Co2 separation system and co2 separation method

Abstract

In this CO2 separation system, CO2 gas is separated from exhaust gas or atmospheric gas by a CO2 separation device. Impurities are removed, by an impurity removal device, from the CO2 gas separated by the CO2 separation device, the CO2 gas is compressed by a compression device, and then a dehydration treatment is performed by a dehydration device. In the dehydration device, a dehydrating agent is brought into contact with the CO2 gas compressed by the compression device in a water absorption tower, whereby at least a portion of the moisture included in the CO2 gas is absorbed by the dehydrating agent. The moisture absorbed by the dehydrating agent and CO2 gas remaining in the dehydrating agent are evaporated, from the dehydrating agent having absorbed the moisture, as evaporation gas in an evaporation unit. The evaporation gas is returned to the upstream side, relative to the impurity removal device, of the flow of CO2 gas from the CO2 separation device to the impurity removal device.

Description

CO₂ separation system and CO₂ separation method

[0001] The present disclosure relates to a CO₂ separation system and a CO₂ separation method. The present application claims priority based on Japanese Patent Application No. 2025-043140 filed with the Japan Patent Office on March 18, 2025, the content of which is incorporated herein by reference.

[0002] CO₂ separation systems for separating CO₂ gas from exhaust gas discharged from industrial equipment such as boilers and gas turbines, or from atmospheric air taken in from the atmosphere are known. Patent Document 1 discloses a technology related to a dehydration apparatus for performing dehydration treatment on a process gas obtained by compressing moisture-containing CO₂ gas separated from exhaust gas discharged from industrial equipment with a compression apparatus in this type of CO₂ separation system.

[0003] Japanese Patent No. 7250957

[0004] In the dehydration apparatus disclosed in the above-mentioned Patent Document 1, dehydration treatment is performed by bringing a dehydrating agent into contact with the process gas, so that moisture contained in CO₂ gas is absorbed by the dehydrating agent. The moisture absorbed by the dehydrating agent becomes evaporated gas by evaporating the dehydrating agent that has absorbed moisture in an evaporation unit (flash tank). In the above-mentioned Patent Document 1, by returning this moisture-containing evaporated gas to the upstream side of the compression apparatus, the evaporated gas is supplied again to the dehydration apparatus together with the process gas, thereby improving dehydration performance.

[0005] In such a configuration, the gas generated in the evaporation unit contains a considerable amount of the dehydrating agent in addition to the moisture contained in the dehydrating agent. If the evaporated gas containing such a dehydrating agent is returned to the upstream side of the compression apparatus as in the above-mentioned Patent Document 1, the dehydrating agent contained in the evaporated gas may cause deterioration of the compression apparatus.

[0006] At least one embodiment of the present disclosure has been made in view of the above circumstances, and an object thereof is to provide a CO₂ separation system and a CO₂ separation method capable of preventing deterioration of a compression apparatus due to evaporated gas containing a dehydrating agent.

[0007] A CO2 separation system according to at least one embodiment of the present disclosure, in order to solve the above problems, comprises: a CO2 separation device for separating CO2 gas from exhaust gas or atmospheric gas; an impurity removal device for removing impurities from the CO2 gas separated by the CO2 separation device; a compression device for compressing the CO2 gas from which the impurities have been removed by the impurity removal device; and a dehydration device for performing a dehydration treatment on the CO2 gas compressed by the compression device, wherein the dehydration device includes: a water absorption tower for bringing a dehydrating agent into contact with the CO2 gas compressed by the compression device to allow at least a portion of the water contained in the CO2 gas to be absorbed by the dehydrating agent; an evaporation section for evaporating the water absorbed by the dehydrating agent and the CO2 gas remaining in the dehydrating agent as an evaporated gas from the dehydrating agent that has absorbed the water in the water absorption tower; and a return line for returning the evaporated gas to the upstream side of the impurity removal device in the flow of the CO2 gas from the CO2 separation device to the impurity removal device.

