engleski

3D-mathematical modelling of limestone calcination

Calcination is an industrial process that uses high temperature to change the chemical and physical properties of limestone, a sedimentary rock composed of the mineral calcite - calcium carbonate and other mineral dolomites. The calcination process is used in many different industries today, such as cement, chemical, pharmaceutical and sugar industry, where limestone CaCO3 is converted by thermal decomposition into lime CaO and carbon dioxide CO2. This reaction is highly endothermic and requires combustion heat released by the fuel where the temperature is between 780°C to 1350°C, indicating that endothermic limestone calcinations and exothermic fuel combustion proceed simultaneously. Fluid flow, transport phenomena, and thermodynamics within these processes are still not well understood in detail. Therefore, understanding the mechanisms of fluid flow and transport phenomena is important. This paper presents 3D mathematical model of limestone calcination reaction mechanism, which was developed and implemented into a commercial code FIRE. The calcination model the effects of temperature, decomposition pressure, diffusion, and pore efficiency since dissociation of the limestone begins at the outer surface of the limestone particle and shifts inward, leaving a porous layer of lime at the surface. Limestone calcinations reactions are calculated using the Arrhenius rate equation for the liberation of CO2. The model is based on the solution of Navier-Stokes equations for the gas phase, and on the Lagrangean dynamics for the discrete particles. The information obtained by these numerical simulations, such as distribution of particles, distribution of temperatures and concentrations can be used for better understanding of particle kinetics and pollutant emissions from calcinations systems and also for investigation and optimization of calcination devices in various industries.

Calcination; limestone; numerical modelling

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