Carbon dioxide capture system

Abstract

To provide a carbon dioxide recovery system capable of efficiently bringing hydrogen and an absorbent which has absorbed carbon dioxide in a distillation tower into contact with gas and liquid and reducing the possibility of condensation of steam evaporated from the absorbent.SOLUTION: This carbon dioxide recovery system comprises: a first distillation tower in which an absorbent which has absorbed carbon dioxide is heated and the carbon dioxide is released from the absorbent; a first reboiler that exchanges heat between the absorbent and steam pulled out from the first distillation tower; and a hydrogen supply unit that supplies hydrogen to the absorbent in the first reboiler or the absorbent which has flown out from the first reboiler.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to carbon dioxide capture systems. [Background technology]

[0002] Patent Document 1 describes a carbon dioxide capture system including an absorption tower that brings a carbon dioxide-containing gas into gas-liquid contact with an absorption liquid to absorb the carbon dioxide into the absorption liquid, and a distillation tower that releases the carbon dioxide from the absorption liquid that has absorbed the carbon dioxide in the absorption tower. In this carbon dioxide capture system, a gas that is almost insoluble in the absorption liquid, such as hydrogen, is supplied to the distillation tower to promote separation of carbon dioxide from the absorption liquid in the distillation tower. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6906766 Summary of the Invention [Problem to be solved by the invention]

[0004] Typically, distillation columns are designed to ensure efficient gas-liquid contact between the absorption liquid that has absorbed carbon dioxide and the water vapor evaporated from the absorption liquid in the distillation column, but when hydrogen is supplied into the distillation column from the bottom end thereof, as in the carbon dioxide recovery system described in Patent Document 1, there is a problem that the water vapor and hydrogen are not mixed sufficiently, preventing efficient gas-liquid contact between the absorption liquid and the hydrogen. Also, when the pressure inside the distillation column is the same in both cases where hydrogen is supplied to the distillation column and where hydrogen is not supplied to the distillation column, the amount of water vapor that transfers from the absorption liquid to the dry hydrogen is greater in the former case than in the latter case, and the reboiler duty increases by the amount of latent heat of this water vapor, which makes the water vapor more likely to condense.

[0005] In view of the above circumstances, at least one embodiment of the present disclosure aims to provide a carbon dioxide recovery system that can efficiently bring an absorption liquid that has absorbed carbon dioxide into gas-liquid contact with hydrogen in a distillation column and that can reduce the risk of condensation of water vapor evaporated from the absorption liquid. [Means for solving the problem]

[0006] In order to achieve the above object, the carbon dioxide recovery system according to the present disclosure includes a first distillation column that heats an absorption liquid that has absorbed carbon dioxide to strip carbon dioxide from the absorption liquid; a circulation line for circulating the absorption liquid so as to extract the absorption liquid in the first distillation column from the first distillation column and return the absorption liquid to the first distillation column; a first reboiler for exchanging heat between the absorption liquid extracted from the first distillation column and steam; and a hydrogen supply unit for supplying hydrogen to the absorption liquid in the first reboiler or the absorption liquid flowing out from the first reboiler. A mixed fluid of the absorption liquid that has been heat exchanged with the steam in the first reboiler and hydrogen, or a mixed fluid of the absorption liquid that has been heat exchanged with the steam in the first reboiler and hydrogen supplied to the absorption liquid that has flowed out of the first reboiler, is returned to the first distillation column. do. [Effects of the Invention]

