Overarching ambition

Giant arched timber columns and what’s thought to be the largest green wall in Europe signal the sustainability credentials of a striking new energy-from-waste facility in Leeds. Stephen Cousins reports

A vast 42 metre-high, 123 metre-long wall of vegetation is the not the first thing you expect to see on an out of town industrial estate, and certainly not the side of a power station, but that is precisely the sight that greets visitors to the new Recycling and Energy Recovery Facility (RERF) in Leeds.

The green wall is a key sustainable element of the 12,000 m2 building, designed by French architects S’pace for Veolia Environmental Services, Leeds City Council’s waste management partner, which will operate the facility under a 25-year PFI contract.

The plant will process around 214,000 tonnes of this waste a year, and features an arc-shaped wooden frame, the tallest of its type in the UK, constructed entirely from giant ‘ribs’ of glulam timber.

The wall was conceived as habitat for birds, animals and insects, and represents the ambitions of a local city council keen to transform public perception of energy-to-waste facilities, which are typically considered undesirable additions to neighbourhoods.

Jean Robert Mazaud, president of S’pace, tells ADF: “The first time I arrived on site, all I could see was a huge parking lot, but sprouting up between the various concrete surfaces were small amounts of grass and flowers.” It was a demonstration of how nature is resistant to the stupid actions of humans.” The wall of vegetation is said to symbolize how people can protect our living environment, “because a dead environment does not need protecting.” A passionate French architect, Mazaud has been designing industrial plants for the past 35 years, 10 of which have been located in the UK. The Leeds facility represents the culmination of many of his ideas, and in many ways is his most ambitious to date. He adds: “I believe we must show in industrial buildings that we are sustainable, planet-orientated and strive to maintain and protect the living environment. We have no choice in this, if a client says they don’t want to go down that route I just quit.”

Ambitious targets

The RERF is located on the Cross Green industrial estate, around five kilometres south east of the city centre. It was constructed by main contractor Clugston and French waste energy specialist CNIM.

The facility will mostly target household bin waste, processing around 214,000 tonnes of material and generating up to 15 MW of electricity for the national grid each year, plus combined heat and power for local businesses. It is also forecast to recover around 16,000 tonnes of recyclable material, removed using specialist machinery.

The facility forms an important part of the council’s 20-year Integrated Waste Strategy, launched in 2005, which targets a minimum 55 per cent reduction in waste by 2016, rising to 60 per cent in the longer term.

Before this project, all of the city’s residual waste was sent to landfill, a costly process made more costly by rising landfill taxes that were pushing up costs by around £1.5m per year. Construction of the RERF is targeted to save the council £200m by 2040.

The plant comprises three connected buildings, a mechanical pre-treatment hall, a main energy recovery facility and an ash storage facility.

Waste first passes through the pre-treatment hall, where materials, such as plastic, cardboard, ferrous and non-ferrous metals are removed for recycling, and non-recyclable materials are carried via conveyor into the main facility.

Here they are incinerated to produce steam to drive turbines and generate enough electricity to power up to 20,000 homes. Ash, a byproduct of the energy generation process, is kept in a dedicated storage building before being taken away for recycling.

“Each phase uses space completely differently, which generated three differently shaped volumes,” says Mazaud. “The first has a huge flat surface, the second a high and narrow volume, the third a pyramidal volume.”

Giant timbers

The main facility is instantly recognisable for its chunky timber superstructure, comprising 20 load-bearing glulam arches designed to fully envelop the processing equipment inside.

Mazaud comments: “The building had to be tall because of the arrangement of the industrial equipment inside. The furnace burns such a large quantity of waste that a large space is required to stabilise the process and cool the air with air-cooled condensers, at the east end of the building, before it is rejected.” The use of 42 metre-long glulam timbers is not unusual in construction, what is unusual is to erect them vertically, The use of 42 metre-long glulam timbers is not unusual in construction, what is unusual is to erect them vertically even though this orientation is fairly straightforward to achieve using existing technology.

A total 2,600 m3 of glulam was supplied, assembled on site by German timber specialist Hess Timber – whose recent work includes the D1 tower in Dubai – and the Museum of Foundation Louis Vuitton, in Paris. Each column is curved at the top and has a cross section of 400 mm x 760 mm.

Engineered timber is very robust and lightweight, recyclable and energy efficient and it worked out cheaper and faster to install than steel or concrete alternatives. In the event of a fire, the timber would (counter-intuitively) burn slowly remaining self-supporting for many hours compared to steel, which transforms and twists relatively quickly.

“The client was initially adamant there should be no wood, but its strong performance in a fire turned out to be one of the arguments I used to persuade them it was the right choice for the project,” says Mazaud, whose fascination with wood goes back to his childhood growing up in a forest where his family ran a saw mill.

A timber frame was also used for the ash storage building, a 12 metre-tall half-dome shaped structure covered by sedum roof.

The arched frame of the main facility is clad in translucent polycarbonate cladding, on its north face, the south elevation is covered by the 1,800 m2 green wall, which runs in vertical strips between the giant timber columns.

The green wall was designed and installed by UK-based firm Biotecture and will provide a live habitat for all types of insects, birds and other animals.

It is inaccessible to humans which should help protect the wildlife from being disturbed or accidentally killed by gardeners or maintenance engineers.

The vegetation is fed using a hydroponic spray irrigation system with intelligent water management. According to Biotecture, the system offers great resilience and fast installation, because most of the work, such as ‘pre-growing’ the walls, is carried out off-site, giving an instant visual impact as the panels are planted with semi-mature plants.

Staying grounded

Such a high level of sustainable design is unusual for an energy-from-waste plant and S’Pace faced challenges trying to convince project stakeholders, whose focus is normally on functionality and cost, that it was the right direction to take.

The project was also subject to a sustained campaign from locals and other organisations, and received 300 formal objections during the planning process.

As a result, Mazaud and the design team met with Leeds City Council’s design committee up to 12 times a month to explain the design and provide various guarantees that the project would succeed.

“This is a very special and unusual way to control the design of an industrial facility,” he says. “The committee was very tough and wanted to check every single detail before signing on the dotted line – they needed reassurances regarding the use of wood, that the traffic around the plant would be under control, that there would be no smell or noise – they wanted guarantees on every single aspect.” However, the architect saw this high level of scrutiny as a benefit rather than an obstacle, he adds: “It was crucial and provided the best support possible

to convince my client, who attended every meeting, that they had to be able to satisfy these people, otherwise there was no project, no contract, and no profit.” The facility officially opened in November and, despite some early teething problems with equipment and processing that have caused it to fall short of recycling targets, serves as an important benchmark for how to build greener, more socially sustainable power plants in the future.