Reboiler and acidic gas recovery system

Abstract

This reboiler comprises a casing which extends in a vertical direction and to which a heating medium capable of raising the temperature of an absorption liquid is supplied, a heat transfer pipe which extends in the vertical direction inside the casing and through which the absorption liquid can flow, and a heat-transfer-promoting body which is disposed inside the heat transfer pipe and generates a turbulent flow in the flowing absorption liquid. The heat transfer pipe has a lower end inlet which is the lower end in the vertical direction and into which the absorption liquid in a liquid-phase state is introduced, and an upper end outlet which is the upper end in the vertical direction and through which the absorption liquid in a gas-liquid two-phase state is discharged. The heat-transfer-promoting body extends in the vertical direction from the lower end inlet upward to a position set apart downward from the upper end outlet.

Description

Reboiler and Acid Gas Recovery System

[0001] This disclosure relates to reboilers and acid gas recovery systems. This application claims priority to U.S. Patent Application No. 18 / 783,524, filed July 25, 2024, the contents of which are incorporated herein by reference.

[0002] In recent years, from the perspective of carbon neutrality, carbon dioxide (CO ２ ) concentration has been attracting attention. From the viewpoint of reducing the concentration of carbon dioxide in the atmosphere, carbon dioxide capture systems that capture carbon dioxide from flue gas are known. In carbon dioxide capture systems, an absorption liquid is circulated between a regeneration tower and an absorption tower to capture carbon dioxide from flue gas.

[0003] For example, Patent Document 1 discloses a carbon dioxide recovery system (CO 2 recovery system) that uses an absorbent that absorbs carbon dioxide to remove carbon dioxide from gas in an absorbent absorption tower and regenerates the absorbent in an absorbent regeneration tower. ２ The document describes an absorbent regeneration tower in which carbon dioxide is absorbed into a rich solution, which is the absorbent, and carbon dioxide is released from the rich solution to regenerate the absorbent. In the absorbent regeneration tower, a portion of the lean solution, which is the absorbent from which carbon dioxide has been released, is supplied to a reboiler. The reboiler exchanges heat between the supplied lean solution and steam to heat the lean solution, and the heated lean solution and steam are supplied into the absorbent regeneration tower.

[0004] Japanese Patent Application Laid-Open No. 2022-180026

[0005] In the carbon dioxide capture system described above, the reboiler heats a multi-component liquid with different boiling points, such as the absorption liquid, which contains amine compounds. The composition ratio of such a multi-component liquid may change from moment to moment depending on the operating conditions of the absorption tower and the regeneration tower. If the composition ratio changes, the boiling point and other flow conditions change when the liquid is heated in the reboiler, making it difficult to heat the liquid under stable conditions. Therefore, it is desirable to improve the heating efficiency of the reboiler even for absorption liquid with a variable composition ratio. At the same time, some kind of disturbance may cause an unstable flow state in the boiling flow within the tube. This unstable flow may cause the flow rate and heating amount to become unstable, potentially resulting in an unstable operating state of the carbon dioxide capture system.

[0006] An object of the present disclosure is to provide a reboiler and an acid gas recovery system that can improve the heating efficiency of an absorption liquid by a reboiler.

[0007] The reboiler according to the present disclosure is a reboiler that heats an absorption liquid containing water and an amine that is supplied from an acidic gas recovery unit, and includes: a casing that extends in a vertical direction and forms an internal heat medium space into which a heat medium capable of heating the absorption liquid is supplied; a heat transfer tube that extends in the vertical direction inside the casing so as to pass through the heat medium space and through which the absorption liquid can flow; and a heat transfer promoter that is disposed inside the heat transfer tube, extends in the vertical direction, and generates turbulence in the flowing absorption liquid, wherein the heat transfer tube has a lower end inlet at its lower end in the vertical direction, through which the absorption liquid in a liquid phase is introduced, and an upper end outlet at its upper end in the vertical direction, through which the absorption liquid in a gas-liquid two-phase state is discharged, and the heat transfer promoter extends upward in the vertical direction from the lower end inlet to a position that is spaced downward from the upper end outlet.

[0008] In addition, the acid gas recovery system according to the present disclosure includes an absorption tower that contacts a gas to be treated containing an acid gas with an absorption liquid containing water and an amine, and discharges the absorption liquid that has absorbed the acid gas and an absorption tower exhaust gas that contains the gas to be treated from which the acid gas has been removed; a regeneration tower that strips the acid gas from the absorption liquid discharged from the absorption tower, and discharges the absorption liquid from which the acid gas has been stripped and a regeneration tower exhaust gas that contains the acid gas; and the reboiler, wherein the absorption liquid in the regeneration tower, which is the acid gas recovery device, is supplied to the reboiler.

[0009] According to the reboiler and acid gas recovery system of the present disclosure, the heating efficiency of the absorption liquid by the reboiler can be improved.

[0010] FIG. 1 is a schematic diagram showing a carbon dioxide recovery system according to the present embodiment. FIG. 2 is a schematic diagram showing the relationship between a regenerator and a reboiler according to the present embodiment. FIG. 3 is a schematic diagram showing a heat transfer tube according to a first embodiment. FIG. 4 is a schematic diagram showing a heat transfer tube according to a second embodiment. FIG. 5 is a schematic diagram showing a heat transfer tube according to a third embodiment. FIG. 6 is a schematic diagram showing a first modified example of a first turbulence structure section. FIG. 7 is a schematic diagram showing a second modified example of a first turbulence structure section. FIG. 8 is a schematic diagram showing a first modified example of a connecting section.

