JP7555296B2 - Carbon dioxide fixation method - Google Patents

Description

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

Conventionally, in order to prevent global warming, there has been a demand for reducing _CO2 emissions into the atmosphere. As one method, Patent Document 1 discloses a technology for immobilizing _CO2 using an alkaline earth metal-containing substance. Examples of alkaline earth metal-containing substances include concrete waste generated by demolishing concrete buildings, and steel slag, a by-product generated in the steelmaking process. Conventionally, these substances have been used as aggregates, etc., but they can be used more effectively by immobilizing _CO2 .

In the method disclosed in the above document, water is added to ready-mixed concrete generated at ready-mixed concrete factories and construction sites to produce slurry-like ready-mixed concrete, and _CO2 is mixed into the mixture to generate _CaCO3 and fix the _CO2 . The generated _CaCO3 is used as a concrete material.

JP 2007-190538 A

However, although methods for immobilizing _CO2 in cement hydrate and methods for using the materials have been developed, there is still no knowledge of highly efficient manufacturing conditions for mass production. In particular, when mass production is assumed, it is necessary to be able to immobilize a certain amount of _CO2 within a certain time.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a highly efficient production method for fixing _CO2 in cement hydrate in a short period of time.

The method of the present invention for fixing _CO2 in cement hydrate includes a CO2 injection step of placing cement hydrate and water in a container, and injecting _CO2 into the container while stirring the mixed liquid of cement hydrate and water, and is characterized in that in the _CO2 injection step, the _CO2 injection rate is 3,600 kg/t-h or more, the _CO2 injection amount is 600 kg/ _t or more , and the CO2 _injection time is 10 minutes or more and 30 minutes or less .

According to the method of fixing _CO2 in cement hydrate of the present invention, _CO2 can be fixed in cement hydrate in a short time. In addition, since the specific surface area of the carbonate generated by fixing _CO2 in cement hydrate is large, it is expected to increase the strength when mixed with cement.

In addition, in the _CO2 injection step of the method of fixing _CO2 in cement hydrate of the present invention, the liquid-solid ratio of water to cement hydrate is 4 to 8, and the ratio of the injection depth in the _CO2 mixed liquid to the maximum bubble diameter of _CO2 at the water depth is 400 or more.

According to the _CO2 injection process of the present invention, the liquid-solid ratio and the ratio of the injection depth in the _CO2 mixture to the maximum bubble diameter of _CO2 at the water depth can be set to values within a suitable range. Therefore, _CO2 can be efficiently fixed in cement hydrate.

FIG. 1 is a schematic diagram of an apparatus 100 for fixing CO ₂ in cement hydrate, which is one embodiment for carrying out the present invention. FIG. 1 is a schematic diagram of a test device embodying the present invention.

<Embodiment>
The present embodiment of the manufacturing method for immobilizing _CO2 in cement hydrate will be described with reference to Fig. 1. The _CO2 immobilization device 100 used in the above method includes a container 10, a _CO2 supply device 20, and a stirring device 30. The _CO2 immobilization device 100 is a device for mass-production of cement hydrate in which _CO2 is immobilized efficiently.

The vessel 10 is a device in which water and waste concrete are put in to fix CO _2. The waste concrete includes waste concrete from demolished concrete buildings, waste sludge from concrete production, waste lightweight aerated concrete (waste ALC), and the like. The waste concrete may contain aggregates other than cement hydrate, and the amount of cement hydrate may be within a specified range. The waste concrete is finely crushed by a crusher (not shown) and put in to fix CO ₂ efficiently. Materials other than cement hydrate, such as aggregates, may also be separated and selected. The finely crushed concrete powder 11 is unlikely to settle even when put in water, and the fixation reaction of CO ₂ can be efficiently performed. The water 12 put in the vessel 10 together with the concrete powder 11 is, for example, industrial water.

Water 12 and concrete powder 11 are put into the container 10 and mixed to generate sludge slurry 13. The liquid-solid ratio, which is the mixing ratio of the water 12 and the concrete powder 11, is preferably in the range of 4 to 8. If the liquid-solid ratio is less than 4, i.e., if the solid content is relatively high, the _CO2 supply device 20 may become clogged and may not be able to supply the necessary _CO2 . Also, if the liquid-solid ratio is 8 or more, i.e., if the solid content is relatively low, the amount of water is in excess of the amount of concrete powder 11, and the container 10 becomes too large. Therefore, the liquid-solid ratio is preferably in the above range.

