Method for producing asphalt mixture, asphalt mixture production plant, and carbon dioxide fixation agent

Abstract

This invention provides a method for producing an asphalt mixture that facilitates the effective use of fixed carbon dioxide. [Solution] A method for producing an asphalt mixture, comprising an aggregate heating step, an aggregate transport step, and a mixing step, wherein in at least one of the aggregate heating step, aggregate transport step, and mixing step, the steps are carried out in the presence of calcium hydroxide and carbon dioxide, so that calcium carbonate is produced by the reaction of calcium hydroxide and carbon dioxide and carbon dioxide is fixed, and in the mixing step, the produced calcium carbonate is mixed with aggregate and asphalt as a filler.

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing an asphalt mixture, a plant for manufacturing an asphalt mixture, and a carbon dioxide immobilizing agent.

Background Art

[0002] In view of the need to recover carbon dioxide in the atmosphere and exhaust gas, Patent Document 1 and Patent Document 2 disclose technologies for solidifying carbon dioxide in the production of asphalt mixtures.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] The technologies of Prior Document 1 and Patent Document 2 have a problem that the immobilized carbon dioxide is not effectively utilized.

[0005] Therefore, an object of the present disclosure is to provide a method for manufacturing an asphalt mixture, a plant for manufacturing an asphalt mixture, and a carbon dioxide immobilizing agent capable of effectively utilizing the immobilized carbon dioxide.

Means for Solving the Problems

[0006] To achieve the above object, the method for manufacturing an asphalt mixture of the present disclosure includes an aggregate heating step, an aggregate conveying step, and a mixing step, wherein the aggregate heating step is a step of heating the aggregate, and the aggregate conveying step is a step of conveying the heated aggregate to the mixing step. The mixing step is a step of mixing the aggregate, asphalt, and filler, In at least one of the aggregate heating step, the aggregate transport step, and the mixing step, the steps are carried out in the presence of calcium hydroxide and carbon dioxide, so that calcium carbonate is produced by the reaction of calcium hydroxide and carbon dioxide and the carbon dioxide is fixed. In the mixing step, the generated calcium carbonate is mixed with the aggregate and the asphalt as the filler. This is the manufacturing method.

[0007] The asphalt mixture manufacturing plant described herein is Including an aggregate heating section, an aggregate transport section, and a mixing section, In the aggregate heating section, a process of heating the aggregate is carried out. In the aggregate transport section, a process is carried out to transport the heated aggregate to the mixing section. In the mixing section, a step is carried out in which the aggregate, asphalt, and filler are mixed. In at least one of the aggregate heating section, the aggregate transport section, and the mixing section, the above steps are carried out in the presence of calcium hydroxide and carbon dioxide, so that calcium carbonate is produced by the reaction of calcium hydroxide and carbon dioxide and the carbon dioxide is fixed. In the mixing section, the step of mixing the generated calcium carbonate with the aggregate and the asphalt as the filler is carried out. It is a manufacturing plant.

[0008] The carbon dioxide fixative of this disclosure is a carbon dioxide fixative used in the method for producing the asphalt mixture of this disclosure, The calcium hydroxide mentioned above, It is a carbon dioxide fixation agent. [Effects of the Invention]

[0009] According to this disclosure, fixed carbon dioxide can be effectively utilized. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a diagram showing an example of a manufacturing plant for the asphalt mixture of this disclosure. [Figure 2] Figure 2 is a graph showing an example of carbon dioxide sequestration according to this disclosure. [Modes for carrying out the invention]

[0011] The present disclosure provides a method for producing an asphalt mixture, further comprising a combustion step, The combustion step is a step of burning fuel to generate heat, and the heat generated in the combustion step is used to perform heating in the aggregate heating step, and the carbon dioxide generated in the combustion step is used as the carbon dioxide in the reaction. In this embodiment, the combustion step may be one or more. Furthermore, the heat generated by the combustion in the combustion step may not be limited to the aggregate heating step, but may also be used for other steps such as the aggregate transport step, the mixing step, or the heating step of the asphalt before mixing.

