阅读说明：本技术 二氧化碳还原系统和二氧化碳还原方法 (Carbon dioxide reduction system and carbon dioxide reduction method ) 是由 R.达萨纳雅克阿鲁特吉 新明健一 御山稔人 于 2019-02-22 设计创作，主要内容包括：本发明的二氧化碳还原系统(1)具备输送二氧化碳的输送路径(4)和使从输送路径(4)导入并且经过了加热的二氧化碳还原的还原装置(5),在输送路径(4)中,通过可再生能源和排出热中的至少一者对二氧化碳进行加热。(A carbon dioxide reduction system (1) is provided with a transport path (4) for transporting carbon dioxide and a reduction device (5) for reducing the heated carbon dioxide introduced from the transport path (4), wherein the carbon dioxide is heated by at least one of renewable energy and exhaust heat in the transport path (4).)

1. A carbon dioxide reduction system is provided with:

a reduction apparatus for reducing carbon dioxide, and

a transport path that transports carbon dioxide to the reduction device, wherein,

in the transport path, the carbon dioxide is heated by at least one of a renewable energy source and exhaust heat.

2. The carbon dioxide reduction system of claim 1,

the renewable energy source utilizes at least 1 selected from the group consisting of solar power generation, wind power generation, hydroelectric power generation, wave power generation, tidal power generation, biomass power generation, geothermal power generation, solar heat, and geothermal heat.

3. The carbon dioxide reduction system of claim 1 or 2,

the exhaust heat is heat generated in the combustion furnace.

4. The carbon dioxide reduction system according to any one of claims 1 to 3, further comprising a carbon dioxide separation device, wherein,

the carbon dioxide in the transport path is obtained by separating carbon dioxide from exhaust gas containing carbon dioxide by the carbon dioxide separation device.

5. The carbon dioxide reduction system according to claim 4, further comprising a combustion furnace, wherein,

the exhaust gas is exhaust gas generated in the combustion furnace,

the transport path is a circulation path that circulates carbon dioxide so as to be heated by heat generated in the combustion furnace.

6. The carbon dioxide reduction system according to claim 5, comprising:

a heat exchanger for cooling an exhaust gas containing carbon dioxide generated in the combustion furnace, wherein,

the circulation path delivers carbon dioxide to the heat exchanger,

in the heat exchanger, the carbon dioxide is heated by exchanging heat with the exhaust gas.

7. The carbon dioxide reduction system of claim 6,

the combustion furnace includes a combustion chamber for combusting a combustion target, and a gas discharge path connected to the combustion chamber, and the heat exchanger is attached to the gas discharge path.

8. The carbon dioxide reduction system according to any one of claims 1 to 7,

the reduction device reduces carbon dioxide to carbon monoxide.

9. The carbon dioxide reduction system according to any one of claims 1 to 8,

the reduction apparatus is a reverse shift reaction apparatus for generating carbon monoxide and water by a reverse shift reaction of carbon dioxide and hydrogen.

10. The carbon dioxide reduction system according to any one of claims 1 to 9,

the reduction apparatus is a chemical circulation type reaction apparatus.

11. A carbon dioxide reduction method comprising:

a step of heating carbon dioxide by at least one of renewable energy and exhaust heat; and

and a step of reducing the heated carbon dioxide.

12. The method for reducing carbon dioxide according to claim 11, further comprising a step of separating carbon dioxide from an exhaust gas containing carbon dioxide.

Technical Field

The present invention relates to a carbon dioxide reduction system and a carbon dioxide reduction method for reducing carbon dioxide.

Background

Conventionally, in power generation facilities, steel making facilities, and the like, a large amount of exhaust gas containing carbon dioxide is discharged by using fossil fuel such as petroleum and coal. In addition, in the incinerator, a large amount of exhaust gas containing carbon dioxide is discharged by burning combustible materials such as waste. In recent years, in order to suppress global warming and build a sustainable society, it is important to suppress the emission of carbon dioxide, and attempts have been made to effectively utilize exhaust gas containing carbon dioxide.

For example, patent document 1 discloses that at least a part of carbon dioxide and hydrogen in an exhaust gas is modified into carbon monoxide and water vapor by a Reverse shift reaction (Reverse shift reaction), and then the modified gas is subjected to microbial fermentation to produce an organic substance.

Disclosure of Invention

Technical problem to be solved by the invention

Carbon dioxide has low thermal energy and needs to be heated to be reduced into useful substances such as carbon monoxide. However, since carbon dioxide is generally generated even when carbon dioxide is heated, it is difficult to contribute to reduction of carbon dioxide even when carbon dioxide is reduced to a useful substance.

