Entrained-flow adsorption of mercury using activated carbon

Bench-scale experiments were conducted in a flow reactor to simulate entrained-flow capture of elemental mercury (Hg-0) by activated carbon. Adsorption of Hg-0 by several commercial activated carbons was examined at different C:Hg ratios (by weight) (350:1-29,000:1), particle sizes (4-44 mum), Hg-0 concentrations (44, 86, and 124 ppb), and temperatures (23-250 degreesC). Increasing the C:Hg ratio from 2100:1 to 11,000:1 resulted in an increase in removal from 11 to 30% for particle sizes of 4-8 Irm and a residence time of 6.5 sec. Mercury capture increased with a decrease in particle size. At 100 degreesC and an Hg-0 concentration of 86 ppb, a 20% Hg-0 reduction was obtained with 4- to 8-mum particles, compared with only a 7% reduction for 24- to 44-mum particles. Mercury uptake decreased with an increase in temperature over a range of 21-150 degreesC. Only a small amount of the Hg-0 uptake capacity is being utilized (less than 1%) at such short residence times. Increasing the residence time over a range of 3.8-13 sec did not increase adsorption for a lignite-based carbon; however, increasing the time from 3.6 to 12 sec resulted in higher Hg-0 removal for a bituminous-based carbon.