JP2010228963A - Carbon dioxide recovery unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To recover carbon dioxide with a lower energy cost and a lower facility cost, and more efficiently than PSA method, when carbon dioxide is recovered from an exhaust gas. <P>SOLUTION: A carbon dioxide recovery unit 10 is used in a facility generating an exhaust gas containing carbon dioxide, and recovers carbon dioxide from the exhaust gas. The carbon dioxide recovery unit comprises heat-exchange means 11, 12 to cool the exhaust gas to make carbon dioxide into a fluid in a gas-liquid mixed state in which carbon dioxide is liquefied, and a gas-liquid separation means 13 to separate and recover liquefied carbon dioxide from the fluid in the gas-liquid mixed state. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a carbon dioxide recovery device for recovering and liquefying carbon dioxide from a gas containing carbon dioxide (hereinafter also referred to as carbon dioxide), and in particular, recovering and liquefying carbon dioxide from a gas containing high-concentration carbon dioxide. The present invention relates to a carbon dioxide recovery device.

  In general, in a fuel cell facility (MCFC), hydrogen is supplied to the fuel electrode (anode) and oxygen and carbon dioxide gas are supplied to the cathode to generate electric power. In some cases, combustion gas (exhaust gas) generated in a coal-fired power plant is supplied to the anode and carbon dioxide contained in the exhaust gas is used.

  In this type of fuel cell, when power is generated, high concentration carbon dioxide gas is discharged at the outlet of the anode when moisture is removed (see, for example, Patent Document 1). It is known to use a so-called physical adsorption method (PSA) in order to recover a concentration of carbon dioxide gas.

  On the other hand, in the molten carbonate fuel cell, the cathode exhaust gas discharged from the cathode of the molten carbonate fuel cell is placed on the cathode side of another molten carbonate fuel cell installed side by side with this molten carbonate fuel cell. There is a battery that is supplied and carbon dioxide produced at an anode of a molten carbonate fuel cell and another molten carbonate fuel cell is recovered by a carbon dioxide recovery device (see, for example, Patent Document 2).

JP 11-333401 A JP 2004-186074 A

  By the way, in a physical adsorption method, for example, an adsorption method using activated carbon or zeolite as an adsorbent, a so-called pressure swing (PSA) method is known in which carbon dioxide gas is desorbed from the adsorbent by decompression. The vacuum pump (compressor) used for carbon dioxide desorption requires high energy. Further, when the scale is increased, the thickness of the packed bed increases, and the pressure difference increases during carbon dioxide desorption. In other words, the required degree of vacuum may not be ensured. In order to secure the required degree of vacuum, a high-performance vacuum pump (large compressor) must be used, which inevitably increases the carbon dioxide desorption energy.

  Further, in the PSA method, it is necessary to pressurize the exhaust gas, and when performing adsorption using a plurality of adsorption towers, a switching valve for selecting the adsorption tower is required. As described above, when a large compressor is provided, the switching valve itself is also enlarged.

  In any case, when the PSA method is used, there is a problem that the energy cost and the equipment cost are increased.

  Therefore, an object of the present invention is to provide a carbon dioxide recovery device with low energy cost and equipment cost.

  (1) The present invention is a carbon dioxide recovery device for recovering carbon dioxide from the exhaust gas, which is used in equipment that generates exhaust gas containing carbon dioxide, and the exhaust gas is cooled to liquefy the carbon dioxide. And a gas-liquid separation means for separating and recovering liquefied carbon dioxide from the gas-liquid mixed fluid.

  In the carbon dioxide recovery device of (1), when recovering carbon dioxide from exhaust gas, the exhaust gas is cooled to liquefy carbon dioxide, and then liquefied carbon dioxide is separated from the fluid in a gas-liquid mixed state. Not only can carbon dioxide be recovered at a high concentration, but also a device such as a vacuum pump becomes unnecessary, so that energy costs and equipment costs can be reduced.

