JPH083917Y2 - Improved continuous firing furnace - Google Patents

Description

[Detailed Description of the Invention] [Technical field to which the invention belongs] The present invention relates to improvement of a continuous firing furnace, particularly a continuous firing furnace suitable for firing large fine ceramics.

[Problems of conventional technology]

As a continuous firing furnace (tunnel kiln) in which so-called ceramics such as bricks and tiles are placed on a trolley and continuously charged into the furnace and fired, gas fuel such as natural gas and butane, liquid fuel such as heavy oil are used. It is used as a heat source, a burner for burning these is provided in the center of the furnace to form a firing zone, and exhaust gas is discharged to the outside from the furnace inlet (carriage carry-in port) to ensure effective use of heat. There is.

In this case, the material to be fired is dried or debindered by heat exchange with the combustion exhaust gas flowing from the firing zone to the firing port while proceeding from the charging port to the firing zone, and is further preheated to near the firing temperature. It At this time, there is an unavoidable tendency that the temperature in the lower part of the furnace becomes lower than that in the upper part. Therefore, an atmosphere circulation system may be adopted for flowing the upper atmosphere downward.

For effective use of heat, the air in the atmosphere heated by heat exchange while the burned product moves through the cooling zone is also used as primary or secondary air for combustion. There is.

In such a conventional type furnace, in order to control the temperature of each part in the pretropical zone, the amount of combustion in the firing zone, the amount of combustion air fed in, the amount of exhaust gas sucked from the inlet, the amount of air fed in the pretropical zone A combination of inlet and exhaust suction means is used.

In recent years, the demand for fine ceramics has increased, and it has been desired to make the firing process continuous for mass production. However, since these raw materials are fine powders, it is difficult to dry or remove the binder at the time of preheating, and this tendency is further increased as the size of the molded product is increased due to poor heat conduction. It is not uncommon for shrinkage during firing to be so great that linear shrinkage exceeds 20%.

When firing such fine ceramics,
If the molded product cracks during preheating, the crack spreads during firing and becomes a defective product. Therefore, meticulous temperature control is required for drying or binder removal. In other words, water or wax inside the molded product is continuously discharged from the surface, and there is no high temperature vapor pressure inside the molded product so that explosion does not occur and the temperature rises within a certain range. You have to maintain speed.

However, in the conventional temperature control, it is possible to provide a continuous temperature gradient from the firing zone to the charging port in the upper part of the furnace, but in the lower part, the same temperature as the upper part,
Or it is very difficult to provide the same temperature gradient.
Especially in the case of molded products that require a large amount of heat for drying or binder removal, the temperature of the hearth remains constant for a long time regardless of the temperature of the furnace top, and rises sharply after approaching the firing zone. There is a tendency to do.

[Means for solving problems]

The present invention is a fuel-fired continuous firing furnace, which is provided with an auxiliary heating means and an auxiliary exhaust means at a position lower than that in the part of the furnace where preheating is essentially performed (pre-tropical zone), and local temperature control is performed. The above problem is solved by performing the following. That is, the pre-tropical zone is divided into a plurality of sections along the flow of the product to be fired, that is, a temperature control unit, and each of them is provided with a pair of an auxiliary burner and an exhaust means, separately from the firing section,
The above-mentioned drawbacks are overcome by performing temperature detection / control for each section.

A single burner or a plurality of burners can be used as the auxiliary combustor, and these can be provided on both sides above the furnace or on the top of the furnace. On the other hand, one or more auxiliary exhaust ports are provided on both sides of the lower part of the furnace to ensure a good temperature distribution. It is not always necessary to provide the same number of combustors and exhaust means, and the exhaust ports do not necessarily have to be directly under the burner, and they may be provided at the outlet side or the inlet side as needed. The temperature of each section is detected by the thermometer of the furnace section and used as control data, and through a known automatic control system,
Alternatively, the firepower and exhaust of the burner are uniformly controlled by manual operation. The surrounding air is directly and strongly heated by the flame from the burner on the side wall of the furnace into the furnace. The high-temperature gas thus generated is sucked from the auxiliary exhaust port below the burner in this section by a known exhaust system to be lowered, and used for heating the bottom of the furnace. In this way, the present invention ensures the temperature rise in the bottom of the furnace, which was difficult to obtain a sufficient temperature in the conventional tunnel furnace,
The temperature difference in the vertical direction in the furnace can be reduced. The temperature difference between adjacent sections is averaged by the main exhaust gas flow flowing from the firing zone towards the furnace inlet,
A gentle temperature rise curve can be obtained over the entire pretropical zone. 200 ° C to obtain a gentler heating curve
It is desirable to provide a pair of an auxiliary burner and an auxiliary exhaust means for each. For the burner, a flat flame type burner that has a short flame and emits a lot of infrared rays is suitable.

