Heating – Work chamber having heating means – Having means by which work is progressed or moved mechanically
Patent
1987-07-06
1989-12-05
Yuen, Henry C.
Heating
Work chamber having heating means
Having means by which work is progressed or moved mechanically
432137, 432145, 432 72, F27B 902
Patent
active
048849693
DESCRIPTION:
BRIEF SUMMARY
The invention relates to continuously operating furnaces (tunnel kilns) for fine ceramic products. In connection with the present invention, the term "tunnel kiln" includes all types of kilns where the products are continuously fired. This includes, for example, roller-hearth kilns, but also sled-type kilns and the like.
Such a tunnel kiln has, from the kiln entrance to the kiln exit, a preheating section, a firing section equipped with burners, and a cooling section subsequent thereto.
The invention relates to such tunnel kiln having gas conveying means at the products entrance, the gas conveying means suctioning, in opposite direction to the conveying direction of the products (from the preheating to the cooling section), gas from at least the firing section to the products entrance, and having at least one air transport means for feeding air to the cooling section. In addition, the invention relates to a method for operating such tunnel kiln.
As shown in DE-C 30 17 434, during firing of earthenware like bricks or roof tiles in tunnel kilns with firing periods of approximately 50 to 60 hours air might be sucked in reversed flow from the cooling to the preheating section in order to save energy. For fine ceramics, for example floor or wall tiles, this is not feasible because of the delicacy of the products, where a certain temperature profile over the length of the kiln has to be exactly maintained. A high throughput and a certain saving of energy may be achieved with fine ceramics by using rapid-firing kilns, for example roller-hearth kilns, because the rollers are maintained at a constant temperature and it is not required to heat up the rollers at each new firing circle.
For adjusting and maintaining the temperature profiles, however, numerous separate means for transporting air and waste gases are required. The counterflow draft must on no account extend over the firing section into the cooling section, because otherwise the firing process is severly disturbed and the rate of rejections increases dramatically.
It is an object of the present invention to provide a continuously operating kiln and a method for operating such a kiln, which make energy savings feasible and reduce the expense for apparatus.
In connection with the kiln the object is achieved by the gas conveying means taking in gases also from the region of the cooling section and conveying them into the firing section, and by arranging, in a transition region between firing section and cooling section, at least one additional burner. In doing so the gases conveyed from the cooling section are heated up to firing temperature.
In a surprising departure from the prior art it is possible, by means of the present invention, to suck (colder) air from the cooling section into the firing section. As the cooling air heated by the ceramic products already has a temperature of approximately 800.degree. to 900.degree. C. at the entrance of the cooling section, the additional burner only has to provide the energy required for heating up to the firing temperature, that is for tiles approximately in the range of 1200.degree. C. Attempts in the past to introduce the hot air of approximately 800.degree. C. which had been sucked from the cooling section to the burners in the firing section have failed, because the pipes with valves, measurement apparatus, and fans arranged therein would withstand this high temperature only for a short time, if at all, thus leading to high costs for repair.
These problems are not present with the solution according to the invention where gases are taken in within the kiln. A disturbance of the temperature profile in the firing section is positively avoided by heating up with additional burners which only have to compensate a considerable smaller temperature difference. The achievable energy savings are considerable and are of the order of 40 to 50%. To begin with, this concerns only the energy consumption of the burners.
As suggested in DE-A 29 47 787 additional burners are provided in the cooling section of a kiln. These bur
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A. Earley John F.
A. Earley III John F.
Ludwig Riedhammer GmbH
Walker P. Michael
Yuen Henry C.
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