Enhancing Desulfurization Performance by Regulating Ca(OH)₂ Hygroscopicity: An Integrated Experimental and DFT Study

Circulating fluidized-bed flue gas desulfurization (CFB-FGD) is a widely employed semidry flue gas desulfurization technology due to its cost-effectiveness and easy operation. However, CFB-FGD cannot satisfy the ultralow emission requirement, particularly under high SO 2 -containing flue gas conditions. This study aimed to enhance the CFB-FGD performance in a cost-effective way by regulating Ca(OH) 2 hygroscopicity in the desulfurization reaction. MgSO 4 was screened out from 7 hygroscopic additives. With a minor addition of 4.8 wt % MgSO 4, the sulfur capacity of Ca(OH) 2 increased significantly by over 15% compared to its pristine benchmark. By synthesizing structural characterization and DFT calculations, the pros and cons of the H 2 O effect on the Ca(OH) 2 desulfurization reactivity were revealed and discussed from an atomic perspective. X-ray diffraction suggested that the introduction of water could activate the Ca(OH) 2 interlayer by expanding the interplanar distance in the (001) orientation, thus enhancing SO 2 adsorption. DFT calculations showed that the desulfurization reaction over Ca(OH) 2 (001) was kinetically promoted in the presence of H 2 O by facilitating proton transfer. By contrast, excessively high hygroscopicity was found to inhibit the desulfurization performance of Ca(OH) 2 by blocking porosity and hindering SO 2 diffusion by absorbing redundant moisture. This work demonstrated that tuning Ca(OH) 2 hygroscopicity is a low-cost and efficient way to boost SO 2 sorption, which advances Ca(OH) 2 -based solution technologies for wider applications in the flue gas decontamination field.