CO2 Separation System

Abstract

A CO2 separation system having first CO2 separation equipment 1, second CO2 separation equipment 2, first piping 14, low-concentration CO2 gas discharge equipment 60, and gas reflux equipment 70 provided with second piping 16 and a high-concentration CO2 gas discharge device 45, the first CO2 separation equipment 1 being configured from a deep-cooling separation device that separates CO2 from gas being treated through a deep-cooling separation process, the first piping 14 supplying the gas discharged from the first CO2 separation equipment 1 to the second CO2 separation equipment 2, the second CO2 separation equipment 2 being provided with an adsorption separation device in which rubber is provided as a CO2 adsorption material, the low-concentration CO2 gas discharge equipment 60 discharging gas that contains a low concentration of CO2 from the second CO2 separation equipment 2, the high-concentration CO2 gas discharge equipment 45 discharging gas that contains a higher concentration of CO2 than the low concentration from the second CO2 separation equipment 2, at least some of the gas discharged from the high-concentration CO2 gas discharge device 45 in the gas reflux equipment 70 being returned to the first CO2 separation equipment 1 via the second piping 16, and the first CO2 separation equipment 1 performing the deep-cooling separation process for separating the CO2 from the gas that is returned by the gas reflux equipment 70.

Description

[Technical Field]

[0001] The present invention relates to a CO2 separation system. [Background technology]

[0002] From the perspective of reducing greenhouse gas emissions, taking into account desorption energy efficiency, there is a strong desire to separate and capture CO2 from natural gas and associated gas containing high concentrations of CO2 using low energy.

[0003] In general, natural gas and associated gas separation processes can be classified as follows based on CO2 concentration: (1) When the CO2 concentration is 2% or less In this case, it is not necessary to separate the CO2, as the impact of corrosion on the pipeline is small if the CO2 concentration is 2% or less. However, when producing liquefied natural gas (LNG), the AGR (Acid Gas Removal) process is applied before applying the cryogenic separation method. (2) When the CO2 concentration is around 30% Older facilities used molten potassium carbonate, but this is being replaced by the AGR process using an amine solvent. Amine solvents allow the adsorbent to be regenerated by heat, making equipment maintenance easy. On the other hand, corrosion of steel is often a problem with molten potassium carbonate. (3) When the CO2 concentration is 30-60% An organic solvent such as propylene carbonate (PC) is used as the adsorbent. High CO2 concentrations require a large amount of heat energy to regenerate the amine solvent, making the AGR process unusable. (4) When the CO2 concentration is 70% or higher Currently, development is difficult, and there is great hope for new CO2 separation technology.

[0004] Under these circumstances, natural gas development is required to separate high-concentration CO2 of over 30% and reduce it to 2% or less. In addition to natural gas, mixed gases containing high concentrations of CO2 are also generated from thermal power plants and biogas production, and hopes are high for low-cost capture technology. However, the method of capturing CO2 using organic solvents as adsorbents (absorbents) requires dissolving the mixed gas in high-pressure microbubbles, which results in a large energy loss. In addition, some of the organic solvent evaporates, which requires costs for recovering the evaporated organic solvent. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Unexamined Utility Model Publication No. 15489-1986 [Non-patent literature]

[0006] [Non-Patent Document 1] Jun Matsumoto et al., Journal of Petroleum Technology, Vol. 76, No. 6, pp. 512-516 (November 2011) [Non-patent document 2] Zenji Fujiyasu, Cryogenic Engineering, Vol. 5, No. 4, pp. 181-185 (1970) [Non-patent document 3] Shigeru Kimura, Hitachi Review, Vol. 48, No. 8, pp. 69-74 (August 1966) [Non-patent document 4] Izumi Ichinose et al., JACI GSC Symposium (June 15-16, 2022) Summary of the Invention [Problem to be solved by the invention]

[0007] In view of the above background, an object of the present invention is to provide a CO2 separation system that efficiently separates CO2 from natural gas, biogas, etc. containing high concentrations of CO2 using low energy and supplies desired gases such as methane. [Means for solving the problem]

