Carbon dioxide recovery system

Abstract

To reduce recovery energy required for recovery of CO2 as much as possible in a CO2 recovery system which is configured to cause an absorbent to absorb the CO2 in a gas and then discharge and recover the CO2 from the absorbent, and in which the amount of CO2 recovered from the adsorbent varies in accordance with the temperature of the gas supplied to the adsorbent.SOLUTION: In a CO2 recovery system: gas temperature adjustment means configured to adjust a temperature of a gas fed to an adsorbent is provided; it is inferred that which of cases requires less energy for recovering CO2 between a case of performing temperature adjustment on the gas fed to the adsorbent and a case of not performing the gas temperature adjustment; and the gas temperature adjustment is performed only when the case of performing the gas temperature adjustment requires less energy than the case of not performing the gas temperature adjustment.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a technology for recovering carbon dioxide (CO2) from gases such as the atmosphere and exhaust gases, and more specifically to a system configured to pass the gas through a solid or liquid adsorbent to adsorb the CO2 in the gas onto the adsorbent, and then desorb the CO2 from the adsorbent to recover the CO2. [Background technology]

[0002] Various technologies for capturing CO2 contained in the atmosphere or exhaust gases have been proposed to prevent global warming. For example, Patent Document 1 proposes a system that introduces a mixed gas containing carbon dioxide into an electrochemical cell having a working electrode with a negatively charged and reduced electroactive material, and executes two modes: an adsorption mode in which the carbon dioxide in the mixed gas is adsorbed onto the electroactive material in the working electrode, and a capture mode in which the working electrode is positively charged and the electroactive material with the adsorbed carbon dioxide is oxidized to release and capture the carbon dioxide. The system is configured to select a combination of the adsorption mode execution time and the capture mode execution time such that the amount of carbon dioxide captured is relatively large and the magnitude of the adsorption mode execution energy and the capture mode execution energy required to capture a predetermined unit amount of carbon dioxide are relatively low, thereby suppressing excessive energy consumption relative to the amount of carbon dioxide captured. Patent Document 2 proposes controlling the temperature, humidity, pressure and flow rate of the supply gas to optimize the gas separation and recovery performance in a system in which biogas, exhaust gas or air is compressed or blown using a gas compressor or gas blower driven by the energy of geothermal fluid, the heat of combustion of biomass, or flowing water, and the compressed or blown gas is supplied to a carbon dioxide separation membrane or a carbon dioxide adsorption and separation device to separate and recover carbon dioxide, and the recovered carbon dioxide gas is compressed using a gas compressor and then cooled using cold energy derived from renewable energy to liquefy or turn into dry ice. Patent Document 3 proposes a method for separating and recovering carbon dioxide gas by using a rotational driving force from the energy of either geothermal fluid or water flow to directly drive a vacuum pump or suction blower installed in the flow path of carbon dioxide gas that has permeated a carbon dioxide gas separation membrane to separate and recover carbon dioxide gas by suction from either air, biogas, or combustion exhaust gas. The proposed configuration controls the temperature of the supply gas upstream of the carbon dioxide separation membrane to achieve the most suitable conditions for separation and recovery by the carbon dioxide membrane, by using one or more of the heat from an electric heater using geothermal fluid or hydroelectric power, cold energy obtained from an absorption or adsorption chiller driven by geothermal fluid, or cold energy obtained from water used for hydroelectric power generation. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2023-161483 [Patent Document 2] Patent Publication No. 2023-10479 [Patent Document 3] Patent Publication No. 2023-36490 Summary of the Invention [Problem to be solved by the invention]

[0004] When capturing CO2 from gases such as the atmosphere or exhaust gas, it is preferable to minimize the energy required for capture per unit amount of CO2. In a system in which CO2 in the gas is adsorbed onto an adsorbent and then released from the adsorbent for capture, the amount of CO2 captured by the adsorbent varies depending on the temperature and humidity of the gas supplied to the adsorbent. Therefore, the amount of CO2 captured can be increased by optimizing the temperature and humidity of the gas supplied to the adsorbent to maximize the amount of CO2 captured. However, heating or humidifying the gas to optimize the temperature and humidity of the gas supplied to the adsorbent consumes energy. Therefore, if heating or humidifying the gas increases the energy required per unit of CO2 captured (hereinafter referred to as "recovery energy"), it is preferable not to heat or humidify the gas. In other words, it is advantageous to heat or humidify the gas only when the recovery energy required when heating or humidifying the gas is smaller than when not heating or humidifying the gas.