Accordingly, an object of the present invention is to provide a carbon dioxide reduction system and a carbon dioxide reduction method that can contribute to reduction of carbon dioxide.

Means for solving the problems

As a result of intensive studies, the present inventors have found that heating carbon dioxide by renewable energy or exhaust heat contributes to reduction of carbon dioxide, and have completed the following invention. The gist of the present invention is as shown in the following [1] to [12 ].

[1] A carbon dioxide reduction system is provided with: a reduction apparatus for reducing carbon dioxide, and

a transport path that transports carbon dioxide to the reduction device, wherein,

the carbon dioxide is heated in the transport path by at least one of a renewable energy source and exhaust heat.

[2] The carbon dioxide reduction system according to the above [1], wherein,

the renewable energy source utilizes at least 1 selected from the group consisting of solar power generation, wind power generation, hydroelectric power generation, wave power generation, tidal power generation, biomass power generation, geothermal power generation, solar heat, and geothermal heat.

[3] The carbon dioxide reduction system according to the above [1] or [2], wherein,

the exhaust heat is heat generated in the combustion furnace.

[4] The carbon dioxide reduction system according to any one of the above [1] to [3], further comprising a carbon dioxide separation device,

the carbon dioxide in the transport path is obtained by separating carbon dioxide from exhaust gas containing carbon dioxide by the carbon dioxide separation device.

[5] The carbon dioxide reduction system according to the above [4], further comprising a combustion furnace, wherein,

the exhaust gas is exhaust gas generated in the combustion furnace,

the transport path is a circulation path that circulates carbon dioxide so as to be heated by heat generated in the combustion furnace.

[6] The carbon dioxide reduction system according to [5], which is provided with a heat exchanger for cooling an exhaust gas containing carbon dioxide generated in the combustion furnace, wherein,

the circulation path delivers carbon dioxide to the heat exchanger,

in the heat exchanger, the carbon dioxide is heated by exchanging heat with the exhaust gas.

[7] The carbon dioxide reduction system according to [6], wherein,

the combustion furnace includes a combustion chamber for combusting a combustion target, and a gas discharge path connected to the combustion chamber, and the heat exchanger is attached to the gas discharge path.

[8] The carbon dioxide reduction system according to any one of the above [1] to [7], wherein,

the reduction device reduces carbon dioxide to carbon monoxide.

[9] The carbon dioxide reduction system according to any one of the above [1] to [8], wherein,

the reduction apparatus is a reverse shift reaction apparatus for generating carbon monoxide and water by a reverse shift reaction of carbon dioxide and hydrogen.

[10] The carbon dioxide reduction system according to any one of the above [1] to [9], wherein,

the reduction apparatus is a chemical circulation type reaction apparatus.

[11] A carbon dioxide reduction method comprising:

a step of heating carbon dioxide by at least one of renewable energy and exhaust heat; and a step of reducing the heated carbon dioxide.

[12] The method for reducing carbon dioxide according to [11], further comprising a step of separating carbon dioxide from an exhaust gas containing carbon dioxide.

The present invention further provides the following [13] to [19 ].

[13] A carbon dioxide reduction system is provided with:

a combustion furnace;

a carbon dioxide separation device that separates carbon dioxide from an exhaust gas containing carbon dioxide generated in the combustion furnace;

a circulation path for circulating the carbon dioxide separated by the carbon dioxide separation device so as to be heated by heat generated in the combustion furnace; and

a reduction device for reducing the heated carbon dioxide.

[14] The carbon dioxide reduction system according to [13], wherein,

the reduction device reduces carbon dioxide to carbon monoxide.

[15] The carbon dioxide reduction system according to the above [13] or [14], wherein,

the reduction apparatus is a reverse shift reaction apparatus for generating carbon monoxide and water by a reverse shift reaction of carbon dioxide and hydrogen.

[16] The carbon dioxide reduction system according to any one of the above [13] to [15], wherein,

the reduction apparatus is a chemical circulation type reaction apparatus.

[17] The carbon dioxide reduction system according to any one of the above [13] to [16], which is provided with a heat exchanger that cools an exhaust gas containing carbon dioxide generated in the combustion furnace,

the circulation path conveys the carbon dioxide separated by the carbon dioxide separation device to the heat exchanger, and the carbon dioxide and the exhaust gas are heated by heat exchange in the heat exchanger.

