New Impulses
for Turbine
Design
The efficiency of gas turbines has been
raised significantly in recent years due
to innovation at various stages of design
and development. Where will future
improvements be found?
Text: Rhea Wessel
Illustration: Mariela Bontempi
Technology
Technology
I
“If there is a trend
in technology that
will revolutionize
gas turbine design,
it is advanced
manufacturing.”
Nicolas Vortmeyer, Head of
Technology and Innovation for Fossil
Power Generation, Siemens
38 Living Energy · No. 9 | December 2013
f power plant designers could
peer into a looking glass and observe the future a decade from
now, most experts would expect to see
further advances in turbine inlet
temperature levels – and thus the efficiency levels – that can be attained by
gas turbines in thermal power plants.
Output and efficiency of the plants
might reach as much as 63 percent in
combined cycle power plants, compared with around 52 percent in the
early 1990s.
Nevertheless, as researchers focus on
raising temperature thresholds in hot
gas paths and increasing the lifetime of
the machinery, their work in advanced
manufacturing technologies may bear
more fruit sooner. Some experts believe advanced manufacturing technologies could have an unrivaled impact on the design of gas turbines and
power plants. Their use could lead to
more cost savings and longer component lifetimes, making gas turbine
power plants even more effective in
their role as a provider of stability in
the grid when increased amounts
of renewable energy are fed in.
One particularly exciting area of advanced manufacturing for gas
turbine development is selective laser
melting technology, a form of
so-called “additive” manufacturing.
The concept behind selective laser
melting technology is similar to that
of the 3D printing technology that
has been in the news recently. 3D
printing allows individuals to manufacture items of their own design in
their own homes using various materials, including powder or granulate,
and a so-called “printer.” One tiny
point at a time, the “printer” melts
and compiles the material into a
three-dimensional object. Selective
laser melting technology can be seen
as the industrial equivalent of 3D
printing in the home.
Improved Heat Transfer
Breakthrough in 3D
Nicolas Vortmeyer, the Head of Technology and Innovation for Fossil
Power Generation at Siemens, says: “If
there is a trend in technology that will
revolutionize how we design gas turbines, it is advanced manufacturing.
This is something totally new, a real
breakthrough. Selective laser melting, for instance, allows us to realize
geometries that can hardly be manufactured right now. We will see new
frontiers for heat transfer and structural integrity.” He adds: “We’re talking smaller and stronger.”
Vortmeyer distinguishes three primary
levels of innovation: gains that come
from an improved ability to manage a
fleet of power plants, for instance
through advanced analytics or predictive analytics using so-called Big
Data; progress at the individual power
plant level, including improvements
in how gas turbines are integrated into plants; and innovation at the component level, such as advances that
improve materials, coatings, or aerodynamics.
Advanced manufacturing technologies
applied at the component level may
bring many benefits, among them improved heat transfer through smaller
cooling channels, lower costs for parts
with complex shapes, and higher R&D
efficiency through rapid prototyping.
“In contrast to competitors, we’re active in R&D in all areas of advanced
manufacturing technologies,” says
Vortmeyer. “The beauty is in the
interdisciplinary effort of combining
design, materials, and manufacturing. I
strongly believe we’re entering a new
era of turbomachinery-based power
generation.”
The following review of technologies
that are driving each benefit offers a
broader perspective of where R&D is
headed in individual areas.
To improve heat transfer, research is
focused on the cooling effects made
possible through blade design, filmcooling technology, and multilayer
coatings that reduce the heat transfer
coefficient. Scientists at Siemens are
developing casting technologies
together with partners from casting
companies, such as those that provide
improvements in the geometric
shapes which can be cast; they are
also working on improved models for
the inside of turbine blades, with the
goal of creating more complex internal
fixtures and cooling channels.
So-called TOMO technology, or tomolithographic molding technology, is
the basis for advances in casting.
With the right core shape, the amount
of cooling air that is consumed can be
reduced, says Willibald Fischer, the
Head of Product Management for Gas
Turbines. “In addition, film-cooling
effectiveness can be improved by laser
engraving the holes on the blades
and vanes. You can improve the cooling effect if you have shaped holes,
not just cylindrical holes. The shape
should widen up at the wall surface in
order to establish an optimal layer of
air for cooling, sometimes called film
cooling,” says Fischer.
Siemens Energy Inc. recently opened
a facility in Charlottesville, Virginia,
for the commercial production of
airfoil ceramic cores for gas turbine
blades and vanes. The TOMO
technology in use there was initially
developed by Mikro Systems with the
support of US government research
funding. Siemens Energy has licensed the TOMO technology from
Mikro Systems.
“In the future, we’ll be able to
achieve new levels of intricacy
in parts using laser melting
technology.”
Willibald Fischer, Head of Product Management
for Gas Turbines, Siemens
Lower Costs for Parts with
Complex Shapes
Selective laser melting technology, as
described above, is one breakthrough
area of materials science that may
help turbine designers create complex parts faster, cheaper, and even remotely. In some applications, it is already being used to produce
complicated parts in a single pass
rather than assembling parts out of
small components.
Says Fischer, “In the future, we’ll be
able to achieve new levels of intricacy
in parts using laser melting technology,
with the shape of the parts built to
custom design using individual layers
of base alloy.” Though the technology
is only in its infancy, Fischer and others see laser melting as a “game
changer” because turbine design will
adapt to the new geometries that will
be able to be manufactured, and it
will be more cost-effective to manufacture parts that are only needed in
small quantities or for prototyping.
In addition, selective laser melting
technology can lead to lower service
costs for power plants. “I can imagine
that someday, our service people will
show up at remote plants with their
own 3D selective laser melting tools.
