JPH0118026B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing lightweight aggregate by granulating and sintering fly ash. The present invention relates to a technology for reliably and economically preventing cracking and collapse of pellets.

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

Such fly ash is collected 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, flammable carbon material (fine powder of coal or coke) is added and kneaded and granulated with a binder (water) to form raw pellets. Dry while being loaded onto a moving grate and transported.
It is preheated, ignited, sintered, heat-retained, and cooled to produce an artificial lightweight aggregate.

Figure 1 is an explanatory diagram showing such a sintering procedure.
A product (sintered) aggregate 2 is charged into the hopper 13, and raw pellets 1 are charged into the hopper 16, and these are stacked on a pellet-shaped movable grate 3 rotating in the direction of the arrow. The product aggregate 2 is supplied as bedding, and the raw pellets 1 are supplied to the hopper 16.
In some cases, it may be charged immediately after granulation. 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,
It undergoes sintering through an ignition furnace 5 and a sintering/retention furnace 6, and reaches a cooling zone 7 where it is sufficiently cooled and becomes a product aggregate. A plurality of wind boxes 8 are arranged along the conveying direction at the bottom of the upper grate that conveys raw pellets 1, etc., and the lower narrow diameter part of the wind boxes 8 is connected to the return side (lower side) fire. In order to avoid the grid, it is deflected in the plane of the paper, and is opened and connected to the exhaust duct 9. The interior 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 mixing pipe to the upper part of each furnace 4, 5, and 6, high-temperature air is introduced into each furnace, passes between the raw material layers, descends, and is discharged into the wind box 8. be done. That is, raw pellets are 5
Since it is spherical with a diameter of ~25 mm, there is relatively little ventilation resistance within the raw material layer, and a downward airflow that passes from top to bottom can be easily formed. Incidentally, the disintegrated materials of the raw pellets that have fallen into the exhaust duct 9 fall through the chute 11 onto the conveyor 12 and are collected, and are generally returned and reused as a raw material for granulating the raw pellets. Sho 1
4 represents a damper, and 18 represents a drive sprocket.

As long as the pellet-shaped product aggregate obtained in this way (hereinafter referred to as "product pellet") is made from ordinary fly ash (for example, low-melting point domestic coal ash), it satisfies the specified standards as a lightweight aggregate. There is.

However, depending on the properties of the fly ash that is the raw material, this may not always be satisfactory. That is, in some types of fly ash (for example, high-melting-point foreign coal ash), moisture in the raw pellets and carbonaceous combustion gas evaporate and expand from inside the pellets, causing cracks in the granulated pellets formed using only water as a binder. In extreme cases, it may cause the pellets to collapse (hereinafter referred to as "bursting").
This resulted in a decrease in product yield and product quality.

The present invention has been completed as a result of intensive research, paying attention to the above-mentioned circumstances, in order to reliably prevent cracking and bursting of pellets during sintering, and to suppress the cost required for prevention as much as possible. Its structure is that an alkali metal compound solution or alkali metal compound powder is adhered to the surface of the raw pellets from the latter half of the granulation process until the ignition process, and then ignition, sintering, heat retention, and cooling are performed. There is a summary in .

The configuration and effects of the present invention will be explained below along with the history of the experiment and with reference to the drawings. First of all, there are various possible causes of bursting, but
One of these is the chemical composition of fly ash, and it has been found that the proportion of alkaline components in particular has a great influence. That is, by adding 1 to 3% by weight of an alkali metal carbonate in advance to a fly ash whose composition is known to be prone to bursting and granulating it, bursting could be almost completely suppressed. . Alkali metal compound (powder) before granulation in this way
The addition of
211673), which is desirable in that it does not require special addition equipment, but it requires a very large amount of expensive alkali metal compounds, resulting in a significant increase in the manufacturing cost of the product pellets. Therefore, we conducted further experiments to determine the minimum amount of alkali metal compounds that can be added to achieve the desired effect, and found that the addition of alkali metal compounds to the skin of a single pellet is sufficient. It has been found. That is, the raw pellets obtained by coating or spraying an alkali metal compound solution over the entire surface of the pellets after granulation are dried, preheated, ignited, sintered, heat-retained, and cooled by the method shown in Figure 1. When product pellets were produced, no bursting was observed and the quality of the product was good. Furthermore, the amount of the alkali metal compound used at this time was extremely small at 1/5 to 1/100 compared to the case where it was added before granulation as described above.

