JPH0930857A - Sintered compact comprising coal ash and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a sintered compact having high strength by carrying out air classification or pulverization treatment and heating treatment of coal ash so as to have specific BET specific surface area value or below and a specific residual content or below on the sieve and forming and sintering the coal ash. SOLUTION: Coal ash such as fry ash, sinter ash, bottom ash generated from fine coal powder burning fire power boiler is subjected to air classification or pulverization treatment and heat treatment to prepare coal ash raw material having <=6.0m<2> /g BET specific surface area and <=5wt.% residual content on 80μm sieve. Then, coal ash raw material is mixed with <= about 20wt.% of a plasticizer, a tacky agent or a fusing agent, etc., and the mixture is subjected to press forming to form a formed article having <=3.0 specific gravity and sintered at 1250-l450 deg.C to provide the objective lightweight sintered compact free from crack having <=1.5 specific gravity and <=5.5 porosity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sintered body which effectively utilizes coal ash discharged from a coal-fired power plant or the like, and a method for producing the same. More specifically, when producing a sintered body from coal ash discharged from a coal-fired power plant, etc., by effectively managing the amount of unburned carbon, there is no crack and a strong sintered body is produced. And a sintered body thereof.

[0002]

2. Description of the Related Art When reviewing the use of coal as an energy source, the treatment of generated coal ash becomes a problem. As an application for effectively utilizing this coal ash, a large amount of it is used as a cement, a concrete admixture, etc., and a high level utilization as a so-called ceramic raw material such as tiles, bricks and artificial aggregates has been attracting attention.

Generally, the manufacturing process of ceramics is roughly divided into raw material adjustment → molding → sintering, but unlike the highly controlled fine ceramics raw material, when coal ash, which is an industrial waste, is used as the raw material of the sintered body. The adjustment of raw materials greatly affects the properties of the product. Among them, the presence of unburned carbon contained in coal ash affects the redox atmosphere and thermal conductivity during sintering, causing not only cracking and expansion in the sintered body, but also internal combustion due to carbon combustion. There is a problem that voids are generated, which causes deterioration of physical properties of the product such as mechanical strength, and a sintered body of stable quality cannot be obtained. In particular, in recent years, coal ash having a high unburned carbon content has been increasing due to the use of foreign coal having a poor ignitability and the need to reduce nitrogen oxides in soot and smoke.

On the other hand, the properties of the ceramics sintered body depend on the particle size of the raw material if the raw material has the same chemical properties and mineral composition, so that the grain size of the raw material has been conventionally controlled. Especially in the field of cement and concrete, the air-permeable brane specific surface area is often used. For example, Japanese Patent Application Laid-Open No. 61-163152 describes a method for producing an artificial aggregate from a raw material of coal ash whose grain size is controlled by the Blaine specific surface area. It is said that the finer the powder has a surface area of 4000 cm ² / g or more, the higher the strength of the sintered body.

[0005]

However, among coal ash containing a large amount of unburned carbon in recent years, the Blaine specific surface area is 5000 cm ²
Even if it reaches / g, the average particle size is as large as 80 μm or more,
For this reason, the moldability is poor, and many of them are not usable at all from the viewpoint of the strength and water absorption of the sintered body. The reason for this is that even if the particles containing unburned carbon are relatively coarse particles, the specific surface area of the powder is significantly increased due to the porosity of the carbon surface. Moreover, in a fluidized bed boiler, the amount of unburned carbon tends to increase further because the coal is crushed and burned at a lower temperature than the pulverized coal boiler, and the particle size tends to become coarse. There is a big problem in using it effectively as a body material. Furthermore, the Blaine specific surface area is based on the assumption that the specific gravity of the powder to be measured is the same as that of ordinary Portland cement, but the physical properties of coal ash are quite different from those of cement, so there are many problems from this point as well.

