Coal ash treatment system and method for producing fly ash for concrete

Abstract

To provide a coal ash treatment system low in unburned carbon content and capable of efficiently providing coal ashes having a high activity index, and a method for manufacturing concrete fly ashes.SOLUTION: This coal ash treatment system comprises: a reformer that reduces an unburned carbon content of coal ashes containing unburned carbons to provide reformed coal ashes; a sampling device that collects some of the reformed coal ashes; a physical property measurement device that measures at least one physical property value selected from the group consisting of the area average particle size of the reformed coal ashes collected by the sampling device and a screening residue of a prescribed particle size; and a distribution device that distributes the reformed coal ashes on the basis of the physical property value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a coal ash treatment system and a method for producing fly ash for concrete. [Background technology]

[0002] Coal ash (fly ash) is a fine particle produced by the aggregation of molten cinders in high-temperature gases generated when pulverized coal is burned in the power generation boilers of coal-fired power plants. Coal ash is a pozzolanic substance primarily composed of SiO2 and Al2O3, and its use in concrete is known to exhibit excellent properties, such as increased long-term strength, improved workability, and suppression of alkali-silica reaction. However, coal ash also contains unburned carbon. The use of coal ash with a high unburned carbon content in concrete can adversely affect concrete quality, such as the occurrence of black spots and a reduction in air content due to adsorption of air-entraining agents. For this reason, efforts have been made to reduce the unburned carbon content of coal ash. Methods for reducing the unburned carbon content of coal ash, such as belt-type electrostatic separation, heat treatment, and flotation, have been investigated (Patent Documents 1 to 3). Furthermore, an attempt to improve the activity index of modified coal ash by classifying and pulverizing modified coal ash, which has had its unburned carbon content reduced by heat treatment, has also been investigated (Patent Document 2).

[0003] Furthermore, the activity index of coal ash can vary depending on factors such as the type of coal used in coal-fired power plants. For this reason, studies have been conducted to predict the activity index of coal ash, select coal ash with a high activity index, and use it in concrete (Patent Documents 4 and 5). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2013-538124 [Patent Document 2] Japanese Patent Application Publication No. 2019-107620 [Patent Document 3] Japanese Patent Application Laid-Open No. 2010-23018 [Patent Document 4] Japanese Patent Application Publication No. 2019-168433 [Patent Document 5] Japanese Patent Application Laid-Open No. 2017-142140 Summary of the Invention [Problem to be solved by the invention]

[0005] Coal ash used in concrete desirably has a low unburned carbon content and a high activity index. However, it is difficult to significantly improve the activity index of coal ash by simply reducing the unburned carbon content of the coal ash. Furthermore, improving the activity index of modified coal ash by classifying or pulverizing the modified coal ash, which has a reduced unburned carbon content, is a complicated process. Furthermore, predicting the activity index of coal ash based on the Blaine specific surface area requires time to measure the Blaine specific surface area, making it difficult to immediately reflect the results in the process, making it difficult to consistently reduce the unburned carbon content of coal ash.

[0006] The present invention has been made in view of the above-mentioned circumstances, and has an object to provide a coal ash treatment system and a method for producing fly ash for concrete, which are capable of efficiently producing coal ash having a low unburned carbon content and a high activity index. [Means for solving the problem]

[0007] In order to solve the above problems, the coal ash treatment system of the present invention includes a modification device that reduces the unburned carbon content of coal ash containing unburned carbon to obtain modified coal ash; a sampling device that collects a portion of the modified coal ash; a physical property measuring device that measures at least one physical property value selected from the group consisting of an area average particle size of the modified coal ash collected by the sampling device and a sieve residue of a predetermined particle size; and a sorting device that sorts the modified coal ash based on the physical property value.

