CO2 capture system

Abstract

To provide a CO2 recovery system which has an excellent CO2 emission suppression effect.SOLUTION: A CO2 recovery system 1 comprises: a CO2 recovery device 10; a temperature sensor 12 as a reaction liquid temperature acquisition part; a first gas passage 21; a second gas passage 22; and an electromagnetic valve 30 as a flow rate adjustment part. The CO2 recovery device 10 recovers CO2 from a CO2-inclusion gas by bringing the CO2-inclusion gas into contact with the reaction liquid stored in a reaction tank 11. The temperature sensor 12 acquires a temperature of the reaction liquid stored in the reaction tank 11. The first gas passage 21 circulates a first CO2-inclusion gas G1. The second gas passage 22 circulates a second CO2-inclusion gas G2 having a higher temperature than that of the first CO2-inclusion gas G1. The electromagnetic valve 30 adjusts a flow rate of the first CO2-inclusion gas G1 in the first gas passage 21 and a flow rate of the second CO2-inclusion gas G2 in the second gas passage 22 such that the temperature of the reaction liquid acquired by the temperature sensor 12 becomes a prescribed temperature.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a CO2 capture system. [Background technology]

[0002] In recent years, there has been a demand to reduce emissions of CO2 gas, a greenhouse gas, and various systems for capturing CO2 gas have been studied. For example, Patent Document 1 discloses a CO2 capture system in which CO2-containing exhaust gas from a power generation boiler or the like is reacted with an NaOH aqueous solution to generate NaHCO3 or Na2CO3, and CO2 is then captured from the exhaust gas. According to this CO2 capture system, the generated NaHCO3 or Na2CO3 is expected to be used as a resource. Furthermore, Patent Document 2 discloses a configuration for utilizing exhaust gas in which high-temperature exhaust gas and low-temperature exhaust gas are mixed together to atomize the exhaust gas. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-288313 [Patent Document 2] Special Publication No. 3-76964 Summary of the Invention [Problem to be solved by the invention]

[0004] In the configuration disclosed in Patent Document 1, the NaHCO3 production reaction is exothermic, and a sudden rise in the temperature of the reaction solution may cause NaHCO3 to decompose and release immobilized CO2. This reduces the CO2 recovery rate and the CO2 emission reduction effect. Furthermore, in the configuration disclosed in Patent Document 1, the exhaust gas supplied to the reaction vessel changes temperature as it flows through the piping connected to the reaction vessel due to heat exchange with the external environment surrounding the piping. Therefore, the temperature of the exhaust gas supplied to the reaction vessel is affected by the temperature surrounding the piping. For example, the temperature of the exhaust gas supplied to the reaction vessel is likely to be low in winter or at night when the ambient temperature is low, and is likely to be high in summer or during the day when the ambient temperature is high. This change in the temperature of the exhaust gas depending on the season and time of day destabilizes the reaction efficiency in the reaction vessel, resulting in a reduction in the CO2 emission reduction effect. Meanwhile, Patent Document 2 makes no mention of the reduction in the CO2 emission reduction effect due to changes in the temperature of the reaction vessel.

[0005] The present invention has been made in view of the above problems, and aims to provide a CO2 recovery system that is highly effective in suppressing CO2 emissions. [Means for solving the problem]

[0006] One aspect of the present invention is a CO2 recovery device that recovers CO2 from a CO2-containing gas by bringing the CO2-containing gas into contact with a reaction liquid stored in a reaction tank; a reaction solution temperature acquisition unit that acquires the temperature of the reaction solution stored in the reaction tank; a first gas flow path through which a first CO2-containing gas flows; a second gas flow path through which a second CO2-containing gas having a temperature higher than that of the first CO2-containing gas flows; a flow rate adjusting unit that adjusts the flow rate of the first CO2-containing gas supplied from the first gas flow path to the CO2 recovery device and the flow rate of the second CO2-containing gas supplied from the second gas flow path to the CO2 recovery device so that the temperature of the reaction liquid acquired by the reaction liquid temperature acquiring unit becomes a predetermined temperature; The CO2 capture system is equipped with [Effects of the Invention]

[0007] In the CO2 capture system, the flow rate of the first CO2-containing gas supplied to the CO2 capture device and the flow rate of the second CO2-containing gas, which is hotter than the first CO2-containing gas, are adjusted so that the temperature of the reaction solution is maintained at a predetermined temperature. This prevents the temperature of the reaction solution from becoming excessively high and suppresses temperature changes in the reaction solution due to changes in outside air temperature depending on the season or time of day. This stabilizes the CO2 fixation reaction in the CO2 capture device and prevents a decrease in the CO2 emission suppression effect. Furthermore, stabilizing the CO2 fixation reaction shortens the operating time of the CO2 capture system, thereby saving energy.

