Method and system for fixing carbon dioxide in cement hydrate-containing material

Abstract

To provide a method and system for fixing carbon dioxide to a cement hydrate-containing material, by using the cement hydrate-containing material to efficiently fix carbon dioxide contained in flue gas or the like, where the hexavalent chromium content in the obtained cement hydrate-containing material is reduced to reduce elution of hexavalent chromium from the cement hydrate-containing material.SOLUTION: The carbon dioxide fixing method and fixing system comprises supplying superheated steam contact heating at a temperature equal to or higher than 120°C to a cement hydrate-containing material and heating the cement hydrate-containing material while adding carbon dioxide, thereby fixing carbon dioxide to the cement hydrate-containing material.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method and system for immobilizing carbon dioxide in a cement hydrate-containing material, and more particularly to a method and system for immobilizing carbon dioxide in a cement hydrate-containing material using superheated steam. [Background technology]

[0002] BACKGROUND ART Various technologies have been developed to fix carbon dioxide in carbon dioxide-containing gases such as factory exhaust gases and reduce the amount of carbon dioxide emitted into the atmosphere. For example, Patent Document 1 discloses a method for reducing carbon dioxide emissions, which involves bringing a CO2-containing exhaust gas into contact with an aggregate of solid particles containing CaO and / or Ca(OH)2 as a composition, thereby fixing the CO2 in the exhaust gas as CaCO3 on the solid particles, thereby reducing the CO2 concentration in the exhaust gas. This method makes it possible to efficiently absorb and remove CO2 from exhaust gases generated in industrial processes, etc., thereby reducing the amount of CO2 emitted into the atmosphere.

[0003] Patent Document 2 describes a method for immobilizing carbon dioxide, which comprises collecting materials obtained by crushing waste concrete, supplying water and stirring them to make them moist, supplying exhaust gas accompanied by exhaust heat to the moistened materials to dry them, and then repeating the alternating steps of supplying water, stirring the materials, and supplying exhaust gas, thereby immobilizing the carbon dioxide in the exhaust gas in the materials. According to this method, the carbon dioxide in the exhaust gas accompanied by exhaust heat can be immobilized using recycled sand from waste concrete.

[0004] Patent Document 3 describes a carbon dioxide fixation concrete structure that is obtained by hardening a concrete composition containing water, cement, admixtures, and aggregate, and that has voids in the surface layer and is provided with carbon dioxide fixation molded bodies that fix carbon dioxide in the atmosphere in the surface layer.This structure can effectively fix carbon dioxide in the atmosphere.

[0005] Patent Document 4 describes a method for immobilizing carbon dioxide, which includes a contacting step of bringing a carbon dioxide-containing gas having a temperature of 350°C or higher into contact with a cementitious hardened body, thereby immobilizing carbon dioxide contained in the carbon dioxide-containing gas in the cementitious hardened body.

[0006] However, the carbon dioxide fixation methods disclosed in Patent Documents 1 to 4 have the problem that hexavalent chromium contained in concrete easily elutes from the treated material after the carbon dioxide fixation treatment, causing environmental pollution, which makes disposal of the treated material itself difficult.

[0007] On the other hand, Patent Document 5 proposes a method for suppressing the elution of hexavalent chromium from soil containing hexavalent chromium, in which soil containing hexavalent chromium is heat-treated at 200 to 600°C in a reducing atmosphere. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-197810 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-90198 [Patent Document 3] Japanese Patent Application Laid-Open No. 2008-75391 [Patent Document 4] Japanese Patent Publication No. 2020-131074 [Patent Document 5] Japanese Patent Application Laid-Open No. 2003-334532 Summary of the Invention [Problem to be solved by the invention]

[0009] The problem that the present invention aims to solve is to solve the above-mentioned problems and to provide a method and system for immobilizing carbon dioxide in a cement hydrate-containing material, which uses a cement hydrate-containing material to efficiently immobilize carbon dioxide contained in combustion exhaust gases and the like, and which reduces the elution of hexavalent chromium from the cement hydrate-containing material by reducing the hexavalent chromium content in the obtained cement hydrate-containing material. [Means for solving the problem]

[0010] In order to solve the above problems, the method and system for immobilizing carbon dioxide in a cement hydrate-containing material of the present invention have the following technical features. (1) A method for immobilizing carbon dioxide, comprising a superheated steam treatment step of contact-heating a cement hydrate-containing material with superheated steam at a temperature of 120°C or higher, and adding carbon dioxide during the superheated steam treatment step to immobilize the carbon dioxide in the cement hydrate-containing material.

