JPS62274560A - Composite type fuel cell power generating system - Google Patents

Abstract

PURPOSE:To lengthen the life by adopting an anode recycling method in which a part of fuel exhaust gas in the upper stream of a fuel cell is supplied to a fuel gas supply line, and controlling fuel utilization in the fuel cell in each step so that fuel utilization is increased as a whole. CONSTITUTION:Raw fuel 2 is mixed with gas returned through an anode recycle line 7, and sulfur in the mixture is removed by desulfurizer 4, and the mixture is supplied to the first step fuel cell main body 1 through a fuel gas supply line 5. In the first step fuel cell main body 1, fuel utilization is made to 30%, and the amount of fuel which is recycled in the anode recycling line 7 is set so that the ratio of to water vapor methane is 2. As the result, the amount of fuel recycled through the anode recycle line 7 is increased to 85% against the amount of gas exhausted from a fuel gas exhaust line 6. Regardless of this increase, partial pressure of hydrogen in the inlet and outlet of the fuel cell main body 1 is about 30%. Thereby, stable perforamance can be obtained over a long period of time.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a fuel cell power generation device, and particularly to a composite fuel cell power generation device that can operate a plurality of fuel cells in a well-balanced manner. be.

[Conventional technology]

FIG.
SEM Engineering NAR) J (1983), published on page 26 of the summary, describes the gas production of conventional fuel cell power generation equipment using an anode recycling method that supplies part of the exhaust gas from the fuel gas exhaust system to the fuel gas supply system. This is a flowchart. In the figure, (1) is the fuel cell main body, and (1a) is the cathode (oxidant electrode) side gas flow path and electrode (1) of the fuel cell main body (1).
Hereinafter, simply referred to as the cathode side > s (1b) is the anode (fuel electrode) side gas flow path and electrode (hereinafter simply referred to as the anode side) of the fuel cell main body (1), (10) is the cathode side of the fuel cell main body (1) (1a) and the anode side (1
(2) is the raw fuel mainly composed of hydrocarbons or alcohols, and (3) is the raw fuel (
(4) is a desulfurizer that desulfurizes the raw fuel (2), (5) is a fuel gas supply system that supplies fuel gas to the inlet of the anode side (1b), (6) That's it,
This is a fuel gas exhaust system in which fuel gas is discharged from the outlet on the side (1b), and a part of the gas in this fuel gas exhaust system (6) passes through the anode recycling system (7) and returns to the fuel gas supply system ( 5), and the remaining gas is heat exchanged with the raw fuel (2) in the heat exchanger (8), and then converted into fuel gas (9).
It is sent to the combustor (10) as a combustor. This combustor (10)
The fuel gas (9) sent to the combustor (10) is completely oxidized and becomes a gas containing a large amount of carbon dioxide.

This gas is then fed to the cathode side (1a) together with air (11) containing oxygen, which acts as an oxidizing agent on the cathode side (1a). A part of the gas discharged from the cathode side (1a) is supplied to the cathode gas supply system (12), and the rest is discharged to the outside of the fuel cell.

The conventional fuel cell power generation device is configured as described above, and the raw fuel (2) heated in the heat exchanger (8) is sent to the desulfurizer (4).
After the sulfur content is removed in the anode recycling system (7
) is mixed with exhaust fuel gas supplied from

This mixed gas is humidified, heated, and supplied to the anode side (vb) through the fuel gas supply system (5).

On the other hand, the air (11) is mixed with part of the outlet exhaust gas on the right side of the combustor (10) and on the cathode side (1a).

After being heated to a predetermined temperature, it is supplied to the cathode side (1a).

Here, the fuel cell main body (1) uses raw fuel (2) containing hydrocarbons or alcohols as its main component.

For example, it operates at a temperature around 650°C. On the anode side (1b) of the fuel cell main body (1), a chemical reaction occurs in which hydrocarbons or alcohols are decomposed to generate hydrogen [Equations (1) to (4) below)] and hydrogen is consumed to generate electricity. An electrochemical reaction [formula (5) below] occurs.

Moreover, on the cathode side (1a), an electrochemical reaction [
The following equation (6)] occurs. Collectively, these reactions exchange the chemical energy of the fuel gas for electrical energy and associated thermal energy.

[Chemical reaction on the anode side (1b)] Hydrocarbon + H
20→H2, Co, 002, OH4 (1) Alcohol + H20→ H2, C! 0,002,OH
a (2) OHa + H2O”: + 31i
2 + Co (RiCo +H20#
H2+CO2(4)H2-)-Cox 4
H2O+ 002 + 28 (
5) [Chemical reaction on the cathode side (1a)] 102
+ (!02 + 26 → CO32 - e.g. 650
According to equations (1 to (4)) at a temperature around °C.