[0011] Hereinafter, an embodiment of an acid gas recovery system according to the present disclosure will be described with reference to the accompanying drawings. However, the present disclosure is not limited to this embodiment.

[0012] First Embodiment (Carbon Dioxide Capture System) A carbon dioxide capture system 1 (acid gas capture system) is a facility that captures acid gas from a gas to be treated from a gas source (not shown). As shown in FIG. 1 , the carbon dioxide capture system 1 of this embodiment separates and captures carbon dioxide contained in the gas to be treated using an absorbent, and is capable of supplying the captured carbon dioxide to another device. Examples of gas sources include waste incinerators, coal- or natural gas-fired power plants, gas turbines, gas engines, cement plants, steel plants, glass melting plants, and ethanol production plants. The gas to be treated from these gas sources contains a gas to be captured, ash, heavy metals, hydrocarbons, and the like. The gas to be captured includes, in addition to carbon dioxide (CO2), nitrogen oxides (NOx) such as nitric oxide (NO), sulfur oxides (SOx) such as sulfur dioxide (SO2), and acid gases such as hydrogen sulfide (HS). In this embodiment, carbon dioxide will be used as an example of the gas to be captured. The gas generation source may also be a facility that is external to the carbon dioxide capture system 1 and sends atmospheric air to the carbon dioxide capture system 1. In other words, the carbon dioxide capture system 1 treats exhaust gases emitted from various facilities and atmospheric air as gases to be treated.

[0013] The absorption liquid preferably has a high absorption rate of acidic gases and low regeneration energy. The absorption liquid contains water and an amine. The absorption liquid is a multi-component aqueous solution containing compounds with different boiling points. For example, when absorbing carbon dioxide, an amine aqueous solution or a non-aqueous amine liquid using a physical absorption solvent instead of water may be used as the absorption liquid. Specific examples of alkanolamines that can be used include monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), methyldiethanolamine (MDEA), diisopropanolamine (DIPA), and diglycolamine (DGA). Hindered amines can also be used. Aqueous solutions of these alone or a mixture of two or more of these can also be used.

[0014] As shown in FIG. 1 , the carbon dioxide recovery system 1 of this embodiment includes an absorption tower 2, a gas line 11 to be treated, a regeneration tower 3, a rich line 13, a lean line 14, an absorbent heat exchanger 4, a regeneration tower discharge line 15, and a reboiler 5.

[0015] The gas to be treated line 11 introduces the gas to be treated into the absorption tower 2. The gas to be treated line 11 cools the gas to be treated sent from the exhaust gas source in a cooling device (not shown) and then sends the cooled gas to the absorption tower 2. The gas to be treated line 11 is connected to the absorption tower 2.

[0016] The absorber discharge line 12 is connected to the top of the absorber 2 and discharges the absorber exhaust gas discharged from the absorber 2 to the outside.

[0017] The regeneration tower 3 strips carbon dioxide from the absorption liquid discharged from the absorption tower 2. The regeneration tower 3 supplies the absorption liquid to the reboiler 5 and heats it. As a result, the regeneration tower 3 strips most of the carbon dioxide from the absorption liquid together with steam, separating the carbon dioxide from the absorption liquid. The regeneration tower 3 separately discharges the absorption liquid from which the carbon dioxide has been stripped and the regeneration tower exhaust gas mainly composed of carbon dioxide.

[0018] The rich line 13 supplies the absorption liquid that has absorbed carbon dioxide from the absorption tower 2 to the regeneration tower 3. Here, the absorption liquid that is discharged from the absorption tower 2 and flows through the rich line 13 is referred to as the rich liquid. The rich liquid is the absorption liquid with a high concentration of carbon dioxide after absorbing carbon dioxide in the absorption tower 2. The rich line 13 connects the bottom of the absorption tower 2 with the top of the regeneration tower 3. A rich pump 35 is arranged in the rich line 13. The rich pump 35 pressurizes the rich liquid and sends it to the regeneration tower 3 via the absorption liquid heat exchanger 4.

[0019] The lean line 14 supplies the absorption liquid from which carbon dioxide has been stripped from the regenerator 3 to the absorber 2. Here, the absorption liquid discharged from the regenerator 3 and flowing through the lean line 14 is referred to as the lean liquid. The lean liquid is the absorption liquid with a low concentration of carbon dioxide after carbon dioxide has been stripped in the regenerator 3. In other words, the lean liquid has a lower concentration of carbon dioxide than the rich liquid. The lean line 14 connects the bottom of the regenerator 3 with the top of the absorber 2. A lean pump 37 is arranged in the lean line 14. The lean pump 37 pressurizes the lean liquid and sends it to the absorber 2 via the absorber heat exchanger 4.

[0020] The absorbent heat exchanger 4 exchanges heat between the rich liquid flowing through the rich line 13 and the lean liquid flowing through the lean line 14. As a result, the absorbent heat exchanger 4 heats the absorbent flowing through the rich line 13 in a state where the pressure has been increased by the rich pump 35 so as to travel from the absorber 2 to the regenerator 3. The absorbent heat exchanger 4 also cools the absorbent flowing through the lean line 14 in a state where the pressure has been increased by the lean pump 37 so as to travel from the regenerator 3 to the absorber 2.

