Carbon dioxide capture system

Abstract

To provide a carbon dioxide recovery system improved in heat efficiency that dissipates carbon dioxide from liquid absorbing the carbon dioxide.SOLUTION: A carbon dioxide recovery system is provided with: a distillation column that heats liquid absorbing carbon dioxide and dissipates the carbon dioxide from the liquid; a first reboiler that performs heat exchange between the liquid extracted from the distillation column and a heat medium; a methanation device including a reactor vessel that makes carbon dioxide with hydrogen to manufacture methane; a reaction gas supply line through which reaction gas flowing out from the reactor vessel is supplied as the heat medium to the first reboiler; and a reaction gas return line through which the reaction gas whose heat is exchanged with the liquid absorbing carbon dioxide in the first reboiler is returned to the methanation device.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a carbon dioxide recovery system.

Background Art

[0002] Patent Document 1 describes an invention in which the heat of reaction of a reaction for producing methane from carbon dioxide and hydrogen is used as thermal energy to separate carbon dioxide from an adsorbent that has adsorbed carbon dioxide.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, since the thermal energy used in Patent Document 1 is used via the vapor generated by the heat of reaction, it is difficult to say that the thermal energy is used efficiently.

[0005] In view of the above circumstances, at least one embodiment of the present disclosure aims to provide a carbon dioxide recovery system with improved thermal efficiency for dissipating carbon dioxide from an absorbent that has absorbed carbon dioxide.

Means for Solving the Problems

[0006] To achieve the above object, the carbon dioxide recovery system according to the present disclosure includes a distillation column that heats an absorbent that has absorbed carbon dioxide to dissipate carbon dioxide from the absorbent, and a first reboiler that exchanges heat between the absorbent withdrawn from the distillation column and a heat medium. In the aforementioned distillation column, the absorbent liquid was releasedThe system includes a methanation apparatus that includes a reactor for producing methane by reacting carbon dioxide and hydrogen, a reaction gas supply line that supplies the reaction gas discharged from the reactor to the first reboiler as the heat transfer medium, and a reaction gas return line that returns the reaction gas, which has undergone heat exchange with the absorbent liquid in the first reboiler, to the methanation apparatus. [Effects of the Invention]

[0007] According to the carbon dioxide capture system of this disclosure, the absorbent liquid that has absorbed carbon dioxide is heated by exchanging heat between the reaction gas that has flowed out of the reactor that produces methane by reacting carbon dioxide and hydrogen, thereby improving the thermal efficiency of releasing carbon dioxide from the absorbent liquid. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic diagram of the configuration of a carbon dioxide capture system according to Embodiment 1 of this disclosure. [Figure 2] This is a schematic diagram of the configuration of a carbon dioxide capture system according to Embodiment 2 of this disclosure. [Figure 3] This is a schematic diagram of the configuration of a carbon dioxide capture system according to Embodiment 3 of this disclosure. [Figure 4] This is a schematic diagram of the configuration of a carbon dioxide capture system according to Embodiment 4 of this disclosure. [Figure 5] This is a schematic diagram of the configuration of a carbon dioxide capture system according to Embodiment 5 of this disclosure. [Modes for carrying out the invention]

[0009] The carbon dioxide capture system according to embodiments of this disclosure will be described below with reference to the drawings. The embodiments described below represent one aspect of this disclosure and are not limiting, and can be modified at will within the scope of the technical idea of ​​this disclosure.

[0010] (Embodiment 1) <Configuration of the carbon dioxide capture system according to Embodiment 1 of this disclosure> As shown in Figure 1, the carbon dioxide recovery system 1 according to Embodiment 1 of the present disclosure is configured by combining a distillation column 2 and a methanation device 20 that produces methane by reacting carbon dioxide with hydrogen. The distillation column 2 is connected to an absorption column (not shown) and an absorption liquid line 3, for example, to absorb carbon dioxide into an absorption liquid by bringing a gas containing carbon dioxide into gas-liquid contact with the absorption liquid.

[0011] The distillation column 2 is equipped with a circulation line 4 for circulating the absorbent liquid in the distillation column 2, drawing it out from the bottom of the column and returning it to the distillation column 2. The circulation line 4 is equipped with a first reboiler 5a, which is a heat exchanger that heats the absorbent liquid by exchanging heat with a heat transfer medium. The heat transfer medium that exchanges heat with the absorbent liquid will be described later.