[0008] A CO2 separation method according to at least one embodiment of the present disclosure, in order to solve the above problems, is a CO2 separation method using a CO2 separation system comprising: a CO2 separation device for separating CO2 gas from exhaust gas or atmospheric gas; an impurity removal device for removing impurities from the CO2 gas separated by the CO2 separation device; a compression device for compressing the CO2 gas from which the impurities have been removed by the impurity removal device; and a dehydration device for performing dehydration treatment on the CO2 gas compressed by the compression device, wherein the dehydration device comprises the steps of: bringing a dehydrating agent into contact with the CO2 gas compressed by the compression device so that at least a portion of the water contained in the CO2 gas is absorbed by the dehydrating agent; evaporating the water absorbed by the dehydrating agent and the CO2 gas remaining in the dehydrating agent as an evaporated gas from the dehydrating agent that has absorbed the water; and returning the evaporated gas to the upstream side of the impurity removal device in the flow of the CO2 gas from the CO2 separation device to the impurity removal device.

[0009] According to at least one embodiment of this disclosure, a CO2 separation system and a CO2 separation method can be provided that can prevent deterioration of a compressor by using an evaporated gas containing a dehydrating agent.

[0010] This is a schematic diagram of a CO2 separation system according to at least one embodiment of the present disclosure. This is a schematic diagram of the dewatering apparatus shown in Figure 1.

[0011] Hereinafter, several embodiments of the present invention will be described with reference to the attached drawings. However, the dimensions, materials, shapes, relative arrangements, etc., of the configurations described as embodiments or shown in the drawings are not intended to limit the scope of the present invention, but are merely illustrative examples.

[0012] Figure 1 is a schematic diagram of a CO2 separation system 1 according to at least one embodiment of the present disclosure. The CO2 separation system 1 is a system for separating CO2 gas from exhaust gas discharged from industrial equipment such as boilers and gas turbines, or from atmospheric gas taken in from the atmosphere. The CO2 separation system 1 comprises a CO2 separation device 2, an impurity removal device 4, a compression device 6, and a dewatering device 8.

[0013] CO2 separation device 2 is a device for separating CO2 gas from exhaust gas or atmospheric gas, and comprises a cooling tower 10, a CO2 absorption tower 12, and an absorbent liquid regeneration tower 14. The exhaust gas or atmospheric gas supplied to the CO2 separation system 1 is first introduced into the cooling tower 10. In the cooling tower 10, the exhaust gas or atmospheric gas is cooled by heat exchange with cooling water. The cooling water, which has been heated by heat exchange with the exhaust gas or atmospheric gas in the cooling tower 10, is guided from the bottom of the cooling tower 10 by a pump 16 through a cooling water line 18 to a cooler 20, where it is cooled and then supplied back to the cooling tower 10.

[0014] The exhaust gas or atmospheric gas cooled in the cooling tower 10 is supplied to the CO2 absorption tower 12 via the supply line L1. In the CO2 absorption tower 12, as the exhaust gas or atmospheric gas passes through the packing material 22, it comes into counter-flow contact with an absorbent liquid (amine solution), for example, an alkanolamine-based liquid. As a result, the CO2 gas contained in the exhaust gas or atmospheric gas is absorbed by the absorbent liquid, and the CO2 gas is removed from the exhaust gas or atmospheric gas. The exhaust gas or atmospheric gas from which the CO2 gas has been removed in the CO2 absorption tower 12 is released outside the system (to the outside) as purified gas via the system discharge line L2 provided at the top 12a of the CO2 absorption tower 12.

[0015] Furthermore, a mist eliminator 24 is provided at the top 12a of the CO2 absorption tower 12 to condense, separate, and remove moisture contained in the purified gas.

[0016] The absorbent liquid that absorbs CO2 gas in the CO2 absorption tower 12 is stored at the bottom 12b of the CO2 absorption tower 12 and transported to the absorbent liquid regeneration tower 14 via the absorbent liquid transport line L3. The absorbent liquid transport line L3 is equipped with a pump 26 for transporting the absorbent liquid. In the absorbent liquid regeneration tower 14, the absorbent liquid supplied via the absorbent liquid transport line L3 is sprayed toward the packing material 28.

[0017] Furthermore, an absorbent liquid transport line L4 is provided between the CO2 absorption tower 12 and the absorbent liquid regeneration tower 14, connecting the bottom 14b of the absorbent liquid regeneration tower 14 to the top of the CO2 absorption tower 12. At the intersection of the absorbent liquid transport line L3 and the absorbent liquid transport line L4, a heat exchanger 30 is provided to exchange heat between the rich solution (absorbent liquid from which CO2 has been absorbed) flowing through the absorbent liquid transport line L3 and the lean solution (absorbent liquid from which CO2 has been removed) flowing through the absorbent liquid transport line L4. In the heat exchanger 30, the rich solution is heated and the lean solution is cooled.

