Pre-treatment method for air separation device, pre-treatment device for the same and carbon dioxide recovery method

Abstract

To propose a pre-treatment device that supplies raw material gas to an air separation device that separates oxygen and nitrogen from the raw material gas, a pre-treatment method for the air separation device, the pre-treatment device for the same, and a carbon dioxide recovery method for recovery of carbon dioxide adhering to an absorbent.SOLUTION: A pre-treatment method for an air separation device comprises: an adsorption process which uses at least two adsorption towers to adsorb and remove carbon dioxide gas and moisture mainly in raw air with the one adsorption tower; and a regeneration process which has a first-stage desorption process that desorbs the carbon dioxide gas and moisture adsorbed by the other adsorption tower by using the carbon dioxide gas. Additionally, the regeneration process has a second-stage desorption process that performs desorption by using impure nitrogen derived from the air separation device instead of the carbon dioxide gas. The carbon dioxide gas and impure nitrogen are preferably heated gases. The adsorption process duration is preferably longer than the regeneration process duration. It is preferable that the adsorption process and the regeneration process are alternately executed between the one adsorption tower and the other adsorption tower.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an air separation unit, and more particularly to a pretreatment method and pretreatment device for removing moisture and carbon dioxide gas contained in feed air, and a carbon dioxide gas recovery method. [Background technology]

[0002] Blast furnaces and converters in steelworks consume large amounts of oxygen. In places where such large amounts of oxygen are required, oxygen production facilities are generally installed within the steelworks, and the oxygen produced by the oxygen production facilities is supplied to the blast furnaces, converters, and other equipment.

[0003] Air separation plants use methods such as cryogenic separation, TSA (Temperature Swing Adsorption), and PSA (Pressure Swing Adsorption) to separate and extract air components such as oxygen and nitrogen from the air and turn them into products. To prevent the moisture and carbon dioxide in the feed air from solidifying in the main body of the air separation plant or to prevent deterioration of the adsorbent in the main body, pretreatment is performed to remove the moisture and carbon dioxide from the feed air before it is introduced into the main body of the air separation plant. Pretreatment is generally carried out by passing the raw air through an adsorber filled with an adsorbent. For example, an adsorber filled with alumina gel (a moisture adsorbent) and zeolite (a carbon dioxide adsorbent) is provided, and the raw air is passed through the adsorber in the order of alumina gel and zeolite, thereby removing moisture and carbon dioxide within the adsorber.

[0004] Such adsorbers are usually provided in pairs, and while feed air is passed through one of the adsorbers to adsorb moisture and the like, high-temperature regeneration gas is introduced into the other adsorber, thereby regenerating the other adsorber (e.g., Patent Document 1 and Patent Document 2). The regeneration gas is obtained by heating nitrogen gas after air separation with a heater. A plurality of adsorption towers are arranged, with some of the adsorption towers being operated for adsorption and the other adsorption towers being operated for desorption.

[0005] In addition, in air separation plants, a two-tower, alternating-switch type adsorption removal unit of the PSA or TSA type is used as a pretreatment unit to remove impurities (moisture, carbon dioxide, etc.) from the feed air. Among these, the TSA method is used in most equipment because it has little pressure fluctuation in the process and long switching times.The TSA method removes impurities (moisture, carbon dioxide, etc.) by utilizing the difference in adsorption capacity of the adsorbent at each temperature. Therefore, the greater the difference between the operating temperature and the regeneration temperature, the greater the adsorption capacity per unit weight of adsorbent. Naturally, when designing a certain device, the greater the temperature difference, the less total amount of adsorbent can be used. Furthermore, the higher the pressure, the lower the saturated moisture content in the feed air, which reduces the total adsorption capacity and therefore the total amount of adsorbent. During desorption, specific components of the adsorbent are desorbed by applying heat to the adsorbent at a pressure lower than the adsorption pressure and heating and cooling the adsorbent.

