Carbon dioxide capture device and carbon dioxide capture method

Abstract

To reduce energy consumption for recovering carbon dioxide.SOLUTION: A carbon dioxide recovery apparatus comprises a separation processing unit that separates carbon dioxide contained in a raw material gas from the raw material gas by a membrane that allows for permeation of carbon dioxide, a suction unit that suctions a processing gas containing carbon dioxide separated from the raw material gas, a cooling unit that is disposed upstream of the suction unit and cools the processing gas using a refrigerant, a vaporization unit that gasifies a liquefied gas using the refrigerant, and a circulation unit that circulates the refrigerant between the cooling unit and the vaporization unit such that the refrigerant repeats a temperature increase accompanying cooling of the processing gas and a temperature decrease accompanying gasification of the liquefied gas.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a carbon dioxide capture device, a combustion system, a power generation system, and a carbon dioxide capture method. [Background Art]

[0002] Technologies for separating and recovering carbon dioxide from a gas containing carbon dioxide are known (see, for example, the following Patent Documents 1 to 3 and Non-Patent Document 1). Patent Document 1 discloses a gas separation device that separates carbon dioxide and water vapor from a mixed gas containing carbon dioxide and water vapor as main component gases. Patent Document 2 discloses a gas recovery device that individually separates carbon dioxide and an inert gas from a mixed gas containing carbon dioxide and an inert gas as main components. Patent Document 3 discloses a gas separation system including a carbon dioxide separation membrane that separates carbon dioxide, and a water vapor removing means that removes water vapor from the gas from which carbon dioxide has been separated. Patent Document 4 discloses a membrane that has high carbon dioxide permeability and can selectively permeate carbon dioxide over nitrogen and the like. Non-Patent Document 1 discloses a technology for recovering carbon dioxide by a chemical absorption method utilizing a chemical reaction between a basic substance and carbon dioxide. [Prior Art Documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. WO 2012 / 086836 [Patent Document 2] International Publication No. WO 2017 / 086293 [Patent Document 3] Japanese Unexamined Patent Publication No. 2017-221864 [Patent Document 4] International Publication No. WO 2017 / 146231 [Non-Patent Documents]

[0004] [Non-Patent Document 1] Shigeo Murai et al., "CCS (CO2 Storage, Capture, and Separation Technology)," Journal of the Japan Society of Mechanical Engineers, April 2011, Vol. 114, No. 1109, pp. 26-28. [Overview of the project] [Problems that the invention aims to solve]

[0005] This disclosure provides a carbon dioxide capture device, combustion system, power generation system, and carbon dioxide capture method that can reduce the energy consumption required to capture carbon dioxide. [Means for solving the problem]

[0006] [1] A separation unit that separates carbon dioxide contained in the raw material gas from the raw material gas using a carbon dioxide permeable membrane, A suction unit for drawing in a processed gas containing carbon dioxide separated from the aforementioned raw material gas, A cooling unit is located upstream of the suction unit and cools the processing gas using a refrigerant, A vaporization unit that gasifies the liquefied gas using the aforementioned refrigerant, A carbon dioxide recovery apparatus comprising a circulation unit that circulates the refrigerant between a cooling unit and a vaporization unit such that the refrigerant repeatedly experiences a temperature rise due to the cooling of the process gas and a temperature decrease due to the gasification of the liquefied gas. [2] The recovery apparatus according to [1] above, wherein the temperature of the refrigerant supplied from the circulation unit to the cooling unit is 1°C to 20°C. [3] Further comprising a water vapor-containing gas supply unit that supplies a water vapor-containing gas containing water vapor to the separation processing unit, The separation processing unit has a membrane that is arranged to separate a first space to which the raw material gas is supplied from a second space. The water vapor-containing gas supply unit is the recovery device of [1] or [2] above, which supplies the water vapor-containing gas to the second space. [4] Another cooling unit located downstream of the suction unit, which uses the refrigerant to cool the gas released by the suction unit, A recovery device according to any of the above [1] to [3], further comprising another suction unit located downstream of the other cooling unit for sucking up the gas released by the suction unit. [5] The recovery device according to [4], wherein the pressure of the gas discharged from the recovery device through at least the suction unit and the other suction unit is 1 atmosphere or more. [6] The liquefied gas is liquefied natural gas, and the recovery device is one of the above [1] to [5]. [7] The recovery device described in [6] above, The system comprises a combustion device for burning natural gas obtained by gasifying the liquefied natural gas in the vaporization section, A combustion system comprising the raw material gas supplied to the separation processing unit, including exhaust gas discharged from the combustion device. [8] The recovery device described in [6] above, The device comprises a power generation apparatus that generates electricity by burning natural gas obtained when the liquefied natural gas is gasified in the vaporization section, A power generation system in which the raw material gas supplied to the separation processing unit includes exhaust gas discharged from the power generation device. [9] A separation step of separating carbon dioxide contained in the raw material gas from the raw material gas using a carbon dioxide permeable membrane, A suction step of drawing in a processed gas containing carbon dioxide separated from the raw material gas, Upstream from the suction in the aforementioned suction step, a cooling step is performed in which the process gas is cooled using a refrigerant, A gasification step in which the liquefied gas is gasified using the aforementioned refrigerant, A method for recovering carbon dioxide, comprising a circulation step of circulating the refrigerant such that the refrigerant repeatedly experiences a temperature rise due to the cooling of the process gas and a temperature decrease due to the gasification of the liquefied gas.

[10] The recovery method according to [9] above, wherein the liquefied gas is liquefied natural gas.

[11] The gasification step further includes a combustion step of burning the natural gas obtained by gasifying the liquefied natural gas, The recovery method of

[10] above, wherein the raw material gas includes exhaust gas discharged in the combustion process.

[12] The method further comprises a power generation step of generating electric power by burning natural gas obtained by gasifying the liquefied natural gas in the gasification step, The recovery method according to

[10] above, wherein the raw material gas comprises exhaust gas discharged in the power generation step.

Effect of the Invention

[0007] According to the present disclosure, there are provided a carbon dioxide recovery apparatus, a combustion system, a power generation system, and a carbon dioxide recovery method that can reduce energy consumption for recovering carbon dioxide.

Brief Description of Drawings

[0008] [Figure 1] Fig. 1 is a schematic diagram showing an example of a carbon dioxide recovery apparatus. [Figure 2] Fig. 2 is a schematic diagram showing an example of a separation apparatus. [Figure 3] Fig. 3 is a schematic diagram showing another example of a separation apparatus. [Figure 4] Fig. 4 is a schematic diagram showing an example of a combustion system. [Figure 5] Fig. 5 is a schematic diagram showing an example of a power generation system.

