Fossil fuels, also known as mineral fuels, are hydrocarbon-containing natural resources such as coal, petroleum and natural gas. The utilization of fossil fuels has fueled industrial development and largely supplanted water driven mills, as well as the burning of wood or peat for heat.
When generating electricity, energy from the combustion of fossil fuels is often used to power a turbine. Older generators used steam generated by the burning of the fuel to turn the turbine, but in newer power plants the gases produced by burning of the fuel turn a gas turbine directly.
The burning of fossil fuels by humans is their major source of emissions of carbon dioxide which is one of the greenhouse gases that is believed to contribute to global warming. A small amount of hydrocarbon-based fuels are biofuels which are derived from atmospheric carbon dioxide and thus do not increase the carbon dioxide in the atmosphere.
There are two theories on the origin of fossil fuels: the mainstream biogenic theory and the abiogenic theory. The two theories have been intensely debated since the 1860s, shortly after the discovery of widespread petroleum. According to the biogenic theory, fossil fuels are the altered remnants of ancient plant and animal life deposited in sedimentary rocks. The organic molecules associated with these organisms forms a group of chemicals known as kerogens which are then transformed into hydrocarbons by the process of catagenesis. According to the abiogenic theory, hydrocarbon deposits are primordial, being part of the Earth as it formed.
The biogenic theory was favored early because in the late 19th century it was believed that the Earth was extremely hot (possibly molten rock) during its formation. This would have precluded the accretion of hydrocarbons, which would have been oxidized into water and carbon dioxide. When it was later discovered that all fossil fuels contain traces of biological debris, the biogenic theory gained further support because the idea that life (even microbial life) could exist at the depths at which petroleum had been found seemed even less plausible.
Research in the abiogenic theory is in progress. For details on the subject see the article Abiogenic petroleum origin.
The reports from the early 1973 energy crisis) that oil supplies would run out in the 1990s have proven wrong, but oil is still believed to be a finite resource. Even if abiogenic oil is the source, the theory is not of practical use unless significant deposits are discovered. Significant usage of hydroelectricity and nuclear power (outside the United States) and scientific advances have reduced the dependency on fossil fuels, of which household usage has increased nonetheless. Petroleum is also important because it is a source of petrochemicals, for which there are a vast variety of uses.
Sooner or later we will have to find alternatives. However, many people share a viewpoint that the time at which we would run out of fossil fuels is far in the future. Some hope that by then we may have presently unavailable power systems such as solar power satellites or nuclear fusion.
The principle of supply and demand suggests that as hydrocarbon supplies diminish, prices will rise. It has therefore been pointed out that higher prices will lead to increased supplies as previously uneconomic sources become more economical to exploit. Artificial gasolines and other renewable energy sources presently require more expensive production and processing technologies than conventional petroleum reserves, but may then become economically viable. See future energy development.
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