[0008] As described above, according to the above-described embodiment, it is possible to provide a CO2 recovery system that is excellent in the effect of suppressing CO2 emissions. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a conceptual diagram showing the configuration of a CO2 recovery system according to a first embodiment. [Figure 2] FIG. 1 is a conceptual diagram showing the correspondence between reaction solution temperature, reaction solution pH, and products in the first embodiment. [Figure 3] FIG. 2 is a flow diagram showing a first usage mode of the CO 2 recovery system in the first embodiment. [Figure 4] FIG. 4 is a flow diagram showing a second usage mode of the CO 2 recovery system in the first embodiment. [Figure 5] FIG. 10 is a conceptual diagram showing the configuration of a CO2 recovery system in a second embodiment. [Figure 6] FIG. 10 is a flow diagram showing a first usage mode of the CO2 recovery system in the second embodiment. [Figure 7] FIG. 10 is a flow diagram showing a second usage mode of the CO2 recovery system in the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] (Embodiment 1) A first embodiment of the CO2 recovery system will be described with reference to FIGS. As shown in FIG. 1, the CO2 capture system 1 of this embodiment is configured to capture CO2 from flue gas, which is a CO2-containing gas emitted from a CO2 emission facility 100. In this specification, the term "CO2-containing gas" refers to a gas that contains CO2 as a constituent component. The CO2-containing gas may be a gas that contains only CO2 as a constituent component, or may be a gas that further contains unavoidable impurities. The CO2-containing gas may also be a mixed gas that contains CO2 and other substances as constituent components. The proportion of CO2 in the mixed gas is not limited, and the main component that accounts for the largest proportion in the mixed gas may be CO2 or a substance other than CO2.

[0011] 1.100 CO2 emission equipment 1 is not particularly limited as long as it is a facility that discharges CO2-containing gas, and examples thereof include a facility having a boiler, a fuel cell, an incinerator, and a heat treatment facility. An exhaust duct 20 is connected to the CO2 discharge facility 100, and exhaust gas G0, which is a CO2-containing gas, is discharged through the exhaust duct 20. The temperature of the exhaust gas G0 discharged from the CO2 discharge facility 100 is not particularly limited, but is preferably high, and can have a temperature in the range of 100°C to 300°C, for example. In this embodiment, the exhaust gas G0 discharged from the CO2 discharge facility 100 has a temperature of 140°C.

[0012] 2.CO2 Capture System 1 The CO2 recovery system 1 of this embodiment mainly includes a CO2 recovery device 10, a first gas flow path 21, a second gas flow path 22, a flow rate adjustment unit (solenoid valve 30), a moisture removal filter 40, an air pump 50, and a filter 60. Each component will be described below.

[0013] 3. First gas flow path 21 The first gas flow path 21 allows a CO2-containing gas to flow. In the first embodiment, the first gas flow path 21 is formed by a pipe connected to an exhaust duct 20 connected to the CO2 discharge facility 100. A portion of the flue gas G0, which is a CO2-containing gas flowing through the exhaust duct 20, flows through the first gas flow path 21. The gas flowing through the first gas flow path 21 is referred to as a first CO2-containing gas G1. The first CO2-containing gas G1 has a lower temperature than a second CO2-containing gas G2, which will be described later. In the first embodiment, the pipe forming the first gas flow path 21 is formed of a material with high thermal conductivity and has lower thermal insulation than the pipe forming the second gas flow path 22, which will be described later. Therefore, as described above, the flue gas G0 discharged from the CO2 discharge facility 100 has a high temperature of about 140°C, but the first CO2-containing gas G1 flowing through the first gas flow path 21 is cooled by heat exchange with the external environment around the pipe during the process of flowing through the first gas flow path 21, and is configured to be in a low temperature state.

[0014] The method for keeping the first CO2-containing gas G1 at a low temperature is not limited to the above-mentioned method, and the first CO2-containing gas G1 may be kept at a low temperature by cooling the exhaust gas flowing through the first gas flow path 21 using a separately provided cooling device or the like. In this case, it is preferable to compare the amount of CO2 equivalent to the amount of energy consumed by cooling with the amount of CO2 that can be captured by the CO2 capture system 1 so that the former is smaller than the latter, thereby saving power throughout the system.

[0015] 4. Second gas flow path 22 The second gas flow path 22 allows a CO2-containing gas to flow. In the first embodiment, the second gas flow path 22 is composed of a pipe connected to an exhaust duct 20 connected to the CO2 emission equipment 100. A portion of the exhaust gas, which is a CO2-containing gas flowing through the exhaust duct 20, flows through the second gas flow path 22. The gas flowing through the second gas flow path 22 is referred to as a second CO2-containing gas G2. The second CO2-containing gas G2 has a higher temperature than the first CO2-containing gas G1 described above. In the first embodiment, the exhaust gas G0 has a high temperature of about 140°C. By covering the outer peripheral surface of the pipe forming the second gas flow path 22 with a heat insulating material 22a, the pipe forming the second gas flow path 22 has higher thermal insulation properties than the pipe forming the first gas flow path 21 described above. This allows the second CO2-containing gas G2 to be maintained at a high temperature.

[0016] The method of bringing the second CO2-containing gas G2 to a high temperature is not limited to the above-mentioned method, and the second CO2-containing gas G2 may be brought to a high temperature by using a separately provided heating device or the like to heat the exhaust gas flowing through the second gas flow path 22. In this case, it is preferable to compare the amount of CO2 equivalent to the amount of energy consumed by heating with the amount of CO2 that can be captured by the CO2 capture system 1 so that the former is smaller than the latter, thereby achieving power saving in the entire system.

[0017] In addition, in this embodiment 1, considering that if the amount of CO2-containing gas bubbling in the reaction tank 11 described later is too large, it becomes difficult to create a state of microbubbles with a sufficiently small bubble size in the reaction liquid, only a portion of the exhaust gas G0 discharged from the CO2 emission equipment 100 is circulated through the first gas flow path 21 and the second gas flow path 22, and the remaining exhaust gas that does not circulate through either of them is released to the outside via the exhaust duct 20.

[0018] 5. Solenoid valve 30 The solenoid valve 30 is connected to a pipe 31 that communicates with the first gas flow path 21, the second gas flow path 22, and a moisture removal filter 40 (described later), and constitutes a flow rate adjusting unit that can change the flow rates of the first CO2-containing gas G1 and the second CO2-containing gas G2 that flow from the first gas flow path 21 and the second gas flow path 22 to the pipe 31. The form of the solenoid valve 30 is not limited, but in the first embodiment, the solenoid valve 30 is configured to be switchable between a first state in which the first gas flow path 21 is opened to maximize the flow rate of the first CO2-containing gas G1 flowing into the pipe 31 and the second gas flow path 22 is closed to reduce the flow rate of the second CO2-containing gas G2 flowing into the pipe 31 to zero, and a second state in which the first gas flow path 21 is closed to reduce the flow rate of the first CO2-containing gas G1 flowing into the pipe 31 to zero and the second gas flow path 22 is opened to maximize the flow rate of the second CO2-containing gas G2 flowing into the pipe 31.

[0019] The operation of the solenoid valve 30 is controlled by a solenoid valve control unit 35. The solenoid valve control unit 35 changes the open / close state of the solenoid valve 30 based on the detection result of a temperature sensor 12 that detects the temperature of the reaction liquid in the reaction tank 11, which will be described later.

[0020] The solenoid valve control unit 35, for example, the solenoid valve 30 as a flow rate control unit, can adjust the flow rates of the first CO2-containing gas G1 and the second CO2-containing gas G2 so that the temperature of the reaction liquid obtained by the temperature sensor 12 described below is higher than a predetermined first reference temperature, or adjust the flow rates of the first CO2-containing gas G1 and the second CO2-containing gas G2 so that the temperature is lower than the first reference temperature.

[0021] The first reference temperature can be set appropriately depending on the target product in the CO2 recovery apparatus. For example, when an aqueous NaOH solution is used as the reaction liquid, the first reference temperature can be set based on the map shown in Figure 2, which shows the correspondence relationship between the pH of the reaction liquid, the reaction liquid temperature, and the product.

[0022] For example, when the purpose is to generate Na2CO3 in a CO2 recovery apparatus, the first reference temperature is set to a value within the range of 45 to 65°C, and the flow rates of the first CO2-containing gas G1 and the second CO2-containing gas G2 can be adjusted so that the temperature is equal to or higher than the first reference temperature. When the temperature of the reaction solution exceeds 65°C, the reverse reaction of Equation 2 (described later) becomes dominant, causing NaHCO3 to disappear and Na2CO3 to be generated. Therefore, by raising the reaction solution to the first reference temperature or higher, Na2CO3 can be actively generated and the purity can be improved. Then, by stopping the bubbling of the CO2-containing gas (described later) when the pH of the reaction solution reaches approximately 10, the aqueous solution of the target product can be obtained. In this embodiment, the first reference temperature is set to 50°C.

[0023] Furthermore, for example, when the objective is to generate a mixture of NaHCO3 and Na2CO3 in a CO2 recovery apparatus, the first reference temperature can be set to a value within the range of 45 to 65°C, and the flow rates of the first CO2-containing gas G1 and the second CO2-containing gas G2 can be adjusted so that the first reference temperature is lower than the first reference temperature. As described above, when the temperature of the reaction solution exceeds 65°C, the reverse reaction of Equation 2 described below becomes dominant and NaHCO3 disappears. Therefore, by lowering the reaction solution temperature below the first reference temperature, the disappearance of NaHCO3 can be suppressed. In this case, the bubbling of the CO2-containing gas described below can be stopped when the pH of the reaction solution reaches about 8, and an aqueous solution of the target product can be obtained.

[0024] Furthermore, for example, when the purpose is to generate NaHCO in a CO recovery apparatus, the first reference temperature is set to a value within the range of 45 to 65°C, and the flow rates of the first CO2-containing gas G1 and the second CO2-containing gas G2 can be adjusted so that they are lower than the first reference temperature. In this case, the bubbling of the CO2-containing gas, which will be described later, is stopped when the pH of the reaction solution reaches about 7.5, thereby obtaining an aqueous solution of the target product.

[0025] Furthermore, the solenoid valve control unit 35, for example, the solenoid valve 30 as a flow rate adjusting unit, can adjust the flow rates of the first CO2-containing gas G1 and the second CO2-containing gas G2 so that the temperature of the reaction solution obtained by a temperature sensor 12 (described later) is higher than a preset second reference temperature. The second reference temperature can be set to a value around room temperature, and in the first embodiment, the second reference temperature is set to 25°C. By controlling the temperature of the reaction solution to be equal to or higher than the second reference temperature, the reaction rates of the reactions shown in Equations 1 and 2 (described later) can be maintained within an appropriate range, and the CO2 fixation reaction can be stabilized.

[0026] 6. Moisture removal filter 40 The moisture removal filter 40 is provided in the pipe 31 and removes moisture from the CO2-containing gas flowing through the pipe 31. The moisture removal filter 40 is configured by a water separator (not shown) that includes a moisture separation section that separates water vapor contained in the CO2-containing gas into liquid, and a gas passage section through which the CO2-containing gas from which the water vapor has been separated and removed passes. The separated moisture is stored in a tank (not shown) and discharged as appropriate. The exhaust gas that has passed through the gas passage section is discharged into the pipe 41 that communicates with the air pump 50, which will be described later. Removing water by the moisture removal filter 40 prevents water from accumulating in the air pump 50 at the downstream stage.

[0027] 7. Air Pump 50 The air pump 50 is connected to the moisture removal filter 40 via a pipe 41 and configured to suck in a CO2-containing gas. Due to the suction of the air pump 50, a portion of the exhaust gas flows from the exhaust duct 20 into the first gas flow path 21 and the second gas flow path 22. The sucked CO2-containing gas is supplied to the reaction vessel 11 described below via the pipe 51. The configuration of the air pump 50 is not limited, but it is preferably a diaphragm pump in which the gas does not come into direct contact with the drive part of the air pump 50.

[0028] The operation of the air pump 50 is controlled by a pump control unit 55. The pump control unit 55 switches the suction operation of the air pump 50 on and off based on the detection result of a pH sensor 13 that detects the pH of the reaction liquid in the reaction tank 11, which will be described later. When the suction operation of the air pump 50 is turned on, bubbling of the CO2-containing gas in the reaction tank 11, which will be described later, begins, and when the suction operation of the air pump 50 is turned off, the bubbling stops.

[0029] 8.CO2 capture device 10 The CO2 recovery device 10 recovers CO2 from the CO2-containing gas by bringing the CO2-containing gas into contact with a reaction liquid stored in a reaction tank 11. The reaction liquid can be an aqueous alkali metal hydroxide solution or an aqueous alkaline earth metal hydroxide solution, and in this embodiment 1, an aqueous NaOH solution was used. The concentration of the NaOH solution is not limited, but in this embodiment 1, a 5.0% NaOH solution was used, which is not a deleterious substance and is therefore easy to handle.

[0030] A CO2-containing gas is supplied to the reaction tank 11 via a pipe 51. The tip of the pipe 51 is located near the bottom inside the reaction tank 11 and is configured to discharge the CO2-containing gas into the reaction liquid to bubble it. The reaction tank 11 is provided with a temperature sensor 12 that detects the temperature of the reaction liquid P and a pH sensor 13 that detects the pH of the reaction liquid P.

[0031] Then, by bringing the CO2-containing gas into contact with the NaOH aqueous solution in the reaction tank 11, the reaction of the following formula 1 takes place in the reaction tank 11, and then the reaction of the following formula 2 takes place. Note that in this specification, the following formulas 1 and 2 are also referred to as CO2 fixation reactions. 2NaOH+CO2→ Na2CO3+H2O (Formula 1) Na2CO3+CO2+H2O → 2NaHCO3 (formula 2)

[0032] Before the start of the reaction, neither NaHCO3 nor Na2CO3 is present in the reaction vessel 11 shown in Figure 1. However, depending on the progress of the reaction, one of the following states occurs: Na2CO3 is produced and no NaHCO3 is present; some Na2CO3 further reacts with CO2 to produce NaHCO3 and both are present; or all Na2CO3 is converted to NaHCO3 and no Na2CO3 remains, resulting in the presence of NaHCO3. Both NaHCO3 and Na2CO3 produced by the reaction are dissolved in water in the reaction vessel 11 and form aqueous solutions. In this specification, NaHCO3, Na2CO3, and a mixture of the two are collectively referred to as the "product," and these aqueous solutions are collectively referred to as the "product aqueous solution."

[0033] In the first embodiment, the reaction can be initiated by bubbling the CO2-containing gas supplied from the pipe 51 into contact with the aqueous NaOH solution in the reaction vessel 11. In order to increase the frequency of contact between the CO2-containing gas and the aqueous NaOH solution, it is preferable to discharge the CO2-containing gas in the form of microbubbles. The microbubbles can be formed by a microbubble generator (not shown) provided at the tip of the pipe 51.

[0034] If the exhaust gas discharged from the CO2 emission facility 100 contains substances that inhibit the above reaction in the reaction tank 11, it is preferable to provide a filter (not shown) that removes substances that inhibit the above reaction at a position upstream of the reaction tank 11, for example, between the solenoid valve 30 and the moisture removal filter 40, between the moisture removal filter 40 and the air pump 50, or between the air pump 50 and the reaction tank 11. Note that if the exhaust gas discharged from the CO2 emission facility 100 does not contain components other than CO2 or if it is clear that it does not contain substances that inhibit the above reaction in the reaction tank 11, there is no need to provide such a filter.

[0035] The exhaust unit 14 shown in FIG. 1 exhausts the CO2-removed gas, from which CO2 has been removed in the reaction tank 11, from the reaction tank 11 to the filter 60. The filter 60 captures harmful components in the CO2-removed gas. The configuration of the filter 60 is not limited, but in the first embodiment, the CO2-removed gas is bubbled through water W stored in the filter 60 and passes through the filter 60, thereby removing the CO2-removed gas from water-soluble substances (for example, NaOH in the reaction liquid that has been sprayed by bubbling in the reaction tank 11 and reached the exhaust unit 14, and nitrogen oxides NO contained in the exhaust gas). x The CO2-removed gas that has passed through the filter 60 is released to the outside of the CO2 recovery system 1.

[0036] Meanwhile, the aqueous product solution produced by the reactions of Equations 1 and 2 above is discharged to the outside via a drain cock 70 provided in the reaction tank 11. The drain cock 70 is configured to be openable and closable. The drain cock 70 is normally closed, but by opening it when recovering the aqueous product solution, the aqueous product solution in the reaction tank 11 can be discharged from the reaction tank 11 and recovered in a recovery container 75. The recovered aqueous product solution can be used as a resource, for example, as a cleaning agent, antiseptic, herbicide, etc. After the aqueous product solution is discharged from the reaction tank 11, the drain cock 70 is closed, and an aqueous NaOH solution, which is the reaction solution to be used in the next reaction, is supplied into the reaction tank 11 from a reaction solution supply unit (not shown).

[0037] 9-1. First Usage of the CO2 Capture System 1 of the First Embodiment Next, a first usage mode of the CO2 recovery system 1 of the present embodiment 1 will be described below with reference to the flow diagram shown in Fig. 3. In the first usage mode, the target product in the CO2 recovery device 10 is a mixture of Na2CO3 and NaHCO3 (sodium sesquicarbonate).

[0038] 3, as a preparation step, an NaOH aqueous solution, which is a reaction liquid, is introduced into the reaction tank 11. Then, in step S2, the air pump 50 is driven, and in step S3, the solenoid valve 30 opens one of the first gas flow path 21 and the second gas flow path 22 and closes the other.

[0039] Then, in step S4, the temperature of the reaction solution is acquired by the temperature sensor 12, and the pH of the reaction solution is acquired by the pH sensor 13. Immediately after the start of the reaction, a large amount of NaOH is present in the reaction solution, so the acquired pH is a high value, and as the reaction progresses, NaOH is consumed, causing the pH of the reaction solution to decrease.

[0040] Next, in step S5, the solenoid valve control unit 35 compares the acquired temperature with 50°C, which is a first reference temperature. If it is determined in step S5 that the acquired temperature is equal to or higher than the first reference temperature, the process proceeds to step S5 (Yes). Then, in step S6, the solenoid valve 30 opens the first gas flow path 21 and closes the second gas flow path 22, and sets the solenoid valve 30 to the first state. As a result, low-temperature exhaust gas is supplied to the reaction vessel 11, and the temperature of the reaction liquid is controlled to be lower than 50°C.

[0041] Thereafter, in step S7, it is determined whether the acquired pH has reached a first target value by the pump control unit 55. The first target value is set appropriately depending on the target product, and in this first usage mode, since the target product is a mixture of NaHCO3 and Na2CO3, the first target value was set to about pH = 8.

[0042] If it is determined in step S7 that the acquired pH has reached the target value, in step S8, the pump control unit 55 stops driving the air pump 50 to stop bubbling in the reaction tank 11. Then, in step S9, the drain cock 70 is opened to recover the aqueous mixture of NaHCO3 and Na2CO3, which is the aqueous product solution, in the recovery container 75. Then, this flow ends.

[0043] On the other hand, if it is determined in step S7 that the acquired pH has not reached the first target value, the process returns to step S4 again, and the subsequent steps are carried out.

[0044] Furthermore, if it is determined in step S5 that the temperature of the acquired reaction liquid is not equal to or higher than the first reference temperature (50°C), the process proceeds to step S5 (No). Then, in step S10, the solenoid valve control unit 35 determines whether the temperature of the acquired reaction liquid is equal to or lower than the second reference temperature, 25°C. If it is determined in step S10 that the temperature of the reaction liquid is equal to or lower than 25°C, the process proceeds to step S11, in which the solenoid valve 30 closes the first gas flow path 21, opens the second gas flow path 22, and sets the solenoid valve 30 to the second state. As a result, a high-temperature second CO2-containing gas is supplied to the reaction vessel 11, and the temperature of the reaction liquid is controlled to be higher than 25°C. Then, the process proceeds to step S7, and the subsequent steps are performed. On the other hand, if it is determined in step S10 that the temperature of the reaction liquid is not equal to or lower than 25°C, the process proceeds to the above-mentioned step S7, and the subsequent steps are performed.

[0045] 9-2. Second Usage of the CO2 Capture System 1 of Embodiment 1 Next, a second usage mode of the CO2 recovery system 1 of the first embodiment will be described below with reference to the flow diagram shown in Fig. 4. In the second usage mode, the target product in the CO2 recovery device 10 is Na2CO3. Note that the same steps as those in the first usage mode described above are denoted by the same reference numerals, and their description will be omitted.

[0046] 4, steps S1 to S5 are the same as those of the first usage mode. If it is determined in step S5 that the temperature of the obtained reaction liquid is not equal to or higher than the first reference temperature, the process proceeds to step S11, in which the solenoid valve 30 closes the first gas flow path 21 and opens the second gas flow path 22. As a result, the high-temperature second CO2-containing gas G2 is supplied to the reaction vessel 11, and the temperature of the reaction liquid is controlled to be 50°C or higher.

[0047] Then, the process proceeds to step S70, where it is determined whether the pH of the obtained reaction solution has reached a second target value. In the second usage mode, since the target product is Na2CO3, the second target value is about pH = 10. If the target product is NaHCO3, the target value can be set to about pH = 7.5.

[0048] If it is determined in step S70 that the pH of the obtained reaction solution has reached the second target value, steps S8 and S9 are carried out in the same manner as in the first mode of use. As a result, in step S9, an aqueous Na2CO3 solution is recovered as the aqueous product solution, and the flow ends.

[0049] Furthermore, if it is determined in step S70 that the pH of the obtained reaction solution has not reached the second target value, the process returns to step S4, and the subsequent steps are carried out.

[0050] On the other hand, if it is determined in step S5 that the temperature of the obtained reaction liquid is equal to or higher than the first reference temperature, the process proceeds from Yes in step S5 to step S70, and the subsequent steps are carried out.

[0051] 10. Effects of the CO2 capture system 1 of the first embodiment Next, the effects of the CO2 capture system 1 of this embodiment will be described in detail. According to the CO2 capture system 1, the flow rate of the first CO2-containing gas G1 supplied to the CO2 capture device 10 and the flow rate of the second CO2-containing gas G2, which has a higher temperature than the first CO2-containing gas G1, are adjusted so that the temperature of the reaction liquid is maintained at a predetermined temperature. This prevents the temperature of the reaction liquid from becoming excessively high and suppresses temperature changes in the reaction liquid due to changes in the outside air temperature depending on the season or time of day. This stabilizes the CO2 fixation reaction in the CO2 capture device 10 and prevents a decrease in the CO2 emission suppression effect. Furthermore, stabilizing the CO2 fixation reaction shortens the operating time of the CO2 capture system 1, thereby saving energy.

[0052] In the first embodiment, the reaction liquid is an aqueous NaOH solution, and the CO2 recovery device 10 recovers CO2 to produce at least one of NaHCO3, Na2CO3, and a mixture of NaHCO3 and Na2CO3. Since all of these products are useful resources, the recovered CO2 can be effectively reused.

[0053] In addition, in the first embodiment, the solenoid valve 30 serving as a flow rate adjusting unit is configured to adjust the flow rates of the first CO2-containing gas G1 and the second CO2-containing gas G2 so that the temperature of the reaction liquid acquired by the temperature sensor 12 constituting the reaction liquid temperature acquiring unit becomes equal to or higher than a first reference temperature set in advance, thereby producing Na2CO3 in the CO2 recovery device 10. This can improve the production efficiency when the target product is Na2CO3.

[0054] In addition, in the first embodiment, the solenoid valve 30 serving as a flow rate adjusting unit is configured to adjust the flow rates of the first CO2-containing gas and the second CO2-containing gas so that the temperature acquired by the temperature sensor 12 constituting the reaction liquid temperature acquiring unit becomes lower than a preset first reference temperature, thereby producing a mixture of NaHCO3 and Na2CO3 in the CO2 recovery device 10. This can improve the production efficiency when the target product is sodium sesquicarbonate, which is a mixture of NaHCO3 and Na2CO3.

[0055] Furthermore, in the first embodiment, the piping forming the first gas flow path 21 has lower thermal insulation than the piping forming the second gas flow path 22, and a portion of the high-temperature exhaust gas is cooled as it flows through the first gas flow path 21 to become the first CO2-containing gas G1, which is at a lower temperature than the second CO2-containing gas G2. As a result, the power consumed to generate the low-temperature first CO2-containing gas G1 and the high-temperature second CO2-containing gas G2 from the high-temperature exhaust gas is essentially the power consumed by the air pump 50 alone, thereby reducing power consumption and improving overall CO2 capture efficiency. Furthermore, since a cooling device for cooling or a heating device for heating the exhaust gas are not required to generate the low-temperature first CO2-containing gas G1 and the high-temperature second CO2-containing gas G2, the device configuration can be simplified and costs can be reduced.

[0056] Furthermore, in this first embodiment, a pH sensor 13 is further provided as a pH acquisition unit that acquires the pH of the reaction solution in the reaction tank 11, and the CO2 recovery system 1 is configured to stop the supply of the first CO2-containing gas G1 and the second CO2-containing gas G2 when the pH acquired by the pH sensor 13 reaches a preset target value. This allows the target value to be set according to the target product, thereby improving the production efficiency of the target product.

[0057] As described above, according to the above embodiment, it is possible to provide a CO2 recovery system 1 that is excellent in the effect of suppressing CO2 emissions.

[0058] (Embodiment 2) A second embodiment of the CO2 recovery system will be described with reference to Figures 5 to 7. In the first embodiment described above, the flow rate adjustment unit is configured with a single solenoid valve 30 that can switch between a first state and a second state. However, in the second embodiment, instead, as shown in Figure 5, the solenoid valve 30 serving as the flow rate adjustment unit includes a low-temperature side solenoid valve 301 and a high-temperature side solenoid valve 302. The low-temperature side solenoid valve 301 is connected to the first gas flow path 21 and is configured to be able to adjust the flow rate of the first CO2-containing gas G1 in the first gas flow path 21. Furthermore, the high-temperature side solenoid valve 302 is connected to the second gas flow path 22 and is configured to be able to adjust the flow rate of the second CO2-containing gas G2 in the second gas flow path 22.

[0059] 6, downstream of the low-temperature side solenoid valve 301 and the high-temperature side solenoid valve 302 is provided a gas mixing unit 32 that mixes the first CO2-containing gas G1 that has passed through the low-temperature side solenoid valve 301 and the second CO2-containing gas G2 that has passed through the high-temperature side solenoid valve 302 and supplies the mixed gas to the CO2 recovery device 10. The gas mixed by the gas mixing unit 32 is supplied to the piping 31. When one of the low-temperature side solenoid valve 301 and the high-temperature side solenoid valve 302 is closed and the other is open, the gas mixing unit 32 can supply to the piping 31 only the CO2-containing gas that has passed through the open one of the low-temperature side solenoid valve 301 and the high-temperature side solenoid valve 302.

[0060] Other configurations in the second embodiment are the same as those in the first embodiment, and the same reference numerals as those in the first embodiment are used, and the description thereof will be omitted.

[0061] 11-1. First Usage of the CO2 Capture System 1 of the Second Embodiment Next, a first usage mode of the CO2 capture system 1 of the second embodiment will be described below with reference to the flow chart shown in Fig. 6. Note that steps equivalent to those in the flow chart shown in Fig. 3 of the first embodiment are denoted by the same reference numerals as in the first embodiment, and descriptions thereof will be omitted.

[0062] In a first mode of use of the CO2 recovery system 1 of the second embodiment, the target product in the CO2 recovery device 10 is a mixture of Na2CO3 and NaHCO3 (sodium sesquicarbonate).

[0063] 6 are the same as in the first embodiment. Then, the process proceeds to step S30, where the low-temperature side solenoid valve 301 and the high-temperature side solenoid valve 302 open both the first gas flow path 21 and the second gas flow path 22. As a result, the first CO2-containing gas G1 and the second CO2-containing gas G2 are mixed in the gas mixing section 32 and supplied to the moisture removal filter 40.

[0064] Next, steps S4 to S11 shown in FIG. 6 are the same as in the first embodiment. If it is determined in step S10 that the acquired temperature is not equal to or lower than 25°C, which is the second reference temperature, the process does not return to step S4 as in the first embodiment, but proceeds to step S12 in the second embodiment. In step S12, the low-temperature side solenoid valve 301 and the high-temperature side solenoid valve 302 open both the first gas flow path 21 and the second gas flow path 22, and the solenoid valve 30 is set to the third state. As a result, the first CO2-containing gas G1 and the second CO2-containing gas G2 are mixed in the gas mixing section 32 and supplied to the moisture removal filter 40, and the temperature of the reaction liquid is controlled to be maintained within the range of 25°C to 50°C. After step S12, the process proceeds to step S7, and the subsequent steps are performed as in the first embodiment.

[0065] 11-2. Second Usage of the CO2 Capture System 1 of the Second Embodiment Next, a second usage mode of the CO2 recovery system 1 of the second embodiment will be described with reference to the flow diagram shown in Fig. 7. In the second usage mode, the target product in the CO2 recovery device 10 is Na2CO3. In the second usage mode of the second embodiment shown in Fig. 7, step S30 described above is performed instead of step S3 in the flow diagram shown in Fig. 4 for the first embodiment. The other steps are the same as those in the first embodiment shown in Fig. 4, and the same reference numerals as those in the first embodiment are used, and their description will be omitted.

[0066] 12. Effects of the CO2 capture system 1 of the second embodiment In the second embodiment, the first CO2-containing gas G1 is a low-temperature exhaust gas obtained by cooling a portion of the high-temperature exhaust gas discharged from the CO2 discharge facility 100, and the second CO2-containing gas G2 is another portion of the high-temperature exhaust gas discharged from the CO2 discharge facility 100. The system further includes a gas mixing unit 32 that mixes the first CO2-containing gas G1 and the second CO2-containing gas G2 and supplies the mixed gas to the CO2 recovery device 10. This makes it easier to adjust the temperature of the gas supplied to the CO2 recovery device 10 to a desired temperature, further stabilizing the reaction in the reaction tank 11. Note that the second embodiment can also achieve the same effects as those of the first embodiment.

[0067] The present invention is not limited to the above-described embodiment and modified forms, and can be applied to various embodiments without departing from the spirit of the present invention. [Explanation of symbols]

[0068] 1: CO2 recovery system, 10: CO2 recovery device, 11: reaction tank, 12: temperature sensor (reaction liquid temperature acquisition unit), 13: pH sensor (pH acquisition unit), 21: first gas flow path, 22: second gas flow path, 22a: heat insulating material, 30: solenoid valve, 301: low temperature side solenoid valve, 302: high temperature side solenoid valve, 32: gas mixing unit, 35: solenoid valve control unit, 40: moisture removal filter, 50: air pump, 55: pump control unit, 60: filter, 70: drain cock, 75: recovery container,

Claims

1. CO is added to the reaction solution stored in the reaction tank. ２ The CO ２ CO from contained gas ２ CO2 recovery ２ A recovery device; a reaction solution temperature acquisition unit that acquires the temperature of the reaction solution stored in the reaction tank; First CO ２ a first gas flow path through which the contained gas flows; The first CO ２ A second CO gas having a higher temperature than the containing gas. ２ a second gas flow path through which the contained gas flows; The CO gas is supplied from the first gas flow path so that the temperature of the reaction liquid acquired by the reaction liquid temperature acquisition unit becomes a predetermined temperature. ２ The first CO supplied to the recovery device ２ The flow rate of the contained gas and the CO ２ The second CO supplied to the recovery device ２ a flow rate adjusting unit that adjusts the flow rate of the contained gas; CO ２ Collection system.

2. The reaction solution is an aqueous NaOH solution. ２ The recovery device is the CO ２ By recovering NaHCO ３ , Na ２ CO ３ , and NaHCO ３ and Na ２ CO ３ and a mixture of the CO ２ Collection system.

3. The flow rate adjusting unit adjusts the first CO 2 so that the temperature of the reaction liquid acquired by the reaction liquid temperature acquiring unit becomes equal to or higher than a first reference temperature set in advance. ２ containing gas and the second CO ２ The flow rate of the CO ２ In the recovery device, Na ２ CO ３ 3. The CO2 of claim 2, ２ Collection system.

4. The flow rate adjusting unit adjusts the first CO 2 flow rate so that the temperature acquired by the reaction solution temperature acquiring unit is lower than a preset first reference temperature. ２ containing gas and the second CO ２ The flow rate of the CO ２ In the recovery device, NaHCO ３ and Na ２ CO ３ 3. The CO2 of claim 2, configured to produce a mixture with ２ Collection system.

5. The first CO ２ The contained gas is CO ２ The low-temperature exhaust gas is obtained by cooling a portion of the high-temperature exhaust gas discharged from the exhaust facility, The second CO ２ The contained gas is the above CO ２ Another part of the high-temperature exhaust gas discharged from the discharge facility, The first CO ２ containing gas and the second CO ２ The CO ２ The CO 2 gas according to any one of claims 1 to 4, further comprising a gas mixing section for supplying the CO 2 gas to a recovery device. ２ Collection system.

6. The piping that forms the first gas flow path has lower thermal insulation than the piping that forms the second gas flow path, and a part of the high-temperature exhaust gas is cooled as it flows through the first gas flow path, and is converted into the second CO ２ The first CO gas is at a lower temperature than the CO gas containing gas. ２ The CO according to claim 5, which is a containing gas. ２ Collection system.

7. Further provided is a pH acquisition unit that acquires the pH of the reaction solution in the reaction tank, When the pH acquired by the pH acquisition unit reaches a preset target value, the first CO ２ containing gas and the second CO ２ The CO2 gas supply system according to any one of claims 1 to 4, wherein the supply of the gas is stopped. ２ Collection system.

Images