Charcoal is an unsung workhorse, a material found in extremely varied and numerous fields and roles. In fact, it's likely that you've used it at some point and may even be unaware. What is charcoal? Basically, charcoal is the carbon and ash left behind from burned wood. It's made by burning wood in an oxygen-depleted environment, to prevent the creation of unwanted and nonburnable oxidation in the finished product. This finished product has many uses, including but certainly not limited to the following: cooking, blacksmithing and forging, heating, filtration, fertilizing, and medicinal purposes. The benefit of charcoal is the versatility of roles it can perform, beyond what you could get from simply burning wood. It is a valuable and useful tool that has benefits over other materials, but can also be perverted to have significant negative impacts.
Charcoal is produced by slow pyrolysis. Pyrolysis is an irreversible thermochemical decomposition of organic material at elevated temperatures and in the absence of oxygen. For making charcoal, this is usually done in the 200–300 °C (390–570 °F) range. Pyrolysis differs from other high-temperature processes like combustion and hydrolysis in that it usually does not involve reactions with oxygen, water, or any other reagents. In practice, it is not possible to achieve a completely oxygen-free atmosphere. Because some oxygen is present in any pyrolysis system, a small amount of oxidation occurs.
Traditional creation was accomplished, at least in Britain, using what's called a clamp. This is essentially a pile of wooden logs standing upright and leaning against a chimney of wooden stakes held by rope. The pile is completely covered by soil, straw, and the like to prevent air from entering, and ensuring the reducing environment. The clamp is lit by introducing burning fuel into the chimney, and allowed to burn down for around five days' time. During this time, the clamp was closely monitored to ensure the soil cover remained intact. Any cracks could allow oxygen into the system and reduce the yield, or spoil the result.
A more simple and modern method of producing charcoal involves a sealed metal container, such as a 55-gallon drum. This has the advantage of preventing fire from breaking through the covering, as was possible with the clamp. This does not mean, of course, that it should be lit and abandoned. Nor should it be done in an enclosed environment, for the fire poses a risk to combustible materials and also produces carbon monoxide: an odorless, colorless, and tasteless gas that is toxic in concentration.
In a DIY environment, once the materials had been gathered, the process is very simple. You would need a sealed metal container with a tight fitting lid, typically a 55-gallon drum would work well. You will also need cured wood to turn into charcoal, and extra wood to burn to produce the charcoal. Cured wood, which means it has been dried to reduce moisture content, can be bought or made yourself by leaving it outside stacked to allow air flow around the pieces. Cherry, oak, and hickory are all good choices, mesquite will work but has a tendency to pop quite violently and throw off sparks. The traditional Japanese white charcoal (binchō-tan) is made from white oak, and has been used for centuries.
Chop the cured wood into four-inch pieces; make sure you have enough to fill the drum to the top (but still replace the lid!) Fill the drum and fit the lid tightly, but don't try and get it "airtight"; you want to prevent the barrel from building up any pressure and rupturing. Take the extra wood and build a bonfire around the drum's base, and stack it up to the rim of the lid. You'll need to make sure you have enough fuel to burn for three to five hours to ensure a complete burn. Let the fire burn out completely and give the drum time to cool off before you approach and open it. You will now have small pieces of charcoal that can be broken up for use in various purposes.
This is only one method of making charcoal, here is a wikihow link that provides two methods with pictures: http://www.wikihow.com/Make-Charcoal. The second method, which I did not describe here, consumes far less fuel in the production. It does, however, take more materials and almost twice as long to complete.
There are several different types of charcoal, which can be broadly broken down into hardwood, briquettes, and biomass or extruded briquettes and logs. Hardwood charcoals, like the lumpcharcoal described above and the Japanese white and black charcoals, create high heat and can be used for cooking as well as forging applications. Briquettes are made of compressed sawdust and wood by-products, sometimes with a binding agent and additives mixed in. They best serve cooking and heating applications. Extruded and biomass charcoal, like Japanese ogatan, is similar to regular briquettes but made from sawdust and ground wood formed with heat and pressure.