[0012] Furthermore, the distillation column 2 is equipped with a condenser 6 that returns the condensate obtained by cooling the gas flowing out from the top of the distillation column 2 (hereinafter referred to as "flowing gas") back to the distillation column 2. The condenser 6 comprises an outflow gas line 6a through which the outflow gas flows, a cooler 6b installed in the outflow gas line 6a, a reflux tank 6c connected to the downstream end of the outflow gas line 6a, and a condensate line 6d that returns the condensate in the reflux tank 6c back to the distillation column 2. The cooler 6b can, for example, be a heat exchanger that cools the outflow gas by exchanging heat with an arbitrary cooling fluid. In addition to the condensate, the reflux tank 6c contains a gas that is mainly carbon dioxide. One end of a carbon dioxide supply line 7, which is connected to a device that uses carbon dioxide, is connected to the top of the reflux tank 6c.

[0013] In Embodiment 1, the apparatus that uses carbon dioxide is a methanation apparatus 20. The methanation apparatus 20 includes a reactor 21 to which the other end of the carbon dioxide supply line 7 is connected. As will be described later, the reactor 21 is provided with a catalyst (not shown), and through the catalytic action of this catalyst, carbon dioxide and hydrogen react to produce methane and water (hereinafter, this reaction is referred to as the "methanation reaction"). The reaction gas flowing out of the reactor 21 contains the produced methane and water, unreacted carbon dioxide and hydrogen, and other unavoidable impurities. To supply hydrogen to the reactor 21, the carbon dioxide supply line 7 has a hydrogen supply line 9, one end of which is connected to a hydrogen supply source 8, and the other end of the hydrogen supply line 9 is connected between the reactor 21 and the reflux tank 6c. The hydrogen supply source 8 is not particularly limited and may be, for example, a tank for storing hydrogen or any apparatus for producing hydrogen. A first heat exchanger 22 is also provided between the reactor 21 and the reflux tank 6c. The first heat exchanger 22 is for exchanging heat between the gas flowing into the reactor 21 (a gas containing at least carbon dioxide and hydrogen, hereinafter referred to as the "raw material gas") and the reaction gas flowing out of the reactor 21.

[0014] A reaction gas supply line 23 is provided to supply the reaction gas flowing out of the reactor 21 to the first reboiler 5a as the aforementioned heat transfer medium. This line connects the reactor 21 and the first reboiler 5a and also passes through the first heat exchanger 22. A reaction gas return line 24 is provided to return the reaction gas, which is used as the heat transfer medium, from the first reboiler 5a to the methanation device 20 after heat exchange with the absorbent liquid in the first reboiler 5a. One end of the reaction gas return line 24 is connected to the first reboiler 5a, and the other end is connected to the first gas-liquid separator 25 provided in the methanation device 20. A second heat exchanger 26 is provided in the reaction gas return line 24 to cool the reaction gas by heat exchange between the reaction gas and an arbitrary cooling medium.

[0015] The methanation apparatus 20 may have a second reaction section 20b downstream of the first reaction section 20a having the above-described configuration, and although not shown in Figure 1, at least one reaction section (e.g., a third reaction section, a fourth reaction section, etc.) may be provided downstream of the second reaction section 20b. For example, the second reaction section 20b, like the first reaction section 20a, includes a reactor 21b and a first gas-liquid separator 25b provided downstream of the reactor 21b. The second reaction section 20b is also provided with a first heat exchanger 22b for heat exchange between the reaction gas from the first reaction section 20a and the reaction gas flowing out of the reactor 21b, and a second heat exchanger 26b for cooling the reaction gas before it flows into the first gas-liquid separator 25b. The first reaction section 20a and the second reaction section 20b are connected by a reaction gas line 27 connecting the first gas-liquid separator 25 and the reactor 21b. Even if a third reaction section, a fourth reaction section, etc., are provided, they can be configured to have the same configuration as the second reaction section 20b.

[0016] Although not essential in Embodiment 1, a steam supply device 30 for supplying steam to the reaction gas supply line 23 may be provided. The configuration of the steam supply device 30 is not limited, but for example, it may consist of a steam supply line 32 with one end connected to a steam supply source 31 and the other end connected to the reaction gas supply line 23, and a flow control valve 33 provided on the steam supply line 32. The configuration of the steam supply source 31 is also not limited, but for example, it may be a boiler.

[0017] <Operation of the carbon dioxide capture system according to Embodiment 1 of this disclosure> Next, the operation of the carbon dioxide recovery system 1 according to Embodiment 1 of this disclosure will be described. The absorbent liquid that has absorbed carbon dioxide flows into the distillation column 2 via the absorbent liquid line 3. The absorbent liquid in the distillation column 2 is circulated so that it is withdrawn from the bottom of the distillation column 2 and then flows through the circulation line 4 to return to the distillation column 2. As the absorbent liquid circulates in this manner, it is heated in the first reboiler 5a.