In order to regularly decompose hydrocarbons or alcohols to generate hydrogen, it is necessary to supply a catalyst for promoting the reaction, such as a reforming catalyst, and the reaction heat necessary for formulas (1) to (4). is necessary. Therefore, in a normal internal reforming type molten carbonate fuel cell, a reforming catalyst is installed adjacent to the electrode, for example, in the gas flow path on the fuel electrode side, and formulas (5) and (6) are used. By supplying thermal energy by-produced in the electrochemical reaction as the reaction heat of equations (1) to (4), steady operation is possible. Formula (5)
, If the reaction heat in (6) is less than the reaction heat in equations (1) to (4), it can be sufficiently covered by using the heat within the power generator, such as by using the heat at the outlet of the combustor (10). . Therefore, in order to operate an internal reforming molten carbonate fuel cell steadily, it is important to maintain the activity of the catalyst.

The above catalysts, such as reforming catalysts, have an active material such as nickel supported on a carrier mainly composed of alumina or magnesia.In order to maintain the activity of this catalyst, the active material such as nickel must be It is necessary to prevent the oxidation represented by the following formula (7).

Ni + H2O # NiO + H2 (7) Decomposition of hydrocarbons or alcohols and hydrogen generation using a general reforming catalyst are carried out by adding steam as shown in equations (1) to (4). The generated hydrogen prevents oxidation of active materials such as nickel, so the activity of the catalyst is maintained.

However, in this type of fuel cell, as shown in equation (5), the hydrogen produced in equations (1) to (4) is consumed to produce water vapor, so the hydrogen concentration decreases and the catalyst Oxidation of the active material, such as nickel, occurs and the catalyst is likely to exhibit a decrease in activity. How easy is this active material to oxidize?

Varies depending on the type of active material. For example, in a catalyst using nickel as an active material, it is known that when the concentration of water vapor to hydrogen becomes 10 to 20 times or more, oxidation of nickel occurs and the activity of the catalyst decreases. Therefore, in order to maintain the activity of the catalyst, the ratio of water vapor concentration to hydrogen concentration must be 10 to 20 or less. In the internal reforming type molten carbonate fuel cell using the above-mentioned anode cycle method, the fuel exhaust gas that is not supplied to the fuel gas supply system (5) is oxidized to a gas mainly composed of carbon dioxide in the combustor (10). As a result, the fuel cell main body (1) has a high fuel utilization rate (ratio of fuel consumed by the fuel cell to the fuel supplied to the fuel cell) and high load operation. This has been done to increase power generation efficiency. However, when the battery is operated at a high fuel utilization rate and high load, the concentration ratio of water vapor to hydrogen near the inlet of the fuel cell main body (1) becomes extremely high partially or transiently, causing the fuel gas flow path to become extremely high. The activity of the placed catalyst decreases, making continuous operation impossible.

Additionally, in general, internal reforming type molten carbonate fuel cells:
For example, when natural gas is supplied as the raw fuel (2), the molar ratio of the water vapor required to convert the natural gas into a fuel whose main components are hydrogen and carbon dioxide to the supplied natural gas is, for example, 1.5. ~4.0, and is supplied to the fuel gas supply system (5).

As a method of supplying this water vapor, for example, a part of the fuel gas exhaust system (6) containing a large amount of water vapor may be connected to the fuel gas supply system (5).
There was an anode recycling method to supply the

[Problem that the invention seeks to solve]

In a power generation device using an internal reforming type molten carbonate fuel cell as described above, if the fuel utilization rate in the fuel cell body (1) is, for example, 80 to 90 inches, the fuel gas exhaust system (6)
The residual fuel components in the fuel will be reduced.

Fuel gas supply system (5) by the above anode recycling
If the fuel utilization rate is, for example, 80, the inlet gas to the anode side (1b) containing the exhaust fuel gas supplied to the
The composition is as shown in the table.

Table 1 When methane is supplied as the raw fuel and the fuel utilization rate is 80 cm, the inlet gas composition of the fuel cell main body (1) (in the case of an internal reforming fuel cell) is 2.0. The electromotive force of a unit cell is determined by the following equation (8), and if the partial pressure of carbon dioxide on the anode side (1″0) is large, the electromotive force of the unit cell will decrease.