[0012] The asphalt mixture manufacturing plant of the present disclosure may further include a combustion section and a gas supply section, wherein the combustion section performs a step of burning fuel to generate heat, the heat generated in the combustion section is used to heat the aggregate in at least the aggregate in the aggregate heating section, and the gas supply section supplies the carbon dioxide generated by the combustion in the combustion section to at least one of the aggregate heating section, the aggregate transport section, and the mixing section where the reaction is carried out, and uses it as the carbon dioxide for the reaction. In this embodiment, the combustion section and the gas supply section may be one or more. Furthermore, the heat generated by the combustion in the combustion section may not only be used to heat the aggregate heating section, but also other sections such as the aggregate transport section, the mixing section, or the heating process of the asphalt before mixing.

[0013] In the present disclosure, the reaction may be carried out in the presence of moisture. As the moisture, for example, water may be sprayed or atomized at a location where carbon dioxide is immobilized. Further, the moisture may be the moisture contained in the aggregate, for example, the moisture contained in sand.

[0014] In the present disclosure, the calcium hydroxide is not particularly limited, and may be, for example, slaked lime and sludge (waste) such as concrete. The carbon dioxide immobilization reaction by calcium hydroxide is represented by the following chemical reaction formula. Ca(OH)2 + CO2 → CaCO3 + H2O

[0015] The slaked lime may be industrial slaked lime or highly reactive slaked lime for removing HCl and SOx in exhaust gas. The highly reactive slaked lime has characteristics such as a larger specific surface area and pore volume than ordinary slaked lime.

[0016] Further, as the calcium hydroxide, calcium hydroxide contained in waste such as sludge, like the calcium hydroxide in sludge, may be used. Examples of the sludge include concrete sludge.

[0017] In a fresh concrete factory, residual concrete that was produced in excess of the order quantity and not shipped, returned concrete that was not used at the supply destination and returned, and their dissolution products; fresh concrete sludge containing cement such as washing wastewater generated by washing equipment such as mixer trucks is generated. In the present disclosure, the fresh concrete sludge generated in a fresh concrete factory can be used as calcium hydroxide.

[0018] Ready-mix concrete sludge typically contains water, calcium compounds such as calcium hydroxide that dissolve in water, and solid components of the sludge (mainly hydration products, aggregate particles, etc. (mainly silica, aluminum, iron, and other metals and their constituents, as well as calcium carbonate)). Sometimes, the solid components are removed from the ready-mix concrete sludge, separating it into supernatant water containing calcium hydroxide, etc., and sludge water containing the solid components of the sludge (mainly hydration products, aggregate particles, etc.). In this case, both the supernatant water and the sludge water can be used as calcium hydroxide.

[0019] Regardless of whether the fresh concrete sludge water used as calcium hydroxide is the supernatant water or the sludge water, the solid content concentration in the fresh concrete sludge water is preferably 40% by mass or less, more preferably 20% by mass or less, even more preferably 10% by mass or less, and even more preferably 5% by mass or less.

[0020] As previously described, fresh concrete sludge water contains dissolved calcium hydroxide as a calcium component, but because calcium hydroxide has low solubility, it also exists as a solid component. In addition, calcium carbonate and other calcium components are also present, mainly as solid components. Thus, fresh concrete sludge water contains calcium components such as calcium hydroxide and calcium carbonate as solid components, as well as sludge solid components (mainly hydrated products, aggregate fine particles, etc.) as described above. These solid components, especially the calcium hydroxide contained as a calcium component, react with carbon dioxide to form calcium carbonate. Furthermore, the calcium carbonate contained in fresh concrete sludge water can be used as a filler in this disclosure.

[0021] From the viewpoint of promoting the formation of calcium carbonate, the solid content concentration in the ready-mix concrete sludge water is preferably 0.001% by mass or more, more preferably 0.0015% by mass or more, and even more preferably 0.002% by mass or more. Furthermore, from a similar viewpoint, the particle size of the solid content in the ready-mix concrete sludge water is preferably 1000 μm or less, more preferably 100 μm or less, even more preferably 10 μm or less, even more preferably 1 μm or less, and particularly preferably 0.1 μm or less.

