Carbon dioxide separation / recovery method

Abstract

To provide a carbon dioxide separation / recovery process which adopts SA-VSA using a carbon dioxide solid absorber, and in which an installation space required for plant construction and steam consumption for regeneration are suppressed.SOLUTION: A method for separating and recovering carbon dioxide from a gas mixture alternately executes a capture process in which carbon dioxide in the gas mixture is captured by a carbon dioxide solid absorber, and a desorption process in which the carbon dioxide solid absorber is brought into contact with steam, thereby desorbing the carbon dioxide, and in addition, executes a separation process in which steam is condensed and separated as water from the gas mixture generated in the desorption process, and a circulation process in which water separated in the separation process is converted into steam again and is circulated to the desorption process. According to this method, a pressure difference is provided between a flow of the gas mixture containing the steam generated in the desorption process or the capture process and a flow including water separated in the separation process, thereby performing indirect heat exchange is performed between both fluids.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a method for separating and recovering carbon dioxide from a gas containing carbon dioxide. [Background technology]

[0002] The problem of global warming caused by rising atmospheric carbon dioxide concentrations has long been recognized. Reducing atmospheric carbon dioxide emissions has become an urgent priority. Along with automobile exhaust, two other sources of carbon dioxide emissions into the atmosphere are waste incinerators and flue gas from thermal power plants. Thermal power plants typically generate electricity by burning fossil fuels such as coal, oil, and natural gas to heat water in a boiler, producing high-temperature, high-pressure steam. This steam is then used to drive a steam turbine, which then rotates a generator directly connected to the rotating shaft. In recent years, gas turbine power generation, which uses natural gas as fuel instead of a steam turbine, and combined-cycle power generation, which uses residual heat from the gas turbine's flue gas to generate steam, have also been put into practical use. These efforts have significantly improved the thermal efficiency and reduced the cost of thermal power generation. Furthermore, air pollution prevention technologies for treating flue gas from these power plants, such as dust removal, desulfurization, and denitrification, have already reached a considerable level. However, while there has been active research into reducing carbon dioxide emissions into the atmosphere, as mentioned above, from the perspective of switching from fossil fuels to renewable energy, there has not yet been sufficient research into post-combustion capture of carbon dioxide (PCC).

[0003] Recently, there has been a growing demand not only for the removal of carbon dioxide from combustion exhaust gas, but also for the capture, storage, and reuse of the removed carbon dioxide (CCS or CCUS). Technologies for separating and capturing carbon dioxide using amine absorbents from combustion exhaust gases from coal-fired boilers with a carbon dioxide concentration of 13-14% by volume have already been put into practical use. However, wet carbon dioxide absorption processes using amine absorbents have been problematic in terms of operating costs when used to separate and capture carbon dioxide from sources with low carbon dioxide concentrations, such as natural gas combustion exhaust gas. Therefore, solid carbon dioxide absorbents have been developed as an alternative to aqueous amine solutions, and carbon dioxide separation and capture processes using these absorbents have been investigated. In particular, separation and capture processes using vacuum swing adsorption (SA-VSA), in which low-temperature (below 100°C) steam is introduced to regenerate the solid carbon dioxide absorbent, have been reported to be extremely effective in reducing operating costs (Non-Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 11-147017 [Non-patent literature]

[0005] [Non-Patent Document 1] Chemical Engineering Journal 307 (2017) 273-282 [Non-patent document 2] Ind. Eng. Chem. Res. 2021, 60,9906-9914 Summary of the Invention [Problem to be solved by the invention]

[0006] Carbon dioxide capture processes that have been investigated to date have primarily focused on the separation and capture of carbon dioxide (concentration 13–14% by volume) contained in flue gas from coal-fired boilers. In contrast, flue gas from oil-fired boilers has a carbon dioxide concentration of less than 10% by volume, and flue gas from natural gas-fired boilers and gas turbines has a carbon dioxide concentration of less than 6% by volume (usually 3–4% by volume), which is about half to one-quarter of the carbon dioxide concentration in flue gas from coal-fired boilers. While this contributes to reducing carbon dioxide emissions, capturing carbon dioxide from such low-concentration flue gas requires processing large volumes of gas, which increases the operating cost per unit of carbon dioxide captured. Therefore, to advance the separation and capture of carbon dioxide from flue gas from natural gas-fired gas turbine power plants and combined-cycle power plants, a process that can process large volumes of flue gas and separate and capture carbon dioxide at low operating costs is required.

