JPH02170368A - Power generating system of fuel battery - Google Patents

Abstract

PURPOSE:To lessen steam supply from outside and enhance the economy by utilizing steam produced at power generating reaction, and securing steam in the amount necessary and sufficient for modifying hydrocarbons. CONSTITUTION:Fuel batteries 1, 2 of internal modification type are furnished in two steps or more, wherein steam necessary for modification of the fuel gas is supplied to the first step for supplying the steam generated in a boiler, and partially part of the fuel chamber 2a outlet gas of fuel battery 2 after the second step or layer is used upon recycle. The crude gas is divided into the first and second steps and supplied, and steam and carbon dioxide gas flowing out of the fuel chamber 1a of an upstream fuel battery 1 are used as material for modification reaction in the fuel battery 2 downstream, and thus power generation is performed. This lessens the amount of steam to be supplied from outside, which enhances the economy.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a fuel cell power generation system, and more specifically to a fuel cell that improves economic efficiency by suppressing the amount of water vapor used in the reforming reaction of fuel gas. Regarding battery power generation systems.

[Prior art] A fuel cell is a device that generates electricity by placing positive and negative electrodes sandwiching an electrolyte, supplying oxygen and hydrogen to each electrode, and artificially performing the reverse process of electrolysis. Depending on the type of electrolyte used, it is broadly classified into alkaline type, phosphoric acid type, molten carbonate type, solid electrolyte type, etc.

Among these, the molten carbonate type and solid electrolyte type operate at high temperatures, have almost no restrictions on fuel gas composition, and are expected to be developed because they can produce fuel cells with higher power generation efficiency.

Hydrogen and carbon monoxide gas are used as fuel gas in these fuel cells, and this fuel gas is used by steam reforming natural gas, methanol, coal gas, or the like. There are two types of reforming: an internal reforming type in which natural gas or the like is reformed with steam inside the fuel cell, and an external reforming type in which steam reforming is performed outside the fuel cell.

In a conventional solid electrolyte internal reforming fuel cell, the following reforming reaction and electrode reaction occur at the cathode (hydrogen electrode) in the structure shown in FIG.

Reforming reaction/shift reaction CH4+H20: CO+3H2 CO+H20: CO2+H2 Electrode reaction (solid electrolyte type, 〇-transmission type) Cathode Q --1/ 202 +e H2+1/20□ → H20 CO+1/20□ → CO2 Anode 1/202 4 0 - -e In this way, when producing (H2+CO) gas by steam reforming raw material hydrocarbons at the fuel electrode of a fuel cell, more than a certain amount of water vapor is required for the hydrocarbons, but this total amount is Supplying from outside is not preferable in terms of thermal efficiency.

[Problems to be Solved by the Invention] In order to improve these problems, in an external reforming type phosphate fuel cell, as a method for effectively utilizing water vapor,
Waste heat generated in the power generation reaction of fuel cells is also recovered as steam and used as a raw material for reforming reactions.

However, such conventional methods do not sufficiently save water vapor.

The present invention has been made in view of the problems of the prior art described above, and an object of the present invention is to reduce the amount of steam supplied from the outside, and to ensure sufficient steam for reforming hydrocarbons. The object of the present invention is to provide a fuel cell power generation system with improved economic efficiency.

[Means and effects for solving the problem] The present inventors:
As a result of intensive studies to achieve the above objectives, we installed an internal reforming fuel cell divided into two or more stages, supplying hydrocarbons and steam to the first stage to reform and generate electricity. By adding hydrocarbons to the gas containing water vapor flowing out from the first stage and supplying it to the second stage for reforming and power generation,
Furthermore, by recycling and reusing the water vapor and carbon dioxide gas generated in the second and subsequent stages in the first stage, we have completed the present invention which solves the above problems.

That is, the present invention is characterized in that, in a power generation system using a fuel cell, the fuel cell is divided into two or more stages, and the water vapor and carbon dioxide gas generated in the fuel cell are used for a reforming reaction to generate power. This is a fuel cell power generation system.

Hereinafter, the present invention will be explained in more detail with reference to the drawings.

FIG. 1 is a schematic diagram showing an internal reforming type fuel cell power generation system of the present invention.

