The influence of sorbent properties and reaction temperature on sorbent attrition, sulfur uptake, and particle sulfation pattern during fluidized-bed desulfurization

The influence of operating parameters such as sorbent properties and reaction temperature on sorbent attrition, sulfur uptake, and particle sulfation pattern during fluidized-bed desulfurization is assessed. Sulfur 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 sulfur mappings of cross sections of sorbent particles are converted into sulfur distribution density functions, which can be directly related to the prevailing particles sulfation pattern. This procedure is applied to samples of three different sorbents (two limestones and one dolomite) sieved in three particle size ranges and batch-wise sulfated in a fluidized bed at three different temperatures. This analysis is complemented by parallel measurement of calcium conversion degree and elutriated calcium mass during the sulfation tests, as well as by visual inspection of scanning electron microscope 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 sulfation degree than the dolomite. For one of the limestones it was found that the maximum sulfation degree was higher the smaller the particle size and the lower the bed temperature. Results of the statistical analysis on spent sorbent particles reveal that, for most samples, a core-shell sulfation 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 sulfur distribution is achieved consistently with sulfation degree results. The influence of particle size and reaction temperature on sulfur uptake is interpreted in light of the significance of kinetic and intraparticle diffusional resistances assessed by the evaluation of particle Thiele moduli.