JP2625218B2 - Method for firing coal ash granules - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for firing coal ash granules, and more particularly to an artificial lightweight aggregate for effectively utilizing coal ash generated from a coal-fired thermal power plant or the like. The present invention relates to a method which can be advantageously applied to a method for producing the same.

[Conventional technology]

Artificial lightweight aggregate made from coal ash is usually made by adding a binder such as clay and water to coal ash,
After granulation into coal, the unburned carbon in the coal ash
It is manufactured by firing at a firing temperature of 00 to 1200 ° C.

Artificial lightweight aggregates are mainly coarse aggregates of structural lightweight concrete (particle size 5-25mmφ) and fine aggregates (particle size 0.15-5mmφ).
Therefore, artificial lightweight aggregates currently in general use must meet the JIS * A * 5002 standard. The quality of coarse aggregate (type M) that is used a lot
Important points for complying with the standards are absolute dry specific gravity of 1.0 to 1.5 and ignition loss of 1% or less. In addition, high strength and low water absorption are required from the viewpoint of workability improvement during concrete construction. . Therefore, in the production of high-quality artificial lightweight aggregate, it is essential to establish a production technique for imparting the above properties.

Coal ash granules are converted into artificial lightweight aggregates through the steps of drying, preheating, ignition, firing, and cooling, and the quality of the product is determined by the firing step. In this firing step, sintering is performed by the combustion reaction between unburned carbon contained in the ignited coal ash granulated material and oxygen in the air. The oxygen concentration is adjusted to the amount of unburned carbon (coal content) in the coal ash. Otherwise, it is difficult to maintain the optimum combustion temperature, and it is not possible to obtain high quality artificial lightweight aggregate.

FIG. 3 shows the relationship between the amount of coal in the coal ash and the O ₂ concentration of the feed gas for combustion. The amount of coal required for sintering and solidification by the self-combustion of coal ash granules is 4% or more. However, if air (O ₂ = 21%) is burned with a coal content of 4% or more, a rapid combustion reaction proceeds. As the surface of the granulated material is melted, the granulated materials are fused and solidified (formation of lumps) after cooling, and before the carbon content in the granulated material does not become less than 1% of ignition loss according to JIS standard. since granule surface combustion reaction by vitrification is stopped, to obtain a good quality of artificial lightweight material with high yield, the firing temperature according to the O ₂ concentration adjustment of combustion feed gas to meet the coal content of the coal ash Moderate adjustment is important. O ₂ required for combustion reaction
If the combustion is continued below the concentration, the temperature of the fired product becomes lower than the appropriate temperature, and an unfired product is generated. Therefore, in order to produce high-quality artificial lightweight aggregate with high yield, the O ₂ concentration of the combustion feed gas is adjusted according to the coal ash properties (coal content and composition) so that it falls within the appropriate range shown in FIG. Thus, the packed bed temperature of the granulated material must be stabilized in an appropriate temperature range. Conventionally, this temperature control has determined the O ₂ concentration of the combustion gas by measuring the coal content of the coal ash.

[Problems to be solved by the invention]

Main component of conventional coal ash _{SiO 2: 34~60%, Al 2} O 3: 17~3
_{1%, Fe 2 O 3:} 2~25%, CaO: 0.5~10%, MgO: a 1~5%, P ₂ O ₅ as a minor _{component, TiO 2, MnO, BaO,} K 2 O, Na 2 O and so on. Since the ranges of these chemical components vary depending on the type of coal ash, if the O ₂ concentration of the combustion feed gas is defined only by the amount of coal, a high-quality artificial lightweight aggregate may not be produced in high yield. This is thought to be due to the change in the properties of coal ash, and in particular, the influence of the change in the content of Fe ₂ O ₃ and CaO is great. In calcinating temperature of coal ash granules is generally 1100~1200 ℃, C ₃ A (C is CaO, A is Al ₂ O ₃₎ is 1050 ° C. or higher, C ₄ A
F (C is CaO, A is Al ₂ O ₃ , F is Fe ₂ O ₃ ) becomes a liquid phase at 1160 ° C. or higher, and it is considered that various other binders are formed in this temperature range. The melting point of the ash is SiO ₂ -Al ₂ O
_The temperature is 1250-1500 ° C. for the ₃ system, but 1100-1250 ° C. for the CaO—SiO ₂ —Al ₂ O ₃ system, and it can be said that the coexistence of CaO has the effect of lowering the melting point.

