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Pyrolysis

Pyrolysis

Related Materials

WoodCharcoalTarMethanolCoalCoke

Pyrolysis & Thermal Decomposition

Pyrolysis is the chemical decomposition of organic materials (biomass, coal, plastics) at high temperatures in the total absence of oxygen (or with severely restricted airflow). Unlike combustion, which consumes biomass to produce carbon dioxide and water, pyrolysis breaks complex chemical polymers into energetic solid, liquid, and gaseous fuels.

Core Process & Phenomena

When biomass (such as wood) is heated in a closed vessel without oxygen:

  1. Drying (up to 200°C): Water vapor escapes as moisture boils off from the cell walls.
  2. Pre-Pyrolysis (200°C - 280°C): Hemicellulose breaks down, yielding pyroligneous acid, carbon monoxide, and carbon dioxide.
  3. Main Pyrolysis Exothermic Reaction (280°C - 500°C): Cellulose and lignin break down rapidly. Heavy volatile vapours boil off, condensing into Tar, bio-oil, and Methanol (wood alcohol), while wood gas (syngas) is released.
  4. Charcoal Finalization (Above 500°C): Nearly pure carbon Charcoal remains in the vessel, possessing high caloric density and smokeless burning properties.

Practical Applications

  • Charcoal Making: Producing concentrated, high-temperature metallurgical fuel for iron smelting.
  • Wood Distillation: Recovering valuable chemical coproducts: methanol, acetic acid, pine pitch, and creosote tar.
  • Biogas & Wood Gas Generation: Feeding volatile gases directly into internal combustion engines or burners via a Wood Gasifier.
  • Coal Coking: Converting bituminous coal into high-purity Coke for blast furnaces.

How to Conduct Pyrolysis (Retort Method)

  1. Airtight Vessel: Place tightly packed dry wood into a sealed steel drum or clay retort with a small gas escape pipe.
  2. External Heating: Build an external fire under and around the vessel to heat the biomass indirectly to 400°C–600°C.
  3. Gas Flaring: As volatile gases vent from the pipe, ignite them; they feed back into the fire, making the process self-sustaining.
  4. Condensation (Optional): Pass escaping gases through a water-cooled copper pipe to condense liquid tar, wood spirit, and pyroligneous acid.
  5. Cooling: Allow the sealed vessel to cool completely before opening to prevent the hot charcoal from spontaneously igniting in fresh air.

Limits and Safety Precautions

  • Explosion Risk: Sealed vessels under pressure can rupture if gas vents become clogged with condensed tar.
  • Toxic Vapors: Released gases contain dangerous levels of Carbon Monoxide (CO) and toxic organic compounds; pyrolysis must always be conducted outdoors or in well-ventilated areas.
  • Spontaneous Combustion: Freshly made charcoal must cool sealed off from oxygen, or it will ignite upon contact with air.