Refuse derived fuel (RDF) is produced by the mechanical processing of solid waste. For use in a kiln, a typical processing scheme for production of RDF might include shredding, screening, and air classification of the wastes. The fuel properties of RDF vary somewhat among plants and processing schemes but in comparison with typical coal properties, refuse derived fuels are generally lower in calorific value and sulphur content but higher in chlorine content. The low sulphur content of RDF is a desirable feature because sulphur dioxide emissions from kilns are subject to air pollution regulations and the use of a low sulphur fuel facilitates meeting these regulations. Also, sulphur is considered a contaminant of some products made in kilns (e.g., lime) and kiln operators prefer to minimise the addition of sulphur to their kilns.