INTRODUCTION: WHAT ARE FOSSIL FUELS?
Nearly 90 percent of the world's energy comes from fossil fuels. Because fossil fuels are the main source, they are not alternative energy sources. Fossil fuels include coal, natural gas, and petroleum (puh-TROH-lee-uhm), which is often called oil. People use fossil fuels to meet nearly all of their energy needs, such as powering cars, producing electricity for light and heat, and running factories. Because their use is so widespread, it is important to understand fossil fuels in order to make informed decisions about present and future alternative energy sources.
Fossil fuels are a popular source of energy because they are considered convenient, effective, plentiful, and inexpensive, but a few nations have most of the world's fossil fuels, a fact that often causes conflicts. Nevertheless, as of 2006, there are no practical and available alternatives to fossil fuels for most energy needs, so they continue to be heavily used.
Types of fossil fuels
Fossil fuels are substances that formed underground millions of years ago from prehistoric plants and other living things that were buried under layers of sediment, which included dirt, sand, and dead plants. To turn into fossil fuels, this organic matter (matter that comes from a life form and is composed mainly of the element carbon) was crushed, heated, and deprived of oxygen. Under the right conditions and over millions of years, this treatment turns dead plants into fossil fuels.
The three main types of fossil fuels correspond to the three states of matter—solid, liquid, and gas:
- Coal is a solid.
- Petroleum is a liquid.
- Natural gas is a gas.
Several fossil fuels are made by refining petroleum or natural gas. These fuels include gases such as propane, butane, and methanol.
Natural Gas Versus Gasoline
Natural gas is not sold at gas stations. The fuel used in cars is liquid petroleum, or gasoline. Although most people call it "gas," this fuel is not the same thing as natural gas. The word gas refers to natural gas, not gasoline. The word oil refers to petroleum.
Words to Know
- A kind of hydrocarbon in which the molecules have the maximum possible number of hydrogen atoms and no double bonds.
- A common unit of measurement of crude oil, equivalent to 42 U.S. gallons; barrels of oil per day, or BOPD, is a standard measurement of how much crude oil a well produces.
- A substance that speeds up a chemical reaction or allows it to occur under different conditions than otherwise possible.
- Clean Air Act
- A U.S. law intended to reduce and control air pollution by setting emissions limits for utilities.
- The by-products of fossil fuel burning that are released into the air.
- Global warming
- A phenomenon in which the average temperature of the Earth rises, melting icecaps, raising sea levels, and causing other environmental problems.
- Greenhouse effect
- A phenomenon in which gases in the Earth's atmosphere prevent the sun's radiation from being reflected back into space, raising the surface temperature of the Earth.
- Octane rating
- The measure of how much a fuel can be compressed before it spontaneously ignites.
- A molecule consisting of three atoms of oxygen, naturally produced in the Earth's atmosphere; ozone is toxic to humans.
- The study of movement within the earth, such as earthquakes and the eruption of volcanoes.
Whether a fossil fuel formed as a solid, liquid, or gas depends on the location, the composition of the materials, the length of time the matter was compressed, how hot it became, and how long it was buried. Coal formed from accumulated layers of plants that died in swamps and were buried for millions of years. Petroleum and natural gas formed from microscopic plants and bacteria in the oceans. Both petroleum and natural gas formed in places that could contain them: pockets, or reservoirs (reh-zuh-VWARS), in the undersea rock.
Earth has a lot of fossil fuels. Scientists in 2005 estimated that the ground contains about ten trillion metric tons of coal, enough to fuel human energy needs for hundreds of years. Petroleum and natural gas deposits are not nearly so extensive. Most scientists believe that if people keep using up oil and gas at 2005 rates, all known petroleum and gas reserves will be used up by the beginning of the twenty-second century.
At the end of the twentieth century, petroleum supplied about 40 percent of the energy needs of the United States. Another 22 percent was covered by coal and 24 percent by natural gas. The International Energy Agency (IEA) has predicted that the world will need almost 60 percent more energy in 2030 than it did in 2002. The IEA believes that fossil fuels will still be supplying most of those needs by 2030.
Dinosaurs in the Gas Tank
It is unlikely that fossil fuels are made of dinosaurs. Most fossil fuels formed about 300 million years ago, and most of them are made mainly of plant matter. Dinosaurs did not appear until about 230 million years ago, so the first dinosaur was not born until the youngest petroleum had already formed. Dinosaur fossils, however, do have something in common with fossil fuels. Fossils, whether they are dinosaurs or coal, are the hardened remains of animals and plants preserved in Earth's crust from an earlier age. Dinosaur fossils formed when dinosaurs were buried in sand or dirt, and their skeletons were hardened by minerals that seeped in through tiny holes in the bone.
Other kinds of fossil fuels exist, but none of them can be extracted, recovered, or used efficiently. These fossil fuels include:
- Gas hydrates, which are deposits of methane and water that form crystals in ocean sediments. There is currently no technology for extracting methane from the crystals, so gas hydrates are not yet considered a part of world energy reserves.
- Tar sands, which are patches of tar in sandstone. Petroleum sometimes gets embedded in sandstone, and the bacteria in the sandstone and the surrounding water make the petroleum turn into tar. Tar sands are difficult to recover and use.
- Oil shale, which is a kind of rock full of a waxy organic substance called kerogen (KEHR-uh-juhn). Kerogen formed from the same microscopic plants and bacteria that make up petroleum, but it never reached the pressure or temperature that would have turned it into oil. It is not currently practical to recover or use oil shale.
How fossil fuels work
Fossil fuels generate energy by burning. This energy can serve a variety of purposes from heating homes to powering automobiles. The simplest devices that use fossil fuels burn them so that people can take advantage of the heat. For example, some homes are heated by furnaces that burn natural gas. The heat from the burning gas warms the house. Camping stoves often burn propane that is fed to the stove burners from an attached bottle. Coal stoves burn lumps of coal.
Most fossil fuel-powered operations, however, use the burning of the fossil fuel to power much more complex machines, such as internal combustion engines. In many cases, other fuels could supply the necessary heat; for example, locomotives could be powered by burning wood instead of burning coal, and power plants can be powered by water instead of coal. The advantage of fossil fuels in these situations is that they produce large amounts of heat for their volume, and they are currently widely available, with some liquid and gas fuels available at pumps.
The internal combustion engine
Automobiles use fossil fuel (gasoline) to power their internal combustion engines. An internal combustion engine burns a fuel to power pistons, which make the engine turn. Internal combustion engines have been around since the 1860s. The four-stroke "Otto" engine was invented in 1867 by Nikolaus August Otto (1832–1891), a German engineer. Another German engineer, Rudolph Diesel (1858–1913), invented the diesel engine in 1892. The basic principles of internal combustion have not changed since then.
An engine contains several cylinders (most cars have between four and eight) that make the engine move. A four-stroke cylinder works like this:
- The intake valve opens to let air and fuel into the cylinder while the piston is down. This is called the intake stroke.
- The piston begins traveling back up. The intake valve closes and the piston compresses the air and fuel in the cylinder. This is called the compression stroke.
- The spark plug creates a spark, which ignites the fuel and air so that it explodes. The explosion pushes the piston down. The piston rotates the crankshaft, which turns the engine. This is called the power stroke.
- The exhaust valve opens. The piston moves back up, forcing the burned gases out through the exhaust valve. The piston travels back down, the exhaust valve opens, and the intake stroke begins again. This is called the exhaust stroke.
One complete cycle of a four-stroke engine will turn the crankshaft twice. A car engine's cylinders can fire hundreds of times in a minute, turning the crankshaft, which transmits its energy into turning the car's wheels. The more air and fuel that can get into a cylinder, the more powerful the engine will be.
Most engines that run on gasoline can also be powered with natural gas or LPGs (liquefied petroleum gas), with some minor modifications to the fuel delivery system. The basic method of combustion is the same.
A diesel engine is similar to a gasoline engine except that only air enters the cylinder during the intake stroke, and only air is compressed during the compression stroke. The fuel is sprayed into the cylinder at the end of the compression stroke, when the air temperature is high enough to cause it to ignite spontaneously without a spark. Diesel engines are usually heavier and more powerful than gasoline engines and have better fuel efficiency; they are used in buses, trucks, ships, and some automobiles. In Europe, a large proportion of personal automobiles are powered by diesel fuel, but diesel fuel is less common in the United States because of clean-air laws. Diesel fuel has more exhaust emissions than gasoline.
What does Octane Mean?
Gasoline comes in several varieties labeled with words such as "regular" or "supreme," each with a number. The higher the number on the gasoline, the more expensive it is. That number is the gasoline's octane rating, which tells how much the fuel can be compressed before it will spontaneously ignite. In a car engine, gasoline is supposed to ignite in one of the engine's cylinders when it is lit by a spark plug; it is not supposed to ignite on its own. When it ignites on its own, the engine "knocks." This can damage the engine. High-performance cars, though, increase their horsepower by increasing the amount of compression in the engine, which makes knocking more likely. That is why high-performance cars have to use expensive, high octane gasoline.
Using coal for heat and cooking can be as straightforward as putting coal in a stove and setting it on fire; the coal burns slowly and emits steady heat. But the way coal really had an effect on people's lives was through its use as a fuel for engines, such as steam engines that powered locomotives that pulled trains. Coal-burning locomotives used steam to power their wheels. A locomotive works like this:
- In order to keep the fire burning, the locomotive has to carry a large pile of coal, which a person called the fireman constantly shovels into the firebed. (More modern locomotives have mechanical shovels to feed the fires.)
- The ashes left over from the burning coal fall through grates into an ashpan below the firebed. The ashes are dumped at the end of the train's run.
- This basic process was not only used in trains. Steam engines also powered riverboats, steamships, and factories.
Most trains in the twenty-first century are powered by diesel fuel or electricity. China still uses coal-burning trains for normal transportation, but in Europe and the United States steam locomotives are only used as part of museum displays to entertain tourists.
Where electricity comes from
Fossil fuels are important for the production of electricity. Most power plants have generators that spin to create electricity, which is then sent out through the wires and poles that distribute it to consumers. Something has to power those generators. The vast majority of power plants burn fossil fuels for this purpose. (The rest use nuclear power or hydroelectric power.)
About one-half of the electricity in the United States comes from coal-burning power plants. These plants store their coal in giant outdoor piles. People driving bulldozers push the coal onto conveyor belts that carry it up to silos or bunkers. The coal is typically crushed so it can be fed into most power station furnaces. Then it is fed into giant burners that burn night and day to create steam to turn the generator. Most plants need constant deliveries of coal to have enough fuel to keep the burners running at all times. They produce large amounts of ash. One of the jobs of plant operators is to keep the ash from clogging up the works.
Natural gas is the other significant fossil fuel source of electrical power in the United States, supplying about one-fifth of the nation's electricity. Natural gas plants use turbines to spin generators. The turbines are connected to pipelines that provide a constant supply of natural gas. Some plants use the natural gas to power the generator directly. Others use the natural gas to create steam, which spins the generator.
The United States government encourages power companies to build plants powered by natural gas because natural gas burns much more cleanly than coal and therefore does not create as much pollution. The U.S. Department of Energy predicts that 90 percent of new power plants built in the early 2000s will be powered by natural gas.
Historical overview: Notable discoveries and the people who made them
Humans have been using fossil fuels for thousands of years, possibly as long ago as twenty thousand years. Oil sometimes seeps up through the ground, so it was easy for people to see it and experiment with it. The ancient Mesopotamians in what is now Iraq may have discovered a way to use oil about five thousand years ago. Historians believe that people first used petroleum as oil for lighting, dipping wood in it and setting it on fire as a torch. Ancient Greeks and Romans used coal as a fuel for heat and cooking. Ancient temples sometimes had eternal flames, which may have been powered by natural gas leaking up from the ground.