The _CO2 supply device 20 supplies CO2 ₁₄ to the container 10. The _CO2 supply device 20 has a supply pipe 21, a flow rate control device 22, and an aeration device 23. One end of the supply pipe 21 is connected to a supply source of _CO2 14 (not shown). The supply pipe 21 has one or more branches in the middle of the supply pipe 21, and the other end of each of the supply pipes 21 is connected to a plurality of aeration devices 23. The gas to be supplied does not need to be 100% _CO2 gas, and factory exhaust gas containing _N2 or _O2 may be used, as long as the actual supply amount of _CO2 is within a specified range.

The _CO2 supply device 20 has at least one of a plurality of flow rate adjustment devices 22 capable of adjusting the amount of _CO2 supplied to each of the plurality of air diffusers 23, or one flow rate adjustment device 22 capable of adjusting the amount of _CO2 supplied to all of the plurality of air diffusers 23, at the intermediate portion of the supply pipe 21. Each of the one or more flow rate adjustment devices 22 may have an electromagnetic valve and be electrically controllable. In addition, the surplus of the supplied _CO2 14 is discharged from the container 10 as exhaust gas 15.

The air diffuser 23 includes a porous structure and is a device that 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 material containing a large number of holes. The porous structure may be covered with other materials except for the surface on which the CO ₂ release surface is formed. Alternatively, the porous structure may be formed of a material that does not have holes formed therein except for the surface on which the CO ₂ release surface is formed. Alternatively, the porous structure may be a material such as a hollow material with a large number of holes processed and opened on the surface. For example, it may be a hollow tube with a large number of holes opened on the surface. Alternatively, a device that uses blades or the like to finely disperse CO ₂ may be used. In addition, it is desirable that the water depth at which the air diffuser 23 is arranged is arranged close to the bottom side of the container 10 so that CO ₂ can be efficiently fixed. For example, the water depth of the aeration device 23 is at least 50% or more, preferably 60% or more, and more preferably 70% or more of the maximum design water depth of the vessel 10. In addition, there may be a plurality of _CO2 fixation devices, and any shape of the device is possible as long as the total contact time of the _CO2 and the sludge slurry is the same.

The CO ₂ 14 introduced into the diffuser 23 is released into the sludge slurry 13 as bubbles having a diameter of 1 mm or less. When the water depth of the CO ₂ 14 injection, i.e., the water depth of the CO ₂ release surface of the diffuser 23 where the CO ₂ 14 bubbles are generated, is L and the diameter of the CO ₂ 14 bubbles at that water depth is M, the diffuser 23 is provided so that L/M≧400. When multiple diffusers 23 are installed at positions with different heights, the water depth of the CO ₂ 14 injection is defined as L, which is the maximum water depth of the CO ₂ release surface of the diffuser 23 where the CO ₂ 14 bubbles are generated.
The diffuser 23 is configured to release CO ₂ 14 from the top, but the CO ₂ release surface of the diffuser 23 may be configured not only as the top surface, but also as the side surface and/or the bottom surface. When the CO ₂ release surface of the diffuser 23 is the side surface and/or the bottom surface, clogging due to the concrete powder 11 in the sludge slurry 13 falling down is less likely to occur compared to when the CO ₂ release surface is the top surface. Therefore, the periodic maintenance period of the diffuser 23 can be extended. The diffuser 23 may be one or more, as long as it can release the specified amount of CO ₂ 14. In addition, when there are more than one diffuser, it is more efficient to arrange them at approximately equal intervals around the periphery along the wall of the container 10.

The agitator 30 is a device that agitates the sludge slurry 13 so as to efficiently fix the CO ₂ 14. The agitator 30 continues to rotate at a constant rotation speed by an electric motor (not shown) to agitate the sludge slurry 13. The agitator 30 is disposed near the approximate center of the vessel 10 so as to efficiently agitate the sludge slurry 13. The agitator 30 has a rotating shaft 31 that is rotated by the electric motor, and an agitator blade 32 that is connected to the lower end of the rotating shaft 31.