[0007] As described above, a carbon dioxide separation and capture process employing SA-VSA with a solid carbon dioxide absorbent is an excellent method with low operating costs. However, when attaching this process to an existing thermal power plant (including gas turbine and combined-cycle power plants), for example, there is often limited space available, making it difficult to install a new carbon dioxide separation and capture plant of the scale required to treat all of the flue gas. Furthermore, to reduce construction and operating costs, it is desirable to rely on the thermal power plant's steam supply facility for regeneration steam. However, this requires minimizing steam consumption at the carbon dioxide separation and capture plant. In other words, the present invention aims to provide a space-saving and energy-efficient carbon dioxide separation and capture process employing SA-VSA with a solid carbon dioxide absorbent. [Means for solving the problem]

[0008] The present invention provides a method for separating and recovering carbon dioxide from a gas mixture containing carbon dioxide, which comprises alternately carrying out a capture step of bringing the gas mixture into contact with a solid carbon dioxide absorbent material to capture the carbon dioxide in the gas mixture in the solid carbon dioxide absorbent material, and a desorption step of bringing the solid carbon dioxide absorbent material that has captured carbon dioxide in the capture step into contact with steam to desorb the carbon dioxide captured in the solid carbon dioxide absorbent material, and further carrying out a separation step of condensing steam from the gas mixture containing carbon dioxide and steam generated in the desorption step to separate it as water, and a circulation step of evaporating the water separated in the separation step to convert it back into steam and circulating this to the desorption step for reuse, and which is characterized by creating a pressure difference between a flow of the gas mixture containing carbon dioxide and steam generated in the desorption step and a flow containing water separated in the separation step, thereby performing indirect heat exchange between the two fluids, thereby solving the above-mentioned problems.

[0009] The present invention also provides a method for separating and recovering carbon dioxide from a gas mixture containing carbon dioxide, comprising alternately performing a capture step of bringing the gas mixture into contact with a solid carbon dioxide absorbent to capture the carbon dioxide in the gas mixture in the solid carbon dioxide absorbent, and a desorption step of bringing the solid carbon dioxide absorbent that has captured carbon dioxide in the capture step into contact with steam to desorb the carbon dioxide captured in the solid carbon dioxide absorbent, and further performing a separation step of condensing steam from the gas mixture containing steam generated in the capture step to separate it as water, and a circulation step of evaporating the water separated in the separation step to convert it back into steam and circulating this to the desorption step for reuse, and providing a pressure difference between a flow of the gas mixture containing steam generated in the capture step and a flow containing water separated in the separation step to perform indirect heat exchange between the two fluids, thereby solving the above-mentioned problems. [Effects of the Invention]

[0010] A space-saving and energy-saving carbon dioxide separation and capture method is provided that is suitable for separating and capturing carbon dioxide from gas mixtures containing carbon dioxide, particularly from the combustion exhaust gas of gas turbine power plants and combined cycle power plants that use natural gas as fuel. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional view showing an example of a radial flow type separation device that can be preferably used in the method of the present invention. [Figure 2] FIG. 1 is a conceptual diagram showing an example of a process for removing and recovering carbon dioxide from combustion exhaust gas by applying the method of the present invention. [Figure 3] FIG. 1 is a schematic diagram illustrating an example of the configuration of a carbon dioxide separation and capture plant for carrying out the method of the present invention. [Figure 4] FIG. 4 is a schematic diagram showing an example of a configuration in which a steam recovery mechanism is further added to the configuration of the carbon dioxide separation and recovery plant shown in FIG. 3. [Figure 5] FIG. 4 is a schematic diagram showing another example of a configuration in which a steam recovery mechanism is further added to the configuration of the carbon dioxide separation and recovery plant shown in FIG. 3. DETAILED DESCRIPTION OF THE INVENTION

[0012] The method of the present invention is a method for separating and capturing carbon dioxide from a gas mixture containing carbon dioxide, particularly from combustion exhaust gas under atmospheric pressure. The method of the present invention is a space-saving and energy-saving method particularly suitable for separating and capturing carbon dioxide from combustion exhaust gas of a gas turbine power plant or a combined cycle power plant that uses natural gas as fuel, and has the advantage that it is relatively easy to install a plant for separating and capturing carbon dioxide from combustion exhaust gas, for example, in an existing power plant.

