JPS583989B2 - Manufacturing method of lightweight aggregate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of producing lightweight aggregate by granulating and sintering fly ash, and particularly relates to a method of producing lightweight aggregate with a low unburned carbon content.

Waste gas generated from boilers, combustion furnaces, incinerators, etc. contains a large amount of extremely fine dust (fly dust: generally 200 mesh or less), which is collected using electrostatic precipitators, etc., but due to the energy situation. It is predicted that if coal-fired coal-fired plants are started due to changes in the amount of carbon dioxide, the amount of flycatcher produced will become extremely large.

As a means to effectively utilize such fly attack,
Technologies for producing lightweight aggregates by granulation and sintering have been proposed, and the basic principles of the manufacturing process are widely known.

FIG. 1 is an explanatory diagram of the process, in which fine coal powder is mixed with fly ash, water is added as a binder, and green pellets 1 having a diameter of 5 to 25 mm are granulated and stored in a hopper.

On the other hand, a bedding 2 (usually made of sintered product aggregate) is formed on the movable grate 3, onto which the raw pellets 1 are charged and moved in the direction of the arrow. .

After passing through a drying and preheating section 4 if necessary, ignition combustion occurs in a sintering section 5, and further, if necessary, a heat retaining section 6.
After that, the aggregate is passed through an air cooling section 7 to be slowly cooled and a product aggregate is obtained.

On the other hand, with the diversification of iron ore, which is the raw material for iron making, the technology of granulating and sintering fine ore powder to obtain sintered ore has been established. Raw pellets usually have a diameter of about 2 to 5 mm, and compared to this, it can be seen that the raw pellets of fly ash have a considerably larger particle size.

Therefore, in the latter sintering process, it is not always easy to completely burn the inside of the pellet and complete the combustion.
Combustible carbon content is often left unburned, making it difficult to achieve the condition of "unburned content: 1% or less", which is the JIS standard for lightweight aggregates.

The present invention has been made in view of the above-mentioned circumstances, and aims to provide a sintering method that can suppress the unburned content (ignition loss) to 1% or less. It is something.

In order to achieve the above objective, we investigated how sintering progresses on a moving grate and found that the situation is as shown in the schematic diagram in Figure 2. This shows the change over time when a layer of pellets is transferred from left to right on the bedding along the arrow, and is ignited and burned from the upper part while forming an air flow from the upper part to the lower part. , white circles represent unburned raw pellets, half-black circles represent pellets that are being burned (sintering in progress), and black circles represent pellets that have been sintered.

However, the beresoto in the upper layer is exposed to low-temperature gas immediately after ignition, and the amount of heat accumulated by itself is small, so sintering progresses insufficiently, unburned matter remains, and the strength does not improve much. It disappears.

On the other hand, since the beresoto in the lower layer receives sufficient combustion heat from the upper layer, sintering progresses sufficiently and the strength of the product aggregate increases.

The present invention was completed as a result of various studies based on such knowledge, and the raw pellet layer charged on the bedding is divided into at least two groups, and the lower layer is made of combustible charcoal. Low carbon raw pellets whose material content has been adjusted to 5% or less on a dry basis are arranged, and on the upper layer side, the combustible carbon material content is adjusted to be higher than the above low carbon raw pellets and below 10% on a dry basis. The key point lies in the fact that continuous sintering is performed by distributing raw high-charcoal pellets.

In the above explanation, we talked about the upper layer side and the lower layer side, but the point is that continuous sintering is performed by placing low-char raw pellets in areas with good combustibility and placing high-carbon raw pellets in areas with poor combustibility. Since raw pellets have bamboo characteristics at points, it is common to charge and form raw pellets in two layers on the bedding, but if necessary, charge and form in three or more layers. However, the scope of the present invention also includes a sintering method in which the lower raw pellets have a lower carbon material content.

Moreover, arbitrary ideas can be added to the structure, size, etc. of the raw pellet itself.

FIG. 3 is an explanatory diagram showing a basic embodiment of the present invention, in which raw pellets 1 are divided into low-charcoal raw pellets) la and high-charcoal raw pellets 1b, and low-charcoal raw pellets Ha are first placed on the bedding 2. Then, high carbon raw pellets Nb were charged.