[0008] The configuration of the present invention is shown below. (Configuration 1) The system includes a gas reflux facility having a first CO2 separation facility, a second CO2 separation facility, a first pipe, a low-concentration CO2 gas discharge facility, a second pipe, and a high-concentration CO2 gas discharge device, the first CO2 separation facility being a cryogenic separation device that separates CO2 from a gas to be treated by cryogenic separation processing, the first pipe supplying gas discharged from the first CO2 separation facility to the second CO2 separation facility, the second CO2 separation facility being equipped with an adsorption separation device having rubber as a CO2 adsorbent, and the low-concentration CO2 gas discharge facility being equipped with a second pipe and a high-concentration CO2 gas discharge device. The equipment discharges gas containing a low concentration of CO2 from the second CO2 separation equipment, the high-concentration CO2 gas discharge device discharges gas containing a higher concentration of CO2 from the second CO2 separation equipment, and the gas reflux equipment returns at least a portion of the gas discharged from the high-concentration CO2 gas discharge device to the first CO2 separation equipment via the second piping, and the first CO2 separation equipment performs a cryogenic separation process to separate CO2 from the gas returned by the gas reflux equipment. (Configuration 2) The CO2 separation system according to configuration 1, wherein the second CO2 separation equipment has a first adsorption tower group consisting of one or more adsorption towers and a second adsorption tower group consisting of one or more adsorption towers, the adsorption towers have a flow path through which gas flows while being retained therein, and the CO2 adsorbent, and the CO2 separation system further comprises a cooling means capable of cooling the flow path and the CO2 adsorbent. (Configuration 3) 3. The CO2 separation system according to claim 2, wherein the first adsorption tower group and the second adsorption tower group are paired adsorption tower groups having the same configuration. (Configuration 4) 3. The CO2 separation system according to claim 2, wherein at least some of the adsorption towers constituting the first adsorption tower group and the second adsorption tower group are arranged in series within the first adsorption tower group and the second adsorption tower group. (Configuration 5) 3. The CO2 separation system according to claim 2, wherein the gas breakthrough time per adsorption tower is 5 minutes or more and 60 minutes or less. (Configuration 6) A CO2 separation system according to any one of configurations 2 to 5, wherein the CO2 concentration in the gas introduced into the first adsorption tower group and the second adsorption tower group is adjusted to be 10 mol% or more and 40 mol% or less, and the CO2 concentration in the gas discharged from the first adsorption tower group and the second adsorption tower group is adjusted to be 2 mol% or more and 10 mol% or less. (Configuration 7) A CO2 separation system according to any one of configurations 2 to 5, wherein the CO2 concentration in the gas introduced into the first adsorption tower group and the second adsorption tower group is adjusted to be 5 mol% or more and 10 mol% or less, and the CO2 concentration in the gas discharged from the first adsorption tower group and the second adsorption tower group is adjusted to be 0 mol% or more and 2 mol% or less. (Configuration 8) 8. The CO2 separation system according to any one of configurations 2 to 7, wherein the adsorption pressure of the adsorption tower is adjusted to 5 MPa or more and 45 MPa or less. (Configuration 9) 3. The CO2 separation system according to claim 2, wherein the cooling temperature is between -50°C and 0°C. (Configuration 10) 2. The CO2 separation system according to claim 1, wherein the concentration of the high concentration CO2 is 50 mol% or more and 99 mol% or less. (Configuration 11) 11. The CO2 separation system according to any one of claims 1 to 10, wherein the rubber is provided in one or more forms selected from the group consisting of pellets, powder, and fine particles. (Configuration 12) 12. The CO2 separation system of claim 11, wherein the rubber is packed in a mesh or perforated bag. (Configuration 13) The CO2 separation system according to configuration 1, wherein the cryogenic separation device comprises a compressor that compresses the supplied gas, a cooling device that cools the gas introduced through the compressor, and a device that discharges the cooled and liquefied CO2. (Configuration 14) 2. The CO2 separation system according to claim 1, wherein the gas to be treated is introduced into the cryogenic separation device via a pressure reduction facility that reduces the pressure of the gas to separate liquid CO2. (Configuration 15) 15. The CO2 separation system according to any one of configurations 1 to 14, wherein the gas to be treated is introduced into the cryogenic separation device via a dehydration facility that performs dehydration. [Effects of the Invention]

[0009] According to the present invention, a CO2 separation system is provided that efficiently separates CO2 from natural gas, biogas, or the like containing high concentrations of CO2 with low energy consumption and supplies desired gases such as methane. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a system configuration diagram showing the overall configuration of a CO2 separation system of the present invention. [Figure 2] FIG. 2 is a configuration diagram showing the configuration of a first CO2 separation facility which is a part of the CO2 separation system of the present invention. [Figure 3] FIG. 2 is a configuration diagram showing the configuration of a second CO2 separation facility which is part of the CO2 separation system of the present invention. [Figure 4] FIG. 2 is a cross-sectional view showing the structure of an adsorption tower. [Figure 5] FIG. 2 is an explanatory diagram illustrating the configuration of an adsorption tower. [Figure 6] FIG. 1 is a characteristic diagram showing the CO2 adsorption and desorption characteristics using rubber. [Figure 7] FIG. 1 is a characteristic diagram showing the relationship between absolute pressure and the amount of CO2 adsorption. [Figure 8] FIG. 1 is a diagram showing a breakthrough curve according to an example. DETAILED DESCRIPTION OF THE INVENTION

[0011] The CO2 separation system according to this embodiment will be described with reference to FIGS.

[0012] 1, the CO2 separation system 101 of this embodiment includes a first CO2 separation facility 1, which is a cryogenic separation device, a second CO2 separation facility 2, a pipe 14 (an example of the "first pipe"), a low-concentration CO2 gas discharge facility 60, a reflux pipe 16 (an example of the "second pipe"), and a gas reflux facility 70 equipped with a high-concentration CO2 gas discharge device 45. FIG. 1 illustrates a configuration in which the CO2 separation system 101 further includes a pressure reduction facility 4, a dehydration facility 5, and pipes 11 to 13.

[0013] However, it is not essential that the CO2 separation system 101 be equipped with the pressure reduction equipment 4 and the dehydration equipment 5. Both or either of the pressure reduction equipment 4 and the dehydration equipment 5 may be omitted from the CO2 separation system 101. Hereinafter, the gas from which CO2 is separated by the CO2 separation system 101 will be referred to as the "gas to be treated." The gas to be treated is, for example, natural gas or associated gas, and contains CO2 in addition to desired components (e.g., methane).

[0014] Here, the first CO2 separation equipment 1 and the second CO2 separation equipment 2 are connected to a cooling equipment 3. The cooling equipment 3 is capable of efficiently and precisely cooling the first CO2 separation equipment 1 and the second CO2 separation equipment 2. There are no particular restrictions on the cooling equipment 3, but a vapor compression refrigerator can be mentioned, for example, and there are no particular restrictions on the refrigerant, but CO2 can be used. The gas to be treated is supplied to the first CO2 separation facility 1, for example, via a pressure reduction facility 4 and a dehydration facility 5. First, the gas to be treated is supplied to the pressure reduction facility 4 via a pipe 11. Next, the gas to be treated that has passed through the pressure reduction facility 4 is supplied to the dehydration facility 5 via a pipe 12. Then, the gas to be treated that has passed through the dehydration facility 5 is supplied to the first CO2 separation facility 1 via a pipe 13. The first CO2 separation facility 1 is connected to the second separation facility 2 through a pipe 14. A return pipe 16 for returning a portion of the gas processed in the second separation facility 2 to the first separation facility 1 is connected between the second separation facility 2 and the first separation facility 1. Furthermore, the first CO2 separation facility 1 is provided with a discharge pipe 17 for discharging liquid CO2 and other condensable gases produced by processing in the first CO2 separation facility 1.

