POWER December 2015 - 57

GAS-FIRED POWER
2. Autopilot. The ECOMAX automated combustion tuning system is capable of monitoring
a range of key turbine operating parameters and keeping output within a specified range to
avoid emissions problems and to maintain peak performance. Courtesy: EthosEnergy
EthosEnergy says the ECOMAX TruCurve
package can improve heat rate by
0.20% to 0.25% and boost power output by
up to 11 MW, depending on the size of the
plant.
Another, more outside-the-box upgrade
will have on performance.
" It can catch up to you over time, and
you are really hurting yourself. You pay
for that pressure drop in your overall efficiency. "
Operational
Adjustments
Another performance element Fassett recommends
that operators think about is the
low-load setpoints on their gas turbines-
not just because of effects on the gas turbine
but also the downstream effects on the
steam turbine.
" When the steam turbine is operating at
low loads, you can exhaust the thermal energy
before the steam reaches the final stages
and get condensation. That can cause erosion
of the turbine blades. "
Fassett said low-load setpoints for the gas
turbines need to consider effects not just on
the turbines themselves but also on the rest
of the plant.
Aftermarket Add-Ons
In addition to relatively simple tweaks, there
are more sophisticated aftermarket tuning solutions
that can be added to existing plants.
EthosEnergy has marketed its ECOMAX
automated combustion tuning system for several
years. ECOMAX is designed to address
performance instabilities that can result from
manual tuning to maintain emissions compliance,
particularly for NOx
. Operating with
lean premixed flames in the combustor keeps
NOx
low but can cause instability in combustion
dynamics, which can damage turbine
components over time. These instabilities are
exacerbated by large ambient temperature
swings-common in many areas where gas
is a major element of the power mix, such as
the U.S. Southwest and West Coast-as well
as by fuel quality and instrument drift. When
the operating envelope strays outside the optimized
range, performance will suffer and
emissions can fall out of compliance.
is the Turbophase compressed air peaking
power system. Offered by Jupiter, Fla.-
based Powerphase, the Turbophase unit
uses a separate reciprocating engine to
add additional compression to the turbine
air inlet, without the use of steam or water
injection, which can cause operational
issues. Powerphase says this system allows
faster peaking response than existing
options, allowing 10% to 20% additional
peaking power capability and up to 7% heat
rate improvement, depending on the model
of turbine. (For more on Turbophase, see
" Quickly Boost Your Combustion Turbine
Response " in the October 2014 issue, online
at powermag.com.)
Low-Load Combined Cycle
Operation
Combined cycle plants often do not operate
in combined cycle mode at low loads because
the system is optimized for baseload operation,
and improper optimization can result in
damage to the heat recovery steam generator,
as well as emissions violations. However,
giving up the ability to operate at low loads
can mean lost revenue.
Many of the newest models of combined
Using [HEPA] filters can recover 6% of
the power output normally lost to engine
fouling.
Other efficiency losses can be found and
eliminated by thinking about ways energy
may be escaping the system.
" One site we worked with has an auxiliary
boiler and is using it to keep vacuum
on the steam turbine generator, " Fassett
said. " All excess steam is being piped to
the heat-recovery steam generator (HRSG)
to keep the boilers warm, so hot restarts
are minimized. " Another relatively simple
tweak is installing heat blankets to insulate
the steam turbine, which cuts down on cold
restarts, he said.
December 2015 | POWER
Using real-time monitoring of combustion
and emissions, the ECOMAX system
automatically tunes combustion to keep the
turbine within the optimized operational envelope
(Figure 2). ECOMAX can communicate
directly with the turbine or integrate
with the plant's digital control system.
ECOMAX can also be used to boost performance,
as necessary, with the addition
of the Tru-Curve option, which raises the
baseload fuel-air ratio while still controlling
emissions and combustion dynamics. TruCurve
can be turned on and off as desired.
www.powermag.com
cycle plants are designed for load following
and low-load operation, but with the right
approach, some older plants can optimize
their operations for low-load generation as
well. The Electric Power Research Institute
(EPRI) recently conducted a proprietary
study determining the best ways to optimize
combined cycle operation at a plant using
GE 7FA turbines. Though proper optimization
procedures will vary from plant to plant
and depend on operational profiles, the EPRI
study found that a tradeoff between lower
exhaust gas temperature and higher exhaust
flow would allow lower-load operation without
damage to the HRSG and without causing
NOx
emissions to spike.
ing of NOx
Making it work requires careful monitorand
CO emission levels, combustion
dynamics, attemperator performance,
main steam-line superheater level, and inletguide
vane position, in order to determine
the minimum generation load at the lowest
possible turbine-exhaust temperature.
Though there are trade-offs with nearly
any performance enhancement, plant operators
have more options these days than
ever. ■
-Thomas W. Overton, JD is a POWER
associate editor.
57

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POWER December 2015

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