JP2000119050A - Production of artificial lightweight aggregate and artificial lightweight aggregate obtained by the method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an artificial lightweight aggregate, capable of inexpensively producing the artificial lightweight aggregate which has a high quality and a small absolute specific gravity and can express a high strength at a relatively low temperature, by adding a small amount of an easily available inexpensive additive, and to provide the artificial lightweight aggregate obtained by the method. SOLUTION: This method for producing the artificial lightweight aggregate comprises adding a binder, a foaming agent and a melting point-lowering agent comprising refuse incineration ash to coal ash, pulverizing the mixture, adding water to the pulverization product, molding the mixture, drying the molded product, and then calcining the molded product. The refuse incineration ash comprises main ash, flied ash or secondary flied ash, and is added in an amount of 1-10 wt.% (converted into an alkali metal oxide). The molded product is calcined in a temperature range of 950-1,300 deg.C. The foaming agent comprises an iron oxide and at least one of silicon carbide and a carbon material. The artificial lightweight aggregate obtained by the method has an absolutely dry specific gravity of 0.5-1.5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an artificial lightweight aggregate, and more particularly, to recycling coal ash generated from a coal-fired power plant or a coal-fired boiler as an artificial lightweight aggregate for civil engineering and construction. TECHNICAL FIELD The present invention relates to a method for producing an artificial lightweight aggregate for effective use by making it into an artificial lightweight aggregate, and an artificial lightweight aggregate obtained by the method.

[0002]

2. Description of the Related Art Coal has abundant resources and lower price per unit calorific value than petroleum. Therefore, domestic energy policy has planned or implemented a significant increase in the use of coal, especially as fuel for power generation. It is getting. As a result, coal ash generated from coal-fired power plants and coal-fired boilers
It increases almost in proportion to the amount of coal used. As a result, the effective use of coal ash, which is rapidly increasing, has become a major issue.

In order to effectively utilize a large amount of coal ash, utilization as an artificial lightweight aggregate is suitable because of its large demand.

[0004] However, coal ash is partially aggregated by the sinter great method, but its use as an artificial aggregate is extremely small in Japan at present. The cause is that coal-fired power plants and coal-fired boilers use coal that generates high melting point ash in order to reduce the adhesion of ash to boiler water pipes and boiler walls. is there.

That is, coal ash generated from a coal-fired power plant or a coal-fired boiler generally has a high melting point. Therefore, in order to produce a lightweight aggregate, a large amount of low-melting clay or shale is mixed and fired. There must be. However, it is difficult to secure a large amount of these clays and shale, and it takes a lot of money to mine, transport, pre-process and mix these clays and shale. And the low utilization rate of coal ash per unit product is not preferable for effective utilization of coal ash, and the absolute dry specific gravity of artificial lightweight aggregate obtained using coal ash It is about 1.3 to 1.4 and its use is limited. Due to problems such as the fact that the technology for producing a light artificial lightweight aggregate with a smaller absolute dry weight has not been developed, coal ash is artificially lightened. It has not been effectively reused as aggregate.

[0006]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above circumstances, and can reduce the absolute specific gravity by adding a small amount of easily available and inexpensive additives.
It is an object of the present invention to provide a method for inexpensively producing a high-quality artificial lightweight aggregate exhibiting high strength at a relatively low temperature and an artificial lightweight aggregate obtained by this method.

[0007]

Means for Solving the Problems The present inventors have increased the use rate of coal ash per unit product to increase its effective utilization rate, can reduce the absolute dry specific gravity, can exhibit high strength, and can reduce the cost. As a result of diligent studies on a simple manufacturing method, it was found that the above-mentioned problems could be solved by using an aggregate containing a melting point depressant consisting of refuse incineration ash, a binder and a foaming agent. The invention has been completed.

