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Refuse derived fuels are secondary fuels that are attained, for example, during the sorting of waste. Among the materials included here are plastics, paper, wood or treated sludge. The concept is defined not by the type of waste, but instead above all by the fact that categorisation and an assessment of the calorific value is made possible by the prior sorting and treatment of the constituents. Whether a product in waste sorting will be recovered materially or thermally depends, among other things, on the quality, severability and degree of contamination. Material recycling often achieves a higher energy efficiency than energetic recovery in some plastics, however the amount of mixed plastics is increasing, particularly in plastic packaging, and individual layers can no longer be separated for recycling. Such plastics are treated to become substitute fuels. To ease handling, the substitute fuels are crushed in shredder plants or die presses or, in the case of paste-like waste, dried and pelleted. Substitute fuels are categorised in special grades using the parameters calorific value, residue on ignition, chlorine content and ash content. The higher the calorific value and the lower the ash content, the more coveted and more expensive the substitute fuel.
As well as being used for co-combustion in waste-to-energy plants, refuse derived fuels are also used in other thermal recovery plants such as cogeneration and cement plants. Some power plants are powered solely by substitute fuels. For the latter, refuse derived fuels with an average calorific value of 12 - 14 MJ/kg are most suitable. In contrast, highly calorific substitute fuels tend to be used for co-combustion in waste incineration plants or cogeneration plants. Refuse derived fuels replace fossil fuels, therefore the market values follow the fluctuations of the market prices for fossil fuels.
Since refuse derived fuels are essentially not different to household waste, the flue gas cleaning requirements are the same as those for a conventional waste incineration plant.