Mode for Carrying Out the Invention

[0009] Hereinafter, an embodiment will be described with reference to the drawings. In the description, the same reference numerals are assigned to the same elements or elements having the same function, and duplicate descriptions are omitted.

[0010] [Carbon Dioxide Recovery Apparatus] Figure 1 is a schematic diagram showing an example of a carbon dioxide recovery device. The carbon dioxide recovery device 10 shown in Figure 1 is a device that recovers carbon dioxide from a raw material gas containing carbon dioxide. Specifically, the recovery device 10 separates the carbon dioxide contained in the supplied raw material gas (hereinafter referred to as "raw material gas G0") from the raw material gas G0 and recovers a gas with a higher purity (concentration) of carbon dioxide than the raw material gas G0. The concentration of carbon dioxide in the gas obtained by recovering carbon dioxide with the recovery device 10 may be 70% or more, 80% or more, or 90% or more.

[0011] As the raw material gas G0, for example, combustion exhaust gas, indoor or outdoor air, biogas, or fossil fuels reformed with steam can be used. Combustion exhaust gas may be exhaust gas discharged after combustion in petroleum refining facilities, petrochemical and chemical plants, steel plants, cement facilities, factories, agricultural heaters, engines of automobiles, gas heat pumps, boilers, combustion water heaters, or power plants (for example, power generation facilities that use fossil fuels, biomass, biogas, garbage, or waste as fuel). Combustion exhaust gas may also be the gas remaining after burning fossil fuels, biomass, biogas, garbage, or waste with a gas containing more oxygen than air. Combustion exhaust gas mainly consists of nitrogen, carbon dioxide, oxygen, and steam, and may also contain trace components such as ash, sulfur oxides, or nitrogen oxides. The concentration of carbon dioxide in the combustion exhaust gas may be 30% or less, 20% or less, or 10% or less.

[0012] The raw material gas G0 contains carbon dioxide and water vapor, as well as gaseous components other than carbon dioxide and water vapor. These gaseous components include, for example, nitrogen, oxygen, methane, or hydrogen. An example of the recovery device 10 will be described in detail below. In this disclosure, the terms "upstream" and "downstream" are used in reference to the gas flow. That is, the gas flows from upstream to downstream in the gas flow path. As shown in Figure 1, the recovery device 10 comprises a vaporizer 20 (vaporization section), a separation device 30, and a circulation device 60 (circulation section).

[0013] The vaporizer 20 is a device that generates gas by vaporizing (converting) liquefied gas. The liquefied gas vaporized by the vaporizer 20 is a gas with a boiling point of 0°C or lower. The type of liquefied gas is not limited, and examples of liquefied gases include liquefied natural gas (LNG), liquefied hydrogen, liquefied ammonia, and liquefied carbon dioxide. Below, an example where the liquefied gas is liquefied natural gas (LNG) will be described. The vaporizer 20 may generate natural gas (Gn) by vaporizing (converting) liquefied natural gas (LNG). In addition to vaporizing liquefied natural gas (LNG), the vaporizer 20 may also have a function to raise the temperature of the natural gas (Gn) after gasification. For example, liquefied natural gas (LNG) is supplied to the vaporizer 20 from a tank in which it is stored by a pump or the like.

[0014] The vaporizer 20 uses the fluid supplied from the circulation device 60 to gasify (re-gasify) liquefied natural gas (LNG). The fluid supplied from the circulation device 60 to the vaporizer 20 is used to cool the gas in the separation device 30, as described later. Therefore, even when the fluid supplied from the circulation device 60 is used for gasification in the vaporizer 20, it is also referred to as "refrigerant." The vaporizer 20 may also use the refrigerant from the circulation device 60 to gasify and heat the liquefied natural gas (LNG). The vaporizer 20 may also supply the generated natural gas (Gn) to a device that generates energy such as electricity or heat using the natural gas (Gn) as fuel.

[0015] The separation device 30 is a device that separates carbon dioxide from the raw material gas G0. The combustion exhaust gas may be supplied to the separation device 30 as the raw material gas G0. The separation device 30 discharges gas Gd1 and gas Gd2. Gas Gd1 is the gas remaining after carbon dioxide has been removed from the raw material gas G0. Gas Gd2 is the gas containing carbon dioxide that has been removed from the raw material gas G0. Figure 2 is a schematic diagram showing an example of the separation device in more detail. Note that some elements of the separation device 30 are omitted in Figure 1. The separation device 30 may have a separation processing unit 40 and an discharge processing unit 50, as shown in Figure 2.

[0016] The separation processing unit 40 is a processing unit that extracts at least a portion of the carbon dioxide in the raw material gas G0. The separation processing unit 40 separates the carbon dioxide contained in the raw material gas G0 from the raw material gas G0 using a membrane that permeates carbon dioxide. The separation processing unit 40 generates a gas (hereinafter referred to as "processed gas Gp") in which the proportion of carbon dioxide to components other than carbon dioxide and water vapor is greater than that of the raw material gas G0. That is, the proportion of carbon dioxide to components other than carbon dioxide and water vapor in the processed gas Gp is ​​greater than the proportion of carbon dioxide to components other than carbon dioxide and water vapor in the raw material gas G0. The separation processing unit 40 has, for example, a housing 42 and a separation member 44. The housing 42 houses the separation member 44 and also forms an internal space.

[0017] The separation member 44 is a component that separates carbon dioxide from the raw material gas G0 by a separation membrane that selectively permeates carbon dioxide contained in the raw material gas G0. The separation member 44 is positioned to divide the internal space formed by the housing 42 into two spaces. Hereinafter, the space to which the raw material gas G0 is supplied will be referred to as the "first space V1" and the other space will be referred to as the "second space V2". In other words, the separation member 44 is positioned inside the housing 42 to separate the first space V1 and the second space V2.

[0018] The separation member 44 includes a separation membrane 46 that selectively permeates carbon dioxide (or carbon dioxide and water vapor) from the raw material gas G0. In this disclosure, selective permeation of one or more components means permeating a portion of the gas such that the amount of permeation of one or more components from among the various components contained in the supplied gas is greater than the amount of permeation of other components. The separation membrane 46 is a membrane that has the property of permeating carbon dioxide and water vapor from among the various components contained in the raw material gas G0 more easily than components other than carbon dioxide and water vapor (for example, nitrogen, oxygen, methane, or hydrogen). The separation membrane 46 may be made of an alkaline material. The separation membrane 46 may be made of the material (gelling polymer particles) described in Patent Document 4 above.