[18] The carbon dioxide reduction system according to [17], wherein,

the combustion furnace includes a combustion chamber for combusting a combustion target, and a gas discharge path connected to the combustion chamber, and the heat exchanger is attached to the gas discharge path.

[19] A carbon dioxide reduction method comprising:

a step of separating carbon dioxide from an exhaust gas containing carbon dioxide generated in a combustion furnace;

a step of heating the carbon dioxide obtained by the separation by heat generated in the incinerator; and

and a step of reducing the heated carbon dioxide.

Effects of the invention

The present invention can contribute to carbon dioxide reduction.

Drawings

FIG. 1 is a schematic view showing a carbon dioxide reduction system according to the present invention.

FIG. 2 is a schematic view showing an embodiment of a carbon dioxide reduction system according to the present invention.

FIG. 3 is a schematic view showing an example of a combustion furnace used in the carbon dioxide reduction system of the present invention.

Detailed Description

The carbon dioxide reduction system and the carbon dioxide reduction method according to the present invention will be described below with reference to the drawings. As shown in fig. 1, a carbon dioxide reduction system 1 of the present invention includes a transportation path 4 and a reduction device 5.

In a preferred embodiment, the carbon dioxide reduction system 1 of the present invention further comprises a carbon dioxide separation unit 3. In general, it cannot be said that the exhaust gas containing carbon dioxide has a sufficiently high carbon dioxide concentration, and it cannot be said that a useful substance can be efficiently produced by direct use. However, the carbon dioxide contained in the exhaust gas is separated by the carbon dioxide separation device 3 and then heated, and the heated carbon dioxide is reduced, whereby the carbon dioxide contained in the exhaust gas can be efficiently reduced.

Hereinafter, a preferred embodiment will be described in detail.

Carbon dioxide (CO)₂) The separation device 3 is a device that separates carbon dioxide from exhaust gas containing carbon dioxide. The apparatus for separating carbon dioxide is not particularly limited, but examples of the separation method include: the details of the chemical absorption method, the solid absorption method, the membrane separation method, and the like are as described in one embodiment described later. The exhaust gas containing carbon dioxide is not particularly limited, and examples thereof include: exhaust gas discharged from a combustion furnace, exhaust gas discharged from a cement plant, exhaust gas discharged from a power plant (thermal power plant), exhaust gas discharged from a steel plant, exhaust gas discharged from an oil refinery, and the like.

The transfer path 4 is a path for transferring the carbon dioxide separated in the carbon dioxide separation device 3 to the reduction device 5. The separated carbon dioxide is heated in the transportation path 4 by the heating means 2. The carbon dioxide can be heated in the transportation path 4, and the heated carbon dioxide can be introduced into the reduction device 5 with a small heat loss.

The transfer path 4 is not particularly limited as long as it is a path connecting the carbon dioxide separation device 3 and the reduction device 5, and may be formed of a pipe (pipe), a tube, or the like. The duct may be of any shape, for example it may be plate-like. The transport path 4 may be provided with a container, a tank, or the like in the middle of the path, and for example, the separated carbon dioxide may be heated in the container, the tank, or the like by the heating means 2. The separated carbon dioxide may be temporarily left in the container, tank, or the like, for example.

The conveyance path 4 is preferably a circulation path as described in the embodiment described later. The circulation path is a path through which the carbon dioxide separated in the carbon dioxide separation device 3 is circulated so as to be heated by heat generated in a combustion furnace or the like as an exhaust gas generation source.

The heating means 2 heats the carbon dioxide obtained by the separation by at least one of renewable energy and exhaust heat. The renewable energy source utilizes at least 1 selected from the group consisting of solar power generation, wind power generation, hydroelectric power generation, wave power generation, tidal power generation, biomass power generation, geothermal power generation, solar heat, and geothermal heat. Further, as the exhaust heat, there are mentioned: heat generated in the reduction apparatus, and heat generated in apparatuses other than the reduction apparatus. Examples of the heat generated in the apparatus other than the reduction apparatus include: heat generated in a combustion furnace, heat generated in a cement plant, heat generated in a power plant (thermal power), heat generated in a steel plant, heat generated in an oil refinery, and the like. These may be used alone in 1 kind, or may be used in combination of 2 or more kinds.

The heating means 2 is not particularly limited as long as it can heat the carbon dioxide separated in the transportation path 4, and is preferably constituted by a heat exchanger. In the case of the heat exchanger, for example, the carbon dioxide is heated by heat exchange between the heating medium heated by at least one of the renewable energy source and the exhaust heat and the carbon dioxide transported in the transport path 4. Examples of the heating medium include fluids such as liquid and gas.

