JP2024106903A - Desulfurization method and desulfurization system circulating and using carbon dioxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a desulfurization method which can reduce a discharge amount of carbon dioxide.

SOLUTION: A desulfurization method using calcium carbonate as a desulfurization agent uses exhaust gas-derived calcium carbonate (X) produced using carbon dioxide in desulfurized exhaust gas (C) discharged from a facility adopting the desulfurization method as a material, as at least a part of a desulfurization agent. The exhaust gas-derived calcium carbonate (X) brings a calcium ion-containing aqueous solution (B) into contact with carbon dioxide-derived carbonate ions in the exhaust gas (C), in the presence of one or more amine compounds (A) selected from the group consisting of amine synthesized in a living body, artificially synthesized amine and a polymer containing a group derived from the amines, and a production method includes a step (S) of suppressing a pH increase of the calcium ion-containing aqueous solution (B) caused by the amine compound (A) using the exhaust gas (C).

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2024,JPO&INPIT

Description

This disclosure relates to a desulfurization method and a desulfurization system.

As a method for suppressing the generation of sulfur oxides (hereinafter also referred to as "SOx"), which are a cause of air pollution, various desulfurization methods, such as a dry method and a wet method, have been proposed in which SOx is removed from combustion exhaust gas using a desulfurizing agent.
For example, Patent Document 1 discloses a technique relating to a dry furnace desulfurization method in which coal is used as fuel and limestone is used as a desulfurization agent and is burned in a combustion device.
Furthermore, Patent Document 2 discloses a technique relating to a wet lime-gypsum process in which the combustion exhaust gas is brought into contact with a water slurry of limestone powder to absorb SOx in the combustion exhaust gas, and the SOx is converted into gypsum and recovered.

Japanese Patent Application Publication No. 07-174471 Japanese Patent Application Publication No. 04-243520

Among greenhouse gases that are said to be the cause of global warming, carbon dioxide has a particularly large impact, and preventing an increase in the concentration of carbon dioxide in the atmosphere could be one means of suppressing global warming.
Therefore, from the perspective of curbing global warming, it is desirable to develop a new method for reducing carbon dioxide emissions from the above-mentioned desulfurization methods.

This disclosure was made in response to such demand, and aims to provide a desulfurization method and desulfurization system that can reduce carbon dioxide emissions.

According to the present disclosure, the following [1] to [4] are provided.
[1] A desulfurization method using calcium carbonate as a desulfurization agent, comprising the steps of:
As at least a part of the desulfurization agent, flue-gas-derived calcium carbonate (X) produced as a raw material for carbon dioxide in desulfurized flue gas (C) discharged from a facility employing the desulfurization method is used,
The exhaust gas-derived calcium carbonate (X) is
A desulfurization method comprising contacting a calcium ion-containing aqueous solution (B) with carbonate ions derived from carbon dioxide in the exhaust gas (C) in the presence of one or more amine compounds (A) selected from the group consisting of amines synthesized in living organisms, artificially synthesized amines, and polymers containing groups derived from these amines, the method including a step (S) of suppressing a pH increase in the calcium ion-containing aqueous solution (B) caused by the amine compound (A) by utilizing the exhaust gas (C).
[2] A desulfurization system for carrying out a desulfurization method using calcium carbonate as a desulfurization agent,
a production system for producing flue-gas-derived calcium carbonate (X) produced using carbon dioxide in a desulfurized flue gas (C) discharged from a facility employing the desulfurization method as a raw material; and a supply device for supplying the flue-gas-derived calcium carbonate (X) produced by the production system as at least a part of the desulfurization agent used in the facility,
The manufacturing system includes:
a first contacting portion (P1-1) for contacting the exhaust gas (C) with an amine aqueous solution (A1) containing one or more amine compounds (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers containing groups derived from these amines, to prepare an amine aqueous solution (A2) containing carbonate ions derived from carbon dioxide in the exhaust gas (C);
a second contact section (P1-2) for contacting the aqueous amine solution (A2) with a calcium ion-containing aqueous solution (B) to precipitate the exhaust gas-derived calcium carbonate (X); and a recovery section (Q) for recovering the exhaust gas-derived calcium carbonate (X).
A desulfurization system comprising:
[3] A desulfurization system for carrying out a desulfurization method using calcium carbonate as a desulfurization agent,
a production system for producing flue-gas-derived calcium carbonate (X) produced using carbon dioxide in flue gas (C) discharged from a facility employing the desulfurization method as a raw material; and a supply device for supplying the flue-gas-derived calcium carbonate (X) produced by the production system as at least a part of the desulfurization agent used in the facility,
The manufacturing system includes:
a contacting section (P2) for simultaneously contacting one or more amine compounds (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers containing groups derived from these amines with a calcium ion-containing aqueous solution (B) and the exhaust gas (C) to precipitate the exhaust gas-derived calcium carbonate (X); and a recovery section (Q) for recovering the exhaust gas-derived calcium carbonate (X).
A desulfurization system comprising:
[4] A desulfurization system for carrying out a desulfurization method using calcium carbonate as a desulfurization agent,
a production system for producing flue-gas-derived calcium carbonate (X) produced using carbon dioxide in a desulfurized flue gas (C) discharged from a facility employing the desulfurization method as a raw material; and a supply device for supplying the flue-gas-derived calcium carbonate (X) produced by the production system as at least a part of the desulfurization agent used in the facility,
The manufacturing system includes:
a first contact portion (P3-1) for preparing a mixed solution (AB) of one or more amine compounds (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers containing groups derived from these amines, and a calcium ion-containing aqueous solution (B);
a second contact section (P3-2) for contacting the mixed liquid (AB) with the flue gas (C) to precipitate the flue gas-derived calcium carbonate (X); and a recovery section (Q) for recovering the flue gas-derived calcium carbonate (X).
A desulfurization system comprising:

This disclosure makes it possible to provide a desulfurization method and desulfurization system that can reduce carbon dioxide emissions.

FIG. 1 is a schematic diagram showing an example of an embodiment of a desulfurization system according to the present embodiment. FIG. 2 is a schematic diagram showing an example of an embodiment in which a dry furnace desulfurization method is applied to the desulfurization system of the present embodiment. FIG. 1 is a schematic diagram showing an example of an embodiment in which a wet lime-gypsum method is applied to the desulfurization system of the present embodiment. FIG. 2 is a process schematic diagram showing an example of the production method of the first embodiment incorporated in the desulfurization method of the present embodiment. FIG. 2 is a process schematic diagram showing an example of a preferred mode of the production method of the first embodiment incorporated in the desulfurization method of the present embodiment. 1 is a schematic diagram showing an example of a production system of a first embodiment incorporated in a desulfurization system of the present embodiment. FIG. FIG. 2 is a schematic diagram showing an example of a preferred embodiment of the production system of the first embodiment incorporated in the desulfurization system of the present embodiment. FIG. 2 is a schematic diagram showing another example of a preferred embodiment of the production system of the first embodiment incorporated in the desulfurization system of the present embodiment. FIG. 2 is a schematic diagram showing an example of a further preferred aspect of the production system of the first embodiment incorporated in the desulfurization system of the present embodiment. FIG. 2 is a process schematic diagram showing an example of a production method according to a second embodiment incorporated in the desulfurization method according to the present embodiment. FIG. 2 is a process schematic diagram showing an example of a preferred mode of the production method of the second embodiment incorporated in the desulfurization method of the present embodiment. FIG. 2 is a schematic diagram showing an example of a production system according to a second embodiment incorporated in the desulfurization system of the present embodiment. FIG. 2 is a schematic diagram showing an example of a preferred embodiment of a production system according to a second embodiment incorporated in the desulfurization system of the present embodiment. FIG. 4 is a process schematic diagram showing an example of a production method according to a third embodiment incorporated in the desulfurization method of the present embodiment. FIG. 2 is a process schematic diagram showing an example of a preferred mode of the production method of the third embodiment incorporated in the desulfurization method of the present embodiment. FIG. 4 is a schematic diagram showing an example of a production system of a third embodiment incorporated in the desulfurization system of the present embodiment. FIG. 4 is a schematic diagram showing an example of a preferred embodiment of a production system according to a third embodiment incorporated in the desulfurization system of the present embodiment. FIG. 2 is a graph showing the change in liquid pH over time when exhaust gas-derived calcium carbonate (X) was produced in the examples. FIG. 1 is a graph showing the change over time in the CO ₂ concentration in the liquid when flue gas-derived calcium carbonate (X) was produced in an example.

The upper and lower limit values of the numerical ranges described in this specification can be combined in any manner. For example, when numerical ranges "A to B" and "C to D" are described, the numerical ranges "A to D" and "C to B" are also included in the scope of the present disclosure.
In addition, unless otherwise specified, a numerical range of "lower limit value to upper limit value" described in this specification means not less than the lower limit value and not more than the upper limit value.
Furthermore, the terms "amine" and "polyamine" used herein mean, unless otherwise specified, amines selected from amines synthesized in vivo and amines synthesized artificially.

[Desulfurization method and desulfurization system according to the present embodiment]
The desulfurization method of the present embodiment is a desulfurization method that utilizes calcium carbonate as a desulfurization agent, and utilizes, as at least a part of the desulfurization agent, flue-gas-derived calcium carbonate (X) produced using carbon dioxide contained in desulfurized flue gas (C) discharged from a facility that employs the desulfurization method as a raw material.
The exhaust gas-derived calcium carbonate (X) is produced by a production method which comprises contacting a calcium ion-containing aqueous solution (B) with carbonate ions derived from carbon dioxide in the exhaust gas (C) in the presence of one or more amine compounds (A) selected from the group consisting of amines synthesized in living organisms, artificially synthesized amines, and polymers containing groups derived from these amines, and which includes a step (S) of suppressing a pH increase in the calcium ion-containing aqueous solution (B) caused by the amine compound (A) by utilizing the exhaust gas (C).