In the British Isles coal began to be used in the late thirteenth century, and it was the dominant fuel in London by 1600. Wood was abundant, so coal took time to become widely adopted. The first widespread use of fossil fuels occurred in the late 1700s, with the development of the steam engine and the start of the industrial revolution. James Watt (1736–1819) is usually credited as the inventor of the first commercially efficient steam engine in 1769, though his work was based on the inventions of others, particularly that of the Cornish engineer Thomas Newcomen (1664–1729), whose atmospheric steam engine was completed in 1711. The steam engine, powered by coal, made the industrial revolution possible. Steam engines could power trains, boats, and factories. The first coal-burning steam locomotive was built in Wales in 1804. In 1825 coal-powered trains became available for commercial use. Robert Fulton (1765–1815) invented the steam-powered riverboat in 1807, and riverboats became a popular way to travel up and down the Mississippi River in the United States. In 1819 a steamship crossed the Atlantic Ocean for the first time. By the mid-1800s people were regularly traveling between Europe and the United States on coal-powered steamships.
People began using natural gas to power lamps in 1785 in England. Natural gas lamps became common in the United States around 1816. The first natural gas well was built in Fredonia, New York, in 1821.
In the 1850s an American lawyer named George Bissell (1821–1884) investigated the possibility of using oil as lamp fuel. He thought he could find more oil if he drilled into the ground, so he hired Edwin Drake (1819–1880) to drill the first oil well. This well was completed in Titusville, Pennsylvania, in 1859. Drake used the oil to make kerosene, which people used in lamps and heaters. Gasoline was a by-product (one of the leftovers) of the process of making kerosene, but no one at the time had a real use for it. Other people began looking for oil, and they found it in places such as Indonesia, Texas, and the Middle East.
By the end of the nineteenth century many people were using light bulbs instead of kerosene lamps, so oil producers began adapting their product for other uses. The first gasoline-powered internal combustion engine was developed in 1886. The first mass-produced gasoline-powered car was the Oldsmobile, introduced in 1902. Henry Ford (1863–1947) introduced the Model T in 1908 and began producing his inexpensive cars on an assembly line. By 1920 there were twenty-three million cars in the world, and it turned out that gasoline was the most practical way to power them.
The Wright brothers, Orville (1871–1948) and Wilbur (1867–1912), flew their first successful airplane in 1903. They used petroleum as their fuel, and from that point on airplanes were powered by petroleum-based fuels. Diesel fuel gradually replaced coal as the dominant fuel for large ships. Diesel locomotives appeared around 1920 and had replaced steam engines by 1960.
Consumption of all fossil fuels increased greatly during the twentieth century. Petroleum was used to power automobiles, airplanes, ships, and electric plants. Coal heated homes, powered factories and trains, and generated electricity at power plants. Toward the end of the twentieth century the oil industry began to develop the potential of natural gas, and this fuel became useful in homes and businesses as well as in industry. Minor fossil fuels such as kerosene, propane, and butane were all widely used at the beginning of the twenty-first century. Perhaps the most notable transition from the twentieth to the twenty-first century is from stationary devices burning solid fuels to mobile sources using liquid fuels.
Current and future technology
Fossil fuels supply a large percentage of the world's energy needs through a variety of technologies. Most automobiles and other vehicles use gasoline to power internal combustion engines, in which the burning that generates power takes place inside the engine. Coal or gasoline is burned to power factory equipment. Coal-fired plants generate much of the world's electricity. Almost every twenty-first century technology uses fossil fuels in some way.
Fossil fuel technology has changed. Scientists are constantly looking for technology that makes fossil fuels work more efficiently and reduces pollution. Fossil fuels are so common and considered so necessary that there is great incentive for engineers to improve methods of acquiring and using fossil fuels. Technology under development includes:
- Clean coal technology
- Vehicles powered by natural gas or substances other than gasoline
- Fuel cells that use small amounts of fossil fuel to make hydrogen
- Safer means of transporting fossil fuels
- Improved techniques for cleaning fossil fuels before, during, and after burning
- Improvements in extracting fossil fuels from the ground
Benefits and drawbacks of fossil fuels
Most existing technology was designed for use with fossil fuels. Fossil fuel transport systems are already in place. Pipelines for oil and natural gas and trucks and ships for petroleum products move the fossil fuels where they are needed. And consumers can buy the fossil fuel products they use on practically every corner.
Yet, fossil fuels are non-renewable resources. Current supplies took a very long time to form under the Earth's crust. These supplies will be gone long before the Earth has a chance to replace them. Even now, getting fossil fuels is a major drawback to using them. Countries that do not have reserves of oil and natural gas must depend on those countries that do. And using fossil fuels contributes to air and water pollution.
Environmental impact of fossil fuels
Fossil fuels cause or contribute to environmental problems such as the following:
- Damage to the landscape
- Air pollution
- Water pollution
- Oil spills
- Radioactivity (Coal contains the radioactive elements uranium and thorium, and most coal-fired plants emit more radiation than a nuclear power plant.)
- Health problems for workers and those nearby (Many fossil fuel byproducts can be harmful to humans: breathing toxic hydrocarbons, nitrogen oxides, and particulate matter can cause ailments such as chest pain, coughing, asthma, chronic bronchitis, decreased lung function, and cancer, and exposure to mercury can lead to nerve damage, birth defects, learning disabilities, and even death.)
Some experts believe the environmental problems are so serious that people need to find alternatives to fossil fuels even before all reserves are used up. Others believe that technological improvements will allow the use of fossil fuels for many years to come.
Damage to the landscape
Fossil fuels are found underground. There is no way to get them out without cutting into or removing the dirt on top of deposits. Strip mining for coal involves removing the dirt and rocks above a deposit of coal and digging out the coal beneath it. Miners sometimes remove the tops of mountains to remove the coal below. Mines below the Earth's surface can collapse, resulting in changes to the landscape on top of them.
Though drilling for oil and natural gas is not always as destructive as coal mining, it still involves machinery that can destroy animal habitats and pipelines that cut across the land for thousands of miles.
Air pollution results from driving cars and trucks, from burning coal and other fossil fuels to create electricity, from industry, from using gas-powered stoves and appliances, and from many other daily activities. As the number of drivers increases and average fuel efficiency declines due to a shift to lower mileage SUVs, air pollution increases. As the number of people using electricity increases, so does air pollution.
There are several types of air pollution:
- Particulate matter is tiny particles of burnt fossil fuels that float in the air. This kind of pollution is sometimes called black carbon pollution. Examples of coarse particulate matter include the smoke that comes from a diesel-poweredtruck or the soot that rises from a charcoal-burning grill. However, in addition to the visible black particulate matter there is the fine material (less than 2.5 microns) that creates large health problems.
- Smog is a mixture of air pollutants, both gases and particles, that create a haze near the ground. Sulfate particles, created when sulfur dioxide combines with other chemicals in the air, and ozone are the main causes of smog and haze in most of the United States.
- Ozone is a form of oxygen that contains three oxygen atoms per molecule. (O2, the form of oxygen that humans need to survive, contains two oxygen atoms per molecule.) It is common in Earth's atmosphere, where it blocks much of the sun's ultraviolet radiation, preventing it from burning up most forms of life. Though it is beneficial and necessary in the atmosphere, ozone is also destructive and highly toxic to humans. Ozone forms spontaneously from the energy of sunlight in the air, but it can also form from other reactions, such as sparks from electrical motors or the use of high
Where Does Air Pollution Come From?
According to the Environmental Protection Agency (EPA), mobile sources, such as cars, trucks, buses, trains, airplanes, and boats, represent the largest contributor to U.S. air toxics. In 1999 as much as 95 percent of the carbon monoxide in typical U.S. cities came from mobile sources, according to EPA studies. More than half of all nitrogen oxide air pollution in the United States came from on road and non-road vehicles. The rest came from industry, such as power plants and factories. But the EPA states that the majority of all hydrocarbons (53 percent) and particulate matter (72 percent) comes from non-mobile sources such as power plants and factories.
- voltage electrical equipment such as televisions. Fossil fuel pollution contributes nitrogen oxides and other organic gases that can react to create ozone. Ozone forms close to the ground on light sunny days, especially in cities.
- Sulfur dioxide is a by-product of burning fossil fuels. It is one of the key ingredients of acid rain. The United States Environmental Protection Agency (EPA) considers the reduction of sulfur dioxide emissions a crucial part of the effort to clean up the nation's air. The United States has set national air quality standards, and state and local governments are required to meet them.
- Nitrogen oxides are gases that contain nitrogen and oxygen in different amounts. Most of them are colorless and odorless. Almost all nitrogen oxides are created by the burning of fossil fuels in motor vehicles, power plants, and industry. Nitrogen oxides react with sulfur dioxide to produce acid rain. They also contribute to the formation of ozone near the ground, and they form particulate matter that clouds vision and toxic chemicals that are dangerous to humans and animals. In addition, they harm water quality by overloading water with nutrients. Finally, they are believed to contribute to global warming.
- Carbon monoxide is one of the main sources of indoor air pollutants. It forms from the burning of fossil fuels in appliances such as kerosene and gas space heaters, gas water heaters, gas stoves and fireplaces, leaking chimneys and
- furnaces, gasoline-powered generators, automobile exhaust in enclosed garages, and other sources. Carbon monoxide binds with the iron atoms in hemoglobin (the part of blood that carries oxygen) and prevents the blood from taking up enough oxygen to keep the brain running.
The United States and the individual states have passed various laws regulating air pollution. The Clean Air Act, passed in 1990, is one of the most important. It requires states to meet air quality standards, creates committees to handle pollution that crosses borders between states or from Mexico or Canada, and allows the EPA to enforce the law by fining polluters. It creates a program allowing polluting businesses to apply for and buy permits that let them release a certain amount of pollutants. Businesses can buy, sell, and trade these permits. They can receive credits if they release fewer emissions than they are allowed to produce.
One major difficulty with controlling air pollution is that some pollutants can travel thousands of miles from their sources. Certain types of air pollution in one state can originate from a coal-burning plant in another. For that reason, air pollution regulations must focus on large regions if they are to have any effect at all.
Burning a charcoal grill or kerosene heater or running a car engine inside an enclosed space, such as a closed garage, can produce enough carbon monoxide to kill a person. Every year people die from inhaling concentrated carbon monoxide. Death comes easily and without warning because the victim often does not notice any symptoms; he or she simply gets sleepy from lack of oxygen, loses consciousness, and dies as carbon dioxide builds up in the blood.
Acid rain is rain with small amounts of acid mixed into it. When sulfur dioxide and nitrogen oxides are released from burning fossil fuels, they mix with water and oxygen in the atmosphere and turn into acids. The acids in acid rain are not strong enough to dissolve a person, but they can contribute to environmental problems, such as the following:
- Polluting lakes and streams, which can kill fish, other animals, and aquatic plants and disrupt entire ecosystems
- Damaging trees at high elevations
- Deteriorating the stone, brick, metal, and paint used in everything from buildings and bridges to outdoor artworks and historical sculptures
- Damaging the paint on cars
- Impairing visibility by filling the air with tiny particles
- Causing health problems in humans when the toxins in the rainfall go into the fruits, vegetables, and animals that people eat.
The EPA has an Acid Rain Program that limits the amount of sulfur dioxide that power plants can produce, and the program has reduced emissions somewhat. Reducing emissions overall should contribute to eliminating acid rain.
A HEPA Filter?
Particulate matter is air pollution in the form of particles suspended in the air. Of special concern to human health are fine particles (of less than 2.5 microns) that are easily inhaled and can cause irritation to the eyes, nose, and throat, and may get into the lungs and either be absorbed by the bloodstream or stay embedded in the lungs to cause more serious breathing problems. Particulate matter has even been linked to an increased risk of heart attack in people with heart disease. Breathing in the particles may cause shortness of breath and chest tightness. A HEPA (HEP-ah) filter cleans particulate matter from indoor air when it is used in vacuum cleaners or air conditioning and heating units. A HEPA filter makes indoor air healthier because it is a "high efficiency particulate arresting" filter.
