Experimental study on the kinetics of magnesium carbonate calcination under elevated heating rates

This paper reports an experimental investigation into the kinetics of magnesium carbonate calcination, conducted using a broad spectrum of heating rates (0.1°C/s to 179.9°C/s) in an air environment for a thin layer bed with Biot number < 0.1. These heating rates surpass those typically employed in thermogravimetric analysers (< 1°C/s) by many orders of magnitude. It was found that higher heating rates led to lower activation energies, as demonstrated by a 24.5% reduction in activation energy, E, from 220.8 kJmol⁻¹ to 166.6 kJmol⁻¹, for an increase in the heating rate from 0.1°C/s to 102.9°C/s. Furthermore, a higher heating rate led to a non-linear reduction in the residence time required to achieve the maximum conversion fraction. For instance, the time required for magnesite calcination to attain a conversion fraction from X=0.1 to X=0.84 decreased by a factor of eight, from 1920 s to 240 s, for only a three-fold increase in the heating rate, from 59.2°C/s to 179.9°C/s. These increases were associated with a higher specific surface area, highlighting the strong influence of the heating rate on the kinetics of magnesium carbonate calcination. It was also found that the highest specific surface area of cases examined for magnesite occurs for a heating rate of 59.2°C/s and a temperature less than 950°C, which avoids significant sintering. Increasing the temperature beyond 950°C reduces the specific surface area by causing sintering.