That is, in order to achieve the above object, the first embodiment of the present invention is obtained by mixing coal ash with a melting point depressant consisting of refuse incineration ash, a binder, and a foaming agent. The mixture is pulverized, molded and dried by adding water to the pulverized material, and then fired, and the refuse incineration ash is
It consists of main ash, fly ash or secondary fly ash, and the amount of the refuse incineration ash is 1 to 10% by weight (in terms of alkali metal oxides).
The method is carried out in a temperature range of ° C., and the method is characterized by a method for producing an artificial lightweight aggregate comprising iron oxide and at least one of silicon carbide and carbonaceous material.

[0009] A second embodiment of the present invention is the above-mentioned first embodiment.
Obtained by the production method according to the embodiment, and 0.5 to
It features an artificial lightweight aggregate having an absolute dry specific gravity of 1.5.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The details of the present invention and its operation will be more specifically described below. The present invention is to add incineration ash to coal ash as a melting point depressant,
The melting point of coal ash is 950 ° C. to 1300 ° C., preferably 10
The temperature is lowered to a temperature easy to industrially bake from 00 ° C to 1250 ° C, and the addition of iron oxide having an average particle size of 10 µm or less and a carbon material such as silicon carbide and / or coal or coke as a foaming agent is performed. An artificial lightweight aggregate having a high dry specific gravity of about 0.5 to 1.5 can be manufactured. Here, in order to set the absolute specific gravity to 1 or less, in particular, Fe ₂ O with respect to the total amount of the aggregate is required.
_The amount of 3 needs to be 3% by weight or more. The carbonaceous material also functions to adjust the reduced state inside the granulated pellets during firing.

Next, a melting point depressant for lowering the melting point of coal ash will be described below. Coal ash often has a very high temperature of generating a liquid phase and sintering at 1400 ° C to 1500 ° C.
Firing is not practical because of the difficulty in selecting the fire resistance and energy cost of the firing equipment and the foaming agent. Conventionally, when firing such a high refractory raw material, natural minerals such as low refractory clay and shale which contain a large amount of alkali metals as a melting point depressant, and JP-A-9-77540 are reported. A method of adding a large amount of waste glass such as bottle glass has been common.

As a result of various studies on the effects of adding clay and shale, the present inventors have confirmed that even a small amount of alkali metals among these constituents significantly lowers the liquidus temperature. Further, the element exhibiting the effect of lowering the liquidus temperature is not limited to the alkali metals, and the element constituting the low-melting oxide, for example, boron, lead, etc., may exhibit the effect. I found it.

Therefore, the present inventors first mixed industrial alkali metal compounds, for example, alkali metal compounds such as sodium carbonate and potassium carbonate, and coal ash to form a mixture.
When melted at 00 ° C. to 1200 ° C. to form a glass, and then cooled and pulverized and added to coal ash, the glass melting point depressant is particularly 5% by weight based on the total amount of the aggregate.
When added in such a manner, the firing temperature becomes 950 ° C. to 1
At 300 ° C., preferably at 1000 ° C. to 1250 ° C., it was found that a high-strength artificial lightweight aggregate uniformly foamed from the inside of the granulated pellets could be fired,
Although this technique was disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 9-77540, it was not satisfactory enough in terms of cost, although industrial chemicals could be used.

The present inventors have studied a more inexpensive production method, and have found that incinerated ash can serve as a melting point depressant, and used it in the present invention. The refuse incineration ash used in the present invention is composed of main ash, fly ash or secondary fly ash.

[0015] In the artificial lightweight aggregate according to the present invention,
The preferable addition amount of the refuse incineration ash is 1 to 10% by weight in terms of alkali metal oxide with respect to the total amount of the aggregate, and this is from the viewpoint of improving the sintering characteristics of the aggregate and the utilization of coal ash. This is the obtained range, and if it is less than 1% by weight, the effect is not sufficiently exhibited, while if it exceeds 10% by weight, fusion between aggregates becomes more remarkable.

