JPS5951513B2 - Method for sintering fly ash granules - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for sintering fly ash granules, and in particular, sintering raw pellets obtained by granulating fly ash by preheating, igniting, retaining heat, and cooling on a moving grate. The present invention relates to a method for simultaneously igniting the surface layer portion of raw pellets introduced into an ignition section and subjected to I'L over the entire width direction, thereby improving and uniformizing the quality of the sintered product.

Exhaust gas generated from boilers, heating furnaces, incinerators, etc. contains large amounts of extremely fine dust (fly ash), which is collected using electrostatic precipitators, etc., but as coal burning increases in the future, It is predicted that the amount of fly ash generated will increase dramatically.

As a technique for effectively utilizing such fly ash, a technique has been proposed in which it is made into lightweight aggregate by granulation and sintering.

In other words, fly ash originally contains unburned carbon, but if necessary, combustible carbon material (coal or coke fine powder) is added, water is added as a binder and kneaded, and this is placed on a moving grate. Drying, preheating, ignition, and
It is made into artificial lightweight aggregate by sintering, heat retention and cooling.

Figure 1 is an explanatory diagram showing such a sintering procedure, and shows the hopper 1.
The product (sintered) aggregate 2 is charged into hopper 16.
The raw pellets 1 are charged and stacked on a pallet-shaped movable grate 3 that rotates in the direction of the arrow.

The product aggregate 2 is supplied as a bed, and the raw pellets 1 may be charged immediately after granulation without using the hopper 16.

The thus formed raw material layer is sequentially transferred from left to right in the drawing as the grate 3 moves, passes through a drying/preheating furnace 4, an ignition furnace 5, a sintering/retention furnace 6, and is sintered, and is sintered in a cooling zone 7.
It is then sufficiently cooled to become 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 direction penetrating the plane of the paper, and is opened and connected to the exhaust duct 1-9.

The inside of Dougs 1 to 9 is exhausted by blower 10.
Due to the suction airflow, a suction airflow is formed that passes downward from the bottom of the raw material layer.

Therefore, each house 4. 5. When the inside of the wind box 6 is heated, high-temperature gas flows down through the raw material layers and flows toward the wind box 8.

Incidentally, the disintegrated material of the raw pellets I that has fallen into the exhaust duct 9 passes through the shoes 1 to 11 and falls onto the conveyor 12 and is collected, and is generally returned and reused as a raw material for granulating raw pellets.

In the figure, 14 indicates a damper, and 18 indicates a drive sprocket 1, respectively.

In such a sintering method, the size of the raw pellets is usually 5 to 25 mmφ, taking into account the JIS standard for artificial lightweight aggregates.
(The average diameter is about 12 mm), so the air permeability during lamination is too good, and the air permeability in the width direction of the charged layer is uneven (the air permeability on both sides is too high).
easy to become

In addition, the currently adopted ignition method is a direct fire method in which the flame from an oil burner or gas burner comes into direct contact with the surface, but it is difficult to spread the fire evenly across the width of the charge. Local overheating is likely to occur in the surface layer and the lower part of the surface layer that are in direct contact with the flame, and the quality and uniformity of the sintered product deteriorates due to local heat fusion.

Moreover, since raw pellets contain a large amount of water (15-20%), when local overheating occurs as mentioned above, the water in the pellet in that area rapidly evaporates, causing the so-called "persting" phenomenon, which deteriorates the quality of the product. Yield and quality decrease.

On the other hand, if the heating power is reduced to prevent local overheating, the sintering of the entire layer will be incomplete due to failure of ignition at both end portions, which have high air permeability. If the entire width of the charge layer surface can be ignited evenly in the ignition section, subsequent dehydration and sintering will proceed evenly over the entire layer, improving the quality and uniformity of the sintered product. I have been researching this idea.

The present invention was completed as a result of such research, and its configuration is that in the sintering method shown in FIG. In the ignition section, hot air of 850 to 1200°C is supplied for 1 to 5 minutes to ignite the surface layer of the preheated laminated pellets all over the width direction, and then sent to the heat retention section where the oxygen concentration is 16%. Send hot air that is more than
The gist is that sintering progresses toward the lower layers of the stacked pellets.

That is, in the present invention, instead of directly igniting the surface of the charging layer with the flame from a burner in the ignition section, the raw pellets 1- are first sufficiently dried and preheated without being ignited in the preheating section, and then the pellets 1- The surface is ignited using hot air that has a high temperature higher than the ignition temperature of the interior carbonaceous material contained in the charcoal material.