The heat exchanger is not particularly limited, and examples thereof include: a heat exchanger that brings a pipe, a duct, or the like, which is a part of the conveyance path 4, into contact with the heating medium; a heat exchanger in which a pipe, a pipeline, and the like are attached to the outer peripheral surface of a structure through which a heating medium passes; a heat exchanger such as a pipe or a duct is disposed in the heating medium.

The heating means 2 may be a heat ray composed of renewable energy, exhaust heat, or the like, and the heat ray may be irradiated from the outer peripheral surface to a pipe, a tube, a container, a tank, or the like constituting the transport path 4, for example. Further, for example, sunlight may be directly irradiated on the outer peripheral surface of a pipe, a tube, a container, a tank, or the like. The heating means 2 may be a heater heated by various types of power generation, and the heater may be disposed inside a pipe, a container, or a tank constituting the transport path 4, or may be heated by an external heater. Further, for example, at least a part of the conveyance path 4 such as a pipe or a tube may be buried in the ground to be heated by geothermal heating.

The reduction device 5 reduces the carbon dioxide introduced from the conveyance path 4 and heated by the heating means 2. The reduction apparatus is not particularly limited as long as it can reduce carbon dioxide, and is preferably a reverse-shift reaction apparatus, a methanation apparatus, a methanol synthesis apparatus, an ethanol production apparatus, or an acrylic acid synthesis apparatus, more preferably a reverse-shift reaction apparatus, and still more preferably a chemical circulation type reaction apparatus. Details of the reduction device 5, details of the reduction of carbon dioxide performed in the reduction device 5, substances produced, and the like are as described later.

As described above, in the present invention, carbon dioxide is heated by renewable energy or exhaust heat, and new carbon dioxide is not exhausted due to heating of carbon dioxide. Therefore, it can contribute sufficiently to carbon dioxide reduction.

The present invention will be described in more detail below with reference to one embodiment. In the carbon dioxide reduction system and the carbon dioxide reduction method of one embodiment described below, the exhaust gas supplied to the carbon dioxide separation device is an exhaust gas generated in a combustion furnace, and carbon dioxide is heated by heat (exhaust heat) generated in the combustion furnace. Therefore, the carbon dioxide reduction method according to the following embodiment further includes a heat recovery step of recovering the exhaust heat by using carbon dioxide.

Fig. 2 shows a carbon dioxide reduction system 10 according to an embodiment of the present invention.

The carbon dioxide reduction system 10 includes: combustion furnace 11, heat exchanger 20, carbon dioxide (CO)₂) A separation device 30, a circulation path 40 and a reduction device 50.

(Combustion furnace)

The combustion furnace 11 in the carbon dioxide reduction system 10 includes, for example, an incinerator for incinerating waste or the like. The type of incinerator is not particularly limited, and any known incinerator such as a Stoker incinerator, fluidized bed incinerator, kiln incinerator, and gasification melter can be used. The incinerator can combine 2 or more of these modes. The combustion furnace 11 is preferably a grate-type incinerator of these. The combustion furnace 11 is not limited to the one that burns waste, and may be one that burns waste other than coke, such as a blast furnace, as long as carbon dioxide is contained in exhaust gas generated by burning a material to be burned. The combustion furnace 11 is preferably an incinerator for incinerating wastes.

Fig. 3 is a schematic view of the case where the combustion furnace 11 is a grate-type incinerator. As shown in fig. 3, the grate-type incinerator includes: an inlet 12 into which a material to be burned such as waste is introduced, a grate (Stoker)13 for burning the introduced material to be burned, and an ash discharge port 14 for discharging incineration ash generated by combustion in the grate 13.

Generally, the grate 13 is stepped or inclined, and the object to be burned fed from the inlet 12 to the upper section of the grate 13 is dried at the upper section of the grate 13, and then is conveyed to the middle section, and the object to be burned is burned at the middle section. Then, the burned material to be burned is transported to the rear stage and post-burned in the rear stage, and is discharged as burned ash from the ash discharge port 14. Further, in the grate 13, oxygen, air, and the like are fed from below the grate 13 or the like in order to burn the combustion target.

In the combustion furnace 11, a combustion chamber 17 for burning a material to be burned is composed of a lower combustion chamber 15 provided with a grate and a gas combustion chamber 16 connected to an upper portion of the lower combustion chamber 15, and gas generated by combustion in the grate 13 is further combusted in the gas combustion chamber 16. The gas further burned in the gas combustion chamber 16 is discharged as an exhaust gas to the outside of the combustion furnace 11 through a gas discharge passage 18 connected to the gas combustion chamber 16 (i.e., combustion chamber 17), and is sent to a carbon dioxide separation device 30 described below.

