Going for the re-burn

Car tyres and other hard-to-dispose-of waste materials could be used to reduce NOx emissions from power stations, a UK research team believes.

A project at Leeds University will attempt to develop technology that uses tyres and waste plastics as an alternative to coal as part of a power plant’s ‘re-burn’ process. If successful, the project team hopes some of the most problematic materials could be turned from an environmental headache into an advantage.

An estimated 40 million old tyres have to be disposed of in the UK each year, and tough new EU regulations will come into force next year banning them from landfill sites.

Re-burning is a well-established technology for reducing NOx emissions. Around 90 per cent of the coal is burned in the main combustion chamber, and the remaining 10 per cent is injected further on in the process. This produces a pool of hydrocarbons that react with the NOx to produce nitrogen, thereby reducing NOx emissions by around 50 per cent.

The team plans to use tyres and waste plastic as the re-burn fuel by injecting them into the chamber in place of coal. Prof Paul Williams, of the University’s Energy Resources Research Unit said: ‘This technology could mean that not only are waste tyres disposed of, but less coal is needed and NOx emissions are reduced at the same time.’

The plastic and tyres are shredded into fine particles before they are injected into the power plant’s combustion chamber.

Using tyres instead of coal in this process should not adversely affect the power output of the plant as the tyres actually have a higher calorific count than coal, claimed Williams.

E.ON UK, the power company that owns Powergen, is a partner in the project and will be offering technical expertise, as well as coal and the use of some of its facilities over the three-year project.

The technology is due to be tested within the next few months at Leeds University’s small 80kW experimental reactor. In preliminary tests using waste plastics a NOx reduction of 85 per cent was achieved, according to the researchers.

An important element of the project will be to test the impact on the process of other harmful by-products released when tyres burn.

Williams said: ‘It’s a three-year project, so we won’t know until late in 2008 whether this technology is beneficial. But with the new EU directives coming in, it is worth investigating.’