COMPARISON OF DESULFURIZATION CHARACTERISTICS OF SHELL WITH LIMESTONE

摘要

Almost of all shell consists of CaCO_3 similar to limestone. It would be proposed that shell could be applied as a desulfurizer. In this study, desulfurization characteristics of shell are fundamentally studied by using a thermobalance and a bubbling fluidized coal combustor comparing with the results obtained by limestone. Under the constant calcination temperature, the desulfurization efficiency for shells attains more than about 70 % after the desulfurization period of 30 h. For the limestones, on the other hand, the desulfurization efficiency after 30 h becomes only 38 %. The desulfurization efficiency depends on the pore size distribution of CaO. From SEM photos of the surface of CaCO_3, CaO and the sulfurized particles the large pores can be observed for the shells even the sulfurized particles. For the limestones, however, the surface structure of each sample seems to be same since the pore size is quite fine. In measuring cross-sectional distribution of sulfur inside the particles by using a two-dimensional XMA, the sulfur in the sulfurized particle of limestone is only trapped near the particle surface. For the shells, on the other hand, the sulfur is distributed over the whole body of particle. The desulfurization efficiency for the shells even under practical coal combustion indicates higher value than that for the limestones.