₂ ) ² × p (CO) ² / p (CH ₄ ) / p (CO ₂ )
K2 = p (H ₂ ) ³ × p (CO) / p (CH ₄ ) / p (H ₂ O)
K3 = p (CO ₂ ) x p (H ₂ ) / p (CO) / p (H ₂ O)
When the carbon activity is Ac and the equilibrium constant in the carbon precipitation reaction of the fuel cell is K4.
Ac = K4 × p (CO) ² / p (CO ₂ )
The determination unit changes the candidate value of the water supply amount H, and the partial pressure p (CO) is derived based on the reaction ratios w, y, and z derived in response to the change. ) And p (CO ₂ ) are derived, and the candidate value in which the carbon activity Ac obtained from each of the derived values falls within the predetermined range is determined as the water supply amount H. Is.

According to this fuel cell system, since the amount of the modifier having the carbon activity within a predetermined range is determined, compared with the case where the amount of the modifier is determined without specifying the range of the carbon activity. , Carbon precipitation can be suppressed more effectively while minimizing the decrease in efficiency.
Further, according to this fuel cell system, even when the first fuel gas is reformed using water as a modifier to generate hydrogen, carbon precipitation is more effective while minimizing the decrease in efficiency. Can be suppressed.
Further, according to this fuel cell system, the carbon activity is predetermined based on the partial pressure and the equilibrium constant of each component in the reforming reaction in the equilibrium state, and the carbon activity and the equilibrium constant in the carbon precipitation reaction. Since the amount of water supplied within the equilibrium range can be determined, carbon precipitation can be suppressed more effectively while minimizing the decrease in efficiency.

Further, in the fuel cell system according to claim 2 , in the fuel cell system according to claim 1 , the reformer further contains a hydrocarbon and the composition ratio of the hydrocarbon is the carbonization of the first fuel gas. A second fuel gas different from the composition ratio of hydrogen is supplied,
The partial pressure p (CH ₄ ), p (H ₂ O), p (CO), p (CO ₂ ), and p (H ₂ ) are units of the second fuel gas supplied to the reformer. When the flow rate per hour is B
p (CH ₄ ) = (c × A + B) × (1-wy)
p (H ₂ O) = H- (c × A + B) × (y + z)
p (CO) = (c × A + B) × (2w + yz)
p (CO ₂ ) = (d × A) − (c × A + B) × (wz)
p (H ₂ ) = (c × A + B) × (2w + 3y + z)
It is represented by.

According to this fuel cell system, even when the second fuel gas is supplied to the reformer in addition to the first fuel gas and reformed with water, carbon precipitation is performed while minimizing the decrease in efficiency. Can be suppressed more effectively.

On the other hand, in order to achieve the above object, the fuel cell system according to claim 3 is supplied with a first fuel gas containing a hydrocarbon and carbon dioxide, and a modifier for reforming the hydrocarbon. A fuel cell including a reformer and a control device for controlling the operation of the fuel cell are provided, and the control device has a predetermined carbon activity amount indicating the ease of carbon dioxide precipitation in the fuel cell. When the reformer uses oxygen in the air as the modifier, the first modification of the hydrocarbon and the carbon dioxide is provided with a determination unit for determining the amount of the modifier that falls within the above range. Hydrogen and carbon monoxide are produced by the quality reaction, and hydrogen and carbon monoxide are produced by the fourth reforming reaction between the hydrocarbon and the oxygen, and the hydrocarbon, the carbon monoxide, the carbon dioxide, and the hydrogen are produced. , And the divided pressures p (CH ₄ ), p (CO), p (CO ₂ ), p (H ₂ ), and p (O ₂ ) of the oxygen in each equilibrium state are the first reforming reaction. The reaction ratio in the above is w, the reaction ratio in the fourth reforming reaction is v, the flow rate of the first fuel gas supplied to the reformer per unit time is A, and the concentration of hydrocarbon in the first fuel gas. C, the concentration of carbon dioxide in the first fuel gas is d, and the amount of oxygen supplied is λ.
p (CH ₄ ) = (c × A) × (1-wv)
p (CO) = (c × A) × (2w + v)
p (CO ₂ ) = (d × A) − (c × A) × w
p (H ₂ ) = (c × A) × (2w + 2v)
p (O ₂ ) = λ- (c × A) × 0.5v
The equilibrium constants K1 and K5 in each of the first reforming reaction and the fourth reforming reaction are represented by.
K1 = p (H ₂ ) ² × p (CO) ² / p (CH ₄ ) / p (CO ₂ )
K5 = p (H ₂ ) ² × p (CO) / p (CH ₄ ) / p (O ₂ ) ^0.5
Represented by
When the carbon activity is Ac and the equilibrium constant in the carbon precipitation reaction of the fuel cell is K4,
Ac = K4 × p (CO) ² / p (CO ₂ )
The determination unit changes the candidate value of the oxygen supply amount λ, and the partial pressure p (CO) and the partial pressure p (CO) are derived based on the reaction ratios w and v derived in response to the change. Each value of p (CO ₂ ) is derived, and the candidate value at which the carbon activity Ac obtained from each derived value falls within the predetermined range is determined as the oxygen supply amount λ. ..

According to this fuel cell system, even when the first fuel gas is reformed using oxygen in the air as a reforming agent to generate hydrogen, carbon precipitation is further suppressed while minimizing the decrease in efficiency. It can be effectively suppressed.
Further, according to this fuel cell system, the carbon activity is predetermined based on the partial pressure and the equilibrium constant of each component in the reforming reaction in the equilibrium state, and the carbon activity and the equilibrium constant in the carbon precipitation reaction. Since the amount of oxygen supplied in the air within the equilibrium range can be determined, carbon precipitation can be suppressed more effectively while minimizing the decrease in efficiency.

Further, in the fuel cell system according to claim 4 , in the fuel cell system according to claim 3 , the reformer further contains a hydrocarbon and the composition ratio of the hydrocarbon is the carbonization of the first fuel gas. A second fuel gas different from the composition ratio of hydrogen is supplied,
The partial pressures p (CH ₄ ), p (CO), p (CO ₂ ), p (H ₂ ), and p (O ₂ ) are unit times of the second fuel gas supplied to the reformer. When the flow rate per hit is B,
p (CH ₄ ) = (c × A + B) × (1-w-v)
p (CO) = (c × A + B) × (2w + v)
p (CO ₂ ) = (d × A) − (c × A + B) × w
p (H ₂ ) = (c × A + B) × (2w + 2v)
p (O ₂ ) = λ- (c × A + B) × 0.5v
It is represented by.

According to this fuel cell system, even when the second fuel gas is supplied to the reformer in addition to the first fuel gas and reformed by oxygen in the air, the decrease in efficiency is minimized. The precipitation of carbon can be suppressed more effectively.

Further, the fuel cell system according to claim 5 is economical in the case where the control device operates the fuel cell by supplying the first fuel gas in the fuel cell system according to claim 2 or 4. Based on the first index shown and the second index showing the economic efficiency when the fuel cell is operated by supplying both the first fuel gas and the second fuel gas, the reformer is equipped with the first index. 2 It is further provided with a determination unit for determining whether or not to supply fuel gas.

According to this fuel cell system, the fuel cell can be operated more economically and is more expensive than the case where the second fuel gas is supplied to the reformer without considering the economic efficiency during the operation of the fuel cell. Economic efficiency can be realized.

Further, in the fuel cell system according to claim 6 , in the fuel cell system according to claim 5 , the determination unit determines whether or not to supply the second fuel gas to the reformer. This is performed when the flow rate of the first fuel gas supplied to the reformer is less than a predetermined amount.

According to this fuel cell system, the second fuel gas is supplied to the reformer without considering the economic efficiency when the flow rate of the first fuel gas supplied to the reformer is smaller than a predetermined amount. It is possible to further improve the economic efficiency in the operation of the fuel cell as compared with the case where the fuel cell is operated.

Further, in the fuel cell system according to claim 7 , in the fuel cell system according to claim 5 or 6 , each value of the first index and the second index is based on the cost of operating the fuel cell. Is also a positive value when the profit is large, and when the value of the first index is equal to or higher than the value of the second index and the value of the first index is a positive value, the above-mentioned It is determined that it is more economical to supply the first fuel gas to the reformer alone, the value of the second index is larger than the value of the first index, and the value of the second index is positive. In the case of the value of, it is determined that it is more economical to supply both the first fuel gas and the second fuel gas, or the second fuel gas alone to the reformer.

According to this fuel cell system, the second fuel gas is supplied to the reformer from the viewpoint of economy by comparing the values of the two indicators indicating economic efficiency and determining the positive or negative of the values of the two indicators. Since it can be determined whether or not to supply the fuel cell, it is possible to further improve the economic efficiency in the operation of the fuel cell.

Further, in the fuel cell system according to claim 8 , in the fuel cell system according to any one of claims 5 to 7 , the value In1 of the first index is supplied to the reformer. The amount of heat per unit flow rate of one fuel gas is α, the purchase price per unit flow rate is ε, the power generation efficiency during partial load operation of the fuel cell is η1, and the first fuel gas is used to generate electricity in the fuel cell. Assuming that the selling price per unit amount of power generated is m
In1 = (η1 × α × A × m) − (ε × A)
Represented by
The value In2 of the second index is β for the amount of heat per unit flow rate of the second fuel gas supplied to the reformer, σ for the purchase price per unit flow rate, and the power generation efficiency during the rated operation of the fuel cell. When the selling price per unit electric energy obtained by generating electricity from the fuel cell with η2 and the second fuel gas is n.
In2 = (η2 × α × A × m) + (η2 × β × B × n) − (ε × A + σ × B)
It is represented by.

