Calcination kinetics of cement raw meals under various CO2 concentrations

Abstract

The calcium looping CO₂ capture process, CaL, represents a promising option for the decarbonisation of cement plants, due to the intrinsic benefit of using the spent CO₂ sorbent as a feedstock for the plant. The generation of sufficiently active CaO from the raw meals entering the cement plant for the CO₂ capture requires calcination of these materials at around 900 °C in various atmospheres of CO₂. This work investigates the calcination kinetics of fine particles (<50 μm) of limestone, natural marls and raw meals in a drop tube reactor, under conditions very similar to those expected in suspension calciners of CaL systems. Experiments have been carried out with very short gas–solid contact times (t < 2 s) and various concentrations of CO₂ (up to 85 vol%). High calcination conversions have been measured under these conditions with all the materials tested regardless of their origin and composition. The kinetic rates of CaCO₃ decomposition depend on the BET surface area of the solid, which is consistent with the model reported by Borgwardt, AIChE J., 1985, 31, 103–111, and yield consistent activation energy (i.e. 195 kJ mol⁻¹) and pre-exponential factors when using a dependency on CO₂, as proposed by J. M. Valverde, P. E. Sanchez-Jimenez and L. A. Perez-Maqueda, J. Phys. Chem. C, 2015, 119, 1623–1641.