・CPco2, Po2'A). (8) In the formula, ΔG: Gibbs free energy, R: gas constant
711 Faraday constant, n: 2, T: temperature (Kelvin)
, Px: Partial pressure of gas component X. Also.

The subscript A indicates that the gas composition is on the anode side (1), and the subscript C indicates that the gas composition is on the cathode side (1).
1a).

Therefore, in order to increase the electromotive force E, the anode side (
In 1b), for example, it is necessary to increase the hydrogen partial pressure and to decrease the water vapor and carbon dioxide partial pressures. In the case of an internal reforming type fuel cell, the above equations (1) and (2) are used.
, (ri) Hydrogen is produced by the reaction (4), but
In general, a reforming catalyst, for example, is often used to accelerate the reaction. When promoting the hydrogen production reaction using this reforming catalyst, it is necessary to maintain the activity of the reforming catalyst continuously for a long period of time. However, on the anode side (1b), the formula (
Hydrogen is continuously consumed by the cell reaction in 5). Therefore, near the inlet of the anode side (1b), hydrogen is consumed before it is sufficiently produced by the reforming reaction, so the load on the reforming catalyst is increased. This poses a problem in that the catalyst becomes larger and the catalyst deteriorates more quickly due to oxidation.

Further, if the fuel utilization rate in the fuel cell body is about 80 inches, the composition of the outlet gas on the anode side (1b) will be as shown in Table 2, for example, and the hydrogen partial pressure will be small.

Table 2 Composition of outlet gas from the fuel cell main body (1) when using methane as fuel (in the case of internal reforming fuel cells) Therefore, some of the gas from the fuel gas exhaust system (6) is transferred to the fuel gas supply system. (5)
If we adopt the method of supplying water vapor by introducing it into the fuel cell, hydrogen used as fuel is supplied at only about 6 SL, whereas carbon dioxide is supplied at 6 SL or more, leading to a decrease in the electromotive force of the fuel cell. There was a point.

As mentioned above, when the fuel utilization rate in the fuel cell body is set to a high rate of 80 to 90%, there is a problem in that the activity of the reforming catalyst decreases and the electromotive force of the fuel cell decreases. .

This invention was made to solve these problems, and it is possible to operate the power generation device, that is, the entire system, with a high fuel utilization rate (this invention also enables the fuel gas supply system to be operated without reducing the electromotive force of the battery). The object of the present invention is to obtain a composite fuel cell power generation device that can supply steam to the fuel cells and maintain the activity of the reforming catalyst for a long period of time.

[Means for solving problems]

The composite fuel cell power generation device according to the present invention arranges a plurality of fuel cells in series with respect to the flow of fuel gas, and adjusts the fuel utilization rate of each fuel cell to achieve a fuel utilization rate of one power generation device as a whole. This allows for high-speed operation for long periods of time.

[For production]

In this invention, by lowering the fuel utilization rate of the first-stage fuel cell located most upstream with respect to the fuel gas supply system than in the conventional case, the hydrogen partial pressure is high and the carbon dioxide and water vapor partial pressures are low. Since a low-temperature fuel gas is supplied to the fuel gas supply system of the second-stage fuel cell, sufficient hydrogen can be supplied in advance to prevent the reforming catalyst from being oxidized at the inlet of the fuel cell main body of the second and subsequent stages. In addition, in the first stage fuel cell, the hydrogen consumption rate is reduced, the load on the reforming catalyst is reduced, and the reaction rate of the reforming reaction has a margin, allowing the activity of the reforming catalyst to be maintained. Since the hydrogen concentration distribution on the electrode surface is smaller than before, the current density distribution within the electrode surface is also smaller, and the average hydrogen partial pressure is also higher than before, resulting in a higher electromotive force.

On the other hand, since the proportion of fuel that is wasted as heat is reduced, power generation efficiency is also improved.

In addition, the fuel cells in the second and subsequent stages use gas containing residual hydrogen, carbon oxide, etc. led from the fuel gas exhaust system of the upstream fuel cell as fuel, so the overall fuel utilization rate of the power generation device is high. Able to drive.