According to this fuel cell system, the values of two indicators indicating economic efficiency can be derived by a simple calculation formula of only addition, subtraction, and multiplication, so that the process of determining economic efficiency can be performed more quickly. be able to.

Meanwhile, in order to achieve the above object, a control apparatus according to claim 9, the first fuel gas containing hydrocarbon and carbon dioxide, and, modifiers for reforming the hydrocarbon is fed, and When water is used as the modifier, hydrogen and carbon monoxide are produced by the first modification reaction between the hydrocarbon and carbon dioxide, and the second modification reaction between the hydrocarbon and the water to produce hydrogen and carbon monoxide, further, the control device for controlling the operation of the fuel cell with a reformer that generates carbon dioxide and hydrogen by the third reforming reaction between the water and the carbon monoxide A determination unit for determining the amount of the modifier whose carbon activity, which indicates the ease of carbon dioxide precipitation in the fuel cell, falls within a predetermined range, is provided , and the hydrocarbon, the water, and the above-mentioned one. The partial pressures p (CH ₄ ), p (H ₂ O), p (CO), p (CO ₂ ), and p (H ₂ ) of carbon oxide, carbon dioxide, and hydrogen at their respective equilibrium states are The reaction ratio in the first reforming reaction is w, the reaction ratio in the second reforming reaction is y, the reaction ratio in the third reforming reaction is z, and the first fuel gas supplied to the reformer. When the flow rate per unit time is A, the hydrocarbon concentration in the first fuel gas is c, the carbon dioxide concentration in the first fuel gas is d, and the water supply amount is H.
p (CH ₄ ) = (c × A) × (1-wy)
p (H ₂ O) = H- (c × A) × (y + z)
p (CO) = (c × A) × (2w + yz)
p (CO ₂ ) = (d × A) − (c × A) × (wz)
p (H ₂ ) = (c × A) × (2w + 3y + z)
The equilibrium constants K1, K2, and K3 in each of the first reforming reaction, the second reforming reaction, and the third reforming reaction are represented by.
K1 = p (H ₂ ) ² × p (CO) ² / p (CH ₄ ) / p (CO ₂ )
K2 = p (H ₂ ) ³ × p (CO) / p (CH ₄ ) / p (H ₂ O)
K3 = p (CO ₂ ) x p (H ₂ ) / p (CO) / p (H ₂ O)
When the carbon activity is Ac and the equilibrium constant in the carbon precipitation reaction of the fuel cell is K4.
Ac = K4 × p (CO) ² / p (CO ₂ )
The determination unit changes the candidate value of the water supply amount H, and the partial pressure p (CO) is derived based on the reaction ratios w, y, and z derived in response to the change. ) And p (CO ₂ ) are derived, and the candidate value in which the carbon activity Ac obtained from each of the derived values falls within the predetermined range is determined as the water supply amount H. Is.
On the other hand, in order to achieve the above object, the control device according to claim 10 is supplied with a first fuel gas containing a hydrocarbon and carbon dioxide, and a modifier for reforming the hydrocarbon. When oxygen in the air is used as the modifier, hydrogen and carbon monoxide are generated by the first modification reaction between the hydrocarbon and the carbon dioxide, and the fourth modification of the hydrocarbon and the oxygen. A fuel cell provided with a reformer that produces hydrogen and carbon monoxide by a quality reaction, and a control device for controlling the operation of the fuel cell are provided, and the control device provides carbon precipitation in the fuel cell. Each of the hydrocarbon, the carbon monoxide, the carbon dioxide, the hydrogen, and the oxygen is provided with a determination unit for determining the amount of the modifier whose carbon activity indicating ease falls within a predetermined range. In the equilibrium state, the partial pressures p (CH ₄ ), p (CO), p (CO ₂ ), p (H ₂ ), and p (O ₂ ) determine the reaction ratio in the first modification reaction. The reaction ratio in the fourth reforming reaction is v, the flow rate of the first fuel gas supplied to the reformer per unit time is A, the concentration of hydrocarbons in the first fuel gas is c, and the first When the concentration of carbon dioxide in the fuel gas is d and the amount of oxygen supplied is λ,
p (CH ₄ ) = (c × A) × (1-wv)
p (CO) = (c × A) × (2w + v)
p (CO ₂ ) = (d × A) − (c × A) × w
p (H ₂ ) = (c × A) × (2w + 2v)
p (O ₂ ) = λ- (c × A) × 0.5v
The equilibrium constants K1 and K5 in each of the first reforming reaction and the fourth reforming reaction are represented by.
K1 = p (H ₂ ) ² × p (CO) ² / p (CH ₄ ) / p (CO ₂ )
K5 = p (H ₂ ) ² × p (CO) / p (CH ₄ ) / p (O ₂ ) ^0.5
Represented by
When the carbon activity is Ac and the equilibrium constant in the carbon precipitation reaction of the fuel cell is K4,
Ac = K4 × p (CO) ² / p (CO ₂ )
The determination unit changes the candidate value of the oxygen supply amount λ, and the partial pressure p (CO) and the partial pressure p (CO) are derived based on the reaction ratios w and v derived according to the change. Each value of p (CO ₂ ) is derived, and the candidate value at which the carbon activity Ac obtained from each derived value falls within the predetermined range is determined as the oxygen supply amount λ. ..

Further, in order to achieve the above object, the program according to claim 11 causes the computer to function as a control device included in the fuel cell system according to any one of claims 1 to 8 .

According to each of the above control devices and programs, the amount of the modifier is determined without specifying the range of the carbon activity in order to determine the amount of the modifier whose carbon activity falls within the predetermined range. It is possible to more effectively suppress the precipitation of carbon while minimizing the decrease in efficiency.

As described in detail above, according to the present invention, carbon precipitation can be effectively suppressed while minimizing the decrease in efficiency.

It is a block diagram which shows an example of the whole structure of the fuel cell system which concerns on 1st Embodiment. It is a flowchart which shows an example of the processing flow by the program which concerns on 1st Embodiment. It is a flowchart which shows an example of the flow of the water supply amount determination process by the program which concerns on 1st Embodiment. It is a schematic diagram which provides the explanation of the example of the processing content by the water supply amount determination part which concerns on 1st Embodiment. It is a schematic diagram provided for the explanation of an example of the processing content by the economic efficiency determination unit which concerns on 1st Embodiment. It is a block diagram which shows an example of the whole structure of the fuel cell system which concerns on 2nd Embodiment. It is a flowchart which shows an example of the processing flow by the program which concerns on 2nd Embodiment.

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

[First Embodiment]
FIG. 1 is a block diagram showing an example of the overall configuration of the fuel cell system 10 according to the first embodiment.
The fuel cell system 10 according to the first embodiment includes a fuel cell 20, a control device 30, and a fuel gas supply device 40. The fuel cell 20 includes a reformer 22, a stack (fuel cell main body) 24, and a combustor 26. The reformer 22, the stack 24, and the combustor 26 are housed in a hot box.

The reformer 22 is arranged in front of the stack 24. Biogas G1 is supplied to the reformer 22 via the fuel gas supply device 40. Biogas G1 is an example of a first fuel gas containing hydrocarbons and carbon dioxide. Further, the reformer 22 may be further supplied with the city gas G2 via the fuel gas supply device 40. The city gas G2 is an example of a second fuel gas containing a hydrocarbon. The composition ratio of the hydrocarbon of the second fuel gas is different from the composition ratio of the hydrocarbon of the first fuel gas. In the case of this example, the composition ratio of the hydrocarbon of the second fuel gas is larger than the composition ratio of the hydrocarbon of the first fuel gas. The typical composition of biogas G1 is about 60% methane (CH ₄ ), which is an example of hydrocarbon, and about 40% carbon dioxide (CO ₂ ). On the other hand, the composition of city gas G2 is about 90% methane in the case of 13A gas.

The reformer 22 has a catalyst for reforming carbon dioxide. For this catalyst, for example, a noble metal catalyst such as nickel-based, ruthenium-based, or rhodium-based catalyst, or a Ni-based catalyst is used. By the action of this catalyst, carbon dioxide in the biogas G1 is used to reform methane with carbon dioxide to generate a reformed gas containing carbon monoxide and hydrogen. The carbon dioxide reforming reaction in the reformer 22 is as shown in the following formula (1). In addition, carbon dioxide may be supplied from the outside to reform methane with carbon dioxide. The formula (1) shows an example of the first reforming reaction.

CH ₄ + CO ₂ → 2H ₂ + 2CO… (1)

As an example, a solid oxide fuel cell (SOFC) 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 (oxidizing agent gas) is supplied to the air electrode of each cell.

At the air electrode, as shown by the following formula (2), oxygen in the air reacts with electrons to generate oxygen ions. This oxygen ion reaches the fuel electrode through the electrolyte layer.