[0013] The method of the present invention utilizes steam-assisted vacuum swing adsorption (SA-VSA) with a solid carbon dioxide absorbent to separate and capture carbon dioxide from a gas mixture containing carbon dioxide, particularly from combustion exhaust gas under atmospheric pressure. Conventionally, the amine absorption method, which uses an aqueous monoethanolamine solution as an absorbent, has been used to remove carbon dioxide from a gas mixture containing carbon dioxide (CO2 concentration of 10% by volume or more). However, when removing carbon dioxide from a gas mixture with a low carbon dioxide concentration (CO2 concentration less than 10% by volume), particularly from the combustion exhaust gas of a natural gas-fueled gas turbine power plant or combined-cycle power plant (CO2 concentration less than 6% by volume), the amine absorption method requires the use of an amine that binds carbon dioxide more tightly. This increases the cost of heating during regeneration and the cost of replacing degraded amines. Therefore, the present invention uses a solid carbon dioxide absorbent that has superior carbon dioxide absorption / desorption properties (especially desorption properties) and, because it does not contain water, does not require the inclusion of the latent heat of vaporization of water in the heating energy required during regeneration.

[0014] A suitable example of such a carbon dioxide solid absorbent is a granular inorganic porous carrier, such as porous silica, prepared by supporting a polyamine compound. Granular porous silica can be obtained, for example, by adding a pore-expanding agent such as trimethylbenzene to an acetic acid-acidic aqueous solution of a hydrophilic polymer (e.g., Sigma-Aldrich P-123) and mixing thoroughly, then adding an aqueous sodium silicate solution and gently mixing at room temperature for 24 hours. The mixture is then left to stand at 100°C for 24 hours, filtered, washed, and the resulting solid is dried at 80°C for 2 days. The resulting dried solid is then calcined in air at 550°C for 4 hours, and the resulting powder is granulated to a particle size of approximately 2 mm. The resulting granular porous silica is dispersed in, for example, methanol, and an appropriate polyamine compound (e.g., tetraethylenepentamine with protected functional groups) is added to the dispersion to impregnate the porous silica with the polyamine compound. The resulting mixture is then dried, yielding a granular porous silica supported with the polyamine compound (see Non-Patent Document 1).

[0015] The removal and recovery of carbon dioxide using SA-VSA is carried out by alternately repeating a capture step in which the gas to be treated, containing carbon dioxide, is brought into contact with a solid carbon dioxide absorbent material under normal pressure to absorb and capture the carbon dioxide contained in the gas, and a desorption step in which the solid carbon dioxide absorbent material that has absorbed carbon dioxide is brought into contact with low-temperature steam under reduced pressure to desorb the carbon dioxide. In SA-VSA, the solid carbon dioxide absorbent is placed under normal pressure during the absorption operation and under reduced pressure during the desorption operation, so these operations are carried out in an airtight container. The gas-solid contact operation between the gas to be treated and the solid carbon dioxide absorbent in the capture step can be carried out in various formats, such as a packed bed, moving bed, or fluidized bed. However, if the concentration of carbon dioxide in the gas to be treated is low and it is desired to achieve almost zero leakage of carbon dioxide into the gas after treatment, a packed bed format with high contact efficiency and little channeling is preferred. On the other hand, the gas-solid contact operation between the steam and the solid carbon dioxide absorbent in the desorption step cannot use a moving bed or fluidized bed because the flow rate of the steam is significantly lower than the flow rate of the gas to be treated, and will be carried out in the same packed bed format as in the capture step.

