JPS6119073A - Molten carbonate type fuel cell system - Google Patents

Abstract

PURPOSE:To reform fuel gas exhausted from an upper stream fuel cell, supply it a downstream fuel cell as fuel gas to increase power generation efficiency, and utilize by-product heat to reform fuel gas by installing a heat supply means which heats a reformer. CONSTITUTION:A reformer 6 is formed in such a way that its piping line passes inside an oxidizing gas piping line 9 for the oxidizing gas exhausted from an upper stream fuel cell 4, and an oxidizing gas piping line 8 is arranged so that a heat supply means which supplies heat of oxidizing gas exhausted to the reformer 6 is formed. Thereby, fuel gas exhausted from an upper stream is reformed by the reformer 6, and again supplied to a downstream fuel cell as fuel gas to prevent power generating efficiency drop, and moreover by-product heat of fuel cells 4 and 5 is utilized to effectively reform fuel gas.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a molten carbonate fuel cell system, and particularly to improving power generation efficiency.

[Prior art]

FIG. 1 is a plan view partially showing a conventional molten carbonate fuel cell, in which (1) is a molten carbonate fuel cell (hereinafter referred to as fuel cell), (2a) and (2b) are fuel cells. Battery (1)
an oxidizing gas inlet manifold and an oxidizing gas outlet manifold for supplying and discharging oxidizing gas, respectively; (3a);
(3b) is a fuel gas inlet manifold and a fuel gas outlet manifold for respectively supplying and discharging fuel gas to the fuel cell (1). In the figure, arrow A indicates the flow direction of oxidizing gas, and arrow B indicates the flow direction of fuel gas.

Next, the operation will be explained. Molten carbonate fuel cell (1
) is, for example, a fuel cell stack that operates at around 650°C.
When fuel gas is supplied through the fuel gas inlet manifold (3a) and oxidizing gas is supplied through the oxidizing gas inlet manifold (2a), both gases are supplied to the fuel cell (1). While flowing through the gas in a cross-flow manner, the following chemical or electrochemical reactions occur at the fuel gas side electrode and the oxidizing gas side electrode, respectively.

Fuel gas side electrode H2+CO knee -+ H,0+ CO2+ 2e
-(1)CO+ H20→H, 10CO□ -
(2) Oxidizing gas side electrode CO2+TO2+2e −+ co, (
3) As shown above, both electrodes convert the chemical energy of hydrogen and carbon oxide into electrical energy and by-product thermal energy.

After this, the reacted fuel gas is transferred to the fuel gas outlet manifold (
3b), and the reacted oxidizing gas is discharged from the oxidizing gas outlet manifold ab>.

Therefore, in order to obtain constant electrical output from the fuel cell (1), it is necessary to continuously supply fuel gas and oxidizing gas to the fuel cell (1).

In a molten carbonate fuel cell system incorporating this fuel cell (1), as shown in equations (1) and (2), the substances that can be directly used as fuel gas in the fuel cell (1) are hydrogen and -oxidation. Since it is carbon, if hydrocarbons, coal, etc. are used as the primary fuel, the primary fuel is transformed into a fuel gas whose main components are hydrogen and carbon oxide in a fuel processing device, and then the fuel cell (1) is supplied to. However, not all hydrocarbons and coal are decomposed in the fuel processing device, but undecomposed hydrocarbons are supplied to the fuel cell (1) and remain unused at the fuel gas outlet manifold (A).
is discharged from. When the amount of undecomposed hydrocarbons and the like is large, this causes a problem in that the power generation efficiency of the system using the fuel cell (1) decreases. Therefore, a desirable fuel processing device for a molten carbonate fuel cell system is limited to one with a small amount of residual hydrocarbons in the outlet fuel gas, and its operating conditions are relatively high temperature and low pressure that promote hydrocarbon decomposition. was limited to.

Conventional molten carbonate fuel cell systems are configured as described above, so hydrocarbons cannot be used directly as fuel, so when fuel gas containing hydrocarbons is used, the power generation efficiency of the system decreases. In addition, in order to reduce this decrease, fuel processing devices that process fuel gas before supplying it to the fuel cell have been limited to those that have a small amount of residual hydrocarbons in the outlet fuel gas. Furthermore, the operating conditions for this fuel processing device are relatively high temperatures.

