Low-pollution diesel created from waste tyres

Waste tyres could be reprocessed into a fuel additive to reduce emissions of NOx and particulates, after successful trials in Australia.

Green Distillation Technologies (GDT) produced 3,000 litres of the liquid from a single seven-tonne tyre taken from a large off-highway dump truck. GDT now aims to produce 8 million litres of the additive annually, with production starting this year.

Director Trevor Bayley said the company used the destructive distillation technique to convert waste rubber into the renewable fuel. Feed stock for the process is plentiful, with a global stockpile of used tyres growing at a rate of over a billion a year.

Waste tyres are heated in an anaerobic chamber, and the vapours given off are collected in a process called destructive distillation, then condensed to form oil.

Some of this ‘tyre oil’ is used to fuel the heating process, meaning that once the plant is established it can be free of external energy inputs. Solid residues from the process are recyclable, consisting of steel and carbon, and no gases are emitted to the atmosphere.

The tyre oil was blended with conventional Australian diesel for testing at Queensland University of Technology’s Biofuel Engine Research facility at concentrations of 10 and 20 per cent. Oils derived from tyres made from both synthetic and natural rubbers were assessed.

Used in a turbocharged six-cylinder diesel engine running at four different load states, the oil caused no impairment in power output. Significantly, NOx emissions were reduced by 30 per cent compared to ‘pure’ conventional diesel, while particulates fell by 33 per cent.

Trevor Bayley said that there was zero waste from the process. Tyre oil could also be used in oil-burning boilers and furnaces and, with further processing, could fuel jet engines.

The implications for the transport industry are positive: currently operators face significant charges for the disposal of end-of-life tyre casings. These could instead possibly retain some value while forming a source of low-pollution fuel.