[0008] The coal ash treatment system of the present invention configured as described above includes a coal ash reforming device that reduces the unburned carbon content of raw coal ash containing unburned carbon to obtain modified coal ash, thereby enabling the production of coal ash with a low unburned carbon content. The coal ash treatment system of the present invention also includes a sampling device that collects a portion of the modified coal ash obtained by the coal ash reforming device, a physical property measuring device that measures at least one physical property selected from the group consisting of the area average particle diameter of the modified coal ash collected by the sampling device and a sieve residue of a predetermined particle size, and a modified coal ash sorting device that sorts the modified coal ash based on the physical property value, thereby enabling the production of coal ash with a high activity index. Therefore, the coal ash treatment system of the present invention makes it possible to efficiently obtain coal ash with a low unburned carbon content and a high activity index.

[0009] Here, in the coal ash processing system of the present invention, the particle size of the sieve residue may be in the range of 3 μm to 15 μm. In this case, the particle size of the sieve residue is within the range of 3 μm to 15 μm, so coal ash with a high activity index can be obtained with higher accuracy.

[0010] In the coal ash treatment system of the present invention, the coal ash reforming device may be a belt-type electrostatic separation device. In this case, raw coal ash can be reformed continuously at room temperature without heating the coal ash, so that coal ash with a low unburned carbon content, a small energy load, and a high activity index can be obtained more efficiently.

[0011] In the coal ash treatment system of the present invention, the physical property measuring device may be a laser diffraction particle size distribution measuring device. In this case, the physical properties of the modified coal ash can be measured continuously in a dry manner, so that coal ash with a low unburned carbon content and a high activity index can be obtained more efficiently.

[0012] The method for producing fly ash for concrete of the present invention includes: a modification step of obtaining modified coal ash by reducing the unburned carbon content of coal ash containing unburned carbon; a sampling step of collecting a portion of the modified coal ash; a physical property measurement step of measuring at least one physical property value selected from the group consisting of an area average particle size and a sieve residue of a predetermined particle size of the modified coal ash collected in the sampling step; a prediction step of predicting an activity index of the modified coal ash at a material age of 28 days based on the physical property value; and a recovery step of recovering modified coal ash whose activity index is predicted to be an arbitrary value of 80% or more in the prediction step.

[0013] The method for producing fly ash for concrete of the present invention includes a modification step of reducing the unburned carbon content of unburned carbon-containing coal ash to obtain modified coal ash, thereby enabling the production of coal ash with a low unburned carbon content. The method for producing fly ash for concrete of the present invention also includes a sampling step of collecting a portion of the modified coal ash obtained in the modification step, a physical property measurement step of measuring at least one physical property selected from the group consisting of the area-average particle size and a sieve residue of a predetermined particle size of the modified coal ash collected in the sampling step, a prediction step of predicting the activity index of the modified coal ash at a material age of 28 days based on the physical property value, and a recovery step of recovering the modified coal ash whose activity index is predicted to be 80% or higher in the prediction step. Therefore, the method for producing fly ash for concrete of the present invention enables the efficient production of coal ash with a low unburned carbon content and a high activity index.

[0014] Here, in the method for producing fly ash for concrete of the present invention, each of the sampling step, the property measuring step, the prediction step, and the recovery step may be configured to be performed while continuously transporting the modified coal ash obtained in the modification step. In this case, there is no need for a facility for temporarily storing the modified coal ash obtained in the modification step, so that fly ash for concrete can be produced more efficiently. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a coal ash treatment system and a method for producing fly ash for concrete that can efficiently produce coal ash with a low unburned carbon content and a high activity index. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a block diagram illustrating a coal ash treatment system according to an embodiment of the present invention. [Figure 2] FIG. 1 is a flow diagram showing a method for producing fly ash for concrete according to one embodiment of the present invention. [Figure 3] FIG. 1 is a correlation diagram between the 5 μm sieve residue and activity index of modified coal ash obtained in the examples. [Figure 4] FIG. 1 is a correlation diagram between the 10 μm sieve residue and activity index of modified coal ash obtained in the examples. [Figure 5] FIG. 1 is a correlation diagram between the area average particle diameter MA and the activity index of modified coal ash obtained in the examples. [Figure 6] FIG. 1 is a correlation diagram between the Blaine specific surface area and activity index of modified coal ash obtained in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a block diagram showing a coal ash treatment system according to one embodiment of the present invention. As shown in FIG. 1 , the coal ash treatment system 10 includes a raw coal ash storage facility 11, a coal ash supply device 12, a coal ash modification device 13, a sampling device 14, a physical property measurement device 15, a calculation device 16, a control device 17, a modified coal ash sorting device 18, and a highly active modified coal ash storage device 19.