Most scientists believe that the use of fossil fuels has changed the world's climate, and that this change is continuing. Burning fossil fuels releases gases called greenhouse gases, which include carbon dioxide, methane, and nitrous oxide. Greenhouse gases are good at trapping heat. When the sun's radiation hits Earth, some of the heat is reflected back into space. When greenhouse gases get into the atmosphere, they act like the walls of a greenhouse, holding the heat in so that it cannot escape back to space. Ordinarily, this would be a good thing, because life on Earth depends on keeping some of the sun's heat on the surface. Since the industrial revolution, however, the amount of greenhouse gases in the atmosphere has increased. The amount of carbon dioxide has increased 30 percent; the amount of methane has increased 100 percent; and the amount of nitrous oxide has risen 15 percent. These gases make the atmosphere better at keeping heat in. As a result, Earth's temperature has risen and continues to rise.
The increase in global temperatures can cause many problems. A possible effect is a rise in sea levels, which can change the shape of coastlines; cause changes in forests, crops, and water supplies; and harm the health of humans and animals. Fossil fuels account for 98 percent of carbon dioxide emissions, 24 percent of methane emissions, and 18 percent of nitrous oxide emissions.
When transporting petroleum, there is always the danger that the oil will leak out of its tank and contaminate the local environment. Many oil spills occur when a giant tanker ship crashes and the petroleum leaks out of the tank into the ocean. Spills can also happen when oil wells or pipelines break, or when tanker ships wash their giant tanks, rinsing the residue straight into the ocean.
When oil gets into the ocean, it quickly spreads over the surface of the water, forming an oil slick. The oil clumps into tar balls and an oil-water mixture called mousse. Seabirds and marine mammals get caught in the oil and die.
The 1989 wreck of the Exxon Valdez in Prince William Sound, Alaska, caused the worst oil spill that has so far occurred in North America. The ship hit and slid onto a coral reef. The accident allowed 38,800 tons of oil from the tanker to spread over 1,200 miles (1,930 kilometers) of shoreline, killing over one thousand sea otters and between 100,000 and 300,000 seabirds. At least 153 bald eagles also died from eating dead seabirds covered with oil. The cleanup cost nearly $3 billion, a large portion of that furnished by the United States government.
In 1997 many of the world's nations agreed to work together to reduce greenhouse gases and stop global warming. These nations signed an agreement in Kyoto, Japan, referred to as the Kyoto Protocol. The Kyoto Protocol sets targets for reducing emissions and deadlines for nations to meet those targets. The United States and Australia have not agreed to participate because the protocol does not place the same requirements on developing nations as it does on industrialized nations.
Almost 14,000 oil spills are reported each year in the United States. Usually, the owner of the oil or the tanker takes responsi-bility for cleanup. Occasionally, local, state, and federal agencies must help. The EPA takes care of spills in inland waters, and the United States Coast Guard responds to spills in coastal waters and deepwater ports.
The long-term effects of oil spills are not known. Though it appears that it is possible to clean up most of the oil and that the local ecosystem can recover, it also seems that some of the effects of oil are very long-lasting. The Prince William Sound environment still had some problems in the early 2000s: many animal species affected by the spill had still not recovered to their pre-spill numbers, and some oil remained on the region's beaches.
Economic impact of fossil fuels
Because they have been plentiful and are usually less expensive than other energy sources, fossil fuels supply nearly all of the world's energy. At the beginning of the twenty-first century the world economy is based on inexpensive fossil fuel. Almost all modes of transportation and industries require fossil fuels. Prices of consumer goods and services from food to airline tickets are partly determined by the cost of fuel. When the price of oil goes up, people who sell goods and services often must raise their prices because it costs more to make or deliver products.
Build a Better Tanker
Transporting oil safely is a big concern for the oil industry. Modern tankers are much stronger than older ones, and they are built with double hulls. Double hull means there are two layers of metal between the oil and the ocean. Double-hulled tankers are much less likely to be torn open if they run into rocks or coral reefs.
As developing nations increase their use of automobiles, electricity, and other goods and services, their demands for fossil fuels increase. For example, oil consumption in China grew rapidly in the early twenty-first century. By 2003 China was consuming the second largest amount of oil in the world, behind the United States. China does not have sufficient fuel reserves to supply its own needs, so it must buy petroleum from other countries. Oil producers can raise their prices because they have several buyers competing to purchase their product.
Yet fossil fuels are still the cheapest source of power in the modern world. Alternative energy sources, such as solar power or hydrogen fuel cells, are much more expensive. Most people will not choose an expensive source of power when a cheap one is available, even if the cheap source contributes to pollution. For example, many coal-burning power plants still produce large amounts of pollution because the cost of controlling the pollution is deemed too expensive.
Societal impact of fossil fuels
Modern life would be impossible without fossil fuels, and in many ways fossil fuels have benefited people. The fact that fossil fuels are everywhere means that it is nearly impossible to take any action without using them. In many houses turning on a light uses fossil fuels. Shopping, eating, going to school, and sleeping in a heated or air conditioned home require the burning of fossil fuels. Fossil fuels are an important global issue. Countries have clashed over the issue of oil.
Air and water pollution are also global issues. The pollutants that come from fossil fuels can spread from country to country. Developing nations, such as Thailand and China, have been rapidly increasing the number of cars owned and of fossil fuel-powered factories and power plants, which has resulted in an increase in air pollution. International groups that want to protect the environment must balance air and water quality with the desire of poorer nations to improve their economies. The less developed countries feel that the countries of Europe and the United States were allowed to use fossil fuels to build their economies, regardless of the environmental consequences, and that they too should be given that opportunity without being forced to worry about pollution.
Issues, challenges, and obstacles in the use of fossil fuels
Fossil fuels are widely used and widely accepted. Nevertheless, there are ways to make fossil fuels less polluting, such as the use of clean coal technology and hybrid automobiles. These technologies have not yet become widespread, in part because they cost more than the methods that are currently used. As pollution increases and fossil fuels become harder to get, new methods of using fossil fuels will probably become more common.
Petroleum is the most widely used fossil fuel, supplying about 40 percent of the world's energy. Petroleum is also called oil. One of the most important uses of petroleum is as fuel for motor vehicles. It can also be used to pave roads, to make other chemicals, and to moisturize skin.
Petroleum is a hydrocarbon, which means it is made up mostly of molecules that contain only carbon and hydrogen atoms. It also contains some oxygen, nitrogen, sulfur, and metal salts. The term petroleum encompasses several different kinds of liquid hydrocarbons. The main ones are oil, tar, and natural gas.
Origins of petroleum
The ingredients in petroleum include microscopic plants and bacteria that lived in the ocean millions of years ago. When they died, these plants and bacteria fell to the bottom of the ocean and mixed with the sand and mud there. This process continued for millions of years, and gradually the layers at the bottom were crushed by the layers above them. The mud became hotter, and the pressure and heat slowly transformed it. The minerals turned into a kind of stone called shale, or mudstone, and the organic matter turned into petroleum and natural gas.
Is Petroleum Really a Fossil Fuel?
Some scientists in Russia and Ukraine believe that petroleum is not actually a fossil fuel but that it formed in Earth's crust from rocks and minerals rather than plants and animals. These scientists believe that the formation of oil requires higher pressure than the formation of coal and that there is not enough organic matter in Earth's deposits to explain the amount of petroleum available in large fields. Scientists in other countries disagree with this idea.
Because they are not solid, petroleum and natural gas can move around. They seep into holes in undersea rocks such as limestone and sandstone, called reservoir rocks. These rocks are porous, meaning they have tiny holes in them that allow liquids and gases to pass through, and function as sponges. Because they are lighter than water, oil and gas migrate upward, although still trapped within Earth's crust. Sometimes the oil and gas end up in an area of rock that is not porous and is shaped in such a way that it can contain liquid and gas. This area becomes a reservoir, or geologic trap, that holds the petroleum and natural gas. Rock formations especially good at trapping hydrocarbons include anticlines, or layers of rock that bend downward; salt domes, or anticlines with a mass of rock salt at the core; and fault traps, or spaces between cracks in Earth's crust.
Within a trap, petroleum, natural gas, and water separate into layers, still within the porous reservoir rocks. Water is the heaviest and stays on the bottom. Petroleum sits on top of the water, and natural gas sits on top of the petroleum. Sometimes the natural gas and petroleum inside a trap find a path to the surface and seep out.
Geologists are scientists who study the history of Earth and its life as recorded in rocks. When looking for oil they want to find underground geologic traps because these traps often contain petroleum that can be removed by drilling. Geologists use a variety of techniques to find oil traps. They use seismology (syze-MAH-luh-jee), sending shock waves through the rock and examining the waves that bounce back. Geologists also study the surface of the land, examining the shape of the ground and the kinds of rocks and soil present. These scientists use gravity meters and magnetometers to find changes in Earth's gravity or magnetic fields that indicate the presence of flowing oil. They use electronic "sniffers" to search for the smell of hydrocarbons. Finding oil is difficult. Scientists searching for oil have only about a ten percent success rate.
Petroleum is present all over the world, but large concentrations of it exist in only a few places. These accumulations are called fields, and they are the places where oil companies drill for oil. The largest fields in the world are in the Middle East, especially in Saudi Arabia, Qatar, and Kuwait, and in North Africa. There are also large fields in Indonesia, Nigeria, Mexico, Venezuela, Kazakhstan, and several U.S. states, including Alaska, California, Louisiana, and Texas.
Once an oil company finds oil in the ground, it has to get the oil out in order to sell it. First the company has to take care of legal matters, such as getting rights to the area it wants to drill. Once that is done, the company builds an oil well, or rig.
All oil rigs have the following basic elements:
- A derrick, which is a tall structure that supports the drill apparatus above ground
- A power source, such as a diesel engine, that powers electric generators
- A mechanical system, including a hoist and a turntable
- Drilling equipment, including drill pipe and drill bits
- Casing to line the drill hole and prevent it from collapsing
- A circulation system that pulls rock and mud out of the hole
- A system of valves to relieve pressure and prevent uncontrolled rushes of gas or oil to the surface
As oil workers drill deeper, they add sections of pipe to the drill and add casings to the hole to keep it stable. They drill until they reach the geologic trap that contains the oil and gas. To get the oil out of reservoir rocks, workers pump in acid or a fluid containing substances to break down the rock and allow the oil to seep into the well. The workers then remove the rig and install a pump in its place. The pump pulls the oil out of the well. Once the oil has been removed from the ground, the oil company must transport the crude oil to a refinery. The most common means of transporting oil are tanker ships, tanker trucks, and pipelines.
Making petroleum useful
Crude oil arrives at the refinery with a great deal of water and salt mixed into it. The water and oil are mixed together in droplets forming an emulsion, which is something like what happens to a salad dressing made of oil and vinegar. The water and oil may eventually separate out into their layers, but this process can take a very long time in thick crude oil. To speed the process, oil refineries heat the crude oil to a temperature at which the water can move more easily. The water molecules then come together and leave the oil. The water also takes the salt out of the oil with it.
The refinery distills crude oil to sort it into its different forms. Crude oil has many different kinds of molecules, some much larger than others. The refinery sorts out these molecules so that molecules of the same size are all together. A refinery is shaped like a tower with trays stacked one above the other. Heating the crude oil makes the molecules turn into gases. These gases move up inside the refinery's tower. As they travel upward in the tower, the gases become colder. At certain temperatures, they become liquids again. The liquids drip back down and are caught in one of the trays. The higher the gas travels, the higher the tray it ends up in. The largest molecules stay at the bottom. The smallest molecules make it all the way to the top of the tower. The lighter molecules are turned into gasoline and other fuels. The heavier ones become engine lubricants, asphalt, wax, and other substances.
