JP5736916B2 - Method for recovering and liquefying carbon dioxide from mixed gas - Google Patents

Description

  The present invention relates to a method for recovering carbon dioxide from a mixed gas containing carbon dioxide such as blast furnace gas and combustion exhaust gas discharged from the top of the blast furnace and liquefying the recovered carbon dioxide.

  Since release of carbon dioxide into the atmosphere causes global warming, it is possible to separate and recover carbon dioxide from gas mixtures containing carbon dioxide such as blast furnace gas and combustion exhaust gas discharged from the top of the blast furnace furnace. Chemical absorption methods, physical adsorption methods, membrane separation methods, and the like have been developed as techniques for separating and recovering carbon dioxide from mixed gases.

  The chemical absorption method uses an amine or the like that absorbs carbon dioxide at 40 ° C. to 50 ° C. and releases carbon dioxide at 100 ° C. to 120 ° C. as an absorbing solution, and selectively absorbs carbon dioxide in the mixed gas. Then, the absorbed carbon dioxide is released by heating the absorbent with steam or the like, and the high purity carbon dioxide is separated and recovered from the mixed gas. The physical adsorption method is a method that separates and recovers components in a mixed gas by utilizing the amount of adsorption that changes due to pressure change or temperature change. Carbon dioxide is adsorbed when pressure is applied. However, it is carried out using zeolite that desorbs carbon dioxide when the pressure is reduced. The membrane separation method is a method for separating and recovering a specific gas component in a mixed gas using a membrane having different permeability depending on substances. For separation / recovery of carbon dioxide, a porous hollow fiber membrane is usually used. It is used.

  As a method for separating carbon dioxide in a mixed gas with low power, a carbon dioxide separation method using hydrate has also been proposed. For example, Patent Document 1 includes a step of cooling an exhaust gas containing carbon dioxide to a predetermined temperature, a step of spraying water into a fine ice generator cooled to a predetermined temperature to generate fine ice, There has been proposed a method for recovering carbon dioxide in exhaust gas, which comprises a step of introducing fine ice and the exhaust gas into a hydrate generator to generate carbon dioxide hydrate. Hydrate is a solid hydrate having a structure in which gas molecules such as carbon dioxide are taken into a basket made of water molecules.

  The separated and recovered carbon dioxide is liquefied and transported to and stored in an aquifer near about 1000 m below ground where it can be stored underground. In this liquefaction process, the higher the purity of carbon dioxide, the less power is used. Therefore, from the viewpoint of reducing the power used during liquefaction, the carbon dioxide to be separated and recovered is required to have high purity. .

  However, although the chemical absorption method and the physical adsorption method can obtain high-purity carbon dioxide, it is necessary to regenerate the absorbent and the adsorbent, and the energy consumption during the separation is large. It is not necessarily suitable as a carbon dioxide separation / recovery method for recovery / storage. In addition, the membrane separation method is a method of separation based on the size of molecules, and the combustion exhaust gas contains nitrogen gas, and the sizes of nitrogen gas molecules and carbon dioxide molecules are comparable, Separation of both is difficult and there is a problem that the purity of the recovered carbon dioxide is low.

  On the other hand, the gas separation method using hydrate can be separated with less power when the concentration of carbon dioxide in the mixed gas is high, but when the concentration of carbon dioxide in the mixed gas is low, that is, dioxide dioxide. When the partial pressure of carbon is low, there is a drawback in that the pressure boosting power of the compressor required for separation increases, and furthermore, the power required for separation increases. Furthermore, since the separation selectivity of the specific gas component from the mixed gas is not 100%, it may be impossible to obtain a high-purity separated gas by a single-stage separation operation. When the carbon concentration is 24% by volume, in order to obtain carbon dioxide having a concentration of 98% by volume, there is a problem that a three-stage hydration treatment is required, and as a result, a large amount of power is required.

  In other words, when recovering carbon dioxide having a purity exceeding 95% by volume from a mixed gas having a carbon dioxide concentration of about 20 to 30% by volume, the gas separation method using hydrate also increases the power used. It is not necessarily suitable as a carbon dioxide separation / recovery method for recovery / storage.

