JP2023147117A - Method for immobilizing carbon dioxide - Google Patents

Abstract

To provide a highly efficient production method of a cement hydrate, capable of immobilizing CO2 to a cement hydrate, and reducing the possibility of occurrence of an alkali aggregate reaction (ASR) of concrete when being added to cement.SOLUTION: A production method of a cement hydrate as a method for immobilizing CO2 to a cement hydrate includes a CO2 blowing step of putting a cement hydrate and water 12 into a container 10 and blowing CO2 14 into the container 10 while stirring the mixed liquid of the cement hydrate and the water 12. In the CO2 blowing step, a CO2 blowing speed is 3,600 kg/t h or less, and a CO2 blowing amount is more than 800 kg/t.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for immobilizing carbon dioxide in cement hydrate.

Conventionally, in order to prevent global warming, it has been required to reduce _CO2 emissions into the atmosphere. As one method, Patent Document 1 discloses a technique of fixing CO ₂ using an alkaline earth metal-containing substance. Examples of the alkaline earth metal-containing substance include concrete waste generated by demolishing concrete buildings, steel slag as a by-product generated in the steel manufacturing process, and the like. Conventionally, these substances have been used for aggregates and the like, but they can be used more effectively by fixing _CO2 .

In the method disclosed in the above-mentioned literature, CaCO ₃ is generated by mixing CO ₂ into the ready-mixed concrete generated at a ready-mixed concrete factory or construction site by adding water to make a slurry-like ready-mixed concrete. Fix _CO2 . The generated CaCO ₃ is used as a material for concrete.

Japanese Patent Application Publication No. 2007-190538

However, although methods for fixing _CO2 in cement hydrate and methods for utilizing the materials have been developed, there is still no knowledge regarding highly efficient manufacturing conditions for the above methods assuming mass production. Not yet. Furthermore, alkaline aggregate reaction (ASR) is known to be one of the factors that decreases the strength of concrete. When alkaline aggregate reaction (ASR) occurs, cracks occur in concrete and the strength of concrete decreases. In order to use concrete structures for as long as possible, it is desirable to reduce the possibility of occurrence of alkaline aggregate reaction (ASR).

The present invention was made to solve the above problems, and it is possible to efficiently fix _CO2 in cement hydrate, and furthermore, when added to cement, it reduces the alkaline aggregate reaction (ASR) of concrete. An object of the present invention is to provide a manufacturing method that can reduce the possibility of such occurrence.

The method of fixing CO ₂ in cement hydrate according to the present invention involves putting cement hydrate and water in a container, and blowing CO ₂ into the container while stirring the mixture of cement hydrate and water. In the CO ₂ injection process, the CO ₂ injection rate is 3600 kg/t·h or less, and the CO ₂ injection amount is more _than 800 kg/t.

According to the method according to the present invention, it is possible to provide a manufacturing method that can efficiently fix _CO2 in cement hydrate and reduce the possibility of occurrence of alkaline aggregate reaction (ASR) in concrete. I can do it.

In addition, in the CO ₂ injection step of the method of fixing CO ₂ to cement hydrate of the present invention, the liquid-solid ratio of water and cement hydrate is 3 to 8, and the injection water depth in the CO ₂ mixture is It is preferable that the ratio of the maximum bubble diameter of CO ₂ at the water depth is 400 or more.

According to the CO ₂ injection process of the present invention, the liquid-solid ratio and the ratio between the injection water depth in the CO ₂ mixture and the maximum bubble diameter of CO ₂ at the water depth are set to values within a suitable range. I can do it. Therefore, CO ₂ can be efficiently fixed in cement hydrate.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of an apparatus 100 for fixing _CO2 into cement hydrate, which is an embodiment of the present invention. FIG. 1 is a schematic diagram of a test device implementing the present invention.

<Embodiment>
With reference to FIG. 1, a manufacturing method for fixing CO ₂ in cement hydrate according to the present embodiment will be described. The CO ₂ fixation device 100 for cement hydrate used in the above method includes a container 10 , a CO ₂ supply device 20 , and a stirring device 30 . The CO ₂ fixation device 100 is a device that efficiently produces cement hydrate in which CO ₂ is fixed in large quantities. The method of the present invention can efficiently fix CO ₂ in cement hydrate, and uses calcium silicate hydrate (C-S-H), which has a low ratio of calcium (Ca) to silicon (Si), and Can produce pozzolan. Furthermore, concrete containing reactive aggregates is known to cause alkaline aggregate reaction (ASR). Since the above-mentioned substance has alkaline substance adsorption properties, concrete to which the above-mentioned substance is added can suppress alkaline aggregate reaction (ASR) and reduce the possibility of a decrease in the strength of concrete.