[0018] When the temperature of the absorption liquid rises due to heating of the absorption liquid in the first reboiler 5a, the carbon dioxide absorbed in the absorption liquid is dissipated from the absorption liquid. The carbon dioxide and other gas components dissipated from the absorption liquid rise in the distillation column 2 and flow out from the top of the distillation column 2, and then flow through the outflow gas line 6a as outflow gas. When the outflow gas flows through the outflow gas line 6a, the outflow gas is cooled in the cooler 6b. When the outflow gas is cooled and its temperature drops, the components with a low boiling point in the outflow gas condense, but most of the carbon dioxide remains in the gaseous state. When the cooled outflow gas flows into the reflux tank 6c, the outflow gas is separated into a gas component and a liquid component. The gas component, which is mainly carbon dioxide, is supplied as a raw material to the methanation device 20 via the carbon dioxide supply line 7. On the other hand, the liquid component is returned into the distillation column 2 via the condensate line 6d.

[0019] On the other hand, in the methanation device 20, the carbon dioxide flowing through the carbon dioxide supply line 7 and the hydrogen supplied from the hydrogen source 8 via the hydrogen supply line 9 are heated in the first heat exchanger 22 as raw material gas and then flow into the reactor 21. In the reactor 21, a methanation reaction occurs by catalysis, generating methane and water. The reaction gas flowing out from the reactor 21 flows through the reaction gas supply line 23, is cooled by heat exchange with the raw material gas in the first heat exchanger 22, and then exchanges heat with the absorption liquid in the first reboiler 5a. Thereafter, the reaction gas flows through the reaction gas return line 24, is cooled in the second heat exchanger 26, and then is gas-liquid separated into a liquid phase and a gas phase in the first gas-liquid separator 25. The liquid phase is mainly water, and the gas phase contains methane, carbon dioxide, hydrogen, etc. Incidentally, when water is used as a cooling medium in the second heat exchanger 26, water vapor can be obtained by utilizing the heat of the reaction gas.

[0020] When the methanation device 20 has a second reaction section 20b, and further has a third reaction section, a fourth reaction section, etc., in the reactors of each reaction section (in the second reaction section 20b, the reactor 21b), carbon dioxide and hydrogen that were not used in the methanation reaction in the previous reaction section are consumed by the methanation reaction, and gas-liquid separation is performed in the gas-liquid separators of each reaction section (in the second reaction section 20b, the first gas-liquid separator 25b). The higher the number of reaction sections, the higher the concentration of methane in the reaction gas flowing out from each reactor.

[0021] Thus, since the absorption liquid is heated by heat-exchanging the reaction gas flowing out from the reactor 21 that reacts carbon dioxide and hydrogen to produce methane and the absorption liquid that has absorbed carbon dioxide, the heat efficiency of dissipating carbon dioxide from the absorption liquid can be improved compared to the case of heat-exchanging the water vapor generated by the heat of the reaction gas and the absorption liquid (for example, Patent Document 1).

[0022] For example, when the production amount of methane in the methanation device 20 is small, or when the amount of the absorption liquid flowing into the distillation column 2 is large, the heat energy for heating the absorption liquid may not be sufficient only with the reaction gas supplied from the methanation device 20 to the first reboiler 5a. In such a case, if the water vapor supply device 30 is provided, water vapor is supplied to the reaction gas by the water vapor supply device 30, so that the heat energy for heating the absorption liquid in the first reboiler 5a can be increased. The supply amount of water vapor from the water vapor supply device 30 can be adjusted by the flow rate control valve 33. Note that even if water vapor is added to the reaction gas, water is separated from the reaction gas in the first gas-liquid separator 25, so that the quality of methane as a product of the methanation device 20 is not adversely affected.

[0023] (Embodiment 2) Next, the carbon dioxide recovery system according to Embodiment 2 will be described. The carbon dioxide recovery system according to Embodiment 2 is obtained by providing another second reboiler 5b in addition to the first reboiler 5a with respect to Embodiment 1. Note that in Embodiment 2, the same components as those in Embodiment 1 are denoted by the same reference numerals, and detailed descriptions thereof are omitted.

[0024] <Configuration of the carbon dioxide capture system according to Embodiment 2 of this disclosure> As shown in Figure 2, in the carbon dioxide recovery system 1 according to Embodiment 2 of the present disclosure, the circulation line 4 includes a first line section 4a and a second line section 4b, which are sections in which the flow of the absorbent liquid is divided into two and flows in parallel to each other. The first line section 4a and the second line section 4b are provided with a first reboiler 5a and a second reboiler 5b, respectively. The second reboiler 5b is a heat exchanger that heats the absorbent liquid by exchanging heat with steam flowing through the second line section 4b. The other configurations are the same as in Embodiment 1.

