JP2017225913A - Method for processing coal ash - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method by which magnetite can be efficiently recovered from coal ash.SOLUTION: A method for processing coal ash has a process in which an exhaust gas, which is generated from coals burned in a boiler 1 of a coal thermal power plant is introduced into an electrical dust collector 2 located on a downstream side of the boiler 1, and coal ash is separated from the exhaust gas. The electric dust collector 2 has such a structure that plural dust chambers 21, 22, etc. are connected in series. The method includes a process in which coal ash is extracted out from the dust chamber 21, which is positioned near an inlet for the exhaust gas, among the plural dust chambers 21, 22, etc., and a process in which magnetite is recovered from the coal ash extracted out in the afore-said process.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for treating coal ash discharged from a coal-fired power plant.

Coal ash generated from coal-fired power plants is mainly composed of quartz and mullite, which are minerals mainly composed of SiO ₂ and Al ₂ O _3. Coal ash has conventionally been made of cement raw materials, concrete admixtures and plastics. It is used for fillers. It is known that coal ash contains a small amount of magnetite. Magnetite has strong magnetism and a reducing function due to the presence of Fe ^{2+ in} the structure. Accordingly, magnetite is expected to be used as a reduction insolubilization material or magnetic material for heavy metals (see Patent Documents 1 and 2).

  As a method for removing and recovering magnetite in coal ash, Patent Document 3 discloses a method for treating coal ash with a magnetic separator. Patent Documents 4 and 5 disclose a method for improving the removal rate of magnetite by magnetic separation treatment by performing dispersion treatment in an air flow before classifying coal ash by a magnetic separator or by performing classification treatment. Has been. According to Patent Documents 4 and 5, the equipment cost and running cost for removing and recovering magnetite from coal ash are required to be low.

  In addition to the above technique, as a technique focusing on the difference in properties of coal ash for each dust collection chamber of the electric dust collector, Patent Document 6 discloses collecting coal ash from the dust collection chamber on the exhaust gas inlet side of the electric dust collector. Thus, a method for obtaining coal ash having a low heavy metal elution amount is disclosed.

JP 2006-205152 A JP 2014-66981 A JP 2011-195399 A JP 2006-255530 A JP 2006255553 A JP 2006-35123 A

  When recovering magnetite by treating coal ash with a magnetic separator, the higher the magnetite content in the coal ash, the higher the magnetite recovery rate. Generally, the magnetite content of coal ash is about 1 to 4% by mass. As in Patent Document 3, when recovering magnetite from coal ash having a high iron content specifically, there is no problem in industrial practicality because the recovery rate can be increased. However, when recovering magnetite from coal ash having a general magnetite content using a magnetic separator, the recovery rate is low and the practicality is poor. Further, as in Patent Documents 4 and 5, a method of suppressing coal agglomeration between magnetite having magnetism and non-magnetic ash by dispersing coal ash particles with a dispersing device or removing fine particles of 10 μm or less with a classifier. Is effective from the viewpoint of improving the recovery rate of magnetite, but it is a problem that a large amount of equipment cost is required to install equipment capable of treating a large amount of coal ash.

  Although the technique described in Patent Document 6 focuses on the difference in properties of coal ash for each dust collection chamber, it focuses on the magnetite content of coal ash for each dust collection chamber, and recovers the magnetite from coal ash. It is not intended to improve.

  Therefore, the subject of this invention is providing the processing method of coal ash which can collect | recover the magnetite in coal ash with high efficiency and low cost.

  As a result of intensive studies by the inventor in order to solve the above problems, the coal ash collected in the dust collection chamber on the exhaust gas inlet side of the electric dust collector composed of a plurality of dust collection chambers contains a large amount of magnetite. By acquiring magnetite from the coal ash collected in the dust collection chamber on the exhaust gas inlet side, we found that magnetite can be recovered with high efficiency and low cost compared to conventional methods, The present invention has been completed.

