Carbon dioxide capture system

Abstract

To provide a carbon dioxide recovery system where heat supply amount from outside to a distillation column diffusing carbon dioxide from an absorbent in which carbon dioxide is absorbed is reduced.SOLUTION: A carbon dioxide recovery system comprises: a first distillation column where an absorbent in which carbon dioxide is absorbed is heated and carbon dioxide is diffused from the absorbent; a first reboiler where heat exchanging is performed between the absorbent taken out from the first distillation column and steam; a second reboiler where heat exchanging is performed between the absorbent taken out from the first distillation column and a fluid which is a different kind from either an outflow gas outflowing from the first distillation column or steam; and a first compressor compressing the fluid before flowing the fluid in the second 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 recovery system including an absorption tower that brings a carbon dioxide-containing gas into gas-liquid contact with an absorption liquid to absorb carbon dioxide into the absorption liquid, and a distillation tower that releases carbon dioxide from the absorption liquid that has absorbed carbon dioxide in the absorption tower. The distillation tower is provided with a reboiler for heating the absorption liquid in the distillation tower. Multiple reboilers may be provided. For example, one reboiler may heat the absorption liquid by exchanging heat between steam and the absorption liquid, and another reboiler may heat the absorption liquid by exchanging heat between the absorption liquid and steam compressed by a compressor after flowing out of the distillation tower. With this configuration, heat from not only the steam but also the steam flowing out from the top of the distillation tower and compressed by a compressor is used as a heat source for heating the absorption liquid, thereby reducing the amount of steam used and the amount of heat supplied from outside. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6064771 Summary of the Invention [Problem to be solved by the invention]

[0004] However, carbon dioxide recovery systems are usually installed as part of a manufacturing plant for any substance, a power generation plant, or the like, and it is thought that there may be more appropriate heat sources for heating the absorption liquid in the distillation column. If such appropriate heat sources are used, it is thought that it will be possible to further reduce the amount of heat supplied from outside.

[0005] In view of the above circumstances, at least one embodiment of the present disclosure aims to provide a carbon dioxide recovery system that reduces the amount of heat supplied from the outside to a distillation column that strips carbon dioxide from an absorption liquid that has absorbed carbon dioxide. [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 second distillation column different from the first distillation column, a first reboiler that performs heat exchange between the absorption liquid extracted from the first distillation column and steam, a second reboiler that performs heat exchange between the absorption liquid extracted from the first distillation column and a fluid different from either the effluent gas or the steam that has flowed out from the first distillation column, a first compressor that compresses the fluid before it flows into the second reboiler, and a condensate obtained by cooling the fluid that has undergone heat exchange with the absorption liquid in the second reboiler and returning the condensate to the second distillation column. Suko compressor (12) and the second reboiler and Recording compressor (12) and a control valve disposed between the first distillation column and the second distillation column for controlling the pressure of the fluid, the fluid being supplied from the second distillation column. [Effects of the Invention]

[0007] According to the carbon dioxide recovery system of the present disclosure, in the first reboiler, the absorption liquid is heated by heat exchange between the steam and the absorption liquid, and in the second reboiler, a fluid different from both the effluent gas and the steam flowing out of the first distillation column is compressed and then heat exchanged with the absorption liquid to heat the absorption liquid, thereby reducing the amount of steam used and the amount of heat supplied to the first distillation column from outside. [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> As shown in Fig. 1, a carbon dioxide capture system 1 according to a first embodiment of the present disclosure will be described using a configuration installed in a methanol production plant as an example. The carbon dioxide capture system 1 includes a first distillation column 2 and a second distillation column 10. The first distillation column 2 is in communication with an absorption column (not shown) via an absorption liquid supply line 3, for example, which absorbs carbon dioxide into the absorption liquid by bringing a carbon dioxide-containing gas into gas-liquid contact with the absorption liquid.

