Charcoal | Research & Encyclopedia Articles

Charcoal

Anyone who has sat around a campfire or witnessed a forest fire knows that wood burns. But they are also aware that wood generates a great deal of smoke as it burns. This is a result of the incomplete combustion of the oils and resin in the wood, along with the high moisture content. Unfortunately, this limits the practicality of wood as a fuel for a variety of purposes including indoor cooking and the smelting of metals. In the latter case, the impurities in the wood smoke result in a lower grade of ore being obtained.

It was for the purposes of smelting copper and subsequently iron that charcoal was first used. Its origin is unknown but it has been used in Europe for over 5,500 years. It was the smelting fuel for the bronze and iron ages of civilization, being used in smelters and the blacksmith's shop.

In essence, charcoal is distilled wood. It is simply the carbon content of the wood with little or no impurities. This almost pure carbon has two distinct advantages. It burns much hotter than wood itself, allowing access to the temperatures necessary to melt ores and it burns without a flame and little smoke. Consider the backyard barbecue. Until some fat or barbecue sauce is spilt on the coals, they do not smoke but simply produce a great deal of heat.

The combustion of wood converts it back into the carbon dioxide and water vapor from which it is made with little ash remaining. Making charcoal, on the other hand, is an art as it requires that wood be burnt to the point of carbon without actually being consumed in flames. The burn removes the impurities from the wood and leaves behind the carbon content. This requires careful control, with limited oxygen, just enough to sustain combustion but not enough to ignite the wood proper. Charcoal making was one of the more time consuming, and expensive, components of the smelting process.

The collier worked from late spring through to early fall, requiring the hot, dry heat of summer to sustain his efforts. During his off season, he traded in his tools for an ax to restock his wood supply for the following burn season. The supply of wood was rapidly depleted in many areas and, in Great Britain, laws were passed to protect the dwindling forests. This resulted in the conversion of English iron works to coke--a partially combusted form of coal generated in much the same way as charcoal. Ironically, this alternative carbon source resulted in an increase in iron production and lead to the demise of the charcoal industry itself.

Charcoal has also been used historically for the production of glass, as a purifier of food and water, in the making of gunpowder and in the hearths of smithies. Its byproducts included a oil that was used as part of the Egyptian embalming process. In more recent times, charcoal finds usage in the backyard barbecue, providing the right combination of heat with little flame.

Another important use for charcoal or carbon is in the "activated" form. The porous structure of charcoal as it is formed fills with the hydrocarbon residue from the combustion of the wood. Removal of this hydrocarbon content, by heating in an inert atmosphere, results in a form of charcoal that is extremely porous. Five pounds of activated charcoal is estimated to have a surface area of approximately one square mile. In addition, the surface atoms are capable of both adsorption and absorption of chemical compounds. Activated charcoal is capable of absorbing between 25percnt; and 100pernct; of its own mass in contaminants.

Activated charcoal is used in the purification of liquid sugar during the production of white sugar, in the purification of water, in the clean up of other solutions including industrial process streams, for air purification in large airport concourses and small personal gas masks, and in the control and recovery of vapors during manufacturing processes. Its large surface area ensures that maximum absorption occurs and it has the advantage that it can be reused. Simple heating results in the desorption of absorbed material. Still, despite its usefulness, activated charcoal is produced on a smaller scale than either charcoal or coke, which are still used in the smelting of ores and other processes.