That is, the present invention relates to a coal ash having a step of introducing exhaust gas generated from coal burned in a boiler of a coal-fired power plant into an electric dust collector installed downstream of the boiler and separating the coal ash from the exhaust gas. Processing method,
The electric dust collector has a structure in which a plurality of dust collection chambers are connected in series,
A step of extracting coal ash from a dust collection chamber located near the inlet of the exhaust gas among the plurality of dust collection chambers;
Recovering magnetite from the coal ash extracted in the step;
This problem is solved by providing a method for treating coal ash containing

  According to the method for treating coal ash of the present invention, the coal ash collected in the dust collecting chamber on the exhaust gas inlet side and the coal ash collected on the outlet side are separately provided downstream of the electric dust collector in the coal thermal power plant. It is possible to recover magnetite more efficiently than conventional methods simply by installing piping so that it can be recovered. Moreover, since no special equipment is required, magnetite can be recovered at low cost.

FIG. 1 is a flowchart showing a method for treating coal ash according to the present invention.

  Hereinafter, the present invention will be described based on preferred embodiments thereof. The present invention relates to coal ash having a process of introducing exhaust gas generated from coal burned in a boiler of a coal-fired power plant into an electric dust collector installed downstream of the boiler, and separating coal ash from the exhaust gas. It relates to a processing method. In a coal-fired power plant, as shown in FIG. 1, coal as fuel is burned in a boiler 1, and high-temperature and high-pressure steam is produced using heat generated thereby. This steam is used to rotate an impeller of a steam turbine (not shown), and a generator connected to the turbine is moved to generate electricity. Exhaust gas generated by the combustion of coal is sent to a denitration device (not shown) and nitrogen oxide is removed, and then introduced into the electrostatic precipitator 2. The electric dust collector 2 has a structure in which a plurality of dust collecting chambers 21, 22,... Are connected in series. Each of the dust collection chambers 21, 22,... Is individually partitioned and has a space independent from other dust collection chambers.

  The electrostatic precipitator 2 is a dust collector that collects the fine particles contained in the exhaust gas by applying electric charges to the fine particles and drawing them to the dust collecting electrode. Each dust collection chamber 21, 22,... Is provided with a discharge electrode and a dust collection electrode (both not shown). When a high voltage is applied between the two electrodes, ions are generated by corona discharge. These ions combine with the fine particles floating around, and the fine particles become charged. The charged fine particles are attracted to the dust collecting electrode to which the opposite voltage is applied, whereby the fine particles are removed from the exhaust gas. These fine particles are called coal ash. Coal ash is usually collected in a hopper installed at the bottom of each dust collection chamber.

  As a result of the present inventors diligently examining the properties of coal ash collected in each dust collection chamber, there is a difference in the content of magnetite contained in coal ash depending on the position of the dust collection chamber from the inlet side of the exhaust gas. It turned out to be. As a result of further investigations by the inventor, it was found that the coal ash removed and collected in the dust collection chamber near the exhaust gas inlet side contained more magnetite. Furthermore, it was found that the particle size of the coal ash removed and collected in the dust collection chamber near the exhaust gas inlet is larger.

  Therefore, in the present invention, the coal ash collected in the dust collection chamber located near the exhaust gas inlet in the electric dust collector and the coal ash collected in the dust collection chamber located near the outlet are separately extracted and exhausted. The coal ash collected in the dust collection chamber located near the gas inlet is preferentially subjected to the magnetite recovery process, so that the magnetite is recovered for coal ash of a quality suitable for magnetite recovery. Yes.

  In contrast, in conventional coal-fired power plants, coal ash collected in each dust collection chamber is transported to a silo through the same pipe and stored. Therefore, the coal ash collected in each dust collection chamber is stored as a mixture thereof. In such a method, coal ash having a high magnetite content, a large particle size, and a quality suitable for recovering magnetite, and a coal having a low magnetite content, a small particle size, not suitable for recovering magnetite. It will be treated with ash. As a result, the recovery efficiency of magnetite is lowered, the amount of coal ash to be processed is increased, and the load on the magnetic separator is increased.

Incidentally, magnetite contained in coal ash is believed to be generated by varying Fe ₂ O ₃ contained in the coal is reduced in the combustion and cooling processes in Fe ₃ O _4. Since the specific gravity of magnetite is larger than that of ash, the inventor believes that a large amount of magnetite is recovered in the dust collection chamber located near the exhaust gas inlet in the electric dust collector.

