Limestone dissolution in modeling of slurry scrubbing for flue gas desulfurization

Batch limestone dissolution experiments were carried out in a pH stat apparatus at 55oC with CO2 sparging and dissolved sulfite. Particle size distribution, utilization, sulfite in solution, limestone type, and the approach to calcite equilibrium were all found to contribute to the limestone reactivity.; In the absence of sulfite limestone dissolution was controlled solely by mass transfer. For a given stone under mass transfer control, film thickness was found to be independent of pH. The dissolution rate in the presence of sulfite was controlled by a combines surface kinetics/mass transfer regime. SEM micrographs supported this conclusion. A surface rate correlation was developed which accounted for observed inhibition by an inverse dependence on calcium sulfite concentration at the limestone surface. While the form of the rate expression was applicable to all stones, the surface rate constant was stone dependent. A computer code which accounted for mass transfer with surface kinetics was tested against experimental observations of four limestone types. Changes in pH and the concentrations of calcium, carbonate, sulfite, sulfate, and adipic acid were accurately modeled.; An overall slurry scrubber model was expanded to predict limestone reactivity from particle size and solution effects. This model predicts scrubber performance and hold tank compositions from the chemistry of the limestone slurry process. Additional subroutines were written to predict particle size distributions from sieve data using the log gamma density function. The expanded model was tested against a limestone type and grind study which investigated utilizations of four limestone types at ten different grinds.; The expanded Slurry Scrubber Model was able to predict both SO{dollar}sb2{dollar} removal and hold tank compositions of the limestone study. The effects of limestone type were handled through changes in the surface rate parameter. Within a given type the effects of grind and utilization were well modeled. Additionally the model indicated that for three runs at very low utilizations of the Fredonia stone, the limestone may have partially blinded. The Slurry Scrubber Model was also able to predict the relatively constant removal observed for Georgia Coarse even though utilization was changed by 12%.