[0021] The regenerator discharge line 15 discharges the regenerator exhaust gas discharged from the regenerator 3 to the outside (outside the system) of the carbon dioxide capture system 1. The regenerator discharge line 15 is connected to the top of the regenerator 3. The regenerator discharge line 15 transfers the regenerator exhaust gas to an external destination depending on the intended use. The regenerator exhaust gas, which is mainly composed of carbon dioxide and discharged from the regenerator discharge line 15, is compressed or liquefied depending on the intended use, and is stored in a tank or transferred via a pipeline to be stored inside an oil field or in an aquifer, etc.

[0022] (Reboiler) The reboiler 5 heats the absorption liquid containing water and amine supplied from the regeneration tower 3, which is an acid gas recovery device. As shown in FIG. 2 , the reboiler 5 is supplied with a portion of the lean liquid stored in the regeneration tower 3 before being discharged. That is, the reboiler 5 is supplied with the absorption liquid containing carbon dioxide in addition to water and amine as the object to be heated. Furthermore, high-temperature steam is supplied to the reboiler 5 from outside the system. The reboiler 5 heats the absorption liquid by performing heat exchange between the supplied steam and the absorption liquid. The reboiler 5 of this embodiment includes a casing 6, a plurality of heat transfer tubes 7, and a plurality of heat transfer promoters 8.

[0023] The casing 6 defines a heat medium space therein, into which a heat medium capable of heating the absorption liquid is supplied. That is, the casing 6 is hollow. The casing 6 extends in the vertical direction Dv. Specifically, the casing 6 is formed in the shape of a cylinder with a bottom extending in the vertical direction Dv. High-temperature steam is supplied to the casing 6 as a heat medium. The casing 6 is formed with an inlet nozzle through which steam flows in and an outlet nozzle through which steam is discharged. The inlet nozzle and the outlet nozzle are arranged at an interval in the vertical direction Dv.

[0024] The plurality of heat transfer tubes 7 are arranged inside the casing 6 so as to pass through the heat medium space. The plurality of heat transfer tubes 7 extend inside the casing 6 in the vertical direction Dv. Each of the plurality of heat transfer tubes is configured so that an absorption liquid can flow therethrough. The absorption liquid is heated by heat exchange between steam flowing through the heat medium space and the absorption liquid flowing inside the plurality of heat transfer tubes 7. The plurality of heat transfer tubes 7 are arranged at intervals in a direction perpendicular to the vertical direction Dv.

[0025] Each heat transfer tube 7 is formed in a hollow cylindrical shape. Each heat transfer tube 7 extends linearly in the vertical direction Dv. As shown in FIG. 3 , each heat transfer tube 7 has a lower end inlet 71 and an upper end outlet 72. The lower end inlet 71 is the lower end of the heat transfer tube 7 in the vertical direction Dv. Liquid-phase absorption liquid is introduced into the lower end inlet 71. The upper end outlet 72 is the upper end of the heat transfer tube 7 in the vertical direction Dv. The upper end outlet 72 is the upper end of the heat transfer tube 7 in the vertical direction Dv. The upper end outlet 72 discharges the gas-liquid two-phase absorption liquid. That is, in the heat transfer tube 7, liquid-phase absorption liquid flows in from the lower end inlet 71, is heated to change state, and the gas-liquid two-phase absorption liquid is discharged from the upper end outlet 72.

[0026] The space inside the heat transfer tube 7 forms a preheating region A1, a bubble flow region A2, and a gas-liquid multiphase flow region A3.

[0027] The preheating zone A1 is a zone in which the absorption liquid can be preheated. Specifically, in the preheating zone A1, the absorption liquid is heated from a liquid state to a state in which no phase change occurs. That is, in the preheating zone A1, the absorption liquid flows in a single phase state consisting of only the liquid phase (single-phase flow). The preheating zone A1 is formed at a position facing the lower-end inlet 71.

[0028] The bubble flow region A2 is a region where bubbles are generated by vaporizing a portion of the absorption liquid. In the bubble flow region A2, a small amount of bubbles is present in the liquid absorption liquid. In other words, in the bubble flow region A2, the liquid phase is in a state where there is little gas phase. The bubble flow region A2 is located above the preheating region A1 in the vertical direction Dv, Dvu. The bubble flow region A2 is connected to the preheating region A1.

[0029] The gas-liquid multiphase flow region A3 is a region where the gas-liquid interface is violently turbulent, generating a flow in which the gas and liquid are mixed together. The gas-liquid multiphase flow region A3 is formed in a position facing the upper-end outlet 72. The gas-liquid multiphase flow region A3 is connected to the bubbly flow region A2. Therefore, the space inside the heat transfer tube 7 is formed, in the vertical direction Dv, with the preheating region A1 in contact with the lower-end inlet 71, the bubbly flow region A2, and the gas-liquid multiphase flow region A3 in contact with the upper-end outlet 72, in that order.

[0030] The heat transfer promoters 8 generate turbulence in the flowing absorption liquid. The heat transfer promoters 8 can change the structure of the flow field of the absorption liquid flowing inside the heat transfer tubes 7 and promote heat transfer. The heat transfer promoters 8 are arranged inside the heat transfer tubes 7. The heat transfer promoters 8 are arranged inside all of the heat transfer tubes 7. The heat transfer promoters 8 extend in the vertical direction Dv. In the vertical direction Dv, the heat transfer promoters 8 extend from the lower end inlet 71 upward Dvu to a position spaced downward Dvd from the upper end outlet 72. In other words, the heat transfer promoters 8 are arranged facing the lower end inlet 71 but spaced apart from the upper end outlet 72. The heat transfer promoters 8A extend so as to be arranged only in the preheating region A1 and the bubbly flow region A2 out of the preheating region A1, the bubbly flow region A2, and the gas-liquid multiphase flow region A3. In other words, the heat transfer promoter 8 is disposed inside the heat transfer tube 7 so as not to be disposed in the gas-liquid multiphase flow region A3. The heat transfer promoter 8 preferably extends to the transition region formed between the bubbly flow region A2 and the gas-liquid multiphase flow region A3. The heat transfer promoter 8 of this embodiment has an axial core portion 81 and a turbulence-forming portion 82.

