Techno-economic analysis of farmer-scale biochar production from agricultural residues in the U.S. Corn Belt: A comparison of three low-cost kiln architectures.

Decentralized, farmer-scale biochar production can valorize agricultural residues for soil amendment and carbon storage while avoiding the feedstock-transport burden of centralized pyrolysis. This study compared three low-capital, field-deployable kiln architectures for an on-farm self-supply user: an open flame-curtain Traditional Oregon Kiln (TOK, Type A), a Controlled-Draft Flame-Curtain Kiln (CDFC, Type B), and an Indirect-Heat Fine-Feedstock Retort (IHFRt, Type C). A unified techno-economic model was parameterized with experimental yields and charring times for corn cob, corn stalk, and sorghum stover (n=15 batches per kiln). At a 50kg batch, 100dyr-1 of operation, a wage of 16.50USDh-1, and a 7% discount rate over a 10-yr life, the estimated minimum selling prices (MSP, oven-dry basis) were 3.06USDkg-1 (Type A), 2.60USDkg-1 (Type B), and 1.74USDkg-1 (Type C). Capital cost was small (876-1416 USD, <3% of levelized cost), whereas labor contributed more than 95% and dominated sensitivity. Type C achieved the lowest MSP because its passive charring phase decoupled operator hours from conversion time, raising biochar output per labor hour by 80%. Against the 3USDkg-1 to 5USDkg-1 U.S. retail price for comparable specialty biochar, Type C undercut even the low end and Type A remained competitive at the upper end. A 10,000-draw Monte Carlo preserved the Type C < Type B < Type A ranking in 99.9% of draws. A paired life-cycle assessment of kiln emissions and the soil-organic-carbon foregone by residue removal is the necessary next step before net climate benefits can be claimed.