JP4315849B2 - Artificial aggregate firing method - Google Patents

Description

The present invention relates to a method for firing an artificial aggregate, and in particular, firing an artificial aggregate capable of firing a high-strength and low water-absorbing artificial aggregate with high productivity even when using a rotary kiln and using coal ash with high unburned carbon. Regarding the method.

When coal is burned, coal ash corresponding to about 10% of its mass is generated. Due to the recent increase in coal-fired thermal power plants, the amount of coal ash generated has increased, and there is a need for an effective method for its use.

When other components are added to the coal ash as necessary, pretreatment such as granulation is performed and then fired, a sintered product having an appropriate strength is obtained and can be used as an aggregate for concrete. Thus, various attempts have been made to produce these artificial aggregates from coal ash and to make effective use thereof.

However, since the first purpose of coal-fired thermal power plants is to provide stable and high-quality power, it is difficult to expect supply of coal ash, which is a by-product, at a certain quality. Eventually, the quality of the generated coal ash varies depending on the power plant or even the same power plant, depending on the brand of coal used and the operating conditions. In particular, the value of so-called unburned carbon, in which carbon in coal remains without being completely burned, varies greatly depending on coal ash, and ranges from less than 1% by mass to several mass%, and sometimes more than 10% by mass. The current situation is that

When calcining artificial aggregate using coal ash as a raw material, unburned carbon in the coal ash is lost by burning in a temperature range of about 600 to 1000 ° C. (calcined range), and a temperature range of about 1200 ° C. or higher. The coal ash powder is fused in the (calcined region) to become a sintered product, which becomes particles having the strength required for the artificial aggregate.

However, when the amount of unburned carbon in the coal ash exceeds 1.5% by mass, the entire amount is not burned in the calcined region, and a part is brought into the calcined region. When the unburned carbon burns after the coal ash powder starts to fuse in the firing zone, bubbles are generated in the sintered product due to the generated carbon dioxide, or in severe cases it may explode, causing high strength artificial There was a phenomenon that aggregates could not be obtained.

Therefore, in Patent Document 1, a projection is provided in a portion corresponding to a temperature region of 800 to 1000 ° C. in the calcined region in the rotary kiln used for firing the artificial aggregate, and coal ash which is a fired product. A technique has been provided in which the agglomerated material is scraped to improve contact with oxygen in the combustion gas so that unburned carbon is sufficiently burnt and removed during the calcining region.

JP-A-6-265271

However, in the technique of Patent Document 1, in order to perform a mechanical operation of providing a protrusion in a high temperature region of 800 to 1000 ° C. and scooping up an object to be fired, the conditions for operating the equipment are severe. It was difficult to leave the object for a long time, and there was a problem that the effect was not sustained unless the rotary kiln was frequently stopped and the protrusions were repaired.

In addition, as a solution without such modification of the equipment, there is a method of suppressing the amount of firing and firing over time, but according to this, the productivity of the artificial aggregate is lowered and the production cost is reduced. Inevitable rise in

Therefore, the present invention has been made in view of the problems in the countermeasure against unburned carbon in the firing of the above-mentioned conventional artificial aggregate, and fires the artificial aggregate using coal ash having high unburned carbon in a rotary kiln as a raw material. Even in this case, an object of the present invention is to provide a method for firing an artificial aggregate that can be fired stably for a long period of time with a high strength and low water absorption artificial aggregate.

In order to solve the above-mentioned problems, the present inventors have conducted intensive studies.As a result, by changing the inner diameter of the rotary kiln on the way, the filling rate of the object to be fired can be adjusted, which is effective for removing unburned carbon. As a result, the present invention has been completed.

That is, in the invention of claim 1, in the firing of the artificial aggregate in which coal ash is the main raw material and the granulated raw material is fired in a rotary kiln, the fired product is discharged from the fired region with respect to the inner diameter from the raw material charging region to the calcined region. A rotary kiln having an inner diameter ratio of 0.90 or more and 0.95 or less is used.

Here, the range from the raw material charging region to the calcining region generally corresponds to a region where the temperature in the rotary kiln is 600 ° C to 1000 ° C. The term “from the firing region to the fired product discharge region” generally corresponds to a region where the temperature in the rotary kiln reaches from 1000 ° C. to a fired product discharge temperature of about 1000 ° C. beyond the burning point of 1200 ° C. or higher. The ratio of the inner diameter from the firing area to the fired product discharge area with respect to the inner diameter from the raw material charging area to the calcining area is 0.90 or more and 0.95 or less, so that the material to be fired can be separated between both inner diameter portions. Filling rate and residence time vary.

