Operational performance and cost–performance trade-offs of low-cost, farmer-scale biochar kilns

Le résumé fourni par la source

Smallholder adoption of biochar remains constrained by the limited availability of affordable, reliable, field-validated production technologies. Here we evaluated the operational performance, repeatability, and cost–performance trade-offs of three locally fabricable, low-cost, farmer-scale biochar kilns spanning a gradient of oxygen control: an open flame-curtain kiln (Type A; Traditional Oregon Kiln), a controlled-draft flame-curtain kiln (Type B), and an indirect-heat retort (Type C). Sixty batch trials ( n = 5 per kiln × feedstock cell) used four representative Midwestern agroforestry residues. Mean gravimetric biochar yields differed sharply: 22.3% (Type A), 31.5% (Type B), and 46.5% (Type C), with corresponding mean peak temperatures of 510, 460, and 385 °C. A linear mixed-effects model (kiln fixed; feedstock and the kiln × feedstock interaction random), complemented by variance partitioning, identified kiln architecture as the dominant driver of yield, accounting for 92.4% of total variance ( η 2 = 0.924; Cliff’s δ = 1.00 for all pairwise contrasts). Feedstock and the interaction together explained less than 1%, and the residual 6.7%. A generalized additive model showed that peak operating temperature alone explained 92% of the deviance in yield ( r = − 0.957 , p < 1 0 − 32 ); processing time was a much weaker, design-driven correlate. Yield repeatability was highest in Type B (CV = 6.8%), comparable in Type C (CV = 7.6%), and considerably lower in Type A (CV = 13.2%). Total fabrication and tooling costs ranged from about US$360 (Type A) to US$1280 (Type C). These benchmarks support evidence-based selection across a “technology ladder” of low-cost kilns and underpin wider deployment of decentralized, farmer-scale biochar systems.

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