A Novel Application of Waste Tyres & plastics as Reburn Fuels for NOx Reduction in Large Scale Combustion Systems

Used tyres and waste plastics represent enormous tonnages of waste generated in the UK and Europe each year requiring disposal. Scrap tyre arisings in the UK are 400,000 tonnes per year amounting to 30 million tyres. In the EU, more than 2.5 million tonnes of tyres and 19.2 million tonnes of plastics are generated each year. Currently the vast majority of the tyre and plastics waste generated is landfilled representing a major waste of a resource. The recent EC Waste Landfill Directive (1999) sets a deadline for the banning of whole and shredded tyres from landfill sites by 2006. In addition, the European Union has recognised scrap tyres as a 'priority waste stream'. Plastics are also regarded as a priority waste stream and the EC Packaging and Packaging Waste Directive (1994) and the EC Waste Electrical and Electronic Equipment (WEEE) Directive (2000) set ambitious recycling and recovery targets for waste plastics.Further, the EC Large Combustion Plant Directive (2001/80/EC) applies to a wide range of plant including power stations, cement kilns and steel based furnaces and sets stringent emissions targets for NOx reduction, for example for existing plant built after 1987 plants are required to reduce NOx levels to below 500 mg/m3 by 2008 and below 200 mg/m3 after 2016 (for plants >500MWt). Whilst reduced NOx levels can be obtained by using existing low NOx burners, there is concern that retrofit systems to reduce NOx to the low levels required of the new EC Large Combustion Plant Directive may not be achievable at reasonable cost.This proposal seeks to investigate the use of two waste streams, tyres and plastics, as potential rebum fuels for the reduction of NOx from large combustion plant by way of a practical large scale experimental approach. The high volatility and reactivity of the tyres and plastics give a process advantage due to the shorter bum-out time required compared to coal which would ease the pressure of retrofitting rebum technology on existing full scale plant. Experiments will be undertaken using a 200kWth pilot-scale reactor. In addition, since wastes combustion Is associated with an adverse public perception of environmental concerns, a section of the work will involve a full emissions survey, including acid gases, particulate, heavy metals and dioxins. All together, the work proposed will provide new information and help to develop a strategy for the retro-fit of this technology to existing plant.