Wheel of fortune spins for worn-out tyres
A waste product of the automobile age could be turned into electricity or used to stop coastal erosion. Tony Newton reports The coast protection plan could use the UK's output of scrap tyres for 30 years
Tuesday 03 January 1995
Alternatives to the open-storage method traditionally used by the tyre industry include landfill and storage in disused coal mines, both of which not only pose a fire hazard, but also may give rise to leaching of noxious gases and liquids as the tyre breaks down. Incinerating scrap tyres in power stations is a superficially attractive option: scrap tyres contain about 21,000 kilojoules of energy per lb, while coal contains around 9,500 kilojoules per lb, and according to government statistics, the weekly electricity needs of a typical home can be met by the incineration of just 10 tyres. The problem is the noxious gases and solid by-products released during the process.
Elm Energy & Recycling (UK) Ltd seems to have found an answer that satisfies everyone. The West Midlands Whole-Tyres-To-Electricity Facility in Wolverhampton, opened in November 1993, is the first power station of its kind in the UK, where scrap tyres are incinerated to generate more than 175,000 megawatt hours of electricity a year for the national grid, with 27,000 tonnes of by-products, including steel wire and zinc oxide, which can be used in other manufacturing processes. The company also profits from the fact that the electricity so produced benefits from the higher-priced Non-Fossil Fuel Obligation of the Department of Trade's Renewable Energy Programme.
The Elm Energy project can make use of only 18 to 20 per cent of scrap-tyre waste. Elm Energy aims to open a similar plant in East Kilbride, Scotland, and the company is searching for a site in southern England.
But until such plants come on-line, that leaves 80 per cent or more of Britain's scrap tyre output needing disposal, and a very different fate for this surplus is being investigated by the Humberside County Council - in conjunction with the Tyre IndustryCouncil and the Ministry of Agriculture, Fisheries and Food - to help protect the Holderness coastline on Humberside, which is being eroded by the sea at a rate of 1.8 metres every year.
While the main towns and villages of this stretch of coast have been protected from erosion since the early years of this century by a series of reinforced concrete walls and timber groynes, similar protection of the land between them has not been economically viable - it would cost between £5,000 and £6,000 per metre of cliff, which far outstrips the commercial value of the land being lost. However, the impact of the erosion on property and livelihoods can no longer be ignored.
A series of artificial rock headlands or shore-parallel breakwaters would halt the erosion, but at prohibitive expense. A third possibility is to create artificial sandbanks that would cause incoming waves to break prematurely and dissipate the energy that would have caused erosion. Computer modelling has shown that such a solution would halt erosion in about 100 years through the formation of stable bays, offering a more gentle and longer-lasting result than shore-based protection.
Experiments showed that in order to be effective, such structures would need to be 1,000m offshore, parallel to the coast in 15 metres of water, with 5 metres of water above them at low tide. They would need to be at least 30 metres wide, with a gentle sea-facing slope to maximise the breaking effect. Each bank would be about 2,000 metres long, with a 500 metre gap between banks to provide continuous coverage for 50 kilometres of coastline.
Such huge structures would require a considerable quantity of material for their construction - and the tyre industry has a considerable quantity of material to dispose of. The Holderness coast project could accept the UK's entire output of scrap-tyre casings for 30 years, to provide a self-financing method of coastal protection. With a likely capacity of one billion tyres, the scheme could even earn revenue by accommodating scrap tyres from abroad. An additional benefit would be the colonisation of these artificial reefs by a variety of fauna and flora, perhaps including shellfish for commercial exploitation.
The tyres would be used as "rubber rocks'', comprising 20 or so compacted tyres filled with concrete. These "rocks'' would be wired and concreted together, and deposited on the seabed through a bottom-opening boat.
Reefs using compacted bundles of tyres similar to those proposed at Holderness have been in use off the New Jersey coast in the US since 1986 and successfully colonised by algae and a wide range of fauna, including coral and shellfish. Tests on mussels from these reefs show no evidence of bioaccumulation of heavy metals or toxic organic compounds above those found at control sites.
It is an interesting thought that projects such as Elm Energy and Holderness could eventually find themselves in competition for tyres. The concept of two bodies actually competing for a waste product that has no value to anyone else is a novel one but, sadly, still a long way off.
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