Attrition of reactivated limestone during fluidized bed sulphation

The attrition behavior of an Italian limestone during fluidized bed calcination and sulphation and, after water reactivation, during further re-sulphation was investigated in a bench scale apparatus. Flue gas SO2 concentration was followed in order to relate attrition data to calcium conversion degree. Operating conditions of the bed were those typical of atmospheric bubbling fluidized bed combustion. Batchwise experiments were carried out in order to study the influence of the chemical reactions and the reactivation step (consisting in the immersion of the spent bed in water until all CaO was converted to Ca(OH)2) on the parallel particle fragmentation and abrasion in the bed. To this end particle-size distribution changes and generated fines elutriation rates were followed throughout conversion. SEM-EDX analysis of polished cross-section of: a) sulphated, b) hydrated and c) re-sulphated particles was carried out in order to follow the particle morphology changes. Results indicated that water reactivation was able to approximately double the final conversion degree of the limestone upon further re-injection of the particles in the bed. On the other hand the reactivation process did not promote any significant enhancement of the attrition of the limestone at hand.