Also, when the same powder is used instead of the alkali metal compound solution to produce product pellets by the above-mentioned calcination operation, similar good results can be obtained, and the amount of the powder used is 1. /3~
It was 1/50. As described above, the purpose can be sufficiently achieved using alkali metal compound powder, but in addition to the effect of reducing the amount added and the ease of handling, it is also possible to uniformly adhere the alkali metal compound to the surface of the raw pellets by using the above compound solution. It is more preferable to use The concentration of the aqueous solution is preferably increased to a concentration that does not impede the smoothness of the coating or spraying operation of the aqueous solution, depending on the solubility of the alkali metal compound used in water. This is to suppress the increase in the moisture content of the raw pellets due to the addition of the aqueous solution as much as possible, and to prevent the deterioration of the properties of the raw pellets and the thermal efficiency during the sintering process due to the increase in moisture content. The recommended ratio of the dry weight of the alkali metal compound added to the dry weight of fly ash is 0.01 to 3%. Although this differs depending on the composition and/or particle size structure of the fly ash to which the additive is added, in general, even if the addition rate of the alkali metal compound exceeds 3%, the bursting suppression effect itself has already been saturated, and it is simply a matter of reducing the manufacturing cost. This is because it only increases it.

Next, when carrying out such adhesion treatment operations such as coating and spraying, for example, as shown in FIG. If the alkali metal compound solution can be supplied from the tank 22 or the solution can be supplied from the tank 24 to the transfer section of the conveyance equipment 23 from the dish-shaped granulator 21 to the movable grate 3, This is preferable because the supplied solution tends to be uniformly attached to the entire surface of each raw pellet.
However, the place where adhesion processing operations such as coating and spraying are performed is not limited to the above, and the point is that the dish-shaped granulator 21
It may be any suitable place between the latter half or the end of the granulation process and the time when the green pellets filled on the movable grate 3 are put into the ignition furnace 5. Spraying can be done using a general spray device, but it is also economical to use a soaking brush or roll it on a belt conveyor whose surface is wetted with the above solution. Relatively effective.

Further, in the above embodiments, coating and spraying were typically used as the adhesion treatment operation, but the present invention is not limited to these, and any method that can be applied to the entire surface of the raw pellets is applicable as long as it can be applied substantially uniformly. Incidentally, when using a powder of an alkali metal compound, a method is adopted in which the powder is granulated using a dish-type granulator or the like, and then the powder is introduced and the surface of the raw pellets is sprinkled with the powder.

The compound used in the present invention may be one that provides alkalinity without decomposing during the sintering process and leaving behind components harmful to the quality of the finished product, or generating harmful substances during the firing process. All can be used, but the most typical ones are
Examples include Na ₂ CO ₃ , NaHCO ₃ , K ₂ CO ₃ , NaOH, and KOH, and these may be used alone or in combination of two or more. In addition, ores containing alkali metals such as those mentioned above, such as soda stone and bicarbonate soda stone, can be crushed and used.
Of course, it is also possible to use glass abrasive powder.

The present invention is roughly constructed as described above, and has an extremely simple construction in which an alkali metal compound solution or powder is attached only to the surface of raw pellets before ignition, thereby preventing cracks and bursting of pellets during sintering. It has become possible to reliably prevent the above-mentioned problems, and the cost required for the above-mentioned prevention can be significantly reduced due to the large reduction in consumption of the alkali metal compound.

Next, examples of the present invention will be shown.

Add 5% by weight of carbonaceous material (as carbon) and 18% water to flyash having the following composition and particle size distribution.
% by weight was added and kneaded, and green pellets with an average diameter of 10 mmφ were formed using a dish-type granulator, and then a 20% aqueous sodium carbonate solution was sprayed onto the pellets at the outlet of the dish-type granulator.

[Fly-assembly molding composition (weight%)]

SiO ₂ : 60%, Al ₂ O ₃ : 25% Fe ₂ O ₃ : 3%, CaO: 3%, MgO: 1% Na ₂ O: 1%, K ₂ O: 2% [Na ₂ CO ₃ adhesion amount (weight%): raw pellets]
0.1% [Fly ash particle size distribution] 200 mesh or less: 60% 325 mesh or less: 55% The obtained raw pellets were sintered according to the method shown in FIG. As a comparative example, the raw pellets obtained by granulation in the above examples were sintered in the same manner without adding sodium carbonate. When examining the ratio (wt%) of bursting-produced pellets to all product pellets for each of the examples and comparative examples, it was 0% in the example and about 24% in the comparative example, indicating that bursting did not occur. It is clear that the method of the present invention is very effective in efficiently suppressing

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram showing a method of drying and sintering raw pellets, and FIG. 2 is a schematic explanatory diagram illustrating the method of the present invention. 1... Raw pellets, 2... Product aggregate, 3... Moving grate, 4... Drying/preheating furnace, 5... Ignition furnace,
6... Sintering/heat retention furnace, 7... Cooling zone, 8...
Wind box, 21...Dish type granulator, 22,
24...Tank, 23...Transportation equipment.

Claims (1)

[Claims] 1. In a method for producing lightweight aggregate by igniting and sintering raw pellets obtained by granulating fly ash on a moving grate, the raw pellets obtained by granulating fly ash are 1. A method for producing lightweight aggregate, which comprises adhering an alkali metal compound solution or an alkali metal compound powder to the surface of pellets.