New Impulses for Turbine Design

The effi ciency of gas turbines has been raised signifi cantly 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

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Technology

f power plant designers could peer into a looking glass and ob-serve the future a decade from

now, most experts would expect to see further advances in turbine inlet temperature levels – and thus the effi-ciency 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, com-pared 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 be-lieve advanced manufacturing tech-nologies could have an unrivaled im-pact on the design of gas turbines and power plants. Their use could lead to more cost savings and longer compo-nent 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 ad-vanced 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 manu-facture items of their own design in their own homes using various mate-rials, 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.

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Breakthrough in 3DNicolas Vortmeyer, the Head of Tech-nology and Innovation for Fossil Power Generation at Siemens, says: “If there is a trend in technology that will revolutionize how we design gas tur-bines, it is advanced manufacturing. This is something totally new, a real breakthrough. Selective laser melt-ing, for instance, allows us to realize geometries that can hardly be manu-factured right now. We will see new frontiers for heat transfer and struc-tural integrity.” He adds: “We’re talk-ing 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 pre-dictive analytics using so-called Big Data; progress at the individual power plant level, including improvements in how gas turbines are integrated in-to plants; and innovation at the com-ponent level, such as advances that improve materials, coatings, or aero-dynamics. Advanced manufacturing technologies applied at the component level may bring many benefits, among them im-proved 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 ac-tive 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.

Improved Heat Transfer To improve heat transfer, research is focused on the cooling effects made possible through blade design, film-cooling 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 tomo-lithographic 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 cool-ing 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 li-censed the TOMO technology from Mikro Systems.

“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

“ 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 ShapesSelective laser melting technology, as described above, is one breakthrough area of materials science that may help turbine designers create com-plex parts faster, cheaper, and even re-motely. In some applications, it is al-ready 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 oth-ers 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 manufac-ture 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 on-site, rather than getting it shipped in,” says Fischer. u

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Higher R&D Effi ciency through Rapid PrototypingA 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 pos-sibility 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 Man-agement for gas turbines, believes rapid prototyping enabled through processes such as selective laser melt-ing and TOMO technology could mean that trials of prototype castings and cores for hot gas parts are undertak-en at least 50 percent faster than at present.Already, the Siemens Corporate Technology (CT) Division in Berlin is testing some parts that were pro-duced 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 applications in mind.

at Jazan Industrial City will be fueled with gasified refinery residues, help-ing preserve the country’s energy re-sources, reduce emissions, and keep costs down.

Integration of Gas Turbines in Power PlantsMoving away from the component level and considering innovation at the power plant level, we see that integra-tion 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 differ-ent 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 tur-bine, you must consider it as part of the complete product or plant.” In other words, buyers should develop the corresponding power plant con-cept in parallel. For example, during the development of the SGT5-8000H gas turbine, Siemens developed a Benson-type heat recovery steam gen-erator 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.

Effi cient, Rapid, FlexibleNo 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 re-newable production, the remaining fossil plants in the fleet will need ex-tra 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

Rhea Wessel is an American freelance business and technology writer based in Frankfurt, Germany.

applicationmaterials, with business

ns in mind.

|

“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

Innovation across the BoardThe 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 perfor-mance, 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 invest-ing 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 com-bustion system with a multifuel capa-ble premixed burner for a low-emis-sion 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 Au-gust 2013. Siemens will supply to Sau-di Aramco ten gas turbines that are specially designed for syngas and fu-el oil, as well as five steam turbines, 15 generators, and ten heat recovery steam generators. The power station