[0016] The method of the present invention is characterized by its ability to treat a large amount of gas to be treated in the capture step. When the space velocity (GHSV) of the gas to be treated in the capture step is set to about 2000 to 6000 / h, the aspect ratio of the packed bed ([layer thickness] / [cross-sectional area of ​​flow path]) is set to about 1500 mm (average superficial column reference linear velocity in the bed is about 0.5 m / s) in order to reduce the pressure loss associated with the energy required to pressurize the gas to be treated, which is at atmospheric pressure, using a blower or the like. 1 / 2) must be significantly reduced. However, increasing the cross-sectional area of ​​the flow path (i.e., the cross-sectional area of ​​the bed) to reduce the aspect ratio of the packed bed can result in a large installation area (footprint) for a conventional packed bed in which the treated gas flows vertically. This is not a problem if space is available to initially install a carbon dioxide capture and recovery system on a large site. However, when a carbon dioxide capture and recovery system is retrofitted to an existing power plant, the installation area is often limited. In such cases, if the gas flows horizontally through the packed bed (horizontal flow type), the cross-sectional area of ​​the flow path can be expanded vertically without increasing the installation area. Typical horizontal flow packed bed types are the leaf type (parallel flow type) and the tubular type (radial flow type). The leaf type is a type in which the packed bed is arranged as an upright hollow plate, and the fluid passes through the packed bed horizontally and in parallel. On the other hand, the radial flow type is a type in which the packed bed is arranged as an upright circular tube, and the fluid passes horizontally and radially through the packed bed, either from the inside to the outside or from the outside to the inside. In either type, multiple packed beds can be arranged in one large airtight container, or one packed bed can be arranged in one airtight container. When one packed bed is arranged in one airtight container, housing a radial flow type packed bed in a cylindrical airtight container is the most compact and space-saving option. In addition, since the packed bed in the radial flow type is arranged in a tubular shape, it has the advantage of having greater pressure resistance than the leaf type, in which the packed bed is arranged in a flat plate shape. In the present invention, since high-speed treatment (vacuuming) of a large amount of gas to be treated is taken into consideration, it is preferable that the packed bed of the solid carbon dioxide absorbent material is of the radial flow type. As can be seen from the above, the reactor type itself having a radial flow type packed bed is already known (see Patent Document 1).

[0017] On the other hand, in the desorption step of the present invention, in order to desorb carbon dioxide from the solid carbon dioxide absorbent that absorbed carbon dioxide in the capture step, a vacuum is drawn inside the container containing the packed bed to reduce the total pressure to less than 1 atmosphere, and steam is simultaneously introduced and passed through the packed bed. However, in SA-VSA, the primary operation in the desorption step is originally the reduction in pressure by vacuum drawing, and the introduction of steam is merely an auxiliary operation. The technical significance of introducing steam is that when carbon dioxide captured in the solid carbon dioxide absorbent is desorbed by the reduction in pressure, the latent heat of desorption is removed from the solid carbon dioxide absorbent, and this is compensated for by the sensible heat and latent heat of condensation of the steam. In other words, introducing steam in the desorption step is thought to have the effect of preventing excessive cooling of the absorbent when carbon dioxide is simultaneously desorbed from the solid carbon dioxide absorbent (adsorbent) due to the reduction in pressure, thereby maintaining a constant temperature and maintaining continuous desorption, thereby promoting desorption. In this sense, it is preferable that at least a portion of the introduced steam condenses within the packed bed and provides the latent heat of condensation to the packed bed. In the desorption step, the atmosphere in which the packed bed is placed is reduced in pressure below 1 atmosphere, and if the temperature of the steam introduced is 100°C or higher, the steam will not condense until the temperature in the packed bed drops below the dew point (less than 100°C) under the reduced pressure conditions. Therefore, it is preferable that the temperature of the steam introduced is less than 100°C. This "steam less than 100°C" is referred to as "low-temperature steam." In practice, it is preferable that the total pressure in the desorption step be reduced to 10 to 45 kPaA (the last "A" indicates absolute pressure), and it is more preferable that the temperature of the steam introduced is less than 80°C.

