Nitrogen oxides
(NOx) are air pollutants produced during coal combustion. The rate
of NOx formation depends on combustion temperature
and
available oxygen and can rise significantly if not properly controlled.
Consequently, combustion control techniques can influence and
minimize the formation of NOx.
The Rawhide Operating
Permit issued by the State of Colorado limits the NOx emission
rate, which is controlled by the tangentially
fired design of Rawhide's
boiler and the use of an enhanced low-NOx combustion control system.
The tangential boiler design provides improved fuel-air mixing and
combustion staging over other boiler designs, resulting in lower
NOx emissions.
Rawhide's enhanced combustion control (ECC) system utilizes the
latest in boiler burner technology, separated over-fire air registers
and a computerized control system that continuously monitors combustion
variables such as air damper positions, burner tilts, coal feeder
speeds and other process parameters and makes adjustments to keep
NOx emissions
below the permitted rate. The ECC system provides an additional 50%
reduction in NOx emission over the emission rates generally achievable
from the
tangential boiler design.
Click for tangentially fired boiler diagram