[0011] (2) The method for fixation of carbon dioxide according to (1) above is characterized in that at least one of a reducing gas, a reducing substance, and an organic substance is present during the superheated steam treatment step, thereby reducing elution of hexavalent chromium from the cement hydrate-containing material after treatment.

[0012] (3) Above (1 ) The carbon dioxide fixation method described teeth The cement hydrate-containing material is characterized in that it is any one of recycled aggregate, waste building materials made of concrete or mortar, waste cement paste, and sludge generated in ready-mix concrete.

[0013] (4) A carbon dioxide fixation system comprising: a superheated steam treatment means for contact heating a cement hydrate-containing material with superheated steam at a temperature of 120°C or higher; and a carbon dioxide fixation system for fixing the carbon dioxide in the cement hydrate-containing material by supplying carbon dioxide to the superheated steam treatment means.

[0014] (5) In the carbon dioxide fixation system described in (4) above, at least one of a reducing gas, a reducing substance, and an organic substance is supplied to the superheated steam treatment means, thereby reducing elution of hexavalent chromium from the cement hydrate-containing material after treatment.

[0015] (6) Above (4 ) The carbon dioxide fixation system described teeth The cement hydrate-containing material is characterized in that it is any one of recycled aggregate, waste building materials made of concrete or mortar, waste cement paste, and sludge generated in ready-mix concrete. [Effects of the Invention]

[0016] The present invention provides a carbon dioxide immobilization method and system in which cement hydrate-containing material is contact-heated with superheated steam at a temperature of 120°C or higher and carbon dioxide is added during heating with the superheated steam, thereby immobilizing the carbon dioxide in the cement hydrate-containing material. This allows the cement hydrate-containing material to be efficiently heated and carbonation to be promoted. Furthermore, the oxygen concentration in the treatment furnace can be kept very low using superheated steam, and a reduced state can be easily maintained by using a reducing substance, etc. As a result, the amount of hexavalent chromium eluted from the treated material treated with the carbon dioxide immobilization method and system of the present invention is reduced, enabling expanded applications such as recycling of the treated material. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a diagram illustrating an outline of the carbon dioxide fixation method of the present invention. [Figure 2] FIG. 1 is a diagram illustrating a method of mixing carbon dioxide and a reducing gas with superheated steam. [Figure 3] FIG. 1 is a flow chart showing an example of the method for fixation of carbon dioxide of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, the method and system for immobilizing carbon dioxide in a cement hydrate-containing material according to the present invention will be described in detail using preferred examples with reference to the drawings. As shown in FIG. 1, the present invention provides a method and system for immobilizing carbon dioxide, which comprises supplying superheated steam contact heating at a temperature of 120°C or higher to a cement hydrate-containing material to heat the material, and simultaneously adding carbon dioxide to immobilize the carbon dioxide in the cement hydrate-containing material.

[0019] In the present invention, superheated steam is used instead of hot gas in order to perform efficient heating. Superheated steam has more energy than hot gas, and therefore can perform heating efficiently. The temperature of the superheated steam supplied to the treatment furnace must be 120°C or higher, preferably 200°C or higher, and more preferably 300°C or higher. Furthermore, as will be described later, a high carbon dioxide solidification rate (solidification amount) can be expected at temperatures between 300°C and 500°C. Furthermore, if the temperature of the superheated steam is too high, a reaction of reconversion to hexavalent chromium occurs, reducing the effect of suppressing the amount of eluted hexavalent chromium and increasing the amount of energy consumed. Therefore, taking into account the treatment effect relative to the energy used (the amount of solidified carbon dioxide and the amount of eluted hexavalent chromium), the temperature is set to 700°C or lower, preferably 600°C or lower, and more preferably 500°C or lower.

[0020] In the present invention, since superheated steam is used, it is possible to maintain an extremely low oxygen concentration inside the treatment furnace where the heat treatment is performed. Furthermore, by using a reducing substance in combination, the material to be treated can be easily maintained in a reduced state, and it is also possible to effectively suppress the amount of hexavalent chromium eluted from the material to be treated.

[0021] By the way, when using superheated steam, not only does it lower the oxygen concentration inside the treatment furnace, but it also makes it possible to generate reducing substances by thermally decomposing organic substances such as high-performance air-entraining water-reducing agents contained in waste concrete with superheated steam (oxygen-free state). In such cases, there is no need to separately supply reducing gas.

