WO2025229962A1 - Transport system for carbon dioxide from exhaust gas - Google Patents

Abstract

Provided is a transport system for carbon dioxide from exhaust gas, wherein the system does not require a special transport means or containers such as tanks having low-temperature resistance and high-pressure resistance, even in a place in which a carbon dioxide (CO₂) recovery location and a CO₂ storage location and a utilization location are separated locations, and has excellent handling and high transport energy efficiency without causing crushing, collapse, etc. since a solidified body obtained by solidifying CO₂ in a form to be transported is provided with constant strength even when vibration or the like is applied by transport means such as a ship and a vehicle.　A transport system for carbon dioxide from exhaust gas, according to the present invention includes: (a) a step for obtaining a slurry containing magnesium carbonate from exhaust gas containing CO₂; (b) a step for solidifying the slurry containing the carbonate; (c) a step for transporting the solidified magnesium carbonate from a first location to a second location; and (d) a step for decomposing the solidified magnesium carbonate into magnesium oxide and CO₂ after transport.

Description

Carbon dioxide transport system from flue gases

The present invention relates to a system for transporting carbon dioxide from exhaust gases, and in particular to a system for transporting carbon dioxide from exhaust gases that uses a magnesium compound to solidify carbon dioxide from exhaust gases emitted from manufacturing facilities such as cement factories, thermal power plants, and chemical plants, as well as from transportation means such as ships, to prepare a solidified body with good strength, improving the transportability of the solidified body and achieving excellent energy efficiency in transportation.

One of the causes of global warming is the greenhouse effect caused by carbon dioxide contained in combustion exhaust gases emitted from large-scale exhaust gas emission sources such as cement factories, thermal power plants, and chemical plants. Various efforts are being made to reduce emissions of such greenhouse gases.
For example, a method has been proposed in which carbon dioxide is separated and recovered from such combustion exhaust gases and then stored underground without being released into the atmosphere.In addition, research has been initiated into artificial photosynthesis, such as the production of plastic products by synthesizing olefins using a catalyst that promotes chemical synthesis, using _H2 gas isolated by a separation membrane and the recovered carbon dioxide, as well as research into energy storage using _CO2 .

One way to reduce carbon dioxide released into the atmosphere is to store it underground. Methods for storing carbon dioxide underground include carbon dioxide capture and storage (CCS), which captures carbon dioxide from exhaust gases and stores it underground, and enhanced oil recovery (EOR), which captures carbon dioxide from large-scale emission sources and injects and stores it in deep underground saline layers, depleted oil and gas fields, oil fields with reduced production efficiency, etc., thereby suppressing the rise of carbon dioxide in the atmosphere.
Known carbon dioxide recovery or removal techniques include chemical absorption, physical absorption, membrane separation, and adsorption, all of which use an absorption solution. A representative recovery technique is the chemical absorption method, which uses an amine aqueous solution.

The following technologies have been proposed as carbon dioxide capture technologies for storing carbon dioxide underground.
Japanese Patent Laid-Open Publication No. 2012-110805 (Patent Document 1) discloses a carbon dioxide recovery method for reducing operating costs by reducing the energy required to regenerate a carbon dioxide absorption liquid. Specifically, the carbon dioxide recovery method described includes an absorption step of bringing a gas containing carbon dioxide into contact with an absorption liquid to cause the absorption liquid to absorb carbon dioxide; a regeneration step of heating the absorption liquid that has absorbed carbon dioxide in the absorption step to release the carbon dioxide from the absorption liquid and regenerate the absorption liquid; a depressurization step of reducing the pressure of the absorption liquid regenerated in the regeneration step to a pressure lower than that in the regeneration step to generate water vapor from the absorption liquid; and a pressurization step of pressurizing the water vapor generated in the depressurization step to a pressure equivalent to that in the regeneration tower step and supplying the water vapor to the regeneration step.