[0018] Figure 1 is a cross-sectional schematic diagram showing an example of a radial flow separation apparatus preferably used in the method of the present invention. Figure 1(a) shows a vertical cross-section of the apparatus, and Figure 1(b) shows a horizontal cross-section of the apparatus taken along line A-A' in Figure 1(a). The separation apparatus 1 in Figure 1 comprises a vertical cylindrical outer shell vessel 10, a cylindrical inner pipe 11, and a cylindrical outer basket 12, which are coaxially arranged inside the shell vessel 10. The solid carbon dioxide absorbent material packed between the pipe 11 and the basket 12 forms a vertically extending cylindrical packed bed 13. Inside the packed bed 13 (inside the cylindrical inner pipe 11) is a cylindrical central space 14, which serves as a first flow path. Outside the packed bed 13 (outside the cylindrical outer basket 12), is a cylindrical peripheral space 15, which serves as a second flow path between the inner wall of the shell vessel 10 and the packed bed 13. The central space (first flow path) 14 and the peripheral space (second flow path) 15 each have a first gas inlet / outlet 16 and a second gas inlet / outlet 17 at their lower ends, and the cylindrical inner pipe 11 and the cylindrical outer basket 12 are each configured to be gas permeable. The cylindrical central space (first flow path) 14 and the cylindrical peripheral space (second flow path) 15 are configured to sandwich the packed bed 13 via the cylindrical inner pipe 11 and the cylindrical outer basket 12, thereby forming a gas flow path from the first gas inlet / outlet 16 through the central space (first flow path) 14, the packed bed 13, and the peripheral space (second flow path) 15 to the second gas inlet / outlet 17, or from the second gas inlet / outlet 17 through the peripheral space (second flow path) 15, the packed bed 13, and the central space (first flow path) 14 to the first gas inlet / outlet 16. The gas to be treated may flow in from the first gas inlet / outlet 16 and out from the second gas inlet 17, or may flow in the opposite direction. Furthermore, although details will be described later, when desorbing carbon dioxide captured in the solid carbon dioxide absorbent (i.e., regenerating the solid carbon dioxide absorbent), a method of drawing a vacuum in the same direction as the flow of the gas to be treated and introducing steam in the same direction (cocurrent regeneration method) can be used, or a method of drawing a vacuum in the opposite direction to the flow of the gas to be treated and introducing steam in the opposite direction (countercurrent regeneration method) can be used.Then, depending on the direction of flow of the gas to be treated in the capture step and the direction of flow of steam due to vacuuming in the desorption step, a first conduit (not shown) for guiding combustion exhaust gas containing carbon dioxide, a second conduit (not shown) for guiding steam, and a conduit (not shown) for discharging outlet gas are switchably connected to the first gas inlet / outlet 16 and the second gas inlet / outlet 17. The second conduit for guiding steam is provided with a steam supply amount control mechanism (not shown) for controlling the amount of steam supplied to the separation device.

[0019] When the gas to be treated is introduced through the first gas inlet / outlet 16, the introduced gas to be treated flows upward through the central space (first flow path) 14, gradually penetrating the packed bed 13 and passing through the peripheral space (second flow path) 15 while absorbing and capturing carbon dioxide, and then flows downward through the peripheral space (second flow path) 15, and the treated gas is discharged from the second gas inlet 17. Here, in the first flow path (central space), the upward speed decreases as the gas to be treated gradually escapes, but the pressure remains almost constant from the bottom to the top (because there are no areas along the way that cause pressure loss). Similarly, in the second flow path (peripheral space), the downward speed increases as the treated gas gradually enters, but the pressure remains almost constant from the top to the bottom. Therefore, the pressure difference between the first flow path (central space) 14 and the second flow path (peripheral space) 15 is approximately uniform from the bottom to the top of the packed bed 13, and the flow rate through the packed bed 13 is approximately uniform from the bottom to the top. When the gas to be treated is introduced through the second gas inlet / outlet 17, the gas flow direction is reversed, but the gas flow velocity and pressure are the same as when the gas to be treated is introduced through the first gas inlet / outlet 16. However, if the difference in horizontal cross-sectional area (flow path cross-sectional area) between the first flow path (central space) 14 and the second flow path (peripheral space) 15 becomes large, the flow velocity ascending through the first flow path (central space) 14 and the flow velocity descending through the second flow path (peripheral space) 15 will differ significantly. Therefore, even if the pressure difference on both sides of the packed bed is uniform from the bottom to the top, it is thought that uneven flow will be more likely to occur. For this reason, it is preferable that the ratio of the horizontal cross-sectional area of ​​the central space (first flow path) 14 to the horizontal cross-sectional area of ​​the peripheral space (second flow path) 15 is approximately 1, specifically 0.8 to 1.25.

