Carbon dioxide fixation method

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

[Technical Field]

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

[0002] To prevent global warming, there has been a demand for reducing CO2 emissions into the atmosphere. As one method for achieving this, Patent Document 1 discloses a technology for immobilizing CO2 using alkaline earth metal-containing substances. 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. While these substances have traditionally been used as aggregates, etc., they can be used more effectively by immobilizing CO2.

[0003] 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 create a slurry-like ready-mixed concrete, and CO2 is then mixed into it to generate CaCO3 and fix the CO2. The generated CaCO3 is used as a concrete material. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-190538 Summary of the Invention [Problem to be solved by the invention]

[0005] However, although methods for immobilizing CO2 in cement hydrate and methods for using these materials have been developed, there is still no knowledge regarding the highly efficient manufacturing conditions for mass production of these methods. Furthermore, alkali-aggregate reaction (ASR) is known to be one of the causes of a decrease in concrete strength. When ASR occurs, cracks form in the concrete, reducing its strength. To ensure the longest possible use of concrete structures, it is desirable to reduce the likelihood of ASR.

[0006] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a production method that can efficiently fix CO2 in cement hydrate and, when added to cement, can reduce the possibility of alkali-aggregate reaction (ASR) occurring in concrete. [Means for solving the problem]

[0007] 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 mixture of cement hydrate and water, and is characterized in that in the CO2 injection step, the CO2 injection rate is 3600 kg / t·h or less and the CO2 injection amount is more than 800 kg / t.

[0008] According to the method of the present invention, it is possible to provide a production method that can efficiently fix CO2 in cement hydrate and reduce the possibility of alkali-aggregate reaction (ASR) occurring in concrete.

[0009] In addition, in the CO2 injection step of the method of fixing CO2 in cement hydrate of the present invention, it is preferable that the liquid-solid ratio of water to cement hydrate is 3 to 8, and the ratio of the injection depth in the CO2 mixed liquid to the maximum CO2 bubble diameter at the water depth is 400 or more.

[0010] According to the CO2 injection process of the present invention, the liquid-solid ratio and the ratio of the injection depth of the CO2 mixture to the maximum CO2 bubble diameter at that depth can be set within suitable ranges, thereby enabling CO2 to be efficiently fixed in cement hydrate. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram of an apparatus 100 for fixing CO2 in cement hydrate, which is one embodiment for carrying out the present invention. [Figure 2] 1 is a schematic diagram of a test device embodying the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] <Embodiment> Referring to FIG. 1, a manufacturing method for immobilizing CO2 in cement hydrate according to the present embodiment will be described. The CO2 immobilization apparatus 100 used in the method includes a container 10, a CO2 supply device 20, and an agitator 30. The CO2 immobilization apparatus 100 is a device for efficiently mass-producing cement hydrate with immobilized CO2. The method of the present invention can efficiently immobilize CO2 in cement hydrate and produce calcium silicate hydrate (CSH) and pozzolan, which have a low ratio of calcium (Ca) to silicon (Si). Furthermore, concrete containing reactive aggregates is known to undergo alkali-aggregate reaction (ASR). Because the above-mentioned substances have alkaline substance adsorption properties, concrete containing these substances can suppress alkali-aggregate reaction (ASR) and reduce the possibility of concrete strength loss.

[0013] The vessel 10 is a device into which water and waste concrete are introduced to immobilize CO2. Examples of waste concrete include waste concrete from demolished concrete buildings, waste sludge generated during concrete production, and waste lightweight aerated concrete (aerated concrete concrete). The waste concrete may contain aggregates other than cement hydrate, as long as the amount of cement hydrate is within a specified range. To efficiently immobilize CO2, the waste concrete is crushed into small pieces using a crusher (not shown) and then introduced. Materials other than cement hydrate, such as aggregates, may also be separated and sorted. The crushed concrete powder 11 is less likely to settle when introduced into water, allowing for an efficient CO2 immobilization reaction. The water 12 introduced into the vessel 10 together with the concrete powder 11 is, for example, industrial water.