[0019] The separation membrane 46 includes, for example, a single layer membrane containing gelling polymer particles containing a basic functional group. Gelating polymer particles are polymer particles that have the property of swelling in water or a polar solvent to become gel-like fine particles. Gelating polymer particles may also be, for example, particles of neutral, alkaline, or acidic polymer compounds impregnated with basic molecules. The thickness of the single layer membrane containing the gelling polymer particles may be less than 50 μm. The functional group contained in the gelling polymer particles may be one or more functional groups selected from the group consisting of amino groups, ammonium groups, carboxylic acids, and sulfuric acids. The polymer compound constituting the gelling polymer particles may be a polymer of monomer components containing monomers having a basic functional group or an acidic functional group. The impregnating basic molecule may contain an amine-containing compound with a molecular weight of 61 to 10000, and the pKa of the conjugate acid of the amine-containing compound may be 5 to 10. The impregnating basic molecule may have a hydroxyl group, a carboxylic acid group, or a sulfonic acid group. Alternatively, the basic molecule to be impregnated may have multiple amino groups or multiple hydroxyl groups.

[0020] The above monomer may include a substituted acrylamide monomer, an N-(aminoalkyl)acrylamide, or a carboxylic acid or sulfonic acid. In the above monomer component, the proportion of monomers having a carboxylic acid or sulfonic acid may be 1 to 95 mol%, or 5 to 95 mol%. The above monomer component may include a monomer having a carboxylic acid or sulfonic acid and a monomer having a hydrophobic group. In this case, the molar ratio of monomers having a carboxylic acid or sulfonic acid to monomers having a hydrophobic group may be 1:95 to 95:5. The monomer having a carboxylic acid may be methacrylic acid or acrylic acid, and the monomer having a hydrophobic group may be N-alkylacrylamide. Alternatively, the monomer having a sulfonic acid may be acrylamide t-butylsulfonic acid or vinylsulfonic acid, and the monomer having a hydrophobic group may be N-alkylacrylamide.

[0021] The gelling polymer particles may be crosslinked polymer compounds. Crosslinking may be formed by copolymerizing monomers having multiple polymerizable functional groups (crosslinking agents) during polymerization, or by forming covalent crosslinking points through chain transfer during polymerization without the use of a crosslinking agent. Crosslinking points may also be formed by generating covalent bonds through reactions between polymer chains after polymerization. Furthermore, crosslinking points may be formed by interactions or entanglement between polymers, even if they are covalent bonds.

[0022] The separation member 44 may include a carrier 46a that supports the separation membrane 46. The carrier 46a may be a porous material (for example, a porous film). The single-layer membrane containing gelling polymer particles may be formed by applying an aqueous solution containing gelling polymer particles to the surface of a porous film and drying the aqueous solution. The gelling polymer particles may be large enough to block the surface pores contained in the porous carrier 46a. The particle diameter of the gelling polymer particles may be larger than the surface pores of the porous carrier 46a. The porous carrier 46a has a first surface and a second surface facing opposite directions, and the surface pores on the first surface may not be blocked by the polymer particles, while the surface pores on the second surface may not be blocked by the polymer particles. In this case, the separation membrane 46 and the carrier 46a may be arranged such that the first surface faces the first space V1 and the second surface faces the second space V2. The carrier 46a may have a regular uneven surface structure that is sufficiently larger than the surface pores.

[0023] The raw material gas G0 is supplied to the first space V1 inside the housing 42. The pressure in the first space V1 to which the raw material gas G0 is supplied may be around 101 kPa (about the same as 1 atmosphere) or may be greater than 1 atmosphere. The second space V2 may be maintained at a lower pressure than the pressure in the first space V1 (for example, a pressure less than 1 atmosphere). The pressure in the second space V2 may be about half or less of the pressure in the first space V1. The pressure in the second space V2 may be 50 kPa or less, 30 kPa or less, or 20 kPa or less. If the diameter of the polymer particles contained in the separation membrane 46 is larger than the pore size of the porous carrier 46a, the separation membrane 46 will be less likely to be damaged by the pressure difference between the first space V1 and the second space V2.

[0024] The separation device 30 may have a water vapor-containing gas supply unit 38. The water vapor-containing gas supply unit 38 supplies water vapor-containing gas to the separation processing unit 40. The water vapor-containing gas (hereinafter referred to as "water vapor-containing gas Gs") supplied by the water vapor-containing gas supply unit 38 to the second space V2 of the separation processing unit 40 promotes the separation of carbon dioxide by the separation member 44 (persistence of carbon dioxide through the separation membrane 46). Specifically, the supply of water vapor-containing gas Gs dilutes the carbon dioxide in the second space V2, and the partial pressure of carbon dioxide in the second space V2 becomes lower than the partial pressure of carbon dioxide in the first space V1. As a result, more carbon dioxide is separated by the separation membrane 46 of the separation member 44 compared to when water vapor-containing gas Gs is not supplied.

[0025] The water vapor-containing gas Gs can be any gas as long as it contains water vapor and allows for the dilution of carbon dioxide in the second space V2. The water vapor-containing gas Gs may also contain other gaseous components besides water vapor. The water vapor-containing gas supply unit 38 may generate the water vapor-containing gas Gs using waste heat generated in a factory or the like. The temperature of the water vapor-containing gas Gs may be adjusted to further promote the permeation of carbon dioxide by the separation membrane 46. The temperature of the water vapor-containing gas Gs supplied from the water vapor-containing gas supply unit 38 to the second space V2 may be between 25°C and 100°C. Alternatively, the temperature of the water vapor-containing gas Gs may be between 30°C and 90°C, or between 35°C and 80°C.

[0026] The separation processing unit 40 discharges gas Gd1, which has been extracted from the raw material gas G0, from the first space V1. The separation processing unit 40 may also discharge gas Gd1 to the outside (into the atmosphere) from the first space V1. The separation member 44 separates carbon dioxide and water vapor from components other than carbon dioxide and water vapor in the raw material gas G0 (by selective permeation from the first space V1 to the second space V2), thereby generating the above-mentioned processed gas Gp in the second space V2. If a water vapor-containing gas supply unit 38 is provided, this processed gas Gp contains, in addition to carbon dioxide, water vapor in the raw material gas G0 and water vapor in the water vapor-containing gas Gs. The relative humidity of the processed gas Gp may be, for example, 50% or more, 60% or more, or 70% or more.

