New developments in precalciners and preheaters

Abstract

The evolving design of the preheater in a modern cement plant has changed very little. Some of the design details, such as low pressure drop cyclones and designs with an eye toward easier and less maintenance are among some of the more significant changes. The preheater must achieve a transfer of heat from the pyroprocessing system exhaust gases to the incoming raw meal in preparation for the energy intensive decarbonation process to occur in the calciner. However, the optimum design is a series of compromises that attempts to balance a lower preheater tower pressure drop (fan electric power) with cyclone collection efficiency (fuel consumption) and cyclone vessel volume (capital cost). Today's preheater cyclones normally are dimensioned smaller, equipped with larger gas inlets and outlets for decreased pressure drop, and don't necessarily yield the highest possible particulate collection efficiency when compared to a decade ago. As a result, the volume occupied in the preheater tower is significantly less for a given capacity resulting in a smaller tower structure to house and support these vessels. With the dynamic environmental regulations constantly becoming more and more strict, equipment suppliers must develop combustion methods to keep pace with the newly imposed limits. Multi-staged combustion, at least for now, offers a relatively low cost approach to meeting the accepted emission levels.