JP2001121084A - Method for refining fly ash and purified fly ash powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain highly refined fly ash by recovering an unburned portion effectively with regard to a method for refining fly ash and refined fly ash powder. SOLUTION: Crude fly ash 1a containing unburned portion of coal is introduced into a coarse screening apparatus 2, and the fly 1b on the screen is discharged from a discharge opening 2b. The fly ash 1c under the screen which has passed through the apparatus 2 is discharged from a discharge opening 2c to a fine screening apparatus 3a and introduced from a discharge opening 2b into a fine screening apparatus 3b to be classified from discharge openings 4a, 4b into the fly ash on the fine screen and the fly ash 2e under the fine screen. Since the resistance of the fine screening apparatuses is large, the apparatuses 3a, 3b are installed in parallel, and ultrasonic vibrators 3a1, 3a2 are installed to prevent the lowering of treatment efficiency by clogging. The fly ash 1b under the course screen containing the unburned portion is obtained from the discharge opening 2b, and high by refined fly ash 1e under fine screen is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention aims to provide a technique for purifying fly ash in order to effectively utilize fly ash generated from a coal-fired boiler.

[0002]

2. Description of the Related Art Coal ash generated from thermal power plants in Japan reaches about 5.3 million tons / year (1996), about 60 tons of which.
% Are used effectively, but the rest is dumped in landfills. Coal ash varies in quality due to JIS
The major reason is that the standard does not satisfy the fly ash standard established in Japan. Also, the breakdown of 60% that is effectively used is mainly made of cement materials instead of clay, and its use as a concrete admixture specified in JIS fly ash standard, which is a characteristic of fly ash itself, is small. is there.

[0003] In the future, with the increase in coal-fired power plants, the amount of fly ash generated is expected to exceed 7 million tons / year, and considering the future where disposal is difficult, the effective utilization rate of coal ash will increase. Is an urgent task. Until now, various efforts have been made for the effective use of fly ash. For example, efforts have been focused on the development of new products, such as a method of granulating and firing fly ash to replace crushed stones, and a method of plasma-melting fly ash to obtain similar crushed stones. However, these methods have a cost disadvantage over alternative crushed stone prices and do not lead to great demand. In addition, as a substitute for clay, the nature of fly ash generated from the power plant varies greatly depending on the power output at the time of sampling, such as unburned matter and particle shape. It was not connected to any use.

[0004] In order to improve these, a classifier using air flow classification has been developed. In this method, a disk collision type classifier having high classification efficiency is used. In this method, fly ash is caused to collide with the airflow classifier and separated by a specific gravity difference. This method is characterized in that the classification efficiency is high and the apparatus can be made compact, unlike the classification method using a sieve proposed by the present invention. However, this method will be described in detail in a later embodiment of the present invention as a comparative method, but has a drawback that it is difficult to use it in large quantities due to a low fly ash recovery rate.
That is, the unburned coal coarse powder that determines the quality of fly ash is crushed by airflow classification, and the unburned content on the fine particle side increases. Therefore, the airflow classification is originally suitable for refining high-quality fly ash having a low unburned content, but is not suitable for improving the high unburned fly ash which leads to mass demand.

The JIS standard for fly ash, which was revised on February 18, 1999, is shown in Table 1 below together with the previous standard.
Shown in

[0006]

[Table 1]

The major feature of the new standard is that ignition loss, fineness, flow value ratio, and activity index are finely divided. Si0 ₂ minutes, moisture, density is essentially a property of fly ash has never whether utilized by the standard is determined. Among the newly subdivided items, ignition loss is based on JISA62 in which part of cement is replaced with fly ash, and standard sand and water are added and kneaded.
01 strongly affects the flow value ratio by mortar. If the ignition loss is large, the flow value ratio cannot be increased. Fineness also affects the activity index of the same test method. If the specific surface area is small, it is difficult to obtain a substance having a high activity index indicating the strength development.

Although it is possible to obtain fly ash that passes this new JISA6201 class by air current classification, the recovery rate of fly ash, which accounts for the majority of the generated amount and has a large ignition loss, remains around 30%. The remaining 70% of the waste that cannot be used as fly ash remains.

