Rotary kilns that produce lime typically have four refractory zones. Long process kilns require abrasion resistant, high strength alumina brick for the charging zone, where abrasion of the stone can be particularly severe. Short preheater kilns normally do not have a charging zone that sees high abrasion as preheated stone is partially softened. In the calcining zone, limestone (calcium carbonate) is heated in preparation for the burning zone. 70% alumina class refractory brick is the most common refractory lining. The burning zone maintains the highest temperatures and drives the decarbonization reaction to completion producing quicklime that is, calcium oxide (CaO).
Since the rate of calcination is related to retention time inside the kiln and the operating temperature, refractory internals can assist in improving kiln efficiency by recovering heat from the kiln exhaust gas, increase production and reduce the fuel ratio for lime product. The discharge zone of a modern lime kiln usually contains a dam construction to increase retention time of the lime in the kiln.
Basic Brick for the Burning Zone:
Basic magnesia brick are more compatible with lime, resist fluxing and offer extended lining reliability. Greenfree KF, features a high content of spinel and gives significantly lower shell temperatures due to improved thermal conductivity. Rescomag 85 is the best option for harsh conditions within the burning zone.
60% to 70% alumina brick linings are the most common brick types in the calcining zones. Rescal 70D offers consistent, economic performance while maintaining good alkali resistance and positive reheat property for improved lining stability. Seneca 60P offers improved abrasion resistance at a competitive cost. Phosphate-bonds give alumina brick high mechanical strength and exceptional abrasion resistance. Alumex P-85-HS is an 80% alumina class burned phosphate-bonded brick. Alumex P-85-HS is effective in charging zones of long rotary lime kilns and for the kiln shell linings where heat exchangers are employed.