[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 includes a first line portion 4a and a second line portion 4b, 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 parallel to each other in the flow direction of the absorption liquid. The first reboiler 5a is a heat exchanger that heats the absorption liquid by heat exchange between the absorption liquid flowing through the first line portion 4a and steam. The second reboiler 5b is a heat exchanger that heats the absorption liquid by heat exchange between the absorption liquid flowing through the second line portion 4b and a fluid other than the steam. Specific examples of fluids in the first embodiment will be described later.

[0012] 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 resulting condensate 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. The cooler 6b can be, for example, a heat exchanger that cools the outlet gas by exchanging heat between the outlet gas and any cooling fluid. In addition to the condensate, gas, mainly carbon dioxide, is present in the reflux tank 6c. The top of the reflux tank 6c may be connected to one end of a line connected to a device that uses carbon dioxide. In the first embodiment, for example, one end of a raw material supply line 7 for supplying carbon dioxide as a raw material to a methanol production plant.

[0013] The configuration of the second distillation column 10 is not particularly limited as long as it is different from the first distillation column 2, but in Embodiment 1, the second distillation column 10 will be described as a distillation column for obtaining a fluid with an increased methanol concentration by rectifying a crude fluid containing methanol as a main component (hereinafter referred to as a "crude methanol fluid") in a methanol production plant. The second distillation column 10 is in communication with a device (not shown) that produces the crude methanol fluid via a crude fluid supply line 16.

[0014] Similar to the first distillation column 2, the second distillation column 10 is provided with a reboiler 11 for heating the crude methanol fluid in the second distillation column 10 and a condenser 12 for condensing the methanol vapor flowing out from the top of the second distillation column 10. The reboiler 11 is, for example, a heat exchanger that exchanges heat between steam and the crude methanol fluid. 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 10 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 10, and a methanol supply line 12d for supplying the remaining liquid methanol in the reflux tank 12b as a product.

[0015] One end of line 13, through which methanol vapor flowing out of second distillation column 10 flows, is connected to the top of second distillation column 10, and the other end of line 13 is connected to reflux tank 12b of condenser 12. Line 13 is provided to pass through second reboiler 5b, i.e., to perform heat exchange 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 1, the aforementioned fluid is the methanol vapor flowing out from the top of second distillation column 10. A first compressor 14 is provided in line 13 between second distillation column 10 and second reboiler 5b, and a control valve 15 for adjusting pressure is provided between second reboiler 5b and condenser 12.

[0016] <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, flows through the circulation line 4, and then returns to the first distillation column 2. When the absorption liquid circulates in this manner, the absorption liquid flowing through each of the first line portion 4a and the second line portion 4b is heated in the first reboiler 5a and the second reboiler 5b, respectively.

[0017] When the temperature of the absorption liquid increases due to heating of the absorption liquid in each of the first reboiler 5a and the second reboiler 5b, the carbon dioxide absorbed in the absorption liquid is stripped from the absorption liquid. The carbon dioxide and other gas components stripped from the absorption liquid rise within the first distillation column 2, exit from the top of the first distillation column 2, and then flow through the outlet gas line 6a as an outlet gas. As the outlet gas flows through the outlet gas line 6a, it is cooled in the cooler 6b. As the outlet gas is cooled and its temperature decreases, components with low boiling points in the outlet gas condense, but most of the carbon dioxide remains in gaseous form. When the cooled outlet gas flows into the reflux tank 6c, it 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 a carbon dioxide consumer (not shown) via the raw material supply line 7. Meanwhile, the liquid component is returned to the first distillation column 2 via the condensate line 6d.

[0018] Meanwhile, the crude methanol fluid that flows into the second distillation column 10 via the crude fluid supply line 16 is heated by the reboiler 11, and its temperature increases. As the temperature of the crude methanol fluid increases, most of the methanol, which has a low boiling point, vaporizes and rises within the second distillation column 10, while most of the components with a high boiling point (mainly water) remain liquid within the second distillation column 10. The vapor, whose main component is methanol (hereinafter referred to as "methanol vapor") that rises within the second distillation column 10 and flows out of the second distillation column 10, flows through line 13.