[0009]

The unburned coal is coal powder that has not been burned in a high-temperature boiler environment. Currently, the power generated by coal-fired thermal power is high during the day, but low during the night because of low demand. At high power output, good fly ash with low unburned content is obtained due to high boiler operating temperature, whereas at low power output, boiler operating temperature is lowered due to reduced fuel input, and unburned coal Increase. The effect of coal type is also large. Since the calorific value and ash component differ depending on the type of coal, the unburned matter and ash properties change. Many types of coal are used in ordinary power plants, and the properties of fly ash change accordingly. These variations in the properties of fly ash hinder the effective utilization of concrete ash and the like.

[0010] At present, large demand cannot be expected for a new utilization technology used as a conventional alternative to crushed stone in terms of cost.
In addition, the airflow classification method that has been established as a method of collecting high-quality fly ash, the coarse unburned coal unburned during the airflow classification increases the unburned fine particles required as fly ash, There was a disadvantage that the recovery rate was extremely reduced.

The present invention has developed a new purification technique capable of correcting the problems of unburned components and non-uniform particle size, which are the inhibiting components of fly ash, and promotes the effective use of a large amount of fly ash, which will increase in the future. It was developed with a view to addressing environmental and resource issues.

[0012]

The present invention provides the following means (1) to (6) to solve the above-mentioned problems.

(1) A method for purifying fly ash, wherein the fly ash collected by an electric dust collector or the like is purified by sieving.

(2) A method for purifying fly ash, wherein the sieve opening size of the apparatus for purifying fly ash according to (1) is 250 μm or more.

(3) The sieve opening size of the apparatus used in the method for purifying fly ash according to (1) is 75 to 150 μm.
A method for purifying fly ash, comprising one or more stages in the m range.

(4) A method for purifying fly ash, comprising a combination of two or more sieves described in (2) and (3).

(5) A powder of purified fly ash, wherein the powder is collected on a sieve having a sieve opening size of 250 μm or more in an apparatus used in the method for purifying fly ash according to (2).

(6) The apparatus used in the method for purifying fly ash according to (3) has a sieve opening size of 75 to 150 μm.
Powder of purified fly ash, wherein one or more stages of m range are mounted and collected under a sieve with the smallest opening.

In (1) of the present invention, coarse brittle and light coal combustion components contained in fly ash can be separated without crushing, and the unburned component recovery rate is increased. Further, in (2) of the present invention, a sieve having an aperture of 250 μm or more is used.
Coarse-grain unburned components in fly ash can be selectively removed.
In addition, in (3) of the present invention, the recovery rate of unburned matter is higher than that of the conventional airflow classification, and condensed particles having high water retention can be removed, and the mortar characteristics are improved. In the method (4) of the present invention, the coarse sieve of the invention (2) and the fine sieve of the invention (3) are simultaneously carried out. There is.

(5) and (6) of the present invention are inventions of particles as a purified product obtained by the fly ash purification method of the present invention. In (5), the particles have a calorific value that can be used as fuel. Since it is porous and has a large specific surface area, it can be used for activated carbon applications. In the case of (6), the ash that has been processed according to the characteristics of fly ash can be given a higher grade of JIS fly ash as compared with as-collected fly ash.

[0021]

Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention. The unfinished fly ash 1a collected by an electric dust collector or the like contains unburned coal. In order to recover the unburned components, the unburned components are passed through a coarse sieving device 2 equipped with a coarse mesh 2a. By passing through this device 2, fly ash 1b on coarse sieve
Collect.

Fly ash 1 having passed through coarse sieving device 2
c flows out from the outlet 2c and flows into the fine sieving device 3a installed under the coarse sieving device 2, where the upper fly ash 1d from the outlet 4a and the lower sieve particles 1e from the lower part. Classified into Similarly, fly ash 1c flowing out from the outlet 2d of the coarse sieving device 2 is
b, where it is classified into upper fly sieve 1d from outlet 4b and lower fine sieve particles 1e from below.

In this embodiment, the fine sieving devices are 3a and 3b.
The reason why a plurality of the fine sieving devices 3 are provided is due to the difference in resistance of the attached mesh. Compared with the coarse sieving device 2 having a small resistance, a plurality of fine sieving devices 3 having a large resistance are required.

Note that the sieving apparatus shown in FIG. 1 is a round apparatus, and it is functionally possible to attach a multi-stage mesh to one apparatus. The sieving device 3a needs to increase the collection efficiency. In order to increase the efficiency, it is desirable to arrange the meshes 5a and 5b respectively.

