JPH03131552A - Method for burning granulated article of coal ash - Google Patents

Abstract

PURPOSE:To obtain a high-quality artificial light-weight aggregate in a high yield by each setting an upper-limit burning temperature from water absorbing characteristics of an artificial light-weight aggregate and a lower-limit burning temperature from an unburned carbon amount contained in the artificial light-weight aggregate and burning a granulated article of coal ash at the set burning temperatures. CONSTITUTION:In burning of a granulated article of coal ash for laminating a granulated article of coal ash containing a coal content on a moving grate of a burning furnace isolated from the air and then producing an artificial light-weight aggregate by burning action with an oxygen-containing gas passing through the layer from upper side to the lower side, burning is carried out as follows: Lower-limit burning temperatures is set from water-absorbing characteristics of the artificial light-weight aggregate which is a burned article of the granulated article and an upper-limit burning temperature is set from an unburned carbon amount contained in the artificial light-weight aggregate and the granulated article is burned at the set temperatures. An optimum burning temperature area characteristic of each granulated article is precisely grasped and control of burning temperature, i.e., an O2 concentration control of a supply gas for burning is facilitated by measuring absolute dry specific gravity specified in JIS, an unburned carbon amount (carbon amount reduced on strong heating) contained in the artificial light-weight aggregate and water absorption important from the viewpoint of application of light-weight concrete. As a result, a high-quality artificial light- weight material can be produced in a higher yield.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for burning coal ash granules, and in particular to an artificial lightweight aggregate for effectively utilizing coal ash generated from coal-fired power generation equipment, etc. The present invention relates to a method that can be advantageously applied to the manufacturing method of.

[Conventional technology]

Artificial lightweight aggregates made from coal ash are usually made by adding and mixing coal ash with a binder such as clay and water to obtain a particle size of 5 to 25 mm.
After granulation, due to the self-combustion action of unburned carbon in the coal ash,
It is manufactured by firing at a firing temperature of 000 to 1200°C.

Artificial lightweight aggregates are mainly coarse aggregates (particle size 5 to 25 mmφ) and fine aggregates (particle size 0.15 to 5 mm) for structural lightweight concrete.
mmφ), the artificial lightweight aggregate currently in general use must meet the JISA 5002 standard. Regarding the quality of coarse aggregate (type M), which is used in large quantities, in order to comply with JIS standards, the important qualities are an absolute dry specific gravity of 1.0 to 1.5 and a loss on ignition of 1% or less. High strength and low water absorption are required from the perspective of improving workability during concrete construction. Therefore, in order to produce high-quality artificial lightweight aggregate, it is essential to establish a manufacturing technology that imparts the above characteristics.

Coal ash granules are turned into artificial lightweight aggregates through the processes of drying, preheating, ignition, calcination, and cooling, but it is the calcination process that determines the quality of the product. In this firing process, the unburned carbon contained in the ignited coal ash granules is sintered by a combustion reaction with oxygen in the air, but the oxygen concentration is
If it is not controlled in accordance with the coal content), it will be difficult to maintain the optimum combustion temperature and it will be impossible to obtain high quality artificial lightweight aggregate.

FIG. 3 shows the relationship between the coal content in coal ash and the 02 concentration in the combustion supply gas. The amount of charcoal required for sintering and hardening of coal ash granules by self-combustion is 4% or more, but if the charcoal amount is 4% or more and air (02-21%) is combusted, the rapid combustion reaction progresses, resulting in hardening. Since the surface of the granules melts, the granules fuse together and solidify after cooling (formation of lumps), and the granules are formed before the charcoal content inside the granules falls below the JIS standard ignition loss of 1%. The surface of the particles becomes vitrified and the combustion reaction stops. Therefore, in order to obtain high-quality artificial lightweight materials at a high yield, it is necessary to adjust the calcination temperature to an appropriate level by adjusting the 02 concentration of the combustion supply gas to match the coal content of the coal ash. Adjustment is key. Also necessary for combustion reactions. If combustion continues below the concentration, the temperature of the fired product will drop below the appropriate temperature, resulting in unfired products. Therefore, in order to produce high-quality artificial lightweight aggregate with a high yield, coal ash properties (charcoal content,
The temperature of the packed bed of granules must be stabilized within the appropriate temperature range by adjusting the 02s degree of the combustion supply gas to fall within the appropriate range shown in FIG. Conventionally, this temperature control determined the 0□ concentration of the combustion supply gas by measuring the coal content of coal ash.