[0014] Water 12 and concrete powder 11 are introduced into container 10 and mixed to produce sludge slurry 13. The liquid-solid ratio, which is the mixing ratio of water 12 to concrete powder 11, is preferably in the range of 3 to 8. If the liquid-solid ratio is less than 3, 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. Furthermore, if the liquid-solid ratio is 8 or more, i.e., if the solid content is relatively low, the amount of water will be in excess of the amount corresponding to the amount of concrete powder 11, and container 10 will become too large. Therefore, the liquid-solid ratio is preferably in the above range.

[0015] 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 regulator 22, and an air diffuser 23. One end of the supply pipe 21 is connected to a CO2 14 supply source (not shown). The supply pipe 21 has one or more branches in the middle, and the other ends of the supply pipes 21 are connected to multiple air diffusers 23. The gas supplied does not need to be 100% CO2 gas; factory exhaust gas containing N2 or O2 may also be used, as long as the actual amount of CO2 supplied is within a specified range.

[0016] The CO2 supply device 20 has at least one of a plurality of flow rate adjusters 22, each capable of adjusting the amount of CO2 supplied to a plurality of diffusers 23, located in the middle of the supply pipe 21, or a single flow rate adjuster 22 capable of adjusting the amount of CO2 supplied to all of the diffusers 23. Each of the one or more flow rate adjusters 22 may have an electromagnetic valve and be electrically controllable. Excess CO2 14 supplied is discharged from the container 10 as exhaust gas 15.

[0017] The air diffuser 23 includes a porous structure or the like and is a device that releases introduced CO2 14 as fine bubbles. One or more air diffusers 23 are disposed within the vessel 10 so that the entire diffuser 23 is immersed in the sludge slurry 13 contained within the vessel 10. The porous structure of the air diffuser 23 is formed of a porous material containing numerous pores. The porous structure may be covered with another material except for the surface on which the CO2 release surface is formed. Alternatively, the porous structure may be formed of a material without pores except for the surface on which the CO2 release surface is formed. Alternatively, the porous structure may be a hollow member or other member with numerous pores machined into its surface. For example, it may be a hollow tube with numerous pores drilled into its surface. Alternatively, a device that uses blades or the like to atomize CO2 may be used. Furthermore, the water depth at which the air diffuser 23 is disposed is preferably close to the bottom of the vessel 10 to efficiently immobilize CO2. For example, the water depth of the aeration device 23 should be 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, multiple CO2 fixation devices may be provided, and any shape of device is possible as long as the total contact time between CO2 and the sludge slurry is the same.

[0018] The CO214 introduced into the diffuser 23 is released into the sludge slurry 13 as bubbles with a diameter of 1 mm or less. When the CO214 injection depth, i.e., the water depth of the CO2 release surface of the diffuser 23 where the CO214 bubbles are generated, is L and the diameter of the CO214 bubbles at that water depth is M, the diffuser 23 is installed so that L / M≧400. When multiple diffusers 23 are installed at different heights, the CO214 injection depth is defined as L, which is the maximum water depth of the CO2 release surface of the diffuser 23 where the CO214 bubbles are generated.

[0019] Although the diffuser 23 is configured to release CO214 from its top surface, the CO2 release surface of the diffuser 23 may be configured not only as the top surface, but also as the side surface, bottom surface, or any combination thereof. When the CO2 release surface of the diffuser 23 is the side surface or bottom surface, clogging due to falling concrete powder 11 in the sludge slurry 13 is less likely to occur than when the CO2 release surface is the top surface. Therefore, the periodic maintenance interval for the diffuser 23 can be extended. The diffuser 23 may be one or multiple, as long as it can release the specified amount of CO214. Furthermore, when multiple diffusers are used, it is more efficient to arrange them at approximately equal intervals around the periphery of the wall of the container 10.

[0020] The agitator 30 is a device that agitates the sludge slurry 13 so as to efficiently fix CO214. The agitator 30 is continuously rotated 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 connected to the lower end of the rotating shaft 31.

