The German town of Erlangen contains both a district energy scheme and the headquarters of Siemens Power Generation. So when the district heating plant needed modernization, it offered a perfect opportunity for the use of modern CHP technology. Harald Dichtl and Lynne Anderson report.

In 2003, Siemens Power Generation was contracted by Stadtwerke Erlangen (ESTW) in the south of Germany to replace a discontinued coal-fired boiler of Erlangen’s district heating power plant with a state-of-the-art, gas-fired combined-cycle plant capable of producing both electricity and district heating for the community. By combining heat and power generation in such a modern plant concept, the emission of the greenhouse gas carbon dioxide (CO2) produced per kilowatt hour was considerably reduced in comparison with other plants.

The plant was required to fit into the existing building and construction needed to be completed within a short period of time.

The gas turbine was commissioned in spring 2005, and the complete combined-cycle plant started operation in September 2005 in time for the winter. The recent upgrade is the first application in Germany of a Siemens industrial gas turbine SGT-400. This gas turbine produces up to 14 MW, depending on the ambient temperature; the SST-300 steam turbine supplies up to 10 MW of electricity.

Background to the project

The modernization of the cogeneration plant was a necessary natural step for two reasons. Firstly, a large utility power plant (Franken II) in the vicinity, which had supplied heat to the city’s district heating network, was closed in 2001. Secondly, certain components of the existing power plant reached the end of their lifespan. The new plant was built partly in the very location where one of the old coal-fired boilers had so faithfully served its city for 45 years. In 1961, the district heating supply for the municipality of Erlangen started with two boiler packages and one steam turbine. Since then the power plant has been continuously modernized.

‘The task for Siemens was not only to build a new combined-cycle power plant but also to dismantle parts of the old plant, such as an old steam generator, including flue gas cleaning and coal-handling systems. An additional challenge was that it needed to be built into the existing building without changes to the architecture,’ says Reinhard Pöhlmann, Project Manager for ESTW.


The steam turbine is being lifted over the roof and lowered into the plant
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‘The new extension was required to incorporate the state-of-the-art gas turbine combined-cycle technology for its efficiency and flexibility in power and heat generation, and also have sufficient flexibility to cover seasonal swings in demand’, adds Pöhlmann. He says further that it was essential for ESTW that the existing plant could continue operation without restrictions throughout the modernization and construction activities.

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The Siemens solution was a SCC-400 1×1, where SCC stands for Siemens Combined Cycle, and 1×1 means one gas turbine combined with one steam turbine. The plant is based on a 13 MW SGT-400 gas turbine, formerly known as the Cyclone, and a back-pressure SST-300 steam turbine, formerly called the ST3. A supplementary-fired boiler as well as electrical and control systems were also included in the Siemens scope of supply. Siemens achieved the promised short planning period and construction time, delivering within 25 months.

The project

On 16 November 2005, in the presence of representatives of Erlangen Stadtwerke and Siemens, the mayor of Erlangen, Siegfried Balleis, inaugurated the municipality’s new combined-cycle plant. It was the biggest single building project that ESTW had yet undertaken.

The SCC-400 (20 MWe) combined-cycle power plant will be used in addition to an existing coal-fired district heating plant. The power and heat demand profile required a high flexibility to adapt to the variations of impact on operational flexibility: during the summer period only a minimum heat output is required (< 10 MW), whereas the peak heat production of the combined-cycle plant reaches more than 25 MW. In order to increase the flexibility of power and heat output, an additionally fired heat recovery steam generator is used, which means that the heat demand is the leading parameter for plant operation.

The Erlangen CHP plant is primarily heat-driven, with the resulting electricity being produced at the highest possible efficiency. The CHP plant reaches a high efficiency, with up to 90% of the fuel converted into power and useful heat, resulting in a considerable saving of fuel and CO2 emission.

In addition to the turnkey modernization of the plant, including dismantling parts of the existing plant and integrating new parts into it, Siemens has undertaken a service contract on the gas turbine for a period of 15 years.

Results of the modernization, apart from a content customer and a satisfied supplier, have been:

  • clean heating and energy supply
  • reduction of CO2 emissions by 70,000 tonnes per year
  • a diversified energy supply for Erlangen (gas and coal).

Installation challenges

Creating a greenfield plant is one thing, extending and partially renewing an existing plant is something quite different. Because of the undertaking to maintain the existing architecture, there were a number of special challenges during construction, such as the use of special cranes, the confined storage spaces, and, of course, the desire of the management to keep the original plant running throughout the procedure. Trucks freighting the gas turbine had to clear 90° corners in tight places, and the steam turbine was dramatically lifted over the roof to be gently lowered and installed from above. But perhaps the most spectacular action was the use of a 170-metre-high, 500-tonne crane to put the pipes of up to 22 metres long into the existing chimney stack from the top. From the outside, the plant serenely remains the same she always was, while precise surgical operations from within have maintained her youth and vigour.

Good neighbours

For Siemens, the project is important since it was executed in the city where Siemens Power Generation has its headquarters and is connected to the power grid of ESTW. Siemens is not just a global player, but also very much a local player, as this project amply illustrates.

From ESTW’s point of view, the investment has made it less dependent on the electricity market. The modified power plant increases the share of self-generated electricity significantly from 11% to 30% of the demand. It also gives ESTW the extra security of a diversified energy supply.


A 170-metre-high crane puts a pipe into the chimney stack
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Since the liberalization of the energy market, the objectives of economy, reliability, and environmental and climatic compatibility are the factors that underpin energy supply. These are the clear factors that influenced the energy-political decision of Erlangen council, backed by the government’s support for cogeneration as an economically viable and ecologically sound solution for power plants in Germany.

Symbiotic relationship

Klaus Voges, Head of Siemens Power Generation, sums up the project quite cogently during the inauguration of the new plant for ESTW: ‘We are proud that Siemens technology has been chosen for the energy supply of Erlangen, the city where Siemens Power Generation has its headquarters. The new combined-cycle plant illustrates exactly how the apparently conflicting aims of reliability of supply, economic operation and environmental compatibility can be united in a single solution. Erlangen has taken a firm step in the direction of sustainable, future-oriented energy supply.’

It is a symbiotic relationship: Siemens provides the municipality with the source of heat and power and is also one of the major users of the plant’s output. And, of course, the proximity of the utility and the supplier both sharpens and sweetens the challenge of satisfying the customer.

Harald Dichtl is Business Development Director for industrial power plants and Lynne Anderson is responsible for external communications at Siemens Power Generation Industrial Applications, based in Duisburg, Germany. Fax: +49 9131 18 2758 e-mail: lynne.anderson@siemens.com

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CHP and combined-cycle plants

Siemens has built more than 300 combined-cycle power plants worldwide. The replacement or extension of an existing heating facility with a gas-fired combined-cycle power plant, as in the case of Erlangen, is a typical application example.

If used as a CHP plant, combined-cycle plants can generate heat levels from 50°C up to 500°C, with a high flexibility of power and heat generation. The main customer groups are the power generation industry, the oil and gas industry and the chemical and process industry.

Also in 2003, Göteborg Energi and Siemens Power Generation signed a contract for the construction of a new cogeneration plant of the combined-cycle SCC-800 at Rya, Gothenburg, Sweden. The decision to build this plant was motivated by the increasing demand for both electricity and district heating in Gothenburg. The project covers a cogeneration plant with three SGT-800 lines, plus the capability to add another line in the future. According to the project schedule, the plant will be ready for test operations during November this year.

Similar plants are currently being built or have recently been put into operation in Riga, Latvia; Moscow, Russia; and Miskolc, Hungary.