The exhaust gas contains carbon dioxide generated by combustion of the combustion target. Further, the fuel system of the combustion furnace 11 may be, for example, a synthesis gas containing carbon dioxide, carbon monoxide, and hydrogen. In addition, the exhaust gas may generally contain nitrogen, oxygen, and water (water vapor) in addition to carbon dioxide, and may further contain carbon monoxide and hydrogen in addition to these.

The exhaust gas may contain, for example, 2 to 30 mass% of carbon dioxide, 15 to 45 mass% of carbon monoxide, 10 to 50 mass% of hydrogen, 25 to 67 mass% of nitrogen, 0.5 to 20 mass% of oxygen, and 5 to 40 mass% of water. Further, for example, the gas may contain 2.5 to 25 mass% of carbon dioxide, 35 to 70 mass% of nitrogen, 4 to 18 mass% of oxygen, and 10 to 35 mass% of water.

The temperature T1 of the exhaust gas sent from the combustion chamber 17 to the gas discharge path 18 is a gas immediately after combustion, and therefore is high. Specifically, the temperature is, for example, 200 to 1300 ℃, preferably 300 to 900 ℃.

Note that, although the combustion chamber 17 is shown as being constituted by the lower stage combustion chamber 15 and the gas combustion chamber 16, the gas combustion chamber 16 may be omitted, and the lower stage combustion chamber 15 may be directly connected to the gas discharge path 18. In the above description, the case where the combustion furnace is a grate-type incinerator has been described as an example, but any combustion furnace may be used as long as a known combustion furnace having a combustion chamber and a gas discharge path is suitably used.

(Heat exchanger)

The carbon dioxide reduction system 10 is provided with the heat exchanger 20 as described above. In the present embodiment, the heat exchanger 20 is attached to the gas discharge path 18. The heat exchanger 20 cools the exhaust gas in the exhaust passage 18 fed from the combustion chamber 17.

The medium passing through the inside of the heat exchanger 20 is carbon dioxide separated by the carbon dioxide separation device 30 described below. The carbon dioxide inside the heat exchanger 20 is heated by heat exchange with the exhaust gas which is fed from the combustion chamber 17, inside the gas exhaust path 18, and has a high temperature.

The heat exchanger 20 may be of any type, either a tube type or a plate type, or a combination thereof. In the case of a tube type, for example, the heat transfer tube may be wound in a coil shape or a capacitor shape, or a plurality of tubes may be bundled. The heat exchanger 20 may be provided inside the gas discharge path 18 as shown in fig. 3, or may be provided along the outer peripheral surface of the gas discharge path 18, and is preferably provided inside the gas discharge path 18.

Further, a heat exchanger (not shown) may be provided in addition to the heat exchanger 20 inside the gas discharge path 18, and the exhaust gas inside the gas discharge path 18 is cooled by the heat exchanger. With such a heat exchanger, for example, a medium inside the heat exchanger, which constitutes a part of the boiler and is heated by the exhaust gas, may be used to drive the boiler.

The exhaust gas cooled by the heat exchanger 20 is discharged from the gas discharge path 18 to the outside of the combustion furnace 11, and is sent to the carbon dioxide separation device 30 as shown in fig. 2. Here, the exhaust gas may be directly sent to the carbon dioxide separation device 30, and preferably sent to the carbon dioxide separation device 30 after being subjected to various treatments.

For example, as shown in fig. 2, a cooling device 21 is provided on a path between the gas discharge path 18 and the carbon dioxide separation device 30, and the exhaust gas cooled by the heat exchanger 20 may be further cooled by the cooling device 21 and then sent to the carbon dioxide separation device 30. The cooling device 21 is not particularly limited, and examples thereof include: heat exchangers, cooling towers, etc. The cooling tower may be of a water spray type, an air cooling type, or the like, which is generally used in an incinerator.

Further, a cleaning device 22 may be provided on a path between the gas discharge path 18 and the carbon dioxide separation device 30, and the exhaust gas cooled by the heat exchanger 20 may be cleaned by the cleaning device 22 and then sent to the carbon dioxide separation device 30. Examples of the cleaning device 22 include: soot removal devices such as bag filters, various adsorption filters such as activated carbon filters, nitrogen oxide removal devices such as denitration reaction towers, acid gas removal devices, and the like, and soot, dioxin, hydrogen chloride, sulfur oxide, nitrogen oxide, organic matter, and the like are removed by these cleaning devices.