Each process, such as drying, preheating, ignition combustion, heat retention, and air cooling, is completely the same as in the case shown in Figure 1, but the raw pellets in each layer can be adjusted depending on the location environment and combustible carbon content. There is absolutely no problem in modifying the fuel so that it can burn more efficiently.

Note that the suction airflow from the chute installed below the movable grate is not processed all at once and discharged as is in the conventional method (Fig. 1), but rather the high temperature exhaust gas H near the sintering zone and the low temperature in other zones It is recommended that a piping line be constructed to separately take out the exhaust gas L and supply the former to the exhaust heat utilization equipment (including the main sintering equipment).

Next, low charcoal raw pellets and high charcoal raw pellets will be explained.

Low carbon raw pellets are charged into the lower layer where there is a large amount of heat storage, so
It is not necessary to increase the combustible carbon content so much, and even if the carbon content is a little, sintering can be completed sufficiently.

As for the upper limit of the content rate, the result of various studies was 5%.
(dry standard, hereinafter the same) is determined to be appropriate, and if the content exceeds 5%, it causes the fly ash to melt over the entire surface and has the disadvantage that it is easy to form large nodules.

Since fly ash originally contains a certain amount of combustible carbon, there is no need to take the trouble of adding coal powder, etc., but if you use a device with high combustion efficiency, you can add a small amount of coal powder. It is recommended to increase the content to nearly 5% to improve the naturalness of the raw pellets and improve the physical properties of the product aggregate.

On the other hand, since high-charcoal raw pellets are placed in an environment (upper layer) where sintering is difficult to proceed, it is necessary to increase the combustible carbon content in the raw pellets to sufficiently raise the temperature of the ignition layer.

By doing so, combustion progressed to the inside of the pellet, and high-strength fired pellets with a small amount of unburned carbon were obtained.

For these reasons, it was decided that the content should be higher than that of low-char raw pellets, but if the content exceeds IO%, there will be a lot of voids in the product aggregate, which may adversely affect the mechanical strength. , the upper limit was set at 10%.

The raw pellets explained above are generally granulated into a single homogeneous structure based on conventional technology, but those with a multilayer structure of two or three or more layers as described below are used. You can also use

In other words, as mentioned above, the green pellets used to produce lightweight aggregates have a fairly large diameter, so there is a difference in combustibility between the surface layer, which is in close contact with the atmosphere, and the core layer, where sufficient contact cannot be expected. There is.

By the way, when we investigated the distribution of unburned carbon in the product aggregate, we found that it tended to be less in the surface layer and more in the core.

From this point of view, the present inventors came up with a multilayer peresot in which the content of the combustible carbon material in the core is reduced and the content of the same is increased in the surface layer.

Figure 4 is a cross-sectional view of a green pellet formed based on this idea, and the combustible carbon material content in the core part A is small (usually 5
% or less), and for the outer skin part B, it is more than the core part (usually 5%).
% or more) and 10% or less.

Regarding the basis for each numerical value in Shodoki, the reasons stated earlier can almost be applied as is.

In addition, the content of combustible carbon material salmon in the raw pellets as a whole is desirably about 4 to 6%.

The reason for this is that if it is less than 4%, it lacks naturalness as a raw pellet (on the contrary, it is predicted that the unburned carbon content will increase), and? This is because if it exceeds 6%, the total blending amount of fine coal powder becomes high, which is uneconomical and may reduce the mechanical strength of the product aggregate.

Next, regarding the size of the multilayer pellet, the core part A should be 2 to 8
It is desirable that the outer skin part B has a diameter of 8 to 25 mm.

If the core part A is less than 2 mm, there is no point in making the raw pellet a multilayer structure and adjusting the carbon content by making the core part A independent from the outer skin part B, and the position near the center of the outer skin part B becomes useless. A large amount of unburned carbon tends to remain in the fuel.

Furthermore, if the core A is formed to have a diameter larger than 8 mm, the influence of the self-combustion that has increased in the outer skin B will be difficult to reach the center of the core A, and there is a danger that a large amount of unburned carbon will be generated in the center. There is.

