Oklahoma Gas & Electric Muskogee Generating Station Best ...

Oklahoma Gas & Electric
Muskogee Generating Station – BART Determination
May 28, 2008
3.2.3.1 Rotating Opposed Fired Air and Rotomix
Rotating opposed fired air (ROFA) is a boosted overfire air system that includes a patented
rotation process which includes asymmetrically placed air nozzles. 6 Like other OFA
systems, ROFA stages the primary combustion zone to burn overall rich, with excess air
added higher in the furnace to burn out products of incomplete combustion. The ROFA
nozzles are designed to increase turbulence within the furnace. Increased turbulence should
prevent the formation of stratified laminar flow, enable the furnace volume to be used more
effectively for the combustion process, and reduce the maximum temperatures of the
combustion zone.
The ROFA system consists of air injection boxes, duct work and supports, the ROFA fan,
and control system instrumentation. A ROFA system was installed on an existing 80-MW
(gross) bituminous-fired utility boiler in the summer of 2002. Test results showed that the
ROFA system reduced NOx emissions from baseline levels between 0.58 and 0.62
lb/mmBtu to approximately 0.22 lb/mmBtu at full load. At lower loads (approximately 40
MW), the ROFA system reduced NOx emissions from 0.59 lb/mmBtu to 0.295 lb/mmBtu. 7
The turbulent air injection and mixing provided by ROFA allows for the effective mixing
of chemical reagents with the combustion products in the furnace. MobotecUSA’s
Rotamix ® system combines the rotating opposed overfire air system with urea injection into
the flue gas to reduce NOx emissions. The turbulent mixing created by the ROFA system is
designed to improve distribution of the ammonia/urea reagent and may reduce the
ammonia/urea injection required by the SNCR control system. A Rotamix control system
was installed on the same 80-MW unit in the spring of 2004.
ROFA and Rotamix ® systems have been demonstrated on smaller coal-fired boilers but
have not been demonstrated in practice on boilers similar in size to Muskogee Units 4 & 5.
As discussed in subsection 3.2.1.1, overfire air control systems are a technically feasible
retrofit control technology, and, based on engineering judgment, the ROFA design could
also be applied to Muskogee Units 4 & 5. However, there is no technical basis to conclude
that the ROFA design would provide additional NOx reduction beyond that achieved with
other OFA designs. Therefore, ROFA control systems will not be evaluated as a specific
6 See, MobotecUSA at www.mobotecusa.com.
7 Coombs, K.A., Crilley, J.S., Shilling, M., Higgins, B., “SCR Levels of NOx Reduction with ROFA and
Rotamix (SNCR) at Dynegy’s Vermilion Power Station,” Presented at 2004 Stack Emissions Symposium,
Clearwater Beach, Florida, July 28-30, 2004.
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