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).
|