Furthermore, Japanese Patent Application Laid-Open No. 2024-030963 (Patent Document 2) discloses a method for underground storage of carbon dioxide that can reliably contain carbon dioxide injected downward by ensuring the strength of a carbon dioxide shielding layer, and can efficiently store large amounts of carbon dioxide. Specifically, the method stores carbon dioxide alone or a liquefied mixed gas containing carbon dioxide as the main component in a geological layer under the seabed consisting of sediments on an acoustic base or in a geological layer on land, and includes a carbon dioxide sealing area consisting of a geological layer that exists from the seabed or ground to a predetermined depth and meets pressure and temperature conditions that allow carbon dioxide hydrate to be generated. The method describes a carbon dioxide underground storage method in which the carbon dioxide is injected below the seabed to form a carbon dioxide reservoir, and at least a portion of the carbon dioxide injected into the carbon dioxide reservoir naturally rises toward the carbon dioxide sealed area due to the buoyancy of the carbon dioxide, thereby generating carbon dioxide hydrate, thereby forming a carbon dioxide shielding layer in the carbon dioxide sealed area.When the carbon dioxide is injected into the subseafloor strata or the terrestrial strata, the pore pressure in the carbon dioxide sealed area is increased by artificial water sealing in which at least one of seawater and water is injected into the carbon dioxide sealed area as pore water.

Furthermore, Japanese Patent Application Laid-Open No. 2023-140554 (Patent Document 3) discloses a method for storing carbon dioxide in soil, which involves mixing at least one of the following mixtures: soil before improvement, an admixture to be mixed with the soil to be improved, or the improved soil; with a gas containing a higher volumetric percentage of carbon dioxide than the air at the construction site, or with a carbonated solution containing dissolved carbon dioxide; and mixing the carbon dioxide into the mixture, thereby storing the carbon dioxide in the improved soil.

However, these underground storage methods are difficult to implement when the location where the carbon dioxide is captured and the location where it is stored are far apart. Furthermore, carbon dioxide liquefied under low temperature and high pressure must be filled into low-temperature and high-pressure resistant transport containers and transported to the carbon dioxide storage location by transport means such as ships or vehicles. This requires maintaining a low temperature during transport and operating under high pressure, which places a heavy burden on transporting liquid carbon dioxide, resulting in extremely poor energy efficiency during transportation.

Another method for reducing atmospheric carbon dioxide is disclosed in Japanese Patent Laid-Open Publication No. 2002-349793 (Patent Document 4), which discloses a method for injecting liquefied carbon dioxide into the sea. Specifically, this method involves injecting liquefied carbon dioxide into the sea using a liquefied carbon dioxide storage and discharge device that includes a liquefied carbon dioxide storage tank into which liquefied carbon dioxide is supplied and the temperature inside the tank is maintained at a predetermined storage temperature, a discharge pump that discharges liquefied carbon dioxide from the storage tank, and a nitrogen gas supply means that supplies nitrogen gas to the storage tank at the same pressure as the predetermined storage pressure of the storage tank so as to maintain the predetermined storage pressure of the storage tank. The nitrogen gas supply means sets the storage pressure higher than the saturation pressure corresponding to the storage temperature inside the storage tank and is configured to have a nitrogen gas supply capacity at the same storage pressure as or greater than the predetermined discharge capacity of the discharge pump.

Furthermore, as a method for transporting captured carbon dioxide, for example, Japanese Patent Application Laid-Open No. 2024-076432 (Patent Document 5) discloses a carbon dioxide transport method comprising: a first transfer step of transporting liquid carbon dioxide captured in equipment for capturing carbon dioxide contained in exhaust gas emitted from a combustion device from the equipment to a first tank installed in a remote location; and a second transfer step of transporting the liquid carbon dioxide from the first tank to a second tank via a first pipeline connecting the first tank to a second tank installed in a remote location; the first transfer step including a transport vehicle transport step of storing the liquid carbon dioxide in a storage tank mounted on a transport vehicle and transporting the liquid carbon dioxide stored in the storage tank to the first tank by the transport vehicle.

However, all of the above methods involve transporting liquefied carbon dioxide, and during transportation, care must be taken to prevent the liquefied carbon dioxide from evaporating or becoming dry ice due to supercooling. Furthermore, when transporting or conveying liquefied carbon dioxide, it is necessary to maintain a certain temperature and pressure, which poses the problem of requiring special tanks and transportation equipment, as well as the energy required to maintain the certain temperature and pressure.

JP 2012-110805 A JP 2024-030963 A JP 2023-140554 A Japanese Patent Application Laid-Open No. 2002-349793 JP 2024-076432 A

The object of the present invention is to solve the above problems and to provide a carbon dioxide ( _CO2 ) transportation system from exhaust _gas that does not require special transportation means, such as containers such as low-temperature-resistant or high-pressure-resistant tanks, even when the carbon dioxide (CO2) recovery site and the _CO2 storage site or utilization site are located far apart, and that produces a solidified CO2 body that has good strength for transportation even when subjected to vibrations from transportation means such as ships or vehicles, and that has excellent transportation energy efficiency.
Preferably, the present invention provides a system for transporting carbon dioxide from exhaust gas, which can be used to construct a circulation system that utilizes exhaust gas containing carbon dioxide emitted from factories and the like.