[0027] The discharge processing unit 50 is a processing unit that sucks in the gas in the second space V2 and removes at least a portion of the water vapor in the processed gas Gp. The discharge processing unit 50 discharges the gas that has been sucked in from the second space V2 and from which the water vapor has been removed as the gas Gd2 described above. The discharge processing unit 50 may also discharge the gas Gd2 to the outside of the separation device 30.

[0028] The discharge processing unit 50 includes, for example, a plurality of suction units (suction devices) and a plurality of cooling units (cooling devices). In the following example, the discharge processing unit 50 will have two suction units and three cooling units. The two suction units will be referred to as "suction unit 52a" and "suction unit 52b," and the three cooling units will be referred to as "cooling unit 54a," "cooling unit 54b," and "cooling unit 54c." The suction units 52a, 52b and the cooling units 54a, 54b, and 54c are connected to each other via a gas flow path that extends from the second space V2 to the gas Gd2 outlet.

[0029] In the gas flow path between the second space V2 and the gas outlet Gd2, the cooling section 54a, suction section 52a, cooling section 54b (another cooling section), suction section 52b (another suction section), and cooling section 54c are arranged in this order from the upstream side. Hereafter, the intermediate stage (in-process) gas released from each of these devices will also be referred to as "processed gas Gp".

[0030] The suction unit 52a is connected to the second space V2 via a gas flow path and is a device that sucks the processing gas Gp in the second space V2. The suction unit 52a may also be a compressor or pump (e.g., a vacuum pump) that reduces the pressure in the second space V2. The suction unit 52a sucks the processing gas Gp in the second space V2, which lowers the pressure in the second space V2. The suction unit 52a may suck the gas in the second space V2 so that the pressure in the second space V2 is maintained at a value lower than the pressure in the first space V1.

[0031] The cooling unit 54a is a device that cools the processed gas Gp released from the second space V2 using a refrigerant supplied from the circulation device 60. The cooling unit 54a is located between the second space V2 and the suction unit 52a. More specifically, the cooling unit 54a is located between the second space V2 and the suction unit 52a (upstream of the suction unit 52a) in the flow path through which the processed gas Gp released from the second space V2 flows. In addition to the function of cooling the processed gas Gp with a refrigerant (heat exchange function), the cooling unit 54a may also have a function of separating gas and liquid.

[0032] Cooling by the cooling unit 54a reduces the amount of water vapor contained in the processed gas Gp. In this way, the cooling unit 54a removes at least a portion of the water vapor in the processed gas Gp, producing a gas with a higher purity of carbon dioxide than the processed gas Gp immediately after it is released from the second space V2. The cooling unit 54a may also discharge the liquid Ld removed from the processed gas Gp to the outside.

[0033] The suction unit 52a, located downstream of the cooling unit 54a, sucks (compresses) the processed gas Gp after at least a portion of the water vapor has been removed by the cooling unit 54a. The suction unit 52a releases the processed gas Gp at a higher pressure than the processed gas Gp immediately after it is released from the second space V2.

[0034] The suction unit 52b is connected in series with the suction unit 52a and is a device that sucks in the processed gas Gp released by the suction unit 52a. The suction unit 52b may be the same type of device as the suction unit 52a, or it may be a different type of device with different performance or cooling method. The cooling unit 54b is located in the gas flow path between the suction unit 52a and the suction unit 52b (downstream of the suction unit 52a). Similar to the cooling unit 54a, the cooling unit 54b may cool the processed gas Gp released from the suction unit 52a using a refrigerant supplied from the circulation device 60. The cooling unit 54b may cool the processed gas Gp with cooling water available at the cooling location instead of or in addition to the refrigerant from the circulation device 60, or it may cool the processed gas Gp by air cooling. Note that the temperature of the processed gas Gp released from the suction unit 52a rises with the suction by the suction unit 52a compared to the temperature of the processed gas Gp before suction (the processed gas Gp immediately after being released from the second space V2).

[0035] The suction unit 52b, located downstream of the cooling unit 54b, sucks (compresses) the processed gas Gp after at least a portion of the water vapor has been removed by the cooling unit 54b. The suction unit 52b releases processed gas Gp at a higher pressure than the processed gas Gp released by the suction unit 52a. The pressure of the processed gas Gp released by the suction unit 52b may be 1 atmosphere or higher.

[0036] The cooling unit 54c is located downstream of the suction unit 52b. Similar to the cooling unit 54b, the cooling unit 54c may cool the processed gas Gp discharged from the suction unit 52b using a refrigerant supplied from the circulation device 60. The cooling unit 54c may cool the processed gas Gp with cooling water available for cooling purposes, instead of or in addition to the refrigerant from the circulation device 60, or it may cool the processed gas Gp by air cooling. The temperature of the processed gas Gp discharged from the suction unit 52b rises compared to the temperature of the processed gas Gp before suction (processed gas Gp after cooling by the cooling unit 54b) due to suction by the suction unit 52b. The cooling units 54b and 54c may be the same type of device as the cooling unit 54a, or they may be different types of devices with different performance or cooling methods. The cooling unit 54c discharges the processed gas Gp, after cooling and removing water vapor, to the outside of the discharge processing unit 50 as the gas Gd2.

[0037] The discharge processing unit 50 described above uses two multi-stage connected suction units (suction units 52a, 52b) to draw gas from the second space V2. In the discharge processing unit 50, the pressure of the processed gas Gp released from the second space V2 is gradually increased by the suction units 52a, 52b. The pressure of the gas Gd2 discharged from the discharge processing unit 50 may be 1 atmosphere or higher. That is, the discharge processing unit 50 may increase the pressure of the processed gas Gp to 1 atmosphere or higher via the suction units 52a, 52b, and then discharge the gas Gd2 at a pressure of 1 atmosphere or higher.

[0038] Returning to Figure 1, the circulation device 60 is a device that circulates the refrigerant between the vaporizer 20 and at least the cooling section 54a of the separation device 30. The refrigerant circulated by the circulation device 60 (hereinafter referred to as "refrigerant Cm") may be of any type as long as it is capable of gasifying (or gasifying and heating) liquefied natural gas LNG in the vaporizer 20 and cooling the processed gas Gp in the separation device 30. Specific examples of refrigerant Cm include water (chiller water), oil, or antifreeze such as glycol. The circulation device 60 has pumps, etc., for sending the refrigerant Cm to the vaporizer 20 and the separation device 30, respectively.

