Kinetic assessment of pulp mill-derived lime mud calcination in high CO2 atmosphere

Abstract

The chemical pulping of biomass involves the recycling of calcium through the calcination of lime mud, which is mostly comprised of calcium carbonate (CaCO3). Lime mud decomposes under elevated temperatures to generate calcium oxide (CaO) and carbon dioxide (CO2), the kinetics of which are strongly influenced by the CO2 partial pressure and temperature. Oxy-fuel combustion and electrified lime kilns for lime mud calcination are intriguing methods to decarbonize this highly polluting operation within the biomass pulping industry. However, the high CO2 concentration in oxy-fuel and electrified calcination processes alters the kinetics and overall reactivity of lime mud. For the first time, a model-fitting method is used to determine the kinetic parameters for lime mud calcination under a wide range of temperatures (550 °C–1250 °C) and under different concentrations of CO2 (0 %, 15 %, 50 %, and 90 %). A kinetic model is developed that accurately predicts the reaction rates as a function of temperature and CO2 concentration. The apparent activation of energy for lime mud calcination is elevated under a high CO2 environment. Relative to inert gas (N2, Ar), the temperature window for calcination is much smaller under high CO2 environments. The presence of Na in lime mud does not seem to affect calcination under a high CO2 environment. Finally, particle size variation does not have a significant effect on calcination under a high CO2 environment.