The fast pyrolysis is a process that organic material in the absence of oxygen is heated within about 2 seconds to about 475 °C. Under these conditions hydrous organic vapours, pyrolysis gas and charcoal arise. The vapours are rapidly cooled and condensed into a reddish-brown liquid, so called pyrolysis oil or Fast Pyrolysis Bio-Oil (FPBO) with typical yields of about two-thirds of the raw material weight. This major product of the fast pyrolysis has about half of the heating value of a conventional fuel oil. Additionally valuable by-products as charcoal (10-15%) and gas (15-20%) arise, which can be used to generate process energy. By the pyrolysis process, the majority of the ash and minerals bound in charcoal and can be removed and recycled. Therefore highly ash-containing biomass streams can be converted into virtually ash less biogenic pyrolysis.

Of the numerous developed reactor configurations the stationary and circulating fluidized sand bed reactors have prevailed, because they are relatively easy to handle and their up-scaling is rather straightforward. The pyrolysis process is energetically self-sustaining and the fast pyrolysis bio-oil contains about 70% of the energy content of the biomass. Fast-pyrolysis bio-oil can be manufactured from a wide range of biomass or biomass residues. Its use is not necessarily linked to the production process, because it is storable and transportable. Fast pyrolysis bio-oil can be used as renewable fuel of 2nd generation in custom oil heaters for space heating.