Reaction mechanism and efficiency enhancement of dry desulfurization at high temperature of magnesian hydrated lime

HE Xuefu; FAN Xiangli; YOU Changfu; WANG Haiming; JIN Yan

doi:10.13225/j.cnki.jccs.2024.0922

Abstract：The non-renewability of limestone resources leads to the gradual scarcity of high-quality limestone,and the de-velopment of calcium-based desulfurizers with low-grade magnesian limestone as the raw material for the production of calcium-based desulfurizers is of great significance for the control of SO2 emissions in highly polluting industries.In this study,the desulfurization performance of magnesian hydrated lime under high temperature flue gas conditions and the in-fluence of Mg on Ca(OH)2 crystal structure were explored by using a fixed-bed desulfurization experimental system com-bined with XRD characterization technology.The role of Ca(OH)2 crystal structure in influencing the surface chemical re-action stage and diffusion control stage of the desulfurization reaction is investigated by the kinetic approach using the equivalent particle model,and the key steps governing the magnesian hydrated lime desulfurization reaction are clarified.Based on Density Functional Theory(DFT),the adsorption behavior and sulfidation reaction of SO2 on clean and Mg-doped Ca(OH)2 surfaces are investigated,and the diffusion behavior of Ca2+in the two lattice systems is probed.Based on the experimental and simulation calculation results,the Na+additive is used to potentiate the desulfurization performance of magnesian hydrated lime,and the potentiation mechanism is revealed.The results show that Mg2+affects the crystal structure of Ca(OH)2 in hydrated lime by substituting Ca2+,and the change in the crystal structure of Ca(OH)2 is the main reason for the change in the desulfurization performance of magnesian hydrated lime.The surface oxygen atom is the act-ive site for SO2 adsorption,and the substitution of Mg2+for Ca2+enhances the adsorption of SO2 on the surface substrate of Ca(OH)2,and the sulfation reaction energy barrier decreases from 1.40 eV to 1.11 eV,so that there is a facilitating ef-fect on the surface chemical reaction phase of desulfurization reaction.At the same time,it also enhances the bonding in-teraction between Ca2+and OH-within the Ca(OH)2 crystals,and the Ca2+diffusion energy barrier increases from 0.98 eV to 1.55 eV,which is not conducive to the ion diffusion inside the crystal,so it has an inhibitory effect on the diffusion con-trol stage.The lattice distortion of Ca(OH)2 is maximized at a NaOH addition concentration of 5%,and the sulfur capacity reaches 98.42 mg/g,which is an enhancement of about 42.92%.Na+doping into the lattice of Ca(OH)2 is able to weaken the bonding cooperation of Ca—O,and the diffusion energy barrier of Ca2+is reduced to 1.26 eV,which can promote the migration of solid ions inside the crystal,and significantly improve the desulfurization performance of magnesian hy-drated lime.