[Embodiment] Fig. 1 is a gas flow diagram showing an embodiment of the present invention, and (1), (21, (4) to (12)) are completely the same as those in the conventional device described above. (13) ) is the second stage molten carbonate fuel cell body provided downstream of the fuel cell body (1), and here the upstream fuel cell body (
1) is the first stage fuel cell main body (1). (13a
) is the cathode side gas flow path and electrode (hereinafter simply referred to as the cathode side) of the second stage fuel cell main body (16), (13
1)) is the anode side gas flow path and electrode (hereinafter simply referred to as the anode side) of the second stage fuel cell main body (13), (
130) is an electrolyte layer of the second stage fuel cell main body (13). The desulfurizer (4) is an anode recycling system (7).
) and the raw fuel supplied (2
) is installed downstream from the mixing position of the heat exchanger (8-1
) and (8-2) are for maintaining the fuel cell bodies (1) and (13) at a predetermined temperature, respectively. Further, (12-1) and (12-2) are cathode gas supply systems in the first stage and second stage fuel cells, respectively.

In the composite fuel cell power generation device configured as described above, the raw fuel (2) is mixed with the gas returned through the anode recycling system (7), and the sulfur component is removed in the desulfurizer (4). Thereafter, it is supplied as fuel from the fuel gas supply system (5) to the first stage fuel cell body (1). 1st
In the stage fuel cell main body (1), the fuel utilization rate is set to 30, and the amount of fuel to be recirculated in the anode recycling system (A) is determined so that the ratio of water vapor to methane is 2. As a result, even though the amount of fuel recirculated in the anode recycling system (7) is as high as 85% of the amount of exhaust gas from the fuel gas exhaust system (6), the fuel cell body (1) Partial pressure of hydrogen at both inlet and outlet is approximately 50%
becomes. Table 3 shows the fuel gas composition at the inlet and outlet of the fuel cell bodies (1) and (13).

Table 3 Fuel gas composition Note: The inlet composition of the fuel cell main body (13) is the same as the outlet composition of the fuel cell main body (1).

The fuel utilization rate is 30 cm for the fuel cell main body (1), 71 cm for the fuel cell main body (15), and 80 cm for the entire power generation device.

Therefore, the reforming catalyst within the fuel cell main body (1) exhibits stable performance over a long period of time without any reduction in activity due to oxidation, carbon deposition, or the like. Also, desulfurizer (4)
For example, when using the hydrodesulfurization method, the following equation (9)
, (Since the sulfur component contained in the fuel is removed by chemisorption through the reaction shown in 1), the desulfurization performance improves as the hydrogen partial pressure in the supplied gas increases.

H2+ sulfur compound → H2S+ hydrocarbon (9)
125 + ZnO4H2O-1-ZnS
(10) Fuel gas containing 30% or more hydrogen (
9) is used as fuel for the second stage fuel cell main body (13).

Assuming that the fuel utilization rate in this fuel cell main body (16) is 71%, the input raw fuel (2) is the sum of the first and second stage fuel cell main bodies (1) and (13). 80 of
This means that you have used Chi. Second stage fuel cell body (1
The fuel exhaust gas emitted from 3) is converted into a gas mainly composed of carbon dioxide in the combustor (10), and then heated together with air (11) in heat exchangers (8-1) and (8-2). After that, it is supplied to the cathode sides (1a) and (15a) of the first and second stage fuel cell bodies (1) and (13).

In addition, in the above embodiment, the first stage fuel cell main body (1)
Although the fuel utilization rate was set at 60%, it can preferably range from 20% to 60%.

Although the fuel utilization rate in the second stage fuel cell main body (13) was set to 71%, it can preferably be set at 60% to 70% for the fuel cells in the second and subsequent stages.

Further, although the fuel utilization rate of the entire power generation device was set to 80%, it can preferably be set to 80% to 90% as in the conventional case.

Further, in the above embodiment, two stages of stacked fuel cells are arranged in series, but three or more stages of stacked fuel cells may be arranged in series, and each stage has a plurality of fuel cells. may be installed in parallel.

Furthermore, in the above embodiment, a part of the gas in the fuel gas exhaust system (6) is guided to the upstream side of the desulfurizer (4) in the fuel gas supply system (5) through the anode recycling system (7). However, as shown in FIG. 2, it may be distributed and supplied to two locations, upstream and downstream of the desulfurizer (4).

A heat exchanger (8-5), a moisture condenser (14), etc. may be used for the gas to be led upstream of the desulfurizer (4), and in this case, the desulfurizer (4) is a dehumidified gas. Since gas is supplied, the hydrogen concentration in the gas increases, increasing the desulfurization effect. Furthermore, since only the gas containing the amount of hydrogen required for desulfurization can be cooled and water condensed, the water condenser (
14) and the heat exchanger (8-5) have a small capacity.

