Method and apparatus for manufacturing recycled aggregate

Abstract

To manufacture a high-purity recycled aggregate from a concrete block at a low cost.SOLUTION: A method for manufacturing a recycled aggregate includes: a heating step of subjecting a concrete block to heat treatment; a kneading step of manufacturing the recycled aggregate from the heated concrete block by performing kneading treatment on the heated concrete block; and a gas supply step of supplying a carbon dioxide gas to at least one of the concrete block during the kneading treatment, the concrete block during the heat treatment, or the concrete block after the heat treatment and before the kneading treatment. In the gas supply step, the carbon dioxide gas having a higher carbon dioxide concentration than that of air is supplied.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method and an apparatus for producing recycled aggregates.

Background Art

[0002] According to the technique described in Patent Document 1 below, recycled aggregates can be produced from a concrete block by subjecting the concrete block heat-treated with hot air to a rubbing process. However, in this technique, it is necessary to use fossil fuel as a heat source for generating hot air for the heat treatment, and there is room for improvement from the viewpoints of manufacturing cost and reduction of carbon dioxide emissions.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The present invention has been made in view of the above problems. The main object of the present invention is to provide a technique capable of suppressing the cost for producing recycled aggregates from a concrete block to a low level and further expecting reduction of carbon dioxide emissions.

Means for Solving the Problems

[0005] The method for manufacturing recycled aggregate according to the first aspect of the present invention includes a heating step of performing heat treatment on a concrete block, a rubbing step of manufacturing recycled aggregate from the concrete block after the heat treatment by performing a rubbing treatment on the concrete block after the heat treatment, and a rubbing step of performing a rubbing treatment on the concrete block during the rubbing treatment. And a gas supply step of supplying carbon dioxide gas to at least one of the concrete block during the heat treatment and the concrete block after the heat treatment and before the rubbing treatment. In the gas supply step, the carbon dioxide gas having a carbon dioxide concentration higher than the carbon dioxide concentration of air is supplied.

[0006] According to the method according to the first aspect, by supplying carbon dioxide gas to the heated concrete block at a high temperature, a chemical reaction (carbonation reaction) between the calcium, sodium, or magnesium content contained in the concrete block and the carbon dioxide contained in the carbon dioxide gas can be caused. The heat generated by this carbonation reaction can increase the temperature of the concrete block. Therefore, it is possible to reduce the amount of fuel used for the heat treatment of the concrete block. That is, the energy efficiency in the heat treatment of the concrete block can be improved. In addition, since the heated cement paste becomes fragile, the production efficiency of recycled aggregate by rubbing can be improved. The cement paste is a component derived from cement separated from the concrete block. Furthermore, since carbon dioxide is fixed in the concrete block (or products such as cement paste fine powder and recycled aggregate separated therefrom) by the carbonation reaction, a reduction in carbon dioxide emissions can be expected. As means for supplying carbon dioxide gas, exhaust gas from a cement factory, exhaust gas from a waste incineration facility, exhaust gas from a thermal power plant, etc. can be preferably used. Further, it may be exhaust gas discharged from the heating device of the concrete block. Further, high-concentration carbon dioxide gas obtained by separating and recovering carbon dioxide from the exhaust gas and increasing the carbon dioxide concentration to 90% or more may be used.

[0007] The method for manufacturing recycled aggregate according to the second aspect of the present invention is such that the carbon dioxide concentration of the carbon dioxide gas is 10% or more and 50% or less, and the temperature of the carbon dioxide gas is 200°C or more and 350°C or less. When the carbon dioxide concentration is within the above range, it becomes about 300 to 1600 times the carbon dioxide concentration of 0.03% in the atmosphere, and the carbonation reaction proceeds more efficiently.

[0008] The method for manufacturing recycled aggregate according to the third aspect of the present invention is to further supply carbon dioxide gas to the recycled aggregate obtained after the grinding treatment in the gas supply step. According to the method according to the above third aspect, carbon dioxide can be further fixed to the recycled aggregate obtained after the grinding treatment.

