Temperature programmed decomposition desorption of the mercury species over spent iron-based sorbents for mercury removal from coal derived fuel gas

Development of an elemental mercury (Hg⁰) removal process for coal derived fuel gas is an important issue in the development of a clean and highly efficient coal power generation system. Recently, iron-based sorbents such as iron oxide (Fe₂O₃), supported iron oxide on TiO₂, and iron disulfide have been proposed as active mercury sorbents. It was supposed that Hg⁰ reacted with H₂S on the iron-based sorbents and captured mercury. However, the mercury species captured on the sorbents have not been directly characterized yet. The captured mercury species was too small to identify because the concentration of Hg⁰ was very low (ppb order). In this study, a temperature programmed decomposition technique is applied in order to understand the decomposition character of the mercury species captured on iron-based sorbents. The Hg⁰ removal experiments were carried out in a laboratory-scale fixed-bed reactor at 80 °C using simulated fuel gas. After the Hg⁰ removal experiments, desorption of the captured mercury species was carried out in the same fixed-bed reactor using an atomic absorption spectrophotometer. Temperature programmed decomposition desorption (TPDD) experiments revealed that the decomposition characteristic of mercury species captured on the sorbent was similar to that of HgS reagents (cinnabar and meta-cinnabar). Furthermore, it was observed that the characteristics of the decomposition of mercury species depended on the sorbent type of sorbents and reaction conditions.