The container 10 is a device into which water and concrete waste are input to fix _CO2 . Concrete waste materials include waste concrete produced from demolished concrete buildings, waste sludge produced during concrete production, waste lightweight aerated concrete (waste ALC), and the like. Concrete waste may contain aggregates other than cement hydrate, as long as the amount of cement hydrate is within a specified range. In order to efficiently fix CO ₂ , the concrete waste is crushed into small pieces by a crusher (not shown) and then input. Furthermore, materials other than cement hydrate, such as aggregate, may be separated and sorted. The finely crushed concrete powder 11 does not easily settle even if it is poured into water, and the CO ₂ fixation reaction can be carried out efficiently. The water 12 put into the container 10 together with the concrete powder 11 is, for example, industrial water.

Water 12 and concrete powder 11 are charged into a container 10 and mixed to produce a sludge slurry 13. The liquid-solid ratio, which is the mixing ratio of water 12 and concrete powder 11, is preferably in the range of 3 to 8. When the liquid-solid ratio is less than 3, that is, when the solid content is relatively large, the CO ₂ supply device 20 may become clogged and the necessary CO ₂ may not be supplied. Further, when the liquid-solid ratio is 8 or more, that is, when the solid content is relatively small, the amount of water is excessive compared to the amount of concrete powder 11, and the container 10 becomes too large. Therefore, the liquid-solid ratio is preferably within the above range.

The CO ₂ supply device 20 supplies CO ₂ 14 to the container 10 . The CO ₂ supply device 20 includes a supply pipe 21 , a flow rate adjustment device 22 , and an aeration device 23 . One end of the supply pipe 21 is connected to a supply source of CO ₂ 14 (not shown). The supply pipe 21 has one or more branches provided in the middle of the supply pipe 21 , and the other ends of each of the supply pipes 21 are connected to a plurality of air diffusers 23 . The gas to be supplied does not need to be 100% CO ₂ gas, and factory exhaust gas containing N ₂ and O ₂ may be used, as long as the actual amount of CO ₂ supplied is within the specified range. good.

The CO ₂ supply device 20 includes a plurality of flow rate adjusting devices 22 that can each adjust the amount of CO 2 supplied to the plurality of air diffusers 23 , or a CO ₂ supply amount to all of the plurality of air diffusers 23 , in the middle part of the supply pipe 21 . _2. It has at least one of one flow rate adjustment device 22 that can adjust the supply amount. Each of the one or more flow regulating devices 22 may include a solenoid valve and be configured to be electrically controllable. Further, a surplus of the supplied CO ₂ 14 is discharged from the container 10 as exhaust gas 15 .

The air diffuser 23 is a device that includes a porous structure and releases the introduced CO ₂ 14 as fine bubbles. One or more air diffusers 23 are arranged in the container 10 so that the entire air diffuser 23 is immersed in the sludge slurry 13 contained in the container 10. The porous structure of the air diffuser 23 is formed of a porous member containing a large number of holes. The porous structure may be covered with another member except for the surface where the CO ₂ release surface is formed. Alternatively, the porous structure may be formed of a member in which no pores are formed except on the surface where the CO ₂ release surface is formed. Alternatively, the porous structure may be a member such as a hollow member having a large number of holes processed on its surface. For example, it may be a hollow tube with many holes drilled on its surface. Alternatively, a device that atomizes CO ₂ using a blade or the like may be used. Moreover, the water depth at which the air diffuser 23 is arranged is desirably arranged close to the bottom side of the container 10 so that CO ₂ is efficiently fixed. For example, the water depth of the aeration device 23 is preferably at least 50% or more, preferably 60% or more, and more preferably 70% or more of the designed maximum water depth of the container 10. Further, a plurality of CO ₂ fixation devices may be provided, and any shape of the device is possible as long as the total contact time of CO ₂ and sludge slurry is the same.

