Nonrenewable energy resources

Summary: A nonrenewable energy resource is a natural resource that cannot be produced or replaced on a scale that can sustain its consumption rate. These resources often exist in a fixed amount and are consumed much more quickly than nature can create them.

Sufficient, reliable sources of energy are a necessity for industrialized nations. Energy is used for heating, cooking, transportation, and manufacturing. Energy can generally be classified as nonrenewable and renewable. More than 85 percent of the energy used in the world is from nonrenewable supplies. A nonrenewable energy resource is a natural resource that cannot be replaced on a scale that can sustain its consumption rate. These resources often exist in a fixed amount and are consumed much more quickly than nature can create them.

The major categories of nonrenewable energy sources are the fossil fuels (oil, natural gas, and coal, including petroleum products such as gasoline, diesel fuel, and propane), and radioactive fuel (nuclear energy). Fossil fuels are continually produced by the decay of plant and animal matter, but the rate of their production is extremely slow, much slower than the rate at which we use them—thus they are nonrenewable. Nuclear energy is also considered nonrenewable in that it uses a relatively rare metal, uranium-235. Nonrenewable energy sources come out of the ground as liquids, gases, and solids. Crude oil (petroleum) is the only commercial nonrenewable fuel that is naturally in liquid form. Natural gas and propane are normally gases, but coal and uranium ore are solid.

Oil and Petroleum Products

Crude oil or liquid petroleum is a fossil fuel that is refined into many different energy products: gasoline, diesel fuel, jet fuel, and heating oil, for example. Oil forms underground in rocks, such as shale, which is rich in organic materials. After the oil forms, it migrates upward into porous reservoir rock, such as sandstone or limestone, where it can become trapped by an overlying impermeable cap rock. Wells are drilled into these oil reservoirs to remove the gas and oil. More than 70 percent of oil fields are found near tectonic plate boundaries, because the conditions there are conducive to oil formation.

More than 50 percent of the world’s oil is found in the Middle East; sizable additional reserves occur in North America. Most known oil reserves are already being exploited, and oil is being used at a rate that exceeds the rate of discovery of new sources. If the consumption rate continues to increase and no significant new sources are found, oil supplies could be exhausted by about 2040.

Despite its limited supply, oil is a relatively inexpensive fuel source. It is preferred over coal as a fuel source because an equivalent amount of oil produces more kilowatts of energy than coal. It also burns cleaner, producing about 50 percent less sulfur dioxide. However, the burning of oil contributes significantly to environment problems and atmospheric pollution in the form of carbon dioxide, carbon monoxide, sulfur dioxide, and nitrogen oxide emissions. These greenhouse gases pollute the air and contribute to global warming.

Oil Shale and Tar Sands

One source of oil, oil shale and tar sands, is currently among the least utilized of fossil fuel sources. Oil shale is sedimentary rock with very fine pores that contain kerogen, a carbon-based, waxy substance. If shale is heated to 490 degrees Celsius, the kerogen vaporizes and can then be condensed as shale oil, a thick, viscous liquid. This shale oil is then further refined into usable oil products. Production of shale oil requires large amounts of energy, however, for mining and processing the shale. Indeed, about half a barrel of oil is required to extract every barrel of shale oil. The largest tar-sand deposit in the world is in Canada and contains enough material (about 500 billion barrels) to supply the world with oil for about 15 years. However, because of environmental concerns and high production costs, these tar sands are not being fully utilized.

Natural Gas

Natural gas production is often a by-product of oil recovery, as the two commonly share underground reservoirs. Natural gas is a mixture of gases, the most common being methane (CH4). It also contains some ethane (C2H5), propane (C3H8), and butane (C4H10).

Natural gas is usually not contaminated with sulfur and is therefore the cleanest-burning fossil fuel. After recovery, propane and butane are removed from the natural gas and made into liquefied petroleum gas (LPG). LPG is shipped in special pressurized tanks as a fuel source for areas not directly served by natural gas pipelines (such as rural communities). The remaining natural gas is further refined to remove impurities and water vapor and is then transported in pressurized pipelines.

Natural gas is highly flammable and odorless. The characteristic smell associated with natural gas is actually that of minute quantities of a smelly sulfur compound (ethyl mercaptan) that is added during refining to allow consumers to smell the gas should it leak from pipes and thus pose a hazard.

