JPS5817141B2 - Fly-assembly sintering method - 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 specifically, a method of forming green pellets with good self-combustibility, drying, and sintering. It is related to.

Dust collectors installed in various boilers, heating furnaces, and even incinerators collect extremely fine dust (fly ash, generally 20%
0 mesh), but the amount generated is quite large.

Moreover, due to sudden changes in the energy situation, switching to coal as a fuel is being considered, and it is predicted that the amount of fly ash generated will become extremely large if the transition to coal-fired combustion occurs. There is an increasing need to establish

Regarding the recycling of fly ash, a technology has been proposed in which it is granulated using a binder and further sintered to produce a lightweight aggregate, and the basic principle of the manufacturing process is already well known.

That is, Figure 1 is an explanatory diagram of the process, in which fly ash is mixed with fine coal powder and water is used as a binder to form a 5 to 25 mm thick powder.
Granulate raw pellets with a diameter of 1.

On the other hand, a bedding (usually sintered product aggregate) 2 is formed on the movable grate 3.

The above-mentioned raw pellets 1 are charged onto it, and if necessary, the raw pellets are dried and preheated 4, and then ignited and burned to proceed with sintering 5. If necessary, hot air is sent during the progress of sintering. Heat retention 6 is carried out, and then air cooling 7 is added in the rear half of the moving grate.

We are getting product aggregates.

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, raw fly ash pellets are quite large.

Therefore, in the latter sintering, while the carbonaceous material on the surface of the particles is efficiently combusted, the carbonaceous material inside the particles is not fully combusted, resulting in what is called a poor naturalness.

As a result, it becomes difficult to achieve the condition of "unburned content = 1% or less" stipulated by the JIS standard for lightweight aggregates.
This had become a bottleneck for recycling flyers.

The present invention has been made in view of the above-mentioned circumstances, and has established a sintering method that can suppress the combustible carbon material residual rate (ignition loss) to 1% or less. This is what I am trying to do.

The sintering method of the present invention has achieved these objectives.
Form a raw pellet of diameter and use it as a nucleus.

The outer surface has a high carbon content that is higher than the core and adjusted to 10% or less on a dry basis, and the total combustible carbon material content in the two-layer green pellet is adjusted to 4 to 6%. The gist of this method is to coat and granulate raw materials to form raw pellets with a diameter of 8 to 25 HIE, which are then dried and sintered.

Figure 2 is a schematic diagram showing the progress of sintering over time, with white circles indicating raw pellets, semi-heated circles indicating pellets in progress of sintering (combustion), and black circles indicating pellets that have been sintered. respectively.

When the pellet layer is transferred from left to right on the bedding along the arrow, air is sent from above and ignited, the pellets in the top layer start burning first, and the combustion layer moves sequentially to the lower layer. Transition.

That is, the pellets in the upper layer are exposed to low-temperature gas after ignition and there is no accumulation of heat, so combustion is difficult to proceed completely and unburned matter tends to remain.

On the other hand, from the middle layer to the lower layer, the combustion heat of the upper layer is sufficiently received and sintering progresses, resulting in a high-strength sintered body with no unburned particles.

In other words, incompletely sintered aggregates burned on the surface layer leave a large amount of unburned carbon, especially in the core, and in order to reduce the unburned content, combustible carbon material present in the core is necessary. It seemed better to keep the amount below the limit and increase the content of combustible carbon material in the skin to increase the self-combustibility of the pellet itself.

Figure 3 is a cross-sectional view of a green pellet formed based on this idea, and the core part A has a combustible carbon material content of 5% on a dry basis.
The combustible carbon material content of the outer skin part B is higher than that of the core part A, but is adjusted to be 10% or less on a dry basis.

The carbon content present in the core part A is small, and includes the carbon content present in normal fly ash.

A very small amount may be added, and especially when the carbon content is relatively high, it is not necessarily necessary to add new carbon to increase the carbon content.

Rather, it is desirable to set the upper limit at 5% to prevent unburned carbon from increasing even if sintering is insufficiently completed.

On the other hand, since it is necessary to improve the self-combustibility of the skin part B for the above-mentioned reasons, it is necessary to make the carbon material content at least higher than that in the core part A, and it is particularly desirable that the content be 5% or more.

As the carbon material content in the outer skin part B increases, the self-combustibility of the raw pellet improves, but if it exceeds 10%, many voids are formed in the outer skin part B of the sintered aggregate. The upper limit was set at 10% because it adversely affected the mechanical strength.