Since the hot air reliably spreads over the entire width of the charging layer, the temperature of the surface layer of the green pellets entering the ignition section is uniformly raised over the entire width, and the pellets can be ignited at approximately the same time.

Therefore, self-combustion and sintering, which sequentially move toward the lower layers while passing through the heat retention section, also progresses uniformly in the width direction.

Since the problems caused by local overheating (collapse, fusion, etc.) that were recently pointed out in the direct fire method are not cut, the yield of sintered products is increased, and the quality and uniformity of the sintered products are also improved.

FIG. 2 is an explanatory diagram showing an embodiment of the present invention, and the other configurations except for the heating methods of the drying/preheating furnace 4, ignition furnace 5, and sintering/retention furnace 6 are substantially the same as the example of FIG. 1. It's the same.

However, in this example, a high-temperature gas generating furnace 19 is provided near the ignition furnace 5, and a burner (oil burner, gas burner, etc.) 20 generates high-temperature combustion gas in this part, and the ducts 1 to 21 generate the high-temperature gas generating furnace 5. It is configured to be introduced in

22 indicates a damper.

In the high temperature gas generating furnace 19, fuel A supplied to the burner 20
and by adjusting the amount and supply ratio of air B,
Combustion gas (hot air) at 850 to 1200°C is generated and sent to the ignition furnace 5.

Although the hot air is deficient in oxygen due to combustion, it is not a problem at all as long as it causes the raw pellets to catch fire.

However, it is necessary to supply an excessive amount of air B and control it so that the hot air contains the oxygen necessary for ignition, or to
9 generates gas at a higher temperature than the above temperature, and
It is also possible to supply an appropriate amount of air B' on the way from the ignition furnace 1 to the ignition furnace 5 to ensure the required amount of oxygen.

Note that the latter air B' may be heated by placing a heat exchange tube in the path of the high-temperature generated gas of the gas generating furnace 19 and passing fresh air through the tube, and this method is also advantageous from a thermoeconomic standpoint.

Further, the hot air may be composed of only fresh air preheated by heat exchange, or may be one in which the suction exhaust gas from the sintering section is further heated and fresh air is supplied for circulation.

In any case, the temperature of the hot air introduced into the ignition furnace 5 is the ignition temperature of the internal carbon material contained in the pellets 1 (usually 600 to 7
It is necessary to set the temperature to 850-1200°C, which is slightly higher than 00°C (approximately 00°C), and if it is lower than 850°C, there may be a small amount of moisture remaining in the pellet, so it may not be possible to reliably ignite the entire surface area. .

On the other hand, when the temperature exceeds 1200℃, the entire surface becomes overheated,
The rapid expansion of water within the pellets causes the pellets to collapse (so-called bursting phenomenon), reducing the yield of sintered products.

In addition, the appropriate time for applying hot air to the charged layer that is continuously conveyed is 1 to 5 minutes; if it is less than 1 minute, there is a risk of insufficient ignition, and if it exceeds 5 minutes, especially high-temperature gas of about 1200℃ is applied. At times, it becomes slightly overheated, and bursting and fusion of the entire layer also occur.

The hot air supply time is determined in relation to the moving speed of the grate 8, the thickness of the layer, etc.

Furthermore, as shown by the broken line in FIG. 2, the combustion gas generated in the high-temperature gas generating furnace 19 can also be introduced into the drying/preheating furnace 4 or the heat retention furnace 6, thereby simplifying the heating source for the entire device. .

When using the gas for drying/preheating, use the duct 23.
An air mixing duct 24 should be provided at a suitable location through which outside air should be mixed in to reduce the gas temperature to 200-500°C.

That is, the raw pellets sent to the ignition furnace 5 are efficiently dried and preheated in the drying/preheating furnace 4, and the stacked pellets 1 are formed in the ignition furnace 5.
In order to ignite the entire surface of ~ at once,
The temperature of the supply gas must be at least 200°C.

However, at this point, the raw pellets 1 are in an undried state and contain a large amount of moisture, so if the gas temperature is too high, there is a risk of bursting, and if a part of the drying/preheating furnace ignites, The temperature of the gas supplied to the drying/preheating furnace 4 should be set at 500° C., since the most important feature of the present invention, ie, “timely ignition in the furnace 5,” cannot be achieved.
Must be kept below.