(Air pole reaction)
1 / 2O ₂ + 2e ⁻ → O ^2- … (2)

On the other hand, at the fuel electrode, as represented by the following formulas (3) and (4), oxygen ions passing through the electrolyte layer react with hydrogen and carbon monoxide in the reformed gas, and steam, carbon dioxide, and so on. And electrons are generated. The electrons generated at the fuel electrode reach the air electrode through an external circuit. Then, the electrons move from the fuel electrode to the air electrode in this way, so that power is generated in each cell. In addition, each cell generates heat due to the above electrochemical reaction during power generation.

(Fuel electrode reaction)
H ₂ + O ^2- → H ₂ O + 2e ⁻ … (3)
CO + O ^2- → CO ₂ + 2e ⁻ … (4)

In addition to steam and carbon dioxide generated by the fuel electrode reaction, the gas generated at the fuel electrode (hereinafter referred to as anode off gas) is generated by the reformer 22 and unreacted at the fuel electrode of the stack 24. Includes 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 after 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 off gas contains unreacted hydrogen and carbon monoxide at the fuel electrode of the stack 24, and the combustor 26 burns the anode off gas using the cathode off gas containing oxygen. The flue gas generated by the combustion of the combustor 26 is discharged to the outside of the fuel cell 20.

In this embodiment, carbon dioxide contained in the biogas G1 is used for reforming, which is efficient. However, on the other hand, since this carbon dioxide reforming reaction is an equilibrium reaction as shown in the above formula (1), there is a possibility that methane becomes surplus in equilibrium and carbon is precipitated. In order to suppress the precipitation of carbon, in the first embodiment, water (H ₂ O) Wa is further supplied to the reformer 22. Water Wa is an example of a modifier. By supplying this water Wa, excess methane can be reformed and carbon precipitation can be suppressed. The reforming reaction when water Wa is supplied to the reformer 22 is as shown in the following formulas (5) and (6). The formula (5) shows an example of the second reforming reaction, and the formula (6) shows an example of the third reforming reaction.

CH ₄ + H ₂ O → 3H ₂ + CO… (5)
CO + H ₂ O → CO ₂ + H ₂ … (6)

On the other hand, the control device 30 controls the operation of the fuel cell 20. The control device 30 is composed of an electronic circuit including a calculation unit 32 and a storage unit 34. In the storage unit 34, a program 34A for determining the supply amount of water Wa capable of suppressing carbon precipitation in the fuel cell 20 and controlling the supply amount of water Wa based on the determination result is stored in advance. Further, the program 34A may realize a function of determining the economic efficiency when the fuel cell 20 is operated and controlling the operation of the fuel cell 20 based on the determination result. The program 34A may be pre-installed in the control device 30, for example. The program 34A may be realized by storing it in a non-volatile storage medium or distributing it via a network and appropriately installing it in the control device 30. Examples of non-volatile storage media include CD-ROM (Compact Disc Read Only Memory), magneto-optical disk, HDD (Hard Disk Drive), DVD-ROM (Digital Versatile Disc Read Only Memory), flash memory, and memory. Cards and the like can be mentioned.

The calculation unit 32 includes a CPU (Central Processing Unit), and by reading and executing the program 34A stored in the storage unit 34, the flow rate determination unit 32A, the heat amount calculation unit 32B, the water supply amount determination unit 32C, and the economy It functions as a sex determination unit 32D and an operation control unit 32E. The economic efficiency determination unit 32D may have the functions of the flow rate determination unit 32A and the calorific value calculation unit 32B. In this case, the flow rate determination unit 32A and the calorific value calculation unit 32B are unnecessary.

By the way, as described above, when carbon dioxide in the biogas G1 is used for reforming, efficient operation is possible, but there is a risk that carbon will precipitate. Precipitation of carbon is not desirable because it may deactivate the catalyst used in the reformer, for example.

On the other hand, the water supply amount determining unit 32C according to the first embodiment is the amount of water Wa in which the carbon activity Ac indicating the ease of carbon precipitation in the fuel cell 20 falls within a predetermined range. To determine. The water supply amount determination unit 32C is an example of the determination unit. The predetermined range is, for example, a range (0 <Ac <1) that is larger than 0 (zero) and smaller than 1. It is said that the larger the carbon activity Ac, the easier it is for carbon to precipitate. The carbon precipitation reaction in the fuel cell 20 is represented by the following formula (7) as an example. The water supply amount determination unit 32C will be described later.

2CO → C + CO ₂ … (7)

On the other hand, since it is difficult to stably supply the biogas G1, it is possible to stably supply methane by using the city gas G2 together. However, on the other hand, when the supply amount of biogas G1 is reduced, etc., from the viewpoint of economy, it is more economical to continue to supply biogas G1 alone without using city gas G2 together. There is.

Therefore, the economic efficiency determination unit 32D according to the present embodiment determines whether or not to supply the city gas G2 to the fuel cell 20 based on the first index and the second index. The economic efficiency determination unit 32D is an example of the determination unit. The first index shows the economic efficiency when the fuel cell 20 is operated by supplying the biogas G1. The second index shows the economic efficiency when the fuel cell 20 is operated by supplying both the biogas G1 and the city gas G2. Each of the first index and the second index is an index indicating economic efficiency, that is, the degree of profit with respect to cost. The economic efficiency determination unit 32D will be described later.

The operation control unit 32E controls the flow rate (supply amount) of each of the biogas G1 and the city gas G2 supplied to the fuel cell 20 according to the determination result of the economic efficiency determination unit 32D. The flow rates of the biogas G1 and the city gas G2 supplied to the fuel cell 20 are adjusted by the operation control unit 32E controlling the fuel gas supply device 40.

That is, the fuel gas supply device 40 includes a first valve 41 provided in the supply path 50 of the biogas G1 and a second valve 42 provided in the supply path 52 of the city gas G2. The opening degree of each of the first valve 41 and the second valve 42 is controlled by the operation control unit 32E. That is, the flow rate of the biogas G1 is adjusted by the operation control unit 32E controlling the opening degree of the first valve 41 of the fuel gas supply device 40. Similarly, the flow rate of the city gas G2 is adjusted by the operation control unit 32E controlling the opening degree of the second valve 42 of the fuel gas supply device 40.

Further, in the supply path 50 of the biogas G1, a concentration meter Cm and a flow meter Fm1 are provided between the fuel gas supply device 40 and the fuel cell 20. The densitometer Cm measures the concentration c [%] of methane contained in the biogas G1 (and the concentration d [%] of carbon dioxide), respectively. The flow meter Fm1 measures the flow rate of the biogas G1. Further, in the supply path 52 of the city gas G2, a flow meter Fm2 is provided between the fuel gas supply device 40 and the fuel cell 20. The flow meter Fm2 measures the flow rate of the city gas G2.

On the other hand, a third valve 43 is provided in the water Wa supply path 54. A flow meter Fm3 is provided in the water Wa supply path 54. The amount of water Wa supplied is adjusted by the operation control unit 32E controlling the opening degree of the third valve 43. The operation control unit 32E controls the amount of water Wa supplied to the fuel cell 20 according to the determination result of the water supply amount determination unit 32C.

A flow meter Fm1 is connected to the flow rate determination unit 32A. The flow rate determination unit 32A continuously inputs the flow rate of the biogas G1 measured by the flow meter Fm1. The flow rate of the biogas G1 measured by the flow meter Fm1 may be input to the flow rate determination unit 32A at predetermined intervals. The flow rate determination unit 32A determines whether or not the input flow rate of the biogas G1 is less than the rated equivalent flow rate. If the flow rate of the biogas G1 is less than the rated equivalent flow rate, it is determined that the flow rate of the biogas G1 is decreasing. The rated equivalent flow rate is, for example, a flow rate at which the supply amount of the biogas G1 is maximized, and is a known amount predetermined according to the specifications of the fuel cell 20 and the like. In the present embodiment, the rated equivalent flow rate is determined by the value of the flow rate, but it may be determined within the range of the flow rate.

Further, the flow rate determination unit 32A converts the flow rate of the biogas G1 measured by the flow meter Fm1 into the flow rate A [mol / h] per unit time, and causes the water supply amount determination unit 32C and the economic efficiency determination unit 32D. Output. The flow rate determination unit 32A calculates the flow rate (F ₀ −A) obtained by subtracting the flow rate A from the rated equivalent flow rate F ₀ [mol / h] per unit time, and calculates the flow rate (F ₀ −A) of the city gas G2 per unit time. Mol / h] is output to the water supply amount determination unit 32C and the economic efficiency determination unit 32D. However, the rated equivalent flow rate F ₀ per unit time is known.

A densitometer Cm is connected to the calorific value calculation unit 32B. The calorific value calculation unit 32B inputs the concentration c (60% as an example) of methane contained in the biogas G1 measured by the densitometer Cm. The calorific value calculation unit 32B derives the calorific value α [kWh / mol] per unit flow rate of the biogas G1 based on the input methane concentration c (= 60%). For example, assuming that the calorific value Q ₀ [kWh / mol] per unit flow rate of methane is known, the calorific value α is derived by the following equation (8).

α = Q ₀ × 60/100… (8)

Further, the calorific value calculation unit 32B derives the calorific value β [kWh / mol] per unit flow rate of the city gas G2, assuming that the concentration of methane contained in the city gas G2 is, for example, 90%. The calorific value β is derived by the following equation (9). Here, the calorific value of hydrocarbons other than methane is ignored.