JP 2006-282403 A

  In this way, for the purpose of global environmental conservation, carbon dioxide is separated and recovered from a mixed gas containing carbon dioxide such as blast furnace gas and combustion exhaust gas, and the recovered carbon dioxide is liquefied and the liquefied carbon dioxide is grounded. For storage, carbon dioxide in mixed gas is conventionally separated by various methods, but carbon dioxide is separated from mixed gas with low carbon dioxide concentration, such as blast furnace gas and combustion exhaust gas, and high purity is obtained. In the case of recovering the carbon dioxide, a great amount of power is required regardless of which method is used, and there is a problem in that the cost in the underground storage of carbon dioxide is increased.

  The present invention has been made in view of such circumstances, and its object is to contain carbon dioxide such as blast furnace gas and combustion exhaust gas in order to store the carbon dioxide contained in the mixed gas in the ground. When separating and recovering carbon dioxide from the mixed gas and liquefying the recovered carbon dioxide, both processes should be performed so that the total power used in both the carbon dioxide separation and recovery process and the liquefaction process is reduced. The object of the present invention is to provide a method for recovering and liquefying carbon dioxide from a mixed gas, which can separate and recover carbon dioxide from a mixed gas and liquefy the recovered carbon dioxide with less power than in the past.

  The present inventors diligently studied and studied in order to solve the above problems. As a result, conventionally, in order to reduce the power cost of the liquefaction process, high purity carbon dioxide is recovered from the mixed gas, and this is the main factor that increases the cost of underground storage treatment of carbon dioxide in the mixed gas. I understood. Therefore, although the power cost of the liquefaction process will increase, the separation / recovery process will be simplified, the purity of the recovered carbon dioxide will be lowered to lower the power cost in the separation / recovery process, and the power cost for the entire process will be reduced. did.

  As a result of the study, the carbon dioxide separation method using hydrate is inherently low in power cost, so the separation method using hydrate is used to improve the purity of carbon dioxide in the mixed gas. The separation and recovery process of carbon dioxide using hydrate was completed at a stage where the purity of carbon dioxide did not increase, and the gas recovered at this stage was liquefied, so that the entire storage process of carbon dioxide was completed. It has been found that the power cost is lower than before.

The present invention has been made based on the above findings, and the gist thereof is as follows.
(1) A mixed gas containing carbon dioxide is introduced into a hydrate generator to form a hydrate of gas and water capable of forming a hydrate in the mixed gas, and then the formed hydrate A separation / recovery step for concentrating the concentration of carbon dioxide in the recovered gas by decomposing the hydrate recovered by recovering the rate into gas and water and recovering the decomposed gas, and the separation A method for recovering and liquefying carbon dioxide from a mixed gas, the method comprising: a liquefying step for liquefying a gas containing carbon dioxide recovered in the recovery step, wherein the separation and recovery step is performed at least on the mixed gas The carbon dioxide in the recovered gas is liquefied by supplying the recovered gas to the liquefaction step when the concentration of carbon dioxide in the recovered gas is 95% by volume or less. Charcoal Element recovery and liquefaction method.
(2) The concentration of carbon dioxide in the gas recovered in the separation / recovery step is liquefied by supplying the recovered gas to the liquefaction step at a stage of 80% by volume or less (above) The method for recovering and liquefying carbon dioxide from the mixed gas according to 1).
(3) The concentration of carbon dioxide in the gas recovered in the separation / recovery step is 30 to 70% by volume, and the recovered gas is supplied to the liquefaction step to be liquefied. The method for recovering and liquefying carbon dioxide from the mixed gas according to (2).

  According to the present invention, when recovering carbon dioxide from a mixed gas, a gas separation method using hydrate is adopted, and the concentration of carbon dioxide recovered by this gas separation method is 95% by volume or less. Since the gas containing carbon dioxide is liquefied after the separation / recovery process is discontinued, the power used in the liquefaction process is increased, but the power used in the separation / recovery process is further reduced and the CO2 in the mixed gas is reduced. It is realized that the carbon underground storage processing cost is significantly reduced as compared with the conventional case.