Either one of the cooling device 21 and the cleaning device 22 may be provided in the carbon dioxide reduction system 10, or both may be provided, or neither may be provided. Further, processing means other than the cooling means 21 and the cleaning means 22 may be provided. Further, the cooling device 21 and the cleaning device 22 may be provided individually or in plural.

The exhaust gas sent to the carbon dioxide separation device 30 is cooled by the heat exchanger 20 as described above, and further cooled by the cooling device 21 as necessary, as described above, to become a low temperature. However, the heat-resistant carbon dioxide separation device 30 and the like may be conveyed to the carbon dioxide separation device 30 without being cooled by the cooling device 21 depending on the type of the carbon dioxide separation device 30. The exhaust gas may be sent to the carbon dioxide separation device 30 without being cooled by the heat exchanger 20 described below or without being cooled by either the heat exchanger 20 or the cooling device 21.

The temperature T2 of the exhaust gas to be sent to the carbon dioxide separation device 30 is preferably, for example, 0 to 500 ℃, and preferably 5 to 450 ℃. By setting the temperature T2 within the above range, it is possible to appropriately separate carbon dioxide from the exhaust gas without placing a burden on the carbon dioxide separation device 30.

The exhaust gas discharged from the gas discharge path 18 may be sent to the carbon dioxide separation device 30 in a state of being pressurized by a blower (not shown) or the like.

(carbon dioxide separation device)

The carbon dioxide separation device 30 separates carbon dioxide from the exhaust gas sent from the fuel furnace 11. The separation method of the carbon dioxide separation device 30 is not particularly limited, and examples thereof include: chemical absorption, solid absorption, membrane separation, and the like. Examples of the apparatus using the chemical absorption method include: an apparatus for absorbing and separating carbon dioxide in the exhaust gas into a solution containing an amine solution or the like, an apparatus utilizing a pressure swing adsorption method (PSA method), or the like. Examples of the apparatus using the solid absorption method include an apparatus in which a solid absorbent capable of absorbing carbon dioxide is supported on a porous support. Further, an apparatus using a TSA (Thermal Swing adsorption) method, or the like may be used. Examples of the apparatus used in the membrane separation method include a carbon dioxide separation membrane. Examples of the carbon dioxide separation membrane include PBI (polybenzimidazole) separation membranes. The PBI-based separation membrane has heat resistance and can separate carbon dioxide even in the case of a relatively high-temperature exhaust gas. Among these, a carbon dioxide separation membrane is preferably used.

In the present invention, the separation of carbon dioxide in the carbon dioxide separation device 30 does not require strict separation of carbon dioxide from the exhaust gas alone, and may be performed as long as the carbon dioxide is separated into a gas having an improved carbon dioxide content and another gas. The carbon dioxide content in the gas with the increased carbon dioxide content is preferably 30 to 100 mass%, more preferably 55 to 99 mass%. In the present specification, for the sake of simplicity of description, the gas having such an improved carbon dioxide content is also referred to simply as the separated carbon dioxide.

The separated carbon dioxide is sent to the heat exchanger 20 through the circulation path 40 and used as a medium passing through the inside of the heat exchanger 20. The temperature T3 of the separated carbon dioxide is, for example, 0 to 550 ℃, preferably 5 to 450 ℃. Therefore, the carbon dioxide separated in the heat exchanger 20 is heated by heat exchange with the exhaust gas generated in the combustion furnace 11. This makes it possible to efficiently use the thermal energy generated by the combustion in the combustion furnace 11.

In the heat exchanger 20, the heated carbon dioxide is sent to the reduction device 50 through the circulation path 40. On the other hand, the exhaust gas generated in the combustion furnace 11 is cooled by the carbon dioxide passing through the inside of the heat exchanger 20, and as described above, is discharged to the outside of the combustion furnace 11 and sent to the carbon dioxide separation device 30.

The carbon dioxide separated in the carbon dioxide separation device 30 may be fed to the reduction device 50 through the circulation path 40 in a pressurized state by, for example, a blower or the like. The pressure in the circulation path 40 is, for example, preferably 101.35 to 999kPa, and more preferably 101.50 to 500 kPa. The carbon dioxide passes through the circulation path 40 after being pressurized, and is efficiently heat-exchanged in the heat exchanger 20.