[0025] <Operation of the carbon dioxide capture system according to Embodiment 2 of this disclosure> Next, the operation of the carbon dioxide recovery system 1 according to Embodiment 2 of this disclosure will be described. The operation in which carbon dioxide is released from the absorbent in the distillation column 2, the operation in which methane and water are produced from carbon dioxide and hydrogen in the methanation device 20, and the operation in which the absorbent is heated in the first reboiler 5a using the reaction gas discharged from the reactor 21 as a heat transfer medium are the same as in Embodiment 1. Embodiment 2 differs from Embodiment 1 in that, of the absorbent circulating in the circulation line 4, the absorbent flowing through the second line portion 4b is heated in the second reboiler 5b by heat exchange with water vapor.

[0026] In Embodiment 2, from the perspective of the reaction gas supplied to the first reboiler 5a as a heat transfer medium, even if the reaction gas alone does not provide enough thermal energy to heat the absorbent liquid, the heat exchange with steam in the second reboiler 5b can compensate for the lack of thermal energy needed to heat the absorbent liquid. On the other hand, from the perspective of the steam in the second reboiler 5b, the amount of steam used in the second reboiler 5b can be reduced by the amount of heat from the reaction gas flowing out of the reactor 21 that is used as thermal energy for heating the absorbent liquid.

[0027] <Modified example of the carbon dioxide capture system according to Embodiment 2 of this disclosure> In Embodiment 2, the first reboiler 5a and the second reboiler 5b were arranged in parallel with respect to the flow direction of the absorbent liquid, but the system is not limited to these configurations. The first reboiler 5a and the second reboiler 5b may also be arranged in series with respect to each other.

[0028] (Embodiment 3) Next, a carbon dioxide recovery system according to Embodiment 3 will be described. The carbon dioxide recovery system according to Embodiment 3 is modified from Embodiment 1 or 2 by adding a plurality of gas-liquid separators to the first reaction section 20a of the methanation device 20. In the following description, the modified form from Embodiment 1 is referred to as Embodiment 3, but the modified form from Embodiment 2 may also be referred to as Embodiment 3. In Embodiment 3, components that are the same as those in Embodiment 1 are given the same reference numerals, and their detailed descriptions are omitted.

[0029] <Configuration of the carbon dioxide capture system according to Embodiment 3 of this disclosure> As shown in Figure 3, in the carbon dioxide recovery system 1 according to Embodiment 3 of this disclosure, a second gas-liquid separator 28 is provided upstream of the second heat exchanger 26 in the reaction gas return line 24. The other configurations are the same as in Embodiment 1.

[0030] <Operation of the carbon dioxide capture system according to Embodiment 3 of this disclosure> Next, the operation of the carbon dioxide recovery system 1 according to Embodiment 3 of this disclosure will be described. The reaction gas that has undergone heat exchange with the absorbent liquid in the first reboiler 5a flows through the reaction gas return line 24 and into the second gas-liquid separator 28, where it is separated into a gas phase and a liquid phase. After the gas phase flows out of the second gas-liquid separator 28, it is cooled in the second heat exchanger 26, similar to Embodiment 1, and then separated into a gas-liquid phase in the first gas-liquid separator 25. Other operations are the same as in Embodiment 1.

[0031] In Embodiment 3, the liquid phase is also separated from the reaction gas in the second gas-liquid separator 28. Since the temperature of the liquid phase separated in the second gas-liquid separator 28 is higher than the temperature of the liquid phase separated in the first gas-liquid separator 25, for example, if the liquid phase separated in the second gas-liquid separator 28 is heated to produce steam, steam can be produced and used with less energy compared to heating the liquid phase separated in the first gas-liquid separator 25. This improves the overall thermal efficiency of the carbon dioxide recovery system 1.

[0032] (Embodiment 4) Next, a carbon dioxide recovery system according to Embodiment 4 will be described. The carbon dioxide recovery system according to Embodiment 4 is modified from Embodiment 1 or 2 by adding a bypass line for a portion of the reaction gas to bypass the first reboiler 5a. In the following description, Embodiment 4 is described as a configuration in which a bypass line is added to Embodiment 1, but Embodiment 4 may also be described as a configuration in which a bypass line is added to Embodiment 2. In Embodiment 4, components that are the same as those in Embodiment 1 are given the same reference numerals, and their detailed descriptions are omitted.