[0031] The axial core portion 81 is formed in a rod shape extending in the vertical direction Dv. The axial core portion 81 is formed with an axial diameter that does not disturb the flow of the absorption liquid flowing inside the heat transfer tubes 7, 7B. The axial core portion 81 extends straight in the vertical direction Dv. The axial core portion 81 extends from the lower end inlet 71 through the preheating region A1 to the bubble flow region A2.

[0032] The turbulent flow forming portions 82 protrude from the axial core portion 81 toward the inner circumferential surface of the heat transfer tube 7. The turbulent flow forming portions 82 are arranged to fill the space between the outer circumferential surface of the axial core portion 81 and the inner circumferential surface of the heat transfer tube 7. The turbulent flow forming portions 82 are composed of multiple wire-shaped members formed in a spiral pattern and randomly arranged without gaps around the outer circumferential surface of the axial core portion 81. Adjacent turbulent flow forming portions 82 are arranged so that at least a portion of each overlaps each other when viewed from the vertical direction Dv. The multiple turbulent flow forming portions 82 are arranged three-dimensionally so as to be interwoven with each other inside the heat transfer tube 7. The turbulent flow forming portions 82 are arranged from the lower end inlet 71 to the preheating region A1 and the bubbly flow region A2. As a result, the multiple turbulent flow forming portions 82 sufficiently fill the space between the outer circumferential surface of the axial core portion 81 and the inner circumferential surface of the heat transfer tube 7 while forming gaps.

[0033] (Operation and Effect) In the reboiler 5 configured as described above, heat exchange occurs between high-temperature steam supplied to the heat medium space inside the casing 6 and the absorption liquid flowing inside the multiple heat transfer tubes 7, thereby heating the absorption liquid. Inside the heat transfer tubes 7, the absorption liquid flowing in from the lower inlet 71 comes into contact with the heat transfer promoters 8, generating turbulence, and flows toward the upper outlet 72. The heat transfer promoters 8 generate turbulence in the absorption liquid, thereby promoting heat transfer and improving the heating efficiency of the absorption liquid. In particular, the extension of the heat transfer promoters 8 from the lower inlet 71 can increase the pressure loss occurring in the absorption liquid that has just flowed into the heat transfer tubes 7. This allows the absorption liquid flowing in from the lower inlet 71 to be agitated and uniformly supplied toward the upper outlet 72. Furthermore, the heat transfer promoters 8 extend in the vertical direction Dv from the lower inlet 71 to a position Dvd below the upper outlet 72, from which the absorption liquid in a gas-liquid two-phase state is discharged. Large bubbles are present at the upper outlet 72 from which the absorption liquid in a gas-liquid two-phase state is discharged. If the large bubbles come into contact with the heat transfer promoters 8, the increase in heat transfer performance relative to the increase in pressure loss will be small. However, the heat transfer promoters 8 are located away from the upper outlet 72, where the absorption liquid in a gas-liquid two-phase state containing large bubbles is present. As a result, the heat transfer performance can be further improved while suppressing the pressure loss due to the heat transfer promoters 8. This improves the heating efficiency of the absorption liquid by the reboiler 5.

[0034] Furthermore, the heat transfer promoters 8 extend so as to be disposed only in the preheating region A1 and the bubble flow region A2 out of the preheating region A1, the bubble flow region A2, and the gas-liquid multiphase flow region A3. In other words, the heat transfer promoters 8 are not disposed in the gas-liquid multiphase flow region A3, where large bubbles are present and the gas phase ratio is highest, inside the heat transfer tube 7. By disposing the heat transfer promoters 8 so as to avoid the gas-liquid multiphase flow region A3, which has the highest gas phase ratio inside the heat transfer tube 7, it is possible to precisely suppress pressure loss due to the heat transfer promoters 8 while further improving heat transfer performance. This allows for highly accurate improvement in the heating efficiency of the absorption liquid in the reboiler 5.

[0035] Furthermore, the absorption liquid continues to circulate for a long period of time as the carbon dioxide capture system 1 is operated for a long period of time. Therefore, various impurities become mixed into the absorption liquid. As a result, the viscosity of the absorption liquid increases, and the heat transfer performance inside the heat transfer tubes 7 decreases. However, by arranging the heat transfer promoters 8 inside the heat transfer tubes 7 through which the absorption liquid flows, the flow of the absorption liquid inside the heat transfer tubes 7 is disturbed. Therefore, even if a highly viscous absorption liquid is circulated, clogging of the heat transfer tubes 7 can be suppressed. Therefore, the heating efficiency of the absorption liquid by the reboiler 5 can be maintained at a high level for a long period of time.

[0036] In addition, the reboiler 5 heats the lean liquid supplied from the regeneration tower 3. Therefore, the absorption liquid circulating between the regeneration tower 3 and the absorption tower 2 can be efficiently heated to release carbon dioxide.