[0018] In the absorbent liquid regeneration tower 14, as the rich solution supplied via the absorbent liquid transport line L3 passes through the packing material 28, the CO2 gas contained in the rich solution is separated by an endothermic reaction due to counterflow contact. By the time the rich solution reaches the bottom 14b of the absorbent liquid regeneration tower 14, most of the CO2 gas has been separated from the rich solution and it is regenerated as a lean solution. The regenerated lean solution is supplied to the CO2 absorption tower 12 by a pump 32 provided in the absorbent liquid transport line L4 and reused. In the absorbent liquid transport line L4, the lean solution is cooled by the aforementioned heat exchanger 30 through heat exchange with the rich solution flowing through the absorbent liquid transport line L3, and further cooled by a water-cooled cooler 34 to a temperature suitable for CO2 gas absorption in the CO2 absorption tower 12.

[0019] The CO2 gas separated from the absorbent liquid in the absorbent liquid regeneration tower 14 is transported to the impurity removal device 4 via the CO2 gas transport line L5 located at the top 14a of the absorbent liquid regeneration tower 14. The impurity removal device 4 is configured to remove impurities contained in the CO2 gas supplied via the CO2 gas transport line L5. For example, the impurity removal device 4 removes the absorbent contained in the CO2 gas as an impurity by washing it, by bringing a washing liquid into gas-liquid contact with the CO2 gas supplied via the CO2 gas transport line L5.

[0020] The CO2 gas from which impurities have been removed by the impurity removal device 4 is transported to the compressor 6 via the CO2 gas transport line L6. The CO2 separation system 1 includes a plurality of compressors 36 as the compressor 6. The plurality of compressors 36 are connected in series with respect to the flow of CO2 gas.

[0021] In the configuration example shown in Figure 1, a dewatering device 8 for removing moisture contained in CO2 gas is installed between adjacent compressors among the multiple compressors 36. Hereinafter, the compressors upstream of the dewatering device 8 will be referred to as "pre-stage compressors," and the compressors downstream of the dewatering device 8 will be referred to as "post-stage compressors." In this embodiment, four compressors 36-1 to 36-4 are installed as the multiple compressors 36, and the dewatering device 8 is connected between compressor 36-2 and compressor 36-3. In this case, compressors 36-1 and 36-2 constitute the pre-stage compressors, and compressors 36-3 and 36-4 constitute the post-stage compressors.

[0022] Furthermore, the number of compressors 36 is not limited to four. Also, the installation location of the dewatering device 8 is not limited to that shown in Figure 1. For example, the dewatering device 8 may be installed between compressor 36-1 and compressor 36-2. Alternatively, the dewatering device 8 may be installed upstream of the compressors 36 (i.e., upstream of compressor 36-1) or downstream of the compressors 36 (i.e., downstream of compressor 36-4).

[0023] Each of the compressors 36-1 to 36-4 is equipped with a cooler 38-1 to 38-4 on its downstream side. The coolers 38-1 to 38-4 are configured to cool the CO2 gas that has been heated by being compressed by the compressors 36-1 to 36-4.

[0024] The upstream compressor 36-1 is connected to the scrubber 40-1 upstream. Scrubber 40-1 removes moisture (mist) contained in the CO2 gas supplied from the impurity removal device 4 via the CO2 gas transport line L6. Scrubbers 40-2 and 40-3 are installed downstream of the coolers 38-1 and 38-2. Scrubbers 40-2 and 40-3 recover moisture (condensed water) produced by condensation in the coolers 38-1 and 38-2. The CO2 gas discharged from scrubber 40-3 is supplied to the dewatering device 8 via the CO2 gas transport line L7.

[0025] The dewatering apparatus 8 is configured to perform dewatering treatment on CO2 gas. The specific configuration of the dewatering apparatus 8 will now be described with reference to Figure 2. Figure 2 is a schematic diagram of the dewatering apparatus 8 shown in Figure 1. The dewatering apparatus 8 comprises a water absorption tower 42, a flux condenser 50, an evaporation section 44, a distillation section 46, and a reboiler 60.

