Bench-scale experimental evaluation of carbon performance on mercury vapour adsorption

Mercury emission in combustion flue gases is a significant environmental concern due to its toxicity and high volatility. The problem is particularly severe for elemental mercury (Hg0) in vapour since it cannot be effectively removed using current air pollution control devices. Activated carbon (AC) adsorption is a technology that offers a great potential for the control of gas-phase mercury emissions. This paper outlines the results of a parametric study conducted with a bench-scale fixed bed, on the capture of trace mercury vapour from simulated flue gas using ACs. The performances of five commercially available ACs, which are claimed to be effective sorbents of mercury, are evaluated. The parameters investigated include carbon loading, reaction temperature, inlet mercury concentration, and particle size of ACs. A full screening of the physical properties of the five carbons using BET, SEM, XRF, and XRD, facilitates a better understanding to the nature of adsorption. The experimental data suggest that the adsorption of mercury is greatly dependent upon the operation conditions. For sulphur-impregnated carbon, adsorption involves both physical and chemical processes. With increasing temperature, physical adsorption decreases due to the nature of exothermal adsorption process whilst chemisorption might be enhanced, evidenced by the better performance of carbon at a higher temperature. The external surface area of AC has a significant contribution to the high performance of ACs. This study provides a good reference for screening the commercial carbon candidates to be used for treating vapour Hg in the actual exhausted flue gas over a wide range of conditions.