[0037] Second Embodiment Next, a reboiler 5A according to a second embodiment of the present disclosure will be described. In the second embodiment described below, components common to those of the first embodiment are denoted by the same reference numerals in the drawings, and descriptions thereof will be omitted. In the second embodiment, the reboiler 5A differs from the first embodiment in the structure of the heat transfer enhancement structure 8A.

[0038] In the reboiler 5A of the second embodiment, the heat transfer enhancement structure 8A has a different structure in the vertical direction Dv. Specifically, the heat transfer enhancement structure 8A of the second embodiment has a first turbulence structure 85, a second turbulence structure 86, and a connecting portion 87.

[0039] The first turbulence structure 85 changes the flow of the absorption liquid into a turbulent state. The first turbulence structure 85 has the same structure as the heat transfer enhancement element 8A of the first embodiment except for its length in the vertical direction Dv. The first turbulence structure 85 is disposed facing the lower-end inlet 71.

[0040] The second turbulence structure 86 is formed with a different shape from the first turbulence structure 85 so as to change the flow of the absorption liquid into a turbulent state different from that of the first turbulence structure 85. The second turbulence structure 86 is disposed above the first turbulence structure 85 in the vertical direction Dv, Dvu. The second turbulence structure 86 is disposed with a gap in the vertical direction Dv from the first turbulence structure 85. The second turbulence structure 86 is disposed away from the upper-end outlet 72. The second turbulence structure 86 has a helical plate portion 861 that is twisted helically to generate a swirling flow in the absorption liquid. When viewed from the vertical direction Dv, the helical plate portion 861 describes a spiral with the center of the heat transfer tube 7 as the base point. The helical plate portion 861 is twisted from a downward direction Dvd to an upward direction Dvu in the vertical direction Dv. The spiral plate portion 861 is formed to have a size that allows it to come into sliding contact with the inner circumferential surface of the heat transfer tube 7 .

[0041] The connecting portion 87 connects the first turbulence structure 85 and the second turbulence structure 86 in the vertical direction Dv. The connecting portion 87 is formed in a rod shape extending in the vertical direction Dv. The connecting portion 87 is formed with an axial diameter that does not disturb the flow of the absorption liquid flowing inside the heat transfer tube 7. The connecting portion 87 is formed with the same diameter as the axial core portion 81. In the vertical direction Dv, the lower end of the connecting portion 87 is connected to the upper end of the first turbulence structure 85. In other words, the connecting portion 87 is formed with a structure in which the axial core portion 81 of the first turbulence structure 85 is extended upward Dvu in the vertical direction Dv. In the vertical direction Dv, the upper end of the connecting portion 87 is connected to the lower end of the second turbulence structure 86.

[0042] (Operation and Effect) In the reboiler 5A of the second embodiment, the heat transfer promoter 8A has a first turbulence structure 85 that changes the flow of the absorption liquid to a turbulent state, and a second turbulence structure 86 that is formed with a different shape from the first turbulence structure 85 so as to change the flow of the absorption liquid to a turbulent state different from that of the first turbulence structure 85. The second turbulence structure 86 is disposed above the first turbulence structure 85 in the vertical direction Dvu. Therefore, inside the heat transfer tube 7, the absorption liquid flows so as to be disturbed by the first turbulence structure 85 and then reach the second turbulence structure 86. As a result, the flow is disturbed by the first turbulence structure 85 in a region close to the lower end inlet 71, and the flow is disturbed by the second turbulence structure 86 in a region close to the upper end outlet 72. Therefore, even if the state of the absorption liquid differs between the region close to the lower end inlet 71 and the region close to the upper end outlet 72, a balance between pressure loss and heat transfer performance can be achieved, thereby optimally improving heat transfer performance. This makes it possible to stably improve the heating efficiency of the absorption liquid by the reboiler 5A.

[0043] Furthermore, the second turbulence structure 86 has a helical plate portion 861 that is twisted helically to generate a swirling flow in the absorption liquid. Therefore, a swirling flow can be generated in the absorption liquid near the gas-liquid mixed-phase flow region A3, where large bubbles are present inside the heat transfer tube 7 and the proportion of gas phase is highest. Therefore, the heat transfer performance can be improved while suppressing an increase in pressure loss near the gas-liquid mixed-phase flow region A3 near the upper-end outlet 72. In particular, when the reboiler 5A is operated under high load with a large flow rate of the absorption liquid circulating inside the heat transfer tube 7, the heat transfer performance can be improved more remarkably while suppressing an increase in pressure loss. This can more efficiently improve the heating efficiency of the absorption liquid by the reboiler 5A.

[0044] The first turbulence structure 85 and the second turbulence structure 86 are connected by a rod-shaped connecting portion 87. The rod-shaped connecting portion 87 does not cause any change in the flow of the absorption liquid. Therefore, in the heat transfer enhancer 8A, the connecting portion 87 functionally separates the first turbulence structure 85, which generates turbulence, and the second turbulence structure 86, which generates swirling flow, in the vertical direction Dv. Therefore, different flows of the absorption liquid can be effectively generated in the first turbulence structure 85 and the second turbulence structure 86, respectively. This allows the reboiler 5A to be configured to heat the absorption liquid more efficiently.

[0045] Third Embodiment Next, a reboiler 5B according to a third embodiment of the present disclosure will be described. In the third embodiment described below, components common to the first and second embodiments are denoted by the same reference numerals in the drawings, and descriptions thereof will be omitted. In the third embodiment, the structure of a heat transfer tube 7B is different from that of the first embodiment.

