Methods for carbon dioxide sequestration

Abstract

To provide a production method that fixes CO2 to cement hydrate with high efficiency.SOLUTION: The present invention discloses a method for fixing cement hydrate to CO2, the method including a CO2 blowing step in which cement hydrate 11 and water 12 are put into a container 10, and the liquid mixture of the cement hydrate 11 and the water 12 are stirred while CO2 14 is blown into the container 10. In the CO2 blowing step, the CO2 blowing speed is 3600 kg / t h or less and the CO2 blowing amount is 800 kg / t or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for immobilizing carbon dioxide in cement hydrates.

Background Art

[0002] Conventionally, in order to prevent global warming, reduction of CO2 emissions into the atmosphere has been demanded. As one of the methods, Patent Document 1 discloses a technique for immobilizing CO2 using an alkaline earth metal-containing substance. The alkaline earth metal-containing substance is, for example, concrete waste generated by demolishing a concrete building, steel slag as a by-product generated in the steelmaking process, and the like. Conventionally, although these substances have been used as aggregates and the like, they can be used more effectively by immobilizing CO2.

[0003] In the method disclosed in the above document, CO2 is mixed into a slurry-like fresh concrete obtained by adding water to fresh concrete generated at a fresh concrete-related factory or a construction site, thereby generating CaCO3 to immobilize CO2. The generated CaCO3 is used as a material for concrete.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, although methods for immobilizing CO2 in cement hydrates and methods for using the materials have been developed, in the above method, findings regarding highly efficient manufacturing conditions on the premise of mass production do not yet exist. In particular, when mass production is assumed, a method with a high CO2 immobilization efficiency that can immobilize as much CO2 as possible out of the supplied CO2 is required.

[0006] The present invention was made to solve the above problems, and aims to provide a highly efficient manufacturing method that can obtain high CO2 fixation efficiency in cement hydrate. [Means for solving the problem]

[0007] The present invention provides a method for fixing CO2 to cement hydrate, which involves placing cement hydrate and water in a container, and stirring the mixture of cement hydrate and water while adding CO2 to the container. 5 to 20 minutes The system includes a CO2 injection process, characterized in that the CO2 injection rate is 3600 kg / t·h or less and the CO2 injection amount is 392 kg / t or less.

[0008] The present invention provides a method for fixing CO2 to cement hydrate, which allows for high-efficiency fixation of CO2 in the cement hydrate. In addition, the low specific surface area of ​​the carbon oxides produced by the fixation of CO2 to the cement hydrate is expected to result in minimal reduction of fluidity when mixed with cement.

[0009] Furthermore, in the CO2 injection step of the method for fixing CO2 to cement hydrate according to the present invention, the liquid-to-solid ratio of water to cement hydrate is 4~ 6 The CO2 mixture is characterized by having a ratio of 400 or more between the injection depth and the maximum CO2 bubble diameter at that depth.

[0010] According to the CO2 injection process of the present invention, the liquid-to-solid ratio and the ratio of the injection water depth in the CO2 mixture to the maximum CO2 bubble diameter at that water depth can be set to values ​​within a suitable range. Therefore, CO2 can be efficiently fixed to the cement hydrate. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram of a CO2 fixation apparatus 100 for cement hydrate, which is one embodiment for carrying out the present invention. [Figure 2]This is a schematic diagram of a test apparatus that implements the present invention. [Modes for carrying out the invention]

[0012] <Embodiment> Referring to Figure 1, a manufacturing method for fixing CO2 into cement hydrate, according to this embodiment, will be described. The CO2 fixation apparatus 100 used in the above method comprises a container 10, a CO2 supply device 20, and a stirring device 30. The CO2 fixation apparatus 100 is a device that produces a large quantity of cement hydrate with fixed CO2 efficiently.

[0013] Container 10 is a device into which water and concrete waste materials are introduced to perform CO2 fixation. Concrete waste materials include waste concrete from demolished concrete buildings, waste sludge generated during concrete production, waste aerated concrete (waste ALC), etc. Concrete waste materials may also contain aggregates other than cement hydrate, as long as the amount of cement hydrate is within the specified range. In order to efficiently fix CO2, the concrete waste materials are finely crushed in a crusher (not shown) and introduced. Materials other than cement hydrate, such as aggregates, may also be separated and sorted. The finely crushed concrete powder 11 does not easily settle when introduced into water, allowing the CO2 fixation reaction to proceed efficiently. The water 12 introduced into container 10 together with the concrete powder 11 is, for example, industrial water.

