Different types of brick kilns 3
The kiln circuit can be oval, rectangular or circular. Because of the counter flow arrangement, the incoming air encounters hot bricks exiting from the combustion zone. As such, air is preheated ( and bricks are cooled ) before entering the combustion zone. The combustion products ( flue gases ) from the combustion zone pass over the green bricks, resulting in the preheating of bricks ( and cooling of flue gases ). The fire travels in the direction of airow. A chimney stack and /or a fan provide the necessary draught. Bull’s Trench Kilns ( the main kiln type for firing bricks in South Asia ) are an example of a moving kiln.
In a moving-ware kiln, there remains stationary, while the bricks and air move in counter-current paths. In a tunnel kiln, a horizontal moving-ware kiln, goods to be fired are passed on cars through a long horizontal tunnel. The firing zone is located at the centre part of its length. Cold air is drawn from the car exit end of the kiln and is cooling the fired bricks. The combustion gases travel towards the car entrance losing a part of their heat to the entering green bricks. The cars can be pushed either continuously or intermittently at fixed time intervals. The tunnel kilns have provision for air extraction and supply, at several points along the length of the kiln.