The present invention has been made in view of the above-mentioned technical problems, and has as its object to provide a method for firing coal ash granules capable of producing a high-quality artificial lightweight aggregate at a high yield.

[Means for solving the problem]

The present invention stacks coal ash granules containing coal on the moving grade of a firing furnace that is isolated from the atmosphere, and produces artificial lightweight aggregates by the action of combustion with an oxygen-containing gas passing through the layer from above to below. In the method for sintering the coal ash granules to be produced, the lower limit sintering temperature is determined from the water absorption performance of the artificial lightweight aggregate which is the sintering product of the granulated product, and the amount of unburned carbon contained in the artificial lightweight aggregate (loss on ignition) This is a method for firing coal ash granulated material, which is fired by setting the upper limit firing temperature from the above.

[Action]

Among the properties of artificial lightweight aggregate obtained by firing coal ash granulated material below the melting temperature of the granulated material, absolute dry gravity and amount of unburned carbon specified in JIS standard (loss on ignition) specified in JIS standards When,
By measuring the water absorption, which is regarded as important from the viewpoint of lightweight concrete construction, and accurately grasping the optimum firing temperature range unique to the granulated material, the firing temperature can be controlled, that is, the supply gas for combustion can be controlled.
Since the control of the O ₂ concentration is facilitated, a high-quality artificial lightweight material can be produced with a higher yield.

〔Example〕

FIG. 2 shows an example of the artificial lightweight aggregate manufacturing apparatus according to the present invention. In FIG. 2, a hopper 2 for storing coal ash discharged from a coal-fired power plant or the like, a tank 1 for storing water mixed with the coal ash, and a binder (clay, bentonite, etc.) for improving granulation and quality. A predetermined amount is supplied to the wet kneader 4 from the hopper 3 for storing the water. The kneaded material kneaded by the wet kneader 4 is formed and granulated to a particle size of 5 to 25 mm by a pan-type granulator 5, and is transferred to a moving great ( (A lattice hearth) 7 '. The bedding pellet hopper 6 ′ supplies burned pellets (particle size: 5 to 25 mm) to the floor and side surfaces to protect the moving grate 7 ′.

The firing furnace 7 is a closed type, and exhaust gas sucked by a blower 9 from a suction box 8 below a great 7 'is supplied from an upper side of the partition plate 12 so as to be blown downward from above the pellet layer. The pellet is circulated and supplied downstream of the partition plate 12 so as to be blown upward from below the pellet layer, and discharged through a chimney.

In the firing furnace 7, the pellets on the great 7 ′ are first dried and preheated in the upstream region of the partition plate 13, and then the igniter 10.
(The raw pellets were heated in an oxygen-free atmosphere at 900 to 1100 ° C for 3 to 4 minutes, and then immediately ignited by introducing air with the air introduction means indicated by arrow 14), and ash contained in air and coal ash Self-combustion and below the melting temperature of coal ash (usually 1050-11
50 ° C), and after firing at this temperature for a predetermined time,
It moves to the cooling zone downstream of the partition plate 12. The cooled fired pellets are discharged out of the system, crushed by the crusher 15, and sieved to obtain artificial lightweight aggregate of the product.

In order to improve the quality and yield of the artificial lightweight aggregate manufactured in this way, it is important to optimize the firing conditions according to the properties of the coal ash.

The specific gravity, the loss on ignition, the water absorption, and the crushing strength of the artificial lightweight aggregate manufactured from two types of coal ash having different properties (see the table below for the properties) were measured. FIG. 1 shows the measurement results.