[0033] <Configuration of the carbon dioxide capture system according to Embodiment 4 of this disclosure> As shown in Figure 4, the carbon dioxide recovery system 1 according to Embodiment 4 of the present disclosure is provided with a bypass line 40 for a portion of the reaction gas flowing out of the reactor 21 to bypass the first reboiler 5a. One end (upstream end) of the bypass line 40 is connected to the reaction gas supply line 23 between the reactor 21 and the first reboiler 5a, preferably between the first heat exchanger 22 and the first reboiler 5a. The other end (downstream end) of the bypass line 40 is connected to the reaction gas return line 24 between the first reboiler 5a and the first gas-liquid separator 25, preferably between the first reboiler 5a and the second heat exchanger 26.

[0034] The bypass line 40 is provided with a third heat exchanger 41 that cools the reaction gas by exchanging heat between the reaction gas flowing through the bypass line 40 and a cooling medium, and a flow control valve 42 that adjusts the flow rate of the reaction gas flowing through the bypass line 40. The cooling medium that exchanges heat with the reaction gas in the third heat exchanger 41 preferably contains water, and more preferably the cooling medium is water. The other configurations are the same as in Embodiment 1.

[0035] <Operation of the carbon dioxide capture system according to Embodiment 4 of this disclosure> Next, the operation of the carbon dioxide recovery system 1 according to Embodiment 4 of this disclosure will be described. By adjusting the opening of the flow control valve 42, a portion of the reaction gas flowing out of the reactor 21 flows through the bypass line 40. In other words, it is possible to prevent a portion of the reaction gas flowing out of the reactor 21 from being supplied to the first reboiler 5a. If the reaction gas flowing out of the reactor 21 has enough heat to heat the absorbent liquid in the first reboiler 5a, the thermal efficiency of the entire carbon dioxide recovery system 1 can be improved by adjusting the flow rate of the reaction gas flowing through the bypass line 40 with the flow control valve 42, taking into account the amount of heat required in the distillation column 2 and the amount of heat generated in the methanation device 20.

[0036] The reaction gas flowing through the bypass line 40 is cooled by heat exchange with a cooling medium in the third heat exchanger 41. If water is used as the cooling medium, water vapor can be obtained by utilizing the heat of the reaction gas. The reaction gas flowing out of the third heat exchanger 41 merges with the reaction gas flowing through the reaction gas return line 24, and is then cooled in the second heat exchanger 26, similar to Embodiment 1, and subsequently separated into gas and liquid in the first gas-liquid separator 25. Other operations are the same as in Embodiment 1.

[0037] <Modified examples of the carbon dioxide capture system according to Embodiments 1-4 of this disclosure> In embodiments 1 to 4, only the reaction gas discharged from reactor 21 is used to heat the absorbent liquid, but the system is not limited to this configuration. Multiple first reboilers 5a may be provided in the circulation line 4, and the reaction gas discharged from reactor 21b of the second reaction section 20b, as well as the reaction gas discharged from reactors such as the third and fourth reaction sections, may be supplied to each of the first reboilers 5a to exchange heat with the absorbent liquid.

[0038] In embodiments 1 to 4, carbon dioxide from reflux tank 6c is supplied to reactor 21 as a raw material for the methanation reaction in the methanation apparatus 20, but the system is not limited to this configuration. The carbon dioxide from reflux tank 6c may be consumed by a device other than the methanation apparatus 20, and carbon dioxide from another device, such as a carbon dioxide storage cylinder or a device that generates carbon dioxide (hereinafter referred to as the "carbon dioxide supply source"), may be supplied to reactor 21. Alternatively, carbon dioxide may be supplied to reactor 21 from both the carbon dioxide supply source and the reflux tank 6c. In other words, carbon dioxide from reflux tank 6c may be used as part of the raw material for the methanation reaction.

[0039] (Embodiment 5) Next, a carbon dioxide recovery system according to Embodiment 5 will be described. The carbon dioxide recovery system according to Embodiment 5 utilizes the liquid phase separated in the first gas-liquid separator 25, compared to Embodiments 1 to 4. In Embodiment 5, components that are the same as those in Embodiments 1 to 4 are given the same reference numerals, and their detailed descriptions are omitted.

[0040] <Configuration of the carbon dioxide capture system according to Embodiment 5 of this disclosure> As shown in Figure 5, the carbon dioxide recovery system 1 according to Embodiment 5 of the present disclosure comprises a first column 51 that brings a gas containing carbon dioxide and a fluid containing water into gas-liquid contact, and a second column 52 that brings the gas discharged from the first column 51 and an absorbent liquid into gas-liquid contact. A line 54 through which the gas containing carbon dioxide flows is connected to the first column 51. The first column 51 and the second column 52 are connected by a line 55. The second column 52 and the distillation column 2 are connected by an absorbent liquid line 3. The circulation line 4 includes a branch line 4c that branches upstream of the first reboiler 5a, and the branch line 4c is connected to the second column 52. The first gas-liquid separator 25 and the first column 51 are connected by a water supply line 53. The water supply line 53 may be connected to the second column 52 instead of the first column 51, or it may be connected to both the first column 51 and the second column 52. Other configurations are omitted in Figure 3 but are the same as in Embodiments 1 to 4.