[0021] The agitator 32 is formed to be at least 30% of the inner diameter or the inner dimensions of the vessel 10, such as the diameter of its largest portion. The water depth of the agitator 32 is at least 50% of the maximum design depth of the sludge slurry 13 to be placed in the vessel 10, i.e., at or deeper than half the water depth. The water depth at which the agitator 32 is placed is preferably as close to the bottom of the vessel 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 vessel 10. For example, the water depth should be at least 50% of the maximum design depth of the vessel 10, preferably at least 60%, and more preferably at least 70%. The agitator 32 is positioned at approximately the same depth relative to the aeration device 23. The agitator 32 can be positioned above the aeration device 23, within the depth 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 cross dimension of the largest part.

[0022] It should be noted that a circulation device for the sludge slurry 13 (not shown) can be provided together with or instead of the agitator 30. The circulation device has a pump and pipes before and after the pump, with the tip of the pipe before the pump being located on or near the bottom of the container 10 and the tip of the pipe after the pump being located at an upper part inside the container 10. The sludge slurry 13 on or near the bottom of the container 10 is sucked by the pump and circulated to above the sludge slurry 13 inside the container 10. This allows for efficient fixation of CO2.

[0023] In the above-described apparatus, water 12 and concrete powder 11 are introduced into a container 10 to achieve a predetermined liquid-solid ratio, and the mixing degree is uniformed by an agitator 30 to produce a sludge slurry 13. The predetermined liquid-solid ratio is 3 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 less. CO2 injection 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 amount is greater than 800 kg / t. This method allows CO2 to be efficiently immobilized in the concrete powder 11. After one CO2 immobilization operation is completed, the sludge slurry 13 is discharged from the container 10. Water 12 and concrete powder 11 are again introduced into the container 10. The discharged sludge slurry 13 is used as is or is dehydrated and dried, and the concrete powder 11 with immobilized CO2 is used as a cement raw material or the like.

[0024] Although the supply of CO214 to the vessel 10 has been described as being from a pressure vessel filled with CO214, other forms are also possible. CO2 derived from exhaust gas from the factory in which the vessel 10 is located or from 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. This reduces the amount of CO2 emitted from the factory.

[0025] In this invention, the target value for the amount of CO2 fixed in cement hydrate in the method for fixing CO2 in cement hydrate is set at 300 kg / t-sludge or more. Among the operating conditions that can achieve a CO2 fixation amount greater than this, we have determined operating conditions that allow for the ratio of calcium silicate hydrate (CSH) with a low calcium (Ca) to silicon (Si) ratio (hereinafter referred to as low-Ca calcium silicate hydrate) to calcium silicate hydrate with a high calcium to silicon (Si) ratio (hereinafter referred to as high-Ca calcium silicate hydrate), as well as for increasing the content of pozzolan. By increasing the amount of the above-mentioned substance with high alkali adsorption, the present invention reduces the alkali concentration in concrete, thereby suppressing alkali-aggregate reaction (ASR) in concrete. Regarding the above-mentioned predetermined values, the ratio of high-Ca calcium silicate hydrate to low-Ca calcium silicate hydrate in the sludge, i.e., high-Ca calcium silicate hydrate / low-Ca calcium silicate hydrate, was set to a target value of 0.9 or less, and the target value for the pozzolan content in the sludge was set to 50 (kg / t-sludge) or more.

[0026] Next, with reference to FIG. 2, the test equipment and results of tests conducted on this embodiment will be described. The test equipment was basically configured to match the above-described equipment. Note that in the test equipment in FIG. 2, the same or corresponding components are designated by the same reference numerals and their description will be omitted. The test equipment 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 constant temperature and humidity chamber 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 CO2 release surface of the aeration device 23 and the agitator blade 32 are positioned so that they are approximately 70% of the water depth.

[0027] The agitator blades 32 are formed to be 30% or more of the inner diameter of the container 10 or the inner dimensions such as the diameter of the largest part. The water depth of the agitator blades 32 is 50% or more of the maximum design water depth of the sludge slurry 13 to be placed in the container 10, i.e., half the water depth or deeper. The water depth at which the agitator blades 32 are placed is desirably 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 even when it sinks to the bottom of the container 10. For example, the water depth may be 60% or more, preferably 70% or more, of the maximum design water depth of the container 10.