  In this specification, “the dust collecting chamber located near the exhaust gas inlet in the electric dust collector” means that the electric dust collector is 2nth from the first dust collecting chamber closest to the exhaust gas inlet (n is a positive integer). In the case of having dust collection chambers up to the following, it is the first to nth dust collection chambers. When the electric dust collector has from the first dust collection chamber closest to the exhaust gas inlet to 2n + 1 dust collection chambers, it means the first dust collection chamber to the nth dust collection chamber.

  On the other hand, “the dust collecting chamber located near the outlet of the exhaust gas in the electric dust collector” means that the electric dust collector has the first dust collecting chamber to the 2nth dust collecting chamber closest to the exhaust gas inlet. , N + 1-th dust collection chamber to 2n-th dust collection chamber. When the electric dust collector has 2n + 1 dust collection chambers from the first dust collection chamber closest to the exhaust gas inlet, it means the n + 1th dust collection chamber to 2n + 1th dust collection chamber.

  When the electric dust collector has the 1st to 2nth dust collection chambers, it is collected from any one of the 1st to nth dust collection chambers or any two or more dust collection chambers. What is necessary is just to collect magnetite for the coal ash which was made. Similarly, when the electric dust collector has 1st to 2n + 1 dust collection chambers, one of the 1st to nth dust collection chambers or any two or more dust collection chambers. What is necessary is just to collect magnetite for the coal ash collected from the chamber. Whether the electric dust collection chamber has 2n dust collection chambers or 2n + 1 dust collection chambers, at least the first dust collection chamber (that is, the dust collection closest to the exhaust gas inlet) It is preferable to recover the magnetite from the coal ash recovered from the chamber from the viewpoint of increasing the recovery efficiency of the magnetite.

  When the electric dust collector has first to 2nth dust collection chambers, it is preferable that the coal ash recovered from the (n + 1) th to 2nth dust collection chambers is not subjected to the magnetite recovery process. As long as the recovery efficiency is not extremely reduced, the magnetite recovery process is not hindered. Similarly, when the electric dust collector has the first to 2n + 1 dust collection chambers, it is preferable that the coal ash recovered from the n + 1th to 2n + 1th dust collection chambers is not subjected to the magnetite recovery process. However, as long as the recovery efficiency of the magnetite is not extremely lowered, it is not hindered to be subjected to the magnetite recovery process.

  FIG. 1 shows a state in which the electric dust collector 2 includes three dust collection chambers. Only the coal ash recovered from the first dust collection chamber 21 closest to the exhaust gas inlet is magnetite. It is preferable that the coal ash that has been subjected to the recovery step and recovered from the second dust collection chamber 22 and the third dust collection chamber 23 is not subjected to the magnetite recovery step.

  As a result of the study by the present inventors, when the electric dust collector 2 has a structure having three dust collection chambers shown in FIG. 1, the mass ratio of coal ash collected in each dust collection chamber is the first dust collection Chamber 21: Second dust collection chamber 22: Third dust collection chamber 23 = 73 to 76: 7 to 26: 1 to 17, and a dust collection chamber 21 located near the exhaust gas inlet suitable for recovery of magnetite It was confirmed that there was a large proportion of coal ash collected in

  In the present invention, the magnetite content of the coal ash extracted from the dust collection chamber located near the exhaust gas inlet of the electrostatic precipitator 2 is preferably 1.5% by mass or more, more preferably 2.0% by mass or more, 5 mass% or more is still more preferable. A magnetite recovery rate can be made high because magnetite content is 1.5 mass% or more. The value of the content is a value for coal ash extracted from one dust collection chamber located near the exhaust gas inlet of the electric dust collector 2 among the plurality of dust collection chambers, or the electric dust collector 2. It is a value about what mixed the coal ash extracted from two or more dust collection chambers located near the entrance of exhaust gas. There is no particular limitation on the upper limit of the magnetite content, and it is preferably as high as possible. However, considering the ratio of iron generally contained in coal, the upper limit is about 25% by mass at the highest.

  In the present invention, the median diameter of the coal ash extracted from the dust collection chamber located near the exhaust gas inlet of the electrostatic precipitator 2 is preferably 25 μm or more, more preferably 30 μm or more, and even more preferably 40 μm or more. The median diameter of coal ash is preferably 100 μm or less, more preferably 75 μm or less, and even more preferably 50 μm or less. When the median diameter of the coal ash is within this range, the fine powder content can be relatively reduced, thereby suppressing a decrease in the recovery rate of the magnetite. The median diameter value of the coal ash is a value for coal ash extracted from one dust collection chamber located near the exhaust gas inlet of the electric dust collector 2 among the plurality of dust collection chambers, or This is a value obtained by mixing coal ash extracted from two or more dust collection chambers located near the exhaust gas inlet of the dust collector 2. A method for measuring the median diameter will be described in detail in Examples described later.

