Forschungs- & Entwicklungsinformationsdienst der Gemeinschaft - CORDIS

Biomass fired superheater for more efficient electricity generation from waste incineration plants

Research was carried out in order to increase steam pressure for a steam cycle, based on a waste-to-energy-plant, avoiding the normal negative effect of high speed corrosion. In the demonstration plant the pyrolysis unit is fed with loosely cut straw. The pyrolyser is a specially designed 2-level horizontal plug-flow reactor, which is indirectly heated to 600 C by flue-gases in a heat jacket. After separation of char particles in a hot cyclone, the 500-550 C hot gas produced fuels a special low nitrogen oxide burner,. installed in an adiabatic combustion chamber designed for up to 1400 C operating temperature. Heat is used initially for superheating of the steam to the maximum allowable limit, secondly for heating the pyrolyser, and finally for preheating of combustion air to 400 C before it is led to the chimney at 150-200 C. Part of the flue gas is recirculated in order to reduce nitrogen oxide and increase efficiency. The separated char is conveyed to the combustion chamber of the steam boiler section where it is added as a top-up fuel. Based on the above, a full scale 3 MW plant was built.

Due to the low process temperature, the alkali/chlorides remain in the char fraction. Therefore a less corrosive pyrolysis gas is used in the external super-heater to boost steam. The actual plant is fed with up to 775 kg/h straw, producing 1 MW of pyrolysis gas and 2 MW of biocoal (300 kg/h). The gas can be converted to 300-780 kW of energy, depending on the steam data. The biocoal is used in the steam boiler of the base plant with an electricity gain of 24% (400 kW). Self consumption of the plant is 70 kW. The heat produced is used in a district heating network. The pay back for a commercial plant is estimated to be 6-9 years.

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COWI Consulting Engineers and Planners AS
Parallelvej 15
DK-2800 Lyngby
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