  (2) The present invention provides the carbon dioxide recovery device according to (1), wherein the heat exchange means includes a first heat exchanger that pre-cools the exhaust gas using the liquefied carbon dioxide, and a predetermined refrigerant. And a second heat exchanger that cools the exhaust gas pre-cooled by the first heat exchanger to form the fluid in the gas-liquid mixed state.

  In the carbon dioxide recovery device of (2), the exhaust gas is precooled using the liquefied carbon dioxide separated by the gas-liquid separation means, so that carbon dioxide can be reliably and efficiently recovered at low cost. it can.

  (3) The present invention provides the carbon dioxide recovery device according to (2), wherein the facility is a fuel cell that is driven by using a liquefied hydrocarbon gas mixture containing liquefied hydrocarbon gas as a raw material. The refrigerant is the liquefied hydrocarbon gas mixture.

  In the carbon dioxide recovery device of (3), when recovering carbon dioxide from the exhaust gas discharged from the fuel cell, the liquefied hydrocarbon gas mixture used in the fuel cell is used as a refrigerant for cooling the exhaust gas. Costs required can be reduced.

  (4) The present invention provides the carbon dioxide recovery device according to (3), wherein the fuel cell is a molten carbonate fuel cell, and an anode of the fuel cell is reformed from the liquefied hydrocarbon gas mixture. Hydrogen is supplied, at least carbon dioxide and oxygen are supplied to the cathode of the fuel cell, and the carbon dioxide supplied to the cathode of the fuel cell is carbon dioxide contained in exhaust gas generated from a thermal power plant. It is characterized by.

  In the carbon dioxide recovery device of (4), when a fuel cell in which carbon dioxide and oxygen are supplied to the cathode is used, in the exhaust gas generated from the thermal power plant as carbon dioxide supplied to the cathode of the fuel cell. The carbon dioxide generated from the thermal power plant can be reduced.

  (5) The present invention is characterized in that in the carbon dioxide recovery device described in (2), it has a recovery tank that recovers the liquefied carbon dioxide that has passed through the first heat exchanger.

  In the carbon dioxide recovery apparatus of (5), since the liquefied carbon dioxide that has passed through the first heat exchanger is recovered, the liquefied carbon dioxide can be efficiently recovered and recovered in the recovery tank.

  (6) The present invention provides the carbon dioxide recovery apparatus according to (3), wherein the fuel cell vaporizes the liquefied hydrocarbon gas mixture to form a hydrocarbon gas mixture, and the hydrocarbon gas mixture. And a reforming section for reforming the liquefied hydrocarbon into hydrogen, wherein the liquefied hydrocarbon gas mixture is vaporized by the second heat exchanger and sent to the reforming section. To do.

  In the carbon dioxide recovery device of (6), since the liquefied hydrocarbon gas mixture is vaporized by the second heat exchanger and sent to the reforming section, exhaust gas can be cooled and liquefied carbonization can be performed at the same time. Vaporization of the hydrogen gas mixture can also be performed.

  (7) The carbon dioxide recovery device according to (6), wherein the fuel cell facility has a combustion chamber to which a gas component other than the liquefied carbon dioxide separated by the gas-liquid separation means is supplied. The reforming section includes a reforming chamber that reforms a hydrocarbon gas mixture that has been pressurized and mixed with steam into hydrogen, and heat necessary for reforming the steam by the combustion gas supplied from the combustion chamber. And a heating chamber for supplying the water.

  In the carbon dioxide recovery device of (7), gas components other than the liquefied carbon dioxide separated by the gas-liquid separation means are supplied to the combustion chamber, and the reforming chamber is heated by the heating chamber according to the combustion gas from the combustion chamber. Therefore, gas components such as hydrogen and methane contained in the exhaust gas can be effectively reused.

  (8) The present invention is the carbon dioxide recovery device described in (7), characterized in that the combustion gas that has passed through the heating chamber is supplied to the cathode of the fuel cell.

  In the carbon dioxide recovery device of (8), since the combustion gas that has passed through the heating chamber is supplied to the cathode of the fuel cell, the carbon dioxide contained in the combustion gas can be used effectively.