Furthermore, the self-combustion improvement effect reaches saturation at about 10%,
It is uneconomical to mix more than that.

The total content of combustible carbon materials in the raw pellets as a whole is preferably about 4 to 6%.

This is because if it is less than 4%, self-combustibility may be insufficient and the unburned carbon content may increase, while if it is more than 6%, it is uneconomical and may reduce the mechanical strength of the product aggregate.

Next, regarding the size of the raw pellet, the core part A needs to have a diameter of 2 to 8 mm, and the outer skin part B needs to have a diameter of 8 to 25 m.

If the diameter of the core part A is less than 2 mm, there is no point in making the raw pellet have a two-layer structure and adjusting the carbon material content by making the core part A independent from the outer skin part B. There is a problem in that a large amount of unburnt carbon material remains (slightly outside the core part A).

Moreover, if the core part A is formed to have a diameter larger than 8IiL, the outer skin part 5
Even if the self-combustibility of the fuel is increased, the effect will hardly reach the center of the core A, and there is a risk that a large amount of unburned carbon will be generated in the center.

On the other hand, the reason why the outer skin part B is made to have a dragon diameter of 8 to 25 mm is mainly due to the required physical properties as a lightweight aggregate.
If it is less than 1, the calorific value of the raw pellet itself becomes insufficient, which tends to lead to incomplete sintering, and if it exceeds 251 m, there is a problem that air infiltration into the core is inhibited, leaving incomplete sintering in the core. there were.

Coal powder is usually used as the combustible carbon material to be blended in the granulation of raw pellets, but this does not preclude the use of coke please or organic substances (sawdust, etc.).

Furthermore, the type of binder, the method of granulating raw pellets, the configuration of the sintering device, etc. are not limiting to the present invention, and can be selected and utilized as desired.

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

Example 1 Water was added to fly ash containing 3% combustible carbon and 70% small particles of 200 mesh or less to prepare a kneaded material with a water content of 15%.

Raw pellets with an average particle size of 6 yen were formed using a pan-type pelletizer and used as core pellets.

On the other hand, 3.5 parts by weight of pulverized coal of the same particle size was added to 96.5 parts by weight of the same fly ash as above, and the combustible carbon content was 6.
Water was added to the 5% mixture to prepare a kneaded product with a water content of 15%.

The above-mentioned core pellets were coated with the kneaded material and granulated to give an average of 101%. m
Two-layered pellets with a diameter of K were produced.

This raw pellet was charged into a batch type sintering machine.

The charging depth was 300 m5.

After preheating the surface with an ignition burner for about 4 minutes and then igniting it, suction was applied from the bottom of the sintering machine at a pressure of 10011L11LAq, air was passed from above to below, and sintering was performed by self-combustion for about 10 minutes.

After completion of sintering, the unburned carbon content in the product aggregate was measured and found to be 0.35% on average.

Comparative Example 1 Water was added to 97 parts by weight of the fly ash used above and 3 parts by weight of pulverized coal of the same particle size to give a combustible carbon content of 6%, to prepare a kneaded product with a water content of 15%.

Green pellets with an average particle size of 101 m were formed using a pan-type pelletizer, and sintered in the same manner as in the examples.

After sintering was completed, the immature carbon content in the product aggregate was measured.
The average was 2.3%.

Since the present invention is configured as described above, the naturalness of the green pellets is improved, and the unburned carbon content in the core can be kept low.

Therefore, the total residual rate of unburnt carbon materials in the sintered product is reduced, making it easier to satisfy the JIS standard values for lightweight aggregates.

Although the content of combustible carbon material in the core is low, effective naturalization takes place in the outer skin, so sufficient sintering has progressed in the core, making it extremely useful as a lightweight aggregate. We were able to.

[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, and FIG. 3 is a cross-sectional view of a two-layered pellet used in the present invention. A: Core part, B: Outer skin part.

Claims (1)

[Claims] 1. Fly ash generated from coal-fired boilers, etc. is granulated by adding an appropriate amount of combustible carbon material and binder.
In the sintering method, first, low-char raw pellets with a diameter of 2 to 8 mm are formed with a combustible carbon material content of 5% or less on a dry basis, and the raw pellets are used as cores, and combustible carbon is coated on the outer surface of the raw pellets. A high carbon raw material whose material content is higher than the core and adjusted to 10% or less on a dry basis, and the total content of combustible carbon materials in the two-layer raw pellet is adjusted to 4 to 6%, is coated and granulated. 8
A fly ash sintering method characterized by forming two-layer green pellets with a diameter of ~25 mm, and then drying and sintering the pellets.