On the relevance of segregation phenomena during bubbling fluidized bed combustion and desulfurization of ebonite

Results of experiments concerning the combustion and desulfurization of ebonite in bubbling fluidized bed are presented in the paper. Two experimental facilities of different scale, the first one operated batchwise, the second one under steady state conditions, were used. Experiments carried out at bench scale were aimed at determining the mechanism of sulfur release during combustion and to evaluate the extent of the contact between released sulfur and sorbent. They demonstrated that a significant amount of sulfur is released during devolatilization stage. Therefore, desulfurization efficiency was limited by occurrence of poor contact between sulfur and calcium. The desulfurization efficiency was very sensitive to the size of sorbent particles and bed solids. Results of steady state combustion, carried out at pre-pilot scale, were elaborated in terms of bed carbon loading and efficiencies of combustion and desulfurization. The comparison with an already tested reference fuel, South African coal, demonstrated similar combustion behavior. Combustion performances were strongly dependent on the excess air ratio. The combustion efficiency was always larger than 90%. Desulfurization efficiency was not satisfactory, approaching a maximum value of 80% at Ca/S molar ratio equal to 10. A theoretical assessment of results, based on a mathematical model, was proposed in both cases. It allowed the determination of the contact efficiency between gaseous sulfur and available sorbent, which was equal to 85% and 65% for the smaller and bigger facilities, respectively.