Co2 absorption amount evaluation method and gas sampling system

Abstract

To provide a method for evaluating a CO2 absorption amount of a CO2 capturing material in soil to be evaluated, and a gas sampling system used for the same.SOLUTION: A method for evaluating a CO2 absorption amount comprises: applying a CO2 capturing material to a first section of soil; measuring an O2 exchange rate and a CO2 exchange rate between the soil and the atmosphere in both the first section and a second section of reference soil; obtaining a reference soil O2 / CO2 exchange ratio as a ratio of the O2 exchange rate to the CO2 exchange rate in the second section; and determining, from the reference soil O2 / CO2 exchange ratio, a contribution of the CO2 exchange rate of the CO2 capturing material in the CO2 exchange rates in the first section. A gas sampling system comprises: chambers which are provided respectively in the first section and the second section, cover a predetermined area of the soil surface and define a closed space; and a suction device for collecting gas components inside the chamber after a predetermined time.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for evaluating the amount of CO2 absorbed by a CO2 trapping material in soil and a gas collection system used therefor, and more particularly to a method for evaluating the amount of CO2 absorbed by a CO2 trapping material in soil to be evaluated and a gas collection system. [Background technology]

[0002] Carbon dioxide (CO2) emitted into the atmosphere is considered a problem as one of the causes of global warming, and methods have been proposed for immobilizing atmospheric CO2 using CO2 capture materials.

[0003] For example, Patent Document 1 discloses a method for mineralizing and immobilizing atmospheric CO2 as carbonates by microparticulating rocks containing alkaline earth metals and exposing them to air at temperatures between 15 and 50°C and relative humidity between 50 and 100%. While CO2 mineralization into rocks occurs naturally over a long period of time, artificial mineralization in a short period of time requires high-temperature and high-pressure environments or the addition of chemicals, which increases the energy load and tends to increase CO2 emissions. The method disclosed in this document, on the other hand, claims to enable low-cost, simple removal of CO2 from the air without the use of chemicals or large-scale facilities. The document lists a wide variety of rocks that can be used, including calcium oxide, magnesium oxide, magnesium-iron oxide, calcium-iron oxide, calcium silicate, and magnesium silicate. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-169854 Summary of the Invention [Problem to be solved by the invention]

[0005] CO2 is emitted not only into the air but also into the soil, and attempts are being made to remove CO2 from soil using CO2 capture materials. However, because the weathering (chemical reaction) rate of CO2 capture materials in soil depends not only on the type of capture material, but also on the CO2 concentration in the soil, moisture, temperature, and the amount of CO2 eluted outside the system, it is necessary to evaluate the amount of CO2 absorbed by CO2 capture materials in actual environments.

[0006] The present invention has been made in consideration of the above-mentioned circumstances, and its purpose is to provide a method for evaluating the amount of CO2 absorption by a CO2 capture material in the soil to be evaluated, and a gas collection system to be used for this method. [Means for solving the problem]

[0007] The evaluation method according to the present invention is a method for evaluating the amount of CO2 absorption by a CO2 trapping material in soil to be evaluated, and is characterized in that it comprises spreading the CO2 trapping material in a first section of the soil, measuring the O2 exchange rate and CO2 exchange rate between the soil and the atmosphere in each of the first section and a second section of a reference soil, determining a standard soil O2 / CO2 exchange ratio, which is the ratio of the O2 exchange rate and the CO2 exchange rate in the second section, and then determining the contribution of the CO2 exchange rate of the CO2 trapping material to the CO2 exchange rate in the first section from the standard soil O2 / CO2 exchange ratio.

[0008] According to this feature, it is possible to determine the amount of CO2 absorbed by the CO2 trapping material in the soil to be evaluated, and to provide an evaluation of the suitability of the CO2 trapping material for the soil to be evaluated.

[0009] In the above-mentioned invention, the O2 exchange rate and the CO2 exchange rate in the first compartment are respectively set to F1 O2 , F1 CO2 and the O2 exchange rate and the CO2 exchange rate in the second compartment are respectively set to F2 O2 , F2 CO2 Then, the O2 exchange rate in the first compartment is F1 O2is the reference soil O2 / CO2 exchange ratio (F2 O2 / F2 CO2 ) and divide by F1, the CO2 exchange rate in the first compartment. CO2 According to this feature, the amount of CO2 absorbed by the CO2 trapping material in the soil to be evaluated can be easily determined.

