Method for recovering co2

Abstract

To provide a CO 2 recovery method capable of recovering CO 2 with high purity and a high recovery rate by a simple system.SOLUTION: A CO2 recovery method according to the present embodiment is a CO2 recovery method for recovering CO2 from an exhaust gas by using an adsorbent 10, and includes a pre-cooling step of cooling the adsorbent 10, a CO2 adsorbing step of adsorbing CO2 contained in the exhaust gas onto the cooled adsorbent 10, a pre-heating step of pre-heating the adsorbent 10 having adsorbed the CO2, and a CO2 desorbing step of desorbing the CO2 from the pre-heated adsorbent 10. In the preheating step, the adsorbent 10 is heated to 60 °C or more and 80 °C or less to desorb a part of CO2 from the adsorbent 10, the impurity gas is pushed out by the desorbed CO2 from the CO2 recovery vessel 100 in which the adsorbent 10 is disposed, and the impurity gas pushed out in the preheating step is returned to the CO2 adsorbing step.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] In systems that separate CO2 from CO2-containing gases using adsorbents, there is a demand for increasing the CO2 purity while also increasing the CO2 capture rate. For example, Patent Document 1 discloses a technology for increasing the CO2 purity by sucking and venting impurity gases while CO2 is adsorbed onto an adsorbent, and then sucking and returning the remaining CO2 to the adsorption process after desorbing the CO2 from the adsorbent, thereby increasing the CO2 recovery rate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2019 / 073866 Summary of the Invention [Problem to be solved by the invention]

[0004] The inventors have found the following problems with the CO2 recovery method. The technology disclosed in Patent Document 1 required the installation of a vacuum pump for suction and exhaust, and the construction of a vacuum pump stop system using a CO2 concentration sensor, making the system complex. Also, when suctioning and exhausting impurity gases, some of the CO2 is desorbed and exhausted to the outside, leaving room for improvement in terms of CO2 capture rate.

[0005] The present disclosure has been made in consideration of such problems, and aims to provide a CO2 recovery method that can recover CO2 with high purity and high recovery rate using a simple system. [Means for solving the problem]

[0006] One aspect of the present invention to achieve the above object is to A method for recovering CO2 from exhaust gas using an adsorbent, comprising: a pre-cooling step of cooling the adsorbent; a CO adsorption step of adsorbing CO contained in the exhaust gas onto the cooled adsorbent; a preheating step of preheating the adsorbent having CO2 adsorbed thereon; a CO2 desorption step of desorbing CO2 from the preheated adsorbent; The preheating step involves heating the adsorbent to a temperature of 60°C or higher and 80°C or lower to desorb some of the CO2 from the adsorbent, and pushing the impurity gas out of the CO2 recovery container in which the adsorbent is placed by the desorbed CO2. The impurity gas pushed out in the preheating step is returned to the adsorption step. [Effects of the Invention]

[0007] According to the present disclosure, a CO2 recovery method can be provided that can recover CO2 with high purity and high recovery rate using a simple system. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram showing an example of the configuration of a CO2 collection container according to the present disclosure. [Figure 2] 1 is a graph showing the relationship between the CO2 adsorption coefficient and the CO2 partial pressure. [Figure 3] 1 is a schematic diagram showing a configuration example of a CO2 recovery system according to the present disclosure. [Figure 4] 1 is a graph showing the change in CO2 desorption amount and partial pressure when the CO2 capture vessel is heated. [Figure 5] 10 is a graph showing the change in purity of the CO2 captured after a relief valve of 1 atm is installed and the CO2 capture vessel is heated. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In each drawing, the same or corresponding elements are designated by the same reference numerals, and for clarity of explanation, duplicate explanations will be omitted as necessary. In addition, for ease of understanding, the scale of each part in the drawings may differ from the actual scale.

[0010] First, an overview of the CO2 recovery method according to the present disclosure will be described with reference to FIGS. 1 and 2. FIG. 1 is a schematic diagram showing an example of the configuration of a CO2 recovery container 100. The CO2 recovery container 100 has an adsorbent 10 disposed therein. The adsorbent 10 adsorbs CO2 in a gas such as exhaust gas, and is configured using, for example, a fixed amount of adsorbent. The CO2 adsorption coefficient of the adsorbent 10 changes depending on the temperature. FIG. 2 is a graph showing the relationship between the CO2 adsorption coefficient of the adsorbent 10 and temperature. As shown in FIG. 2, as the temperature of the adsorbent 10 increases, the CO2 adsorption coefficient decreases, and the amount of CO2 that can be adsorbed decreases.

