Viennese watts: a model for future CHP activity in central Europe

Vienna’s high-efficiency CHP facilities at Donaustadt provides both power and heat through the existing district heating network. Is this a model for Austria’s eastern neighbours? David Appleyard reports.

The district heating network of Vienna is some 800 km in length and supplies around 240,000 dwellings and 5000 industrial customers with energy for space- and water-heating purposes. Operated by Fernwàƒ¤rme Wien, energy-from-waste and cogeneration accounts for 97% of the heat output in what is one of Europe’s largest district heating networks, through the operation of 10 interconnected heating and combined heat and power (CHP) facilities.

With a population of more than 1.6 million people, Vienna covers an area of 415 km2. Donaustadt, in the north-east part of the city, is the largest of the local districts, occupying about one-quarter of the Vienna city area. It is also home to the Donaustadt heat and power complex and a modern baseload facility with some 350 MW of electrical capacity and a further 250 MW of thermal energy capacity for supply to the local distribution network.

Planning development

The decision to develop a new plant on the site of a pair of existing facilities was taken almost a decade ago when the local utility company, the municipally owned Wien Energie Wienstrom, began to consider efficiency improvements to its generation portfolio. Although at the time electricity prices were very low, potentially precluding significant investment in new generation assets, several considerations necessitated action. These included the liberalization of the Austrian energy market – which opened to competition in October 2001 – and the City of Vienna’s climate protection programme, which advocated reducing carbon dioxide emissions from the by then ageing Donaustadt heat and power complex.

The Donaustadt plant with its district heating pipes (All photos: David Appleyard)
Click here to enlarge image

The two existing gas-fired plants, units 1 and 2, each rated at 140 MW electrical, had been commissioned in 1973 and 1975 respectively, and although selective catalytic NOx reduction equipment had been fitted in 1986-7, the overall combined heat and electrical efficiency of just 38% fell far short of modern requirements.

The site was one of three considered and the decision to develop a new plant was finalized in 1996 as preferable to either refurbishing existing plant or purchasing significantly more power from alternative sources.

In addition, its location on a site adjacent to the two older units allowed the maximum use of existing infrastructure while reducing potential environmental impacts, a key consideration given the tough local planning laws. Consequently, the new facility uses pre-existing cooling water feed lines to the Danube, together with the gas lines and links to the 110 kV transmission network. Cooling water is used during condensing operations when the plant is generating electricity only.

As no additional cooling water lines could be built, the decision was taken to decommission the older and far less efficient unit 2 station in 2001, leaving unit 1 at the site to act as an occasional peaking plant for use on particularly high demand days when spot prices reach more than E70-80/MWh. Wienstrom had considered decommissioning unit 1 also, but as spot power prices have reached as much as 2000/MWh, the facility confers considerable economic advantage to the utility. Unlike the older unit, the latest addition at Donaustadt can also be co-fired with oil during winter months when gas prices are at a peak.

Technology and advantage

The newest conventional CHP facility in the region, the gas-fired combined-cycle plant was developed by Siemens Power Generation (PG) on a turnkey basis. Preliminary site construction on the plant began in December 1999, allowing the generator to arrive on site by November 2000. The turbine, delivered by barge up the Danube, was installed and commissioned by June 2001 with commercial operations beginning in September of that year. The plant is operated by existing personnel relieved from duties at unit 2.

The facility uses a V94.3A gas-fired turbine – now marketed as the SGT5-4000F – a technology brought to the market in 1996 as the ‘workhorse’ among Siemens’ 50 Hz machines with an electrical efficiency of 38.6% in simple cycle and a design output of 266 MW.

There is also a steam turbine. When generating heat, the V94.3A in service at the Donaustadt achieves a fuel efficiency of over 86%, with an inlet temperature of 1230à‚°C, and an efficiency of 58% for electrical generation only.

Electrical efficiency during heating is slightly reduced at 52%. This compares with electrical efficiencies of around 28% and inlet temperatures of about 800à‚°C for gas turbines from the 1970s.

Gunter Kappacher, Head of Power Group Siemens Austria, explains: ‘We have made enormous advances in recent years, particularly in terms of materials for turbine blading, ceramic airfoil coatings and the design of compressor and turbine airfoils.’

The three-stage steam turbine uses an SSS (synchronous self-shifting) clutch which automatically synchronizes the turbines on a single shaft when the steam turbine reaches speed with the gas unit. During start-up the gas turbine is used to power up the generator which is then used as a motor to accelerate the steam turbine to speed.

The district heating line out of the facility uses two reheaters from the steam turbine and an additional reheater in the steam generator and operates at 130à‚°-150à‚°C on the outward line and returns at 65à‚°-70à‚°C. There is no additional over-firing or duct-firing capacity.


At Donaustadt the gas turbine is used to control total output while the local dispatcher issues requests for both electrical and heat requirements. The dispatcher has an output curve for the plant and is aware of the possible parameters available for the combination of heat and power values.

Priority dispatch is on the basis of thermal output, and while overall heating demand usually tails off by about 11 pm, electrical output is generally tailored to match thermal demand conditions.

The steam turbine and the clutch arrangement on the single shaft
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The plant operates for some 35,000 hours between major inspections – equivalent to some six years of normal operations – and the recently completed first major inspection revealed no major problems with the facility.

Cost advantages

The Donaustadt facility operates as a baseload plant for around 6000 hours per year and 395 MW of electrical capacity with full condensing capability, when producing electricity only during the summer months, and 350 MWe when producing an additional 250 MW of thermal capacity.