The CO ₂ 14 introduced into the aeration device 23 is released into the sludge slurry 13 as bubbles with a diameter of 1 mm or less. When the CO ₂ 14 injection water depth, that is, the water depth of the CO ₂ release surface of the diffuser 23 where CO ₂ 14 bubbles are generated, is L, and the diameter of the CO ₂ 14 bubbles at that water depth is M, L/ The air diffuser 23 is provided so that M≧400. When a plurality of air diffusers 23 are installed at different heights, the CO ₂ 14 injection water depth is determined by the maximum water depth of the CO ₂ release surface of the air diffuser 23 where CO ₂ 14 bubbles are generated. Let it be L.

The air diffuser 23 is configured to emit CO ₂ 14 from the upper surface, but the CO ₂ emitting surface of the air diffuser 23 is not only the upper surface but also the side and/or lower surfaces. It may also be configured in combination. When the CO ₂ release surface of the air diffuser 23 is on the side surface or the bottom surface, clogging due to falling concrete powder 11 in the sludge slurry 13 is less likely to occur than when the CO ₂ release surface is on the top surface. Therefore, the period of periodic maintenance of the air diffuser 23 can be extended. The diffuser 23 may be one or more as long as it can release a specified amount of CO ₂ 14 blown into the air diffuser 23 . Furthermore, in the case of a plurality of containers, it is efficient to arrange them at approximately equal intervals along the wall of the container 10 in the periphery.

The stirring device 30 is a device that stirs the sludge slurry 13 so that CO ₂ 14 can be efficiently fixed. The stirring device 30 continues to rotate at a constant rotation speed by an electric motor (not shown) and stirs the sludge slurry 13. The stirring device 30 is arranged approximately at the center of the container 10 so that the stirring device 30 efficiently stirs the sludge slurry 13. The stirring device 30 includes a rotating shaft 31 rotated by an electric motor, and stirring blades 32 connected to the lower end of the rotating shaft 31.

The stirring blades 32 are formed so as to have an inner diameter of the container 10 or an inner dimension such as a maximum width across the container 10 by 30% or more. Further, the water depth of the stirring blades 32 is arranged so as to be at least 50% of the designed maximum water depth of the sludge slurry 13 placed in the container 10, that is, at a position that is half of the water depth or deeper. The water depth at which the stirring blades 32 are arranged is set as close to the bottom side of the container 10 as possible so that even when the concrete powder 11 contained in the sludge slurry 13 sinks to the bottom of the container 10, it can be easily scooped up. It is desirable that it be placed. For example, the water depth may be at least 50% or more, preferably 60% or more, and more preferably 70% or more of the maximum designed water depth of the container 10. Regarding the relationship between the stirring blades 32 and the aeration device 23 in the water depth direction, they are arranged at substantially the same water depth position. The positional relationship of the stirring blade 32 with respect to the aeration device 23 in the water depth direction can be above the aeration device 23, within the range of the aeration device 23 in the water depth direction, or below the aeration device 23. A plurality of stirring blades 32 may be arranged, and the total length thereof may be 30% or more of the inner diameter of the container 10 or the inner dimension such as the width across the maximum part.

Note that a circulation device for the sludge slurry 13 (not shown) may be provided together with the stirring device 30 or in place of the stirring device 30. The circulation device has a pump and piping in front and behind the pump, and the tip of the piping in front of the pump is placed at or around the bottom of the container 10, and the tip of the piping behind the pump is placed in the container 10. It is placed at the top within 10. The bottom surface of the container 10 or the sludge slurry 13 around the bottom surface is sucked by the pump and circulated to the upper part of the sludge slurry 13 in the container 10. Thereby, CO ₂ is efficiently fixed.