Moreover, an example of a desulfurization system according to this embodiment is shown in FIG.
The desulfurization system Z1 shown in FIG. 1 is a desulfurization system for carrying out a desulfurization method using calcium carbonate as a desulfurization agent, and includes a production system 1 that produces flue-gas-derived calcium carbonate (X) using carbon dioxide in flue gas (C) discharged from a facility Z11 that employs the desulfurization method as a raw material, and a supply device Z21 that supplies the flue-gas-derived calcium carbonate (X) produced by the production system 1 as at least a part of the desulfurization agent used in the facility Z11.

That is, in the desulfurization method and desulfurization system of the present embodiment, a manufacturing method or system for manufacturing flue-gas-derived calcium carbonate (X) is added to a facility employing a conventional desulfurization method that uses calcium carbonate as a desulfurization agent. By using the flue-gas-derived calcium carbonate (X) as at least a part of the desulfurization agent, the carbon dioxide in the flue gas (C) is recycled and the amount of carbon dioxide emission is reduced.
Representative examples of facilities that employ a conventional desulfurization method that utilizes calcium carbonate as a desulfurization agent include facilities that burn fossil fuels, such as thermal power plants, but are not limited thereto. Examples of such facilities include paper manufacturing plants, cement manufacturing plants, oil refineries, and waste incinerators.

The exhaust gas-derived calcium carbonate (X) may be used as at least a part of the desulfurization agent, and is preferably 1 mass% or more, more preferably 5 mass% or more, and even more preferably 10 mass% to 100 mass% of the total amount of the desulfurization agent used in the desulfurization method and desulfurization system. From the viewpoint of further reducing carbon dioxide emissions, it is preferable to increase the replacement amount of the exhaust gas-derived calcium carbonate (X) in the desulfurization agent used in the desulfurization method and desulfurization system.

<Desulfurization method using calcium carbonate as a desulfurization agent>
The desulfurization method using calcium carbonate as a desulfurization agent is not particularly limited, but examples thereof include a dry furnace desulfurization method and a wet lime-gypsum method.

(Dry furnace desulfurization method)
In the dry furnace desulfurization method, sulfur-containing fuel such as coal and limestone (calcium carbonate) as a desulfurizing agent are supplied to a combustion furnace and combusted. As a result, SOx generated by the combustion of the sulfur-containing fuel reacts with the desulfurizing agent, and exhaust gas (C) with a reduced sulfur concentration is discharged. The exhaust gas (C) contains carbon dioxide. In this embodiment, the carbon dioxide is used to generate exhaust-gas-derived calcium carbonate (X). As a result, the carbon dioxide in the exhaust gas (C) is recycled and reused, reducing the amount of carbon dioxide emissions.

An example of an embodiment of a desulfurization system of the present embodiment using a dry furnace desulfurization method is shown in Fig. 2. The desulfurization system Z1a shown in Fig. 2 includes a combustion device Z11a, a production system 1 that produces exhaust-gas-derived calcium carbonate (X) using carbon dioxide contained in an exhaust gas (C) discharged from the combustion device Z11a as a raw material, and a supply device Z21 that supplies the exhaust-gas-derived calcium carbonate (X) produced by the production system 1 as at least a part of a desulfurization agent used in the combustion device Z11a.
The combustion device Z11a is not particularly limited, and any combustion device (e.g., a fluidized bed boiler, etc.) that is generally used in the dry furnace desulfurization method can be appropriately used.
Although not shown, the downstream of the combustion apparatus Z11a may be provided with one or more devices selected from a denitration device, a dust collection device, a heat exchanger, etc., and the exhaust gas (C) discharged from the combustion apparatus Z11a may be subjected to one or more processes selected from a denitration process, a dust collection process, and a heat exchange process (cooling process).

(Wet lime-gypsum method)
In the wet lime-gypsum process, the flue gas discharged from a combustion device that burns sulfur-containing fuels such as coal is brought into contact with a water slurry of limestone powder to absorb the SOx in the flue gas, which is then converted into gypsum and recovered. As a result, the SOx generated by the combustion of the sulfur-containing fuel reacts with the desulfurizing agent, and exhaust gas (C) with a reduced sulfur concentration is discharged. The exhaust gas (C) contains carbon dioxide. In this embodiment, the carbon dioxide is used to generate calcium carbonate (X) derived from exhaust gas. This allows the carbon dioxide in the exhaust gas (C) to be recycled and reduces the amount of carbon dioxide emissions. There are.

An example of an embodiment of the desulfurization system of the present embodiment using a wet lime-gypsum method is shown in Fig. 3. The desulfurization system Z1b shown in Fig. 3 includes a combustion device Z11b, a desulfurization device Z12b equipped with a limestone (calcium carbonate) water slurry that absorbs SOx by contacting with the combustion exhaust gas discharged from the combustion device Z11b, a production system 1 that produces exhaust-gas-derived calcium carbonate (X) using carbon dioxide contained in the exhaust gas (C) discharged from the desulfurization device Z12b as a raw material, and a supply device Z21 that supplies the exhaust-gas-derived calcium carbonate (X) produced by the production system 1 as at least a part of the desulfurization agent used in the desulfurization device Z12b.
The combustion device Z11b and the desulfurization device Z12b are not particularly limited, and any combustion device and desulfurization device generally used in the wet lime-gypsum method can be appropriately used.
Although not shown in the figure, the downstream of the combustion device Z11b may be provided with one or more devices selected from a denitration device, a dust collection device, a heat exchanger, etc., and the exhaust gas (C) discharged from the combustion device Z11b may be subjected to one or more processes selected from a denitration process, a dust collection process, and a heat exchange process (cooling process).
The rear stage of the combustion apparatus Z11b means the rear stage of the combustion apparatus Z11b, but the front or rear stage of the desulfurization apparatus Z12b, or the desulfurization apparatus Z12b itself.

(Preferred embodiment of desulfurization method)
The desulfurization method that can be used in this embodiment is not limited to the above-mentioned examples, and various desulfurization methods that utilize calcium carbonate can be appropriately used.
Here, in this embodiment, from the viewpoint of further reducing the amount of carbon dioxide emissions, it is preferable to employ a dry furnace desulfurization method.

[Manufacturing method and manufacturing system]
Hereinafter, first to third embodiments will be described in detail as specific examples of a manufacturing method and a manufacturing system incorporated in a desulfurization method and a desulfurization system that utilize calcium carbonate as a desulfurization agent.
In the following description, the production systems 1a, 1a', 1a'', 11a, 1b, 11b, 1c, and 11c correspond to the production system 1 of the desulfurization system shown in FIGS.

[Manufacturing method of the first embodiment]
An example of the manufacturing method of the first embodiment is shown in FIG.
The production method shown in FIG. 4 includes a step (S) (hereinafter sometimes abbreviated as "step (S)") of suppressing an increase in pH of a calcium ion-containing aqueous solution (B) caused by an amine compound (A) by utilizing exhaust gas (C), and includes a first contact step (S1-1) of contacting an amine aqueous solution (A1) containing one or more amine compounds (A) selected from the group consisting of amines synthesized in a living body, artificially synthesized amines, and polymers containing a group derived from these amines with exhaust gas (C) to prepare an amine aqueous solution (A2) containing carbonate ions derived from carbon dioxide in the exhaust gas (C).
The production method shown in FIG. 4 further includes, as step (S), a second contact step (S1-2) of contacting an aqueous amine solution (A2) with an aqueous calcium ion-containing solution (B) after the step (S1-1).
Furthermore, the production method shown in FIG. 4 further includes a recovery step (T) of recovering the exhaust gas-derived calcium carbonate (X) after the step (S).

FIG. 5 shows an example of a preferred embodiment of the manufacturing method according to the first embodiment.
The production method shown in FIG. 5 further includes, in addition to the step (S) and the recovery step (T), an amine compound recovery/supply step (U) of recovering an amine compound (A) from the liquid phase after precipitation of the exhaust-gas-derived calcium carbonate (X) and supplying the amine compound (A) as at least a part of the amine compound (A) used in the step (S).

Next, an example of a manufacturing system for carrying out the manufacturing method of the first embodiment is shown in FIG.
The production system 1a shown in FIG. 6 includes at least a first contact section (P1-1), a second contact section (P1-2), and a recovery section (Q).
In the first contacting section (P1-1), an aqueous amine solution (A1) containing one or more amine compounds (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers containing groups derived from these amines is contacted with exhaust gas (C) to prepare an aqueous amine solution (A2) containing carbonate ions derived from carbon dioxide in the exhaust gas (C).
In the second contact section (P1-2), the aqueous amine solution (A2) is brought into contact with the aqueous calcium ion-containing solution (B) to precipitate calcium carbonate (X) derived from the exhaust gas.
In the recovery section (Q), calcium carbonate (X) derived from the exhaust gas is recovered.
Exhaust gas (C) is supplied from a facility Z11. In addition, exhaust gas-derived calcium carbonate (X) is supplied to the facility Z11 by a supply means Z21. As a result, carbon dioxide discharged from the facility Z11 is recycled within the system, and the amount of carbon dioxide emission is reduced.