If Petroleum Formed in the Ocean, Why are Oil Wells on Land?
When petroleum was forming, much of the area that is now dry land was covered with water. The ocean has moved away since then, but the oil is still there. In addition, many oil wells are out in the ocean, not on land at all.
There is a much larger market for gasoline and other fuels than for the products made from heavier molecules, so refineries try to make as much gasoline as possible. They can sometimes break down larger molecules into smaller ones. They do this through a process called cracking, which uses either heat or chemical catalysts to break down the large molecules.
The Oil Sands of Canada
Since the 1960s, investors and developers have been working to extract crude oil stored in the oil sands of Alberta, Canada. Some experts put the amount of proven oil reserves in the western Canadian oil sands at roughly 175 billion barrels. This would put it second only to Saudi Arabia (with 260 billion) in terms of proven oil reserves. Others believe that the amount of reserve oil in Alberta is much higher, possibly at 300 billion barrels, with more potentially buried deep underground.
Though people dreamed for decades of striking it rich by getting the oil out of Canada's sand, techniques are still in the early stages because of the difficulty of removing it. When compared to the relative ease of getting the oil that comes gushing out of oil fields in the Middle East and Texas, the existing process for turning oil sand into crude oil is difficult and expensive. It requires oversized trucks and shovels to dig out the sand and various machines to crush it, mix it with hot water, spin it to separate out the oil, and heat it to remove impurities. The expense concerned oil investors until political issues in the Middle East and other oil-producing nations and increasingly high demand in the early 2000s drove up oil prices to record levels, finally making oil removal from Alberta's sands profitable. With demand for crude oil on the world market growing, in particular to meet the needs of the United States and China, many of the residents and government officials of Alberta and Canada saw the potential for job creation and huge profits for the province and the rest of the country. In addition to making money by selling the oil, Canada could also potentially use the oil to negotiate with other countries on trade and political issues.
In the decades to come, Canada may become one of the biggest players in the fossil fuel economy, though the benefits may come at a high cost. The large amounts of natural gas and water used in the separation process create concerns for environmentalists. So does the excavation of thousands of tons of mud and sand, which creates large mining pits in Alberta's landscape. Though the oilmen who run Alberta's oil sand industry have promised to improve technology to clean up their greenhouse gas emissions and refill the mines and replant trees, groups like the Sierra Club of Canada have their doubts about whether technology will progress fast enough or trees grow quickly enough to make it worth the environmental damage. With little encouragement for conservation and the use of alternate energy sources by the worldwide community, demand for crude oil will most certainly transform Canada's economy and landscape as the oil sands become a valuable energy source for the world.
Current and potential uses of petroleum
Petroleum has many uses. It can take on different consistencies depending on how much it is refined. About 90 percent of the petroleum used in the United States is used as fuel for vehicles. Fuel types include:
- Motor gasoline used to power automobiles, light trucks, or pickup trucks that people drive as their daily transportation, boats, recreational vehicles, and farm equipment such as tractors
- Distillate fuel oil, including the diesel fuel used to power diesel engines in trucks, buses, trains, and some automobiles
- Heating oil to heat buildings and power industrial boilers
- LPGs (liquid petroleum gases), including propane and butane. Propane is used for heating and to power appliances. Butane is used as fuel and is blended with gasoline
- Jet fuel, which is a kerosene-based fuel that ignites at a higher temperature and freezes at a lower temperature than gasoline, making it safer to use in commercial airplanes
- Residual fuel oil used by utilities to generate electricity
- Kerosene used to heat homes and businesses and to light lamps
- Aviation gasoline, which is a high-octane gasoline used to fuel some aircraft
- Petroleum coke used as a low-ash solid fuel for power plants and industry
Petroleum has many other uses, including:
- Petrolatum, or petroleum jelly, used as a moisturizer and lubricant
- Paraffin wax used in candles, candy making, matches, polishes, and packaging
- Asphalt or tar used to pave roads or make roofs
- Solvents used in paints and inks
- Lubricating oils for engines and machines
- Petroleum feedstock used to make plastics, synthetic rubber, and chemicals
The United States uses over 250 billion gallons of oil every year. About one-half of that amount comes from domestic wells; the other half is imported.
Stopping the Knocking
The question of how to prevent engine knocking has occupied petroleum engineers for many years. In the mid-twentieth century, they added lead to gasoline to make it burn more efficiently. In 1979 leaded gasoline became illegal in the United States due to fears of lead poisoning in children. Since that time MTBE (methyl tertiary-butyl ether) has been added to gasoline in the United States to enhance octane. It has done a great job of reducing emissions from car engines, but it is not perfect. People are concerned that MTBE is dangerous when it gets into drinking water, and they want to find a substitute. Ethanol has been used in some cases, but it has drawbacks, too. As of the early 2000s, oil companies were still looking for the perfect fuel additive.
Benefits and drawbacks of petroleum
As compared to other fossil fuels, petroleum is easy to retrieve, refine, and use. It is fairly easy to transport and store. It is not prone to exploding spontaneously, so it is relatively safe to keep near homes. Petroleum burns easily, making it the ideal fuel for internal combustion engines. Petroleum has many applications in addition to fueling vehicles. These uses range from paving materials to skin moisturizers.
Using petroleum, however, has many drawbacks. It contributes to various types of environmental problems, including air and water pollution. There is only a limited supply of petroleum, which means that at some time in the future, the world's petroleum will be gone. When that happens, people will have to find another way of powering their vehicles, factories, and utilities.
Impact of petroleum
Using petroleum as fuel contributes to many environmental problems. These include oil spills, which typically happen during the transportation of petroleum; the destruction done by drilling for oil; contamination from oil wells and pipelines; and air pollution. Drilling for oil, for instance, requires massive pieces of equipment and results in giant holes in the ground. Contamination happens when oil seeps into local soil and water. The people who live near oil wells and refineries sometimes suffer health problems as a result of exposure to petroleum.
When gasoline burns, it releases carbon dioxide and water into the atmosphere. It also produces carbon monoxide, nitrogen oxides, and unburned hydrocarbons, all of which can contribute to air pollution. Modern automobiles use catalytic converters to remove some of the pollutants from car emissions. Because of this improvement in car technology, automobiles in 2005 produced much less pollution than cars in 1970.
The economic impact of petroleum is enormous. The United States uses more than seventeen million barrels of oil daily and 250 billion gallons of oil a year. More than one-third of that petroleum powers cars and trucks. The country must import more than one-half of that amount from other countries. The United States has more oil reserves than it currently uses, but as of the early twenty-first century it was much less expensive to import oil than it was to extract reserves within the country. Foreign oil is becoming more expensive, however, especially as other countries increase their oil consumption. Some people support opening new U.S. sites to oil exploration and drilling partly because the oil industry can create so many good jobs.
A sudden change in oil prices can be disruptive to the United States and world economies. For example, oil prices rose steeply in the 1970s, creating an oil shock and inspiring car manufacturers to improve fuel economy. Oil prices were low and stable during the late 1980s and most of the 1990s. Rising prices in the early 2000s reflected increased demand for oil and other complicated economic factors.
Issues, challenges, and obstacles in the use of petroleum
There is a limited supply of petroleum on Earth. Some experts believe that oil production will peak by 2020 and that current oil reserves will run out by 2050, if not earlier. Other experts disagree, believing that there are enough oil reserves to provide for the world's energy needs throughout the twenty-first century. Many areas in the Middle East and Russia are still unexplored. Oil companies can now drill in much deeper parts of the ocean than they previously could; oil rigs in the Gulf of Mexico now drill into wells below 10,000 feet (3,048 meters) of water. Improved drilling technology such as drills that can twist and turn underground allows oil companies to reach petroleum deposits miles away from rigs.
Pessimists argue that improved technology will only deplete oil reserves faster, especially as more of the world uses oil to power its vehicles and industry. Optimists believe that should not matter and that innovation will allow oil companies to keep furnishing the world with petroleum.
Along with coal and petroleum, natural gas is one of the three main fossil fuels in use in the early twenty-first century. People use natural gas for heating, electrical power, and other purposes. Natural gas produces much less pollution than petroleum, so some people believe it could be an ideal substitute for petroleum and coal in the future.
Natural gas is a gaseous hydrocarbon. It is colorless, odorless, and lighter than air. Natural gas is made up of 75 percent methane, 15 percent ethane, and small amounts of other hydrocarbons such as propane and butane.
The Middle East holds a great deal of the world's petroleum. Middle Eastern nations and a few others have formed an organization called the Organization of the Petroleum Exporting Countries, or OPEC (OH-peck), which coordinates the prices that the individual countries charge for oil. Most OPEC member countries are developing nations, which means they are working on making their countries more modern. Oil is extremely important for these countries because it brings in a huge amount of money. Furthermore, as long as petroleum is needed, the OPEC nations will have power over the rest of the world.
The substance that oil companies sell as natural gas is almost pure methane, with the other gaseous components removed. When it burns, methane releases a large amount of energy, which makes it a useful fuel. Methane is sometimes called marsh gas because it forms in swamps as plants and animals decay underwater. Methane is naturally odorless, but gas companies add traces of smelly compounds to natural gas so that people will be able to smell gas leaks and avoid danger.
Origins of natural gas
Natural gas formed from underwater plants and bacteria. These microscopic organisms fell to the bottom of the ocean when they died and over the course of millions of years were crushed and heated by the pressure of layers of sand, dirt, and other organic matter that accumulated on top of them. The mineral components of the undersea mud gradually turned into shale, and some of the organic components turned into natural gas. Natural gas can move around within porous reservoir rocks. It can also be trapped in underground reservoirs, or geologic traps. Natural gas is lighter than petroleum, so it usually sits on top of the petroleum in a reservoir. Natural gas sometimes seeps up through Earth's crust and appears on the surface.
Fuel Economy in Cars
The average fuel economy of cars sold in the United States has decreased steadily since 1985. That means that on average, a new car today uses more fuel for the same performance than an equivalent car built 20 years ago. Sport utility vehicles (SUVs) are partly to blame for this. The Clean Air Act required car manufacturers to build vehicles to certain specifications that limited pollution. Certain types of vehicles, such as trucks, did not have to meet the same standards as cars because they were larger and there were relatively few people driving them at the time. Because SUVs are classified as light trucks under the law, they do not have to have the same level of fuel economy that a passenger car has. Car manufacturers like SUVs because they are inexpensive to make and can be sold for relatively high prices. SUVs have also been fashionable among consumers. In 2005 a proposed reform of the government's Corporate Average Fuel Economy (CAFE) program for light trucks by the National Highway Traffic Safety Administration (NHTSA) required carmakers to make gradual changes to their designs to meet stricter fuel economy requirements for light trucks by 2011. The proposed plan was scheduled to go into effect in April 2006.
As gas prices rose and concerns about America's dependence on foreign oil began to concern Americans in the early 2000s, hybrid cars became fashionable. These cars were powered by a combination of gasoline and battery power and had considerably better mileage than gasoline-powered cars. In their first years only a few were available so they were hard to buy. Some critics complained that hybrid cars were too expensive and that they did not in fact provide the fuel economy that a small, light, efficient gasoline-powered car could.
Finding and extracting natural gas
Natural gas is usually found with petroleum. When geologists (scientists who deal with the history of Earth and its life as recorded in rocks) search for underground oil, they find natural gas along with it. Sometimes there are pockets of natural gas in coal beds. Geologists occasionally find reservoirs that contain mostly or all natural gas with no oil. The largest reserves of natural gas in the United States are in Texas, Alaska, Oklahoma, Ohio, and Pennsylvania. Some experts believe that there is enough natural gas in the Earth to last two hundred years, although much of this gas may be difficult to reach.
