POWER June 2013 - 41

PLANT DESIGN
the 560 MW minimum net rating with a
small amount of duct firing, while the 7FA
5-Series plant exceeds the standard without
duct firing. The heat rate of the new plant
is slightly higher than that of the repowered
options because the 2 x 1 plants are
based on current F-Class technology rather
than the H-Class unit used as a basis for the
repowered unit. However, the 2 x 1 plants
offer substantially higher power output and
the 2 x 1 configurations allow greater turndown
range for part-load operation.
The plant based on the new 7FA 5-Series
provides about 70 MW more output at essentially
the same unfired heat rate as the
7FA 3-Series. Therefore, the 7FA 5-Series
was selected as the basis for developing the
capital and operating cost estimates.
Capital Cost Estimates
URS prepared total plant cost (TPC) estimates
for three options. A TPC estimate includes
equipment costs, labor costs, indirect
The 7FA 5-Series was selected as the basis
for developing the capital and operating
cost estimates.
construction costs, engineering, startup and
testing costs, and contingencies. It excludes
taxes, interest during construction, costs to
obtain permits, and owner's engineer cost.
The TPC estimates were based on first quarter
2013 dollars.
■ Repower existing steam turbine unit: $407
million or $979/kW, based on 416.1 MW
annual average power rating.
■ Repower existing steam turbine unit and
upgrade HP/IP steam paths: $414 million
or $965/kW, based on 429.5 MW annual
average power rating.
Table 4. Estimated performance of a new 2 x 1 combined cycle. Note that
the 7FA 3-Series option requires a slight amount of duct firing to achieve the minimum plant net
output of 560 MW, while the 7FA.05-based plant does not. Source: URS Corp.
Combustion turbines
Duct firing (%)
Total CTG output (MW)
STG output (MW)
Total auxiliary loads and
losses (MW)
Net output (MW)
Combined CTG fuel
Combined HRSG fuel
Net plant heat rate
2 x 1 7FA 3-Series
Plant power generation (MW)
361.6
186.4
15.3
532.6
Fuel consumption (MMBtu/hr)
3,588
6,737
2 x 1 7FA 3-Series
100
361.6
215.2
16.1
560.6
3,588
244
6,835
2 x 1 7FA 5-Series
NA
412.2
208.2
17.4
603.1
4,065
NA
6,740
Notes: NA = not applicable. Fuel calorific value used is HHV. CTG = combustion turbine generator, HRSG = heat recovery
steam generator, STG = steam turbine generator.
Table 5. Levelized cost of electricity analysis. The analysis is based on a 30-year
plant life and operation at an average annual 50% capacity factor. The repower option with upgraded
steam path was found to have a 5% cost of electricity advantage. Source: URS Corp.
Configuration
Levelized cost of electricity
components ($/MWh)
Fuel cost
Fixed charges
Variable O&M
Fixed O&M
Levelized COE ($/MWh)
1 x 1 Repower 1 x 1 Repower
Existing STG
New HP/IP
$82.62
$28.53
$7.49
$4.54
$123.17
$81.82
$28.39
$7.49
$4.54
$122.24
New 2 x 1
NGCC
$82.02
$34.76
$7.65
$3.57
$128.00
Notes: STG = steam turbine generator, HP = high pressure, LP = low pressure, NGCC = natural gas combined cycle.
June 2013 | POWER
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■ New 2 x 1 7FA.05 combined cycle: $678
million or $1,124/kW, based on 603 MW
annual average power rating.
It is interesting to observe that the cost
of the steam paths upgrade increases TPC
by $7 million for the repowered option but
reduces the plant installed cost per kilowatt.
The repowering with steam path upgrades
option also improved the plant heat rate
and extends the life of the steam turbine.
The cost per kilowatt for the new combined
cycle plant is about 15% higher
than for the repowered option. This cost
penalty will be offset to some extent by
reduced maintenance on the new steam
turbine and new condenser and a slightly
lower heat rate.
Cost of Electricity Estimates
The cost of electricity was estimated for
each of the three options over an assumed
30-year plant life. Operation and maintenance
costs were derived from a URS database
for similar plants, and life-cycle fuel
cost was estimated using the Department of
Energy Annual Energy Outlook forecast of
natural gas prices. An annual capacity factor
of 50% was assumed for each analysis.
The results of the case study show that repowering
of the existing steam unit provided
better life-cycle economics than construction
of a new combined cycle plant. Table
5 shows the cost components that form the
levelized cost of electricity (LCOE) estimate.
The repowered options show a LCOE
advantage of about 5% relative to the new
combined cycle. The benefits of lower construction
cost and the higher efficiency of
the H-Class combustion turbine technology
for the repowered unit outweigh the lower
efficiency of the existing steam turbine.
Many site-specific constraints and design
and construction decisions made in
the course of the study led to this conclusion.
A key finding was that the investment
in upgrading the existing turbine's
HP/IP steam paths with modern technology
is a good investment. Your site-specific
factors may lead you to a different conclusion,
even for a similar plant. ■
-R.B Boulay, PE, and M.S. Massoudi,
PE, PhD, URS Corp., Energy &
Construction Division.
41

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POWER June 2013

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