The use of natural gas is growing rapidly. Besides being a clean-burning fuel source, natural gas is easy and inexpensive to transport, once pipelines are in place. In developed countries, natural gas is used primarily for heating, cooking, and powering vehicles. It is also used in a process for making ammonia fertilizer. The current estimate of natural gas reserves is about 100 million metric tons. At current usage levels, this supply will last an estimated 100 years. Most of the world’s natural gas reserves are found in Eastern Europe and the Middle East.

Coal

Coal is the most abundant fossil fuel in the world, with estimated reserves of 1 trillion metric tons. Most of the world’s coal reserves exist in Eastern Europe and Asia, but the United States also has considerable reserves. Coal formed slowly over millions of years from the buried remains of ancient swamp plants. During the formation of coal, carbonaceous matter was first compressed into a spongy material called peat, which is about 90 percent water. As the peat became more deeply buried, the increased pressure and temperature turned it into coal.

Different types of coal resulted from differences in the pressure and temperature that prevailed during formation. The softest coal (about 50 percent carbon), which also has the lowest energy output, is called lignite. Lignite has the highest water content (about 50 percent) and relatively low amounts of smog-causing sulfur. With increasing temperature and pressure, lignite is transformed into bituminous coal (about 85 percent carbon and 3 percent water). Anthracite (almost 100 percent carbon) is the hardest coal and also produces the greatest energy when burned.

Currently, the world is consuming coal at a rate of about 7 billion metric tons per year. The main use of coal is for power generation, because it is a relatively inexpensive way to produce power. Coal is used to produce more than 50 percent of the electricity in the United States. In addition to electricity production, coal is sometimes used for heating and cooking in less developed countries and in rural areas of developed countries. If consumption continues at the current rates, reserves will last for more than 200 years.

Coal mining creates several environmental problems. Coal is most cheaply mined from near-surface deposits using strip-mining techniques. Strip mining causes considerable environmental damage in the form of erosion and habitat destruction. Subsurface mining of coal is less damaging to the surface environment, but it is much more hazardous for miners because of tunnel collapses and gas explosions. The burning of coal results in significant atmospheric pollution. The sulfur contained in coal forms sulfur dioxide when burned. Harmful nitrogen oxides, heavy metals, and carbon dioxide are also released into the air during coal burning. The harmful emissions can be reduced by installing scrubbers and electrostatic precipitators in the smokestacks of power plants. The toxic ash remaining after coal burning is also an environmental concern and is usually disposed into landfills.

Radioactive Fuel

The use of nuclear technology requires a radioactive fuel. Uranium ore is present in the ground at relatively low concentrations and is mined in 19 countries. Uranium is used to create plutonium; uranium-238 is fissionable and can be transmuted into fissile plutonium-239 in a nuclear reactor. Nuclear fuel is used in nuclear power stations to create electricity. Nuclear power provides about 6 percent of the world’s energy and 13–14 percent of the world’s electricity. Nuclear technology is a volatile and contaminating source of fuel production, with the expense of the nuclear industry predominantly reliant on subsidies.

In most electric power plants, water is heated and converted into steam, which drives a turbine generator to produce electricity. Fossil-fueled power plants produce heat by burning coal, oil, or natural gas. In a nuclear power plant, the fission of uranium atoms in the reactor provides the heat to produce steam for generating electricity.

Originally, nuclear energy was expected to be a clean and cheap source of energy. Nuclear fission does not produce atmospheric pollution or greenhouse gases, and its proponents expected that nuclear energy would be cheaper and last longer than fossil fuels. Unfortunately, because of construction cost overruns, poor management, and numerous regulations, nuclear power has become much more expensive than predicted. The nuclear accidents at Three Mile Island in Pennsylvania (1979) and Chernobyl in the Ukraine (1986) raised concerns about the safety of nuclear power. Furthermore, the problem of safely disposing spent nuclear fuel remains unresolved.

Sustainable Development

It is our responsibility to use scarce nonrenewable energy resources judiciously and sustainably, so that we do not contribute to their fast depletion. Although today’s society will remain dependent on nonrenewable energy resources for the next few decades, the development of alternative energy sources and the technology to harness them at the nascent stage should be our aim. Also, we need to have proper technology in place and devise newer methods to eliminate the negative environmental impact of fossil fuels. Overexploitation of nonrenewables will lead to excessive pollution and rising threats of global warming. The judicious use of nonrenewables can save us from an energy crisis in the immediate future until we develop alternative sources.

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