  There is no particular limitation on the means for recovering magnetite from the coal ash, and any means known so far can be appropriately employed. In particular, it is preferable to employ a method of treating coal ash with a magnetic separator 3 as shown in FIG. As the magnetic separator 3, either a dry type or a wet type may be used. When the recovered magnetite is effectively used as a magnetic material or a heavy metal reduction and insolubilization material, it is preferable to use a dry magnetic separator. This is because a drying step is required when magnetite obtained using a wet magnetic separator is used as a magnetic material or a heavy metal reduction / insolubilization material.

  The operating magnetic force of the magnetic separator 3 is preferably 10,000 gauss or more and 15000 gauss or less, more preferably 11000 gauss or more and 14000 gauss or less, and further preferably 12000 gauss or more and 13000 gauss or less. By setting the magnetic force to 10,000 gauss or more, the recovery rate of magnetite can be sufficiently increased. In addition, by setting the magnetic force to 15000 gauss or less, it is possible to effectively prevent the ash content in the vicinity of the magnetite from being unintentionally attracted together with the magnetite and the purity of the recovered magnetite to be lowered.

  Examples of the magnetic separator 3 include a screen type, a drum type, and a hanging type, and any of them can be used in the present invention. For the purpose of improving the recovery rate of magnetite, a screen type magnetic separator capable of processing with a higher magnetic force than the drum type or the suspension type is preferable. For the purpose of treating a large amount of coal ash, a drum type magnetic separator is preferred. Which method is adopted may be appropriately selected according to the properties of the coal ash to be treated, but it is preferable to adopt a screen type and / or a drum type. Examples of the screen-type magnetic separator include an electromagnetic separator CG type (manufactured by Nippon Magnetics).

  In the present invention, the coal ash from which magnetite has been removed in the magnetite recovery process may be repeatedly processed by the magnetic separator 3 to further recover the magnetite. Generally, since the recovery rate of magnetite from coal ash tends to be higher when it is repeatedly treated, it may be appropriately selected in consideration of the recovery rate and cost of magnetite. As a method of repeated processing, for example, a method of arranging a plurality of magnetic separators 3 in series, a method of returning coal ash from which magnetite has been removed to a line that supplies the magnetic separator 3 together with coal ash extracted from the electrostatic precipitator 2, etc. Is mentioned.

  The magnetite thus recovered can be effectively used as a magnetic material or a heavy metal reduction insolubilization material as shown in FIG. 1, for example. On the other hand, the coal ash from which the magnetite has been removed can be effectively used as a concrete admixture or a cement additive as shown in FIG.

  The unburned carbon is removed from the coal ash from which the magnetite has been removed by an unburned carbon removing device 4 as shown in FIG. 1, and the coal ash from which the unburned carbon has been removed is used, for example, as shown in FIG. It can also be used effectively as an additive. As the unburned carbon removing device 4, for example, electrostatic classification, heating, and a flotation treatment device can be used.

  Alternatively, after coal ash from which magnetite has been removed is granulated with a granulator 5 as shown in FIG. 1, it can be effectively used as a civil engineering material as shown in FIG. The coal ash from which the magnetite has been removed can be suitably used as a civil engineering material because the amount of arsenic and / or selenium eluted is reduced compared to the coal ash before removal. Moreover, by granulating coal ash, harmful substances such as arsenic and selenium that may be contained in the coal ash become more difficult to elute. Instead of granulating the coal ash from which the magnetite has been removed, after the coal ash from which the unburned carbon has been removed is granulated, it can also be used effectively as a civil engineering material. When used as a civil engineering material, coal ash is a mixture of coal ash from which magnetite has been removed and at least one selected from the group consisting of cement, slaked lime, magnesium oxide and gypsum. This is preferable because elution of heavy metals can be further suppressed.