It is the schematic which shows the example of the whole structure of the collection | recovery and liquefaction facility of the carbon dioxide which implemented this invention. It is a figure which shows the relationship between the carbon dioxide concentration in mixed gas, and the carbon dioxide concentration of the hydrate phase formed from this mixed gas. It is a figure which shows the relationship between the carbon dioxide concentration in the gas isolate | separated and collect | recovered by the gas separation method by a hydrate, and the motive power required for isolation | separation and collection | recovery. It is a figure which shows the relationship between the carbon dioxide concentration in the gas isolate | separated and collect | recovered by the gas separation method by hydrate, and the gas flow rate which passes a hydrate generator. It is a figure which shows the relationship between the carbon dioxide density | concentration in the gas isolate | separated and collect | recovered by the gas separation method by hydrate, and the motive power required for liquefaction of collection | recovery gas. It is a figure which shows the relationship between the carbon dioxide density | concentration in the gas isolate | separated and collect | recovered by the gas separation method by hydrate, and the gas flow rate which passes the liquefying apparatus at the time of liquefying gas. It is a figure which shows the relationship between the carbon dioxide concentration in the gas isolate | separated and collect | recovered by the gas separation method by a hydrate, and the motive power required for isolation | separation, collection | recovery, and liquefaction. It is a figure which shows the relationship between the carbon dioxide concentration in the gas isolate | separated and collect | recovered by the gas separation method by a hydrate, and the cost required for isolation | separation, collection | recovery, and liquefaction of gas.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic diagram showing an example of the overall configuration of the carbon dioxide recovery / liquefaction facility used in carrying out the present invention.

  As shown in FIG. 1, a carbon dioxide recovery / liquefaction facility 1 embodying the present invention includes a hydrate generator 5 for mixing carbon dioxide in a mixed gas with water to form a hydrate of carbon dioxide. And a hydrate separator 6 for decomposing the hydrate of carbon dioxide formed by the hydrate generator 5 into a gas containing carbon dioxide and water. A liquefaction device 8 is installed at the subsequent stage of the hydrate separator 6, and the gas containing carbon dioxide recovered by the hydrate separator 6 is introduced into the liquefaction device 8 and liquefied by the liquefaction device 8. It is comprised so that. In addition, the compressor 2 is disposed in front of the hydrate generator 5, and the first cooler 3 and the second cooler 4 are connected in series between the compressor 2 and the hydrate generator 5. Has been placed.

  In the carbon dioxide recovery / liquefaction facility 1, the compressor 2 to the hydrate separator 6 are the devices used in the carbon dioxide separation / recovery step, and the liquefaction device 8 is the device used in the carbon dioxide liquefaction step. In addition, since hydrocarbon gas such as carbon monoxide, nitrogen gas or methane gas contained in the mixed gas also forms hydrate, the gas decomposed from the hydrate by the hydrate separator 6 is not carbon dioxide. Gas species are mixed.

  Hereinafter, a method of separating and recovering carbon dioxide from a mixed gas containing carbon dioxide and liquefying it using the carbon dioxide recovery / liquefaction facility 1 configured as described above will be described.

  Carbon dioxide, such as blast furnace gas discharged from the top of the blast furnace furnace, converter gas discharged from a converter in a steelmaking factory, coke oven gas discharged from a coke oven, or combustion exhaust gas discharged from a heating facility at a steelworks Is supplied to the compressor 2, and the compressed gas b is compressed by the compressor 2 to form a compressed gas b that has been increased to a pressure (for example, 1400 kPa) required for the production of carbon dioxide hydrate. . The compressed gas b is continuously introduced into the first cooler 3 and the second cooler 4 provided in the subsequent stage of the compressor 2 to a temperature necessary for hydrate generation (for example, 5 ° C. or less). Cooling.

  Here, the first cooler 3 uses the unreacted gas c in the hydrate generator 5 as the cooling gas, and the unreacted after heat exchange with the compressed gas b in the first cooler 3. Since the gas c is maintained in a compressed state, the gas c is introduced into the expansion turbine 9 to drive the expansion turbine 9. The power of the expansion turbine 9 can be used, for example, to assist the power of the compressor 2 or to generate power. As the coolant for the second cooler 4, cooling water is used. This cooling water is cooled by a cooling device (not shown) after heat exchange with the compressed gas b, and is circulated and used as a coolant for the second cooler 4. The expansion turbine 9 is an attached device, and is not an essential device for the carbon dioxide recovery / liquefaction facility 1.

