Computer Simulation Increases Power Plant Efficiency

Siemens is developing the most efficient combined cycle power plants in the world with the aid of complex simulations. The research magazine Pictures of the Future reports that experts are using computer models to improve the form of the turbine blades in combined cycle plants in order to optimize the flow. This development, along with continued improvement of materials, is resulting in efficiency levels of more than 60 percent in combined cycle facilities. Today these power plants operate at around 58 percent efficiency.

First, combusted natural gas drives the gas turbine; then it heats water, which is converted into steam used to drive another turbine, a steam turbine. A generator changes this mechanical energy into electrical energy. The shape of the turbine blades plays a definitive role in the efficiency of the system. The better they are formed lesser natural gas is needed to produce electricity.

That’s why turbine experts from Power Generation (PG) and Corporate Technology in Munich are using computers to simulate the flows of the gases – which can be as hot as 1,500 degrees Celsius – at the turbine. The turbine blades are described mathematically by a tightly-woven net, and the gas flow is translated into so-called Navier-Stokes equations. The solutions to these equations reveal the optimal blade shape to the experts. At the PC, the experts can detect irregularities in flow and correct them by making changes to the shape of the blade.

In addition, the experts from PG use an acoustic simulation process that calculates turbine vibration. During operation, unfavourable conditions in the burners in the gas turbine can develop a hum at frequencies that reinforce one another. This would lead to damage to the turbine, which therefore has to be switched off immediately, resulting in expensive downtime.

The acoustic simulation is able to determine at which phase of turbine operation these frequencies arise, and controls the process sequence so that the vibrations no longer occur in step. This new thermo-acoustic design will be employed for the first time in 2007 in the new gas turbine generation. The prototype of the turbine is currently under construction in the Berlin plant.