How Biochar is Made

Four production pathways exist, each with tradeoffs. Traditional kilns—earthen mounds or steel drums—are cheapest ($500-$5,000) but inefficient (20-30% biochar yield) and smoky. Smallholder farmers in Kenya, India, and Central America use simple kilns to convert crop residues. Low tech, locally built, but high labor and air pollution.

Retort pyrolyzers improve yield to 40-50%. Biomass heats in sealed chamber; gases burn externally to maintain temperature. Less smoke, better carbon retention, heat recovery possible. Capital cost: $50k-$2M depending on scale. Commercial biochar producers (Carbo Culture, Pacific Biochar) use retorts. Still batch process—load, heat, cool, unload—limiting throughput.

Continuous feed systems achieve 50-60% efficiency. Biomass continuously enters reactor, biochar exits opposite end. Automated temperature control, syngas capture for energy, minimal labor. Auger or screw conveyors move material through hot zone. Capital intensive ($1M-$5M+) but necessary for industrial scale (50-100+ t/day). Companies like Bioforcetech, CharGrow pioneering these.

Gasification systems co-generate electricity. Partial oxidation converts biomass to syngas (H₂, CO, CH₄) which powers generators. Biochar is byproduct (~30-40% yield). Economics depend on power prices—works well for off-grid or industrial heat applications. More complex operation but dual revenue stream (biochar + electricity) improves payback.