[0007] According to the carbon dioxide recovery system of the present disclosure, by supplying hydrogen to the absorption liquid in the first reboiler or to the absorption liquid that has flowed out of the first reboiler, the hydrogen and the absorption liquid are returned in a mixed state to the first distillation column. In this way, a gas that is a good mixture of hydrogen and water vapor evaporated from the absorption liquid rises inside the first distillation column, and the absorption liquid that has absorbed carbon dioxide can efficiently come into gas-liquid contact with not only water vapor but also hydrogen. Furthermore, because hydrogen is supplied to the absorption liquid that is being heated in the first reboiler or the absorption liquid that has been heated in the first reboiler, the risk of water vapor condensing can be reduced by controlling the temperature in the first reboiler. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram illustrating the configuration of a carbon dioxide capture system according to a first embodiment of the present disclosure. [Figure 2] FIG. 10 is a schematic diagram illustrating the configuration of a carbon dioxide capture system according to a second embodiment of the present disclosure. [Figure 3] FIG. 10 is a schematic diagram illustrating the configuration of a carbon dioxide capture system according to a third embodiment of the present disclosure. [Figure 4]FIG. 10 is a schematic diagram illustrating the configuration of a carbon dioxide capture system according to a fourth embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, a carbon dioxide capture system according to an embodiment of the present disclosure will be described with reference to the drawings. The embodiment described below shows one aspect of the present disclosure, and is not intended to limit the present disclosure. Any modification can be made within the scope of the technical concept of the present disclosure.

[0010] (Embodiment 1) <Configuration of carbon dioxide capture system according to embodiment 1 of the present disclosure> 1, a carbon dioxide capture system 1 according to a first embodiment of the present disclosure includes a first distillation column 2. The first distillation column 2 is in communication with an absorption column (not shown) via an absorption liquid supply line 3, for example, for causing gas containing carbon dioxide to come into gas-liquid contact with an absorption liquid, thereby causing the absorption liquid to absorb carbon dioxide.

[0011] The first distillation column 2 is provided with a circulation line 4 for circulating the absorption liquid in the first distillation column 2 by extracting the absorption liquid from the bottom of the first distillation column 2 and returning it to the first distillation column 2. The circulation line 4 is provided with a first reboiler 5a. The first reboiler 5a is a heat exchanger that heats the absorption liquid by exchanging heat between the absorption liquid flowing through the circulation line 4 and steam (for example, water vapor).

[0012] The first reboiler 5a is provided with a hydrogen supply unit 8 that supplies hydrogen to the absorption liquid in the first reboiler 5a. The configuration of the hydrogen supply unit 8 is not particularly limited, but for example, the hydrogen supply unit 8 may include a hydrogen supply source 8a and a hydrogen supply line 8b having one end connected to the hydrogen supply source 8a and the other end connected to a circulation path of the absorption liquid in the first reboiler 5a. The hydrogen supply source 8a may be, for example, a hydrogen cylinder or a hydrogen tank that stores hydrogen, or a hydrogen production device that produces hydrogen by any method. A compressor may be provided in the hydrogen supply line 8b to supply hydrogen from the hydrogen supply source 8a to the circulation path of the absorption liquid in the first reboiler 5a. In addition, a heat exchanger may be provided in the hydrogen supply line 8b in order to supply hydrogen in a heated state.

[0013] The other end of the hydrogen supply line 8b may be connected to the circulation line 4 between the first reboiler 5a and the first distillation column 2, instead of to the circulation path of the absorption liquid in the first reboiler 5a. In this case, hydrogen is supplied to the absorption liquid flowing out of the first reboiler 5a.

[0014] The first distillation column 2 is also provided with a condenser 6 that cools the gas flowing out from the top of the first distillation column 2 (hereinafter referred to as the "outlet gas") and returns the condensate obtained to the first distillation column 2. The condenser 6 includes an outlet gas line 6a through which the outlet gas flows, a cooler 6b provided in the outlet gas line 6a, a reflux tank 6c connected to the downstream end of the outlet gas line 6a, and a condensate line 6d through which the condensate in the reflux tank 6c is returned to the first distillation column 2. As an example, the cooler 6b can be a heat exchanger that cools the outlet gas by exchanging heat between the outlet gas and an arbitrary cooling fluid. In addition to the condensate, the reflux tank 6c contains gas mainly containing carbon dioxide and hydrogen, as described below. A gas supply line 7 connected to a device 10 that uses the gas may be connected to the top of the reflux tank 6c. A compressor 9 for pressurizing the gas may be provided in the gas supply line 7.

