JPH0411501B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for firing refractory bricks, and particularly to preventing black core formation in large refractory bricks. Conventionally, when large-sized refractory bricks are fired using heavy oil or kerosene burners in batch-type firing kilns such as single kilns or shuttle kilns, combustion exhaust gas and moisture are In order to discharge the materials out of the furnace in a short time, the pressure inside the furnace was set to negative pressure, and the heating conditions were set as shown below to perform preheating, calcination, and low-temperature heat treatment before firing. (1) The temperature increase rate shall be 4.5℃/h or less up to 700℃. (2) For moisture evaporation, the heating temperature should be around 100℃ and the heating time should be at least 24 hours. (3) For decomposition of crystal water, the heating temperature is 300 to 700°C and the heating time is 50 hours or more. (4) If an organic binder is added, increase the heating temperature.
Heat at 300-500℃ for 30 hours or more. If the above conditions are not met, an explosion phenomenon due to water vapor may occur, or a black core may form in the center of the refractory brick. Such a black core part is denser and has a lower porosity than other good parts, and the spalling resistance is lowered, so the quality characteristics of the refractory brick with the black core deteriorate. However, the method of firing refractory bricks using a conventional heavy oil or kerosene burner as described above has the following drawbacks. (1) Since the firing time is long in the low temperature firing area, a large amount of fuel is used. (2) Since it is nearly impossible to control combustion in the low-temperature firing range with a normal burner, the generation of soot (C, CO) due to incomplete combustion causes decarburization of the refractory bricks, making it even more difficult to decarburize. Not only does it take a long time to heat up, but there is a risk of burning the burner. (3) Since heavy oil or kerosene is burned with negative pressure inside the furnace, it is difficult to make the temperature inside the furnace uniform regardless of the size of the furnace. It is necessary to hold at temperature for a long time. The present invention has been made in order to eliminate the above-mentioned drawbacks, and provides a refractory brick that can shorten the heating time and reduce the amount of fuel used by uniformizing the temperature inside the furnace, and improve the quality of large refractory bricks. The purpose of this invention is to provide a firing method. That is, the method for firing refractory bricks of the present invention is as follows:
When firing refractory bricks with a surface area/volume ratio (ratio of surface area and volume calculated by measuring dimensions in the same unit, the same applies hereinafter) in a batch firing kiln of 0.4 or less and a minimum thickness of 150 mm or more, the above-mentioned A high velocity burner is attached to the batch-type firing kiln, and the firing rate is 600 to 700.
It is characterized by preheating and calcination while maintaining positive atmospheric pressure in the furnace up to ℃, then switching to a heavy oil or kerosene burner to perform low temperature heat treatment, and then raising the temperature and firing. . In the present invention, the high velocity burner attached to the batch type firing kiln has a structure as shown in FIG. 2, for example. In Figure 2,
An internal cylinder 2 is inserted into one end of the main body cylinder 1 and fixed with a flange part 3. A combustion chamber 4 is formed inside the internal cylinder 2, and a combustion nozzle 5 is inserted into the combustion chamber 4. Furthermore, an air intake hole is formed in the inner cylinder 2. An air supply hole 6 is formed in the main body cylinder 1 at a position on the side surface of the internal cylinder 2. A cone 7 is provided at the other end of the main body tube 1 and is fixed by a flange portion 8. This high velocity burner supplies a large amount of air from the air supply hole 6,
A part of the air is used to burn heavy oil or kerosene inside the combustion chamber 4, and the other large part is used as dilution air, and hot air is blown out from the tip of the cone 7. The hot air is adjusted within a range of, for example, a hot air temperature of 200 to 1300°C and a hot air volume of 12 to 33 Nm ³ /min. According to such a method, the pressure inside the furnace can be made positive by a large amount of hot air supplied from the high velocity burner, so that the temperature distribution inside the furnace can be made uniform. In addition, by setting the pressure in the furnace to positive pressure, moisture evaporation from the surface of the bricks is suppressed, and because the moisture concentration gradient is small, it is possible to quickly raise the temperature, shortening the heating time.
It is possible to evaporate water, decompose crystal water, and burn organic binder all the way to the inside of the brick in a short time.
Furthermore, since a large amount of air is supplied to the high velocity burner in order to make the pressure inside the furnace positive, the fuel is completely combusted and no soot is generated. In addition, in the present invention, the reason why the temperature is raised to 600 to 700°C using the high velocity burner as described above is to prevent the concentration gradient of moisture due to the diffusion of moisture from the inside of the refractory brick to the surface and the evaporation of moisture from the surface. This is to make it possible to reduce the temperature and increase the temperature quickly, thereby shortening the heating time and effectively evaporating moisture. In addition, in the present invention, the refractory brick to be fired has a surface area/volume ratio of 0.4 or less and a minimum thickness of
Those with a surface area/volume ratio exceeding 0.4 or a minimum thickness of 150mm are limited to those with a surface area/volume ratio of over 0.4.
This is because fire bricks of less than mm can be fired with sufficient high quality using a normal burner without using the method of the present invention. Examples of the present invention will be described below. Refractory brick (viscous refractory brick,
In order to fire 70 tons of Al ₂ O ₃ (32%), the brick molded bodies were loaded into a single kiln and heated to 700℃ using a high-velocity burner to supply a large amount of hot air to maintain positive pressure inside the furnace. After preheating and calcination, a heavy oil burner was used to perform low-temperature heat treatment at 600 to 900°C, and the temperature was further increased to 1300°C for firing. The firing conditions at this time and the quality of the obtained refractory bricks are shown in the table below. Comparative Examples 1 and 2 shown in the table below show the firing conditions and the quality of the refractory bricks obtained using a conventional method using only a heavy oil burner. Here, the pressure in the furnace up to 700° C. was positive pressure in Examples, and negative pressure in Comparative Examples 1 and 2. Furthermore, the firing conditions for these Examples and Comparative Examples 1 and 2 are shown in the figure.