The fine sieving devices 3a and 3b are 75-1
It is equipped with a fine mesh of 50 microns,
In the horizontal discharge type sieving machine of the shaker lower type of the coarse sieving apparatus 2, the processing speed is reduced. Therefore, in order to increase the processing efficiency, the ultrasonic vibrators 3a1 and 3b1
It is desirable to use the lower discharge type ultrasonic sieves 3a and 3b which can prevent clogging by being attached. Still, since the processing speed is different from that of the coarse sieving apparatus 2, an example of a multi-stage arrangement type is shown.

Next, sieving was performed using fly ash by using the above apparatus. Upon sieving, fly ash property tests in accordance with the respective recovery rates and JIS standards shown in Table 1 were performed. The results are described in Table 2. In the table, the types of coal of fly ash collected at low power output, the refining yield when the refining method is changed, powder properties, mortar test results, and grade evaluation based on JIS standards are shown.

[0027]

[Table 2]

Table 2 shows the results of processing ash collected under low power output. As-collected fly ash is 81A, 8
2A. 81 is a co-firing of domestic coal and Australian coal, and 82 is a co-firing of Indonesia coal and Australian coal.
Each co-firing ratio is approximately 1: 1. Unburned fly ash as generated is 4% and 5.9, respectively.
%, But the flow value ratio in the mortar test was lower than 92% of the old JIS standard, and it was not adopted as fly ash.

The most important factor in using fly ash as mortar is the flow value ratio. Fly ash is used for mortar as a substitute for cement, but cannot be used at a ratio of 90 or less to a standard mortar flow value ratio of 100 in which only cement is added. The new JIS standard recognizes three types having a flow value ratio of 85 or more, but cannot be expected to be used due to the conventional JIS standard.
It is necessary to pass at least the old standard. Also,
With regard to coal types, Indonesian coal-blended fly ash 82A, for which the amount of coal used will increase in the future, has a high unburnt content, and it is expected that the utilization rate of fly ash will decrease further as it is.

In the purification test, sieving was performed using these ashes. B following the number in the table is above the 250 μm sieve (shown by a black circle in the figure), and C is below the sieve (shown by a white circle in the figure). The as-collected sieve was used even at 150 μm. D is above the 150 μm sieve and E is below the sieve. 81B on the coarse sieve has a yield of 1% when 81A is set to 100 as it is generated.
However, this 1% powder has a loss on ignition of about 50%, which is 1% lower than that of 81A where the loss on ignition is still generated under the coarse sieve.
It decreased by 0%. Then, in 81C under the coarse sieve, the most important flow value ratio as fly ash was improved to 91%, which is close to two types.

Similarly, 82A of the Indonesian coal co-fired contained 2.7% of coarse particles on a 250 μm sieve, and the unburned content of the particles under the sieve, which had been removed therefrom, was reduced by 40% as compared with the as-collected state. And the ignition loss of the particles 82B on the coarse sieve is 5
The value was as high as 5%.

Based on the above results, the first aspect of the present invention is to recover fly ash by sieving. If a sieve is used, coarse and brittle unburned coal contained in fly ash can be recovered without destroying it. In the air stream classification, the unburned coal cannot be recovered as coarse particles, and the unburned coal is light and easily broken, so that the recovery rate of purified fine particles is reduced.

Based on the above results, the second aspect of the present invention
Means that the mesh of the coarse sieve is 250 μm or more. The reason is that unburned coal can be efficiently recovered. Sieve powder 81 at 150 μm for comparison
D, 81E are also shown. In this comparative example, ignition loss was significantly reduced, and not only coal unburned matter but also fly ash aggregated particles were included. The calorific value of particles with a 50% loss on ignition is 4000 cal / g, which is a level that can be reused as fuel.

The coal particles heated by the heat in the boiler are not dense but have a high specific surface area, such as activated carbon, and have activated carbon characteristics such as iodine adsorption amount, and can be used as activated carbon. It has potential. For these reasons, the size of the mesh of the coarse sieve is set to 250 μm or more, at which unburned coal can be efficiently recovered.

Further, as a fifth aspect of the present invention, a 250 μm
This is the powder collected on the sieve. Since it has a calorific value that can be reused as fuel and has a porous form and has characteristics of activated carbon, it can be used as a water quality improver or the like. If it is less than this, coagulated coarse particles are also included, and the amount of unburned coal is reduced and cannot be used.