The carbon dioxide separated in the carbon dioxide separation device 30 may be circulated so as to pass through the inside of the heat exchanger 20, and may be circulated so as to pass through the inside of the heat exchanger used in the cooling device 21, for example. That is, the separated carbon dioxide may be sequentially passed through the heat exchanger inside of the cooling device 21 and the heat exchanger inside of the heat exchanger 20, and then may be sent to the reduction device 50. In this manner, the separated carbon dioxide is more efficiently heated by the heat energy generated in the combustion furnace 11.

(reduction apparatus)

As described above, carbon dioxide heated by the heat exchanger 20 or the like is supplied to the reduction device 50. The temperature T4 of the carbon dioxide supplied to the reduction apparatus 50 is preferably 200 to 900 ℃, and more preferably 300 to 700 ℃. By setting the temperature T4 of carbon dioxide within the above range, the additive heating in the reduction device 50 can be reduced, and carbon dioxide can be reduced without heating.

In the reduction device 50, the supplied carbon dioxide is reduced. The substance obtained by the reduction of carbon dioxide may be carbon monoxide, or an organic substance such as methane, methanol, acetic acid, ethane, or ethylene, but carbon monoxide is preferred. The reduction apparatus 50 is preferably a reverse-shift reaction apparatus that can perform a reduction reaction by an endothermic reaction, more preferably a chemical circulation type reaction apparatus.

In order to obtain the substance by reduction of carbon dioxide, it is preferable to supply gas components other than carbon dioxide to the reduction device 50, and specifically, as shown in fig. 2, it is preferable to supply hydrogen gas. When hydrogen gas is supplied, carbon monoxide and water are produced from carbon dioxide and hydrogen by a reverse shift reaction represented by the following formula (1).

CO₂+H₂→CO+H₂O (1)

It is preferable that the hydrogen supplied to the reduction device 50 is heated. Specifically, the supplied hydrogen may be heated to 200 ℃ or higher, for example, but in the case of a one-pot reaction described later, the hydrogen may be heated to 300 to 900 ℃ or higher, and more preferably 350 to 750 ℃. In addition, in the case of chemical cycling reaction, the temperature is preferably 200 to 700 ℃, and more preferably 200 to 650 ℃.

The method of heating hydrogen is not particularly limited, and the hydrogen may be heated by passing the hydrogen as a medium through the inside of a heat exchanger installed in the combustion furnace (gas discharge path) or the inside of a heat exchanger of the cooling device 21, or may be heated by another method, as in the case of carbon dioxide.

The reverse-flow reaction apparatus is, for example, a reactor in which a catalyst for the reverse-flow reaction for promoting the reaction of the above (1) is filled, and is a reactor in which both reduction of carbon dioxide and oxidation of hydrogen are carried out in the same reactor. In this way, the reverse shift reaction of both the reduction of carbon dioxide and the oxidation of hydrogen is carried out in the same reactor, and is also referred to as a one-pot reaction in the present specification.

In the one-pot type reaction, carbon monoxide and water (steam) are generated inside the same reactor by passing carbon dioxide and hydrogen through the reactor, and carbon monoxide and water (steam) are discharged from the reactor.

The gas temperature inside the reactor in the one-pot reaction is, for example, 300 to 1000 ℃, preferably 450 to 850 ℃. As described above, the carbon dioxide or the carbon dioxide and the hydrogen supplied to the reduction device 50 are heated in advance. Therefore, the reactor may not be heated, but heating may be performed in the case where the gas temperature does not reach the temperature or the like.

Examples of the catalyst for the reverse shift reaction used in the one-pot reaction include catalysts containing a noble metal catalyst such as ruthenium (Ru) or rhodium (Ru), and a metal catalyst such as Mn, Fe, or Co.

Further, as a more preferable mode for the reverse shift reaction, there is a chemical circulation type reaction. The reaction apparatus used in the chemical circulation type reaction (chemical circulation type reaction apparatus) includes the 1 st and 2 nd reactors, and the reaction represented by the above formula (1) is carried out as the 1 st and 2 nd reactions in the 1 st and 2 nd reactors, respectively. Specifically, the 1 st and 2 nd reactors are filled with a metal oxide catalyst, respectively, and the 1 st reaction for reducing carbon dioxide to carbon monoxide is performed in one reactor, and the 2 nd reaction for oxidizing hydrogen to water is performed in the other reactor. The 1 st and 2 nd reactions are represented by the following reaction formulae (2) and (3), respectively.

The 1 st and 2 nd reactions are carried out by supplying carbon dioxide to one reactor and hydrogen to the other reactor, respectively, and a gas containing carbon monoxide is discharged from one reactor and a gas containing water (water vapor) is discharged from the other reactor.