In order to solve the above problems, the present invention has discovered that the problem can be solved by preparing a slurry containing magnesium carbonate that fixes carbon dioxide, and then mixing the slurry with magnesium oxide and/or magnesium oxychloride cement (MOC) and/or magnesium oxysulfate cement (MOS), a magnesium compound that dissolves and reprecipitates in water and/or a magnesium compound that undergoes a phase transition in water, and solidifying the mixture. This led to the development of the present invention, which has the following technical features.

(I) The carbon dioxide transport system from exhaust gas of the present invention comprises the following steps:
(a) obtaining a slurry containing magnesium carbonate from a _CO2 -containing flue gas;
(b) solidifying the carbonate-containing slurry;
(c) transporting the solidified magnesium carbonate from the first location to a second location; and
(d) A system for transporting carbon dioxide from exhaust gas, comprising a step of decomposing the solidified magnesium carbonate after transportation into magnesium oxide and _CO2 .

(II) Preferably, in the above-mentioned carbon dioxide transport system from exhaust gas of the present invention, step (b) comprises mixing magnesium oxide and/or magnesium oxychloride cement (MOC) and/or magnesium oxysulfate cement (MOS) with the slurry containing magnesium carbonate obtained in step (a) and solidifying the mixture.

(III) More preferably, in the above-mentioned carbon dioxide transport system of the present invention,
The step (a) comprises:
(a1) obtaining a carbonate of an alkali other than an alkaline earth metal from a flue gas containing _CO2 ; and
(a2) A step of reacting the alkali carbonate obtained in the step (a1) with magnesium hydroxide to obtain the magnesium carbonate.

(IV) Preferably, in the system for transporting carbon dioxide from exhaust gas of the present invention,
(p) after step (d), a step of reacting the magnesium oxide obtained in step (d) with water to obtain magnesium hydroxide;
(q) transporting the magnesium hydroxide obtained in step (p) to a first location; and
(r) Any of the above systems for transporting carbon dioxide from exhaust gas, further comprising a step of recycling the magnesium hydroxide after transport as the magnesium hydroxide in step (a).

(V) Preferably, in the system for transporting carbon dioxide from exhaust gas of the present invention,
(f) transporting the magnesium oxide obtained in step (d) to a first location;
(g) reacting the transported magnesium oxide with water to obtain magnesium hydroxide; and
(h) Any of the above systems for transporting carbon dioxide from exhaust gas, further comprising a step of recycling the magnesium hydroxide obtained in the step (g) as the magnesium hydroxide in the step (a).

(VI) Furthermore, preferably, in the above-mentioned system for transporting carbon dioxide from exhaust gas of the present invention,
The system for transporting carbon dioxide from exhaust gas is characterized in that in step (g), the reaction heat generated when the magnesium oxide is reacted with water to obtain magnesium hydroxide is used for solidification in step (b).

(VII) More preferably, in the above-mentioned carbon dioxide transport system of the present invention,
Any of the above carbon dioxide transportation systems from exhaust gases is characterized in that the exhaust gas is exhaust gas generated from a transportation means during transportation.

(VIII) More preferably, in the above-mentioned carbon dioxide transport system from exhaust gas of the present invention,
(e) Any of the above carbon dioxide transport systems from exhaust gases, further comprising a step of injecting the _CO2 obtained by decomposition in the step (d) underground.

In the present invention, "solidification" refers to the process of blending a magnesium compound that dissolves and reprecipitates in water, such as magnesium oxide and/or magnesium oxychloride cement (MOC) and/or magnesium oxysulfate cement (MOS), and/or a magnesium compound that undergoes a phase transition in water, with a magnesium-containing carbonate slurry, and solidifying the carbonate slurry containing the magnesium compound as a result of the blended magnesium compound having a solidifying function.
Additionally, "transport" is meant to include the concepts of transfer and transportation.