β = Q ₀ × 90/100… (9)

In the case of city gas G2, since the main component is a hydrocarbon such as methane, the calorific _value β of the city gas G2 may be approximated by the calorific _value Q0 of methane. The calorific value calculation unit 32B outputs the calorific values α and β derived above to the economic efficiency determination unit 32D.

A densitometer Cm is connected to the water supply amount determining unit 32C. The water supply amount determination unit 32C inputs each of the concentration c of methane and the concentration d of carbon dioxide contained in the biogas G1 measured by the concentration meter Cm. Each of the flow rate A of the biogas G1 and the flow rate B of the city gas G2 is input from the flow rate determination unit 32A to the water supply amount determination unit 32C. The gas constant R (unit: J / mol · K), the operating temperature T (unit: K) of the fuel cell 20, and the Faraday constant F (unit: C / mol) are input to the water supply amount determination unit 32C. .. The value g1 [J / mol] of the Gibbs free energy ΔG1 determined by the above equation (1) is input to the water supply amount determination unit 32C. Similarly, the water supply amount determination unit 32C is subjected to the Gibbs free energy ΔG2 value g2 determined by the above formula (5), the Gibbs free energy ΔG3 value g3 determined by the above formula (6), and the above formula (7). The value g4 of the Gibbs free energy ΔG4 to be determined is input. Further, a range (0 <Ac <1) of the carbon activity Ac is input to the water supply amount determining unit 32C.

The water supply amount determining unit 32C has an equilibrium constant K1 corresponding to the above equation (1), an equilibrium constant K2 corresponding to the above equation (5), an equilibrium constant K3 corresponding to the above equation (6), and the above equation (7). The equilibrium constant K4 corresponding to is derived from the following equations (10) to (13). However, g1 to g4 are values of Gibbs free energy ΔG1 to ΔG4 [J / mol], R is a gas constant, and T is an operating temperature.

K1 = Exp (−ΔG1 / RT) = Exp (−g1 / RT)… (10)
K2 = Exp (−ΔG2 / RT) = Exp (−g2 / RT)… (11)
K3 = Exp (−ΔG3 / RT) = Exp (−g3 / RT)… (12)
K4 = Exp (−ΔG4 / RT) = Exp (−g4 / RT)… (13)

On the other hand, the partial pressures of methane, water, carbon monoxide, carbon dioxide, and hydrogen at equilibrium p (CH ₄ ), p (H ₂ O), p (CO), p (CO ₂ ), and p. (H ₂ ) is represented by the following equations (14) to (18). However, w is the reaction ratio in the above formula (1), y is the reaction ratio in the above formula (5), z is the reaction ratio in the above formula (6), and H is the supply amount [mol / h] of water Wa. Further, c is the methane concentration [%] in the biogas G1, d is the carbon dioxide concentration [%] in the biogas G1, and A is the flow rate [mol / h] per unit time of the biogas G1.

p (CH ₄ ) = (c × A) × (1-wy)… (14)
p (H ₂ O) = H- (c × A) × (y + z)… (15)
p (CO) = (c × A) × (2w + yz)… (16)
p (CO ₂ ) = (d × A) − (c × A) × (wz)… (17)
p (H ₂ ) = (c × A) × (2w + 3y + z)… (18)

The initial value of p (CH ₄ ) is (c × A), the initial value of p (H ₂ O) is (H), and the initial value of p (CO) is 0 (zero). The initial value of p (CO ₂ ) is (d × A), and the initial value of p (H ₂ ) is 0 (zero). The sum of these partial pressures p is 1.

The equilibrium constants K1, K2, and K3 in each of the above equations (1), (5), and (6) are represented by the following equations (19) to (21).

K1 = p (H ₂ ) ² × p (CO) ² / p (CH ₄ ) / p (CO ₂ )… (19)
K2 = p (H ₂ ) ³ × p (CO) / p (CH ₄ ) / p (H ₂ O)… (20)
K3 = p (CO ₂ ) × p (H ₂ ) / p (CO) / p (H ₂ O)… (21)

Further, the carbon activity Ac is represented by the following formula (22). However, K4 is an equilibrium constant corresponding to the above equation (7) and is derived by the above equation (13).

Ac = K4 × p (CO) ² / p (CO ₂ )… (22)

From the above, the water supply amount determination unit 32C changes the candidate value of the water supply amount H of the water Wa, and based on the reaction ratios w, y, and z derived according to the change, the partial pressure p (CO) and Each value of p (CO ₂ ) is derived. Then, the water supply amount determining unit 32C selects a candidate value in which the carbon activity Ac obtained from each of the derived partial pressure p (CO) and p (CO ₂ ) values is, for example, greater than 0 and less than 1. It is determined as the supply amount H of water Wa.

That is, since the equilibrium constants K1 to K3 are known values under a certain operating temperature T, if the candidate value of the supply amount H is set to an arbitrary value, the relationship between the above equations (14) to (21) can be obtained. , Three simultaneous equations with the reaction ratios w, y, and z as unknowns are established. By solving these three simultaneous equations, the values of the reaction ratios w, y, and z are obtained, and each of the above partial pressures p is determined. Since the equilibrium constant K4 is also a known value under an operating temperature T, the carbon activity Ac is determined from the above equation (22). Further, when the determined carbon activity Ac is not in the range of 0 <Ac <1, the candidate value is incremented and the same calculation is performed, and when the determined carbon activity Ac is in the above range, it is set. The candidate value is determined as the water supply amount H.

Here, when the city gas G2 is further supplied to the fuel cell 20, the partial pressures p (CH ₄ ) and p (H ₂ O) of methane, water, carbon monoxide, carbon dioxide, and hydrogen in each equilibrium state are supplied. ), P (CO), p (CO ₂ ), and p (H ₂ ) are represented by the following equations (23) to (27). However, B is the flow rate [mol / h] of the city gas G2 per unit time, and is represented by (F ₀ −A). Here, it is assumed that the entire composition of city gas G2 is regarded as methane.

p (CH ₄ ) = (c × A + B) × (1-wy)… (23)
p (H ₂ O) = H- (c × A + B) × (y + z)… (24)
p (CO) = (c × A + B) × (2w + yz)… (25)
p (CO ₂ ) = (d × A) − (c × A + B) × (wz)… (26)
p (H ₂ ) = (c × A + B) × (2w + 3y + z)… (27)

The initial value of p (CH ₄ ) is (c × A + B), the initial value of p (H ₂ O) is (H), and the initial value of p (CO) is 0 (zero). The initial value of p (CO ₂ ) is (d × A), and the initial value of p (H ₂ ) is 0 (zero). The sum of these partial pressures p is 1.

When biogas G1 and city gas G2 are used in combination, water Wa can be similarly supplied by using the above formulas (23) to (27), formulas (19) to (21), and formula (22). The quantity H can be determined.

On the other hand, the economic efficiency determination unit 32D derives the value In1 of the first index (hereinafter referred to as the first index value In1) and the value In2 of the second index (hereinafter referred to as the second index value In2). The first index value In1 is an index value indicating the economic efficiency when the fuel cell 20 is operated by supplying the biogas G1. The second index value In2 is an index value indicating the economic efficiency when the fuel cell 20 is operated by supplying both the biogas G1 and the city gas G2. Each of these first index value In1 and second index value In2 becomes a positive value when the profit is larger than the cost for operating the fuel cell 20. Hereinafter, specific examples of the first index value In1 and the second index value In2 will be described, but the unit of each parameter is an example and is not limited thereto.

The first index value In1 (unit: yen / h) is A [mol / h] for the flow rate of the biogas G1 supplied to the fuel cell 20 per unit time, and α [kWh / mol] for the amount of heat per unit flow rate. , The purchase price per unit flow rate is ε [yen / mol], the power generation efficiency during partial load operation of the fuel cell 20 is η1 [%], and the unit power amount obtained by generating power with the fuel cell 20 by the biogas G1. When the selling price per unit is m [yen / kWh], it is expressed by the following formula (28). In addition, the partial load operation shall represent the state of operating at an output less than the rated output.

In1 = (η1 × α × A × m) − (ε × A)… (28)

On the other hand, the second index value In2 (unit: yen / h) is B [mol / h] for the flow rate of the city gas G2 supplied to the fuel cell 20 per unit time and β [kWh / h] for the amount of heat per unit flow rate. mol], the purchase price per unit flow rate is σ [yen / mol], the power generation efficiency during rated operation of the fuel cell 20 is η2 [%], and the unit power obtained by generating power with the fuel cell 20 using city gas G2. When the selling price per unit is n [yen / kWh], it is expressed by the following formula (29). The rated operation means the state of operating at the rated output.

In2 = (η2 × α × A × m) + (η2 × β × B × n)-(ε × A + σ × B)… (29)

However, the flow rates A and B are input from the flow rate determination unit 32A to the economic efficiency determination unit 32D, and the heat quantities α and β are input to the economic efficiency determination unit 32D from the heat quantity calculation unit 32B. Further, the purchase prices ε and σ, the power generation efficiencies η1 and η2, and the power sales prices m and n are input to the economic efficiency determination unit 32D via an input unit (not shown) or the like. The input purchase prices ε and σ, power generation efficiencies η1 and η2, and power sales prices m and n may be stored in the storage unit 34 and used repeatedly as long as there is no fluctuation.

