JP2004186074A - Method for recovering carbon dioxide using molten carbonate type fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for recovering a carbon dioxide using a molten carbonate type fuel cell having a high carbon dioxide recovery. <P>SOLUTION: The method for recovering the carbon dioxide using the molten carbonate type fuel cell includes the steps of supplying a gas containing an oxygen to be exhausted from an exhaust gas generator (9) and the carbon dioxide to the cathode (2) side of the molten carbonate type fuel cell for constituting the cell by holding an electrolyte plate (1) between an anode (3) and a cathode (2), supplying a cathode exhaust gas to be exhausted from the cathode (2) of the molten carbonate type fuel cell to the cathode side of the other molten carbonate type fuel cell installed in alignment with the molten carbonate type fuel cell, and recovering the carbon dioxides generated from the anodes (3) of the molten carbonate type fuel cell and the other molten carbonate type fuel cell by a carbon dioxide recovering unit (11). <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
[Industrial applications]
The present invention relates to a method for recovering carbon dioxide using a molten carbonate fuel cell.
[0002]
[Prior art]
Molten carbonate fuel cells have features that are not found in conventional power generators, such as high efficiency and little impact on the environment, and have attracted attention as a power generation system following hydro, thermal and nuclear power. Is underway.
[0003]
FIG. 4 is a diagram schematically illustrating the power generation principle of a molten carbonate fuel cell. Hydrogen is supplied to the anode (fuel electrode), and oxygen and carbon dioxide are supplied to the other cathode (air electrode). Carbonate ions are generated at the cathode by an electrochemical reaction of oxygen with carbon dioxide and electrons that have passed through an external circuit. The carbonate ions travel through the electrolyte to the anode, where they react with the hydrogen ions that have released electrons to produce water and carbon dioxide. The emitted electrons travel to the cathode through an external circuit and become carbonate ions at the cathode. Then, the electrons emitted from the anode move to the anode through an external circuit to generate power.
[0004]
In this molten carbon dioxide fuel cell, carbon dioxide is required for the reaction at the cathode, and the same amount of carbon dioxide is generated for the reaction at the anode. That is, the carbon dioxide that has entered the cathode of the molten carbonate fuel cell passes through the electrolyte, is concentrated from the anode, and is discharged.
[0005]
By the way, in recent years, the global warming phenomenon has become a global problem, and reducing the emission of CO ₂ gas has become an important issue. One of such CO ₂ emission reduction targets is industrial combustion exhaust gas such as thermal power plant exhaust gas, which is characterized in that a large amount of CO ₂ gas with low concentration is emitted at high temperature. Currently, in addition to thermal power generation, power generation systems such as hydropower, thermal power and nuclear power are used, but thermal power generation plays a central role in these power generation systems, and it is not possible to satisfy electricity demand without thermal power generation . Therefore, it can be said that if the amount of CO ₂ gas emitted from the thermal power plant can be suppressed, it greatly contributes to the prevention of global warming.
[0006]
A typical method for concentrating and separating and recovering the low-concentration CO ₂ gas is as follows: (1) CO ₂ is separated and recovered by absorbing CO ₂ by a chemical reaction in an absorbing solution and heating it. Chemical absorption method, (2) Physical adsorption method in which CO ₂ is physically adsorbed in pores of a solid adsorbent such as zeolite, and CO ₂ is separated and recovered by lowering pressure, (3) Airframe for polymer membrane A membrane separation (permeation) method for separating and recovering CO ₂ by utilizing the difference in the permeation speed of a membrane is known (for example, see Patent Document 1).
[0007]
However, in the case of the above chemical absorption method (1), since the temperature of the CO ₂ gas needs to be lowered due to the restriction on the absorption liquid (solvent) side, a large heating energy is required for separation. In addition, there is a problem in that the amount of the absorbing solution used is large and expensive. Further, in the case of the physical adsorption method of the above (2), there is a problem that very large energy is required for separating CO ₂ and it is difficult to increase the capacity. On the other hand, in the case of the membrane separation method of the above (3), the cost is high because the membrane is very expensive, and it is difficult to increase the capacity because a large area of the membrane is required. There are problems such as the need to develop a suitable film.
[0008]
On the other hand, by utilizing the carbon dioxide concentration function of the molten carbonate fuel cell described above, the low concentration carbon dioxide discharged from the thermal power plant is utilized at the cathode of the molten carbonate fuel cell, thereby further improving this. Means for discharging low-concentration carbon dioxide and recovering carbon dioxide concentrated at the anode have been considered.
[0009]
[Patent Document 1]
JP-A-11-33340
[Problems to be solved by the invention]
In the means for recovering carbon dioxide using a molten carbonate fuel cell, an exhaust gas containing carbon dioxide is supplied to the cathode, but the carbon dioxide utilization of the cathode is limited (for example, 300 kW class molten carbonate fuel cell). As a result, carbon dioxide remains in the cathode exhaust gas (for example, about 300 m ³ / h at the time of a rated 300 kW class molten carbonate fuel cell). However, since the gas discharged from the cathode outlet is released to the atmosphere as it is by the means currently considered, the carbon dioxide remaining in the cathode exhaust gas has not yet been recovered.