[0015] <Decompression equipment 4> The pressure reduction facility 4 is a facility designed to reduce the pressure of gas to be treated at high pressures of 60 MPa or higher (e.g., high-pressure gas rising from deep underground). It consists of, for example, a choke and a temperature control device. For example, if the gas to be treated has an initial pressure of nearly 120 MPa and contains water, rapid cooling due to pressure reduction can lead to the formation of methane hydrate. A temperature control device is required to prevent this. A typical pressure reduction operation involves gradually reducing the pressure, for example, from 120 MPa to 60 MPa, 15 MPa, and 3 MPa, while maintaining the temperature above room temperature. Note that if the gas to be treated contains a large amount of CO2, the pressure reduction facility 4 may be equipped with a CO2 discharge pipe, since liquid CO2 can be produced by appropriate pressure reduction. Furthermore, water and condensate (liquid hydrocarbons) may be produced by cooling in the pressure reduction facility 4, and these can also be discharged from the CO2 discharge pipe. If the gas to be treated is natural gas containing condensate, it is preferable to discharge the condensate, which is a valuable product.

[0016] <Dehydration equipment 5> The dehydration equipment 5 is a facility equipped for the purpose of removing moisture from the gas to be treated. The dehydration equipment 5 contains a moisture remover. Examples of moisture removers that can be used include molecular sieves (zeolite, a registered trademark), silica gel, activated carbon, activated alumina, and ethylene glycol derivatives. Dehydration equipment 5 using silica gel or activated alumina, which can achieve a dew point of approximately -40°C, is particularly suitable. Water in the gas to be treated becomes almost liquid by lowering the temperature. The dehydration equipment 5 is used to remove moisture from the gas phase, which does not condense even at temperatures near room temperature. Although not shown, the dehydration equipment 5 may be equipped with a heater and a desorption steam cooler to regenerate the moisture remover. Furthermore, it is desirable to operate the dehydration equipment 5 at temperatures above 0°C to prevent hydrate formation. Furthermore, for continuous operation, the dehydration equipment 5 may be equipped with multiple adsorption towers. For example, the dehydration equipment 5 is installed when the gas to be treated is natural gas.

[0017] <First CO2 Separation Facility 1> The first CO2 separation equipment 1 is an apparatus that performs cryogenic separation processing to separate CO2 from the gas to be treated. The first CO2 separation equipment 1 can be a cryogenic separation equipment that is normally used, except that it has a path through which at least a portion of the gas returned through the return pipe 16 is treated in the first CO2 separation equipment 1. Fig. 2 is a configuration diagram of an example of the first CO2 separation facility 1 of this embodiment. As shown in Fig. 2, the first CO2 separation facility 1 includes, for example, a compression device 21, a dehydration device 22, a cooling device 23, and a liquefied CO2 emission device 24.

[0018] The compressor 21 is connected to a pipe 13 for supplying the gas to be treated, and a reflux pipe 16 for supplying the gas refluxed from the second CO2 separation facility 2. The gas compressed in the compressor 21 is supplied to the dehydrator 22 via a pipe 31. Here, the pressure of the gas after compression is, for example, 10 MPa or more and 50 MPa or less. Because the temperature rises when the gas is compressed, the first CO2 separation facility 1 is preferably equipped with a cooling device 23. The dehydration device 22 is a device that performs a dry gasification process (dehydration process) to remove moisture from the gas after compression. A method that uses silica gel or zeolite is an excellent method for dry gasification. Here, the amount of water contained in the dry gas that has been subjected to the dry gasification process is preferably controlled to 10 ppm or less. Note that dehydration using silica gel is preferably performed at 30°C or less, since the amount of adsorption decreases at high temperatures. Note that if sufficient dehydration is performed in the dehydration equipment 5, the dehydration device 22 can be omitted. The gas that has been subjected to the dry gasification process is supplied to the cooling device 23 via a pipe 32. The cooling device 23 is not particularly limited, but for example, a vapor compression refrigerator using CO2 as a refrigerant can be used to utilize the cold heat. Cooling by adiabatic expansion can also be used in combination as long as the solidification of CO2 does not occur. The cooling device 23 cools the supplied gas to a temperature between -40°C and 0°C. Since the gas supplied to the cooling device 23 has already been dehydrated and no hydrate is formed, it is desirable that the temperature of the cooling device 23 be low enough that solidification of CO2 does not occur. The pressure is also 10 MPa to 50 MPa, but it is desirable that it be high enough that the safety of the pressure-resistant container can be ensured. The cooled gas is transported via piping 33 to the liquefied CO2 discharge device 24, and liquid substances such as liquefied CO2 produced by cooling are discharged via discharge piping 17. The liquefied CO2 discharge device 24 is a pump that discharges liquid CO2, and like the cooling device 23, it needs to be cooled by the cooling equipment 3.

[0019] <Second CO2 Separation Facility 2> Fig. 3 is a configuration diagram of an example of the second CO2 separation facility 2 according to this embodiment. The second CO2 separation facility 2 is a facility for removing CO2 that was not completely separated by the cryogenic separation process in the first CO2 separation facility 1. As shown in Fig. 3, the second CO2 separation facility 2 includes an adsorption separation device 80 that uses rubber as an adsorbent.

[0020] The adsorption / separation device 80 is a device that adsorbs and separates CO2 in the gas supplied from the pipe 14, and performs desorption of CO2. Specifically, the adsorption / separation device 80 includes two adsorption towers 41 (adsorption towers 41a and 41b) that incorporate, for example, rubber, which will be described later, as a CO2 adsorbent. When there is no need to distinguish between the adsorption tower 41a and the adsorption tower 41b, they will be referred to as adsorption towers 41. However, the number of adsorption towers 41 included in the adsorption / separation device 80 is not limited to two, and may be three or more towers or one tower. However, from the viewpoint of continuously treating the gas to be treated, it is preferable that the number of adsorption towers 41 be two or more.

[0021] As described above, the adsorption tower 41 contains rubber, which is a CO2 adsorbent, and adsorbs and desorbs CO2. The adsorption tower 41a and the adsorption tower 41b are identical and are arranged as a pair. The gas processed in the first CO2 separation facility 1 is introduced into either the adsorption tower 41a or the adsorption tower 41b via the pipe 14 and the valve 51. The adsorption towers 41a and 41b are connected to the reflux pipe 16 via the valve 52 and the high-concentration CO2 gas exhaust device 45. The adsorption towers 41a and 41b are also connected to the pipe 15 via the valve 53 and the flow regulator 46. By switching the valves 51, 52, and 53, one of the adsorption towers 41a and 41b is used for CO2 adsorption, and the other is used for CO2 desorption. In other words, CO2 adsorption and CO2 desorption are performed in parallel. CO2 adsorption and CO2 desorption are performed alternately in the adsorption tower 41a, and CO2 adsorption and CO2 desorption are performed alternately in the adsorption tower 41b.