The artificial lightweight aggregate must satisfy JIS A 5002. Among them, the absolute dry specific gravity of the coarse aggregate (type M) must be 1.0 or more and less than 1.5, and the ignition loss must be 1% or less. In Fig. 1, the absolute dry specific gravity of both A ash and B ash satisfies the JIS standard in all firing temperature ranges, and there is no problem, but the ignition loss, that is, the amount of unburned carbon increases as the firing temperature increases. 1205 ° C
Is the upper limit temperature at which firing is possible. The higher the temperature, the higher the ignition loss is, the higher the melting temperature of the coal ash or higher, the surface layer of the pellets melts and becomes vitreous, making it difficult for oxygen gas necessary for burning the residual carbon inside the pellets to enter That's why.

On the other hand, when using artificial lightweight aggregate as aggregate for lightweight concrete, it is preferable that the fluidity of concrete is stable until concrete is mixed and then constructed, in order to saturate the water absorption performance of artificial lightweight aggregate itself. Is usually performed. From this viewpoint, the lower the water absorption of the pellet, the better.
For pellets made from 25 ° C and B ash, 1160 ° C is the minimum temperature at which firing is possible (however, the maximum water absorption is 15%). It should be evaluated as a lump, and should be kept as a reference value when determining the firing temperature, but there is a close correlation with the water absorption rate, and the lower limit temperature at which firing is possible is based on the case where the water absorption rate is used as an index. It turns out that it is the same.

As described above, the measurement results of the water absorption and crushing strength were determined according to the absolute dry weight and loss on ignition specified in JIS A 5002 as the quality of fired pellets (artificial lightweight aggregate). In this case, it is possible to produce a high-quality artificial lightweight aggregate at a high yield.

As described above, according to the present invention, in order to produce a high-quality artificial lightweight aggregate with a high yield, the properties of the product (absolute dry specific gravity, ignition loss, water absorption, crushing strength) are determined by using coal ash granulated material. Is used as a guideline for determining the firing temperature.

〔The invention's effect〕

According to the method of the present invention described above, in producing an artificial lightweight aggregate using coal ash as a raw material, the properties of the obtained artificial lightweight aggregate are accurately grasped and fed back to the setting of the firing temperature. The yield can be improved, and an economical method for producing an artificial lightweight aggregate using coal ash as a raw material can be achieved.

[Brief description of the drawings]

FIG. 1 is a table showing the relationship between the burning temperature and the product properties of two types of coal ash granules according to an embodiment of the present invention, and FIG. 2 is a diagram showing an artificial lightweight aggregate manufacturing apparatus for carrying out the present invention. FIG. 3 is a schematic diagram of the embodiment, and FIG. 3 is a table showing the relationship between the amount of coal in coal ash and the O ₂ concentration of the combustion supply gas.

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Takeshi Otake 1-1, Higashiyatabe-cho, Tsukuba-gun, Ibaraki Pref., Ministry of International Trade and Industry Ministry of Industry and Technology (72) Inventor Kunihisa Fujiwara 4-chome Kannonshinmachi, Nishi-ku, Hiroshima-shi, Hiroshima No. 6-22 Mitsubishi Heavy Industries, Ltd. Hiroshima Research Institute (72) Inventor Shigeo Itano 4-62 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture Mitsubishi Heavy Industries Co., Ltd. Hiroshima Research Center (72) Inventor Toshio Kai, Hiroshima City, Hiroshima Prefecture 4-62 Kannon Shinmachi Mitsubishi Heavy Industries, Ltd. Hiroshima Research Laboratory (72) Inventor Toshikuni Sera 2-5-1 Marunouchi, Chiyoda-ku, Tokyo Examiner for Mitsubishi Heavy Industries, Ltd. Noriko Suzuki

Claims (1)

(57) [Claims] An artificial lightweight bone is produced by laminating coal ash granules containing coal on the moving grade of a firing furnace which is isolated from the atmosphere, and combusting with oxygen-containing gas passing through the layer from above to below. In the method of calcining coal ash granules for producing the aggregate, the lower limit firing temperature is determined from the water absorption performance of the artificial lightweight aggregate which is the fired product of the granulated product, and the upper limit firing is determined based on the amount of unburned carbon contained in the artificial lightweight aggregate. A method for firing coal ash granulated material, comprising firing at a set temperature.