Significations et usages de Charcoal

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Charcoal is the black residue consisting of impure carbon obtained by removing water and other volatile constituents from animal and vegetation substances. Charcoal is usually produced by slow pyrolysis, the heating of wood, sugar, bone char, or other substances in the absence of oxygen (see pyrolysis, char and biochar). The resulting soft, brittle, lightweight, black, porous material resembles coal and is 50% to 95% carbon with the remainder consisting of volatile chemicals and ash.^[1]

Etymology

The first part of the word is of obscure origin, but the first use of the term "coal" in English was as a reference to charcoal. In this compound term, the prefix "chare-" meant "turn", with the literal meaning being "to turn to coal". The independent use of "char", meaning to scorch, to reduce to carbon, is comparatively recent and is assumed to be a back-formation from the earlier charcoal. It may be a use of the word charren or churn, meaning to turn; i.e. wood changed or turned to coal, or it may be from the French charbon. A person who manufactured charcoal was formerly known as a collier (also as a wood collier). The word "collier" was also used for those who mined or dealt in coal, and for the ships that transported it.

Charcoal, or biochar, is also an essential element in the composition of terra preta.

History

Historically, production of wood charcoal in districts where there is an abundance of wood dates back to a very ancient period, and generally consists of piling billets of wood on their ends so as to form a conical pile, openings being left at the bottom to admit air, with a central shaft to serve as a flue. The whole pile is covered with turf or moistened clay. The firing is begun at the bottom of the flue, and gradually spreads outwards and upwards. The success of the operation depends upon the rate of the combustion. Under average conditions, 100 parts of wood yield about 60 parts by volume, or 25 parts by weight, of charcoal; small scale production on the spot often yields only about 50%, large scale was efficient to about 90% even by the seventeenth century. The operation is so delicate that it was generally left to colliers (professional charcoal burners).

The massive production of charcoal (at its height employing hundreds of thousands, mainly in Alpine and neighbouring forests) was a major cause of deforestation, especially in Central Europe. In England, many woods were managed as coppices, which were cut and regrew cyclically, so that a steady supply of charcoal would be available (in principle) forever; complaints (as early as the Stuart period) about shortages may relate to the results of temporary over-exploitation or the impossibility of increasing production to match growing demand. The increasing scarcity of easily harvested wood was a major factor for the switch to the fossil fuel equivalents, mainly coal and brown coal for industrial use.

The modern process of carbonizing wood, either in small pieces or as sawdust in cast iron retorts, is extensively practiced where wood is scarce, and also for the recovery of valuable byproducts (wood spirit, pyroligneous acid, wood tar), which the process permits. The question of the temperature of the carbonization is important; according to J. Percy, wood becomes brown at 220 °C, a deep brown-black after some time at 280 °C, and an easily powdered mass at 310 °C.^{[citation needed]} Charcoal made at 300° is brown, soft and friable, and readily inflames at 380 °C; made at higher temperatures it is hard and brittle, and does not fire until heated to about 700 °C.

In Finland and Scandinavia, the charcoal was considered the by-product of wood tar production. The best tar came from pine, thus pinewoods were cut down for tar pyrolysis. The residual charcoal was widely used as substitute for metallurgical coke in blast furnaces for smelting. Tar production led to rapid deforestation: it has been estimated all Finnish forests are younger than 300 years. The end of tar production in the end of the 19th century meant also rapid re-forestation.

The charcoal briquette was first invented and patented by Ellsworth B. A. Zwoyer of Pennsylvania in 1897^[2] and was produced by the Zwoyer Fuel Company. The process was further popularized by Henry Ford, who used wood and sawdust byproducts from automobile fabrication as a feedstock. Ford Charcoal went on to become the Kingsford Company.

Types

Commercial charcoal is found in either lump, briquette, or extruded forms:

• Lump charcoal is made directly from hardwood material and usually produces far less ash than briquettes.
• Briquettes are made by compressing charcoal, typically made from sawdust and other wood by-products, with a binder and other additives. The binder is usually starch. Some briquettes may also include brown coal (heat source), mineral carbon (heat source), borax, sodium nitrate (ignition aid), limestone (ash-whitening agent), raw sawdust (ignition aid), and other additives like paraffin or petroleum solvents to aid in ignition.^[3]
• Extruded charcoal is made by extruding either raw ground wood or carbonized wood into logs without the use of a binder. The heat and pressure of the extruding process hold the charcoal together. If the extrusion is made from raw wood material, the extruded logs are then subsequently carbonized.

The characteristics of charcoal products (lump, briquette, or extruded forms) vary widely from product to product. Thus it is a common misconception to stereotype any kind of charcoal, saying which burns hotter, etc.

Charcoal is sometimes used to power commercial road vehicles—usually buses—in countries where oil is scarce or completely unavailable. In the years immediately after the Second World War, charcoal buses were in regular use in Japan and are still used today in North Korea.^[4]

Uses

An application of wood charcoal was as a constituent of gunpowder. It was also used in metallurgical operations as a reducing agent, but its application has been diminished by the introduction of coke, anthracite smalls, etc. For example, charcoal may be used to smelt a variety of metals from aluminum to copper as it burns at the necessary temperature: 1,100 °C (2,010 °F).^[5] A limited quantity is made up into the form of drawing crayons; but the greatest amount is used as a fuel, which burns hotter and cleaner than wood. Charcoal is often used by blacksmiths, for cooking, and for other industrial applications.

Cooking fuel

Charcoal briquettes are widely used for outdoor grilling and barbecues in backyards and on camping trips.