[0022] The CO2 adsorption / desorption method in the adsorption tower 41 will be described in detail below. The adsorption tower 41a is operated for CO2 adsorption and the adsorption tower 41b is operated for CO2 desorption by opening the valve 51 to the adsorption tower 41a side and closing it to the adsorption tower 41b side, closing the valve 52 to the adsorption tower 41a side and opening it to the adsorption tower 41b side, and opening the valve 53 to the adsorption tower 41a side and closing it to the adsorption tower 41b side. The adsorption tower 41a is then operated for CO2 desorption and the adsorption tower 41b is operated for CO2 adsorption by closing the valve 51 to the adsorption tower 41a side and opening it to the adsorption tower 41b side, opening the valve 52 to the adsorption tower 41a side and closing it to the adsorption tower 41b side, and closing the valve 53 to the adsorption tower 41a side and opening it to the adsorption tower 41b side. This process is then repeated to perform CO2 adsorption / desorption. Here, adsorption and desorption are controlled by pressure. Adsorption towers 41a and 41b are insulated, but cooling equipment 3 is used for pre-cooling and maintaining low temperatures. Here, the temperature inside adsorption towers 41a and 41b during adsorption is preferably -50°C or higher and 0°C or lower, and more preferably -40°C or higher and -20°C or lower. Cooling equipment 3 is an example of cooling means capable of cooling the flow path (flow path 42 described below) through which gas flows while being retained inside, and the CO2 adsorbent. By controlling the temperature inside the adsorption towers 41a and 41b during adsorption within this range, solidification of CO2 during desorption can be prevented, resulting in improved separation efficiency. It is desirable that the temperature of the adsorption tower 41 of the second CO2 separation equipment be lower than that of the first CO2 separation equipment (cryogenic separation device). This is because the second CO2 separation equipment has a lower CO2 concentration in the gas than the first CO2 separation equipment, making solidification of CO2 less likely to occur, and lower temperatures result in higher CO2 separation efficiency in the adsorption tower 41.

[0023] The adsorption / desorption switching of the adsorption towers 41a and 41b (switching of valves 51, 52, and 53) is preferably performed based on the breakthrough time characteristics of CO2 gas in the adsorption tower 41, as shown in Figure 6. The adsorption / desorption switching of the adsorption towers 41a and 41b is preferably performed by switching valves 51-53 when the CO2 concentration (C / C0) at the outlet of the adsorption tower performing adsorption, either 41a or 41b, reaches approximately 1 / 3 (although this should be within the range of 1 / 4 to 1 / 2). Switching between adsorption and desorption at this timing maximizes the adsorption / desorption efficiency. Note that C0 represents the maximum CO2 adsorption amount in that adsorption tower.

[0024] The pressure during CO2 adsorption inside adsorption towers 41a and 41b is preferably adjusted to between 5 MPa and 45 MPa. The CO2 adsorption capacity of the CO2 adsorbent depends on the pressure, increasing as the pressure increases. However, since it becomes difficult to increase the size of the adsorption towers at high pressures, it is preferable to adjust the pressure to between 5 MPa and 45 MPa. Note that 45 MPa is the maximum filling pressure of a 250 L container made of chromium-molybdenum steel with a wall thickness of 22 mm, and it is not easy to manufacture an adsorption tower that can withstand pressures higher than this.

[0025] The gas discharged from the second CO2 separation equipment 2 (adsorption tower 41) is separated into treated gas (low-concentration CO2 gas) controlled to a low concentration of CO2, as shown below, and high-concentration CO2 gas (high-concentration CO2 gas) with a higher CO2 concentration. The low-concentration CO2 gas (treated gas) is discharged by the low-concentration CO2 gas discharge equipment 60. On the other hand, the high-concentration CO2 gas is returned to the first CO2 separation equipment by the gas reflux equipment 70 (high-concentration CO2 gas discharge device 45, reflux piping 16). The low-concentration CO2 gas discharge equipment 60 and the gas reflux equipment 70 (high-concentration CO2 gas discharge device 45, reflux piping 16) will be described in detail below.

[0026] <Low concentration CO2 gas emission equipment> The low-concentration CO2 gas discharge equipment 60 is an equipment that discharges the low-concentration CO2 gas after CO2 has been adsorbed by the adsorption / separation device 80. That is, the low-concentration CO2 gas discharge equipment 60 discharges gas (low-concentration CO2 gas) containing CO2 at a concentration lower than the CO2 concentration in the gas supplied to the adsorption / separation device 80 from the pipe 14.

[0027] Specifically, the low-concentration CO2 gas discharge equipment 60 is, for example, a device (treated gas discharge equipment) including a flow regulator 46 and piping 15. The low-concentration CO2 gas discharged from the second CO2 separation equipment 2 is discharged from the CO2 separation system 101 via a valve 53 and the low-concentration CO2 gas discharge equipment 60. The flow regulator 46 adjusts the flow rate so that the gas pressure in piping 15 is slightly lower than the pressure during CO2 adsorption in the adsorption towers 41a and 41b, thereby ensuring the pressure and gas residence time within the adsorption tower 41. Because the treated gas discharged from the low-concentration CO2 gas discharge equipment 60 has a low CO2 concentration, it will not freeze and clog, even in polar regions, and can be delivered to consumption areas via pipelines, etc. Furthermore, once CO2 is removed, it becomes possible to transport more natural gas through the same pipeline, reducing natural gas transportation costs.