[0020] 1, the first gas inlet / outlet 16 and the second gas inlet / outlet 17 are provided at the bottom of the first flow path 14 and the second flow path 15, respectively, but both may be provided at the top, or one may be provided at the top and the other at the bottom. When both are provided at the top, the only difference is that the piping for the gas to be treated and the piping for the treated gas are at the top rather than the bottom, and the gas flow within the device is the same as when both are provided at the bottom. However, when one is provided at the top and the other at the bottom, the flow direction in the first flow path and the flow direction in the second flow path are the same, and the vertical change in the flow velocity ascending or descending through the first flow path is opposite to the vertical change in the flow velocity ascending or descending through the second flow path (gradually slowing down on the inlet side and gradually increasing on the outlet side). Therefore, even if the horizontal cross-sectional areas of the central space and the peripheral space are made approximately equal, the flow velocities on both sides of the packed bed cannot be made approximately equal throughout the entire length from the bottom to the top. Therefore, it is thought that flow bias is likely to occur regardless of the ratio of the horizontal cross-sectional areas of the central space and the peripheral space. For these reasons, it is preferable to provide the first gas inlet / outlet and the second gas inlet / outlet at the ends on the same side of the first and second flow paths.

[0021] The solid carbon dioxide absorbent that absorbs and captures carbon dioxide in the capture step is regenerated by desorbing the captured carbon dioxide in the subsequent desorption step, and is then used again to absorb and capture carbon dioxide in the subsequent capture step. In the desorption step, the entire space within the shell vessel 1, including the packed bed and the first and second flow paths, is depressurized by a vacuum pump, which is connected to either the first or second gas inlet / outlet to perform evacuation. Meanwhile, steam is introduced through the gas inlet / outlet not connected to the vacuum pump and flows through the same flow path as the gas to be treated. As mentioned above, if the flow direction of the gas to be treated in the capture step and the flow direction of the steam in the desorption step are the same, this is called cocurrent desorption (cocurrent regeneration), and if they are opposite, this is called countercurrent desorption (countercurrent regeneration). Countercurrent regeneration is preferable in the desorption step because countercurrent regeneration is superior to cocurrent regeneration in terms of desorption efficiency and purity of the desorbed carbon dioxide. Although the mass flow rate of steam in the desorption step is much smaller than the mass flow rate of the gas to be treated in the capture step, the total pressure, including the steam, in the shell vessel is preferably reduced to 10 to 45 kPaA (approximately 0.1 to 0.45 atm) in the desorption step, so the volumetric flow rate is not that small, and it is thought that the flow rate changes in the first and second flow paths are similar to those in the capture step. However, because the total pressure is lower in the desorption step, it is thought that uneven flow is more likely to occur than in the capture step. Therefore, it is more preferable to provide the first gas inlet / outlet and the second gas inlet / outlet at the ends of the same side of the first and second flow paths than in the capture step.

[0022] FIG. 2 is a conceptual diagram showing an example of a flow chart for separating and capturing carbon dioxide from a combustion flue gas, which is a mixed gas containing carbon dioxide, using the method of the present invention. Generally, combustion flue gas discharged from a combustion device such as an incinerator or boiler is cooled to approximately 90°C by recovering residual heat as needed, and then discharged into the atmosphere through a chimney. In the method of the present invention, at least a portion of the flue gas is extracted through a flue and guided by a flue gas blower 100 to a carbon dioxide capture and separation plant 200, where the carbon dioxide contained in the combustion flue gas is separated and captured, and the remaining gas is returned to the flue. Meanwhile, the carbon dioxide capture and separation plant 200, which implements the method of the present invention, is supplied with low-temperature steam used to regenerate a solid carbon dioxide absorbent. The captured carbon dioxide is compressed by a CO compressor 300 and stored or put to useful use.

[0023] FIG. 3 is a schematic diagram illustrating an example of the configuration of a carbon dioxide separation and capture (PCC) plant 200 for implementing the method of the present invention, including the separation device 1 (1A, 1B) that forms the core of the PCC plant 200 and its associated equipment. In FIG. 3, two separation towers, 1A and 1B, are used, and one is programmed to be in the capture (absorption) process while the other is in the desorption process, allowing for continuous carbon dioxide separation and capture by alternating between the capture and desorption processes. Alternatively, three or more separation towers may be used, with some of the towers programmed to be in the desorption process and the others in the capture process, allowing for continuous carbon dioxide separation and capture by rotating between the towers. The combustion exhaust gas drawn from the flue is pressurized by a flue gas blower 100 and enters a scrubber unit 400. After being cleaned with wash water, the gas is introduced into separation tower 1A, which is in the capture process. The gas, from which carbon dioxide has been removed, passes through a packed bed of solid carbon dioxide absorbent material and is returned to the flue. 3 does not show the flow of the combustion exhaust gas in the separation tower 1A, and does not specifically show that the combustion exhaust gas flows in from the top of the separation device and flows out from the bottom. Meanwhile, the diagram shows that steam for regenerating the solid carbon dioxide absorbent is introduced into separation device 1B in the desorption step, the pressure inside separation device 1B is reduced to desorb carbon dioxide, the desorbed carbon dioxide is extracted from the separation device together with the steam, and then the steam accompanying the carbon dioxide flow is separated as drain, and the remaining carbon dioxide is recovered. If the combustion exhaust gas is emitted from a thermal power plant, the regeneration steam can be supplied from the facilities of the thermal power plant.