[0039] The circulation device 60 circulates the refrigerant Cm between at least the cooling section 54a of the separation device 30 and the vaporizer 20 so that the refrigerant Cm repeatedly rises in temperature due to the cooling of the process gas Gp and falls in temperature due to the gasification of liquefied natural gas (LNG). When the vaporizer 20 performs gasification of liquefied natural gas (LNG) and also raises the temperature of the gas, the refrigerant Cm repeatedly rises in temperature due to the cooling of the process gas Gp and falls in temperature due to the gasification and heating of liquefied natural gas (LNG). Figure 2 shows the cases in which refrigerant Cm is supplied to the cooling sections 54a, 54b, and 54c, respectively, and below, the cases in which the cooling of the process gas Gp by refrigerant Cm is performed in each of the cooling sections 54a, 54b, and 54c will be described. Furthermore, an example will be given in which both gasification and heating are performed in the vaporizer 20.

[0040] The circulation device 60 supplies refrigerant Cm to the vaporizer 20 and recovers the refrigerant Cm after it has been used for gasification and heating in the vaporizer 20. The temperature of the refrigerant Cm supplied from the circulation device 60 to the vaporizer 20 (first temperature) may be 5°C to 50°C, 8°C to 45°C, or 10°C to 40°C. In the vaporizer 20, all or part of the liquefied natural gas (LNG) supplied to the vaporizer 20 is gasified by removing heat from the refrigerant Cm. As the liquefied natural gas (LNG) is gasified and the temperature rises after gasification, the temperature of the refrigerant Cm decreases by about 5°C to 20°C.

[0041] The circulation device 60 supplies refrigerant Cm to the cooling sections 54a, 54b, and 54c of the separation device 30 and recovers the refrigerant Cm after it has been used to cool the processed gas Gp in the cooling sections 54a, 54b, and 54c. The circulation device 60 supplies the refrigerant Cm recovered from the vaporizer 20 to the cooling sections 54a, 54b, and 54c. The temperature of the refrigerant Cm supplied from the circulation device 60 to the cooling sections 54a, 54b, and 54c (second temperature) is lower than the temperature of the refrigerant Cm supplied from the circulation device 60 to the vaporizer 20 (first temperature). The temperature of the refrigerant Cm supplied from the circulation device 60 to the cooling sections 54a, 54b, and 54c may also be lower than the temperature of the water vapor-containing gas Gs supplied from the water vapor-containing gas supply section 38 to the second space V2. The temperature of the refrigerant Cm supplied from the circulation device 60 to the cooling units 54a, 54b, and 54c may be 1°C to 20°C, 2°C to 15°C, or 3°C to 10°C.

[0042] In the cooling sections 54a, 54b, and 54c, the refrigerant Cm absorbs heat from the processing gas Gp, thereby cooling the processing gas Gp. As a result, water vapor is removed from the processing gas Gp. As the processing gas Gp cools, the temperature of the refrigerant Cm rises by approximately 5°C to 20°C. The circulation device 60 supplies the refrigerant Cm recovered from the cooling sections 54a, 54b, and 54c to the vaporizer 20. As described above, the circulation device 60 is used to cool the processing gas Gp in the cooling sections 54a, 54b, and 54c, and supplies the refrigerant Cm, whose temperature has risen, to the vaporizer 20.

[0043] The circulation device 60 is used for gasifying liquefied natural gas (LNG) in the vaporizer 20 and for raising the temperature after gasification, and supplies the refrigerant Cm, after its temperature has decreased, to the cooling units 54a, 54b, and 54c. The refrigerant Cm circulating through the circulation device 60 alternately undergoes temperature increases due to the cooling of the processed gas Gp in the cooling units 54a, 54b, and 54c, and temperature decreases due to the gasification and heating of liquefied natural gas (LNG) in the vaporizer 20. The refrigerant Cm may also be used to adjust the temperature of the raw material gas G0 supplied to the separation device 30 by performing heat exchange with it.

[0044] (modified version) Figure 3 is a schematic diagram showing another example of a separation device. The separation device 30 shown in Figure 3 has a discharge processing unit 50A instead of a discharge processing unit 50. The discharge processing unit 50A has two suction units and two cooling units. The discharge processing unit 50A differs from the discharge processing unit 50 shown in Figure 2 in that it does not have a cooling unit 54c. In the discharge processing unit 50A, the processed gas Gp sucked in and released by the suction unit 52b is discharged to the outside of the discharge processing unit 50A as gas Gd2. In the discharge processing unit 50A, the cooling units 54a and 54b cool the processed gas Gp using a refrigerant Cm supplied from the circulation device 60. Note that the cooling unit 54b may use another refrigerant instead of refrigerant Cm to cool the processed gas Gp.

[0045] The discharge processing units 50 and 50A have multiple suction units and multiple cooling units, but the number of these devices is not limited to the examples described above. The discharge processing units 50 and 50A may have one suction unit and one cooling unit. When the number of suction units and cooling units are the same, the number of these units may be three or more. When the number of suction units is one less than the number of cooling units, the number of suction units may be one and the number of cooling units may be two. Alternatively, the number of suction units may be three or more and the number of cooling units may be four or more. The number of suction units may be set according to the performance of each device and the target pressure of the gas Gd2 (application of gas Gd2).

[0046] [Combustion System] Next, we will describe the case where a carbon dioxide capture device is applied to a combustion system that uses natural gas as fuel. Figure 4 is a schematic diagram showing an example of a combustion system. The combustion system 80 shown in Figure 4 is a system that captures carbon dioxide while burning liquefied natural gas. The combustion system 80 comprises a capture device 10 and a combustion device 82. The combustion system 80 may also include a storage device 2.

[0047] The storage device 2 stores liquefied natural gas (LNG) and supplies it to the vaporizer 20 of the recovery device 10. The storage device 2 is located, for example, at or near an LNG receiving terminal installed in a port or the like. The storage device 2 may be located in a different location from the LNG receiving terminal (for example, a factory), and may store liquefied natural gas (LNG) transported from the LNG receiving terminal. In one example, the storage device 2 has a tank for storing liquefied natural gas (LNG) and a pump for sending the liquefied natural gas (LNG) to the vaporizer 20.