[0026] CO2 gas supplied to the dehydration device 8 via the CO2 gas transport line L7 is first introduced into the water absorption tower 42. The water absorption tower 42 is configured to absorb the moisture contained in the CO2 gas by bringing the dehydrating agent into contact with the moisture-containing CO2 gas. A packing material 45 is housed inside the water absorption tower 42, and the dehydrating agent is sprayed from the top of the packing material 45. The dehydrating agent is a liquid capable of absorbing moisture contained in CO2 gas, such as triethylene glycol (TEG) or diethylene glycol (DEG). As the sprayed dehydrating agent passes through the packing material 45, the CO2 gas and the dehydrating agent are in counterflow contact. As a result, the moisture contained in the CO2 gas is absorbed by the dehydrating agent, but at this time, a portion of the CO2 gas (for example, about 0.2 to 5%) is also absorbed by the dehydrating agent.

[0027] Furthermore, a mist eliminator 47 is installed at the top of the water absorption tower 42. After the water is removed in the water absorption tower 42, the CO2 gas passes through the mist eliminator 47 and is sent to the downstream compressors 36-3 and 36-4 via the CO2 gas transport line L8, where it is compressed. The CO2 gas compressed by the downstream compressors 36-3 and 36-4 is supplied to other equipment (not shown) via the supply line L16.

[0028] Meanwhile, the dehydrating agent that has absorbed moisture in the water absorption tower 42 is transported from the bottom of the water absorption tower 42 by the dehydrating agent transport line L10. The dehydrating agent transported by the dehydrating agent transport line L10 passes through the flux condenser 50 and is sent to the evaporation section 44. As will be described later, high-temperature (for example, about 100 to 200°C) CO2 gas and a gas containing moisture flows through the flux condenser 50, and the dehydrating agent passing through the dehydrating agent transport line L10 is heated by indirect heat exchange with this high-temperature gas. The dehydrating agent heated in the flux condenser 50 is introduced to the upper part of the evaporation section 44 via the dehydrating agent transport line L10.

[0029] The evaporation section 44 is configured to evaporate the water adsorbed on the dehydrating agent and the CO2 gas remaining in the dehydrating agent from the dehydrating agent that has adsorbed water in the water absorption tower 42. The evaporation section 44 is configured as a flash drum that evaporates the water adsorbed on the dehydrating agent and the CO2 gas remaining in the dehydrating agent by reducing the pressure of the dehydrating agent that has adsorbed water in the water absorption tower 42. In the evaporation section 44, an evaporated gas is obtained by flashing (evaporating) the dehydrating agent. This evaporated gas contains most of the CO2 gas (80% to 90%) that was absorbed by the dehydrating agent, as well as a small amount of water and a trace amount of dehydrating agent.

[0030] The evaporated gas obtained in the evaporation section 44 is configured to be returned to the upstream side of the impurity removal device 4 via the return line L9. In this embodiment, as shown in Figure 1, the return line L9 is configured to merge with the CO2 gas transport line L5 that connects the absorption liquid regeneration tower 14 and the impurity removal device 4. As mentioned above, the evaporated gas transported by the return line L9 contains a small amount of dehydrating agent, but by supplying the evaporated gas to the impurity removal device 4 via the return line L9 together with the CO2 gas flowing through the CO2 gas transport line L5, the dehydrating agent contained in the evaporated gas can be removed as an impurity. As a result, the evaporated gas transported by the return line L9 is supplied to the compressor 6 in a clean state from which the dehydrating agent has been removed by the impurity removal device 4, thus effectively preventing the compressor 6 from deteriorating due to the dehydrating agent. Furthermore, as mentioned above, the evaporated gas obtained in the evaporation section 44 contains a relatively large amount of CO2 gas, so instead of discharging it outside the system, it is merged with the CO2 gas flowing through the CO2 gas transport line L5 via the return line L9. Therefore, it is possible to suppress the deterioration of the compressor 6 while increasing the CO2 gas recovery efficiency.

[0031] In Figure 1, the return line L9 is configured to merge with the CO2 gas transport line L5, allowing the evaporated gas from the return line L9 to be supplied to the impurity removal device 4. However, the return line L9 may also be directly connected to the impurity removal device 4, allowing the evaporated gas from the return line L9 to be supplied to the impurity removal device 4.