[0019] Methanol vapor circulating through line 13 is compressed by first compressor 14. Compression by first compressor 14 increases the temperature of the methanol vapor. The methanol vapor compressed by first 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, it 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 10 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.

[0020] 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.

[0021] A simulation was performed on the fluid characteristics and energy consumption of each device in each device and line of the carbon dioxide recovery system 1 under the conditions that the amount of carbon dioxide recovered in the first distillation column 2 was 3 t / day, the amount of methanol supplied as a product from the second distillation column 10 was 2 t / day, and all of the methanol vapor that had exchanged heat with the absorption liquid in the second reboiler 5b was condensed to become liquid methanol.The results of this simulation showed that the amount of steam used in the first reboiler 5a could be reduced by 40 to 50% compared to when the absorption liquid was heated only in the first reboiler 5a.

[0022] In this way, 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 flowing out from the second distillation column 10 is compressed and then heat exchanged with the absorption liquid to heat the absorption liquid, thereby reducing the amount of steam used.

[0023] (Embodiment 2) Next, a carbon dioxide recovery system according to embodiment 2 will be described. The carbon dioxide recovery system according to embodiment 2 is modified from embodiment 1 in that the fluid that has undergone heat exchange with the absorption liquid in second reboiler 5b is used as a cooling fluid for cooling the effluent gas from first distillation column 2 in condenser 6. 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.

[0024] <Configuration of carbon dioxide capture system according to embodiment 2 of the present disclosure> As shown in Fig. 2, in the carbon dioxide capture system 1 according to the second embodiment, the condenser 6 includes a cooler 6e provided on the effluent gas line 6a upstream of the cooler 6b. A bypass line 20 is provided between the second reboiler 5b and the control valve 15, with one end connected to the line 13 and the other end connected to the line 13, between the first compressor 14 and the second distillation column 10. The bypass line 20 is configured to pass through the cooler 6e, i.e., to perform heat exchange in the cooler 6e between the effluent gas flowing through the effluent gas line 6a and the fluid flowing through the bypass line 20. A control valve 21 for adjusting the pressure is provided in the bypass line 20 between the second reboiler 5b and the cooler 6e. The other configurations are the same as those in the first embodiment.

[0025] <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 generating methanol vapor from the crude methanol fluid in the second distillation column 10 are the same as those in the first embodiment. In the second embodiment, the fluid that has undergone heat exchange with the absorption liquid in the second reboiler 5b becomes a methanol vapor or a fluid in which at least a portion of the methanol is condensed, flows through the bypass line 20, and flows into the cooler 6e. This fluid exchanges heat with the outflow gas in the cooler 6e to cool the outflow gas. If this fluid contains at least liquid methanol, the liquid methanol is vaporized by heat exchange with the outflow gas. The methanol vapor flowing out of the cooler 6e flows through the bypass line 20 into the line 13 between the second distillation column 10 and the first compressor 14, where it is mixed with the methanol vapor flowing through the line 13 and compressed by the first compressor 14. The other operations are the same as those in the first embodiment.

[0026] In this way, a portion of the fluid after heat exchange with the absorption liquid in second reboiler 5b is used to cool the effluent gas flowing out from first distillation column 2, thereby improving the thermal efficiency of the entire carbon dioxide recovery system 1. In addition, the cooling fluid after heat exchange with the effluent gas in cooler 6e is mixed with the fluid from the top of second distillation column 10, compressed by first compressor 14, and then supplied to second reboiler 5b, thereby improving the thermal efficiency of the entire carbon dioxide recovery system 1.

[0027] In the same manner as in the first embodiment, in the second embodiment, the recovery amount of carbon dioxide in the first distillation column 2 was set to 3 t / day, the supply amount of methanol as a product from the second distillation column 10 was set to 2 t / day, all of the methanol vapor that exchanged heat with the absorption liquid in the second reboiler 5b was condensed to liquid methanol, and all of the liquid methanol that exchanged heat with the outflow gas in the cooler 6e was vaporized. The results of this simulation showed that the amount of steam used in the first reboiler 5a could be reduced by 80 to 90% compared to when the absorption liquid was heated only by the first reboiler 5a.

