X-ray photoelectron spectroscopy analysis of mercury sorbent surface chemistry

Abstract

During coal combustion, mercury completely volatilizes and can remain in the vapor phase throughout the combustion and environmental control system. Mercury is partitioned into elemental, oxidized and particulate phases in the flue gas stream. Air pollution control devices such as wet scrubbers can remove the oxidized and particulate-bound mercury. Elemental mercury cannot be effectively removed by current control technologies. One proposed new technology involves injecting a powdered carbon-based sorbent upstream of the air pollution control device to capture mercury. Previous work has identified lignite-derived activated carbon as a possible sorption material for mercury in flue gas atmospheres. This study is focused on determining the chemical changes taking place on the surface of two activated carbons that may influence mercury sorption and desorption. The carbons tested included the Norit FGD lignite activated carbon and an activated carbon derived from high-sodium lignite. The sorbents were tested for their ability to sorb and retain elemental mercury in a simulated baseline flue gas containing relatively high concentrations of SO 2, NO 2 and HCl, representative of bituminous coal firing. The breakthrough of mercury was determined for each sorbent under different flue gas compositions. The effect of SO 2, NO 2, HCl and H 2O on the carbon's ability to sorb mercury was evaluated for both activated carbons.