[0005] In view of the above circumstances, the main object of the present invention is to provide a CO2 recovery system that adsorbs CO2 in a gas onto an adsorbent and then releases and recovers the CO2 from the adsorbent, in which the amount of CO2 recovered by the adsorbent varies depending on the temperature and humidity of the gas supplied to the adsorbent, thereby reducing the energy required to recover CO2 as much as possible. [Means for solving the problem]

[0006] According to the present invention, the above problem is solved by a system for recovering CO2 in a gas, the system being configured such that in an adsorption mode, the gas is fed into an adsorbent so that CO2 in the gas is adsorbed by the adsorbent, and in a desorption mode, the adsorbent is heated to desorb the CO2 adsorbed by the adsorbent and the CO2 is recovered in a recovery vessel, a gas temperature adjusting means configured to adjust the temperature of the gas fed to the adsorber; a recovery energy magnitude estimation means configured to estimate which of the CO2 recovery energy when the temperature of the gas fed to the adsorbent is not adjusted and the CO2 recovery energy when the temperature of the gas fed to the adsorbent is adjusted is smaller; Including, This is achieved by a system in which the gas temperature adjustment means is configured to perform temperature adjustment of the gas only when the recovered energy when temperature adjustment of the gas is performed is smaller than the recovered energy when temperature adjustment of the gas is not performed.

[0007] In the above configuration, the "system for capturing CO2 from gas" may be any type of system configured to, as described above, in an adsorption mode, introduce a gas, such as the atmosphere or exhaust gas, containing CO2 to be captured into an adsorbent, where the CO2 in the gas is adsorbed by the adsorbent, and in a desorption mode, heat the adsorbent to desorb the CO2 adsorbed in the adsorbent and capture it in a capture vessel. The adsorbent may be, for example, a solid or liquid containing an amine, which is used in a technology for selectively capturing CO2 gas from gas using the reversible adsorption reaction between amines and CO2 (the amine method). The basic operation of such a CO2 capture system alternates between an adsorption mode in which a blower fan or the like is driven to flow gas through the adsorbent, whereby the CO2 in the gas is adsorbed by the adsorbent, and a desorption mode in which a heater or the like is used to heat the adsorbent with CO2 adsorbed thereon, whereby the CO2 is desorbed from the adsorbent, and a pump or the like is driven to send the desorbed CO2 to a capture vessel. Thus, CO2 is captured from the gas.

[0008] In the above system, the "gas temperature adjusting means" may be a means configured to adjust the temperature of the gas fed to the adsorbent by any method, and may include a sensor for detecting the gas temperature and a heater for heating the gas, and may be configured to adjust the gas temperature to an appropriately set target temperature value in a manner described later. In this regard, since the amount of CO2 captured by the adsorbent varies depending on the gas temperature, the target temperature value may specifically be set to a temperature (optimum temperature) at which the amount of CO2 captured is maximized.

[0009] In the above system, the "recovered energy magnitude estimation means" may be configured to estimate, by any method, which of the CO2 recovered energy when the temperature of the gas fed to the adsorbent is not adjusted, and the CO2 recovered energy when the temperature of the gas fed to the adsorbent is adjusted, is smaller. The recovered energy magnitude estimation means is realized by the operation of a computer device in accordance with a program.

[0010] Here, the "recovery energy" of CO2 refers to the total amount of energy required to recover a unit amount of CO2 in the system of the present invention. More specifically, the recovery energy when the temperature of the gas fed to the adsorbent is not adjusted is given by the sum of the energy required to drive the blower fan and other devices to feed the gas to the adsorbent in the adsorption mode, the energy required to heat the adsorbent to desorb CO2 from the adsorbent in the desorption mode (the sum of the energy required to heat the adsorbent and the energy required to vaporize CO2), and the energy required to drive the pump and other devices to send the desorbed CO2 to the capture container, divided by the amount of CO2 recovered at that time. Furthermore, the recovery energy when the temperature of the gas fed to the adsorbent is adjusted is given by the sum of the energy required in the adsorption mode and the desorption mode plus the energy required to adjust the gas temperature (particularly heating), divided by the amount of CO2 recovered at that time.

[0011] Regarding each parameter required for estimating the above-mentioned recovery energy, the energy required in each of the adsorption mode and desorption mode can be detected, estimated, or determined by any method, for example, by measuring or predicting power consumption. When the desorption mode is executed, the amount of CO2 recovered can be detected by any method, for example, by detecting the amount of CO2 flowing into the recovery container (using a CO2 concentration sensor and a flow rate sensor). Alternatively, the amount of CO2 recovered by the adsorbent per unit amount of gas fed to the adsorbent (amount of recovered CO2) is uniquely determined by the partial pressure (or concentration) of CO2 in the gas, and the temperature and humidity of the gas. Therefore, the amount of CO2 recovered by the adsorbent under various conditions of partial pressure (or concentration) of CO2 in the gas, gas temperature, and humidity can be experimentally investigated in advance, and the amount of CO2 recovered during the actual recovery of CO2 from the gas can be determined or estimated from the partial pressure (or concentration), temperature, and humidity of CO2 in the gas at that time, which are detected or determined using any sensor, etc., with reference to the previously investigated relationship between the partial pressure (or concentration), gas temperature, and humidity of CO2 in the gas and the amount of recovered CO2. In an embodiment, a map is prepared that provides an estimated value of the amount of CO2 recovered per unit amount of gas, using the relationship between the partial pressure (or concentration) of CO2 in the gas, the temperature and humidity of the gas, and the amount of CO2 recovered, which has been investigated in advance, and the amount of CO2 recovered during the execution of CO2 recovery from the gas may be estimated by multiplying the value of the amount of CO2 recovered per unit amount of gas estimated using the map from the partial pressure (or concentration) of CO2, temperature and humidity of the gas at that time, by the amount of gas fed to the adsorbent.

