New TOXECON™ II sorbent injection system delivers high mercury capture short term, but with O&M issues.

The improved lance and sorbent distribution system, for injection ahead of the last two fields in the electrostatic precipitator (ESP) at Entergy’s Independence station unit 2 (842 MWe), captured 80-90% of the mercury but required off-line cleaning due to lance pluggage every 1-2 days.

The TOXECON II system injects activated carbon (or other sorbent) ahead of the last or second-to-last fields of the ESP. This process retains salability for 90-95% of the ash captured before reaching these last fields while still capturing mercury emissions. Using computational fluid dynamics (CFD) modeling and visual observations, the team designed a new injection system that distributes the sorbent according to mercury flow. These new lances were tested for 30 days on 1/4 of one of four ESP boxes in unit 2 (1/16 of total flue gas flow) , enabling the system to achieve 80-90% mercury removal across the ESP with brominated carbon at an injection rate of 5 lb/Macf. These results are similar to those from sorbent injection ahead of the ESP. However, carbon deposits in the lances made it difficult to operate for more than a day or two without bringing the lances off-line for cleaning. Method 5 measurements showed no increase in particulate emissions at the ESP outlet as a result of the injection, but stack data (full unit) suggest a slight increase in both opacity and particulate emissions. The test team is reviewing the results to better understand the inconsistency. An updated sorbent distribution and injection system has been designed to address the lance pluggage issue. This system was installed while unit 2 was online in May and is being tested. For more information, contact Ramsay Chang at 650.855.2535 (rchang@epri.com).