JPS59111971A - Manufacture of lightweight aggregate - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing lightweight aggregate by granulating and sintering fly ash. When self-combusting the pellets by burning the material, the combustion speed of the next material is controlled to prevent cracks and collapse of the pellets during sintering, improving the yield of product pellets (@mass aggregate). and the same quality as above.

The exhaust gas generated from various boilers, heating furnaces, incinerators, etc. contains a large amount of glazed dust (fly ash), but as the energy source changes, the switch to coal-fired combustion is progressing. It is predicted that the noise generated by fly ash will increase dramatically as time goes on.

Such praiatunyu is recovered using an electrostatic precipitator or the like, but in order to effectively utilize it, a method of sintering it into Δ grains and turning it into artificial @mass aggregate has become necessary. In other words, fly ash originally contains some wood-burning carbon material, but if necessary, combustible carbon material (coal or coke fine powder) is added, and it is kneaded and granulated with nokinder (water). The pellets are charged onto a moving grate and transported while being dried, preheated, ignited, sintered, heat-retained, and cooled to become artificial lightweight aggregate.

FIG. 1 is an explanatory diagram showing such a sintering procedure, in which the product (sintered) aggregate 2 is charged into the hopper 18, the raw pellet 1 is charged into the hopper 16, They are stacked on a pallet-shaped movable grate 8 that rotates in the direction of the arrow. Meat product aggregate 2 is to be supplied as bedding, raw beret l
may be charged immediately after granulation without depending on the hopper 16. The raw material layer thus formed is sequentially transferred from the left side of the drawing to the stones as the grate moves, passes through a drying/preheating furnace 4, an ignition furnace 5, and a combustion/retention furnace 6, undergoes sintering, and is then transferred to a cooling zone 7. It is sufficiently cooled and becomes product aggregate. At the bottom of the upper grate that conveys the raw pellets, a wind box 8 is fixedly placed along the conveying direction.
The lower diameter of the wind box 8 is the return side (lower 111
1) In order to avoid the grate, it is deflected in the direction penetrating the plane of the paper, and is opened and connected to the exhaust duct 9. Duct 9 is a blower
10, and due to the suction airflow, a suction airflow that passes through the raw material layer from top to bottom is formed.

Therefore, if a high-heat air introduction pipe is connected to the upper part of the 6 rectangles 4 and 5.6, the same high-temperature air will be introduced into each furnace, and it will descend between the raw material layers and enter the wind box 6. It is discharged. That is, since the green pellets are spherical with a diameter of 5 to 25 .phi., the ventilation resistance within the raw material layer is relatively small, and a descending airflow passing through from the top to the bottom is formed in the spacer. Further, the disintegrated waste of the green pellets that has fallen into the exhaust duct 9 falls through the chute 11 onto the conveyor 12 and is collected, and is generally returned and reused as a raw material for granulating the green pellets. 14 is a damper,
Reference numeral 18 indicates a driving sprocket.

The pellet-shaped product aggregate obtained in this way (hereinafter referred to as "product pellet") is limited to those made from ordinary fly ash (e.g., low melting point domestic return ash) and satisfies the specified standards as a lightweight aggregate. are doing.

However, depending on the properties of the raw material fly ash, it may not always be satisfactory. In other words, fly ash (e.g. daytime melting point overseas coal ash) on a certain shelf evaporates and expands from the moisture in the raw pellets and the inside of the carbonaceous combustion gas pellets, forming granulated pellets with only water as a binder. This causes cracks in the pellets and, in extreme cases, causes the pellets to collapse (hereinafter referred to as "bursting"), resulting in lower product yields and lower product quality.

By the way, even with fly ash that generates bursting, it is necessary to make the drying/preheating zone sufficiently long to dry all the pigeons almost completely before igniting them on the moving grate. If you carry out the processing,
It is known that the occurrence of bursting can be largely prevented. However, if such a pretreatment process were to be newly established, compared to the general conventional method in which only the surface layer of the filled pellet is dried and preheated, then ignited, and the lower layer is subjected to dry formation using the combustion heat of the upper layer. However, there are major problems in terms of equipment economy and heat economy, such as the need for long firing equipment and the need to secure a large amount of hot air for drying.

The present invention focused on the above-mentioned circumstances and was completed as a result of intensive research in order to almost completely prevent the above-mentioned bursting and produce high-quality product pellets at a high yield without making the drying/preheating zone particularly long. The gist of the structure is that air containing lower oxygen concentration than normal air is supplied from above the packed pellet layer that is at least in the first half of sintering and heat retention.

