Q6Power Generation Sources

Pyrolysis is a thermochemical conversion process in which organic biomass material is heated to moderately high temperatures (typically 300°C to 900°C) in an oxygen-starved or completely oxygen-free environment, so that instead of burning (which requires oxygen), the material thermally decomposes into simpler chemical compounds. Because there is no combustion, no ash-forming oxidation occurs in the primary reaction; instead, the biomass breaks down into three product streams: a solid residue called char (or charcoal, rich in fixed carbon), a liquid condensate called bio-oil or pyrolysis oil (a complex mixture of oxygenated organic compounds), and a non-condensable gas mixture (pyrolysis gas, containing CO, CO₂, H₂, CH₄ and other light hydrocarbons).

Pyrolysis is broadly classified by heating rate and residence time into: slow pyrolysis (low heating rate, long residence time, favors maximum char yield — traditional charcoal-making), fast pyrolysis (very rapid heating, short vapor residence time of under 2 seconds, favors maximum liquid bio-oil yield, up to 70-75% by weight), and flash pyrolysis (extremely rapid heating with very fine particle sizes, maximizing gas/liquid yield). The relative proportions of char, oil and gas depend on the pyrolysis temperature, heating rate and residence time. Pyrolysis products serve as renewable substitutes for fossil fuels — bio-oil can be refined into transport fuels or chemicals, char can be used as a fuel or soil amendment (biochar), and the gas can be burnt to supply process heat for the pyrolysis reactor itself, making the process partly self-sustaining.