[0028] <Modification of the carbon dioxide capture system according to the second embodiment of the present disclosure> In the second embodiment, the condenser 6 includes two coolers 6b and 6e, but may include only the cooler 6e instead of the cooler 6b. The number of coolers 6e is not limited to one, and multiple coolers 6e may be provided in series or in parallel with respect to the flow direction of the outflow gas.

[0029] (Embodiment 3) Next, a carbon dioxide capture system according to embodiment 3 will be described. The carbon dioxide capture system according to embodiment 3 is modified from embodiment 2 by providing a third reboiler 5c in addition to the first reboiler 5a and the second reboiler 5b to heat the absorption liquid. 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.

[0030] <Configuration of carbon dioxide capture system according to embodiment 3 of the present disclosure> As shown in Fig. 3, in the carbon dioxide capture system 1 according to the third embodiment, the circulation line 4 includes a third line portion 4c that is provided in parallel with each of the first line portion 4a and the second line portion 4b. The third line portion 4c is provided with a third reboiler 5c that heats the absorption liquid by heat exchange between the absorption liquid flowing through the third line portion 4c and the second fluid. That is, the third reboiler 5c is provided in parallel with each of the first reboiler 5a and the second reboiler 5b in the flow direction of the absorption liquid. Specific examples of the second fluid in the third embodiment will be described later.

[0031] Unlike Embodiment 2, Embodiment 3 does not include a bypass line 20. Instead, a line 13, one end of which is connected to the top of the second distillation column 10, passes through the second reboiler 5b, then the cooler 6e, and then the third reboiler 5c, with the other end of the line 13 being connected to the reflux tank 12b of the condenser 12. A second compressor 30 is provided on line 13 between the cooler 6e and the third reboiler 5c, and a control valve 31 for adjusting the pressure is provided between the third reboiler 5c and the condenser 12. The other configurations are the same as those of Embodiment 2.

[0032] <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 operation of stripping carbon dioxide from the absorption liquid in the first distillation column 2, the operation of generating methanol vapor from the crude methanol fluid in the second distillation column 10, and the operation of heat exchanging the methanol vapor with the absorption liquid in the second reboiler 5b and with the effluent gas in the cooler 6e are the same as those in the second embodiment. In the third embodiment, the methanol vapor after heat exchange with the effluent gas in the cooler 6e is compressed by the second compressor 30. The temperature of the methanol vapor increases as a result of compression by the second compressor 30. The methanol vapor compressed by the second compressor 30 exchanges heat with the absorption liquid as the second fluid in the third reboiler 5c, and its temperature decreases. The second fluid after heat exchange with the absorption liquid in the third reboiler 5c is supplied to the condenser 12. The operation of the condenser 12 is the same as that in the second embodiment.

[0033] In the same manner as in the second embodiment, the amount of carbon dioxide recovered in the first distillation column 2 was set to 3 t / day, the amount of methanol supplied from the second distillation column 10 was set to 2 t / day, and a simulation was performed on the fluid characteristics in each device and line of the carbon dioxide recovery system 1 and the energy consumption of each device under the following conditions: all methanol vapor that exchanged heat with the absorption liquid in the second reboiler 5b was condensed to liquid methanol, all liquid methanol that exchanged heat with the effluent gas in the cooler 6e was vaporized, and all methanol vapor that exchanged heat with the absorption liquid in the third reboiler 5c was condensed to liquid methanol. The simulation results showed that the amount of steam used in the first reboiler 5a could be reduced by 80 to 90% compared to when the absorption liquid was heated only by the first reboiler 5a.