On the other hand, the reason why the outer skin part B is made to have a diameter of 8 to 25 mm is mainly due to the required physical properties of the lightweight aggregate itself.
If it is less than 8 mm, the calorific value of the raw pellet itself will be insufficient, which may lead to incomplete sintering. If it is more than 25 mm, air will not be able to enter the core, resulting in incomplete sintering of the core. There is a fear that.

Coal powder is usually used as the combustible carbon material for granulating the above-mentioned raw pellets, but coke breeze, organic substances (sawdust, etc.), etc. may also be used.

Water is usually used as the binder, but there are no particular restrictions on its type or the method of granulating raw pellets.

Next, Examples and Comparative Examples of the present invention will be shown.

Example 1 Pulverized coal of the same particle size was added to the fly ash, in which the content of combustible carbon material was 3%, and the small particle size of 200 mesh or less was 70%, to make the total content 4%.

Water was added to the mixture to adjust the moisture content to 15%, and raw pellets I having an average particle size of 10 mm were granulated using a pan-shaped pelletizer.

In addition, pulverized coal of the same particle size was added to increase the total content of combustible carbon material to 7%.
Raw pellets ■ were obtained in the same manner from the prepared fly atsushi.

Raw pellets I were charged into a batch type sintering machine to a depth of 200 mm, and raw pellets II were further charged to a thickness of 100 mm.

The surface was preheated for about 2 minutes with an ignition burner, then ignited, and natural sintering was performed for about 10 minutes while suctioning from the bottom of the sintering machine under a pressure of 100 mmAq and passing air from above to below.

Twenty samples were taken out at random from the obtained product and the crushing strength was measured, and the average was 63 kg/lOCmφ.
There was almost no variation between the pellets in the upper and lower layers.

The average unburned carbon content in the upper layer was 0.83% and the average in the lower layer was 0.65%.

Comparative Example 1 Following the same procedure as Example 1, the town-burnable carbon material content was 6%.
The raw pellets are granulated and placed in a batch type sintering machine at a depth of 300m
It was charged at m.

Then, when it was sintered in the same way and the same measurements were performed,
The average crushing strength was 41 kg/10 Cmφ, and large variations were observed in the pellet crushing strength between the upper layer and the lower layer.

The average unburned carbon content in the upper layer was 2.8%, and the average in the lower layer was 1.5%.

Example 2 A core with a diameter of 8 mm (combustible carbon material content: 4%) was coated with a muddy mixture having a combustible carbon material content of 8%, and the core was 13 mm in diameter.
Fresh fly pellets were prepared.

This is charged into the upper layer, and the lower layer has a combustible carbon material content of 4%.
raw pellets (diameter lomm) were charged.

When this was sintered according to Example 1, the upper pellet had a crushing strength of 90 kg/1.3 Cmφ and an unburned carbon content of o. 72%, lower pellet crushing strength: 64kg
/1 cmφ, unburned carbon content: 0.60%.

Since the present invention is configured as described above, the sintering of the green pellets progresses sufficiently, and the unburned carbon content in the product aggregate, particularly in the lower layer, can be suppressed to a low level.

Therefore, the physical properties as a lightweight aggregate were improved, and its utility value was made extremely high.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the sintering process, Fig. 2 is a schematic diagram showing the progress of sintering, Fig. 3 is an explanatory diagram showing the manufacturing process of the present invention, and Fig. 4 is a two-layer diagram that can be used in the present invention. FIG. 3 is a cross-sectional view of raw pellets. 1a: Low charcoal raw pellets, 1b: High charcoal raw pellets.

Claims (1)

[Claims] 1. Green pellets are obtained by adding an appropriate amount of combustible carbon material and a binder to fly ash generated from a coal-fired boiler, etc., and granulating the mixture, and charging the green pellets onto a moving grate. In a method for producing lightweight aggregate by sintering, a bedding material made of the product lightweight aggregate is charged onto a moving grate, and a combustible carbon material content of 5% on a dry basis is placed on top of it. % or less, and on top of that, charge high-charcoal raw pellets whose combustible carbon material content is higher than the low-charcoal raw pellets and adjusted to 10% or less on a dry basis. A method for producing lightweight aggregate characterized by continuous sintering. 2. In claim 1, the high-charcoal raw pellets are manufactured by producing lightweight aggregate, which is obtained by coating and granulating a material with a high combustible carbon material content around a core with a low combustible carbon material content. Law.