  (9) The present invention is characterized in that, in the carbon dioxide recovery device described in (6), the second heat exchanger and the heat exchange unit are shared.

  In the carbon dioxide recovery device of (9), since the second heat exchanger and the heat exchange unit are shared, the number of heat exchangers can be reduced, and as a result, the cost required for the equipment can be reduced. Can do.

  As described above, according to the present invention, the exhaust gas is cooled to form a gas-liquid mixed state fluid in a state where carbon dioxide is liquefied, and then the liquefied carbon dioxide is separated from the gas-liquid mixed state fluid. Since the carbon dioxide can be collected at a high concentration, there is an effect that an energy cost and a manufacturing cost can be reduced because a device such as a vacuum pump is not necessary.

It is a block diagram showing an example of a carbon dioxide recovery device by an embodiment of the invention. FIG. 2 is a block diagram showing an example of a fuel cell facility in which the carbon dioxide recovery device shown in FIG. 1 is used. It is a figure which shows the thermal mass balance of the waste gas containing the high concentration carbon dioxide in the gas-liquid separator shown in FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  A carbon dioxide recovery device according to an embodiment of the present invention is used, for example, to recover and liquefy carbon dioxide gas discharged from a fuel cell. In a device that discharges exhaust gas containing carbon dioxide gas, carbon dioxide gas is recovered. It can also be used when liquefied.

  FIG. 1 is a block diagram illustrating an example of a carbon dioxide recovery device according to an embodiment of the present invention. The illustrated carbon dioxide recovery device 10 includes a first heat exchanger 11 and a second heat exchanger 12 and a gas exchanger. A liquid separator 13 is provided for collecting carbon dioxide gas discharged from a fuel cell maintenance described later.

  Here, a fuel cell facility in which the carbon dioxide recovery apparatus 10 shown in FIG. 1 is used will be described. FIG. 2 is a diagram illustrating an example of a fuel cell facility (MCFC). The illustrated MCFC 20 is, for example, a 50 KW class, and includes a reforming unit 23, a fuel cell 24, and a catalytic combustor 26. And these reforming part 23, the fuel cell 24, and the catalytic combustor 26 are accommodated in the pressure vessel 27, for example. The MCFC 20 is supplied with a liquefied hydrocarbon gas mixture (for example, liquefied natural gas (LNG)) containing a plurality of types of liquefied hydrocarbon gases having different boiling points. The liquefied hydrocarbon gas mixture is a fuel tank. (LNG tank) 21 is stored. The liquefied hydrocarbon gas mixture supplied from the fuel tank 21 is vaporized in the heat exchange unit 22. The reforming unit 23 generates hydrogen by reacting the hydrocarbon gas mixture, boil-off gas, and water vapor under high temperature conditions and the presence of a metal catalyst, and the boil-off gas generated inside the fuel tank 21 is discharged from the exhaust unit 25. Exhausted outside.

  The heat exchanging unit 22 is for supplying heat to the liquefied hydrocarbon gas mixture to vaporize the liquefied hydrocarbon gas, and the heat source in the heat exchanging unit 22 is not particularly limited. , Outside air, or water or warm water.

  The reforming unit 23 has a reforming chamber 23a and a heating chamber 23b that reforms a hydrocarbon gas mixture that has been pressurized and mixed with water vapor into hydrogen, and the reforming chamber 23a includes a hydrocarbon. A reforming medium for reforming the gas mixture into hydrogen is filled. A catalytic combustor 26 is connected to the heating chamber 23b, combustion gas in the catalytic combustor 26 is given to the heating chamber 23b, and heat necessary for steam reforming is supplied to the reforming chamber 23a by the heating chamber 23b.

  As the fuel cell 24, various types of fuel cells can be used. Here, for example, a molten carbonate fuel cell is used. The molten carbonate fuel cell includes a fuel electrode (anode) 31, an air electrode (cathode) 32, and an electrolyte layer (not shown) sandwiched between the fuel electrode 31 and the air electrode 32.

