CO2 recovery method

Abstract

Provided is an O 2 recovery method capable of recovering O 2 with high purity and high recovery rate using a simple system. A CO2 recovery method according to the present disclosure is a CO 2 recovery method for recovering CO 2 from exhaust gas using an adsorbent (10), the method comprising: a preliminary cooling step for cooling the adsorbent (10); an O (2) adsorption step in which O (2) included in the exhaust gas is adsorbed on the cooled adsorbent (10); a pre-heating step for pre-heating the adsorbent (10) on which the CO (2) has been adsorbed; and a CO (2) detachment step for detaching the CO (2) from the preheated adsorbent (10), in which the adsorbent (10) is heated to 60-80 DEG C (inclusive) to detach a portion of the CO (2) from the adsorbent (10), and foreign gas is extruded from the inside of the CO2 recovery container (100) in which the adsorbent (10) is disposed by the detached CO (2) to the outside, and the adsorbent (10) is removed from the adsorbent (10) by heating the adsorbent (10) to 60-80 DEG C (inclusive). The foreign gas extruded in the pre-heating step is returned to the CO 2 adsorption step.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a CO2 recovery method. BACKGROUND

[0002] In a system for separating CO2 from a CO2-containing gas using an adsorbent material, it is desirable to increase the CO2 recovery rate while increasing the CO2 purity. For example, in Patent Literature 1, a technique is disclosed in which, in a state in which CO2 is adsorbed to an adsorbent material, an impurity gas is suction-exhausted to increase the CO2 purity, and after the CO2 is desorbed from the adsorbent material, the remaining CO2 is suctioned to be returned to the adsorption process again to increase the CO2 recovery rate. PRIOR ART DOCUMENTS PATENT LITERATURE

[0003] Patent Literature 1: International Publication No. 2019 / 073866 SUMMARY PROBLEMS TO BE SOLVED BY THE INVENTION

[0004] Regarding the CO2 recovery method, the inventors have found the following problems. In the technique disclosed in Patent Literature 1, a vacuum pump for suction-exhaustion needs to be provided and a vacuum pump stop system based on a CO2 concentration sensor needs to be further constructed, and the system is complicated. In addition, when the impurity gas is suction-exhausted, a part of the CO2 is desorbed and discharged to the outside, so there is room for improvement in order to increase the CO2 recovery rate.

[0005] The present disclosure was made in view of such problems, and aims to provide a CO2 recovery method capable of recovering CO2 at a high purity and a high recovery rate using a simple system. TECHNICAL MEANS FOR SOLVING THE PROBLEMS

[0006] One way for achieving the above object is a CO2 recovery method for recovering CO2 from an exhaust gas using an adsorbent material, comprising: a preliminary cooling process of cooling the adsorbent material; a CO2 adsorption process of adsorbing CO2 contained in the exhaust gas to the adsorbent material after cooling; a preliminary heating process of preliminarily heating the adsorbent material to which CO2 is adsorbed; and a CO2 desorption process of desorbing CO2 from the adsorbent material after the preliminary heating, in the preliminary heating process, a part of the CO2 is desorbed from the adsorbent material by heating the adsorbent material to 60°C or higher and 80°C or lower, and an impurity gas is extruded from a CO2 recovery container in which the adsorbent material is disposed to the outside using the desorbed CO2, The impurity gas extruded in the preliminary heating process is returned to the adsorption process. Effects of Invention

[0007] According to the present disclosure, a CO2 recovery method capable of recovering CO2 at high purity and high recovery rate using a simple system can be provided. BRIEF DESCRIPTION OF DRAWINGS

[0008] Figure 1 is a schematic view showing a configuration example of a CO2 recovery vessel according to the present disclosure. Figure 2 is a graph showing a relationship between an adsorption coefficient of CO2 and a CO2 partial pressure. Figure 3 is a schematic view showing a configuration example of a CO2 recovery system according to the present disclosure. Figure 4 is a graph showing changes in a CO2 desorption amount and a partial pressure in a case where the CO2 recovery vessel is heated. Figure 5 is a graph showing changes in a purity of recovered CO2 after a 1 atm overflow valve is provided and the CO2 recovery vessel is heated. DETAILED DESCRIPTION

[0009] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In each drawing, the same or corresponding elements are denoted by the same reference numerals, and repeated description will be omitted as necessary for the sake of clear description. In addition, the proportions of each portion in the drawings are sometimes different from the actual proportions for easy understanding.

