Elemental Mercury In Flue Gas Research Articles

Removal of Gas-Phase Elemental Mercury in Flue Gas by Inorganic Chemically Promoted Natural Mineral Sorbents

A variety of natural mineral sorbents were synthesized and tested on a lab-scale fixed-bed system to evaluate mercury removal efficiencies under a simulated flue gas condition that contains 84% N2, 4% O2, and 12% CO2 in volume fraction. Three types of natural minerals, bentonite (Ben), mordenite (Mor), and attapulgite (Atp), were selected as raw sorbents, and several chemical promoters, such as CuCl2, NaClO3, KBr, and KI, were employed to enhance mercury removal abilities of the raw sorbents. The physical-chemical characteristics of these minerals were analyzed by an X-ray diffractometer (XRD), an accelerated surface area and porosimeter (ASAP) using the N2 isotherm adsorption/desorption method, and X-ray fluorescence (XRF) spectrometry. The mercury concentration was detected continuously using a VM3000 online mercury analyzer. The results showed that CuCl2-impregnated Atp (Cu-Atp) and CuCl2-impregnated Ben (Cu-Ben) presented about 90% average Hg0 removal efficiencies at 120 °C, respectively. In addition, as the temperature increased, the removal efficiencies decreased. Although NaClO3-impregnated Atp showed an average Hg0 removal efficiency more than 90% at 120 °C, its performance was limited by the testing temperature, and that was probably due to the high iron oxide content in Atp. For the KI-impregnated sorbents, high mercury removal efficiencies could be observed, and the efficiencies increased steadily with the temperature increased from 70 to 150 °C. The three natural minerals presented poor adsorption abilities for bromine, which resulted in the disappointing mercury removal efficiencies. Generally, Cu-Atp, Cu-Ben, and KI-impregnated sorbents were promising cost-effective mercury sorbents.

Oxidation efficiency of elemental mercury in flue gas by SCR De-NOx catalysts

The oxidation efficiency of elemental mercury (Hg0) by fresh and 40000 h SCR (Selective Catalytic Reduction) catalysts was studied with the help of simulated experiments under oxidation and SCR conditions, respectively. The structural and textural properties of the catalysts were characterized by various techniques, including N2 adsorption/desorption, SEM-EDS, FT-IR, and ion chromatography. It was found that the Hg0 oxidation efficiency over the 40000 h catalyst is about 5%–20% lower than that of the fresh one under the oxidation condition (with HCl and O2), whereas it just decreases by about 5%–10% under the SCR condition (when NH3 and NO are added). The particles agglomeration phenomenon was observed for the 40000 h catalyst, of which the BET, V content, and V5+ = O quantity decrease to some extent. The contents of the water-soluble ions (such as Na+, K+, NH4+, and SO42–) of the 40000 h catalyst are higher than those of the fresh one. All these factors have a negative influence on the pore structure and active sites distribution over the 40000 h catalyst, thereby reducing its Hg0 oxidation efficiency.