Ramping up when the sun takes a break

Today, Duke Energy is one of the major providers of solar energy in the United States. Yet, the supply of electricity needs to be ensured even when the sun doesn’t shine. But how? In North Carolina the Duke Energy’s gas-fired Lincoln Combustion Turbine Station helps out – with top performances, which earned it two entries in the Guinness Book of records in 2022: First the title of the world’s “most powerful simple-cycle gas power plant” with an output of around 410 MW. And then also for the world’s fastest ramp-up rate by a 60Hz gas power plant at more than 100 MW-per-minute, enabling it to reach its full capacity in just a few minutes.

The power plant’s top performances are thanks to a new heavy-duty gas turbine, which is operating while also being tested under real conditions for the first time in North Carolina. It is packed with numerous innovations, including the combustion system design for hotter temperatures and fuel flexibility, the number of premix burners, the overall thermal management of the turbine, and the compressor- and turbine-blade design.

Last but not least, it also features new rotor disks designed and built based on innovative material simulations. They need to withstand many more quick starts than were previously required as renewable power’s share of electricity is continually rising, while also strongly fluctuating. Gas-fired power stations have to step in at short notice to ensure a stable supply of electricity. As gas turbines are capable of starting up quickly to deliver high power outputs, they´re the preferred choice for this task.

The high number of quick starts causes extreme stresses on the rotor disk’s material. The disks, with forty or more blades installed around the outer diameter, are colossuses forged from steel. They weigh up to seven metric tons and measure up to two meters in diameter. During fast cold starts, for example, different areas on the disks heat up at different speeds, subjecting the overall disk to high stress.

“If these starts happen regularly, the result can be dangerous, because it can lead to disk fractures over the longer term,” says Kai Kadau, Siemens Energy simulation expert in North Carolina. “That´s not trivial. When it’s in full swing, a large turbine rotor with 20 disks has the kinetic energy of 200 trucks driving at full speed. The consequences of a disk fracture aren’t something you want to think about.”

In order to ensure that dangers like these are avoided a team around Kadau developed a simulation program that allowed it to design large generators and turbines. Its probabilistic data analytics tools tap into a wide array of data sources, including operational data or vendor data. Kadau and his team applied it to rotor disks for the new flagship gas turbine at Duke Energy, calculating the strength of its forged-steel components, and thereby the risk of their fracturing.

This tool has already played a critical part in ruling out the risk of disk fractures for a number of years in various turbines. It is used daily in turbine development to ensure that the disks can cope with new demands, assessing the rotor’s expected wear and tear and how this should affect its maintenance schedule. And even more, when inspected, the tool allows a user to determine whether, based on is condition, the rotor should be replaced.

This success wouldn’t have been possible without the help of an expert Siemens Technology team in graphics processor-based computing and software performance optimization for simulation and digital twins in Bangalore. They reorganized and reprogrammed key parts of the tool to enable its maximum performance when running on graphics processor-based high-performance computers. This way, Kadau’s team was able to calculate the fracture strength within minutes and even seconds rather than hours. An impressive feat, as the probabilistic tool runs through several million calculation sequences to cover all the material and load combinations that determine fracture strength.

The new turbine at Duke Energy’s Lincoln Combustion Turbine Station shows what the tool is capable of. “We can ramp the turbine up really fast, as the Guinness world record confirmed”, says Hans Maghon, who has been monitoring the development of the new gas turbine as program director at Siemens Energy. “But even more, the turbine also guarantees 1,250 starts between inspections, the level of flexibility that’s a precondition for commercial viability in the energy market of the future.” Maghon also counts on super-fast material simulations for future innovations.

One of these innovations is AI. “Taking in the data of multiple sensors installed in turbines and combining it with Artificial Intelligence ultimately should tell operators how a whole turbine will behave under various loads”, says Georg Rollmann, leading a group dedicated to advanced analytics and AI at Siemens Energy. “This allows us not only to continue to improve the design and maintenance of our products, but also to run simulations of operating power plants in real time. It can enable us to get the most of what’s physically possible out of energy assets – be it maximizing its efficiency, optimizing its maintenance schedule, and keeping the flexibility we need for dispatchable power.”

Ramping up in record time when sun and wind take a break

Many contributors to success

Fracture strength of rotor disks

Innovative simulation push material innovations

1,250 starts between inspections guaranteed