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Waste not want not

Roof trusses will remain fully exposed as feature elements

Representing the largest single capital project ever commissioned by the Jersey Government, a new energy from waste facility, which will provide 7% of the island’s electricity, is under construction at La Collette. Martin Cooper reports.

FACT FILE: La Collette Energy from Waste facility, Jersey

Main client: States of Jersey
Architect: EPR
Main contractor: Spie Batignolles Camerons
Structural engineer: Campbell Reith
Steelwork contractor: Bourne Steel
Steel tonnage: 900t

The UK needs to find alternative sources of energy as well as methods for waste disposal that do not involve landfill sites. Many local authorities believe energy from waste facilities, where rubbish is incinerated to produce a renewable source of electricity, are the answer to both of these pressing questions.

A number of these plants are currently under construction across the UK and one such facility is at La Collette near St Helier on the island of Jersey. Once commissioned in 2011, it will replace an existing incinerator and provide the Channel Island with a reliable means of waste disposal for the next 25 years. It will also be able to produce 10MW of power, equivalent to 7% of the island’s electricity usage.

The facility will be accompanied by a bulky waste recycling plant, with the capacity to pre-treat up to 40,000t of household, commercial and industrial waste per year.

Commenting on the project, the States of Jersey’s Director of Waste Strategy Projects, Will Gardiner, said the plant’s development represents the end of a lengthy process, involving the consideration of numerous technological options.

Energy from waste is regarded as the best option for an island with few waste management facilities and a limit on the use of compost and digestate on its unique agricultural land, which is primarily given over to the production of potatoes.Although the new plant sits adjacent to an existing power station, with which it will share a chimney, cooling water and other auxillary services, the facility will not resemble a run-of-the-mill industrial building. The majority of the structure’s steel frame will be left exposed, with the large circular columns and roof trusses aiding a modernist architectural vision.

“Steel was chosen for the structure’s main frame to fit the overall architectural concept,” says Will Shaw, Campbell Reith Project Engineer. “And in order to get the required open internal spans steel was the obvious option.”

The gable end of the steel framed energy centre is formed with large box sections positioned inside the column line

Trusses are brought to site in two pieces and welded together at the site’s assembly yard

The completed 36m long sections are then lifted into place

Working on behalf of main contractor Spie Batignolles Camerons, Bourne Steel is fabricating, supplying and erecting approximately 900t of steelwork for the project’s main frame.

The frame is formed by six large 36m long roof trusses supported on 37m high CHS columns, which are spaced at 16m intervals. At roof level the main trusses are tied together by a series of 16m long secondary trusses. Each gable end is formed with a box section (500mm x 30mm with 805mm x 20mm wide plates welded either side) goal post structure which stands approximately 800mm inside of the main perimeter column line.

Completing the steelwork concept, the columns are connected together with seven lines of bespoke fabricated cladding wind rails, which begin 6m above ground level and extend upwards to the roof at 4m intervals. These rails with preformed feature openings are designed to remain exposed beyond the line of the cladding and aid the overall vision for the structure. This is further enhanced as each bay of windrails is connected to the roof structure at midspan by two vertical macalloy bars which run the full height of the elevation.

Much of the project’s substantial concreting works had already been completed prior to this year’s steelwork programme kicking off. Large concrete walls and structures housing offices at one end of the building, and the 30m deep refuse tipping bunker, all provide the steelwork with some stability. Where there are no concrete walls to tie back into, such as the two gable ends and near to the roof, the steelwork is braced.

Delivering structural steelwork to a site in Jersey from mainland UK has been a logistical challenge. From Bourne’s facility in Poole, Dorset the steel is transported by road to Portsmouth and then shipped overnight by ferry. However, once on Jersey the loads are too big to be moved from the harbour to the site, as parking restrictions have to be put in place to make sure the loads can be manouevred around some tight bends. This means all deliveries to the site from the harbour are made only on Sundays.

The tubular columns are transported to site in three sections – two 15m lengths and a third 7m piece. The 5m deep roof trusses arrive in two equal sections, while the majority of the remaining steelwork is delivered complete.

“We have an assembly yard on site where the tubular columns and roof trusses are welded, shotblasted and painted, before being lifted into place as complete sections,” explains Neil Senior, Bourne Steel Contracts Manager.

Steelwork erection has been done with a combination of the on-site tower crane and an 80t crawler crane. “We started erecting the structure from one gable end and then worked our way down the building,” adds Mr Senior. “There are points further down the structure which are out of reach for the tower crane.”

As well as the main concreting works having mostly been completed prior to the steel frame erection beginning, the majority of the facility’s equipment, such as boilers, were also installed earlier in the construction programme.

Interestingly, as part of another separate contract, a further 400t of structural steelwork has been erected to support the internal equipment and to provide maintenance walkways. The internal steelwork is completely independent from the main frame as the two steel elements are not connected at any point.

“We’ve had to leave a couple of areas open for machinery installation,” says Mr Senior. “But the majority of our steelwork is covering over areas which are largely completed.”

Steelwork for the main facility is scheduled to be completed by July, when Bourne will begin erecting the adjacent bulky waste recycling plant. This building will comprise of a large portal shed measuring approximately 70m x 25m with a maximum eaves height of 14m.

It is anticipated the facility will be up and running, providing Jersey with a clean and renewable source of energy and waste disposal, by May 2011.

Situated on a headland at La Collette, the new energy centre will share a chimney with an existing power station

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