Start of Operation
1986, expansion estimated to open 2010
A new 850MW gas combined-cycle power plant is being added to the Mellach power plant in Austria. The plant is being built for ATP by Siemens, and will cost an estimated €400m. It will also provide 250MW of district heating for the Greater Graz Region, so generating around 5,000GWh a year.
The existing Mellach power plant already has an installed electrical power of 245MW and 230MW district heating. The plant is powered by hard coal, and exhaust gas cleaning (reducing nitrogen, dust and sulphur emissions) has been fitted.
It has recently begun burning up to 6t/h or 99t/d of wet sludge, so 34,900t/a. With dry matter, the amount is about 10,500t/a.
The tightening of the regulations of the Austrian Federal Waste Management Act has greatly reduced the extent to which sewage sludge can be used on agricultural ground. Since 1 January 2004, no untreated or only drained sludge from commercial sewage plants has been allowed to be deposited.
The simultaneous combustion of sewage sludge at Mellach is a way of disposing of this. CO2 emissions are reduced as the sewage sludge is used as a substitute for coal. At the Fast Forward Awards 2005, ATP won the special prize for eco-technology for the project.
A test operation was performed in Mellach in December 2003 on sludge burning. The drying capacity of the coal mills is sufficient for an average water content of coal and a maximum sludge amount of 1.5t/h per mill. If the coal water content rises, the sludge amount has to be reduced. The chemical and physical properties of fly ash and gypsum are similar to those without burning sludge.
Emissions from flue gas include dust, SO2, NOx, CO2, polychlorinated dibenzodioxins and -furans, polycyclic aromatic hydrocarbons, heavy metals, ammonia, hydrogen chloride (HCI) and hydrogen fluoride (HF). Emission parameters are below the required limits. A decision was therefore made to implement the sludge-burning project as soon as the required licences and the proof of profitability were available.
The test operation started in November 2005. The sewage sludge plant consists primarily of a receiving bunker, a buffer silo and a dosage into the coal mills. Sewage sludge and coal are blended in the coal mills, grinded and blown into the existing burners.
Steam is generated in a steam generator through the combustion of coal, natural gas, crude oil, biomass and substitute fuels. The steam leaves the steam generator and flows through the guide and rotor blades of the turbine, which drives the generator via gear transmission. Electricity from the generator is fed into the interregional grid.
The steam that exits the turbine is converted back into water in the condenser unit. This water is then fed back into the steam generator and the water-steam cycle starts again. In co-generation plants that produce heat and electricity, part of the steam is taken from the turbine and used to heat the water of the district heating network.
Austrian Thermal Power GmbH & Co KG (ATP) is a subsidiary of Österreichische Elektrizitätswirtschafts AG (Verbund) with headquarters in Graz.ATP was founded in 2001 and now has thermal power plants from Draukraft, Verbundkraft and STEWEAG.
ATP erects and operates thermal power plants with and without power/heat cogeneration. The company currently has around 400 employees at its power plants in Graz.
ATP has a total of nine power plants with an overall installed capacity of 1,850MW.
The four power plants Dürnrohr, Voitsberg, Mellach and Neudorf-Werndorf 2 have an overall capacity of 1,145MW, and generate an average of 4,600GWh of electrical energy per year. Four further plants are mothballed and one plant is leased.
The selective catalytic reduction (SCR) was installed by AE&E. SCR has been regarded as the most efficient process for reducing nitrous oxides emissions in the incinerator flue gases. Since the installation of the first SCR system in Austria at the beginning of the 1980s, AE&E has been a European pioneer in the field.
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