The purpose of this study is to experimentally investigate the desulfurization and dechlorination characteristics of seashell and limestone in two waste-coal co-firing circulating fluidized beds of 50 kg⁄h with different heights (15 m and 6 m). The tested wastes were Japanese RDF and Chinese waste, whilst the employed coals had varied fuel ratios of either 4.5 or 8.8. It was shown that the efficiencies of desulfurization and dechlorination were both higher for seashell than for limestone. At four times and beyond of the stoichiometric ratio of Ca over sulfur and chlorine, i.e. at Ca⁄(S+2Cl) › 4.0, the efficiencies of seashell for desulfurization and dechlorination reached more than 99 % and 80 %, respectively. Under the quoted conditions these efficiencies were only 95 % and 70 % for limestone. Meanwhile, it was found that the calcined seashell had a mean pore size four times bigger than that of calcined limestone, and this was considered to be the cause for the preceding different efficiencies. That is, when the bigger pores existing in calcined seashell allowed the desulfurization and dechlorination reactions to take place throughout the sorbent particles, those reactions were possible only on particles′ surface for limestone. Furthermore, the work clarified that the dusulfurization and dechlorination efficiencies for the tested different wastes, coals and circulating fluidized beds could be unified according to Ca⁄(S+2Cl) ratio.
