Preheater Rotary Kiln

Preheater Rotary Kilns are the preferred technology for the burning of limestone and dolomite when the following requirements need to be met:

• high production capacity, preferably >1000 tpd
• small stone feed size, e.g. 15 to 45 mm
• maximum flexibility in the selection of fuels
• production of low sulphur lime using cheap, high sulphur fuels.

The energetic performance of a rotary kiln is much enhanced by a shaft preheater. The shaft preheater uses the kiln exhaust gases to preheat and partially precalcine the limestone. The modular designed preheater, developed by Polysius and Maerz, combines highly efficient heat transfer with optimal accessibility for maintenance during operation.

The technology is based on the joint know-how of Polysius and Maerz. Polysius contributes its long-standing experience in the building of rotary kilns as well as its R&D capabilities, whereas Maerz contributes profound process knowledge in the manufacture of lime, e.g. gas flow patterns in material beds as well as the handling of dust formation and coatings that naturally occur when processing limestone.

A special feature is the sulphur bypass, which was developed by Polysius. It allows for the production of low sulphur lime, as often required in the steel industry, whilst using cheap but often high sulphur fuel. In this novel system, the flow of material and the flow of exhaust gas between the kiln head and the preheater are separated, and the material undergoes a hot screening and further classification, in order to section off the fine fraction with high sulphur content.