Ceramic roller-hearth kiln with controlled combustion and cooling

A ceramic kiln through which objects to be baked are moved by a conveyor, said kiln comprising a preheating zone, a baking zone downstream of the preheating zone, burner means in said baking zone for baking objects moving through the baking zone, a cooling section downstream of the baking zone and comprising in succession, a fast cooling zone, an induction cooling zone, an air cooling zone, and a fan cooling zone, said fast cooling zone comprising means for directing cold air jets onto objects on the conveyor, said induction cooling zone comprising first and second indirect heat exchanger tube bundles disposed immediately above and below the conveyor for removing heat by conduction to air flowing through tubes of the tube bundles without adding air to the atmosphere in the induction cooling zone of the kiln, each tube bundle comprising coplanar bundles of horizontal transversely extending tubes connected to respective external atmospheric cooling air supply headers and external hot air discharge headers;

• fan means for supplying atmospheric air to the atmospheric air headers, and control means for controlling the discharge of air from the hot air headers, to control the flow of cooling air through the tubes, said air cooling zone comprising means for admitting cooling air through apertures below the conveyor and means for withdrawing said cooling air from above the conveyor, said fan cooling zone comprising a plurality of fans blowing cooling air toward the conveyor, means for collecting hot gaseous products of combustion from the burner means of the baking zone, and comprising means for withdrawing the hot products of combustion from the baking zone at a location between the preheating zone and the upstream end of the baking zone, means for mixing the hot products of combustion with air and feeding the mixture to the preheating zone, and means for removing cooling air introduced in the fast cooling zone at a location downstream of the fast cooling zone, and upstream of said air cooling zone.