Calcination kinetics of cement raw meals under various CO2 concentrations
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.