[0015] <Operation of the carbon dioxide capture system according to the first embodiment of the present disclosure> Next, the operation of the carbon dioxide capture system 1 according to the first embodiment of the present disclosure will be described. The absorption liquid that has absorbed carbon dioxide flows into the first distillation column 2 via the absorption liquid supply line 3. The absorption liquid in the first distillation column 2 is circulated so that it is extracted from the bottom of the first distillation column 2, then flows through the circulation line 4 and returns to the first distillation column 2. As the absorption liquid circulates in this manner, it flows through the first reboiler 5a. As the absorption liquid flows through the first reboiler 5a, hydrogen is supplied to the absorption liquid by the hydrogen supply unit 8. In the first reboiler 5a, a mixed fluid of hydrogen and the absorption liquid is heated by heat exchange with steam. The mixed fluid heated in the first reboiler 5a flows into the first distillation column 2.

[0016] When the heated mixed fluid flows into the first distillation column 2, the temperature of the absorption liquid remaining in the first distillation column 2 rises, and the carbon dioxide absorbed in the absorption liquid is stripped from the absorption liquid and rises within the first distillation column 2. Furthermore, as water evaporates from the absorption liquid, water vapor also rises within the first distillation column 2. Furthermore, hydrogen in the mixed fluid heated in the first reboiler 5a is also stripped from the absorption liquid within the first distillation column 2 and rises within the first distillation column 2. That is, carbon dioxide, water vapor, and hydrogen rise within the first distillation column 2.

[0017] The absorption liquid that has flowed into the first distillation column 2 via the absorption liquid supply line 3 is heated as it falls within the first distillation column 2 by gas-liquid contact with the carbon dioxide, water vapor, and hydrogen that rise within the first distillation column 2. Meanwhile, the temperatures of the carbon dioxide, water vapor, and hydrogen decrease, and some of the water vapor condenses into a liquid that falls within the first distillation column 2. As a result, the effluent gas flowing out from the top of the first distillation column 2 contains carbon dioxide, water vapor, and hydrogen.

[0018] In the first embodiment, hydrogen is supplied to the absorption liquid in the first reboiler 5a, and therefore the hydrogen and absorption liquid flow into the first distillation column 2 in a sufficiently mixed state. In this way, the water vapor and hydrogen come into gas-liquid contact with the absorption liquid in the first distillation column 2 in a sufficiently mixed state, and therefore the absorption liquid can efficiently come into gas-liquid contact not only with the water vapor but also with the hydrogen. The same applies when hydrogen is supplied to the absorption liquid that has flowed out from the first reboiler 5a. In contrast, when hydrogen is directly supplied into the first distillation column 2, the water vapor and hydrogen are not necessarily sufficiently mixed, and a mixing device or the like may be required to sufficiently mix the two. Therefore, the hydrogen supply method as in the first embodiment is considered to be advantageous in the configuration of the carbon dioxide capture system 1 from the viewpoint of gas-liquid contact between the absorption liquid, the water vapor, and the hydrogen.

[0019] Furthermore, as described above, supplying hydrogen to the first distillation column 2 tends to cause water vapor to condense. However, in the first embodiment, hydrogen is supplied to the absorption liquid whose temperature is being increased in the first reboiler 5a or the absorption liquid whose temperature has been increased in the first reboiler 5a. Therefore, the risk of water vapor condensation can be reduced by controlling the temperature in the first reboiler 5a.

[0020] The effluent gas discharged from the top of the first distillation column 2 flows through the effluent gas line 6a. As the effluent gas flows through the effluent gas line 6a, it is cooled in the cooler 6b. When the effluent gas is cooled and its temperature decreases, components with low boiling points in the effluent gas condense, but most of the carbon dioxide and hydrogen remain in gaseous form. When the cooled effluent gas flows into the reflux tank 6c, it is separated into gas and liquid components. The gas component, which mainly contains carbon dioxide and hydrogen, is supplied to the apparatus 10 via the gas supply line 7. Meanwhile, the liquid component is returned to the first distillation column 2 via the condensate line 6d.