In the portion from the raw material charging area having a large inner diameter to the calcining area, the filling rate of the object to be fired is low. As a result, the entire object to be fired comes into contact with the remaining air in the combustion exhaust gas, and the unburned carbon in the coal ash is sufficiently burned and removed. When unburned carbon is burned and removed, bubbles will not be generated after coal ash powder starts fusing in the firing zone near the burning point, producing high-strength and low water-absorbing artificial bone. It can be fired with good performance.

On the other hand, since the inner diameter of the rotary kiln is narrowed at a ratio of 0.90 or more and 0.95 or less, the material to be fired that has reached the firing region has a slow passage speed and a long residence time. Thereby, the powder of coal ash is fused, and it becomes possible to give sufficient sintering time to the process which becomes a sintered product.

When the ratio of the inner diameters is less than 0.90, there is a problem that the material to be fired is softened and fused inside the rotary kiln, and the consumption of bricks becomes severe, which may hinder stable operation. When the ratio of the inner diameters exceeds 0.95, it is not preferable because the effect of removing and burning unburned carbon cannot be sufficiently obtained.

In addition, since the change in the inner diameter of the rotary kiln can be performed by adjusting the construction thickness of the refractory, it is more durable in a high temperature atmosphere than a projection with a scraping action, and stable operation over a long period of time. Is possible.

The invention according to claim 2 is the method for firing an artificial aggregate according to claim 1, wherein coal ash containing 1.5% by mass or more of unburned carbon is used as a raw material.

Since the present invention prevents the unburned carbon in the coal ash from adversely affecting the firing of the artificial aggregate, when using coal ash whose unburned carbon is 1.5 mass% or more as a raw material, The effect can be used effectively.

According to the invention of claim 3, the properties of the artificial aggregate obtained by the main firing are such that the absolute dry density value is 1.50 g / cm 3 or more and 2.10 g / cm 3 or less, and the 24-hour water absorption value is 0.00. 1 or more and 6% or less, and the value of the pressing load is 0.5 kN or more of aggregate having a diameter of 5 mm to 10 mm, or 1.0 kN or more of aggregate having a diameter of 10 mm to 15 mm. 2. The method for firing an artificial aggregate according to any one of 2 above.

The firing method of the present invention can prevent the generation of bubbles and explosion in the sintered product due to the combustion of unburned carbon, so that the absolute dry density value is 1.50 g / cm 3 or more, 2.10 g / cm 3 or less, and 24 hours. Dense and strong with a water absorption value of 0.1% or more and 6% or less, and a compressive weight value of 0.5 to 5 kN aggregate with a diameter of 5 to 10 mm, or 1.0 kN or more with 10 to 15 mm in diameter. This is a firing method for obtaining a high-quality artificial aggregate.

According to the present invention, even when an artificial aggregate is calcined using coal ash with high unburned carbon in a rotary kiln, the filling rate of the material to be fired during the period from the raw material charging area to the calcining area is low, and combustion Effective contact with residual air in exhaust gas, unburned carbon in coal ash can be sufficiently reduced by combustion removal, and dense and high-strength artificial aggregate can be fired, and productivity is reduced. And stable operation for a long time.

In the present invention, coal ash is used as the main raw material for the artificial aggregate. Coal ash is discharged from a coal-fired power plant, and is adjusted in particle size using fly ash that is scattered from a pulverized coal boiler and collected by an electric dust collector, PFBC ash that is collected from a circulating fluidized bed boiler, etc. It can be used with no raw powder. If necessary, various types of cements as a binder, bentonite as a binder, kaolin mineral, sodium silicate, lignin contained in the waste liquid during pulp production, and the like are added to the coal ash. Furthermore, a component adjusting material is added as necessary. The component adjusting material is added to adjust the softening and melting temperature of the raw material mainly composed of coal ash. For example, silica powder and kaolin as the SiO ₂ source, alumina powder and aluminum as the Al ₂ O ₃ source As the CaO source such as ash, lime powder, cement, gypsum and the like are used.

After mixing the above raw materials, granulate. Any method can be used as long as the granulation can be molded to a particle size within the specified range. Rolling granulation using a pan pelletizer, press granulation using a pressure molding machine, Henschel mixer (Mitsui Engineering & Shipbuilding Co., Ltd., registration) Agitation granulation using a trademark) or the like can be used.

Next, the granulated raw material is fired to produce an artificial aggregate. By using a rotary kiln as the firing device, mass production is possible and a homogeneous fired product can be obtained. In the present invention, a rotary kiln having a ratio of the inner diameter from the firing area to the fired product discharge area to the inner diameter from the raw material charging area to the calcining area is 0.90 or more and 0.95 or less.

Below, the difference between the rotary kiln used in the prior art and the rotary kiln used in the present invention will be described with reference to the drawings.

FIG. 2 shows a side cross-section of a conventional rotary kiln that has been used conventionally, and the inner diameter is the same from the bottom of the kiln where the raw material is charged to the front of the kiln where the fired product is discharged.

