The characterisation and recycling of incinerated tyres
In excess of 1,000 million tyres are manufactured worldwide every year. The average tyre lasts for approximately 50,000 kilometres before it must be replaced. Each year in the UK approximately 37 million tyres reach the end of their useful life. The used tyre, which is almost identical to the replacement, then requires disposal. As the volume of road traffic increases alternative disposal routes are required to take up the resulting shortfall in capacity. SITA Tyre Recycling operate an incinerator in the West Midlands which solely burns scrap tyres. The plant receives a significant proportion of UK scrap tyre waste stream as well as reject tyres from manufacturers. The main waste stream generated is disposed to landfill. The objective of this research was to determine if the waste had potential for recycling which would reduce the burden on landfill and possibly generate revenue through the sale of products. By developing methods to sample and characterise the waste stream it was found to consist of multiple phases that could be individually treated to generate valuable products. Products based on carbon and steel were derived from the combusted rubber and bead wire respectively. Detailed examination of the carbon phase using a range of techniques revealed that many compounds used in the manufacture of the tyre rubber were highly dispersed in a carbon dominated matrix. The success of physical separation processes was limited by the difficulties associated with liberation of the valuable carbon from contaminating elements. The post-combustion steel was found to have an unacceptable sulphur concentration, which was mainly associated with surface coatings of the carbon phase. Through the application of traditional attrition scrubbing the surface coatings were removed and a reduced sulphur content steel product generated. Pilot scale trials were used to generate large samples for industrial assessment and process optimisation purposes.