[0034] (Embodiment 4) Next, a carbon dioxide capture system according to embodiment 4 will be described. The carbon dioxide capture system according to embodiment 4 is modified from embodiment 1 by providing a third reboiler 5c in addition to the first reboiler 5a and second reboiler 5b to heat the absorption liquid. In embodiment 4, the same components as those in embodiment 1 are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0035] <Configuration of carbon dioxide capture system according to embodiment 4 of the present disclosure> As shown in Fig. 4, the carbon dioxide capture system 1 according to the fourth embodiment, like the third embodiment, is equipped with a third reboiler 5c in addition to the first reboiler 5a and the second reboiler 5b to heat the absorption liquid in the first distillation column 2. In the fourth embodiment, one end of an outlet gas line 6a connected to the top of the first distillation column 2 passes through the third reboiler 5c, and the other end of the outlet gas line 6a is connected to a reflux tank 6c of the condenser 6. Two third compressors 40a, 40b are provided in series between the first distillation column 2 and the third reboiler 5c in the outlet gas line 6a, and a heat exchanger 41 is further provided between the third compressors 40a, 40b to cool the outlet gas by heat exchange between the outlet gas and an arbitrary cooling fluid. The other configurations are the same as those of the first embodiment.

[0036] Although not an essential configuration in the fourth embodiment, a condensate withdrawal line 42 may be provided, the condensate withdrawal line 42 having one end connected to the condensate line 6d and the other end connected to a discharge line 4d branched from the circulation line 4, which is a line for discharging the absorption liquid to the outside of the system. In this case, in order to adjust the amount of condensate returned to the first distillation column 2 and the amount of condensate flowing through the condensate withdrawal line 42, control valves 43 and 44 for adjusting the flow rates may be provided in the condensate line 6d and the condensate withdrawal line 42, respectively.

[0037] <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 operation of stripping carbon dioxide from the absorption liquid in the first distillation column 2, the operation of generating methanol vapor from the crude methanol fluid in the second distillation column 10, and the operation of heat exchange between the absorption liquid and the fluid (methanol vapor) in the second reboiler 5b and condensing the fluid that has exchanged heat with the absorption liquid in the condenser 12 are the same as those in the first embodiment. In the fourth embodiment, the effluent gas flowing out from the first distillation column 2 is compressed by each of the third compressors 40a and 40b while its temperature is adjusted by the heat exchanger 41 as it flows through the effluent gas line 6a. The temperature of the effluent gas increases due to compression by each of the third compressors 40a and 40b. The effluent gas compressed by each of the third compressors 40a and 40b exchanges heat with the absorption liquid as the second fluid in the third reboiler 5c. The effluent gas that has exchanged heat with the absorption liquid in the third reboiler 5c is treated in the condenser 6 in the same manner as that described in the first embodiment.

[0038] When a condensate discharge line 42 is provided, a portion of the condensate can be discharged to the outside of the system via the condensate discharge line 42 and the discharge line 4d. Discharging a portion of the condensate to the outside of the system reduces the reflux flow rate of the first distillation column 2. Reducing the reflux flow rate of the first distillation column 2 reduces the reboiler duty of the first distillation column 2. For example, according to a simulation performed by the inventors of the present disclosure, reducing the reflux flow rate of the first distillation column 2 by 50% can reduce the reboiler duty of the first distillation column 2 by 10 to 20%.

[0039] In the same manner as in the first embodiment, in the fourth embodiment, a simulation was performed on the fluid characteristics in each device and line of the carbon dioxide recovery system 1 and the energy consumption of each device under the conditions that the amount of carbon dioxide recovered in the first distillation column 2 was set to 3 t / day, the amount of methanol supplied as a product from the second distillation column 10 was set to 2 t / day, and all of the methanol vapor that had exchanged heat with the absorption liquid in the second reboiler 5b was condensed to liquid methanol. According to the results of this simulation, the amount of steam used in the first reboiler 5a can be reduced by 90 to 100% compared to when the absorption liquid is heated only by the first reboiler 5a.