Fig.1 (a) shows the side cross section of an example of the rotary kiln used for the baking method of the artificial aggregate which concerns on this invention. 2 from the raw material charging area to the calcining area has a constant inner diameter φA. 3 from the firing region to the fired product discharge region has a constant inner diameter φB. The relationship is 0.90φA ≦ φB ≦ 0.95φA.

FIG.1 (b) shows the side cross section of an example of the rotary kiln used for baking of the artificial bone of the other form which concerns on this invention. 2 from the raw material charging area to the calcining area has a constant inner diameter φA. Although the inner diameter of 3 from the firing region to the fired product discharge region is gradually narrowed, the average inner diameter φB has a relationship of 0.90φA ≦ φB ≦ 0.95φA. In the present invention, the inner diameter from the firing region to the fired product discharge region refers to the inner diameter when the interval is a constant inner diameter, and refers to the average inner diameter when there is a change in the inner diameter. Shall.

Coal ash containing 2.8% by mass of unburned carbon discharged from a coal-fired power plant (chemical components are shown in Table 1) as a main raw material and 15% by mass of ordinary Portland cement as a binder The mixed powder was granulated with a pan pelletizer at a water content of 15% by mass to a particle size of 5 to 15 mm. Next, the granulated material was cured for 2 hours in an atmosphere having a curing temperature of 85 ° C. and a relative humidity of 90% or more using a rotary curing machine. The granulated product after curing was fired in the rotary kiln having the following specifications under the described conditions, and the properties of the artificial aggregate of the fired product were measured. The results are shown in Table 2.

Example 1
Change the construction thickness of the brick inside the rotary kiln (φ1.5m × 20mL), the inner diameter φA from raw material input area to calcination area (from 0 to 8m) = 1.4m, from firing area to fired product discharge area (15m ~ 20 m), an inner diameter φB = 1.26 m, and a rotary kiln having the configuration shown in FIG.
This rotary kiln was fired at a raw material feed rate of 1.2 tons / h, a residence time of 1.5 hours, and a firing temperature of 1240 ° C.
(Example 2)
Change the construction thickness of the brick inside the rotary kiln (φ1.5m × 20mL), the inner diameter φA from the raw material input area to the calcination area (from 0 to 7.5m) = 1.4m, from the firing area to the fired product discharge area ( The inner diameter of 15m to 20m was narrowed to a taper shape, and an average inner diameter φB = 1.32 m was obtained to obtain a rotary kiln having the form of FIG. 1B (inner diameter ratio = 0.94).
This rotary kiln was fired at a feed rate of 1.4 ton / h, a residence time of 1.2 hours, and a firing temperature of 1265 ° C.
(Comparative example)
The inner diameter of the rotary kiln (φ1.5 m × 20 mL) from the raw material charging area to the calcining area (from 0 to 8 m) and the inner diameter from the baking area to the fired product discharge area (15 m to 20 m) are the same (φA = φB = 1) 4 m) to obtain a rotary kiln having the form of FIG. 2 (inner diameter ratio = 1).
This rotary kiln was fired at a raw material feed rate of 1.3 tons / h, a residence time of 1.4 hours, and a firing temperature of 1250 ° C.

(Table 1)

(Table 2)

As is clear from the data in Table 2, in Examples 1 and 2 fired by the firing method according to the present invention, far better numerical values were obtained in terms of absolute dry density, 24-hour water absorption rate, and compressive load as compared with the comparative example. Of artificial aggregate.

Side surface sectional drawing of the rotary kiln used for the baking method of the artificial aggregate which concerns on this invention Side sectional view of a rotary kiln used in a conventional method for firing artificial aggregates

Explanation of symbols

1 Rotary kiln 2 From raw material input area to calcined area 3 From calcined area to fired product discharged area 4 Inner diameter φA
5 Inner diameter φB

Claims (3)

The ratio of the inner diameter from the firing area to the fired product discharge area to the inner diameter from the raw material input area to the calcined area is 0 in the firing of the artificial aggregate in which the coal ash is the main raw material and the granulated raw material is fired in the rotary kiln. A method for firing an artificial aggregate, comprising using a rotary kiln that is 90 or more and 0.95 or less. The method for firing an artificial aggregate according to claim 1, wherein coal ash containing 1.5% by mass or more of unburned carbon is used as a raw material. The properties of the artificial aggregate obtained by the main firing are such that the absolute dry density value is 1.50 g / cm 3 or more and 2.10 g / cm 3 or less, and the 24-hour water absorption value is 0.1% or more and 6% or less. 3. The compressive weight value is 0.5 kN or more of aggregate having a diameter of 5 mm to 10 mm, or 1.0 kN or more of aggregate having a diameter of 10 mm to 15 mm. A method for firing the described artificial aggregate.

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