According to the present invention, since the system contains magnesium compounds such as magnesium oxide and/or magnesium oxychloride cement (MOC) and/or magnesium oxysulfate cement (MOS), the solidification of the compounds firmly solidifies the carbonate slurry in which the _CO2 contained in the exhaust gas is fixed, making it easy to store. Furthermore, the solidified body has the strength to maintain its solid state even when subjected to vibrations and the like from transportation means such as ships, vehicles, and trains. Therefore, even if the carbon dioxide ( _CO2 ) capture site and the _CO2 storage site or utilization site are located far apart, there is no need for special transport containers or the like for transporting the solidified body in which the carbon dioxide is fixed, such as tanks or other low-temperature or high-pressure resistant containers. This improves the stability of transportation and provides a system for transporting carbon dioxide from exhaust gas with excellent transportation energy efficiency.
Furthermore, according to the preferred embodiment of the present invention, it is possible to construct an effective circulation system that utilizes exhaust gas containing carbon dioxide emitted from factories and the like.

Furthermore, the _CO2 obtained by decomposition of the carbon dioxide solidified body transported energy-efficiently by the transportation system of the present invention can be efficiently injected and stored in deep underground saline layers such as CSS and EOR, depleted oil and gas fields, producing oil fields with reduced production efficiency, and abandoned mines in shallow layers less than 800 meters underground.Furthermore, the _CO2 obtained by decomposition can be used for known purposes, such as as an industrial raw material for plastic production, or in _CO2 batteries that use _CO2 to store energy, making it possible to curb the increase in carbon dioxide in the atmosphere, which is an environmental problem.

FIG. 1 is a diagram showing a schematic diagram of an example of the outline of a system for transporting carbon dioxide from exhaust gas according to the present invention. FIG. 2 is a diagram showing a schematic diagram of another example of the outline of the system for transporting carbon dioxide from exhaust gas according to the present invention.

The present invention will be described below with reference to the following preferred examples, but is not limited thereto.
The carbon dioxide transport system from exhaust gas of the present invention comprises:
(a) obtaining a slurry containing magnesium carbonate from a flue gas containing _CO2 ;
(b) solidifying the carbonate-containing slurry;
(c) transporting the solidified magnesium carbonate from the first location to a second location; and
(d) a system for transporting carbon dioxide from flue gas, comprising a step of decomposing the solidified magnesium carbonate after transport into magnesium oxide and _CO2 .

Preferably,
Following the step (d),
(p) a step of reacting the magnesium oxide obtained in step (d) with water to obtain magnesium hydroxide;
(q) transporting the magnesium hydroxide obtained in step (p) to a first location; and
(r) further comprising a step of recycling the magnesium hydroxide after transportation as the magnesium hydroxide in the step (a), or
(f) transporting the magnesium oxide obtained in step (d) to a first location;
(g) reacting the transported magnesium oxide with water to obtain magnesium hydroxide; and
(h) A system for transporting carbon dioxide from exhaust gas, further comprising a step of recycling the magnesium hydroxide obtained in the step (g) as the magnesium hydroxide in the step (a).

The above-mentioned carbon dioxide transport system from exhaust gas of the present invention will be explained using the following preferred examples, but is not limited thereto.
The following description will be given based on the examples shown in FIGS.
Step (a) Step (a) in the system for transporting carbon dioxide from flue gas of the present invention is a step of obtaining a slurry containing magnesium carbonate from flue gas containing _CO2 (Figure 1).
Examples of _CO2 -containing exhaust gases to which the present invention can be applied include any _CO2 -containing exhaust gases, such as exhaust gases generated from manufacturing facilities such as cement factories, and from transportation means such as ships and vehicles. The exhaust gases may contain at least _CO2 , and may also contain other components, such as sulfur oxides (SOx) and nitrogen oxides (NOx).

As shown in FIG. 1, step (a) is specifically a step in which exhaust gas containing CO ₂ is brought into contact with a solution of magnesium hydroxide, and the CO ₂ in the exhaust gas is reacted with the magnesium hydroxide to produce a slurry containing magnesium carbonate.
The exhaust gas may be preheated to 60° C. or higher in order to increase the efficiency of the reaction with the magnesium hydroxide.
Furthermore, if necessary, the magnesium hydroxide obtained in the step (g) described below or the magnesium hydroxide in the step (r) may be used as the magnesium hydroxide to be contacted with the exhaust gas containing _CO2 .

