5-9
Potential (new) coal-fired, combined cycle, and IGCC units are modeled to be constructed with
SCR systems and designed to have emission rates ranging between 0.01 and 0.06 lb
NO
x
/MMBtu. EPA Base Case v.4.10 cost assumptions for these units include the cost of SCR
5.2.3 Methodology for Obtaining SCR Costs for Coal Units
As with the update of SO
2
control costs, Sargent and Lundy employed an engineering build-up of
the capital, fixed and variable operating and maintenance components of cost to update post-
combustion NO
x
control costs. This section describes the approach used for SCR. The next
section treats SNCR. Detailed example cost calculation spreadsheets for both technologies can
be found in Appendix 5-2.
For cost calculation purposes the Sargent and Lundy methodology calculates plant specific NO
x
removal efficiencies, i.e., the percent difference between the uncontrolled NO
x
rate
29
for a model
plant and the cost calculation floor NO
x
rate corresponding to the predominant coal rank used at
the plant ( 0.07 lb/MMBtu for bituminous and 0.05 lb/MMBtu for subbitumionus and lignite coals).
For example, a plant that burns subbitumionus coal with an uncontrolled NO
x
rate of 0.1667
lb/MMBtu, and a cost calculation floor NO
x
rate of 0.05 lb/MMBtu would have a removal efficiency
of 70%, i.e., (0.1667 – 0.05)/0.1667 = 0.1167/0.1667 = .70. The NO
x
removal efficiency so
obtained figures in the capital, VOM, and FOM components of SCR cost.
Capital Costs
: In building up SCR capital costs, four separate cost modules were included: SCR
island (e.g., inlet ductwork, reactor, and bypass), reagent preparation, air pre-heater modification,
and balance of plan (e.g., ID or booster fans, piping, and auxiliary power modification). Air pre-
heater modification cost only applies for plants that burn bituminous coal whose SO
2
content is 3
lbs/MMBtu or greater, where SO
3
control is necessary. Otherwise, there is no air pre-heat cost.
For each of the four modules the cost of foundations, buildings, electrical equipment, installation,
and average retrofit difficulty were taken into account.
The governing cost variables for each module are indicated in Table 5-3. All four capital cost
modules, except reagent preparation, are functions of retrofit difficulty, coal rank, heat rate, and
unit size. NO
x
rate (expressed via the NO
x
removal efficiency) affects the SCR and reagent
preparation cost modules. Not shown in Table 5-3, heat input (in Btu/hr) also impacts reagent
preparation costs. As noted above, the SO
2
rate becomes a factor in SCR cost for plants that
combust bituminous coal with 3 lbs SO
2
/MMBtu or greater, where air pre-heater modifications are
needed for SO
3
control.
As with FGD capital costs, the base module costs for SCR are summed to obtain total bare
module costs. This total is increased by 30% to account for additional engineering and
construction fees. The resulting value is the capital, engineering, and construction cost (CECC)
subtotal. To obtain the total project cost (TPC) the CECC subtotal is increased by 5% to account
for owner’s home office costs, i.e., owner’s engineering, management, and procurement costs.
Whereas the resulting sum is then increased by another 10% for FGD, for SCR it is increased by
6% to factor in an Allowance for Funds used During Construction (AFUDC) over the 2-year
engineering and construction cycle (in contrast to the 3-year cycle assumed for FGD). The
resulting value, expressed in $/MW, is the capital cost factor that is used in EPA Base Case
v.4.10.
Variable Operating and Maintenance Costs (VOM)
: For SCR Sargent and Lundy identified four
components of VOM: (a) costs for the urea reagent, (b) costs of catalyst replacement and
disposal, (c) cost of required steam, and (d) cost of additional power required to run the control
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More precisely, the uncontrolled NO
X
rate for a model plant in EPA Base Case v.4.10 is the
capacity weighted average of the Mode 1 NO
X
rates of the generating units comprising the model
plant. The meaning of “Mode 1 NO
X
rate” is discussed in section 3.9.2 and Appendix 3-1 (“NO
X
Rate Development in EPA Base Case v.4.10).