When they first began drilling for oil, people believed natural gas was an unpleasant by-product. They would burn the natural gas away before removing the oil from the ground. Now oil companies know that natural gas is a valuable commodity in its own right, and they extract it carefully. The process of drilling for natural gas is similar to that of drilling for petroleum. In many cases natural gas comes out of wells that have already been dug to extract oil. Oil companies also drill wells to extract natural gas by itself. There are three main kinds of natural gas wells:
- Gas wells, which are dug into a reservoir of relatively pure natural gas
- Oil wells, which are dug for extracting oil but also extract any natural gas that happens to be in the reservoir
- Condensate wells, which are dug into reservoirs that contain natural gas and a liquid hydrocarbon mixture called condensate but contain no crude oil
Natural gas that comes from oil wells is sometimes called associated gas. Natural gas from gas wells and condensate wells is called non-associated gas because it is extracted on its own and not as a by-product of oil drilling.
Make Your Own Methane
Although most of the world's methane is very old, it is possible to make new methane through chemical reactions. The Sabatier process combines hydrogen and carbon dioxide with a nickel catalyst and high temperatures to synthesize methane and water. This method of producing methane could be used to generate fuel in outer space to power spacecraft. One common natural process also results in large amounts of methane: When cattle digest food, they produce methane that they emit into the atmosphere.
Making natural gas useful
The natural gas that consumers use is almost pure methane. The natural gas that comes out of a well is not pure and may contain a mixture of hydrocarbons and gases, including methane, ethane, propane, and butane. It also may contain small amounts of oxygen, argon, and carbon dioxide, but methane is by far the largest component.
An oil or gas company processing natural gas separates the gases into individual components, dividing them into pure methane, pure propane, pure butane, and so on. The liquid forms of the non-methane gas components, such as propane and butane, are called natural gas liquids, or NGLs, and sometimes are called liquid petroleum gas, or LPG. All of these products can be sold individually, so it is cost-effective to separate them.
The first step in processing is to remove any oil mixed with the gas. Natural gas that comes out of an oil well is separated from petroleum at the well. Sometimes the gas is dissolved in the oil, like the carbonation in a soft drink, and through the force of gravity the gas bubbles come out of the oil. In other cases the oil workers use a separator that applies heat and pressure to the mixed oil and gas to make them separate. The workers must also remove any water from the natural gas, using heat, pressure, or chemicals. They then remove NGLs using similar techniques.
Once they have been removed from natural gas, NGLs must be separated from one another. This is done through a process called fractionation, which involves boiling the NGLs until each one has evaporated. A similar process is used to refine petroleum. The different NGLs have different boiling points. As the NGLs boil, the different hydrocarbons evaporate and can be captured.
Some natural gas comes out of the ground with large amounts of sulfur in it. It is called sour gas because the sulfur makes the gas smell like rotten eggs. The gas company must remove the sulfur before selling the gas because sulfur in significant amounts is poisonous for humans to breathe and because it corrodes metal. The companies can sell the sulfur for industrial uses once it is separated out.
Sometimes a processing plant turns natural gas into liquid before transporting it. Liquid natural gas is one six-hundredth the volume of natural gas in gas form. Liquefying it makes it possible to store and transport natural gas around the world.
Once it has been refined and liquefied, natural gas can be transported and sold. The most common way to transport natural gas is through pipelines, which crisscross the United States and many other countries. If the gas is not sold right away, the gas company must store it. Natural gas is usually stored underground in formations such as empty gas reservoirs; in aquifers, or underground rock formations that hold water; and in salt caverns.
Current and potential uses of natural gas
People have known about natural gas for thousands of years. The eternal flames in ancient temples may have been fueled by natural gas. In the early nineteenth century people began using natural gas as a light source, but as soon as oil was discovered in the 1860s and electricity became widespread, people abandoned natural gas except for limited use in cooking and heating.
Even so, the natural gas industry built the first large natural gas pipeline in 1891 and a large network of pipelines in the 1920s. Gas companies built more pipelines between 1945 and 1970, which made it convenient to use natural gas for heating homes and for use in appliances.
Natural gas has become more appealing as a fuel in recent years. Some uses are:
- Powering heaters and air conditioners. Because so many homes and businesses use gas heat, natural gas consumption typically is much higher in the winter than in the summer.
- Running appliances such as water heaters, stoves, washers and dryers, fireplaces, and outdoor lights.
- Serving as an ingredient in plastics, fertilizer, antifreeze, and fabric.
- Producing methanol, butane, ethane, and propane, which can be used in industry and as fuel.
- Dehumidifying, or drying the air in, factories that make products that can be damaged by moisture.
Scientists are considering the use of natural gas in applications such as the following:
- Powering natural gas-fueled vehicles, which produce far fewer emissions than vehicles powered by gasoline.
- Powering fuel cells in which hydrogen is used to produce electricity with few emissions.
- Reburning, or adding natural gas to coal- or oil-fired boilers to reduce the emission of greenhouse gases.
- Cogeneration, a technology for generating electricity as it burns fuel, requiring less total fuel and producing fewer emissions.
- Combined cycle generation, a technology that captures the heat generated in producing electricity and uses it to create more electricity. Combined cycle generation units powered by natural gas are much more efficient than those powered by petroleum or coal.
Scientists are especially interested in technologies that combine natural gas with other fossil fuels to increase efficiency and reduce emissions. Natural gas is seen as a good source of fuel for the future, and as a result scientists are constantly inventing new ways to use it.
Benefits of natural gas
Natural gas has advantages over petroleum and coal. It burns cleanly, producing no by-products except for carbon dioxide and water, so it does not cause the same degree of air pollution as the other fossil fuels. It does not produce the sludge that results from coal-burning emissions.
Natural gas can take the place of gasoline as a fuel for cars, trucks, and buses. Most natural gas vehicles are powered by compressed natural gas (CNG); the technology used to pump CNG into a car is almost identical to the process of fueling a gasoline-powered car. Some vehicles can use either gasoline or CNG. Natural gas cars have no trouble meeting environmental standards because of their low emissions. Natural gas is very safe; it does not pollute groundwater.
For many years natural gas has been cheaper than gasoline. Many cities have converted their buses, taxis, construction vehicles, garbage trucks, and public works vehicles to natural gas. These organizations are well suited to use natural gas as fuel because their vehicles do not travel long distances and can afford the cost of converting the vehicles in the first place.
Drawbacks of natural gas
Natural gas historically was hard to transport and store, but modern technology has for the most part removed that difficulty. One reason natural gas is not a perfect substitute for petroleum is that supplies are limited. At current rates of use, all of the world's natural gas could be used up in forty to ninety years.
Natural gas vehicles have not become widespread because it is more expensive to convert gasoline vehicles for natural gas use; there are very few natural gas refueling stations; and the vehicles cannot travel long distances without refueling.
Impact of natural gas
Natural gas is the cleanest fossil fuel. The burning of natural gas releases no ash and produces low levels of carbon dioxide, carbon monoxide, and other hydrocarbons and very small amounts of sulfur dioxide and nitrogen oxides. Vehicles powered by natural gas emit 90 percent less carbon monoxide and 25 percent less carbon dioxide than gasoline-powered vehicles.
Natural gas is becoming an increasingly common fuel for electrical power plants and in industry. Electrical power plants fueled by natural gas produce far fewer emissions than coal-powered plants. Burning natural gas does not contribute significantly to the formation of smog.
Natural gas does contribute to some environmental problems. Burning natural gas emits carbon dioxide, which is considered a greenhouse gas that contributes to global warming. On the other hand, natural gas produces 30 percent less carbon dioxide than burning petroleum and 45 percent less carbon dioxide than burning coal, so it is still preferable to either of those.
On an economic level, the cost of natural gas has dropped considerably. The development of LNG technology means that natural gas is easier and less expensive to store and to transport, and liquefaction techniques (turning gas into a liquid) improve every year. Petroleum engineers are constantly getting better at finding and extracting natural gas from the ground.
Natural gas may change the way people use power in their daily lives. In the twenty-first century natural gas is a fairly minor fuel compared with gasoline, but it has the potential to be much more important. If power plants switch to the use of natural gas during summer when demand for natural gas is lowest and smog is highest, they could emit fewer pollutants and improve air quality. Using natural gas instead of other fossil fuels could reduce acid rain and particulate emissions. As people become concerned about emissions and fuel economy, they may want vehicles powered by natural gas. The vehicles will then become more widely available, less expensive, and easier to refuel.
Issues, challenges, and obstacles in the use of natural gas
Natural gas technology is not widespread. The fuel has many possible applications, but car manufacturers will have to decide that it is cost-effective for them to build natural gas vehicles before they do so on a large scale. Consumers will not buy natural gas vehicles until they are convinced that it will be convenient, safe, and inexpensive for them to buy natural gas as fuel. A final large issue is the supply of natural gas, which could run out in a few decades.
Coal supplies about one-fourth of the world's energy needs. Coal is a solid hydrocarbon made primarily of carbon and hydrogen with small amounts of other elements such as sulfur and nitrogen. Coal looks like black rock, and it leaves black dust on things that it touches.
Origins of coal
Millions of years ago Earth was covered with swamps full of giant trees and other plants. When they died, these trees fell into the swampy water and were gradually covered by other plants and soil. All living things, including plants and animals, are composed mainly of carbon. Over millions of years, the carbon in the swamp plants was compressed and heated. This caused it to rot, exactly the way fruit and vegetables rot if kept too long. This rotting produced methane gas, also known as swamp gas.
Over several thousand years, the weight of the upper layers compacted the lower layers into a substance called peat. Peat is the first step on the way to the formation of coal and other fuels. People can use peat as fuel simply by cutting chunks of it out of the ground and burning them. Ireland used to be covered with peat, which was the main source of fuel there for years. The Great Dismal Swamp in North Carolina and Virginia contains almost one billion tons of peat.
As the peat continued to be compacted by new layers of dead plants, it became hotter as it was being pushed closer to the heat inside the Earth. The heat and pressure gradually turned it into coal. Most of Earth's coal was formed during one of two periods: the Carboniferous (360 million-290 million years ago) or the Tertiary (65 million-1.6 million years ago).
There are large reserves of coal all over the world. China has nearly one-half of the world's coal reserves and produces nearly one-fourth of the coal that is used every year. There are also large reserves of coal in North America, India, and central Asia. In the United States, most coal comes from mines in Montana, North Dakota, Wyoming, Alaska, Illinois, and Colorado. There are also coal deposits in the Appalachian area, especially in West Virginia and Pennsylvania.
Getting coal out of the ground
Coal is extracted from the earth through mining techniques that vary depending on where the coal is located. If a coal seam (or deposit) is deep below the surface of the Earth, miners use subsurface mining. They dig vertical tunnels into the ground to reach the seam and then dig horizontal tunnels at the level of the seam. The miners ride elevators down to the seam, dig out the coal, and transport it back up to the surface. To prevent the earth from collapsing, miners leave pillars of coal standing to hold up the tunnel roof. Despite this precaution, coal mines sometimes collapse, killing miners trapped inside.
Surface mining, or strip mining, is a process of taking coal off the surface of the Earth without going underground. Miners use giant shovels to remove dirt, called overburden, from the coal seam and then use explosives to blast the coal out of the rock. Strip mining is much safer than subsurface mining, but it leaves huge scars on the land and can contribute to water pollution.
Making coal useful
Coal comes out of the ground in chunks up to 3 or 4 feet (0.9-1.2 meters) across, and coal processors crush it into chunks about the size of a person's fist. These chunks of coal then go through a screen that separates out the smallest pieces. Coal plants sometimes clean coal by setting it, which washes out the heavier particles of stone. The plant may then dry the coal to make it lighter and help it burn better. Once processing is complete, coal is transported to buyers using trains, barges (flat cargo-carrying boats), and trucks.