[0048] The vaporizer 20 vaporizes and heats the liquefied natural gas (LNG) supplied from the storage unit 2 using the refrigerant Cm supplied from the circulation unit 60. The vaporizer 20 may also use other refrigerants in addition to the refrigerant Cm to vaporize and heat the liquefied natural gas (LNG). The vaporizer 20 supplies the natural gas (Gn) produced by the vaporization and heating of the liquefied natural gas (LNG) to the combustion unit 82.

[0049] The combustion device 82 is a device for burning natural gas Gn. The combustion device 82 is, for example, a boiler that generates hot water or steam by burning natural gas Gn. The combustion device 82 may also generate hot water or steam by heating water or a heat transfer medium with the combustion gas generated by burning natural gas Gn. The hot water or steam generated by the combustion device 82 may be used for any purpose. The combustion device 82 cools the combustion exhaust gas generated after heating water, etc., by heat exchange with a refrigerant, etc., as needed (the part where the cooling is performed is not shown in the illustration) and then supplies it to the separation device 30. In this case, the raw material gas G0 supplied to the separation processing unit 40 of the separation device 30 includes the combustion exhaust gas discharged from the combustion device 82.

[0050] The separation unit 40 generates treated gas Gp by separating carbon dioxide from the exhaust gas discharged from the combustion device 82. The separation unit 40 of the separation device 30 discharges the gas remaining after carbon dioxide has been separated from the exhaust gas by the combustion device 82 as gas Gd1. Gas Gd1 may be released to the outside through a chimney installed in a factory or the like.

[0051] In this combustion system 80 as well, the circulation device 60 circulates the refrigerant Cm between the vaporizer 20 and at least the cooling section 54a (for example, cooling sections 54a, 54b, 54c) of the separation device 30. Various modifications described above may be applied to the recovery device 10 of the combustion system 80.

[0052] [Power generation system] Next, we will describe the application of a carbon dioxide capture device to a power generation system that generates electricity using liquefied natural gas. Figure 5 is a schematic diagram showing an example of a power generation system. The power generation system 90 shown in Figure 5 is a system that generates electricity using liquefied natural gas while capturing carbon dioxide. The power generation system 90 comprises a capture device 10 and a power generation device 92. The power generation system 90 may also include a storage device 2. The power generation system 90 is constructed, for example, at or near an LNG receiving terminal.

[0053] The vaporizer 20 gasifies liquefied natural gas (LNG) to produce natural gas (Gn) and supplies the natural gas (Gn) to the power generator 92. The power generator 92 may generate electricity using the natural gas (Gn) in any manner. For example, the power generator 92 may burn the natural gas (Gn) to generate steam, and then use that steam to rotate a steam turbine and operate a generator. The power generator 92 may also burn the natural gas (Gn) to generate combustion gas, and then use that combustion gas to rotate a gas turbine and operate a generator. The power generator 92 may also generate electricity using a combined cycle power generation method that combines these steam turbines and gas turbines.

[0054] The power generation device 92 supplies the exhaust gas after generating steam, or the exhaust gas after rotating the gas turbine, to the separation device 30 after cooling it by heat exchange with a refrigerant or the like as needed (the part performing the cooling is not shown in the illustration). In this case, the raw material gas G0 supplied to the separation processing unit 40 of the separation device 30 includes the exhaust gas discharged from the power generation device 92. The separation processing unit 40 generates processed gas Gp by separating carbon dioxide from the exhaust gas discharged from the power generation device 92. The separation processing unit 40 discharges the gas remaining after carbon dioxide has been separated from the exhaust gas by the power generation device 92 as gas Gd1. Gas Gd1 may be released to the outside through a chimney installed at the power plant or the like.

[0055] In this power generation system 90 as well, the circulation device 60 circulates the refrigerant Cm between the vaporizer 20 and at least the cooling section 54a (for example, cooling sections 54a, 54b, 54c) of the separation device 30. Various modifications described above may be applied to the recovery device 10 of the power generation system 90.

[0056] Next, as an example of a carbon dioxide recovery method, a method for recovering carbon dioxide from raw gas G0 using the recovery device 10 described above will be explained. The recovery method performed in the recovery device 10 includes a separation step, a suction step, a discharge step, a cooling step, a gasification step, and a circulation step. These steps are performed in parallel so that at least a portion of their execution period overlaps with each other.

[0057] In the separation process, carbon dioxide is separated from the raw material gas G0 using a separation member 44 to generate the processed gas Gp. Specifically, in the separation process, the separation processing unit 40 supplies the raw material gas G0 to a first space V1 within the housing 42. Along with the supply of the raw material gas G0, a water vapor-containing gas Gs is supplied from a water vapor-containing gas supply unit 38 to a second space V2 within the housing 42. Due to the pressure difference between the first space V1 and the second space V2, and the supply of the water vapor-containing gas Gs, the carbon dioxide and water vapor contained in the raw material gas G0 supplied to the first space V1 are introduced into the second space V2 by permeating through a separation membrane 46 that is positioned to separate the first space V1 and the second space V2. As a result, the processed gas Gp is ​​generated in the second space V2.

[0058] In the suction step, the gas in the second space V2 is drawn in by the suction units 52a and 52b so that the processed gas Gp is ​​released from the second space V2. The execution of the suction step creates the above pressure difference between the first space V1 and the second space V2, and the above separation step continues. In the cooling step, the processed gas Gp released from the second space V2 is cooled using the refrigerant Cm in at least the cooling unit 54a (for example, cooling units 54a, 54b, and 54c). In the cooling step, the refrigerant Cm may be supplied to the cooling units 54a, 54b, and 54c from the circulation device 60. In the cooling step, the processed gas Gp is ​​cooled by the refrigerant Cm absorbing heat from the processed gas Gp, and the temperature of the refrigerant Cm rises by about 5°C to 20°C.

[0059] In the discharge process, the gas that has been drawn in from the second space V2 by the suction units 52a and 52b and from which water vapor has been removed by the cooling units 54a, 54b, and 54c is discharged as the gas Gd2 described above. In the discharge process, the gas Gd2 may also be discharged to the outside of the separation device 30. Carbon dioxide is recovered when the gas Gd2 is discharged.

