Siemens nabs three efficiency world records with Fortuna combined-cycle gas plant

Its electrical efficiency is at an unprecendented 61.5%.

When utility firm Stadtwerke Düsseldorf (SWD) set out to have its power plant in Lausward, Germany to meet its environmentally responsible investment strategy, it was Siemens that stepped up to meet the utility firm’s needs.

Under SWD and Siemens’ partnership, the Lausward Power Station evolved from a coal-fired plant into combined-cycle gas turbine (CCGT). The station came to house the CCGT unit Fortuna, which hails from Siemens’ H-Class line of turbines. Thanks to Fortuna, the Lausward power plant economically generates environmentally friendly electric power as well as district heat.

Breaking world records

With a performance capacity that far exceeds what is customarily achieved by similar power generating units, the Fortuna CCGT has raised the bar in terms of efficiency.

The Fortuna unit boasts electrical efficiency of 61.5%. This exceeds even Siemens’ previous world record of 60.75% net power-generating efficiency set in May 2011 by the company’s Ulrich Hartmann combined-cycle unit at located in Irsching in the south of Germany. The efficiency is achieved thanks partly to a triple-recovery steam generator that heats steam to temperatures of up to 600°C at 170 bar.

In addition, the Lausward plant pairs a 422-MW producing Siemens H-class turbine together with a downstream steam turbine from Siemens SST5-5000 series. During the test run before SWD’s acceptance of the unit, the two turbines achieved a maximum electrical net output of 603.8 MW, which is unmatched by any other single-shaft combined cycle configuration in the world.

Lastly, the Fortuna unit prevents any waste heat to go unused. To supply the city of Düsseldorf with city heat, steam is extracted from the low-pressure steam turbine section in volumes of up to 300 MW of thermal energy in a combined-cycled operation—the most thermal energy extracted from a single power plant unit anywhere in the world.

Overall, the plant’s fuel efficiency of the natural gas clocks in at roughly 85%, thanks to the plant’s electrical efficiency combined with its use of heat generated in the power production process.

Accelerated hot starts

The Fortuna unit utilises Siemens’ Co-Start technology, allowing the power plant to shorten startup times under hot-start conditions by simultaneously starting the gas and steam turbines. The gas turbine starts and runs up, boosting the power plant’s output at the steepest gradient possible right up to full load. This means that the plant does not need to wait for staggered startup of the steam turbine, as customarily practiced by conventional combined-cycle units.

In addition, the Co-Start technology is also used to increase Fortuna’s warm starts, meaning unit re-start after a weekend shutdown lasting typically up to 48 hours. The improved startup procedure is essentially achieved by implementing the same technical measures of the startup process for hot starts.

The difference for warm starts lies, however, in the temperature and pressure conditions in the heat recovery steam generator considered by the instrumentation and control system after the longer period of shutdown.

Rapid shutdown system

To accelerate the shutdown process, the Lausward power plant’s gas turbine is shut down as rapidly as possible independently of the steam turbine. In addition, the gas turbine shuts down without regard to customary waiting periods and holdpoints observed in conventional combined-cycle plant operations.

At the same time, enhanced instrumentation and control logic operations enable the steam turbine to begin shut-down very early.

As with the rundown process, the shaft train is brought to a standstill quickly thanks to a modified operating code.

Siemens notes that in test runs, it verified that its Quick-Stop technology allows for a massive cut in the shutdown time of a combined cycle power plant to 25 minutes—nearly half the usual shutdown period of 45 minutes.

Decoupling heat, power generation

Dusseldorf’s district heating system is poised to be expanded this year to include a large hot-water district heat accumulator system. It is slated to commence operation as of January 2017, further expanding the Lausward plant’s flexibility.

The principle of the thermal energy storage is simple—if more thermal energy is extracted from the power generation process than is currently required by the city of Dusseldorf, the district heat accumulator stores the surplus thermal energy. Meanwhile, if power demand reaches a low while simultaneous demand for heat is high, the accumulator storage system can cover the increased demand.

The system allows temporary decoupling of heat and power generation from the city’s demand for thermal energy, and climate friendly plant operation can continue while fulfilling the given market demand in the intended manner.