US3487135A - Method of firing continously operating kilns for ceramic products - Google Patents

Description

Dec. 30, 1969 A. HASSLER 3,487,135

METHOD OF FIRING CONTINUOUSLY OPERATING KILNS FOR CERAMIC PRODUCTS Filed Feb. 25, 1966 Sheets-Sheet 1 IN V EN TOR.

w I p d 1 H 1 m w. m

HTTORNEVS Dec. 30, 1969 A. HASSLER 3,487,135 METHOD OF FIRING CONTINUOUSLY OPERATING KILNS FOR CERAMIC "PRODUCTS Filed Feb. 25, 1966 2 Sheets-Sheet 2 3 1\ s Q h Lk {I i i I no I 4 I N l l l t N l l I '0 IN VEN TOR.

Hnareas Haas/e United States Patent 3 487,135 METHOD OF FIRING CONTINOUSLY OPERATING KILNS FOR CERAMIC PRODUCTS Andreas Hassler, Jahnstrasse 45, 7904 Erbach/Wurttemberg, Germany Filed Feb. 25, 1966, Ser. No. 530,192 Claims priority, application Germany, Mar. 1, 1965, H 55,338; Nov. 25, 1965, H 57,838 Int. Cl. C04b 33/32, 35/64; M71: 9/10; F27d 19/00 US. Cl. 264-56 6 Claims ABSTRACT OF THE DISCLOSURE A method of firing continuously operating kilns for ceramics and like products including the step of causing the firing gas to flow alternately with and against the movement of material being fired. The alternate flow is preferably rhythmic and adjustable.

The operation of continuous kilns, for example tunnel kilns, for ceramic products, as counterfiow heat exchanges, wherein a stream of air or gas is moved in the opposite direction to the direction of travel of the material to be fired, and finally exhausted as flue gas adjacent the inlet to the kiln, is known. Fuel is fed to the kiln, for example by means of a lateral heater or of a ceilin heater, in the main firing zone, substantially in the middle of the kiln. The fuel fed into hte firing zone gives its heat at each burner or row of burners to the air in the combustion chamber, which until it reaches the next burner or row of burners gives olf heat to the material to be fired. [During this time the firing air drops in temperatures so that at the next burner or row of burners it is heated up. A constant reheating of the firing air repeatedly occurs in the spaces between the heaters in the length of the kiln. I

As the kiln uses, on the one hand, a given amount of fuel and, as on the other hand, a given amount of air passes through the kiln, exceptional heat exchange relationships result herefrom. The amount of air passing through the kiln over a unit of time, is in the main determined, because of the counter flow heat exchange method, by the amount of material to be fired passing through per unit of time. As large differences of temperature are undesirable for the firing of ceramics, inadmissa bly large falls in temperature are produced from one burner or row of burners to the other in the counter flow method with intermediate heating up of the firing air. Drops in temperature of from 50100 C. are not uncommon. Consequently the employment of continuous longitudinal and transverse circulation of air in the heating up and cooling down zones of such kilns, has already been adopted in order to improve the heat transfer relationships between air or firing air on the one hand and on the material to be fired on the other. Hitherto, success has not been achieved in obtaining an improvement in the heat transfer relationships due to the high temperatures in the firing zones of such kilns.

In contrast to this, a method is provided according to the invention, which, in a simple manner, makes it possible considerably to improve the heat exchange in a continuous kiln so that higher throughput and quality can be achieved.

The invention will now be described further by way of example with reference to the accompanying drawings.

FIG. 1 illustrates the known counter flow method in a tunnel kiln, the flue gas being exhausted at the entry to the kiln by a chimney 1.

The firing air is moved in the opposite direction to that of the material to be fired placed on the trolley 2.

In the mehod according to the invention illustrated in FIG. 2, in contrast thereto, the direction of the air flow in the kiln is periodically reversed so that the chamber of the kiln is operated at short intervals of the time with the air flowing alternately in the opposite and in the same direction as the material to be fired is moving. The duration of the flow in each direction may be selected as is suitable and if desired, may be different in each direction. Further, the air pressures in each direction may be selected at will in accordance with requirements. For carrying out the method devices known per se can be used, for example, a fan 3 at the inlet to the kiln and a further fan 4 at the outlet from the kiln. A connection pipe 5 may also be provided. Instead of the fan 3, a fan located in the flue gas chimney 1 may be used.

The firing method according to the invention may be partially used also in firing kilns forceramics which are operated in the continuous or reversing principle, as shown in FIGS. 3 and 4.

The reference numbers 1, 2 and 5 indicate in FIGS. 3 and 4 the corresponding parts similarly marked in FIGS. 1 and 2. Only the fans 6 to 10 which replace to the fans 3 and 4 in FIG. 2 have been remarked due to the altered arrangement of the flow circuits.

The method can be used for example only in the heating up, cooling, or firing zone. A use is furthermore also possible in such a way that, in the reversing method according to the invention, in each case only two zones are inclnded.

The method may also be used in such a way that the individual reversed flows overlap (FIG. 4). According to the prior art, the heating up and the cooling, especially the latter, of ceramic products present considerable difficulties which are only met in an imperfect manner by the known counter-flow firing method with which tunnel kilns for example are frequently operated. The new reversing flow firing method makes it possible, for example in the cooling process, to move a considerably larger amount of air in alternating directions, and indeed, does not damage the throughput of air through the cooling zone. Thereby very good heat transfer relationships are provided for an even cooling or heating up.

Ifseveral kilns are available or could conveniently be included, it is advantageous that the rhythmic reversible flow circuit through one kiln is returned through at least a second kiln. By this separate return pipes 5 are saved.

I claim:

1. A method of firing continuously operating kilns for ceramic products comprising the steps of causing a firing gas to flow through at least part of the kiln opposite to the direction of passage through the kiln of the material to be fired, and superposing on said flow a rhythmically lengthwise oscillating gas flow alternately opposite to and in the same direction as the direction of passage through the kiln of the material to be fired.

2. A method as set forth in claim 1 in which the respective durations of flow in the two directions are adjustable.

3. A method as set forth in claim 1 in which the gas pressure during the flow in the one direction is different from the gas pressure during the flow in the other direction.

4. A method vas set forth in claim 1 in which the said alterante flow is caused to occur over one longitudinal part of the kiln only,

5. A method as set forth in claim 1 in which alternate flow is caused to occur independently over more than one longitudinal part of the kiln.

6. A method as set forth in claim 1 in which said alternate flow is caused to occur over those zones of the kiln where the material to be fired is first heated and secondly fired.

References Cited UNITED STATES PATENTS US. Cl. X.R.

Images