Wood and charcoal as fuel resources
Wood and charcoal are longstanding fuel resources that have supported human energy needs since prehistoric times. Wood can be burned directly or transformed into charcoal through a charring process, which involves heating wood in the absence of air. Globally, more than half of all wood is used for energy, with wood accounting for up to 80% of energy needs in some developing countries, contrasting sharply with its minimal contribution in most developed nations. While wood is often sourced sustainably, high demand in certain regions, particularly in Africa, has led to consumption rates that exceed the natural replenishment of trees.
Charcoal, which is lighter and more energy-dense than wood, requires about 2.5 kilograms of wood to produce 1 kilogram of charcoal. It is typically regarded as a cleaner-burning option, producing fewer emissions compared to wood. Both wood and charcoal are used in various applications, from domestic heating and cooking to industrial processes, including paper production and metalworking. However, reliance on wood fuel can lead to environmental issues such as deforestation and air pollution, particularly in densely populated areas. The combustion of wood contributes to air quality concerns, as it produces harmful emissions, including particulates and carbon monoxide, which can have adverse health effects.
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Wood and charcoal as fuel resources
Globally, the amount of wood utilized for fuel exceeds the total amount of wood utilized for all other purposes. Between 15 and 80 percent of the total energy needs of some developing countries are met by wood.
Background
Wood and charcoal are some of the oldest energy sources: They have provided fuel for human energy needs since prehistoric times. Rough wood and bark may be burned directly for fuel, or wood may be converted into charcoal by charring in a kiln from which air has been excluded. According to the Food and Agriculture Organization of the United Nations, more than half of all the wood utilized in the world is used for energy production. Wood provides up to 80 percent of the total energy needs of some developing countries, but it provides less than 5 percent of the total energy requirement in most developed countries. In some developing areas of the world, fuelwood demand is greater than the supply; particularly in parts of Africa, significantly exceeds replacement of the stock of trees.
Wood fuel also finds some use in industry, as in the paper industry. Industrial uses often burn waste material from other manufacturing processes. Bark removed from raw logs, sawdust, planer shavings, sander dust, edges, and trim pieces may all be burned to generate power while disposing of the unwanted material. Small wood particles such as sawdust and shavings may be compressed to produce briquets or “logs” for use as fuel.
Increasing numbers of forests have been planted and cultivated for the sole purpose of energy production. Entire trees are chipped and burned for energy production at the end of a rotation. These forests may be known as forest plantations, tree farms, or energy forests. This type of wood production and fuel use has the potential to reduce dependency on fossil fuels. Energy forests remove carbon from the over their life spans, then release this carbon in various forms during combustion for energy production.
Types of Combustion
The direct burning of wood occurs when the surface is intensively irradiated so that the temperature is raised to the point of spontaneous ignition, anywhere from 260° to more than 480° Celsius, depending on the conditions. More common is indirect combustion, in which the wood breaks down into gases, vapors, and mists, which mix with air and burn. About 1.3 kilograms of oxygen are required for the complete combustion of 1 kilogram of wood. At normal atmospheric concentrations, this implies that about 5 kilograms of air are needed for the complete combustion of 1 kilogram of wood. During combustion, gases such as carbon dioxide and carbon monoxide, water vapor, tars, and charcoal are produced, along with a variety of other hydrocarbons. Dry wood or bark and charcoal burn relatively cleanly; wetter wood produces a larger amount of emissions. Collectors may be used to remove particulate matter from industrial sources. It is less feasible to reduce emissions from cooking stoves (either chemically or mechanically), however, and cooking stoves are a major source of human exposure to emissions from wood burning in much of the world.
Charcoal
Charcoal is lighter than wood and has a higher energy content. It takes approximately 2.5 kilograms of wood to produce 1 kilogram of charcoal. The exact conversion ratio depends on the tree species, the form of wood utilized, and the kiln technology used. Charcoal is more efficient to transport than wood, and it can be burned at higher temperatures. It is used both for domestic purposes and, in some countries—Brazil for example—as an industrial fuel. In general, charcoal is considered a cleaner, less polluting fuel than wood in that its combustion produces fewer particulates. Charcoal was used extensively as an energy source for and metalworking from prehistoric times into the Industrial Revolution, but coal eventually became the principal alternative energy source for these processes in areas where it was available. Today, and are major sources of energy for industrial processes.
Energy Content
The average recoverable heat energy from 0.5 kilogram of wood is about 8,500 British thermal units (Btus). The value ranges from 8,000 to 10,000 Btus per 0.5 kilogram for different species. In some efficient processes, 12,500 Btus can be recovered from 0.5 kilogram of charcoal. If wood with a high moisture content is burned, some of the energy produced by combustion is absorbed as the moisture evaporates, reducing the recoverable energy.
Impacts on Environment and Health
Traditional uses of wood fuel for cooking and home heating utilize woody material obtained from tree pruning or agroforestry systems. These uses are sustainable and have relatively little environmental impact in areas with low human population levels, but they may be associated with serious air pollution problems as well as widespread and if they are the major sources of energy for a large or concentrated population. In most of the areas that have deforestation problems, the problem is primarily attributable to changes in land use, particularly the opening of land for agriculture and grazing. Fuelwood is often recovered during such land-use changes, but the need for fuelwood production is often a secondary cause or by-product of deforestation.
Industrial power production that utilizes available technology to ensure high-temperature, virtually complete combustion minimizes hydrocarbon and particulate emissions and can be designed to meet most existing air quality standards. Less efficient domestic combustion may be associated with unacceptable levels of human exposure to airborne particulates, carbon monoxide, and other produced by incomplete combustion. The health effects of exposure to domestic wood fires are difficult to determine, since it often occurs along with other factors known to increase health risks. However, as noted by the nonprofit organization Environment and Human Health and other organizations, wood smoke contains particulates as well as recognized carcinogenic compounds that, depending on the circumstance of exposure, can pose risks similar to those of cigarette smoke.
Bibliography
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"Where Does Charcoal Come From - and Is It Sustainable?" Penn Today, 16 Nov. 2022, penntoday.upenn.edu/news/where-does-charcoal-come-and-it-sustainable. Accessed 29 Dec. 2024.