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.
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