Sv. Krishnan et Sv. Sotirchos, EFFECTIVE DIFFUSIVITY CHANGES DURING CALCINATION, CARBONATION, RECALCINATION, AND SULFATION OF LIMESTONES, Chemical Engineering Science, 49(8), 1994, pp. 1195-1208
This study investigates the changes occurring in the intraparticle mas
s transport resistance of gases in limestone particles used to control
SO2 emissions from coal-fired power plants. The evolution of intrapar
ticle mass transfer resistance in calcined limestones undergoing carbo
nation and sulfation and carbonated calcines undergoing recalcination
is investigated experimentally using the pulse chromatographic techniq
ue. The large quantities of calcined, carbonated, recalcined, or sulfa
ted samples needed to pack the chromatographic column are produced in
a fluidized-bed reactor and two types of limestones containing more th
an 95% CaCO3 are employed. Effective diffusivities are estimated by ma
tching the experimental and theoretical chromatographic response curve
s in the time domain. The analysis of the experimental data show that
the intraparticle diffusion resistance in calcined limestone particles
(both reacted and unreacted) depends not only on the pore size distri
bution but on the connectivity of the pore structure as well. This con
clusion is in agreement with a result reached in past studies from the
analysis of sulfation data for the same solids.