The electrolyte layer is, for example, a porous flat plate in which a molten salt that is an electrolyte is impregnated, and a matrix composed of lithium aluminate (LiAlO ₂ ) is impregnated with a molten salt mainly composed of a carbonate that is an electrolyte. Use The carbonate is not particularly limited, and examples thereof include alkali metal carbonates such as lithium carbonate, potassium carbonate, and sodium carbonate, and alkaline earth metal carbonates such as magnesium carbonate and calcium carbonate. Can be mentioned.

  As the fuel electrode 31 and the air electrode 32, a conductive metal oxide that can withstand high temperatures and an oxidizing atmosphere is used. For example, nickel oxide, iron oxide, copper oxide, or other metal oxide doped with lithium Is used alone or a mixture of a plurality of types.

In the molten carbonate fuel cell shown in the figure, for example, exhaust gas (coal-fired exhaust gas) generated at a coal-fired power plant is supplied to the exhaust gas pre-treatment device 29, where it is pre-treated and then mixed with air. (The combustion gas that has passed through the heating chamber 23b is mixed with the pretreatment exhaust gas from the exhaust gas pretreatment device 29). On the air electrode 32 side, an electrochemical reaction represented by the following chemical formula (1) is performed, and carbonate ions are generated (a gas containing unreacted carbon dioxide and oxygen in the air electrode 32 is an air electrode). 32 is discharged as exhaust gas, and a part thereof is given to the catalytic combustor 26).

The generated carbonate ions migrate through the electrolyte layer and reach the fuel electrode 31. On the fuel electrode 31 side, an electrochemical reaction represented by the following chemical formula (2) is performed, and electrons are deprived. Carbon dioxide is generated from the ions, and a gas (exhaust gas) containing carbon dioxide is discharged from the gas outlet.

  As these electrochemical reactions proceed, power generation is performed and hydrogen is oxidized to produce water. The exhaust gas from the fuel electrode 31 is supplied to the catalytic combustor 26 and to the combustion electrode (anode) return gas preheater 28. The carbon dioxide recovery device 10 is connected to the anode return gas preheater 28, where carbon dioxide is recovered. The exhaust gas after the carbon dioxide is recovered by the carbon dioxide recovery device 10 is returned to the anode return gas preheater 28 and is preheated and then supplied to the catalytic combustor 26.

  By the way, as a liquefied hydrocarbon gas mixture used for the fuel cell 24, it is preferable to use liquefied natural gas (LNG) from a viewpoint of availability. In liquefied natural gas, methane and the like are contained as low-boiling hydrocarbons. For this reason, when liquefied natural gas is used as a liquefied hydrocarbon gas mixture, boil-off gas containing methane gas is generated. This boil-off gas is exhausted from the exhaust unit 25 via the first self-pressure adjusting valve 41 and the second self-pressure adjusting valve 42.

  For example, the first self-pressure adjusting valve 41 is opened when the pressure on the inflow side to the valve becomes equal to or higher than a first predetermined pressure, and the second self-pressure adjusting valve 42 is connected to the valve. When the pressure on the inflow side becomes equal to or higher than a second predetermined pressure lower than the first predetermined pressure, the valve is opened.

  The hydrocarbon gas from the heat exchanging unit 22 is given to the reforming unit 23 via the third self-pressure regulating valve 43 and the flow rate control valve 45. The valve is closed when the pressure on the inflow side becomes equal to or higher than a third predetermined pressure. Further, as shown, the outlet side of the first self-pressure adjusting valve 41 is connected to the fourth self-pressure adjusting valve 44, and the outlet side of the fourth self-pressure adjusting valve 44 is the third self-pressure adjusting valve. 43 and the flow control valve 45 are connected. The fourth self-pressure adjusting valve 44 is closed when the pressure on the inflow side of the valve becomes equal to or higher than a fourth predetermined pressure that is lower than the second predetermined pressure.

  By the way, as described above, exhaust gas containing high-concentration carbon dioxide gas is discharged from the fuel electrode 31, but in the present embodiment, the carbon dioxide recovery device 10 uses carbon dioxide from the exhaust gas discharged from the fuel electrode 31. The gas is collected and liquefied.