Coal comes in several types, depending on how pure the carbon is, which also corresponds to how old the coal is. Coal is rated by heat value (how much heat it can produce when it burns). The purer the carbon is, the higher the heat value. Heat value is measured in British thermal units, or Btu, per pound. A Btu is the amount of heat required to raise the temperature of one pound of water one degree Fahrenheit.
- Anthracite (AN-thruh-syte) contains between 86 and 98 percent pure carbon and has a heat value of 13,500 to 15,600 Btu per pound.
- Bituminous (bye-TOO-muh-nuhs) coal contains between 60 and 86 percent pure carbon and has a heat value of 8,300 to 13,500 Btu per pound.
- Lignite contains between 46 and 60 percent pure carbon and has a heat value of 5,500 to 8,300 Btu per pound.
Current and potential uses of coal
Coal became a popular fuel in England in the nineteenth century because England sits on top of huge coal deposits. Coal was more plentiful than wood, which meant it was less expensive. The availability of coal along with inventions such as the steam engine allowed England to become the first truly industrialized nation.
During the nineteenth century and in the early part of the twentieth century, many people had coal-burning stoves in their homes. This system of heating had many drawbacks. It was messy, and people had to make sure they did not run out of coal. By the late twentieth century coal was no longer a common fuel for heating homes. As individual homeowners used less coal, industry used more.
Between 1940 and 1980 the amount of coal used by electrical power plants doubled every year. Coal also powers factories that make paper, iron, steel, ceramics, and cement. At the beginning of the twenty-first century over one-half of the electrical power plants in the United States were powered by coal.
Benefits and drawbacks of coal
Coal burns hotter and more efficiently than wood, and in many places it is more readily available. There is a great deal of coal in the world, so supplies are not likely to run out in the near future.
One of the drawbacks of using coal is that it has to be dug out. All methods of mining coal have problems associated with them. Coal is also very dirty. Coal dust coats anything it falls on, from buildings to people. Gases released by burning coal are big contributors to air pollution.
Environmental impact of coal
Coal is not environmentally friendly. It produces large amounts of pollution, which may contribute to acid rain and global warming. Mining it is often damaging to the environment, and transporting it is destructive as well. Most coal is moved around on trains, which are powered by pollution-causing diesel fuel.
The difficulty with burning coal is that it rarely produces only carbon dioxide, water, and energy. If the temperature is not high enough or if not enough oxygen is available to keep the fire burning high, the coal is not completely burned. When that hap-pens, the coal releases other substances into the air. These substances include:
- Carbon monoxide, which is toxic to humans and animals
- Soot, which is pure carbon dust and can turn buildings, trees, and animals black (The English invented glass-covered bookcases in the 1800s so their books would not get covered with soot.)
- Sulfur dioxide, sulfur trioxide, and nitrogen oxides, which become part of acid rain
- Lead, arsenic, barium, and other dangerous compounds that are in coal ash, which can float in the air or stay where the coal was burned and cause people to become ill
As mentioned, electrical power plants produce 67 percent of the United States sulfur dioxide emissions, 40 percent of carbon dioxide emissions, 25 percent of nitrogen oxide emissions, and 34 percent of mercury emissions. Coal-fired power plants account for over 95 percent of all these emissions.
Eternal Coal Fires
Sometimes the coal inside a mine will catch on fire by accident. It can be nearly impossible to put out this kind of fire; drilling into the mine only adds oxygen to fuel the flames. A coal deposit in Tajikistan has supposedly been burning underground since 330 BCE when Alexander the Great visited the area. A network of coal mines in Centralia, Pennsylvania, caught fire in 1962 and is still burning. Someone had burned trash in an abandoned coal pit, and the coal vein ignited. The town had to be evacuated in the 1980s. Hundreds of coal mines are burning in the United States, but many more are burning in China and India, where mining development is proceeding too rapidly to control. In addition, coal mining produces tailings (coal mining wastes) that are put in large piles above ground; the tailings can also catch fire and burn for decades.
New power plants may be less polluting than older ones, but most power plants operating in the United States as of 2005 still used older technology. Under the Clean Air Act older plants were prevented from expanding, in the hope that they would gradually close down and be replaced by modern facilities. The Clear Skies program enacted in 2003 by President George W. Bush removed this requirement, allowing older plants to keep operating and to expand their operations if they chose to do so.
Regardless of what developed countries of the twenty-first century do about emissions, China and other developing nations are using outdated technology that releases huge amounts of pollution. As the developing nations move towards resembling the developed world technologically, vast amounts of pollution travel around the world and end up in countries elsewhere.
Surface coal mining can leave huge holes in the land and even destroy entire mountains. Water that flows over the mine site can flush pollutants into streams and rivers. Underground coal mining leaves behind tunnels in the ground, which can collapse suddenly. In the old days of mining, abandoned surface mines would turn into forbidding deserts, full of old rusted equipment.
Modern coal mining is very different, at least in the industrialized world. Due to several decades of pressure from consumers and environmental groups and new environmental laws, twenty-first century coal mining companies are much more careful about restoring the landscape after they take the coal from it. Miners save the topsoil and store local plants in greenhouses. Mining companies hire biologists, botanists (scientists who study plants), and fisheries experts to restore the environment as it was before mining began. Before laws required it, no mining company spent the money to avoid environmental harm.
Economic impact of coal
Coal started the industrial revolution in Europe in the late eighteenth century. Without coal, there would have been no factories, no steel, no trains, no steamships, and no electric lights. In the early twenty-first century coal is still a huge business. Coal mines bring in a great deal of money. In areas that have large coal deposits, most of the local population may be employed by the coal industry. The closing of a coal mine can harm a community by putting many townspeople out of work.
Societal impact of coal
Coal mining was one of the first industries to attract the attention of socially conscious lawmakers, who passed laws protecting workers. Coal mining was also one of the first industries in which workers organized, leading to the development of trade unions. Although mining techniques in the United States are much better than they were in the nineteenth century, coal miners still face more daily risks than most workers. Some health problems are much more common in coal miners than in other groups of people. Aside from the danger of being killed in a mine collapse, coal miners are at risk of life-threatening lung diseases. People who live in coal mining regions depend on the coal industry for their income and do not want to see coal mining disappear. At the same time, they would like to see coal mining become safer and less destructive.
Issues, challenges, and obstacles in the use of coal
The demand for coal is expected to triple in the twenty-first century. Coal is the only fossil fuel that is likely to be in large supply in the year 2100, so people may become even more dependent on it. The U.S. Congress has encouraged coal producers to clean up coal technology since 1970. Scientists are trying to invent ways to use coal for fuel without causing pollution. These methods are called clean coal technologies and include the following:
- Coal gasification, by which coal is turned into gas that can be used for fuel, leaving the dangerous solid components in the mine
- Coal liquefaction, by which coal is turned into a petroleum-like liquid that can be used to power motor vehicles
- Coal pulverization, by which coal is broken into tiny particles before it is burned
- Use of hydrosizers, which are machines that use water to extract (take out or remove) the usable coal from mining waste to increase the amount of coal that can be retrieved from a mine
- Use of scrubbers and other devices to clean coal before, during, and after combustion to reduce the amount of pollution released into the atmosphere
- Use of bacteria to separate pollutants from organic components in coal so that the sulfur and other pollutants can be removed before burning
- Fluidized bed technology, which burns coal at a lower temperature or adds elements to the furnaces in coal plants to remove pollutants before they burn
Coal gasification is a process that converts coal to a gas that can be used as fuel. The main advantage of gasification is that it can remove pollutants from coal before the coal is burned, so the harmful substances are not released into the air. Coal gasification is a clean coal technology.
Coal gasification is done in stages. The first step is to crush and dry the coal. The crushed coal is placed in a boiler, where it is heated with air and steam. This heat causes chemical reactions that release a mix of gases that can then be used as fuel. The solid waste, or ash, remains in the boiler, where it can be collected and thrown away. Dangerous gases such as carbon dioxide and sulfur dioxide are removed in scrubbers like the ones in smokestacks at coal plants.
Gasification has been around for at least 100 years. It was widely piped and used as a fuel in Britain and many other European countries by 1900. Although it was used in other countries, in the United States it wasn't utilized during the first half of the century because petroleum and natural gas were inexpensive and plentiful. In the 1970s utility companies began considering gasification as a way to obey stricter environmental laws. Many people hope that coal gasification will be a valuable technology in the twenty-first century.
Current and potential uses of coal gasification
Coal gasification produces the following kinds of gases that can be used as fuel:
- Methane, which can be used as a substitute for natural gas
- Chemical synthesis gas consisting of carbon monoxide and hydrogen, which is used in the chemical industry to produce other chemicals, such as ammonia and methyl alcohol
- Medium-Btu gas, which is also made of carbon monoxide and hydrogen and used by utilities and industrial plants
Benefits and drawbacks of coal gasification
Plants and factories that run on coal gasification technology have much lower emissions than traditional coal-burning plants, and their solid wastes are not hazardous. The waste products themselves can be useful. The sulfur dioxide scrubbers produce pure sulfur that can be used in other processes, and some scientists believe the ash can be used to build roads and buildings. Some people believe it may even be possible to use sewage or hazardous wastes to power the coal gasification boilers.
The greatest problem with coal gasification is cost. Using coal gasification technology to provide power to an industrial plant costs three times as much as using natural gas. Supporters of the technology hope that researchers will develop ways to make gasification less expensive. Coal gasification requires vast amounts of water, which creates a problem. For gasification to be cost-effective, the plants must be built near coal mines so that the coal does not have to travel far, and most coal mines in the United States are in western states, where water is limited and expensive.
Impact of coal gasification
On an environmental level, gasification has the potential to make coal a much less polluting fossil fuel. It will not have any impact on the environmental destruction caused by coal mining itself. However, coal mining is now much less destructive than it used to be.
Economically, coal gasification is much less efficient than burning coal directly; 30 to 40 percent of coal's energy is lost during the process of converting it to gas. Gasification would hardly be worth the cost of production if it were not for the environmental benefits it offers.
Issues, challenges, and obstacles in the use of coal gasification
Scientists in Europe and the United States have been working to improve coal gasification techniques. They have been experimenting with using chemicals called catalysts to release the gases from coal. Using catalysts would allow gasification to occur at a lower temperature, which would make the process less expensive. Some scientists believe that the answer is to carry out gasification inside coal mines. Miners could pipe up the useful gases and leave the solid wastes underground. This idea is attractive because a large portion of coal reserves are nearly impossible to remove by the usual methods, and underground gasification would make those reserves available.
LIQUEFIED PETROLEUM GAS: PROPANE AND BUTANE
Liquefied petroleum gas, or LPG, is petroleum gas that can easily be turned into a liquid at ordinary temperatures simply through the application of pressure. The main types of LPG are propane and butane. Propane is the most common LPG and is usually what people mean when they refer to LPGs. Propane and butane are both colorless, flammable gases that belong to the category of hydrocarbons called paraffins or alkanes. Unprocessed natural gas contains both propane and butane, which are removed during the purifying process. Petroleum refining also creates LPGs.
The first step in processing LPG is to remove any oil that might be mixed with the gas. Sometimes the natural gas is dissolved in oil, and the gas bubbles will come out of the oil through the force of gravity. In other cases oil workers use a separator that applies heat and pressure to the mixed oil and gas to make them separate.
Once the methane has been removed from the natural gas, the workers separate the remaining components, which include propane, butane, and ethane in a liquid form. The process is called fractionation, which basically involves boiling until each one of the gases has evaporated. The different gases have different boiling points. As each different boiling point is reached, the gases evaporate and can be captured separately. Because LPGs are naturally odorless, oil companies often add a substance called ethanethiol (eth-THAN-ee-thee-all) to it so people can smell the gas if it leaks. Ethanethiol smells like rotten eggs.
