Unloading of Wood Pellets for a co-fired Power Plant

For unloading of wood pellets from barges Electrabel selected a pneumatic ship unloader from Vigan. (Picture: Vigan)

Electrabel has increased the amount of biomass fuel at its co-fired Gelderland power plant in the Netherlands by a factor of ten. The wood pellets are delivered by barges and unloaded efficiently and dust-free by means of a mobile pneumatic unloader.

Alternative and renewable sources of energy are a major concern not only due to limited resources of fossil origin but also within the context of the world-wide efforts against gas emissions. New power plants as well as some existing energy producers are upgrading their existing technologies with latest innovations in order to fulfill their legal obligations of protecting the environment while containing costs.

The French group Suez is a major player in Europe and on worldwide level with about 200 000 workers and an annual turnover of more than USD 110 billions. Suez has integrated this approach for many years with very significant investment in engineering developments and state-of-the art industrial installations.

Electrabel, the electricity division of the group developed a special project during the last few years for its power plant in Gelderland (city of Nijmegen in The Netherlands) of a capacity of about 600 megawatts.

Tractebel, its Belgian engineering affiliate was in charge of developing this biomass and coal co-firing project by increasing the amount of wood pellets from 8 to 75 tonnes per hour, which is a rate of up to 20 per cent of the total energy produced by this up-graded plant. Since its operational start in 2010, this Electrabel power plant has become one of the world largest co-firing plant with wood pellets

Thanks to the excellent hinterland river and canal system in the Netherlands for bulk transport, the wood pellets are transported to the power plant by barges from various locations. Because coal fired power plants can not be switched on and off easily and because of the importance of a continuous power supply, the discharge of such volume requires a 24 hours per day reliability, and, consequently, the highest quality and the most efficient operational performances of the fuel handling systems.

The turnkey installation of the wood pellet handling plant for the project was carried out by the Belgium company Geldof. The main components of the plant include a 500 tonnes per hour mobile pneumatic barge unloader, quai belt conveyors of the same capacity, silo feeding with pipe belt conveyors and two carbon steel silos with a capacity of 5000 cubic metres, each. The silos are equipped with screw reclaimers to deliver the pellets via chain conveyors to the pellet dosing bins at 120 tonnes per hour from where the pellets are processed for combustion. The processing facility was also part of the installation by Geldof and includes hammer mills and wood dust screens, wood dust silos, pneumatic transport/boiler injection.

Barges are unloaded pneumatically at this site at the rate of 500 tonnes per hour via a mobile unit that eliminates dust emissions. According to Geldof, the complete circuit from quay to boiler uses completely closed conveyer belts, silos, hammer mill and buildings kept at a small under pressure to avoided any possibility for wood dust to escape. It is obviously unavoidable, however, that wood dust is present within the system, Therefore secondary containment measures such as dedusting and fire and explosion protection equipment are in place.

The scope of Geldof's work for the project included design, engineering, fabrication, mounting, testing, and commissioning of the civil and mechanical construction, including foundation and steel construction, ferro-non ferro separation, fire and explosion protection and detection, dedusting, and other components.

Vigan Engineering, also a Belgium company, was selected to manufacture and install the pneumatic unloader. The company, specialised in pneumatic and mechanical ship unloaders mainly for agribulk cargoes, looks back at 40 years of experience and more than 1150 pieces of equipment installed around the world.

Pneumatic Unloading

The transport of any wood residue is usually facing the challenge of the low density of those materials. Therefore the most common process is pelletizing in order to condense them into granules (usually about 10 to 15 millimetre length and a diameter around 5 to 6 millimetre).

Thanks to this process and with a reasonable content of humidity, the wood pellets are quite free flowing and there-fore allows for an easy conveying from the production facility up to its use as an input in the power co-firing with coal.