[0011] The CO2 recovery container 100 is provided with a heating mechanism and an exhaust mechanism. The heating mechanism heats the adsorbent 10. The heat medium input section 20 shown in FIG. 1 is an example of the heating mechanism. The heat medium input section 20 is a component into which a heat medium such as oil is input, and is disposed within the CO2 recovery container 100. Note that the heating mechanism is not limited to this and may be, for example, an external heater. The exhaust mechanism exhausts gas from within the CO2 recovery container 100. The relief valve 30 shown in FIG. 1 is an example of the exhaust mechanism. The relief valve 30 opens when the pressure within the CO2 recovery container 100 exceeds a set value. The set pressure of the relief valve 30 is, for example, above atmospheric pressure and below 2 atmospheres.

[0012] The CO2 capture method according to the present disclosure comprises a pre-cooling step, a CO2 adsorption step, a pre-heating step, and a CO2 desorption step. In the pre-cooling step, the adsorbent 10 is cooled. In the CO2 adsorption step, exhaust gas is sent to the CO2 capture vessel 100 after the pre-cooling step, and the CO2 contained in the exhaust gas is adsorbed by the adsorbent 10. In the pre-heating step, the adsorbent 10, which has adsorbed CO2 in the adsorption step, is heated to a temperature of 60°C or higher and 80°C or lower. In the CO2 desorption step, CO2 is desorbed from the pre-heated adsorbent 10.

[0013] In the CO2 adsorption process, exhaust gas containing CO2 is sent to the adsorption CO2 capture vessel 100. When the exhaust gas is introduced, the CO2 in the exhaust gas is adsorbed by the adsorbent 10, and gases other than CO2, i.e., impurity gases, remain as residual gases in the gas phase of the CO2 capture vessel 100. In the CO2 capture method disclosed herein, a preheating process is performed to heat the adsorbent 10 in this state by, for example, introducing a heat medium into the heat medium input section 20. Preheating reduces the CO2 adsorption coefficient of the adsorbent 10, causing some of the CO2 adsorbed by the adsorbent 10 to desorb. At this time, the desorbed CO2 increases the CO2 partial pressure in the gas phase, thereby increasing the CO2 adsorption coefficient and enabling the adsorption of more CO2 than during desorption. In other words, the CO2 capture vessel 100 is balanced between the decrease in the adsorption coefficient due to heating and the increase in the adsorption coefficient due to the increase in CO2 partial pressure.

[0014] When a portion of the CO2 is desorbed from the adsorbent 10 by preheating, the combined gas of the desorbed CO2 and residual gas expands due to heating, increasing the pressure inside the CO2 capture vessel 100. When the pressure inside the CO2 capture vessel 100 exceeds the set value of the relief valve 30, the relief valve 30 opens, and the combined gas is expelled from the CO2 capture vessel 100 to the outside. As will be described in detail later, the expelled combined gas is returned to the CO2 adsorption process and adsorbed onto the adsorbent 10. In this way, the preheating process can increase the CO2 purity inside the CO2 capture vessel 100. Therefore, the CO2 capture method according to the present disclosure does not require the construction of a vacuum pump and a vacuum pump stop system, thereby simplifying the system. Furthermore, the CO2 released during the preheating process is re-adsorbed and not discharged outside the capture system. In other words, the CO2 capture method according to the present disclosure can capture CO2 with a high capture rate. As such, the CO2 capture method according to the present disclosure can capture CO2 with high purity and a high capture rate using a simple system.

[0015] Next, a specific embodiment of the CO2 capture method according to the present disclosure will be described with reference to FIGS. 3 to 6. FIG. 3 shows an example configuration of a CO2 capture system 200 for performing the CO2 capture method according to the present disclosure. The CO2 capture system 200 includes four CO2 capture vessels 100a, 100b, 100c, and 100d. The CO2 capture vessels 100a to 100d each perform a pre-cooling process, a CO2 adsorption process, a pre-heating process, and a CO2 desorption process. In the example shown in FIG. 3, the CO2 capture vessel 100a performs the pre-cooling process, the CO2 capture vessel 100b performs the CO2 adsorption process, the CO2 capture vessel 100c performs the pre-heating process, and the CO2 capture vessel 100d performs the CO2 desorption process. The CO2 capture vessels 100a to 100d are connected to each other via openable and closable valves, allowing gas exchange between them. The black valves shown in Figure 3 indicate that the valves are in a closed state. The white valves shown in Figure 3 indicate that the valves are in an open state.