[0006] The pretreatment devices for air separation plants are generally of the type that adsorb moisture and carbon dioxide onto an adsorbent. For example, Patent Document 3 discloses a pretreatment method for a cryogenic air separation plant that includes multiple adsorption towers filled with adsorbents that adsorb and remove moisture, carbon dioxide, and other substances from the feed air, and that continuously purify the feed air. It also describes the use and optimization of adsorption towers filled with a moisture adsorbent such as activated alumina and a carbon dioxide adsorbent such as X-type zeolite. Furthermore, used adsorption towers are regenerated by desorbing the adsorbed material using high-temperature purge gas, and are reused. Patent Documents 4 and 5 disclose techniques for predicting the usage limit of an adsorption tower and the amount of energy required for regeneration.

[0007] Various efficient methods for pre-treatment of air separation units are being investigated. Patent Document 1 discloses a method for pretreating feed air without using a fluorocarbon refrigerator. Specifically, in this pretreatment method, moisture and carbon dioxide gas are removed from the feed air by passing the feed air through an adsorber before the feed air is introduced into the main body of an air separation unit. After passing the feed air through a moisture adsorption section that adsorbs and removes moisture, the feed air is cooled and then passed through a carbon dioxide adsorption section that adsorbs and removes carbon dioxide gas.

[0008] Patent Document 2 discloses a pretreatment method for an air separation unit that can eliminate the need for a refrigerator, and an apparatus used therein. Specifically, the air separation unit includes a first adsorption tower that adsorbs and dehumidifies moisture in the feed air, a heat exchanger that cools the feed air that has been heated by the adsorption and dehumidification in the first adsorption tower, and a second adsorption tower that adsorbs and removes carbon dioxide and moisture from the feed air that has passed through the heat exchanger.

[0009] Patent Document 3 discloses a method and apparatus for pretreatment of a cryogenic air separation unit for removing moisture and carbon dioxide gas from a cryogenic air separation unit, in which high-temperature pressurized feed air leaving an air- or water-cooled aftercooler is directly introduced into an adsorber in a pretreatment unit, without the need for special equipment such as a precooling system or dehumidifier to replace a fluorocarbon refrigerator or water-wash cooling tower. The method and apparatus then enable operation at high air temperatures. Specifically, the pretreatment method for a cryogenic air separation unit includes multiple adsorption columns, each filled with an adsorbent that adsorbs and removes impurities such as moisture and carbon dioxide gas from the feed air, and is switchable between them to continuously purify the feed air. The method is characterized by an adsorption process, a depressurization process, a heating process, a cooling process, a thermal regeneration process, and a pressurization process.

[0010] Patent Document 4 discloses a pretreatment device that effectively utilizes the adsorbent so as not to switch between adsorption and regeneration when sufficient adsorption capacity remains in the adsorption tower, thereby suppressing excessive consumption of regeneration energy and further being able to handle cases where CO2 in the air significantly exceeds the design value. Specifically, this pretreatment device supplies a raw gas to an air separation unit that separates oxygen and nitrogen from the raw gas, and is characterized by comprising at least two adsorption towers through which air passes and removes H2O, CO2, and N2O from the air, and an N2O sensor that measures the concentration of N2O in the gas that has passed through one of the adsorption towers, and by switching the adsorption towers when the N2O concentration measured by the N2O sensor reaches a specified value.

[0011] Patent Document 5 describes a pretreatment device that effectively utilizes the adsorbent so that switching between adsorption and regeneration does not occur when sufficient adsorption capacity remains in the adsorption tower, thereby reducing excessive consumption of regeneration energy and also coping with cases where CO2 in the air significantly exceeds the design value. Specifically, a pretreatment device is disclosed that supplies a raw material gas to an air separation unit that separates oxygen and nitrogen from the raw material gas, and is characterized by comprising at least two adsorption towers through which the gas passes and removes at least CO2 from the gas, a CO2 sensor that measures the concentration of CO2 in the gas before it passes through the adsorption towers, a gas meter that measures the amount of gas that has passed through the adsorption towers, a CO2 amount integrating unit that integrates the total amount of CO2 that has passed through one of the adsorption towers based on the CO2 concentration and the gas amount, and switching between the adsorption towers before the total amount of CO2 reaches a predetermined value. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-66245 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-209474 [Patent Document 3] Japanese Patent Application Publication No. 9-38446 [Patent Document 4] JP 2014-113593 A [Patent Document 5] JP 2014-113594 A Summary of the Invention [Problem to be solved by the invention]

[0013] Recently, society has been calling for a reduction in CO2 emissions, and CCU (Carbon dioxide Capture and Utilization) technology has been attracting attention. However, the conventional technology does not recover the adsorbed carbon dioxide gas, which is problematic from the viewpoint of reducing carbon dioxide gas emissions.

