JP2003086225A - Solid oxide type fuel cell and its operating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell with a long term stability wherein a precipitation of a carbonaceous matter to the battery constituting material and its peripheral member is suppressed when a power generation is carried out by using a hydrocarbon fuel, even in case a solid oxide type fuel cell is made to be large-sized or operated for a long period. SOLUTION: In the solid oxide type fuel cell in which the hydrocarbon fuel is directly used, and the partial oxidation reaction of the hydrocarbon fuel is made to be a prior power generation reaction, this has a steam feeder 5 which is a means to supply a steam so that the steam/carbon ratio (S/C) in the fuel gas becomes 0.5 or less and larger than 0, an adaptive control part 6, a carbon deposition forecasting/detecting part 8, and other fuel cells 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid oxide fuel cell in which a hydrocarbon fuel such as city gas or natural gas is directly used, and a partial oxidation reaction of this hydrocarbon fuel is preferentially used as a power generation reaction. Regarding the driving method.

[0002]

2. Description of the Related Art In a solid oxide fuel cell using a hydrocarbon-based fuel, the hydrocarbon-based fuel is mainly composed of water vapor or carbon dioxide in order to avoid carbonaceous deposition due to decomposition of the hydrocarbon-based fuel. A method is generally used in which it is heated and reacted with a gas, reformed into hydrogen and carbon monoxide, and then used as a fuel for a solid oxide fuel cell (Japanese Patent Laid-Open No. 9-12.
9256).

However, in a fuel cell including this type of reforming process, the reforming reaction does not contribute to power generation and is an endothermic reaction that requires heat for the reaction. There is a loss in movement and it is necessary to take in heat efficiently.

As a means for solving this problem, in a solid oxide fuel cell using methane as a main component of natural gas as a fuel, a high ion conductive substance is used as an electrolyte material,
By preferentially causing the partial oxidation reaction shown in Formula 1 as the reforming reaction without adding steam, a method has been found which can perform reforming and power generation without deposition of carbonaceous matter ( 8th SOFC Research Presentation Abstracts by Ishihara et al., P. 93, 1999).

CH ₄ + 1 / 2O ₂ = CO + 2H ₂ Equation 1 This reaction not only functions as a power generation reaction itself, but also produces carbon monoxide and hydrogen that can be used as a fuel for a fuel cell. By using the fuel thus produced in another fuel cell to generate electricity, it is possible to generate electricity with high efficiency. However, the above method has only been considered in small, short-term trials.

[0006]

In the solid oxide fuel cell in which the above partial oxidation reaction is preferentially used as the power generation reaction, the solid oxide fuel cell has a high temperature range during long-term operation or the cell and its surrounding structure become large. If the fuel cell becomes large and the fuel is present there for a long time, the
Carbonaceous matter is deposited as typified by the direct decomposition of methane shown in.

CH ₄ → C + 2H _{2 (} Formula 2) When carbonaceous matter is deposited on the cell constituent materials, the catalyst performance is lowered, and if it is deposited on the cell peripheral members such as the fuel flow pipe, the pipe is blocked. There was a problem of doing.

The present invention has been made in view of the above problems, and even when a solid oxide fuel cell is upsized or is operated for a long period of time when power is generated using a hydrocarbon fuel. It is an object of the present invention to provide a solid oxide fuel cell and a method for operating the same, which suppresses the deposition of carbonaceous materials on the cell constituent members and their peripheral members and realizes a fuel cell having long-term stability.

[0009]

In order to solve the above-mentioned problems, the solid oxide fuel cell according to claim 1 of the present invention comprises:
In a solid oxide fuel cell in which a hydrocarbon-based fuel is directly used and a partial oxidation reaction of the hydrocarbon-based fuel is preferentially used as a power generation reaction, a steam / carbon ratio in a fuel gas is greater than 0 and 0.5 or less. It is characterized by having a means for supplying water vapor so that

In the method for operating a solid oxide fuel cell according to the present invention, the amount of water vapor supplied is controlled by predicting and detecting the deposition of carbonaceous matter. , A first step of determining whether or not there is a load change by detecting a change in output power, and a first mode of maintaining the amount of water vapor mixed in the fuel gas when there is no load change. In the case of the above load fluctuation, the third step of determining whether or not the carbonaceous deposits are predicted by the adaptive control, and the above-mentioned carbonaceous deposits are not predicted. Is a fourth step of operating in the first mode,
If the precipitation of carbonaceous matter is predicted, a fifth step of increasing the amount of water vapor and a sixth step of judging whether or not the carbonaceous matter precipitation detection threshold value is exceeded after the fifth step When the carbonaceous deposition detection threshold value is exceeded, the operation is performed in the second mode in which excessive steam is supplied regardless of the steam supply amount suitable for the output fluctuation and the reaction with the precipitated carbonaceous matter is promoted. Doing and returning to the 6th step 7th
And in the sixth step, if the carbonaceous precipitation detection threshold value is not exceeded, the third step is performed.
It is characterized by returning to the step of.