[0021] As described above, supplying hydrogen to the first distillation column 2 increases the reboiler duty of the first distillation column 2. On the other hand, supplying hydrogen to the first distillation column 2 lowers the temperature inside the first distillation column 2 compared to when hydrogen is not supplied to the first distillation column 2, and therefore the pressure inside the first distillation column 2 can be increased. This also increases the pressure inside the reflux tank 6c, so when carbon dioxide and hydrogen are supplied to the device 10 by the compressor 9, the energy consumption of the compressor 9 can be reduced. Furthermore, in this case, the pressure inside the first distillation column 2 increases, and the reboiler duty is reduced to the same level as when hydrogen is not supplied. This allows the operating costs of the carbon dioxide capture system 1 as a whole to be reduced.

[0022] (Embodiment 2) Next, a carbon dioxide capture system according to embodiment 2 will be described. The carbon dioxide capture system according to embodiment 2 is configured by adding a second reboiler for heating the absorption liquid in addition to the first reboiler 5a to embodiment 1. In embodiment 2, the same components as those in embodiment 1 are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0023] <Configuration of carbon dioxide capture system according to embodiment 2 of the present disclosure> As shown in FIG. 2, the carbon dioxide capture system 1 according to the second embodiment includes, in addition to the first distillation column 2, a second distillation column 20 that is different from the first distillation column 2. The circulation line 4 includes a first line portion 4a and a second line portion 4b, which are portions in which the flow of the absorption liquid is divided into two and flows parallel to each other. The first line portion 4a and the second line portion 4b are provided with a first reboiler 5a and a second reboiler 5b, respectively. That is, the first reboiler 5a and the second reboiler 5b are provided in parallel to each other in the flow direction of the absorption liquid. The second reboiler 5b is a heat exchanger that heats the absorption liquid by exchanging heat between the absorption liquid flowing through the second line portion 4b and a fluid supplied from the second distillation column 20.

[0024] The configuration of the second distillation column 20 is not particularly limited as long as it is different from the first distillation column 2, but in Embodiment 2, the second distillation column 20 is described as a distillation column for obtaining a fluid with an increased methanol concentration by rectifying crude methanol containing methanol as the main component in a methanol production plant. The second distillation column 20 is in communication with a methanol production unit 30 that produces crude methanol via a crude methanol supply line 16.

[0025] Similar to the first distillation column 2, the second distillation column 20 is provided with a reboiler 11 for heating the crude methanol in the second distillation column 20 and a condenser 12 for condensing the methanol vapor flowing out from the top of the second distillation column 20. The reboiler 11 is, for example, a heat exchanger that exchanges heat between steam (e.g., water vapor) and crude methanol. The condenser 12 is, for example, provided with a cooler 12a that is a heat exchanger that exchanges heat between the methanol vapor flowing out from the second distillation column 20 and an arbitrary cooling fluid, a reflux tank 12b into which the fluid (mainly liquid methanol) cooled in the cooler 12a flows, a return line 12c for returning a portion of the liquid methanol in the reflux tank 12b to the second distillation column 20, and a methanol supply line 12d for supplying the remaining liquid methanol in the reflux tank 12b as a product.

[0026] One end of line 13, through which methanol vapor flowing out of second distillation column 20 flows, is connected to the top of second distillation column 20, and the other end of line 13 is connected to reflux tank 12b of condenser 12. Line 13 is provided so as to pass through second reboiler 5b, i.e., so that heat exchange occurs in second reboiler 5b between the absorption liquid flowing through second line portion 4b and the methanol vapor flowing through line 13. Therefore, in Embodiment 2, the aforementioned fluid is the methanol vapor flowing out from the top of second distillation column 20. The other configurations are the same as those of Embodiment 1.

[0027] <Operation of the carbon dioxide capture system according to the second embodiment of the present disclosure> Next, the operation of the carbon dioxide capture system 1 according to the second embodiment of the present disclosure will be described. The operation of stripping carbon dioxide from the absorption liquid in the first distillation column 2 and the operation of supplying hydrogen to the absorption liquid being heated in the first reboiler 5a or the absorption liquid whose temperature has been raised in the first reboiler 5a are the same as those in the first embodiment. The second embodiment differs from the first embodiment in that the absorption liquid extracted from the bottom of the first distillation column 2 is heated not only in the first reboiler 5a but also in the second reboiler 5b. Below, the operations that differ from the first embodiment will be described.