[0022] When the ready-mix concrete sludge water is the supernatant water described above, the calcium concentration in the ready-mix concrete sludge water is usually 100 mg / L or more, preferably 250 mg / L or more, more preferably 500 mg / L or more, and even more preferably 800 mg / L or more. The higher the upper limit, the better, and there are no particular restrictions, but it is usually 1500 mg / L or less. Furthermore, if the ready-mix concrete sludge water is the sludge water described above, the calcium concentration in the ready-mix concrete sludge water is usually 1,000 mg / L or more, preferably 10,000 mg / L or more, more preferably 100,000 mg / L or more, and even more preferably 300,000 mg / L or more. As for the upper limit, the higher the better, and there is no particular limit, but it is usually 3,000,000 mg / L or less.

[0023] Furthermore, as the ready-mix concrete sludge water, a mixture obtained by mixing the above-mentioned solids from ready-mix concrete sludge with water, from which the solids have been removed, can also be used. The aforementioned solids contain calcium components such as calcium hydroxide, and the hydration products mainly contained in the solids contain calcium components such as calcium hydroxide and calcium silicate hydrate. Therefore, even the mixture from which the solids have been removed still contains calcium dissolved from the solids in water, making it possible to convert more calcium into calcium carbonate from ready-mix concrete sludge.

[0024] In this disclosure, the aggregate may be new aggregate or recycled aggregate. For example, new aggregate may include crushed stone, gravel, and sand. Recycled aggregate may include recycled aggregate manufactured from construction waste. Construction waste may include, for example, asphalt pavement waste excavated by road construction, or concrete waste (crushed stone) from demolished buildings.

[0025] Examples of crushed stone include single-sized crushed stone (No. 1 to No. 7), crushed stone run (C-20 to C-40), and graded crushed stone (M-25 to M-40) as specified in JIS A5001:2008. Standard products include crushed stone for concrete as specified in JIS A5005:2020. It is also possible to use non-standard crushed stone similar to these as crushed stone.

[0026] Examples of crushed sand include concrete crushed sand as specified in JIS A5005:2020. It is also possible to use materials that do not meet the specifications of crushed sand as crushed sand.

[0027] Examples of recycled aggregates include concrete-grade recycled aggregates H, M, and L, as specified in JIS A5021:2018, JIS A5022:2018, and JIS A5023:2018, respectively. It is also possible to use non-standard recycled aggregates similar to these as recycled aggregates.

[0028] Examples of recycled crushed stone include recycled crushed stone made from recycled crushed stone and graded crushed stone (e.g., RC-40), and recycled graded crushed stone (e.g., RM-30).

[0029] In this disclosure, the filler is a fine aggregate, for example, fine particles that pass through a 75 μm sieve. Examples of fillers include limestone and igneous rock powder, slaked lime, cement, and fly ash. The main component of limestone powder is calcium carbonate, and this disclosure has the advantage that calcium carbonate produced by fixing carbon dioxide can be used as a filler.

[0030] Next, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments. In the following drawings, the same parts are denoted by the same reference numerals. Furthermore, unless otherwise specified, the descriptions of each embodiment can be used interchangeably with those of the others, and unless otherwise specified, the configurations of each embodiment can be combined.

[0031] [Embodiment 1] Figure 1 shows an example of the configuration of an asphalt mixture manufacturing plant according to the present disclosure. As shown in Figure 1, the manufacturing plant in this example has as its main components a new aggregate dryer 11a, a recycled aggregate dryer 11b, a burner 15a, a burner 15b, a hot elevator 12, a mixer 13, a classifier 14, a filler hopper 16a, an asphalt storage tank 16b, a dust collection filter 17, and a chimney 18. The new aggregate dryer 11a and burner 15a, and the recycled aggregate dryer 11b and burner 15b each constitute two aggregate heating sections. The hot elevator is an aggregate transport section that transports the heated new aggregate to the classifier 14. The heated recycled aggregate is also transported to the classifier 14 by an aggregate transport section (not shown). Mixer 13 is a mixing unit that mixes aggregate supplied from classifier 14, filler supplied from filler hopper 16a, and asphalt supplied from asphalt storage tank 16b. Some of the exhaust gas discharged from burner 15a is introduced into new aggregate dryer 11a, while the rest passes through dust collection filter 17 and is discharged from chimney 18. Similarly, some of the exhaust gas discharged from burner 15b is introduced into recycled aggregate dryer 11b by the exhaust gas unit (indicated by arrows in Figure 1), while the rest passes through dust collection filter 17 and is discharged from chimney 18. In addition, the exhaust gas from new aggregate dryer 11a and recycled aggregate dryer 11b also passes through dust collection filter 17 and is discharged from chimney 18.