According to the solid oxide fuel cell and the method of operating the same of the present invention, with the above configuration, even when the solid oxide fuel cell is upsized or is operated for a long period of time, the cell constituent material and its peripheral members are provided. It is possible to suppress the precipitation of the carbonaceous substance and realize a fuel cell having long-term stability.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. In the drawings described below, components having the same function are designated by the same reference numeral, and repeated description thereof will be omitted.

FIG. 1 (a) is a diagram showing the concept of the present invention and shows the difference from the conventional solid oxide fuel cell which preferentially uses the partial oxidation reaction shown in FIG. 1 (b). It is a figure.

In FIG. 1, 1 is a hydrocarbon, 2 is steam, 3 is a power generation section, 4 is hydrogen and carbon monoxide.

As shown in FIG. 1B, in the conventional solid oxide fuel cell which preferentially uses the partial oxidation reaction of the hydrocarbon 1, only the hydrocarbon 1 as the fuel is directly supplied to the power generation section 3. To be done. On the other hand, in the solid oxide fuel cell according to the present invention, steam is supplied so that the steam / carbon ratio (S / C) in the supplied fuel gas is more than 0 and 0.5 or less ( That is, 0 <S
/C≦0.5).

The steam / carbon ratio (S / C)
Is the molar ratio of carbon to water vapor in the fuel gas supplied. For example, when simultaneously supplying 1 mol / min of methane and 0.5 mol / min of steam, the S / C is 0.5 / 1 = 0.5.
Becomes Also, for example, ethane 1 mol / min and water vapor 0.
When 5 mol / min is simultaneously supplied, ethane is C ₂ H ₆ and ₂ mol of carbon is contained with respect to 1 mol of ethane.
Is 0.5 / 2 = 0.25.

In the present invention, any hydrocarbon can be used as the hydrocarbon-based fuel as long as it is a hydrocarbon that undergoes a reforming reaction with steam and produces carbon monoxide and hydrogen by a partial oxidation reaction. Specifically, methane, ethane,
It is preferable to use propane, butane or the like alone or a mixture thereof, and among them, methane or natural gas containing methane as a main component is more preferable. Further, in order to partially react the above hydrocarbon-based fuel with steam, for example, considering hydrocarbon as methane, hydrogen and carbon monoxide that can participate in the power generation reaction by the steam reforming reaction shown in Formula 3 before the power generation reaction. And the hydrogen and carbon monoxide cause the power generation reaction shown in Formulas 4 and 5 and the water gas shift reaction shown in Formula 6 to generate carbon dioxide and water different from the products of the partial oxidation reaction.

CH ₄ + H ₂ O = CO + 3H ₂ Equation 3 H ₂ + 1 / 2O ₂ = H ₂ O Equation 4 CO + 1 / 2O ₂ = CO ₂ Equation 5 CO + H ₂ O = CO ₂ + H ₂ Equation 6 However, Carbon dioxide reacts with methane, which is the main component, according to Formula 7, resulting in the production of hydrogen and carbon monoxide. Water is utilized in the steam reforming reaction of methane shown in Formula 3, and similarly produces hydrogen and carbon monoxide.

CH ₄ + CO ₂ = 2CO + 2H ₂ Formula 7 In other words, although a steam reforming reaction that does not partially contribute to power generation occurs, hydrogen and carbon monoxide that can be used as fuel are the main components in the produced gas. There is expected. Equation 3,
Reactions 6 and 7 are reactions that do not directly contribute to the power generation reaction, but are supplied only in the range where the amount of water vapor added is in the range of 0 <S / C ≦ 0.5, and the precipitation of carbonaceous matter is suppressed,
This does not significantly reduce the power generation efficiency. Further, even if carbon dioxide and water remain in the produced gas due to the reactions of equations 4, 5, and 6, only the range (0 <S / C ≦ 0.5) in which the added steam suppresses the precipitation of carbonaceous matter. Therefore, the utility value of the discharged substance as a fuel will not be significantly reduced.

