POWER March 2015 - 46

COMBINED CYCLE GAS TURBINES
Are Flexible Generation Plants
Performing as Expected?
Highly flexible, fast-ramping, fast-cycling combined cycle plants hit the market
with a big splash a few years ago. But are they performing as advertised?
Though the few operational plants are still new and still learning, the initial
results are encouraging.
Thomas W. Overton, JD
T
he Lodi Energy Center (LEC) is a 296MW
1 x 1 combined cycle plant in
Lodi, Calif., just north of Stockton and
east of the San Joaquin River delta (Figure 1).
From the outside, there's little to distinguish
it from the many other combined cycle plants
large and small that power the California Independent
System Operator (CAISO) grid.
On the inside, though, there's much to set
this plant, which began commercial operations
in November 2012 and earned a POWER
Top Plant award that year, apart from its older
brethren. LEC was one of the first plants in
a new generation of combined cycle facilities
specifically designed for fast starts and fast
ramping while maintaining both high efficiency
and low emissions.
LEC is operated by the Northern California
Power Agency (NCPA) and owned by NCPA
and a coalition of local public power agencies
in the area. A turnkey plant delivered by
Siemens, which refers to the design as a FlexPlant
30, it's built around Siemens' SCC65000F
gas turbine, which is paired with a
Nooter Eriksen triple-pressure reheat heatrecovery
steam generator (HRSG) equipped
with a once-through Benson high-pressure
section, high-capacity steam attemperation,
and full-capacity steam bypass systems.
LEC also utilizes innovative piping warmup
strategies, a Siemens SPPA-T3000 control
system and steam turbine stress controller,
and optimized plant stand-by using auxiliary
steam to maintain vacuum. The plant has as
many analyzers and system drains as a conventional
3 x 1 plant.
Another Siemens Flex-Plant, NRG Yield's
two-unit, 550-MW El Segundo Energy Center,
came online in 2013; two more, Panda
Power Funds' Temple I and Sherman plants
(both 2 x 1 758-MW plants), started up in
Texas in 2014.
Designed for intermediate to continuous
cycling duty, LEC manages efficiencies
above 57% with startup times that are as
short as half those of earlier plants due to the
integration of fast-start features. Ramping at
13.4 MW/minute from a cold start, the plant
can reach 150 MW output in a little over
10 minutes, and the fast ramp rate means it
reaches CO compliance in 23 minutes and
NOx
compliance in 40 minutes.
That's performance that is becoming
critically important with continually increasing
amounts of renewable generation being
added to CAISO. California already has the
nation's highest state renewable portfolio
standard, 33% by 2020, and Governor Jerry
Brown announced in January that he would
seek to raise it even further, to 50% by 2030.
That means the state's gas-fired fleet will be
called upon to back up an enormous amount
1. Fast start for a fast starter. The Lodi Energy Center in California was the first U.S. plant
to employ Siemens' Flex-Plant technology. In the first two years, it's totaled 380 starts and achieved
94% availability. Courtesy: Siemens
of variable wind and solar generation.
But Does It Work?
All that, at least, was the intent. But are LEC
and the new highly flexible plants like it living
up to the hype?
The question is not an idle one. A 2012
study by the National Renewable Energy
Laboratory and Intertek APTECH found that
shifting to faster ramping and startups from a
baseload role resulted in considerably higher
operational and maintenance costs for typical
combined cycle plants. Worse, these costs
increased with greater penetration of renewable
generation into the energy mix.
In the case of LEC, at least, according to
Plant Manager Michael DeBortoli, the answer
is an unqualified yes.
" It has lived up to our expectations, " he
told POWER in an interview in January. " So
far, the plant has been running very well. We
cycle a lot and have a lot of starts and stops
almost on a daily basis, and everything has
been running fine. "
DeBortoli confessed some concern with
being what amounted to a guinea pig for the
new design. " Being the first one in the country
with this new technology, " he said, " I thought
we were going to encounter a few hiccups, but
the plant has been operating to expectations. "
LEC has been a workhorse since it came online.
From November 2012 through the end of
January 2015, the plant racked up an impressive
380 starts despite two planned outages. Over
that period, it's achieved 94% availability.
The plant is regularly being ramped from
165 MW minimum load to maximum output.
" That's basically achieved within a 10-minute
interval, " DeBortoli said. " The gas turbine is
being run at the max ramp rate. "
And it's being done without any excessive
wear and tear on the HRSG. " The Benson
technology, which is the once-through HP
section, we have not had any issues on that, "
DeBortoli said. " All of our bypass valves
have been working very well. "
In the Benson once-through natural-circu46
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