[0028] Here, the CO2 concentration in the gas introduced into the adsorption towers 41a and 41b (i.e., the gas supplied via the pipe 14) is preferably adjusted to 2 mol% or more and 40 mol% or less by the first CO2 concentration separation equipment. The CO2 concentration in the low-concentration CO2 gas discharged from the low-concentration CO2 gas discharge equipment 60 is preferably adjusted to 0.5 mol% or more and 10 mol% or less. The CO2 concentration in the gas introduced into the adsorption towers 41a and 41b is more preferably adjusted to 10 mol% or more and 40 mol% or less by the first CO2 concentration separation equipment. The CO2 concentration in the low-concentration CO2 gas discharged from the low-concentration CO2 gas discharge equipment 60 is more preferably adjusted to 2 mol% or more and 10 mol% or less. If the CO2 concentration in the gas introduced into the adsorption towers 41a and 41b and the CO2 concentration in the low-concentration CO2 gas discharged from the low-concentration CO2 gas discharge equipment 60 are adjusted to be within this concentration range, a significant greenhouse gas reduction effect can be achieved. Alternatively, the CO2 concentration in the gas introduced into the adsorption towers 41a and 41b is more preferably adjusted to between 2 mol% and 10 mol% by the first CO2 concentration separation equipment. The CO2 concentration in the low-concentration CO2 gas discharged from the low-concentration CO2 gas discharge equipment 60 is more preferably adjusted to between 0 mol% and 2 mol%, but may be between 0.5 mol% and 2 mol%. When the CO2 concentration in the gas introduced into the adsorption towers 41a and 41b and the CO2 concentration in the low-concentration CO2 gas discharged from the low-concentration CO2 gas discharge equipment 60 are adjusted to within this range, corrosion prevention effects for the pipeline can be obtained.

[0029] <Gas reflux equipment> As described above, the gas reflux equipment 70 includes the high-concentration CO2 gas discharge device 45 and the reflux piping 16. Note that the reflux piping 16 is a piping that is generally used for transporting gas. Specifically, the gas reflux equipment 70 functions as an element that returns at least a portion of the gas discharged from the high-concentration CO2 gas discharge device 45 to the first CO2 separation equipment 1 via the reflux piping 16.

[0030] The high-concentration CO2 gas discharge device 45 is a device that desorbs and discharges CO2 from the adsorption / separation device 80 (adsorption tower 41) after CO2 adsorption. That is, the high-concentration CO2 gas discharge device 45 discharges gas (high-concentration CO2 gas) containing CO2 at a higher concentration than the CO2 concentration in the low-concentration CO2 gas discharged by the low-concentration CO2 gas discharge equipment 60. In this embodiment, a pump that desorbs CO2 from the adsorption / separation device 80 by reducing pressure is exemplified as the high-concentration CO2 gas discharge device 45.

[0031] The high-concentration CO2 gas is returned to the first CO2 separation facility 1 via valve 52 and gas reflux equipment 70 (high-concentration CO2 gas exhaust device 45 and reflux piping 16) for reprocessing (i.e., cryogenic separation). The CO2 concentration of the high-concentration CO2 gas is preferably 50 mol% to 99 mol%, more preferably 50 mol% to 90 mol%. Adjusting the CO2 concentration in the high-concentration CO2 gas within this range improves the efficiency of the CO2 separation system. The CO2 concentration in the high-concentration CO2 gas can be adjusted by the temperature and pressure during CO2 adsorption in the adsorption towers 41a and 41b, and the filling rate of the rubber CO2 adsorbent. Here, returning the high-concentration CO2 gas to the first CO2 separation facility 1 is extremely important for increasing the methane recovery rate. This is because, in the present invention, pelletized, powdered, and microparticle rubber is used as the CO2 adsorbent, and high-pressure gaseous methane is present around these CO2 adsorbents. Therefore, when high-concentration CO2 gas is discharged, methane is also discharged, and disposing of this results in a loss of methane. However, the methane contained in this high-concentration CO2 gas is returned to the first CO2 separation facility 1 and then returned to the second CO2 separation facility 2, so there is essentially no loss of methane.

[0032] In order to improve the CO2 adsorption amount and adsorption / desorption efficiency, it is preferable that the adsorption tower 41 has a long flow path 42 inside the adsorption tower 41 to ensure residence time, and that rubber, which is a CO2 adsorbent, is placed in a space 43 in the flow path 42, as shown in FIG.

[0033] The rubber used as a CO2 adsorbent is preferably a crosslinked PDMS (PolyDiMethylSiloxane). The preferred crosslinking methods are those using a radical crosslinking agent and those crosslinking multiple vinyl groups within the molecules of both PDMS by hydrosilation. The latter method typically uses a platinum catalyst. Considering cost and resource recycling, it is also preferable to use recycled rubber, such as scrap tires, as the rubber for the CO2 adsorbent. The rubber should have a glass transition temperature of -150°C or higher and -10°C or lower, and an SP value of 7.0 (cal / cm) at room temperature. 3 ) 0.5 More than 10.0(cal / cm 3 ) 0.5 The following is desirable: The modulus of elasticity at 25°C is preferably 0.03 MPa or more and 8 MPa or less. Rubber that satisfies these conditions has a high CO2 adsorption capacity and adsorption / desorption efficiency. The relationship between absolute pressure and CO2 adsorption amount at a temperature of 245 K when using PDMS rubber is shown in Figure 7. The glass transition temperature of this rubber is -150°C, and the SP value at room temperature is 7.5 (cal / cm 3 ) 0.5 , and the elastic modulus at 25°C is approximately 4 MPa. It is clear that it has good CO2 adsorption properties.

[0034] The SP value at room temperature is 10.5 (cal / cm 3 ) 0.5 The rubbers listed below are generally hydrophobic, but some are prone to adsorbing water. In such cases, making the rubber hydrophobic makes it possible to absorb large amounts of CO2 below freezing. At sub-freezing points, water tends to adsorb to the rubber's interfaces and voids, and even a small amount of water can easily reduce the adsorption performance. In such cases, it is effective to adsorb hydrophobic molecules such as decane onto the rubber. This reduces water adsorption, making it easier to maintain high CO2 adsorption capacity. The water contact angle of the CO2 adsorbent surface should be between 80° and 150°. It is important that the SP value of rubber at room temperature is close to that of CO2, but it is known that the SP value of CO2 increases as the temperature decreases. The SP value of rubber also increases with decreasing temperature, but the increase in the SP value of PDMS rubber is somewhat slower than that of CO2. For this reason, in the range of -20°C to -40°C, a rubber with a slightly higher SP value than PDMS rubber is desirable. An example of such a rubber is one in which the methyl groups in the PDMS rubber molecule have been replaced with phenyl groups or the like.