The concentration of the magnesium hydroxide solution can be appropriately determined depending on the CO ₂ concentration contained in the exhaust gas.
Furthermore, depending on the components contained in the exhaust gas other than _CO2 , the exhaust gas is brought into contact with magnesium hydroxide to produce a slurry containing magnesium carbonate, but there are also cases where a slurry containing magnesium sulfate, magnesium nitrate, etc. is produced.
For example, when sulfur oxides are contained in the exhaust gas, a slurry containing magnesium sulfate, which is a reaction product of magnesium hydroxide and sulfur oxide, may be produced, and when nitrogen oxides are contained in the exhaust gas, a slurry containing magnesium nitrate, which is a reaction product of magnesium hydroxide and nitrogen oxide, may be produced.

Among the components contained in the exhaust gas, those that have low reactivity with magnesium hydroxide are preferably removed by emitting them outside the system during the process of contacting the exhaust gas with magnesium hydroxide.

If the slurry containing magnesium carbonate also contains magnesium sulfate or magnesium nitrate, it is desirable to separate the magnesium carbonate from the magnesium sulfate or magnesium nitrate from the perspective of looping and recycling the magnesium. However, if the exhaust gas contains only trace amounts of sulfur oxides and nitrogen oxides, it is not necessary to separate the magnesium sulfate or magnesium nitrate that is produced.

A method for separating magnesium carbonate from components other than magnesium carbonate, such as magnesium sulfate and magnesium nitrate, can be, for example, a method in which the solid-liquid ratio of the slurry is adjusted by utilizing the difference in solubility in water to dissolve the component in the water of the slurry, and then a solid-liquid separation means such as a filter press is combined. Such a separation method may involve applying a plurality of known separation methods for separation, or may involve using a plurality of separation devices for separation.
The components other than the separated magnesium carbonate are discharged as a solution to the outside of the system and removed.
The removed sulfates and nitrates other than magnesium carbonate can be separated into magnesium hydroxide, sulfuric acid, and nitric acid, for example, by electrodialysis using a bipolar membrane.

As shown in FIG. 2 , the step (a) preferably includes the following steps (a1) and (a2), and suitable examples of the steps (a1) and (a2) are as follows:
Step (a1) Step (a1) is a step of preparing a solution and/or slurry containing a carbonate of an alkali other than an alkaline earth metal from exhaust gas containing _CO2 .
Specifically, this is a process in which exhaust gas containing _CO2 is brought into contact with an alkaline solution other than an alkaline earth metal, and the _CO2 in the exhaust gas is absorbed by the alkaline solution to produce a solution and/or slurry containing an alkali carbonate.
The exhaust gas may be preheated to 60° C. or higher to increase the absorption efficiency in the alkaline solution. Hereinafter, the alkaline solution refers to an alkaline solution containing an alkali other than alkaline earth metals.

The alkaline solution for absorbing _CO2 in exhaust gas is not particularly limited as long as it is an alkaline solution that can absorb _CO2 , and any alkaline solution can be used. Examples of alkaline solutions include aqueous solutions containing hydroxides of alkali metals (potassium, sodium, etc.), aqueous solutions containing ammonia, and amines.

The concentration of the alkaline solution can be appropriately determined depending on the type of alkali contained, the _CO2 concentration in the exhaust gas, etc. For example, when the _CO2 concentration in the exhaust gas is 7 to 10 mass % and the alkaline solution is a sodium hydroxide solution, the concentration of the sodium hydroxide solution can be set to 1 to 20 mass %.

When the exhaust gas containing _CO2 comes into contact with the alkaline solution, a solution and/or slurry containing carbonate and/or hydrogencarbonate of the contained alkali (alkali metal, ammonia, amine, etc.) (hereinafter referred to as "slurries containing alkali metal carbonates") is produced. For example, when the alkaline solution is an alkali metal hydroxide, a slurry containing alkali metal carbonates is produced.

Furthermore, depending on the components contained in the exhaust gas other than _CO2 , contacting the exhaust gas with an alkaline solution may produce a solution and/or slurry containing alkali sulfates, alkali nitrates, etc. in addition to the alkali carbonates and/or hydrogen carbonates contained in the alkaline solution.
For example, when the alkaline solution is an aqueous solution containing an alkali metal hydroxide, in addition to the alkali metal carbonate and/or hydrogen carbonate, if sulfur oxide is contained in the exhaust gas, a solution and/or slurry containing an alkali metal sulfate, which is a reaction product between the alkali metal hydroxide and sulfur oxide, may be produced, or if nitrogen oxide is contained in the exhaust gas, a solution and/or slurry containing an alkali metal nitrate, which is a reaction product between the alkali metal hydroxide and nitrogen oxide.For example, when the alkali metal is sodium or potassium, in addition to sodium carbonate or potassium carbonate, a solution and/or slurry containing sodium sulfate or potassium sulfate, sodium nitrate or potassium nitrate is produced.

