JPH11126628A - Fuel cell power generating device fitted with carbon deposition preventing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell power generating device preventing carbon deposition, by converting CO contained in anode exhaust gas into another. SOLUTION: This device is equipped with a fuel cell 20 composed of a cathode and anode for generating power from oxygen-contained cathode gas and hydrogen-contained anode gas, a reformer 22 for reforming steam-contained fuel gas into hydrogen-contained anode gas and supplying it to the anode, an anode exhaust gas line 4 for cooling anode exhaust gas exhausted from the anode by a heat exchanger 36, separating water from it by a steam separator 40, heating it by the heat exchanger 36, and then supplying it to the reformer 22 as gas for combustion, and a shift converter 44 provided between the heat exchanger 36 and the steam separator 40 for converting carbon monoxide and water in the anode exhaust gas into carbon dioxide and hydrogen gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell power generator equipped with a carbon deposition preventing device for converting carbon monoxide in anode exhaust gas to carbon dioxide and preventing carbon deposition on equipment passing therethrough.

[0002]

2. Description of the Related Art Molten carbonate fuel cells have features not found in conventional power generators, such as high efficiency and low environmental impact, and have attracted attention as power generation systems following hydro, thermal and nuclear power. Currently, intensive research is underway.

FIG. 3 is a diagram showing an example of a power generation facility using a molten carbonate fuel cell using city gas as fuel. In the figure, a power generation facility is a reformer 22 for reforming a fuel gas (city gas) mixed with steam into an anode gas containing hydrogen.
And a fuel cell 20 that generates power from a cathode gas containing oxygen and an anode gas containing hydrogen.
The anode gas produced in the fuel cell 20 is supplied to the fuel cell 20 by the anode gas line 2, and the most of the anode gas is consumed in the fuel cell 20 to become an anode exhaust gas. It is supplied to the combustion chamber.

In the combustion chamber, combustible components (hydrogen, carbon monoxide, methane, etc.) in the anode exhaust gas are burned together with the cathode exhaust gas containing oxygen to produce high-temperature combustion exhaust gas.
The heating chamber of the reformer 22 is heated, and the fuel gas is reformed by the reforming catalyst in the reforming chamber to become anode gas. The anode gas exchanges heat with the fuel gas mixed with the steam flowing through the fuel gas line 1 by the fuel preheater 24, and is supplied to the anode of the fuel cell 20. The flue gas discharged from the combustion chamber is passed through a carbon dioxide gas recycling line 7 to a carbon dioxide gas recycling blower 3.
2 to the cathode. The combustion exhaust gas contains a large amount of carbon dioxide, and serves as a supply source of carbon dioxide required for the battery reaction. Air from the air line 8 is supplied to the outlet side of the carbon dioxide gas recycle blower 32 to supply oxygen required for a cathode cell reaction. Part of the cathode exhaust gas discharged from the cathode is supplied to the cathode by the circulation line 3. The cathode exhaust gas, the combustion exhaust gas, and the air are mixed to form a cathode gas, which is supplied to the cathode.

The cathode gas undergoes a cell reaction in the fuel cell 20 to produce a high-temperature cathode exhaust gas. A part of the cathode gas is circulated through the circulation line 3 and the other part is burned in the reformer 22 by the cathode exhaust line 5. The power is recovered by a turbine compressor 28 that drives a compressor that compresses air in a waste heat utilization line 6, and the rest is recovered by a waste heat recovery steam generator 30 to recover thermal energy. Is discharged. The steam generated by the exhaust heat recovery steam generator 30 enters the fuel gas line 1 via the steam line 9,
The mixture with the fuel gas is sent to the reformer 22.

The anode exhaust gas line 4 includes a heat exchanger 36 for cooling the high-temperature anode exhaust gas discharged from the anode, a gas cooler 38 for further cooling the cooled anode exhaust gas, and a water cooler for cooling the anode exhaust gas. And an exhaust gas blower 42 which heats the anode exhaust gas from which water has been separated by the heat exchanger 36 and sends it to the combustion chamber. The water separated by the steam separator 40 becomes steam in the exhaust heat recovery steam generator 30.