[0028] Crude methanol produced in the methanol production apparatus 30 flows into the second distillation column 20 via a crude methanol supply line 16. The crude methanol that flows into the second distillation column 20 is heated in the reboiler 11, and its temperature increases. As the temperature of the crude methanol increases, most of the methanol, which has a low boiling point, vaporizes and rises within the second distillation column 20, while most of the components with a high boiling point (mainly water) remain liquid within the second distillation column 20. The vapor, which rises within the second distillation column 20 and is mainly composed of methanol, flows out of the second distillation column 20 and flows through a line 13.

[0029] The methanol vapor flowing through line 13 exchanges heat with the absorption liquid in second reboiler 5b, lowering its temperature. Depending on the temperature, at least a portion of the methanol may condense. The methanol vapor that has exchanged heat with the absorption liquid in second reboiler 5b flows through line 13 either as methanol vapor or containing at least liquid methanol, and is cooled by cooler 12a in condenser 12 before flowing into reflux tank 12b. A portion of the condensate (liquid methanol) in reflux tank 12b is returned to second distillation column 20 via return line 12c, while the remaining condensate is supplied via methanol supply line 12d to a device (not shown) for consuming or storing methanol.

[0030] In this way, in the first reboiler 5a, the absorption liquid is heated by heat exchange between steam and the absorption liquid, and in the second reboiler 5b, the absorption liquid is heated by heat exchange between the fluid supplied from the second distillation column 20 and the absorption liquid. Therefore, the amount of steam used in the first reboiler 5a is reduced, and the amount of heat supplied to the first distillation column 2 from outside can be reduced.

[0031] In the second embodiment, at least a portion of the methanol vapor is condensed in the second reboiler 5b, making it possible to provide the absorbing liquid with heat equivalent to the latent heat of condensation. As a result, the line 13 functions as a heat pump, thereby reducing the energy consumption of the entire carbon dioxide recovery system 1. To further enhance this effect, the inside of the second distillation column 20 may be pressurized. To pressurize the inside of the second distillation column 20, for example, a pump may be provided on the crude methanol supply line 16 to increase the pressure of the crude methanol supplied to the second distillation column 20.

[0032] (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 different from embodiment 2 in that a compressor that compresses methanol vapor supplied from second distillation column 20 to second reboiler 5b is added to line 13. In embodiment 3, the same components as those in embodiment 2 are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0033] <Configuration of carbon dioxide capture system according to embodiment 3 of the present disclosure> 3, in the carbon dioxide capture system 1 according to the third embodiment, a compressor 14 is provided in the line 13 between the second distillation column 20 and the second reboiler 5b, and a control valve 15 for adjusting the pressure is provided between the second reboiler 5b and the condenser 12. The other configurations are the same as those of the second embodiment. This compressor 14 is used to pressurize the methanol vapor supplied from the second distillation column 20 toward the second reboiler 5b, instead of pressurizing the interior of the second distillation column 20 in the second embodiment.

[0034] <Operation of the carbon dioxide capture system according to the third embodiment of the present disclosure> Next, the operation of the carbon dioxide capture system 1 according to the third embodiment of the present disclosure will be described. The third embodiment differs from the second embodiment in the operation of heat exchange between the absorption liquid and the methanol vapor in the second reboiler 5b. Only the operation different from the second embodiment will be described below.

[0035] Methanol vapor flowing from the top of the second distillation column 20 and circulating through line 13 is compressed by compressor 14. Compression by compressor 14 increases the temperature of the methanol vapor. The methanol vapor compressed by compressor 14 exchanges heat with the absorption liquid in second reboiler 5b, lowering its temperature. Depending on the temperature, at least a portion of the methanol may condense. The methanol vapor that has exchanged heat with the absorption liquid in second reboiler 5b flows through line 13 either as methanol vapor or containing at least liquid methanol. In condenser 12, the methanol vapor is cooled by cooler 12a and then flows into reflux tank 12b. A portion of the condensate (liquid methanol) in reflux tank 12b is returned to second distillation column 20 via return line 12c, while the remaining condensate is supplied via methanol supply line 12d to a device (not shown) for consuming or storing methanol.