[0014] The present invention has been made in consideration of the above circumstances, and aims to propose a pretreatment method and pretreatment device for an air separation unit, and a carbon dioxide recovery method, relating to pretreatment for supplying a raw material gas to an air separation unit that separates oxygen and nitrogen from the raw material gas. [Means for solving the problem]

[0015] The pretreatment method for an air separation unit according to the present invention, which advantageously solves the above problems, is configured as follows. [1] A pretreatment method for an air separation unit, which uses at least two adsorption towers and includes an adsorption step in which one adsorption tower adsorbs and removes mainly carbon dioxide and moisture from the feed air, and a regeneration step in the other adsorption tower, which includes a first desorption step in which the adsorbed carbon dioxide and moisture are desorbed using heated carbon dioxide. [2] In the above [1], the carbon dioxide gas discharged from the other adsorption tower is separated into a discharge channel and a heated channel, a portion of the carbon dioxide gas is discharged, and the remainder of the carbon dioxide gas is circulated for heating and heated by a heater, and the heated carbon dioxide gas is supplied to the other adsorption tower in the regeneration step. This is a pretreatment method for an air separation unit. [3] In the above [1], the regeneration step is a pretreatment method for an air separation unit, including a second desorption step in which impure nitrogen led from an air separation unit is used instead of the carbon dioxide gas. [4] In the above [1] or [3], the pretreatment method for an air separation unit uses heated gas in the regeneration step. [5] The pretreatment method for an air separation unit according to the above [1] or [3], wherein the duration of the adsorption step is longer than the duration of the regeneration step. [6] In any one of [1] to [3] above, a pretreatment method for an air separation unit is provided, in which the adsorption step and the regeneration step are alternately carried out in the one adsorption tower and the other adsorption tower by switching a switching valve in a gas distribution path.

[0016] The pretreatment device for an air separation plant according to the present invention, which advantageously solves the above problems, is configured as follows. [7] A pretreatment device for an air separation unit, comprising at least two adsorption towers, each filled with an adsorbent that adsorbs and removes mainly carbon dioxide and moisture from the feed air, the adsorbed carbon dioxide and moisture being desorbed by heated gas, and configured such that when one adsorption tower adsorbs and removes mainly carbon dioxide and moisture from the feed air, the other adsorption tower desorbs the adsorbed carbon dioxide and moisture with heated carbon dioxide gas. [8] In the above [7], the pretreatment device for an air separation unit is provided with a carbon dioxide gas circulation path in which the flow of carbon dioxide gas derived from the other adsorption tower is divided into a path for discharge and a path for heating, and a carbon dioxide gas circulation path in which the carbon dioxide gas flows for heating and the heated carbon dioxide gas is supplied to the other adsorption tower. [9] In the above [7], the pretreatment device for an air separation unit further comprises a switching valve that can switch between the supply of raw air to the one adsorption tower and the circulation path of treated air, and the supply of heated gas to the other adsorption tower and the circulation path of carbon dioxide gas.

[0017] The carbon dioxide gas recovery method according to the present invention, which advantageously solves the above problems, is configured as follows.

[10] A carbon dioxide gas recovery method in which the carbon dioxide gas that is discharged and led out from the adsorption tower is recovered by using the pretreatment method according to any one of [1] to [3] above. [Effects of the Invention]

[0018] The present invention provides a pretreatment method and pretreatment device for an air separation unit to remove moisture and carbon dioxide gas from feed air, making it possible to recover carbon dioxide gas that was previously unrecovered. Furthermore, clean carbon dioxide gas from the atmosphere can be utilized as a material for clean CCUs. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a configuration diagram illustrating an air separation facility according to an embodiment of the present invention. [Figure 2] FIG. 1 is a configuration diagram illustrating a conventional air separation facility. [Figure 3] FIG. 1 is an explanatory diagram of the regeneration of an adsorbent when the present invention is applied compared to the conventional method. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, a detailed description will be given of a pretreatment method for an air separation unit according to one embodiment of the present invention, together with a pretreatment device used therein.