[0007]

In order to convert the water in the anode exhaust gas into steam in the exhaust heat recovery steam generator 30, the water is cooled by the heat exchanger 36 and the gas cooler 38, and the water is separated by the steam separator 40. After that, it is heated again by the heat exchanger 36 and supplied to the combustion chamber. The anode exhaust gas after separating this water is:
If the partial pressure of water vapor is lowered and heated in the heat exchanger 36, carbon is deposited on the heat exchanger 36 by the following reaction, which hinders the operation of the heat exchanger 36. Budoir reaction: 2CO → C + CO ₂ Duking reaction: H ₂ + CO → C + H ₂ O This carbon precipitation is more likely to occur due to a decrease in steam partial pressure and an increase in CO partial pressure.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a fuel cell power generator which converts CO contained in an anode exhaust gas to another to prevent carbon deposition.

[0009]

In order to achieve the above object, according to the first aspect of the present invention, there is provided a fuel cell comprising a cathode and an anode, generating electricity from a cathode gas containing oxygen and an anode gas containing hydrogen, and a fuel cell containing steam. A reformer for reforming the gas to an anode gas containing hydrogen and supplying the reformed gas to the anode;
An anode exhaust gas line for cooling the anode exhaust gas discharged from the anode with a heat exchanger, separating water with a steam separator, heating the heat with the heat exchanger and then supplying the reformed gas as a combustion gas to the reformer; A shift converter provided between the exchanger and the steam separator for converting carbon monoxide and moisture in the anode exhaust gas into carbon dioxide and hydrogen gas.

After cooling the anode exhaust gas with a heat exchanger,
By converting the contained carbon monoxide and water to carbon dioxide and hydrogen gas, even if the anode exhaust gas after water separation by the steam separator is heated by a heat exchanger, carbon monoxide is almost contained. Therefore, carbon deposition can be prevented from occurring in the heat exchanger.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of an embodiment of the present invention. In this drawing, components having the same functions as those in FIG. 3 are denoted by the same reference numerals. The fuel cell 20 is supplied with the anode gas containing hydrogen from the anode gas line 2 and the cathode gas containing oxygen and carbon dioxide gas from the circulation line 3 to generate power. From the fuel cell 20, anode exhaust gas is discharged from the anode exhaust gas line 4, and cathode exhaust gas is discharged from the cathode exhaust gas line 5. A heat exchanger 36 is provided in the anode exhaust gas line 4 to cool the anode exhaust gas. The cooled anode exhaust gas converts carbon monoxide contained in shift converter 44 into carbon dioxide. The anode exhaust gas is further cooled by a gas cooler 38, water is separated by a steam separator 40, and the exhaust gas blower 4
2 heats the heat in the heat exchanger 36. Then the reformer 22
And combusts with oxygen contained in the cathode exhaust gas from the cathode exhaust gas line 5.

The shift converter 44 comprises a container and a catalyst filled in the container, and converts carbon monoxide and moisture contained in the anode exhaust gas into carbon dioxide and hydrogen gas by the following reaction formula. CO + H ₂ O⇔CO ₂ + H ₂ (1) Since carbon monoxide is removed from the anode exhaust gas by this reaction, the generation of carbon precipitation when heated in the heat exchanger 36 is prevented. It should be noted that the shift converter 44 may be of such an extent that the shift catalyst is filled in the pipe.

