An Experimental Study of Calcination of South Australian Caroline Limestone

Abstract

AbstractCalcination experiments were conducted on Caroline Limestone from 53μm to 1.0 mm in size, under a range of partial pressures of CO2 and total pressures and temperatures between 700–900°C using both an atmospheric and a pressurised thermogravimetric apparatus. Results revealed that under these conditions the calcination of Caroline Limestone was unaffected by particle size. The behaviour was attributed to particle explosion that allowed less diffusion resistances for the larger particles. It still needs to be determined whether the explosion was a result of thermally induced fractures (TIFs) or low‐temperature decomposition of MgCO3. The calcination of Caroline Limestone conducted under a variety of partial pressures of CO2 was found to be proportional to the equilibrium partial pressure of CO2 minus the partial pressure of CO2 at interface, PCO2e ‐ PCO2i, for the 0.21–0.35 and 0.5–0.6mm particle size fractions. For the larger particle size fractions between 0.85–1.0mm and 0.5–0.6mm in N2 environment under higher pressures (up to 5 atm), the use of a constant mole fraction y1, was necessary to correlate the calcination rates with effect of CO2 partial pressure. The calcination rate under these conditions was therefore found proportional to PCO2e ‐ PCO2i ‐ Py1. Calcination rates calculated from data up to 100% conversion for the 0.2–0.35mm particles also required the inclusion of y1 and its value was also found to increase from 0.03 at 850°C to 0.22 at 900°C. The observed trends in the value and requirement of the constant mole fraction, y1 clearly indicates that it is included to account for heat and mass transport processes which supports previous justification for its introduction in the rate equation.