[0040] <Modification of the carbon dioxide capture system according to the fourth embodiment of the present disclosure> In the fourth embodiment, two third compressors 40a, 40b are provided to compress the outflow gas as the second fluid. However, a configuration in which only one third compressor is provided may also be used. However, by using multiple compressor stages, the compression ratio per stage can be reduced, power consumption can be reduced, and efficiency can be improved. Therefore, the number of third compressors is not limited to two, and three or more third compressors may also be provided. In the fourth embodiment, the heat exchanger 41 is provided between the third compressors 40a, 40b. However, any device capable of cooling the gas flowing out from each compressor may be used. An exemplary alternative may be a pump that sprays liquid into the line through which the gas flowing out from each compressor flows. The gas can be cooled by quenching with the liquid sprayed from such a pump.

[0041] <Modifications of the carbon dioxide capture system according to each embodiment> In the first to fourth embodiments, the second distillation column 10 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 10, which is a distillation column, methanol is supplied from, for example, a methanol storage facility and a methanol heating system. Particularly in the second embodiment, when such a configuration is adopted, the entire amount of methanol after heat exchange with the absorbing liquid in the second reboiler 5b may be used as a cooling fluid for the cooler 6e. The methanol heated by heat exchange with the effluent gas in the cooler 6e may be supplied to the second reboiler 5b again for heat exchange with the absorbing liquid. Furthermore, in embodiments 1 to 4, the second distillation column 10 is a single distillation column, but the second distillation column 10 may be composed of two or more distillation columns, or may be composed of a combination of one or more distillation columns and an apparatus other than a distillation column.

[0042] In the first 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 physical properties in which the saturation temperature is 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.

[0043] In the first to fourth embodiments, the first distillation column 2 and the second distillation column 10 are in the same plant (for example, a methanol production plant), but they may be provided in separate plants.

[0044] In the first and second 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, and in the third and fourth embodiments, the third reboiler 5c is provided in parallel with each of the first reboiler 5a and the second reboiler 5b 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 be provided in series with each other, and the third reboiler 5c may be provided in series with at least one of the first reboiler 5a and the second reboiler 5b.

[0045] In addition, in the first to fourth embodiments and their modifications, the pressure in the second distillation column 10 may be higher than the pressure in the first distillation column 2. In this case, the compression ratio in the first compressor 14 can be reduced, and the amount of energy consumed in the carbon dioxide recovery system 1 as a whole can be reduced.

[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 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 second reboiler (5b) that exchanges heat between the absorption liquid withdrawn from the first distillation column (2) and a fluid different from both the effluent gas flowing out from the first distillation column (2) and the vapor; a first compressor (14) for compressing the fluid before it enters the second reboiler (5b); Equipped with.

[0048] According to the carbon dioxide recovery system of the present disclosure, in the first reboiler, the absorption liquid is heated by heat exchange between the steam and the absorption liquid, and in the second reboiler, a fluid different from both the effluent gas and the steam flowing out of the first distillation column is compressed and then heat exchanged with the absorption liquid to heat the absorption liquid, thereby reducing the amount of steam used and the amount of heat supplied to the first distillation column from outside.

[0049] [2] A carbon dioxide capture system according to another aspect is the carbon dioxide capture system of [1], 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.

[0050] [3] A carbon dioxide capture system according to yet another embodiment is the carbon dioxide capture system according to [1] or [2], The system further includes a second distillation column (10) different from the first distillation column (2), The fluid is supplied from the second distillation column (10).

[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 fluid supplied from the second distillation column is compressed and then heat exchanged with the absorption liquid to heat the absorption liquid, thereby reducing the amount of steam used and the amount of heat supplied to the first distillation column from outside.

[0052] [4] A carbon dioxide capture system according to yet another embodiment is the carbon dioxide capture system according to [3], The pressure in the second distillation column (10) is higher than the pressure in the first distillation column (2).

[0053] With this configuration, the compression ratio of the first compressor can be reduced, and the amount of energy consumed by the entire carbon dioxide capture system can be reduced.

[0054] [5] A carbon dioxide capture system according to yet another embodiment is the carbon dioxide capture system according to [3] or [4], a condenser (6) for cooling the effluent gas flowing out from the first distillation column (2) and returning the condensate obtained to the first distillation column (2), The condenser (6) includes a cooler (6e) that cools the outflow gas by heat exchange between the outflow gas and a cooling fluid, The cooling fluid is at least a portion of the fluid after it has exchanged heat with the absorption liquid in the second reboiler (5b).