[0032] After the evaporation gas is obtained in the evaporation section 44, a small amount (10% to 20%) of CO2 gas and moisture remains absorbed in the dehydrating agent and is stored at the bottom of the evaporation section 44. This absorbent is transported to the distillation section 46 via the dehydrating agent transport line L11. A filter 54 is installed in the dehydrating agent transport line L11 to remove solid matter (such as rust) contained in the dehydrating agent before it is transported to the distillation section 46.

[0033] Furthermore, a heat exchanger 56 is installed downstream of the filter 54 in the dehydrating agent transport line L11. In the heat exchanger 56, heat exchange takes place between the dehydrating agent discharged from the filter 54 and the dehydrating agent discharged from the reboiler 60, which will be described later. Through this heat exchange, the dehydrating agent transported in the dehydrating agent transport line L11 is heated to approximately 150°C.

[0034] The distillation section 46 is configured to release any remaining moisture from the dehydrating agent by heating the dehydrating agent conveyed via the dehydrating agent conveying line L11. The dehydrating agent supplied from the dehydrating agent conveying line L11 is heated in the distillation section 46, and any CO2 gas and moisture remaining in the dehydrating agent are released as vent gas. The vent gas passes through the reflux condenser 50 and is supplied to the separator 70 via the vent gas conveying line L12.

[0035] Furthermore, a dehydrating agent removal device 51 is provided at the top 46a of the distillation section 46 for removing the dehydrating agent contained in the vent gas. The dehydrating agent removal device 51 is, for example, a demister for removing the mist-like dehydrating agent contained in the vent gas.

[0036] The separator 70 is configured to separate moisture from the vent gas as condensed water. The condensed water separated by the separator 70 is discharged out of the system via a condensed water discharge line L13 equipped with a pump 72. The vent gas from which the condensed water has been separated by the separator 70 is transported via a vent gas transport line L14.

[0037] As shown in Figure 1, the vent gas transport line L14 is configured to merge with the system-external discharge line L2 located at the top 12a of the CO2 absorption tower 12. The vent gas transported in the vent gas transport line L14 is released outside the system together with the purified gas from the system-external discharge line L2. This makes it possible to configure the CO2 separation system 1 with fewer emission points compared to the case where the purified gas and vent gas are released outside the system separately. Furthermore, the vent gas transported in the vent gas transport line L14 contains a smaller amount of CO2 gas than the evaporated gas transported via the return line L9. Therefore, it is appropriate to release it outside the system by merging it with the system-external discharge line L2 located at the top 12a of the CO2 absorption tower 12, rather than merging it with the CO2 gas flowing through the CO2 gas transport line L5.

[0038] Furthermore, the dehydrating agent, which has released CO2 gas and moisture in the distillation section 46, is transported to the reboiler 60 and heated. The dehydrating agent heated in the reboiler 60 is transported to the water absorption tower 42 via the dehydrating agent transport line L15. The dehydrating agent transport line L15 is equipped with a pump 62 for transporting the dehydrating agent. In addition, the aforementioned heat exchanger 56, located midway along the dehydrating agent transport line L15, performs heat exchange between the dehydrating agent transported along the dehydrating agent transport line L11 and the dehydrating agent transported along the dehydrating agent transport line L15. After heat exchange, the dehydrating agent is cooled in the cooler 64 and then supplied to the water absorption tower 42.

[0039] As described above, according to the above embodiment, the CO2 gas separated from the exhaust gas or atmospheric gas by the CO2 separation device 2 passes through the impurity removal device 4 and the compression device 6 in order, and then undergoes dewatering treatment in the dewatering device 8. In the dewatering device 8, the CO2 gas is brought into contact with a dewatering agent in the water absorption tower 42, and the moisture contained in the CO2 gas is absorbed by the dewatering agent, thereby performing dewatering treatment. The dewatering agent that has absorbed moisture from the CO2 gas is evaporated in the evaporation section 44, generating evaporated gas containing moisture contained in the dewatering agent and CO2 gas remaining in the dewatering agent. This evaporated gas contains a considerable amount of dewatering agent and is returned to the upstream side of the impurity removal device 4 via the return line. As a result, the evaporated gas returned to the upstream side of the impurity removal device 4 via the return line L9 is supplied to the compression device 6 after the dewatering agent contained in the evaporated gas is removed as an impurity in the impurity removal device 4. Therefore, the dewatering agent contained in the evaporated gas is not supplied to the compression device 6, and deterioration of the compression device 6 by the dewatering agent can be effectively prevented.

