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Helsinki, Finland -- Europe's largest vertical Trellex Pocketlift conveyor system from Metso Minerals Wear Protection & Conveying (WPC), feeds coal over a distance of 98,50 m from unique purpose-built underground coal silos to the surface of Helsinki's Salmisaari power station; in a move to redevelop valuable building land.
The Finnish capital of Helsinki, mainly located on a peninsula, suffers a chronic shortage of building space in the city. In a move to redevelop land, the city owned Helsinki Energy has moved its large 500,000 t open-air coal stockpiles to underground storage at the Salmisaari power plant. The open-air storage occupied 100 000 m2 of land and is to be redeveloped with offices for the high-tech industries; providing an excellent seaside location.
The new storage system includes crushing and conveying the coal to large underground silos from where it is fed into consumption storage for daily use. This system of storing coal underground in the bedrock is thought to be the first of its kind in the world. A 98,50 m high vertical Trellex Pocketlift conveyor from Metso Minerals Wear Protection & Conveying (WPC), the same source for the well known Trellex Flexowell belts, forms part of the transportation system, taking coal to the surface.
The Salmisaari power plant, located within the harbour of Helsinki, is a combined heat and power (CPH) plant. It generates an average 700 GWh of electricity and 1500 GWh of heat annually. At full capacity, approximately 70 t of coal per hour is burned at the plant.
Coal is delivered by ship from Poland and Russia to the power station's own docks. Directly after unloading, it is crushed to a fraction of its normally max 100 mm - being the most efficient size for handling and transportation.
This is transported from the harbour by conveyors into the four underground silos, excavated in the granite bedrock.
"Each silo measures 40 m diameter and 65 m high," explains Jari Kottonen, Team Manager at Helsinki Energy. The silos total capacity is approximately 200,000 t of coal representing about half of the Salmisaari plant's annual consumption.
"This ensures sufficient security to take us through the hardest winters when it may not be possible for the coal ships to enter the harbour," says Jari Kottonen.
Construction
The main part of the project was the excavation of some 1,000, 000 m3 of crushed stone to make the 3.7 km tunnels and galleries plus the four silos; undertaken by a consortium of Finnish contractors.
According to Jari Kottonen, "The granite is a very high grade and although we are located in the harbour, we have no problems with leakages in the tunnels or silos. At the lowest point the tunnels are 126 m below sea level, which is the lowest point in Helsinki."
The project was started in 2000 and completed in July 2004 when the silos started to be filled with coal. The coal is tightly packed into the silos for safety reasons so as to prevent self-combustion.
Europe's largest
Coal is fed from the bottom of each silo into vibrating hoppers and on to a belt conveyor taking the coal to the Trellex Pocketlift conveyor. This lifts the coal vertically 86.5 m on what is thought to be Europe's largest vertical Trellex Pocketlift conveyor system, for distribution on the surface. The coal is then conveyed to the power stations consumption storage area.
The Trellex Pocketlift system, delivered by Metso Minerals Wear Protection & Conveying (WPC) in cooperation with Arthur Loibl GmbH, has a capacity of 500 t/h. The conveyor is driven by two 110 kW motors, lifting the coal at over 2 m per second.
A Trellex Pocketlift system is an ideal solution for handling high mass flow of bulk material for high lift heights up to 500m by means of a vertical conveying process. At Salmisaari the angle is 90 degrees with a lifting height of 86.5 m. The charge and discharge units are both 10 m.
"An ordinary conveyor solution would have meant a long conveyor belt at a low angle. This would have taken too much space," says Olli Patosaari, Manager at Metso Minerals in Finland.
In comparison to a standard Trellex Flexowell conveyor belt which consist of a cross-rigid base belt with textile or steel cord reinforcements, corrugated sidewalls and transverse cleats preventing the material conveyed from sliding backward the Trellex Pocketlift belt has a complete different design.
The Trellex Pocketlift belt (new development of Metso Minerals ( Moers ) GmbH) at Salmisaari comprises two narrow steel cord base belts each 300 mm wide, forming the band which has a total width of 1600 mm. On a total, endless belt lengths of 229,50 m, 459 triangulated cross bars are screwed onto both base belts in a distance of 500 mm. Between this cross bars 800 mm wide rubber pockets are fixed by screws to convey the coal. Cross bars as well as pockets can easily be replaced if required.
Helsinki Energy has signed a service agreement with Metso Minerals, which includes regular monthly service inspections. The status of the installation is documented in a written report each month.
"The Trellex Pocketlift system has proved to be a real alternative to conventional conveyor solutions as well as bucket elevators," says Olli Patosaari, Manager at Metso Minerals, Finland, "It is less noisy and demands less maintenance. It is also more flexible than bucket elevators as the discharge can be angled in relation to the loading point."
For more information contact,
Metso Minerals Oy
P.O. Box 307, Lokomonkatu 3
FIN-33101 Tampere
Finland
Telephone: +358 20 484 100
Fax: +358 20 484 141
Email: minerals.info@metso.com
Web site: http://www.metso.com/
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