Model-based sensitivity analysis and experimental investigation of perlite grain expansion in a vertical electrical furnace

The new vertical electrical furnace which has been designed and operated at NTUA successfully produces expanded perlite of superior quality, unleashing its potential for high-performance thermal and acoustic insulation applications in the manufacturing and construction industries. A detailed sensitivity analysis has been performed on the basis of our dynamic model for perlite grain expansion, in order to quantitatively understand and systematically evaluate the effect and relative importance of feed quality and operating conditions on macroscopic (grain velocity and temperature evolution) and microscopic (steam bubble pressure, grain size) perlite particle state variables. Experimental campaign
observations illustrate furnace efficiency and are in acceptable agreement with the model. Perlite feed quality (origin, chemical composition, effective water content, initial particle size distribution) is critical for adequate expansion and must be determined in advance of high-temperature processing. Process operating conditions (air feed flow rate and temperature, heating chamber wall temperature) are instrumental towards achieving adequate expansion for a given perlite feed. Ambient air injection accomplishes sufficient expansion of the finer raw perlite fractions only, while preheated air injection achieves coarse fraction expansion but induces a risk of grain overheating and disintegration. Process
efficiency increases dramatically when the furnace wall temperature is maintained within the 1100-1200 °C range.