Irsching power plant: Incubator for high-efficiency gas turbines

Extensive engineering development, test validation, and implementation of advanced gas turbines have taken place at Irsching over recent years. In May 2011 these developments culminated in the officially certified, record-setting 60.75% net thermal efficiency mark in combined-cycle operation for Siemens’ H-class gas turbine. See aerial photos.


Six exhaust stacks of the five-unit Irsching gas-fired power plant reach for the sky above green fields around the Bavarian village of the same name, near Ingolstadt, Germany. Three of the stacks, for Units 1, 2, and 3, at 200-m (656-ft) high, are remarkably taller than the others. They’re reminders of older power plant technology. Units 4 and 5 have compact buildings with stylish façades and exhaust stacks less than half the height—but more importantly, they represent the latest in combined-cycle gas turbine (CCGT) plant technology. 

A facility of major electricity provider E.ON Kraftwerke, Irsching comprises one of the largest gas-fired power plants in Germany. Located near the country’s main North-South high-voltage electric grid, the site has total gas-based installed capacity of about 1,850 MW, noted Klaus Hammer, COO of Gas-CCGT at E.ON Generation GmbH. 

Extensive engineering development, test validation, and implementation work for advanced gas turbines have taken place at Irsching over recent years. In May 2011, these efforts culminated in a record-setting 60.75% net thermal efficiency mark for Siemens’ H-class gas turbine in CC operation. Siemens’ turbine and its 8000H CC power plant system went into commercial operation in late July 2011 at Unit 4. (See August 2011 CE gas turbine article linked below).

42 years young

Irsching power plant started in a quieter way. Unit 1 (151 MW) went online in 1969, followed by Units 2 (312 MW) and 3 (415 MW) in 1972 and 1974, respectively. At first, heavy heating oil was burned but boilers were converted to use either light heating oil or natural gas in 1980. At one time the three-unit complex was the largest power plant in the region.

Unit 2 was shut down in 1995 and, when activities for new Units 4 and 5 began, Unit 1 was closed in 2006. Unit 3 still operates in a peak load and reserve power role, and is capable of 415 MW output. This unit runs as a conventional power plant, using a steam turbine, generator, and boiler as main components.

While Unit 4 has made the most recent news, prior noteworthy CCGT developments took place at Unit 5 as well. Construction of this unit started in 2007 as a “multi-shaft” plant arrangement. Here, two gas turbines and a steam turbine each run on separate shafts. Each gas turbine drives its own generator and exhausts hot gases to its own heat-recovery steam generator (HRSG). Hence there are two 97-m exhaust stacks for Unit 5. Two HRSGs deliver steam to the steam turbine, which drives a separate generator. A total of three generators deliver power to the grid via individual transformers.

Siemens installed its 4000 F combined-cycle plant in Unit 5, the latest system available at the time. Major equipment supplied included two F-class gas turbines, steam turbine, three generators, HRSG, and SPPA-T3000 power plant automation control system, which handles all control functions. Unit 5 went online in 2010 and attained noteworthy 59.5% net thermal efficiency in CC operation, according to Siemens.

New turbine class

Unit 4 was a special case because a new H-class gas turbine being developed by Siemens was key to implementing that CC plant. Construction of Unit 4 began in 2006. Siemens partnered with the customer E.ON to build the CC system on-site with direct connection to the national grid. Extensive testing and design validation of the H-class turbine was done at E.ON’s plant site. The project was implemented in two phases: first in simple-cycle operation and then in combined-cycle operation (read more at Refs. 1 and 2, below).

The “single-shaft” plant arrangement of the 8000H CC system at Unit 4 is especially compact. The steam turbine, generator, and gas turbine line up along one shaft. Also, the HRSG inlet is in line with the gas turbine’s exhaust diffuser. As mentioned above, Unit 4 went into commercial operation not long after the CC system achieved its certified record-setting thermal efficiency.

A central control room directs the operation of Irsching Units 3, 4, and 5. One large screen display for each unit monitors numerous plant variables, including instantaneous power output. Easy-to-read graphics are used, eliminating small dials or gages. The latest communication interfaces and information technology are in place for the operators.

Valuable development experience has been gained with advanced gas turbines at Irsching Units 4 and 5. This is expected to translate into further application of high-efficiency turbines and the combined-cycle plants in which they have a key role. See related information, below.

Speaking of exhaust stacks...

What’s the connection between toppling exhaust stacks at a power plant and advanced gas turbines? The short answer is new technology replacing the old. Exhaust stack demolition at FPL’s outdated Riviera Beach power plant took place in June 2011 as part of modernizing that facility into a next generation clean-energy center. Courtesy: Florida Power and Light Co.

Normally, the toppling of exhaust stacks is not a good sign for a power plant. However, in this case it means a positive development—an early step in the dismantling of outdated facilities to prepare for new construction. The metaphor of exhaust stacks connects developments at two power plants in Florida with those that took place at the Irsching power plant in Germany (see above).

In 2010, Florida Power & Light Co. (FPL) took significant steps to modernize its 1960s-vintage Cape Canaveral and Riviera Beach power plants. Objective of the $2.4 billion investment was to increase fuel efficiency by 33%, generate power with 90% fewer air emissions, and cut CO2 emissions in half—compared to the predecessor plants, according to FPL. “Next generation” clean-energy centers being built at Cape Canaveral (Cocoa, FL) and Riviera Beach (near Palm Beach, FL) will implement state-of-the-art combined-cycle gas turbine (CCGT) technology. When completed in 2013 and 2014, respectively, each new energy center will have a compact, three-unit layout and deliver 1,250 megawatt (MW) rated output.

Exhaust stacks and structures at the old Cape Canaveral plant were demolished in August 2010, and construction of the new energy center started in March 2011. Dismantling of the Riviera Beach plant began in December 2010, with stack demolition taking place in mid-2011 (see photo). As an aside, the photo shows one of the stacks experiencing classical bending stress failure as it topples over—but prior to impact with the ground. It’s an interesting example of strength of materials theory in practice.

H-class turbines coming

High-efficiency gas turbines will be at the core of FPL’s new CC plants. Siemens Energy will supply six 60-Hz, H-class gas turbines to the project—three machines going to each plant (read more at the link, below: Ref. 3). The SGT6-8000H gas turbines are rated at 410 MW and predicated by Siemens to achieve over 60% thermal efficiency in combined-cycle operation. They’re a scaled version of the successful 50-Hz machine that went into commercial operation at the Irsching power plant in Germany in July.

Design and engineering of the air-cooled 60-Hz H-class gas turbine was done at Siemens Energy's North America headquarters in Orlando. First machines for this order are expected to be delivered to FPL in 2012.

Frank J. Bartos, PE, is a Control Engineering contributing content specialist. Reach him at braunbart(at) 


Further reading online

Ref. 1 – “Largest gas turbine: 2,838 sensors, 90 GB data per hour of testing” 

Ref. 2 – “Siemens gas turbine breaks 60% efficiency barrier” 

Ref. 3 - “First order for Siemens’ 60-Hz, H-class gas turbine” 

- Posted by Chris Vavra, Control Engineering,

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