In the above device, water 12 and concrete powder 11 are put into a container 10 so as to have a predetermined liquid-solid ratio, and a sludge slurry 13 is generated with a uniform mixing degree by a stirring device 30. . The predetermined liquid-solid ratio is 3-8. In this state, the CO ₂ supply device 20 starts supplying CO ₂ at a predetermined CO ₂ blowing rate. The predetermined CO ₂ blowing rate is 3600 kg/t·h or less. The CO ₂ injection continues for a predetermined CO ₂ injection time, and a predetermined amount of CO ₂ is blown into the sludge slurry 13 . The predetermined CO ₂ injection amount is greater than 800 kg/t. By the above method, CO ₂ is efficiently fixed in the concrete powder 11. After one CO ₂ fixation operation is completed, the sludge slurry 13 is discharged from the container 10. Water 12 and concrete powder 11 are put into the container 10 again. The discharged sludge slurry 13 is left as it is, or is dehydrated and dried, and the concrete powder 11 in which CO ₂ is fixed is used as a raw material for cement.

Regarding the supply of CO ₂ 14 to the container 10, the embodiment has been described in which the CO ₂ 14 is supplied from a pressure vessel filled with the CO 2 14, but other embodiments may be used. CO ₂ originating from exhaust gas from the factory where the container 10 is located or an adjacent factory may be supplied via piping installed in the factory. For example, CO ₂ discharged from a cement factory may be continuously supplied through a supply pipe. By doing so, the amount of CO ₂ emitted from the factory will be reduced.

In the present invention, in the method of fixing CO ₂ in cement hydrate, the target value of the amount of CO ₂ fixed in cement hydrate is set to be 300 kg/t-sludge' or more. Among the implementation conditions that can obtain a higher amount of CO ₂ fixed, calcium silicate hydrate (C-S-H) has a low ratio of calcium (Ca) to silicon (Si). (hereinafter referred to as low Ca calcium silicate hydrate) and calcium silicate hydrate with a high ratio of calcium (Ca) to silicon (Si) (hereinafter referred to as high Ca calcium silicate hydrate) ) and the implementation conditions that can increase the content of pozzolan were determined. The present invention can reduce the alkali concentration in concrete by increasing the above-mentioned substances having high alkali adsorption properties, and as a result, can suppress the alkaline aggregate reaction (ASR) of concrete. Regarding the predetermined value, the production ratio of high Ca calcium silicate hydrate and low Ca calcium silicate hydrate in the sludge, that is, high Ca calcium silicate hydrate/low Ca calcium silicate water For Japanese products, the target value was set to 0.9 or less. Further, the target value for the content of pozzolan in the sludge was set at 50 (kg/t-sludge) or more.

Next, with reference to FIG. 2, a test apparatus and results regarding tests conducted regarding this embodiment will be described. The test apparatus was basically configured according to the above apparatus. In addition, in the test apparatus shown in FIG. 2, the same or corresponding members are given the same reference numerals, and the description thereof will be omitted. The test device includes a container 10, a CO ₂ supply device 20, and a stirring device 30, and has basically the same configuration as the CO ₂ fixation device 100 in FIG. 1. The container 10 was placed in a constant temperature and humidity device 40, and the test was started at 20°C. The stirring device 30 includes a rotating shaft 31 rotated by an electric motor, and stirring blades 32 connected to the lower end of the rotating shaft 31. The position of the CO ₂ release surface of the aeration device 23 and the stirring blade 32 are arranged at a depth of about 70% of the water depth.

The stirring blades 32 are formed so as to have an inner diameter of the container 10 or an inner dimension such as a maximum width across the container 10 by 30% or more. Further, the water depth of the stirring blades 32 is arranged so as to be at least 50% of the designed maximum water depth of the sludge slurry 13 placed in the container 10, that is, at a position that is half of the water depth or deeper. The water depth at which the stirring blades 32 are arranged is set as close to the bottom side of the container 10 as possible so that even when the concrete powder 11 contained in the sludge slurry 13 sinks to the bottom of the container 10, it can be easily scooped up. It is desirable that it be placed. For example, the water depth may be 60% or more, preferably 70% or more of the designed maximum water depth of the container 10.

[Preparation of raw materials]
Container 10 was charged with powdered ready-mixed concrete sludge supplied from a ready-mixed concrete factory. The provided ready-mix concrete sludge was selected from the time it had been produced for a short period of time, and the drying process started 24 hours after it was supplied. The provided raw concrete sludge was pulverized and thoroughly dried using a drying oven to obtain dried sludge. The Blaine specific surface area of the dried sludge at this time was Bl'=14230 cm ² /g (ρ=2.61 g ^{/cm 3} , e=0.74). Thereafter, the dried sludge was crushed. In the crushing process, a 10 kg sample was crushed for 30 seconds using a ball mill. Table 1 shows the chemical composition of the dried sludge used. As is clear from Table 1, the chemical composition of the dried sludge used in this test is comparable to that of commercially available cement, and it can be treated as a cement hydrate that does not contain aggregate. The particle size of the dried sludge used is 0.4 mm or less.