In Fig. 1, 1 and 2 are fuel cells, 1as2a is a fuel chamber, 1b and 2b are air chambers, 3 is a fuel gas supply line, 4 is a steam supply line, 5 is a compressor, 6 is a cooler, and 7 is a gas-liquid separator. 8a, 8b are combustors, 9a, 9
b indicates an air supply line, and 10a and tab indicate exhaust gas lines.

In the present invention, first, as shown in FIG. 1, two or more stages of internal reforming fuel cells are provided. The steam necessary for reforming the fuel gas is supplied to the first stage. The method of supplying steam is to supply steam generated in a boiler, and part of it is recycled and used as part of the gas at the outlet of the fuel chamber of the fuel cell in the second and subsequent stages.

Adding excessive water vapor during the reforming reaction in the fuel chamber of the fuel cell is undesirable because it lowers the hydrogen partial pressure PH2 and lowers the motive force. In order to reduce the amount of steam used by generating steam from the boiler feed water, the steam generated by the electrode reaction is used.

The raw material gas (CH4) is divided and supplied to each of the - stage and the second stage. Even if the raw material is liquefied petroleum gas or naphtha, if a low-temperature steam reforming process is added, CH4, H2, C01
Since the gas reformed to C02 is i-1, it can be applied to the present invention. The purpose of split injection of CH4 into each fuel chamber is to use the water vapor generated in each fuel chamber, which can average the hydrogen partial pressure within the fuel cell and reduce the electromotive force. It has an effect that can be maintained constant.

A portion of the fuel cell outlet gas is cooled to condense and remove H20, and then mixed with air for catalytic combustion and sent to the air chamber, or is not cooled and is mixed with air and combusted to produce air. The temperature of the reforming reaction/power generation reaction is maintained.

As described above, in the present invention, water vapor and carbon dioxide flowing out from the fuel chamber of the upstream fuel cell are used as raw materials for the reforming reaction of the downstream fuel cell to generate electricity.

Additionally, water vapor and carbon dioxide gas flowing out of the fuel chamber are recycled and used as raw materials for reforming reactions in each fuel cell to generate electricity.

The electrode reactions in the fuel cell are as follows.

■Air electrode (anode) 1/202 → 0 -e ■Fuel electrode (cathode) 0 → 1/202 + C H2→ 1/20□+H20 In the reforming reaction, (CH4+2H20→ CO2+4H2,4H2+20
□ → 4H20) Therefore, in the end, the following reaction occurs at the fuel electrode: CH, +202 → CO2+2H20.

Even if the water vapor generated at the fuel electrode is used for the reforming reaction in this way, 2 moles of H20 are generated per 1 mole of CH, so H20/CH4-2 can be maintained.

The present invention can be preferably applied to either a molten carbonate type fuel cell or a solid electrolyte type fuel cell.

In the molten carbonate type, a carbonate such as potassium carbonate or lithium carbonate, which is liquid at a humidity of 500° C. or higher, is used as an electrolyte. In solid electrolyte fuel cells, zirconia stabilized with calcium oxide, thorium oxide, cerium oxide, yttrium oxide, or the like is preferably used.

In addition to internal reforming type fuel cells that reform fuel gas with steam inside the fuel chamber, external reforming type fuel cells can also be used if an external reformer is installed just before each fuel cell. The invention can be suitably applied.

[Examples] Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples.

Example 1 Methane gas was converted into
．． 000 NJ/hr, water vapor 200.000
It was introduced into the first stage supply line 1 as S/C-2,0 at a rate of Nj/hr.

A steam reforming reaction was carried out at a temperature of 900° C. and a pressure of 1.5 atmospheres in each reformer, and the gas composition in the first stage discharge port line 2 was as follows.

CH40,02NJ/hr H2125,257NJ/br CO37,749NJ/hr C0,62,249NJ/hr H20274,746NJ/hr Under these operating conditions of the fuel cell, the numbered second stage The gas components at the supply port and discharge port of each stage after the second stage were measured, and the results are shown in Table 1.

The total amount of hydrogen gas consumed in the power generation reaction in the internal reforming multi-stage fuel cell power generation device used in this example was 229
It was 7.815Nj/hr.

