 The purpose of the refractory lining is to insulate the steel shell from the high temperatures inside the kiln, and to protect it from the corrosive properties of the process material.It may consist of refractory bricks or cast refractory concrete, or may be absent in zones of the kiln that are below approximately 250 °C.The refractory selected depends upon the temperature inside the kiln and the chemical nature of the material being processed.