FIG. 7 shows an example of a preferred embodiment of a manufacturing system for carrying out the manufacturing method of the first embodiment.
The manufacturing system 1a′ shown in Fig. 7 includes a plurality of first contact parts. In Fig. 7, two first contact parts are included (reference symbols (P1-1) and (P1-1)′), but the number of first contact parts may be three or more.
The manufacturing system 1a′ shown in Fig. 7 includes a plurality of second contact parts. In Fig. 7, two second contact parts are included (reference symbols (P1-2), (P1-2)′), but the number of second contact parts may be three or more.
The manufacturing system in the first embodiment is not limited to a configuration in which both the first contact portion and the second contact portion are provided in multiple numbers, and may be a configuration in which the first contact portion is provided in multiple numbers and only one second contact portion is provided, or may be a configuration in which the second contact portion is provided in multiple numbers and only one first contact portion is provided.

Furthermore, another example of a preferred embodiment of a manufacturing system for carrying out the manufacturing method of the first embodiment is shown in FIG.
The production system 1a'' shown in FIG. 8 does not include a second contact portion (P1-2), and the amine aqueous solution (A2) is brought into contact with the calcium ion-containing aqueous solution (B) in the first contact portion (P1-1).
Although not shown, the manufacturing system 1a'' shown in FIG. 8 may also be provided with a plurality of first contact portions.

FIG. 9 shows an example of a more preferable embodiment of the manufacturing system of this embodiment for carrying out the manufacturing method of the first embodiment.
The production system 11a shown in FIG. 9 further includes, in addition to the first contact part (P1-1), the second contact part (P1-2), and the recovery part (Q), an amine compound recovery/supply part (R) that recovers an amine compound (A) from the liquid phase after precipitation of the exhaust gas-derived calcium carbonate (X) and supplies the amine compound (A) as at least a part of the amine compound (A) used in the first contact part (P1-1).
It should be noted that the production system 11a shown in FIG. 9 further includes an amine compound recovery and supply unit (R) in addition to the production system 1a shown in FIG. 6, but is not necessarily limited to this embodiment.
For example, the production system 1a' shown in Fig. 7 may further include an amine compound recovery/supply unit (R). Also, the production system 1a'' shown in Fig. 8 may further include an amine compound recovery/supply unit (R).

The manufacturing method of the first embodiment will be described in detail below, along with the configuration of the manufacturing system for carrying out the method.

<First contact step (S1-1)>
In the first contact step (S1-1), an amine aqueous solution (A1) containing one or more amine compounds (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers containing groups derived from these amines is contacted with exhaust gas (C) to prepare an amine aqueous solution (A2) containing carbonate ions derived from carbon dioxide in the exhaust gas (C). By contacting the amine aqueous solution (A1) containing one or more amine compounds (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers containing groups derived from these amines with exhaust gas (C), carbon dioxide in the exhaust gas (C) is efficiently absorbed into the amine aqueous solution (A1), and an amine aqueous solution (A2) containing carbonate ions derived from carbon dioxide in the exhaust gas (C) is efficiently prepared. The carbon dioxide-derived carbonate ions contained in the amine aqueous solution (A2) function as a carbonate ion source for precipitating exhaust gas-derived calcium carbonate (X) in the second contact step (S1-2).

The following provides a detailed explanation of the aqueous amine solution (A1), the exhaust gas (C), and the method for contacting the aqueous amine solution (A1) with the exhaust gas (C).

(Amine aqueous solution (A1))
The aqueous amine solution (A1) contains one or more amine compounds selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers containing groups derived from these amines.

The present inventors have been studying marine bacteria that form calcium carbonate granules as part of a study to elucidate calcium carbonate formation in marine organisms. When this marine bacterium is cultured in an artificial medium containing calcium, it forms calcium carbonate (calcite) in a dumbbell or spherical shape outside the bacterial cell. In the course of studying this mechanism, the present inventors have determined that amines produced by the marine bacteria play a major role.
In other words, it was found that the dumbbell- and spherical-shaped calcium carbonate granules seen in marine bacterial cultures promote the crystallization of calcium carbonate by increasing the concentration of carbonate ions in the medium due to the increase in amines in the medium as the marine bacteria grow.
The amines in the culture medium of the marine bacteria in which calcium carbonate granule formation was observed were fluorescently derivatized with dansyl chloride and analyzed by HPLC in accordance with the "Analysis of non-volatile putrefactive amines in foods" in the Food Sanitation Inspection Guidelines. As a result, amines such as 1,3-propanediamine, putrescine, kataberin, spermine, spermidine, norspermidine, and norspermine were detected.
From the above, it was found that the amines produced by marine bacteria bind with carbon dioxide in the air and are then hydrolyzed, increasing the carbonate ion concentration in the culture medium and causing calcium carbonate to precipitate. Note that calcium carbonate precipitation was also confirmed when the amines and calcium chloride were mixed in an aqueous solution in the absence of marine bacteria and allowed to stand. This shows that calcium carbonate precipitation occurs even in the absence of marine bacteria. In other words, it was found that the amines produced by marine bacteria can efficiently generate carbonate ions by forming salts with carbon dioxide, even in the absence of marine bacteria.

However, as a result of further intensive research by the present inventors, it was found that when amines such as polyamines are mixed with seawater, calcium carbonate cannot be produced sufficiently efficiently. It was presumed that the reason for this is that when amines are added to seawater, the pH of the seawater temporarily rises, and magnesium ions, which are present in seawater in three times the amount of calcium ions, become magnesium hydroxide, which inhibits the production of calcium carbonate.

In the manufacturing method of the first embodiment, in the first contact step (S1-1), an amine aqueous solution (A1) containing one or more amine compounds (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers containing groups derived from these amines is contacted with the exhaust gas (C). As a result, carbonate ions for precipitating the exhaust gas-derived calcium carbonate (X) in the second contact step (S1-2) are efficiently generated in the amine aqueous solution (A2). Moreover, since carbonate ions for precipitating the exhaust gas-derived calcium carbonate (X) are efficiently generated in the amine aqueous solution (A2), an increase in the pH of the amine aqueous solution (A2) is also suppressed. Therefore, when the amine aqueous solution (A2) is contacted with the calcium ion-containing aqueous solution (B), an increase in the pH of the calcium ion-containing aqueous solution (B) (pH of the mixture of the amine aqueous solution (A2) and the calcium ion-containing aqueous solution (B)) is also suppressed. Therefore, even if the calcium ion-containing aqueous solution (B) contains magnesium ions, inhibition of calcium carbonate production caused by the production of magnesium hydroxide is also suppressed. Therefore, calcium carbonate is produced extremely efficiently in the second contact step (S1-2).

As the amine compound (A), amines (monoamines and polyamines) synthesized in a living organism (for example, in the living organism of a marine bacterium) can be used without any particular limitation. Among these amines, from the viewpoint of facilitating an increase in carbonate ions in the amine aqueous solution (A2), it is preferable to use one or more polyamines selected from the group consisting of 1,3-propanediamine, putrescine (butane-1,4-diamine), cataverin (pentane-1,4-diamine), spermine (1,11-diamino-4,9-diazaundecane), spermidine (1,8-diamino-4-azaoctane), norspermidine (3,3'-iminobis(propan-1-amine)), and norspermine (3,3'-[(propane-1,3-diyl)bisimino]bis(propan-1-amine)).
In addition, according to the experiments of the present inventors, it has been confirmed that even when an artificially synthesized amine is used as the amine compound (A), the same effect as that of an amine synthesized in vivo can be achieved. Therefore, an artificially synthesized amine can also be used. Examples of the artificially synthesized amine include monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), diisopropanolamine (DIPA), diglycolamine (DGA), methyldiethanolamine (MDEA), and diamines such as piperazine and ethylenediamine.
As the amine compound (A), a polymer containing a group derived from the above-mentioned amine (a polymer containing a group derived from an amine synthesized in a living body, or a polymer containing a group derived from an artificially synthesized amine) may be used.
The polymer containing the group derived from the amine is preferably a polymer containing the group derived from the amine at least at the end. Examples of such a polymer include a polymer having a structural unit derived from a compound having the group derived from the amine and an ethylenically unsaturated double bond, polyalkyleneimine, etc., and preferably polyalkyleneimine.
The alkylene group of the polyalkyleneimine preferably has 2 to 4 carbon atoms, more preferably 2 to 3 carbon atoms, and even more preferably 2 carbon atoms.
The term "group derived from the above amine" refers to a monovalent or higher group obtained by removing at least one hydrogen atom from the above amine (amine synthesized in vivo or artificially synthesized amine). For example, an example of a group derived from ethylenediamine is the monovalent group -NHCH ₂ CH ₂ NH ₂ .
The number average molecular weight of the polymer containing the above amine-derived group, as measured by the boiling point elevation method, is preferably 500 to 50,000, more preferably 500 to 40,000, and even more preferably 500 to 35,000.
The amine compound (A) may be used alone or in combination of two or more kinds.
In addition, it is preferable to use an amine synthesized in a living body as the amine compound (A). By using an amine synthesized in a living body, it is possible to reduce carbon dioxide emitted by synthesizing and transporting the amine, etc. Therefore, it is possible to more effectively reduce the amount of carbon dioxide emitted.

It is presumed that when an aqueous amine solution (A1) containing one or more amine compounds (A) selected from the group consisting of amines synthesized in living organisms, artificially synthesized amines, and polymers containing groups derived from these amines is contacted with exhaust gas (C) and carbon dioxide is absorbed into the aqueous amine solution (A1), the carbon dioxide reacts with the amine compound (A) in the aqueous amine solution (A1) to generate carbonate ions in the aqueous amine solution (A1), and the amine compound (A) becomes a cation.
The reaction scheme assumed when the amine compound (A) is putrescine is shown below.