[0022] When carbon monoxide is used as a reducing substance in the treatment furnace, the concentration of carbon monoxide is set to 50 ppm or more, preferably 100 ppm or more.

[0023] The cement hydrate-containing materials used in this invention include materials that contain or adhere to cement hydrates, such as demolished concrete blocks, finely crushed concrete blocks, recycled aggregates produced from concrete blocks and their finely powdered parts, ready-mixed concrete sludge discharged from water treatment facilities in ready-mixed concrete plants, wood cement boards, and ALC waste. Among these, recycled aggregates, waste building materials made of concrete or mortar, waste cement paste, and sludge generated in ready-mixed concrete are more preferable from the standpoint of material cost and effective use of waste materials.

[0024] In the present invention, as shown in Fig. 1, it is possible to directly charge the cement hydrate-containing material into the treatment furnace, but as shown in Fig. 2, it is also possible to preheat the material using hot gas (hot air) before heating it with superheated steam. As the hot gas, high-temperature exhaust gas or the like can be used. Furthermore, by preheating the cement hydrate-containing material, it is possible to efficiently superheat it with superheated steam.

[0025] Furthermore, as shown in Figure 2, after heating and drying the cement hydrate-containing material in a heating furnace, grinding or milling the particle size to make it easier to absorb carbon dioxide can be achieved. It can also be expected to have the effect of removing mortar from the aggregate. Furthermore, treatment with superheated steam makes it even easier to remove mortar from the aggregate. The treated material discharged from the treatment furnace can be separated by particle size, for example, into fine powder with a particle size of 1 mm or less and recycled aggregate with a particle size of 1 mm or more, and each can be used for different purposes. It is also possible to subject the treated material to a pulverization process, such as grinding or milling, before separation.

[0026] As shown in Figure 1, carbon dioxide and reducing gas can be supplied separately to the processing furnace that supplies superheated steam. However, as shown in Figure 3, carbon dioxide and reducing gas (CO) can also be mixed with superheated steam and supplied.

[0027] As an example, water is converted to steam in a steam boiler, generating saturated steam at approximately 120°C and approximately 0.5 MPa. Carbon dioxide is then mixed with the steam and fed to a superheated steam generator. While there are various methods for converting saturated steam into superheated steam, induction heating of a heating element using high-frequency waves generated by a high-frequency power source is preferred because it allows for precise temperature control and simplifies the construction. The temperature of the superheated steam can be set between 120°C and 1000°C, depending on the capacity of the treatment furnace and the amount of cement hydrate-containing material being treated. Furthermore, to sufficiently reduce the amount of hexavalent chromium leaching, it is more preferable to set the temperature of the superheated steam between 300°C and 500°C.

[0028] In the present invention, when treatment is performed with superheated steam, at least one of a reducing gas, a reducing substance, and an organic substance is present, and treatment is performed in a reducing atmosphere. This makes it possible to reduce the elution of hexavalent chromium from the cement hydrate-containing material after treatment. As shown in Figure 3, carbon monoxide can be supplied as a reducing substance to the superheated steam between the superheated steam generator and the treatment furnace, and the superheated steam can be supplied to the treatment furnace.

[0029] As shown in FIG. 1, in the processing furnace, if the temperature cannot be maintained sufficiently by heating with superheated steam alone, it is possible to use a heating means such as an auxiliary electric heater in combination. In addition, in order to maintain an appropriate pressure inside the processing furnace, unnecessary gases are released into the atmosphere after dust and harmful substances have been removed. Furthermore, in order to operate the processing furnace continuously, it is also possible to use an inclined rotary furnace as shown in Patent Document 5, for example.

[0030] In order to confirm the effect of the carbon dioxide fixation method of the present invention, the following experiment was carried out. (Experimental Procedure) (1) 100 kg / h of saturated steam (0.2 MPa, 120°C) was generated in a steam boiler and supplied to a superheated steam generator. (2) Using a superheated steam generator (Nomura Giko Co., Ltd., GE-100 model, high-frequency power output 20 kW), superheated steam at a maximum temperature of 550°C was generated and supplied to the processing furnace (internal dimensions W400 mm x H400 mm x D400 mm). (3) The temperature inside the furnace was controlled by controlling the temperature of the supplied superheated steam. (4) An electric heater was used as an auxiliary to recover the initial temperature drop to the set temperature as quickly as possible. (5) The sample (using RC10 roadbed material made from waste concrete) was laid out to a thickness of about 10 mm and placed in the treatment furnace. (6) The carbon dioxide partial pressure was adjusted using a flow meter so that it could be controlled between 0 and 20%. (7) Carbon monoxide was also adjusted using a flow meter so that the concentration was 0-200 ppm.