[0012] Thus, since the CO2 recovery energy when the temperature of the gas fed to the adsorbent is not adjusted and the CO2 recovery energy when the temperature of the gas fed to the adsorbent is adjusted can each be determined or estimated by any method as described above, it is also possible to estimate their magnitude. In the system of the present invention, the CO2 recovery energy when the temperature of the gas fed to the adsorbent is not adjusted and when the temperature of the gas fed to the adsorbent is adjusted may each be estimated, but as long as the magnitude is known, the value of the recovery energy itself does not need to be calculated.

[0013] In the system of the present invention, the gas temperature adjustment means adjusts the gas temperature only when the energy required to recover the CO2 when the gas temperature adjustment is performed is smaller than the energy required to recover the CO2 when the gas temperature adjustment is not performed. As mentioned above, the CO2 recovery amount of the adsorbent varies depending on the temperature of the gas supplied to the adsorbent in the adsorption mode (which is approximately equal to the temperature of the adsorbent). Therefore, if the temperature of the gas currently being fed to the adsorbent is lower than the optimal temperature, raising the gas temperature using the gas temperature adjustment means will increase the CO2 recovery amount. However, raising the gas temperature generally requires energy. Even if the CO2 recovery amount increases as a result of such a temperature increase, if the increase in energy is too great and the recovery energy increases, energy efficiency will decrease. Furthermore, as will be explained later, if CO2 is released during the generation of energy used for CO2 capture, increasing the recovery energy will be disadvantageous because the increase in CO2 release during energy generation will exceed the increase in the CO2 recovery amount. Therefore, as described above, the system of the present invention is configured to perform gas temperature adjustment only when the recovered energy when gas temperature adjustment is performed is smaller than the recovered energy when gas temperature adjustment is not performed.

[0014] The system of the present invention may further include a gas humidity adjustment means configured to adjust the humidity of the gas fed to the adsorbent, and the recovery energy magnitude estimation means may be configured to estimate which of the CO2 recovery energy when the humidity adjustment of the gas fed to the adsorbent is not performed and the CO2 recovery energy when the humidity adjustment of the gas fed to the adsorbent is performed is smaller. The gas humidity adjustment means may be configured to adjust the humidity of the gas only when the recovery energy when the humidity adjustment of the gas is performed is smaller than the recovery energy when the humidity adjustment of the gas is not performed. Here, the "gas humidity adjustment means" may be a means configured to adjust the humidity of the gas fed to the adsorbent by any method, and may include a sensor for detecting the humidity of the gas and a humidifier for humidifying the gas. The "gas humidity adjustment means" may be configured to adjust the humidity of the gas to an appropriately set target humidity value in a manner described below. As already mentioned, the amount of CO2 captured by the adsorbent varies depending on the humidity of the gas. Therefore, the target humidity value may be set to a humidity (optimum humidity) at which the amount of CO2 captured is maximized. When gas humidity adjustment is performed by the gas humidity adjustment means, energy is consumed to drive the humidifier, and therefore, in calculating the CO2 recovery energy when humidity adjustment of the gas fed to the adsorbent is performed, the energy required to drive the humidifier is added to the energy required in the adsorption mode. For the same reason as in the case of gas temperature adjustment, gas humidity adjustment by the gas humidity adjustment means may be performed only when the recovered energy when gas humidity adjustment is performed is smaller than the recovered energy when gas humidity adjustment is not performed, in order to reduce the recovered energy as much as possible.