The content of the amine compound (A) in the amine aqueous solution (A1) is preferably 1% by mass to 50% by mass, more preferably 10% by mass to 40% by mass, and even more preferably 25% by mass to 35% by mass, based on the total amount of the amine aqueous solution (A1), from the viewpoint of facilitating efficient absorption of carbon dioxide in the amine aqueous solution (A1).

The pH of the aqueous amine solution (A1) before contacting with the exhaust gas (C) is determined taking into consideration the amount of carbon dioxide to be absorbed and the reactivity in the second contact step (S1-2). Specifically, the pH of the aqueous amine solution (A1) before contacting with the exhaust gas (C) is adjusted so that the pH of the aqueous amine solution (A2) containing carbonate ions derived from carbon dioxide after contacting with the exhaust gas (C) is preferably 6 or more, more preferably 7 or more, and even more preferably 8 or more.
In addition, the pH of the amine aqueous solution (A1) before contacting with the exhaust gas (C) may be adjusted depending on the type of carbonate to be precipitated in the second contact step (S1-2). For example, from the viewpoint of facilitating precipitation of calcium carbonate, the pH of the amine aqueous solution (A1) before contacting with the exhaust gas (C) may be adjusted so that the pH of the amine aqueous solution (A2) containing carbonate ions derived from carbon dioxide after contacting with the exhaust gas (C) is preferably 7 to 12, more preferably 7 to 9. In addition, from the viewpoint of facilitating precipitation of calcium carbonate, the pH of the amine aqueous solution (A1) before contacting with the exhaust gas (C) may be adjusted so that the pH of a mixture of the amine aqueous solution (A2) containing carbonate ions derived from carbon dioxide and the calcium ion-containing aqueous solution (B) when they are contacted in the second contact step (S1-2) is preferably 8 to 9.

The temperature of the aqueous amine solution (A1) when it is brought into contact with the exhaust gas (C) is preferably 10°C or higher, more preferably 30°C to 50°C, from the viewpoint of efficiently absorbing carbon dioxide and facilitating an increase in the carbonate ion concentration in the aqueous amine solution (A2). In this process, in order to prevent the loss of bonds between the amine and carbon dioxide, it is preferable to maintain the temperature of the aqueous amine solution (A1) at 50°C or lower when it is brought into contact with the exhaust gas (C).

The time for contacting the aqueous amine solution (A1) with the exhaust gas (C) is appropriately set depending on the contact method, the temperature of the aqueous amine solution (A1), the content of the amine compound (A) in the aqueous amine solution (A1), the temperature of the exhaust gas (C), the carbon dioxide concentration, the gas flow rate of carbon dioxide, the size of the container (reaction tank), etc. It is generally 30 minutes to 3 hours, and preferably 1 hour to 24 hours.

(Exhaust gas (C))
The flue gas (C) is desulfurized flue gas discharged from a facility that uses calcium carbonate as a desulfurizing agent. Since the flue gas contains carbon dioxide, it can be used as a raw material for producing flue gas-derived calcium carbonate (X).
From the viewpoint of improving the production efficiency of the exhaust gas-derived calcium carbonate (X) and facilitating further reduction in carbon dioxide emission, the exhaust gas (C) is preferably an exhaust gas having a high carbon dioxide concentration. Specifically, the exhaust gas (C) is preferably an exhaust gas discharged from a desulfurization system that uses coal as a sulfur-containing fuel.

(Method for contacting aqueous amine solution (A1) with exhaust gas (C))
The method for contacting the aqueous amine solution (A1) with the exhaust gas (C) is not particularly limited as long as the method can efficiently absorb carbon dioxide into the aqueous amine solution (A1).

Here, an example of a method for contacting the aqueous amine solution (A1) with the exhaust gas (C) will be described based on the production system in the first embodiment.
In the production systems 1a, 1a', 1a'', and 11a of the first embodiment, the first contacting step (S1-1) is carried out in a first contacting section (P1-1) in which an aqueous amine solution (A1) containing one or more amine compounds (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers containing groups derived from these amines is contacted with exhaust gas (C) to prepare an aqueous amine solution (A2) containing carbonate ions derived from carbon dioxide in the exhaust gas (C).
An aqueous amine solution (A1) containing one or more amine compounds (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers containing groups derived from these amines is contained in a storage tank 21 and supplied to the first contact part (P1-1) via a supply line 21a.
On the other hand, exhaust gas (C) is supplied from the facility Z11 and is supplied to the first contact portion (P1-1) by, for example, a blower 22 via a supply line 22a.
Furthermore, the exhaust gas (C) may be subjected to one or more treatments selected from a denitrification treatment, a dust collection treatment, and a heat exchange treatment (cooling treatment) as necessary.

Examples of a method for contacting the aqueous amine solution (A1) with the exhaust gas (C) in the first contact part (P1-1) include the following methods (1) to (4), but are not limited thereto. Various methods for dissolving a gas in a liquid may be used.
(1) An aqueous amine solution (A1) is placed in a reaction tank and stirred with a stirring blade or the like while spraying an exhaust gas (C) near the liquid surface of the aqueous amine solution (A1).
(2) An aqueous amine solution (A1) is placed in a reaction tank, and exhaust gas (C) is directly blown into the aqueous amine solution (A1).
(3) An exhaust gas (C) is introduced from the bottom of a sealed reaction tower and allowed to rise, while an aqueous amine solution (A1) is sprayed from the top of the reaction tower using a nozzle or the like, thereby bringing the exhaust gas (C) and the aqueous amine solution (A1) into countercurrent contact with each other.
(4) The exhaust gas (C) is converted into fine bubbles and introduced into the aqueous amine solution (A1), thereby increasing the contact area between the aqueous amine solution (A1) and the exhaust gas (C), and allowing carbon dioxide to be more efficiently absorbed into the aqueous amine solution (A1).
The contact between the aqueous amine solution (A1) and the exhaust gas (C) in the first contact portion (P1-1) is preferably carried out at 50° C. or less and under normal pressure, more preferably at normal temperature (25±15° C.) and under normal pressure.

The aqueous amine solution (A2) rich in carbonate ions derived from carbon dioxide, prepared in the first contact step (S1-1), is supplied to the second contact step (S1-2).
Since the amine aqueous solution (A2) is rich in carbonate ions derived from carbon dioxide, the flue-gas-derived calcium carbonate (X) is more likely to precipitate in the second contact step (S1-2). Furthermore, since the amine aqueous solution (A2) is rich in carbonate ions derived from carbon dioxide, a rapid increase in pH of the mixture of the amine aqueous solution (A2) and the calcium ion-containing aqueous solution (B) is suppressed when the amine aqueous solution (A2) and the calcium ion-containing aqueous solution (B) are brought into contact with each other in the second contact step (S1-2). Therefore, the flue-gas-derived calcium carbonate (X) can be more likely to precipitate immediately when the amine aqueous solution (A2) and the calcium ion-containing aqueous solution (B) are brought into contact with each other in the second contact step (S1-2). In other words, carbon dioxide can be efficiently fixed.
In addition, since the amine aqueous solution (A2) contains a large amount of carbonate ions derived from carbon dioxide, it is possible to precipitate the exhaust-gas-derived calcium carbonate (X) even if the calcium ion-containing aqueous solution (B) has a low calcium ion concentration. For example, even when a calcium ion-containing aqueous solution (B) having a calcium ion concentration of 300 ppm by mass (or even 400 ppm by mass) is used, it is possible to precipitate the exhaust-gas-derived calcium carbonate (X).

<Second Contact Step (S1-2)>
In the second contact step (S1-2), the aqueous amine solution (A2) prepared in the first contact step (S1-1) is contacted with a calcium ion-containing aqueous solution (B) to precipitate exhaust gas-derived calcium carbonate (X).
By contacting the aqueous amine solution (A2) prepared in the first contact step (S1-1) with the calcium ion-containing aqueous solution (B), carbonate ions in the aqueous amine solution (A2) react with calcium ions in the aqueous calcium ion-containing solution (B), and exhaust-gas-derived calcium carbonate (X) precipitates. Since the carbonate ions in the aqueous amine solution (A2) are generated using carbon dioxide in the exhaust gas (C) as a raw material, the carbon dioxide is fixed as the exhaust-gas-derived calcium carbonate (X).

The calcium ion-containing aqueous solution (B) used in the second contact step (S1-2) and the method for contacting the amine aqueous solution (A2) with the calcium ion-containing aqueous solution (B) are described in detail below.

(Calcium ion-containing aqueous solution (B))
The calcium ion-containing aqueous solution (B) is used as a calcium source for the exhaust gas-derived calcium carbonate (X).
Here, the calcium ion-containing aqueous solution (B) may contain magnesium ions.
In the first embodiment, in the first contact step (S1-1), an amine aqueous solution (A1) containing one or more amine compounds (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers containing groups derived from these amines is contacted with the exhaust gas (C). This suppresses an increase in pH of the amine aqueous solution (A2) containing carbonate ions derived from carbon dioxide in the exhaust gas (C), and therefore suppresses an increase in pH of the mixture of the amine aqueous solution (A) and the calcium ion-containing aqueous solution (B) when the amine aqueous solution (A2) is contacted with the calcium ion-containing aqueous solution (B). Therefore, even if the calcium ion-containing aqueous solution (B) contains magnesium ions, inhibition of calcium carbonate production caused by the production of magnesium hydroxide is also suppressed. Therefore, in the second contact step (S1-2), calcium carbonate derived from the exhaust gas (X) is produced extremely efficiently.

