Study of elemental mercury re-emission through a lab-scale simulated scrubber

Abstract

This paper describes a lab-scale simulated scrubber that was designed and built in the laboratory at Western Kentucky University’s Institute for Combustion Science and Environmental Technology. A series of tests on slurries of CaO, CaSO 3, CaSO 4/CaSO 3 and Na 2SO 3 were carried out to simulate recirculating slurries in different oxidation modes. Elemental mercury (Hg 0) re-emission was replicated through the simulated scrubber. The relationship between the oxidation–reduction potential (ORP) of the slurries and the Hg 0 re-emissions was evaluated. Elemental mercury re-emission occurred when Hg 2+ that was absorbed in the simulated scrubber was converted to Hg 0; then, Hg 0 was emitted from the slurry together with the carrier gas. The effects of both the reagents and the operational conditions (including the temperature, pH, and oxygen concentrations in the carrier gas) on the Hg 0 re-emission rates in the simulated scrubber were investigated. The results indicated that as the operational temperature of the scrubber and the pH value of the slurry increased, the Hg 0 concentrations that were emitted from the simulated scrubber increased. The Hg 0 re-emission rates decreased as the O 2 concentration in the carrier gas increased. In addition, the effects of additives to suppress Hg 0 re-emission were evaluated in this paper. Sodium tetrasulfide, TMT 15, NaHS and HI were added to the slurry, while Hg 2+, which was absorbed in the slurry, was retained in the slurry as mercury precipitates. Therefore, there was a significant capacity for the additives to suppress Hg 0 re-emission.