  The compressed gas b cooled to the temperature necessary for hydrate generation by the first cooler 3 and the second cooler 4 is introduced into the hydrate generator 5 installed at the subsequent stage of the second cooler 4. Then, carbon dioxide in the compressed gas reacts with water to form carbon dioxide hydrate. Inside the hydrate generator 5, a cooler 5a using cooling water as a coolant is installed in order to prevent the temperature of the cooled compressed gas b from rising. This cooling water is cooled by a cooling device (not shown) after heat exchange with the compressed gas b, and is circulated and used as a coolant for the cooler 5a.

  As the hydrate generator 5, for example, the compressed gas b is made into fine bubbles, and the outer surface is blown into the water passing through the reaction pipe cooled by the cooler 5a. An apparatus of the type that reacts with water can be used. As described above, the mixed gas a includes carbon monoxide and nitrogen gas, and may further include hydrocarbon-based gas such as methane gas, and some of these gases included in the mixed gas a. Also form hydrates. However, the amount of hydrate produced is smaller than that of carbon dioxide, and most is separated by the hydrate generator 5 as unreacted gas c. As described above, the unreacted gas c is used as a cooling gas for the first cooler 3 and a driving gas for the expansion turbine 9.

  Next, the hydrate-water mixture d (also referred to as “hydrate slurry”) formed by the hydrate generator 5 is introduced into the hydrate separator 6 connected to the subsequent stage of the hydrate generator 5. . Moisture in the hydrate slurry d introduced into the hydrate separator 6 is immediately separated from the hydrate and circulated to the hydrate generator 5 via the circulation pump 7 to form a new hydrate. Served as moisture e. On the other hand, moisture e is removed from the hydrate slurry d introduced into the hydrate separator 6, and hydrate is accumulated in the separator 6.

  The hydrate separator 6 is provided with a heat exchanger 6a using seawater. Generally, seawater in the sea near Japan is 15 ° C. or higher, and the hydrate accumulated in the hydrate separator 6 is heated. The heat is exchanged with the exchanger 6a and the temperature is increased, and the gas is decomposed into a gas f containing carbon dioxide and moisture e. Although seawater is used as the heating medium here, river water, industrial water, tap water, or the like may be used as long as the temperature is 15 ° C. or higher. The water e is circulated to the hydrate generator 5 via the circulation pump 7, while the recovered gas f containing carbon dioxide is introduced into the liquefaction apparatus 8 in the next step.

  The liquefying device 8 is configured such that the mixed gas a that has not been subjected to the separation / recovery process by hydrate is introduced, and the recovered gas f containing carbon dioxide has not been subjected to the separation / recovery process. A predetermined amount is mixed with the mixed gas a, and then compressed and cooled in the liquefying device 8 to be liquefied to generate liquefied carbon dioxide g. The produced liquefied carbon dioxide g is transported as it is to the ground and stored there, or once stored in a low-temperature storage tank (not shown) and then transported and stored in the ground.

  When carbon dioxide in a mixed gas is separated and recovered using hydrate, the concentration of carbon dioxide in the mixed gas and the hydrate phase formed from this mixed gas (= gas formed by decomposition of hydrate) 2) is known to be related to carbon dioxide concentration (see publication: Nguyen Hong Duc, et al., Center SPIN, France, Energy Conversion and Management 2006). As shown by a broken line in FIG. 2, carbon dioxide having a purity exceeding 95% by volume is recovered from a mixed gas such as blast furnace gas having a carbon dioxide content of 24% by volume by applying a gas separation method using hydrate. In this case, the concentration of carbon dioxide in the recovered gas is 24 vol% → 68 vol% in the first stage separation / recovery, and 68 vol% → 92 vol% in the second stage separation / recovery. The separation / recovery is 92% by volume → 98% by volume, which requires a total of three separation / recovery steps.

FIG. 3 is a diagram showing the relationship between the concentration of carbon dioxide in the gas separated and recovered by the gas separation method using hydrate and the power required for the separation and recovery. FIG. FIG. 3 is a diagram showing the relationship between the carbon dioxide concentration in the recovered gas and the gas flow rate passing through the hydrate generator 5. In FIG. 4, when the CO ₂ concentration after separation / collection is 98% by volume, it is indexed and displayed as a reference (= 1.0). As shown in FIGS. 3 and 4, the higher the carbon dioxide concentration in the gas separated and recovered by the hydrate gas separation method, the higher the required power and equipment costs in the separation and recovery process. I understand.

