Charcoal Production in Kilns

When wood is ignited in a limited, controlled air supply a form of decomposition occurs which yields charcoal. Kilns, located mainly in the Eastern half of the United States, produced a substantial portion of the 264,900 ton total in 1956. Kilns used were the primitive earth type, the small portable sheet-metal type, the large beehive type, and the modern high-yield masonry block type. Preferred wood species for firm, heavy charcoal are the medium-dense hardwoods. Charcoal from lighter woods is less dense but can be ground and reformed into briquets. Briquetting also utilizes the usual 8 to 10 percent of fines produced in each kiln charge. Best quality charcoal contains 74 to 81 percent fixed carbon, 18 to 23 percent volatiles, 2 to 4 percent ash, and 2 to 4 percent moisture. A higher percentage of fixed carbon may be produced for special markets by accelerated combustion or overburning, but yield is reduced. Underburning produces a degraded charcoal high in volatiles which tends to smoke excessively when used. Wood yields about 50 percent of its dry weight in charcoal. The Forest Service is conducting research on commercial kiln design, operating methods, economics of production, and mechanization. The most economical kiln design to date is a 7-cord double-walled masonry unit. Capital costs in commercial installations are low (150 to 200 dollars per cord capacity) compared to raw material and labor costs. Raw material cost can be minimized by integration with local sawmills since mill residues are a good cheap source of wood. Labor costs can be minimized by operating several kilns and staggering the load-unload cycles. A growing market demand for charcoal is being met by expanding facilities and more unified groups as compared to the widely scattered operations of previous years.

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