Sulphation of limestones in a fluidized bed combustor: the relationship between particle attrition and microstructure

Sulphation of two limestones in a fluidized bed combustor has been investigated. One limestone (coarse-grained) was characterized by a significant population of relatively large pores after calcination; the other (fine-grained) presented a finer and fairly unimodal pore size distribution. Differences in the microstructure were reflected by different thickness of the sulphate shell formed upon sulphation and ultimate calcium conversion degree. Particle attrition/fragmentation were fairly small under moderately bubbling fluidization conditions. Fragmentation upon impact was significant. The fine-grained limestone, characterized by a thinner sulphate shell, was more susceptible to fragmentation than the other. Particle fragmentation discloses unreacted CaO enabling secondary sulphation of exhausted particles.