[0035] Furthermore, by making the rubber into a powder or fine particles, the surface area increases, allowing it to absorb CO2 quickly. From the viewpoint of CO2 adsorption and desorption speed, it is preferable to use rubber such as PDMS that has been powdered or microparticulated to a size of 500 μm or less.

[0036] Moreover, pellet-shaped rubber is preferably used because it is easy to handle, such as for replacement work. Furthermore, CO2 adsorption into rubber pellets begins near the rubber surface, but the adsorption rate slows significantly at depths of 2.5 mm or more from the surface. Therefore, from the perspective of CO2 adsorption rate, the thickness of rubber pellets is preferably 5 mm or less. While there is no particular lower limit on the rubber thickness, a thickness of 0.1 mm or more is preferred for ease of handling and quality stability. Therefore, when rubber is made into pellets, its thickness is preferably between 0.1 mm and 5 mm. CO2 desorption using rubber can be achieved by reducing the pressure, and does not require heating, which means it consumes little energy.

[0037] Here, in order to facilitate replacement of the rubber, it is preferable that the rubber be packed in a mesh or porous bag and provided in the adsorption tower 41.

[0038] The adsorption / separation device 80 may have a first adsorption tower group consisting of a plurality of adsorption towers 41a and a second adsorption tower group consisting of a plurality of adsorption towers 41b. The first adsorption tower group may, for example, include a plurality of adsorption towers 41a arranged in series. Similarly, the second adsorption tower group may, for example, include a plurality of adsorption towers 41b arranged in series. The adsorption / separation device 80 may include the first adsorption tower group and the second adsorption tower group, thereby improving the amount and efficiency of CO2 adsorption. FIG. 5 illustrates an example of an adsorption tower group (first adsorption tower group, second adsorption tower group) in which three adsorption towers 41_1, 41_2, and 41_3 are arranged in series. Note that when each adsorption tower group (first adsorption tower group, second adsorption tower group) includes three or more adsorption towers 41, not all of the three or more adsorption towers 41 need to be directly connected, and some of the adsorption towers 41 (i.e., two or more adsorption towers 41) may be connected in series. Furthermore, the first and second adsorption tower groups are preferably paired adsorption tower groups with the same configuration, i.e., the first and second adsorption tower groups preferably have the same number of adsorption towers and the same arrangement of the adsorption towers, as well as the same internal configuration of each adsorption tower.

[0039] After conducting various experiments, it was found that the breakthrough time per adsorption tower (41) was optimal for improving the amount of CO2 adsorption and the adsorption / desorption efficiency when it was between 5 and 60 minutes.

[0040] In the present invention, rubber is used as the CO2 adsorbent, and powder or particulate form is preferably used to improve the adsorption amount and adsorption efficiency. In this case, the gaps between the rubber particles are large and the pressure during adsorption is high, between 5 MPa and 45 MPa, so desired gases such as methane are easily trapped there, which causes the problem of a low recovery rate of the desired gas. To solve this problem, the present invention provides a gas recirculation system 70 including a high-concentration CO2 gas discharge device 45 and a recirculation pipe 16, and reprocesses the gas containing high concentrations of CO2 using a cryogenic separation device, which is the first CO2 separation facility 1, thereby increasing the recovery rate of the desired gas. This process achieves a recovery rate of 90% or more of the desired gas.

[0041] It is essential that the gas reflux equipment 70 includes a reflux pipe 16. In the above embodiment, a pump is used as the high-concentration CO2 gas discharger 45, but various other devices can be used for the high-concentration CO2 gas discharger 45. For example, if a compressor (a type of pump) is used as the high-concentration CO2 gas discharger 45, gas containing a high concentration of CO2 can be pressurized and forcibly sent to the first CO2 separation equipment 1. On the other hand, if a pump is used as the high-concentration CO2 gas discharger 45, the temperature of the adsorption tower can be raised by sending a heat medium to the second CO2 separation equipment 2, and the desorbed CO2 is then sent to the first CO2 separation equipment 1. That is, in addition to the reflux pipe 16, the gas reflux equipment 70 may include, for example, a pump (compressor), a heating device, or both a pump (compressor) and a heating device. Gas can also be refluxed by applying heat to the adsorption / separation equipment 80 using a heating device. When a large amount of CO2 is to be desorbed, a compressor capable of reducing the pressure inside the adsorption tower of the second CO2 separation equipment 2 is preferably used.

[0042] The CO2 separation system using rubber as an adsorbent is capable of separating high-concentration CO2 and requires less energy than chemical absorption methods using amine solvents. Furthermore, the reflux of gas containing the high-concentration CO2 mentioned above allows for a high recovery rate of the desired gas.

[0043] When the equipment of this embodiment was used to process a mixed gas mainly composed of methane with a CO2 concentration of approximately 70%, it was confirmed that CO2 could be separated efficiently with low energy consumption and that methane gas with a CO2 concentration of 2% or less could be efficiently supplied. The CO2 separation system of the present invention can be said to make it possible to transport natural gas extracted in polar regions via pipeline at low cost. Since biogas also generally contains high concentrations of CO2, the CO2 separation system of the present invention is also effective in treating biogas. [Example]

[0044] The present invention will be described in detail with reference to examples, but the present invention is not limited to the examples.

