Oil from old tyres…

Bolsover-based Coalite has discovered that its low temperature process for 'cooking' coal to remove the smoke which caused the smog problems of the 1950s and 60s, can be modified to cook tyres. The process produces a range of useful by-products, including oil, in useable and cost-efficient quantities.

The increased use of gas and other fuels for home heating has reduced the demand for Coalite such that the Bolsover plant, built in 1936, now has spare capacity. Following research into alternative applications for the under-utilised assets, a tyre pyrolysis – heat-induced chemical decomposition – process has been developed.

The existing process involves the low-temperature carbonisation of bituminous coals in vertical, cast iron retorts at around 640°C. Forty retorts are assembled in two rows of 20 to form a unit known as a battery. Each retort holds around 300kg of coal, which is carbonised in the absence of air for four hours.

Coalite engineers and technical staff have, with Environment Agency approval, utilised existing technology and converted existing retorts to a pyrolysis chamber. The diagram (left) illustrates how the stainless steel chamber fits comfortably into an existing battery arrangement.

Recycled gas

Around 50 baled tyres weighing 350kg are placed into the pyrolysis chamber, the lid is bolted down and the chamber is lowered into the battery setting. Using gas generated from the process, heating is applied via a radiation chamber constructed with ceramic bricks. As with the Coalite process, the gas flame does not come into direct contact with the chamber. The process is self-sufficient in gas usage. After cleaning by electrostatic precipitation and cooling, the gas is recycled for use in the next pyrolysis cycle.

Based on a charge of 350kg and an eight-hour residence time, each battery is capable of pyrolysing around 7,500 tonnes or one million tyres every year. Markets for all of the products produced by the process – oil, char, steel and gas – have been identified: char can be added back into the Coalite blend in lieu of coal, or may be suitable as a low-grade carbon black; steel will be baled and sold as scrap; the oil has been described as similar to Brent Crude, and will be blended or sold as a fuel oil; and gas, as stated, will be recirculated to heat the pyrolysis process.

Funding for the project has been agreed by Coalite’s parent company, Anglo United Ltd. Negotiations are underway to secure adequate and continuous supplies of tyres for processing, scheduled to start in April 2001.

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