Rawhide
Unit One was originally constructed with best available control technology
air pollution emission controls including fabric filter
baghouses for particulate control, tangentially fired boiler combustion
controls using low-nitrogen oxides (NOx) burners and over-fire
air and a lime spray dry absorber sulfur dioxide (SO2) scrubber.
Over time, Platte River has strived to not only achieve its emission
limits for these substances, but to do better than its permit
requirements. Consequently, actual average emissions rates have consistently
been lower than what is permitted.
In early 2002,
Platte River approached the Colorado Department of Public Health
and Environment's Air Pollution Control Division about the formulation of a Voluntary Emissions
Reduction Agreement (VERA) for Rawhide Unit One. The agreement included accepting
significantly more stringent NOx and SO2 emission limits in
exchange for an exemption from new "state-only" emission
reduction requirements for a regulatory assurance period of
up to 15 years. The VERA was finalized in September 2002.
Platte River has
successfully implemented emission control system enhancements and
upgrades and consistently complies with the VERA-related NOx and SO2 emission limits. To comply with the new NOx
limit, Platte River updated boiler combustion control equipment that
included a new low-NOx concentric firing burner system with separated
over-fire air. Since implementation, NOx emissions are two–thirds
lower than the prior permit limit.
Ensuring continuous
compliance with the new SO2 limit required implementing a number
of SO2 scrubber enhancements. Though not a VERA requirement,
Platte River also tightened the acceptable coal specifications
and now purchases premium lower sulfur and higher heat content coal.
Due to Platte River's longstanding practice of striving
to minimize emissions, the post-VERA annual Rawhide SO2 emissions
rates are now about one-third lower than the prior permit limit.
NOx Limit Pre-VERA (lb/mmBtu) |
NOx Limit Post-VERA (lb/mmBtu) |
2010 NOx Emission Rate (lb/mmBtu) |
SO2 Limit Pre-VERA (lb/mmBtu) |
SO2 Limit Post-VERA (lb/mmBtu) |
2010 SO2 Emission Rate (lb/mmBtu) |
0.5 |
0.18 |
0.17 |
0.13 |
0.09 |
0.08 |
Platte River continues
to evaluate options for upgrading Rawhide's
emission controls. Additional enhancements have been made
to the NOx combustion controls since the VERA upgrades and more
changes will be implemented in 2012 to ensure compliance with the
U.S. environment
Protection Agency’s Regional Haze Rule's additional
NOx reduction requirements. Recently implemented NOx emissions control
enhancements include adding more extensive boiler combustion process
monitoring equipment and integrating "artificially intelligent" neural-net
combustion optimization computing (hardware and software)
into the boiler's coordinated combustion control system. It is
anticipated that these new enhancements will reduce NOx emissions
an additional 20 percent below the VERA permit limit.
