Investigation into Mercury Removal with Different Sorbents Injection in Simulated and Coal-Fired Flue Gas

摘要

Mercury and its compounds have been brought into global focus for their heavy damages on both environment and human health. Coal burning remains one of the most significant anthropogenic sources of mercury emissions to atmosphere, roughly one quarter of total anthropogenic amount. Activated carbon draws attention to its feasibility of adsorbing Hg effectively in flue gas injection demercuration, but its high cost prevents its large-scale application in coal-fired power plants especially in China.Agricultural biomass residues are kinds of waste with high carbon content, which are potential precursors to develop low-cost and high efficient sorbents for mercury removal. In this work, the demercurization performance of rice husk char and a kind of activated carbon was investigated in both simulated and coal-fired flue gas. Both of these two kinds of sorbents were modified by low concentration ammonium halide solutions. The addition of halogen was found to enhance the fixed-bed mercury removal efficiency up to 80%~95% even after 2 hours. The simulated flue jet experiments results demonstrated that the mercury removal levels in excess of 90% were achievable at the residence time 2 seconds and the C/Hg ratio greater than 9×l0~4. Lastly, these newly developed modified sorbents were tested in a bench scale coal-fired circulating fluidized bed facility to verify the mercury removal behavior by injecting them into a coal-fired flue gas duct. High mercury removal efficiency (82.05%~90.45%) was achieved, and a co-removal rates of 30.62%~36.07% and 9.8%~38.25% for SO_2 and NO_x respectively. It has been shown that ammonium bromide modified biomass-based sorbents possesses as high mercury removal efficiency as commonly used activated carbon.