58
OPERATIONAL FLEXIBILITY
Shorter start-up times:
overall start-up
efficiency increased
by 14 percent
Part-load
efficiency:
less CO2
emissions
Flexible and Efficient Fossil Fuel Plants to Make
the Vision of Renewable Energy a Reality
Combined cycle power plants that are flexible in operation and are
optimized for efficiency are ushering in the rapid growth of renewable
energy sources. A recent Siemens study examines how operational
efficiency can be improved.
FACY TM: The first
steam generated
can be delivered
to the turbine
H CLASS GAS TURBINE
MODERN GAS
TURBINES
designed with air cooling to
allow for maximum operational
flexibility.
fitted with variable pitch
guide vanes at the inlet to
the gas turbine compressor.
Text: Rhea Wessel, Illustration: Mariela Bontempi
OPERATIONAL FLEXIBILITY AT HIGHEST EFFICIENCY
Future market drivers
HEAT RECOVERY
STEAM GENERATOR
(HRSG)
• Highest efficiency
throughout the
whole load range
• Optimized start-up
and shutdown
operation
with HP Benson section
is optimized for daily startstop operation.
FAST CYCLING
Plants equipped with a complete
FACY TM package are designed for daily
start-up and shutdown at high fullload efficiency. They offer part-load
efficiency with the air preheater at
the compressor inlet.
• Load ramps
• Stable operation in
case of grid incidents
• Fast starts
• Backup power
• Park load
• Load ramps
DAILY LOAD CYCLE (SCHEMATIC) AND ITS IMPLICATIONS ESPECIALLY FOR COMBINED CYCLE POWER PLANTS
load
control
PEAK LOAD
INTERMEDIATE LOAD
over a service life of
25 years
Fuel
consumption can be
reduced by
14,700 t/year
CO2 can be
reduced by
43,000 t/year
Global renewable
capacity* reached
1,320 GW (+8%)
in 2010
* incl. hydro
POWER »
300 x 25:
7,500 starts
TIME OF DAY »
Source: Renewables 2011 Global Status Report, dena, IEA, Siemens
Pumped storage, gas turbine
peaker plants, etc.
Mainly CCPP
RENEWABLES
Replacing base load units due
to feed-in legislation
BASE LOAD
Nuclear power, hydropower,
coal-fired power plants
PRODUCT
REQUIREMENTS:
• Low generating cost
• Fast start-up
• High starting reliability
• Good part-load
capability
60
OPERATIONAL FLEXIBILITY
OPERATIONAL FLEXIBILITY
Combined cycle power plants that have
been optimized for maximum flexibility and efficiency will play an important role in stabilizing the grid as the
transition to renewable energy takes
place over the next decades and beyond. By providing flexible, on-demand
energy that is more efficient due to
features such as improved start-up
times, preheater components, and advanced gas turbines, the plants will
do their part in making the vision and
promise of renewable energy a reality.
These were the results of a study
led by Andreas Pickard, the Head of
Product Line Marketing for Combined
Cycle Power Plants in the Energy Solutions business unit of Siemens Energy.
Pickard and his colleague Gero
Meinecke, Product Line Manager for
reference power plants in the same
department, released the paper entitled
The Future Role of Fossil Power Generation in early 2011. Later that year, it
won the Best Paper Award at PowerGen
Europe 2011. The paper is based on
the VDE AT40 study that estimated residual loads for the year 2020 considering the expanding share of renewable energy.
Pickard and Meinecke’s paper, presented at the PowerGen conference in
June 2011, approaches the subject of
fossil power generation from a holistic
perspective by examining how to
improve fast-start capabilities as well
as full- and part-load efficiencies
and to increase power reserves. These
Paper Summary
The Future Role of Fossil Power Generation, a paper
by Andreas Pickard and Gero Meinecke, explores
how combined cycle power plants must become more
flexible and efficient as they supply backup power
when energy from renewable sources is not available.
Improved start-up times and better part-load efficiency
will help the plants reduce their own emissions and
meet the fluctuating demand that is expected when
32 percent of the power mix around the world comes
from renewable sources in 2035.
www.siemens.com/energy/ccpp
are widely seen as key areas to
improve if maximum operational
flexibility and efficiency are to
be achieved.
Improved Start-up Times
and Other Ways to Increase
Efficiency
Shorter start-up times make it possible to feed reserve power into the grid
and to sell that power on the spot market at short notice. Typically, when a
conventional combined cycle plant is
started up, steam is discharged via the
condenser not contributing to power
generation. With the FACYTM solution
from Siemens, the first steam generated can be delivered to the steam turbine, resulting in shorter start-up times
and improving start-up efficiency by
14 percent, at a start-up reliability
of more than 98 percent. In addition,
FACYTM limits the service-life expenditure caused by start-ups, allowing
combined cycle power plants to sustain up to 300 starts per year.
