United States
Environmental Protection
Agency
National Risk Management
Research Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/SR-01/087 January 2002
Cost of Catalytic
Reduction (SCR) Application for
NO Control on Coal-fired
Boifers
Wojciech Jozewicz
The report provides a methodology
for estimating budgetary costs associ-
ated with retrofit applications of selec-
tive catalytic reduction (SCR) technology
on coal-fired boilers. SCR is a post-
combustion nitrogen oxides (NOX) con-
trol technology capable of providing NOX
reductions >90%. With SCR, NOX reduc-
tions are achieved by injecting ammo-
nia into the flue gas, which then passes
through layers of catalyst in a reactor.
The ammonia and NOX react on the sur-
face of the catalyst, forming nitrogen
and water. In the U.S., SCR has been
applied mainly to electrical utility boil-
ers firing coal and natural gas and tang-
ing in capacity from 25 to 800 MW.
The costing methodology presented
in the report is applicable to SCR retro-
fits on coal-fired boilers tanging in ca-
pacity from 100 to about 850 MW and
with design efficiencies of 80-95% NOX
removal. The cost equations and vari-
ables used in the methodology are
based on information obtained from
SCR system suppliers and reflect ex-
perience gained from >200 SCR appli-
cations. Note, however, that the
budgetary cost estimates for typical
SCR applications that this methodology
provides cannot replace the detailed
site-specific engineering cost studies
or cost quotations that are developed
by SCR system suppliers.
This Project Summary was developed
by the National Risk Management Re-
search Laboratory's Air Pollution Pre-
vention and Control Division, Research
Triangle Park, NC, to announce key find-
ings of the research project that is fully
documented in a separate report of the
same title (see Project Report ordering
information at back).
Background
Selective catalytic reduction (SCR) is a
postcombustion nitrogen oxides (NOX)
control technology capable of providing
NOX reductions >90%. With SCR, NOX
reductions are achieved by injecting am-
monia into the flue gas, which then passes
through layers of catalyst in a reactor.
The ammonia and NOX react on the sur-
face of the catalyst, forming molecular
nitrogen (N2) and water. In the U.S., SCR
has been applied mainly to electric utility
boilers firing coal and natural gas.
The report provides algorithms for esti-
mating costs and performance of generic
SCR retrofit applications on coal-fired
boilers. Specifically, the algorithms are
applicable to SCR systems with design
efficiencies of 80-95% NOX removal that
can operate on coal-fired boilers ranging
in size from approximately 100 to 850 MW.
The cost equations and variables are
based on industrial experience gained
from >200 SCR applications. Note that
the algorithms presented in this work are
not meant to replace the detailed engi-
neering studies or cost quotations that
are developed by system suppliers, nor
should these algorithms be used to de-
termine detailed site-specific costs for ret-
rofit SCR applications.
The Costing Algorithms
SCR budgetary costing algorithms for
capital as well as fixed and variable op-
erating and maintenance (O&M) costs (in
January 2000 dollars) are given below.
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The capital cost, D ($/kW), of an SCR
retrofit application is estimated using
Equation (1):
D = 75 {300,000 Z/A}035 (1)
where:
Z = [(B/1.5)° °5(C/100)°4]
and
D = capital cost ($/kW)
75 = capital cost ($/kW) associated with a
typical SCR retrofit on a 300,000 kW
coal-fired unit
300,000 = reference to a 300,000 kW
baseline unit (basis for the economy-
of-scale adjustment in the equation)
B = NOX (lb/106 Btu) at the inlet of the
SCR reactor; range of approximately
0.15-2.5 lb/106 Btu
0.05 = exponent for inlet NOX concentra-
tion
C = NOX removal efficiency (%); range of
80-95%
0.4 = exponent for NOX removal efficiency
A = plant capacity (kW); range of approxi-
mately 100,000-850,000 kW
0.35 = exponent for an economy-of-scale
adjustment factor (scaled from a
300,000 kW unit)
The complexity of an SCR system design
is dependent on the plant layout. For ex-
ample, a relatively constrained plant lay-
out may involve a more difficult SCR system
design compared to a relatively uncon-
strained layout and, therefore, may require
more ductwork and air heater modifica-
tions. In contrast, a relatively uncon-
strained layout may not need air heater
modifications and more than the typical
amount of ductwork. To account for vary-
ing levels of design complexity, a degree
of difficulty is associated with an SCR
retrofit application. In this context, the av-
erage degree of difficulty is assigned to a
retrofit where the SCR installation is rela-
tively simple (i.e., the facility has adequate
space for the SCR system). Equation (1)
assumes this average degree of difficulty.
