The 570MW Avedøre-2 power plant can work from biomass, and incorporates other measures to reduce environmental impacts. The Danish Energy Agency approved E2’s plans for the new plant at Avedøre, south of Copenhagen in September 1994. It was jointly developed between Energi E2 and Vattenfall.
The plant is located adjacent to an existing coal fired 250MW CHP plant, Avedøre-1, and was required to make minimum impact on the environment. As a condition of the project approval, SK Power had to decommission three older coal-fired power plants to reduce net emissions of CO2 (10%), NOx (20%) and SO2 (30%).
The Avedøre-2 plant has been designed for multi-fuel operation and uses a unique combination of gas turbines, fossil fuel boiler and biomass boiler. These offer high operational flexibility and plant availability. In cogeneration mode the new plant, inaugurated in early 2002, uses up to 95% of the input fuel’s energy content.
Electric power output from the new plant will meet 20% of power demand in eastern Denmark. The plant will also supply 485MW of electricity and 570MW of heat to Greater Copenhagen’s district heating system. The unit will be able to supply district heat to about 180,000 homes and provide electricity consumption for 800,000 households.
For even greater power availability, SK Power has an agreement with Vattenfall of Sweden whereby the Swedish company can take up to 200MW of Avedøre-2 power. In return, SK Power can call on 200MW of hydropower from the Indalseiven plant in the North of Sweden.
In 1996 the Danish authorities banned the burning of coal. When the plant was built, natural gas was expected to contribute 85% of Avedøre-2’s total fuel consumption in the main boiler. However, the price of natural gas then rocketed, so in early 2001 biofuel was decided upon for the main fuel source. Half of the 300,000t of the needed bioenergy pellets come from a plant run by E2, and the other half from local sources. A straw boiler uses approximately 150,000t of supplementary fuel per year.
The biomass plant comprises the straw storage facility, a boiler, an ash separator and ash and fly-ash handling equipment. A flue gas filter restricts particle discharge into the atmosphere. Bottom ash is recycled as a fertiliser. The steam is fed into an ultra-supercritical steam system. Because the combined plant uses a large steam turbine the efficiency of the biomass plant is 45%.
Avedøre-2 combines power from a biomass steam cycle and a fossil fuel fired ultra-supercritical steam cycle with heat recovery steam generators.
The ultra supercritical steam turbine operates at steam temperatures up to 600°C and at the time was the most advanced and efficient steam turbine in the world. The steam system operates at 300bar pressure and 580°C steam temperature. Reheat temperature is 600°C. Condenser pressure is 0.22bar. Boiler feedwater is partly heated by the exhaust flue gas from the gas turbines and is fed into the boiler at 310°C. The efficiency of the fossil fuel steam cycle is rated at 48.2%.
South of the main building, another building is under construction for the flue gas cleaning plant and the biomass plant. They will be separated from each other by a full-height concrete wall.