As described above, the coarse sieve using the 250 μm mesh is for collecting unburned coal. In the experiment, a general lower vibration type φ1 m device was used, but 0.5 to 1 to
Processing speed was high at n / hr. As a secondary effect, the properties of the under-sieved particles can be improved, but a fine sieving treatment is required to obtain two or more kinds of fly ash that are competitive in quality.

As a comparative example, the results of airflow classification are shown as F on the coarse particle side and G on the fine particle side. The apparatus used for this airflow classification test was a typical airflow classification (Yaskawa Shoji;
(YM micro cut), a centrifugal force is applied to the rotating collision plate to classify the particles based on the difference in specific gravity. The fly ash used in the test was subjected to a 150 μm sieving process in advance because the unburned matter on the fine particle side was predicted to increase in advance.
The symbol fly ash was used. As is clear from the table, the unburned matter on the fine particle side G was high, and did not reach JIS grade 2.

The increase in the unburned portion does not lead to an improvement in the flow value ratio, and the activity index is improved because of only fine particles. However, a large amount of coarse particles F cannot be used as fly ash. This phenomenon is due to the fact that unburned coal is crushed by the airflow classification device as described above, and the airflow classification method cannot contribute to improving the utilization rate of poor-quality fly ash.

On the other hand, fly ash under the sieve classified by the sieve does not increase the ignition loss. E shown in Table 2
Are 150 μm below, I is below 100 μm, and J is below 75 μm. The loss on ignition decreases as the sieve mesh becomes smaller, and the fly ash properties are improved.

The biggest difference from the air classification is that the yield of the improved fly ash is high. 75
Approximately 80% of fly ash still generated even with particles under μm sieve
Can be recovered. This is the same phenomenon for both the domestic coal-mixed fly ash 81 and the Indonesian coal-mixed fly ash 82. It has been confirmed that it is possible to improve the low power output fly ash by using a sieve of 75 μm for 81 and a 100 μm for 82.

[0041]

[Table 3]

Next, Table 3 above shows the results of the refining test at high power output. In the table, the refining yield, powder characteristics, mortar test results, and J
The grade evaluation based on IS standard was shown. 91A is a domestic coal-blended fly ash, and 92A is an Indonesian coal-blended fly ash. As for 91A, two kinds passed as it occurred, and there was no need for purification. In contrast, 92A
Has only three types of low flow value ratios. This 92A
Was subjected to a fine sieving test. At high power output, the boiler temperature was high, so that unburned coal was not included so much, so that the coarse sieving treatment with a 250 μm mesh could be omitted.

As for the coarse particles of the fine sieve particles, unburned coal and agglomerated particles are recovered on the sieve. As a result, the properties of the under-sieved particles are improved. The flow value ratio was improved even with a 150 μm mesh. The flow value is reduced by the highly water-absorbing particles. A typical example is the unburned portion which has been heated and made porous in a high temperature of a boiler, but the aggregated particles also have high water absorption. The improvement effect of the 150 μm sieve on the high power output ash is due to the effect of reducing the flow value because the condensed particles are collected on the sieve.

Table 3 also shows the results of airflow classification performed for comparison. 92F, 9 of this airflow classification process
As with low-power output fly ash, 2G recovered 20% of fly ash that passed the two types, but the increased ignition loss and the coarse-grained side that accounted for 80% showed fly ash properties. Decreased.

Based on the results in Tables 2 and 3, above, the third aspect of the present invention is that the size of the mesh of the fine sieve is 75 μm to 1 μm.
The present invention proposes a device having one or more stages selected from 50 μm. The idea of fly ash purification proposed by the present invention is to treat what is not available. The sieving process is not as good as the air flow classification from the viewpoint of production efficiency. In particular, the smaller the mesh size of the sieve, the lower the efficiency. As described above, in the experiment using the lower-excitation type general φ1 m sieving apparatus of the present invention, the coarse sieving at 250 μm is 1 ton per hour.
Near fly ash could be processed, but half at 150 μm, 1/10 at 100 μm, 1/15 at 75 μm
Became. This is because finer particles are easier to clog,
100 in the bottom discharge type sieving device with ultrasonic vibrator.
The processing speeds of μm and 75 μm are increased about three times as compared with those without the ultrasonic vibrator, but the equipment cost is increased. Accordingly, the present invention provides a minimum necessary means for removing unburned matters and aggregates required for improving the properties of fly ash.

