Experimental Study On Adsorption Of Mercury By Activated Carbon Fibres At Low Temperature

Coal-fired plants is a main emission source for mercury in atmosphere, which exists in flue gas as gas phase, and without control the released mercury will contaminate the environment. Elemental mercury possess high volatility and low water-solubility, thus is one of the most intractable form. Herein experimental researches are carried out to study the adsorption ability for mercury and to investigate influencing factors using activated carbon fibres (ACFs) as adsorbent at low temperature.Research on mercury adsorption by three different ACFs in coal-fired flue gas is conducted on a one-dimensional combustion test facility to investigate mercury speciation using Ontario-Hydro method and to discuss adsorption efficiency of different ACFs and the influence of moisture and temperature to mercury adsorption. The experimental results indicate that surface oxygen and nitrogen functional groups on ACFs and moisture show positive effects on mercury adsorption especially for the sorption and oxidation of element mercury. Under the specific experimental conditions, increasing reaction temperature is favorable to chemical adsorption while it leads to decrease of physical adsorption, therefore, according to the catalyzed polyacrylonitrile-based ACF sample, at 70℃increasing moisture content is advantageous to the adsorption of mercury.Moreover, by adopting fixed-bed experimental system and simulating flue gas components, researches are done to study the influence of temperature and varied inlet mercury concentration and SO₂ and NOx to mercury adsorption using viscose-based ACF. It is indicated that with the increase of inlet elemental mercury concentration the adsorptive capacity enhances; ACF is a low temperature adsorbent, the physical adsorption ability of which is stronger at low temperature if untreated while the ability decreases when the reactive temperature increases; SO₂ would make adsorption ability decline; with the existence of O₂, NO enhances the adsorption capacity of ACF for mercury viz. NO₂ is in favor of adsorption of element mercury. When SO₂ and NO coexists, there would be a series of reactions among SO₂ and NO and mercury happening on surface of ACF attributed to catalyzed effects of activated sites while too high concentration of SO₂ is disbenefit to the adsorption of mercury. The interaction among these gases indicates that the process of elemental mercury adsorption by ACF is not only a physical adsorptive course but also a chemical adsorptive one, thus cannot be ignored. Finally, based on mass balance of gas in the packed bed reactor and inside the pores of fiber, a dynamical model of elemental mercury adsorption is established using isothermal adsorption equilibrium equation, which is fitted with experiment results to obtain some parameters, therefore provides reference for further forecasting.