[Problem to be solved by the invention]

The main component of normal coal ash is 5102: 34-60%, ^
120. : 17-31%, Fe20a: 2-25%, C
aO: 0.5-10%, MgO: 1-5%, and minor components include P2O3, Ti0z, MnO, and BaO.

Examples include K2O, Na, 0, etc. The range of these chemical components varies depending on the type of coal ash, so if the 02 concentration of the combustion supply gas is defined only by the amount of coal, it may not be possible to produce high-quality artificial lightweight aggregate at a high yield. This is thought to be due to changes in coal ash properties, especially Fe2
The influence of O2 and Can content fluctuations is large. The firing temperature of coal ash granules is usually 1100 to 1200°C, but C3
8 (C is CaO, A is Al2O3) is in liquid phase at 1050℃ or higher, C, AF (C is CaO, A is A1.03, F is FeJ3) is in liquid phase at 1160℃ or higher, and other than these also It is thought that they form various combinations. In addition, the melting point of ash is 1250 to 1500°C for 5I02 Al2O3 system, but CaO-3iO2-
In the A12D3 system, the temperature is 1100-1250℃, and CaO
It can be said that coexistence has the effect of lowering the melting point.

In view of the above-mentioned technical problems, the present invention aims to provide a method for firing coal ash granules that can produce high-quality artificial lightweight aggregate at a high yield.

[Means to solve the problem]

In the present invention, coal ash granules containing coal are layered on a moving grade of a kiln isolated from the atmosphere, and artificial lightweight aggregate is produced by the combustion action with oxygen-containing gas that passes through the layer from above to below. In the method of firing the coal ash granules to be produced, the lower limit firing temperature is determined from the water absorption performance of the artificial lightweight aggregate, which is the fired product of the granules, and the amount of unburned carbon contained in the artificial lightweight aggregate (ignition loss). This is a method for firing coal ash granules, in which the upper limit firing temperature is set and fired.

[Effect]

Among the properties of the artificial lightweight aggregate obtained by firing coal ash granules at a temperature below the melting temperature of the granules, the absolute dry specific gravity and amount of unburned carbon contained (ignition By measuring the water absorption rate, which is important from the perspective of lightweight concrete construction, and accurately understanding the optimal firing temperature range unique to the granules, it is possible to control the firing temperature, that is, to reduce the amount of gas supplied for combustion to zero. □Since concentration control becomes easier, high-quality artificial lightweight materials can be produced at higher yields.

[Example] FIG. 2 shows an example of the artificial lightweight aggregate production apparatus according to the present invention. In Fig. 2, a hopper 2 for storing coal ash discharged from coal-fired power plants, a tank 1 for storing water to be mixed with the coal ash, and a binder (for improving granulation and quality) are shown.
A predetermined amount of clay, bentonite, etc.) is supplied to a wet kneader 4 from a hopper 3 that stores the clay, bentonite, etc. The kneaded material kneaded by this wet kneader 4 is molded and granulated in a pan-type granulator 5 to have a particle size of 5 to 25, and then passed through the pellet charging hopper 6 of the kiln 7 to the moving grating of the kiln 7. (grid hearth) 7'. The bedding pellet feeding hopper 6' supplies fired pellets (particle size 5 to 25 mm) to the floor and side surfaces in order to protect the moving grate 7'.

This firing furnace 7 is of a closed type, and the exhaust gas sucked by a blower 9 from a suction box 8 at the bottom of the grate 7' is supplied to the upstream side of the partition plate 12 so as to be blown from above the pellet layer to below. It is circulated, and on the downstream side of the partition plate 12, it is supplied so as to be blown from below to above the pellet layer, and is discharged through the chimney.