Charcoal has been used for millenia in a range of purposes, but the most principle role has been as a metallurgical fuel. It is the traditional blacksmith's fuel for forging, and other applications where intense heat was required. It burns at very high temperatures, up to 2700 °C ( 4800 °F), which exceeds the melting point of iron. Because charcoal is porous, it is sensitive to air flow and thus the head generated by it can be controlled by limiting or increasing the air flow to the fire. It also produces an excellent reducing environment, limited oxygen in the forge, which prevents the metal from scaling and degrading. In this application it is superior to its counterpart, coal, because it lacks sulfur and is capable of burning hotter.
For many years, charcoal was used in blast furnaces, and millenia before that in foundries for the production of various grades of iron and steel, known as "cast iron", "pig iron", and "steel." It was only with industrialization that the use of cheaper coke fuel began, as the demand for charcoal was rapidly increasing beyond production capability. For centuries and continuing even in the modern age, traditional steel for Japanese swords, known as tamahagane, is still made using a tatara pit furnace. Over the course of 72 hours, charcoal and iron sand will be continuously added and burned in the pit to create approximately 2.5 tons of steel. In many places, charcoal was still used up until World War II to make high quality steel.
A wood gas generator, or gasifier, can burn charcoal or wood to produce combustible gasses that are then usable by gasoline powered machines. It does so by mixing atmospheric nitrogen with flammable gasses released during the fuel's combustion, such as carbon monoxide. These machines can range from a simple gasoline-powered generator to an automobile once converted. In fact, a Chinese engineer named Tang Zhongming developed an automobile powered by charcoal in 1931 that remained popular in his home country until the 1950s.
Regular charcoal or activated charcoal can both be used in filtration, odor absorption, and purification. Activated charcoal is a processed form of charcoal reheated in the presence of a gas to fill it with tiny pores that easily absorb organic compounds from liquids or gasses. When the organic compounds pass through the charcoal, they are removed from the original medium and held within the charcoal. You have most likely seen this being used in a water purifier available from most grocery stores without even knowing it. In addition to purifying and filtering, it can also aid in indigestion. Traditionally it was consumed in small biscuits to aid in relieving gastric problems, but today it can be taken via capsule or tablet. An interesting anecdote is the fact that some African monkeys, whom possess a leafy diet high in cyanide, have been observed consuming charcoal to absorb the cyanide and relive their indigestion. This is why it's modern medicinal use is primarily in the absorption of ingested poisons and toxins in the body.
As a fuel, charcoal is generally cleaner burning and free of impurities when compared with coal and coke. The major benefits that coal or coke have over charcoal is that, besides their undesirable sulfer content, they are cheaper to obtain and use. Charcoal, however, is a superior fuel because it lacks the sulfur and burns hotter. This esd "rediscovered" in 2010 when PKS charcoal (palm kernel shell) was determined to be a better alternative to fossil fuels for use in foundry electric arc furnaces. A Brazilian program for eco-friendly steel production was implemented after the 2009 United Nations Climate Change Conference (COP15) in Copenhagen, Denmark. This program phased out the use of coal and coke in favor of wood from eucalyptus plantations.
While charcoal possesses many positive uses and benefits in certain applications, it also has some serious historical and potential drawbacks. For example, charcoal is cleaner burning and more pure as a fuel source than coal or coke. However, the irresponsible production of charcoal can rapidly lead to deforestation of an area as all suitable trees are harvested and burned. Most of the drawbacks could be alleviated with responsible and sustainable woodland management. With a little consideration and extra effort, charcoal can be a lasting and sustainable tool in many roles and industries.
Stoughton, Bradley Ph. B., B. S. (1934) The Metallurgy of Iron and Steel. New York, NY: McGraw-Hill Book Company.
Kapp, Leon and Hiroko. (2012) The Art of the Japanese Sword. The Craft of Swordmaking and its Appreciation. Rutland, Vermont: Tuttle Publishing.
HQ, Department of the Army. (2012) FM 21-76 Reprint of Department of the Army Field Manual. U.S. Army Survival Manual. New York, NY: Mud Puddle Inc.
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Originally posted: Friday April 4, 2014