On the other hand, when using it as a heat-retaining gas, an oxygen-containing gas supply duct 26 is provided at an appropriate location of the duct 25, and an appropriate amount of oxygen-containing gas (for example, air) is mixed into the high-temperature gas so that the oxygen content becomes 16% or more. should be introduced into the heat retention furnace 6.

However, sintered products used as artificial lightweight aggregates have
An extremely low carbon content of usually 1% or less is required, and in order to meet such requirements, it is necessary to completely burn the charged carbonaceous material contained in the pellets in the heat retention and sintering process.

Therefore, the gas introduced into the heat retention furnace 6 should contain oxygen necessary for complete combustion of the residual carbonaceous material, and in order to reduce the content of the sintered product to 1% or less, must contain 16% or more oxygen.

The present invention is generally constructed as described above, but the point is that the ignition method using high-temperature gas is used instead of the conventional direct combustion method using flames, so that the surface layer of the charge is ignited over the entire width in the ignition section. This made it possible to ignite evenly, and it became possible to proceed uniformly throughout the sintering process, which is then transferred in the depth direction.

In particular, the high-temperature gas ignition method does not cause the problem of local overheating that occurs with the flame ignition method, so there is no risk of bursting or uneven firing, and high-quality, uniform sintered products can be manufactured at a high yield. .

Next, Examples and Comparative Examples will be given to clarify the effects of the present invention.

Comparative Example 1 Fly ash containing 3% unburned carbon (-44 μm near 0
%) to adjust the carbon content to 5% by adding pulverized coal (-74 μm: 67%), and further adding water as a binder, and then using a pan-type granulator to obtain an average particle size of 12 mm and a moisture content of 17.
% raw pellets were granulated.

The raw pellets are charged into a Dry 1 to Lloyd type sintering machine so that the layer height is approximately 300 mm, and the raw pellets are sufficiently dried and preheated by blowing hot air at 350°C in a drying/preheating furnace before being sent to an ignition furnace. , 16,000Kcal by propane burner in ignition furnace
After ignition by applying a heat amount of /r12·min for 2 minutes, self-combustion and sintering were performed while suctioning from below.

Example 1 2ONm3 of 1000℃ hot air obtained by burning heavy oil
Comparative example 1 except that it was ignited by blowing at 7 minutes/m2 for 2 minutes
Sintering was carried out in the same manner.

Due to this ignition, the entire surface layer was ignited simultaneously in the width direction, and the temperature at the ignited part reached 1050℃, but no bursting occurred at all, and subsequent self-combustion and sintering proceeded smoothly. This was confirmed.

Example 2 Sintering was carried out in the same manner as in Example 1, except that hot air at 900°C was blown at 2ONm37min/m2 for 3 minutes.

Due to this ignition, the surface layer ignited simultaneously across the entire width direction, and the temperature at the ignition part reached 980°C, but no bursting occurred at all, and subsequent self-combustion and sintering proceeded smoothly. was confirmed.

Table 1 shows the variations in yield and crushing strength of the sintered products obtained in the above Comparative Examples and Examples.

As is clear from Table 1, the yield in the comparative example is low and the variation in crushing strength is extremely large, whereas the yield in the example is extremely high (8-5% in terms of loss) and the variation in crushing strength is also compared. The number has drastically decreased to less than 172 as in the previous example.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing a conventional sintering method, and FIG. 2 is an explanatory diagram illustrating the sintering method of the present invention. 3...Movable grate, 4...Drying/preheating furnace, 5...Ignition furnace, 6...Sintering/heat retention furnace, 19... ...High-temperature gas generating furnace, 20...
・Burna.

Claims (1)

[Claims] 1. A method in which raw pellets obtained by granulating fly ash from a coal-fired boiler, etc. are stacked on a moving grate and sintered while forming an airflow that passes through the layers from above to below. After drying and preheating the raw pellets without igniting them in the ignition section, the raw pellets are sent to the ignition section, where the
Supplying hot air at ~1200°C for 1 to 5 minutes to ignite the surface layer part of the preheated laminated pellets all over the width direction, and then sending hot air with an oxygen concentration of 16% or more to the heat storage part, A method for sintering fly ash granules, characterized in that sintering progresses toward the lower layer of laminated pellets.