Federico II coal plant retrofit: wood domes have got it covered

ENEL's Federico II coal fired power plant, located in southern Italy, 12 km from the city of Brindisi, on the Adriatic Sea coast, is one of Europe's largest coal fired power plants. The power plant, built in the 1990s, is located on a 270 hectare site, with 16 hectares of buildings and covered areas.

The plant has four 660 MW units, which share a single 200 m stack with a diameter of 28 m. The table opposite summarises some of the key features.

The units have been extensively retrofitted, with upgrading of the coal mills, revamping of the selective catalytic reduction systems, and replacing of ESP systems with fabric filters on units 3 and 4 (2010-2012), bringing particulates emissions down to less than 10 mg/Nm3.

Currently the main focus of retrofit activity at the site is the construction of two large and highly innovative coal storage domes employing laminated wood, to reduce dust. Construction started on these domes in January 2013.

The supply of coal to the plant (6.5 million tons/year) is via a 13 km long system of conveyor belts and towers, plus service road, which connects the port area of Brindisi to the power plant. The coal is unloaded from ships via the conveyor belts which transport it to the central coal storage area of the power station.

To help minimise the environmental footprint of the power plant and to contain coal dust it was decided to create a coal storage park completely covered by storage domes with a system for conveying coal to the power plant boilers completely isolated from the atmosphere.

This is in line with ENEL's efforts to reduce its environmental impact while remaining competitive and providing its customers with affordable power, which entails investment in R&D, innovation and best available technologies.

Improved coal storage

The main measures to improve coal handling at Federico II include the following:

• construction of two new covered coal bunkers employing wooden geodesic domes (259C and 259B in the drawings opposite);
• installation of two new stacker/reclaimer machines with a high degree of automation;
• installation of new coal conveyors, with towers (T19, T20, T21 and T22) of prefabricated reinforced concrete, to connect the existing system to the new coal bunkers.

The two new geodesic domes, currently under construction, employ laminated wood. Each dome has a diameter of about 144 m and a height of about 49 m, providing a storage capacity of 210 000 m3 of coal, equivalent to about 180 000 tons.

In terms of diameter, these domes will be the largest of their type in Europe. The geodesic configuration and choice of materials, notably wood, have been guided by considerations of lightness, stiffness and strength, but above all because wood needs less maintenance and because, contrary to what one might think, it provides greater resistance to fire at relatively low cost.

The 15 month long design phase for the domes included wind tunnel tests to evaluate wind pressure, testing of the effect of lightning on the roof material to ensure electrical continuity of the coating, tests on structural nodes to verify their behaviour was in accordance with expectation, testing and fluid dynamic calculations relating to ventilation inside the domes, and testing and thermodynamic calculations relating to fires. Static and dynamic tests will carried out on the completed dome structure to confirm structural integrity and agreement between measurements of its actual behaviour and the mathematical modelling.

The domes will be equipped with fire protection control systems based on IR cameras and thermo sensitive fibre optic cables able to activate fire protection systems when specific temperature thresholds are exceeded.

The total investment in the two domes plus associated coal conveyors and stacker/reclaimers amounts to about €140 million.

The main suppliers include the following: stacker/reclaimer, Bedeschi; conveyors, FAM; wooden coal storage domes, Rubner Holzbau. Completion of construction is expected by September 2015.

An international example

Roberto Tomasi, senior VP, power plant development and construction area, Enel engineering and research division, describes this "great project at Federico II power station" as an "interesting challenge for engineering and research" and a clear sign from Enel of its intention to pursue "sustainable clean coal combustion."

Roberto Giazzi, site manager, says the implementation of the ambitious and innovative dome project requires a combination of "attention to detail and a passion for the project" while project director Franco Maffei notes that the coal storage project further improves the environmental credentials of a "facility essential for Italy" (building on other recent upgrades such as modernisation of the coal landing quay at Costa Morena port and particulate emissions reduction) and represents "international best practice in terms of technology technical adopted, not least the choice of laminated wood for the construction of the dome roofs."

Further information

Giancarlo Benelli, ENEL, Coal storage at Federico II: wood domes have got it covered