[0028] [Ingredient preparation] Powdered ready-mixed concrete sludge supplied from a ready-mixed concrete plant was placed in container 10. The provided ready-mixed concrete sludge was selected from those that had been produced a short time ago, and those that began drying 24 hours after being supplied were used. The provided ready-mixed concrete sludge was crushed and then thoroughly dried in 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=2.61g / cm 3 , e=0.74). The dried sludge was then crushed. For the crushing process, a 10 kg sample was pulverized in a ball mill for 30 seconds. 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 similar to that of commercially available cement, and it can be treated as cement hydrate without aggregate. The particle size of the dried sludge used was 0.4 mm or less.

[0029] [Table 1]

[0030] [Carbonation treatment] Sludge slurry 13 was prepared by adding the dried sludge prepared as described above to 1,000 mL of ion-exchanged water to achieve a predetermined liquid-solid ratio. Then, while stirring the sludge slurry 13 in a constant temperature and humidity chamber (incubator), CO2 was injected into the slurry at a predetermined flow rate and for a predetermined time using an air diffuser 23. The CO2 flow rate was controlled using a float flow meter connected to a gas cylinder. After injection, 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 and passed through a 600 μm sieve, after which various analyses were performed.

[0031] The calculation method for each characteristic value is as follows. (1) CO2 injection amount (CO2 supply amount) (kg-CO2 / t-sludge) CO2 / Sludge = (QCO2×t) / Msludge QCO2: CO2 gas 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) CO2 fixed amount (kg / t-sludge') CO2 cap =CO2 TG ×(100 / (100-ig.loss TG ) CO2 cap : Amount of CO2 contained in ignited carbonated sludge (%) CO2 TG : CO2 amount (%) calculated by TG-DTA ig.loss TG : Weight loss (%) up to 1000°C in TG-DTA TG-DTA was performed using a simultaneous differential thermal and thermogravimetric analyzer TG-DTA6300 manufactured by Seiko Instruments Inc., under the conditions of a temperature range of room temperature to 1000°C, a heating rate of 10°C / min, and an atmosphere of N2. The following unit correction was also performed. CO2(kg / t-sludge')=CO2 cap×1000 / 100

[0032] The formation rate of low-Ca calcium silicate hydrate was measured by infrared spectroscopy at 900-1000 cm -1 The peak of calcium silicate hydrate with high Ca and Si in the vicinity and the peak of calcium silicate hydrate in the range of 1000 to 1030 cm -1 The peak height was calculated by taking the ratio of the peak height of the low-Ca, low-Si calcium silicate hydrate to the peak height of the nearby low-Ca, low-Si calcium silicate hydrate.

[0033] Here, the infrared spectroscopy measurement was performed using a JASCO FTIR-6100, and the measurement range was 4000 to 400 cm -1 The KBr (potassium bromide) pellet measurement method was used. For the measurement, approximately 1 mg of carbonated sludge and approximately 100 mg of KBr were thoroughly mixed in an agate mortar, and the mixture was pressed into a disk-shaped pellet for use in the measurement. The transmittance spectrum obtained in the measurement was converted to absorbance using the following equation (Beer-Lambert equation), and the peak ratio was calculated. Absorbance=log[1 / transmittance]

[0034] The amount of pozzolan produced was calculated as follows: Pozzolana production (kg / t-sludge) = [(Ma'-M') / 100] x 1000 M': Insoluble residue (%) determined by the hydrochloric acid-sodium carbonate method according to JIS R5202 "Chemical analysis method for cement" Ma': Insoluble residue (%) when only hydrochloric acid is dissolved in the above quantitative method

[0035] The results of the tests carried out using the above test equipment are shown in Table 2. [Table 2]

[0036] [result] (1) Test results for CO2 fixation amount by CO2 injection Table 2 shows the results of Examples 1 to 9, which were carried out under specified conditions. It was confirmed that the method of the present invention can fix the amount of CO2 in the sludge to 300 (kg / t-sludge') or more, which is significantly higher than the amount of CO2 fixed in the raw material, 82 (kg / t-sludge'). In the present invention, the sludge production conditions were determined with a target of fixing the amount of CO2 of 300 (kg / t-sludge') or more.