[0046] In the reboiler 5B of the third embodiment, the cross section of the heat transfer tube 7B varies in the vertical direction Dv. The heat transfer tube 7B of the third embodiment is a spiral tube twisted from a lower position Dvd to an upper position Dvu in the vertical direction Dv. The heat transfer tube 7B has a spiral inner circumferential surface formed to generate a swirling flow in the absorption liquid flowing therethrough. As a result, the internal flow path cross section of the heat transfer tube 7B varies in the vertical direction Dv so as to repeatedly increase and decrease.

[0047] (Operation and Effect) In the reboiler 5B of the third embodiment, the heat transfer tubes 7, 7B are formed as spiral tubular members so that the cross section of the heat transfer tube 7B changes in the vertical direction Dv. Therefore, the flow of the absorption liquid can be disturbed not only by the heat transfer promoter 8 but also by the heat transfer tube 7B. This further improves the heating efficiency of the absorption liquid by the reboiler 5B.

[0048] In particular, in this embodiment, the heat transfer tubes 7B are formed in a spiral shape, which allows the inner circumferential surfaces of the heat transfer tubes 7B to generate a swirling flow in the absorption liquid. Therefore, regardless of the structure of the heat transfer promoters 8, it is possible to improve heat transfer performance near the gas-liquid multiphase flow region A3 while suppressing an increase in pressure loss.

[0049] (Other Embodiments) Although the embodiments of the present disclosure have been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and design changes and the like within the scope that does not deviate from the gist of the present disclosure are also included.

[0050] It should be noted that the reboilers 5, 5A, 5B are not limited to a structure in which they are directly connected to the regenerator 3 in the carbon dioxide recovery system 1. For example, the reboilers 5, 5A, 5B may be arranged in an absorption liquid circulation line in which a filtration device that removes impurities from the absorption liquid or a reclaiming device that performs a reclaiming process to remove degraded substances and the like that have accumulated in the absorption liquid at high temperatures is arranged.

[0051] Furthermore, the reboilers 5, 5A, 5B are not limited to being disposed in the carbon dioxide recovery system 1. The reboilers 5, 5A, 5B may also be disposed in a power generation system such as a gas turbine that burns fossil fuel, a cement manufacturing system, an iron and steel manufacturing system, a system for recovering energy from waste, a gas engine system, or a chemical plant.

[0052] The shape of the heat transfer promoters 8, 8A is not limited as long as they are disposed inside the heat transfer tubes 7, 7B and can generate turbulence in the absorbing liquid.

[0053] Furthermore, the heat transfer promoters 8, 8A are not limited to those having an axial core portion 81. The heat transfer promoters 8, 8A may have any structure that generates turbulence. Therefore, the turbulence generating portion 82 and the first turbulence generating portion 85 are not limited to the structures described in the above-described embodiment. For example, as shown in FIG. 6 , the first turbulence generating portion 85A may have a turbulence generating portion 82A that does not have an axial core portion 81 but has a steel wool-like structure in which very fine and flexible iron fibers are randomly arranged. Furthermore, as shown in FIG. 7 , the first turbulence generating portion 85B may have a turbulence generating portion 82B that does not have an axial core portion 81 but has a coil-like structure in which wire-like members are arranged in a spiral.

[0054] Furthermore, the connecting portion 87 is not limited to a structure formed integrally with the axial portion 81 and having the same diameter as that of the second embodiment. The connecting portion 87 may have any structure as long as it connects the first turbulence structure 85 and the second turbulence structure 86. Therefore, as shown in FIG. 8, the connecting portion 87A may have a structure in which the first turbulence structure 85 and the second turbulence structure 86 are fixed together by a rivet 871. Furthermore, as shown in FIG. 9, the connecting portion 87B may have a structure in which the first turbulence structure 85 and the second turbulence structure 86 are fixed together by a wire 872.

[0055] <Additional Notes> The reboilers 5, 5A, 5B and the acid gas recovery system described in each embodiment can be understood, for example, as follows.

[0056] (1) The reboiler 5, 5A, 5B according to the first aspect is a reboiler 5, 5A, 5B that heats an absorption liquid containing water and an amine supplied from an acidic gas recovery unit, and includes a casing 6 that extends in a vertical direction Dv and forms a heat medium space therein to which a heat medium capable of heating the absorption liquid is supplied, heat transfer tubes 7, 7B that extend in the vertical direction Dv inside the casing 6 so as to pass through the heat medium space and through which the absorption liquid can flow, and a heat transfer tube 7, 7B that is disposed inside the heat transfer tubes 7, 7B and that is arranged in the vertical direction Dv. The heat transfer tubes 7, 7B are provided with heat transfer promoters 8, 8A extending in the vertical direction Dv and generating turbulence in the flowing absorption liquid, and the heat transfer tubes 7, 7B have a lower end inlet 71 at the lower end in the vertical direction Dv into which the absorption liquid in a liquid phase is introduced, and an upper end outlet 72 at the upper end in the vertical direction Dv from which the absorption liquid in a gas-liquid two-phase state is discharged, and the heat transfer promoters 8, 8A extend in the vertical direction Dv from the lower end inlet 71 upward Dvu to a position distant downward Dvd from the upper end outlet 72.