Therefore, seawater can be used as the calcium ion-containing aqueous solution (B). Although seawater is easy to obtain, it contains more magnesium ions than calcium ions as well as calcium ions. Therefore, as described above, there is a problem of calcium carbonate production inhibition. However, according to the manufacturing method of the first embodiment, even when seawater is used as the calcium ion-containing aqueous solution (B), the inhibition of calcium carbonate production caused by the production of magnesium hydroxide is suppressed, so that exhaust gas-derived calcium carbonate (X) is produced extremely efficiently even when seawater, which is easily available, is used as the calcium ion-containing aqueous solution (B). Moreover, when seawater is used, carbon dioxide emitted can be reduced by synthesizing or transporting a calcium source material. Therefore, carbon dioxide emissions can be reduced more effectively.

In addition, as the calcium ion-containing aqueous solution (B), other than seawater, for example, waste seawater obtained when seawater is desalinized, concentrated seawater generated when magnesium hydroxide, salt, or bittern is produced from seawater, salt lake brine, underground brine, and brackish water can be used.
The brine is water containing salts such as sodium chloride, and usually contains one or more alkaline earth metal ions (particularly calcium ions) selected from the group consisting of calcium ions, magnesium ions, strontium ions, and barium ions. Therefore, by using the brine as the calcium ion-containing aqueous solution (B), it is possible to easily supply calcium ions for producing the flue-gas-derived calcium carbonate (X).
Here, since the waste seawater and the concentrated seawater contain calcium ions at high concentrations, calcium ions that are the source of the exhaust gas-derived calcium carbonate (X) can be efficiently supplied in the second contact step (S1-2). Therefore, the production efficiency of the exhaust gas-derived calcium carbonate (X) can be further improved, and the yield of the exhaust gas-derived calcium carbonate (X) can be improved. This allows for a further reduction in carbon dioxide emissions. In addition, the second contact section (P1-2) in which the second contact step (S1-2) is performed can be made compact to reduce the size of the production system. In addition, salt lake brines such as those typified by the Uyuni Salt Lake and warm water brines such as those typified by the Salton Lake in the United States are also preferred because they have a high calcium ion concentration. In recent years, the development of geothermal power generation as a renewable energy source has been actively carried out. These underground warm water brines are also preferred.
Therefore, the calcium ion-containing aqueous solution (B) to be used has a calcium ion concentration of preferably 400 ppm by mass or more, more preferably 600 ppm by mass or more, even more preferably 800 ppm by mass or more, still more preferably 1,000 ppm by mass or more, even more preferably 1,500 ppm by mass or more, and even more preferably 1,800 ppm by mass or more.
The calcium ion-containing aqueous solution (B) exemplified above may be used alone or in combination of two or more.

Concentrated seawater can be produced using seawater as a raw material by known methods such as the ion exchange membrane method, evaporation method, and reverse osmosis method.

In addition, as the calcium ion-containing aqueous solution (B), calcium ion-containing water having a magnesium ion concentration of 500 ppm by mass or less (preferably 400 ppm by mass or less, more preferably 300 ppm by mass or less) may be used.
For example, in an industrial process for producing magnesium hydroxide from seawater, calcium ion-containing water having a magnesium ion concentration of 500 mass ppm or less is generated as a by-product. In the first embodiment, it is possible to effectively utilize such a by-product.
In addition, in an industrial magnesium hydroxide production process from seawater, by adding milk of lime to seawater, calcium ion-containing water having a magnesium ion concentration of 500 mass ppm or less is generated as a by-product after extracting the generated magnesium hydroxide slurry. By adding milk of lime to seawater, the calcium ion concentration of the by-product calcium ion-containing water is increased compared to seawater (for example, preferably 400 mass ppm or more, more preferably 600 mass ppm or more, even more preferably 800 mass ppm or more, even more preferably 1,000 mass ppm or more, even more preferably 1,500 mass ppm or more, and even more preferably 1,800 mass% ppm or more). Therefore, in order to recover all the calcium ions from the by-product calcium ion-containing water, it is necessary to increase the amine compound concentration of the amine aqueous solution (A1). When the concentration of the amine compound (A) in the amine aqueous solution (A1) is increased, the pH of the amine aqueous solution (A1) increases, making it difficult for the reaction of generating calcium carbonate (X) derived from exhaust gas to proceed. However, in the first embodiment, by bringing the exhaust gas (C) into contact with the aqueous amine solution (A1), even if calcium ion-containing water having a calcium ion concentration higher than that of seawater is used as the calcium ion-containing aqueous solution (B), an increase in pH can be suppressed and exhaust gas-derived calcium carbonate (X) can be efficiently produced.

(Method of contacting an aqueous amine solution (A2) with an aqueous calcium ion-containing solution (B))
The method for bringing the aqueous amine solution (A2) into contact with the calcium ion-containing aqueous solution (B) is not particularly limited as long as the method can efficiently produce exhaust gas-derived calcium carbonate (X).

Here, an example of a method for contacting the aqueous amine solution (A2) with the calcium ion-containing aqueous solution (B) will be described based on the production system in the first embodiment.
In the production systems 1a, 1a′, and 11a in the first embodiment, the second contact step (S1-2) is carried out in a second contact part (P1-2) in which the aqueous amine solution (A2) is brought into contact with the calcium ion-containing aqueous solution (B) to precipitate exhaust gas-derived calcium carbonate (X).
The aqueous amine solution (A2) is supplied from the first contact portion (P1-1) to the second contact portion (P1-2) via a supply line 2a.
On the other hand, the calcium ion-containing aqueous solution (B) is stored in a storage tank 31 and is supplied to the second contact part (P1-2) via a supply line 31a.

Examples of the method for contacting the aqueous amine solution (A2) with the aqueous calcium ion-containing solution (B) in the second contact portion (P1-2) include the following methods (5) and (6).
(5) The aqueous amine solution (A2) and the aqueous calcium ion-containing solution (B) are introduced into a reaction vessel, and are mixed by stirring using a stirring blade or the like.
(6) The aqueous amine solution (A2) and the aqueous calcium ion-containing solution (B) are introduced into a line mixer or the like, and mixed by turbulent stirring or the like without stirring using an impeller or the like.
In the method (5), it is preferable to use a thickener sedimentation device as the reaction tank, which can separate the flue-gas-derived calcium carbonate (X), which is precipitated and dispersed in the liquid phase, from the liquid phase by sedimenting it under the action of gravity. In this case, the second contact section (P1-2) can also function as a recovery section (Q) described later.
The temperature of each solution during contact between the aqueous amine solution (A2) and the aqueous calcium ion-containing solution (B) in the second contact portion (P1-2) is 10°C to 45°C, preferably 25°C to 40°C.
In addition, the ratio of the amount of the amine aqueous solution (A2) supplied to the second contact portion (P1-2) to the amount of the calcium ion-containing aqueous solution (B) supplied is appropriately adjusted so that the molar amount of carbon dioxide (carbonate ions) in the amine aqueous solution (A2) is approximately equivalent to the molar amount of calcium ions.
The precipitation of the exhaust-gas-derived calcium carbonate (X) occurs in a short time. In addition, the use of the polyamine can prevent the pH from becoming high, which has the advantage of making it easier to precipitate the exhaust-gas-derived calcium carbonate (X) while suppressing the precipitation of magnesium hydroxide.

<Preferable aspects of the first contact step (S1-1) and the second contact step (S1-2)>
The first contact step (S1-1) is preferably carried out at a plurality of first contact portions as shown in FIG.
Moreover, the second contact step (S1-2) is also preferably carried out at a plurality of second contact portions as shown in FIG.
Specifically, in the first unit (first contact part (P1-1)), an amine aqueous solution (A1) is produced, and the exhaust gas (C) is brought into contact with the aqueous amine solution (A2) to prepare an aqueous amine solution (A2) containing carbonate ions derived from carbon dioxide in the exhaust gas (C). Then, by preparing an already prepared aqueous amine solution (A2) in the second unit (first contact part (P1-1)'), while the aqueous amine solution (A2) is being prepared in the first unit, the aqueous amine solution (A2) can be supplied from the second unit to the second contact part to carry out the second contact step (S1-2).
Similarly, in the second contact section, the amine aqueous solution (A2) is brought into contact with the calcium ion-containing aqueous solution (B) in the first contact section (second contact section (P1-2)) to precipitate the exhaust-gas-derived calcium carbonate (X). Meanwhile, the amine aqueous solution (A2) can be received in the second contact section (second contact section (P1-2)'). Alternatively, the exhaust-gas-derived calcium carbonate (X) can be discharged to a recovery section.

Also, as shown in FIG. 8, it is possible to carry out the first contact step (S1-1) and the second contact step (S1-2) in the first contact section (P1-1) without providing a second contact section (P1-2). In this case, too, by providing multiple first contact sections (P1-1), it becomes possible to continuously supply the exhaust gas-derived calcium carbonate (X) to the recovery section (Q).

Whether the first contact section (P1-1) and the second contact section (P1-2) are multiple or single, or whether the first contact step (S1-1) and the second contact step (S1-2) are carried out in the first contact section, can be selected according to conditions and requirements such as the desired amount of carbon dioxide fixed.

In addition, the entire process can be made continuous by using an alternating current contact method with a sealed reaction tower in the first contact section (P1-1) and a continuous stirred tank reactor or line mixer in the second contact section (P1-2).