[0024] Figure 4 shows an example of a configuration in which a steam recovery mechanism is further added to the configuration of the PCC plant shown in Figure 3. In Figure 3, the steam accompanying the carbon dioxide flow desorbed in the separation device was separated and then discharged as drain without being recovered. However, in Figure 4, a configuration is added in which the flow containing carbon dioxide and steam generated in the desorption process is pressurized by a first-stage vacuum pump to condense the steam, and the condensation heat is imparted to condensed water separated in a drum under reduced pressure by a second-stage vacuum pump through indirect heat exchange, thereby evaporating the condensed water separated in the drum and recovering it as steam (steam circulation using self-heat). In this way, a pressure difference is created between the flow of the gas mixture containing carbon dioxide and steam generated in the desorption process and the flow containing water separated in the separation process, and indirect heat exchange is performed between the two fluids in heat exchanger 500, thereby reducing the amount of regeneration steam supplied from an external source.

[0025] Figure 5 shows another example of a PCC plant configuration in which a steam recovery mechanism is further added to the configuration of the PCC plant shown in Figure 3. Figure 4 shows a configuration in which steam is recovered by applying self-heated steam circulation to the flow of a gas mixture containing carbon dioxide and steam generated in the desorption step, while Figure 5 shows a configuration in which steam is recovered by applying self-heated steam circulation to the flow of a gas mixture containing treated flue gas and steam generated in the capture step. In Figure 4, self-heated steam circulation is applied to the depressurized gas mixture from the desorption step, so steam is condensed from the gas mixture downstream of the first-stage vacuum pump. However, in Figure 5, self-heated steam circulation is applied to the atmospheric pressure gas mixture from the capture step, so steam is condensed directly from the gas mixture, and the heat of condensation is imparted to the depressurized condensed water by indirect heat exchange to evaporate and recover as steam. This is a difference. In this way, by creating a pressure difference between the flow of the gas mixture containing steam generated in the capture step and the flow containing water separated in the separation step, and performing indirect heat exchange between the two fluids, the amount of regeneration steam supplied from the outside can be reduced, as in the case of Figure 4.

[0026] Steam recovery using the configuration of Figure 4 or steam recovery using the configuration of Figure 5 may be performed alone, or both may be performed by switching the piping. Normally, when countercurrent regeneration is performed in the desorption step, depending on the operating conditions of the capture step and desorption step, the gas discharged at the beginning of the desorption step may contain only desorbed carbon dioxide and little steam. If the desorption step is continued as is, steam will eventually be contained, but if the desorption step is terminated at that point and the process moves to the capture step, steam captured in the packed bed of the solid carbon dioxide absorbent material in the desorption step may flow out at the beginning of the capture step. In such cases, steam is contained in large amounts not in the gas discharged from the desorption step but in the gas discharged from the capture step (at the beginning). Therefore, steam can be recovered more efficiently using the configuration of Figure 5 than using the configuration of Figure 4. On the other hand, in the desorption step, if steam is hardly captured by the solid carbon dioxide absorbent material and carbon dioxide is discharged together with steam, the steam will be contained in large amounts in the gas discharged from the desorption step and will be almost completely contained in the gas discharged from the capture step, and therefore steam can be recovered more efficiently by using the configuration of Figure 4 than the configuration of Figure 5. The point at which steam becomes contained in large amounts in the gas discharged varies depending on the type of solid carbon dioxide absorbent material and the operating conditions of the desorption step and the capture step, so steam can be recovered by selecting the configuration of Figure 4 or the configuration of Figure 5 accordingly. [Explanation of symbols]