[0021] <Pretreatment device for air separation unit> The pretreatment device of this embodiment of the air separation unit includes at least two adsorption towers, each filled with an adsorbent that adsorbs and removes mainly carbon dioxide and moisture from the feed air, and the packing has the function of desorbing the adsorbed carbon dioxide and moisture with heated gas. Furthermore, the pretreatment device is configured so that when one adsorption tower adsorbs and removes mainly carbon dioxide and moisture from the feed air, the other adsorption tower desorbs the adsorbed carbon dioxide and moisture with heated carbon dioxide gas.

[0022] An example of an air separation facility is shown in Figure 1. The arrows indicate the direction of gas flow. This pretreatment device 1 supplies raw gas compressed by a gas compressor 4 to an air separation device 2, which separates oxygen and nitrogen from the raw gas. The pretreatment device 1 also includes at least two adsorption towers (11, 12) through which the gas passes and removes at least carbon dioxide from the gas; the air separation device 2 to which purified air 8 purified in the adsorption tower 11 is introduced; and a heater 3 that heats regeneration gas 7. It is preferable to install a control device (not shown) in the carbon dioxide gas recovery system.

[0023] A heat exchanger (not shown) may be disposed in the circulation path where a part of the nitrogen gas or carbon dioxide gas discharged from the air separation unit is used as the regeneration gas, and a circulation path for supplying the regeneration gas heated by the heater to the adsorption tower may be provided. The regeneration gas may be heated by a heat exchanger instead of a heater.

[0024] The gas compressor 4 compresses gas (for example, air) taken in through a filter, and then cools it in a cooler (not shown) such as an aftercooler, and supplies the gas to the pretreatment device 1 as a raw material gas.

[0025] In pretreatment device 1, compressed feed gas supplied by gas compressor 4 is supplied to adsorption towers (11, 12) and purified. In the adsorption towers, impurities such as moisture, hydrocarbons, and carbon dioxide gas in the passing feed gas are removed by adsorbing them onto an adsorbent. The purified feed gas (purified air) 8 is cooled to near the dew point in a heat exchanger (not shown) installed on the outlet side of pretreatment device 1, and then supplied to air separation device 2.

[0026] In the air separation facility, it is preferable to install a two-way selector valve and a three-way selector valve in the gas flow path to switch the gas flow. In the switching valve in Fig. 1, the open state is indicated by the white part, and the closed state is indicated by the black part. Therefore, in the state of the switching valve in Fig. 1, air 9 is compressed by compressor 4, and then passes through adsorption tower 1, air separation unit 2, heater 3, and adsorption tower 2 in the flow indicated by the arrows, before being separated into discharge carbon dioxide gas 5 and circulating carbon dioxide gas 6.

[0027] In the air separation unit 2, for example, when a cryogenic separation unit is used, the purified feed air (purified air 8) supplied by the pretreatment unit is further cooled and separated into nitrogen, oxygen, and argon by rectification using the difference in liquefaction temperature. The oxygen and nitrogen separated in the rectification tower are supplied to their destinations via the gas supply lines for each product. For example, in a steelworks, oxygen is supplied to the blast furnace, converter, and other use plants.

[0028] <Pretreatment method for air separation unit> The pretreatment method for an air separation unit according to this embodiment uses at least two adsorption towers, and includes an adsorption step in which one adsorption tower adsorbs and removes mainly carbon dioxide and moisture from the feed air, and a regeneration step including a first-stage desorption step in which the adsorbed carbon dioxide and moisture are desorbed using carbon dioxide in the other adsorption tower.

[0029] The carbon dioxide gas discharged from the other adsorption tower is divided into two sections for discharge and heating, and the heated carbon dioxide gas that flows for heating is introduced into the other adsorption tower to carry out the first-stage dissociation step. The carbon dioxide gas discharged from the other adsorption tower is again divided into two sections for discharge and heating and flows, forming a circulation path through which the carbon dioxide gas that flows for heating is circulated.

[0030] Specifically, while one adsorption tower, for example, adsorption tower 1, is used to adsorb and remove impurities from the air, another adsorption tower, for example, adsorption tower 2, is regenerated with heated gas. Furthermore, by alternately switching the switching valve of the flow path and alternately using the removal and regeneration adsorption towers, it is possible to continuously purify the raw material gas. Note that three or more adsorption towers, including at least one removal adsorption tower and at least one regeneration adsorption tower, may be used by switching the switching valve of the flow path.

