The influence of sorbent properties and reaction temperature on sorbent attrition, sulphur uptake and particle sulphation pattern during fluidized bed combustion

The influence of operating parameters such as sorbent properties and reaction temperature on sorbent attrition, sulphur uptake and particle sulphation pattern during fluidized bed desulphurization is assessed. Sulphur distribution throughout the particles is evaluated by means of a novel quantitative automated statistical procedure. With the aid of this technique, energy dispersive X-ray sulphur mappings of cross sections of sorbent particles are converted into sulphur distribution density functions, which can be directly related to the prevailing particles sulphation pattern. This procedure is applied to samples of three different sorbents (two limestones and one dolomite), sieved in three particle size ranges batchwise sulphated in fluidized bed at three different temperatures. This analysis is complemented by parallel measurement of calcium conversion degree and elutriated calcium mass during the sulphation tests, as well as by visual inspection of scanning electron micrographs of cross sections of spent sorbent particles discharged at the end of the tests. Experimental results show that the two limestones achieve a larger final sulphation degree than the dolomite, and that, for a fixed sorbent type, the smaller the particle size and the lower the bed temperature, the higher the maximum sulphation degree obtained. Results of the statistical analysis on spent sorbent particles reveal that, for most samples, a core-shell sulphation pattern is established. Departure from the core-shell pattern is shown by the finest sorbent particles and by sorbent reacted at the lowest bed temperature investigated, in which a uniform sulphur distribution is achieved consistently with sulphation degree results. Observed fractional sulphated areas are interpreted in the light of the significance of kinetic and intraparticle diffusional resistances independently assessed by the evaluation of particle Thiele moduli.