Explain in detail the difference between continuous and intermittent kilns. – NABTEB QUESTION

ANSWER

CONTINUOUS KILN

In this type of kiln, dried clay bricks otherwise known as green bricks are loaded into steel trucks to form a continuous line that passes into a long chamber that has a firing zone of high temperatures at the centre of its length. The trucks are then passed gradually through the kiln. The bricks get warmed as they reach the firing zone. The bricks then get cautiously burnt at controllable temperatures and are allowed to gradually cool before emerging at the exit end of the kiln for unloading and subsequent delivery to site. One notable example of the continuous kiln is the Hoffman type.

INTERMITTENT KILN

In intermittent kilns, bricks are molded, dried and stacked either in enclosures like in the scotch kiln or down-draught kiln. Sometimes the bricks are loaded in exposed sites out the sides and tops of stacks, green bricks are covered with under-burnt bricks to protect the bricks from weather effects likely to affect it before firing. In both cases of intermittent kilns, however, fire-holes are provided at bases of the stocks or sides as the case maybe. During burning, the fire-holes are filled with burning material such as coal or coke breeze. The fire material is then ignited and heat gradually rises as the fire works increases thereby burning the bricks to the required temperature which bakes and hardened the bricks to a useful building
material.