[0015] The system of the present invention may be configured to stop CO2 capture when the CO2 capture energy required when the temperature of the gas fed to the adsorbent is not adjusted and when the temperature of the gas fed to the adsorbent is adjusted is both equal to or greater than a threshold, or when the CO2 capture energy required when the humidity of the gas fed to the adsorbent is not adjusted and when the humidity of the gas fed to the adsorbent is adjusted is both equal to or greater than a threshold. As mentioned above, when the energy required for CO2 capture is generated by a method that involves CO2 emissions, such as thermal power generation, the net amount of CO2 captured by the system of the present invention is the amount of CO2 captured in the capture container by the system minus the amount of CO2 released during the generation of the energy required for CO2 capture. Therefore, if the latter is equal to or greater than the former, the system of the present invention is not able to capture CO2. Since the amount of CO2 released during energy generation increases with the energy of CO2 recovery, when the energy of CO2 recovery is a value that makes the amount of CO2 released during energy generation equal to or greater than the amount of CO2 recovered by the operation of the present system, CO2 is not being recovered, and operation of the present system should be stopped. Thus, as described above, when the energy of CO2 recovery, both with and without gas temperature or humidity adjustment, is greater than a predetermined threshold, CO2 recovery may be stopped. The predetermined threshold may be set appropriately based on the value at which the energy of CO2 recovery matches the amount of CO2 released during energy generation and the amount of CO2 recovered by the operation of the present system. In an embodiment, the threshold may typically be set to a value significantly lower than the value at which the energy of CO2 recovery matches the amount of CO2 released during energy generation and the amount of CO2 recovered by the operation of the present system.

[0016] In the system of the present invention, as already described, the CO2 recovery energy may be estimated using a pre-prepared map that estimates the amount of CO2 recovered by the adsorbent based on the partial pressure or concentration of CO2 in the gas fed to the adsorbent and the gas temperature or the gas temperature and humidity. In this regard, since the amount of CO2 recovered by the adsorbent relative to the partial pressure (or concentration) of CO2 in the gas, the gas temperature, and the humidity changes as the performance of the adsorbent changes over time, it is preferable that the above map reflects the change in the performance of the adsorbent over time in order to accurately estimate the recovery energy. Specifically, a map may be prepared in advance for each period of use of the adsorbent, and the CO2 recovery energy may be estimated using the map corresponding to the period during which the adsorbent was actually used. [Effects of the Invention]

[0017] Thus, in the system of the present invention, in which CO2 in a gas is adsorbed onto an adsorbent and then released and captured from the adsorbent, a means for adjusting the temperature or humidity of the gas fed to the adsorbent is provided, and such temperature or humidity adjustment of the gas is performed only when performing such adjustment would reduce the energy required to capture CO2, thereby suppressing the energy required for capture. The system of the present invention may be used to selectively capture CO2 from any gas containing CO2.

[0018] Other objects and advantages of the present invention will become apparent from the following description of preferred embodiments of the invention. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a block diagram showing the configuration of the system according to this embodiment. [Figure 2] 2(A), (B), and (C) are diagrams each showing a schematic representation of the change in the amount of CO2 recovered by the adsorbent RA relative to the incoming gas temperature T, the incoming gas humidity H, and the CO2 partial pressure Pp in the incoming gas in the system of this embodiment. [Figure 3] FIG. 3 is a flowchart showing the process for determining the mode of CO2 recovery operation in the system of this embodiment. [Explanation of symbols]

[0020] 1...CO2 recovery system, 2...blower fan, 3...air supply pipe, 4...adsorption tower (adsorbent), 4a...adsorbent heater, 5...suction pump, 6...recovery container, 10...gas heater, 11...gas humidifier, 20...CO2 concentration sensor, 21...gas temperature sensor, 22...gas humidity sensor, 23...flow rate sensor, 24...CO2 recovery amount detection means, 50...control device BEST MODE FOR CARRYING OUT THE INVENTION

[0021] The present invention will now be described in detail with reference to some preferred embodiments thereof with reference to the accompanying drawings, in which like reference numerals indicate like parts.

[0022] CO 2 Collection system configuration As already described, the CO2 capture system according to this embodiment is a system that captures CO2 from gas by alternately executing an adsorption mode in which a gas containing CO2, such as the atmosphere or exhaust gas, is fed into an adsorbent and the CO2 in the gas is adsorbed by the adsorbent, and a desorption mode in which the adsorbent is heated to desorb the CO2 adsorbed on the adsorbent and capture it in a capture vessel. As shown in FIG. 1 , in the specific configuration of the CO2 capture system 1, in the adsorption mode, a gas a containing the CO2 to be captured is fed by an electrically driven blower fan 2 through an air pipe 3 into an adsorption tower 4 containing an adsorbent. Here, the gas comes into contact with the adsorbent, and the CO2 in the gas is adsorbed by the adsorbent. The adsorbent may typically be a solid or liquid containing an amine, as used in the amine method, which selectively captures CO2 gas from gas using the reversible adsorption reaction between amines and CO2, as already mentioned, but is not limited thereto. After CO2 is adsorbed by the adsorbent in the adsorption mode, in the desorption mode, the adsorbent in the adsorption tower 4 is heated by an electrically driven heater 4a, and CO2 desorbed from the adsorbent is sucked by an electrically driven suction pump 5 and sent to a capture vessel 6, where the CO2 is captured. Here, the temperature of the adsorbent may be controlled by the heater 4a so that it is raised to a target temperature equal to or higher than the temperature at which the CO2 adsorbed in the adsorbent is desorbed from the adsorbent (the temperature of the adsorbent may be detected by a temperature sensor, not shown). The heater 4a may utilize waste heat such as geothermal energy, heat of a chemical reaction, or heat of combustion.