In addition, a moisture condenser (1) or a humidifier may be used in combination with the above embodiments, and in another embodiment as shown in FIG. 14) was installed, dehumidified gas with high hydrogen concentration was supplied to the desulfurizer (4), and a steam supply device (not shown) was installed downstream of the desulfurizer (4), so the fuel cell Fuel gas with an adjusted amount of humidification can be supplied to the main bodies (1) and (13).

In the above example, a molten carbonate fuel cell was used as the second-stage fuel cell, but the second-stage fuel cell and subsequent stages may use an internally reformed or externally reformed molten carbonate fuel cell. A type fuel cell, a phosphoric acid type fuel cell, or a phosphoric acid type fuel cell can be used.

[Effects of the Invention] As explained above, this invention arranges at least two stages of fuel cells in series in the fuel gas system, and directs a portion of the fuel exhaust gas from the upstream fuel cell to the fuel gas supply system of the fuel cell. In addition, the fuel utilization rate of each stage of fuel cells was adjusted to increase the fuel utilization rate of the entire power generation device, so the high activity of the reforming catalyst used in the fuel cell can be maintained for a long time. It is maintained over a period of time and has the effect of extending the life of the fuel cell without reducing the electromotive force of the fuel cell.

[Brief explanation of drawings]

Fig. 1 is a gas flow diagram showing an embodiment of the present invention;
FIG. 3 is a gas flow chart showing another embodiment of the invention, FIG. 3 is a gas flow chart showing still another embodiment of the invention, and FIG. 4 is a gas flow chart of a conventional fuel cell power generation device. In the figure numbers, (1) is the fuel cell body, (1a) is the cathode side gas flow path and electrode, (1b) is the anode side gas flow path and electrode, (1C) is the electrolyte layer, and (2) is the raw material. Fuel, (6) is raw fuel supply system, (4) is desulfurizer, (5) is fuel gas supply system, (6) is fuel gas discharge system, (7) is anode recycling system, (81, (8- 1) , (8-2)
, (8-5) is a heat exchanger, (9) is a fuel gas, (10
) is the combustor, (11) is air, (12), (12-1)
, (12-2) is the cathode gas supply system, (13) is the second
The fuel cell main body in the third stage, (15a) is the cathode side gas flow path and electrode, (131) is the anode side gas flow path and electrode, and (1) water condenser. Note that the same reference numerals are used in each figure. indicates the same or equivalent part.

Claims (8)

[Claims] (1) A fuel gas system consisting of a fuel gas supply system and a fuel gas exhaust system is used to operate a fuel cell that causes an electrochemical reaction between the fuel gas supplied from the fuel gas supply system and the oxidizing gas supplied from the oxidizing gas supply system. are arranged in series in at least two stages, and out of the fuel gas discharged from the upstream fuel cell, at least a portion of the discharged fuel gas that was not supplied to the fuel gas supply system of the downstream fuel cell is transferred to the upstream fuel cell. A composite type that uses an anode recycling method that recirculates the fuel gas to the fuel gas supply system of the fuel cell, and also adjusts the fuel utilization rate of each stage of fuel cells so that the fuel utilization rate of the entire power generation device is high. Fuel cell power generation device. (2) The composite fuel cell power generation device according to claim 1, wherein the upstream fuel cell is an internal reforming type molten carbonate fuel cell. (3) A patent claim characterized in that the upstream fuel cell is a molten carbonate fuel cell in which raw fuel is reformed into a gas containing hydrogen as a main component and the reformed gas is used as the fuel gas. The combined fuel cell power generation device according to item 1. (4) Claim 1, characterized in that a reformer for reforming raw fuel into fuel gas containing hydrogen as a main component is provided in the fuel gas supply system of the upstream fuel cell. The composite fuel cell power generation device described in 2. (5) The fuel cells in the second and subsequent stages are at least one selected from the group consisting of internally reforming molten carbonate fuel cells, externally reforming molten carbonate fuel cells, and phosphoric acid fuel cells. The composite fuel cell power generation device according to claim 1, characterized in that it is one type of fuel cell power generation device. (6) A desulfurizer is installed in the fuel supply system of the first stage fuel cell to remove the sulfur content of sulfur compounds in the fuel gas and the exhaust fuel gas recirculated by the anode recycling method. A composite fuel cell power generation device according to claim 1. (7) The composite fuel cell power generation device according to claim 6, wherein the desulfurizer is a hydrodesulfurization device. (8) The composite fuel cell power generation device according to claim 1, wherein the raw fuel used as the fuel gas contains hydrocarbons or alcohols as a main component.