Simultaneous removal of NO and elemental mercury from coal-fired flue gas using natural ferruginous manganese ore at low temperature

Abstract

Natural ferruginous manganese ore (FMO) was developed as a cost-effective NH3-SCR catalyst for the simultaneous removal of NO and elemental mercury (Hg0) from coal-fired flue gas. The chemical composition, pore structure, crystal structure and surface chemistry of FMO were characterized by different methods. The results showed that FMO was constructed with sheet-like structures. There were massive slit-shaped pores in the FMO. Manganese and iron oxides existed in an amorphous form. After calcination, the NO removal performance of FMO was obviously decreased due to the decomposition of MnO2. A high NH3/NO ratio was conductive to NO removal but excessive NH3 was unnecessary for NO removal. NO could promote Hg0 removal whereas Hg0 had little effect on NO removal. The effects of different SCR atmosphere (inlet, middle layer, and outlet), reaction temperature (100 °C–400 °C), and flue gas composition (O2 and SO2) on NO/Hg0 removal was also studied. At the optimal temperature (200 °C), the NO removal efficiency was greater than 80% and the Hg0 removal efficiency was close to 100%. To some extent, FMO presented preferable SO2 poisoning resistance probably because of the presence of iron oxide. The mechanism of NO/Hg0 removal over FMO was further described. Both fast SCR and conventional SCR reactions happened over FMO during NO removal. Mn4+, Fe3+, and lattice oxygen were first consumed and then replenished by gaseous O2. FMO served as a catalyst for Hg0 oxidation during a long period of denitration process.