FIG. 2 shows S / C and the amount of carbonaceous deposits (μmo
It is a figure which shows the relationship with 1 / s).

In the solid oxide fuel cell according to the present invention,
As shown in FIG. 2, when S / C = 0, the precipitation of carbonaceous material occurs rapidly, but within the range of 0 <S / C ≦ 0.5, there is no precipitation of carbonaceous material.

When the S / C is from 0 to 0.1, the amount of carbonaceous matter is drastically reduced from 20 μmol / s, but carbonaceous matter is precipitated. Therefore, S / C is 0.1 <S /
The range of C ≦ 0.5 is more preferable.

Further, in the range of 0.5 <S / C, although the precipitation of carbonaceous matter does not occur, the main power generation reaction is the power generation reaction by hydrogen generated by the steam reforming reaction shown in Formula 3 (Formula 4, Since the formula (5) is used, the production costs are carbon dioxide and water, and the partial oxidation reaction in the present invention is preferentially used, and the function of producing carbon monoxide and hydrogen is lost.

FIGS. 3 (a) and 3 (b) are schematic views showing examples of water vapor supply means used in the present invention.

In FIG. 3A, 5 is a steam supply device, 6 is an adaptive control unit, 7 is water, 8 is a carbon deposition prediction / detection unit, and in FIG. 3B, 9 is another fuel cell. 1
0 is carbon dioxide.

The means for supplying water vapor in the present invention is shown in FIG.
As shown in (a), a single steam supply facility may be used.

Alternatively, as shown in FIG. 3 (b), since the substance produced from the solid oxide fuel cell which preferentially uses the partial oxidation reaction can be used as the fuel of the fuel cell, another fuel cell can be used. It is also possible to use part or all of the steam 2 generated from the other fuel cell 9 in the subsequent stage in combination with 9, depending on the required amount.

At this time, in either case of the independent equipment of (a) or the use of water vapor from the other fuel cell 9 of (b), the output fluctuation of the solid oxide fuel cell which preferentially uses the partial oxidation reaction, etc. Adaptive control is required to predict and detect the precipitation of carbonaceous substances due to changes in the operating conditions of, and to supply an appropriate amount of water vapor. For this adaptive control, it is desirable to use control means such as robust, neuro, fuzzy, etc., but in addition, any control means capable of predicting and detecting precipitation of carbonaceous matter due to output fluctuation and performing appropriate control may be used. Available.

As described above, the solid oxide fuel cell of the present embodiment uses a hydrocarbon-based fuel directly and preferentially uses the partial oxidation reaction of the hydrocarbon-based fuel as a power generation reaction. In fuel cells, steam in fuel gas /
A means for supplying water vapor so that the carbon ratio (S / C) becomes greater than 0 and equal to or less than 0.5 (in FIG. 3A, the water vapor supply device 5, the adaptive control unit 6, the carbon deposition prediction / detection unit 8). 3 (b), it has a steam supply device 5, an adaptive control unit 6, a carbon deposition prediction / detection unit 8, and another fuel cell 9).

FIG. 4 is a flow chart showing an example of the operating method of the solid oxide fuel cell of the present invention.

As shown in FIG. 4, it is determined whether or not there is a load change by detecting a change in output power (S1 in FIG. 4).

If there is no load fluctuation, operation is performed in the first mode for maintaining the amount of water vapor mixed in the fuel gas, that is, mode 1 (S2).

If there is a load change, it is judged whether or not carbonaceous precipitation is predicted by the adaptive control (S).
3).

Even if there is a load change, if the precipitation of carbonaceous matter is not predicted, the operation is performed in mode 1 in which the amount of water vapor mixed in the fuel gas is maintained (S4).

On the other hand, when carbonaceous precipitation is predicted by the above adaptive control, an appropriate amount of water vapor is supplied, that is,
The amount of steam supply is increased (S5). At the same time, feedback control is provided to detect the deposition of carbonaceous matter.

That is, it is determined whether or not the carbonaceous deposition detection threshold is exceeded (S6).

When the carbonaceous deposition detection threshold is exceeded,
Regardless of the amount of steam supply suitable for output fluctuations, operation is performed in the second mode, that is, mode 2, in which excess steam is supplied to promote reaction with the precipitated carbonaceous matter, and the process returns to S6 (S
7). As a result, although the battery output is temporarily reduced, the device can be regenerated to a state in which power can be generated.

