Waste incineration and pyrolysis

Waste materials may be treated by incineration (burning) or by thermal processing in the absence of air or oxygen (pyrolysis), or, similarly, by thermal processing with a limited amount of air or oxygen (gasification).

Incineration gives waste reduction by weight and volume, a sterile residue, and the possibility of heat recovery as hot water and/or steam. Thermal processing gives waste reduction by weight and volume, a sterile residue, plus the following products and possibilities: (i) gas with a low to medium calorific value for use as a fuel or feedstock for chemical conversion; (ii) a solid or char which can be used as a fuel, or alternatively an ash; or (iii) liquid tars and/or heavy oils which may be used as a fuel oil substitute or as a feed for thermal cracking, accompanied by a volume of water containing dissolved organic materials. The latter may pose a considerable disposal problem.

The waste material used as a feed for thermal processing may be: raw refuse; sorted material in that the combustible portion has been separated or concentrated (termed refuse-derived fuel); sorted and prepared material in that most of the noncombustible portion has been removed and the combustible portion densified into a form meeting a specification as a fuel (termed densified refuse-derived fuel). The incineration of waste may yield steam or hot water which can be used to do work (e.g. generate electricity). Thermal processing may yield a storable, transportable fuel.