[0010] In the above-described invention, a chamber that covers a predetermined area on the surface of the soil and defines a closed space may be provided in each of the first and second compartments, and gas components in the chambers may be sampled after a predetermined time to measure the O2 exchange rate and the CO2 exchange rate. According to this feature, the amount of CO2 absorbed by the CO2 capture material in the soil to be evaluated can be easily determined using a simple device.

[0011] In the above-described invention, the CO2 capture material may be characterized in that it absorbs CO2 through chemical weathering. With this characteristic, the amount of CO2 absorbed by the CO2 capture material in the soil to be evaluated through chemical weathering can be easily determined using a simple device.

[0012] In the above-described invention, the reference soil may be set in the soil, and the second section may be provided in a section other than the first section of the soil. With this feature, the amount of CO2 absorbed by the CO2 capture material in the soil to be evaluated can be easily determined.

[0013] Furthermore, the gas sampling system according to the present invention is a gas sampling system used in the above-mentioned method for evaluating CO2 absorption amount, characterized in that it includes a chamber provided in each of the first and second compartments, covering a predetermined area on the surface of the soil and defining a closed space, and a suction device that samples gas components in the chamber after a predetermined time.

[0014] According to this feature, the amount of CO2 absorbed by the CO2 trapping material in the soil to be evaluated can be determined using a simple device, and an evaluation of the suitability of the CO2 trapping material for the soil to be evaluated can be provided.

[0015] In the above-described invention, the suction device may further include a circulation path that guides the gas components in the chamber to the outside and returns them to the chamber, and a collection mechanism that collects the gas components from the circulation path after a predetermined time. With this feature, the amount of CO2 absorbed by the CO2 capture material in the soil to be evaluated can be easily determined. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a block diagram of an example gas sampling system according to the present invention. [Figure 2] This figure shows the exchange of CO2 and O2 between (a) soil sprayed with CO2 capture material, (b) soil without CO2 capture material sprayed, and the atmosphere. [Figure 3] 1 is a graph showing the CO2 exchange rate separated into the contribution of the CO2 trapping material and other factors in an example using the evaluation method according to the present invention. [Figure 4] 1 is a graph showing an example of separating the CO2 exchange rates of the first and second compartments, assuming a reference soil O2 / CO2 exchange ratio of -1.1. DETAILED DESCRIPTION OF THE INVENTION

[0017] The method for evaluating the CO2 absorption amount of a CO2 trapping material according to the present invention and the gas sampling system used therein will now be described. First, the gas sampling system will be described.

[0018] As shown in Figure 1, gas sampling system 10 includes chamber 1, which covers a predetermined area on the surface of the soil to define a closed space, and suction device 2, which is in communication with the space within chamber 1 and collects gas components within the chamber. Suction device 2 includes circulation path 2a, which guides gas components within chamber 1 to the outside and then returns them to chamber 1. Circulation path 2a is equipped, in this order, with dehumidifying tube 21, which dehumidifies the gas circulating through circulation path 2a, pump 22, which sucks gas into circulation path 2a, a collection mechanism, which collects gas components from circulation path 2a, and back pressure valve 24.

[0019] For example, magnesium perchlorate can be used for the dehumidifying tube 21. For example, a diaphragm pump can be suitably used for the pump 22. For example, a gas sampling flask 23 can be used as the gas sampling mechanism. The gas sampling flask 23 can be attached to the circulation path 2a to communicate with its interior, and has valves on both ends so that it can be removed after achieving an airtight seal. Furthermore, a valve is provided at the end of the circulation path 2a where the gas sampling flask 23 is attached so that the portion can also be airtight.

[0020] The back pressure valve 24 is provided to maintain a constant pressure within the chamber 1 when gas is introduced from the chamber 1 to the circulation path 2a. This pressure is preferably set to, for example, atmospheric pressure plus 0.1 MPa. A thin tube 11 is provided on the top surface of the chamber 1, connecting the chamber 1 to the outside air. The thin tube 11 may be, for example, a tube with an inner diameter of 1 / 16 inch. The back pressure valve 24 and thin tube 11 are provided to suppress pressure fluctuations within the chamber 1 that accompany the collection of gas from the circulation path 2a, and to prevent forced gas exchange that differs from soil respiration due to a pressure difference between the soil and the atmosphere within the chamber 1. The chamber 1 is also provided with a thermometer (not shown) that measures the temperature of the atmosphere inside.

[0021] Next, a method for evaluating the CO2 absorption amount of a CO2 trapping material using the gas sampling system 10 will be described.