Next, the operation of the control device 30 according to the first embodiment will be described with reference to FIG. Note that FIG. 2 is a flowchart showing an example of the processing flow by the program 34A according to the first embodiment.
When the operation start of the fuel cell 20 is instructed, the calculation unit 32 reads out and executes the program 34A stored in the storage unit 34.

First, in step 100 of FIG. 2, the operation control unit 32E fully opens the first valve 41 of the fuel gas supply device 40, fully closes the second valve 42, starts supplying the biogas G1, and starts supplying the biogas. The rated operation of the fuel cell 20 is started by G1. At the time of this rated operation, the reformer 22 is supplied with the biogas G1 having a rated equivalent flow rate capable of performing the rated operation of the fuel cell 20. In this case, the supply amount of city gas G2 is set to 0 (zero).

In step 102, the water supply amount determination unit 32C inputs each of the concentration c [%] of methane and the concentration d [%] of carbon dioxide contained in the biogas G1 measured by the concentration meter Cm.

In step 104, the flow rate determination unit 32A determines whether or not the flow rate of the biogas G1 has decreased from the rated equivalent flow rate. If it is determined that the flow rate of the biogas G1 has decreased (in the case of an affirmative determination), the process proceeds to step 106, and if it is determined that the flow rate of the biogas G1 has not decreased (in the case of a negative determination), the process proceeds to step 112. To do.

In step 106, the flow rate determination unit 32A converts the flow rate of the biogas G1 measured by the flow meter Fm1 into the flow rate A [mol / h] per unit time, and further, the flow rate of the city gas G2 per unit time. B [mol / h] is derived. On the other hand, the calorific value calculation unit 32B derives calorific values α and β [kWh / mol] based on the above equations (8) and (9).

Next, in step 108, the economic efficiency determination unit 32D determines whether or not the first index value In1 is equal to or higher than the second index value In2 and the first index value In1 is a positive value. When the economic efficiency determination unit 32D determines that the first index value In1 ≥ the second index value In2 and the first index value In1> 0 (in the case of affirmative determination), the process proceeds to step 110 and the first index value When it is determined that the value In1 ≥ the second index value In2 and the first index value In1> 0 (in the case of a negative determination), the process proceeds to step 114.

Next, in step 110, the economic efficiency determination unit 32D determines that it is more economical to supply the biogas G1 alone without supplying the city gas G2. Then, according to the determination result by the economic efficiency determination unit 32D, the operation control unit 32E, for example, the supply amount of the biogas G1 becomes A [mol / h], and the supply amount of the city gas G2 becomes 0 (zero). The state is maintained to control the operation of the fuel cell 20. Further, the operation control unit 32E controls the operation of the fuel cell 20 so that the current density in the fuel cell 20 becomes J [A / cm ² ] during the partial load operation.

In step 112, the water supply amount determining unit 32C determines the supply amount H of water Wa when the biogas G1 is supplied alone by using the above formulas (10) to (22).

On the other hand, in step 114, the economic efficiency determination unit 32D determines whether or not the second index value In2 is larger than the first index value In1 and the second index value In2 is a positive value. When it is determined that the second index value In2> the first index value In1 and the second index value In2> 0 (in the case of affirmative judgment), the process proceeds to step 116, and the process proceeds to step 116, where the second index value In2> the first index value is determined. When it is determined that In1 and the second index value In2> 0 is not satisfied (in the case of a negative determination), the process proceeds to step 120.

In step 116, the economic efficiency determination unit 32D determines that both the biogas G1 and the city gas G2 are supplied. The economic efficiency determination unit 32D may determine that the city gas G2 is supplied alone when the flow rate of the biogas G1 is extremely reduced, such as when the flow rate of the biogas G1 becomes 0 (zero). .. Then, according to the determination result by the economic efficiency determination unit 32D, the operation control unit 32E maintains the supply amount of the biogas G1 as A [mol / h], and the supply amount of the city gas G2 is B [. The opening degree of the second valve 42 of the fuel gas supply device 40 is controlled so as to be mol / h]. Here, the supply amount of the city gas G2 is measured by the flow meter Fm2. The operation control unit 32E controls the opening degree of the second valve 42 so that the measured value of the flow meter Fm2 is B [mol / h].

In step 118, the water supply amount determining unit 32C uses the above equations (10) to (13), the above equations (19) to (22), and further, instead of the above equations (14) to (18). Using the formulas (23) to (27), the supply amount H of water Wa when both the biogas G1 and the city gas G2 are supplied is determined.

On the other hand, in step 120, when the economic efficiency determination unit 32D determines that the first index value In1 ≦ 0 and the second index value In2 ≦ 0, that is, when the profit is not positive, the power generation is stopped or Judged to shift to the hot standby state. Then, the operation control unit 32E controls to temporarily stop the power generation in the fuel cell 20 as an example according to the determination result by the economic efficiency determination unit 32D. The flow rate of the biogas G1 shall be measured even when the power generation is stopped.

Next, in step 122, the operation control unit 32E controls the opening degree of the third valve 43 so that the supply amount of water Wa becomes the supply amount H according to the determination result by the water supply amount determination unit 32C. Here, the supply amount of water Wa is measured by the flow meter Fm3. The operation control unit 32E controls the opening degree of the third valve 43 so that the measured value of the flow meter Fm3 is H [mol / h].

Next, in step 124, the flow rate determination unit 32A determines whether or not the flow rate of the biogas G1 has fluctuated based on the measurement result of the flow meter Fm1. If it is determined that there is a fluctuation in the flow rate (in the case of an affirmative determination), the process proceeds to step 106, and if it is determined that there is no fluctuation in the flow rate (in the case of a negative determination), the process proceeds to step 126.

In step 126, the operation control unit 32E 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 affirmative determination), the process proceeds to step 128, 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 It shifts to 124 and becomes a standby. As an example, when the operation end instruction by the operator is received, it may be determined that the operation of the fuel cell 20 is ended.

In step 128, the operation control unit 32E fully closes the first valve 41 and the second valve 42 of the fuel gas supply device 40, and further the third valve 43, and supplies biogas G1, city gas G2, and water Wa. To stop. The operation control unit 32E controls to end the operation of the fuel cell 20, and ends the series of processes.

FIG. 3 is a flowchart showing an example of the flow of the water supply amount determination process by the program 34A according to the first embodiment.
This flowchart shows the flow of subroutine processing in step 112 or step 118 shown in FIG.

First, in step 200, the water supply amount determination unit 32C inputs the values of each parameter. The values of each parameter include gas constant R, operating temperature T of fuel cell 20, faraday constant F, flow rate A of biogas G1, flow rate B of city gas G2, methane concentration c in biogas G1, and biogas. Contains the carbon dioxide concentration d in G1. Further, the values of each parameter include the Gibbs free energies ΔG1 to ΔG4 values g1 to g4 and the carbon activity Ac.

In step 202, the water supply amount determination unit 32C sets a candidate value (initial value) of the water supply amount H of the water Wa.

In step 204, the water supply amount determination unit 32C has the above equations (10) to (21) (however, when the city gas G2 is supplied, the above equations (14) to (14) to the above equations (14) to (21)) based on the candidate values set above. The reaction ratios w, y, and z are derived by using the above formulas (23) to (27) instead of (18). The reaction ratio w corresponds to the above formula (1), the reaction ratio y corresponds to the above formula (5), and the reaction ratio z corresponds to the above formula (6).

In step 206, the water supply amount determining unit 32C determines the above formulas (14) to (18) (or the above formulas (23) to (27)) based on the above-derived reaction ratios w, y, and z. , P (CH ₄ ), p (H ₂ O), p (CO), p (CO ₂ ), partial pressures of methane, water, carbon monoxide, carbon dioxide, and hydrogen at their respective equilibrium states. And p (H ₂ ) are determined.

In step 208, the water supply amount determining unit 32C determines the carbon activity Ac using the above formula (22) based on each of the determined partial pressures p.

In step 210, the water supply amount determination unit 32C determines whether or not the carbon activity Ac determined above falls within the range of 0 <Ac <1. When it is determined that the carbon activity Ac does not fall within the range of 0 <Ac <1 (in the case of a negative determination), the process proceeds to step 212, and when it is determined that the carbon activity Ac falls within the range of 0 <Ac <1. (In the case of affirmative determination), the process proceeds to step 214.

In step 212, the water supply amount determining unit 32C increments the candidate value of the water supply amount H of the water Wa, returns to step 204, and repeats the process.

In step 214, the water supply amount determination unit 32C determines the candidate value set above as the water supply amount H, and ends the series of processes.

FIG. 4 is a schematic diagram provided for explaining an example of the treatment content by the water supply amount determining unit 32C according to the first embodiment.

As shown in FIG. 4, input value group 1 to input value group 4 are input to the water supply amount determination unit 32C. The input value group 1 includes a gas constant R [J / mol · K], an operating temperature T [K] of the fuel cell 20, and a Faraday constant F [C / mol]. The input value group 2 includes the Gibbs free energies ΔG1 to ΔG4 values g1 to g4 [J / mol]. The input value group 3 includes the flow rate A [mol / h] of the biogas G1, the flow rate B [mol / h] of the city gas G2, the methane concentration c [%] contained in the biogas G1, and the carbon dioxide concentration. d [%] and are included. However, the flow rate B is a value obtained by subtracting the flow rate A from the rated equivalent flow rate F ₀ . The input value group 4 includes a range of carbon activity Ac (0 <Ac <1).