[0057] With this configuration, the heat medium supplied to the heat medium space inside the casing 6 exchanges heat with the absorption liquid flowing inside the heat transfer tubes 7, 7B, thereby heating the absorption liquid. Inside the heat transfer tubes 7, 7B, the absorption liquid flowing in from the lower inlet 71 comes into contact with the heat transfer promoters 8, 8A, generating turbulence, and flows toward the upper outlet 72. The heat transfer promoters 8, 8A generate turbulence in the absorption liquid, thereby promoting heat transfer and improving the heating efficiency of the absorption liquid. In particular, the extension of the heat transfer promoters 8, 8A from the lower inlet 71 increases the pressure loss of the absorption liquid that has just flowed into the heat transfer tubes 7, 7B. This allows the absorption liquid flowing in from the lower inlet 71 to be agitated and uniformly supplied toward the upper outlet 72. Furthermore, the heat transfer promoters 8, 8A extend in the vertical direction Dv from the lower inlet 71 to a position Dvd below the upper outlet 72 through which the two-phase gas-liquid absorption liquid is discharged. Large bubbles are present at the upper outlet 72 through which the two-phase gas-liquid absorption liquid is discharged. If the large bubbles come into contact with the heat transfer promoters 8, 8A, the increase in heat transfer performance relative to the increase in pressure loss is reduced. However, the heat transfer promoters 8, 8A are located away from the upper outlet 72 where the two-phase gas-liquid absorption liquid containing large bubbles is present. As a result, heat transfer performance can be further improved while suppressing pressure loss due to the heat transfer promoters 8, 8A. This improves the heating efficiency of the absorption liquid by the reboilers 5, 5A, 5B.

[0058] (2) A reboiler 5, 5A, 5B according to a second aspect is the reboiler 5, 5A, 5B of (1), wherein the internal space of the heat transfer tubes 7, 7B is formed at a position facing the lower end inlet 71 and is configured to form a preheating region A1 in which the absorption liquid can be preheated, a bubbly flow region A2 located Dvu above the preheating region A1 in the vertical direction Dv and in which bubbles are generated by vaporizing a part of the absorption liquid, and a gas-liquid multiphase flow region A3 formed at a position facing the upper end outlet 72 and in which a gas-liquid interface is disturbed and a flow in which gas and liquid are mixed together is generated, and the heat transfer promoters 8, 8A extend so as to be disposed only in the preheating region A1 and the bubbly flow region A2 out of the preheating region A1, the bubbly flow region A2, and the gas-liquid multiphase flow region A3.

[0059] With this configuration, the heat transfer enhancers 8, 8A are not disposed in the gas-liquid multiphase flow region A3, where large bubbles are present and the gas phase ratio is highest, within the heat transfer tubes 7, 7B. By disposing the heat transfer enhancers 8, 8A to avoid the gas-liquid multiphase flow region A3, where the gas phase ratio is highest, within the heat transfer tubes 7, 7B, it is possible to precisely suppress pressure loss due to the heat transfer enhancers 8, 8A while further improving heat transfer performance. This allows for highly accurate improvement in the heating efficiency of the absorption liquid in the reboilers 5, 5A, 5B.

[0060] (3) A reboiler 5A according to a third aspect is the reboiler 5, 5A, 5B of (1) or (2), in which the heat transfer promoter 8A has a first turbulence structure 85 that changes the flow of the absorption liquid to a turbulent state, and a second turbulence structure 86 that is arranged above the first turbulence structure 85 in the vertical direction Dvu and has a shape different from that of the first turbulence structure 85 so as to change the flow of the absorption liquid to a turbulent state different from that of the first turbulence structure 85.

[0061] According to this configuration, inside the heat transfer tubes 7, 7B, the absorption liquid flows so as to reach the second turbulence structure 86 after being turbulent in the first turbulence structure 85. As a result, the flow is turbulent by the first turbulence structure 85 in the region close to the lower end inlet 71, and the flow is turbulent by the second turbulence structure 86 in the region close to the upper end outlet 72. Therefore, even if the state of the absorption liquid differs between the region close to the lower end inlet 71 and the region close to the upper end outlet 72, the pressure loss and heat transfer performance can be balanced, and the heat transfer performance can be improved in an optimal manner. This allows the heating efficiency of the absorption liquid by the reboiler 5A to be stably improved.

[0062] (4) A reboiler 5A according to a fourth aspect is the reboiler 5A of (3), wherein the second turbulent flow structure portion 86 has a spiral plate portion 861 that is twisted spirally so as to generate a swirling flow in the absorption liquid.

[0063] With this configuration, a swirling flow can be generated in the absorption liquid near the large bubbles present inside the heat transfer tubes 7, 7B. Therefore, the heat transfer performance can be improved while suppressing an increase in pressure loss near the upper end outlet 72. This can more efficiently improve the heating efficiency of the absorption liquid by the reboiler 5A.

[0064] (5) A reboiler 5A according to a fifth aspect is the reboiler 5, 5A, 5B of (3) or (4), wherein the heat transfer promoter 8A further has a connecting portion 87 that connects the first turbulence structure portion 85 and the second turbulence structure portion 86 in the vertical direction Dv and extends in the vertical direction Dv.

[0065] With this configuration, the connecting portions 87 are formed in a rod shape, and therefore do not cause any change in the flow of the absorption liquid. Therefore, in the heat transfer promoter 8A, the connecting portions 87 functionally separate the first turbulence structure 85 and the second turbulence structure 86 in the vertical direction Dv. Therefore, different flows of the absorption liquid can be effectively generated in the first turbulence structure 85 and the second turbulence structure 86, respectively. This allows the reboiler 5A to be configured to heat the absorption liquid more efficiently.