It has the disadvantage that it is limited to low pressures and can only be applied to fuel processing devices with a narrow operating range.

[Summary of the invention]

This invention was made to eliminate the drawbacks of the conventional ones as described above, and includes an upstream fuel cell and a catalyst that are supplied with fuel gas and oxidizing gas to cause an electrochemical reaction, and the upstream fuel cell generates electricity. A reformer that introduces fuel gas discharged after a chemical reaction and reforms this fuel gas, and a downstream fuel cell that is supplied with the reformed fuel gas and oxidizing gas to cause an electrochemical reaction. , and a heat supply means for supplying the oxidizing gas discharged from at least one of the upstream cell and the downstream fuel cell to the reformer and applying heat to the reformer. The fuel gas discharged from the cell is reformed in a reformer and supplied as fuel gas to the downstream fuel cell again, reducing the reduction in power generation efficiency. It is an object of the present invention to provide a #d carbonate fuel cell system that can efficiently reform fuel gas by utilizing the above-described method and has a wide range of desirable fuel processing devices.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. Second
In the figure, (4) is composed of a fuel cell stack, and is an upstream fuel cell placed upstream of the fuel gas flow path in the system, and (5) is a fuel cell stack, which is arranged on the upstream side of the fuel gas flow path in the system. The downstream fuel cell (6) is arranged on the downstream side of the fuel gas passage, and the downstream fuel cell (6) is arranged on the fuel gas passage between the upstream fuel cell (4) and the downstream fuel cell (5). a reformer that introduces the fuel gas discharged from the fuel cell (4), reforms the fuel gas, and leads it to the downstream fuel cell (5);
(7) is a catalyst held by a perforated plate (8) inside the reformer (6), which promotes the decomposition of hydrocarbons, and is composed of, for example, a Ni catalyst using alumina as a carrier. Further, the reformer (6) is arranged to pass through the inside of the oxidant gas pipe (9) discharged from the upstream fuel cell (4), for example, so that the heat of the discharged oxidant gas is transferred to the reformer (6). ) is equipped with heat supply means.

In such a molten carbonate fuel cell system, a fuel gas composed of coal gasified gas containing, for example, about 5 to 10 hydrocarbons such as methane in addition to hydrogen and carbon oxide is supplied to the upstream fuel cell. (4) The fuel gas is introduced through the fuel gas inlet manifold (3a) as shown by arrow B, and is supplied to the fuel gas side electrode.

At the same time, oxidizing gas is introduced from the oxidizing gas inlet manifold (2a) as shown by arrow A, and is supplied to the oxidizing gas side electrode. At both electrodes, water vapor and carbon dioxide are generated from hydrogen and carbon oxide in the fuel gas according to the electrochemical reactions shown in equations (1), (2), and (3), and at the same time, electrical energy and thermal energy are generated. The fuel gas at about 650° C. after this electrochemical reaction is discharged from the fuel gas outlet manifold (3b) and introduced into the reformer (6). Since the catalyst (7) is held inside the reformer (6), hydrocarbons in the fuel gas are decomposed according to the following formula, for example.

CHa + H2O-+CO+ 3H2+ 49.3
Km/mol −(4)CnHm +nH2O−+
nco + “%”-H2-(5)CO+ H2O-+
■2 + H2-9,8KaIVmol -(6
) Next, the fuel gas containing hydrogen and carbon oxide that can be used in the fuel cell produced in the reformer (6) is transferred to the downstream fuel cell (
6) is supplied from the fuel gas inlet manifold (3a), and oxidizing gas is also supplied from the oxidizing gas inlet manifold (2a), causing an electrochemical reaction at the oxidizing gas side electrode and the fuel gas side electrode, and generating electrical energy and thermal energy. generate.

The decomposition of hydrocarbons in the reformer (6) is expressed by equations (4) and (
As shown in 5), the lower the hydrogen concentration in the fuel gas and the higher the water vapor concentration, the higher the concentration of water vapor. In this invention, as described above, the upstream fuel cell (4) consumes hydrogen and generates water vapor. Since the fuel gas discharged at approximately 650°C is introduced into the reformer (6), the hydrogen concentration in the introduced fuel gas is low and the water vapor concentration is high. Furthermore, the reaction to decompose hydrocarbons is a large endothermic reaction as a whole, and the reaction heat is composed of the heat of the oxidizing gas flowing through the oxidizing gas pipe (9) and the heat of the fuel gas itself. It is supplied by the sensible heat it possesses, and the reaction is carried out efficiently.