Then, the water supply amount determination unit 32C determines the supply amount H of the water Wa by using each parameter included in the input value group 1 to the input value group 4. The supply amount H of water Wa is the above formulas (10) to (22) (however, when the city gas G2 is supplied, the above formulas (23) to (22) are used instead of the above formulas (14) to (18). 27) is applied).

According to the first embodiment, in order to determine the supply amount H of water Wa whose carbon activity Ac falls within a predetermined range, the supply amount H of water Wa is not specified without defining the range of carbon activity Ac. Carbon precipitation can be suppressed more effectively than in the case of determining. Further, since the supply amount H of water Wa is determined in consideration of carbon dioxide in the biogas, it is possible to prevent a decrease in power generation efficiency due to the addition of a modifier more than necessary.
Furthermore, the cost of the equipment can be reduced by using the carbon dioxide in the biogas G1 for reforming without separating it.

FIG. 5 is a schematic diagram for explaining an example of the processing content by the economic efficiency determination unit 32D according to the first embodiment.

As shown in FIG. 5, the economic efficiency determination unit 32D inputs the input value group 1 to the input value group 5. The input value group 1 includes the purchase price ε [yen / mol] of the biogas G1 and the purchase price σ [yen / mol] of the city gas G2. The input value group 2 includes the electricity selling price m [yen / kWh] of the biogas G1 and the electricity selling price n [yen / kWh] of the city gas G2. The input value group 3 includes the calorific value α [kWh / mol] of the biogas G1 and the calorific value β [kWh / mol] of the city gas G2. The input value group 4 includes a flow rate A [mol / h] of the biogas G1 and a flow rate B [mol / h] of the city gas G2. However, the flow rate B is a value obtained by subtracting the flow rate A from the rated equivalent flow rate F ₀ . The input value group 5 includes a power generation efficiency η1 [%] during the partial load operation of the fuel cell 20 and a power generation efficiency η2 [%] during the rated operation of the fuel cell 20.

Then, the economic efficiency determination unit 32D uses each parameter included in the input value group 1 to the input value group 5 to set the first index value In1 [yen / h] and the second index value In2 [yen / h]. Derived. The first index value In1 is derived by the above formula (28), and the second index value In2 is derived by the above formula (29).

Then, the economic efficiency determination unit 32D determines whether or not to supply the city gas G2 to the fuel cell 20 based on the first index value In1 and the second index value In2. That is, (1) When the first index value In1 ≥ the second index value In2 and the first index value In1> 0, it is more economical to supply the biogas G1 alone without supplying the city gas G2. Judged as having high sex. (2) When the second index value In2> the first index value In1 and the second index value In2> 0, it is more economical to supply both the biogas G1 and the city gas G2 (or only the city gas G2). Judged as having high sex. (3) When the first index value In1 ≦ 0 and the second index value In2 ≦ 0, it is determined that the power generation is stopped (or the state shifts to the hot standby state).

According to the first embodiment, when the flow rate of the biogas G1 is smaller than the rated equivalent flow rate and the rated operation cannot be performed, it is economical based on the first index value In1 and the second index value In2. From the viewpoint, it can be determined whether or not the city gas G2 is supplied to the fuel cell 20. Therefore, the cost of operating the fuel cell 20 can be suppressed, and high economic efficiency can be realized. Further, by using the biogas G1, the environmental load can be reduced.

[Second Embodiment]
FIG. 6 is a block diagram showing an example of the overall configuration of the fuel cell system 12 according to the second embodiment.
In the fuel cell system 12 according to the second embodiment, the configuration of the control device 30 is different from the configuration of the control device 30 according to the first embodiment. That is, the control device 30 includes an oxygen supply amount determining unit 32F instead of the water supply amount determining unit 32C. Further, in the first embodiment, water Wa is used as the modifier, but in the second embodiment, oxygen (O ₂ ) Va in the air is used as the modifier. Since the other configurations are the same as the configurations of the fuel cell system 10 according to the first embodiment, the repeated description here will be omitted.

In the second embodiment, oxygen Va is supplied to the reformer 22. Oxygen Va is an example of a modifier. By supplying this oxygen Va, excess methane can be reformed and carbon precipitation can be suppressed. The reforming reaction when oxygen Va is supplied to the reformer 22 is as shown in the following formula (30). The formula (30) shows an example of the fourth reforming reaction.

CH ₄ + 0.5O ₂ → 2H ₂ + CO… (30)

In addition, also in this 2nd Embodiment, the said formula (10), the formula (13), the formula (19), and the formula (22) shall be used in the same manner as the said 1st Embodiment.

A third valve 43 is provided in the oxygen Va supply path 54. A flow meter Fm3 is provided in the oxygen Va supply path 54. The supply amount of oxygen Va is adjusted by the operation control unit 32E controlling the opening degree of the third valve 43. The operation control unit 32E controls the amount of oxygen Va supplied to the fuel cell 20 according to the determination result of the oxygen supply amount determination unit 32F.

A densitometer Cm is connected to the oxygen supply amount determining unit 32F. The oxygen supply amount determination unit 32F inputs each of the concentration c of methane and the concentration d of carbon dioxide contained in the biogas G1 measured by the concentration meter Cm. Each of the flow rate A of the biogas G1 and the flow rate B of the city gas G2 is input from the flow rate determination unit 32A to the oxygen supply amount determination unit 32F. The gas constant R, the operating temperature T of the fuel cell 20, and the Faraday constant F are input to the oxygen supply amount determination unit 32F. The value g1 [J / mol] of the Gibbs free energy ΔG1 determined by the above equation (1) is input to the oxygen supply amount determination unit 32F. Similarly, the value g5 of the Gibbs free energy ΔG5 determined by the above formula (30) and the value g4 of the Gibbs free energy ΔG4 determined by the above formula (7) are input to the oxygen supply amount determination unit 32F. Further, a range (0 <Ac <1) of the carbon activity Ac is input to the oxygen supply amount determining unit 32F.

The oxygen supply amount determining unit 32F derives the equilibrium constant K1 corresponding to the above equation (1) by the above equation (10), and derives the equilibrium constant K4 corresponding to the above equation (7) by the above equation (13). The equilibrium constant K5 corresponding to the above equation (30) is derived by the following equation (31). However, g5 is the value [J / mol] of the Gibbs free energy ΔG5, R is the gas constant, and T is the operating temperature.

K5 = Exp (−ΔG5 / RT) = Exp (−g5 / RT)… (31)

On the other hand, the partial pressures of methane, carbon monoxide, carbon dioxide, hydrogen, and oxygen at equilibrium p (CH ₄ ), p (CO), p (CO ₂ ), p (H ₂ ), and p ( O ₂ ) is represented by the following equations (32) to (36). However, w is the reaction ratio in the above formula (1), v is the reaction ratio in the above formula (30), and λ is the supply amount [mol / h] of oxygen Va. Further, c is the methane concentration [%] in the biogas G1, d is the carbon dioxide concentration [%] in the biogas G1, and A is the flow rate [mol / h] per unit time of the biogas G1.

p (CH ₄ ) = (c × A) × (1-wv)… (32)
p (CO) = (c × A) × (2w + v)… (33)
p (CO ₂ ) = (d × A) − (c × A) × w… (34)
p (H ₂ ) = (c × A) × (2w + 2v)… (35)
p (O ₂ ) = λ- (c × A) × 0.5v… (36)

The initial value of p (CH ₄ ) is (c × A), the initial value of p (CO) is 0 (zero), and the initial value of p (CO ₂ ) is (d × A). , The initial value of p (H ₂ ) is 0 (zero), and the initial value of p (O ₂ ) is (λ). The sum of these partial pressures p is 1.

The equilibrium constant K1 in the above formula (1) is represented by the above formula (19), and the equilibrium constant K5 in the above formula (30) is represented by the following formula (37).

K5 = p (H ₂ ) ² × p (CO) / p (CH ₄ ) / p (O ₂ ) ^0.5 … (37)

Further, the carbon activity Ac is represented by the above formula (22) used in the above-mentioned first embodiment.

From the above, the oxygen supply amount determining unit 32F changes the candidate value of the supply amount λ of oxygen Va, and based on the reaction ratios w and v derived according to the change, the partial pressures p (CO) and p ( Each value of CO ₂ ) is derived. Then, the oxygen supply amount determining unit 32F is a candidate value in which the carbon activity Ac obtained from each of the derived partial pressure p (CO) and p (CO ₂ ) values is, for example, greater than 0 and less than 1. Is determined as the supply amount λ of oxygen Va.

That is, since the equilibrium constants K1 and K5 are known values under a certain operating temperature T, if the candidate value of the supply amount λ is set to an arbitrary value, the above equations (19) and (32) to (Equations) ( From the relationship between 36) and equation (37), two simultaneous equations with reaction ratios w and v as unknowns are established. By solving these two simultaneous equations, the values of the reaction ratios w and v are obtained, and each of the above partial pressures p is determined. Since the equilibrium constant K4 is also a known value under an operating temperature T, the carbon activity Ac is determined from the above equation (22). Further, when the determined carbon activity Ac is not in the range of 0 <Ac <1, the candidate value is incremented and the same calculation is performed, and when the determined carbon activity Ac is in the above range, it is set. The candidate value is determined as the supply amount λ of oxygen Va.