[0041] <Operation of the carbon dioxide capture system according to Embodiment 5 of this disclosure> Next, the operation of the carbon dioxide recovery system 1 according to Embodiment 5 of this disclosure will be described. Embodiment 5 differs from Embodiment 1 or 2 in that the operation until the absorbent liquid that has absorbed carbon dioxide flows into the distillation column 2 is the same as that of Embodiment 1 or 2, but the other operations are the same as those of Embodiment 1 or 2. For this reason, only the operation until the absorbent liquid that has absorbed carbon dioxide flows into the distillation column 2 will be described below.

[0042] Gas containing carbon dioxide, such as exhaust gas discharged from various combustion devices, flows into the first tower 51 via line 54 and rises within the first tower 51. Additionally, the liquid phase from the first gas-liquid separator 25, i.e., water, is supplied to the first tower 51 via water supply line 53 and falls within the first tower 51. Within the first tower 51, the gas containing carbon dioxide and water come into gas-liquid contact, removing sulfur oxides (e.g., sulfur dioxide) and solid matter such as dust contained in the gas by absorption and capture by the water, while simultaneously providing cooling.

[0043] The gas flowing out from the top of the first column 51 flows into the second column 52 via line 55 and rises within the second column 52. In the second column 52, the absorbent liquid withdrawn from the bottom of the second column 52 is sent to the distillation column 2 via absorbent liquid line 3, and the absorbent liquid withdrawn from the bottom of the distillation column 2 is sent to the second column 52 via branch line 4c, thus circulating the absorbent liquid between the second column 52 and the distillation column 2. Through gas-liquid contact between the gas and the absorbent liquid in the second column 52, carbon dioxide in the gas is absorbed by the absorbent liquid, reducing the concentration of carbon dioxide in the gas, and the gas is released from the top of the second column 52.

[0044] In this way, by using the water separated from the reaction gas in the first gas-liquid separator 25 of the methanation device 20 for cooling and washing the gas containing carbon dioxide, the amount of water consumed in the carbon dioxide recovery system 1 can be reduced.

[0045] <Modified example of the carbon dioxide capture system according to Embodiment 5 of this disclosure> In Embodiment 5, only the liquid phase separated by the first gas-liquid separator 25 is supplied to the first column 51, but the system is not limited to this configuration. The liquid phase separated by the first gas-liquid separator 25b of the second reaction section 20b, and the liquid phase separated by gas-liquid separators in the third and fourth reaction sections, etc., may also be supplied to the first column 51. Furthermore, the system is not limited to supplying only the liquid phase from the gas-liquid separator of the methanation device 20 to the first column 51; only a portion of the liquid phase from the gas-liquid separator of the methanation device 20 may be used, or water from other water sources may be supplied to the first column 51. In addition, in Embodiment 5, the liquid phase separated by the first gas-liquid separator 25 is supplied directly to the first column 51, but it may be cooled to the required temperature in the first column 51 before being supplied to the first column 51, the second column 52, or both. As for the cooling method, a method using a heat exchanger or any other method may be used.

[0046] The contents described in each of the above embodiments can be understood, for example, as follows:

[0047] [1] A carbon dioxide capture system according to one embodiment is: A distillation column (2) heats the absorbent liquid that has absorbed carbon dioxide to release carbon dioxide from the absorbent liquid, A first reboiler (5a) that exchanges heat between the absorbent liquid extracted from the distillation column (2) and the heat transfer medium, A methanation apparatus (20) including a reactor (21) that reacts carbon dioxide and hydrogen to produce methane, A reaction gas supply line (23) supplies the reaction gas discharged from the reactor (21) to the first reboiler (5a) as the heat transfer medium, A reaction gas return line (24) returns the reaction gas that has exchanged heat with the absorbent liquid in the first reboiler (5a) to the methanation device (20), and It is equipped with.

[0048] According to the carbon dioxide capture system of this disclosure, the absorbent liquid that has absorbed carbon dioxide is heated by exchanging heat between the reaction gas that has flowed out of the reactor that produces methane by reacting carbon dioxide and hydrogen, thereby improving the thermal efficiency of releasing carbon dioxide from the absorbent liquid.

[0049] [2] A carbon dioxide capture system according to another embodiment is the carbon dioxide capture system of [1], The system includes a second reboiler (5b) that exchanges heat between the absorbent liquid (2) and steam extracted from the distillation column (2).