In the combustion chamber, the combustible components in the anode exhaust gas are burned together with the cathode exhaust gas containing oxygen to generate high-temperature combustion exhaust gas, and the reforming chamber of the reformer 22 is heated, and the reforming catalyst is reformed in the reforming chamber. Thus, the city gas is desulfurized by the desulfurizer 26, and the fuel gas generated by adding steam is reformed to be the anode gas. The anode gas exchanges heat with the fuel gas flowing through the fuel gas line 1 by the fuel preheater 24 and is supplied to the anode of the fuel cell 20. Further, the flue gas discharged from the combustion chamber is supplied to a cathode by a carbon dioxide gas recycling blower 32 in a carbon dioxide gas recycling line 7. The combustion exhaust gas contains a large amount of carbon dioxide, and serves as a supply source of carbon dioxide required for the battery reaction. Air from the air line 8 is supplied to the outlet side of the carbon dioxide gas recycle blower 32 to supply oxygen required for a cathode cell reaction. Part of the cathode exhaust gas discharged from the cathode is supplied to the cathode by the circulation line 3. The cathode exhaust gas, the combustion exhaust gas, and the air are mixed to form a cathode gas, which is supplied to the cathode. The flow rate of the circulation line 3 is controlled by a flow control valve 50.

This cathode gas undergoes a cell reaction in the fuel cell 20 to become a high-temperature cathode exhaust gas. A part of the cathode gas is circulated through the circulation line 3 and the other part is burned in the reformer 22 by the cathode exhaust line 5. The power is recovered by a turbine compressor 28 that drives a compressor that compresses air in a waste heat utilization line 6, and the rest is recovered by a waste heat recovery steam generator 30 to recover thermal energy. Is discharged. The exhaust heat recovery steam generator 30 generates steam from water supplied from the steam separator 40 and supplies the steam to the fuel gas line 1 through the steam line 9. The air enters the compressor of the turbine compressor 28, where it is pressurized and
Supplied to

FIG. 2 shows a comparison of the equilibrium constant between the conventional type (without using a shift converter) shown in FIG. 3 and the shift converter of the present embodiment. The equilibrium constant Kp of the Boudouard reaction is represented by the following equation. Kp = Pco ₂ / (Pco) ² (2) where Pco ₂ is the partial pressure of CO _{2 in} the equation (1), and Pco is the partial pressure of CO in the equation (1). The horizontal axis in FIG. 2 shows the temperature of the anode exhaust gas (° C.), and the vertical axis shows the equilibrium constant Kp of the Boudouard reaction. The curve represents the theoretical equilibrium constant. The lower side of the curve represents the theoretical carbon deposition region, and the upper side represents the theoretical non-carbon deposition region. Anode exhaust gas is 420-430 ° C in heat exchanger 36
When the shift converter 44 shown by the black circle is installed, the carbon enters the theoretical non-carbon deposition region, and the generation of carbon deposition is prevented.

[0016]

As is apparent from the above description, according to the present invention, a shift converter is provided, and carbon monoxide contained in anode exhaust gas is converted into carbon dioxide and then heated.
It is possible to prevent carbon deposition from occurring in equipment such as a heat exchanger to be heated.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a diagram showing a comparison of equilibrium constants when a conventional type and a shift converter of the present embodiment are installed.

FIG. 3 is a configuration diagram of a conventional fuel cell power generator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fuel gas line 2 Anode gas line 3 Circulation line 4 Anode exhaust gas line 5 Cathode exhaust gas line 6 Exhaust heat utilization line 7 Carbon dioxide gas recycling line 8 Air line 9 Steam line 12 Bypass line 13 Tie line 20 Fuel cell 22 Reformer 24 Fuel Preheater 26 Desulfurizer 28 Turbine compressor 30 Exhaust heat recovery steam generator 32 Carbon dioxide gas recycle blower 36 Heat exchanger 38 Gas cooler 40 Steam separator 42 Exhaust gas blower 44 Shift converter 50 Flow control valve

Claims (1)

[Claims] 1. A fuel cell comprising a cathode and an anode and generating electricity from a cathode gas containing oxygen and an anode gas containing hydrogen, and a reformer for reforming a fuel gas containing water vapor to an anode gas containing hydrogen and supplying it to the anode An anode exhaust gas line that cools an anode exhaust gas discharged from the anode with a heat exchanger, separates moisture with a steam-water separator, heats the heat with the heat exchanger, and supplies the reformed gas as a combustion gas to the reformer; A shift converter provided between the heat exchanger and the steam separator to convert carbon monoxide and moisture in the anode exhaust gas into carbon dioxide and hydrogen gas. Battery power generator.