(364f) Functionalized Nanometal Aggregates For Vapor-Phase Mercury Capture

Meyer, D., University of Kentucky
Sikdar, S. K., National Risk Management Research Lab / US EPA
Hutson, N., US EPA

Coal-fired power plants in the United States emit roughly 48 tons of mercury annually. In 2005, the U.S. EPA promulgated the Clean Air Mercury Rule (CAMR), calling for a nearly 70% reduction in these Hg emissions by 2018. As a result, there has been considerable work in the development and testing of innovative and cost-effective mercury control technologies. There are two main approaches that have been studied for Hg vapor control at elevated temperatures. One involves direct capture of Hg0 by injection of sorbents, usually powdered activated carbons. The other approach focuses on the development of oxidation catalysts to transform Hg vapor to Hg2+ for removal during scrubbing processes. Our work deals with non-carbon-based sorbents. The use of copper-doped Fe nanoaggregates silanized with organic sulfur as bis-(triethoxy silyl propyl)-tetra sulfide has been investigated for the capture of elemental mercury from the vapor phase for potential power-plant applications. Silanization procedures resulted in 70% deposition of the targeted sulfur (S) level, with particles containing approximately 4 wt% S. The addition of copper (Cu) was found to increase the fixed-bed (total) capacity of this type of sorbent from 170 microgram Hg/g sorbent with no copper doping to 2730 microgram Hg/g sorbent at 1.3 wt% Cu. When no S is deposited, the capacity of Fe/Cu nanoaggregates was only 180 microgramHg/g sorbent. These findings suggest that a combined Cu-S mechanism is responsible for Hg capture. Moving-bed (injection) testing of the Fe-based sorbents in a simulated flue gas stream showed the 1.3 wt% Cu sample was able to achieve significant removal of Hg. At a modest sorbent injection rate of 3.6 x 10-3 g/L-hr, this material showed a steady-state removal capacity of 107.5 microgram Hg/g sorbent for an inlet concentration of 17.8 microgram/m3. Based on only 4% usage of the total capacity during single-pass injection, it is possible that these materials can be separated and recycled to reduce power plant operation costs for Hg emissions control. Comparison results will also be provided for benchmark activated carbon. This work is made possible with funding provided by the U. S. Environmental Protection Agency in cooperation with the University of Cincinnati. Mercury analysis by ICP for fixed-bed testing was carried out at the University of Kentucky's Environmental Research and Training Laboratory. Dr. Yongxin Zhao of Arcadis, an on-site contractor to NRMRL/RTP, performed the tests on the EPA's Entrained Flow Reactor.