[0010] First, an outline of a CO2 recovery method according to the present disclosure will be described with reference to Figures 1-2 Figure 1 is a schematic view showing a configuration example of a CO2 recovery vessel 100. The CO2 recovery vessel 100 is internally configured with an adsorption material 10. The adsorption material 10 adsorbs CO2 in a gas such as exhaust gas, and is configured using, for example, a fixed adsorption material. The adsorption coefficient of CO2 of the adsorption material 10 varies depending on the temperature. Figure 2 is a graph showing a relationship between the CO2 adsorption coefficient of the adsorption material 10 and the temperature. As Figure 2 indicated, when the temperature rises, the CO2 adsorption coefficient of the adsorption material 10 decreases, and the amount of adsorbable CO2 decreases.

[0011] A heating mechanism and an exhaust mechanism are provided in the CO2 recovery vessel 100. The heating mechanism is a mechanism that heats the adsorption material 10. Figure 1 ​The heat medium injection portion 20 shown is an example of a heating mechanism. The heat medium injection portion 20 is a member that injects a heat medium such as oil, and is disposed inside the CO2 recovery container 100. In addition, the heating mechanism is not limited to this, and can be, for example, an external heater. The exhaust mechanism is a mechanism for exhausting gas from inside the CO2 recovery container 100. Figure 1 The overflow valve 30 shown is an example of an exhaust mechanism. The overflow valve 30 opens when the pressure inside the CO2 recovery container 100 becomes a set value or more. The set pressure of the overflow valve 30 is, for example, about atmospheric pressure or more and 2 atmospheres or less.

[0012] The CO2 recovery method according to the present disclosure includes a preliminary cooling step, a CO2 adsorption step, a preliminary heating step, and a CO2 desorption step. In the preliminary cooling step, the adsorbent material 10 is cooled. In the CO2 adsorption step, after the preliminary cooling step, exhaust gas is fed to the CO2 recovery container 100, and CO2 contained in the exhaust gas is adsorbed to the adsorbent material 10. In the preliminary heating step, the adsorbent material 10 to which CO2 is adsorbed in the adsorption step is heated to 60°C or more and 80°C or less. In the CO2 desorption step, CO2 is desorbed from the adsorbent material 10 after the preliminary heating.

[0013] In the CO2 adsorption step, CO2-containing exhaust gas is fed to the CO2 recovery container 100. When the exhaust gas is fed, the state in which CO2 in the exhaust gas is adsorbed to the adsorbent material 10 and gas other than CO2, that is, impurity gas, remains as residual gas in the gas phase inside the CO2 recovery container 100. In the CO2 recovery method according to the present disclosure, the preliminary heating step of heating the adsorbent material 10 by injecting a heat medium or the like to the heat medium injection portion 20 in this state is performed. When the preliminary heating is performed, the CO2 adsorption coefficient of the adsorbent material 10 decreases, and a part of the CO2 adsorbed to the adsorbent material 10 is desorbed. At this time, the CO2 partial pressure in the gas phase increases due to the desorbed CO2, so the CO2 adsorption coefficient increases, and more CO2 than at the time of desorption can be adsorbed. That is, the inside of the CO2 recovery container 100 is balanced by the decrease in the adsorption coefficient due to heating and the increase in the adsorption coefficient due to the increase in the CO2 partial pressure.

[0014] When a portion of the CO2 is desorbed from the adsorbent material 10 by the preliminary heating, the total gas of the desorbed CO2 and the residual gas is expanded by heating, and the internal pressure of the CO2 recovery container 100 rises. When the pressure in the CO2 recovery container 100 becomes equal to or higher than the set value of the overflow valve 30, the overflow valve 30 opens, and the total gas is expelled from the inside of the CO2 recovery container 100 to the outside. Details will be described later, but the expelled total gas returns to the CO2 adsorption process and is adsorbed to the adsorbent material 10. As such, by performing the preliminary heating process, the purity of the CO2 in the CO2 recovery container 100 can be increased. Thus, the CO2 recovery method according to the present disclosure can make the system simple without constructing a vacuum pump and a vacuum pump stop system or the like. In addition, since the CO2 discharged in the preliminary heating process is adsorbed again, it is not discharged to the outside of the recovery system. That is, the CO2 recovery method according to the present disclosure can recover CO2 at a high recovery rate. As such, the CO2 recovery method according to the present disclosure can recover CO2 at a high purity and a high recovery rate using a simple system.

[0015] Next, a specific mode of the CO2 recovery method according to the present disclosure will be described with reference to Figures 3-5 Figure 3 is a configuration example of a CO2 recovery system 200 for performing the CO2 recovery method according to the present disclosure. The CO2 recovery system 200 is provided with four CO2 recovery containers 100a, 100b, 100c, and 100d. The CO2 recovery containers 100a to 100d perform a preliminary cooling process, a CO2 adsorption process, a preliminary heating process, and a CO2 desorption process, respectively. In the example shown in Figure 3 , it is assumed that the CO2 recovery container 100a performs the preliminary cooling process, the CO2 recovery container 100b performs the CO2 adsorption process, the CO2 recovery container 100c performs the preliminary heating process, and the CO2 recovery container 100d performs the CO2 desorption process. The CO2 recovery containers 100a to 100d are connected to each other via valves that can be opened and closed, and can exchange gas. Figure 3 The black valve shown in Figure 3 indicates that the valve is in a closed state.

