Charcoal Kiln Yields Compared from Stated Assumptions: A Saleable-Yield Bound for Earth-Mound, Brick, and Metal Retort Kilns

This study compares three charcoal-making methods — the earth-mound kiln, the brick kiln, and the sealed metal retort — on a single accounting basis, so that their yields can be compared without mixing definitions. All results are simulated, not measured. Starting from 1 kg of oven-dry wood with a lower heating value of 19.0 MJ/kg, and applying stated gross solid fractions, stated fines fractions, and stated fractions of unburned brands for each method, the saleable mass yields are 0.192 kg of charcoal per kg of wood for the earth mound, 0.2848 kg/kg for the brick kiln, and 0.3534 kg/kg for the metal retort. The corresponding wood requirements are 5.208, 3.511, and 2.830 kg of oven-dry wood per kg of charcoal, and the fractions of the wood energy retained in the saleable charcoal are 0.288, 0.4422, and 0.5673. A maker who sizes a burn on the central yield and is then met with the low yield in the stated range will be short of wood: for 1000 kg of saleable charcoal the prudent, low-yield wood order is 6250.0 kg for an earth mound, 4012.8 kg for a brick kiln, and 3162.6 kg for a retort, against central estimates of 5208.3, 3511.2, and 2829.7 kg. The practical contribution is the separation itself: much of the apparent disagreement between published kiln yields disappears once fines and unburned brands are counted the same way for every method.