  Here, the carbon dioxide recovery apparatus 10 will be described with reference to FIG. 1 again. The exhaust gas discharged from the fuel electrode (anode) 31 (that is, the exhaust gas supplied from the anode return gas preheater 28 shown in FIG. 2) is first supplied to the first heat exchanger 11. This exhaust gas has a pressure of about 0.9 MPa, and the carbon dioxide concentration is about 88%. In addition, about 12% of hydrogen, methane, carbon monoxide and the like are included.

  On the other hand, concentrated carbon dioxide (liquefied carbon dioxide) separated by the gas-liquid separator 13 is given to the first heat exchanger 11 through the expansion valve 14 as a refrigerant. The exhaust gas is precooled. The liquefied carbon dioxide that has passed through the first heat exchanger 11 is sent to a carbon dioxide recovery tank (not shown).

  The exhaust gas precooled by the first heat exchanger 11 is given to the second heat exchanger 12. LNG (about −160 ° C.) is supplied to the second heat exchanger 12 as a refrigerant, and the exhaust gas is further cooled by the second heat exchanger 12 (not shown in FIG. 1, Supplied from the fuel tank 21 to the second heat exchanger 12). At this time, LNG is heated in advance with seawater or the like, and is set to a temperature at which carbon dioxide in the exhaust gas is liquefied. That is, in the second heat exchanger 12, only carbon dioxide in the exhaust gas is liquefied.

  In this way, after pre-cooling the exhaust gas using liquefied carbon dioxide, the exhaust gas is cooled using LNG to liquefy the carbon dioxide, so that the exhaust gas can be cooled more efficiently than when cooling with LNG alone. The carbon dioxide can be liquefied. In the exhaust gas in a gas-liquid mixed state, it was confirmed that the concentration of carbon dioxide was concentrated to about 99%.

  Since the LNG that has passed through the second heat exchanger 12 exchanges heat with the exhaust gas, the LNG is vaporized and becomes hydrocarbon gas. Then, this hydrocarbon is sent to the reforming section 23 (that is, the reforming chamber 23a). In addition, if the heat exchange part 22 shown in FIG. 1 is used as the 2nd heat exchanger 12, the number of heat exchangers can be reduced.

  The exhaust gas in a gas-liquid mixed state is sent to the gas-liquid separator 13 where gas-liquid separation is performed. That is, the liquefied carbon dioxide and the gas component are separated by the gas-liquid separator 13, and the liquefied carbon dioxide is sent to the first heat exchanger 11 via the expansion valve 14. On the other hand, gas components, that is, hydrogen, methane, and the like are sent to the catalytic combustor 26 via the anode return gas preheater 28, for example.

  FIG. 3 is a diagram showing a thermal mass balance of exhaust gas containing high-concentration carbon dioxide in the gas-liquid separator 13. The exhaust gas (indicated by A in FIG. 3) is about 88% carbon dioxide gas and about 6% hydrogen. About 3% carbon monoxide and about 2% methane. And when this exhaust gas is cooled gradually and it will be in a gas-liquid mixed state and will be in the state shown by the code | symbol E in FIG. 3, it turns out that the density | concentration (ratio) of liquefied carbon dioxide will be about 99%.

  As described above, in the present embodiment, when carbon dioxide is liquefied and recovered from the exhaust gas from the fuel cell, the carbon dioxide is liquefied using LNG used in the fuel cell as a refrigerant. The power can be reduced during the carbon dioxide recovery, and as a result, the carbon dioxide can be efficiently recovered while saving energy.

  Furthermore, in the present embodiment, since the liquefied carbon dioxide is used for precooling the exhaust gas from the fuel cell, the exhaust gas is cooled more efficiently than in the case of cooling only with LNG, and the carbon dioxide is liquefied. be able to.

  In the present embodiment, since the gas component (hydrogen etc.) recovered by the gas-liquid separator is supplied again to the fuel cell as fuel, hydrogen which is a component other than carbon dioxide contained in the exhaust gas. Can be used effectively.