[0009] The manufacturing apparatus for recycled aggregate according to the fourth aspect of the present invention includes a heating device for performing heat treatment on a concrete block, a grinding facility for manufacturing recycled aggregate from the concrete block after the heat treatment by performing a grinding treatment on the concrete block after the heat treatment, the concrete block during the grinding treatment, the concrete block during the heat treatment, and at least one of the concrete blocks after the heat treatment and before the grinding treatment, and a gas supply means for supplying carbon dioxide gas, and the gas supply means supplies the carbon dioxide gas having a carbon dioxide concentration higher than the carbon dioxide concentration of air.

[0010] According to the apparatus according to the above fourth aspect, the same effect as the method according to the first aspect can be achieved.

[0011] The manufacturing apparatus for recycled aggregate according to the fifth aspect of the present invention further supplies carbon dioxide gas to the recycled aggregate obtained after the grinding treatment by the gas supply means. According to the apparatus according to the above fifth aspect, the same effect as the method according to the third aspect can be achieved.

Effects of the Invention

[0012] According to the present invention, it is possible to improve the energy efficiency in manufacturing recycled aggregates from concrete blocks and keep the manufacturing cost of the recycled aggregates low. Further, according to the present invention, it is possible to expect a reduction in carbon dioxide emissions.

Brief Description of the Drawings

[0013]

Figure 1

Embodiments for Carrying Out the Invention

[0014] A manufacturing apparatus 1 of recycled aggregates according to an embodiment of the present invention will be described. This manufacturing apparatus 1 manufactures recycled aggregates from concrete blocks, and as shown in FIG. 1, includes a heating device 10, a grinding device 20, a classification device 30, a first dust collection device 40, a second dust collection device 50, and a gas supply means 70. The concrete block means a hardened body of concrete. Examples of the concrete block include concrete scraps (such as fragments of concrete discharged during construction or demolition work). Since the concrete block contains various foreign matters, such as steel materials such as reinforcing bars, wood, plastics, etc., it is preferable to appropriately select and remove these foreign matters. In particular, since plastics may generate harmful substances such as dioxins by heat treatment, it is necessary to remove them. Further, before the concrete block is put into the heating device, it is preferable to crush it to a maximum size of 10 to 60 mm, preferably 20 to 40 mm, and remove large blocks by sieving. Thereby, damage to the heating device 10 itself or refractory bricks inside the heating device 10 can be reduced, and grinding in the subsequent grinding process can be efficiently performed.

[0015] The heating device 10 heat-treats the concrete block with combustion gas. As the heating device 10, for example, a rotary kiln, a roller hearth kiln, a fluidized bed heating furnace, etc. can be used if it is a continuous type, and a general heating furnace can be used if it is a batch type.

[0016] The rubbing device 20 rubs and processes the concrete blocks (concrete blocks after heat treatment) discharged from the heating device 10. Inside the rubbing device 20, cement paste fine powder (powder of hardened cement paste) is removed from the concrete blocks to produce recycled aggregates. Here, the recycled aggregates are, for example, the recycled aggregates defined in "JIS A 5021:2018", "JIS A 5022:2018", and "JIS A 5023:2018". In addition, in the process of manufacturing the recycled aggregates, cement paste fine powder (powder of hardened cement paste) is also manufactured at the same time.

[0017] As the rubbing device 20, for example, a crusher, a pulverizer, or a grinder for concrete waste can be used (see Patent Document 1). More specifically, for example, a grinder "Product Name: Marumar" manufactured by Kurimoto Iron Works can be used as the rubbing device 20. In addition, as the rubbing device 20, it is preferable that the residence time of the concrete blocks inside it can be made as long as necessary to ensure the contact time between the concrete blocks and carbon dioxide gas in the rubbing device 20.

[0018] The classification device 30 classifies the recycled aggregates discharged from the rubbing device 20. By the classification device 30, the recycled aggregates are separated into recycled coarse aggregates and recycled fine aggregates. As the classification device 30, for example, a vibrating screen can be used. Here, the recycled coarse aggregates are, for example, the recycled coarse aggregates defined in "JIS A 5021:2018", "JIS A 5022:2018", and "JIS A 5023:2018". Also, the recycled fine aggregates are, for example, the recycled fine aggregates defined in "JIS A 5021:2018", "JIS A 5022:2018", and "JIS A 5023:2018".

[0019] The first dust collecting device 40 sucks the exhaust gas from the heating device 10 and recovers the cement paste fine powder contained in this exhaust gas. As the first dust collecting device 40, for example, a bag filter or an electrostatic precipitator can be used.