[0055] According to this configuration, at least a portion of the fluid after heat exchange with the absorption liquid in the second reboiler is used to cool the effluent gas flowing out from the first distillation column, thereby improving the thermal efficiency of the entire carbon dioxide recovery system.

[0056] [6] A carbon dioxide capture system according to yet another embodiment is the carbon dioxide capture system according to [5], The cooling fluid after heat exchange with the effluent gas in the cooler (6e) is mixed with the fluid from the second distillation column (10) and compressed in the first compressor (14).

[0057] According to this configuration, the cooling fluid after heat exchange with the effluent gas in the cooler is mixed with the fluid from the second distillation column, compressed in the first compressor, and then supplied to the second reboiler, thereby improving the thermal efficiency of the entire carbon dioxide recovery system.

[0058] [7] A carbon dioxide capture system according to yet another embodiment is the carbon dioxide capture system according to [5], The absorption liquid extracted from the first distillation column (2) is subjected to heat exchange with a second fluid. Third a reboiler (5c); a second compressor (30) for compressing the cooling fluid after heat exchange with the outflow gas in the cooler (6e); Equipped with The second fluid is the cooling fluid after being compressed by the second compressor (30).

[0059] According to this configuration, a third reboiler is provided that heats the absorption liquid by exchanging heat between the absorption liquid and a second fluid, which is obtained by compressing the cooling fluid after heat exchange with the outflow gas in the cooler. This reduces the amount of steam used in the first reboiler, thereby making it possible to further reduce the amount of heat supplied from outside to the first distillation column.

[0060] [8] A carbon dioxide capture system according to yet another embodiment is the carbon dioxide capture system according to [1] or [2], a third reboiler (5c) for exchanging heat between the absorption liquid discharged from the first distillation column (2) and a second fluid; a third compressor (40a, 40b) that compresses an effluent gas flowing out from the first distillation column (2) and supplies the compressed gas to the third reboiler (5c) as the second fluid; a condenser (6) for returning at least a portion of the condensate obtained by cooling the second fluid after heat exchange with the absorption liquid in the third reboiler (5c) to the first distillation column (2); Equipped with.

[0061] According to this configuration, the third reboiler is provided, which heats the absorption liquid by exchanging heat between the absorption liquid and a second fluid, which is a gas obtained by compressing the effluent gas flowing out from the first distillation column, and thereby the amount of steam used in the first reboiler can be reduced, and the amount of heat supplied from the outside to the first distillation column can be further reduced. Also, by returning a portion of the condensate to the distillation column and discharging the remaining condensate to the outside of the system together with the waste absorption liquid extracted from the first distillation column, the amount of condensate returned to the first distillation column can be reduced, and the amount of heat supplied from the outside to the first distillation column can be further reduced.

[0062] [9] A carbon dioxide capture system according to yet another embodiment is any one of the carbon dioxide capture systems [1] to [8], The fluid is methanol. [Explanation of symbols]

[0063] 1. Carbon dioxide capture system 2. First distillation tower 5a No. 1 reboiler 5b Second reboiler 5c Third reboiler 6 Condenser Place 6e cooler 10. Second distillation tower 12 Condenser Place 14 First compressor 15 Control valve 30 Second compressor 40a Third compressor 40b Third compressor

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 second distillation column different from the first distillation column; a first reboiler for exchanging heat between the absorption liquid discharged from the first distillation column and steam; a second reboiler that performs heat exchange between the absorption liquid withdrawn from the first distillation column and a fluid different from both the effluent gas flowing out from the first distillation column and the vapor; a first compressor for compressing the fluid before it enters the second reboiler; a condenser (12) for cooling the fluid that has been heat exchanged with the absorption liquid in the second reboiler and returning the condensate obtained to the second distillation column; a control valve provided between the second reboiler and the condenser (12) for adjusting the pressure of the fluid; Equipped with The carbon dioxide capture system, wherein the fluid is supplied from the second distillation column.