[0014] Water 12 and concrete powder 11 are added to container 10 and mixed to produce sludge slurry 13. The liquid-to-solid ratio, which is the mixing ratio of water 12 to concrete powder 11, is preferably in the range of 4 to 8. If the liquid-to-solid ratio is less than 4, i.e., if the solid content is relatively high, the CO2 supply device 20 may become clogged and unable to supply the necessary CO2. Also, if the liquid-to-solid ratio is 8 or higher, i.e., if the solid content is relatively low, the amount of water is excessive compared to the amount of concrete powder 11, and the container 10 becomes too large. Therefore, the liquid-to-solid ratio is preferably within the above range.

[0015] The CO2 supply device 20 supplies CO214 to the container 10. The CO2 supply device 20 includes a supply pipe 21, a flow rate adjuster 22, and an aeration device 23. One end of the supply pipe 21 is connected to a CO214 supply source (not shown). The supply pipe 21 has one or more branches in the middle, and the other end of each branch is connected to a plurality of aeration devices 23. The supplied gas does not need to be 100% CO2 gas; factory exhaust gas containing N2 and O2 may be used, as long as the actual amount of CO2 supplied is within the specified range.

[0016] The CO2 supply device 20 has at least one of the following in the middle of the supply pipe 21: a plurality of flow rate adjusters 22 capable of adjusting the amount of CO2 supplied to each of the plurality of aeration devices 23, or a single flow rate adjuster 22 capable of adjusting the amount of CO2 supplied to all of the plurality of aeration devices 23. Each of the one or more flow rate adjusters 22 may be configured to be electrically controllable by having a solenoid valve. Any excess CO2 14 supplied is discharged from the container 10 as exhaust gas 15.

[0017] The aeration device 23 includes a porous structure and is a device that releases the introduced CO2 14 as fine bubbles. One or more aeration devices 23 are placed inside the container 10 so that the entire aeration device 23 is submerged in the sludge slurry 13 contained in the container 10. The porous structure of the aeration device 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 CO2 release surface is formed. Alternatively, the porous structure may be formed of a material in which no holes are formed except for the surface on which the CO2 release surface is formed. Alternatively, the porous structure may be a hollow material or the like with a large number of holes processed into its surface. For example, it may be a hollow tube with a large number of holes on its surface. Alternatively, a device that atomizes CO2 using blades or the like may be used. Furthermore, it is desirable that the aeration device 23 be placed at a water depth close to the bottom surface of the container 10 so that CO2 fixation is carried out efficiently. For example, the water depth of the aeration device 23 should be at least 50% of the maximum design water depth of the container 10, preferably 60% or more, and more preferably 70% or more. Furthermore, there may be multiple CO2 fixation devices, and any shape of the device is acceptable as long as the total contact time between the CO2 and the sludge slurry is the same.

[0018] CO214 introduced into the diffuser 23 is released into the sludge slurry 13 as bubbles with a diameter of 1 mm or less. The diffuser 23 is configured such that L / M ≥ 400, where L is the water depth at which CO214 bubbles are generated at the CO2 discharge surface of the diffuser 23, and M is the diameter of the CO214 bubbles at that water depth. If multiple diffusers 23 are installed at different heights, the water depth at which CO214 bubbles are generated is defined as L, which is the maximum water depth at the CO2 discharge surface of the diffuser 23 where CO214 bubbles are generated. The aeration device 23 is configured to release CO214 from its top surface, but the CO2 release surface of the aeration device 23 may be the top surface, the side surface, the bottom surface, or a combination of any of these. When the CO2 release surface of the aeration device 23 is the side surface or the bottom surface, clogging due to the concrete powder 11 in the sludge slurry 13 falling is less likely to occur compared to when the CO2 release surface is the top surface. Therefore, the periodic maintenance interval of the aeration device 23 can be extended. The aeration device 23 may be one or multiple, as long as it can release the specified amount of CO214 injected. Also, in the case of multiple devices, it is more efficient to arrange them at approximately equal intervals along the wall of the container 10 in the surrounding area.

[0019] The stirring device 30 is a device that stirs the sludge slurry 13 so that CO214 can be immobilized efficiently. The stirring device 30 rotates at a constant speed using an electric motor (not shown) to stir the sludge slurry 13. The stirring device 30 is positioned near the center of the container 10 so that it can efficiently stir the sludge slurry 13. The stirring device 30 has a rotating shaft 31 that is rotated by an electric motor and a stirring blade 32 that is connected to the lower end of the rotating shaft 31.

[0020] The stirring blade 32 is formed to be at least 30% of the inner diameter of the container 10, or the maximum cross-section dimension of the container 10. The stirring blade 32 is positioned at a depth of at least 50% of the design maximum water depth of the sludge slurry 13 placed in the container 10, i.e., half the water depth or deeper. It is desirable that the stirring blade 32 be positioned as close to the bottom of the container 10 as possible so that the concrete powder 11 contained in the sludge slurry 13 can be easily scooped up when it settles to the bottom of the container 10. For example, it is good to set the depth at least 50% of the design maximum water depth of the container 10, preferably 60% or more, and more preferably 70% or more. The stirring blade 32 is positioned at approximately the same water depth as the aeration device 23 in the water depth direction. The positional relationship of the stirring blade 32 to the aeration device 23 in the direction of water depth can be any of the following: above the aeration device 23, within the range of the dimensions of the aeration device 23 in the direction of water depth, or below the aeration device 23. A plurality of stirring blades 32 may be arranged, and they may be installed such that the total length thereof is 30% or more of the inner dimensions such as the inner diameter of the container 10 or the span dimension of the largest part.

