Biochar Production through Pyrolysis

Biochar is a carbon-rich solid produced by heating biomass with little or no oxygen. In pyrolysis, agricultural residues are thermally decomposed without allowing complete combustion, producing biochar along with liquid vapours and combustible gases.

Feedstock preparation

Crop residues such as straw, husk, shells and stalks can serve as feedstock. Proper preparation makes heating more uniform and reduces avoidable emissions.

• The biomass is cleaned to remove soil, stones and non-biomass contaminants.
• It is dried because excess moisture consumes heat and lowers process efficiency.
• Large or irregular residues are size-reduced before being placed in the reactor.

Oxygen-limited thermal conversion

The prepared biomass is heated in a sealed or controlled-air reactor. Limited oxygen prevents burning and causes devolatilisation, in which biomass separates into solid carbon and volatile compounds.

• The main products are solid biochar, condensable vapours that can form bio-oil, and non-condensable combustible gas.
• Compared with fast pyrolysis, slow pyrolysis generally employs slower heating and longer residence time, thereby favouring solid-char production.
• Process temperature, heating rate and residence time determine char yield, carbon content, porosity and other properties.

Recovery and safe handling

Hot biochar must be cooled while air remains excluded because exposure to oxygen can cause oxidation or ignition. The cooled material may be crushed, screened and characterised before soil or environmental use.

• Combustible gases and vapours should be captured and used for process heat or treated rather than released as smoke.
• Controlled reactors are preferable to open or poorly controlled kilns because they reduce incomplete combustion and pollutant emissions.
• Pyrolysis converts part of the biomass carbon into relatively stable aromatic carbon, slowing its return to the atmosphere compared with rapid residue decomposition or burning.