[0036] When the methanol vapor circulating through line 13 is used as the heat medium, the heat medium can be heated by compressing it, and heat exchange in second reboiler 5b can provide the absorbing liquid with heat equivalent to the latent heat of condensation. As a result, line 13 and the equipment attached to line 13 function as a heat pump, thereby reducing the energy consumption of the entire carbon dioxide recovery system 1.

[0037] In this way, in the first reboiler 5a, the absorption liquid is heated by heat exchange between steam and the absorption liquid, and in the second reboiler 5b, the fluid supplied from the second distillation column 20 is compressed and then heat exchanged with the absorption liquid to heat the absorption liquid. Therefore, the amount of steam used in the first reboiler 5a is reduced, and the amount of heat supplied to the first distillation column 2 from outside can be reduced.

[0038] (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 a modification of Embodiment 2 or 3, in which the heat of crude methanol produced in the methanol production apparatus 30 is utilized in the second reboiler 5b. In the following description, Embodiment 4 is configured as a configuration in which the above-described modifications are made to Embodiment 3, but it may also be configured as a configuration in which the above-described modifications are made to Embodiment 2. In Embodiment 4, the same components as those in Embodiment 3 are designated by the same reference numerals, and detailed description thereof will be omitted.

[0039] <Configuration of carbon dioxide capture system according to embodiment 4 of the present disclosure> As shown in Fig. 4, in the carbon dioxide recovery system 1 according to the fourth embodiment, a heat exchanger 32 for removing heat generated during methanol synthesis is provided in the methanol production apparatus 30. The heat exchanger 32 is configured to exchange heat between the heat generated during methanol synthesis and methanol supplied from a methanol purification apparatus 40 composed of a condenser 12 and a second distillation column 20 (including a reboiler 11). There are no particular limitations on where in the methanol purification apparatus 40 the methanol is supplied from. However, as a specific example, in the fourth embodiment, a branch line 31 branching from the methanol supply line 12d passes through the heat exchanger 32 and is connected to the line 13 between the second distillation column 20 and the compressor 14. The other configurations are the same as those of the third embodiment.

[0040] <Operation of the carbon dioxide capture system according to the fourth embodiment of the present disclosure> Next, the operation of the carbon dioxide capture system 1 according to the fourth embodiment of the present disclosure will be described. The fourth embodiment differs from the third embodiment in a part of the operation of heat exchange between the absorption liquid and the methanol vapor in the second reboiler 5b. Only the operation different from the third embodiment will be described below.

[0041] Crude methanol produced in the methanol production system 30 is cooled in the heat exchanger 32 by heat exchange with methanol supplied from the methanol purification system 40. Meanwhile, the temperature of the methanol increases and it turns into methanol vapor. The methanol vapor flows into the line 13 between the second distillation column 20 and the compressor 14 and is combined with the methanol vapor flowing through the line 13 from the second distillation column 20 toward the second reboiler 5b. As in the third embodiment, the combined methanol vapor is further heated by being compressed in the compressor 14 and then undergoes heat exchange with the absorption liquid in the second reboiler 5b. The subsequent operation is the same as in the third embodiment.

[0042] In this way, the methanol vapor heated in the heat exchanger 32 is supplied to the second reboiler 5b together with the methanol vapor supplied from the second distillation column 20, thereby further reducing the amount of steam used in the first reboiler 5a and further reducing the amount of heat supplied from outside to the first distillation column 5a.

