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● ● ● Particularity : valorisation of composted refuse through heat production.
The wood energy Trail
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Lausanne : an alternative use for forest waste-energy
Lausanne
• Population : 110 000 inhabitants.
Valorisation of wood waste
Vaud region
Fuel supply
Photo AJENA
La Tuilière is a composting platform which treats more than 65,000 m3 of waste from tree pruning and felling (more than 80 % of its acti-
The grinding and composting platform at La Tuilière
Photo AJENA
vity) as well as assorted plant waste collected from households. The increasing volume of this wood waste, and difficulties in selling the resulting compost, prompted the managers of the site to seek an alternative arrangement for the recycling of wood waste in the Lausanne region. They finally decided to install a boiler fired by shredded wood with a capacity of 3 MW. The town of Lausanne has a great advantage in its extensive heating network, which made it possible to join this installation, thus providing a new source of energy in a sector distant from other boiler plants. To connect the boiler to the network it was necessary to implant link of 1,600 m in length. The town of Lausanne plans to develop its urban expansion around this extension of the heating network, which has saved the town the equivalent of 1,300 tonnes of oil.
The boiler house and his silo
Information on the community • Altitude : 400 to 800 m,
The fuel used comes in part from the wood waste received at the composting site (trunks, stumps, refuse after screening), but the majority (two-thirds of the annual consumption, 7,000 steres) is refuse from the wood industry and by-products from forest clearing. The annual consumption is estimated at 25 000 m3 of shredded chips and defibred mulch. The wood is shredded in a tub grinder with blades to an average granulometry of 4 x 4 x 1 cm. This fuel is then taken to the feeder silo, or stored outside if there is no immediate need for it. The concrete feeder silo has a moveable covering and hydraulic scrapers for removing the fuel as well as two guillotines to avoid fuel build-up. When the fuel enters the boiler furnace, it passes through a funnel equipped with blades that chop up any bits of fuel that are too long for the boiler. Its capacity of 150 m3 suffices for two days with the boiler burning at full capacity.
A self-operating boiler Installed at the end of 1995, the boiler, with an output of 3,000 kW, is equipped with a Tiba Müller combustion chamber with moveable grates which is capable of burning wood with a moisture content of up to 50 % of gross weight. In the heat exchanger with smoke flues, the extremely hot gaseous effluents attain speeds of up to 20 m/s, which promotes the self-cleaning process. Also to reduce the need for cleaning, electromagnetic valves blow compressed air (10 bars) into the smoke flues in sequence. Grates transport the ashes to an ash-clearing screw, where they are taken by a chain conveyor to a magnetic drum which separates the particles of metal from the smoke. The ashes are then collected in a receptacle with the dust extracted by the extractor filter. These residues have an extremely low heavy metal content and can thus be used for compost. Another system, called DeNOX, considerably reduces
© ITEBE- july 1999
Switzerland