[0060] In the gasification process, liquefied gas is gasified in the vaporizer 20 using a refrigerant Cm. In the gasification process, liquefied natural gas (LNG), which is an example of liquefied gas, may be gasified (or gasified and heated). In the gasification process, liquefied natural gas (LNG) is supplied to the vaporizer 20, and refrigerant Cm is supplied from the circulation device 60. In the gasification process, the liquefied natural gas (LNG) is regasified by absorbing heat from the refrigerant Cm. This generates natural gas (Gn) from the liquefied natural gas (LNG). In the gasification process, the gas generated by the regasification of liquefied natural gas (LNG) may be heated by the refrigerant Cm. The natural gas (Gn) generated in the gasification process is supplied to the combustion system 80 or the power generation system 90, etc.

[0061] In the circulation process, the refrigerant Cm circulates between the vaporizer 20 and the separation unit 30 (for example, cooling units 54a, 54b, 54c) so that the refrigerant Cm repeatedly rises in temperature as the process gas Gp is ​​cooled and falls in temperature as the liquefied natural gas LNG is gasified and heated. Through this circulation process, the refrigerant Cm, which has risen to the first temperature as the process gas Gp is ​​cooled, is used to cool the liquefied natural gas LNG in the gasification process. Furthermore, the refrigerant Cm, which has fallen to the second temperature as the liquefied natural gas LNG is gasified and heated, is used to cool the process gas Gp in the cooling process.

[0062] In the circulation process, the refrigerant Cm, which has been used for heat exchange with the processed gas Gp in the cooling process, is recovered by the circulation device 60. The refrigerant Cm recovered from the cooling sections 54a, 54b, and 54c is supplied to the vaporizer 20 by the circulation device 60. In the gasification process, the refrigerant Cm, which has been used for heat exchange with liquefied natural gas LNG, is recovered by the circulation device 60. The refrigerant Cm recovered from the vaporizer 20 is supplied to the cooling sections 54a, 54b, and 54c by the circulation device 60.

[0063] In a combustion system 80 equipped with a recovery device 10, the carbon dioxide recovery method described above may also be performed. In the combustion system 80, in addition to the separation step, suction step, discharge step, cooling step, gasification step, and circulation step included in the recovery method described above, a combustion step is performed. In the combustion step, natural gas Gn obtained by gasifying liquefied natural gas LNG in the gasification step is burned. In the combustion step, water or the like may be heated using natural gas Gn as fuel. In the separation step, the raw material gas G0 supplied to the separation device 30 includes the exhaust gas discharged in the combustion step.

[0064] In a power generation system 90 equipped with a recovery device 10, the carbon dioxide recovery method described above may also be performed. In the power generation system 90, in addition to the separation step, suction step, discharge step, cooling step, gasification step, and circulation step included in the recovery method described above, a power generation step is performed. In the power generation step, electricity is generated by burning natural gas Gn obtained when liquefied natural gas LNG is gasified in the gasification step. In the separation step, the raw material gas G0 supplied to the separation device 30 includes exhaust gas discharged in the power generation step.

[0065] [Effects of the Embodiment] The recovery device 10 according to the embodiment described above includes a separation processing unit 40 that separates carbon dioxide contained in the raw material gas G0 from the raw material gas G0 using a carbon dioxide permeable membrane, a suction unit 52a that sucks in the processed gas Gp containing carbon dioxide separated from the raw material gas G0, a cooling unit 54a located upstream of the suction unit 52a and cooling the processed gas Gp using a refrigerant Cm, a vaporizer 20 that vaporizes the liquefied gas using the refrigerant Cm, and a circulation device 60 that circulates the refrigerant Cm between the cooling unit 54a and the vaporizer 20 so that the refrigerant Cm repeatedly rises in temperature due to the cooling of the processed gas Gp and falls in temperature due to the vaporization of the liquefied gas.

[0066] In this recovery device 10, by circulating the refrigerant Cm between the vaporizer 20 and the cooling unit 54a, the processed gas Gp released from the second space V2 can be cooled by utilizing at least the cold energy generated when vaporizing the liquefied gas (for example, the cold energy generated during gasification and heating). As a result, the temperature of the processed gas Gp is ​​further reduced before it is drawn in by the suction unit 52a, and a large amount of moisture contained in the processed gas Gp is ​​condensed and removed. Therefore, the performance required of the suction unit 52a can be reduced. Consequently, it is possible to reduce the energy consumed to recover carbon dioxide.

[0067] The temperature of the refrigerant Cm supplied from the circulation device 60 to the cooling unit 54a may be between 1°C and 20°C. Having the above temperature of the refrigerant Cm allows for the removal of a significant amount of heat from the processed gas Gp before it is drawn in by the suction unit 52a, thereby increasing the amount of water removed from the processed gas Gp. Consequently, it becomes possible to reduce the amount of energy required to recover the gas containing carbon dioxide.

[0068] The recovery device 10 may further include a water vapor-containing gas supply unit 38 that supplies water vapor-containing gas Gs to the separation processing unit 40. The separation processing unit 40 may have a membrane that separates a first space V1 to which raw material gas G0 is supplied and a second space V2. The water vapor-containing gas supply unit 38 may supply water vapor-containing gas Gs to the second space V2. The supply of water vapor-containing gas Gs to the second space V2 promotes the separation of carbon dioxide by the membrane. When water vapor-containing gas is supplied, the processed gas Gp generated in the second space V2 may contain a lot of water vapor, but by utilizing the above-mentioned cold energy, a lot of water vapor can be removed from the processed gas Gp. Therefore, it is possible to achieve both efficient separation of carbon dioxide and a reduction in the amount of energy required for recovery.

[0069] The recovery device 10 may further include a cooling unit 54b located downstream of the suction unit 52a and cooling the gas released by the suction unit 52a using a refrigerant Cm, and a suction unit 52b located downstream of the cooling unit 54b and sucking in the gas released by the suction unit 52a. By providing multiple stages of suction units, including suction units 52a and 52b, it is easy to increase the gas pressure. Therefore, it is easy to obtain gas in which carbon dioxide is concentrated and the pressure is increased.

[0070] The pressure of the gas discharged from the recovery device 10 via at least the suction section 52a and the suction section 52b may be 1 atmosphere or more. By setting the pressure of the gas discharged from the recovery device 10 to 1 atmosphere or more, the gas recovered from the recovery device 10 can be easily sent from the recovery device 10 to another device or another location.

[0071] The liquefied gas may be liquefied natural gas (LNG). Even when liquefied natural gas (LNG) is vaporized using a refrigerant (Cm), the processing gas (Gp) released from the second space (V2) can be cooled by utilizing the cold energy generated during the vaporization of the LNG. As a result, the temperature of the processing gas (Gp) is lowered further before the suction unit (52a) draws it in, increasing the amount of water condensation in the processing gas (Gp) and allowing for the removal of more water. Therefore, the performance requirements for the suction unit (52a) can be reduced. Consequently, it becomes possible to reduce the energy consumed to recover carbon dioxide.

