Oklahoma Gas & Electric Muskogee Generating Station Best ...

Oklahoma Gas & Electric
Muskogee Generating Station – BART Determination
May 28, 2008
term boiler NOx emissions will be higher under certain operating conditions. Furthermore,
the mechanisms used to reduce NOx formation (e.g., cooler flame and reduced O2
availability) also tend to increase the formation and emission of CO and VOCs.
Based on information available from burner control vendors, emissions achieved in practice
at existing similar sources, and engineering judgment, it is expected that combustion
controls, including LNB and OFA, on the tangentially-fired Muskogee boilers can be
designed to meet the presumptive NOx BART emission rate of 0.15 lb/mmBtu
(approximately 110 ppmvd @ 3% O2). An average emission rate of 0.15 lb/mmBtu should
be achievable on a 30-day rolling average basis under all normal boiler operating
conditions and while maintaining acceptable CO and VOC emission rates.
3.2.1.2 Flue Gas Recirculation
Flue gas recirculation (FGR) controls NOx by recycling a portion of the flue gas back into
the primary combustion zone. The recycled air lowers NOx emissions by two mechanisms:
(1) the recycled gas, consisting of products that are inert during combustion, lowers the
combustion temperatures; and (2) the recycled gas will reduce the oxygen content in the
primary flame zone. The amount of recirculation is based on flame stability.
FGR control systems have been used as a retrofit NOx control strategy on natural gas-fired
boilers, but have not generally been considered as a retrofit control technology on coalfired
units. Natural gas-fired units tend to have lower O2 concentrations in the flue gas and
low particulate loading. In a coal-fired application, the FGR system would have to handle
hot particulate-laden flue gas with a relatively high O2 concentration. Although FGR has
been used on coal-fired boilers for flue gas temperature control, it would not have
application on a coal-fired boiler for NOx control. Because of the flue gas characteristics
(e.g., particulate loading and O2 concentration), FGR would not operate effectively as a
NOx control system on a coal-fired boiler. Therefore, FGR is not considered an applicable
retrofit NOx control option for Muskogee Units 4 & 5, and will not be considered further in
the BART determination.
3.2.2 Post-Combustion Controls
Post-combustion NOx control systems with potential application to Muskogee Units 4 & 5 are
discussed below.
3.2.2.1 Selective Non-Catalytic Reduction
Selective non-catalytic reduction (SNCR) involves the direct injection of ammonia (NH3)
or urea (CO(NH2)2) at high flue gas temperatures (approximately 1600ºF - 1900ºF). The
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