[Carbonation treatment]
Sludge slurry 13 was prepared by adding the dried sludge prepared in the above manner to 1000 mL of ion-exchanged water so as to have a predetermined liquid-solid ratio. Thereafter, while stirring the sludge slurry 13 in a constant temperature and humidity device (incubator), CO ₂ was blown in at a predetermined flow rate and time using an aeration device 23. The flow rate of _CO2 was controlled using a float flow meter connected to the gas cylinder. After the blowing, the slurry 13 was subjected to suction filtration to separate the solid phase and the liquid phase. The separated solid phase was dried at 105°C to obtain carbonated sludge. The carbonated sludge was crushed and passed through a sieve with a roughness of 600 μm before various analyses.

The calculation method for each characteristic value is as follows.
(1) CO ₂ injection amount (CO ₂ supply amount) (kg-CO ₂ /t-sludge)
_CO2 /sludge=( _QCO2 ×t)/Msludge
QCO ₂ : CO ₂ gas flow rate (kg-CO ₂ /h) measured by a flow meter connected to a CO ₂ gas cylinder
t: Time from start to end of blowing (h)
Msludge: Mass of input sludge (kg)
(2) Amount of _CO2 fixed (kg/t-sludge')
CO ₂ ^cap = CO ₂ ^TG × (100/(100-ig.loss ^TG )
CO ₂ ^cap : CO ₂ amount (%) contained in ignited carbonated sludge
CO ₂ ^TG : CO ₂ amount (%) calculated by TG-DTA
ig. loss ^TG : Loss value (%) up to 1000℃ in TG-DTA
TG-DTA was performed using a differential thermogravimetric simultaneous measuring device TG-DTA6300 manufactured by Seiko Instruments Co., Ltd. under the conditions of temperature range: room temperature to 1000°C, heating rate: 10°C/min, atmosphere: _N2. Measurements were taken. In addition, the following unit corrections were made.
CO ₂ (kg/t-sludge') = CO ₂ ^cap × 1000/100

The production ratio of low Ca calcium silicate hydrate is determined by the peak of high Ca, high Si calcium silicate hydrate near 900 to 1000 cm ^-1 measured by infrared spectroscopy, and the peak of high Si calcium silicate hydrate near 1000 to 1030 cm ^-1 . It was calculated by taking the height ratio to the peak of low Ca, low Si calcium silicate hydrate.

Here, the measurement by infrared spectroscopy was analyzed using FTIR-6100 manufactured by JASCO Corporation, the measurement range was 4000 to 400 cm ⁻¹ , and the KBr (potassium bromide) tablet measurement method was used. For the measurements, a mixture of about 1 mg of carbonated sludge and about 100 mg of KBr was thoroughly mixed using an agate mortar and molded into disc-shaped pellets using a pressure molding method, and used for the measurements. The transmittance spectrum obtained in the measurement was converted into absorbance using the following formula (Beer-Lambert formula), and the peak ratio was calculated.
Absorbance = log [1/transmittance]

The amount of pozzolan produced was calculated as follows.
Pozzolan production amount (kg/t-sludge) = [(Ma'-M')/100] x 1000
M': Insoluble residual amount (%) determined by the hydrochloric acid-sodium carbonate method according to JIS R5202 "Cement chemical analysis method"
Ma': In the above quantitative method, the amount of undissolved residue (%) when only hydrochloric acid is dissolved

Table 2 shows the results of the tests conducted using the above test equipment.

[result]
(1) Test results of CO ₂ fixation amount by CO ₂ injection Table 2 shows the results of Examples 1 to 9 conducted under predetermined conditions. In the method according to the present invention, the amount of CO ₂ fixed in the sludge can be 300 (kg/t-sludge') or more, which far exceeds the amount of CO ₂ fixed in the raw material, which is 82 (kg/t-sludge'). It was confirmed that In the present invention, the sludge production conditions were determined using a CO ₂ fixed amount of 300 (kg/t-sludge') or more as a guideline.