<Recovery process (T)>
In the recovery step (T), the exhaust-gas-derived calcium carbonate (X) produced in the second contact step (S1-2) is recovered.
The exhaust gas-derived calcium carbonate (X) precipitates and can be separated and recovered by one or more solid-liquid separation treatments selected from filtration, centrifugation, and the like.
The exhaust-gas-derived calcium carbonate (X) is recovered in a recovery section (Q). In the production systems 1a, 1a', 1a'', and 11a shown in Figs. 6 to 9, the recovery section (Q) is, for example, a sub-tank, and the liquid phase containing the exhaust-gas-derived calcium carbonate (X) obtained in the second contact step (S1-2) is transferred to the sub-tank or the like, and solid-liquid separation treatment is performed in the sub-tank, and the exhaust-gas-derived calcium carbonate (X) is recovered.
As described above, when a thickener sedimentation apparatus is used as a reaction tank in the second contact section (P1-2), the second contact section (P1-2) can also function as a recovery section (Q).

The recovered exhaust gas-derived calcium carbonate (X) may be washed with water, if necessary, and then dried before being supplied to facility Z11.

<Amine compound recovery and supply step (U)>
In the amine compound recovery step (U), the amine compound (A) is recovered from the liquid phase remaining after precipitation of the exhaust gas-derived calcium carbonate (X) and supplied as at least a part of the amine compound (A) in the aqueous amine solution (A1) used in the first contact step (S1-1).
The amine recovery/supply step (U) enables the amine compound (A) to be repeatedly reused in the production method and immobilization system, thereby reducing the costs, etc., associated with the amine compound (A).
In addition, recycling the amine compound (A) also has the effect of reducing the amount of carbon dioxide emission generated during procurement of raw materials for synthesis of the amine compound (A) and during synthesis, etc.

The method for recovering amine compound (A) and the method for supplying the recovered amine compound (A) carried out in the amine compound recovery/supply step (U) are described in detail below.

(Method for recovering amine compound)
The recovery of the amine compound (A) from the liquid phase after the flue gas-derived calcium carbonate (X) has precipitated can be carried out, for example, by a method using an adsorbent, which will be described below. The method described here is equivalent to the principle and method of ion exchange chromatography. The recovery of the amine compound (A) can be carried out by any known method, and is not limited to a method using an adsorbent. Specifically, an electrodialysis method, a dialysis membrane method, or an ultrafiltration method can be used.

- Adsorbent -
As the adsorbent, a solid adsorbent capable of recovering the amine compound (A) by contacting the liquid phase after precipitation of the exhaust gas-derived calcium carbonate (X) is used.
As the solid adsorbent, for example, one having a substituent represented by -SO ₃ M (M represents a hydrogen atom or an alkali metal) is used.
The alkali metals that may be selected for M are lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), or francium (Fr).
From the viewpoints of water solubility and operability, M is preferably an Na or hydrogen atom.
The solid adsorbent may be used alone or in combination of two or more solid adsorbents having different M's.

The solid adsorbent exerts a recovery function of the amine compound (A) by bonding the above-mentioned substituent to the carrier. The carrier is not particularly limited as long as the above-mentioned substituent can be bonded thereto, and examples thereof include silica gel, alumina, glass, kaolin, mica, talc, clay, hydrated alumina, wollastonite, iron powder, potassium titanate, titanium oxide, zinc oxide, silicon carbide, silicon nitride, calcium carbonate, carbon, barium sulfate, boron, ferrite, cellulose, and activated carbon.
The carrier may be used alone or in combination of two or more kinds.

The shape of the solid adsorbent is not particularly limited, and may be, for example, a powder, granule, or sheet. It may also be a cartridge, column, or funnel filled with powder or particles of the solid adsorbent.

- Contact between liquid phase and solid adsorbent -
The liquid phase after the flue gas-derived calcium carbonate (X) is precipitated is brought into contact with a solid adsorbent, whereby the amine compound (A) is recovered in the solid adsorbent. In this case, the pH of the liquid phase is preferably 1 to 7. The temperature of the liquid phase is not particularly limited, but is preferably 20° C. to 40° C.

The method for contacting the liquid phase after the flue gas-derived calcium carbonate (X) has precipitated with the solid adsorbent is not particularly limited, but from the standpoint of ease of handling, etc., it is preferable to use a cartridge, column, or funnel filled with powder or particles of the solid adsorbent and pass the liquid phase through it.

-Elution of amine compound (A)-
The amine compound (A) recovered in the solid adsorbent can be recovered by being eluted in an eluate by contacting the solid adsorbent with the eluate.
The eluent may be an aqueous solution containing a basic compound (including an aqueous solution to which an organic solvent has been added or partly substituted).
The basic compound may be any compound that does not substantially undergo a chemical reaction with the amine compound (A) to be recovered and is soluble or miscible in water. Preferred basic compounds include, for example, ammonia, sodium hydroxide, ammonium hydroxide, triethylamine, pyridine, histidine, diazabicycloundecene, and mixtures thereof.

From the viewpoint of improving the elution efficiency of the amine compound (A), the concentration of the basic compound is preferably 0.5% by mass to 10% by mass, based on 100% by mass of the total of the basic compound and the organic solvent.

As the organic solvent, a general organic solvent capable of dissolving the amine compound (A) and the basic compound to be recovered can be used, but from the viewpoint of operability, etc., an organic solvent having a low viscosity and a low boiling point is preferred, and furthermore, one that can be mixed uniformly with water is preferred. Examples of the organic solvent include lower alcohols having 1 to 3 carbon atoms, such as methanol, ethanol, and 2-propanol; acetone; acetonitrile, etc.
Although a small amount of an organic solvent may be added or mixed in order to adjust the aqueous solution containing the basic compound, it is preferable that the aqueous solution containing the basic compound does not contain an organic solvent.

The temperature of the eluent when dissolving the amine compound (A) into the eluent is not particularly limited, but is generally 20 to 40°C.

The method for eluting the amine compound (A) recovered in the solid adsorbent is not particularly limited. From the viewpoint of ease of handling, etc., when a cartridge, column, or funnel filled with powder or particles of a solid adsorbent is used, a method may be mentioned in which a liquid phase after precipitation of the exhaust gas-derived calcium carbonate (X) is passed through the cartridge, column, or funnel to recover the amine, and then the eluate is passed through the solid adsorbent in which the amine compound (A) has been recovered, to elute and recover the amine compound (A) in the eluate.
Therefore, the amine compound recovery means constituting the amine compound recovery/supply section (R) may be, for example, a configuration including a cartridge, column, or funnel filled with solid adsorbent powder or particles for circulating the liquid phase supplied from supply line 51a to recover amine compound (A), and a supply line (not shown) for circulating the eluate through the cartridge, column, or funnel.

(Method of Supplying Amine Compound (A))
The amine compound (A) recovered in the eluate is supplied to the storage tank 21 via the supply line 51b. In this way, in the production method and immobilization system of the first embodiment, the amine compound (A) is circulated within the system.
The amine compound (A) recovered in the eluate may be supplied to the storage tank 21 together with the eluate, or at least a portion of the eluate may be separated to concentrate the amine compound (A) and then supplied to the storage tank 21.

In the above-mentioned amine compound recovering/supplying step (U), an example in which amine compound (A) is recovered using a solid adsorbent has been described. However, the recovery of amine compound (A) is not limited to this method, and may be performed using, for example, an ion exchange membrane electrolysis device, a reverse osmosis membrane device, an electrodialysis device, a diffusion dialysis device, a device equipped with an ion exchange resin, or the like.
Therefore, the production system of the first embodiment may include an ion exchange membrane electrolysis device, a reverse osmosis membrane device, an electrodialysis device, a diffusion dialysis device, or a device equipped with an ion exchange resin as the amine compound recovery/supply section (R) for carrying out the amine compound recovery/supply step (U). In addition, when a polymer containing a group derived from a biogenic amine is used as the amine compound (A), the amine compound may be recovered using an ultrafiltration membrane (UF membrane).

[Manufacturing method of the second embodiment]
An example of the manufacturing method according to the second embodiment is shown in FIG.
The production method shown in FIG. 10 includes, as step (S), a contacting step (S2) of simultaneously contacting one or more amine compounds (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers containing groups derived from these amines with a calcium ion-containing aqueous solution (B) and exhaust gas (C).
Furthermore, the production method shown in FIG. 10 includes a recovery step (T) of recovering the exhaust gas-derived calcium carbonate (X) after the step (S).
Exhaust gas (C) is supplied from a facility Z11. In addition, exhaust gas-derived calcium carbonate (X) is supplied to the facility Z11 by a supply means Z21. As a result, carbon dioxide discharged from the facility Z11 is recycled within the system, and the amount of carbon dioxide emission is reduced.

In the manufacturing method of the second embodiment, in the contact step (S2), the amine compound (A), the calcium ion-containing aqueous solution (B), and the exhaust gas (C) are contacted simultaneously. Therefore, exhaust gas-derived calcium carbonate (X) can be efficiently produced while suppressing the increase in pH of the calcium ion-containing aqueous solution (B) caused by the amine compound (A) by carbonate ions derived from carbon dioxide in the exhaust gas (C) produced in the calcium ion-containing aqueous solution (B).

In addition, in the manufacturing method of the second embodiment, as shown in FIG. 11, it is preferable to further include an amine compound recovery/supply step (U) in which amine compound (A) is recovered from the liquid phase after the exhaust gas-derived calcium carbonate (X) has precipitated, and supplied as at least a part of the amine compound (A) used in step (S).

Next, an example of a manufacturing system for carrying out the manufacturing method of the second embodiment is shown in FIG.
A production system 1b shown in FIG. 12 includes at least a contact section (P2) and a recovery section (Q).
In the contacting section (P2), one or more amine compounds (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers containing groups derived from these amines, a calcium ion-containing aqueous solution (B), and an exhaust gas (C) are simultaneously contacted with each other to precipitate exhaust-gas-derived calcium carbonate (X).
In the recovery section (Q), calcium carbonate (X) derived from the exhaust gas is recovered.

