Volume 24, No.08 - August 2016

Waste not, want not: FROM CONSUMPTION TO POWER


 

Arguably almost every building type can nowadays be formed from wood: recent - and credible - design explorations for tall timber residential structures rising as high as 80 storeys may well be  deemed over-ambitious and beyond current technological reach, but concepts such as these have the considerable benefit of stimulating highly advanced structural engineering research and development, the results of which filter into more mainstream engineered timber construction. 

 

The building types (i.e. not civil engineering structures such as dams) that are the most obvious exceptions to this new rule are undoubtedly those facilities associated with the generation of nuclear power. Traditionally, their construction has consumed enormous quantities of in-situ reinforced concrete, the 14500m3 of this material in the foundation work currently being completed at the Hinkley C site being the most immediate example of this well-tried and tested technological approach - and this before the main bodies of the nuclear reactors themselves are constructed. However, it can be argued that the process used in the production of the cement required to manufacture concrete is one of the world’s largest contributors to greenhouse gases - and that calculation of this should be set against the anticipated carbon efficiency of the nuclear facility once it is up and running. 
But we nowadays live in a world where other options are not only possible but, for many, also broadly desirable. Whether for economic, environmental or sustainability reasons, the search for alternatives to fossil fuels to generate energy continues apace, as does the debate between the advocates of nuclear power and those who would give primacy to the development and application of renewable sources of electricity and heat. Ever increasing consumption of energy - especially in the world’s more developed economies - can also be directly correlated to profligacy in its use: instead of implementing approaches that reduce energy requirements, we simply seek more effective ways to produce greater amounts of what is nowadays considered to be an indispensable human requirement. 
 
Of course, in the modern global economy, those who have the means to produce energy are also able to exert other kinds of power - should they choose to do so - whether financial, industrial or strategically political. In such an unpredictable environment, the case for considerably more nuanced policies able to deliver energy independence is indisputable: the discussion, however, too often revolves around subsidies rather than efficiencies. 

The 20 huge glulam timber frames that make up the RERF’s structure endow it with a highly visible, cathedral-like quality, whilst the transparent polycarbonate cladding delivers ample daylight its interior

The 42m high engineered timber arches of the Recycling and Energy Recovery Facility (RERF) form the tallest ,and possibly the largest, glulam project in the UK

Having stated at the outset that almost every building type can nowadays be formed from wood, it should be said that this is not necessarily the case for the engineered structures required by some forms of renewable power generation: hydro dams, wave energy and offshore wind turbines being examples for which timber solutions have yet to appear*. This is not to say that they won’t: simply that the development finance required to take engineered timber, wood modification and timber /concrete hybrid technologies to the necessary advanced and scaled-up levels, especially with subsidies in the renewables sector being reduced or withdrawn completely, has yet to emerge. And whilst biomass might be a more immediate thought when one considers the use of wood in the generation of energy, in a circular economy this is very possibly the last option to contemplate for something that is, after all, a highly reusable natural resource. Whilst infinitely better CO2-wise than its previous coal fired process, some 98% of the biomass required to feed the huge demands of the Drax power station, for example, comes from overseas (73% from north America). Even allowing for it being sourced from sustainably managed forests and the fact that the carbon emissions associated with its transportation are relatively small, biomass is not perhaps the ‘silver bullet’ needed to deliver long-term energy independence, especially if rolled out more widely on a similar scale. 
Which, of the five W’s of renewable energy generation - waste, water (hydro), wave, wind and wood (biomass) leaves us with the first of these: power and heat generated from the detritus produced by consumer society and the types of buildings required to house the plant and equipment involved. In the past these facilities have been constructed using steel frames and steel cladding and have hardly been objects of great beauty, but a new breed has begun to emerge. 
 
Consumer waste is indeed one of the challenges of our times, and one that requires local solutions. Many would argue that we should focus our endeavours on encouraging people to reduce the amount of waste they produce, but the cold hard reality is that it will take some considerable time before the mainstream public willingly reduces its consumption and fully engages in the recycling options available and there will be an ongoing need to dispose of massive quantities of domestic rubbish. Black bin waste that goes to landfill currently costs taxpayers almost £85 per tonne in Landfill Tax and so, for local authorities, it is imperative to find other solutions such as energy and waste plants, of which there are now quite a number around the country.
What singles out the new Recycling and Energy Recovery Facility (RERF) at Leeds is that it is the first energy recovery centre to feature a recycling element before the rubbish is processed into energy. Designed by Jean-Robert Mazaud of S’pace Architectes who, for over 20 years has made something of a specialisation in this particular building type - he has delivered at least five other energy and waste management facilities in the UK as well as many more throughout France. Its distinctive physical form lies in the engineering and materials used in its construction: a series of arched, engineered timber frames that stand 42 metres high (only slightly shorter than the 52 metres of Leeds Civic Hall). These have been formed by Hess Timber, one of Europe’s leading manufacturers of glulam timber from sustainably sourced European larch and which, when manufactured as here into a large scale engineered timber product, can deliver a structural solution distinctly different from the heavy materials traditionally used for this type of facility. Adding to this unusual characteristic is the extensive green ‘living’ wall of its 125m long south facade and which is one of the largest in Europe. This not only enhances the visual impact of the building but also contributes to its biodiversity, a feature that helps fulfil Leeds City Council’s brief that the facility should not only provide a landmark (given that it was going to be big anyway) in the Aire Valley but that it should also visually communicate its sustainability credentials. 
 
When fully operational (the building only recently opened), the RERF will process up to 214,000 tonnes of the city’s annual black bin waste - around 75% of Leeds’ total bin output - and up to 75% of the total waste that will be brought to the site, the remainder being made up of commercial waste. Recyclable materials (i.e. those that didn’t already find their way into a green bin or civic skip and which make up 20% of the total that comes in) will be harvested and the remainder incinerated. The combustion process is anticipated to generate 11 megawatts of electricity - enough to power 20,000 homes - which will be fed into the National Grid. Also in development is a district heating scheme designed to pipe heat from the steam created in the incineration processes to municipal buildings, swimming pools, libraries and high-rise council flats. 
 
Overall, it is anticipated the 25-year, PFI-funded project will save taxpayers more than £200m in Landfill tax and environmental levies and, whilst all such estimates should be taken with a pinch of salt given experience to date of this method of finance for new hospitals and schools, there is no doubt the facility is a key element in this particular local authority’s long-term waste and recycling strategy. To help the city break through the 60% barrier for overall recycling rates within the next few years, the RERF has a visitor facility to give people the opportunity to learn more about how it works and what they can do to contribute to better waste management and recycling in Leeds. Other sustainability elements such as rainwater harvesting and drainage techniques integrated throughout the design only add to the characteristics that distinguish this building from the more prosaic industrial facilities normally associated with the processes involved here. 
 
Some measure of the design and construction achievement can be measured by the fact that the facility - in the face of stiff competition - won the title of ‘Project of the Year’ in the 2015 Structural Timber Awards, no mean feat for a building type never previously associated with the use of wood and which has opened many eyes to the potential to do so for more such unusual situations. As a valuable contribution the UK’s energy mix, the RERF has many characteristics replicable in other conurbations and with its use of timber as a primary structural material, is a positive contributor to the environment. The debate about what to do long-term with waste is not therefore solely about nuclear: but in confronting the domestic waste challenge we may finally be developing viable and locally sustainable - timber - solutions.
 
 
* (although operational wind turbine towers and blades made from engineered timber exist in Austria and Germany)
Credit all photographs to HESS TIMBER © RenstephThompson

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