The agitator 32 is formed to be 30% or more of the inner diameter of the container 10 or the inner dimension such as the cross dimension of the maximum part. The water depth of the agitator 32 is 50% or more of the design maximum water depth of the sludge slurry 13 to be put into the container 10, that is, half the water depth or deeper. The water depth at which the agitator 32 is placed is preferably as close to the bottom side of the container 10 as possible so that the concrete powder 11 contained in the sludge slurry 13 can be easily scooped up even when it sinks to the bottom of the container 10. For example, it is good to set it to at least 50% or more, preferably 60% or more, and more preferably 70% or more of the design maximum water depth of the container 10. The agitator 32 is placed at approximately the same water depth position with respect to the air diffuser 23 in the water depth direction. The position of the agitator 32 relative to the aeration device 23 in the water depth direction may be above the aeration device 23 , within the range of the water depth direction dimension of the aeration device 23 , or below the aeration device 23 .
A plurality of stirring blades 32 may be arranged, and they may be installed so that their total length is 30% or more of the inner diameter of the vessel 10 or the inner dimension such as the span dimension of the maximum part.

In addition, a circulation device for the sludge slurry 13 (not shown) can be provided together with the stirring device 30 or instead of the stirring device 30. The circulation device has a pump and pipes before and after the pump, with the end of the pipe before the pump being disposed on the bottom surface of the container 10 or near the bottom surface, and the end of the pipe after the pump being disposed at the upper part inside the container 10. The sludge slurry 13 on the bottom surface of the container 10 or near the bottom surface is sucked by the pump and circulated to the upper part of the sludge slurry 13 inside the container 10. This allows for efficient fixation of _CO2 .

In the above apparatus, water 12 and concrete powder 11 are put into the container 10 so as to have a predetermined liquid-solid ratio, and the sludge slurry 13 is generated with a uniform degree of mixing by the stirring device 30. The predetermined liquid-solid ratio is 4 to 8. In this state, the _CO2 supply device 20 starts supplying _CO2 at a predetermined _CO2 injection rate. The predetermined _CO2 injection rate is 3600 kg/t·h or more. The injection of _CO2 is continued for a predetermined _CO2 injection time, and a predetermined _CO2 injection amount is injected into the sludge slurry 13. The predetermined _CO2 injection time is 35 minutes or less, and the predetermined _CO2 injection amount is 600 kg/t or more. By the above method, _CO2 is efficiently fixed in the concrete powder 11. When one _CO2 fixation operation is completed, the sludge slurry 13 is discharged from the container 10. Water 12 and concrete powder 11 are again put into the container 10. The discharged sludge slurry 13 is used as is or is dehydrated, dried, etc., and the concrete powder 11 with the _CO2 fixed therein is used as a cement raw material, etc.

Although the supply of CO ₂ 14 to the container 10 has been described as being supplied from a pressure container filled with CO ₂ 14, other forms are also possible. CO ₂ originating from exhaust gas from the factory in which 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 via a supply pipe. In this way, the amount of CO ₂ emitted from the factory is reduced.

In the present invention, the goal is to develop a method for fixing a certain amount of _CO2 in cement hydrate in a short period of time, which can fix 200 kg/t-cem or more of _CO2 in cement hydrate within 35 minutes.

Next, the test apparatus and the results of the test performed on this embodiment will be described with reference to FIG. 2. The test apparatus was basically configured according to the above apparatus. In addition, in the test apparatus in FIG. 2, the same or corresponding members are denoted by the same reference numerals and their description will be omitted. The test apparatus includes a container 10, a _CO2 supply device 20, and an agitator 30, and is basically configured the same as the _CO2 fixation device 100 in FIG. 1. The container 10 was placed in a thermo-hygrostat 40, and the test was started at 20°C. The agitator 30 has a rotating shaft 31 rotated by an electric motor and an agitator blade 32 connected to the lower end of the rotating shaft 31. The position of the _CO2 release surface of the aeration device 23 and the agitator blade 32 are arranged so as to be about 70% of the water depth.

The agitator blades 32 are formed to be 30% or more of the inside diameter of the container 10 or the inside dimension such as the diameter of the largest part. The water depth of the agitator blades 32 is 50% or more of the designed maximum water depth of the sludge slurry 13 to be put into the container 10, that is, half the water depth or deeper. It is desirable to arrange the water depth at which the agitator blades 32 are arranged as close as possible to the bottom side of the container 10 so that the concrete powder 11 contained in the sludge slurry 13 can be easily scooped up even when it sinks to the bottom of the container 10. For example, it is good to make it 60% or more, preferably 70% or more, of the designed maximum water depth of the container 10.

[Preparation of ingredients]
The container 10 was filled with powdered ready-mixed concrete sludge supplied from a ready-mixed concrete factory. The ready-mixed concrete sludge provided was selected from those that had been produced for a short time, and those that started drying 24 hours after being supplied were used. The ready-mixed concrete sludge provided was crushed and then 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). The dried sludge was then crushed. In the crushing process, a 10 kg sample was crushed in a ball mill for 30 seconds. The chemical composition of the dried sludge used at this time is shown in Table 1. 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 can be treated as a cement hydrate that does not contain aggregate.