Oil companies usually store large amounts of LPGs in underground salt domes and pressurized empty mines near gas production facilities and pipeline hubs. These reservoirs are tied directly to pipelines so the LPGs can be delivered rapidly. LPG merchants store the gas in large pressurized above-ground tanks. Consumers then store LPGs in smaller above-ground tanks at their homes or businesses.
Most LPGs in the United States are transported through a network of about 70,000 miles (113,000 kilometers) of pipelines. Most of these pipelines are concentrated along the Gulf Coast and in the Midwest. The Midwest also receives LPGs from two pipelines running from Canada. The east coast of the United States has only two pipelines serving the area. LPGs can be delivered by trucks, trains, barges, and ocean tankers. The United States imports about ten percent of its total LPG supply from other countries, including Saudi Arabia, Algeria, Venezuela, Norway, and the United Kingdom.
Current and potential uses of LPG
LPGs are useful as substitutes for natural gas for purposes such as powering stoves, furnaces, and water heaters. LPGs, often sold as or called propane, can be used in many ways, including:
- As a fuel for internal combustion engines, such as the ones in cars and buses
- To power home appliances, such as hot water heaters, heat pumps, space heaters, fireplaces, stoves, and clothes dryers
- As a fuel for devices such as forklifts
- For industrial purposes such as soldering, cutting, heat treating, and space heating
- To power campers and recreational vehicles
- As a solvent and refrigerant in the petroleum industry
- As a propellant in aerosol sprays, replacing CFCs (chlorofluorocarbons)
- For agricultural purposes such as weed control, crop drying, and as fuel for irrigation pumps and farm equipment
Butane by itself is used in cigarette lighters and portable stoves, such as the stoves people take camping. Petroleum refineries leave some butane in gasoline to make it easier to start engines since butane ignites quickly.
Ethane, which is another kind of LPG, is used as a starting material in the production of ethylene and acetylene, which are used as fuel in welding. It is possible to power automobiles and other vehicles with LPG. Some people have converted their cars to burn LPG instead of gasoline.
Homeowners and private consumers use about 45 percent of the LPGs sold in the United States. Most of this LPG, that is, propane for heat and other home purposes, is usedduringthe winter. The petrochemical industry uses about 38 percent of the LPGs in the manufacture of plastics. Farms and factories use another seven percent each. Farms use the most LPGs in the fall,but factories use a steady amount year-round. Transportation accounts for only three percent.
Benefits of LPG
LPG is a good fuel for internal combustion engines. LPG is no more dangerous than gasoline when contained in a fuel tank. Because LPG becomes liquid easily, it is possible to put it in pressurized tanks for storage and transport. People can keep tanks of LPG in their yards, and tanker trucks can deliver it to rural areas that are not served by natural gas companies.
Propane is an excellent fuel for automobiles and is becoming one of the most popular alternative fuels. Propane vehicles produce between 30 and 90 percent less carbon monoxide and 50 percent fewer smog-producing pollutants than gasoline-powered vehicles. In the early 2000s there were about 350,000 propane-powered vehicles in the United States and about four million in the world. These vehicles include cars, vans, pickup trucks, buses, and delivery trucks. The U.S. Department of Energy has encouraged consumers to consider using propane-powered vehicles.
In many ways propane is superior to electricity and to other fuels. It does not produce nearly as much pollution as gasoline or coal. Propane furnaces are more efficient at heating and release fewer air pollutants than heaters powered by electricity or fuel oil. Propane fireplaces are cheaper and less polluting than wood-burning fireplaces, and they can be turned on and off with a switch. Many professional cooks prefer propane stoves to electric stoves because they produce heat instantly and are easier to control. Moreover, propane appliances will still work during power outages, unlike electric appliances.
Drawbacks of LPG
LPG is more expensive to produce than gasoline. It is not widely available, so it can be difficult to refuel a car that runs on LPG, although in the early 2000s this situation was improving. It can be difficult to find an LPG-powered vehicle because not many are made. Propane-powered vehicles usually have a slightly lower driving range than gasoline-powered vehicles because the energy content of propane is lower than that of gasoline.
LPG is highly explosive. It is important to maintain propane appliances in good condition and have them inspected regularly. Consumers should find out where gas lines run under their yards so they can avoid striking them with shovels or other hard metal objects. Anyone who smells a propane leak should immediately evacuate the building and call the fire department. No one should flip light switches, turn on other electrical appliances, or use the telephone if near a propane leak.
Impact of LPG
LPG emissions of nitrogen oxides, carbon monoxide, hydrocarbons, and particulate matter are very low. LPG releases almost no emissions through evaporation, as gasoline and diesel fuel do. Engines that run on LPG are quieter than those that run on gasoline. LPGs do not cause carbon to accumulate inside machinery.
Economically, because propane and LPGs are produced as a by-product of natural gas and petroleum refining, their prices are directly tied to petroleum and natural gas prices. Prices for LPGs fluctuate (go up and down) according to seasonal demand. They are usually most expensive in winter, when people are using them for heat. Prices also vary by distance from source, so that consumers who live far away from sources of LPGs often pay more for them than consumers who live close by. Automobile manufacturers do not build LPG-burning cars because LPG is more expensive than gasoline.
On a societal level, LPG is invaluable to people in rural areas because it is a source of power that can be transported to areas not otherwise served by natural gas and electricity.
Issues, challenges, and obstacles in the use of LPG
Since LPG comes from the production of petroleum and natural gas, when those supplies run out, so will LPG. At the beginning of the twenty-first century many organizations are trying to encourage consumers to use more propane and LPGs as fuel for their homes or vehicles, and interest in LPGs has increased somewhat as people become concerned about the environment. In order for more people to use LPGs as fuel for transportation, companies will have to make it easier to refuel the vehicles and less expensive to buy them.
Methanol is a kind of alcohol that can be used as fuel. It is also called methyl alcohol and is used primarily in industry and in racecars. Some people hope it can be used to power fuel cells.
Methanol is a clear, colorless liquid with a distinctive odor. Methanol used to be called wood alcohol because people made it by burning wood and condensing the vapors that emerged. The ancient Egyptians created methanol in this way and used it to embalm mummies. Robert Boyle (1627–1691) isolated methanol in the 1660s, and Pierre Eugène Marcelin Berthelot synthesized it in about 1860. In the twenty-first century methanol usually is produced from natural gas. It may be possible to use coal or wood to produce methanol in order to avoid using natural gas resources.
Current and potential uses of methanol
Methanol has several uses. Chemists use it to manufacture plastics and formaldehyde, which is used to preserve organic matter. It is useful as a solvent and as antifreeze. Methanol also can be used to power fuel cells, such as those in cellular telephones or laptop computers, and to manufacture the fuel additive MTBE (methyl tertiary-butyl ether).
Automakers have experimented with using methanol as a fuel for cars, either alone or mixed with gasoline. A mix of 85 percent methanol and 15 percent unleaded regular gasoline (called M85) emits only half the pollutants of gasoline alone. Between 1978 and 1996 several automobile manufacturers made demonstration vehicles that could use both M85 and regular gasoline. Two companies offered these fuel-flexible vehicles for sale to consumers in 1995 and 1996. Methanol is a popular fuel for race cars largely because methanol fires can be put out with water, which makes it safer than gasoline.
Benefits and drawbacks of methanol
When used as an automobile fuel, methanol produces fewer emissions and has better performance than gasoline. It is also less flammable. Methanol can be made from a variety of substances, including natural gas, coal, and wood. Use of methanol could reduce dependence on petroleum. Methanol can easily be made into hydrogen so it has potential as a fuel source for hydrogen fuel cells.
However, methanol has several drawbacks as a fuel. The flame produced by burning methanol is colorless and almost invisible, which makes it dangerous for people working near it. Methanol vapors are poisonous and can burn skin. People who handle methanol without adequate protection can absorb it through their skin or lungs and quickly become ill, because methanol is highly poisonous.
Methanol is also more expensive to produce than gasoline, which makes methanol-gasoline mixes more expensive than plain gasoline. Anyone who owns a methanol-powered vehicle has a hard time finding a place to refuel. Automobile manufacturers stopped making methanol-powered vehicles in 1998, switching their attention to ethanol instead.
Do Not Drink the Methanol
The alcohol people drink in beer, wine, and whiskey is ethyl alcohol, or ethanol. Methanol, although it is a type of alcohol, is not the sort of thing anyone would want to drink. Drinking even a small amount can cause blindness. Drinking a larger amount can kill a person.
Impact of methanol
Methanol produces fewer greenhouse gases than gasoline. Vehicles powered with mixed gasoline and methanol emit just one-half the smog-forming pollutants that a comparable gasoline-powered vehicle emits. The formaldehyde it produces when it burns, however, is quite poisonous.
Many industries use methanol in their daily business. Because most methanol is made from natural gas, changes in natural gas prices affect methanol prices. Some factories that produce methanol stop production if natural gas prices go too high, a practice that can cause methanol shortages.
Issues, challenges, and obstacles in the use of methanol
Many people believe methanol has potential as a fuel. Federal and state governments have passed laws encouraging the development of alternative fuels such as methanol. The California Energy Commission has encouraged car manufacturers to experiment with methanol since 1978. Twenty-five years of experimenting did little to increase public support for using methanol as a fuel. As of 2005 most car manufacturers had abandoned methanol research.
Japanese cellular telephone manufacturers have been developing fuel cells powered by methanol. They hope that by 2007 people will be able to provide hours of power for their cellular telephones by squirting drops of methanol into them. The main drawback to this technology is the need to carry flammable methanol in public places, such as on airplanes. Researchers hope that this technology will have a wider application in the near future.
METHYL TERTIARY-BUTYL ETHER
Methyl tertiary-butyl ether, or MTBE, is a substance added to gasoline to make it burn more completely and produce fewer polluting emissions. It has been added to gasoline in the United States since the late 1970s. In the 1990s communities discovered that MTBE was getting into their water supplies, which led to a movement to eliminate MTBE use.
MTBE is a chemical compound made of methanol and isobutylene. At room temperature, MTBE is a colorless liquid that dissolves easily in water. It is volatile (or unstable) and flammable. It has a strong odor, and small amounts of it can make water taste bad. MTBE is an oxygenate, which is a substance that raises the oxygen content of another substance. MTBE is used to raise the oxygen content of gasoline.
Current and potential uses of MTBE
MTBE, used as a fuel additive, increases the octane level of gasoline and reduces emissions of carbon monoxide and pollutants that form ozone. The U.S. Clean Air Act was passed in 1963 and updated in 1970 and 1990, requiring people in certain areas to use oxygenated gasoline. MTBE is one of the least expensive oxygenates, so most oil companies chose it as a fuel additive. Gasoline with oxygenates added to it is sometimes called reformulated gasoline, or RFG. At the end of the twentieth century about 30 percent of the gasoline sold in the United States was RFG, and MTBE was the oxygenate most commonly mixed into it. MTBE is the primary oxygenate because it is relatively inexpensive.
Benefits and drawbacks of MTBE
MTBE blends easily with gasoline, and it can be shipped through existing pipelines. Gasoline with MTBE mixed into it burns more cleanly than plain gasoline, reducing tailpipe emissions. This has resulted in an improvement in air quality. The U.S. Environmental Protection Agency estimated that the addition of MTBE to gasoline reduces toxic chemical emissions by twenty-four million tons a year and smog-forming pollutants by 105 million tons.
MTBE dissolves easily in water, which can pose a hazard. When gasoline tanks or pipelines leak above or below the ground, the MTBE can dissolve in groundwater and travel to water supplies. Urban runoff, rain, motorboats and jet skis, and car accidents can all result in gasoline and MTBE getting into groundwater. Gasoline tends to stick to soil so it does not travel very far when it is spilled, but MTBE moves freely with water and can easily contaminate water supplies. It does not break down in the environment, so it can stay in groundwater for years.
