Charcoal
From Wikipedia, the free encyclopedia
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). They often lived alone in small huts in order to tend their
wood piles. For example, in the Harz Mountains of Germany, charcoal burners
lived in conical huts called Köten which are still much in evidence today.
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 use of
charcoal as a smelting fuel has been experiencing a resurgence in South America
following Brazilian law changes in 2010 to reduce carbon emissions as part of
President Lula da Silva's commitment to make a "green steel".[2][3]
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 (428 °F), a deep brown-black after some time at 280 °C
(536 °F), and an easily powdered mass at 310 °C (590 °F).[4]
Charcoal made at 300°C (572 °F) is brown, soft and friable, and readily
inflames at 380 °C (716 °F); made at higher temperatures it is hard and
brittle, and does not fire until heated to about 700 °C (1,292 °F).
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 at the end of the 19th century resulted in rapid
re-forestation.
The charcoal briquette was
first invented and patented by Ellsworth B. A. Zwoyer of Pennsylvania in 1897[5]
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.
Production methods
Charcoal has
been made by various methods. The traditional method in Britain
used a clamp. This is essentially a pile of wooden logs
(e.g. seasoned oak) leaning against a chimney (logs are placed in a circle).
The chimney consists of 4 wooden stakes held up by some rope. The logs are
completely covered with soil and straw allowing no air to enter. It must be lit
by introducing some burning fuel into the chimney; the logs burn very slowly
(cold fire) and transform into charcoal in a period of 5 days' burning. If the
soil covering gets torn (cracked) by the fire, additional soil is placed on the
cracks. Once the burn is complete, the chimney is plugged to prevent air from
entering.[6]
The last
section of the film Le Quattro Volte (2010) gives a good and long, if
poetic, documentation of the traditional method of making charcoal.[7]
The Arthur
Ransome children's series Swallows and Amazons, (particular the second
book Swallowdale),
features carefully drawn vignettes of the lives and the techniques of charcoal
burners at the start of the 20th century, in the Lake District of the UK.
Modern methods
use a sealed metal container, as this does not require watching lest fire break
through the covering.[8]
However, on-site attendance is required. This is often carried out by the last
forestry workers to live in working woodland in the western world. There has
been a resurgence of this, particularly in the UK. A good example of this is
Bulworthy Project where charcoal production supports an experiment in
low-impact living and nature conservation.[9]
The properties
of the charcoal produced depend on the material charred. The charring
temperature is also important. Charcoal contains varying amounts of hydrogen
and oxygen as well as ash and other impurities that, together with the
structure, determine the properties. The approximate composition of charcoal
for gunpowders
is sometimes empirically described as C7H4O. To obtain a
coal with high purity, source material should be free of non-volatile compounds
(sugar and a high charring temperature can be used). After charring, partial
oxidation with oxygen or chlorine can reduce hydrogen levels. For activation of
charcoal see activated carbon.
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.
- Pillow Shaped
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.
- Hexagonal
Sawdust Briquette Charcoal are made by compressing sawdust without binders or
additives, making it completely natural. Hexagonal Sawdust Briquette
Charcoal is the preferred charcoal in countries like Taiwan, Korea, Middle
East, Greece. It has a round hole through the center, with a hexagonal
intersection. Mainly for BBQ uses as it does not emit odor, no smoke,
little ash, high heat, and long burning hours (exceeding 4 hours). Just
pure wood aroma for the BBQ meat.
- 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.[10]
- Japanese
charcoal removes pyroligneous acid during the charcoal
making. Therefore when burning, there are almost no stimulating smells or
smoke. The charcoal of Japan is classified into three kinds.
- White
charcoal (Binchōtan), It is very hard and having a metallic
sound.
- Black
charcoal
- Ogatan, Black charcoal that is made
from hardened sawdust. Used in the Izakaya or Yakiniku
restaurant.
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 or
longer etc.[11]
Uses
Charcoal has
been used since the earliest times for a range of purposes including art and
medicine, but by far its most important use has been as a metallurgical fuel.
Charcoal is the traditional fuel of a blacksmith's forge and other applications
where an intense heat is wanted. Charcoal was also used historically as a
source of carbon black by grinding it up. In this form charcoal
was important to early chemists and was a constituent of formulas for mixtures
such as gunpowder.
Due to its high surface area charcoal can be used as a filter, as a catalyst
or as an adsorbent.