The fixed O&M cost, E ($/yr), is as-
sumed to be 0.66% of the capital cost
and is estimated using Equation (2):
E = D«A«C (2)D
where: D
E = fixed O&M cost ($/yr)D
D = capital cost ($/kW) from Equation (1)D
A = plant capacity (kW); range of approxi-D
mately 100,000-850,000 kW
C = a constant; 0.0066 yr1
The variable O&M cost, F ($/yr), is esti-
mated using Equation (3):
F = G {225«[0.37B«H«(C/100)«
(8760/2000)]«1.005«1.05 +
0.025. D.A.Z+ 1.45.A} (3)
where:
F = variable O&M cost ($/yr)
G = annual capacity factor (expressed as
a fraction)
B = inlet NOX (lb/106 Btu); range of 0.15-
2.5 lb/106 Btu
H = heat input (106Btu/hr)
C = NOX removal efficiency (%); range of
80-95%
D = capital cost ($/kW)
A = plant capacity (kW); range of approxi-
mately 100,000-850,000 kW
Validation of the Costing
Algorithms
The costing methodology presented
above was derived from information pro-
vided by SCR system suppliers and is
deemed valid for typical coal-fired SCR
retrofit applications for NOX removal effi-
ciencies in the range of 80-95%. Note,
however, that this methodology is in-
tended and valid for developing budget-
ary cost estimates and assumes typical
installations. Therefore, the methodology
should not be expected to account for
reported costs of each site-specific SCR
retrofit application.
In a 1998 study conducted for North-
east States for Coordinated Air Use Man-
agement (NESCAUM) and Mid-Atlantic
Regional Air Management Association
(MARAMA), the capital cost for SCR ret-
rofit on dry-bottom wall- and tangentially
fired boilers to achieve 85% NOV reduc-
tion was estimated to be 70-90 $/kW. Simi-
larly, the study estimated that the capital
cost of SCR retrofits to achieve 90% NOX
reduction from wet-bottom boilers would
also be 70-90 $/kW. Note that these esti-
mates were based on 330 MW units. In
comparison, the costing methodology re-
sults in an estimate of approximately 70
$/kW for similar units.
Recent literature reflects a range of 55-
140 $/kW as being typical of site-specific
retrofit SCR capital costs for all types of
utility boilers. By comparison, the costing
methodology estimates a capital cost of
approximately 50-110 $/kW to achieve
85-95% NOX removal efficiency.
The NESCAUM/MARAMA report esti-
mated a combined fixed and variable
O&M cost of reducing NOX by 70-80% for
a 330 MW dry-bottom boiler at approxi-
mately $1.1 million/yr and approximately
$2.8 million/yr for a similar-sized wet-bot-
tom boiler. The costing methodology esti-
mates the combined fixed and variable
O&M costs for all boiler types to be about
$1.0 to 1.7 million/yr for 85% NOX re-
moval. In another economic analysis of
SCR retrofits on 300 and 500 MW boilers
to reduce NOX by 80-85%, combined
O&M costs were estimated to be $1.6-3.2
million/yr.
Based on the above comparisons, the
capital and O&M cost estimates derived
from applying this methodology are
deemed reasonably accurate and fall well
within the ranges reported elsewhere.
Actual cost reported from site-specific
SCR retrofit applications, as well as indi-
vidual facility engineering studies, would
more accurately reflect the circumstances
of individual facilities. As a result, it is
also reasonable to expect that reported
actual costs may not always conform to
budgetary cost estimates that have been
designed around typical installations.
While the methodology has been shown
to consistently estimate costs that fit well
with other reported actual and estimated
costs, occasionally it can be expected
that there will be data with higher or lower
costs.
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Wojciech Jozewicz is with ARCADIS Geraghty & Miller, Inc., Research Triangle
Park, NC 27709.
Ravi K. Srivastava is the EPA Project Officer (see below).
The complete report, entitled "Cost of Selective Catalytic Reduction (SCR) Appli-
cation for NOX Control on Coal-Fired Boilers," will be available at http://
www.epa.gov/ORD/NRMRLyPubs/600R01087/600R01087all.pdf. It will also
be available from NTIS (Order No. PB2002-100499; Cost: $23.00, subject to
change) at the following address:
National Technical Information ServiceO
5285 Port Royal RoadD
Springfield, VA 22161-0001D
Telephone: (703) 605-60000
(800) 553-6847 (U.S. only)
The EPA Project Officer can be contacted at:
Air Pollution Prevention and Control Division
National Risk Management Research Laboratory
U. S. Environmental Protection Agency
Research Triangle Park, NC 27711-0001
United StatesD
Environmental Protection Agency D
CenterforEnvironmental Research InformationD
Cincinnati, OH 45268D
PRESORTED STANDARDD
POSTAGES FEES PAIDD
EPAD
PERMIT No. G-35D
Official Business
Penalty for Private Use
$300
EPA/600/SR-01/087
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