Among the components contained in the exhaust gas, those that are less reactive with the alkaline solution are preferably removed by emitting them outside the system during the process of contacting the exhaust gas with the alkaline solution.

Step (a2) Step (a2) is a step of reacting the slurry containing the alkali metal carbonates produced in step (a1) with magnesium hydroxide to produce magnesium carbonate, thereby preparing a slurry containing magnesium carbonate.
When the alkali carbonate is an alkali metal carbonate, a slurry containing magnesium carbonate is prepared by adding magnesium hydroxide to a slurry containing alkali metal carbonate and allowing the mixture to react.

When the slurry containing alkali metal carbonates produced in the above step (a1) also contains alkali sulfates or alkali nitrates, magnesium sulfate or magnesium nitrate is produced in the slurry by contact with magnesium hydroxide.
When the slurry containing magnesium carbonate prepared in step (a2) contains magnesium sulfate or magnesium nitrate, it is desirable to separate the magnesium carbonate from the magnesium sulfate or magnesium nitrate from the viewpoint of looping and circulating the magnesium. However, when the amount of sulfur oxides and nitrogen oxides contained in the exhaust gas is small, the produced magnesium sulfate or magnesium nitrate does not need to be separated.

As a method for separating magnesium carbonate from components other than magnesium carbonate, such as magnesium sulfate and magnesium nitrate, a separation method utilizing the difference in solubility in water can be used, as described above. Such a separation method may involve applying a plurality of known separation methods or may involve using a plurality of separation devices.
The components other than the separated magnesium carbonate are discharged as a solution to the outside of the system and removed.

The removed sulfates and nitrates, excluding magnesium carbonate, can be separated into magnesium hydroxide, sulfuric acid, and nitric acid, for example, by electrodialysis using a bipolar membrane.

Step (b) Step (b) in the system for transporting carbon dioxide from exhaust gas of the present invention is a step of solidifying the slurry containing magnesium carbonate obtained in step (a).
As described above, "solidification" refers to the process of blending a magnesium compound that dissolves and reprecipitates in water and/or a magnesium compound that undergoes a phase transition in water, such as magnesium oxide and/or magnesium oxychloride cement (MOC) and/or magnesium oxysulfate cement (MOS), with a magnesium-containing carbonate slurry, and solidifying the carbonate slurry containing the magnesium compound as a result of the blended magnesium compounds, such as magnesium oxide and/or magnesium oxychloride cement (MOC) and/or magnesium oxysulfate cement (MOS), exhibiting a solidifying function.

Specifically, the resulting slurry containing magnesium carbonate is mixed with a magnesium compound that dissolves and reprecipitates in water and/or a magnesium compound that undergoes a phase transition in water, such as magnesium oxide and/or magnesium oxychloride cement (MOC) and/or magnesium oxysulfate cement (MOS). The mixed magnesium compounds, such as magnesium oxide and/or magnesium _oxychloride cement (MOC) and/or magnesium oxysulfate cement (MOS), act as nuclei during phase transition to magnesium hydroxide, 5Mg(OH) ₂ + _MgCl2.8H2O , 5Mg(OH) ₂ + _{MgSO4.8H2O ,} etc., and can increase the strength of the resulting solidified body.

In this way, by blending magnesium oxide and/or magnesium oxychloride cement (MOC) and/or magnesium oxysulfate cement (MOS) or other magnesium compounds with a slurry containing magnesium carbonate and solidifying the magnesium carbonate, the strength of the solidified body produced can be increased. When transporting the solidified body, even during transport involving vibration, the shape of the solidified body can be maintained without shattering or scattering, making it easy to store and resulting in a solidified body that is easy to handle.

In solidification, the carbonate slurry containing the magnesium compound can be solidified by dissolving and reprecipitating the mixture at, for example, 60 to 90°C, preferably 70 to 80°C, and/or by causing a phase transition in water.
When a slurry is dried, if fine powder is present in the dried slurry, the fine powder may scatter during transportation. However, as in the present invention, even if the solidified product contains moisture or is left to evaporate, scattering of the fine powder can be suppressed.
As a heat source for solidification, a heat source from exhaust gas emitted from a factory or the like, or a heat source generated in step (g) described below, as necessary, can be suitably used, but is not limited to these heat sources.