[0045] <CO2 Separation System>

[0046] Using a mixed gas of CO2 and N2 as the gas to be treated, CO2 was separated from the gas to be treated by the following CO2 separation system. The CO2 separation system according to the embodiment was composed of the following elements. Each of the following elements is connected through pipes. Gas cylinder for the gas to be treated (CO2 gas cylinder and N2 gas cylinder) Gas flow meter for adjusting the flow rate of the CO2 gas cylinder Gas flow meter for adjusting the flow rate of the N2 gas cylinder First cooling device for removing a part of CO2 and moisture contained as impurities in the gas to be treated Column filled with rubber as a CO2 adsorbent (KMP-602 manufactured by Shin-Etsu Chemical Co., Ltd. (true specific gravity 0.98, particle size distribution 4 - 60 μm) or crushed product of K-125 manufactured by Tokawa Rubber Co., Ltd. (true specific gravity 1.20, particle size distribution 350 - 1000 μm)) (Column volume: 22.6 cm 3 , rubber filling rate: 76.7% (KMP-602), 77.0 (K-125)) Second cooling device for controlling the column temperature Pressure gauge for measuring the pressure of the column and the CO2 recovery container Column flow meter for controlling the column pressure Gas chromatograph for measuring the concentration of components in the gas discharged from the column CO2 recovery container for recovering CO adsorbed on the rubber Third cooling device for controlling the temperature of the CO2 recovery container Note that the above first cooling device, third cooling device, and CO2 recovery container are examples of the first CO2 separation facility (cryogenic separation device), and the above column is an example of the second CO2 separation facility.

[0047] Using the above CO₂ separation system, a CO₂ adsorption test and a CO₂ desorption recovery test were conducted. The piping connection after the column is different between the CO₂ adsorption test and the CO₂ desorption recovery test, and is switched by a valve installed in the pipe immediately after the column. Specifically, during the CO₂ adsorption test, the column is connected to a gas chromatograph via a flow meter that controls the column pressure, and during CO₂ desorption recovery, it is connected to a CO₂ recovery container.

[0048] The pressure of the gas to be treated was adjusted with the secondary pressure gauge of the regulator. The gas to be treated was passed through a first cooling device that removes moisture, and the gas after removing moisture was supplied to the column.

[0049] <Calculation method of CO₂ adsorption amount> The CO₂ adsorption amount was adopted as the CO₂ adsorption amount at the time when the time change of the outlet concentration of the adsorption tower that can maximize the adsorption and desorption efficiency became C / C₀ = 1 / 3 in the characteristic diagram (breakthrough time characteristic of CO₂ gas) showing the adsorption and desorption characteristics of CO₂ using the rubber in Fig. 6. The CO₂ adsorption amount is the area of the shaded part in the figure and was calculated from "adsorption amount = CO₂ concentration (C / C₀) × time (time when C / C₀ = 1 / 3) × flow rate".

[0050] [Example 1] KMP-602 manufactured by Shin-Etsu Chemical Co., Ltd. was used as the CO₂ adsorbent. The gas to be treated had 20 mol% CO₂ and 80 mol% N₂. The column pressure was 6 MPa and the column temperature was -30°C. Specifically, first, the column temperature was maintained at -30°C with the second cooling device, only N₂ was flowed into the column, and the column pressure was increased to 6 MPa by setting the flow rate of the column flow meter that controls the column pressure to zero. Thereafter, the supply gas flow rates of the CO₂ gas cylinder and the N₂ gas cylinder were adjusted to 40 sccm and 120 sccm, respectively, with the gas flow meters connected thereto, and the mixed gas to be treated was flowed into the column. At the same time, the CO₂ adsorption test was started by adjusting the flow rate of the column flow meter that controls the column pressure to 200 sccm, the CO₂ concentration at a predetermined time was measured with a chromatograph, and the CO₂ adsorption amount was calculated.

[0051] After the CO2 adsorption amount on the rubber adsorbent reached saturation (C / C0 = 1), the supply of the gas to be treated was stopped, and the valve immediately downstream of the column was connected to a CO2 capture vessel to initiate the CO2 desorption and capture test. The CO2 desorption and capture amount was measured. The column temperature during CO2 desorption and capture was 23°C, and the capture vessel temperature was -40°C. The CO2 desorption and capture test was terminated when the pressure between the column and the CO2 capture vessel became constant. The CO2 desorption and capture amount was calculated from the weight change of the CO2 capture vessel before and after the test. In the configuration of the separation system of the present invention, a pump, more specifically a compressor, is preferably used as the high-concentration CO2 gas discharge device, a component of the gas reflux equipment, to forcibly transfer the high-concentration CO2 gas discharged from the column to the cryogenic separation device. However, in experiments with CO2 capture amounts of 1 kg or less, it is not possible to stably transfer the gas by pressurizing it with a compressor. Therefore, in this example, the temperature of the CO2 adsorption tower is increased to reflux the gas to the cryogenic separation device in order to achieve pressure-driven mass transfer (gas transfer) similar to that achieved by a compressor.

[0052] Figure 8 shows the breakthrough curve for Example 1. The amount of CO2 adsorbed was 1.8 g based on the area of ​​the shaded portion in Figure 8, and the breakthrough time was 23 minutes, compared to the target value of 5 to 60 minutes, indicating good adsorption characteristics. Table 1 shows the results of the CO2 adsorption test and the CO2 desorption and recovery test.

[0053] The pressure in the column and recovery vessel during CO2 desorption and recovery was 2.9 MPa, and the amount of CO2 desorbed and recovered was 1.3 g, with a recovery rate of 72 mol%, indicating that a sufficiently high concentration of CO2 was recovered. In addition, since CO2 liquefies at -40°C and 1 MPa, the desorbed and recovered CO2 is considered to be liquefied CO2.

[0054] As described above, Example 1 showed good adsorption characteristics with a breakthrough time of 23 minutes and an adsorption amount of 1.8 g under conditions of an adsorption pressure of 6 MPa and a CO2 concentration of 20 mol% in the gas to be treated.Furthermore, the temperature during desorption and recovery was -40°C, and the liquefied CO2 recovery rate was 72%, demonstrating good desorption and recovery characteristics.

[0055] [Table 1]

[0056] [Example 2] Crushed K-125 manufactured by Togawa Rubber Co., Ltd. was used as the CO2 adsorbent. A desorption experiment was conducted on 1.8 g of CO2 adsorbed using the same equipment as in Example 1. Table 2 shows the results of the CO2 adsorption test and the CO2 desorption and recovery test. The pressure in the column and recovery vessel during CO2 desorption and recovery was 1.0 MPa, and the amount of CO2 desorbed and recovered was 1.7 g, giving a recovery rate of 94 mol%, indicating that a very high concentration of CO2 was recovered.