[0016] The CO2 recovery vessels 100a-100d use 500 kg of zeolite as the adsorbent 10. The gas phase volume of the CO2 recovery vessels 100a-100d is 250 L, and the CO2 concentration in the exhaust gas before CO2 adsorption is 10%. In this case, the amount of CO2 adsorbed in the CO2 adsorption process is calculated to be approximately 1100 mol by multiplying the adsorption coefficient [mol / kg] at 20°C and a CO2 partial pressure (10 kPa) by the weight [kg] of the adsorbent 10.

[0017] Figure 4 shows the change in CO2 desorption amount and partial pressure when the adsorbent 10 is heated by adding high-temperature oil in this state. The pressure inside the CO2 recovery vessel 100c increases due to thermal expansion of the gas phase gas (total gas), causing the gas phase gas to leak through the relief valve 30. If the relief valve is set to atmospheric pressure, i.e., 1 atm, a directional control valve (check valve) may be used instead of the relief valve 30.

[0018] Furthermore, with regard to the CO2 partial pressure, which was about 10 kPa (O2 concentration set at 10%) during CO2 adsorption, 9.6 mol are desorbed at 60°C, balancing at a partial pressure of 51 kPa, which is roughly equal to the impurity gas (N2), and the CO2 concentration in the gas phase is 50%.Furthermore, at 80°C, 62.7 mol are desorbed, resulting in a partial pressure of 88 kPa, and at 100°C, 242.7 mol are desorbed, resulting in a partial pressure of 98 kPa, and the gas phase is almost entirely CO2 gas.

[0019] Figure 5 is a graph showing the gas-phase gas leaking from the relief valve 30 at 1 atm and the purity of the captured CO2 gas. As the temperature rises, CO2 desorbed from the adsorbent 10 forces impurity gas (N2) to leak from the relief valve 30, causing the impurity gas in the gas phase to decrease with increasing temperature. At 60°C, 4.5 mol of impurity gas (N2) remains in the gas phase. When CO2 is captured, including this, the purity of the captured CO2 gas is 99.6%, an improvement of 0.5 points compared to the 99.1% purity during adsorption. At 80°C, 1.1 mol of impurity gas (N2) remains, resulting in a captured CO2 purity of 99.89%. At 90°C, 0.5 mol of impurity gas (N2) remains, resulting in a captured CO2 purity of 99.95%. Thus, the purity of the captured CO2 increases with increasing temperature. However, as the temperature increases, the amount of leaked CO2 also increases. As mentioned above, the leaked CO2 is returned to the CO2 adsorption process and does not escape to the outside, but it does cause an increase in the amount of CO2 that cannot be captured. Therefore, from a cost perspective, it is preferable that preheating be carried out at a temperature between 60°C and 80°C.

[0020] As described above, when the preheating step is performed, the purity of the recovered CO2 can be increased from about 99.1% to about 99.8% compared to when the preheating step is not performed. In this way, the CO2 recovery method according to the present disclosure can increase the purity of the recovered CO2 without providing a pump for discharging impurity gases, thereby achieving cost reduction and a downsized system.

[0021] The present disclosure is not limited to the above-described embodiment, and can be modified as appropriate within the scope of the present disclosure. [Explanation of symbols]

[0022] 100(100a, 100b, 100c, 100d) CO2 capture container 10. Adsorbent 20 Heat medium input part 30 Relief valve

Claims

[Claim 1] CO2 from exhaust gas using adsorbent ２ CO to collect ２ A recovery method comprising: a pre-cooling step of cooling the adsorbent; The cooled adsorbent is then cooled to remove CO contained in the exhaust gas. ２ CO that adsorbs ２ an adsorption step; CO ２ a preheating step of preheating the adsorbent that has adsorbed the CO from the preheated adsorbent ２ CO that desorbs ２ a desorption step, The preheating step is a step of heating the adsorbent to a temperature of 60° C. or higher and 80° C. or lower to remove a part of CO from the adsorbent. ２ is released, and the release CO ２ The adsorbent is placed by ２ The impurity gas is pushed out from the collection container. The impurity gas pushed out in the preheating step is ２ Returned to the adsorption process CO ２ Recovery method.

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