  The above explanation is about coal ash after recovering magnetite from coal ash extracted from the dust collection chamber located near the exhaust gas inlet of the electrostatic precipitator 2. As for the coal ash extracted from the dust collection chamber located closer, the particle size is relatively small and the content of unburned carbon is relatively small. It can be effectively used as a cement additive (see FIG. 1).

  According to the above method, the coal ash collected in the dust collecting chamber on the exhaust gas inlet side and the coal ash collected on the outlet side can be separately collected downstream of the electric dust collector in the coal thermal power plant. Magnetite can be recovered more efficiently than conventional methods simply by installing piping. Moreover, since no special equipment is required, magnetite can be recovered at low cost.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, “%” means “mass%”. Prior to the description of the examples and comparative examples, the coal ash used in these examples will be described.

  In Example 1 and Comparative Examples 1 to 3, the three dust collection chambers of the electrostatic precipitator installed in the coal-fired power plant are sequentially arranged from the inlet side to the outlet side of the exhaust gas, one room, two rooms, and three rooms. Call. The coal ash collected from each chamber is called coal ash A to C. Also, coal ash collected from a silo that mixes and stores coal ash collected from each chamber of the electric dust collector as in the past is called coal ash D. These four types of coal ash were used. The properties of coal ash A to D are shown in Table 1 below. The analysis values shown in the table are values measured by the following method.

(I) SiO ₂ , Al ₂ O ₃ , Fe ₂ O ₃ content Measured according to JIS M 8853 “Chemical analysis method of aluminosilicate materials for ceramics”.

(Ii) Magnetite content 5 g of coal ash, 150 g of distilled water, and a stirring magnet were put into a 300 mL beaker and stirred for 5 minutes with a magnetic stirrer. Next, the stirring magnet with the magnetic substance attached was taken out of the beaker. Thereafter, a new stirring magnet was put in a beaker and the same operation was performed. This repeated operation was performed until no magnetic substance adhered to the stirring magnet. After the stirring magnet with the magnetic material adhered was dried at 40 ° C. for 24 hours, the magnetic material was removed from the stirring magnet, and the mass of the magnetic material was measured. The magnetite content (% by mass) was calculated by dividing the mass of the magnetic material recovered as an adhering matter by the mass of coal ash charged into the beaker and multiplying by 100.

(Iii) Median Diameter and Ratio of Particles of 10 μm or Less Measurement was performed with a laser diffraction particle size distribution measuring apparatus (SALD-2200, manufactured by Shimadzu Corporation). The proportion of particles of 10 μm or less is a volume-based proportion.

  As shown in Table 1, coal ash A collected from one chamber has a higher magnetite content and median diameter than coal ash B and C collected from two and third chambers and coal ash D collected from silos. It can be seen that the proportion of fine powder of large and 10 μm or less is low. Therefore, coal ash collected in the dust collection chamber located near the exhaust gas inlet in the electric dust collector is extracted separately from the coal ash collected in the dust collection chamber located near the exhaust gas outlet. Coal ash suitable for recovering magnetite can be obtained.

  The following Example 1 and Comparative Examples 1 to 3 compare the magnetite recovery rates from coal ash from different collection locations.

[Example 1]
Coal ash A (magnetite content 2.26%) collected in one room is put into a lattice-type magnet type magnetic separator (manufactured by Nippon Magnetics, 3 permanent magnets, surface magnetic force 12,000 gauss), The adhering component (hereinafter referred to as magnetized material) and the component not adhering to the magnet (hereinafter referred to as non-magnetized material) were selected and each mass was measured. The magnetite was assumed to be magnetite, and the magnetite recovery rate was calculated by dividing the mass of the magnetized material by the mass of magnetite in the charged coal ash A. The results are shown in Table 2.

[Comparative Example 1]
A test was conducted in the same manner as in Example 1 except that coal ash B (magnetite content 0.76%) collected in two chambers was used, and the magnetite recovery rate was calculated. The results are shown in Table 2.

[Comparative Example 2]
A test was performed in the same manner as in Example 1 except that coal ash C (magnetite content: 0.36%) collected in three chambers was used, and the magnetite recovery rate was calculated. The results are shown in Table 2.

[Comparative Example 3]
A test was performed in the same manner as in Example 1 except that coal ash D (magnetite content: 1.47%) collected from a coal ash silo was used, and the magnetite recovery rate was calculated. The results are shown in Table 2.