Next, as an example, when a fuel gas in which methane is decomposed is introduced into a fuel processing device, unreacted methane is produced when a conventional molten carbonate fuel cell system is used and when a fuel cell system according to an embodiment of the present invention is used. A comparative example of quantity will be described.

As a condition for calculation, the operating temperature of the fuel processing device is 650℃.
, the molar ratio of steam and methane supplied to the fuel processor is 4 = 1. The total amount of hydrogen reacted in the molten carbonate fuel cell is when the methane supplied to the fuel processor is completely decomposed into hydrogen. Assume that the amount of hydrogen is 80 t.

When using a conventional molten carbonate fuel cell system (1), when the fuel processing device operates at atmospheric pressure, 4.8% of the input methane is discharged undecomposed and unused. .

Furthermore, when the fuel processing device is operated at high pressure, the undecomposed rate of methane increases rapidly.For example, in the case of 4 atmosphere operation, the undecomposed rate of methane reaches 29.9%, which makes it difficult for the system to operate effectively. becomes impossible.

On the other hand, when using a molten carbonate fuel cell system according to an embodiment of the present invention, the ratio of reaction hydrogen in the upstream fuel cell (4) and the downstream fuel cell (5) is set to 3=1.
When set to , the undecomposed rate of methane is 0.06% when the fuel processing device operates at atmospheric pressure, and 1.3% when operated at 4 atmospheres, and the system operates efficiently under both operating conditions. I understand that.

Furthermore, in recent years, with the aim of improving power generation efficiency, progress has been made in the development of fuel processing devices that utilize thermal energy by-produced in molten carbonate fuel cell stacks. Since this fuel processing device operates at a relatively low temperature of, for example, 550°C to 650°C, in principle there is a large amount of undecomposed hydrocarbons, and conventional systems cannot generate a large amount of power, especially in the case of high-pressure operation that improves battery characteristics. Although this results in a decrease in efficiency, according to the present invention, together with the effect of recovering exhaust heat from by-product thermal energy, a large improvement in power generation efficiency can be obtained.

In the above embodiment, the reaction hydrogen amount ratio between the upstream fuel cell (4) and the downstream fuel cell (5) is set to 3=1, but the ratio is not limited to this. However, if the fuel gas introduced into the reformer (6) contains enough steam, the reformer (6)
), it is desirable that the amount of hydrogen in the upstream fuel cell (4) is larger than that in the downstream fuel cell (5).

In addition, as another embodiment, a reformer (
6) to the fuel gas outlet manifold (5) of the upstream fuel cell (5).
If heat is supplied to the reformer (6) through the oxidizing gas pipe (9) inside the reformer (6), the same effect as in the above embodiment can be obtained. In addition, there is an effect that thermal energy radiated from the side of the fuel cell can be efficiently used as reaction heat.

Likewise, the reformer (6) may be arranged inside the fuel gas inlet manifold (3a) of the downstream fuel cell (5), and furthermore - in the fuel gas outlet manifold (3a) of the upstream fuel cell (4). 3b) It may be disposed across the inside and the inside of the fuel gas inlet manifold (3a) of the downstream fuel cell (5).

Further, still another embodiment is shown in FIG. In the above embodiment, the stack forming the upstream fuel cell (4) and the stack forming the F-stream fuel cell (5) are formed separately, but in this embodiment, the stack forming the upstream fuel cell (4) is formed separately. ) and the laminate forming the downstream fuel cell (5) constitute one laminate. In this embodiment, in addition to the effects of the above embodiment, it is possible to miniaturize the system that can also serve as the flow path for the oxidation residue of the C1 upstream and downstream fuel cells (4) and (5), and furthermore, This has the effect of reducing heat loss and providing a highly efficient system. Furthermore, FIG. 5 shows the fuel gas outlet manifold (
3b) and the fuel gas inlet manifold (3a) of the downstream fuel cell (5), and a reformer (6) is installed inside this.
This is an example in which a This configuration is more effective in downsizing and reducing heat loss.