Next, a binder is added for imparting the formability and strength of the granulated material. The type of the binder is not particularly limited, but examples thereof include inorganics such as bentonite and water glass, and starch. , Molasses, lignin, polyvinyl alcohol, methylcellulose, natural rubber, pulp waste liquor and the like. Although the amount of addition is not particularly limited, it is 0.5% by weight to 1% in consideration of the effect of addition and cost.
A range of 0% by weight is preferred.

The blowing agent is added to control the absolute dry specific gravity of the artificial lightweight aggregate to about 0.5 to 1.5. In the present invention, iron oxide, silicon carbide and It is preferable to use a carbon material. In general, the foaming agent is not particularly limited as long as it exerts the above-mentioned effects. However, in the present invention, preferably, an agent composed of iron oxide, silicon carbide and / or carbonaceous material is used. Hematite with a high degree of oxidation is desirable.

[0018] The particle size of the iron oxide is not particularly limited.
It is preferable that the thickness be 0 μm or less. The preferable amount of Fe ₂ O _{3 to be} added to the total amount of the aggregate is 1% by weight to 1%.
When the amount is less than 1% by weight, the effect as a foaming agent is small and the absolute dry specific gravity of the artificial lightweight aggregate cannot be controlled to about 0.5 to 1.5. On the other hand, even if it is added in excess of 10% by weight, the effect of weight reduction by foaming does not further increase.

When only iron oxide is used as the foaming agent, the specific gravity of iron oxide is significantly higher than that of coal ash, and if foaming is not promoted, the specific gravity of the artificial lightweight aggregate will increase. Therefore, in the present invention, silicon carbide and / or carbonaceous material for promoting foaming of iron oxide are added. When the granulated pellets generate a large amount of liquid phase by heating, silicon carbide is produced by reacting efficiently with iron oxide to form CO, C.
O ₂ gas is captured to promote foam swelling of the pellets. The amount of silicon carbide to be added to the total amount of the aggregate is preferably 0.1% by weight to 10% by weight, more preferably 0.1% by weight.
If less, the effect on the weight reduction of the absolute dry weight is not sufficient,
It is not possible to obtain aggregates with absolute specific gravity of 1.0 or less.
Even if it exceeds 0% by weight, the lightening effect does not increase any more.

Although the carbon material has a small effect, it reacts with iron oxide to exert a function of foaming. Therefore, it is possible to replace a part of the hydrocarbon with the carbon material or to use it in combination with silicon carbide. . The carbonaceous material also has a secondary function that the effect of adjusting the degree of reduction inside the pellet during firing is large. The carbon material is not particularly limited as long as it has the above-described effects, and examples thereof include coal and coke.
It is preferably from 0.2% by weight to 10% by weight. 0.
If the amount is less than 2% by weight, the effect of weight reduction by foaming cannot be obtained. If the amount exceeds 10% by weight, the effect of weight reduction by foaming expansion does not increase any more. And the strength of the artificial lightweight aggregate may be reduced.

Further, the coal ash used in the present invention is not particularly limited. For example, all coal ash including, for example, raw powder which is a mixture of fly ash and synda ash, fly ash conforming to JIS A6201, coarse powder, and clinker ash Can be used. The particle size of the coal ash is not particularly limited.

In the pulverization method used in the present invention, the mixed raw material of the aggregate mixture has an average particle size of 20 μm or less, preferably 15 μm or less.
m, any method can be used as long as it can be finely pulverized, and examples thereof include a ball mill such as a pot mill, a vibration mill, and a planetary mill, a collision-type jet pulverizer, and a turbo pulverizer.

Next, the pulverized mixture of coal ash, melting point depressant, binder and foaming agent is wet-kneaded if necessary.
The kneading method used is not particularly limited, and a general-purpose kneading apparatus can be used.

Any molding method can be used as long as it can be molded to a predetermined diameter. For example, it is convenient to use a pan pelletizer or an extruder. The drying method is not particularly limited.