[0072] [Simulation Results] Next, we will explain the simulation results of the energy consumption required to recover carbon dioxide using the recovery device 10 shown in Figures 1 and 2. For each of the following Reference Example 1, Reference Example 2, Example 1, and Example 2, we evaluated (simulated) the energy consumption required to recover 1 ton of carbon dioxide when recovering gas with a carbon dioxide concentration of approximately 95% or higher. Reference Example 1 is a case in which carbon dioxide is recovered by chemical absorption, while Reference Example 2 and Examples 1 and 2 are cases in which carbon dioxide is recovered by membrane separation.

[0073] Reference Example 2 is a case where the carbon dioxide concentration in the combustion exhaust gas is relatively high, and carbon dioxide is recovered from coal combustion exhaust gas using a membrane separation method with general cooling water. Example 1 is a case in which the refrigerant in Reference Example 2 is changed from general cooling water to refrigerant Cm that is circulated between the vaporizer 20 and the combustion exhaust gas, and Example 2 is a case where the carbon dioxide concentration in the natural gas combustion exhaust gas is relatively low, and carbon dioxide is recovered from the combustion exhaust gas using a membrane separation method with refrigerant Cm. In Reference Example 2, there is no vaporizer 20 and circulation device 60 shown in Figures 1 and 2, and the evaluation was performed with a configuration in which general cooling water is circulated between the separation device 30 and the combustion exhaust gas, while in Examples 1 and 2, the evaluation was performed with the apparatus configuration shown in Figures 1 and 2. The main differences between Reference Examples 1 and 2 and Examples 1 and 2 and their evaluation results are shown in Table 1. [Table 1]

[0074] The following describes the details of Reference Examples 1 and 2 and Examples 1 and 2. In Reference Example 1, the energy consumption evaluation value was obtained by referring to the separation and recovery energy of the atmospheric pressure chemical absorbent shown in Non-Patent Document 1 mentioned above. For Reference Example 2 and Examples 1 and 2, the main assumptions and calculation results of the simulation are shown in Table 2, and the calculation process and calculation results of the carbon dioxide recovery energy are shown in Table 3.

[0075] [Table 2]

[0076] [Table 3]

[0077] In Reference Example 2 and Examples 1 and 2, the main energy consumption includes the power consumption of the motors used to operate the suction devices (suction sections 52a and 52b) in the suction process, and the power consumption of the motors used to operate the pumps that circulate the refrigerant in the circulation device. In Reference Example 1, the main energy consumption is the thermal energy required to generate steam used for the regeneration of the chemical absorbent. In Reference Examples 1 and 2 and Examples 1 and 2, it is necessary to compare the energy required for carbon dioxide recovery equally as thermal energy, in line with Reference Example 1. Therefore, in Reference Example 2 and Examples 1 and 2, the thermal energy required for power generation to supply electricity is calculated and compared with the thermal energy in Reference Example 1.

[0078] In Reference Example 2 and Examples 1 and 2, it is assumed that the necessary electricity is supplied from a power plant that emits the combustion exhaust gas assumed in each example. The power generation efficiency at the power plant end, based on the lower heating value (LHV), was set to approximately 40% for both the coal-fired power plant and the natural gas-fired power plant. Furthermore, a transmission and distribution loss of approximately 5% was assumed, and the thermal energy required to supply the necessary electricity was calculated.

[0079] From the evaluation results in Table 1 or Table 3, it can be seen that even in Reference Example 2, which uses ordinary cooling water as the refrigerant, energy consumption is reduced by approximately 35% compared to Reference Example 1. Furthermore, in Examples 1 and 2, where refrigerant Cm is circulated by the circulation device 60, energy consumption is reduced by more than half compared to Reference Example 1. [Explanation of Symbols]

[0080] 10...Recovery unit, 20...Vaporizer, 30...Separation unit, 38...Water vapor-containing gas supply unit, 40...Separation unit, 46...Separation membrane, V1...First space, V2...Second space, 50, 50A...Discharge unit, 52a, 52b...Suction unit, 54a, 54b, 54c...Cooling unit, 60...Circulation unit, 80...Combustion system, 82...Combustion unit, 90...Power generation system, 92...Power generation unit, G0...Raw material gas, Gp...Processed gas, Gs...Water vapor-containing gas, LNG...Liquefied natural gas, Gn...Natural gas, Cm...Refrigerant.

Claims

1. A separation device for separating carbon dioxide contained in the raw material gas from the raw material gas, a vaporizer, and a circulation device, The separation device is A suction unit for drawing in a processed gas containing carbon dioxide separated from the aforementioned raw material gas, It has a cooling unit located upstream of the suction unit, which cools the processing gas using a refrigerant, The vaporization device uses the refrigerant to vaporize the liquefied gas, The circulation device is a carbon dioxide recovery device that circulates the refrigerant between the cooling unit and the vaporizer such that the refrigerant repeatedly experiences a temperature rise due to the cooling of the process gas and a temperature decrease due to the gasification of the liquefied gas.

2. The recovery apparatus according to claim 1, wherein the separation apparatus separates carbon dioxide contained in the raw material gas from the raw material gas by absorption.

3. The recovery device according to claim 1 or 2, wherein the temperature of the refrigerant supplied from the circulation device to the cooling unit is 1°C to 20°C.

4. A separate cooling unit is located downstream of the suction unit and uses the refrigerant to cool the gas released by the suction unit, The recovery device according to any one of claims 1 to 3, further comprising another suction unit located downstream of the other cooling unit and for sucking up the gas released by the suction unit.

5. The recovery apparatus according to any one of claims 1 to 4, wherein the liquefied gas is liquefied natural gas.

6. A separation step of separating carbon dioxide contained in the raw material gas from the raw material gas, a gasification step, and a circulation step, The separation step is, A suction step of drawing in a processed gas containing carbon dioxide separated from the raw material gas, The cooling step includes cooling the process gas using a refrigerant upstream of the suction step, The gasification step is a step of gasifying the liquefied gas using the refrigerant, A method for recovering carbon dioxide, wherein the circulation step is a step of circulating the refrigerant such that the refrigerant repeatedly experiences a temperature rise due to the cooling of the process gas and a temperature decrease due to the gasification of the liquefied gas.

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