However, the particles having a size of 150 μm or more contain agglomerated coarse particles having high water retention as described above, and the upper limit of the sieve mesh is set to 150 μm in order to remove the particles. The lower limit of 75 μm is a lower limit economically established by using a sieving apparatus with an ultrasonic vibrator. There is also a 44 μm mesh smaller than this, which is technically possible but is not economically feasible due to the extremely low throughput.

The sixth aspect of the present invention is the under-sieved fly ash powder of the third aspect of the invention, which can be obtained in a high yield in which the ignition loss and the flow value ratio are incomparable with those obtained by airflow classification. The fourth aspect of the present invention is an image of FIG. 1 in which the second 250 μm upper sieve of the second aspect and the third aspect of the invention are arranged in multiple stages, and this method is the configuration that is most easily systemized.

[0048]

According to the present invention, (1) is a method for purifying fly ash by sieving. Because brittle and light coal unburned matter contained in fly ash can be separated without crushing, it is possible to reduce ignition loss on the fine particle side and achieve high yield compared to conventional airflow classification. Can be purified.

(2) of the present invention is a processing method using a sieve having an opening size of 250 μm or more in the invention of (1). Coarse-grain unburned components contained in fly ash can be selectively removed.

The method (3) of the present invention is a method for purifying fly ash using the sieve having a sieve opening size in the range of 75 to 150 μm in the invention of (1). Since it is possible to remove not only unburned components but also aggregated particles having high water retention, it is effective in improving the flow value of mortar characteristics. Further, compared with the airflow classification, the purified fly ash can be recovered in a higher yield.

The method (4) of the present invention is a method for simultaneously carrying out the coarse sieve of the invention (2) and the fine sieve of the invention (3). There is an economical effect that can be omitted rather than improving work efficiency and separately providing space.

(5) The present invention is on-screen particles treated by the method of (2). Since it has a calorific value that can be used as a fuel, and is porous and has a large specific surface area, it can be used for purposes such as activated carbon.

The (6) of the present invention is the under-sieved particles treated by the method of (3). Compared with as-collected fly ash, those treated according to the characteristics of fly ash can be given a higher grade of JIS standard fly ash.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a processing mode according to an embodiment of the present invention.

[Explanation of symbols]

 1a Fly ash before purification 1b Fly ash above coarse sieve 1c Fly ash under coarse sieve 1d Fly ash above fine sieve 1e Fly ash under fine sieve 2 coarse sieve 3a, 3b coarse sieve 3a1, 3b1 ultrasonic vibrator

Continuation of the front page (72) Inventor Akio Saito 1-3-6 Uchisaiwaicho, Chiyoda-ku, Tokyo New day Hiya Building Inside Joban Kyodo Thermal Power Co., Ltd. (72) Keiichi Ozawa 1-3-6 Uchisaiwaicho, Chiyoda-ku, Tokyo No. Shinichi Hiya Building Joban Kyodo Co., Ltd. F-term (reference) 4D004 AA37 AC05 AC07 BA02 BB03 CA08 CA12 DA03 DA20 4D021 AA02 AB02 AC01 BA18 CA07 CB11 CB18 DA01 DA13 DC02 EA10 EB00 4G012 MA01

Claims (6)

[Claims] 1. A method for purifying fly ash, comprising purifying fly ash collected by an electric dust collector or the like by sieving. 2. A method for purifying fly ash, wherein a sieve opening size of an apparatus used for the method for purifying fly ash according to claim 1 is 250 μm or more. 3. An apparatus used in the method for purifying fly ash according to claim 1, wherein a sieve opening size is 75 to 150 μm.
A method for purifying fly ash, wherein one or more stages of the fly ash are mounted. 4. A method for purifying fly ash, comprising combining two or more sieves according to claim 2 and 3. 5. A powder of a purified fly ash product, which is collected on a sieve having a sieve opening size of 250 μm or more in an apparatus used in the method for purifying fly ash according to claim 2. 6. An apparatus used in the method for purifying fly ash according to claim 3, wherein a sieve opening size is 75 to 150 μm.
A powder of purified fly ash, wherein the powder in the range is mounted in one or more stages and collected under a sieve having the smallest opening.