[0020] The second dust collecting device 50 sucks the exhaust gas from the grinding device 20 and recovers the cement paste fine powder contained in this exhaust gas. As the second dust collecting device 50, the same device as the first dust collecting device 40 can be used, but a device with different functions or structures may also be used.

[0021] The gas supply means 70 can supply carbon dioxide gas from a gas supply source (not shown) to the required location. Here, the carbon dioxide concentration of the carbon dioxide gas is higher than the carbon dioxide concentration in the air (usually about 0.03 to 0.04%), for example, 1% or more and 50% or less, preferably 10% or more and 50% or less. Also, the temperature of the carbon dioxide gas is, for example, 200°C or more and 350°C or less. Examples of the gas supply source include a factory (specifically, a cement manufacturing factory, a waste treatment facility, etc.) or a thermal power plant. Examples of the carbon dioxide gas include the exhaust gas from a factory or a thermal power plant (for example, the exhaust gas during cement firing in a cement manufacturing factory).

[0022] Specifically, the gas supply means 70 includes pipes 71, 72, and 73 for transferring carbon dioxide gas from a gas supply source (not shown). The gas supply means 70 may be configured to supply carbon dioxide gas to the recycled aggregate or cement paste fine powder after being separated by the grinding device and immobilize the carbon dioxide. Here, when immobilizing carbon dioxide on the recycled aggregate, the contact between the recycled aggregate and carbon dioxide can be improved by injecting carbon dioxide gas while stirring the recycled aggregate in a container (not shown). When fixing carbon dioxide to cement paste fine powder, the contact between the cement paste fine powder and carbon dioxide can be improved by injecting carbon dioxide while stirring the cement paste fine powder in a container (not shown), or by injecting carbon dioxide in a state where the cement paste fine powder is dispersed in a fluidized bed.

[0023] The pipe 71 is configured to supply carbon dioxide gas to the concrete mass being heat-treated inside the heating device 10. The pipe 71 is inserted into the heating device 10, for example, from a concrete mass supply port (not shown) of the heating device 10.

[0024] The pipe 72 is configured to supply carbon dioxide gas to the concrete mass (the concrete mass after heat treatment and before grinding treatment) being conveyed from the heating device 10 toward the grinding device 20. The pipe 72 is disposed above a conveying means (not shown, such as a hot elevator, a belt conveyor, etc.) that conveys the concrete mass from the heating device 10 to the grinding device 20 so as to be able to spray carbon dioxide gas onto the concrete mass.

[0025] The pipe 73 is configured to supply carbon dioxide gas to the concrete mass being ground inside the grinding device 20. The pipe 73 is inserted into the grinding device 20, for example, from a concrete mass supply port (not shown) of the grinding device 20 so as to be able to supply carbon dioxide gas.

[0026] Next, a method for manufacturing recycled aggregate according to an embodiment of the present invention will be described. First, combustion gas is supplied into the heating device 10. Also, carbon dioxide gas from a gas supply source is supplied into the heating device 10 through the pipe 71 of the gas supply means 70. Thereby, the inside of the heating device 10 can be set to a high temperature (for example, 200°C to 350°C) and a high carbon dioxide gas concentration (for example, 10% to 50%).

[0027] Next, a concrete lump (for example, one crushed so that the maximum particle size is 40 mm or less) is supplied into the heating device 10. Inside the heating device 10, as the heat of the combustion gas is transferred to the concrete lump, the temperature of this concrete lump rises. Then, a chemical reaction (carbonation: in this example, the production reaction of calcium carbonate, sodium carbonate, or magnesium carbonate) occurs between the calcium component, sodium component, or magnesium component contained in the high-temperature concrete lump and the carbon dioxide in the carbon dioxide gas. Since the carbonation reaction is an exothermic reaction, the temperature of this concrete lump further rises. Therefore, the amount of fuel required to keep the temperature conditions inside the heating device 10 constant can be saved. That is, it becomes possible to improve the energy efficiency and reduce the amount of carbon dioxide emissions during the production of recycled aggregates by heating and grinding.