[0023] In addition to the basic configuration described above, the system of this embodiment is provided with a gas heater 10 and a gas humidifier 11 in the air supply pipe 3, and in the adsorption mode, the temperature or humidity of the gas a fed to the adsorbent is selectively adjusted according to the manner described later.

[0024] The operation of each part of the above system is controlled by a control device 50, which may be a computer device operating according to a program. The control device 50 receives inputs of detected values ​​from sensors 20, 21, and 22 that detect the CO concentration (partial pressure), temperature, and humidity of gas a introduced into the gas supply pipe 3, respectively, and a detected value from a flow sensor 23 that detects the total amount of gas a introduced into the adsorption tower 4, in order to estimate which of the CO2 recovery energies is smaller when temperature or humidity control of the gas introduced into the adsorbent is performed and when it is performed, as described below, or whether the minimum of these recovery energies is smaller than a predetermined threshold value set in a manner described below. Note that a CO2 recovery amount detection means 24 (a CO2 concentration sensor and a flow sensor) may be provided to detect the amount of CO2 recovered from the adsorption tower 4 to the recovery vessel 6 in the desorption mode. In the adsorption mode, the control device 50 issues control commands to the blower fan 2, the gas heater 10, and the gas humidifier 11 to selectively activate or deactivate them, and in the desorption mode, it issues control commands to the adsorbent heater 4a and the suction pump 5 to activate them.

[0025] System Operation (a) Overview In the CO2 capture system described above, the amount of CO2 captured using the adsorbent generally varies depending not only on the CO2 partial pressure of the gas fed to the adsorbent but also on the temperature and humidity. Experiments conducted by the inventors of this embodiment have revealed that, when the gas temperature is varied, there exists a temperature (optimum temperature) at which the amount of CO2 captured by the adsorbent is maximized, as illustrated in FIG. 2(A). Furthermore, when the gas humidity is varied, as illustrated in FIG. 2(B), the amount of CO2 captured by the adsorbent increases with increasing gas humidity, but the rate of increase decreases and the adsorbent reaches a saturation point. Furthermore, the amount of CO2 captured by the adsorbent increases with the CO2 partial pressure or concentration in the gas contacting the adsorbent, as illustrated in FIG. 2(C). Therefore, to increase the amount of CO2 captured, it is necessary to adjust the temperature of the gas fed to the adsorbent to the optimal temperature and increase the humidity of the gas. However, when the gas heater 10 and gas humidifier 11 installed in the air supply pipe 3 are operated to heat or humidify the gas, energy is consumed for this purpose. Generally, this consumed energy is used to release CO2 during production, and in this case, even if the amount of CO2 recovered is increased by adjusting the temperature or humidity of the gas, if the amount of CO2 released during production is greater than the increase in the amount of CO2 recovered by adjusting the temperature or humidity of the gas, it is better not to adjust the temperature or humidity of the gas.

[0026] Whether the increase in the amount of CO2 recovered by adjusting the temperature or humidity of the gas is greater than the amount of CO2 released during production due to the energy required to adjust the temperature or humidity of the gas can be detected by the energy (recovered energy) required to recover a unit amount of CO2 when adjusting the temperature or humidity of the gas and when not adjusting the temperature or humidity of the gas. Specifically, if the energy recovered when adjusting the temperature or humidity of the gas is less than the energy recovered when not adjusting the temperature or humidity of the gas, the increase in the amount of CO2 recovered by adjusting the temperature or humidity of the gas will exceed the amount of CO2 released during production due to the energy required to adjust the temperature or humidity of the gas.

[0027] More specifically, when the energy required to recover the amount of CO2 X when the temperature or humidity of the gas is not adjusted is E, the increase in the amount of CO2 recovered when the temperature or humidity of the gas is adjusted is ΔX1, and the increase in energy is ΔE, if the recovered energy (E+ΔE) / (X+ΔX1) when the temperature or humidity of the gas is adjusted is smaller than the recovered energy E / X when the temperature or humidity of the gas is not adjusted, then (E+ΔE) / (X+ΔX1) <E / X Here, if the amount of CO2 released when generating energy E is αX, the above equation becomes: (αX+αΔX2) / (X+ΔX1)<αX / X Here, ΔX2 is the amount of CO2 released when ΔE is generated, that is, the increase in the amount of CO2 released. The above equation is ΔX1>ΔX2 Therefore, in this case, the increase ΔX1 in the amount of CO2 recovered when adjusting the temperature or humidity of the gas is greater than the increase ΔX2 in the amount of CO2 released due to the increased energy generation for adjusting the temperature or humidity of the gas. Thus, when the energy recovered when adjusting the temperature or humidity of the gas is smaller than when adjusting the temperature or humidity of the gas, the amount of CO2 recovered can be increased.