Here, when the city gas G2 is further supplied to the fuel cell 20, the partial pressures p (CH ₄ ) and p (CO) of methane, carbon monoxide, carbon dioxide, hydrogen, and oxygen in each equilibrium state. , P (CO ₂ ), p (H ₂ ), and p (O ₂ ) are represented by the following equations (38) to (42). However, B is the flow rate [mol / h] of the city gas G2 per unit time, and is represented by (F ₀ −A). Here, it is assumed that the entire composition of city gas G2 is regarded as methane.

p (CH ₄ ) = (c × A + B) × (1-w-v)… (38)
p (CO) = (c × A + B) × (2w + v)… (39)
p (CO ₂ ) = (d × A) − (c × A + B) × w… (40)
p (H ₂ ) = (c × A + B) × (2w + 2v)… (41)
p (O ₂ ) = λ- (c × A + B) × 0.5v… (42)

The initial value of p (CH ₄ ) is (c × A + B), the initial value of p (CO) is 0 (zero), and the initial value of p (CO ₂ ) is (d × A). , The initial value of p (H ₂ ) is 0 (zero), and the initial value of p (O ₂ ) is (λ). The sum of these partial pressures p is 1.

When biogas G1 and city gas G2 are used in combination, oxygen Va can be similarly supplied by using the above formulas (19), (22), (37), and formulas (38) to (42). The quantity λ can be determined.

Next, the operation of the control device 30 according to the second embodiment will be described with reference to FIG. 7. Note that FIG. 7 is a flowchart showing an example of the processing flow by the program 34A according to the second embodiment.
When the operation start of the fuel cell 20 is instructed, the calculation unit 32 reads out and executes the program 34A stored in the storage unit 34. By executing this program 34A, the calculation unit 32 functions as a flow rate determination unit 32A, a heat quantity calculation unit 32B, an economic efficiency determination unit 32D, an operation control unit 32E, and an oxygen supply amount determination unit 32F.

The program 34A according to the second embodiment determines the supply amount of oxygen Va capable of suppressing the precipitation of carbon in the fuel cell 20, and controls the supply amount of oxygen Va based on the determination result.

Since the processes described in the first embodiment (see FIG. 2) described above are the same except for the processes in steps 312, 318, and 322 in the second embodiment, the process is repeated here. The description of is omitted.

In step 312, the oxygen supply amount determining unit 32F uses the above equations (10), (13), (19), (22), (31), (32) to (36), and equations. (37) is used to determine the supply amount λ of oxygen Va when the biogas G1 is supplied alone.

In step 318, the oxygen supply amount determining unit 32F uses the above equations (10), (13), (19), (22), (31), (37), and (38) to (38). (42) is used to determine the supply amount λ of oxygen Va when both the biogas G1 and the city gas G2 are supplied.

In step 322, the operation control unit 32E controls the opening degree of the third valve 43 so that the supply amount of oxygen Va becomes the supply amount λ according to the determination result by the oxygen supply amount determination unit 32F. Here, the supply amount of oxygen Va is measured by the flow meter Fm3. The operation control unit 32E controls the opening degree of the third valve 43 so that the measured value of the flow meter Fm3 is λ [mol / h].

According to the second embodiment, in order to determine the supply amount of oxygen Va in the air in which the carbon activity Ac falls within a predetermined range, the supply of oxygen Va without specifying the range of the carbon activity Ac. Compared with the case of determining the amount, carbon precipitation can be suppressed more effectively. Further, since the supply amount λ of oxygen Va is determined in consideration of carbon dioxide in the biogas, it is possible to prevent a decrease in power generation efficiency due to the addition of a modifier more than necessary.
Furthermore, the cost of the equipment can be reduced by using the carbon dioxide in the biogas G1 for reforming without separating it.

In the above embodiment, the case where the carbon dioxide in the biogas G1 is not separated has been described, but the case where the carbon dioxide is separated is also within the scope of the present application.

The fuel cell system and its control device have been illustrated and described above as embodiments. The embodiment may be in the form of a program for causing a computer to execute the functions of each part included in the control device. The embodiment may be in the form of a storage medium that can be read by a computer that stores this program.

In addition, the configuration of the control device described in the above embodiment is an example, and may be changed depending on the situation within a range that does not deviate from the gist.

Further, the processing flow of the program described in the above embodiment is also an example, and even if unnecessary steps are deleted, new steps are added, or the processing order is changed within a range that does not deviate from the purpose. Good.

Further, the various mathematical formulas described in the above-described embodiment may also be modified within a range that does not deviate from the gist.

Further, in the above-described embodiment, the case where the processing 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, 12 Fuel cell system 20 Fuel cell (hot box)
22 Reformer 24 stack (fuel cell body)
26 Combustor 30 Control device 32 Calculation unit 32A Flow rate determination unit 32B Heat quantity calculation unit 32C Water supply amount determination unit 32D Economic efficiency determination unit 32E Operation control unit 32F Oxygen supply amount determination unit 34 Storage unit 34A Program 40 Fuel gas supply device 41 1 valve 42 2nd valve 43 3rd valve 50, 52, 54 Supply path

Claims (11)