[0028] Furthermore, the heat-treated concrete lump is transported from the heating device 10 to the grinding device 20 using a transport means such as a hot elevator. Here, carbon dioxide gas from a gas supply source is supplied to the transported concrete lump through the pipe 72. As a result, a chemical reaction (carbonation) occurs between the calcium component, sodium component, or magnesium component contained in the concrete lump whose high temperature is maintained after the heat treatment and the carbon dioxide in the carbon dioxide gas. As described above, since the carbonation reaction is an exothermic reaction, the temperature drop of this concrete lump can be suppressed by the heat generated by this chemical reaction (depending on the conditions, the temperature can be maintained or increased).

[0029] Subsequently, carbon dioxide gas from the gas supply source is supplied into the rubbing device 20 through the pipe 73. Then, the concrete block conveyed from the heating device 10 is supplied into the rubbing device 20. As a result, inside the rubbing device 20, a chemical reaction (carbonation) occurs between the calcium, sodium, or magnesium content contained in the concrete block and the carbon dioxide in the carbon dioxide gas. And, the rubbing process by the rubbing device 20 is performed on the concrete block that has become high temperature due to the heat generated by this chemical reaction. Then, inside the rubbing device 20, the aggregate and the cement paste fine powder (powder of the cement paste hardened body) are separated from this concrete block. That is, recycled aggregate and cement paste fine powder can be generated thereby. In the present embodiment, since the concrete block processed by the rubbing device 20 is at a high temperature, the cement paste adhering to the aggregate constituting the concrete block can be weakened. Also, due to the action of the temperature increase, the adhesion force between the aggregate and the cement paste is weakened. Thereby, the crushing of the concrete block and the separation between the recycled aggregate and the cement paste can be facilitated.

[0030] Subsequently, the recycled aggregate generated by the rubbing device 20 is supplied to the classification device 30. The classification device 30 separates the recycled aggregate into recycled coarse aggregate and recycled fine aggregate. These recycled coarse aggregate and recycled fine aggregate are, for example, usable as aggregate for recycled aggregate concrete.

[0031] Note that the cement paste content remains in the recycled coarse aggregate and the recycled fine aggregate, and they have the remaining capacity for the carbonation reaction. Therefore, carbon dioxide can be fixed to the recycled coarse aggregate or / and the recycled fine aggregate. For example, when the recycled fine aggregate or the recycled coarse aggregate is put into a stirring container and carbon dioxide gas is injected while stirring, the carbonation reaction proceeds effectively.

[0032] In this embodiment, while the above operations are being performed, the first dust collector 40 sucks the gas inside the heating device 10 and collects the fine cement paste powder contained in the sucked exhaust gas. Also, the second dust collector 50 sucks the gas inside the grinding device 20 and collects the fine cement paste powder contained in the sucked exhaust gas. The fine powder thus collected can be used, for example, as a filler for cement. Note that the exhaust gas from the first dust collector 40 and the second dust collector 50 is treated by an appropriate method.

[0033] Note that the fine cement paste powder has cement paste as a main component and has a margin for carbonation reaction. Therefore, carbon dioxide can be fixed in the fine cement paste powder. For example, when the fine cement paste powder is put into a stirring container and carbon dioxide gas is injected while stirring, the carbonation reaction proceeds effectively. Also, when carbon dioxide is injected in a state where the fine cement paste powder is dispersed in a fluidized bed, the carbonation reaction proceeds more efficiently.

[0034] As described above, according to this embodiment, by supplying carbon dioxide gas to the concrete mass that has become high temperature by heat treatment, a chemical reaction occurs between the calcium content, sodium content, or magnesium content contained in this concrete mass and the carbon dioxide in the carbon dioxide gas, and due to the heat generation accompanying this chemical reaction, the temperature of the concrete mass can be further increased. For this reason, the fuel required for heat-treating the concrete mass at a predetermined temperature can be saved, the energy efficiency in the production process of recycled aggregate can be improved, and furthermore, the amount of carbon dioxide emissions during the production of recycled aggregate by heat grinding can be reduced.

[0035] Moreover, according to the present embodiment, by supplying carbon dioxide gas to the high-temperature concrete mass, carbon dioxide can be fixed in the concrete mass (or products such as cement paste fine powder or recycled aggregate separated therefrom). Therefore, there is also an advantage that the carbon dioxide concentration in the exhaust gas discharged from a plant such as a cement manufacturing plant can be reduced. As a result, it is possible to expect a reduction in the amount of carbon dioxide emissions from a plant such as a cement manufacturing plant.