Below, we will explain the structure and effects of this button light according to the research history and with reference to the drawings. First, the present inventor places emphasis on the fact that bursting hardly occurs in the firing mode in which green pellets are completely dried and then ignited and sintered. Even with a firing method in which drying and preheating proceed at the same time,
B to the extent that bursting does not occur in the middle and lower layers of the pellet packed bed! We established a solution guideline that if we control the rate of cyst formation so that it is completely dry and preheated until it reaches ignition, combustion, and sintering, especially through delay control, bursting should be suppressed. Research has been carried out in search of such a means for controlling the firing S degree delay. By the way, since the firing speed delay control is nothing but the control of the combustion speed of the carbon material applied to the green pellets, it can be determined that the air amount should be considered as a control element and the air amount should be reduced. In other words, when the green pellet passes through the ignition zone and moves to the next sintering/heat retention zone, it is expected that the firing speed can be easily delayed and controlled by adjusting the degree of decrease in the amount of air supplied in this zone. Ta. However, simply reducing the amount of air in this way can cause overheating and fusion of the civet due to the retention of combustion heat, resulting in a decline in product quality, especially in the case of frying with a high content of unburned I# elements. Since the amount of hot air passing through to the lower layer itself will be reduced, the intended purpose of completely drying and preheating the bamboo before ignition cannot be achieved.

Therefore, we conducted further research to find a way to slow down the firing speed while still allowing adequate ventilation to prevent excess combustion heat from accumulating. It has been found that it is sufficiently effective if the oxygen content is lower than that of normal air. In other words, when the raw pellet passes through the ignition zone and moves to the sintering/heat retention zone,
When the pellets were self-combusted by supplying air with a lower oxygen concentration than normal air from above the filled pellets), the firing rate slowed down, but no bursting was observed, and no bursting was observed. The quality of the product pellets was also good. Therefore, even with a firing method in which combustion sintering of the packed and stacked pellet layer and drying and preheating of the lower layer proceed simultaneously, the middle and lower layers of the packed pellet layer are completely dried and preheated to the extent that bursting does not occur. After that, ignition, P sintering, and sintering can be performed.
without increasing the length of the sintering equipment by lengthening the preheating zone.
Bursting can be almost completely prevented and high-quality product pellets can be manufactured at a high yield.

In this case, the recommended target for reducing the oxygen concentration in the air is 12 to 19 qb. This is because when the oxygen concentration decreases by a factor of 12, the sintering rate becomes extremely slow, causing problems in productivity and even stopping the sintering reaction itself.On the other hand, when the oxygen concentration exceeds 19%, the gF 4
This makes it difficult to control the temperature delay, and ignition and sintering will begin before the middle and lower parts of the pellet packed bed are completely dried and preheated, making it difficult to obtain a bursting suppression effect. be.

By the way, when producing air with a lower oxygen concentration than normal air, it is necessary to be able to easily change and adjust the oxygen concentration according to differences in the properties of fly ash. For example, the method shown in FIG. 2 may be used. That is, a high temperature air introduction pipe 26 is installed in the front half of the sintering/heat retention furnace 6.
and an oxygen concentration meter 2 on the downstream side of the introduction pipe 26.
0, and furthermore, an inert gas supply pipe 21 is connected to the front side of the concentration meter 20. Further, a valve 22 is provided in the high temperature air introduction pipe 26 on the upstream side of the connecting portion, and a valve 28 is also provided in the inert gas supply pipe 21. Then, the concentration of oxygen contained in the temperate air after mixing with the inert gas is determined by the acid concentration a.
The oxygen concentration can be freely controlled by setting and constantly recording the oxygen concentration using the temperature meter 20 and opening and closing the valves 22 and 28 according to the set value or the recorded value. Like the above configuration,
It is not necessary to introduce the inert gas mixture only into the first half of the sintering/heat retention zone until all layers of the packed pellets have been sintered (and it is necessary to maintain productivity as much as possible). Therefore, from this point of view, normal air (oxygen-enriched air if necessary) should be supplied in the zone υ behind (in the direction of pellet advance) from the position where all layers of the filled pellet have been dried in Fig. 2. If the firing speed is increased to a point where there is no problem by actively supplying it, productivity can be improved accordingly, and the firing equipment can also be downsized.

The present invention is constructed as described above, but the key point is that the middle and lower layers of the pellet packed bed on the moving grate are sufficiently dried and preheated before the combustion sintering zone from the upper layer reaches the bed. Because of this structure, bursting can be almost completely prevented and high-quality product pellets can be manufactured at a high yield even if the drying/preheating zone is lengthened and the sintering equipment is made longer as in the past.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the sintering process, and FIG. 2 is a diagram of an embodiment of the present invention. 8...Movable grate 4...Drying/preheating furnace 5...
・Ignition furnace 6...Sintering/heat retention furnace 7...Cooling zone 20...Oxygen meter 21...Inert gas supply pipe 22.28...Valve 26...High temperature air introduction Pipe applicant Kobe Steel, Ltd.

Claims (1)

[Claims] +11 After adding an appropriate amount of combustible carbon material and binder to the fly ash and granulating the pellets, the pellets are loaded onto a moving grate, and are sequentially and continuously dried, preheated, and ignited along the direction of travel. In the method of producing bulk aggregate by sintering, heat retention, and cooling, the air supplied from above the bed at least in the first half of the sintering and heat retention stage has a higher oxygen content than normal air. A method for manufacturing light air conditioning materials characterized by producing low air quality.