[0040] Furthermore, it is possible to replace the components in the above-described embodiments with well-known components as appropriate, without departing from the spirit of this disclosure, and the above-described embodiments may also be combined as appropriate.

[0041] The contents described in each of the above embodiments can be understood, for example, as follows:

[0042] (1) A CO2 separation system according to one embodiment comprises: a CO2 separation device for separating CO2 gas from exhaust gas or atmospheric gas; an impurity removal device for removing impurities from the CO2 gas separated by the CO2 separation device; a compression device for compressing the CO2 gas from which the impurities have been removed by the impurity removal device; and a dehydration device for performing a dehydration treatment on the CO2 gas compressed by the compression device, wherein the dehydration device includes: a water absorption tower for bringing a dehydrating agent into contact with the CO2 gas compressed by the compression device to allow at least a portion of the water contained in the CO2 gas to be absorbed by the dehydrating agent; an evaporation section for evaporating the water absorbed by the dehydrating agent and the CO2 gas remaining in the dehydrating agent as an evaporated gas from the dehydrating agent that has absorbed the water in the water absorption tower; and a return line for returning the evaporated gas to the upstream side of the impurity removal device in relation to the flow of the CO2 gas from the CO2 separation device to the impurity removal device.

[0043] According to the embodiment of (1) above, the CO2 gas separated from the exhaust gas or atmospheric gas by the CO2 separation device passes through an impurity removal device and a compression device in sequence, and then undergoes dewatering treatment in a dewatering device. In the dewatering device, the CO2 gas is brought into contact with a dewatering agent in a water absorption tower, and the moisture contained in the CO2 gas is absorbed by the dewatering agent, thereby performing dewatering treatment. The dewatering agent, which has absorbed moisture from the CO2 gas, is evaporated in the evaporation section, generating evaporated gas containing moisture contained in the dewatering agent and CO2 gas remaining in the dewatering agent. This evaporated gas contains a considerable amount of dewatering agent and is returned to the upstream side of the impurity removal device via a return line. As a result, the evaporated gas returned to the upstream side of the impurity removal device via the return line is supplied to the compression device after the dewatering agent contained in the evaporated gas is removed as an impurity in the impurity removal device. Therefore, the dewatering agent contained in the evaporated gas is not supplied to the compression device, and deterioration of the compression device by the dewatering agent can be effectively prevented.

[0044] (2) In another aspect, according to the aspect of (1) above, the dehydration apparatus further comprises: a distillation section configured to heat the dehydrating agent from which the evaporated gas has been evaporated in the evaporation section, so as to release the moisture remaining in the dehydrating agent from the dehydrating agent; and a vent line configured to discharge the vent gas containing moisture released in the distillation section to the outside of the system.

[0045] According to the aspect of (2) above, the dehydrating agent after the evaporated gas is evaporated in the evaporation section is heated in the distillation section, thereby releasing vent gas containing moisture remaining in the dehydrating agent. The vent gas released in the distillation section has a low CO₂ content and can be discharged to the outside of the system through the vent line.

[0046] (3) In another aspect, according to the aspect of (2) above, the CO₂ separation apparatus comprises an absorption tower that separates the CO₂ gas by bringing an absorption liquid into contact with the exhaust gas or the atmospheric air, and discharges the exhaust gas or the atmospheric air from which the CO₂ gas has been separated to the outside of the system as purified gas; and the vent line is configured to introduce the vent gas into the absorption tower and discharge the vent gas to the outside of the system together with the purified gas.

[0047] According to the aspect of (3) above, the vent gas generated in the distillation section is introduced into the absorption tower through the vent line, and is discharged to the outside of the system together with the purified gas discharged from the absorption tower. This can suitably avoid an increase in the number of emission points that discharge gas to the outside of the system.

[0048] (4) In another aspect, according to the aspect of (2) or (3) above, the distillation section comprises a dehydrating agent removal apparatus for removing the dehydrating agent contained in the vent gas.