[0028] From the above, in the system of this embodiment, gas temperature adjustment or humidity adjustment is performed only when the recovered energy when gas temperature adjustment or humidity adjustment is performed is less than when gas temperature adjustment or humidity adjustment is not performed.

[0029] (b) Estimation of recovered energy The recovered energy Ep and Ef when the temperature or humidity of the gas is not adjusted and when it is adjusted are given as follows: If gas temperature or humidity control is not performed: Ep = (Ea + Eb + Ec) / Xp + Er … (1) Here, Ea is the power consumption of the blower fan in adsorption mode, Eb is the power consumption for heating the adsorbent in desorption mode, Ec is the power consumption of the suction pump in desorption mode, Xp is the amount of CO2 recovered when gas temperature or humidity control is not performed, and Er is the heat of vaporization of CO2 (the amount of heat absorbed when CO2 per unit amount bound to the adsorbent is desorbed as gas molecules, i.e., the value obtained by dividing the energy required to vaporize CO2 by the amount of CO2 recovered). If gas temperature or humidity control is performed: Efi=(Ea+Eb+Ec+Et+Eh) / Xf+Er …(2) where i=1, 2, 3 are the symbols for when only temperature control is performed, when only humidity control is performed, and when both temperature and humidity control are performed, respectively. Also, Et is the power consumption of the gas heater in adsorption mode, Eh is the power consumption of the gas humidifier in adsorption mode, and Xf is the amount of CO2 recovered when gas temperature or humidity control is performed.

[0030] In the above, the power consumption Ea of the blower fan in adsorption mode and the power consumption Ec of the suction pump in desorption mode are determined by their respective operating amounts. These operating amounts are preset and therefore known. The power consumption Eb for heating the adsorbent in desorption mode is the energy required to raise the temperature of the adsorbent to a target temperature set appropriately enough to desorb CO2 from the adsorbent. Since the temperature of the adsorbent before desorption mode is approximately equal to the gas temperature, the power consumption Eb for heating each adsorbent can be uniquely determined if the temperature of the gas fed to the adsorbent is known. Therefore, the power consumption required to raise the temperature from various ambient temperatures to the target temperature in desorption mode and maintain that temperature can be calculated in advance, and a map providing estimated values ​​of power consumption for each ambient temperature can be prepared. During CO2 capture, the power consumption Eb for heating the adsorbent can be calculated from the map based on the detected or estimated ambient temperature. Er is a characteristic of CO2 and the adsorbent and is a known, fixed value. Note that Er does not depend on whether or not temperature or humidity adjustment of the gas is performed, and therefore does not contribute to determining the magnitude relationship of the recovered energy, and therefore may not be taken into consideration.

[0031] Et is the amount of power required to heat a gas from a certain temperature to a target temperature during temperature adjustment. Therefore, Et is calculated by multiplying the amount of gas fed to the adsorbent by the amount of power consumed by the gas heater required to heat a unit amount of gas from the temperature before temperature adjustment to the target temperature. Here, the target temperature may be the optimal temperature (ta in FIG. 2(A)) at which the amount of CO2 captured by the adsorbent is maximized. Since the amount of power consumed by the gas heater to heat a unit amount of gas from the temperature before temperature adjustment to the target temperature is uniquely determined for the temperature before temperature adjustment, the amount of power consumed by the gas heater to heat a unit amount of gas from various gas temperatures to the target temperature when temperature adjustment is performed may be calculated in advance, and a map may be prepared that provides an estimated amount of power consumed for each temperature before temperature adjustment. During CO2 capture, the amount of power consumed to heat a unit amount of gas for the detected gas temperature may be obtained from the map. Similarly, Eh is the amount of power required to humidify gas at a certain humidity level to the target humidity level during humidity adjustment. Therefore, Eh is calculated by multiplying the amount of gas fed to the adsorbent by the amount of power consumed by the gas humidifier to humidify a unit amount of gas from the humidity level before humidity adjustment to the target humidity level. Here, the target humidity level may be the humidity at which the amount of CO2 captured by the adsorbent is approximately maximized (ta in FIG. 2B). The power consumption of the gas humidifier to heat a unit amount of gas from the humidity level before humidity adjustment to the target humidity level is uniquely determined for the temperature and humidity before temperature adjustment. Therefore, the power consumption of the gas humidifier to heat a unit amount of gas from the humidity level before humidity adjustment to the target humidity level when humidity adjustment is performed may be calculated in advance, and a map may be prepared that provides estimated power consumption values ​​for the humidity and temperature before humidification. During CO2 capture, the power consumption for humidifying a unit amount of gas may be estimated from the map for the detected gas humidity and temperature (the detected gas temperature if temperature adjustment is not performed, or the target temperature if temperature adjustment is performed). The amount of gas fed to the adsorbent in one adsorption mode may be set appropriately.

