Modeling expanded perlite production in a vertical electrical furnace

Expanded perlite has outstanding thermal and acoustic insulating properties and is widely used in the manufacturing and construction industries. The conventional perlite expansion method has certain disadvantages which affect the quality of expanded perlite products, thus limiting their performance and range of applications. A new perlite expansion process has been designed and a vertical electrical furnace for perlite expansion has been constructed in our laboratory in order to overcome these drawbacks, enabling precise control of experimental conditions in order to prescribe the temperature profile and residence time within the new heating chamber. A novel dynamic model for perlite grain expansion has been developed and validated so as to study and optimize the new furnace operation. Perlite ore origin, size distribution and water content are key parameters affecting expanded perlite quality. Moreover, air feed flow rate and temperature, as well as the imposed wall temperature distribution along the heating chamber are experimentally known to have a profound, measurable effect on grain residence time and expansion. A detailed sensitivity analysis has been performed so as to quantitatively understand the effect and relative importance of all foregoing operational parameters on macroscopic furnace operation (perlite particle velocity and temperature evolution) as well as on inaccessible microscopic characteristics (internal steam bubble pressure and size). Perlite grain radius and expansion ratio are probed in detail as a function of time, and furnace operation can be tuned vs. feed variation toward optimal product quality. Particle critical characteristics along trajectories as well as final particle size plots are presented; also, optimal furnace operating condition ranges are determined for variable initial size and water content.