When they have determined what
needs repair, the service people will
be able to manufacture the part onsite, rather than getting it shipped
in,” says Fischer.
u
Living Energy · No. 9 | December 2013
39
Technology
Higher R&D Efficiency
through Rapid Prototyping
A third key point is rapid prototyping.
In the past, it took years to develop a
prototype part and test it in a gas
turbine. Now, designers have the possibility of generating an idea and
testing it in short order. Vortmeyer
notes: “A lot of the effort of developing
gas turbines involves trial and error.
If we can quickly manufacture our
own components, we can try out our
ideas really fast.”
Fischer, who leads the Product Management for gas turbines, believes
rapid prototyping enabled through
processes such as selective laser melting and TOMO technology could mean
that trials of prototype castings and
cores for hot gas parts are undertaken at least 50 percent faster than at
present.
Already, the Siemens Corporate
Technology (CT) Division in Berlin is
testing some parts that were produced with rapid prototyping. The
CT Division conducts research in
materials technology with a team of
interdisciplinary experts. Researchers
are focused on the development,
engineering, and manufacturing of
innovative materials, with business
application
ns in mind.
applications
40 Living Energy · No. 9 | December 2013
Innovation across the Board
The promise of better heat transfer,
lower costs for intricate parts, and
rapid prototyping is what gets turbine
designers excited, and innovation in
advanced manufacturing technologies
is moving quickly. But that doesn’t
mean innovation isn’t taking place in
other areas of gas turbine and power
plant design as well. On a broad basis,
steady gains are expected in performance, efficiency, emissions reduction,
and fuel and operational flexibility,
including more frequent and rapid
start-up capabilities. These gains will
come from even more innovation at
the component level (besides those
made with advanced manufacturing
technologies), such as improvements in
aerodynamics, aeromechanics, and
combustion.
In aerodynamics, Siemens is focused
on improving compressor efficiency
with the best shapes and aerodynamic
profiles. Fischer says, “We are investing a lot in aerodynamic codes and the
further development of aerodynamic
design tools.”
In combustion, researchers are
working to achieve a better premixing
quality of compressed air and fuel for
better flame distribution. Siemens
has also developed an advanced combustion system with a multifuel capable premixed burner for a low-emission syngas turbine in an integrated
gasification combined cycle plant.
“Our advanced combustion system
has shown promising results in low
emission levels, increased firing
temperatures, and reduced dilution,”
says Vortmeyer.
Many of the latest developments will
be incorporated into a new plant to be
built in the Kingdom of Saudi Arabia,
as was announced by Siemens in August 2013. Siemens will supply to Saudi Aramco ten gas turbines that are
specially designed for syngas and fuel oil, as well as five steam turbines,
15 generators, and ten heat recovery
steam generators. The power station
at Jazan Industrial City will be fueled
with gasified refinery residues, helping preserve the country’s energy resources, reduce emissions, and keep
costs down.
Integration of Gas Turbines
in Power Plants
Moving away from the component level
and considering innovation at the
power plant level, we see that integration of gas turbines into power plants
is another key focus of research. “In
the end, the power plant is not just the
gas turbine,” says Andreas Pickard,
who leads Innovation Management for
Fossil Power Plants at Siemens.
Before the 1990s, power producers
tended to purchase plants from different suppliers, putting them together
based on their own lot specifications.
Now, power producers typically prefer
turnkey solutions, since the overall
design of the plant must be fine-tuned
for the equipment selected.
It works the other way around as well,
Pickard says. “To optimize a gas turbine, you must consider it as part of
the complete product or plant.” In
other words, buyers should develop
the corresponding power plant concept in parallel. For example, during
the development of the SGT5-8000H
gas turbine, Siemens developed a
Benson-type heat recovery steam generator in parallel. It is able to provide
steam with a temperature of 600 °C and
makes use of the exhaust gas energy
of the gas turbine without jeopardizing
the operational flexibility of the power
plant solution, as Pickard notes.
Those responsible for plant design at
Siemens work closely with all areas
of R&D to develop integrated solutions
during the gas turbine development
process. Their goal is to ensure that
an optimized plant concept will be
available when the product goes to
market. “There are so many things to
keep in mind when you introduce a
new gas turbine generator, for
instance the water-steam cycle or the
heat recovery steam generator, and
even more mundane things such as
access and space for maintenance
activities,” says Pickard.
Efficient, Rapid, Flexible
No matter what new heights of
innovation designers reach, in the end,
experts agree that combined cycle
power plants will remain a leading
power generation technology over
many years. That’s because of their
high levels of base- and part-load
efficiency, quick start-up times, and
the ability of the plants to stabilize
frequency in the grid. Accordingly,
power plants must be designed
for maximum flexibility to adapt to
changing market conditions and new
technologies over the long term.
If the energy mix includes fewer fossil
power plants and more fluctuating renewable production, the remaining
fossil plants in the fleet will need extra flexibility to deal with the demand
at peak times. They will need to handle
increased load ramps to control
the frequency in the grid. Many of the
plants will be confronted with longer
standby periods, on one hand, and
demand for just-in-time power, on the
other hand, says Pickard. “With these
new requirements, we have to develop
new systems, such as the standby
mode for power plants. We need fast
start-ups even after longer standby
periods.” p
“To optimize a gas
turbine, you must
consider it as part of
the complete
product or plant.”
Andreas Pickard, Head of Innovation
Management for Fossil Power
Plants, Siemens
Rhea Wessel is an American freelance business
and technology writer based in Frankfurt, Germany.
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