Waste tyre rubber as a secondary fuel for power plants

Approximately 1 billion waste tyres are generated worldwide each year, with the US producing 300 million and the EU 260 million tyres, representing an enormous waste management problem. At the same time, increasingly stringent emission control targets are being imposed on electric power generating plants. The development of science and technology for clean coal combustion is crucial for a sustainable environment which is dependent on a mix of energy production systems. In this pilot scale study we have shown that tyre rubber can be fired with pulverised coal and may have a role to play in co-firing configurations in full scale power plant boilers as wastes are beginning to feature in ‘fuel switching’ scenarios for CO2 mitigation. Utilisation of waste tyres in a coal combustion plant can, in one step, reduce NO emissions and recover energy from waste tyres, efficiently. Therefore, through this process, a problem waste stream is effectively utilised to help solve a major environmental pollution problem. We present data demonstrating reburning and co-firing configurations utilising waste tyre rubber. Low levels of NO emission (up to 80% reduction at reburning fuel fractions <12%th) can be achieved, when using a lower volatile South African coal as the primary fuel. The results for tyre reburning are compared with the performance of a suite of reburning fuels with differing volatile hydrocarbon contents. Direct co-firing of tyre with coal can also reduce NO levels but the degree of reduction is dependent on the reactivity of the coal and the prevailing combustion conditions in the primary zone of the mixed fuel flame.