Performance of Hg⁰ removal from coal-fired flue gas over coal gasification slag

Mercury (Hg), a kind of heavy metal pollutant, has a great impact on the environment and human health. The highly efficient technology for Hg removal has attracted widespread attention from researchers. In this study, the coal gasification slag (CGS) and the slag after sorting were used as sorbents, and the Hg⁰ removal performance of the sorbents were investigated through the fixed-bed reactor and entrained flow reactor. The characterization methods such as N₂ adsorption-desorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) were performed to analyze the physical and chemical characteristics of the sorbents. According to the results of fixed-bed Hg⁰ removal experiment, the Hg⁰ removal efficiency of the origin slag (OS) and high carbon slag (HCS) could maintain more than 91% at 60−120 ℃. The high ash slag (HAS) showed the highest Hg⁰ removal efficiency of 97% at 60 ℃, which was greatly affected by the Hg⁰ removal temperature. The Hg-TPD (Hg-temperature program desorption) and XPS results indicated that the chemisorbed oxygen on the sorbent participated in the Hg⁰ oxidation process with HgO formed on the surface of the sorbent. According to the results of entrained flow Hg⁰ removal experiments, the Hg⁰ removal efficiencies of OS and HCS were 56% and 57% at C/Hg ratio of 40000 and the Hg⁰ removal temperature of 60 ℃, respectively. When the C/Hg ratio was 80000 and the Hg⁰ removal temperature was 60 ℃, the Hg⁰ removal efficiencies of OS and HCS were 100% and 82%, respectively.