[0022] As shown in Figure 2, CO2 is released and O2 is absorbed between the soil and the atmosphere through respiration by soil microorganisms and plant roots, a process known as soil respiration (see Figure 2(b) in particular). Meanwhile, in soil where CO2 capture materials are sprayed (see Figure 2(a)), CO2 absorption by the CO2 capture materials occurs in addition to soil respiration. Here, CO2 absorption by CO2 capture materials is considered to include all CO2 absorption without the involvement of O2, such as chemical weathering. Figure 2 shows an example in which mafic rock, which absorbs CO2 through chemical weathering, is used as the CO2 capture material. As mentioned above, to evaluate the CO2 absorption amount by CO2 capture materials in a real environment, this example sprays CO2 capture materials on soil and measures CO2 concentration. However, even if the CO2 exchange rate is calculated from the changes in CO2 concentration, changes in CO2 concentration in a real environment are affected by soil respiration.

[0023] Therefore, in the method for evaluating the CO absorption amount of a CO2 trapping material according to this embodiment, the soil-atmosphere O2 exchange rate and CO2 exchange rate are measured in a first section where the CO2 trapping material is sprayed (see (a) in the figure) and a reference soil where the CO2 trapping material is not sprayed, typically a second section other than the first section (see (b) in the figure). Next, the ratio of the O2 exchange rate to the CO2 exchange rate in the second section, i.e., the reference soil O2 / CO2 exchange ratio, is calculated. The reference soil O2 / CO2 exchange ratio is then used to calculate the contribution of the CO2 exchange rate due to chemical weathering of the CO2 trapping material to the CO2 exchange rate in the first section. Note that the reference soil is a simulated soil located in a location other than the soil where the first section is located and that can provide the above-mentioned reference soil O2 / CO2 exchange ratio. It is preferable that factors affecting the O2 / CO2 exchange ratio, such as absorption and release of O2 and CO2, other than the CO2 trapping material in the soil to be evaluated, are common between the reference soil and the soil to be evaluated. For example, if the only factor in the soil to be evaluated is soil respiration, and does not include absorption or release of O2 or CO2 resulting from chemical changes in inorganic components that vary from region to region, it is preferable that the same is true for the reference soil.

[0024] Specifically, the experiment was carried out as follows. First, a first section was prepared in which CO2 capture material was sprayed onto the soil, and a second section was prepared in which CO2 capture material was not sprayed. In the first section, crushed peridotite powder (olivine sand) was mixed into the soil at 10% by mass to a depth of 15 cm from the surface. Peridotite is a type of mafic rock that absorbs CO2 through chemical weathering. Chamber 1 of the gas sampling system 10 was installed in each of the first and second sections. That is, chamber 1 covered a predetermined area of the soil surface to define a closed space. Chamber 1 was a cylindrical metal chamber with an inner diameter of 50 cm and a height of 30 cm. Yams were grown in both the first and second sections, but yam leaves were prevented from entering chamber 1 to avoid interference with the respiration and photosynthesis of the yam leaves.

[0025] Chamber 1 was provided with a lid (not shown), allowing outside air to be introduced into chamber 1. After the lid was closed, gas was sampled multiple times at predetermined time intervals. Here, after closing the lid, gas was sampled four times every seven minutes, yielding four gas sampling flasks 23 in each of the first and second compartments. The volume of gas sampling flask 23 was 760 mL, and gas was sampled at atmospheric pressure + 0.1 MPa.

[0026] The CO2 and O2 concentrations of each sampled gas were measured using a mass spectrometer. An isotope ratio mass spectrometer, for example, can be suitably used as the mass spectrometer. The Ar concentration was also measured to correct for minute changes in the O2 concentration due to temperature changes during gas sampling. Correction of the O2 concentration by Ar is well known, and therefore will not be described here.

[0027] The soil / atmosphere O2 and CO2 exchange rates were calculated from the measured O2 and CO2 concentrations. First, the total volume of air in chamber 1 was calculated from the volume and temperature of chamber 1, and this was multiplied by the measured O2 and CO2 concentrations, respectively, to calculate the O2 and CO2 amounts in chamber 1. The rates of change in O2 and CO2 amounts were calculated from the changes in the O2 and CO2 amounts of each gas sampled at specified time intervals. This was divided by the area of the soil surface covered by chamber 1 to obtain the soil / atmosphere O2 and CO2 exchange rates per unit area of the soil surface.