[0037] (2) CO2 injection rate Referring to the results in Table 2, at a CO2 injection rate of 3528 (kg / t·h) in Example 10, a CO2 fixation amount of 359 (kg / t-sludge') was obtained. Taking into consideration this result and the fact that the CO2 fixation amount was 302 (kg / t-sludge') at a CO2 injection rate of 4704 (kg / t·h) in Comparative Example 5, the CO2 injection rate was set to 3600 (kg / t·h) or less. Furthermore, even under the conditions of Example 2, where the CO2 injection rate was 588 (kg / t·h), the CO2 fixation amount was 358 (kg / t-sludge'), which is well above the target CO2 fixation amount of 300 (kg / t-sludge'), so the lower limit of the CO2 injection rate was set to 500 (kg / t·h).

[0038] (3) CO2 injection amount Regarding the lower limit of the CO2 injection rate, even at 882 kg / t in Example 2, there was still room for improvement compared to the CO2 fixation rate of 300 kg / t-sludge, so the CO2 injection rate was determined to be greater than 800 kg / t. Regarding the upper limit of the CO2 injection rate, the test results showed that even when a large amount was injected, the CO2 fixation rate, absorbance ratio, and pozzolan content did not necessarily change in proportion to the injection rate. Therefore, based on the test results, the upper limit of the CO2 injection rate was set at 6,300 kg / t, based on the maximum value confirmed in the test, 6,272 kg / t, in Example 9.

[0039] (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 fixed CO2 could be produced. When the liquid-solid ratio was less than 3, i.e., when the solid content was relatively high, the CO2 supply device 20 could become clogged, and the required amount of CO2 could not be supplied. Also, when the liquid-solid ratio was greater than 8, i.e., when the solid content was relatively low, the amount of water was in excess of the amount corresponding to the amount of concrete powder 11, and the container 10 would become too large. Therefore, the liquid-solid ratio was set to 3 or more and 8 or less.

[0040] (5) The ratio of the injection depth in the CO2 mixture to the maximum CO2 bubble diameter at the injection depth. In Example 4 of Table 2, sludge was successfully produced when the ratio was 400. Therefore, the ratio was set to 400 or greater. In the equipment embodying the present invention, the shape and dimensions of the vessel 10 and the CO2 supply device 20 are determined so that the ratio is 400 or greater. Regarding the upper limit of the ratio, one approach is to consider the 1000 ratio confirmed in Examples 1 to 3 and 5 to 11 by testing. However, the larger the ratio, the more advantageous it is. Specifically, in the test results, the larger the ratio, the greater the amount of CO2 fixed, the smaller the absorbance ratio, and the higher the pozzolan content. Therefore, the larger the ratio, the better.

[0041] According to the method of the present invention for fixing CO2 in cement hydrate, it is possible to efficiently fix CO2 and obtain cement hydrate that, when added to cement, can reduce the possibility of alkali-aggregate reaction (ASR) occurring in concrete. [Explanation of symbols]

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

Claims

[Claim 1] CO ２ A method for fixing a hydrated material to a cement hydrate, comprising the steps of: Cement hydrate, which is dry sludge with a particle size of 0.4 mm or less, and water are placed in a container, and CO is added to the container while stirring the mixture of cement hydrate and water. ２ CO ２ The CO ２ In the blowing process, CO ２ The injection rate is less than 3600 kg / t h, and CO ２ The injection rate is more than 800 kg / t. The CO ２ In the blowing process, The liquid-solid ratio of water to cement hydrate is 3 to 8, and CO ２ the injection depth in the mixed liquid of ２ The ratio of the maximum bubble diameter to the maximum bubble diameter of CO is 400 or more. ２ A method of fixing the material in cement hydrate.

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