[0043] <Modifications of the carbon dioxide capture system according to each embodiment> In the second to fourth embodiments, the second distillation column 20 is a distillation column for rectifying methanol in a methanol production plant. However, the present invention is not limited to such a distillation column and may be a methanol-derived product production system, such as a system for producing dimethyl carbonate from carbon dioxide and methanol, a system for producing olefins from methanol (MTO), or a system for producing gasoline from methanol (MTG). Furthermore, the methanol is not limited to that produced in the plant (product or intermediate), and may be procured from an external source. In this case, instead of the second distillation column 20, which is a distillation column, methanol is supplied from, for example, a methanol storage facility and a methanol heating system. Furthermore, in the second to fourth embodiments, the second distillation column 20 is a single distillation column. However, the second distillation column 20 may be composed of two or more distillation columns, or may be composed of one or more distillation columns combined with a system other than a distillation column.

[0044] In the second to fourth embodiments, the fluid used as the heat source in the second reboiler 5b is methanol vapor, but this is not limited to methanol. Water, or a hydrocarbon or hydrocarbon containing oxygen atoms having a saturation temperature of 100°C or less at atmospheric pressure and 120°C or less at 10 atmospheres or less may also be used as the fluid. Furthermore, the fluid is not limited to pure substances such as these, and may contain such substances as a part of the fluid. Examples of such substances include ethanol, acetone, 2-propanol, hexane, and mixtures thereof.

[0045] In the second to fourth embodiments, the first reboiler 5a and the second reboiler 5b are provided in parallel with each other in the flow direction of the absorption liquid, but the present invention is not limited to these embodiments. The first reboiler 5a and the second reboiler 5b may also be provided in series with each other.

[0046] In the present disclosure, no particular mention is made of the configuration of the apparatus 10 that uses a gas that mainly contains carbon dioxide and hydrogen. However, the apparatus is not particularly limited as long as it uses such a gas, and in the cases of embodiments 2 to 4, the apparatus 10 may be a methanol production apparatus 30.

[0047] The contents described in each of the above embodiments can be understood, for example, as follows.

[0048] [1] A carbon dioxide capture system according to one aspect includes: a first distillation column (2) for heating an absorption liquid that has absorbed carbon dioxide to strip the carbon dioxide from the absorption liquid; a first reboiler (5a) for exchanging heat between the absorption liquid discharged from the first distillation column (2) and steam; a hydrogen supply unit (8) that supplies hydrogen to the absorption liquid in the first reboiler (5a) or to the absorption liquid that has flowed out of the first reboiler (5a); Equipped with.

[0049] According to the carbon dioxide recovery system of the present disclosure, by supplying hydrogen to the absorption liquid in the first reboiler or to the absorption liquid that has flowed out of the first reboiler, the hydrogen and the absorption liquid are returned in a mixed state to the first distillation column. In this way, a gas that is a good mixture of hydrogen and water vapor evaporated from the absorption liquid rises inside the first distillation column, and the absorption liquid that has absorbed carbon dioxide can efficiently come into gas-liquid contact with not only water vapor but also hydrogen. Furthermore, because hydrogen is supplied to the absorption liquid that is being heated in the first reboiler or the absorption liquid that has been heated in the first reboiler, the risk of water vapor condensing can be reduced by controlling the temperature in the first reboiler.

[0050] [2] A carbon dioxide capture system according to another aspect is the carbon dioxide capture system of [1], a second distillation column (20) different from the first distillation column (2); a second reboiler (5b) for exchanging heat between the absorption liquid withdrawn from the first distillation column (2) and a fluid supplied from the second distillation column (20); Equipped with.

[0051] According to this configuration, in the first reboiler, the absorption liquid is heated by heat exchange between steam and the absorption liquid, and in the second reboiler, the absorption liquid is heated by heat exchange between the fluid supplied from the second distillation column and the absorption liquid, so that the amount of steam used in the first reboiler is reduced and the amount of heat supplied from outside to the first distillation column can be reduced.

[0052] [3] A carbon dioxide capture system according to yet another embodiment is the carbon dioxide capture system according to [2], A compressor (14) is provided to compress the fluid before it enters the second reboiler (5b).

[0053] According to this configuration, in the first reboiler, the absorption liquid is heated by heat exchange between steam and the absorption liquid, and in the second reboiler, the fluid supplied from the second distillation column is compressed and then heat exchanged with the absorption liquid to heat the absorption liquid. This reduces the amount of steam used in the first reboiler and makes it possible to reduce the amount of heat supplied from outside to the first distillation column.