In 2005, the overall Donaustadt plant (units 1 and 3) generated 2408 GWh of electrical energy and 881 GWh of thermal energy. This includes around 900 GWh of electrical energy from the older unit 1 (used only occasionally during periods of peak demand).

The development saves its owner Wienstrom some €18 million annually in generation costs, including some 150 million cubic metres of natural gas, and also reduces carbon dioxide emissions by some 330,000 tonnes per annum. These are significant impacts for a utility with an €18 billion annual turnover, and the utility now operates CHP facilities exclusively.

Future markets

Given the current power demand boom, commercial incentives, and policy support for high-efficiency generation, Donaustadt appears as a forerunner for a swathe of CHP development in Austria over the coming years.

Energie AG (EAG) has recently awarded Siemens’ Austrian subsidiary, Siemens àƒ—sterreich, a €200 million contract to build a 400 MW gas-fired combined-cycle CHP plant at Timelkam, in Upper Austria.

The plant, which is expected to generate some 2.5 TWh annually when it is commissioned at the end of 2008, will supply energy to some 700,000 customers. The station claims the highest technically possible efficiency at present of nearly 60%, EAG says, a key consideration in awarding the contract. With building preparations due to begin immediately, the licensing procedure (currently in process) for the power station could be completed in the record time of only six months.

Meanwhile, Austria’s biggest power producer and distributor, Verbund, has received a favourable environmental impact assessment for its planned 850 MW electrical and 250 MW thermal gas-fired combined-cycle CHP plant in Mellach, south of Graz in southern Austria.

Commenting on the conclusions reached by the Styrian provincial government, Verbund’s general manager, Hans Haider, said: ‘This is an important step for the long-term security of supply for the low-generation region of southern Austria, and a markedly positive signal for our project regarding the smaller affiliated, 400 MW power plant near Klagenfurt.’

Stadtwerke Klagenfurt, 49% of which was bought by Verbund last year, is developing a new gas-fired CHP development on the town edge of Klagenfurt, also in southern Austria, at a cost of approximately €250 million.

An existing district heating power plant, now located close to the centre, will be decommissioned when the new plant is operating. Construction, which is expected to take some 30 months, is to commence immediately upon receiving all necessary approvals.

The €400 million Mellach project, due to be commissioned in 2009, is being developed by Verbund subsidiary, Verbund Austrian Thermal Power (ATP). ATP owns 17 thermal power plants through it subsidiaries Draukraft, Verbundkraft and Steweag with a combined capacity of 1960 MW, covering about one ninth of Austria’s electricity consumption and it is also the second-largest supplier of district heat in Austria.

Anton Smolak, ATP Chief Executive, added that the state-of-the-art plant will have an efficiency of 80% and will produce less than half the emissions of an equivalent coal-fired plant.

a model for central europe

Further afield, according to the conference ‘District Heating in South Eastern Europe – Opportunities for Business and the Environment’ a few years ago, district heating covers the heat supply of about 60% of all buildings in central and eastern Europe.

While the Baltic and Central/eastern European members of the EU, plus its newest entrants Bulgaria and Romania, supply some 41 million customers with district heating, many of the systems have been in place for some time and have the potential to be upgraded with more efficient technology. Meanwhile, the number of district heating customers in the EU-15 countries is only around 20 million, leaving vast opportunities for regional CHP development.

According to recent figures, a total of 575,000 households, or every sixth dwelling in Austria, was heated via district heating in 2005. This is up from 83,000 households in 1980 and amply illustrates the rise of CHP in the country.

Together with proposed plants at Mellach, Klagenfurt and Timelkam, CHP looks set to spread its influence in Austria and across the wider south-eastern European region.

David Appleyard is a freelance journalist specializing in the energy and process sectors.

Austrian policy

Within Austria a large proportion of electricity generation is produced from renewable energy sources. Most of this renewable energy is hydro power, which provided almost 68% of the total energy generation in 1999.

Some 50% of electricity demand is met by hydro projects on the Danube alone, but the current demand-driven capacity growth in Austria is expected to require the equivalent of another Danube within a decade. With some 100 MW of additional thermal capacity required annually, the current demand-led boom is expected to last for at least another three or four years.

However, while gas and coal still account for about 23% of production, Austria has set out its ambition to generate 78.1% of electricity from renewable sources by 2008. At the Kyoto conference, Austria committed to reduce its greenhouse gas emissions by 13% towards around 6.6 tonnes CO2e per capita by 2010.

In order to achieve these objectives, the country aims to increase generation from renewables and CHP as set out in the Green Electricity Act or àƒ—kostromgesetz, which proposes measures to generate 9% of electricity from small-scale hydroelectric plants and 4% from renewable energy, the rest being generated from large-scale hydro.

This is to be achieved by providing federally decreed aid in the form of supply tariffs until 2015. In July 2006 the European Commission approved the Austrian feed-in tariffs for electricity from renewable sources and the support tariff for CHP installations for public district heating.

This decision, which retroactively authorizes the support measures contained in the àƒ—kostromgesetz 2002, paves the way for the continuation of the support under the new Green Electricity Act.

Commenting on the decision, EU Competition Commissioner Neelie Kroes said: ‘I am happy to approve aid for the promotion of green electricity, especially as this is a very important objective of the Community policy for environmental protection and serves the development of sustainable energy.’

Through the àƒ—kostromgesetz, in force since 2003, fees which had varied from state to state are replaced with a uniform fee for power generated by CHP plants, renewable sources and small hydro power plants from 2007. For CHP the current feed-in tariff for district heating is a little over €0.05/kWh.

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