Waste incineration and pyrolysis

Abstract

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.