[0011]
The present invention has been made to solve the above problems. That is, an object of the present invention is to provide a carbon dioxide recovery method using a molten carbonate fuel cell having a higher carbon dioxide recovery rate than before.
[0012]
[Means for Solving the Invention]
According to the present invention, the electrolyte plate (1) is sandwiched between the anode (3) and the cathode (2) and discharged from the exhaust gas generator (9) to the cathode (2) side of a molten carbonate fuel cell constituting a cell. A gas containing oxygen and carbon dioxide to be supplied is supplied, and the cathode exhaust gas discharged from the cathode (2) of the molten carbonate fuel cell is subjected to another molten carbonate fuel cell arranged in parallel with the molten carbonate fuel cell. Supplying carbon dioxide to the cathode side of the fuel cell and recovering carbon dioxide generated at the anode (3) of the molten carbonate fuel cell and the other molten carbonate fuel cell by a carbon dioxide recovery device (11); A method for recovering carbon dioxide using a molten carbonate fuel cell is provided.
[0013]
According to a preferred embodiment of the present invention, a gas containing oxygen and carbon dioxide discharged from the exhaust gas generator (9) is supplied to the cathode side of the other molten carbonate fuel cell.
[0014]
According to the above means, the cathode exhaust gas discharged from the cathode (2) of the molten carbonate fuel cell is supplied to the cathode (2) side of another molten carbonate fuel cell, so that the discharge of the cathode exhaust gas to the atmosphere is minimized. The process is performed only in the molten carbonate fuel cell on the downstream side, and the carbon dioxide generated at the anode (3) of each molten carbonate fuel cell is recovered by the carbon dioxide recovery device (11). Recovery rate is improved.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In addition, the same reference numerals are given to the common parts in the respective drawings, and the duplicate description will be omitted.
[0016]
FIG. 1 shows a carbon dioxide recovery system according to the first embodiment of the present invention installed downstream of a facility (exhaust gas generation facility 9) such as a thermal power plant that emits a low concentration and large amount of CO ₂ gas at a low temperature. FIG. 1 is an overall configuration diagram of equipment for performing a method. In the figure, reference numeral 4 denotes a molten carbonate fuel cell (hereinafter, referred to as MCFC).
An exhaust gas line 5 for supplying a gas obtained by mixing an exhaust gas containing carbon dioxide discharged from the exhaust gas generator and air compressed by the compressor 12 is connected to a cathode side of the MCFC 4 on the most upstream side. Except for the most upstream MCFC 4, the cathode side of each MCFC 4 and the cathode outlet of the MCFC 4 adjacent to the upstream side of the MCFC 4 are connected by a cathode exhaust gas line 6. In the figure, reference numeral 11 denotes a carbon dioxide capture device that captures carbon dioxide generated at the anode of each MCFC, and is connected to the anode side of each MCFC by a carbon dioxide capture line 8.
[0017]
In the figure, reference numeral 10 denotes a reformer for reforming a fuel gas containing water vapor into an anode gas containing hydrogen, and is connected to the anode side of each MCFC 4 by a fuel line 7. Natural gas is pressurized by a fuel blower (not shown), desulfurized by a desulfurizer, mixed with steam, and supplied to the reformer 10 as fuel gas. The reformer 10 includes a combustion chamber and a reforming chamber that reforms fuel gas by heat transfer from the combustion chamber to generate anode gas. The fuel chamber is filled with a combustion medium so that sufficient combustion is performed, and the reforming chamber is filled with a reforming medium for reforming the fuel gas into an anode gas mainly composed of hydrogen.
[0018]
FIG. 3 is a conceptual diagram of the MCFC 4 according to the method of the present invention. As shown in this figure, the MCFC comprises an enrichment cell comprising an electrolyte plate 1 using molten carbonate as an electrolyte and a porous cathode 2 and anode 3 sandwiching the electrolyte plate 1 from both sides.
[0019]
The electrolyte plate 1 is a porous flat plate impregnated with a molten salt as an electrolyte. For example, a matrix made of lithium aluminate (LiAlO ₂ ) is impregnated with a molten salt mainly composed of a carbonate as an electrolyte. Use what has been done. As the electrolyte, a carbonate of an alkali metal such as lithium, sodium, potassium or the like, or a carbonate of an alkaline earth metal such as magnesium or calcium is used alone or in a mixed state.
[0020]
The cathode 2 and the anode 3 are each made of nickel oxide, iron oxide, copper oxide or other metal oxides alone or in combination as conductive metal oxides that can withstand high temperatures and oxidizing atmospheres. A porous material doped with lithium is used.
[0021]
On the cathode side,
CO ₂ + 1 / 2O ₂ + 2e ⁻ → CO ₃ ^2-
Electrochemical reaction takes place, the carbonate ion _CO ^{3 2-} is generated. The gas containing unreacted carbon dioxide and oxygen at the cathode is discharged from the cathode outlet.
