Low Concentration Mercury Sorption Mechanisms and Control by Calcium-Based Sorbents: Application in Coal-Fired Processes.

The capture of elemental mercury (Hg0) and mercuric chloride (HgCl2) by three types of calcium (Ca)-based sor-bents was examined in this bench-scale study under conditions prevalent in coal-fired utilities. Ca-based sorbent performances were compared with that of an activated carbon. Hg0 capture of about 40% (nearly half that of the activated carbon) was achieved by two of the Ca-based sorbents. The presence of sulfur dioxide (SO2) in the simulated coal combustion flue gas enhanced the Hg0 capture from about 10 to 40%. Increasing the temperature in the range of 65-100 °C also caused an increase in the Hg0 capture by the two Ca-based sorbents. Mercuric chloride (HgCl2) capture exhibited a totally different pattern. The presence of SO2 inhibited the HgCl2 capture by Ca-based sorbents from about 25 to less than 10%. Increasing the temperature in the studied range also caused a decrease in HgCl2 capture. Upon further pilot-scale confirmations, the results obtained in this bench-scale study can be used to design and manufacture more cost-effective mercury sorbents to replace conventional sorbents already in use in mercury control.