[0066] (6) A reboiler 5B according to a sixth aspect is any one of the reboilers 5, 5A, and 5B according to (1) to (5), in which the cross section of the heat transfer tube 7B is different so as to change in the vertical direction Dv.

[0067] With this configuration, the flow of the absorption liquid can be disturbed not only by the heat transfer promoters 8, 8A but also by the heat transfer tube 7B, thereby further improving the heating efficiency of the absorption liquid by the reboiler 5B.

[0068] (7) The acidic gas recovery system according to the seventh aspect includes an absorption tower 2 that contacts a gas to be treated containing an acidic gas with an absorption liquid containing water and an amine, and discharges the absorption liquid that has absorbed the acidic gas and an absorption tower exhaust gas that contains the gas to be treated from which the acidic gas has been removed; a regeneration tower 3 that strips the acidic gas from the absorption liquid discharged from the absorption tower 2, and discharges the absorption liquid from which the acidic gas has been stripped and a regeneration tower exhaust gas that contains the acidic gas; and a reboiler 5, 5A, 5B selected from any one of (1) to (5), and the reboilers 5, 5A, 5B are supplied with the absorption liquid in the regeneration tower 3, which is the acidic gas recovery device.

[0069] According to this configuration, the absorption liquid supplied from the regeneration tower 3 is heated. Therefore, the absorption liquid circulating between the regeneration tower 3 and the absorption tower 2 can be efficiently heated to dissipate acidic gases.

[0070] According to the reboiler and acid gas recovery system of the present disclosure, the heating efficiency of the absorption liquid by the reboiler can be improved.

[0071] DESCRIPTION OF SYMBOLS 1 Carbon dioxide recovery system 2 Absorption tower 11 Gas line to be treated 12 Absorption tower discharge line 3 Regeneration tower 13 Rich line 35 Rich pump 14 Lean line 37 Lean pump 4 Absorbent heat exchanger 15 Regeneration tower discharge line 5, 5A, 5B Reboiler 6 Casing 7, 7B Heat transfer tube A1 Preheating region A2 Bubble flow region A3 Gas-liquid multiphase flow region 71 Lower end inlet 72 Upper end outlet 8, 8A Heat transfer promoter 81 Axial core portion 82 Turbulence forming portion 85, 85A, 85B First turbulence structure portion 86 Second turbulence structure portion 861 Spiral plate portion 87, 87A, 87B Connecting portion Dv Vertical direction Dvu Upward Dvd Downward

Claims

1. A reboiler for heating an absorption liquid containing water and an amine supplied from an acid gas recovery unit, comprising: a casing extending in a vertical direction and forming an internal heat medium space into which a heat medium capable of heating the absorption liquid is supplied; a heat transfer tube extending in the vertical direction inside the casing so as to pass through the heat medium space and through which the absorption liquid can flow; and a heat transfer promoter disposed inside the heat transfer tube, extending in the vertical direction, and generating turbulence in the flowing absorption liquid, wherein the heat transfer tube has a lower end inlet at its lower vertical end, through which the absorption liquid in a liquid phase is introduced, and an upper end outlet at its upper vertical end, through which the absorption liquid in a gas-liquid two-phase state is discharged, and the heat transfer promoter extends upward in the vertical direction from the lower end inlet to a position spaced downward from the upper end outlet.

2. A reboiler as claimed in claim 1, wherein the space inside the heat transfer tube is formed into a preheating region, which is formed at a position facing the lower end inlet and is capable of preheating the absorption liquid, a bubbly flow region, which is located vertically above the preheating region and in which bubbles are generated by vaporizing a portion of the absorption liquid, and a gas-liquid multiphase flow region, which is formed at a position facing the upper end outlet and in which a flow in which the gas-liquid interface is disturbed and gas and liquid are mixed together is generated, and wherein the heat transfer promoter extends so as to be positioned only in the preheating region and the bubbly flow region out of the preheating region, the bubbly flow region and the gas-liquid multiphase flow region.

3. A reboiler as claimed in claim 1 or 2, wherein the heat transfer promoter has a first turbulence structure portion that changes the flow of the absorption liquid into a turbulent state, and a second turbulence structure portion that is arranged vertically above the first turbulence structure portion and is formed in a shape different from that of the first turbulence structure portion so as to change the flow of the absorption liquid into a turbulent state different from that of the first turbulence structure portion.

4. A reboiler according to claim 3, wherein the second turbulent flow structure has a spiral plate portion twisted in a spiral shape to generate a swirling flow in the absorption liquid.

5. A reboiler according to claim 3, wherein the heat transfer promoter further comprises a connecting portion extending in the vertical direction, connecting the first turbulence structure portion and the second turbulence structure portion in the vertical direction.

6. A reboiler according to claim 1 or 2, wherein the cross sections of the heat transfer tubes vary in the vertical direction.

7. An acidic gas recovery system comprising: an absorption tower that brings a gas to be treated containing an acidic gas into contact with an absorption liquid containing water and an amine, and discharges the absorption liquid that has absorbed the acidic gas and an absorption tower exhaust gas that contains the gas to be treated from which the acidic gas has been removed; a regeneration tower that strips the acidic gas from the absorption liquid discharged from the absorption tower, and discharges the absorption liquid from which the acidic gas has been stripped and a regeneration tower exhaust gas that contains the acidic gas; and a reboiler as defined in claim 1 or 2, wherein the reboiler is supplied with the absorption liquid in the regeneration tower, which is the acidic gas recovery device.

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