CO₂(gas) + MO_x-1(solid) → CO (gas) + MO_x(solid) (2)

H₂(gas) + MO_x(solid) → H₂O (gas) + MO_x-1(solid) (3)

(in the formulae (2) and (3), M represents a metal and x represents a positive integer.)

The chemical circulation type reaction apparatus includes a reaction apparatus having a catalyst circulation path for circulating a metal oxide catalyst between two reactors. In this chemical circulation type reactor, carbon dioxide is supplied to the 1 st reactor to perform a reduction reaction and carbon monoxide is discharged, and hydrogen is supplied to the 2 nd reactor to perform an oxidation reaction and water is discharged. Further, the metal oxide catalyst oxidized in the 1 st reactor is transferred to the 2 nd reactor, and the metal oxide catalyst reduced in the 2 nd reactor is transferred to the 1 st reactor, thereby circulating the metal oxide catalyst. By thus circulating the metal oxide catalyst, the metal oxide catalyst can be continuously used for a long time without being deactivated even if reduction and oxidation are respectively repeated in the 1 st and 2 nd reactors, respectively.

Further, the chemical circulation type reactor may be a reactor in which a catalyst is fixed and gas to be supplied to each reactor is switched. This type of chemical circulation type reactor is provided with a 1 st reactor and a 2 nd reactor each filled with a metal oxide catalyst, and the 1 st reactor and the 2 nd reactor are each provided with a line for supplying carbon dioxide and hydrogen thereto. Carbon dioxide is supplied to one reactor, where a reduction reaction is performed to discharge carbon monoxide, while hydrogen is supplied to the other reactor, where an oxidation reaction is performed to discharge water.

The reactor to which carbon dioxide is supplied and the reactor to which hydrogen is supplied are appropriately switched over with the passage of time, whereby oxidation and reduction of the metal oxide catalyst are repeatedly performed in each reactor, and the metal oxide catalyst can be continuously used for a long time without being deactivated.

In the chemical circulation type reaction apparatus, the gas temperature in the 1 st reactor (i.e., the reactor in which the reduction of carbon dioxide is performed) is, for example, 450 to 1000 ℃, and preferably 500 to 850 ℃. The gas temperature in the 2 nd reactor (i.e., the reactor in which hydrogen oxidation is performed) is, for example, 300 to 800 ℃, and preferably 300 to 750 ℃.

The 1 st and 2 nd reactors may not be heated, but may be heated when the gas temperature of carbon dioxide and hydrogen supplied to these reactors does not reach the above temperature or the like.

The metal oxide catalyst in the chemical circulation reactor may be any known metal oxide catalyst, and examples thereof include oxides of 1 or 2 or more metals selected from La, Sr, Co, Ce, Zr, Y and Fe. The oxide may be an oxide having a perovskite crystal structure.

The carbon monoxide obtained in the reduction apparatus 50 can be further converted into an organic substance or the like by microbial fermentation or the like. The water obtained in the reduction apparatus 50 may be removed by appropriate liquefaction or the like.

As described above, according to the present embodiment, carbon dioxide separated by the carbon dioxide separation device is heated by the thermal energy generated in the combustion furnace and then reduced, whereby carbon dioxide contained in the exhaust gas generated in the combustion furnace can be efficiently reduced. In the present embodiment, the heat generated in the furnace can be recovered safely and efficiently by using carbon dioxide, which has a large heat capacity and is inactive, as the heat recovery medium.

In the above embodiment, the heat exchanger for cooling the exhaust gas containing carbon dioxide generated in the combustion furnace is provided, but the heat exchanger may not be provided, and the exhaust gas containing carbon dioxide generated in the combustion furnace may be sent to the carbon dioxide separation device without being cooled by the heat exchanger.

However, in this case, since the separated carbon dioxide needs to be heated by heat generated in the combustion furnace, for example, a pipe or the like may be passed through the combustion chamber, and the carbon dioxide separated in the carbon dioxide separation device may be passed through the pipe to heat the carbon dioxide.

Description of the symbols

1 carbon dioxide reduction system

2 heating means

3 carbon dioxide separation device

4 conveying path

5 reduction device

10 carbon dioxide reduction system

11 combustion furnace

12 throwing-in mouth

13 fire grate

14 ash discharge port

15 lower combustion chamber

16 gas combustion chamber

17 combustion chamber

18 gas discharge path

20 heat exchanger

21 cooling device

22 cleaning device

30 carbon dioxide separation device

40 circulation path

50 reduction device