In the production system 1b shown in FIG. 12, the amine compound (A) is stored as an aqueous amine solution (A1) in a storage tank 21, and the aqueous amine solution (A1) is supplied to the contact part (P2) via a supply line 21a.
The calcium ion-containing aqueous solution (B) is stored in a storage tank 31 and supplied to the contact part (P2) via a supply line 31a.
Exhaust gas (C) is supplied from the facility Z11 and is supplied to the contact section (P2) via a supply line 22a, for example, by a blower 22.
The amine compound (A) in the aqueous amine solution (A1), the calcium ion-containing aqueous solution (B), and the exhaust gas (C) are simultaneously contacted at the contact portion (P2) to produce exhaust-gas-derived calcium carbonate (X).
The amine compound (A) is not limited to being supplied to the contact portion (P2) as the aqueous amine solution (A1), and may be directly supplied to the contact portion (P2).

Although not shown, a manufacturing system for implementing the manufacturing method of the second embodiment may be provided with multiple contact portions (P2).

FIG. 13 shows an example of a preferred embodiment of a manufacturing system of this embodiment for carrying out the manufacturing method of the second embodiment.
The production system 11b shown in FIG. 13 further includes, in addition to the contact section (P2) and the recovery section Q, an amine compound recovery/supply section (R) that recovers the amine compound (A) from the liquid phase after the precipitation of the exhaust gas-derived calcium carbonate (X) and supplies it as at least a part of the amine compound (A) to be used in the contact section (P2).

In the second embodiment, the aspects and configurations common to the first embodiment are also similar to the first embodiment in terms of the preferred aspects and configurations, and therefore the description thereof will be omitted.
For example, the amine compound (A), the amine aqueous solution (A1), the calcium ion-containing aqueous solution (B), and the exhaust gas (C) used in the second embodiment are the same as those in the first embodiment, and preferred aspects and the like are also the same as those in the first embodiment.
In addition, the recovery step (T), the amine compound recovery/supply step (U), the recovery section (Q), and the amine compound recovery/supply section (R) are also the same as those in the first embodiment, and preferred embodiments and the like are also the same as those in the first embodiment.

[Manufacturing method of the third embodiment]
An example of a manufacturing method according to the third embodiment is shown in FIG.
The production method shown in FIG. 14 includes, as steps (S), a first contact step (S3-1) of contacting one or more amine compounds (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers containing groups derived from these amines with a calcium ion-containing aqueous solution (B) to prepare a mixed solution (AB) of the amine compound (A) and the calcium ion-containing aqueous solution (B), and a second contact step (S3-2) of contacting the mixed solution (AB) with exhaust gas (C) after the first contact step (S3-1).
Furthermore, the production method shown in FIG. 14 includes a recovery step (T) of recovering the exhaust gas-derived calcium carbonate (X) after the step (S).
Exhaust gas (C) is supplied from a facility Z11. In addition, exhaust gas-derived calcium carbonate (X) is supplied to the facility Z11 by a supply means Z21. As a result, carbon dioxide discharged from the facility Z11 is recycled within the system, and the amount of carbon dioxide emission is reduced.

By bringing the exhaust gas (C) into contact with a mixed liquid (AB) of the amine compound (A) and the calcium ion-containing aqueous solution (B), it is also possible to efficiently produce the exhaust gas-derived calcium carbonate (X) while suppressing an increase in pH of the calcium ion-containing aqueous solution (B) caused by the amine compound (A).
However, from the viewpoint of more easily suppressing an increase in pH and more efficiently producing the exhaust gas-derived calcium carbonate (X), it is preferable to contact the mixed liquid (AB) with the exhaust gas (C) as soon as possible after the preparation of the mixed liquid (AB).

In addition, in the manufacturing method of the third embodiment, as shown in FIG. 15, it is preferable to further include an amine compound recovery/supply step (U) in which an amine compound (A) is recovered from the liquid phase after the flue gas-derived calcium carbonate (X) has precipitated, and supplied as at least a portion of the amine compound (A) used in the first contact step (S3-1).

Next, an example of a manufacturing system for carrying out the manufacturing method according to the third embodiment is shown in FIG.
A production system 1c shown in FIG. 16 includes at least a first contact section (P3-1), a second contact section (P3-2), and a recovery section (Q).
In the first contact portion (P3-1), a mixed solution (AB) of one or more amine compounds (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers containing groups derived from these amines, and a calcium ion-containing aqueous solution (B) is prepared.
In the second contact section (P3-2), the mixed liquid (AB) is brought into contact with the exhaust gas (C) to precipitate calcium carbonate (X) derived from the exhaust gas.
In the recovery section (Q), calcium carbonate (X) derived from the exhaust gas is recovered.

In the production system 1c shown in FIG. 16, the amine compound (A) is stored as an aqueous amine solution (A1) in a storage tank 21, and the aqueous amine solution (A1) is supplied to the first contact part (P3-1) via a supply line 21a.
The calcium ion-containing aqueous solution (B) is stored in a storage tank 31 and is supplied to the first contact part (P3-1) via a supply line 31a.
The amine compound (A) in the aqueous amine solution (A1) and the calcium ion-containing aqueous solution (B) are contacted and mixed at the first contact portion (P3-1) to prepare a mixed solution (AB).
The mixed liquid (AB) is supplied to a second contact section (P3-2) via a supply line 2a. The mixed liquid (AB) in the second contact section (P3-2) comes into contact with an exhaust gas (C) that is supplied from a facility Z11 and is supplied to the second contact section (P3-2) via a supply line 22a by, for example, a blower 22, to generate an exhaust gas-derived calcium carbonate (X).
The amine compound (A) is not limited to the embodiment in which it is supplied to the first contact portion (P3-1) as the aqueous amine solution (A1), and may be directly supplied to the first contact portion (P3-1).

Although not shown, in a manufacturing system for carrying out the manufacturing method of the second embodiment, the number of the first contact portion (P3-1) may be one or more, and the number of the second contact portion (P3-2) may be one or more.
16 does not include the second contact section (P3-2), and the mixed liquid (AB) and the exhaust gas (C) are preferably brought into contact with each other in the first contact section (P3-1). By adopting such a configuration, after the mixed liquid (AB) is prepared in the first contact section (P3-1), the mixed liquid (AB) is easily brought into contact with the exhaust gas (C) quickly, and the production efficiency of the exhaust gas-derived calcium carbonate (X) is easily improved.

FIG. 17 shows an example of a preferred embodiment of a manufacturing system of this embodiment for carrying out the manufacturing method of the third embodiment.
A production system 11c shown in FIG. 17 includes, in addition to the first contact part (P3-1), the second contact part (P3-2), and the recovery part (Q), an amine compound recovery/supply part (R) that recovers an amine compound (A) from the liquid phase after precipitation of the exhaust gas-derived calcium carbonate (X) and supplies the amine compound (A) as at least a part of the amine compound (A) used in the first contact part (P3-1).

In the third embodiment, aspects and configurations common to the first embodiment, including preferred aspects and configurations, are the same as those in the first embodiment, and therefore description thereof will be omitted.
For example, the amine compound (A), the amine aqueous solution (A1), the calcium ion-containing aqueous solution (B), and the exhaust gas (C) used in the third embodiment are the same as those in the first embodiment, and preferred aspects and the like are also the same as those in the first embodiment.
In addition, the recovery step (T), the amine compound recovery/supply step (U), the recovery section (Q), and the amine compound recovery/supply section (R) are also the same as those in the first embodiment, and preferred embodiments and the like are also the same as those in the first embodiment.

In the manufacturing method of the first embodiment, the manufacturing method of the second embodiment, and the manufacturing method of the third embodiment described above, the calcium ion-containing aqueous solution (B) is contacted with carbonate ions derived from carbon dioxide in the exhaust gas (C) in the presence of the amine compound (A). However, when the magnesium ion concentration of the calcium ion-containing aqueous solution (B) is low compared to the calcium ion concentration and calcium ions are the main constituent, the magnesium ions are unlikely to inhibit calcium carbonate precipitation. In such a case, a base other than the amine compound (A), such as sodium hydroxide, may be used instead of the amine compound (A).

[Production of exhaust gas-derived calcium carbonate (X)]
<Bases Used>
"Base 1": an aqueous amine solution (A2) containing carbonate ions derived from carbon dioxide, obtained by using putrescine (1,4-butanediamine) as the amine compound (A) and introducing carbon dioxide into an aqueous amine solution (A1) in which the putrescine concentration was adjusted to 10 mass%.
Carbon dioxide was introduced into 0.4 L of the amine aqueous solution (A1) via an air stone at a rate of 11 to 3 L/min, with an average of 1.3 L/min (both calculated under standard conditions), for 5 hours to obtain an amine aqueous solution containing _carbonate ions (A2). The results are shown in Figure 18 (changes in pH over time) and Figure 19 (changes in the amount of _CO2 gas absorbed into the amine aqueous solution over time).
The _CO2 concentration in the liquid was measured using a portable carbon dioxide concentration meter CGP-31 manufactured by DKK Toa Corporation.
The pH in the solution was measured using a pH meter TPX-999 manufactured by Toko Chemical Laboratory Co., Ltd.