【table】

[Table] As is clear from the above table and figure, when the firing time is shortened to 700℃ using the conventional method (Comparative Example 1), black cores are generated, the porosity decreases, and the scratch resistance decreases. Polling performance has also deteriorated. In addition, when the conventional method was used to increase the firing time up to 700°C (Comparative Example 2), it was possible to obtain refractory bricks of good quality without the generation of black core, but the amount of fuel used was large. The generation of soot and smoke due to incomplete combustion of burners has increased significantly. In contrast, in the example, even though the firing time up to 700°C is short, the pressure inside the furnace is kept positive, which makes it possible to equalize the temperature inside the furnace and effectively remove moisture with a low moisture concentration gradient. can be evaporated, so it is possible to obtain high-quality refractory bricks that do not generate black core, have high porosity, and have good spalling resistance. Furthermore, since the amount of fuel used is small and the fuel is completely combusted by the large amount of air supplied, the amount of soot and smoke generated is also extremely small. For example, refractories using alumina cement or chemically bonded refractories both use 4 to 14% moisture during molding, but when heated using conventional methods, only about 50% of the added moisture evaporates. For example, 250 x 300 x 600 mm, surface area/volume =
0.187 and weighs 100 kg, only 30% of the added water evaporates. On the other hand, by drying according to the method of the present invention, most of the added moisture can be evaporated. As detailed above, according to the method for firing refractory bricks of the present invention, it is possible to significantly shorten the heating time and reduce the amount of fuel used, and to obtain high-quality large-sized refractory bricks that do not generate black core. It is something.

[Brief explanation of drawings]

FIG. 1 is a diagram showing firing conditions for refractory bricks according to an embodiment of the method of the present invention and a conventional method, and FIG. 2 is a sectional view of a high velocity burner. DESCRIPTION OF SYMBOLS 1... Main body cylinder, 2... Internal cylinder, 3, 8... Flange part, 4... Combustion chamber, 5... Combustion nozzle, 6...
...Air supply hole, 7...Cone.

Claims (1)

[Claims] 1 The surface area/volume ratio in the batch firing kiln is 0.4.
When firing refractory bricks with a minimum thickness of 150 mm or more, a high-velocity burner is attached to the batch-type firing kiln, and the furnace is preheated and calcined to 600 to 700°C while maintaining positive atmospheric pressure. A method for firing refractory bricks, which is characterized in that after performing the above steps, the burner is switched to a heavy oil or kerosene burner to perform low-temperature heat treatment, and the temperature is further increased for firing.