[Carbonation treatment]
The sludge slurry 13 was prepared by adding the dried sludge prepared as described above to 1000 mL of ion-exchanged water to obtain a predetermined liquid-solid ratio. Then, while stirring the sludge slurry 13 in a thermo-hygrostat (incubator), _CO2 was blown in at a predetermined flow rate and time using the air diffuser 23. The flow rate of _CO2 was controlled using a float flowmeter connected to a gas cylinder. After the blowing was completed, 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 a carbonated sludge. The carbonated sludge was pulverized and passed through a 600 μm sieve, after which various analyses were performed.

The calculation method for each characteristic value is as follows:

1. Amount of _CO2 injected (amount of _CO2 supplied to sludge) (kg- _CO2 /t-sludge)
_CO2 /sludge = ( _QCO2 x t)/Msludge
_QCO2 : _CO2 flow rate (kg- _CO2 /h) measured by a flow meter connected to a _CO2 gas cylinder
t: Time from start to finish of blowing (h)
Msludge: Mass of sludge added (kg)

2. Amount of _CO2 fixed in sludge (kg/t-sludge)
CO ₂ cap=CO ₂ TG×(100/(100-ig.lossTG)
_CO2 cap: The amount of _CO2 contained in the ignited carbonated sludge (%)
_CO2 TG: _CO2 amount (%) calculated by TG-DTA
ig. lossTG: Weight loss (%) up to 1000°C in TG-DTA

TG-DTA was performed using a Seiko Instruments Inc. thermogravimetry and differential thermal analyzer TG-DTA6300 under the following conditions: temperature range: room temperature to 1000°C, heating rate: 10°C/min, atmosphere: 20°C. The following unit corrections were also performed.

CO ₂ (kg/t-sludge') = CO ₂ cap x 1000/100

The results of the tests conducted using the above test equipment are shown in Table 2. Table 3 shows the results of tests conducted by changing the liquid-solid ratio. Table 4 shows the results of tests conducted by changing the injection depth/maximum bubble diameter.

[result]
(1) From Table 2, it was confirmed that in Examples 1 to 10, the amount of CO ₂ fixed in the sludge was 200 (kg/t-cem) or more. From this, it was found that if the liquid-solid ratio of water to cement hydrate was 4 to 8, the CO ₂ injection rate was 3600 kg/t-h or more, the CO ₂ injection amount was 600 kg/t or more, and the ratio of the injection depth of CO ₂ in the mixed liquid to the maximum bubble diameter of CO ₂ at the water depth was a predetermined value or more, the target amount of CO ₂ fixed in the cement hydrate of 200 kg/t-cem or more could be achieved within 30 minutes. In addition, the specific surface area of the generated carbonate is large, and when added to cement concrete, it is expected to increase the strength when mixed with cement. For reference, tests in which the CO ₂ injection time was set to 40 minutes, which is longer than the target, were conducted as Reference Examples 1 to 3. These are for reference because they are longer than the target CO ₂ injection time.
(2) Table 3 shows that the amount of _CO2 fixed in the sludge is highest when the liquid-solid ratio is 6, and is slightly lower when the liquid-solid ratio is 4 or 8 compared to when the liquid-solid ratio is 6.
(3) Table 4 shows that the amount of _CO2 fixed in the sludge varies depending on the water injection depth/maximum bubble diameter.

According to the method of fixing _CO2 in cement hydrate of the present invention, _CO2 can be fixed in cement hydrate in a short period of time.

10 container, 11 concrete powder 11, 12 water.

Claims (2)

A method for fixing _CO2 in cement hydrate, comprising the steps of:
The method includes a _CO2 injection step of injecting _CO2 into a container while stirring the mixture of cement hydrate and water,
In the _CO2 blowing step,
_CO2 injection rate is 3600 kg/t・h or more,
_CO2 injection amount is 600 kg/t or more ,
_The CO2 blowing time is 10 minutes or more and 30 minutes or less .
A method for fixing _CO2 in cement hydrate. In the _CO2 blowing step,
The liquid-solid ratio of water to cement hydrate is 4 to 8.
2. The method for fixing _CO2 in cement hydrate according to claim 1, wherein a ratio of an injection depth of _CO2 in the mixed liquid to a maximum bubble diameter of _CO2 at the injection depth is 400 or more.

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