[0049] According to the aspect of (4) above, the distillation section comprises the dehydrating agent removal apparatus, which removes the dehydrating agent contained in the vent gas, thereby suitably preventing the dehydrating agent from being discharged to the outside of the system.

[0050] (5) In another aspect, according to the aspect of (4) above, the dehydrating agent removal apparatus is a demister for removing mist of the dehydrating agent contained in the vent gas.

[0051] According to the embodiment of (5) above, the distillation section has a demister as a dehydrating agent removal device, which allows for the effective removal of mist-like dehydrating agents contained in the vent gas.

[0052] (6) In other embodiments, in any one embodiment of (1) to (5) above, the return line is configured to merge with a CO2 gas transport line for supplying the CO2 gas separated by the CO2 separation device to the impurity removal device.

[0053] According to the embodiment of (6) above, the return line is configured to merge with the CO2 gas transport line upstream of the impurity removal device. This effectively prevents the supply of evaporated gas containing the dehydrating agent to the compressor downstream of the impurity removal device, as the dehydrating agent contained in the evaporated gas is removed by the impurity removal device.

[0054] (7) In other embodiments, in any one embodiment of (1) to (6) above, the evaporation section is a flash tank that evaporates the water adsorbed on the dehydrating agent and the CO2 gas remaining in the dehydrating agent by reducing the pressure of the dehydrating agent that has absorbed the water in the water absorption tower.

[0055] According to the embodiment of (7) above, in the evaporation section, the dehydrating agent that has absorbed moisture is depressurized (flashed), causing the evaporation gas to evaporate from the dehydrating agent. The evaporation gas thus generated contains a considerable amount of dehydrating agent, but as mentioned above, by returning the evaporation gas to the upstream side of the impurity removal device via the return line, the dehydrating agent contained in the evaporation gas can be suitably removed by the impurity removal device.

[0056] (8) In other embodiments, in any one embodiment of (1) to (7) above, the dehydrating agent is triethylene glycol or diethylene glycol.

[0057] According to the embodiment of (8) above, in a CO2 separation system having a dehydration device that uses triethylene glycol or diethylene glycol as a dehydrating agent, deterioration of the compression device due to the dehydrating agent can be effectively prevented.

[0058] (9) A CO2 separation method according to one embodiment is a CO2 separation method using a CO2 separation system comprising: a CO2 separation device for separating CO2 gas from exhaust gas or atmospheric gas; an impurity removal device for removing impurities from the CO2 gas separated by the CO2 separation device; a compression device for compressing the CO2 gas from which the impurities have been removed by the impurity removal device; and a dehydration device for performing dehydration treatment on the CO2 gas compressed by the compression device, wherein the dehydration device comprises the steps of: bringing a dehydrating agent into contact with the CO2 gas compressed by the compression device so that at least a portion of the water contained in the CO2 gas is absorbed by the dehydrating agent; evaporating the water absorbed by the dehydrating agent and the CO2 gas remaining in the dehydrating agent as an evaporated gas from the dehydrating agent that has absorbed the water; and returning the evaporated gas to the upstream side of the impurity removal device in relation to the flow of the CO2 gas from the CO2 separation device to the impurity removal device.

[0059] According to the embodiment of (9) above, the CO2 gas separated from the exhaust gas or atmospheric gas by the CO2 separation device passes through an impurity removal device and a compression device in sequence, and then undergoes dewatering treatment in a dewatering device. In the dewatering device, the CO2 gas is brought into contact with a dewatering agent in a water absorption tower, and the moisture contained in the CO2 gas is absorbed by the dewatering agent, thereby performing dewatering treatment. The dewatering agent, which has absorbed moisture from the CO2 gas, is evaporated in the evaporation section, generating evaporated gas containing moisture contained in the dewatering agent and CO2 gas remaining in the dewatering agent. This evaporated gas contains a considerable amount of dewatering agent and is returned to the upstream side of the impurity removal device via a return line. As a result, the evaporated gas returned to the upstream side of the impurity removal device via the return line is supplied to the compression device after the dewatering agent contained in the evaporated gas is removed as an impurity in the impurity removal device. Therefore, the dewatering agent contained in the evaporated gas is not supplied to the compression device, and deterioration of the compression device by the dewatering agent can be effectively prevented.