[0021] In addition, a circulation device for the sludge slurry 13 (not shown) may be provided together with the stirring device 30 or instead of the stirring device 30. The circulation device has a pump and pipes on both the front and rear sides of the pump. The tip of the pipe in front of the pump is arranged at the bottom surface of the container 10 or around the bottom surface, and the tip of the pipe behind the pump is arranged at the upper part inside the container 10. The sludge slurry 13 at the bottom surface of the container 10 or around the bottom surface is sucked by the pump and circulated to the upper part of the sludge slurry 13 inside the container 10. Thereby, the fixation of CO2 is efficiently performed.

[0022] In the above device, water 12 and the concrete powder 11 are put into the container 10 so as to have a predetermined liquid-solid ratio, and a sludge slurry 13 with a uniform mixing degree is generated by the stirring device 30. The predetermined liquid-solid ratio is 4 to 8. In that state, the supply of CO2 is started by the CO2 supply device 20 at a predetermined CO2 injection rate. The predetermined CO2 injection rate is 3600 kg / t·h or less. The injection of CO2 is continued for a predetermined CO2 injection time, and a predetermined amount of CO2 is injected into the sludge slurry 13. The predetermined amount of CO2 injection is 800 kg / t or less. By the above method, CO2 is efficiently fixed to the concrete powder 11. When one CO2 fixation operation is completed, the sludge slurry 13 is discharged from the container 10. Water 12 and the concrete powder 11 are again put into the container 10. The discharged sludge slurry 13 is left as it is, or dehydrated, dried, etc., and the concrete powder 11 with CO2 fixed thereto is used as a cement raw material or the like.

[0023] Regarding the supply of CO214 to container 10, the description has been of a form in which CO214 is supplied from a pressure vessel filled with CO214, but other forms are also possible. CO2 originating from the exhaust gas of the factory where container 10 is located, or an adjacent factory, may be supplied via piping installed in the factory. For example, CO2 emitted from a cement factory may be continuously supplied via a supply pipe. Doing so would reduce the amount of CO2 emitted from the factory.

[0024] In this invention, the goal was to achieve a method that provides high CO2 fixation efficiency in cement hydrate, specifically one that results in a CO2 fixation efficiency of 15% or more in cement hydrate.

[0025] Referring to Figure 2, the test apparatus and results of the test conducted with respect to this embodiment will now be described. The test apparatus was basically configured to match the apparatus described above. In the test apparatus in Figure 2, the same or corresponding components are denoted by the same reference numerals and their descriptions are omitted. The test apparatus comprises a container 10, a CO2 supply device 20, and a stirring device 30, and is basically the same configuration as the CO2 fixation device 100 in Figure 1. The container 10 was placed in a constant temperature and humidity chamber 40, and the test was started at 20°C. The stirring device 30 has a rotating shaft 31 that is rotated by an electric motor, and a stirring blade 32 connected to the lower end of the rotating shaft 31. The position of the CO2 discharge surface of the aeration device 23 and the stirring blade 32 are positioned at a depth of approximately 70% of the water depth.

[0026] The stirring blade 32 is formed to be at least 30% of the inner diameter of the container 10, or the maximum cross-section dimension of the container 10. Furthermore, the water depth of the stirring blade 32 is positioned at least 50% of the design maximum water depth of the sludge slurry 13 placed in the container 10, i.e., half the water depth or deeper. It is desirable that the stirring blade 32 be positioned as close to the bottom of the container 10 as possible so that the concrete powder 11 contained in the sludge slurry 13 can be easily scooped up when it settles to the bottom of the container 10. For example, it is good to set it at least 60%, preferably 70%, of the design maximum water depth of the container 10.

[0027] [Preparation of raw materials] Container 10 was filled with powdered ready-mix concrete sludge supplied from a ready-mix concrete plant. The provided ready-mix concrete sludge was selected based on the shortest time elapsed since its preparation, and drying was started 24 hours after supply. After crushing, the provided ready-mix concrete sludge was thoroughly dried in a drying oven to obtain dried sludge. The Blaine specific surface area of ​​the dried sludge at this stage was Bl' = 14230 cm². 2 / g(ρ=2.61g / cm 3 The result was e=0.74). Subsequently, the dried sludge was subjected to crushing treatment. For the crushing treatment, 10 kg of the 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 similar to that of commercially available cement and can be treated as cement hydrate without aggregate.