On the other hand, conventionally, the amount of unburned carbon in coal ash is controlled by the ignition loss value (Ig. Loss) by heating at 750 ° C. However, even if a small amount of carbon is present, it has a great influence on the physical properties of the sintered body. Since it is given, the product properties may be impaired even if the ignition loss value is small. Therefore, it is insufficient to manage the coal ash containing carbon by the ignition loss value, and it is the current situation that the properties of the sintered body cannot be grasped unless the coal ash is actually molded and burned. In addition, as a substitute measurement item for the unburned content of coal ash, the adsorbed amount of methylene blue pigment is often measured in the concrete field, but the unburned content is 5%.
If it is more than%, the difference becomes unclear, and it is not possible to accurately grasp it with this method.

[0007]

As described above, with regard to coal ash containing carbon, it is not possible to sufficiently grasp the physical properties of the sintered body as a raw material for the sintered body by the conventional Blaine specific surface area and ignition loss value. The present invention is to solve the above-mentioned problems in the conventional manufacturing method, and grasps the amount of carbon which has been conventionally controlled by the loss on ignition value as a BET specific surface area as an index, and expresses this as a residual amount on a sieve. The quality of the coal ash is selected as a raw material of the sintered body by using it as a control index together with the grain size to be obtained, and a high-strength and crack-free sintered body is obtained.

That is, according to the present invention, a sintered body having the following constitution and a method for manufacturing the same are provided. (1) BET specific surface area of 6.0 m ² / g or less and 80 μm
A sintered body obtained by molding coal ash with a residue of 5% by weight or less on a sieve and sintering it. (2) The sintered body according to claim 1, wherein the coal ash is fly ash, cinder ash, or bottom ash generated from a pulverized coal combustion coal-fired boiler. (3) The sintered body according to claim 1, wherein the coal ash is coal ash generated from a fixed bed combustion boiler or a fluidized bed boiler. (4) BET specific surface area of 6.0 m ² / g by air classification or pulverization or heat treatment together with these treatments.
The sintered body according to (1) above, which is made of coal ash prepared as follows, and having a residual content of 5% by weight or less on a 80 μm sieve. (5) BET specific surface area of 6.0 m ² / g or less and 80 μm
A molded product having a specific gravity of 3.0 or less is produced from coal ash having a residue on the sieve of 5% by weight or less as a raw material, and the molded product is 1250 to 1
A method for producing a sintered body having a specific gravity of 1.5 or less by sintering at 450 ° C.

The present invention manages the amount of carbon in advance by using the BET specific surface area as an index, instead of the conventional particle size management by the brane specific surface area. Blaine specific surface area is a method of measuring the specific surface area of powder by the time when a certain amount of air passes through the powder layer and is absorbed, but since carbon is porous, it has a high specific surface area. The error is large. On the other hand, the BET specific surface area is a method used for evaluation of activated carbon and the like, and is a method of measuring the specific surface area including surface pores by adsorbing and desorbing nitrogen gas and measuring the difference between them to obtain an accurate specific surface area for carbon. Represent

Table 1 shows the composition and physical properties such as loss on ignition and the Blaine specific surface area and the BET specific surface area of various types of coal ash. As shown in this result,
The BET value is about 2 to 20 times higher than the Blaine value, but the BET value is large even if the Blaine value is smaller than other samples like Sample E, and the Blaine values are similar to Samples C and G. However, there are some cases where the BET values are significantly different, and there is no specific correlation between the Blaine value and the BET value.
Further, as compared with Sample B and Samples A and G, there are some samples having a small ignition loss value but a high BET value. That is, when various types of coal ash are used as the raw material for the calcined body, the physical properties of the raw material cannot be accurately grasped by grain size control based on the Blaine specific surface area or control by ignition loss.

Regarding the BET values, the BET values of Samples B and G after firing (B1, G1) and after particle size adjustment (B2, B3, G2, G3) were examined. Is high, but the BET value of the fired product is extremely small. The BET value after firing is a specific surface area of an inorganic part other than unburned carbon, for example, fly ash balloons. Therefore, it is considered that most of the specific surface area of the entire coal ash before firing is due to unburned carbon.

By the way, in the pulverized product, unburned carbon confined by vitrification and the like by pulverization appears on the surface, so that the specific surface area and the loss on ignition value become high.
Further, in the air-classified product, the unburned carbon is reduced in weight by pulverization or the like, and therefore the specific surface area and the ignition loss are increased as compared with the raw powder due to the fine powder portion.