Metallurgical fuel
Charcoal burns
at intense temperatures, up to 2700 degrees Celsius. By comparison the melting
point of iron is
approximately 1200 to 1550 degrees Celsius. Due to its porosity it is sensitive
to the flow of air and the heat generated can be moderated by controlling the
air flow to the fire. For this reason charcoal is an ideal fuel for a forge and
is still widely used by blacksmiths. Charcoal is also an excellent reducing
fuel for the production of iron and has been used that way since Roman times.
In the 16th century England had to pass laws to prevent the country from
becoming completely denuded of trees due to production of iron. In the 19th
century charcoal was largely replaced by coke,
baked coal, in steel making due to cost. Charcoal is far superior fuel to coke,
however, because it burns hotter and has no sulfur. Until World War II charcoal
was still being used in Sweden to make ultra high-quality steel. In
steel-making, charcoal is not only a fuel, but a source for the carbon in the
steel according to some scholars such as Moronda, 2011.
After the 2009 United Nations
Climate Change Conference (COP15) in Copenhagen, Denmark, steel industry in
Brazil proposed to replace coal and coke with charcoal in their high
temperature furnaces. The program "Green Steel for the Brazilian Steel
Industry" converted wood from Eucalyptus plantations into charcoal that
will be used in steel making.[12]
In 2010, Japan
Consulting Institute took an action in search of a better, 'greener', and even
cheaper alternative to replace fossil fuels like coke in steelmaking. The research
revealed that Palm Kernel Shell charcoal (PKS charcoal) is proven to be a
better fuel in Electric arc furnace (EAF) as coke
replacement.[13]
As auxiliary energy in EAF, in many aspects, PKS charcoal outperforms coke.[14]
Cooking fuel
Prior to the
industrial revolution charcoal was occasionally used as a cooking fuel. Modern
"charcoal briquettes", widely used for outdoor grilling and barbecues in
backyards and on camping
trips, imitate this use, but are not pure charcoal.[15]
They are usually compacted mixtures of sawdust with additives like coal or coke
and various binders.
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.[citation needed]
Syngas production, automotive fuel
Like many other
sources of carbon, charcoal can be used for the production of various syngas
compositions; i.e., various CO + H2 + CO2 + N2
mixtures. The syngas is typically used as fuel, including automotive
propulsion, or as a chemical feedstock.
In times of
scarce petroleum, automobiles and even buses have been converted to burn wood gas (a
gas mixture consisting primarily of diluting atmospheric
nitrogen,
but also containing combustible gasses, mostly 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.[16]
Gunpowder
Charcoal
(mostly together with sulphur) is the fuel component of gunpowders
and blasting powders and is also used in other pyrotechnic mixtures.[17]
This coal is usually made from specific hardwoods charred at low temperature.
Carbon source
Charcoal may be
used as a source of carbon in chemical reactions. One example of this is the
production of carbon disulphide through the reaction of sulphur
vapours with hot charcoal. In that case the wood should be charred at high temperature
to reduce the residual amounts of hydrogen and oxygen that lead to side
reactions.
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. In certain industrial processes, 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
gases, 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.[18]
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 (commonly known as a fart or flatulence)
in the digestive tract.[19]
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.[citation needed]
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.[20]
- Powdered
charcoal is often
used to "tone" or cover large sections of a drawing surface.
Drawing over the toned areas darkens it further, but the artist can also
lighten (or completely erase) within the toned area to create lighter
tones.
- Compressed
charcoal charcoal
powder mixed with gum binder compressed into round or square
sticks. The amount of binder determines the hardness of the stick.[21]
Compressed charcoal is used in charcoal pencils.
Horticulture
Main article: Biochar
One additional
use of charcoal was rediscovered recently 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.[citation needed]
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 effects.[citation needed] Research
regarding its effectiveness is controversial.[22]
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.[23]
Also, see Activated charcoal, medicinal applications.
Smoking
Special
charcoals are used in smoking the hookah. Lit charcoals are placed on top of foil that is placed
over the tobacco bowl. The charcoals "cook" the tobacco to a
temperature that does not burn it but produces smoke. Normally, charcoal for
hookah or shisha smoking must be hard, high density, easy to ignite, and burn
longer with persistent heat.[24]
Environmental implications
Charcoal
production at a sub-industrial level is one of the primary causes of
deforestation in the Developing World. Charcoal production is usually illegal
and nearly always unregulated as in Brazil where
charcoal production is actually a huge illegal industry for making pig iron [25][26]
Massive forest destruction has been documented in areas such as Virunga National Park in the Democratic Republic of Congo, where it
is considered a primary threat to the survival of the mountain gorillas.[27]
Similar threats are found in Zambia.[28]
The entire wiki link can be found
at: http://en.wikipedia.org/wiki/Charcoal
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