Furthermore, in the embodiment shown in FIGS. 4 and 5, the fuel gas is supplied by separating the fuel cells into upstream and downstream fuel cells (4) and (5) in the planar direction of the fuel cell stack. However, they may be separated and configured by lamination capacity.

Further, as shown in FIG. 6, the reformer (6) is configured to pass through the oxidant gas outlet manifold (2b) of the upstream or downstream fuel cell (4), (5), The heat of the gas may be supplied to the reformer (6).

Further, the catalyst (7) is not limited to an Nt catalyst using alumina as a carrier, and does not promote the decomposition of hydrocarbons.

〔Effect of the invention〕

As described above, according to the present invention, the upstream fuel cell includes an upstream fuel cell that oxidizes fuel gas and causes an electrochemical reaction, and a catalyst, and the upstream fuel cell causes an electrochemical reaction and discharges the fuel gas. A reformer that introduces the fuel gas and reforms the fuel gas, a downstream fuel cell that is supplied with the reformed fuel gas and an oxidizing gas that causes an electrochemical reaction, and an upstream fuel cell and a downstream fuel cell. By supplying at least one of the discharged oxidizing gases to the reformer and providing heat supply means for applying heat to the reformer, the fuel gas discharged from the upstream fuel cell can be used in the reformer. A more desirable fuel processing device that can reform the fuel gas and supply it again to the downstream fuel cell as fuel gas to reduce the deterioration of the power generating vehicle, and can efficiently reform the fuel gas by using the heat by-produced in the fuel cell. This has the effect of providing a molten carbonate fuel cell system with a wide range of conditions.

[Brief explanation of the drawing]

FIG. 1 is a partially sectional plan view of a conventional molten carbonate fuel cell, FIG. 2 is a configuration diagram showing a molten carbonate fuel cell system according to an embodiment of the present invention, and FIG. 3 is a plan view of a conventional molten carbonate fuel cell. FIGS. 4 and 5 are a cross-sectional view showing a fuel gas outlet manifold of an upstream fuel cell according to another embodiment of the present invention, respectively, and FIGS. FIG. 6 is a sectional view showing an oxidizing gas outlet manifold of a fuel cell according to still another embodiment of the present invention. In the figure, (2a) is the oxidizing gas inlet manifold, (2a)
b) is the oxidizing gas outlet manifold, (3a) is the fuel gas inlet manifold, (3b) is the fuel gas outlet manifold, (
4) is an upstream fuel cell, (5) is a downstream fuel cell, and (6) is a downstream fuel cell.
) is a reformer, (7) is a catalyst, and (8) is an oxidizing gas pipe, which constitutes a heat supply means. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (7)

[Claims] (1) It has an upstream fuel cell that is supplied with fuel gas and oxidizing gas to cause an electrochemical reaction, and a catalyst, and the fuel gas discharged from the upstream fuel cell that causes an electrochemical reaction is introduced, and this fuel gas a downstream fuel cell to which the reformed fuel gas is supplied as well as an oxidizing gas to cause an electrochemical reaction, and at least any of the upstream fuel cell and the downstream fuel cell. A molten carbonate fuel cell system comprising heat supply means for supplying one of the discharged oxidizing gases to the reformer and applying heat to the reformer. (2) The molten carbonate fuel cell system according to claim 1, wherein the laminate forming the upstream fuel cell and the laminate forming the downstream fuel cell are separated. (3) The molten carbonate fuel cell according to claim 1, wherein the laminate forming the upstream fuel cell and the laminate forming the downstream fuel cell form one laminate. system. (4) According to any one of claims 1 to 3, the heat supply means is characterized in that an exhaust oxidant gas flow path is provided in the reformer to exchange heat with the exhaust oxidant gas. The molten carbonate fuel cell system described. (5) The heat supply means is characterized in that a reformer is provided in the exhaust oxidant gas flow path and the heat of the exhaust oxidant gas is applied to the reformer. The molten carbonate fuel cell system according to any one of paragraphs. (6) The molten carbonate fuel cell system according to claim 4, characterized in that a reformer is provided in the fuel gas manifold of the fuel cell. (7) The molten carbonate fuel cell system according to claim 5, characterized in that a reformer is provided in the oxidizing gas manifold of the fuel cell.