Sv. Krishnan et Sv. Sotirchos, A VARIABLE DIFFUSIVITY SHRINKING-CORE MODEL AND ITS APPLICATION TO THE DIRECT SULFATION OF LIMESTONE, Canadian journal of chemical engineering, 71(5), 1993, pp. 734-745
A variable diffusivity shrinking-core model that allows for temporal a
nd spatial variation of the effective diffusivity in the solid product
layer was developed in this study. The model was used to analyze a se
t of experimental data for the direct sulfation of three limestones (t
hat is, their reaction with SO2 under noncalcining conditions), and a
parameter estimation procedure was formulated for extracting the effec
tive diffusivity as a distributed parameter from the experimental conv
ersion vs. time curves. Very strong effects of temperature, concentrat
ion, and depth in the product layer on the effective diffusivity were
revealed by the analysis. On the basis of the obtained results, it was
concluded that despite being essentially nonporous, uncalcined limest
ones can react with SO2 under noncalcining conditions at rates compara
ble to those of calcined samples because they present much lower resis
tance for diffusion Of SO2 through the product layer than the latter.