Impact fragmentation of limestone-based sorbents for calcium looping: The effect of steam and sulphur dioxide

Calcium Looping (CaL) for CO2 capture and utilisation is affected by the presence of SO2 and/or H2O in the flue gases that are processed in the carbonator. The influence regards both the course of carbonation as well as the mechanisms and extent of attrition and fragmentation phenomena to which sorbent particles are exposed in Dual Interconnected Fluidised Beds (DIFB) that are commonly used for this process. Fragmentation by impact has been comparatively less investigated with reference to operating conditions entailing the presence of SO2 and/or H2O. In this study, two high-calcium commercial limestones, similar in chemical composition but different in reactivity, have been subjected to CaL tests in a lab-scale DIFB apparatus in presence of sulphur dioxide and/or steam. Calcination was carried out at 940 °C in an atmosphere containing 70% CO2. Carbonation was carried out at 650 °C in an atmosphere containing 15% CO2. The effect of SO2 and/or H2O was assessed with reference to six carbonation atmospheres, with different concentrations of steam (0 and 10%v) and sulphur dioxide (0, 75 and 1500 ppmv). After ten CaL cycles, the particles were tested ex-situ in an impact test rig, consisting of a duct where samples were entrained in a gas stream at a controlled velocity and impacted against a target. The apparatus was operated at room temperature at various impact velocities (six values from 10 to 45 m/s). The extent and pattern of impact fragmentation was assessed by characterising the particle size distribution of the debris and the fractional mass of generated fragments. Results are discussed in the light of the different sorbent nature and of the CaL FB operating conditions.