A fuel cell provided with a first fuel gas containing hydrocarbons and carbon dioxide, and a reformer to which a reformer for reforming the hydrocarbons is supplied.
A control device that controls the operation of the fuel cell and
With
The control device includes a determination unit for determining the amount of the modifier whose carbon activity, which indicates the ease of carbon precipitation in the fuel cell, falls within a predetermined range .
When water is used as the reforming agent, the reformer produces hydrogen and carbon monoxide by the first reforming reaction between the hydrocarbon and carbon dioxide, and the hydrocarbon and the water have the first reformer. 2 The reforming reaction produces hydrogen and carbon monoxide, and the third reforming reaction between the carbon monoxide and the water produces carbon dioxide and hydrogen.
Divided pressures p (CH ₄ ), p (H ₂ O), p (CO), p (CO ₂ ) of the hydrocarbon, the water, the carbon monoxide, the carbon dioxide, and the hydrogen at their respective equilibrium states. ) And P (H ₂ ), the reaction ratio in the first reforming reaction is w, the reaction ratio in the second reforming reaction is y, the reaction ratio in the third reforming reaction is z, and the reformer. The flow rate of the first fuel gas supplied to the first fuel gas per unit time is A, the concentration of hydrocarbon in the first fuel gas is c, the concentration of carbon dioxide in the first fuel gas is d, and the amount of water supplied is. When set to H,
p (CH ₄ ) = (c × A) × (1-wy)
p (H ₂ O) = H- (c × A) × (y + z)
p (CO) = (c × A) × (2w + yz)
p (CO ₂ ) = (d × A) − (c × A) × (wz)
p (H ₂ ) = (c × A) × (2w + 3y + z)
Represented by
The equilibrium constants K1, K2, and K3 in each of the first reforming reaction, the second reforming reaction, and the third reforming reaction are
K1 = p (H ₂ ) ² × p (CO) ² / p (CH ₄ ) / p (CO ₂ )
K2 = p (H ₂ ) ³ × p (CO) / p (CH ₄ ) / p (H ₂ O)
K3 = p (CO ₂ ) x p (H ₂ ) / p (CO) / p (H ₂ O)
Represented by
When the carbon activity is Ac and the equilibrium constant in the carbon precipitation reaction of the fuel cell is K4,
Ac = K4 × p (CO) ² / p (CO ₂ )
Represented by
The determination unit changes the candidate value of the water supply amount H, and the partial pressures p (CO) and p (CO) are derived based on the reaction ratios w, y, and z derived according to the change. A fuel cell system in which each value of ₂ ) is derived, and the candidate value in which the carbon activity Ac obtained from each of the derived values falls within the predetermined range is determined as the water supply amount H. The reformer is further supplied with a second fuel gas containing a hydrocarbon and having a composition ratio of the hydrocarbon different from that of the hydrocarbon of the first fuel gas.
The partial pressures p (CH ₄ ), p (H ₂ O), p (CO), p (CO ₂ ), and p (H ₂ ) are units of the second fuel gas supplied to the reformer. When the flow rate per hour is B
p (CH ₄ ) = (c × A + B) × (1-wy)
p (H ₂ O) = H- (c × A + B) × (y + z)
p (CO) = (c × A + B) × (2w + yz)
p (CO ₂ ) = (d × A) − (c × A + B) × (wz)
p (H ₂ ) = (c × A + B) × (2w + 3y + z)
The fuel cell system according to claim 1 . A fuel cell provided with a first fuel gas containing hydrocarbons and carbon dioxide, and a reformer to which a reformer for reforming the hydrocarbons is supplied.
A control device that controls the operation of the fuel cell and
With
The control device includes a determination unit for determining the amount of the modifier whose carbon activity, which indicates the ease of carbon precipitation in the fuel cell, falls within a predetermined range.
When oxygen in the air is used as the reforming agent, the reformer produces hydrogen and carbon monoxide by the first reforming reaction between the hydrocarbon and carbon dioxide, and the hydrocarbon and the oxygen. Hydrogen and carbon monoxide are produced by the fourth reforming reaction with
Differential pressures p (CH ₄ ), p (CO), p (CO ₂ ), p (H ₂ ) of the hydrocarbon, the carbon monoxide, the carbon dioxide, the hydrogen, and the oxygen in their respective equilibrium states. , And p (O ₂ ) are w for the reaction ratio in the first reforming reaction, v for the reaction ratio in the fourth reforming reaction, and per unit time of the first fuel gas supplied to the reformer. When the flow rate of A is A, the concentration of hydrocarbon in the first fuel gas is c, the concentration of carbon dioxide in the first fuel gas is d, and the supply amount of oxygen is λ.
p (CH ₄ ) = (c × A) × (1-wv)
p (CO) = (c × A) × (2w + v)
p (CO ₂ ) = (d × A) − (c × A) × w
p (H ₂ ) = (c × A) × (2w + 2v)
p (O ₂ ) = λ- (c × A) × 0.5v
Represented by
The equilibrium constants K1 and K5 in each of the first reforming reaction and the fourth reforming reaction are
K1 = p (H ₂ ) ² × p (CO) ² / p (CH ₄ ) / p (CO ₂ )
K5 = p (H ₂ ) ² × p (CO) / p (CH ₄ ) / p (O ₂ ) ^0.5
Represented by
When the carbon activity is Ac and the equilibrium constant in the carbon precipitation reaction of the fuel cell is K4,
Ac = K4 × p (CO) ² / p (CO ₂ )
Represented by
The determination unit changes the candidate value of the oxygen supply amount λ, and the partial pressures p (CO) and p (CO ₂ ) are derived based on the reaction ratios w and v derived according to the change. A fuel cell system in which the respective values of the above are derived, and the candidate value in which the carbon activity Ac obtained from the derived values falls within the predetermined range is determined as the oxygen supply amount λ . The reformer is further supplied with a second fuel gas containing a hydrocarbon and having a composition ratio of the hydrocarbon different from that of the hydrocarbon of the first fuel gas.
The partial pressures p (CH ₄ ), p (CO), p (CO ₂ ), p (H ₂ ), and p (O ₂ ) are unit times of the second fuel gas supplied to the reformer. When the flow rate per hit is B,
p (CH ₄ ) = (c × A + B) × (1-w-v)
p (CO) = (c × A + B) × (2w + v)
p (CO ₂ ) = (d × A) − (c × A + B) × w
p (H ₂ ) = (c × A + B) × (2w + 2v)
p (O ₂ ) = λ- (c × A + B) × 0.5v
The fuel cell system according to claim 3 . The control device has a first index showing economic efficiency when the fuel cell is operated by supplying the first fuel gas, and the fuel by supplying both the first fuel gas and the second fuel gas. The second or fourth aspect of claim 2 or 4 , further comprising a determination unit for determining whether or not to supply the second fuel gas to the reformer based on a second index indicating economic efficiency when a battery is operated. Fuel cell system. The determination unit determines whether or not to supply the second fuel gas to the reformer, and the flow rate of the first fuel gas supplied to the reformer is reduced from a predetermined amount. The fuel cell system according to claim 5 , wherein the fuel cell system is performed in the case. Each value of the first index and the second index becomes a positive value when the profit is larger than the cost for operating the fuel cell.
When the value of the first index is equal to or higher than the value of the second index and the value of the first index is a positive value, the determination unit uses the first fuel gas alone in the reformer. If it is determined that it is more economical to supply with, and the value of the second index is larger than the value of the first index and the value of the second index is a positive value, the reformer is used. The fuel cell system according to claim 5 or 6, wherein it is determined that it is more economical to supply both the first fuel gas and the second fuel gas, or the second fuel gas alone. The value In1 of the first index is α for the amount of heat per unit flow rate of the first fuel gas supplied to the reformer, ε for the purchase price per unit flow rate, and power generation during partial load operation of the fuel cell. When the efficiency is η1 and the selling price per unit electric energy obtained by generating electricity from the fuel cell with the first fuel gas is m.
In1 = (η1 × α × A × m) − (ε × A)
Represented by
The value In2 of the second index is β for the amount of heat per unit flow rate of the second fuel gas supplied to the reformer, σ for the purchase price per unit flow rate, and the power generation efficiency during the rated operation of the fuel cell. When the selling price per unit electric energy obtained by generating electricity from the fuel cell with η2 and the second fuel gas is n.
In2 = (η2 × α × A × m) + (η2 × β × B × n) − (ε × A + σ × B)
The fuel cell system according to any one of claims 5 to 7 , represented by. When a first fuel gas containing a hydrocarbon and carbon dioxide and a modifier for reforming the hydrocarbon are supplied and water is used as the modifier, the hydrocarbon and the carbon dioxide are used. Hydrogen and carbon monoxide are produced by the first reforming reaction of the above, hydrogen and carbon monoxide are produced by the second reforming reaction of the hydrocarbon and the water, and further, the carbon monoxide and the water are used. the third reforming reaction and a control device for controlling the operation of the fuel cell with a reformer that generates carbon dioxide and hydrogen,
A determination unit for determining the amount of the modifier whose carbon activity, which indicates the ease of carbon precipitation in the fuel cell, falls within a predetermined range is provided .
Divided pressures p (CH ₄ ), p (H ₂ O), p (CO), p (CO ₂ ) of the hydrocarbon, the water, the carbon monoxide, the carbon dioxide, and the hydrogen at their respective equilibrium states. ) And P (H ₂ ), the reaction ratio in the first reforming reaction is w, the reaction ratio in the second reforming reaction is y, the reaction ratio in the third reforming reaction is z, and the reformer. The flow rate of the first fuel gas supplied to the first fuel gas per unit time is A, the concentration of hydrocarbon in the first fuel gas is c, the concentration of carbon dioxide in the first fuel gas is d, and the amount of water supplied is. When set to H,
p (CH ₄ ) = (c × A) × (1-wy)
p (H ₂ O) = H- (c × A) × (y + z)
p (CO) = (c × A) × (2w + yz)
p (CO ₂ ) = (d × A) − (c × A) × (wz)
p (H ₂ ) = (c × A) × (2w + 3y + z)
Represented by
The equilibrium constants K1, K2, and K3 in each of the first reforming reaction, the second reforming reaction, and the third reforming reaction are
K1 = p (H ₂ ) ² × p (CO) ² / p (CH ₄ ) / p (CO ₂ )
K2 = p (H ₂ ) ³ × p (CO) / p (CH ₄ ) / p (H ₂ O)
K3 = p (CO ₂ ) x p (H ₂ ) / p (CO) / p (H ₂ O)
Represented by
When the carbon activity is Ac and the equilibrium constant in the carbon precipitation reaction of the fuel cell is K4,
Ac = K4 × p (CO) ² / p (CO ₂ )
Represented by
The determination unit changes the candidate value of the water supply amount H, and the partial pressures p (CO) and p (CO) are derived based on the reaction ratios w, y, and z derived according to the change. A control device for deriving each value of ₂ ) and determining the candidate value in which the carbon activity Ac obtained from each of the derived values falls within the predetermined range as the water supply amount H. When a first fuel gas containing a hydrocarbon and carbon dioxide and a reformer for reforming the hydrocarbon are supplied and oxygen in the air is used as the reformer, the hydrocarbon and the reformer are used. A fuel cell equipped with a reformer that produces hydrogen and carbon monoxide by the first reforming reaction with carbon dioxide, and produces hydrogen and carbon monoxide by the fourth reforming reaction between the hydrocarbon and the oxygen. ,
A control device that controls the operation of the fuel cell and
With
The control device includes a determination unit for determining the amount of the modifier whose carbon activity, which indicates the ease of carbon precipitation in the fuel cell, falls within a predetermined range.
Differential pressures p (CH ₄ ), p (CO), p (CO ₂ ), p (H ₂ ) of the hydrocarbon, the carbon monoxide, the carbon dioxide, the hydrogen, and the oxygen in their respective equilibrium states. , And p (O ₂ ) are w for the reaction ratio in the first reforming reaction, v for the reaction ratio in the fourth reforming reaction, and per unit time of the first fuel gas supplied to the reformer. When the flow rate of A is A, the concentration of hydrocarbon in the first fuel gas is c, the concentration of carbon dioxide in the first fuel gas is d, and the supply amount of oxygen is λ.
p (CH ₄ ) = (c × A) × (1-wv)
p (CO) = (c × A) × (2w + v)
p (CO ₂ ) = (d × A) − (c × A) × w
p (H ₂ ) = (c × A) × (2w + 2v)
p (O ₂ ) = λ- (c × A) × 0.5v
Represented by
The equilibrium constants K1 and K5 in each of the first reforming reaction and the fourth reforming reaction are
K1 = p (H ₂ ) ² × p (CO) ² / p (CH ₄ ) / p (CO ₂ )
K5 = p (H ₂ ) ² × p (CO) / p (CH ₄ ) / p (O ₂ ) ^0.5
Represented by
When the carbon activity is Ac and the equilibrium constant in the carbon precipitation reaction of the fuel cell is K4,
Ac = K4 × p (CO) ² / p (CO ₂ )
Represented by
The determination unit changes the candidate value of the oxygen supply amount λ, and the partial pressures p (CO) and p (CO ₂ ) are derived based on the reaction ratios w and v derived according to the change. A control device for deriving each value of the above, and determining the candidate value in which the carbon activity Ac obtained from each of the derived values falls within the predetermined range as the oxygen supply amount λ . A program that causes a computer to function as a control device included in the fuel cell system according to any one of claims 1 to 8 .