At this time, the supply amount of CHl is 828.248 N i/
The supply amount of 11r, H, and O is 200.000 N J /
Since it is hr, H,O/CH4-200,000/
It was 828.248-0.242. However, as described above, H20/CH4-2,0 is maintained at each stage.

In this way, by utilizing the water vapor contained in the gas composition in the discharge port line 2 of the first stage, from the second stage onwards, S/C is applied to the water vapor in the gas flowing out from the upper stage.
Only methane gas was supplied to the inlet of each stage so as to maintain -2.0.

Comparative Example 1 Reforming and power generation reactions were carried out in a conventional internal reforming type molten carbonate fuel cell power generation device consisting of one stage as shown in FIG.

Methane gas and water vapor were introduced into the reforming reaction as shown below so that the amount of hydrogen gas consumed in the power generation reaction was the same as in Example 1.

CH4989,587N l / hrH201939
, 174 NJ/hr A reforming reaction was carried out with this gas composition, and as in Example 1, power generation was carried out using 75% of the hydrogen gas.

The gas composition at the exhaust port of the fuel cell after the electrode reaction was completed was as follows.

CH40,019N! / hr H21214,478N j / hrC03G (i,
009N j / hrCO2GO3,558N J
/ hrH2026 [i3.844N i / hrThe total amount of hydrogen gas consumed in the power generation reaction of the internal reforming type one-stage fuel cell power generation device used in this comparative example is also 2297.815
It was NJ/hr.

At this time, the supply amount of CH4 is 969.587N J /
hr, the supply amount of H7O is 1939.174N J /
Since it is hr, H20/CH4-1939,174
/989.587 = 2.0.

As described above, when the fuel cell is operated with the same amount of hydrogen consumption and the same amount of power generation in both the example and the comparative example, the amount of power generation is the same, but according to the present invention, which utilizes the water vapor generated in the upper stage, the amount of water vapor used is It can be seen that the savings are extremely significant.

In this way, the fuel cell power generation system according to the present invention utilizes the steam generated by the power generation reaction and secures the amount of steam necessary and sufficient for reforming hydrocarbons, thereby significantly reducing the amount of steam supplied from the outside. Can be done.

[Effects of the Invention] As explained above, the fuel cell power generation system of the present invention has the following effects.

■ The steam necessary for reforming hydrocarbons is generated from the fuel electrode of the fuel cell, so the amount of steam used can be reduced.

■ Since the hydrogen partial pressure is averaged, a constant electromotive force can be obtained.

- Applicable not only to solid electrolyte fuel cells but also to molten carbonate fuel cells.

(2) Furthermore, the same effect can be obtained not only with an internal reforming type fuel cell but also with an external reforming type in which a reforming device is provided between the fuel cells.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an internal reforming type molten carbonate fuel cell showing the power generation system of the present invention. FIG. Figure 3 is a schematic diagram of a conventional single-stage internal reforming type molten carbonate fuel cell; Figure 4 is a schematic diagram of a conventional molten carbonate fuel cell. FIG. 2 is a cross-sectional view showing the structure of a battery. In the figure: 1.2: fuel cell, 1 as 2 a: fuel chamber, lb, 2b: air chamber, 3: fuel gas supply port line, 4: steam supply port line, 5: compressor 6: cooler, 7 : Gas-liquid separator 8 a s 8 b : Combustor, 9 as 9 b : Air supply port line, 10 a, lO
b is the exhaust gas line. Patent applicant: JGC Co., Ltd. Company agent
Patent Attorney Tatsuo Ito Agent Patent Attorney Tetsuya Ito Figure 1 Figure 2 Figure Figure

Claims (1)

[Claims] 1. In a power generation system using a fuel cell, the fuel cell is divided into two or more stages, and the water vapor and carbon dioxide gas generated in the fuel cell are used for a reforming reaction to generate power. Features a fuel cell power generation system. 2. The power generation system according to claim 1, wherein water vapor and carbon dioxide flowing out from the fuel chamber of the upstream fuel cell are used as raw materials for a reforming reaction in the downstream fuel cell. 3. The power generation system according to claim 1, wherein the water vapor and carbon dioxide gas flowing out from the fuel chamber are recycled and used as raw materials for the reforming reaction of each fuel cell.