[0032] In the manufacturing plant described here, the production of asphalt mixture is carried out, for example, as follows: First, new aggregate (crushed stone, gravel, sand, etc.) and calcium hydroxide (slaked lime, etc.) are put into a new aggregate dryer 11a and heated with a burner 15a. At this time, the exhaust gas from the burner 15a is introduced into the new aggregate dryer 11a. Inside the new aggregate dryer 11a, the new aggregate is dried by heating, and the carbon dioxide in the exhaust gas reacts with the calcium hydroxide to produce calcium carbonate. The calcium carbonate produced in the new aggregate dryer 11a is supplied to the classifier 14 by the hot elevator 12 along with the dried new aggregate. Next, recycled aggregate and calcium hydroxide (slaked lime, etc.) are put into a recycled aggregate dryer 11b and heated with a burner 15b. At this time, the exhaust gas from the burner 15b is introduced into the recycled aggregate dryer 11b. Inside the recycled aggregate dryer 11b, the recycled aggregate is dried by heating, and carbon dioxide in the exhaust gas reacts with calcium hydroxide to produce calcium carbonate. The calcium carbonate produced in the new aggregate dryer 11b, along with the dried recycled aggregate, is supplied to the classifier 14 by the aggregate transport unit (not shown). The new aggregate, recycled aggregate, and calcium carbonate supplied to the classifier 14 are classified and then supplied to the mixer 13. Filler (stone powder, etc.) is supplied to the mixer 13 from the filler hopper 16a as needed. Asphalt is supplied to the mixer 13 from the asphalt storage tank 16b. In the mixer 13, the new aggregate, recycled aggregate, calcium carbonate (filler), and asphalt are mixed to produce an asphalt mixture. The produced asphalt mixture is loaded onto dump trucks and delivered to road construction sites, etc. The exhaust gas from burners 15a and 15b passes through the dust collection filter 17 and is released into the atmosphere by the chimney 18, but the exhaust gas contains recovered carbon dioxide.

[0033] In this disclosure, the method of adding calcium hydroxide is not particularly limited; for example, it may be added manually or automatically using a machine. Furthermore, if added in a dispersed state in water, it may be added by spraying or misting.

[0034] In this disclosure, the carbon dioxide to be fixed is not particularly limited and may be, for example, carbon dioxide generated during the combustion of a burner, or carbon dioxide in the atmosphere.

[0035] In this disclosure, the location where carbon dioxide fixation is carried out is not particularly limited and may be any of the aggregate heating section, aggregate transport section, or mixing section, or it may be fixed in a location other than these.

[0036] [Embodiment 2] This embodiment is an experimental example of fixing carbon dioxide using calcium hydroxide.

[0037] A carbon dioxide measuring device and a calcium hydroxide sample were placed in a plastic bag and the bag was sealed. Three types of samples were used: ready-mix concrete sludge, industrial slaked lime, and highly reactive slaked lime. Air was removed from the sealed plastic bag using a syringe. Carbon dioxide-containing gas was introduced into the plastic bag from which the air had been removed. The carbon dioxide-containing gas had a carbon dioxide concentration of 3 vol% and a nitrogen gas concentration of 97 vol%. The plastic bag containing the carbon dioxide-containing gas was placed in a shaker and shaken at a shaking amplitude of 50 mm and 200 rpm, and the carbon dioxide concentration inside the plastic bag was measured. The results are shown in the graph in Figure 2.

[0038] In Figure 2, graph A represents sludge, graph B represents industrial slaked lime, and graph C represents highly reactive slaked lime. As shown in the graphs in Figure 2, the carbon dioxide concentration decreased over time in all three samples, confirming the fixation of carbon dioxide by the samples. When highly reactive slaked lime was used as the sample, the decrease in carbon dioxide concentration occurred rapidly. A decrease in carbon dioxide concentration was also confirmed when sludge was used as the sample. On the other hand, the formation of calcium carbonate was confirmed in all samples.

