Charcoal has widespread uses include metallurgy, tobbaco curing, water purification (activated carbon), poultry and animal feeds, soil Amendment, and other miscellaneous uses. Charcoal is made by a certain process conditions to achieve the specifications according to their usefulness.
The amounts of moisture (2 to 4 percent), volatiles (18 to 23 percent), ash (1 to 4 percent), and fixed carbon (74 to 81 percent) in charcoal provide an average index of quality for general market acceptance either in lump or briquette form. Charcoal with relatively low volatile content and correspondingly higher amounts of fixed carbon is desirable for specialized industrial uses. Temperatures somewhat higher than the normal kiln operating temperatures of 850° to 950° F (454° to 510° C) are required to produce it. The volatiles, when present in proportions greater than about 24 percent, will cause smoking when charcoal is burned and will give product degrade in some areas of recreational use.
In a continuous process raw organic material of any kind is passed through the retorts and cooked into marketable products. While some of the biogas is used to fuel its own process, on site gas turbines or steam boilers can be fueled by the same gas. Variable speed drives give the operator total control on product quality by altering the residence time of the feed stock. The operator can also vary the percentage split between the bio-oil and charcoal by changing the temperature.
Chemical properties can be precisely determined only with analytical equipment. A rough quality test for volatiles can be made, however, by burning samples of charcoal and observing the absence or extent of smoking. A metallic ring when a piece of charcoal is dropped onto a hard surface provides a further rough test for good quality. Too rapid coaling at high temperature usually results in the formation of crumbly charcoal easily broken into small pieces and fines. The species of wood does not influence the chemical quality of charcoal; the physical properties, however, are influenced by wood density and structure. For example, the low-density woods produce charcoal in greater bulk, while some woods will produce brittle charcoal. In general, the lump charcoal obtained from the medium-dense to dense hardwoods is considered a cleaner product because of less breakage and dusting with handling.