Step (c) Step (c) in the system for transporting carbon dioxide from exhaust gas of the present invention is a step of transporting the solidified body containing magnesium carbonate obtained in step (b) from a first location to a second location.
Examples of transportation means include vehicles such as trucks, ships, trains such as electric trains and locomotives, and belt conveyors, but are not limited to these as long as they are capable of transporting the solidified body.

Furthermore, unlike conventional methods, the solidified body containing magnesium carbonate can be transported at room temperature and pressure. The first location may be a _CO2 capture location, and the second location may be a location where _CO2 from the solidified magnesium body is stored or utilized.

The first location may be any location within the same country as the second location, a vessel or other conveyance, or a different country from the second location. Conversely, the second location may be any location within the same country as the first location, a vessel or other conveyance, or a different country from the first location.
Furthermore, the first location may be a location, region, country, etc. that has more CO ₂ emissions than the second location, or may be a region, country, etc. that has less CO ₂ emissions.

Step (d) in the system for transporting carbon dioxide from exhaust gas of the present invention is a step of decomposing the solidified magnesium carbonate after transport to the second location via step (c) into magnesium oxide and _CO2 . As a method for such decomposition, for example, thermal decomposition can be used.
For example, by heating solidified magnesium carbonate to the decomposition temperature of the carbonate, for example, 700 to 1000°C, it can be decomposed into magnesium oxide and _CO2 .

Step (e) Step (e), which is a further preferably added step in the system for transporting carbon dioxide from flue gas of the present invention, is a step of injecting the _CO2 produced by the decomposition of magnesium carbonate in step (d) underground, for example, via a pipeline, for storage or utilization. Underground storage includes not only CCS and EOR, but also known underground storage, such as in an abandoned mine in a shallow layer less than 800 m underground. Any method used in known CCS, EOR, etc. can be applied as the method for injecting _CO2 underground.
Additionally, any known method for increasing the concentration of _CO2 produced by decomposition can be applied to increase the concentration of _CO2 stored underground.

Steps (p), (q), and (r) Step (p), which is a further step that is preferably added to the system for transporting carbon dioxide from exhaust gas of the present invention, is a step of reacting magnesium oxide produced by decomposition in step (d) with water to produce magnesium hydroxide.

In step (g) described below, magnesium hydroxide is generated at a first location, and the generated heat can be utilized in step (b) above. However, when the present invention is applied to a transportation means, for example, to capture and fix _CO2 emitted from a ship or the like during transportation, it is desirable to generate magnesium hydroxide by reacting magnesium oxide with water, as in step (p). This makes it possible to apply the present invention to a transportation means such as a ship.

Step (q) is a step of transporting the magnesium hydroxide obtained in step (p) to the first location. The magnesium hydroxide produced in step (p) can be transported from the second location to another location by, for example, a transport means, and it is preferable that the transport is from the second location to the first location.
As mentioned above, examples of the transportation means include vehicles such as trucks, ships, trains, locomotives, etc., but are not limited to these as long as they can transport magnesium hydroxide.
Furthermore, the magnesium hydroxide obtained in the step (p) can be transported to, for example, the first location at room temperature and atmospheric pressure.
Step (r) is a step of utilizing the magnesium hydroxide transported to the first location in step q as a raw material (magnesium hydroxide) for the slurry containing magnesium carbonate in step (a). All or part of the magnesium hydroxide obtained in step (r) can be used as the magnesium hydroxide in step (a).

When the present invention is applied to the capture and fixation of _CO2 emitted from a ship or the like during transportation within a means of transportation, it is desirable to generate magnesium hydroxide by reacting magnesium oxide with water in step (p) as described above, which makes it possible to apply the present invention within a means of transportation such as a ship.

Steps (f), (g), and (h): Instead of the steps (p) to (r) above, the following steps (f) to (h) can also be applied.
Step (f) is a step of transporting the magnesium oxide obtained in step (d) from the second location to the first location.
As mentioned above, examples of transportation means include vehicles such as trucks, ships, trains, locomotives, and belt conveyors, but are not limited to these as long as they can transport magnesium oxide, and the magnesium oxide can be transported at room temperature and normal pressure.
The magnesium oxide transported to the first location can also be used as a raw material for magnesium oxide, MOC, and MOS to be used in the subsequent step (g) or for solidification in the above step (b).

