POWER July 2013 - 60

ELECTRIC POWER 2013: FLEXIBILITY AND ADAPTABILITY
Is Gas Getting Too Hot to Handle?
With ever-increasing demands for fast ramping and flexibility, natural gas-fired
plants are grabbing a bigger share of the generation pie. But uncertainty
about future prices and concerns about overreliance on a single fuel are
dampening enthusiasm during what may be the most exciting time for gas
ever. Natural gas is hot-but will generators and the market get burned?
By Thomas Overton
I
n a series of standing-room-only sessions
in Track 2: Gas Turbine/Combined
Cycle Power Plants at ELECTRIC
POWER 2013, an array of speakers
from generating companies, manufacturers,
and service providers reported on best
operation and maintenance practices and
new options in gas-fired power generation,
particularly cycling existing plants and
building distributed and combined heat and
power plants (Figure 1).
The Challenges of Frequent Cycling
With the rapidly expanding role of wind in
the generation mix, the ability to ramp up
and down quickly is a gas-fired plant's biggest
advantage. Rapid cycling, however, can
come with hidden costs, explained Douglas
Hilleman of Intertek. Too often, plant owners
make assumptions about these costs
without drilling down into the details, even
though small changes can reap big returns
in more profitable operations. Not knowing
the true costs of cycling operations can
leave a substantial amount of money on the
table. " It's not just fuel, " Hilleman said, " it's
the latent costs. "
Hilleman reported on Intertek's cycling
analysis for Xcel Energy's peaking plant in
Riverside, California. A full understanding
of cycling costs allowed Xcel to tailor its
dispatch plans to the true costs, and do it
without capital investments or hardware
modifications. While a comprehensive
analysis of cycling operations can be costly,
the returns are big enough that it can
pay for itself in a few months. In the case
of the Riverside plant, simply reducing the
ramp rate by 33% saved thousands of dollars
in maintenance costs.
When a plant owner needs to shift gears
in a changing market, careful analysis is
key, reported Brian Eskra of Power Engineers
Collaborative. Eskra described a
study performed for a client in Southern
California that needed to retire its steam
electric plants and replace them with combined
cycle plants in order to meet the demands
of the CAISO market and changing
60
1. Full house. Attendees in the gas track learned about meeting the challenges of the gas
market. Source: POWER
regulations in the state. Recognizing that
intermediate and peaking generation offered
the best market niche was only the
start, Eskra said. Analysis of the various
options, market demands, and the returns
on investment led to development of a 3 x
1 block configuration utilizing Mitsubishi
Heavy Industries D/E class turbines.
Scott Polemus of LTSA Options described
ways that plant owners can optimize their
long-term service agreements (LTSAs). The
market has changed in the past few years,
and it's worth reevaluating and renegotiating
existing LTSAs for cost savings and/or
increased benefits. Owners can restructure
agreements to provide for more cost and risk
sharing, Polemus explained. With the growing
role of and demands on gas-fired plants,
it's time to determine if an LTSA is still serving
a plant's needs.
Even when a plant is optimized for its
market, however, there's no guarantee it's
going to stay that way: Wear and tear from
www.powermag.com
frequent cycling and ramping, along with
changes in weather and fuel properties, can
reduce a plant's operating windows. That's
why regular tuning is important, explained
Donald Gauthier, senior technical lead for
Power Systems Manufacturing (PSM).
These kinds of changes will increase turbine
dynamics, and running with high dynamics
can be very expensive, whether the
costs result from lean blowouts (LBOs) or
accelerated equipment wear.
While manual tuning will work, automated
tuning systems are preferable because
of faster response and reduced maintenance.
PSM's AutoTune system offers one solution
for 7FA units. AutoTune automatically manages
combustion dynamics to reduce the risk
of LBO and improve emission control, while
maximizing power output.
In combined cycle plants, however,
proper tuning extends beyond the turbine.
Rapid cycling also places demands on the
heat recovery steam generator (HRSG), exPOWER
| July 2013
http://www.powermag.com
POWER July 2013

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