[0032] Furthermore, in the above formulas (1) and (2), the CO2 recovery amount Xp when gas temperature or humidity control is not performed and the CO2 recovery amount Xf when gas temperature or humidity control is performed are amounts obtained by multiplying the amount of gas fed to the adsorbent by the amount of CO2 recovered by the adsorbent when a unit amount of gas is fed to the adsorbent. Here, the amount of CO2 recovered by the adsorbent when a unit amount of gas is fed to the adsorbent is determined by the CO2 partial pressure, temperature, and humidity of the gas, as explained in relation to Figures 2(A) to 2(C). In one aspect of this embodiment, the amount of CO2 recovered by the adsorbent (per unit amount of gas fed) under various conditions of CO2 partial pressure (or concentration), gas temperature, and humidity is experimentally investigated in advance. Using the previously investigated relationship between the amount of CO2 recovered and the partial pressure (or concentration), gas temperature, and humidity of the gas, a map is prepared that provides an estimate of the amount of CO2 recovered per unit amount of gas, with the partial pressure (or concentration), temperature, and humidity of the gas as variables. The amount of CO2 recovered during the gas CO2 recovery process may be estimated by multiplying the amount of CO2 recovered per unit amount of gas estimated using the map based on the partial pressure (or concentration), temperature, and humidity of the gas at that time by the amount of gas fed to the adsorbent. Here, the partial pressure or concentration of CO2 may be determined using the value detected by the CO2 concentration sensor 20. For the temperature, the detection value of the gas temperature sensor 21 may be used when temperature adjustment is not performed, and the target temperature value may be used when temperature adjustment is performed. Similarly, for the humidity, the detection value of the gas humidity sensor 22 may be used when humidity adjustment is not performed, and the target humidity value may be used when humidity adjustment is performed.

[0033] The amount of CO2 captured by an adsorbent varies (usually decreases) over the period of use. Therefore, in order to accurately estimate the CO2 capture amounts Xp and Xf, it is preferable to use a map that uses the partial pressure (or concentration), temperature, and humidity of CO2 in the gas as variables to provide an estimate of the amount of CO2 captured per unit amount of gas. The map preferably uses the partial pressure (or concentration), temperature, and humidity of CO2 in the gas as variables to determine the relationship between the amount of CO2 captured and the partial pressure (or concentration), temperature, and humidity of the gas, and the amount of CO2 captured, which is adapted to changes over the period of use of the adsorbent. Therefore, in this embodiment, the amount of CO2 captured by the adsorbent (per unit amount of gas fed) under various conditions of the partial pressure (or concentration), temperature, and humidity of CO2 in the gas may be investigated in advance for each period of use of the adsorbent. Using the results, a different map may be prepared for each period of use of the adsorbent. The period of use of the adsorbent for which the map is prepared may be set as appropriate.

[0034] When CO2 recovery is in progress, the amount of CO2 recovered may be obtained by directly detecting the amount of CO2 sent from the suction pump 5 to the recovery container 6. In this case, the detected value of the CO2 recovery amount detection means 24 (CO2 concentration sensor and flow rate sensor) may be used.

[0035] (c) Deciding whether or not to implement CO2 capture As already mentioned, when CO2 is released during the generation of energy required to operate the CO2 capture system according to this embodiment, if the amount of released CO2 exceeds the amount of captured CO2, the system is not being captured, and operation of the system should be stopped. More specifically, when an amount of CO2 Y is released during the generation of energy E required to capture an amount of CO2 X by operating the system, X>Y …(3) should be true. Here, if the energy E=αY, then X>E / α(=Y) Therefore, the recovered energy E / X is E / X<α …(4) When this is the case, equation (3) is established. That is, when the recovered energy E / X exceeds the threshold value α, the amount of CO2 released Y exceeds the amount of CO2 recovered X, and therefore the execution of CO2 recovery by this system is stopped. In an embodiment, the threshold value may be appropriately set to a value smaller than α at which the amount of CO2 released Y becomes equal to the amount of CO2 recovered X. It should be understood that the threshold value may be changed depending on the energy generation method. For example, the greater the amount of CO2 released during energy generation, the lower the threshold value is set. If no CO2 is released during energy generation (α ← infinity), no threshold value is set, and there is no need to stop the system due to the large amount of recovered energy.