[0031] The treated products obtained by the above-mentioned experimental procedures were analyzed by the following methods. (Analysis method) (1) The amount of hexavalent chromium leaching complies with Ministry of the Environment Notification No. 46. (2) Increase in calcium carbonate content In TG thermogravimetric analysis, the weight change between 500 and 850°C is considered to be calcium carbonate. Analysis was performed before and after superheated steam treatment to determine the amount of increase. Calculations were made on a dry sample basis. Specifically, it was calculated using the following formula. (Formula) Calcium carbonate increase (%) = (Qb - Qa) / Qa x 100 Here, the meanings of Qa and Qb are as follows: Qa: Amount of calcium carbonate contained in the untreated sample per unit sample (105°C dry basis) Qb: Amount of calcium carbonate contained in the treated sample per unit sample (105°C dry basis)

[0032] Experiments were conducted in two cases: one in which carbon dioxide was fixed using superheated steam alone (Table 1), and the other in which carbon dioxide was fixed using a combination of superheated steam and reducing gas (CO) (Table 2). The results of each experiment are as follows. The carbon dioxide supply time in each experiment was 60 minutes. As a comparative example, heating was performed using an electric heater instead of using superheated steam.

[0033] [Table 1]

[0034] [Table 2]

[0035] From the results in Tables 1 and 2, with reference to Comparative Example 1 and Example 3, or Comparative Example 2 and Example 7, it was confirmed that when superheated steam was used, the amount of calcium carbonate increased by about 20 times or more compared to when heating with an electric heater, even at the same temperature of 300°C, and it was confirmed that carbon dioxide fixation was more efficient when superheated steam was used.

[0036] Furthermore, it can be seen that the amount of hexavalent chromium eluted from the treated material is effectively suppressed when superheated steam of 300°C or higher is used, particularly with reference to Examples 3 and 4. This is presumably due to the fact that the use of superheated steam reduces the amount of oxygen supplied, and that organic matter contained in the waste concrete is thermally decomposed by the superheated steam to generate reducing substances.

[0037] Naturally, as shown in Examples 5 to 9, it is possible to effectively suppress the elution of hexavalent chromium by supplying a reducing substance (CO) for treatment. Moreover, it was confirmed that the amount of eluted hexavalent chromium was suppressed even at temperatures lower than 300°C. [Industrial Applicability]

[0038] As described above, according to the present invention, it is possible to provide a method and system for immobilizing carbon dioxide in a cement hydrate-containing material, which uses a cement hydrate-containing material to efficiently immobilize carbon dioxide contained in combustion exhaust gases and the like, and reduces the elution of hexavalent chromium from the cement hydrate-containing material by reducing the hexavalent chromium content in the obtained cement hydrate-containing material.

Claims

1. The cement hydrate-containing material is subjected to superheated steam treatment, which involves contact heating with superheated steam at a temperature of 120°C or higher. adding carbon dioxide during the superheated steam treatment to fix the carbon dioxide in the cement hydrate-containing material; A method for fixation of carbon dioxide, characterized in that the cement hydrate-containing material is any one of recycled aggregate, waste building materials made of concrete or mortar, waste cement paste, and sludge generated in ready-mix concrete.

2. 2. The method for fixation of carbon dioxide according to claim 1, wherein at least one of a reducing gas, a reducing substance, and an organic substance is made present during the superheated steam treatment, thereby reducing elution of hexavalent chromium from the cement hydrate-containing material after the treatment.

3. a superheated steam treatment means for contact heating the cement hydrate-containing material with superheated steam at a temperature of 120°C or higher; supplying carbon dioxide to the superheated steam treatment means and immobilizing the carbon dioxide in the cement hydrate-containing material; A carbon dioxide fixation system characterized in that the cement hydrate-containing material is any one of recycled aggregate, waste building materials made of concrete or mortar, waste cement paste, and sludge generated in ready-mix concrete.

4. 4. The carbon dioxide fixation system according to claim 3, wherein at least one of a reducing gas, a reducing substance, and an organic substance is supplied to the superheated steam treatment means, thereby reducing elution of hexavalent chromium from the cement hydrate-containing material after treatment.

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