[0028] [Table 1]

[0029] [Carbonation treatment] Sludge slurry 13 was prepared by adding the dried sludge prepared in the manner described above to 1000 mL of deionized water to achieve a predetermined liquid-to-solid ratio. Then, while stirring the sludge slurry 13 in a constant temperature and humidity chamber (incubator), CO2 was blown in at a predetermined flow rate and time using an aeration device 23. The CO2 flow rate was controlled using a float flow meter connected to a gas cylinder. After the blowing was complete, the slurry 13 was subjected to suction filtration to separate the solid and liquid phases. The separated solid phase was dried at 105°C to obtain carbonated sludge. The carbonated sludge was pulverized, passed through a 600 μm coarse sieve, and then subjected to various analyses.

[0030] The calculation method for each characteristic value is as follows:

[0031] 1. CO2 injection amount (amount of CO2 supplied to sludge) (kg-CO2 / t-sludge) CO2 / Sludge = (QCO2 × t) / Msludge QCO2: CO2 flow rate (kg-CO2 / h) measured by a flow meter connected to a CO2 gas cylinder. t: Time from the start to the end of the recording (h) Msludge: Mass of sludge added (kg)

[0032] 2. Amount of CO2 fixed into sludge (kg / t-sludge) CO2cap=CO2TG×(100 / (100-ig.lossTG)) CO2cap: Amount of CO2 contained in strongly heated carbonated sludge (%) CO2TG: CO2 amount (%) calculated by TG-DTA ig.lossTG: Loss of weight up to 1000°C in TG-DTA (%)

[0033] TG-DTA measurements were performed using a Seiko Instruments TG-DTA6300 differential thermogravimetric analyzer under the following conditions: temperature range: room temperature to 1000°C, heating rate: 10°C / min, and ambient temperature: 20°C. The following unit corrections were also applied.

[0034] CO2(kg / t-sludge')=CO2cap×1000 / 100

[0035] 3. CO2 fixation efficiency in sludge (%) CO2 fixation efficiency = [CO2cap - CO2O] / [QCO2 × t] CO2cap: CO2 (kg) contained in strongly heated carbonated sludge CO2O: Amount of CO2 (kg) contained in sludge before carbonation after strong heating. QCO2: Gas flow rate (kg-CO2 / h) measured by a regulator connected to a CO2 gas cylinder. t: Time from the start to the end of the recording (h)

[0036] The results of the tests conducted using the above-described test apparatus are shown in Table 2. The results of tests conducted with varying liquid-to-solid ratios are shown in Table 3. Furthermore, the results of tests conducted with varying injection water depth / maximum bubble diameter values ​​are shown in Table 4.

[0037] [Table 2]

[0038] [Table 3]

[0039] [Table 4]

[0040] [result] (1) From Table 2, it was confirmed that the CO2 fixation efficiency to sludge in Examples 1 to 10 was 15% or more. From this, it was found that if the liquid-to-solid ratio of water to cement hydrate is 4 to 8, the CO2 injection rate is 3600 kg / t·h or less, the CO2 injection amount is 800 kg / t or less, and the ratio of the injection depth of CO2 in the CO2 mixture to the maximum bubble diameter of CO2 at that depth is 400 or more, the target CO2 fixation efficiency to cement hydrate of 15% or more can be achieved. Furthermore, the specific surface area of ​​the generated carbon oxide is small, and it can be expected that there will be little decrease in fluidity when added to cement concrete. (2) From Table 3, it was found that the CO2 fixation efficiency in sludge was highest when the liquid-to-solid ratio was 4, and when the liquid-to-solid ratio was 6 or higher, it was slightly lower than when the liquid-to-solid ratio was 4. (3) From Table 4, it was found that the CO2 fixation efficiency in sludge varies depending on the injection water depth / maximum bubble diameter.

[0041] According to the method for fixing CO2 to cement hydrate of the present invention, a high CO2 fixation efficiency to cement hydrate can be obtained. [Explanation of Symbols]

[0042] 10 containers, 11 concrete powder, 12 water.

Claims

[Claim 1] CO 2 A method for fixing to cement hydrate, Place cement hydrate and water in a container, and while stirring the mixture of cement hydrate and water, add CO2 to the container. 2 Blowing CO2 for 5 to 20 minutes 2 It includes a blowing process, The aforementioned CO 2 In the blowing process, CO 2 The injection speed is 3600 kg / t·h or less. CO 2 The amount of air blown in is 392 kg / t or less. The liquid-to-solid ratio of water to cement hydrate is 4-6. CO 2 The injection water depth in the aforementioned mixed liquid and the CO at the injection water depth 2 The ratio to the maximum bubble diameter is 1000 or more. CO 2 Method for fixing to cement hydrate

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