POWER July 2012 - 73

ELECTRIC POWER 2012: WHERE THE GENCOS MEET
Gas Glut Drives Action in
Combined Cycle Power
A diverse range of speakers reviewed the state of gas-fired generation at
ELECTRIC POWER, but there was one constant: flexibility.
By Thomas W. Overton, JD
L
ow gas prices and increasing demand
for highly flexible power generation
are driving innovation and expanded
use of gas-fired power, according to numerous
speakers in the gas turbine/combined
cycle power plant track at ELECTRIC
POWER.
The track began with presentations from
representatives of Alstom, Mitsubishi, GE,
and Siemens, who outlined upgrades to their
workhorse gas turbine models. All stressed
the importance of being able to respond to
rapidly changing demand. The impact of
greater renewable generation, and its varying
and often unpredictable output, was a theme
that many speakers returned to during the
week.
No One-Size-Fits-All Approach
Case study and best practices presentations
on Wednesday and Thursday made clear that
with gas-fired power growing in significance,
efficient operation requires attention to detail.
Flexibility is key: One-size-fits-all approaches
are not allowed.
Colleen Layman, water treatment engineering
manager at Bechtel, delivered a lively
talk on plant chemistry. Chemistry programs
for heat recovery steam generators (HRSGs)
have their own demands and constraints
distinct from those for water-tube boilers,
largely because they operate at multiple pressures
and temperatures. For example, while
maintaining proper phosphate levels to prevent
corrosion is important across all steam
boilers, HRSGs have a particular problem
with " phosphate hideout " (a condition under
which phosphate concentrates in certain
areas, causing inaccurate test readings and
overfeed of phosphates) due to plant cycling.
Phosphate hideout is known to be increased
by the use of duct burners.
Layman cautioned that plant chemistry
needs to be based on the highest system pressure,
and that careful thought needs to be given
to each plant's unique characteristics and
operating parameters. Different approaches
can be taken for specific plants, but operators
need to be aware of the consequences of
their choices.
July 2012 | POWER
1. Up to the challenge. Panel members for the CCGT Design & Engineering Challenges
session were (left to right) Richard Boulay, URS Corp.; Colleen Layman, Bechtel Power Corp.;
and Harpreet Singh, Alstom. Source: POWER
Because of phosphate hideout issues,
plants that cycle frequently, and those that
fast start, are better served by the use of allvolatile
treatment rather than phosphate treatment,
provided that high water quality can be
maintained. Full flow condensate polishing
is also recommended for such units.
Plant Case Studies
Richard Boulay, consulting engineer with
URS, reviewed his firm's experience converting
a Midwestern coal plant to gasfired
generation. Engineers compared
options for repowering the plant and reusing
its existing 180-MW steam turbine
or replacing it with a new combined cycle
power plant. Several considerations went
into the decision:
■ There was only room for a single H-class
turbine in the existing plant, but room for
a 2 x 1 F-class configuration elsewhere on
the site if the plant were replaced.
■ The existing plant used once-through
cooling, which would have to be replaced
with a cooling tower.
■ The repowered steam cycle would have
all existing feedwater heater extractions
blanked off with a low-pressure admission
introduced at the crossover point.
www.powermag.com
After analyzing the options, URS found
that although a new plant would generate
more total power (603 MW vs. 429 MW), a
repowered plant would produce lower costs
per kilowatt over the projected 30-year lifetime
based on a 50% capacity factor. However,
they found that a repowered plant would
have a slightly higher forced outage rate.
Harold Guidotti, engineering director with
Pratt & Whitney Power Systems, gave an
update on Northwestern Energy's regulating
reserve plant, which was profiled in the
December 2011 issue of POWER. Though
the plant showed premature distress on some
components, the modular design project engineers
chose allowed rapid change-out with
minimal downtime.
Ben Frerichs, assistant mechanical
engineer with Burns & McDonnell, described
an ongoing repowering project at
the Moselle Generating Plant, owned and
operated by South Mississippi Electric
Power Association. Two of the three existing
gas-fired boilers are being replaced by
a 1 x 1 arrangement of GE 7FA turbines
and Vogt Power HRSGs, which will boost
output from 60 MW to 150 MW. Much of
the original steam cycle is being reused,
including the steam turbines (which were
refurbished), feed pumps, condensate
69

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POWER July 2012

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