JPH0142906B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention mainly relates to an improvement in a method for producing lightweight aggregate using coal ash generated from coal-fired boilers as a main raw material.

Coal ash generated from conventional coal-fired boilers is broadly divided into clinker ash, which accumulates at the bottom of the furnace, cinder ash, which accumulates near the economizer, and fly ash, which is collected by a dust collector.

Fly atsushi is further classified into coarse powder and fine powder.
The fine powder has been standardized by the JIS as a raw material for fly ash cement, opening the door to its use, but most of the coal ash is disposed of through landfill. However, in recent years it has become increasingly difficult to secure land for landfills, and as a result, even the survival of coal-fired power generation is in jeopardy.

Against this background, various uses have been proposed to expand the use of coal ash, and the lightweight aggregate of the present invention is also intended to expand the use of coal ash as part of this. .

As a method for producing lightweight aggregate from coal ash,
Conventionally, rotary kiln method and sinter grate method are well known, but recently coal ash has been mixed with 2 to 5%
It is said that the method of obtaining lightweight aggregate by mixing and granulating pulverized coal, drying it on the sintering plate of a sintering machine, and then igniting it using a burner is superior in terms of manufacturing cost and quality. This method is the first
This is implemented in the manner shown in the figure. That is, the first
In the figure, pellets as a bedding layer are first supplied from a bedding supply feeder 021 onto a grate 020 that is moving endlessly. Then, granulated coal ash is deposited onto this bedding layer through a granulated coal ash feeder 02.
2 to form a moving packed bed. This moving packed bed then enters a preheating furnace 023 where it is dried, and then the top of the bed is ignited in an ignition furnace 024. After exiting the ignition furnace 024, air 027 is sucked from the upper part of the bed, the coal mixed in the granulated coal ash is burned, and the temperature in the bed gradually increases, causing a sintering reaction. When the coal burns out, it is sequentially cooled by suction air 027.

When the series of reactions of combustion, sintering, and cooling have been carried out to the bottom of the layer, the material is discharged from the discharge port 028 onto the conveyor 029. After that, the finished product relay tank 03
The particles are sent to a finished product storage bin 031 through a filter 0, where they are sieved by a screen 032 and stored according to particle size.

In addition, in the figure, 025 and 026 are the ignition furnace 024
033 is a line that supplies preheated air for drying into the preheating furnace 023, 034 is a dust collector that removes dust from the exhaust gas discharged from the preheating furnace 023, the ignition furnace 024, etc., 35
is the main exhaust fan, and 36 is the chimney.

In such a conventional granulated coal ash firing method, the coal content of the granulated coal ash supplied to the calcination machine is almost the same; With bed layer)
Figure 2 shows the concentration distribution of coal in the direction of the bed height when the coal is supplied to the coal and forms a bed. That is, in Fig. 2a, 020 indicates the grade, 1 indicates the bedding layer, and 2 indicates the granulated coal ash layer, and the coal concentration distribution in the layer height direction in this case is as shown in Fig. 2b. It is uniform in the layer height direction.

By the way, since the combustion of coal in a layer progresses from the upper layer to the lower layer, the air sucked from the upper layer to the lower layer is heated while passing through the upper layer, so the combustion temperature of coal in the combustion zone toward the lower layer increases. will gradually rise. That is, the maximum temperature in the bed (coal combustion temperature) at each position in the bed height direction is as shown in FIG. 2c. In this case, if the amount of coal mixed into the granulated coal ash is set so that the maximum temperature in the upper layer is a temperature suitable for combustion, the maximum temperature in the lower layer will be too high than the appropriate value, and the lower layer will There are problems such as melting, which deteriorates air permeability and reduces productivity, and severe melting that makes it difficult to produce lightweight aggregates for finished products. If the mixing amount is such that the maximum temperature of the upper layer becomes an appropriate value, the disadvantage is that the maximum temperature of the upper layer becomes low, the proportion of unfired products increases, and the yield as a finished product decreases.

The present invention is proposed for the purpose of solving the drawbacks of the conventional calcination method as described above, and involves preparing granulated coal ash with different amounts of pulverized coal in advance, and producing granulated coal with a small amount of pulverized coal mixed in. Ash is placed at the bottom and granulated coal ash containing a large amount of fine coal is placed at the top to form a layer on the moving grate, and then various processes necessary for firing such as drying, ignition, firing, and cooling are sequentially performed. Provided is a method for producing lightweight aggregate, which is characterized by applying.

In the method of the present invention, the granulated coal ash with a smaller amount of pulverized coal mixed is placed in the lower layer to form a layer of granulated coal ash on the grate. This allows for high yields of high quality lightweight aggregates,
It can be manufactured at a high production rate and the time required for firing can be significantly shortened.

An example of an apparatus for carrying out the method of the present invention will be explained in detail below with reference to FIG. 3 and FIGS. 4a, b, and c.

In FIG. 3, all symbols other than 22a and 22b are the same as those in FIG. 1, and indicate the same members. Bedding layer material is first supplied from a bedding supply feeder 21 onto the grate 20 moving on an endless track. Next, granulated coal ash containing a small amount of pulverized coal is supplied onto the bedding layer from the feeder 22a.
On this layer of granulated coal ash with a small amount of pulverized coal,
Granulated coal ash containing a large amount of pulverized coal is supplied from the feeder 22b to form the final layer.

