Iterative design through EIA

19th March 2015

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Nicola Mableson

Richard Kevan, technical director at Wardell Armstrong, discusses the benefits using EIA to inform modifications to project design.

What’s the point of an environmental impact assessment (EIA)? Some might regard it simply as an unavoidable legal obligation. But at best it can play a vital part in good decision making. Its real value is often as part of an iterative design process – especially when it results in mitigation measures that can save money, keep the programme on track and help gain public approval. A good case in point is the Keighley clean energy facility. Here, a full EIA is helping to inform the development of a pioneering three-pronged Energy-from-Waste (EfW) scheme that will generate electricity from commercial waste and old tyres as well as converting waste plastic into diesel.

In the late 19th century, a far-sighted Keighley Corporation set out to be at the forefront of generating gas for lighting and heating. The town gas works that they built and opened in 1876 supplied Keighley’s gas for more than 100 years. After the works were finally demolished, the site at Aire Valley Road lay vacant for decades. But with a good planning allocation for waste, it was bought in 2010 by Halton Homes. By 2017, it will be transformed into a £120 million state-of-the-art facility with three interconnected EfW plants. The site will be restored once again to its historical role of generating energy for the region – but in a more sustainable way than previously.

As is often the case with EfW plants, potential air quality and visual impact issues were high on the EIA agenda. This was especially so in view of the nearby Rombald’s Moor, a sensitive ecological grassland and special protection area (SPA) under EU protection. Close by too is East Riddlesden Hall, a historic seventeenth century manor house and gardens that is open to visitors and a popular wedding venue. Although the development site is located in a largely industrial area, there are also some residential properties on its southern side.

In the light of detailed modelling of air quality and emissions, a number of design modifications were made and mitigation measures introduced to minimise environmental impact. Along with real-time monitoring, these should make sure that the facility will operate within the Environment Agency’s strict air quality requirements. They included raising the height of the stack from 40-60 metres and installing carbon filters, also known as scrubbers. As well as using landscaping and colouring to limit visual impact, the stack itself was moved 30 metres to the right so that its view from East Riddlesden Hall would be obscured by trees.

Similarly, a detailed noise assessment led to mitigation measures including cladding on the buildings; acoustic fencing along the access road; air curtains at entrance doors; fast opening and closing roller shutter doors and negative air pressure to control dust, odour and litter as well as noise.

Commercial and industrial waste from local businesses in and around Bradford will be delivered by HGV into a materials reception hall in the main 12MW refuse derived fuel plant. From here it will be craned onto a conveyor and taken into the plant to be combusted. The heat from the combustion process will be converted to steam and driven through a turbine to generate electricity, while the bottom ash that falls through a grate will be sold as aggregate for road building. Residual fly ash will be sent to a hazardous landfill site or long term storage, although the option of vitrification is also being explored. In addition to the revenue stream gained from selling electricity to the grid, the site will charge a gate fee positioned competitively against the cost of landfill.

In an adjacent building on the same site, a tyre crumb melting plant with a capacity of 10,000 tpa will use pyrolysis to convert pre-processed, shredded, end-of-life tyres into electricity. Superheating the rubber crumb to 900°C will produce a syngas which can be burned in a gas engine to generate power. The residual biochar, which has a calorific content even higher than coal, can also be put back through the main EfW plant to produce yet more electricity to be sold back to the grid.

A major concern that emerged during the public consultation process was that of fire risk – heightened by an actual fire at Sherburn in Elmet that was in the news at the time. This concern was successfully addressed by giving reassurance to stakeholders that only two to three days’ stock of tyre crumb would be held at any time – a much lower level than elsewhere and therefore a greatly reduced fire risk.

Here again, the findings of the EIA informed an iterative design process. In the light of sophisticated air quality and emissions modelling, the design was modified so that instead of having a separate stack for the tyre crumb melting plant, it would share a stack with the main EfW plant while still having its own flue – a further reduction in visual impact. Similarly, a tyre crumb storage unit originally designed as a separate building was merged into a single building for ergonomic and operational reasons, and also to help further reduce noise.

The third element of the planned Keighley Clean Energy facility is a 30,000 tpa capacity plant that will convert waste plastics into diesel. Using fractional depolymerisation, it will apply superheating to plastic bags and bottles to change their hydrocarbon chains into liquid diesel. By recovering the energy embedded in waste plastic, it will help to avoid landfill and save the need to burn fossil fuel. The diesel it creates can be used as a biofuel for heating, to power vehicles and for other potentially emerging applications.

So as this pioneering new EfW facility takes shape, what does it tell us about the importance and role of an EIA? The clear conclusion is that an effective EIA is far more than a mere legal planning obligation. Where developers and their designers are willing to listen to specialists, take their studies into account and make modifications, it can play a critical role in providing clear information and bringing an early understanding about the possible effects on the environment of any planned project. This in turn means that mitigation measures can be taken at the earliest possible stage, potentially streamlining the project programme and saving money as well as reducing environmental impact. And this can only be to the good in terms of gaining public understanding and acceptance of a scheme, especially when some difficult conversations may be needed.

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