Siemens' newest combined cycle power plant converts up to 60.75 percent of the energy contained in natural gas into electricity - a world record. It can be started up and shut down in approximately 30 minutes, which is necessary to compensate for fluctuating infeeds from renewable sources.
History was made in a power plant in May 2011. The plant houses a turbine that has been entered in the Guinness World Records and recognized with numerous environmental and innovation awards. The combined cycle gas turbine — the world’s largest and most efficient system of its kind — is the centerpiece of the Irsching Block 4 power plant in Germany. Measuring 13 meters, and weighing 444 metric tons, the turbine, following years of testing, entered commercial service at E.ON, a power company, on July 22, 2011.
The plant, which has an output of 375 megawatts (MW), achieves an efficiency of 40 percent. In combination with a steam turbine and a heat recovery steam generator, which was specially developed by Siemens, the plant posted a world-record efficiency of 60.75 percent with a net output of 578 MW — more than originally planned. The power plant is thus capable of supplying enough electricity for a city the size of Berlin, with its 3.4 million inhabitants. Compared to power plants that had previously been considered the most advanced the plant is 2.0 percent more efficient, thus saving about 43,000 metric tons of CO2 per year — equivalent to the emissions of some 10,000 mid-size cars traveling 20,000 km. And in comparison to the global average for the installed fleet of combined cycle power plants, the new plant uses one third less natural gas and expels one third less CO2 per kilowatt hour generated.
The speed with which the gas turbine can be started up and shut down is also unmatched. After being shut down for several hours, the unit can be brought up to full power in approximately 30 minutes. This flexibility is the combined cycle power plant’s second trump card alongside its environmental compatibility. Willibald Fischer, product manager for the gas turbine, says that “with renewable power generating facilities, which are now coming online in increasing numbers, a cloud or a slight lull in the wind is enough to cause fluctuations in the grid. Such fluctuations will have to be offset very quickly in the future, by using combined cycle power plants as a backup solution, for example. And quick startup is necessary to prevent them from having to idle continuously while on standby.”
Backbone for Renewables. Some elements of Fischer’s scenario are now reality. On sunny days, photovoltaic systems in Bavaria already provide over half of the electricity needed, and significant expansion of renewable energy generating facilities is expected during the next few years.By as soon as 2020, according to Fischer, it may be possible to meet Germany’s entire electricity demand for several hours on windy summer days solely with electricity from renewable energies.
But when the weather changes suddenly, fossil fuel power plants would then have to kick in as quickly as possible. “By 2020 we will need an additional power plant reserve of roughly 30 to 50 gigawatts, or 20 to 30 percent of Germany’s currently-installed power plant capacity. Flexible gas-fired power plants are very well suited for this purpose. Capital expenditures are low and natural gas has the best CO2 balance of any fossil energy source,” says Lothar Balling, general manager for gas-fired power plants.
More than 750 employees, including 250 engineers, worked on the development, assembly, and testing of the SGT5-8000H and its combined cycle power plant (see Pictures of the Future, Fall 2007, Unmatched Efficency). Siemens invested over €500 million in a prototype plant before it was handed over to E.ON.
All in all, the turbine was developed from the ground up, rather than being the next generation of an existing model. Most of the effort that went into achieving the plant’s record-setting efficiency and flexibility involved improvements to the gas turbine and the overall design.
Engineers increased the turbine’s operating temperature, optimized the material and geometry of the compressor and turbine blades, reduced air cooling losses, and adapted the boiler, steam turbine, and generator to the Amerigas turbine. But the engineers’ greatest contribution to the plant’s record-breaking efficiency was increasing its combustion temperature from about 1,400 degrees Celsius in the previous model to around 1,500 degrees in the new gas turbine. Because the temperature on the surface of the turbine blades is also correspondingly higher, even better protection against heat is needed.
The turbine’s blades are thus made of a nickel alloy that solidifies as a single crystal in the direction of load, making them particularly resistant to fracture. Next there is a two-layer thermal barrier coating that provides heat insulation. The blades’ air cooling characteristics were also optimized. Developers also optimized the blade profiles to reduce losses caused by turbulence at the tip of the compressor blades. They did this by simulating the three-dimensional fluid dynamics within the compressor — a particularly challenging case for computer simulation.
Achieving the gas turbine’s high efficiency also requires all of its components to be optimally matched. The steam turbine, for example, (see Pictures of the Future, Spring 2008, Preparing for a Fiery Future) was designed specifically for the turbine’s exhaust gas temperature.
The gigantic size of the boiler between the steam turbine and the gas turbine is necessary in order to efficiently convert the huge volume of exhaust gas into steam. The boiler weighs 7,000 metric tons and contains heat exchangers with a surface area of 510,000 square meters. “A combined cycle power plant must be perfectly coordinated down to the last detail,” says Fischer. “It’s like a car — the best engine is worthless if it isn’t matched to the optimum chassis.”
The Fine Art of Engineering. Developers achieved the plant’s fast startup and shutdown times by cooling the gas turbine exclusively with air and hydraulically optimizing the gap between the rotating blades and the casing. This was achieved by adjusting the position of the rotors by three millimeters, which, in turn, prevents collisions between the blades and the casing during a fast start. This approach to air cooling is better suited for the desired flexibility than partial or complete steam cooling because it eliminates the need to wait for steam generation when starting up the turbine. Another secret of the turbine’s success is the combination of the best technologies from Siemens and the U.S. company Westinghouse, which Siemens acquired in 1998. While a superior Siemens turbine rotor design was retained, engineers chose to use a Westinghouse combustion chamber because it was easier to test on the test bed than a combustion chamber from Siemens.
Thorough testing characterized the entire development of the SGT5-8000H. The partnership with E.ON made it possible to conduct tests under actual conditions in Irsching from 2007 to 2009. To precisely analyze the plant’s behavior, 3,000 sensors were installed for the test runs. They measured parameters including pressure and temperature, rotating blade vibrations, clearance at the tip of the rotating blades, flows, mechanical stresses, and rotational speeds. The results were used to finetune and optimize the SGT5-8000H.
Worldwide Demand. Customers are lining up for the record-breaking gas turbine. South Korea has ordered a combined cycle power plant that is scheduled for delivery starting in 2012, and a power provider in Florida has ordered six of the new gas turbines in the 60-hertz version, which will allow it to save approximately $1 billion in operating, maintenance, and capital expenditure costs over the life cycle of the turbines.
Combined cycle power plants in the U.S. currently have an average efficiency of less than 40 percent. If all of these units used the new gas turbine from Siemens, additional electricity equal to that used by 25 million Americans could be generated each year — without causing additional CO2 emissions. In order to thoroughly test the 60-hertz turbine, Siemens spent over €17 million to upgrade and expand the testing area at its Berlin gas turbine plant. A turbine for the customer in Florida has been undergoing extensive testing there since July 2011. And the record-chasers at Siemens are determined that their turbines will continue to be champions. “I expect we can improve the combined cycle power plant’s efficiency by an additional percentage point in five years using an even bigger and hotter gas turbine. That will make the technology even more economical and environmentally compatible,” says Balling.