Pyrolysis is the thermal decomposition of materials at elevated temperatures in the absence of oxygen. The process simultaneously changes the physical phase and chemical composition of materials and is an irreversible.. When applied to organic materials (Biomass) pyrolysis results in a range of volatile liquid (bio-oil) and gas (Syngas) products and solid enriched carbon (Char) – each having different potential uses for the Bioenergy sector and bioeconomy.

There are three main types of pyrolytic reactions each applying different processing times and temperatures and resulting in a different breakdown of products.

Slow pyrolysis describes pyrolytic reactions that take place over a long period of time where the solid and gaseous materials are gradually heated at 10°C per second with prevailing temperatures of 400-500°C. The primary products from slow pyrolysis are gases, ‘thicker’ bio-oil (tar) and Char that are released from as the Biomass Feedstock is slowly devolatilised. epolymerisation/ recombination reactions occur after the primary reactions take place. The residence time of gases within the reaction vessel may be over five seconds, whilst the Biomass material is typically 5-30 minutes.

Fast pyrolysis describes pyrolytic reactions where the Biomass Feedstock is rapidly heated at 100 °C per second to temperatures of 400-650°C. This is carried out to produce a ‘thinner’ bio-oil and gases, the specific temperatures applied will influence this proportions of liquid and gas product. Char accumulates in large quantities and has to be removed frequently.

Flash pyrolysis describes rapid pyrolytic reactions where heating rates of >500 °C per second are applied to achieve temperatures 700-1000°C. The residency time of materials within the vessel is less than 2s, favouring the production of gases and bio-oil.