The firing method is not particularly limited. For example, a rotary kiln is preferably used in consideration of continuous operation and uniformity of quality, and the atmosphere can be arbitrarily selected in accordance with desired aggregate characteristics. Is 950 ° C
To 1300 ° C, preferably 1000 ° C to 1250 ° C.

[0026]

EXAMPLES Examples of the present invention will be described below together with comparative examples.
You. However, the present invention is not limited to the following examples.
No. Coal used in the following Examples and Comparative Examples of the present invention
The main component of the ash is SiO₂: 56.20% by weight, Al₂O
₃: 32.10% by weight, Fe₂O₃: 3.57% by weight,
CaO: 0.59% by weight, MgO: 1.40% by weight, N
a₂O: 0.22% by weight, K₂O: 0.48% by weight
It is. On the other hand, incineration fly ash used as melting point depressant
The minute is SiO₂: 21.9% by weight, Al₂O₃: 13.
0% by weight, Fe₂O₃: 1.51% by weight, CaO: 1
5.7% by weight, MgO: 3.31% by weight, Na₂O:
8.7% by weight, K₂O: 7.39% by weight;
The main component of the incineration main ash is SiO₂: 32.8% by weight,
Al₂O₃: 20.8% by weight, Fe ₂O₃: 6.5 weight
%, CaO: 24% by weight, MgO: 4.6% by weight, Na
₂O: 5% by weight, K₂O: 5.4% by weight.

Example 1 67.5% by weight of coal ash, 5% by weight of bentonite, 5% by weight of hematite, 0.1% of silicon carbide
An aggregate-mixed raw material composed of 5% by weight, 2% by weight of coke and 20.0% by weight of incinerated fly ash was mixed and pulverized by a ball mill to have an average particle size of 14 μm. At this time, the amount of fly ash added was 3.2% by weight in terms of alkali metal oxide with respect to the total amount of aggregate. Next, while adding water in which molasses in an amount of 1% by weight based on the total amount of the aggregate raw material was added to the pulverized material, a diameter of about 5 to 15 mm was obtained with a pan pelletizer.
After granulating into a spherical shape, it was dried by ventilation at 105 ° C. The dried aggregate is put into a rotary kiln (brick inner diameter 400 mm × length 6
000 mm), the oxygen concentration of the combustion gas is 6%,
The aggregate A was obtained by firing under the condition of 120 ° C. . In order to evaluate the aggregate A thus obtained, JIS A111
Based on 0, the absolute dry specific gravity was measured, and the crushing strength was measured by a uniaxial compressive breaking load. The results are shown in Table 1 below. The crushing strength was measured for each aggregate having a diameter of 10 mm by a crushing tester, and the average value was obtained.

As can be seen from Table 1, the commercially available artificial lightweight aggregate has an absolute dry specific gravity of 1.3 to 1.4 and a crushing strength of 50 to 60 kgf.
In contrast, the aggregate A of Example 1 had an absolute dry specific gravity of 1.27 and
High strength of 0 kgf or more.

Examples 2 to 8 and Comparative Example 1 Coal ash 7
Bone in the same manner as in Example 1 except that 0.5% by weight, 2% by weight of bentonite, 5% by weight of hematite, 0.5% by weight of silicon carbide, 2% by weight of coke and 20.0% by weight of incinerated fly ash were used. Material B (Example 2) was prepared by mixing 61.2% by weight of coal ash, 5% by weight of bentonite, 5% by weight of hematite, 0.5% by weight of silicon carbide, 2% by weight of coke, and incinerated fly ash.
Aggregate C (Example 3) was replaced with incinerated fly ash as a melting point depressant in the same manner as in Example 1 except that the content was 3% by weight. Aggregate D (Example 4) was heated in a rotary kiln at 900 ° C., 1080 ° C., 1100 ° C., and 1130 ° C. in the same manner as in Example 1 except that 3% by weight was added.
C. and 1150 ° C., respectively, in the same manner as in Example 1, respectively, aggregate E (Comparative Example 1), aggregate F (Example 5), aggregate G (Example 6), and aggregate H (Example). 7) Aggregate I (Example 8) was obtained. The same measurement as in Example 1 was performed for the obtained aggregates B to I, and the results are shown in Table 1.

