Pictures of the Future Spring 2008
Energy for Everyone – Water Demand in Coal-Fired Power Plants
Fit for the Desert
In Australia’s Kogan Creek, Siemens has built a coal-fired power plant that requires very little cooling water and is therefore ideal for use in arid regions.
The world’s largest cooling condenser (below) ensures that this Australian coal-fired power plant operates with 90 % less water than comparable systems
Drive straight ahead for 200 km," says the navigation system. And once the skyline of Brisbane has disappeared in the rear-view mirror, a well-nigh endless road stretches through the dry back country of the eastern coast of Australia. Only after another 250 km does a huge power line raise hopes that the destination is near. But another 30 km pass before a smokestack emerges near the little town of Chinchilla, indicating the location of the Kogan Creek Power Plant. In front of a corrugated iron hut, the visitor is greeted by red dust, aggressive flies and Thomas Scherer, who has been directing construction of the plant for six years on behalf of Siemens.
"The first ideas for the project date from the early 1990s," says Scherer, and the first contract was signed in 1999. But since there was a glut on the energy market, the project was halted by the government of Queensland, which owns CS Energy Ltd, the plant’s operator. In 2004, forecasts again predicted increased demand for energy, and Kogan Creek was given a new lease on life. This particular location was chosen for the plant because coal was readily available just below ground and there is a major high-voltage transmission line 28 km away. In fact, it’s the main artery for the transmission of power between the federal states of Queensland and New South Wales. Energy fed to the line supplies major cities on the east coast, including Brisbane and Sydney, which account for approximately half of the Australian population.
During a tour in Scherer’s all-terrain vehicle, it quickly becomes clear what else makes the power plant so special. For a start, there is Kogan Creek, which, like most creeks in Australia, is dry. And where there’s no water, there’s not much sense in having cooling towers—features that are as much a part of a coal-fired power station as boilers and turbines.
The eye lingers not on imposing cooling towers but on a roof the size of a football field that stands on 15-m-high stilts and has no apparent function, since it serves neither to hold off the non-existent rain nor to provide shade for any equipment beneath it. Scherer climbs up a steel staircase and discloses the answer to this mystery. Beneath huge corrugated steel sheets arranged like gable roofs, two low-pressure turbines emit hot steam at 60 to 80 °C. Each second, about half a ton of the gas flows through large heat exchangers that resemble giant automobile radiators. Fans nine meters in diameter blow air against the metal sheets from below and cool the steam so that it condenses. Each second, 500 liters of water flow into a collector at the lower end of the heat exchanger clusters and then into a tank, from which the water is fed back into the power plant via pumps and is again heated to 540 °C in the boiler.
Full Power in an Arid Climate. The huge cooling condenser, which comes from the GEA Group in Bochum, Germany, is not the first of its kind, but it is the largest in the world. And the power plant is not only Australia’s most efficient but, with an output of 750 MW, it is also the country’s largest. History is no doubt being written here and Siemens and Babcock Hitachi expect others will imitate Kogan Creek. Siemens supplies the turbines, generator, transformers, and control systems while Babcock Hitachi is responsible for the boiler, steam lines, and flue-gas treatment.
Australia’s increasingly dry climate is now affecting the builders of power plants. At Tarong Power Station, a coal-fired facility about a hundred kilometers northeast of Kogan Creek, three of the four units have had to be shut down at times because of dryness. There, the cooling water comes from storage dams via two pipelines 96 and 78 km in length. Each second, about 600 liters of cooling water is vaporized in the two cooling towers.
Despite cooling problems, however, coal power will continue to form the backbone of Australian power generation, because it is extremely cheap. The reason for this can be seen four kilometers away from Kogan Creek, where hard coal lies in abundance at the surface, covered by nothing more than red loam and withered grass. Excavators shovel up to 1,100 t of coal per hour—2.8 mill. t per year—onto a conveyor belt that leads directly to the boiler. Each hour, 75 t of ash is mixed with water to form a slurry, which is fed into a sink behind the site, where it hardens. In three years, the ash will be deposited where the coal is being extracted now.
Kogan Creek cannot operate entirely without water. Three tanks that draw water from deep bores make it available for drinking and fire fighting. They also replenish losses in the steam cycle of the turbines and supply cooling water for electrical equipment that cannot be cooled with air alone.
Nonetheless, the amount of water used is low enough to break records. Compared to similar power plants, the air cooler reduces water consumption by 90 %. That offers extra reserves in extremely dry periods, during which water-cooled power plants are forced to scale back their output. At Kogan Creek, water can be sprayed beneath the condenser surfaces for additional cooling. "That means we can operate the plant at its full capacity of 750 MW even at temperatures well over 40 °C, or tease out a few more megawatts when there are bottlenecks in the grid," says Scherer.
Kogan Creek’s commissioning ceremony took place on November 28, 2007. According to Albert Goller, Managing Director of Siemens Ltd. Australia and New Zealand, it is "the most efficient coal-fired power plant in Australia." The plant is designed for an efficiency rating of 45 % for comparable water-cooled facilities, which is one of the highest in the world, even though it gives up a few percentage points of efficiency due to Australia’s climate. Policy makers are satisfied too. Anna Bligh, Premier of Queensland, commented: "Kogan Creek will set new standards in environmental compatibility for coal-fired power plants."
Bernd Müller
Respect for Aboriginal Culture
In the tradition of the Australian Aborigines, people have no right to own land; they are instead merely its users. That applies as well to the site where Siemens erected the Kogan Creek power plant. According to Australian law, the builder must take into account the interests of the Aborigines, who claim the right to use the land. At Kogan Creek, there were five such families. In August 2003, the owner of the plant and representatives of the clans went over the entire area on foot to collect or document archeological evidence of earlier land use, including pits for water storage, stone tools, and markings on trees. During excavation work, there was likewise always an Aborigine present. About 22,000 artifacts were collected. When it was not possible to remove the objects, the layout of the power plant was modified. In the middle of the site, for instance, there is an island with trees scored with markings, and water holes. "Sometimes the discussion was very emotional," recalls Thomas Scherer, but the respect shown for this cultural heritage was worthwhile. It was the mutual agreement that made the construction of the facility possible in the first place.