TM 5-815-1/AFR 19-6
d. Procedure. A technical program for implementing
c. Copper oxide is used as the acceptor for SO2
a NOx reduction program should proceed with the aid
removal, forming copper sulfate. Subsequently both
of equipment manufacturers and personnel who have
the copper sulfate which was formed and the copper
had experience in implementing each of the NOx
oxide catalyze the reduction of NO to nitrogen and
reduction techniques that may be required in the
water by reaction with ammonia. A regeneration step
following manner:
produces an SO2 rich steam which can be used to man-
ufacture by-products such as sulfuric acid.
should be performed during normal boiler
load times to ascertain actual on-site NOx
11-5.
Step-by-step NOx reduction method
generation. This test should include recording
a. Applicability. The application of NOx reduction
of normal boiler parameters such as: flame
techniques in stationary combustion boilers is not
temperature; excess air; boiler loads; flue-gas
extensive. (However, NOx reduction techniques have
temperatures; and firing rate. These
been extensively applied on automobiles.) These tech-
parameters can be referred to as normal
niques have been confined to large industrial and utility
operating parameters during subsequent
boilers where they can be more easily implemented
changes in operation.
where NOx emissions standards apply, and where
(2) Reduction capabilities. The desired reduction
equipment modifications are more economically justi-
in NOx emissions, in order to comply with
fied. However some form of NOx control is available
standards, should be estimated based on mea-
for all fuel-burning boilers without sacrificing unit
sured NOx emission data. Specific NOx re-
output or operating efficiency. Such controls may
duction techniques can then be selected based
become more widespread as emission regulations are
on desired reductions and reduction capa-
broadened to include all fuel-burning boilers.
bilities outlined in preceding paragraph 11-3.
b. Implementation. The ability to implement a par-
(3) Equipment optimization. Any realistic pro-
ticular combustion modification technique is dependent
gram for NOx reduction should begin with an
upon furnace design, size, and the degree of equipment
evaluation and overhaul of all combustion
operational control. In many cases, the cost of con-
related equipment. A general improvement of
version to implement a modification such as flue-gas
boiler thermal efficiency and combustion effi-
recirculation may not be economically justified. There-
ciency will reduce the normal level of NOx
fore, the practical and economic aspects of boiler
emissions. Of major importance are:
design and operational modifications must be
(a) the cleanliness of all heat transfer surfaces
ascertained before implementing a specific reduction
(especially those exposed to radiative heat
technique.
absorption),
(1) Temperature reduction through the use of
(b) maintaining proper fuel preparation (siz-
two stage combustion and flue-gas
ing, temperature, viscosity),
(c) insuring control and proper operation of
recirculation is most applicable to high heat
combustion equipment (burners nozzles,
release boilers with a multiplicity of burners
air registers, fans, preheaters, etc.),
such as utility and large industrial boilers.
(d) maintaining equal distribution of fuel and
(2) Low excess air operation (LEA) coupled with
air to all burners.
flue-gas recirculation offers the most viable
(4) Low excess air operation. Low excess air
solution in smaller industrial and commercial
operation is the most recommended modific-
size boilers. These units are normally
ation for reducing NOx emission. Possible
designed for lower heat rates (furnace
reductions are given in preceding table 11-2.
temperature) and generally operate on high
How-ever, a control system is needed to
levels of excess air (30 to 60%).
accurately monitor and correct air and fuel
c. Compliance. When it has been ascertained that
flow in response to steam demands. Of the
NOx emissions must be reduced in order to comply
control systems available, a system incorpo-
with state and federal codes, a specific program should
rating fuel and air metering with stack gas O2
be designed to achieve the results desired. The
correction will provide the most accurate
program direction should include:
control. A system of this nature will generally
-- an estimate of the NOx reduction desired,
pay for itself in fuel savings over a 2 to 3-year
-- selection of the technique or combination
period, and is economically justified on
thereof, which will achieve this reduction;
industrial boilers rated as low as 40,000 lb of
-- an economic evaluation of implementing each
steam/hr.
technique, including equipment costs, and
(5) Flue-gas recirculation. Flue-gas recirculation
changes in operational costs;
is the second most effective NOx reduction
-- required design changes to equipment
technique for boilers where two stage
-- the effects of each technique upon boiler
combustion cannot be applied. Low excess
performance and operational safety.
11-5
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