[0036] In the present embodiment, carbon dioxide gas is supplied to all of the concrete mass being heat-treated inside the heating device 10, the concrete mass after heat treatment and before the rubbing treatment (i.e., the concrete mass being conveyed from the heating device 10 to the rubbing device 20), and the concrete mass being rubbed inside the rubbing device 20. However, a configuration in which carbon dioxide gas is supplied to at least one of these may also be used.

[0037] In the present embodiment, a concentration device (not shown) for increasing the carbon dioxide concentration of the carbon dioxide gas discharged from the gas supply source may be used to increase the carbon dioxide concentration of the carbon dioxide gas supplied through the pipes 71 to 73.

[0038] In the present embodiment, a part of the exhaust gas from the rubbing device 20 may be circulated so as to be returned inside the rubbing device 20 again. Then, the heat of the exhaust gas and the carbon dioxide gas can be reused. Similarly, it is also possible to circulate and reuse a part of the exhaust gas from the heating device 10 to the heating device 10.

[0039] Furthermore, in this embodiment, it may further include either or both of a classifier (not shown) for classifying the cement paste fine powder collected by the first dust collector 40 and a classifier (not shown) for classifying the cement paste fine powder collected by the second dust collector 50. In this case, among the fine powder (powder with a particle size less than a predetermined particle size) and the coarse powder (powder with a particle size greater than or equal to the predetermined particle size) obtained by these classifiers, the fine powder may be used as a filler for cement production, and the coarse powder may be returned to the inside of the heating device 10 or the grinding device 20 for reprocessing. Here, the particle size of the fine powder is, for example, less than 30 μm, and the particle size of the coarse powder is, for example, 30 μm or more, but it is not limited to this. Also, it may be configured to supply carbon dioxide gas to at least one of the recycled aggregate generated by heat grinding, the cement paste fine powder generated by heat grinding, and the cement paste fine powder recovered from the heating device.

[0040] Since the coarse powder has a larger specific surface area than the concrete block, the carbonation reaction by carbon dioxide in the carbon dioxide gas is promoted, and it can be expected to increase the calorific value.

Explanation of Signs

[0041] 1 Manufacturing apparatus for recycled aggregate 10 Heating device 20 Grinding device 30 Classifier 40 First dust collector 50 Second dust collector 70 Gas supply means 71·72·73 Piping

Claims

1. A heating step of performing a heat treatment on a concrete block; A rubbing step of manufacturing recycled aggregate from the heat-treated concrete block by performing a rubbing treatment on the heat-treated concrete block; A gas supply step of supplying carbon dioxide gas to at least one of the concrete block during the rubbing treatment, the concrete block during the heat treatment, and the concrete block after the heat treatment and before the rubbing treatment; A method for manufacturing recycled aggregate, characterized in that in the gas supply step, the carbon dioxide gas having a carbon dioxide concentration higher than the carbon dioxide concentration of air is supplied.

2. The carbon dioxide concentration of the carbon dioxide gas is 10% or more and 50% or less; The temperature of the carbon dioxide gas is 200°C or more and 350°C or less. The method for manufacturing recycled aggregate according to Claim 1, characterized in that.

3. The method for manufacturing recycled aggregate according to Claim 1 or 2, wherein in the gas supply step, carbon dioxide gas is further supplied to the recycled aggregate obtained after the rubbing treatment.

4. A heating device for performing a heat treatment on a concrete block; A rubbing device for manufacturing recycled aggregate from the heat-treated concrete block by performing a rubbing treatment on the heat-treated concrete block; Gas supply means for supplying carbon dioxide gas to at least one of the concrete block during the rubbing treatment, the concrete block during the heat treatment, and the concrete block after the heat treatment and before the rubbing treatment; A manufacturing apparatus for recycled aggregate, characterized in that the gas supply means supplies the carbon dioxide gas having a carbon dioxide concentration higher than the carbon dioxide concentration of air.

5. The manufacturing apparatus for recycled aggregate according to Claim 4, wherein the gas supply means is configured to further supply carbon dioxide gas to the recycled aggregate obtained after the rubbing treatment.

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