[0027] 1 Separation device 1A First Separation Device 1B Second Separation Device 10 Outer shell container 11 Inner cylindrical pipe 12 outer cylindrical basket 13 Filled bed 14 Central space (first flow path) 15 Surrounding space (second flow path) 16 First gas inlet / outlet 17 Second gas inlet / outlet 100 Flue gas blower (booster) 200 Carbon Dioxide Separation and Capture Plant 300 CO2 Compressor 400 Scrubber Unit 500 heat exchanger

Claims

1. 1. A method for separating and recovering carbon dioxide from a gas mixture containing carbon dioxide, comprising: a capturing step of bringing the gas mixture into contact with a solid carbon dioxide absorbent to capture carbon dioxide in the gas mixture in the solid carbon dioxide absorbent, and a desorption step of bringing the solid carbon dioxide absorbent that has captured carbon dioxide in the capturing step into contact with steam to desorb the carbon dioxide captured in the solid carbon dioxide absorbent, and a separation step of condensing steam from the gas mixture containing carbon dioxide and steam generated in the desorption step to separate it as water, and a circulation step of evaporating the water separated in the separation step to convert it back into steam, which is then circulated to the desorption step for reuse, a pressure difference is created between a gas mixture stream containing carbon dioxide and steam generated in the desorption step and a stream containing water separated in the separation step, thereby performing indirect heat exchange between the two fluids.

2. 1. A method for separating and recovering carbon dioxide from a gas mixture containing carbon dioxide, comprising: a capturing step of bringing the gas mixture into contact with a solid carbon dioxide absorbent to capture carbon dioxide in the gas mixture in the solid carbon dioxide absorbent, and a desorption step of bringing the solid carbon dioxide absorbent that has captured carbon dioxide in the capturing step into contact with steam to desorb the carbon dioxide captured in the solid carbon dioxide absorbent, and a separation step of condensing steam from the steam-containing gas mixture generated in the capture step and separating it as water, and a circulation step of evaporating the water separated in the separation step and converting it back into steam, which is then circulated to the desorption step for reuse; A method characterized by creating a pressure difference between the stream of the gas mixture containing steam generated in the capturing step and the stream containing water separated in the separation step, thereby performing indirect heat exchange between the two fluids.

3. 3. The method according to claim 1 or 2, wherein the gas mixture containing carbon dioxide is a combustion exhaust gas under atmospheric pressure, the capturing step causes the combustion exhaust gas to flow through a packed bed of the solid carbon dioxide absorbent material under atmospheric pressure, and the desorption step causes the solid carbon dioxide absorbent material to be contacted with steam at a temperature of less than 100°C under reduced pressure.

4. The method according to claim 3, wherein the desorption step involves contacting the solid carbon dioxide absorbent with steam at a temperature of less than 80°C under a reduced pressure of 10 to 45 kPaA.

5. 2. The method of claim 1, wherein the pressure difference is established by pressurizing a stream of a gas mixture comprising carbon dioxide and steam generated in the desorption step.

6. The method of claim 2 , wherein the pressure differential is established by reducing the pressure of the water-containing stream separated in the separation step.

7. 2. The method of claim 1, wherein the gas mixture stream containing carbon dioxide and steam generated in the desorption step is further cooled after indirect heat exchange with the water-containing stream separated in the separation step.

8. 3. The method of claim 2, wherein the steam-containing gas mixture stream generated in the capturing step is further cooled after indirect heat exchange with the water-containing stream separated in the separation step.

9. 3. The method according to claim 1, wherein the solid carbon dioxide absorbent is an inorganic porous carrier having a polyamine compound supported thereon.

10. 3. The method according to claim 1, wherein the carbon dioxide concentration in the carbon dioxide-containing gas mixture is 10% by volume or less.

11. 3. The method according to claim 1, wherein the carbon dioxide concentration in the carbon dioxide-containing gas mixture is 6% by volume or less.

12. 3. The method of claim 1, wherein the gas mixture containing carbon dioxide is the exhaust gas of a gas turbine fueled by natural gas.

13. 13. The method according to claim 12, wherein the gas turbine constitutes a first stage of a combined cycle, and a part of steam supplied to a steam turbine constituting a second stage of the combined cycle is used as the steam.

Images