<Production of calcium carbonate>
Next, 0.2 L of base 1 (amine aqueous solution (A2)) was added to 2 L of demagnesium seawater.
The demagnesium-free seawater was produced by adding milk of lime to seawater (natural seawater) and then removing the resulting magnesium hydroxide slurry. The magnesium concentration of the demagnesium-free seawater was 500 ppm by mass or less.
Next, the precipitated calcium carbonate was filtered using a PTFE membrane filter having a pore size of 0.1 μm and dried in a dryer to obtain 20 g of exhaust gas-derived calcium carbonate (X).

<Use as limestone for desulfurization using the lime-gypsum process>
A mixture of 90 g of commercially available limestone (purchased from Taiheiyo Cement Corporation) and 10 g of calcium carbonate (X) derived from exhaust gas was added as a desulfurization agent to the above-mentioned coal boiler owned by Idemitsu Kosan Co., Ltd. There was no effect on desulfurization at all.

[Estimated carbon dioxide reductions]
The carbon dioxide reduction amount was estimated for the desulfurization system Z1a (see FIG. 2) at the facility Z11 that adopted the dry furnace desulfurization method.
Assume that the amount of coal fed into the furnace per day is 600 tons (600 tons/day).
Also, it is assumed that the amount of calcium carbonate (X) derived from the exhaust gas fed into the furnace per day is 35 tons (35 tons/day).
The amount of calcium carbonate (X) derived from the exhaust gas relative to the coal charged into the furnace (ratio to coal) was assumed to be 6%, which is typical in the dry furnace desulfurization method.
The carbon dioxide content in the calcium carbonate in the exhaust gas (C) is 44 mass %. The molar mass of calcium carbonate is 100 g/mol, and the molar mass of carbon dioxide is 44 g/mol.
Therefore, the amount of carbon dioxide captured and circulated can be estimated as 35 tons/day x 0.44, which is 15.4 tons/day. When this value is annualized (365 days/year), it is estimated to be 5,621 tons/year.
Therefore, it was found that the desulfurization system of this embodiment has excellent efficiency in reducing carbon dioxide emissions.

Z1 Desulfurization system Z11 (incorporating a production system) Facility Z21 employing a desulfurization method using calcium carbonate Supply device 1 (for exhaust gas-derived calcium carbonate (X)) Production systems 1a, 1a', 1a'', 11a Production systems 1b, 11b (in the first embodiment) Production systems 1c, 11c (in the second embodiment) Production systems (P1-1), (P1-1)' (in the third embodiment) First contact section (P2) (in the first embodiment) Contact section (P3-1) (in the second embodiment) First contact section 2a (in the third embodiment) Supply line 21 (from the first contact section to the second contact section) Storage tank 21a (for the aqueous amine solution (A1)) Supply line 22 (for the aqueous amine solution (A1)) Blower 22a Supply line (P1-2), (P1-2)' (for the exhaust gas (C)) Second contact section (P3-2) (in the first embodiment) Second contact section 31 (in the third embodiment) Storage tank 31a (for the calcium ion-containing aqueous solution (B)) Supply line (Q) (for the calcium ion-containing aqueous solution (B)) Recovery section (R) Amine compound recovery/supply section 51a Supply line 51b (from the recovery section to the amine compound recovery/supply section) Supply line (from the amine compound recovery/supply section to the storage tank for the aqueous amine solution (A1))

Claims (17)

A desulfurization method using calcium carbonate as a desulfurization agent, comprising the steps of: using, as at least a part of the desulfurization agent, flue-gas-derived calcium carbonate (X) produced from carbon dioxide contained in desulfurized flue gas (C) discharged from a facility employing the desulfurization method;
The exhaust gas-derived calcium carbonate (X) is
A desulfurization method comprising contacting a calcium ion-containing aqueous solution (B) with carbonate ions derived from carbon dioxide in the exhaust gas (C) in the presence of one or more amine compounds (A) selected from the group consisting of amines synthesized in living organisms, artificially synthesized amines, and polymers containing groups derived from these amines, the method including a step (S) of suppressing a pH increase in the calcium ion-containing aqueous solution (B) caused by the amine compound (A) by utilizing the exhaust gas (C). The step (S)
a first contact step (S1-1) of contacting an aqueous amine solution (A1) containing the amine compound (A) with the exhaust gas (C) to prepare an aqueous amine solution (A2) containing carbonate ions derived from carbon dioxide in the exhaust gas (C);
The desulfurization method of claim 1 , comprising: The step (S)
After the first contact step (S1-1),
A second contact step (S1-2) of contacting the aqueous amine solution (A2) with the aqueous calcium ion-containing solution (B).
The desulfurization method of claim 2, comprising: The step (S)
a contacting step (S2) in which the amine compound (A), the calcium ion-containing aqueous solution (B), and the exhaust gas (C) are simultaneously contacted with each other;
The desulfurization method of claim 1 , comprising: The step (S)
a first contact step (S3-1) of contacting the amine compound (A) with the calcium ion-containing aqueous solution (B) to prepare a mixed solution (AB) of the amine compound (A) and the calcium ion-containing aqueous solution (B); and a second contact step (S3-2) of contacting the mixed solution (AB) with the exhaust gas (C) after the first contact step (S3-1).
The desulfurization method of claim 1 , comprising: The desulfurization method according to any one of claims 1 to 5, wherein the amine synthesized in the living body is one or more selected from the group of biogenic amines consisting of 1,3-propanediamine, putrescine, cadaverine, spermidine, spermine, norspermidine, and norspermine. The desulfurization method according to any one of claims 1 to 6, wherein the artificially synthesized amine is one or more selected from the group consisting of monoethanolamine, diethanolamine, triethanolamine, diisopropanolamine, diglycolamine, methyldiethanolamine, piperazine, and ethylenediamine. The desulfurization method according to any one of claims 1 to 6, wherein the amine compound (A) is an amine synthesized in the living body. The desulfurization method according to any one of claims 1 to 8, wherein the calcium ion-containing aqueous solution (B) is seawater. The desulfurization method according to any one of claims 1 to 9, further comprising an amine compound recovery/supply step (U) of recovering the amine compound (A) from the liquid phase after the flue gas-derived calcium carbonate (X) has precipitated and supplying the amine compound (A) as at least a portion of the amine compound (A) used in step (S). A desulfurization system for carrying out a desulfurization method using calcium carbonate as a desulfurization agent, comprising: a production system for producing flue-gas-derived calcium carbonate (X) produced from carbon dioxide contained in desulfurized flue gas (C) discharged from a facility employing the desulfurization method, and a supply device for supplying the flue-gas-derived calcium carbonate (X) produced by the production system as at least a part of the desulfurization agent used in the facility,
The manufacturing system includes:
a first contacting portion (P1-1) for contacting the exhaust gas (C) with an amine aqueous solution (A1) containing one or more amine compounds (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers containing groups derived from these amines, to prepare an amine aqueous solution (A2) containing carbonate ions derived from carbon dioxide in the exhaust gas (C);
a second contact section (P1-2) for contacting the aqueous amine solution (A2) with a calcium ion-containing aqueous solution (B) to precipitate the exhaust gas-derived calcium carbonate (X); and a recovery section (Q) for recovering the exhaust gas-derived calcium carbonate (X).
A desulfurization system comprising: The desulfurization system according to claim 11, wherein the production system includes a plurality of the first contact parts (P1-1). The desulfurization system according to claim 11 or 12, wherein the production system includes a plurality of the second contact parts (P1-2). The desulfurization system according to claim 11 or 12,
A desulfurization system, comprising: a first contact portion (P1-1) that is not provided with a second contact portion (P1-2); and a second contact portion (P1-2) that is not provided with the second contact portion (P1-2); and the first contact portion (P1-1) that is not provided with the second contact portion (P1-2); A desulfurization system for carrying out a desulfurization method using calcium carbonate as a desulfurization agent,
a production system for producing flue-gas-derived calcium carbonate (X) produced using carbon dioxide in a desulfurized flue gas (C) discharged from a facility employing the desulfurization method as a raw material; and a supply device for supplying the flue-gas-derived calcium carbonate (X) produced by the production system as at least a part of the desulfurization agent used in the facility,
The manufacturing system includes:
a contacting section (P2) for simultaneously contacting one or more amine compounds (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers containing groups derived from these amines with a calcium ion-containing aqueous solution (B) and the exhaust gas (C) to precipitate the exhaust gas-derived calcium carbonate (X); and a recovery section (Q) for recovering the exhaust gas-derived calcium carbonate (X).
A desulfurization system comprising: A desulfurization system for carrying out a desulfurization method using calcium carbonate as a desulfurization agent,
a production system for producing flue-gas-derived calcium carbonate (X) produced using carbon dioxide in the flue gas (C) discharged from a facility employing the desulfurization method as a raw material, and a supply device for supplying the flue-gas-derived calcium carbonate (X) produced by the production system as at least a part of the desulfurization agent used in the facility,
The manufacturing system includes:
a first contact portion (P3-1) for preparing a mixed solution (AB) of one or more amine compounds (A) selected from the group consisting of amines synthesized in vivo, artificially synthesized amines, and polymers containing groups derived from these amines, and a calcium ion-containing aqueous solution (B);
a second contact section (P3-2) for contacting the mixed liquid (AB) with the flue gas (C) to precipitate the flue gas-derived calcium carbonate (X); and a recovery section (Q) for recovering the flue gas-derived calcium carbonate (X).
A desulfurization system comprising: an amine compound recovery/supply section (R) for recovering the amine compound (A) from the liquid phase after precipitation of the exhaust gas-derived calcium carbonate (X) and supplying the recovered amine compound (A) as at least a part of the amine compound (A) to be used in the first contact section (P1-1), the contact section (P2), or the first contact section (P3-1);
The desulfurization system according to any one of claims 11 to 16, further comprising: