Co2 recovery method

Abstract

To provide a CO2 recovery method capable of suppressing deterioration of both silica and amine contained in an adsorbent.SOLUTION: A CO2 recovery method includes the steps of: measuring the temperature and the relative humidity of CO2-containing gas; supplying the CO2-containing gas to the inside of a desorption tower, and thereby adsorbing CO2 on an adsorbent; estimating scheduled relative humidity of the internal atmosphere of the desorption tower when the CO2 is desorbed, from the measured temperature and relative humidity of the CO2-containing gas, and a scheduled raised temperature of the internal atmosphere of the desorption tower when the CO2 is desorbed, on the basis of a relation between the temperature and relative humidity of the atmosphere of the CO2-containing gas, and an adsorption water amount of a carrier; determining whether or not the scheduled relative humidity is within a predetermined humidity range; and adjusting the relative humidity of the internal atmosphere of the desorption tower when it is determined that it is not within the predetermined humidity range, and then raising the temperature of the internal atmosphere of the desorption tower to the predetermined raised temperature, and thereby desorbing the CO2 from the adsorbent.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for recovering CO2 by using an adsorbent capable of adsorbing and desorbing CO2 to recover CO2.

Background Art

[0002] Conventionally, as a method for recovering CO2 (carbon dioxide), after adsorbing CO2 from a CO2-containing gas onto an adsorbent, the atmosphere in which the adsorbent is disposed is heated to desorb CO2 from the adsorbent, thereby recovering CO2. A method is known.

[0003] As such a method, for example, after adsorbing CO2 by introducing a CO2-containing gas into a honeycomb (adsorbent) carrying an adsorbent containing an amine, CO2 is desorbed from the honeycomb by introducing high-temperature steam into the honeycomb. A method is known (Patent Document 1). Further, in an adsorption tower, an adsorption step of adsorbing one or more gas components (CO2) in a mixed gas onto a gas adsorbent and a regeneration step of desorbing the gas component by heating with steam to regenerate the gas adsorbent are alternately performed. A method is known (Patent Document 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In conventional CO₂ recovery methods such as Patent Documents 1 and 2, a method is adopted in which water vapor is used to raise the temperature of the atmosphere where the adsorbent is disposed, thereby desorbing CO₂ from the adsorbent. On the other hand, as the adsorbent, an adsorbent containing a carrier containing silica and an adsorbent containing an amine supported on the carrier may be used. However, the carrier containing silica and the adsorbent containing an amine have a problem that they are likely to deteriorate when the processes of adsorbing and desorbing CO₂ to and from the adsorbent are repeated depending on conditions such as the temperature and relative humidity of the atmosphere where the adsorbent is disposed.

[0006] The present invention has been made in view of the above problems, and the main object thereof is to provide a method for recovering carbon dioxide that can suppress the deterioration of both the carrier containing silica and the adsorbent containing an amine included in the adsorbent.

Means for Solving the Problems

[0007] In order to solve the above problems, the CO₂ recovery method of the present invention includes a desorption tower and an adsorbent stored inside the desorption tower, and uses a recovery device including a carrier containing silica and an adsorbent containing an amine supported on the carrier to recover CO₂ from a CO₂-containing gas. The method comprises: a step of measuring the temperature and relative humidity of the CO₂-containing gas; a step of adsorbing the CO₂ onto the adsorbent by supplying the CO₂-containing gas inside the desorption tower; a step of estimating the predicted relative humidity of the atmosphere inside the desorption tower during CO₂ desorption for desorbing the CO₂ from the adsorbent, based on the relationship between the temperature and relative humidity of the atmosphere of the CO₂-containing gas where the carrier is disposed and the water adsorption amount of the carrier, from the measured temperature and relative humidity of the CO₂-containing gas and the predicted temperature rise of the atmosphere inside the desorption tower during CO₂ desorption; a step of determining whether the predicted relative humidity is within a predetermined humidity range that can suppress the progress of deterioration of both the carrier and the adsorbent contained in the adsorbent within an allowable range; a step of adjusting the relative humidity of the atmosphere inside the desorption tower so that the predicted relative humidity is within the predetermined humidity range when the predicted relative humidity is not within the predetermined humidity range; and a step of desorbing the CO₂ from the adsorbent by raising the temperature of the atmosphere inside the desorption tower to the predicted temperature rise after adjusting the relative humidity.

Effect of the Invention

[0008] According to the present invention, it is possible to suppress the deterioration of both the carrier containing silica and the adsorbent containing an amine contained in the adsorbent.

[0009] Problems, configurations, and effects of the present invention other than those described above will be clarified by the description of the embodiments for carrying out the following invention.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments of the CO2 (carbon dioxide) recovery method of the present invention will be described. First, regarding the outline of the CO2 recovery method according to the embodiment, the CO2 recovery method according to one embodiment will be exemplified and described.

[0012] Prior to the description of the CO2 recovery method according to one embodiment, the CO2 recovery apparatus according to one embodiment used therefor will be described. Fig. 1(a) is a schematic diagram showing a CO2 recovery apparatus according to one embodiment, and Fig. 1(b) is a schematic perspective view showing an adsorbent according to one embodiment. In Fig. 1(b), an enlarged view of the cells of the honeycomb substrate of the adsorbent as viewed in plan from the stretching direction is shown in the inset.

[0013] As shown in FIG. 1(a), a CO2 recovery apparatus 100 according to an embodiment includes a desorption tower 10, an intake fan 24 connected to a CO2-containing gas source (e.g., the atmosphere) 22, a water vapor gas supply device 26, a dry gas supply device 28, a vacuum pump 32, a condenser 34, a CO2 recovery tank 36, and a control device 50. The recovery apparatus 100 further includes a CO2 supply flow path 12, a temperature sensor 12t and a humidity sensor 12r installed in the CO2 supply flow path 12, a water vapor gas supply flow path 14, a dry gas supply flow path 16, and a recovery flow path 18. The recovery apparatus 100 further includes an inlet valve 10a, an outlet valve 10b, a water vapor gas control valve 10c, a dry gas control valve 10d, an electric heater 10h, a temperature sensor 10t, and a humidity sensor 10r installed in the desorption tower 10.

[0014] The recovery apparatus 100 further includes an adsorbent 2 shown in FIG. 1(b). The adsorbent 2 is stored inside the desorption tower 10. The adsorbent 2 has a honeycomb substrate 4 and an adsorption layer 6. The honeycomb substrate 4 is a porous substrate in which a cylindrical frame portion 4f and a partition wall 4w that partitions the space inside the frame portion 4f in a honeycomb shape are integrally formed. The partition wall 4w defines a plurality of cells 4c extending from the gas inflow side end face to the outflow side end face of the honeycomb substrate 4. The shape of the partition wall 4w includes a plurality of wall portions arranged parallel to each other with a gap therebetween, and a plurality of wall portions perpendicular to and arranged parallel to each other with a gap therebetween, and the cross section perpendicular to the extending direction is in a lattice shape. The plurality of cells 4c are adjacent to each other with the partition wall 4w interposed therebetween, and the inflow side end and the outflow side end are open. As shown in the blowout, the adsorption layer 6 is provided on the surface of the partition wall 4w on the cell 4c side from the inflow side end to the outflow side end. The adsorption layer 6 includes a granular porous carrier (not shown) containing silica and an adsorbent (not shown) containing an amine supported on the porous carrier.

[0015] The control device 50 of the recovery device 100 stores, as information representing the relationship between the temperature [°C] and relative humidity [%RH] of the atmosphere of the CO2-containing gas in which the porous carrier is disposed and the water adsorption amount [g] of the porous carrier, an adsorption isotherm representing the change in the water adsorption amount per unit weight [g / g] of the porous carrier with respect to the relative humidity [%RH] at each temperature [°C] of the atmosphere of the CO2-containing gas when the temperature of the atmosphere of the CO2-containing gas in which the porous carrier is disposed is changed. The control device 50 stores the weight [g] of the porous carrier included in the adsorbent 2, the planned temperature increase temperature [°C] of the atmosphere inside the desorption tower 10 during CO2 desorption for desorbing CO2 from the adsorbent 2, the saturated water vapor amount [g / m 3 of the supplied CO2-containing gas, and the saturated water vapor amount [g / m 3 of the CO2-containing gas at the planned temperature increase temperature, the volume [m 3 of the inside of the desorption tower 10, the relative humidity [%RH] of the water vapor gas, and the relative humidity [%RH] of the dry gas. The control device 50 stores in advance a predetermined humidity range [%RH] that can suppress the progress of deterioration of both the porous carrier and the adsorbent included in the adsorbent 2 within an allowable range. The control device 50 may further store other information used in the CO2 recovery method. The control device 50 controls various devices and equipment included in the recovery device 100 and performs various calculations.

[0016] Subsequently, a CO2 recovery method according to an embodiment will be described. FIG. 2 is a flowchart showing an outline of the CO2 recovery method according to an embodiment.

[0017] In the CO2 recovery method according to an embodiment, as shown in FIG. 2, first, in the measurement step S10, the temperature and relative humidity of the CO2-containing gas (for example, normal-temperature air) supplied from the CO2-containing gas source 22 (for example, the atmosphere) into the desorption tower 10 are measured. Specifically, under the control of the control device 50, the temperature [°C] and relative humidity [%RH] of the CO2-containing gas are measured by the temperature sensor 12t and the humidity sensor 12r installed in the CO2 supply flow path 12, and then the measured temperature and relative humidity of the CO2-containing gas are stored in the control device 50.

[0018] Next, in the adsorption step S20, the adsorbent 2 adsorbs CO2 by supplying a CO2-containing gas from the CO2-containing gas source 22 into the desorption tower 10. Specifically, under the control of the control device 50, the inlet valve 10a and the outlet valve 10b of the desorption tower 10 are opened, the steam gas control valve 10c and the dry gas control valve 10d are closed, and then the intake fan 24 continuously feeds the CO2-containing gas from the CO2-containing gas source 22 into the CO2 supply passage 12 at a predetermined flow rate for a predetermined time or more. As a result, the CO2-containing gas is continuously supplied from the CO2 supply passage 12 into the desorption tower 10 through the inlet valve 10a at a predetermined flow rate for a predetermined time or more. Thereby, the atmosphere inside the desorption tower 10 is made into an atmosphere of a single CO2-containing gas, and the CO2-containing gas is caused to flow into the plurality of cells 4c of the honeycomb substrate 4 of the adsorbent 2 from the inflow side end, and is brought into contact with the adsorption layer 6 provided on the surface of the partition wall 4w of the honeycomb substrate 4 on the cell 4c side. In this way, CO2 is adsorbed by the adsorbent (amine) contained in the adsorbent 2. Then, the gas after being brought into contact with the adsorption layer 6 flows out of the adsorbent 2 from the outflow side ends of the plurality of cells 4c, and further flows out from the inside of the desorption tower 10 into the recovery passage 18 through the outlet valve 10b.

[0019] Next, in the estimation step S30, based on the relationship between the temperature [°C] and relative humidity [%RH] of the atmosphere of the CO2-containing gas in which the porous carrier is disposed and the water adsorption amount [g] of the porous carrier, from the measured temperature [°C] and relative humidity [%RH] of the CO2-containing gas and the expected temperature rise temperature [°C] of the atmosphere inside the desorption tower 10 at the time of CO2 desorption for desorbing CO2 from the adsorbent 2, the expected relative humidity [%RH] of the atmosphere inside the desorption tower 10 at the time of CO2 desorption is estimated.

[0020] In the estimation step S30, the control device 50 selects, from the adsorption isotherms representing the change in the water adsorption amount per unit weight of the porous carrier [g / g] with respect to the relative humidity [%RH] at each temperature [°C] of the atmosphere of the CO₂-containing gas in which the porous carrier is disposed when the temperature of the atmosphere of the CO₂-containing gas in which the porous carrier is disposed is changed, the adsorption isotherm in which the temperature of the atmosphere of the CO₂-containing gas in which the porous carrier is disposed is equal to the measured temperature of the CO₂-containing gas. Then, using the selected adsorption isotherm, the control device 50 calculates the water adsorption amount per unit weight of the porous carrier when the relative humidity of the atmosphere of the CO₂-containing gas in which the porous carrier is disposed becomes equal to the measured relative humidity of the CO₂-containing gas. Then, the value obtained by multiplying the calculated amount by the weight [g] of the porous carrier included in the adsorbent 2 is acquired as the water adsorption amount [g] adsorbed by the porous carrier included in the adsorbent 2 when the CO₂-containing gas is supplied into the inside of the desorption tower 10 in the adsorption step S20. Further, the control device 50 selects, from the above adsorption isotherms, the adsorption isotherm in which the temperature of the atmosphere of the CO₂-containing gas in which the porous carrier is disposed is equal to the planned temperature increase temperature. Then, using the selected adsorption isotherm, the control device 50 calculates the water adsorption amount per unit weight of the porous carrier when the relative humidity of the atmosphere of the CO₂-containing gas in which the porous carrier is disposed becomes equal to the relative humidity at the planned temperature increase temperature of the CO₂-containing gas. Then, the value obtained by multiplying the calculated amount by the weight [g] of the porous carrier included in the adsorbent 2 is acquired as the water adsorption amount [g] adsorbed by the porous carrier included in the adsorbent 2 at the time of CO₂ desorption. Next, the control device 50 calculates the amount of evaporated water vapor [g] evaporated from the adsorbent 2 into the atmosphere inside the desorption tower 10 at the time of CO₂ desorption by subtracting the water adsorption amount adsorbed by the porous carrier included in the adsorbent 2 at the time of CO₂ desorption from the water adsorption amount adsorbed by the porous carrier included in the adsorbent 2 at the time of CO₂-containing gas supply. Next, the control device 50 calculates the planned relative humidity [%RH] of the atmosphere inside the desorption tower 10 at the time of CO₂ desorption by using the following formula (1). Thus, the planned relative humidity is estimated.

[0021] RH x0 =(RH0×SV0+W V / V R ) / SVR (1) RH x0 : Predicted relative humidity [%RH] of the atmosphere inside the desorption tower 10 during CO2 desorption RH0: Measured relative humidity [%RH] of the CO2-containing gas SV0: Saturated water vapor amount [g / m 3 W V : Evaporated water vapor amount [g] during CO2 desorption V R : Volume [m 3 SV R : Saturated water vapor amount [g / m 3

[0022] Next, in the first determination step S41, the control device 50 determines whether the predicted relative humidity of the atmosphere inside the desorption tower 10 during CO2 desorption is equal to or higher than the lower limit of a predetermined humidity range that can suppress the progress of deterioration of both the porous carrier and the adsorbent contained in the adsorbent 2 within an allowable range. If it is determined that the predicted relative humidity is not equal to or higher than the lower limit of the predetermined humidity range, the process proceeds to the water vapor gas supply step S51. On the other hand, if it is determined that the predicted relative humidity is equal to or higher than the lower limit of the predetermined humidity range, the process proceeds to the second determination step S42.

[0023] In the water vapor gas supply step (adjustment step) S51, by supplying water vapor gas from the water vapor gas supply device 26 into the desorption tower 10, the relative humidity of the atmosphere inside the desorption tower 10 is adjusted so that the predicted relative humidity of the atmosphere inside the desorption tower 10 during CO2 desorption falls within the predetermined humidity range.

[0024] ​​​In the steam gas supply step S51, under the control of the control device 50, the inlet valve 10a of the desorption tower 10 is closed, the outlet valve 10b is opened, the steam gas control valve 10c is further opened, and the dry gas control valve 10d is closed. Then, steam gas is supplied from the steam gas supply device 26 into the desorption tower 10 through the steam gas supply passage 14 and the steam gas control valve 10c. At this time, by pushing out with the steam gas supplied into the desorption tower 10, for example, a CO2-containing gas in an amount equal to the supply amount of the steam gas flows out from the inside of the desorption tower 10 through the outlet valve 10b into the recovery passage 18. After the supply of the steam gas is completed, the outlet valve 10b and the steam gas control valve 10c of the desorption tower 10 are closed. In this way, the atmosphere inside the desorption tower 10 is changed from an atmosphere of the CO2-containing gas alone to a humidified atmosphere in which the CO2-containing gas is humidified with the steam gas. Thereby, the relative humidity of the atmosphere inside the desorption tower 10 is adjusted from RH0 (the relative humidity of the measured CO2-containing gas) to RH1 (RH0 < RH1) so that the planned relative humidity falls within the above-mentioned predetermined humidity range. As the steam gas, it is a gas in which the relative humidity is increased to a predetermined value by generating steam in the CO2-containing gas (for example, air), and the temperature is adjusted to the same temperature as the CO2-containing gas (for example, normal temperature) or a temperature slightly higher than the CO2-containing gas. Further, the supply amount of the steam gas supplied into the desorption tower 10 can be calculated in advance by the control device 50 as an amount such that the planned relative humidity when the steam gas is supplied into the desorption tower 10 falls within the above-mentioned predetermined humidity range. The planned relative humidity when the steam gas is supplied into the desorption tower 10 can be calculated, for example, by using the following formulas (2-1) and (2-2).

[0025] RH x1 =(RH1×SV0 + W V / V R ) / SV R (2-1) RH1=(RH WG ×V WG +RH0×(V R -V WG )) / V R (2-2) RH x1: Predicted relative humidity [%RH] when supplying steam gas into the inside of the desorption tower 10 RH1: Relative humidity [%RH] of the humidification atmosphere in which the CO2-containing gas is humidified with steam gas SV0: Saturated water vapor amount of the supplied CO2-containing gas [g / m 3 W V : Amount of evaporated water vapor [g] during CO2 desorption V R : Volume [m 3 SV R : Saturated water vapor amount of the CO2-containing gas at the predicted temperature rise temperature [g / m 3 RH WG : Relative humidity of steam gas [%RH] V WG : Supply amount of steam gas [m 3 RH0: Measured relative humidity of the CO2-containing gas [%RH]

[0026] On the other hand, in the second determination step S42, the control device 50 determines whether the predicted relative humidity of the atmosphere inside the desorption tower 10 during CO2 desorption is equal to or lower than the upper limit of the predetermined humidity range. And when it is determined that the predicted relative humidity is not equal to or lower than the upper limit of the predetermined humidity range, the process proceeds to the dry gas supply step S52.

[0027] In the dry gas supply step (adjustment step) S52, by supplying dry gas from the dry gas supply device 28 into the inside of the desorption tower 10, the relative humidity of the atmosphere inside the desorption tower 10 is adjusted so that the predicted relative humidity of the atmosphere inside the desorption tower 10 during CO2 desorption falls within the predetermined humidity range.

[0028] ​​​​In the dry gas supply step S52, under the control of the control device 50, the inlet valve 10a of the desorption tower 10 is closed, the outlet valve 10b is opened, the steam gas control valve 10c is further closed, and the dry gas control valve 10d is opened. Then, dry gas is supplied from the dry gas supply device 28 into the desorption tower 10 through the dry gas supply passage 16 and the dry gas control valve 10d. At this time, by pushing out with the dry gas supplied into the desorption tower 10, for example, a CO2-containing gas in an amount equal to the supply amount of the dry gas flows out from the inside of the desorption tower 10 to the recovery passage 18 through the outlet valve 10b. After the supply of the dry gas is completed, the outlet valve 10b and the dry gas control valve 10d of the desorption tower 10 are closed. In this way, the atmosphere inside the desorption tower 10 is changed from an atmosphere of the CO2-containing gas alone to a humidity-adjusted atmosphere in which the CO2-containing gas is humidity-adjusted with the dry gas. Thereby, the relative humidity of the atmosphere inside the desorption tower 10 is adjusted from RH0 (relative humidity of the measured CO2-containing gas) to RH2 (RH0>RH2) so that the planned relative humidity is within the above-mentioned predetermined humidity range. As the dry gas, a gas whose relative humidity has been reduced to a predetermined value by drying a CO2-containing gas (for example, air) and whose temperature has been adjusted to the same temperature as the CO2-containing gas (for example, normal temperature) is used. Further, the supply amount of the dry gas supplied into the desorption tower 10 can be calculated in advance by the control device 50 as an amount such that the planned relative humidity when the dry gas is supplied into the desorption tower 10 is within the above-mentioned predetermined humidity range. The planned relative humidity when the dry gas is supplied into the desorption tower 10 can be calculated, for example, by using the following formulas (3-1) and (3-2).

[0029] RH x2 =(RH2×SV0+W V / V R ) / SV R (3-1) RH2=(RH DG ×V DG +RH0×(V R -V DG )) / V R (3-2) RH x2 : Planned relative humidity [%RH] when the dry gas is supplied into the desorption tower 10 RH2: Relative humidity [%RH] of the humidity-controlled atmosphere in which the CO2-containing gas is humidity-controlled with dry gas SV0: Saturated water vapor amount of the supplied CO2-containing gas [g / m 3 W V : Amount of evaporated water vapor [g] during CO2 desorption V R : Volume inside the desorption tower 10 [m 3 SV R : Saturated water vapor amount of the CO2-containing gas at the planned temperature increase [g / m 3 RH DG : Relative humidity of the dry gas [%RH] V DG : Supply amount of the dry gas [m 3 RH0: Measured relative humidity of the CO2-containing gas [%RH]

[0030] And when it is determined in the first determination step S41 and the second determination step S42 that the planned relative humidity is equal to or greater than the lower limit and equal to or less than the upper limit of the predetermined humidity range (within the predetermined humidity range), or after the water vapor gas supply step S51 or the dry gas supply step S52, the process proceeds to the desorption step S60.

[0031] In the desorption step S60, CO2 is desorbed from the adsorbent 2 by raising the temperature of the atmosphere inside the desorption tower 10 to the planned temperature increase. Specifically, under the control of the control device 50, with the inlet valve 10a and the outlet valve 10b of the desorption tower 10 closed and the water vapor gas control valve 10c and the dry gas control valve 10d closed, the temperature of the atmosphere inside the desorption tower 10 measured by the temperature sensor 10t is raised from room temperature to the planned temperature increase (for example, 100°C) by the electric heater 10h. Thereby, CO2 is desorbed from the adsorbent (amine) contained in the adsorbent 2 stored inside the desorption tower 10.

[0032] ​​​​Next, in the recovery step S70, the CO2 desorbed from the adsorbent 2 is recovered. Specifically, under the control of the control device 50, the inlet valve 10a of the desorption tower 10 is closed, the outlet valve 10b is opened, and further, with the steam gas control valve 10c and the dry gas control valve 10d closed, the inside of the desorption tower 10 is forced to intake air by the vacuum pump 32, so that the gas containing the desorbed CO2 flows out from the inside of the desorption tower 10 as the recovered gas through the outlet valve 10b into the recovery flow path 18. Then, the moisture contained in the recovered gas is condensed and removed by the condenser 34, and the recovered gas from which the moisture has been condensed and removed is recovered by the CO2 recovery tank 36.

[0033] In the method for recovering CO2 according to the above-described one embodiment, before the desorption step S60, in the estimation step S30, the predicted relative humidity of the atmosphere inside the desorption tower 10 at the time of CO2 desorption is estimated. And when the estimated predicted relative humidity is not within a predetermined humidity range that can suppress the progress of the deterioration of both the porous carrier (silica) and the adsorbent (amine) contained in the adsorbent 2 within an allowable range, the relative humidity of the atmosphere inside the desorption tower 10 is adjusted in the steam gas supply step S51 or the dry gas supply step S52 so that the predicted relative humidity falls within the above-described predetermined humidity range. Thereby, in the desorption step S60, when the temperature of the atmosphere inside the desorption tower 10 is raised to the predicted temperature rise temperature in order to desorb CO2 from the adsorbent 2, the relative humidity of the atmosphere inside the desorption tower 10 can be made within the above-described predetermined humidity range. Therefore, the deterioration of both the porous carrier (silica) and the adsorbent (amine) contained in the adsorbent 2 can be suppressed. Accordingly, according to the embodiment of the present invention, as in the above-described one embodiment, the deterioration of both the carrier containing silica and the adsorbent containing amine contained in the adsorbent 2 can be suppressed.

[0034] Note that in the CO₂ recovery method according to one embodiment, after the water vapor gas supply step S51 and before the desorption step S60, and after the dry gas supply step S52 and before the desorption step S60, the relative humidity of the above humidification atmosphere is measured by the humidity sensor 10r, and the control device 50 determines whether the measured relative humidity of the humidification atmosphere is within the humidity range where the above planned relative humidity is within the predetermined humidity range. When it is determined as "no" in the inspection step, the control device 50 may further include a readjustment step of readjusting the relative humidity of the humidification atmosphere so that the above planned relative humidity is within the predetermined humidity range. Hereinafter, the CO₂ recovery method according to the embodiment will be described in more detail.

[0035] The CO₂ (carbon dioxide) recovery method according to the embodiment is a method of recovering CO₂ from a CO₂-containing gas by using a recovery device, and includes at least a measurement step, an adsorption step, an estimation step, a determination step, an adjustment step, and a desorption step.

[0036] The recovery device is not particularly limited as long as it includes a desorption tower and an adsorbent stored inside the desorption tower. For example, a device such as the recovery device according to the above one embodiment can be mentioned. The adsorbent is not particularly limited as long as it includes a carrier containing silica and an adsorbent containing an amine supported on the carrier. For example, an adsorbent such as the one according to the above one embodiment can be mentioned. Examples of the carrier containing silica include silica, silica alumina, clay minerals, etc. Examples of the adsorbent containing an amine include an adsorbent containing monoethanolamine, allylamine, polyethyleneimine, ethylenediamine, etc. The CO₂-containing gas to be the target for CO₂ recovery is not particularly limited as long as it is a gas containing CO₂ (carbon dioxide). For example, air supplied from the atmosphere, exhaust gas from an internal combustion engine or an industrial furnace, etc. can be mentioned.

[0037] In the measurement step, the temperature and relative humidity of the CO2-containing gas are measured. The method for measuring the temperature and relative humidity of the CO2-containing gas is not particularly limited as long as it is a method for measuring the temperature and relative humidity of the CO2-containing gas before it is supplied into the desorption tower. For example, the method in the measurement step according to the above-described one embodiment can be mentioned.

[0038] In the adsorption step, the CO2-containing gas is supplied into the desorption tower to adsorb the CO2 onto the adsorbent. The method for adsorbing CO2 onto the adsorbent is not particularly limited. For example, the method in the adsorption step according to the above-described one embodiment can be mentioned.

[0039] In the estimation step, based on the relationship between the temperature and relative humidity of the atmosphere of the CO2-containing gas in which the carrier is disposed and the water adsorption amount of the carrier, from the measured temperature and relative humidity of the CO2-containing gas and the planned temperature increase of the atmosphere inside the desorption tower at the time of CO2 desorption for desorbing the CO2 from the adsorbent, the planned relative humidity of the atmosphere inside the desorption tower at the time of CO2 desorption is estimated. The method for estimating the planned relative humidity is not particularly limited. For example, the method in the estimation step according to the above-described one embodiment can be mentioned. Here, the "relationship between the temperature and relative humidity of the atmosphere of the CO2-containing gas in which the carrier is disposed and the water adsorption amount of the carrier" specifically refers to the relationship between the temperature and relative humidity of the atmosphere of the CO2-containing gas and the water adsorption amount of the carrier when the temperature of the atmosphere of the CO2-containing gas in which the carrier is disposed is changed. For example, like the relationship according to the above-described one embodiment, it is the change in the water adsorption amount per unit weight of the carrier with respect to the relative humidity at each temperature of the atmosphere of the CO2-containing gas when the temperature of the atmosphere of the CO2-containing gas in which the carrier is disposed is changed.

[0040] In the determination step, it is determined whether or not the planned relative humidity is within a predetermined humidity range that can suppress the progress of deterioration of both the carrier and the adsorbent contained in the adsorbent within an allowable range. The method for determining whether or not the planned relative humidity is within the predetermined humidity range is not particularly limited, and examples thereof include the methods in the first determination step and the second determination step according to the above-described one embodiment.

[0041] Here, a predetermined humidity range that can suppress the progress of deterioration of both the carrier and the adsorbent contained in the adsorbent within an allowable range will be described. The carrier is a granular carrier containing silica. For this reason, when the process of adsorbing CO2 to the adsorbent and the process of desorbing CO2 from the adsorbent are repeatedly performed under conditions where the relative humidity of the atmosphere is too high, the carrier may aggregate and the surface area may decrease, leading to deterioration of the performance as a carrier for supporting the adsorbent. On the other hand, the adsorbent enables adsorption and desorption of CO2 by containing an amine having CO2 adsorption and desorption performance. Here, FIG. 3 is a diagram for explaining the chemical reaction of ethylenediamine, which is an example of an amine. As shown in FIG. 3, ethylenediamine becomes a carbamate by adsorbing CO2, and the carbamate becomes ethylenediamine by desorbing CO2. On the other hand, when the relative humidity of the atmosphere is too low and the water vapor in the atmosphere is too little, as shown in FIG. 3, the carbamate becomes ethyleneurea irreversibly by separating H2O and bonding C and N derived from CO2, and is likely to be deactivated. For this reason, under conditions where the relative humidity of the atmosphere is too low, for example, like ethylenediamine shown in FIG. 3, it is likely that the amine absorbs CO2 and is deactivated. Therefore, when the process of adsorbing CO2 to the adsorbent and the process of desorbing CO2 from the adsorbent are repeatedly performed under conditions where the relative humidity of the atmosphere is too low, the deterioration of the CO2 adsorption and desorption performance of the adsorbent may progress due to the progress of amine deactivation.

[0042] Therefore, the above predetermined humidity range is artificially set on the premise of the characteristics of the carrier containing silica and the adsorbent containing amine included in the adsorbent as described above, taking into account the usage conditions such as the temperature of the atmosphere in which the adsorbent is used and the service life of the adsorbent. Therefore, when the planned relative humidity is not above the lower limit of the above predetermined humidity range, there is a risk that the progress of the deterioration of the adsorbent (amine) cannot be suppressed within the allowable range when the adsorbent is used under the planned usage conditions. On the other hand, when it is not below the upper limit of the above predetermined humidity range, there is a risk that the progress of the deterioration of the carrier (silica) cannot be suppressed within the allowable range when the adsorbent is used under the planned usage conditions.

[0043] In the adjustment step, when the planned relative humidity is not within the above predetermined humidity range, the relative humidity of the atmosphere inside the desorption tower is adjusted so that the planned relative humidity is within the above predetermined humidity range. The method for adjusting the relative humidity of the atmosphere inside the desorption tower is not particularly limited. For example, the relative humidity of the atmosphere inside the desorption tower can be increased by supplying water vapor gas into the desorption tower as in the water vapor gas supply step according to one of the above embodiments, or the relative humidity of the atmosphere inside the desorption tower can be decreased by supplying dry gas into the desorption tower as in the dry gas supply step according to one of the above embodiments. Examples include methods of reducing the relative humidity of the atmosphere inside the desorption tower by supplying an inert gas such as N2 (nitrogen) or He (helium) into the desorption tower.

[0044] In the desorption process, after adjusting the relative humidity, the temperature of the atmosphere inside the desorption tower is raised to the scheduled temperature increase to desorb the CO2 from the adsorbent. The method of desorbing CO2 from the adsorbent by raising the temperature of the atmosphere inside the desorption tower to the scheduled temperature increase is not particularly limited. For example, like the desorption process according to the above-described one embodiment, a method of raising the temperature of the atmosphere inside the desorption tower to the scheduled temperature increase by a heater installed in the desorption tower can be mentioned. The scheduled temperature increase is not particularly limited as long as it is a temperature (for example, 100°C) at which the CO2 adsorbed by the adsorbent contained in the adsorbent can be desorbed.

Example

[0045] Hereinafter, the CO2 recovery method according to the embodiment will be described more specifically with reference to reference examples.

[0046] [Reference Example] Four adsorbents, which are examples of the adsorbent according to the above-described one embodiment, were prepared. As the carrier containing silica contained in the prepared adsorbent, Carrieract manufactured by Fuji Silysia Chemical Ltd. was used, and as the adsorbent containing an amine, polyethyleneimine manufactured by Fujifilm Wako Pure Chemical Corporation was used. For these adsorbents, after conducting a durability test using an example of the desorption tower according to the above-described one embodiment, a CO2 adsorption / desorption test was conducted to evaluate the performance retention rate.

[0047] (Durability Test) Durability tests 1 to 4 were respectively carried out on four adsorbents. The durability test conditions for durability tests 1 to 4 are shown in Table 1 below. Different types of durability test gases were used in durability tests 1 to 4. In each of durability tests 1 to 4, first, the adsorbent was stored inside the desorption tower. Next, the durability test gas shown in Table 1 below was heated to the durability temperature shown in Table 1 below, and then continuously supplied into the desorption tower through the inlet valve at a predetermined flow rate for the durability time shown in Table 1 below. Thereby, the durability test gas was made to flow into the cells of the honeycomb substrate of the adsorbent from the inflow side end. Then, the gas after contacting the adsorption layer of the adsorbent was made to flow out of the adsorbent to the outside from the outflow side end of the cell, and further flowed out to the outside from the inside of the desorption tower through the outlet valve.

[0048] (CO2 Adsorption and Desorption Test) For the adsorbent after each durability test, a CO2 adsorption and desorption test was carried out. In each adsorption and desorption test, first, an inert gas (He) was heated to 100 °C and then continuously supplied into the desorption tower through the inlet valve at a predetermined flow rate for 1 hour (pretreatment). Next, a CO2-containing gas at 30 °C was continuously supplied into the desorption tower through the inlet valve at a predetermined flow rate for 3 hours (adsorption treatment). Next, an inert gas (He) at 30 °C was continuously supplied into the desorption tower through the inlet valve at a predetermined flow rate for 30 minutes (purge treatment). Next, an inert gas (He) was heated to 100 °C and then continuously supplied into the desorption tower through the inlet valve at a predetermined flow rate for 1 hour (desorption treatment). And in the desorption treatment, the amount of CO2 desorbed from the adsorbent (hereinafter, may be abbreviated as "desorbed CO2 amount") was measured.

[0049] (Evaluation) For the adsorbent of the same kind of initial product (the adsorbent of the same kind for which the durability test has not been carried out), a CO₂ adsorption / desorption test under the same conditions was carried out, and in the desorption process, the amount of CO₂ desorbed from the adsorbent of the initial product (hereinafter, may be abbreviated as "desorbed CO₂ amount of the initial product") was measured. Then, by dividing the desorbed CO₂ amount of the adsorbent after each durability test by the desorbed CO₂ amount of the initial product, the performance retention rate (initial product ratio of desorbed CO₂ amount) [-] of the adsorbent after each durability test was determined. The results are shown in Table 1 below. Further, Fig. 4(a) is a graph showing the change in the performance retention rate with respect to the relative humidity of the durability test gas for two adsorbents for which durability tests 1 and 2 were respectively carried out, and Fig. 4(b) is a graph showing the change in the performance retention rate with respect to the relative humidity of the atmosphere of the adsorbent of the durability test gas for two adsorbents for which durability tests 3 and 4 were respectively carried out.