In the present invention, coal ash having a BET specific surface area of 6.0 m ² / g or less and a residue of 5% by weight or less on an 80 μm sieve is used as a raw material for a sintered body. If the BET value exceeds the above range, it contains a large amount of unburned carbon and is not suitable as a raw material for a sintered body. That is, the carbon causes voids due to combustion to affect the physical properties of the sintered body, and
At the same time, air is entrained in the porous surface and the air expands and deaerates during heating, which causes cracks in the sintered body. Thirdly, sintering in an oxidizing atmosphere is partially due to carbon combustion. In addition, there is a problem that the atmosphere becomes a reducing atmosphere and sintering failure occurs, and this is remarkable when the BET value exceeds the above range.

Further, the coal ash used as a raw material is 80 μm
The particle size of the residue on the sieve is 5% by weight or less. If the particle size is larger than this, not only the sintering is delayed, but also the voids around the particles become large, causing defects in the structure of the sintered body.
By the way, if the residue on the 80 μm sieve exceeds 5% by weight, the artificial aggregate with a diameter of φ50 or a large brick (100 × 100 × 10
mm), the physical properties are likely to be remarkably deteriorated, and as an example, the mechanical strength is reduced by 50% or more, the occurrence rate of cracking or warping is 30% or more, and color unevenness occurs.
The residue on the 80 μm sieve is placed on a sieve with a mesh of 80 μm ± 2 μm, a certain amount of the powder to be measured, and air or water is made to flow, or vibration is applied to force the sieve to pass through the sieve. It can be measured by the amount of powder remaining in the.

BET value of 6.0 m ² / g or less, 80
Coal ash with a residual content of 5% by weight or less on the μm sieve is obtained by adjusting the particle size of coal ash discharged from a thermal power plant or the like by air classification, mechanical pulverization or the like, and further subjecting it to heat treatment if necessary.

The above coal ash is sintered after molding, but it can be molded by adding a general plasticizer, an adhesive or a melting agent in an amount of 20% by weight or less at the time of molding. The addition amount of these is 2
If it exceeds 0% by weight, the density of the sintered body is lowered by the combustion of these and the strength is impaired, which is not preferable. Also,
As for the density of the molded body, it is preferable to mold so that the porosity after firing is 5.5% or less. Porosity of sintered body is 5.5%
If it exceeds, the water absorption is increased and the strength is decreased, which is not preferable.

In order to obtain an artificial lightweight aggregate using the above-mentioned coal ash, the specific gravity of the compact is adjusted to 3.0 or less and 1200 to 1
Baking is preferably performed in the temperature range of 450 ° C. Those using coal ash as a raw material which is out of the scope of the present invention do not have a significant decrease in specific gravity even if the sintering temperature is raised, and it is difficult to obtain a lightweight fired body having a specific gravity of 1.5 or less.

[0018]

Embodiments of the present invention will be described below. It should be noted that the present embodiment is an example and does not limit the scope of the invention.

Example 1 The BET specific surface area of various commercially available coal ash was measured together with its main components and physical properties, and the Blaine specific surface area. The results are shown in Table 1. Sample B,
Heat treatment for G (Sample B1, G1), Air classification (Sample B)
2, G2), mechanical pulverization treatment (samples B3, G3) and those subjected to heat treatment and mechanical pulverization (sample B4, G4), the physical property values, the Blaine specific surface area and the BET specific surface area are shown in Table 2.
For comparison, the physical property values of Portland cement are shown in comparison with Table 1. 10 tap water to these coal ash
The mixture was added by weight% and granulated to a particle size of about 10 mm. Table 3 shows the crush strength of this molded product according to JIS Z 8841.

In addition, 1% of PVA liquid was added to the above coal ash and mixed well, charged into a mold press, and a pressure of 1 t / m ² was applied to form a large brick (115 × 115 × 15 mm). , Heating the molded body to 1350 ° C. at a temperature rising rate of 5 ° C./min, and
After holding at 350 ° C. for 1 hour, it was allowed to cool to room temperature. The appearance of the obtained fired body was colored with a red dye, and the number of defective products such as cracks, cracks, and warpage was examined. In addition, a specimen (3 × 4 × 40 mm) was cut out from a sample with no abnormal appearance and JIS R
According to 6201, 3-point bending strength, Vickers hardness and porosity were measured. The results are summarized in Table 3.
Each measured value is an average value of 10 samples, and the specific gravity of the molded body was adjusted to 1.5 ± 0.1.

