Pyrolysis (or piroscission) is a process of thermo-chemical decomposition of organic materials, obtained by applying heat and in the absence of an oxidant (normally oxygen).  In practice, if the material is heated in the presence of oxygen, it produces a heat-producing combustion and produces oxidized gaseous compounds; while performing the same heating in anoxic conditions (total absence of oxygen), the material undergoes the splitting of the original chemical bonds with the formation of simpler molecules. The heat provided in the pyrolysis process is then used to break down the chemical bonds, implementing what is termed induced omolysis.
Waste pyrolysis, using temperatures between 400 and 800 ° C, converts solid state material into liquid products (so-called tar or pyrolysis oil) and / or gases (syngas), which can be used as fuels or raw materials for subsequent use chemical processes. The solid carbonaceous residue obtained can be further refined by providing products such as activated carbon. Pyrolysis products are both gaseous, both liquid and solid, proportions that depend on pyrolysis methods (fast, slow, or conventional pyrolysis) and reaction parameters. A pyrolyzer differs from a gasifier because working in the absence of oxygen (often takes advantage of a hot stream of an inert gas such as nitrogen) realizes pyrolysis properly said, while a gasifier actually working in the presence of small amounts of oxygen realizes even partial oxidation and technology is a middle ground between the incinerator and the pyrolyzer.