[0028] Here, the O2 exchange rate and CO2 exchange rate in the first compartment are respectively expressed as F1 O2 , F1 CO2 The O2 exchange rate and the CO2 exchange rate in the second compartment are respectively set as F2 O2 , F2 CO2 Then, the standard soil O2 / CO2 exchange ratio is calculated from the exchange rate of the second plot where no CO2 capture material was spread, F2 O2 / F2 CO2 Since there is no absorption or emission of O2 by the CO2 capture material, the O2 balance is considered to be entirely due to the reference soil. If the reference soil O2 / CO2 exchange ratio is the same for the first and second sections, then the O2 exchange rate for the first section, F1 O2 The reference soil O2 / CO2 exchange ratio of F2 O2 / F2 CO2 Dividing this by 1 gives the CO2 exchange rate F1 CO2 This is the contribution of the reference soil. Therefore, this CO2 exchange rate F1 CO2 Subtracting the contribution of the reference soil from the CO2 exchange rate F1 CO2 The contribution of the CO2 exchange rate of the CO2 capture material can be obtained.

[0029] In other words, if the contribution of the CO2 exchange rate of the CO2 capture material is x, it can be calculated using the following formula. x=F1 CO2 -F1 O2 / (F2 O2 / F2 CO2 )

[0030] In this way, by determining the contribution of the CO2 exchange rate due to chemical weathering of the CO2 capture material, it is possible to evaluate the amount of CO2 absorbed by the CO2 capture material due to chemical weathering in the soil being evaluated, which in turn makes it possible to evaluate the suitability of the CO2 capture material for the soil being evaluated.

[0031] Figure 3 shows an example of separating the CO2 exchange rate measured using the method described above into the contribution of the reference soil and the contribution of the CO2 trapping material. The left half of the figure shows the contribution of the reference soil, and the right half shows the contribution of the CO2 trapping material. In this way, it was possible to separate the contribution of the CO2 trapping material from the CO2 exchange rate. Note that the CO2 exchange rate in the figure is shown in carbon equivalent units.

[0032] The reference soil O2 / CO2 exchange ratio in the second plot, where no CO2 capture material was applied, was -1.51. According to data accumulated by the inventors, the reference soil O2 / CO2 exchange ratio is generally approximately -1.1. Note that this data was obtained from soil where factors such as O2 and CO2 absorption and release that affect the O2 / CO2 exchange ratio are solely due to soil respiration. Therefore, the reference soil O2 / CO2 exchange ratio is equal to the soil respiration O2 / CO2 exchange ratio. In other words, the above-mentioned "-1.51" value suggests that CO2 absorption occurs in addition to soil respiration. Therefore, investigation of the measured soil revealed that it contained weakly alkaline limestone. This suggests that inorganic CO2 exchange between the soil and the atmosphere was occurring even without the application of CO2 capture material.

[0033] Therefore, as shown in Figure 4, the CO2 exchange rates were separated in the same manner as above for both the first plot where the CO2 capture material was sprayed and the second plot where it was not sprayed, using the above-mentioned standard soil O2 / CO2 exchange ratio (soil respiration O2 / CO2 exchange ratio of "-1.1") instead of the standard soil O2 / CO2 exchange ratio.

[0034] First, the left half of the figure (contribution of the reference soil) will be explained. The left side is the second section, and the right side is the first section. In other words, the left side is the CO2 exchange rate of soil where no CO2 trapping material was applied, with the contribution of the reference soil (soil respiration with an O2 / CO2 exchange ratio of -1.1) separated from the CO2 exchange rate. The right side is the CO2 exchange rate of soil where CO2 trapping material was applied, with the contribution of the reference soil (soil respiration with an O2 / CO2 exchange ratio of -1.1) separated from the CO2 exchange rate.

[0035] Meanwhile, in the right half of the figure (CO2 capture material and other contributions), the left side is the second section and the right side is the first section. In other words, the left side is the CO2 exchange rate of soil where no CO2 capture material was applied, separated from the contributions of the reference soil (soil respiration with an O2 / CO2 exchange ratio of -1.1) (inorganic contributions from limestone, etc.). The right side is the CO2 exchange rate of soil where CO2 capture material was applied, separated from the contributions of the reference soil (soil respiration with an O2 / CO2 exchange ratio of -1.1) (inorganic contributions from the CO2 capture material and limestone, etc.). In other words, the difference A between the left and right sides of the right half of the figure corresponds to the contribution of the CO2 capture material to the CO2 exchange rate, and matches the separation of the contribution of the CO2 capture material from the CO2 exchange rate in Figure 3 above.