[0018] The raw coal ash storage facility 11 is a facility for temporarily storing raw coal ash before the coal ash is processed. The raw coal ash is coal ash generated, for example, in a power generation boiler of a coal-fired power plant.

[0019] The coal ash supplying device 12 is a device that supplies raw coal ash stored in the raw coal ash storage facility 11 to the coal ash reforming device 13. The coal ash supplying device 12 is, for example, a combination of a belt conveyor, an air slider, a rotary valve, and the like.

[0020] The coal ash reformer 13 is a device that reduces the unburned carbon content of raw coal ash by removing coal ash containing a large amount of unburned carbon, thereby obtaining reformed coal ash. Examples of the coal ash reformer 13 include a belt-type electrostatic separator and a heating device. The belt-type electrostatic separator has a pair of parallel electrodes and a mesh belt disposed between the pair of electrodes (positive and negative electrodes). In the belt-type electrostatic separator, raw coal ash is supplied to a rotating mesh belt, and the raw coal ash is caused to collide or come into contact with each other, thereby positively charging the unburned carbon and negatively charging the coal ash (pozzolanic substance). The positively charged unburned carbon is then moved to the negative electrode side, and the negatively charged coal ash is moved to the positive electrode side, thereby separating the unburned carbon from the coal ash. The heating device is a device that heats the raw coal ash to volatilize and remove unburned carbon. The belt-type electrostatic separator is preferable in that it can be operated at room temperature, does not require thermal energy, and can continuously modify raw coal ash.

[0021] The sampling device 14 is a device that collects a portion of the modified coal ash obtained in the coal ash reformer 13. The portion of the modified coal ash is an amount necessary for measuring the physical properties of the modified coal ash with the physical property measuring device 15. The remainder of the modified coal ash is sent from the coal ash reformer 13 to the modified coal ash sorting device 18. The sampling device 14 may be arranged at a position where it can sample a portion of the modified coal ash as a measurement sample from the line that transports the modified coal ash from the coal ash reformer 13 to the modified coal ash sorting device 18.

[0022] The physical property measuring device 15 is a device that measures the physical properties of the modified coal ash sampled by the sampling device 14. The physical properties of the modified coal ash to be measured are the area average particle size and the sieve residue of a predetermined particle size. The particle size of the sieve residue is preferably in the range of 3 μm to 15 μm, and preferably in the range of 5 μm ± 2 μm or 10 μm ± 2 μm. A laser diffraction particle size distribution measuring device can be used as the physical property measuring device 15. The physical properties are preferably measured continuously in a dry state using the laser diffraction particle size distribution measuring device. By measuring in a dry state, the physical properties of the modified coal ash can be measured continuously.

[0023] The calculation device 16 is a device that calculates a predicted value of the activity index of the modified coal ash at a material age of 28 days based on the physical property values ​​measured by the physical property measurement device 15. The calculation device 16 may, for example, be a device having a memory unit that stores a correlation equation between the previously measured physical property values ​​of the modified coal ash and the activity index at a material age of 28 days, and a calculation unit that calculates a predicted value of the activity index of the modified coal ash at a material age of 28 days by substituting the physical property values ​​measured by the physical property measurement device 15 into the correlation equation stored in the memory unit. Examples of the calculation device 16 include a personal computer and a smartphone. The calculation device 16 and the physical property measurement device 15 may be connected by wire or wirelessly.