  In the above-described embodiment, an example in which carbon dioxide is recovered from exhaust gas discharged from the fuel cell has been described. However, it is also used in facilities (carbon dioxide generating facilities) that generate a large amount of carbon dioxide such as thermal power plants. Can do. In this case, it is preferable to use LNG stored in a thermal power plant as a refrigerant. Further, a gas component such as hydrogen separated by the gas-liquid separator may be supplied as fuel to another fuel cell.

  As mentioned above, although embodiment of this invention was described, this invention is not restricted to embodiment mentioned above. The effects described in the embodiments of the present invention are only the most preferable effects resulting from the present invention, and the effects of the present invention are limited to those described in the embodiments of the present invention. is not.

DESCRIPTION OF SYMBOLS 10 Carbon dioxide recovery device 11,12 Heat exchanger 13 Gas-liquid separator 14 Expansion valve 20 Fuel cell power generation facility (MCFC)
DESCRIPTION OF SYMBOLS 21 Fuel tank 22 Heat exchange part 23 Reformer part 24 Fuel cell 25 Exhaust part 26 Catalytic combustor 27 Pressure vessel 28 Anode return gas preheater 29 Exhaust gas pretreatment device 31 Fuel electrode (anode)
32 Air electrode (cathode)

Claims (9)

A carbon dioxide recovery device that is used in equipment that generates exhaust gas containing carbon dioxide, and that recovers carbon dioxide from the exhaust gas,
Heat exchange means for cooling the exhaust gas to form a gas-liquid mixed state fluid in a state in which carbon dioxide is liquefied;
And a gas-liquid separation means for separating and recovering liquefied carbon dioxide from the gas-liquid mixed fluid. The heat exchange means includes a first heat exchanger that pre-cools the exhaust gas using the liquefied carbon dioxide,
2. A second heat exchanger comprising: a second heat exchanger that cools the exhaust gas pre-cooled by the first heat exchanger using a predetermined refrigerant to form the fluid in the gas-liquid mixed state. The carbon dioxide recovery device described. The facility is a fuel cell driven using a liquefied hydrocarbon gas mixture containing liquefied hydrocarbon gas as a raw material,
The carbon dioxide recovery apparatus according to claim 2, wherein the predetermined refrigerant is the liquefied hydrocarbon gas mixture. The fuel cell is a molten carbonate fuel cell,
Hydrogen separated from the liquefied hydrocarbon gas mixture is supplied to the anode of the fuel cell,
At least carbon dioxide and oxygen are supplied to the cathode of the fuel cell,
The carbon dioxide recovery apparatus according to claim 3, wherein carbon dioxide supplied to the cathode of the fuel cell is carbon dioxide contained in exhaust gas generated from a thermal power plant.   The carbon dioxide recovery apparatus according to claim 2, further comprising a recovery tank that recovers the liquefied carbon dioxide that has passed through the first heat exchanger. The fuel cell is a part of a fuel cell facility having a heat exchange unit that vaporizes the liquefied hydrocarbon gas mixture to form a hydrocarbon gas mixture, and a reforming unit that reforms the hydrocarbon gas mixture into hydrogen. Yes,
The carbon dioxide recovery apparatus according to claim 3, wherein the liquefied hydrocarbon gas mixture is vaporized by the second heat exchanger and sent to the reforming unit. The fuel cell facility has a combustion chamber to which gas components other than liquefied carbon dioxide separated by the gas-liquid separation means are supplied,
The reforming unit is configured to reform a hydrocarbon gas mixture that has been pressurized and mixed with steam into hydrogen, and to generate heat necessary for reforming the steam by the combustion gas supplied from the combustion chamber. The carbon dioxide recovery device according to claim 6, further comprising a heating chamber to be supplied.   8. The carbon dioxide recovery apparatus according to claim 7, wherein the combustion gas that has passed through the heating chamber is supplied to the cathode of the fuel cell.   The carbon dioxide recovery apparatus according to claim 6, wherein the second heat exchanger and the heat exchange unit are shared.

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