[0036] As described above, the method of this embodiment uses the reference soil O2 / CO2 exchange ratio in the second section, where no CO2 trapping material was sprayed, to separate the contribution of the CO2 trapping material from the CO2 exchange rate in the first section, where the CO2 trapping material was sprayed. Therefore, according to this method, even if the soil contains substances that exchange inorganic CO2 other than soil respiration, as shown in Figure 3, it is possible to separate only the contribution of the CO2 trapping material from the CO2 exchange rate. In other words, the CO2 absorption amount of the CO2 trapping material can be evaluated regardless of the soil.

[0037] Furthermore, by comparing the O2 / CO2 exchange ratio with a reference value (value at a reference point) (which can be set arbitrarily, for example, -1.1, the soil respiration value accumulated by the inventors), CO2 capture materials with CO2 absorption properties that do not affect the O2 exchange ratio, as with chemical weathering, can be evaluated. Furthermore, just as in this example, the soil itself contains limestone, which absorbs CO2 in addition to soil respiration, and its CO2 absorption amount was evaluated, it is also possible to evaluate the CO2 absorption amount of soil in a specific region. The mafic rock used as a CO2 capture agent in this example is also naturally occurring, and in areas where this rock is produced, it can be used to evaluate the impact of excavation, etc. on surrounding soil, in addition to evaluating the existing soil in the surrounding area.

[0038] Although the embodiments of the present invention and modifications based thereon have been described above, the present invention is not necessarily limited thereto, and a person skilled in the art will be able to find various alternative embodiments and modifications without departing from the spirit of the present invention or the scope of the appended claims. [Explanation of symbols]

[0039] 1 chamber 2 Suction device 2a Circulation Route 10 Gas sampling system 23 Gas sampling flask (gas sampling mechanism)

Claims

1. CO in the soil being evaluated ２ CO of the adsorption material ２ A method for evaluating an absorption amount, comprising: adding the CO ２ Spreading the collection material, The soil / air O in each of the first section and the second section of the reference soil. ２ Exchange rate and CO ２ Measure the exchange rate, In the second section, ２ Exchange rate and the CO ２ The ratio of the exchange rates of the reference soil O ２ / CO ２ After determining the exchange ratio, ２ The CO exchange rate ２ CO of the adsorption material ２ The contribution of the exchange rate to the reference soil O ２ / CO ２ CO ２ Methods for assessing absorption.

2. The O in the first section ２ Exchange rate and the CO ２ The exchange rate is F1 Ｏ２ , F1 ＣＯ２ year, The O in the second section ２ Exchange rate and the CO ２ The exchange rate is F2 Ｏ２ , F2 ＣＯ２ Then, The O in the first section ２ F1, which is the exchange rate Ｏ２ the reference soil O ２ / CO ２ The exchange ratio is (F2 Ｏ２ / F2 ＣＯ２ ) and then dividing the CO ２ F1, which is the exchange rate ＣＯ２ Subtract the CO ２ CO of the adsorption material ２ 2. The method according to claim 1, wherein the CO exchange rate is determined. ２ Methods for assessing absorption.

3. A chamber covering a predetermined area on the surface of the soil and defining a closed space is provided in each of the first section and the second section, and gas components in the chamber are sampled after a predetermined time. ２ Exchange rate and the CO ２ 3. The CO exchange rate measurement method according to claim 1, wherein the CO exchange rate is measured. ２ Methods for assessing absorption.

4. The CO ２ The adsorption material is chemically weathered to remove CO ２ 3. The CO absorber according to claim 1, wherein the CO absorber is a ２ Methods for assessing absorption.

5. 3. The CO2 measurement method according to claim 1, wherein the reference soil is set in the soil, and the second section is provided in a section other than the first section of the soil. ２ Methods for assessing absorption.

6. CO according to claim 1 or 2 ２ A gas sampling system for use in an absorption amount evaluation method, comprising: a chamber provided in each of the first and second sections, covering a predetermined area on the surface of the soil and defining a closed space; and a suction device that collects gas components in the chamber after a predetermined time.

7. 7. The gas sampling system according to claim 6, wherein the suction device includes a circulation path that guides the gas components in the chamber to the outside and then returns them to the chamber, and further includes a sampling mechanism that samples the gas components from the circulation path after a predetermined time.

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