How does a tunnel kiln fire and cool bricks or tiles?

In modern brick and tile production, a tunnel kiln operates as a continuous system rather than a batch process. Dried bricks or tiles are loaded onto railcars, which can carry 3,000 or more units at a time.1

These cars enter the long tunnel at the cool end and move slowly forward through the structure. As they traverse the kiln, the materials pass through zones of gradually increasing temperatures until they reach the central firing zone, where they are heated to temperatures typically ranging from 870° to 1,100° C (1,600° to more than 2,000° F). After passing through this hot zone, the cars continue moving through zones of decreasing heat, allowing the products to cool gradually before they emerge from the kiln at room temperature. This continuous movement ensures efficient, large-scale production compared to periodic kilns.12