Well worth going underground

The Finnish capital of Helsinki suffers a chronic shortage of land for building. In a move to free up valuable land for redevelopment, Helsinki Energy has moved its 500 000 t open-air coal stockpiles to an underground storage facility at the Salmisaari power plant. The open-air storage base occupied 100 000 m2 of land, which is now to be redeveloped with offices for the high-tech industries.

The new storage system at Salmisaari includes crushing and conveying facilities, large underground silos and consumption storage facilities. This system of storing coal underground in the bedrock is thought to be the first of its kind in the world, and includes a 98.5 m high vertical Trellex Pocketlift conveyor from Metso Minerals Wear Protection & Conveying (WPC) to take coal to the surface.

The Salmisaari power plant, located within the harbour of Helsinki, is a combined heat and power (CHP) plant. It generates an average 700 GWh of electricity and 1500 GWh of heat annually. At full capacity, it burns approximately 70 t of coal per hour.

Coal is delivered by ship from Poland and Russia to the power station’s own docks. Directly after unloading, it is crushed before transportation by conveyors to 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, equivalent to 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 Kottonen.

The underground storage system, thought to be the first in the world, features a 98.5 m high vertical Trellex Pocketlift conveyor to take coal to the surface
Click here to enlarge image

The main part of the €65 million project, undertaken by a consortium of Finnish contractors, 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. The project was started in 2000 and completed in July 2004 when the silos started to be filled with coal.

According to 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.”

Coal is fed from the bottom of each silo into vibrating hoppers and on to a belt conveyor 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 station’s consumption storage area.

The Trellex Pocketlift system, delivered by Metso Minerals 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/s.

A Trellex Pocketlift system is an ideal solution for handling high mass flow of bulk material for heights up to 500 m by means of a vertical conveying process. At Salmisaari the angle is 90° with a lifting height of 86.5 m. The charge and discharge units are both 10 m.

The new storage facility at Salmisaari, Finland, includes crushing and conveying facilities, large underground silos and consumption storage facilities
Click here to enlarge image

“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.

The Trellex Pocketlift belt 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 with a length of 229.5 m, 459 triangulated cross bars are screwed onto both base belts at 500 mm intervals. Between these 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.

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.”

LCPD rule lowers NOx

As companies prepare for the impact of the Large Plant Combustion Directive (LCPD), Mitsui Babcock has been awarded NOx reduction contracts worth a combined £14 million ($24 million).

The LCPD will become effective in 2008 and will control the levels of permissible NOx emissions from power stations.

Mitsui Babcock will work on three UK power stations including EDF Energy’s Cottam, Drax in North Yorkshire and Didcot in Oxfordshire.

Peter Emery, production director at Drax Power Limited, said: “In early 2004 we became one of the first to take the initiative further to reduce our NOx emissions well ahead of the implementation of the LCPD.”

Mitsui Babcock will design, supply and install a full boosted over-fire air system and an Forced Draft over-fire air system for all three power plants.

Iain Miller, COO of the UK based company, said: “We are seeing a significant surge in demand for NOx reduction technology.”

Stimulating simulators

A subsidiary of L-3 Communications is to extensively upgrade the nuclear power plant simulator operated by a large utility in North Carolina, USA.

The project will see L-3 Communications MAPPS replace the majority of the simulator’s current systems, including the primary, containment, emergency core cooling and Balance Of Plant process systems.

All of the new replacement models will be developed with the company’s ROSE simulation environment, which has been emplyed by L-3 MAPPS for almost 15 years.

The order is an extension to ongoing work that company is carrying out to replace the simulator’s electrical system models.

With both projects underway, the improved simulator is expected to be ready for action in early 2007.