Decomposition mechanism of lumpy dolomite particles

Abstract

Cylindrical cm-sized dolomite particles were decomposed using the two steps decomposition scheme. Several studies on dolomite decomposition have been done using µm- to mm-sized samples over the years. However, these sizes are too small for industrial kiln application and ignore the influence of important parameters, e.g. thermal conductivity, on the decomposition process. In this work, the decomposition behavior of lumpy dolomite particles in each step was investigated. Experimentally measured sample temperature and conversion profiles in steps 1 and 2 are respectively similar to those obtained for the decomposition of pure magnesite and limestone. To measure the core temperature and conversion is to essentially analyze the decomposition behavior. The thermophysical material properties of the decomposition product in each step as a function of temperature was estimated using the shrinking core model. Finite difference method was employed in solving the 1D heat equation describing the process. The reaction rate coefficient in step 1 is shown to have a weak temperature dependence, the thermal conductivity of the product, MgO∙CaCO3, slightly increases with temperature but the permeability is not dependent. In step 2, the reaction coefficient and MgO∙CaO thermal conductivity and pore diffusivity do not show a clear temperature dependence. Finally, the sensitivity of the material and transport properties on the decomposition process was studied under shaft kiln condition. Thermal conductivity is observed to have the highest influence on decomposition with a value of up to 60 % at 1400 °C and for 120 mm particles.