Advanced SNCR Chemical Injection Model Visualization
Source: Doosan Power Systems America
Temperature window and chemical injection model visualization Chemical droplet trajectories tuned to
change in temperature window
Department of Energy (DOE) of fuel
gas reburning combined with LNB on a
wall-fired boiler reported that 70 percent
NOx reduction could be achieved, with
estimated installed capital cost of around
$26 per k W for a hypothetical 300-MW
cyclone boiler fired with 3 percent sulfur
Fuel Biasing: Fuel biasing diverts fuel
from the upper-level burners to the lower
ones to create a fuel-rich lower zone and a
fuel-lean upper zone in operation, resulting in a reduction in NOx emissions of up
to 30 percent.
Flue Gas Recirculation: Flue gas recirculation (FGR) recirculates 20 to 30
percent of the boiler flue gas from either
the airheater inlet (hot FGR) or the ID
fan outlet (cold FGR) into the furnace
or burner. The resulting dilution in the
flame reduces flame temperature and
availability of oxygen, thereby reducing thermal NOx formation. The
FGR technique is used mainly in low-NOx gas burners in gas-fired plants.
In coal-fired plants, the FGR can inhibit the combustion efficiency to an
with NOx to turn it into Nitrogen gas.
The combustion is completed in an oxy-gen-lean environment to minimize additional NOx formation.
A low-NOx burner retrofit can achieve
NOx reduction on the order of 40 to 70
percent, at an installation cost of $5 to $10
per kilowatt (k W).
Over-Fire Air: Furnace OFA technology
separates combustion air into two separate streams. A primary flow of between
70 to 90 percent of the total combustion
air is routed to the burners, and a secondary flow of 10 to 30 percent of the
total combustion air is injected above the
burner elevation. This allows two-stage
combustion to take place.
In the first stage, the air flow to the
burner is mixed with the fuel at the
burner, producing an oxygen-deficient,
fuel-rich zone in which the formation of
fuel NOx is minimized, and the fuel is
In the second stage, the balance of the
combustion air is injected through the
OFA nozzles into the furnace, where the
combustion is completed.
Optionally, boosted over-fire air
(BOFA) can be used, where a fan is used
to inject the OFA into the unit at a higher
velocity. This promotes improved mixing
of the OFA and the furnace gases.
OFA technology alone can achieve
NOx reduction on the order of 20 to 45
percent, at an installation cost of $4 to $7
per k W.
Fuel Reburning: Fuel reburning is a
form of fuel-staged combustion usually combined with LNB and OFA. This
method separates the combustion into
three-stages: the primary combustion
zone, the reburn zone, and the burnout
In the primary zone, coal is fired
through conventional burners or LNB in
low excess-air conditions to reduce initial
NOx formation. A secondary fuel is injected into the upper section of the furnace to create a secondary sub-stoichio-metric reburn zone without combustion
air. Natural gas is widely used for this
purpose, although coal and oil are being
In 2001, an evaluation by the U.S.