HEATED FLY-ASH HYDRATED LIME SLURRIES FOR SO2 REMOVAL IN SPRAY DRYER ABSORBERS

Coal fly ashes have been slurried with quicklime at elevated temperatu res to determine their reactivity with SO2 in a minipilot spray dryer. Bench-scale experimental results indicate that this hydration process greatly increases the total surface area of the solids. Minipilot-sca le spray dryer tests reveal that the slurry reaction step can signific antly increase calcium utilization and SO2 removal of these fly ash/qu icklime sorbents, depending on the type of fly ash used. One type of f ly ash showed considerably better reactivity in the spray dryer tests. This enhancement is considered due to the presence of calcium silica hydrate material formed from the reaction between calcium and the alum ina silicate found in the fly ashes and the difference in reactivity d ue to the type of calcium silica hydrate material formed. The benefit, however, decreases with the calcium feed rate. Pozzolanic strength te sts were performed on the fly ashes used, and the measured unconfined compressive strengths followed the reactivity results in the spray dry er; the most reactive fly ash possessed the highest pozzolanic activit y.