[0054] [4] A carbon dioxide capture system according to yet another embodiment is the carbon dioxide capture system according to [3], The fluid includes water, or a hydrocarbon having physical properties such that the saturation temperature is 100° C. or less at atmospheric pressure and 120° C. or less at 10 atmospheres or less, or a hydrocarbon containing oxygen atoms.

[0055] [5] A carbon dioxide capture system according to yet another embodiment is any one of the carbon dioxide capture systems [2] to [4], a methanol production unit (30) for producing crude methanol to be supplied to the second distillation column (20), The fluid is methanol vapor.

[0056] With this configuration, in the first reboiler, the absorption liquid is heated by heat exchange between the steam and the absorption liquid, and in the second reboiler, the absorption liquid is heated by heat exchange between the methanol vapor supplied from the second distillation column and the absorption liquid. This reduces the amount of steam used in the first reboiler and the amount of heat supplied from outside to the first distillation column.

[0057] [6] A carbon dioxide capture system according to yet another embodiment is the carbon dioxide capture system according to [5], a heat exchanger (32) for exchanging heat between the crude methanol produced in the methanol production apparatus (30) and methanol supplied from a methanol purification apparatus (40) including the second distillation column (20) and purifying the crude methanol; The methanol vapor produced by heat exchange between the crude methanol and the methanol in the heat exchanger (32) is combined with the methanol vapor supplied from the second distillation column (20).

[0058] With this configuration, the methanol vapor heated in the heat exchanger is supplied to the second reboiler together with the methanol vapor supplied from the second distillation column, thereby further reducing the amount of steam used in the first reboiler and the amount of heat supplied from outside to the first distillation column. [Explanation of symbols]

[0059] 1. Carbon dioxide capture system 2. First distillation tower 5a No. 1 reboiler 5b Second reboiler 8 Hydrogen supply unit 14 Compressor 20 Second distillation tower 30 Methanol production equipment 32 Heat exchanger 40 Methanol Purification Unit

Claims

1. a first distillation column for heating an absorption liquid that has absorbed carbon dioxide to strip carbon dioxide from the absorption liquid; a circulation line for circulating the absorption liquid so that the absorption liquid in the first distillation column is extracted from the first distillation column and returned to the first distillation column; a first reboiler provided in the circulation line for exchanging heat between the absorption liquid extracted from the first distillation column and steam; a hydrogen supply unit that supplies hydrogen to the absorption liquid in the first reboiler or the absorption liquid that has flowed out of the first reboiler; Equipped with a mixed fluid of the absorption liquid that has been heat exchanged with the steam in the first reboiler and hydrogen, or a mixed fluid of the absorption liquid that has been heat exchanged with the steam in the first reboiler and hydrogen that has been supplied to the absorption liquid that has flowed out of the first reboiler, is returned to the first distillation column.

2. a second distillation column different from the first distillation column; a second reboiler for exchanging heat between the absorption liquid extracted from the first distillation column and a fluid supplied from the second distillation column; The carbon dioxide capture system of claim 1 , comprising:

3. 3. The carbon dioxide capture system of claim 2, further comprising a compressor that compresses the fluid before it enters the second reboiler.

4. 4. The carbon dioxide recovery system according to claim 3, wherein the fluid comprises water, or a hydrocarbon having physical properties such that the saturation temperature is 100°C or less at atmospheric pressure and 120°C or less at 10 atmospheres or less, or a hydrocarbon containing oxygen atoms.

5. a methanol production unit for producing crude methanol to be supplied to the second distillation column, The carbon dioxide recovery system according to any one of claims 2 to 4, wherein the fluid is methanol vapor.

6. a heat exchanger that exchanges heat between the crude methanol produced in the methanol production apparatus and methanol supplied from a methanol purification apparatus that includes the second distillation column and purifies the crude methanol, 6. The carbon dioxide recovery system according to claim 5, wherein the methanol vapor produced by heat exchange between the crude methanol and the methanol in the heat exchanger is combined with the methanol vapor supplied from the second distillation column.

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