[0050] With this configuration, even if the reaction gas supplied from the methanation unit to the first reboiler is insufficient to heat the absorbent, the heat exchange with steam in the second reboiler can compensate for the lack of heat energy needed to heat the absorbent. Furthermore, the amount of steam used in the second reboiler can be reduced by using the heat from the reaction gas supplied from the methanation unit to the first reboiler as thermal energy for heating the absorbent.

[0051] [3] A carbon dioxide capture system according to yet another embodiment is the carbon dioxide capture system of [1], The system includes a steam supply device (30) that supplies steam to the reaction gas supply line (23).

[0052] With this configuration, if the reaction gas supplied from the methanation unit to the first reboiler is insufficient to heat the absorbent liquid, the steam supply unit provides steam to the reaction gas, thereby increasing the amount of heat needed to heat the absorbent liquid in the first reboiler.

[0053] [4] A carbon dioxide capture system according to yet another embodiment is any of the carbon dioxide capture systems described in [1] to [3], The methanation apparatus (20) includes a first heat exchanger (22) that exchanges heat between the reaction gas flowing through the reaction gas supply line (23) and carbon dioxide and hydrogen before they flow into the reactor (21).

[0054] With this configuration, the heat from the reaction gas is used not only to heat the absorbent liquid in the first reboiler, but also to heat the carbon dioxide and hydrogen before they flow into the reactor, thereby improving the overall thermal efficiency of the carbon dioxide capture system.

[0055] [5] A carbon dioxide capture system according to yet another embodiment is any of the carbon dioxide capture systems described in [1] to [4], The methanation apparatus (20) includes at least one gas-liquid separator (first gas-liquid separator 25, second gas-liquid separator 28) for separating the reaction gas into gas-liquid and gas-liquid components. The carbon dioxide capture system (1) is A first tower (51) brings a gas containing carbon dioxide and water into a gas-liquid contact, A second tower (52) brings the gas flowing out of the first tower (51) into gas-liquid contact with the absorbent liquid, An absorption liquid line (3) supplies the absorption liquid from the second column (52) to the distillation column (2), A water supply line (53) supplies the liquid phase separated by at least one gas-liquid separator (25, 28) as water to the first tower (51), and It is equipped with.

[0056] With this configuration, the water separated from the reaction gas in the gas-liquid separator of the methanation device can be used to cool and wash the gas containing carbon dioxide, thereby reducing the amount of water consumed in the carbon dioxide recovery system.

[0057] [6] A carbon dioxide capture system according to yet another embodiment is the carbon dioxide capture system of [5], The methanation device (20) comprises two or more gas-liquid separators (25, 28).

[0058] If the temperature of the liquid phase separated in one gas-liquid separator is higher than the temperature of the liquid phase separated in the other gas-liquid separator, heating the higher-temperature liquid phase to produce steam requires less energy than heating the lower-temperature liquid phase. This improves the overall thermal efficiency of the carbon dioxide capture system.

[0059] [7] A carbon dioxide capture system according to yet another embodiment is any of the carbon dioxide capture systems described in [1] to [5], The methanation apparatus (20) includes a bypass line (40) for at least a portion of the reaction gas to bypass the first reboiler (5a).

[0060] With this configuration, if the reaction gas flowing out of the reactor has enough heat to heat the absorbent in the first reboiler, the overall thermal efficiency of the carbon dioxide capture system can be improved by adjusting the flow rate of the reaction gas circulating through the bypass line, taking into account the amount of heat required in the distillation column and the amount of heat generated in the methanation unit.

[0061] [8] A carbon dioxide capture system according to yet another embodiment is the carbon dioxide capture system of [7], The methanation apparatus (20) includes a gas-liquid separator (25) to which the reaction gas return line (24) is connected. The bypass line (40) is connected to the reaction gas return line (24) between the first reboiler (5a) and the gas-liquid separator (25).

[0062] With this configuration, all of the reaction gas flowing out of the reactor can be separated into liquid and gas phases by a gas-liquid separator.

[0063] [9] A carbon dioxide capture system according to yet another embodiment is the carbon dioxide capture system of [7] or [8], The methanation apparatus (20) includes a second heat exchanger (26) that cools the gas formed by the convergence of the reaction gases that have flowed through the reaction gas return line (24) and the bypass line (40), respectively.

[0064] With this configuration, water vapor can be obtained by utilizing the heat of the reaction gas by exchanging heat between the reaction gas and water, which acts as a cooling medium, in the second heat exchanger.

[0065]

[10] A carbon dioxide capture system according to yet another embodiment is any of the carbon dioxide capture systems described in [7] to [9], The bypass line (40) is provided with a third heat exchanger (41) that recovers the heat of the reaction gas flowing through the bypass line (40).

