High Calcium Utilization and Gypsum Formation for Dry Desulfurization Process

Abstract

The high-active sorbent for SO2 removal was developed by mixing CaO particles with fly ash in water at ambient temperature. The calcium utilization rate in the sorbent was achieved to 60% after the desulfurization reaction at 450 °C for 90 min, while the utilization rate for original pure CaO particles was only 21% under the identical conditions. The surface of the sorbent was examined by SEM, EDX, and BET analysis to study the activation mechanism. Results indicated that CaO particles were separated to several small particles of Ca(OH)2 in water due to a significant heat release, while a small amount of Ca(OH)2 dissolved in water. Under the condition of coexistence with fly ash particles, the tiny Ca(OH)2 particles and its solute covered the surface of fly ash particles with the drying process. Therefore, SO2 could react efficiently with the Ca(OH)2 on the surface of fly ash particles. XRD analysis showed that the composition of sorbent was not apparently changed in the sorbent preparation process. Moreover, the mixture time of CaO and fly ash in water did not play a significant role on calcium utilization rate. These results revealed that the hydration reactions between CaO and the materials such as SiO2 or Al2O3 in fly ash were limited in sorbent preparation process at ambient temperature. The IR analysis of reaction products indicated that gypsum could be produced efficiently at high reaction temperature by using the sorbent.