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 SO2-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. MgSO4 was screened out from 7 hygroscopic additives. With a minor addition of 4.8 wt % MgSO4, 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 H2O 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 SO2 adsorption. DFT calculations showed that the desulfurization reaction over Ca(OH)2(001) was kinetically promoted in the presence of H2O 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 SO2 diffusion by absorbing redundant moisture. This work demonstrated that tuning Ca(OH)2 hygroscopicity is a low-cost and efficient way to boost SO2 sorption, which advances Ca(OH)2-based solution technologies for wider applications in the flue gas decontamination field.