(2) CO ₂ injection rate Referring to the results in Table 2, at the CO ₂ injection rate of 3528 (kg/t・h) in Example 10, the sludge with a fixed amount of CO ₂ of 359 (kg/t-sludge') was gotten. In addition to this result, taking into consideration that the amount of CO ₂ fixed at the CO ₂ injection rate of 4704 (kg/t・h) in Comparative Example 5 was 302 (kg/t-sludge'), the CO ₂ injection The speed was set to 3600 (kg/t·h) or less. Furthermore, regarding the lower limit of the CO ₂ injection rate, even under the conditions of Example 2 where the CO ₂ injection rate is 588 (kg/t・h), the amount of CO ₂ fixed is 358 (kg/t-sludge'). , it was set at 500 (kg/t·h) because there was some margin compared to the standard CO ₂ fixation amount of 300 (kg/t-sludge').

(3) CO ₂ injection amount Regarding the lower limit of the CO ₂ injection amount, the CO ₂ injection amount of 882 (kg/t) in Example 2 is also compared to the CO ₂ fixed amount of 300 (kg/t-sludge'). Since there _was a margin, the CO ₂ injection amount was determined to be more than 800 (kg/t). Regarding the upper limit of the amount of CO ₂ blown, looking at the test results, we find that even if a large amount is blown, the amount of CO ₂ fixed, the absorbance ratio, and the pozzolan content do not necessarily change in proportion to the amount of blown CO 2. . From this, the upper limit of the CO ₂ injection amount is set at 6300 (kg/t) based on the maximum value confirmed in the test, 6272 (kg/t) in Example 9, from this test result. .

(4) Liquid-solid ratio As shown in Examples 1 to 11 in Table 2, when the liquid-solid ratio was 3 or more and 8 or less, sludge with a predetermined amount of CO ₂ fixed could be produced. When the liquid-solid ratio is less than 3, that is, when the solid content is relatively large, the CO ₂ supply device 20 may become clogged and the necessary CO ₂ may not be supplied. Further, when the liquid-solid ratio is greater than 8, that is, when the solid content is relatively small, the amount of water is excessive compared to the amount of concrete powder 11, and the container 10 becomes too large. Therefore, the liquid-solid ratio was set to 3 or more and 8 or less.

(5) Ratio between the blown water depth in the CO ₂ mixed liquid and the maximum bubble diameter of CO ₂ at the blown water depth When the above ratio of Example 4 in Table 2 is 400, sludge can be generated. Ta. Therefore, the above ratio was set to 400 or more. In the equipment implementing the present invention, the shapes and dimensions of the container 10 and the CO2 supply device 20 are determined so that the above ratio is 400 or more. Regarding the upper limit of the above ratio, one way of thinking is 1000 in Examples 1 to 3 and 5 to 11, which were confirmed in the test. However, the larger the value of the above ratio, the better. Specifically, in the present test results, the larger the above ratio is, the more the amount of CO ₂ fixed increases, the absorbance ratio becomes smaller, and the pozzolan content increases. Therefore, the above ratio is considered to be a magnifying characteristic, and preferably, the larger the ratio, the better.

According to the method of fixing CO ₂ in cement hydrate of the present invention, CO ₂ can be efficiently fixed, and furthermore, when added to cement, there is a possibility of occurrence of alkaline aggregate reaction (ASR) in concrete. It is possible to obtain cement hydrate that can reduce the

10 container, 11 concrete powder, 12 water.

Claims (2)

A method of fixing _CO2 in cement hydrate, the method comprising:
The method includes a CO _{2 blowing step of putting cement hydrate and water in a container and blowing CO 2 into} the container while stirring the mixture _of the cement hydrate and water. In the embedding process,
A method of fixing CO ₂ to cement hydrate, with a CO 2 injection rate of 3600 kg/t·h or less and _{a CO 2 injection} amount of more than 800 kg/t. In the CO ₂ injection step,
The liquid-solid ratio of water and cement hydrate is 3 to 8, and
The method for fixing CO ₂ in cement hydrate according to claim 1, wherein the ratio of the depth of CO _{2 blown into the mixed liquid and the maximum bubble diameter of CO 2 at} the blown water depth is 400 or more. .

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