  In other words, although the power used decreases as the number of separation / recovery steps increases, the power required for each separation / recovery step increases. Add to increase.

On the other hand, FIG. 5 is a diagram showing the relationship between the concentration of carbon dioxide in the gas separated and recovered by the gas separation method using hydrate and the power required for liquefying the recovered gas, and FIG. 6 is the gas separation method using hydrate. It is a figure which shows the relationship between the carbon dioxide concentration in the gas isolate | separated and collect | recovered by (1), and the gas flow rate which passes the liquefying apparatus 8 at the time of liquefying gas. In FIG. 6, when the CO ₂ concentration after separation / collection is 98% by volume, it is indexed and displayed as a reference (= 1.0). As shown in FIG. 5 and FIG. 6, it can be seen that the higher the carbon dioxide concentration in the gas separated and recovered by the gas separation method using hydrate, the lower the required power and equipment cost in the liquefaction process. . This is because the power required for gas compression other than carbon dioxide decreases as the carbon dioxide concentration increases.

That is, since the relationship between the carbon dioxide concentration after separation / recovery and the required power shows an opposite tendency between the separation / recovery process and the liquefaction process, the total power including both is shown in FIG. There is a minimum carbon dioxide concentration range. In addition, the cost including the required power and the equipment cost also has a minimum carbon dioxide concentration range as shown in FIG. FIG. 7 is a diagram showing the relationship between the carbon dioxide concentration in the gas separated and recovered by the gas separation method using hydrate and the power required for both the separation, recovery and liquefaction steps. It is a figure which shows the relationship between the carbon dioxide density | concentration in the gas isolate | separated and collect | recovered by the gas separation method by a rate, and the cost required in both process of gas isolation | separation / collection | recovery and liquefaction. In FIG. 8, when the CO ₂ concentration after separation / collection is 98% by volume, it is indexed and displayed as a reference (= 1.0).

  In the present invention, the carbon dioxide concentration of the recovered gas f is controlled to at least 95% by volume or less in order to reduce the total power and cost of use in both the gas separation / recovery and liquefaction steps. That is, the gas f having a carbon dioxide concentration of 95% by volume or less is introduced into the liquefying device 8 to liquefy the carbon dioxide contained in the gas f. A gas having a low liquefaction temperature such as nitrogen gas contained in the gas f is cooled but not liquefied. In this case, in order to further reduce power and cost, the carbon dioxide concentration of the recovered gas f is preferably controlled to 80% by volume or less, more preferably 30 to 70% by volume.

  In FIG. 1 described above, carbon dioxide is recovered in a single-stage separation / recovery process. When the single-stage separation / recovery process is applied to blast furnace gas (the carbon dioxide concentration of the blast furnace gas is about 24% by volume). As the gas f, a gas having a carbon dioxide concentration of 68% by volume is recovered. In the two-stage separation / recovery step, carbon dioxide having a purity of 92% by volume is recovered. In the separation and recovery process after the second stage, one or more sets of hydrate generators and hydrate separators are arranged in series in this order on the downstream side of the hydrate separator 6 shown in FIG. This can be done. The unreacted gas in each hydrate generator is mixed with the unreacted gas c and effectively used as a coolant for the first cooler 3 and a driving gas for the expansion turbine 9.

  Therefore, when the present invention is applied and, for example, carbon dioxide is separated and recovered from blast furnace gas having a carbon dioxide content of 24% by volume, the one-stage separation / recovery process shown in FIG. 1 is used. Or the gas whose purity of a carbon dioxide is 95 volume% or less is collect | recovered as the gas f by using a two-stage separation / recovery process. Moreover, when the content of carbon dioxide in the mixed gas a is 50% by volume or more, it can be seen from the relationship shown in FIG. Furthermore, when the content of carbon dioxide in the mixed gas a is 75% by volume or more, from the relationship shown in FIG. 2, a gas whose carbon dioxide purity exceeds 95% by volume is recovered in the single separation / recovery step. The result is out of the scope of the present invention. That is, the number of separation / recovery steps may be determined so that the carbon dioxide concentration of the recovered gas f is 95% by volume or less according to the carbon dioxide content of the mixed gas a. The smaller the number of separation / recovery steps, the less power is used.