[0057] [Table 2] [Industrial Applicability]

[0058] The present invention makes it possible to efficiently remove CO2 from natural gas, biogas, and other sources that contain large amounts of CO2. This makes it possible, for example, to process natural gas containing high concentrations of CO2 at low cost and supply it via pipelines at low cost. In this way, the present invention makes it possible to effectively utilize gases that have been difficult to utilize until now, and is believed to greatly contribute to the development of industry and society.

[0059] Taking the case of natural gas development as an example, a CO2 separation system is provided that separates CO2 from natural gas containing high concentrations of CO2 of 30% or more and supplies it at 2% or less. Natural gas containing large amounts of CO2 can cause problems with freezing in cold regions such as polar regions. Furthermore, natural gas containing 2% or more of CO2 can corrode pipelines. However, by using the CO2 separation system of the present invention, natural gas containing high concentrations of CO2 can be efficiently processed at low cost, enabling it to be transported inexpensively via pipeline. [Explanation of symbols]

[0060] 1: First CO2 separation facility (cryogenic separation device) 2: Second CO2 separation facility 3: Cooling equipment 4: Pressure reducing equipment 5: Dehydration equipment 11: Piping 12: Piping 13: Piping 14: Piping (first piping) 15: Piping 16: Reflux piping (second piping) 17: Discharge piping 21: Compression device 22: Dehydration equipment 23: Cooling device 24:Liquefied CO2 emission device 31: Piping 32: Piping 33: Piping 41:Adsorption tower 41a: Adsorption tower 41b: Adsorption tower 41_1:Adsorption tower 41_2:Adsorption tower 41_3:Adsorption tower 42: Flow path 43: Space 45: High concentration CO2 gas exhaust device 46:Flow regulator 51: Switching valve 52: Switching valve 53: Switching valve 60: Low concentration CO2 gas emission equipment 70: Gas reflux equipment 80: Adsorption separation device 101: CO2 separation system

Claims

1. First CO ２ Separation equipment; Second CO ２ Separation equipment; A first pipe; low concentration CO ２ Gas exhaust equipment; Second pipe and high concentration CO ２ a gas return facility having a gas exhaust device; The first CO ２ The separation equipment separates CO from the gas to be treated by cryogenic separation. ２ and a cryogenic separation device for separating the The first pipe is ２ The gas discharged from the separation equipment is ２ Supply to separation equipment, The second CO ２ The separation facility separates the rubber into CO ２ An adsorption separation device is provided as an adsorbent, The low concentration CO ２ The gas exhaust equipment is ２ Low concentration CO ２ Discharge gas containing The high concentration CO ２ The gas discharge device ２ CO with a concentration higher than the low concentration is separated from the separation equipment. ２ It emits gas containing In the gas reflux facility, the high concentration CO ２ At least a part of the gas discharged from the gas discharge device is discharged to the first CO ２ Return to the separation facility The first CO ２ The separation equipment separates CO from the gas returned by the gas reflux equipment. ２ A cryogenic separation process is carried out to separate CO ２ Separation system.

2. the adsorption separation device includes a first adsorption tower group consisting of one or more adsorption towers and a second adsorption tower group consisting of one or more adsorption towers, The adsorption tower has a flow path through which the gas flows while being retained therein, and ２ having an adsorbent, The CO in question ２ The separation system includes the flow path and the CO ２ The adsorbent further includes a cooling means capable of cooling the adsorbent. The CO according to claim 1 ２ Separation system.

3. the first adsorption tower group and the second adsorption tower group are paired adsorption tower groups having the same configuration; The CO according to claim 2 ２ Separation system.

4. at least some of the adsorption towers constituting the first adsorption tower group and the second adsorption tower group are arranged in series within the first adsorption tower group and the second adsorption tower group; The CO according to claim 2 ２ Separation system.

5. 3. The CO 2 adsorption system according to claim 2, wherein the gas breakthrough time per adsorption tower is 5 minutes or more and 60 minutes or less. ２ Separation system.

6. CO in the gas introduced into the first group of adsorption towers and the second group of adsorption towers ２ The concentration is adjusted to 10 mol% or more and 40 mol% or less, CO in the gas discharged from the first group of adsorption towers and the second group of adsorption towers ２ The concentration was adjusted to 2 mol% or more and 10 mol% or less. The CO according to claim 2 ２ Separation system.

7. CO in the gas introduced into the first group of adsorption towers and the second group of adsorption towers ２ The concentration is adjusted to 5 mol% or more and 10 mol% or less, CO in the gas discharged from the first group of adsorption towers and the second group of adsorption towers ２ The concentration was adjusted to 0 mol% or more and 2 mol% or less. The CO according to claim 2 ２ Separation system.

8. The adsorption pressure of the adsorption tower is adjusted to 5 MPa or more and 45 MPa or less. The CO according to claim 2 ２ Separation system.

9. The cooling temperature is −50° C. or higher and 0° C. or lower. The CO according to claim 2 ２ Separation system.

10. The high concentration of CO ２ The concentration of is 50 mol% or more and 99 mol% or less, The CO according to claim 1 ２ Separation system.

11. The rubber is provided in one or more states selected from the group consisting of pellets, powder, and fine particles. The CO according to claim 1 ２ Separation system.

12. The rubber is provided in a mesh or perforated bag. The CO according to claim 11 ２ Separation system.

13. The cryogenic separation device includes a compressor that compresses the supplied gas, a cooling device that cools the gas introduced through the compressor, and a CO liquefied by the cooling. ２ and a device for discharging the The CO according to claim 1 ２ Separation system.

14. The gas to be treated is decompressed to form liquid CO ２ is introduced into the cryogenic separation device through a decompression facility that separates The CO according to claim 1 ２ Separation system.

15. The gas to be treated is introduced into the cryogenic separation device through a dehydration facility that performs dehydration. The CO according to claim 1 ２ Separation system.

Images