Preparation, Characterization, and Calcium Utilization of Fly Ash/Ca(OH)2 Sorbents for Dry Desulfurization at Low Temperature

Abstract

Sorbents for SO2 removal were prepared by hydration at 90 °C of calcium hydroxide and coal fly ash at different fly ash/Ca(OH)2 initial ratios, from 1/3 to 15/3, and slurring times, from 3 to 37 h. Properties characterized in the sorbents included the particle size, the Brunauer−Emmett−Teller surface area, and the porosity distribution. The Ca(OH)2 conversion as a measure of the pozzolanic reaction extent was also determined; all of these sorbent properties were related to the preparation variables. The obtained sorbents were tested in a flue gas desulfurization reaction at 57 °C and 52% relative humidity. The calcium utilization in this reaction was quantified as moles of SO2 captured per moles of calcium × 100. The Ca(OH)2 conversion in the hydration reaction and the raw material ratios have been revealed as the most efficient parameters to predict the behavior of the sorbent in the desulfurization process. The hydration reaction between fly ash and Ca(OH)2 should be performed just until the completion of the pozzolanic reaction and with a fly ash/Ca(OH)2 initial weight ratio of 5/3 or 9/3 to have an optimum sorbent in the reaction with SO2.