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.

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.

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