According to the present invention, it is possible to select the best temperature rising curve suitable for the material to be fired. The object to be fired has different temperature rising curves depending on the particle size of the raw material, the type and amount of the molding binder, and the size of the molding. For example, in the case of alumina-based fine ceramics that is formed by using glue dissolved in water as a binder, it takes 20% to remove water up to 400 ° C.
Although it is necessary to raise the temperature at a rate of ℃ / hour or less, we have found that at a temperature of 500 ℃ or more, the temperature can be raised at a rate of 30 ℃ / hour or more. However, in the conventional type tunnel kiln, the traveling speed of the trolley is controlled by the lowest temperature rise curve, so it takes a longer time than necessary as a whole, and not only time and fuel loss but also burning zone By staying for a long time, there is a disadvantage that the strength of the product is reduced due to abnormal grain growth.

On the other hand, in the tunnel kiln according to the present invention, it is possible to increase the distance in the temperature region where the temperature raising rate needs to be decreased and shorten the distance in the temperature region where the temperature raising rate can be increased. Although the fuel consumption rate is slightly larger than that of the tunnel kiln, the rate of defective products due to firing cracking can be significantly reduced, and the firing time as a whole can be shortened.

〔Example〕

The continuous firing furnace (tunnel kiln) according to the present invention is shown in FIG. Furnace 1 has a total length of 74 m and a cross-sectional dimension of a firing zone of 2.3.
m × 2.6m, pretropics I, cooling zone III are 2.2m × 2.5m,
It is 2.2m x 2.4m. The burning zone II has 10 burners 2 on each side, and the total calorific value is about 1 million KCal / hour. A main exhaust port 3 is provided substantially symmetrically on the side surface of the furnace near the charging port.

The preheater consists of 8 sections (A to H). Each section has an auxiliary burner 4 with a calorific value of 30,000 KCal / h on both sides of the upper part, and an auxiliary exhaust port 5 with a damper on both sides of the lower part. The temperature of each section is detected and controlled by a thermometer 6 provided at the top of the furnace.

Figure 2 uses an auxiliary burner to load 3.7 tons of alumina molding with an outer diameter of 26 cm, an inner diameter of 10 cm, and a height of 16 cm on each trolley.
It is a curve showing the temperature of the upper part (solid line) and the lower part (broken line) of each part in the furnace when charging at a speed of 0.7 m / hour. The temperature is almost uniform for each section, and no discontinuity in temperature between sections is observed. The obtained fired product had a fine structure and exhibited a compressive strength of 14 ton / cm ² .

[Comparative example]

In the above furnace, firing was performed without using an auxiliary burner. FIG. 3 shows the temperatures of the upper part (solid line) and the lower part (broken line) of each part in the furnace when a molded product having the same weight as the above was charged at the same speed. It is possible to make the upper part of the furnace equal to that of Fig. 2, but the temperature of the lower part is abnormally low near the charging port, and it is recognized that it rises sharply from the middle.
In this case, more than half of the molded products were cracked and became defective.

In order to make the temperature curve almost the same as in Fig. 2 under these firing conditions, it was necessary to reduce the loading speed of the truck by 0.2 m / hour. Abnormal grain growth was observed in the fired product obtained in this case, and the compressive strength decreased to 9 ton / cm ² .

As is clear from the above description, in the furnace of the present invention, 1) it is possible to select the best temperature rising curve suitable for the material to be fired, so it is only necessary to significantly reduce the rate of defective products due to cracking. Therefore, the firing time as a whole can be shortened.

2) Further, it becomes possible to arbitrarily set the residence time in the firing zone, and by preventing abnormal grain growth, it is possible to obtain a fired product having high strength and the like.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a continuous firing furnace according to the present invention,
FIG. 2 is a temperature rise curve by the original operation of the furnace, and FIG. 3 is a temperature rise curve when the furnace is operated by the same operation as the conventional one. 1 ... Furnace; 2 ... Main burner; 3 ... Main exhaust port; 4 ... Auxiliary burner; 5 ... Auxiliary exhaust port; 6 ... Thermometer.

Claims (1)

[Scope of utility model registration request] 1. For firing ceramics of a type in which a material to be fired is placed on a truck and loaded into a furnace, preheating, firing and cooling are performed from the front in the traveling direction of the truck and a gas fuel or a liquid fuel is used as a heating source. In the continuous firing furnace, the part of the furnace to be used for preheating is divided into a plurality of temperature control units, a thermometer is provided at the top of each control unit, and an auxiliary heating means including one or a plurality of burners on the upper side surface. It is possible to reduce the temperature difference between the upper and lower parts of the furnace for each temperature control unit by providing auxiliary exhaust means provided below the means and passing the high temperature exhaust of the burner generated above the inside of the furnace through the bottom of the furnace. A continuous firing furnace characterized by the above.