Another implication of fluctuating
power feed-in due to rising renewable
capacity is the necessity to improve
part-load efficiency so that a power
plant can be operated at as low a part
load as possible without breaching
the maximum allowable CO2 emissions
threshold. Excellent part-load efficiency helps to cut down on fuel consumption and emissions and can be
achieved with modern gas turbines
that are fitted with variable pitch guide
vanes as well as with air preheaters.
Finally, by improving flexibility, operators can comply with the regulations
in certain markets that are designed
to avoid island formation and provide
peak-load power in reserve that could
be sold on the spot market. Patented
Siemens technology, the fast wet compression system, allows combined
cycle power plants to provide required
power reserves during low-frequency
operation. For the 60-Hz market, the
SGT6-5000F gas turbine has been
developed to deliver up to 10 percent
stand-by load over and above the load
point, by opening the variable guide
vanes of the compressor.
Living Energy · Issue 6/February 2012
Designed for Fast Start-ups
and High Load Efficiency
In general, the promise of renewable
energy has captured the popular
imagination so much that a majority
of subsidies and investment are focused on renewable energy, while investment in fossil fuel plants is lagging due to various political uncertainties.
“Given the shorter day-to-day operation times expected for fossil fuel plants
now that renewables are coming online, operators are trying to extend the
service life of plants. Some are letting
their older plants run longer rather
than investing in new ones. You can
do this for a certain amount of time,
but at some point, the technology will
meet its limit and there will be no
way around implementing solutions
to improve flexibility and efficiency or
investing in new plants,” says Pickard.
In Ritthem in the Netherlands, such
investments have already been made.
The Sloe Centrale plant, for instance,
has increased efficiency using a number of the solutions discussed above
(see Living Energy Issue 2, April 2010).
In operation since the end of 2009,
the plant, which is equipped with a
complete FACYTM package, was designed
for daily start-up and shutdown and
runs with high full-load efficiency. It
has also achieved optimized part-load
efficiency with the air preheater at
the compressor inlet.
At Irsching 4 in Germany, which went
into commercial operation last summer, an H class gas turbine, designed
with air cooling to allow for maximum
operational flexibility (see Living
Energy Issue 5, July 2011), was installed. Tests that were independently
verified and certified by TÜV SÜD in
Germany show that the H class combined cycle power plant can start up
within half an hour. This plant delivers
efficiency improvements of about
1.5 percent points compared to a stateof-the-art F class.
For large plants, such improvement
rates mean substantial savings and
a contribution to the overall goal
of protecting the environment: At
Living Energy · Issue 6/February 2012
a 1.5 percent points improvement
for a plant with 570 MW of electrical
output and 8,000 base load hours for
the year, fuel consumption would go
down by 14,700 t/year and CO2 would
be reduced by 43,000 t/year.
Pickard’s study shows that fossil power
plants with highly flexible operating
capabilities are the key to integrating
renewables into the power grid and
an essential prerequisite for the rapid
growth of these energy sources; based
on the cases of Sloe Centrale and
Irsching, the study also illustrates that
many solutions for achieving such
flexibility have left the realm of theory
and are already available on the
market.
Looking Forward
In 2035, the mix of energy produced
worldwide will be very different from
today’s. At that point, 32 percent of the
world’s energy will come from renewable sources such as wind, solar, and
hydropower, and the rest will be generated by fossil fuel and nuclear plants.
The trend means a new focus for operators of combined cycle power plants.
They will be asked to ensure grid
stability by accommodating a fluctuating energy supply from renewable
sources when the wind is not blowing
or the sun is not shining. At the same
time, they will need to focus on improving full-load and part-load efficiencies in order to minimize their own
fuel consumption.
“We expect that in Germany by 2020,
nearly all the nonrenewable fleet
of plants will require daily start-stop
operation. To be an effective and profitable backup for renewables, plants
will need rapid availability and optimized start-up and shutdown operations,” says Pickard, adding: “Our forecast shows that demand for uninterrupted operation of fossil-fired plants
in base load, which is the rule today,
will virtually disappear from the market except for frequency control.” p
Rhea Wessel is a freelance writer based
in Frankfurt, Germany.
61
Glossary
Residual Load
The difference between power
demand (load) in a power grid and
the fluctuating infeed from noncontrollable power sources (mostly
renewable based, e.g., wind power).
Negative or Zero
Residual Load
The point at which the fluctuating
infeed (mostly renewable based)
exceeds power demand, thus rendering fossil backup power unnecessary. A negative residual load will
be a problem for grid operators and
can only be countered with large
capacity energy storage.
Load Ramps
Change in electrical power output
during a certain period of time,
which is mostly stated as ratio
of MW/min.
Island Formation
The unexpected breakdown of the
power grid into two sections (mainly
due to grid faults or load shedding)
– one with a high excess supply and
one with a large shortfall of power.
Full-Load Efficiency
Efficiency at the point of maximum
power output (the plant’s design
point).
Part-Load Efficiency
Efficiency at operation points below
full load that in general entail lower
efficiency compared to operation
at the design point.