[0031] In this embodiment, after regenerating the adsorbent with carbon dioxide and recovering the carbon dioxide, it is preferable to use nitrogen (waste nitrogen) of lower purity than the product nitrogen in the regeneration gas discharge circulation path to regenerate the adsorbent in the adsorption tower.

[0032] It is preferable to use a heater to heat the regeneration gas. Examples of the heater include an electric heater and a heat exchanger. When a heat exchanger (not shown) is used, it is placed in the same circulation path as the heater.

[0033] A portion of the nitrogen gas discharged from the air separation unit, i.e., waste nitrogen, is supplied to a heat exchanger via a circulation path and heated to become regenerated gas. The generated regenerated gas is then supplied to an adsorption tower, which performs regeneration treatment, via a circulation path for the regenerated gas supply, where carbon dioxide and moisture adsorbed on the used adsorbent are removed, regenerating the adsorption tower so that it can be used repeatedly.

[0034] Regeneration gas is supplied to the adsorption tower 1 (11) through the regeneration gas supply flow path, and regeneration is performed to remove carbon dioxide and moisture adsorbed in the used adsorbent. It is preferable that the flow path for the regeneration gas supply is alternately switched to alternately supply and stop the regeneration gas at the same time that the switching valve alternately switches between the adsorption towers 1 (11) and 2 (12) for removal and regeneration. The positions of the switching valves of the flow paths in Fig. 1 indicate a gas flow path in which adsorption tower 1 (11) performs the removal function and adsorption tower 2 (12) performs the regeneration function. It is preferable to provide two adsorption towers, adsorption tower 1 (11) and adsorption tower 2 (12), and alternately switch the switching valves of the flow paths to alternately perform the removal and regeneration functions of the adsorption towers.

[0035] An image of the regeneration flow of the adsorbent to which the present invention is applied is shown in Figure 3, in comparison with the conventional method.

[0036] The carbon dioxide gas recovery system of this embodiment may be provided with a control device (not shown). The control device is configured by a computer equipped with, for example, a CPU, a memory, etc., and can control each device and equipment. For example, it is preferable to incorporate a concentration meter that measures the concentration of carbon dioxide gas, a flow meter that measures the amount of gas, and a control device that determines whether carbon dioxide gas is to be recovered based on the gas concentration and amount, and to control the concentration and amount of carbon dioxide gas to be recovered. The carbon dioxide gas recovery method of this embodiment can be applied to an air separation process that includes a pretreatment step, which has not been done conventionally. [Example]

[0037] The effects of this embodiment will be specifically described below based on examples, but the present invention is not limited to these examples.

[0038] [Example 1] The equipment configuration shown in Figure 1 was used to carry out the pretreatment of the air separation unit described below. In an air separation plant equipped with an adsorption device that adsorbs and removes primarily carbon dioxide and moisture from feed air, a pretreatment method was carried out to regenerate the adsorption tower in the first-stage desorption step, in which carbon dioxide gas is used for desorption, during the regeneration process of the adsorption device. In this case, carbon dioxide gas was circulated and recovered from the exhaust gas flow path. Two adsorption towers, adsorption tower 1 (11) and adsorption tower 2 (12), were installed, and the flow path switching valves were alternately switched to alternately perform removal and regeneration of the adsorption towers. According to the embodiment of the present invention, it was possible to recover the carbon dioxide gas adsorbed in the adsorption step and also to regenerate the adsorption tower. In addition, when heated regeneration gas was used in the regeneration step, carbon dioxide gas could be recovered more efficiently than when the gas was not heated.

[0039] [Example 2] The following pretreatment for an air separation unit was carried out using the equipment configuration shown in Figure 1. In the regeneration process of the adsorption unit, a pretreatment method was carried out to regenerate the adsorption tower in a first desorption step using carbon dioxide gas, and a second desorption step using impure nitrogen led from the air separation unit. According to the embodiment of the present invention, the carbon dioxide gas adsorbed in the adsorption step could be recovered, and the adsorption tower could be regenerated to a state of higher purity than in Example 1.