  As is apparent from the results shown in Table 2, when coal ash A collected in one chamber, that is, coal ash having a magnetite content of 1.5% or more and a median diameter of 25 μm or more is processed by a magnetic separator, Most magnetite could be recovered from coal ash. From this, it can be seen that the magnetite recovery rate is higher when the coal ash having a high magnetite content and a large particle size is subjected to magnetic separation.

  Reference Examples 1 to 3 below compare the relationship between the operating magnetic force of the magnetic separator and the magnetite recovery rate.

[Reference Example 1]
Coal ash E (magnetite content 2.59%, median diameter 40.2 μm) collected from a coal ash silo at a thermal power plant was put into the same grid type magnetic magnetic separator (surface magnetic force 12,000 gauss) as in Example 1. Then, it was classified into a component adhering to the magnet (hereinafter referred to as magnetized material) and a component not adhering to the magnet (hereinafter referred to as non-magnetized material), and each mass was measured. The magnetite was assumed to be magnetite, and the magnetite recovery rate was calculated by dividing the mass of the magnetized material by the mass of magnetite in the input coal ash E. The results are shown in Table 3.

[Reference Example 2]
A magnetite recovery rate was calculated by conducting a test in the same manner as in Reference Example 1 except that the surface magnetic force of the lattice magnet type magnetic separator was 9000 Gauss. The results are shown in Table 3.

[Reference Example 3]
A magnetite recovery rate was calculated by performing a test in the same manner as in Reference Example 1 except that the surface magnetic force of the lattice magnet type magnetic separator was set to 6000 gauss. The results are shown in Table 3.

  As is clear from the results shown in Table 3, it can be seen that when the operating magnetic force of the magnetic separator is 9000 gauss or less, the magnetite recovery rate from coal ash is significantly reduced.

  Reference Examples 4 to 6 below compare the relationship between the magnetite content and particle size of coal ash and the magnetite recovery rate.

[Reference Example 4]
Same as Reference Example 1 except that the coal ash F (magnetite content: 7.17%, particle size of 45 μm or more) obtained by sieving the coal ash E used in Reference Example 1 at 45 μm as a sieve residue is used. The test was conducted by this method, and the magnetite recovery rate was calculated. The results are shown in Table 4.

[Reference Example 5]
Except for using the coal ash G (magnetite content 5.01%, particle size 20-45 μm) obtained by sieving the coal ash F used in Reference Example 4 at 20 μm as a sieve residue, The test was conducted in the same manner, and the magnetite recovery rate was calculated. The results are shown in Table 4.

[Reference Example 6]
Same as Reference Example 1 except that the coal ash F used in Reference Example 4 was sieved at 20 μm and obtained as a sieve passing part using coal ash H (magnetite content 0.96%, particle size 20 μm or less). The test was conducted by this method, and the magnetite recovery rate was calculated. The results are shown in Table 4.

  As is clear from the results shown in Table 4, it can be seen that the magnetite recovery rate is higher when coal ash having a high magnetite content and a large particle size is treated with a magnetic separator. Therefore, as in the present invention, the coal ash having a high magnetite content and a large particle size extracted from the dust collection chamber located near the exhaust gas inlet in the electric dust collector is processed with a magnetic separator, thereby improving efficiency. The magnetite recovery rate can be improved well.

  In the following Reference Examples 7 to 9 and Comparative Examples 4 to 6, the elution test for heavy metals from coal ash was performed.

[Reference Example 7]
The coal ash E used in Reference Example 1 is put into the same grid-type magnet type magnetic separator (surface magnetic force 12,000 gauss) as in Example 1, and does not adhere to the component (hereinafter referred to as magnetic attachment 1) and the magnet. It separated into the component (henceforth non-magnetic thing 2), and measured each mass. The obtained non-magnetized material 1 is again put into the same magnetic separator, and after sorting into the magnetic material 2 and the non-magnetized material 2, each mass is measured, and the magnetite recovery rate is obtained in the same manner as in Example 1. Calculated. The results are shown in Table 5. Next, a heavy metal elution test was performed using the non-magnetic product 2 in accordance with Ministry of the Environment Notification No. 46 (1998) to prepare a test solution. The arsenic and selenium concentrations of the test solution were measured. The results are shown in Table 5.