  Thus, according to the present invention, when recovering carbon dioxide from a mixed gas, a gas separation method using hydrate is employed, and the concentration of carbon dioxide recovered by the gas separation method using hydrate is 95. The separation / recovery process is discontinued at the stage of volume% or less, and the recovered gas f containing carbon dioxide is liquefied, so the power used in the liquefaction process increases, but the power used in the separation / recovery process is more than that. This makes it possible to significantly reduce the underground storage treatment cost of carbon dioxide in the mixed gas as compared with the conventional case.

  In addition, this invention is not limited to the range of the said description, A various change is possible. For example, the cooling device for the compressed gas b has two stages, but may have one stage, and may further have three stages or more. A filter for separating hydrate and water from the hydrate slurry d may be disposed between the hydrate generator 5 and the hydrate separator 6.

  By applying the present invention, carbon dioxide was recovered and liquefied from blast furnace gas containing 24% by volume of carbon dioxide, 23% by volume of carbon monoxide, 4% by volume of hydrogen, and the balance being nitrogen gas.

  In addition, as shown in FIG. 2 mentioned above, when recovering a blast furnace gas having 24% by volume of carbon dioxide by applying a separation method using hydrate, the concentration of carbon dioxide in the recovered gas is the first stage. 24 volume% → 68 volume% in the second stage separation / recovery, and 68 volume% → 92 volume% in the second stage separation / recovery, and 92 volume% → 98 volume% in the third stage separation / recovery.

  In Example 1 of the present invention, the separation / recovery process is only one stage, and the obtained gas having a carbon dioxide concentration of 68% by volume is liquefied. In Example 2, the separation / recovery process is performed in two stages. Further, a gas having a carbon dioxide concentration of 92% by volume was liquefied. In the comparative example, a high-purity gas having a carbon dioxide concentration of 98% by volume obtained by the separation / recovery process using three stages of hydrates was liquefied. Table 1 shows the power used in the separation / recovery process and the liquefaction process.

In the comparative example in which carbon dioxide is concentrated to 98% by volume, the power used in the liquefaction process is as low as 71 kWh / t-CO ₂ , but the power used in the separation / recovery process is as high as 529 kWh / t-CO ₂ for separation. -A total of 600 kWh / t-CO ₂ was required for the recovery and liquefaction processes.

On the other hand, in Example 1 of the present invention, the power used in the liquefaction process increases to 92 kWh / t-CO ₂ , but the power used in the separation / recovery process is as low as 314 kWh / t-CO _2, and the separation / recovery process. And the total of the liquefaction processes only required 406 kWh / t-CO ₂ . Similarly, in Example 2 of the present invention, 516 kWh / t-CO ₂ was required in total for the separation / recovery step and the liquefaction step, and it was confirmed that the power used was greatly reduced compared to the comparative example.

DESCRIPTION OF SYMBOLS 1 Recovery and liquefaction equipment 2 Compressor 3 1st cooler 4 2nd cooler 5 Hydrate generator 5a Cooler 6 Hydrate separator 6a Heat exchanger 7 Circulation pump 8 Liquefaction device 9 Expansion turbine

Claims (3)

A gas mixture containing 20-30% by volume of carbon dioxide is introduced into the hydrate generator to form a hydrate of gas and water capable of forming a hydrate in the gas mixture, and then formed. A separation / recovery step for concentrating the concentration of carbon dioxide in the recovered gas by decomposing the recovered hydrate into a gas and water, and recovering the decomposed gas; A method for recovering and liquefying carbon dioxide from a mixed gas, the method comprising: a liquefying step for liquefying a gas containing carbon dioxide recovered in the separation / recovery step, wherein the separation / recovery step includes at least the mixed gas performed once for at carbon dioxide concentrations below 95 vol% steps in the gas is recovered, the recovered gas is liquefied and supplied to the liquefaction step, the separation and recovery step and the liquefaction Characterized by reducing the total value of the used power in the extent of both processes, recovery and liquefaction process of carbon dioxide from a gas mixture.   The liquefied gas is supplied to the liquefaction step and liquefied when the concentration of carbon dioxide in the gas recovered in the separation / recovery step is 80% by volume or less. To recover and liquefy carbon dioxide from mixed gas.   The liquefied gas is supplied to the liquefaction step and liquefied when the concentration of carbon dioxide in the gas recovered in the separation / recovery step is 30 to 70% by volume. A method for recovering and liquefying carbon dioxide from the described mixed gas.

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