In many non-industrialized countries, charcoal is used for everyday cooking by a large portion of the population. This is potentially a serious health problem when used indoors since carbon monoxide (CO) is a combustion product.^[6]

Industrial fuel

Historically, charcoal was used in great quantities for smelting iron in bloomeries and later blast furnaces and finery forges. This use was replaced by coke during the Industrial Revolution. For this purpose, charcoal in England was measured in dozens (or loads) consisting of 12 sacks or shems or seams, each of 8 bushels.

Automotive fuel

In times of scarce petroleum, automobiles and even buses have been converted to burn wood gas (gas mixture containing primarily carbon monoxide) released by burning charcoal or wood in a wood gas generator. In 1931 Tang Zhongming developed an automobile powered by charcoal, and these cars were popular in China until the 1950s. In occupied France during World War II, wood and wood charcoal production for such vehicles (called gazogènes) increased from pre-war figures of approximately fifty thousand tons a year to almost half a million tons in 1943.^[7]

Purification and filtration

Charcoal may be activated to increase its effectiveness as a filter. Activated charcoal readily adsorbs a wide range of organic compounds dissolved or suspended in gases and liquids. Charcoal is often used to filter water to remove bacteria and undesired tastes. In certain industrial process, such as the purification of sucrose from cane sugar, impurities cause an undesirable color, which can be removed with activated charcoal.It is also used to absorb odors and toxins in gasses, such as air . Charcoal filters are also used in some types of gas masks. The medical use of activated charcoal is mainly the adsorption of poisons, especially in the case of suicide attempts in which the patient has ingested a large amount of a drug. Activated charcoal is available without a prescription, so it is used for a variety of health-related applications. For example, it is often used to reduce discomfort (and embarrassment) due to excessive gas in the digestive tract.

Animal charcoal or bone black is the carbonaceous residue obtained by the dry distillation of bones. It contains only about 10% carbon, the remainder being calcium and magnesium phosphates (80%) and other inorganic material originally present in the bones. It is generally manufactured from the residues obtained in the glue and gelatin industries. Its decolorizing power was applied in 1812 by Derosne to the clarification of the syrups obtained in sugar refining; but its use in this direction has now greatly diminished, owing to the introduction of more active and easily managed reagents. It is still used to some extent in laboratory practice. The decolorizing power is not permanent, becoming lost after using for some time; it may be revived, however, by washing and reheating. Wood charcoal also to some extent removes coloring material from solutions, but animal charcoal is generally more effective.

Art

Charcoal is used in art for drawing, making rough sketches in painting and is one of the possible media for making a parsemage. It must usually be preserved by the application of a fixative. Artists generally utilize charcoal in three forms:

• Vine charcoal is created by burning sticks of wood (usually willow or linden/Tilia) into soft, medium, and hard consistencies.
• Compressed charcoal charcoal powder mixed with gum binder compressed into round or square sticks. The amount of binder determines the hardness of the stick. Compressed charcoal is used in charcoal pencils.
• Powdered charcoal is often used to "tone" or cover large sections of a drawing surface. Drawing over the toned areas will darken it further, but the artist can also lighten (or completely erase) within the toned area to create lighter tones.

Horticulture

One additional use of charcoal rediscovered recently is in horticulture. Although American gardeners have been using charcoal for a short while, research on Terra preta soils in the Amazon has found the widespread use of biochar by pre-Columbian natives to turn otherwise unproductive soil into very rich soil. The technique may find modern application, both to improve soils and as a means of carbon sequestration.

Medicine

Charcoal was consumed in the past as dietary supplement for gastric problems in the form of charcoal biscuits. Now it can be consumed in tablet, capsule or powder form, for digestive benefits. Charcoal absorbs gases and toxins to help heartburn, flatulence or indigestion.^[8]

Red colobus monkeys in Africa have been observed eating charcoal for the purposes of self-medication. Their leafy diets contain high levels of cyanide, which may lead to indigestion. So they learned to consume charcoal, which absorbs the cyanide and relieves indigestion. This knowledge about supplementing their diet is transmitted from mother to infant.^[9]

Also, see Activated charcoal, medicinal applications.

Smoking

Special charcoals are used in the smoking of the hookah" Argeeleh en Arabic or Nargeleh en turkesh. Lit coals are placed on top of foil, which is placed over the bowl of tobacco, and through indirect heat "cook" the tobacco to a temperature that produces smoke, but does not burn.

See also

• Biochar
• Pyrolysis
• Slash-and-char
• Terra preta
• Biomass briquettes

References

External links

• On Charcoal
• The Lump Charcoal Database - Information about lump charcoal
• Charcoal Making - Charcoal making community for livelihood
• How to Make Charcoal - Traditional charcoal production method, India
• The River Wey and Wey Navigations Community Site—a non-commercial site of over 200,000 words all about the Wey Valley and includes a photo file on charcoal production and information relating to gunpowder manufacture at Chilworth
• Catoctin Mountain Park - Charcoal and Iron Industry (U.S. National Park Service) Catoctin Mountain Park, Maryland, USA, includes interpretive features ("Charcoal Trail", etc) on the history of charcoal making in the area
• Coconut Charcoal - Facts
• Discovery of new charcoal production process and ARTI, Appropriate Rural Technologies Institute - Making powdered charcoal directly from sugar cane leaves and trash
• The "Adam-retort", or ICPS (Improved Charcoal Production System)
• Flash Carbonization is a pressurised highly efficient charcoal making process
• A photo of traditional charcoal production in Cuba. Photo by Robert Frigault

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