[0024] The control device 17 is a device that determines whether the predicted value of the activity index predicted by the calculation device 16 is a preset value. Then, based on the determination result, the control device 17 transmits a control signal to the modified coal ash sorting device 18. For example, when the predicted value of the activity index of the modified coal ash predicted by the calculation device 16 is 80% or more, the control device 17 transmits a control signal to recover the modified coal ash as high-activity modified coal ash, and when the predicted value of the activity index of the modified coal ash is less than 80%, the control device 17 transmits a control signal to recover the modified coal ash as low-activity modified coal ash. The control device 17 and the calculation device 16 may be connected by wire or wirelessly. The control device 17 and the modified coal ash sorting device 18 may be connected by wire or wirelessly.

[0025] The modified coal ash sorting device 18 is a device that sorts the modified coal ash transported from the coal ash reforming device 13 into high-activity modified coal ash and low-activity modified coal ash based on a control signal transmitted from the control device 17. The high-activity modified coal ash can be used, for example, as fly ash for concrete. The low-activity modified coal ash can be used, for example, as a cement raw material.

[0026] The highly active modified coal ash storage device 19 is a device that stores the highly active modified coal ash sorted by the modified coal ash sorting device 18.

[0027] In the coal ash treatment system 10 of this embodiment, it is preferable that the time required from when the modified coal ash is collected by the sampling device 14 until when the control device 17 sends a control signal to the modified coal ash sorting device 18 is within the time required for the modified coal ash obtained by the coal ash reformer 13 to be transported to the modified coal ash sorting device 18. In this case, there is no need to provide equipment for temporarily storing the modified coal ash between the coal ash reformer 13 and the modified coal ash sorting device 18, and the coal ash can be treated continuously.

[0028] Next, a method for producing fly ash for concrete according to one embodiment of the present invention will be described. FIG. 2 is a flow diagram showing a method for producing fly ash for concrete according to one embodiment of the present invention. 2, the method for producing fly ash for concrete of this embodiment is a method for producing fly ash for concrete from raw coal ash. The method for producing fly ash for concrete includes a modifying step S01, a sampling step S02, a physical property measuring step S03, a prediction step S04, a determination step S05, and a recovery step S06.

[0029] The reforming step S01 is a step of reducing the unburned carbon content of raw coal ash to obtain reformed coal ash. The reforming step S01 can be performed using the coal ash reforming device 13 described above.

[0030] The sampling step S02 is a step of collecting a portion of the modified coal ash obtained in the modification step S01. The sampling step S02 can be performed using the above-mentioned sampling device 14. The remainder of the modified coal ash obtained in the modification step S01 is transported to the recovery step S06.

[0031] The physical property measuring step S03 is a step of measuring the physical properties of the modified coal ash collected in the sampling step S02. The physical property measuring step S03 can be performed using the physical property measuring device 15 described above.

[0032] The prediction step S04 is a step of calculating a predicted value of the activity index of the modified coal ash at an age of 28 days based on the physical property values ​​measured in the physical property measurement step S03. The prediction step S04 can be performed using the calculation device 16 described above.

[0033] The determination step S05 is a step of determining whether the predicted value of the activity index predicted in the prediction step S04 is a preset value. The determination step S05 can be performed using the above-mentioned control device 17. In this embodiment, it is determined whether the predicted value of the activity index of the modified coal ash is 80% or more.

[0034] The recovery step S06 is a step of recovering the modified coal ash, whose predicted value of the activity index is determined to be 80% or more in the determination step S05, as fly ash for concrete. The recovery step S06 can be performed using the above-mentioned modified coal ash sorting device 18. The modified coal ash, whose predicted value of the activity index is determined to be less than 80% in the determination step S05, can be recovered separately from the fly ash for concrete and used as a cement raw material, for example.

[0035] In the method for producing fly ash for concrete of this embodiment, it is preferable to perform the sampling step S02, the physical property measurement step S03, the prediction step S04, and the recovery step S06 while continuously transporting the modified coal ash obtained in the modification step S01. That is, it is preferable that the time required for the sampling step S02, the physical property measurement step S03, the prediction step S04, and the determination step S05 is within the time required for the modified coal ash obtained in the modification step S01 to be transported to the recovery step S06. Since there is no need for equipment to temporarily store the modified coal ash obtained in the modification step S01, fly ash for concrete can be produced more efficiently.