[Reference Example 8]
Except for using coal ash I (magnetite content 2.40%), tests were conducted in the same manner as in Example 2 to calculate the magnetite recovery rate. The results are shown in Table 5. Next, using the obtained non-magnetic deposit 2, a heavy metal elution test was performed, and arsenic and selenium concentrations in the test solution were measured. The results are shown in Table 5. Coal ash I is coal ash collected from a coal ash silo that mixes and stores coal ash collected in each room of an electric dust collector of a thermal power plant as in the past.

[Reference Example 9]
Except for using coal ash J (magnetite content 2.16%), tests were conducted in the same manner as in Example 2 to calculate the magnetite recovery rate. The results are shown in Table 5. Next, using the obtained non-magnetic deposit 2, a heavy metal elution test was performed, and arsenic and selenium concentrations in the test solution were measured. The results are shown in Table 5. Coal ash J is coal ash collected from a coal ash silo that mixes and stores coal ash collected in each room of an electric dust collector of a thermal power plant as in the past.

[Comparative Example 4]
Using coal ash E used in Reference Example 1, a heavy metal elution test was conducted in accordance with Ministry of the Environment Notification No. 46 (1998) to prepare a test solution. The arsenic and selenium concentrations of the test solution were measured. The results are shown in Table 5.

[Comparative Example 5]
Using coal ash I used in Reference Example 8, a heavy metal elution test was conducted in accordance with Ministry of the Environment Notification No. 46 (1998) to prepare a test solution. The arsenic and selenium concentrations of the test solution were measured. The results are shown in Table 5.

[Comparative Example 6]
Using coal ash J used in Reference Example 9, a heavy metal elution test was conducted in accordance with Ministry of the Environment Notification No. 46 (1998) to prepare a test solution. The arsenic and selenium concentrations of the test solution were measured. The results are shown in Table 5.

  As is clear from the results shown in Table 5, it can be seen that coal ash from which magnetite has been removed has a lower elution amount of arsenic and selenium than coal ash from which magnetite has been removed. Therefore, it can be seen that the coal ash from which magnetite is removed can be effectively used as civil engineering materials. Reference Examples 7 to 9 are not measurement results when using coal ash from which magnetite has been removed by the method of the present invention, but also when using coal ash from which magnetite has been removed by the method of the present invention, It can be easily estimated that similar results are obtained.

DESCRIPTION OF SYMBOLS 1 Boiler 2 Electric dust collector 21, 22, 23 Dust collection chamber 3 Magnetic separator 4 Unburned carbon removal apparatus 5 Granulator

Claims (7)

A method for treating coal ash comprising a step of introducing exhaust gas generated from coal burned in a boiler of a coal-fired power plant into an electric dust collector installed downstream of the boiler and separating coal ash from the exhaust gas. And
The electric dust collector has a structure in which a plurality of dust collection chambers are connected in series,
A step of extracting coal ash from a dust collection chamber located near the inlet of the exhaust gas among the plurality of dust collection chambers;
Recovering magnetite from the coal ash extracted in the step;
Coal ash treatment method including   2. The method according to claim 1, further comprising a step of obtaining a civil engineering material by mixing coal ash from which magnetite has been removed by the magnetite recovery step and at least one selected from the group consisting of cement, slaked lime, magnesium oxide and gypsum. The processing method of coal ash as described.   The method for treating coal ash according to claim 1 or 2, wherein the coal ash is extracted from a dust collection chamber closest to an exhaust gas inlet side among the plurality of dust collection chambers installed in the electric dust collector.   The method for treating coal ash according to any one of claims 1 to 3, wherein the coal ash extracted from the dust collection chamber is magnetically selected by a magnetic separator to recover magnetite.   The method for treating coal ash according to claim 4, wherein the magnetic separator is a screen type or drum type magnetic separator.   The coal ash treatment according to any one of claims 1 to 5, wherein a magnetite content of the coal ash extracted from the dust collection chamber is 1.5 mass% or more, or a median diameter is 25 µm or more. Method.   The coal according to any one of claims 1 to 6, wherein the coal ash with reduced elution amount of arsenic and / or selenium is obtained by recovering magnetite from the coal ash extracted from the dust collection chamber. Ash processing method.

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