Application of Spent H2S Scavenger of Iron Oxide in Mercury Capture from Flue Gas

A commercial H2S scavenger of iron-oxide base, namely TG-4 in the Chinese market, was found to have activity for mercury (Hg) capture from flue gas after its use in H2S removal. The technical feasibility of using this industrial spent material to replace expensive activated carbon for mercury capture from coal-fired power plant flue gas was studied in this paper. The effects of temperature, space velocity, and compositions of the flue gas on the efficiency of Hg removal was investigated using a packed-bed tubular reactor on the benchtop scale. The mercury sorbents prepared from the spent TG-4 H2S sorbent were characterized by sulfur measurement, thermogravimetric and differential thermal analysis (TG-DTA), and X-ray absorption spectroscopy (XAS). The Hg L-3-edge XAS was used to analyze the material after its contact with Hg. The results show that the spent TG-4 can efficiently remove elemental mercury from the gas at a temperature range between 80 and 240 degrees C and at reasonable space velocity. The efficiency of Hg removal slightly decreased when acidic gases such as SO2, NO, and HC1 were present in the gas stream. HgS was observed in the adsorbent after its reaction with gases containing Hg vapor, indicating that the elemental sulfur was the active component for mercury capture. However, compared with the benchtop experimental results, the spent TG-4 gave lower Hg capture efficiency in the scaled-up test at SaskPower's Emission Control Research Facility.