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

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, CaSO3, CaSO4/CaSO3 and Na2SO3 were carried out to simulate recirculating slurries in different oxidation modes. Elemental mercury (Hg0) re-emission was replicated through the simulated scrubber. The relationship between the oxidation–reduction potential (ORP) of the slurries and the Hg0 re-emissions was evaluated. Elemental mercury re-emission occurred when Hg2+ that was absorbed in the simulated scrubber was converted to Hg0; then, Hg0 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 Hg0 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 Hg0 concentrations that were emitted from the simulated scrubber increased. The Hg0 re-emission rates decreased as the O2 concentration in the carrier gas increased. In addition, the effects of additives to suppress Hg0 re-emission were evaluated in this paper. Sodium tetrasulfide, TMT 15, NaHS and HI were added to the slurry, while Hg2+, 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 Hg0 re-emission.