Figure 4 shows the appearance of the layers at that time.
In the figure, 20 is the grade, 1 is the bedding layer, 2a is the lower layer consisting of granulated coal ash with a small amount of pulverized coal mixed, 2
4b shows the upper layer consisting of granulated coal ash with a large amount of coal mixed, and FIG. 4b shows the coal concentration distribution in the layer in the layer height direction at this time. In other words, a layer is formed in which the coal concentration in the upper layer is high and the coal concentration in the lower layer is low. After this layer is dried in a preheating furnace 23, it enters an ignition furnace 24 where the upper part of the layer is ignited. After leaving the ignition furnace 24, air 2 flows from the top of the layer.
The coal mixed in the granulated coal ash is combusted by suctioning 7, and the temperature in the bed increases sequentially from the top of the bed to the bottom, so that a sintering reaction occurs sequentially within the bed. At this time, the maximum temperature reached in each part of the layer is influenced by the coal concentration in the layer, and as shown in FIG. 4c, a substantially uniform red-hot temperature is obtained in the layer height direction. In other words, the coal concentration in the upper part of the bed is set to reach the appropriate temperature through combustion, and the coal concentration in the lower part of the bed is reduced, so there is no excess heat in the lower part of the bed, and almost all of the temperature is maintained throughout the height of the bed. Uniform combustion and glowing temperature can be obtained, so
Lightweight aggregate of constant quality can be fired under conditions of high yield and high production rate.

In addition, as for how to give the coal concentration distribution in the bed height direction, concentration changes may be provided in three or more stages, without being limited to the two stages described above.

Next, examples of the method of the present invention will be described.

Example 1 First, pre-fired lightweight aggregate pellets with a grain size of 6 to 15 mm were charged as a bedding layer onto the grate of a testing firing pot with a diameter of 300 mm so that the layer thickness was approximately 20 mm.

Next, granulated coal ash with a particle size of 5 to 25 mm mixed with 3% pulverized coal was charged to a layer thickness of 100 mm, and finally granulated coal ash with a particle size of 5 to 25 mm mixed with 5% pulverized coal was charged. Thickness 100mm (total height is bedding layer 20mm + coal 3%
100mm mixed layer + 100mm mixed layer of 5% coal = 220mm), and after forming the layer, heat it to about 270℃.
It was dried with hot air for about 8 minutes and then the surface of the layer was ignited with a propane burner for 2 minutes. The flame temperature of the burner at this time was 1270°C.

Immediately after ignition, combustion in the burner was stopped, and cold air was sucked in from above the layer. This operation resulted in a maximum temperature of approximately 1240°C at each location within the layer. When the pellets were completely cooled to the bottom of the bed and discharged from the firing pot, they were found to have been fired almost uniformly to the extent that the pellets at various positions in the bed height were separated by a light shock.

Approximately 75% of the total was made into finished products.

Comparative Example 1 In the same test firing pot as in Example 1, pre-fired lightweight aggregate pellets were first charged to a layer thickness of 20 mm, and then pulverized coal was charged into the same pot as in Example 1.
% mixed granulated coal ash with a particle size of 5 to 25 mm, with a total layer thickness of
A layer of 220 mm was charged to form a layer.

When this layer was subjected to drying, ignition, and cooling operations under the same conditions as in Example 1, the temperature of the upper layer was approximately
The temperature rose only to 1,160°C, while the lower layer reached 1,300°C or higher, creating a melting zone, and the cooling time was about four times that of Example 1. When the fired material was discharged from the pot after cooling, it was found that the upper layer was unfired and had weak strength, while the lower layer had particles fused together to form a single lump. Therefore, only about 40% of the products were made into finished products.

As described above, it can be seen that the method of the present invention is significantly superior to the conventional method in terms of firing yield and shortening of firing time.

[Brief explanation of drawings]

Figure 1 is a process diagram showing the conventional lightweight aggregate manufacturing method, Figure 2 a is a cross-sectional view showing a granulated coal ash layer on a grate in the conventional method, and Figures 2 b and c are the coal concentration in the layer. A diagram showing the distribution and the maximum temperature distribution in the layer height direction during firing, FIG. 3 is a process diagram showing an example of an apparatus for carrying out the method of the present invention, and FIG. 4 a
is a cross-sectional view showing the granulated coal ash layer on the grate in the method of the present invention, and Figures 4b and 4c are diagrams showing the coal concentration distribution in the layer and the maximum temperature distribution in the layer height direction during firing. be. 1: bedding layer, 2,: 2a, 2b: granulated coal ash layer,
020,20: Great, 021,21: Bedding supply feeder, 022: Granulated coal ash supply feeder,
22a: Granulated coal ash supply feeder with low coal content;
22b: Granulated coal ash supply feeder with high coal content;
023, 23: Preheating furnace, 024, 24: Ignition furnace,
027, 27: Supply air, 028, 28: Product discharge port, 030, 30: Product relay tank, 031, 3
1: Product storage, 034, 34: Dust collector, 035,
35: Main exhaust fan.

Claims (1)

[Claims] 1 In a method of producing lightweight aggregate by laying coal ash granulated by mixing pulverized coal in a layer on a moving grate and burning the coal ash while moving the heating area of the grate, the amount of pulverized coal mixed is A lightweight aggregate characterized in that two or more different types of granulated coal ash are prepared in advance, and a layer of coal ash is formed on the grate so that the granulated coal ash with a smaller amount of pulverized coal is placed in the lower layer. Production method.