Energy - Green electricity comes out the woods
Dortmund, at the heart of the Ruhr area: Where once the chimneys of the coal mines and coking plants puffed smoke into the sky, green electricity is now being generated from wood. The thermal process that makes this possible has been known for 200 years. What had been lacking was the required technology to utilise wood in an energetically sensible and economically profitable manner, not only for the production of heat, but also of electricity. Biomass Energiesysteme GmbH & Co. KG has now closed this gap. The Dortmund plant manufacturers make innovative wood gas production plants and use GEA Küba heat exchangers for the wood drying and dry cooling process.
The new environmentally friendly gasification technology produces a combustible gas from fresh wood. This is done by thermal conversion in a DC fixed bed gasifier. The CO2 neutral gas fires a block heating power station which cogenerates heat and electricity.
After the Dortmund plant manufacturers put the first pilot system in Germany into operation in Arnsberg, Westphalia in 2006, they followed it up with the second wood gas plant in Schmallenberg in 2007. The third and fourth wood gasifiers went on line in Dortmund in June 2008. These were realised
in cooperation with DEW 21, the Dortmund Energy and Water Suppliers. What was unique about the plant in dortmund was that for the first time, a plant was built with two parallel production lines so that the conventional energetic power of the gasifier plants was approximately doubled.
Together, they invested a good 3.3m euros in the future of energy supply and built a wood gas production plant over an area of 4000 square metres which could supply around 1000 households with electricity. The plant is designed to output 540 kilowatts (kW) of electric power and 800 kW of thermal power.
Wood that ist gasified is fresh leftover wood which has been rejected by the sawmills. Unlike in conventional wood burning, the type of wood is of no significance. 5,000 tonnes of wood are consumed a year. This corresponds to a consumption per household of around 5 cubic metres a year. The system is filled with wood chips, which has been chipped by the system operator after the wood has been delivered. The Dortmund pilot plant feeds the generated electricity into the netword according to the EEG (Renewable Energy Act) and supplies heat to the DEW 21 premises, also called “Zinkhütte”. The remaining heat which arises during the generation of electricity is used to dry the wood chips. The drying process takes around 24 hours on average. During this procedure, water flows through the GEA Küba air heater at a temperature of 90°. There is one Küba air heater per process line. The fins dissipate the heat into the drying air and heat the air to 70°C. High-performance fans provide the required air circulation. The hot air removes the core moisture from the wood and therefore replaces the necessity of a longer storage process. This is because only dry wood can be used.
“The gas-liquid heat exchangers from GEA Küba provide the best possible heat transfer, thanks to their large surfaces and their fin structures, and are ideally suited for the drying process,” said Dr Thomas Wienands, managing director of Biomass Energiesysteme GmbH. The company was founded in 2006 and is located in Dortmund.
Biomass Engineering Ltd., whose owner is also a partner in Biomass Energiesysteme, has been carrying out research for the optimisation of gasification technology since 1995, and launched a mature gasification process in 1997. The innovative technology was originally developed in the UK by Biomass Engineering Ltd. for the British leather industry to dispose of the waste in an environmentally friendly manner.
In the meantime, a larger number of plants have been in operation in the UK and Ireland for many years, helping to reduce dependency on fossil fuels and simultaneously accelerating the change to ecological solutions in energy generation. The core of the plant is the gas generator in which the wood chips
are thermally decomposed. Wood gas is created in this process. The wood gas is purified at approx. 500°C in the downstream ceramic filter, where tar, as well as other hydrocarbon compounds, are removed. It is the innovative filter technology which makes the utilisation of the gas possible at all. When ligneous biomass is gasified, a tar substance is automatically created which, through combustion, would destroy any combustion machine. The tar content in the gas is therefore reduced
to the analytical detection limit of 20 milligrams per cubic meter.