[0016] The CO2 recovery containers 100a to 100d use 500 kg of zeolite as the adsorbent material 10. In addition, the gas phase capacity of the CO2 recovery containers 100a to 100d is set to 250 L, and the CO2 concentration in the exhaust gas before CO2 adsorption is set to 10%. In this case, the amount of CO2 adsorbed in the CO2 adsorption process is the product of the adsorption coefficient [mol / kg] at 20°C and a CO2 partial pressure (10 kPa) and the weight [kg] of the adsorbent material 10, so it is calculated to be about 1100 mol.

[0017] ​The amount of CO2 desorbed and the change in partial pressure in the case where the adsorbent 10 is heated by introducing high-temperature oil or the like in this state are shown in FIG. 6. Figure 4 The pressure in the CO2 recovery container 100c rises due to thermal expansion of the gas-phase gas (total gas), and the gas-phase gas leaks from the overflow valve 30. In the case where the overflow valve is set to atmospheric pressure, i.e., 1 atm, a directional control valve (one-way valve) can be used instead of the overflow valve 30.

[0018] In addition, with respect to the CO2 partial pressure, at the time of CO2 adsorption, it is about 10 kPa (O2 concentration is set to 10%) and, at 60°C, 9.6 mol is desorbed and the equilibrium is at a partial pressure of 51 kPa, which is almost equal to the impurity gas (N2), and the CO2 concentration in the gas phase becomes 50%. Further, at 80°C, 62.7 mol is desorbed and the partial pressure becomes 88 kPa, and at 100°C, 242.7 mol is desorbed and the partial pressure becomes 98 kPa, and almost all of the gas in the gas phase is CO2 gas.

[0019] Figure 5 is a graph showing the purity of the gas-phase gas that leaks from the overflow valve 30 set to 1 atm and the recovered CO2 gas. The impurity gas (N2) leaks from the overflow valve 30 due to the pressure of the CO2 that is desorbed from the adsorbent 10 due to the temperature rise, and thus the impurity gas in the gas phase decreases as the temperature rises. At 60°C, 4.5 mol of the impurity gas (N2) remains in the gas phase, and in the case where CO2 is recovered including this, the purity of the recovered CO2 gas becomes 99.6%, which is improved by 0.5 percentage points compared to 99.1% at the time of adsorption. At 80°C, 1.1 mol of the impurity gas (N2) remains, and the purity of the recovered CO2 becomes 99.89%. In addition, at 90°C, 0.5 mol of the impurity gas (N2) remains, and the purity of the recovered CO2 becomes 99.95%. As such, as the temperature rises, the purity of the recovered CO2 increases. However, as the temperature increases, the amount of CO2 that leaks also increases. Although the leaked CO2 returns to the CO2 adsorption process as described above and does not go outside, an increase in the amount of CO2 that cannot be recovered occurs. Thus, from the viewpoint of cost, it is preferable that the preparatory heating be performed at a temperature of 60°C or higher and 80°C or lower.

[0020] As described above, if the preparatory heating process is performed, the purity of the recovered CO2 can be increased from about 99.1% to about 99.8% compared to the case where the preparatory heating process is not performed. As such, the CO2 recovery method according to the present disclosure can increase the purity of the recovered CO2 without providing a pump for discharging the impurity gas, and can achieve cost reduction and system size reduction.

[0021] Furthermore, the present disclosure is not limited to the above-described embodiments and can be appropriately changed within the scope of the gist. Reference Signs List

[0022] 100 (100a, 100b, 100c, 100d) CO2 recovery container 10 adsorbent material 20 heat medium feeding portion 30 overflow valve

Claims

1. A CO2 recovery method of recovering CO2 from exhaust gas using an adsorbent material, comprising: a preliminary cooling step of cooling the adsorbent material; a CO2 adsorption step of adsorbing CO2 contained in the exhaust gas to the adsorbent material after the cooling; a preliminary heating step of preliminarily heating the adsorbent material to which CO2 is adsorbed; and a CO2 desorption step of desorbing CO2 from the adsorbent material after the preliminary heating, wherein in the preliminary heating step, a part of the CO2 is desorbed from the adsorbent material by heating the adsorbent material to 60°C or higher and 80°C or lower, and impurity gas is extruded from a CO2 recovery vessel in which the adsorbent material is disposed to the outside by the desorbed CO2, and wherein the impurity gas extruded in the preliminary heating step is returned to the CO2 adsorption step. ​ ​ ​ ​ ​ ​

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