EFFECTIVE DIFFUSIVITY CHANGES DURING CALCINATION, CARBONATION, RECALCINATION, AND SULFATION OF LIMESTONES

This study investigates the changes occurring in the intraparticle mass transport resistance of gases in limestone particles used to control SO2 emissions from coal-fired power plants. The evolution of intraparticle mass transfer resistance in calcined limestones undergoing carbonation and sulfation and carbonated calcines undergoing recalcination is investigated experimentally using the pulse chromatographic technique. The large quantities of calcined, carbonated, recalcined, or sulfated samples needed to pack the chromatographic column are produced in a fluidized-bed reactor and two types of limestones containing more than 95% CaCO3 are employed. Effective diffusivities are estimated by matching the experimental and theoretical chromatographic response curves 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 distribution but on the connectivity of the pore structure as well. This conclusion is in agreement with a result reached in past studies from the analysis of sulfation data for the same solids.