Samples included in the scope of the present invention (A, B2, B3, G2,
All of G3) have significantly higher crushing strength than other samples, and almost no defective products are generated, and bending strength and hardness are also significantly higher. Also, the porosity is small, and a dense sintered body can be obtained.

Example 2 10% by weight of tap water was added to the above coal ash to give a specific gravity of 2.95.
A molded product having a particle size of about 2.45 and a particle size of about 10 mm was granulated. The molded body was heated to 1100 to 1450 ° C. in an electric furnace and fired. The specific gravity of the obtained sintered body is shown in Table 4. Here, the coal ash of Sample E, which is outside the scope of the present invention, has a loss on ignition of 2
It is 5.5%, which is the largest amount of carbon in all the samples, but the weight loss due to this combustion is small, and the specific gravity does not decrease much even if the sintering temperature is raised, and it becomes rather high when it exceeds 1250 ° C. On the other hand, samples included in the scope of the present invention (A, B2, G2, G3)
Adjust the specific gravity to 3.0 or less, 1250 to 1450 ℃
In each case, a lightweight fired body having a specific gravity of 1.5 or less can be obtained by firing.

Example 3 1 % by weight of PVA was added to the coal ash of sample B3 and granulated into particles having a particle size of 0.6 mm using a spray dryer. The granules are packed in a rubber mold and pressed with a hydrostatic press (CIP) (1.
5t / m ² ) and a pipe having an inner diameter of 450 mm, a thickness of 10 mm and a length of 200 mm was formed. Charge this compact into a gas furnace, and 2 ℃ / min
After heat-sintering at 1350 ° C. at a temperature rising rate of 4 ° C., holding at this temperature for 4 hours, and cooling at −2 ° C./min temperature decreasing rate. Ten of the obtained ceramic pipes were joined together and connected to a cement crushed product pressure feed pipe. When 2 kg / min of cement was passed through this pipe for 1 year, the internal wear amount was 1 mm.
The wear amount of the steel pipe (SUS 304) under the same conditions was significantly less than 12 mm.

[0024]

EFFECT OF THE INVENTION The sintered body of the present invention grasps the amount of carbon in advance for coal ash containing carbon by using the BET specific surface area as an index, and uses this as a management index together with the particle size represented by the residual amount on the screen. As a result, high-quality coal ash is selected and produced as a raw material for the sintered body, and it has high strength and is free from cracks, and thus can be widely used for various purposes. Further, according to the present invention, a large amount of coal ash discharged from a coal-fired power plant or the like can be effectively used.

[Table 1]

[Table 2]

[Table 3]

[Table 4]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kenji Nozaki Kenji Nozaki 2-4-2 Daisaku Sakura, Chiba Prefecture Chichibu Konoda Central Research Institute

Claims (5)

[Claims] 1. A BET specific surface area of 6.0 m ² / g or less and 8
0 μm A sintered body obtained by molding coal ash having a residue of 5% by weight or less on a sieve and sintering it. 2. The sintered body according to claim 1, wherein the coal ash is fly ash, cinder ash or bottom ash generated from a pulverized coal burning coal fired boiler. 3. The sintered body according to claim 1, wherein the coal ash is a coal ash generated from a fixed bed combustion boiler or a fluidized bed boiler. 4. A BET specific surface area of 6.0 by subjecting to air classification or pulverization or heat treatment together with these treatments.
The sintered body according to claim 1, wherein the raw material is coal ash prepared to a m ² / g or less and a residue on an 80 µm sieve of 5% by weight or less. 5. A BET specific surface area of 6.0 m ² / g or less and 8
A molded body having a specific gravity of 3.0 or less was produced from a coal ash having a residue of 0 μm on a sieve at 5% by weight or less as a raw material, and the molded body was subjected to 1250
A method for producing a sintered body having a specific gravity of 1.5 or less by sintering at ˜1450 ° C.