[0036] (d) Control process In the system of this embodiment, whether to adjust the temperature or humidity of the gas fed to the adsorbent and whether to perform CO2 capture operation are determined based on the estimated value of the captured energy, as described above. More specifically, as shown in FIG. 3, the captured energy Ep (Step 1) when neither gas temperature nor humidity control is performed, and the captured energies Ef1, Ef2, and Ef3 (Step 2) when only gas temperature control is performed, when only gas humidity control is performed, and when both gas temperature control and humidity control are performed are estimated using equations (1) and (2), respectively. Here, as already mentioned, in estimating the CO2 capture amounts Xp and Xf, it is preferable to use maps prepared corresponding to the period of use of the adsorbent, taking into account changes in the performance of the adsorbent over time. Then, it is determined whether the minimum value of Ep, Ef1, Ef2, and Ef3 is greater than the threshold value Eth set as described above (step 3), and if the minimum value of Ep, Ef1, Ef2, and Ef3 is greater than the threshold value Eth, no significant net CO2 recovery amount is expected, so the CO2 recovery operation may be stopped (step 11).

[0037] When the minimum value of Ep, Ef1, Ef2, and Ef3 is smaller than the threshold value Eth, the CO2 capture operation is performed in the following manner. First, when Ep is minimum (step 4), the CO2 capture operation is performed without adjusting the temperature or humidity of the gas (step 5). When Ef1 is minimum (step 6), the CO2 capture operation is performed with only the temperature of the gas adjusted (step 7). When Ef2 is minimum (step 8), the CO2 capture operation is performed with only the humidity of the gas adjusted (step 9). When Ef3 is minimum (step 8), the CO2 capture operation is performed while adjusting both the temperature and humidity of the gas (step 10). As a result, the CO2 capture operation is performed with the energy required for capture minimized, optimizing the amount of CO2 captured per unit of energy consumed.

[0038] Thus, in the system configuration of this embodiment described above, a means is provided for adjusting the temperature or humidity of the gas fed to the adsorbent, and such gas temperature or humidity adjustment is performed only when performing it would reduce the energy required to recover CO2, i.e., only when it would increase the amount of CO2 recovered per unit of energy consumed, thereby improving energy efficiency in CO2 recovery.

[0039] The above description has been made in relation to the embodiments of the present invention, but it will be apparent that many modifications and changes will be readily apparent to those skilled in the art, and the present invention is not limited to the above-described exemplary embodiments, but can be applied to various devices without departing from the concept of the present invention.

Claims

1. CO in gas ２ In an adsorption mode, the gas is fed to an adsorbent to recover CO ２ is adsorbed to the adsorbent, and in the desorption mode, the adsorbent is heated to remove the CO ２ and collecting the same in a collection container, a gas temperature adjusting means configured to adjust the temperature of the gas fed to the adsorber; CO when the temperature of the gas fed to the adsorber is not adjusted ２ and CO when the temperature of the gas fed to the adsorbent is adjusted. ２ a recovered energy magnitude estimation means configured to estimate which of the recovered energies is smaller, Including, A system configured such that the gas temperature adjustment means performs temperature adjustment of the gas only when the recovered energy when temperature adjustment of the gas is performed is smaller than the recovered energy when temperature adjustment of the gas is not performed.

2. 2. The system according to claim 1, further comprising a gas humidity adjusting means configured to adjust the humidity of the gas fed to the adsorbent, wherein the recovered energy magnitude estimating means further estimates the CO ２ and CO when humidity control of the gas fed to the adsorbent is performed. ２ and the gas humidity adjustment means is configured to perform humidity adjustment of the gas only when the recovered energy when humidity adjustment of the gas is performed is smaller than the recovered energy when humidity adjustment of the gas is not performed.

3. 2. The system of claim 1, wherein the CO 2 concentration is determined by a comparison between when the temperature of the gas fed to the adsorber is not adjusted and when the temperature of the gas fed to the adsorber is adjusted. ２ When the recovered energy of each of the above is equal to or greater than the threshold, CO ２ The system is configured to stop collection of

4. 3. The system of claim 2, wherein the CO 2 ratio is calculated by comparing a case where the humidity adjustment of the gas fed to the adsorbent is not performed and a case where the humidity adjustment of the gas fed to the adsorbent is performed. ２ When the recovered energy of each of the above is equal to or greater than the threshold, CO ２ The system is configured to stop collection of

5. 3. The system according to claim 1, wherein the recovery energy magnitude estimation means estimates the amount of CO contained in the gas fed to the adsorbent. ２ and the temperature of the gas or the temperature and humidity of the gas. ２ The system is configured to estimate the recovered energy using a pre-prepared map that estimates the amount of the adsorbent, the map reflecting changes in performance of the adsorbent over time.

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