[0039] Although the present disclosure has been described above with reference to embodiments, the present disclosure is not limited to the embodiments described above. Various modifications to the structure and details of the present disclosure are possible, as can be understood by those skilled in the art within the scope of the present disclosure. Furthermore, each embodiment can be combined with other embodiments as appropriate. [Industrial applicability]

[0040] According to this disclosure, fixed carbon dioxide can be effectively utilized as a filler in asphalt mixtures. According to this disclosure, for example, carbon dioxide fixation and effective utilization can be achieved by making simple modifications to existing asphalt mixture manufacturing plants. According to this disclosure, for example, carbon dioxide generated in asphalt mixture manufacturing plants can be fixed, and furthermore, carbon dioxide in the atmosphere and carbon dioxide contained in exhaust gases from other factories can be fixed and effectively utilized. For this reason, the asphalt mixture manufacturing method and the like of this disclosure are useful, for example, for reducing carbon dioxide and effectively utilizing resources. [Explanation of symbols]

[0041] 1. Asphalt mixture manufacturing plant 11a New aggregate dryer 11b Recycled aggregate dryer 12 Hot Elevator 13 Mixer 14 Classifier 15a, 15b burners 16a Filler Hopper 16b Asphalt storage tank 17 Dust collection filter 18 Chimney

Claims

1. This process includes an aggregate heating process, an aggregate transport process, and a mixing process. The aggregate heating step is a step of heating the aggregate, The aggregate transport step is a step of transporting the heated aggregate to the mixing step, The mixing step is a step of mixing the aggregate, asphalt, and filler, In at least one of the aggregate heating step, the aggregate transport step, and the mixing step, the steps are carried out in the presence of calcium hydroxide and carbon dioxide, so that calcium carbonate is produced by the reaction of calcium hydroxide and carbon dioxide and the carbon dioxide is fixed. In the mixing step, the generated calcium carbonate is mixed with the aggregate and the asphalt as the filler. A method for producing asphalt mixtures.

2. Furthermore, including the combustion process, The aforementioned combustion process is a process of burning fuel to generate heat. The heat generated in the combustion process is used to carry out heating in at least the aggregate heating process. The carbon dioxide generated in the combustion of the combustion step is used as the carbon dioxide in the reaction. A method for producing the asphalt mixture according to claim 1.

3. A method for producing an asphalt mixture according to claim 1, wherein the above reaction is carried out in the presence of water.

4. The method for producing an asphalt mixture according to claim 3, wherein the moisture is moisture contained in the aggregate.

5. The calcium hydroxide is slaked lime. A method for producing the asphalt mixture according to claim 1.

6. Including an aggregate heating section, an aggregate transport section, and a mixing section, In the aggregate heating section, a process of heating the aggregate is carried out. In the aggregate transport section, a process is carried out to transport the heated aggregate to the mixing section. In the mixing section, a step is carried out in which the aggregate, asphalt, and filler are mixed. In at least one of the aggregate heating section, the aggregate transport section, and the mixing section, the above steps are carried out in the presence of calcium hydroxide and carbon dioxide, so that calcium carbonate is produced by the reaction of calcium hydroxide and carbon dioxide and the carbon dioxide is fixed. In the mixing section, the step of mixing the generated calcium carbonate with the aggregate and the asphalt as the filler is carried out. A plant that manufactures asphalt mixtures.

7. Furthermore, including the combustion section and the gas supply section, In the aforementioned combustion section, a process is carried out in which fuel is burned to generate heat. A step is performed in which the heat generated in the combustion section is used to heat the aggregate in at least the aggregate heating section. The gas supply unit supplies the carbon dioxide generated by the combustion in the combustion unit to at least one of the aggregate heating unit, the aggregate transport unit, and the mixing unit where the reaction is carried out, and uses it as the carbon dioxide for the reaction. A manufacturing plant for the asphalt mixture according to claim 6.

8. The above reaction is carried out in the presence of water. A manufacturing plant for the asphalt mixture according to claim 6.

9. The moisture mentioned above is the moisture contained in the aggregate. A manufacturing plant for the asphalt mixture according to claim 8.

10. The calcium hydroxide is slaked lime. A manufacturing plant for the asphalt mixture according to claim 6.

11. A carbon dioxide fixing agent used in the method for producing the asphalt mixture according to claim 1, A carbon dioxide fixation agent containing the aforementioned calcium hydroxide.

12. The calcium hydroxide mentioned above includes slaked lime. The carbon dioxide fixative according to claim 11.

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