Investigation of Elemental Mercury Removal from Coal-Fired Boiler Flue Gas over MIL101-Cr

摘要

In this work, the MIL101-Cr sorbent with a large BET surface area was prepared and used to remove He from simulated coal-fired boiler flue gas. The chemical and physical properties of the prepared sorbent were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) analysis, and X-ray photoelectron spectroscopy (XPS). A range of experiments was conducted in a fixed-bed reactor to investigate the effects of reaction temperature, Hg-0 inlet concentration, gas hourly space velocity (GHSV), and flue gas composition on the Hg-0 removal for the prepared sorbent. The mechanisms and kinetics of the Hg-0 adsorption were also studied. The results showed that the MIL101-Cr sorbent achieved a Hg-0 removal efficiency of more than 85% for 4 hat 200 degrees C under the conditions of a relatively high Hg-0 inlet concentration (203 mu g/m(3)) and GHSV (8 x 10(5) h(-1)). The O-2 in the flue gas was found to be beneficial for Hg-0 removal. The NO in the flue gas favored He removal both in the presence and absence of O-2. The SO2 in the flue gas notably inhibited Hg-0 adsorption in the absence of O-2, whereas a low concentration of SO2 slightly inhibited He removal in the presence of O-2. However, high concentrations of SO2 in the flue gas still significantly weakend Hg-0 removal ability, even in the presence of O-2, due to the competitive adsorption of SO2 with Hg-0 on the sorbent and the sulfation of the sorbent. The simultaneous presence of O-2 and NO in the flue gas could overcome the adverse impact of SO2 on Hg-0 adsorption. The H2O has little influence on Hg-0 removal due to the competitive adsorption. XPS analysis indicated that the surface Cr3+, oxygen species, and C=O group in MIL101-Cr acted as the active adsorption/oxidation sites for Hg-0. The Hg-0 removal by MIL101-Cr was due to chemisorption and could be described by the pseudo-second-order model. The equilibrium adsorption capacity calculated for the sorbent amounted to 25 656 mu g/g at 200 degrees C, which indicated that MIL101-Cr could be used as a promising sorbent to remove Hg-0 from coal-fired boiler flue gas.