As can be seen from Table 1, the aggregates B, C, D, F, G and H of Examples 2 to 7 have absolute dry specific gravities of 1.12 to 1.
At 50, the crushing strength was 100 kgf or higher. Further, the aggregate I of Example 8 had a crushing strength of 87 kgf even when the absolute dry specific gravity was less than 1, which was higher than that of a commercially available artificial lightweight aggregate. On the other hand, the aggregate E of Comparative Example 1 was insufficient in foaming due to a low firing temperature, and as a result, had an absolute dry specific gravity of 1.65 and was not a desired lightweight aggregate.

[Comparative Examples 2-3] 82.5% by weight of coal ash
5% by weight of bentonite, 5% by weight of hematite, 0.5% by weight of silicon carbide, 2% by weight of coke and 5% by weight of incinerated fly ash (0.8% by weight in terms of alkali metal oxide based on the total amount of aggregate mixed) Aggregate J (Comparative Example 2) was prepared in the same manner as in Example 1 except that coal ash was 72.5% by weight, bentonite was 0% by weight, hematite was 5% by weight, silicon carbide was 0.5% by weight, and coke was 2% by weight. % And incinerated fly ash 20.0% by weight
Aggregate K (Comparative Example 3) in the same manner as in Example 1 except that
I got The same measurement as in Example 1 was performed for the obtained aggregates J and K, and the results are shown in Table 1.

As can be seen from Table 1, in the aggregate J of Comparative Example 2, the incinerated fly ash contained 0.8% by weight in terms of alkali metal oxide.
As a result, the melting point was insufficient, and the absolute density was 1.75, which was not a desired lightweight aggregate. Further, in the aggregate K of Comparative Example 3, the strength of the dried aggregate was low because the binder was not added, and cracking and chipping frequently occurred due to the impact when the rotary kiln was charged.

[0033]

[Table 1]

[0034]

As described above, according to the present invention, an extremely light, high-strength, and high-quality artificial lightweight aggregate is reduced using coal ash generated from a coal-fired power plant or a coal-fired boiler as a raw material. It can be produced efficiently at low cost. Therefore, industrial waste can be recycled into civil engineering and building materials, etc., which need to be reduced in weight, without having to bury and dispose of it, which greatly contributes to environmental conservation and stable supply of energy.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shingo Sudo 3-18-5, China, Ichikawa, Chiba Prefecture Sumitomo Metal Mining Co., Ltd. Central Research Laboratory (72) Inventor Koji Kawamoto 3-18-, China, Ichikawa, Chiba 5 Sumitomo Metal Mining Co., Ltd. Central Research Laboratory F-term (reference) 4G019 JA01 JA02

Claims (6)

[Claims] 1. A mixture obtained by mixing a melting point depressant consisting of refuse incineration ash, a binder, and a foaming agent with coal ash, and pulverizing the mixture. A method for producing an artificial lightweight aggregate, comprising drying and firing. 2. The method for producing an artificial lightweight aggregate according to claim 1, wherein said incineration ash is made of main ash, fly ash or secondary fly ash. 3. The method for producing an artificial lightweight aggregate according to claim 1, wherein the amount of the waste incineration ash is 1 to 10% by weight (in terms of an alkali metal oxide). 4. The method for producing an artificial lightweight aggregate according to claim 1, wherein the firing is performed in a temperature range of 950 ° C. to 1300 ° C. 5. The method for producing an artificial lightweight aggregate according to claim 1, wherein said foaming agent comprises iron oxide and at least one of silicon carbide and carbonaceous material. . 6. An artificial lightweight aggregate obtained by the method according to any one of claims 1 to 5, having an absolute dry specific gravity of 0.5 to 1.5.