[0040] [Example 3] Using the equipment configuration shown in Figure 1 and the pretreatment conditions shown in Example 1 as a base, the effect of heating the regeneration gas on carbon dioxide recovery was investigated. As a result, when heated regeneration gas was used, carbon dioxide gas could be recovered more efficiently than when it was not heated.

[0041] [Example 4] Using the equipment configuration shown in Figure 1 and the pretreatment conditions shown in Example 1 as a base, the effect of the time difference between the adsorption process and the regeneration process on carbon dioxide recovery was investigated. As a result, when the adsorption step time was longer than the desorption (regeneration) step time, carbon dioxide gas could be recovered without reducing the productivity of air separation, compared to when the adsorption step time was shorter. Here, 60,000 Nm 3 The air separation unit can produce oxygen at a rate of 1000 kJ / h and capture up to 2,000 tonnes of CO2 per year.

[0042] In the conventional equipment configuration shown in Figure 2, air separation can be performed without any problems, but the carbon dioxide gas adsorbed in the adsorption process is released into the atmosphere during regeneration. [Industrial Applicability]

[0043] The pretreatment method for air separation of the present invention is applicable not only to specific processes but also to any process for producing oxygen-utilizing products. [Explanation of symbols]

[0044] 1 Pretreatment equipment 11 Adsorption tower 1 12 Adsorption tower 2 2. Air Separation Unit 3 Heater 4 Compressor 5 Carbon dioxide (including water) 6 Circulating carbon dioxide 7 Regeneration gas (nitrogen) 8. Purified Air 9. Air 10 Gas after air separation 13 Nitrogen (including water and carbon dioxide)

Claims

1. 1. A method for pretreatment of an air separation unit, comprising the steps of: Use at least two adsorption towers, an adsorption step of adsorbing and removing mainly carbon dioxide gas and moisture from the feed air in a single adsorption tower; A regeneration process including a first desorption step in which the adsorbed carbon dioxide gas and moisture are desorbed using heated carbon dioxide gas in another adsorption tower; A method for pretreatment of an air separation unit, comprising:

2. The flow of carbon dioxide gas discharged from the other adsorption tower is divided into a discharge gas and a heating gas. A portion of the carbon dioxide gas is discharged, The remainder of the carbon dioxide gas is circulated for heating and heated by a heater, The heated carbon dioxide gas is supplied to another adsorption tower in the regeneration step. The method for pretreatment of an air separation unit according to claim 1.

3. The regeneration process includes a second desorption step in which impure nitrogen derived from an air separation unit is used in place of the carbon dioxide gas. The method for pretreatment of an air separation unit according to claim 1.

4. In the regeneration step, a heated gas is used. The method for pretreatment of an air separation unit according to claim 3.

5. 4. The method for pretreatment of an air separation unit according to claim 1 or 3, wherein the duration of the adsorption step is longer than the duration of the regeneration step.

6. 4. The pretreatment method for an air separation unit according to claim 1, wherein an adsorption step and a regeneration step are alternately carried out in the one adsorption tower and the other adsorption tower by switching a switching valve in a gas flow path.

7. At least two adsorption towers are provided, Each adsorption tower is filled with an adsorbent that adsorbs and removes mainly carbon dioxide and moisture from the feed air. The adsorbent has a function of desorbing the adsorbed carbon dioxide gas and moisture by heated gas, When the carbon dioxide and moisture in the feed air are mainly adsorbed and removed in one adsorption tower, In another adsorption tower, the adsorbed carbon dioxide gas and moisture are desorbed by heated carbon dioxide gas, in a pretreatment device for an air separation plant.

8. a carbon dioxide gas flow path in which the carbon dioxide gas discharged from the other adsorption tower is divided into a discharge path and a heating path; a carbon dioxide gas flow path for heating the carbon dioxide gas and supplying the heated carbon dioxide gas to the other adsorption tower; The pretreatment device of claim 7, comprising:

9. a supply path for feed air to the first adsorption tower and a flow path for treated air therethrough; 8. The pretreatment device for an air separation plant according to claim 7, further comprising a switching valve capable of switching between a supply path for the heated gas to said other adsorption tower and a flow path for the carbon dioxide gas.

10. A carbon dioxide gas recovery method, comprising recovering carbon dioxide gas that is led out of an adsorption tower and circulated for discharge, by using the pretreatment method according to any one of claims 1 to 3.

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