If the carbonaceous deposition detection threshold value is not exceeded, the process returns to the adaptive control (return to S3).

Although the present invention has been specifically described based on the embodiments, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the invention. Is.

For example, in the mode 1, the operation was carried out while maintaining the amount of water vapor mixed with the fuel gas, but the conditions for depositing carbonaceous materials on the cell constituent materials and the peripheral members are different for each of the developed devices. Therefore, it is not always necessary to mix steam in mode 1 when there is no possibility of carbon deposition in the apparatus without supplying steam.

In addition, the carbonaceous deposition detection threshold value in the above-described embodiment is apparently a decrease in output during long-term operation due to a reduction in catalyst ability and the deposition of carbonaceous substances in the cell peripheral members such as the fuel distribution pipe. You need to set the expected value for. For example, the carbon-based material balance of the input hydrocarbon fuel and the output material is tested by gas chromatography, and if the input / output error is 5% or more, the mode 2 is switched to.

The solid oxide fuel cell according to the above-described embodiment is applicable to any fuel cell having any of a cylindrical type, a flat plate type, and a hollow flat plate type, and the same effect can be expected.

Further, the solid oxide fuel cell in the above embodiment can be expected to have the same effect not only in the single cell but also in the cell assembly.

[0044]

As described above, according to the present invention,
Prevents the deposition of carbonaceous materials on the cell components and peripheral members when a solid oxide fuel cell that preferentially uses the partial oxidation reaction of the hydrocarbon fuel as a fuel to generate electricity is operated for a large size or for a long period of time. It becomes possible and stable power generation becomes possible for a long period of time.

[Brief description of drawings]

FIG. 1A is a diagram showing a concept of a solid oxide fuel cell of the present invention, and FIG. 1B is a diagram showing a concept of a conventional solid oxide fuel cell.

FIG. 2 is a diagram showing the relationship between S / C and the amount of carbonaceous deposits.

3 (a) and 3 (b) are schematic views showing examples of water vapor supply means used in the present invention.

FIG. 4 is a flow chart showing an example of an operating method of the solid oxide fuel cell of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Hydrocarbon, 2 ... Steam, 3 ... Power generation part, 4 ... Hydrogen, carbon monoxide, 5 ... Steam supply device, 6 ... Adaptive control part, 7 ...
Water, 8 ... Carbon deposition prediction / detection unit, 9 ... Other fuel cells, 1
0 ... carbon dioxide.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hitoshi Watanabe             2-3-1, Otemachi, Chiyoda-ku, Tokyo             Inside Telegraph and Telephone Corporation (72) Inventor Masayasu Arakawa             2-3-1, Otemachi, Chiyoda-ku, Tokyo             Inside Telegraph and Telephone Corporation F term (reference) 5H026 AA06 BB08 EE11 HH05                 5H027 AA06 BA01 BA13 KK31 MM14

Claims (2)

[Claims] 1. A solid oxide fuel cell in which a hydrocarbon-based fuel is directly used and a partial oxidation reaction of the hydrocarbon-based fuel is preferentially used as a power generation reaction.
A solid oxide fuel cell, comprising means for supplying water vapor so that the carbon ratio is greater than 0 and 0.5 or less. 2. The method for operating a solid oxide fuel cell according to claim 1, wherein a first step of determining whether or not there is a load change by detecting a change in output power, and the load change If there is not, the second step of operating in the first mode to maintain the amount of water vapor mixed in the fuel gas, and if there is the above load fluctuation, is it possible to predict the precipitation of carbonaceous matter by adaptive control? A third step of judging whether or not the above-mentioned carbonaceous deposits are predicted, a fourth step of operating in the above-mentioned first mode, and a case where the above-mentioned carbonaceous deposits are predicted, steam A fifth step of increasing the amount, a sixth step of judging whether or not the carbonaceous deposition detection threshold value is exceeded after the fifth step, and the carbonaceous deposition detection threshold value is exceeded. If the water vapor is suitable for output fluctuation A seventh step of returning to the sixth step while operating in a second mode in which an excess amount of steam is supplied regardless of the gas supply amount to promote a reaction with the precipitated carbonaceous matter; In step 6, if the carbonaceous deposition detection threshold value is not exceeded, the method is returned to the third step, wherein the solid oxide fuel cell is operated.