[0066] With this configuration, water vapor can be obtained by utilizing the heat of the reaction gas by exchanging heat between the reaction gas flowing through the bypass line and water, which is used as a cooling medium, in the third heat exchanger.

[0067]

[11] A carbon dioxide capture system according to yet another embodiment is the carbon dioxide capture system of

[10] , The cooling medium that exchanges heat with the reaction gas in the third heat exchanger (41) includes water.

[0068] With this configuration, water vapor can be obtained by utilizing the heat of the reaction gas by exchanging heat between the reaction gas flowing through the bypass line and water, which is used as a cooling medium, in the third heat exchanger.

[0069]

[12] A carbon dioxide capture system according to yet another embodiment is any of the carbon dioxide capture systems described in [1] to

[11] , The system includes a carbon dioxide supply line (7) that supplies carbon dioxide released in the distillation column (2) to the reactor (21).

[0070] With this configuration, the recovered carbon dioxide is used as at least part of the raw material for methane, thus enabling the effective utilization of carbon dioxide. [Explanation of Symbols]

[0071] 1. Carbon dioxide capture system 2 Distillation column 3. Absorption line 5a First Reboiler 5b Second Reboiler 7. Carbon dioxide supply lines 20 Methanation device 21 Reactor 22 1st heat exchanger 23 Reaction gas supply line 24. Reaction gas return line 25 1st gas-liquid separator (gas-liquid separator) 26 Second heat exchanger 28 Second gas-liquid separator (gas-liquid separator) 30. Steam supply device 40 Bypass Line 41 Third heat exchanger 51 Tower 1 52 Second Tower 53 Water supply lines

Claims

1. A distillation column that heats the absorbent liquid that has absorbed carbon dioxide to release carbon dioxide from the absorbent liquid, A first reboiler that exchanges heat between the absorbent liquid extracted from the distillation column and a heat transfer medium, A methanation apparatus including a reactor that produces methane by reacting carbon dioxide released from the absorbent in the distillation column with hydrogen, A reaction gas supply line supplies the reaction gas discharged from the reactor to the first reboiler as the heat transfer medium, A reaction gas return line returns the reaction gas, which has undergone heat exchange with the absorbent liquid in the first reboiler, back to the methanation device. A carbon dioxide capture system equipped with [the necessary components].

2. The carbon dioxide recovery system according to claim 1, further comprising a second reboiler for heat exchange between the absorbent liquid extracted from the distillation column and steam.

3. The carbon dioxide recovery system according to claim 1, further comprising a steam supply device that supplies steam to the reaction gas supply line.

4. The carbon dioxide recovery system according to any one of claims 1 to 3, wherein the methanation apparatus comprises a first heat exchanger that exchanges heat between the reaction gas flowing through the reaction gas supply line and carbon dioxide and hydrogen before they flow into the reactor.

5. The methanation apparatus comprises at least one gas-liquid separator for separating the reaction gas into gas-liquid, The carbon dioxide recovery system is A first tower brings a gas containing carbon dioxide and water into a gas-liquid contact, A second tower brings the gas discharged from the first tower into gas-liquid contact with the absorbent liquid, An absorption liquid line for supplying the absorption liquid from the second column to the distillation column, A water supply line supplies the liquid phase separated by the at least one gas-liquid separator as water to the first tower. A carbon dioxide capture system according to any one of claims 1 to 4, comprising:

6. The carbon dioxide recovery system according to claim 5, wherein the methanation device comprises two or more gas-liquid separators.

7. The carbon dioxide recovery system according to any one of claims 1 to 5, wherein the methanation apparatus includes a bypass line for at least a portion of the reaction gas to bypass the first reboiler.

8. The methanation apparatus includes a gas-liquid separator to which the reaction gas return line is connected. The carbon dioxide recovery system according to claim 7, wherein the bypass line is connected to the reaction gas return line between the first reboiler and the gas-liquid separator.

9. The carbon dioxide recovery system according to claim 7 or 8, wherein the methanation apparatus comprises a second heat exchanger for cooling the gas formed by the convergence of the reaction gases that have flowed through the reaction gas return line and the bypass line, respectively.

10. The carbon dioxide recovery system according to any one of claims 7 to 9, wherein the bypass line is provided with a third heat exchanger for recovering heat from the reaction gas flowing through the bypass line.

11. The carbon dioxide recovery system according to claim 10, wherein the cooling medium that exchanges heat with the reaction gas in the third heat exchanger includes water.

12. A carbon dioxide recovery system according to any one of claims 1 to 11, comprising a carbon dioxide supply line for supplying carbon dioxide released in the distillation column to the reactor.

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