In step (g), the magnesium oxide transported to the first location in step (f) is reacted with water to produce magnesium hydroxide, similar to step (p) above. In step (h), the obtained magnesium hydroxide is recycled and reused as magnesium hydroxide for immobilizing _CO2 in step (a).

The reaction between magnesium oxide and water in step (g) is an exothermic reaction, and the generated heat can be used in the solidification step in step (b). There is no particular limitation on whether the generated heat is used in the step (b) or not.
Furthermore, before using the obtained magnesium hydroxide in step (a), it is desirable to separate unreacted magnesium oxide, water, etc., in order to increase the purity.

In this way, in the carbon dioxide transportation system from exhaust gas of the present invention, even if the first location where _CO2 is captured and the second location where _CO2 is stored or utilized are far apart, the solidified magnesium carbonate body that fixes carbon dioxide has good strength, which improves ease of storage.Furthermore, when transporting, the solidified body does not shatter or crumble, but retains its shape, and can be transported to the second location at room temperature and normal pressure by transportation means such as a ship or vehicle.Compared to the conventional method of transporting _CO2 in liquid form, no special equipment such as a storage tank or energy to maintain the specified temperature and pressure is required, which improves transportation stability and makes it possible to realize a carbon dioxide transportation system that is highly energy efficient.

The carbon dioxide transportation system of the present invention is an energy-efficient system that can reduce carbon dioxide emissions into the atmosphere, effectively fix _CO2 , and transport it energy-efficiently. Therefore, it can be efficiently injected and stored underground in deep underground saline layers such as CSS and EOR, depleted oil and gas fields, producing oil fields with reduced production efficiency, and abandoned mines in shallow layers. The _CO2 obtained by decomposition can also be used for known purposes, such as as an industrial raw material for plastic production, or in _CO2 batteries that store energy using _CO2 , making it suitable for use in coastal and inland factories that emit carbon dioxide.

Claims (8)

(a) obtaining a slurry containing magnesium carbonate from a _CO2 -containing flue gas;
(b) solidifying the carbonate-containing slurry;
(c) transporting the solidified magnesium carbonate from a first location to a second location; and
(d) A system for transporting carbon dioxide from flue gas, comprising a step of decomposing the solidified magnesium carbonate after transportation into magnesium oxide and _CO2 . The carbon dioxide transport system from exhaust gas described in claim 1, characterized in that in step (b), magnesium oxide and/or magnesium oxychloride cement (MOC) and/or magnesium oxysulfate cement (MOS) are mixed with the magnesium carbonate-containing slurry obtained in step (a) and solidified. The step (a) comprises:
(a1) obtaining a carbonate of an alkali other than an alkaline earth metal from a flue gas containing _CO2 ; and
3. The system for transporting carbon dioxide from exhaust gas according to claim 1 or 2, further comprising: (a2) a step of reacting the alkali carbonate obtained in step (a1) with magnesium hydroxide to obtain the magnesium carbonate. (p) after step (d), a step of reacting the magnesium oxide obtained in step (d) with water to obtain magnesium hydroxide;
(q) transporting the magnesium hydroxide obtained in step (p) to a first location; and
3. The system for transporting carbon dioxide from exhaust gas according to claim 1 or 2, further comprising a step (r) of recycling the magnesium hydroxide after transport as the magnesium hydroxide in step (a). (f) transporting the magnesium oxide obtained in step (d) to a first location;
(g) reacting the transported magnesium oxide with water to obtain magnesium hydroxide; and
3. The carbon dioxide transport system from exhaust gas according to claim 1 or 2, further comprising: (h) a step of recycling the magnesium hydroxide obtained in the step (g) as the magnesium hydroxide in the step (a). The carbon dioxide transport system from exhaust gas described in claim 5, characterized in that in step (g), the reaction heat generated when the magnesium oxide is reacted with water to obtain magnesium hydroxide is used for solidification in step (b). The carbon dioxide transport system from exhaust gas described in claim 1 or 2, characterized in that the exhaust gas is exhaust gas generated from a transportation means during transportation. The carbon dioxide transport system from flue gas according to claim 1 or 2, further comprising: (e) a step of injecting the CO ₂ obtained by the decomposition in the step (d) into the ground.