JPS583990B2 - Sintering method using a moving grate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for sintering fly ash granules, and particularly to a method for preventing uneven sintering due to the occurrence of partial half-burning.

Exhaust gas generated from various boilers, heating furnaces, incinerators, etc. contains a large amount of fine dust (fly dust), but as the energy source changes and the switch to coal-fired combustion progresses, It is predicted that the amount of fly attack will increase dramatically.

Such fly ash is recovered using an electrostatic precipitator or the like, but in order to effectively utilize it, a method of granulating and sintering it into artificial lightweight aggregate has been put into practical use.

In other words, fly ash originally contains some unburned carbon material, but if necessary, combustible carbon material (fine powder of coal or coke) is added, kneaded and granulated with a binder (water) to form raw pellets, which are then transported. It is charged onto a grate and transported while being dried, preheated, ignited, sintered, heat-retained, and cooled to produce an artificial lightweight aggregate.

Figure 1 is an explanatory diagram showing such a sintering procedure.
Product (sintered) aggregate 2 is charged into hopper 13.
6 is loaded with raw pellets 1, and the cross-sectional view (
They are sequentially stacked onto a pallet-shaped movable grate 3 that has a groove shape as shown in FIG. 2) and rotates in the direction of the arrow in FIG.

The product aggregate 2 is initially charged as a bedding in order to prevent pellets that become red-hot due to sintering from directly contacting and adhering to the grate 3 and further causing heat loss to the grate 3. The raw pellets 1 may be charged immediately after granulation, without using the hopper 16.

The raw material layer thus formed is sequentially transferred from left to right in the drawing as the grate moves, and is transferred to the drying/preheating furnace 4 and the ignition furnace 5.
and undergoes sintering through a sintering/retention furnace 6 and a cooling zone 7.
It is then sufficiently cooled to become product aggregate.

A plurality of wind boxes 8 are arranged along the conveyance direction at the bottom of the upper grate through which fresh pellets 1, etc. are conveyed. It is deflected to avoid the return grate and is opened and connected to the exhaust duct 9.

The inside of the duct 9 is evacuated by a blower 10, and due to the suction airflow, a suction airflow is formed that passes through the raw material layer from top to bottom.

Therefore, by connecting a high-temperature air introduction pipe to the upper part of each furnace 4, 5.6, high-temperature air is introduced into each furnace, descends between the raw material layers, and is discharged into the wind box 8. Ru.

The decayed raw pellets, etc. that fall with the discharged air fall through the chute 11 onto the conveyor 12 and are collected.
Generally, raw pellets 1 are returned as raw materials for granulation and reused.

Note that 14 represents a damper, and 18 represents a drive sprocket.

In the above sintering method, the size of the raw pellet 1 is
Considering the JIS standard for artificial lightweight aggregate, the length is usually 5 to 25 m.
Since it is formed into a spherical shape with mφ (about 12 mmφ on average), the air resistance within the raw material layer is relatively small, and a downward airflow passing from the top to the bottom is easily formed.

However, this air permeability is not uniform and the air permeability of the part in contact with the side wall is large, so the air permeability of the side wall 3a side is ten times lower than that of the central part, and in order to achieve sintering to the inside of the pellet, it is necessary to Even if the preheated air is passed through, the pellets being sintered are strongly air-cooled on the side wall side, resulting in incomplete sintering (half-baked).

Therefore, uneven sintering will occur as a sintered product,
For example, the unburned carbon content (measured as loss on ignition) is
There was a problem that the limit value (1%) in the JIS standard was exceeded.

The present invention has been made in view of these circumstances, and it is an object of the present invention to provide a sintering method that can comprehensively suppress the occurrence of sintering unevenness.

That is, the gist of the present invention is to charge sintered pellets so as to be arranged on both side walls of a groove-shaped grate, and to perform sintering by charging green pellets inside the sintered pellets. As a result, the problem of uneven sintering was completely avoided as a result of not originally expecting sintering on both side walls, but rather sintering concentrated on the center side.

In addition, when using pellets with a smaller particle size than the charged raw pellets as the sintered pellets placed on both side walls, the ventilation resistance on both side walls increases and the overall sintering progresses more uniformly. Now I can do it.

FIG. 3 is a sectional view showing the raw material charging situation in the movable grate 3, in which the bedding 2 described in FIG. 2' (side layer) is charged.

The green pellets 1 to be sintered are then charged into the center.

Therefore, even if the air permeability becomes excessive on the side layer side, the air permeability at the contact point between the side layer and the raw pellet is improved, and the sintering progress at that point no longer needs to be a problem, and the sintering can be controlled. It was decided that it would be better to focus only on the central area.

Therefore, the amount of green pellets 1 charged onto the grate is smaller than in the conventional method, which at first glance seems to be inconvenient in terms of productivity, but with regard to sintering speed control, etc. Comprehensively considering the advantages of the present invention, such as requiring only centralized control, improving product yield, and reducing the need for separation operations due to uneven sintering, the present invention is advantageous. Gender is easily understood.

The particle size of the pellets in the side layer is not particularly limited, but if it is made smaller than the particle size of green pellets 1, the ventilation resistance in the part that comes into contact with the green pellets will be reduced, so it will be easier to Even if a portion of the pellets may be mixed into the side layer, half-cooking is prevented and the overall breathability becomes more uniform.

Therefore, it is preferable to reduce the particle size of the sintered pellets charged as a side layer, but charging small particles of non-standard size will complicate the classification work after sintering is completed, so in the case of bedding 2 Similarly, it is recommended to use particles with as small a particle size as possible within the standard range.

Since the present invention is configured as described above, it is possible to prevent raw pellets from being half-burned, and to provide a sintered product whose unburned carbon content satisfies JIS standards at a high yield.

Next, embodiments of the present invention will be described.

Example 1 On a groove type grate with depth: 40 cm and width: 120 cm, 3
A bed of product pellets (particle size: 5 to 10 mm) was formed at a height of Cm.

Next, product pellets (particle size: 5 to 8 mm) are charged from the side wall surface to an average thickness of 3 cm, and raw pellets (average particle size: 12 mm, moisture: 17%, carbon material content (rate: 5%) was charged to a height of 27 (m).

When charging side layers and green pellets separately, a partition plate was used during the charging stage, and the partition plate was pulled out after charging was completed.

The powder ratio (ratio of particles less than 5 mm in diameter) of the product obtained by sintering by a conventional method was 24%, and the unheated carbon content was 0.3%.

Comparative Example 1 Sintering was carried out in the same manner as in Example 1 except that the side layer was not formed. The powder ratio of the sintered product was 13% and the immature carbon content was 1.5%.

[Brief explanation of the drawing]

FIG. 1 is an overall view of the sintering process, FIG. 2 is a cross-sectional view taken along the line n-1, and FIG. 3 is a cross-sectional view showing the state of charging into the grate in the present invention. 1...Raw pellets, 2...Bedding, 2/
...Side layer, 3...Grate.

Claims (1)

[Claims] 1. Raw pellets obtained by granulating fly ash generated from a coal-fired boiler etc. are stacked on a moving grate,
When performing sintering by forming a through-air flow in the vertical direction of the layer, sintered pellets are placed on both side walls of a groove-shaped grate, and green pellets are charged inside and sintered. A sintering method using a moving grate. 2. A sintering method according to claim 1, in which sintered pellets having a smaller diameter than raw pellets are mainly charged as sintered pellets placed on both side walls of a groove-shaped grate.