In the firing furnace 7, the pellets on the grate 7' are first dried and preheated in the upstream region of the partition plate 13, and then passed through the ignition device 1.
0 (after heating the raw pellets in an acid-free cumulative atmosphere at 900 to 100°C for 3 to 4 minutes, air is immediately introduced by the air introduction means shown by arrow 14 and ignited), and the coal ash is contained in the air and coal ash. It self-combusts with carbon and is heated to below the melting temperature of coal ash (usually 1050 to 1150°C), and after being fired at this temperature for a predetermined period of time, it is moved to a cooling zone downstream of the partition plate 12. The cooled fired pellets are discharged from the system, crushed by crushing a15, and then sieved to obtain artificial lightweight aggregate for the product.

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

The bone-dry specific gravity, ignition loss, and
Water absorption rate and crushing strength were measured. Figure 1 shows the results of this measurement.

Artificial lightweight aggregates must satisfy JIS A 5002, of which the absolute dry specific gravity must be 1.0 or more and less than 1.5 for coarse aggregate (type M), and the ignition loss must be 1% or less. .

In Figure 1, the absolute dry specific gravity of both A ash and B ash satisfies the JIS standard in all firing temperature ranges, so there is no problem.
That is, the amount of unburned carbon increases as the firing temperature increases, and 1205° C. is the upper limit temperature at which firing is possible. The reason why the ignition loss increases as the temperature increases is because when the temperature reaches or exceeds the melting temperature of coal ash, the surface layer of the pellet melts and becomes glassy, making it difficult for the oxygen gas required to burn the residual carbon inside the pellet to enter. It's for a reason.

On the other hand, when using artificial lightweight aggregate as an aggregate for lightweight concrete, it is preferable that the fluidity of the concrete is stable until the concrete mixer is used, and the water absorption performance of the artificial lightweight aggregate itself is saturated. Brella etching is usually carried out. From this point of view, the lower the water absorption rate of the pellets, the better; in the case of pellets made from A ash, it is 11
For pellets made from B ash, the minimum temperature for firing is 1160°C (however, the maximum water absorption rate is 15%). It should be evaluated as a lump, and should be used 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 can be determined by using the water absorption rate as an indicator. It turns out that they are similar.

As mentioned above, the quality of fired pellets (artificial lightweight aggregate) is determined by measuring the water absorption rate and crushing strength in accordance with the absolute dry specific gravity and ignition loss specified in JIS A 5002 under the firing conditions, especially the firing temperature range. By reflecting this in the decision-making process, it becomes possible to produce better quality artificial lightweight aggregate at a higher yield.

As explained above, in order to produce high-quality artificial lightweight aggregate at a high yield, the present invention aims to improve the product properties (absolute dry specific gravity, loss on ignition, water absorption, crushing strength) of coal ash granules. This is a guideline for determining the firing temperature.

〔Effect of the invention〕

According to the method of the present invention described above, when producing artificial lightweight aggregate using coal ash as a raw material, the properties of the obtained artificial lightweight aggregate can be accurately grasped and fed back to the setting of the firing temperature. , it becomes possible to improve the product yield and achieve an economical method for producing artificial lightweight aggregate using coal ash as a raw material.

[Brief explanation of the drawing]

FIG. 1 is a chart showing the relationship between the firing temperature and product properties of two types of coal ash granules according to examples of the present invention, and FIG. 2 is an illustration of an artificial lightweight aggregate manufacturing apparatus for carrying out the present invention. A schematic diagram of the example, Figure 3 shows the amount of coal in coal ash and the amount of gas supplied for combustion.
It is a chart showing the relationship with concentration.

Claims (1)

[Claims] Coal that produces artificial lightweight aggregate by layering coal-containing coal ash granules on a moving grade in a kiln isolated from the atmosphere, and by combustion with oxygen-containing gas that passes through the layer from above to below. In the method for firing ash granules, the lower limit firing temperature is determined from the water absorption performance of the artificial lightweight aggregate that is the fired product of the granules.
A method for firing coal ash granules, comprising setting an upper limit firing temperature based on the amount of unburned carbon contained in the artificial lightweight aggregate.