2. a condenser (6) for cooling the effluent gas flowing out from the first distillation column and returning the condensate obtained to the first distillation column; The condenser (6) includes a cooler that cools the outflow gas by heat exchange between the outflow gas and a cooling fluid; 2. The carbon dioxide capture system of claim 1, wherein the cooling fluid is at least a portion of the fluid after the fluid has exchanged heat with the absorption liquid in the second reboiler.

3. 3. The carbon dioxide recovery system of claim 2, wherein the cooling fluid after heat exchange with the effluent gas in the cooler is mixed with the fluid from the second distillation column and compressed in the first compressor.

4. a third reboiler for exchanging heat between the absorption liquid withdrawn from the first distillation column and a second fluid; a second compressor for compressing the cooling fluid after heat exchange with the effluent gas in the cooler; Equipped with The carbon dioxide capture system of claim 2 , wherein the second fluid is the cooling fluid after being compressed by the second compressor.

5. a first distillation column for heating an absorption liquid that has absorbed carbon dioxide to strip carbon dioxide from the absorption liquid; a second distillation column different from the first distillation column; a first reboiler for exchanging heat between the absorption liquid discharged from the first distillation column and steam; a second reboiler that performs heat exchange between the absorption liquid withdrawn from the first distillation column and a fluid different from both the effluent gas flowing out from the first distillation column and the vapor; a first compressor for compressing the fluid before it enters the second reboiler; a condenser (6) for cooling the effluent gas flowing out from the first distillation column and returning the condensate obtained to the first distillation column; Equipped with the fluid is supplied from the second distillation column; The condenser (6) includes a cooler that cools the outflow gas by heat exchange between the outflow gas and a cooling fluid; the cooling fluid is at least a portion of the fluid after the fluid has exchanged heat with the absorption liquid in the second reboiler; A carbon dioxide recovery system configured such that the cooling fluid after heat exchange with the effluent gas in the cooler is mixed with the fluid from the second distillation column and compressed in the first compressor.

6. a first distillation column for heating an absorption liquid that has absorbed carbon dioxide to strip carbon dioxide from the absorption liquid; a second distillation column different from the first distillation column; a first reboiler for exchanging heat between the absorption liquid discharged from the first distillation column and steam; a second reboiler that performs heat exchange between the absorption liquid withdrawn from the first distillation column and a fluid different from both the effluent gas flowing out from the first distillation column and the vapor; a first compressor for compressing the fluid before it enters the second reboiler; a condensation device (6) for returning a condensate obtained by cooling the effluent gas flowing out from the first distillation column to the first distillation column, the condensation device (6) including a cooler that cools the effluent gas by heat exchange with a cooling fluid; a third reboiler for exchanging heat between the absorption liquid withdrawn from the first distillation column and a second fluid; a second compressor for compressing the cooling fluid after heat exchange with the effluent gas in the cooler; Equipped with the fluid is supplied from the second distillation column; the cooling fluid is at least a portion of the fluid after the fluid has exchanged heat with the absorption liquid in the second reboiler; A carbon dioxide capture system, wherein the second fluid is the refrigerated fluid after being compressed by the second compressor.

7. The carbon dioxide recovery system according to any one of claims 1 to 6, wherein the fluid comprises water, or a hydrocarbon having physical properties such that a 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.

8. The carbon dioxide recovery system according to any one of claims 1 to 7, wherein the pressure of the second distillation column is higher than the pressure of the first distillation column.

9. a third reboiler for exchanging heat between the absorption liquid withdrawn from the first distillation column and a second fluid; a third compressor that compresses the effluent gas flowing out from the first distillation column and supplies the compressed gas to the third reboiler as the second fluid; a condenser (6) for returning at least a portion of the condensate obtained by cooling the second fluid after heat exchange with the absorption liquid in the third reboiler to the first distillation column; The carbon dioxide capture system of claim 1 , comprising:

10. The carbon dioxide recovery system according to any one of claims 1 to 9, wherein the fluid is methanol.

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