[0050]

Table 1

[0051] As shown in Table 1 above and Fig. 4(a), for the adsorbent for which durability test 1 using dry N₂ gas (relative humidity: 0%RH, CO₂ component ratio: 0 vol.%) as the durability test gas was carried out, the performance retention rate was "1.00", while for the adsorbent for which durability test 2 using wet N₂ gas (relative humidity: 80%RH, CO₂ component ratio: 0 vol.%) as the durability test gas was carried out, the performance retention rate was "0.84". Since there is no CO₂ component in dry N₂ gas and wet N₂ gas, in durability tests 1 and 2, it is impossible for the adsorbent (amine) contained in the adsorbent to absorb CO₂ and become deactivated. Therefore, the reason why the performance retention rate of the adsorbent for which durability test 2 was carried out decreased to "0.84" is considered to be that due to the high-humidity atmosphere of wet N₂ gas, the carrier (silica) contained in the adsorbent aggregated, resulting in a decrease in its surface area and a decrease in the frequency of contact between CO₂ and the adsorbent supported on the carrier. On the other hand, the reason why the performance retention rate of the adsorbent for which durability test 1 was carried out was maintained at "1" is considered to be that in the low-humidity atmosphere of dry N₂ gas, aggregation of the carrier (silica) contained in the adsorbent did not occur.

[0052] On the other hand, as shown in Table 1 and FIG. 4(b) above, in the adsorbent for which durability test 3 was carried out using a dry CO2-containing gas (relative humidity: 0%RH, CO2 component ratio: 10 vol.%) as the durability test gas, the performance retention rate was "0.06", whereas in the adsorbent for which durability test 4 was carried out using a moist CO2-containing gas (relative humidity: 80%RH, CO2 component ratio: 10 vol.%) as the durability test gas, the performance retention rate was "0.84". Since a CO2 component is present in the dry CO2-containing gas and the moist CO2-containing gas, in durability tests 3 and 4, when the relative humidity of the durability test gas is too low, the adsorbent (amine) contained in the adsorbent may absorb CO2 and become deactivated. On the other hand, since the dry CO2-containing gas has a low humidity like the dry N2 gas, it is considered that the carrier (silica) contained in the adsorbent did not aggregate in durability test 3 in the same manner as in durability test 1. For this reason, it is considered that the performance retention rate of the adsorbent for which durability test 3 was carried out decreased to "0.06" because the relative humidity of the durability test gas was too low and the reaction in which the adsorbent (amine) contained in the adsorbent absorbed CO2 and became deactivated occurred significantly. In addition, since the performance retention rate of the adsorbent for which durability test 4 was carried out was "0.84", which is about the same as the performance retention rate of the adsorbent for which durability test 2 with the same relative humidity of the durability test gas was carried out, it can be inferred that in durability test 4, the reaction in which the adsorbent (amine) contained in the adsorbent became deactivated did not occur and the carrier (silica) contained in the adsorbent aggregated.

[0053] As described above, the embodiments of the method for recovering CO2 of the present invention have been described in detail. However, the present invention is not limited to the above-described embodiments, and various design changes can be made without departing from the spirit of the present invention described in the claims.

Explanation of symbols

[0054] 2: Adsorbent, 4: Honeycomb substrate, 6: Adsorption layer, 10: Desorption tower, 10h: Electric heater, 10t: Temperature sensor, 10r: Humidity sensor, 12: CO2 supply channel, 12t: Temperature sensor, 12r: Humidity sensor, 50: Control device

Claims

【Claim 1】 A recovery device comprising a stripping tower and an adsorbent stored inside the stripping tower, the adsorbent including a carrier containing silica and an adsorbent containing an amine supported on the carrier is used, whereby CO ２ is recovered from a CO ２ -containing gas, which is a method of the CO ２ a step of measuring the temperature and relative humidity of the gas containing The foregoing CO ２ By supplying the containing gas into the inside of the desorption tower, the adsorbent adsorbs the CO ２ adsorbing step; and The temperature and relative humidity of the atmosphere of the CO-containing gas in which the carrier is disposed and the amount of adsorbed water of the carrier, based on which the measured CO ２ The temperature and relative humidity of the CO-containing gas and the CO desorbed from the adsorbent ２ From the planned temperature rise temperature of the atmosphere inside the desorption tower at the time of desorbing the CO ２ The step of estimating the planned relative humidity of the atmosphere inside the desorption tower at the time of desorbing the CO ２ when desorbing the CO ２ and estimating the planned relative humidity of the atmosphere inside the desorption tower at the time of desorbing the CO a step of determining whether or not the planned relative humidity is within a predetermined humidity range that can suppress the progress of deterioration of both the carrier and the adsorbent contained in the adsorbent within an allowable range; a step of adjusting the relative humidity of the atmosphere inside the desorption tower so that the planned relative humidity is within the predetermined humidity range when the planned relative humidity is not within the predetermined humidity range; After adjusting the relative humidity, the temperature of the atmosphere inside the desorption tower is raised to the planned temperature increase temperature, thereby desorbing the CO from the adsorbent ２ and a step of desorbing, characterized in that it comprises a method for recovering CO ２ .

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