[0060] 1 CO2 separation system 2 CO2 separation device 4 Impurity removal device 6 Compressor 8 Dehydration device 10 Cooling tower 12 CO2 absorption tower 12a Top section 12b Bottom section 14 Absorbent liquid regeneration tower 16 Pump 18 Cooling water line 20 Cooler 22 Packing material 24 Mist eliminator 26 Pump 28 Packing material 30 Heat exchanger 32 Pump 34 Water-cooled cooler 36 (36-1 to 36-4) Compressor 38-1 to 38-4 Cooler 40-1 to 40-3 Scrubber 42 Water absorption tower 44 Evaporation section 45 Packing material 46 Distillation section 47 Mist eliminator 50 Reflux condenser 51 Dehydrating agent removal device 54 Filter 56 Heat exchanger 60 Reboiler 62 Pump 64, Cooler 70, Separator 72, Pump

Claims

1. A CO2 separation system comprising: a CO2 separation device for separating CO2 gas from exhaust gas or atmospheric gas; an impurity removal device for removing impurities from the CO2 gas separated by the CO2 separation device; a compression device for compressing the CO2 gas from which the impurities have been removed by the impurity removal device; and a dehydration device for performing dehydration treatment on the CO2 gas compressed by the compression device, wherein the dehydration device includes: a water absorption tower for bringing a dehydrating agent into contact with the CO2 gas compressed by the compression device to allow at least a portion of the water contained in the CO2 gas to be absorbed by the dehydrating agent; an evaporation section for evaporating the water absorbed by the dehydrating agent and the CO2 gas remaining in the dehydrating agent as an evaporated gas from the dehydrating agent that has absorbed the water in the water absorption tower; and a return line for returning the evaporated gas to the upstream side of the impurity removal device in the flow of the CO2 gas from the CO2 separation device to the impurity removal device.

2. The CO2 separation system according to claim 1, further comprising: a distillation section for releasing the water remaining in the dehydrating agent from the dehydrating agent by heating the dehydrating agent from which the evaporated gas has evaporated in the evaporation section; and a vent line for releasing the vent gas containing the water released in the distillation section to the outside of the system.

3. The CO2 separation system according to claim 2, wherein the CO2 separation device has an absorption tower that separates the CO2 gas by bringing an absorbent liquid into contact with the exhaust gas or the atmospheric gas, and releases the exhaust gas or the atmospheric gas from which the CO2 gas has been separated as a purified gas outside the system, and the vent line is configured to introduce the vent gas into the absorption tower and release it outside the system together with the purified gas.

4. The CO2 separation system according to claim 2, wherein the distillation section has a dehydrating agent removal device for removing the dehydrating agent contained in the vent gas.

5. The CO2 separation system according to claim 4, wherein the dehydrating agent removal device is a demister for removing mist of the dehydrating agent contained in the vent gas.

6. The CO2 separation system according to claim 1 or 2, wherein the return line is configured to merge with a CO2 gas transport line for supplying the CO2 gas separated by the CO2 separation device to the impurity removal device.

7. The CO2 separation system according to claim 1 or 2, wherein the evaporation section is a flash tank that evaporates the water adsorbed on the dehydrating agent and the CO2 gas remaining in the dehydrating agent by reducing the pressure of the dehydrating agent that has absorbed the water in the water absorption tower.

8. The CO2 separation system according to claim 1 or 2, wherein the dehydrating agent is triethylene glycol or diethylene glycol.

9. A CO2 separation method using a CO2 separation system comprising: a CO2 separation device for separating CO2 gas from exhaust gas or atmospheric gas; an impurity removal device for removing impurities from the CO2 gas separated by the CO2 separation device; a compression device for compressing the CO2 gas from which the impurities have been removed by the impurity removal device; and a dehydration device for performing dehydration treatment on the CO2 gas compressed by the compression device, the method comprising: in the dehydration device, a step of bringing a dehydrating agent into contact with the CO2 gas compressed by the compression device so that at least a portion of the water contained in the CO2 gas is absorbed by the dehydrating agent; a step of evaporating the water absorbed by the dehydrating agent and the CO2 gas remaining in the dehydrating agent as an evaporative gas; and a step of returning the evaporative gas upstream of the impurity removal device in the flow of the CO2 gas from the CO2 separation device to the impurity removal device.

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