[0036] The coal ash treatment system 10 of this embodiment, configured as described above, includes a coal ash reformer 13 that reduces the unburned carbon content of raw coal ash containing unburned carbon to obtain reformed coal ash, thereby enabling the production of coal ash with a low unburned carbon content. The coal ash treatment system 10 of this embodiment also includes a sampling device 14 that samples a portion of the reformed coal ash obtained by the coal ash reformer 13, a physical property measuring device 15 that measures at least one physical property selected from the group consisting of the area-average particle size of the reformed coal ash sampled by the sampling device 14 and a sieve residue of a predetermined particle size, and a reformed coal ash sorting device 18 that sorts the reformed coal ash based on the physical property value, thereby enabling the production of coal ash with a high activity index. Therefore, the coal ash treatment system 10 of this embodiment allows the efficient production of coal ash with a low unburned carbon content and a high activity index.

[0037] In the coal ash processing system 10 of this embodiment, if the particle size of the sieve residue is in the range of 3 μm to 15 μm, coal ash with a high activity index can be obtained with higher accuracy. Furthermore, in the coal ash treatment system 10 of this embodiment, when the coal ash reformer 13 is a belt-type electrostatic separator, raw coal ash can be reformed continuously at room temperature, making it possible to more efficiently obtain coal ash with a low unburned carbon content and a high activity index. Furthermore, when the physical property measuring device 15 is a laser diffraction particle size distribution measuring device, the physical property values ​​of the modified coal ash can be measured continuously in a dry state, making it possible to more efficiently obtain coal ash with a low unburned carbon content and a high activity index.

[0038] The method for producing fly ash for concrete of this embodiment includes a modification step S01 in which the unburned carbon content of unburned carbon-containing coal ash is reduced to obtain modified coal ash, thereby enabling the production of coal ash with a low unburned carbon content. The method for producing fly ash for concrete of this embodiment also includes a sampling step S02 in which a portion of the modified coal ash obtained in the modification step S01 is collected, a physical property measurement step S03 in which at least one physical property value selected from the group consisting of the area-average particle size and a sieve residue of a predetermined particle size of the modified coal ash collected in the sampling step S02 is measured, a prediction step S04 in which the activity index of the modified coal ash at a material age of 28 days is predicted based on the physical property value, and a recovery step S06 in which the modified coal ash predicted to have an activity index of 80% or higher in the prediction step S04 is recovered. Therefore, the method for producing fly ash for concrete of this embodiment allows the efficient production of coal ash with a low unburned carbon content and a high activity index.

[0039] Although the embodiment of the present invention has been described above, the present invention is not limited to this and can be modified as appropriate within the scope of the technical idea of ​​the invention. For example, in the coal ash treatment system 10 of this embodiment, the calculation device 16 is used to calculate a predicted value of the activity index of the modified coal ash at an age of 28 days based on the physical property values ​​measured by the physical property measurement device 15, but this is not limited to this. The modified coal ash may also be sorted based on the physical property values ​​measured by the physical property measurement device 15, such as the area average particle diameter of the modified coal ash and the sieve residue of a predetermined particle size. [Example]

[0040] Twenty types of coal ash were prepared. Each type of coal ash was separated into positively and negatively charged particles using a belt-type electrostatic separator, and the negatively charged particles were collected as modified coal ash. The particle size distribution of the collected modified coal ash was measured using a laser diffraction particle size analyzer (Insitec Dry, Malvern Instruments) in a dry state to determine the volume mean diameter (MV), number mean diameter (MN), area mean diameter (MA), calculated specific surface area (CS), 95 μm sieve residue, 45 μm sieve residue, 20 μm sieve residue, and 5 μm sieve residue. The Blaine specific surface area, 45 μm sieve residue (measured by the mesh sieve method), and activity index (at 28 days) of the modified coal ash were also measured. The Blaine specific surface area was measured in accordance with the method specified in JIS R 5201:2015 (Physical Testing Methods for Cement). The 45 μm sieve residue measured using the mesh sieve method was measured in accordance with the method specified in Appendix B of JIS A 6201:2015 (fly ash for concrete). The activity index was measured in accordance with the method specified in Appendix C of JIS A 6201:2015. The results are shown in Table 1.