[0022]
Next, the generated carbonate ion CO ₃ ^2- permeates in the electrolyte plate 1 and reaches the anode 3, and on the anode side,
H ₂ + CO ₃ ^2- → H ₂ O + CO ₂ + 2e ⁻
Is performed and CO ₂ is concentrated and separated from the carbonate ions, and is discharged from the gas outlet.
[0023]
Water vapor and carbon dioxide discharged from the anode outlet of each MCFC 4 are cooled by a first cooling device (not shown). By this cooling, the steam is condensed and liquefied to be separated and collected. The carbon dioxide separated from the water vapor is liquefied by being cooled to −78.5 ° C. or lower by a second cooling device (not shown), and is recovered by the carbon dioxide recovery device 11.
[0024]
The cathode exhaust gas discharged from the cathode outlet of each MCFC 4 is supplied to the cathode side of the MCFC 4 adjacent to the downstream side. The gas supplied to the cathode side of the most upstream MCFC 4 is a gas discharged by the exhaust gas generator 9, and its CO ₂ gas concentration is about 8%. On the other hand, the CO ₂ gas concentration of the cathode exhaust gas discharged from the cathode outlet of the MCFC 4 on the most upstream side is 5%. As described above, the CO ₂ gas concentration of the cathode exhaust gas discharged from the cathode outlet of the MCFC 4 on the most downstream side by passing through the cathode of the MCFC 4 on the downstream side from the upstream side is discharged from the cathode outlet of the MCFC 4 on the most upstream side. Concentration is lower than that of the cathode exhaust gas. This reduces the amount of CO ₂ gas emitted into the atmosphere and also collects high-concentration CO ₂ gas with the carbon dioxide capture device, thereby improving the carbon dioxide capture rate.
[0025]
FIG. 2 is an overall configuration diagram of a facility for performing a carbon dioxide recovery method according to a second embodiment of the present invention, in which oxygen and carbon dioxide discharged from an exhaust gas generator 9 are disposed on the cathode side of all MCFCs 4. An exhaust gas line 5 for supplying a gas obtained by mixing a gas containing carbon and air compressed by the compressor 12 is connected. Other configurations are the same as those in the first embodiment.
[0026]
According to the second embodiment, the gas containing oxygen and carbon dioxide discharged from the exhaust gas generator 9 is compressed by the compressor 12 in order to secure the concentration of oxygen and carbon dioxide necessary for power generation by the MCFC 4. Since the gas mixed with the air is supplied to the cathode side of each MCFC 4, the carbon dioxide recovery rate can be improved without lowering the power generation efficiency of the MCFC 4.
[0027]
It should be noted that the present invention is not limited to the above-described embodiment, and it is needless to say that various changes can be made without departing from the spirit of the present invention.
[0028]
【The invention's effect】
As described above, according to the method for recovering carbon dioxide using the molten carbonate fuel cell of the present invention, the cathode exhaust gas discharged from the cathode of the molten carbonate fuel cell is used for the other molten carbonate fuel cell. Since the cathode exhaust gas is supplied to the cathode side, the discharge of cathode exhaust gas into the atmosphere is performed only in the molten carbonate fuel cell on the most downstream side, and the carbon dioxide generated at the anode of each molten carbonate fuel cell is converted into a carbon dioxide capture device. As a result, the carbon dioxide recovery rate is improved.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of equipment for performing a carbon dioxide recovery method using a molten carbonate fuel cell according to a first embodiment of the present invention.
FIG. 2 is an overall configuration diagram of equipment for performing a carbon dioxide recovery method using a molten carbon dioxide fuel cell according to a second embodiment of the present invention.
FIG. 3 is a conceptual diagram of a molten carbonate fuel cell according to an embodiment of the present invention.
FIG. 4 is a diagram schematically showing the power generation principle of a molten carbonate fuel cell.
[Explanation of symbols]
1 electrolyte plate 2 cathode (air electrode)
3 Anode (fuel electrode)
4 Molten carbonate fuel cell 5 Exhaust gas line 6 Cathode exhaust gas line 7 Fuel line 8 Carbon dioxide recovery line 9 Exhaust gas generation equipment 10 Reformer 11 Carbon dioxide recovery device 12 Compressor

Claims (2)

A gas containing oxygen and carbon dioxide discharged from an exhaust gas generator (9) on the cathode side of a molten carbonate fuel cell constituting a cell by sandwiching an electrolyte plate (1) between an anode (3) and a cathode (2) And supplying the cathode exhaust gas discharged from the cathode (2) of the molten carbonate fuel cell to the cathode side of another molten carbonate fuel cell juxtaposed to the molten carbonate fuel cell, Carbon dioxide produced at the anode (3) of the molten carbonate fuel cell and the other molten carbonate fuel cell is recovered by a carbon dioxide recovery device (11). A carbon dioxide recovery method using a battery. The molten carbonate fuel according to claim 1, wherein a gas containing oxygen and carbon dioxide discharged from the exhaust gas generator (9) is supplied to the cathode side of the other molten carbonate fuel cell. A carbon dioxide recovery method using a battery.

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