[0041] [Table 1]

[0042] The correlation coefficients between the Blaine specific surface area, the 45 μm sieve residue measured by the mesh sieve method, and each physical property measured with a laser diffraction particle size analyzer and the activity index (material age: 28 days) were calculated. The results showed that the 5 μm sieve residue, 10 μm sieve residue, area-average particle diameter MA, and Blaine specific surface area showed a high correlation with the activity index, with a coefficient of determination of 0.88 or higher. Figure 3 shows the correlation between the 5 μm sieve residue and the activity index, Figure 4 shows the correlation between the 10 μm sieve residue and the activity index, Figure 5 shows the correlation between the area-average particle diameter MA and the activity index, and Figure 6 shows the correlation between the Blaine specific surface area and the activity index.

[0043] The results in Figures 3 to 6 confirm that the activity index of modified coal ash (at age: 28 days) can be accurately predicted using the 5 μm sieve residue, 10 μm sieve residue, area-average particle diameter MA, and Blaine specific surface area. However, continuous measurement of Blaine specific surface area is difficult. On the other hand, the 5 μm sieve residue, 10 μm sieve residue, and area-average particle diameter MA can be continuously measured using a laser diffraction particle size distribution analyzer. Therefore, the activity index can be continuously predicted for modified coal ash that is continuously modified using a modification device. [Explanation of symbols]

[0044] 10 Coal Ash Treatment System 11 Raw coal ash storage facility 12 Coal ash supply equipment 13 Coal ash reforming equipment 14 Sampling Device 15 Physical property measuring equipment 16 Computing equipment 17 Control device 18 Modified coal ash separator 19 Highly active modified coal ash storage facility

Claims

1. a reforming device for reducing the unburned carbon content of coal ash containing unburned carbon to obtain reformed coal ash; a sampling device for sampling a portion of the modified coal ash; a physical property measuring device that measures at least one physical property value selected from the group consisting of an area average particle size of the modified coal ash sampled by the sampling device and a sieve residue having a predetermined particle size; a sorting device that sorts the modified coal ash based on the physical property value, A coal ash treatment system, wherein the particle size of the sieve residue measured by the physical property measuring device is in the range of 3 μm or more and 12 μm or less.

2. 2. The coal ash treatment system according to claim 1, wherein the particle size of the sieve residue is in the range of 5 μm to 10 μm.

3. 3. The coal ash treatment system according to claim 1, wherein the reforming device is a belt-type electrostatic separator.

4. The coal ash treatment system according to any one of claims 1 to 3, wherein the physical property measuring device is a laser diffraction particle size distribution measuring device.

5. a modification step of reducing the unburned carbon content of coal ash containing unburned carbon to obtain modified coal ash; a sampling step of collecting a portion of the modified coal ash; a physical property measuring step of measuring at least one physical property value selected from the group consisting of an area average particle size of the modified coal ash sampled in the sampling step and a sieve residue having a predetermined particle size; a prediction step of predicting an activity index of the modified coal ash at a material age of 28 days based on the physical property values; a recovery step of recovering the modified coal ash whose activity index is predicted to be an arbitrary value of 80% or more in the prediction step, A method for producing fly ash for concrete, wherein the particle size of the sieve residue in the physical property measurement step is in the range of 3 μm or more and 12 μm or less.

6. 6. The method for producing fly ash for concrete according to claim 5, wherein the sampling step, the physical property measuring step, the prediction step, and the recovery step are performed while continuously transporting the modified coal ash obtained in the modification step.

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