Some people fear that MTBE causes health problems. Research animals exposed to large amounts of MTBE have developed cancer and other health problems. So far researchers do not believe that MTBE in gasoline poses any major health risks to humans. Researchers do, however, believe MTBE may cause cancer in people who drink water contaminated with large amounts of it.
Impact of MTBE
The use of MTBE in gasoline has improved air quality in the United States since 1995. But MTBE has gotten into the groundwater in some areas. This happens easily when gasoline leaks out of storage containers or is spilled during transport. Rain can carry MTBE into shallow groundwater, and it can then get into deeper water supplies. MTBE can make water undrinkable. Some states have set limits on the amount of MTBE allowed in drinking water. Most public water systems must monitor their water supplies for the presence of MTBE.
Although MTBE can spread through the ground and water very easily, it does not break down easily. Getting MTBE out of water is difficult, so once it has polluted a water source, MTBE can be very hard to clean up. In 1996 the city of Santa Monica, California, found that two wells supplying the city's water were contaminated with MTBE and that levels of MTBE were increasing. After discovering more areas contaminated with MTBE, the state issued an order requiring that MTBE be removed from all California gasoline by the end of 2003.
On an economic level, MTBE is one of the least expensive and most convenient fuel additives. A huge amount of MTBE is produced in the United States. In 1999 more than two hundred thousand barrels were produced every day. Production of MTBE is very profitable, but cleaning MTBE out of the U.S. water supply is very expensive. MTBE has caused a number of lawsuits over cleanups that have cost both cities and oil companies huge amounts of money.
Issues, challenges, and obstacles in the use of MTBE
Many U.S. states have decided that the risks associated with MTBE are too great. Following California's lead, many states have called for MTBE to be phased out completely by 2014. A proposed $2 billion may be spent between 2005 and 2013 to help MTBE manufacturers switch their operations to some other substance.
In the early 2000s most of the world is utterly dependent on fossil fuels for its energy needs. A number of nations are deeply concerned about this dependence because the use of fossil fuels contributes to air pollution and sometimes leads to strife between nations, and because the supply of some types of fossil fuel is likely to run out in the not-too-distant future. Many governments have begun looking for ways to end their dependence on oil, by exploring alternative sources of energy and developing systems of public transportation.
For More Information
Gelbspan, Ross. Boiling Point: How Politicians, Big Oil and Coal, Journalists and Activists Are Fueling the Climate Crisis. New York: Basic Books, 2004.
Leffler, William L. Petroleum Refining in Nontechnical Language. Tulsa, OK: Pennwell Books, 2000.
"Alternative Fuels." U.S. Department of Energy Alternative Fuels Data Center. http://www.eere.energy.gov/afdc/altfuel/altfuels.html (accessed on July 20, 2005).
"Black Lung." United Mine Workers of America. http://www.umwa.org/blacklung/blacklung.shtml (accessed on July 20, 2005).
"Classroom Energy!" American Petroleum Institute. http://www.classroom-energy.org (accessed on July 20, 2005).
"Oil Spill Facts: Questions and Answers." Exxon Valdez Oil Spill Trustee Council. http://www.evostc.state.ak.us/facts/qanda.html (accessed on July 20, 2005).
"The Plain English Guide to the Clean Air Act." U.S. Environmental Protection Agency. http://www.epa.gov/air/oaqps/peg_caa/pegcaain.html (accessed on July 20, 2005).
Since the beginning of the industrial revolution , fossil fuels have been important sources of energy. European industrialization began in the late 1700s in England, and coal soon became a major fuel. In 1850 wood was still the main energy source in the United States. During the latter half of the nineteenth century, the United States and other industrialized nations relied on coal (a fossil fuel) to provide the energy for industrialization. Coal remained the major fuel source for many years, and then, in the latter half of the twentieth century, oil and natural gas became the primary energy sources. The first oil well was drilled in Pennsylvania in 1859.
In 2000, fossil fuels accounted for almost 90 percent of the world's energy production (see Table 1). Nuclear power and hydroelectric plants supplied about 13 percent and geochemical, wind, and solar energy sources supplied only a fraction of 1 percent. Biomass , including the burning of wood, is not included in the table because it is so difficult to estimate.
Although coal combustion produces substantially greater air pollution problems than does oil or natural gas combustion, because of its great abundance in the United States and other countries (such as Russia), there has been renewed interest in developing technology to burn coal more cleanly. However, all fossil fuels consist mainly of hydrocarbons (compounds that contain only carbon and hydrogen), which, upon complete combustion, yield carbon dioxide, a major greenhouse gas.
It is widely accepted in the scientific community that fossil fuels (coal, oil, and gas) have a biological origin and are ultimately derived from the buried remains of plant and animal matter, although some still argue in favor of a nonbiological or inorganic source. It is believed that a small fraction (much less than 1%) of dead plant and animal matter accumulates as deposited matter, is removed from contact with atmospheric oxygen, is subject to elevated temperatures and pressures (inhibiting decomposition by bacteria), and over geological time, is transformed into fossil fuels.
|WORLD ENERGY SOURCES IN 2000|
|Source||Percent of Energy|
Coal is considered the remnant of plants that grew in swamps hundreds of millions of years ago, and thus its source is often characterized as terrestrial, signifying its association with continental land masses. Terrestrial plant material characteristically contains lignin, a carbon-based natural polymer that provides rigidity to nonaquatic plants and enables them to stand upright against the pull of gravity. Lignin is much more resistant to bacterial degradation than other botanical components, such as cellulose, and is considered a significant contributor to the chemical composition of coal.
The extent to which lignin and other plant matter has been metamorphosed by the high temperatures and pressures associated with the gradual burial of this material determines the grade of the coal produced. As the process of coal formation (coalification) proceeds, the product is increasingly characterized by lower moisture content, greater carbon and energy content, and a greater hardness. Lignite is the softest and least metamorphosed type of coal, with a relatively high moisture content, a low fixed carbon (nonvolatile carbon) content, and a low energy content. Subbituminous coal is the next highest grade, and upon further coalification it can be transformed to bituminous coal, or ultimately to anthracite. Anthracite is the hardest coal, possessing about 95 percent fixed carbon, the lowest moisture content, and the best energy content. Coals from different sources also contain differing amounts of inorganic mineral matter (ash), which remains as a residue upon burning and thus lowers the energy content of the coal. Table 2 compares the compositions of the various types of coal.
One mineral often associated with coal is pyrite, FeS2. The burning of coal contributes to pollution of the atmosphere, owing to the presence in coal of pyrite and organic sulfur-containing compounds. Coal is commonly burned in power plants that generate electricity, and both the inorganic (pyrite-containing) and organic forms of coal are oxidized to yield sulfur dioxide (SO2). Sulfur dioxide reacts in air to form sulfuric acid (H2SO4), which is a major cause of acid rain . Sulfuric acid and sulfur dioxide are also lung irritants, and thus health hazards, and contribute to the corrosion of structures by their acidification of all forms of precipitation (rain, snow, fog, sleet). The impact of the atmospheric precipitation of SO2 and H2SO4 has been minimized by chemical and physical processes that remove inorganic sulfur from coal (desulfurization), and by the use of coals with low sulfur content. One positive effect of higher H2SO4 levels in the atmosphere is the increase in cloud cover, due to the hygroscopic (water-absorbing) nature of this acid, and this may help to lower the average surface temperature of the planet—although CO2 produced as a result of oxidization of the carbon in coal is a major contributor to global warming.
|Type of Coal||%C||%H||%O||%N||%Moisture||Heating Value (kcal/kg)|
|*Peat is a dark, woody soil that has not yet been coalified to lignite.|
Coal can be transformed into coke and other fuels by various industrial and experimental processes. Coke is produced by the pyrolysis (heating in the absence of air) of coal and is used in the production of iron and steel. The coking procedure removes moisture and other volatile components from coal, yielding an extremely carbon-rich material. Coal can also be transformed (via intrafuel conversion) into relatively clean liquid and gaseous fuels (liquifaction and gasification). However, this is accomplished at high cost—in money and energy.
Petroleum is an extremely complex mixture of hydrocarbons, which can be separated into liquid (oil) and gas fractions. Compared to coal, petroleum being a liquid is easier to transport. It probably originated in marine sediments, in contrast to the terrestrial origins of coal.
Because petroleum varies greatly in composition and distribution throughout the world, elaborate systems of refining and transport have been developed. Major oil fields or giant petroleum fields ("giant" indicating oil fields capable of producing at least 500 million barrels of oil) are found primarily in the Middle East, North and South America, and countries that made up the former Soviet Union. The uneven natural distribution of oil, and the consequent need to transport oil across vast distances, has led to instances of contamination due to oil spills. Coastal waters are particularly vulnerable, not only to oil spills, but also to contamination by bilge water and tank-washing water from commercial oil tankers. Even though it is a major producer of oil, the United States has found it necessary to import significant additional amounts of oil in order to meet ever-increasing industrial and home-related energy demands. Most plastics and other petrochemicals are made from petroleum, along with almost all gasoline, diesel fuel, jet fuel, heating oil, and lubricants. However, Earth's supply of petroleum is limited. Some experts estimate that world production of oil could climax as early as 2004. Although most, if not all, of the major oil-producing fields associated with continental masses have been discovered, and many offshore wells have been drilled, there still may be other major oil discoveries in less accessible areas such as under the ocean—a largely unexplored territory.
The history of natural gas dates back to 900 b.c.e., when its use was mentioned in China. It was apparently unknown in Europe until 1659, when it was discovered in England. It was not discovered in the United States until 1815 in West Virginia. In the early twenty-first century, natural gas has become the favorite fuel of industrial nations. The United States is the largest producer as well as the largest consumer of natural gas. The largest natural gas reserves are located in Russia, Kazakhstan, and Iran.
Natural gas, which consists mainly of methane (CH4), can contain up to 20 percent of other gases—mainly ethane (C2H6), and possibly propane (C3H8), butane (C4H10), pentane (C5H12), carbon dioxide (CO2), and nitrogen (N2). Some natural gases contain small amounts of hydrogen, argon, carbon monoxide, or even hydrogen sulfide. Certain gas wells in Oklahoma also contain helium. In fact, they are a major source of helium in the United States. Natural gas is also colorless, odorless, and nontoxic but very flammable. (The odor we associate with natural gas is because of a mercaptan added to make gas leaks detectable.) Most natural gas is burned as fuel; however, ethane and the higher alkanes can be separated out and cracked to ethylene and propylene for making plastics. Although it is considered a "clean" and environmentally friendly fuel, compared to oil and coal, it is itself a major greenhouse gas and upon combustion yields carbon dioxide, the other major greenhouse gas. Like carbon dioxide, methane is also a greenhouse gas. However, natural gas fuel is thought to be only a minor contributor to methane in the atmosphere. Methane is constantly being generated by marsh and swamp terrain and by certain animals. Some experts believe that animals are the main source of atmospheric methane.
Other Sources of Fossil Fuels
Oil shales and tar sands also contain significant amounts of hydrocarbon materials that might eventually prove to be important energy sources. Oil shales are fine-grained sedimentary rocks (shales) that contain hydrocarbons that are dispersed within the matrix of the rock. A ton of shale contains from 10 to 100 gallons of kerogen, a waxy material that breaks down to oils when heated in the absence of air. It is estimated that three states (Utah, Colorado, and Wyoming) contain shale bearing more oil than exists in all the proven reserves in the world. Tar sands are the extremely viscous petroleum deposits associated with sedimentary rocks. They are mixtures of clay, sand, and extremely viscous oils called bitumens. The utility of oil shales and tar sands is currently limited, because of problems having to do with hydrocarbon recovery and the disposal of large amounts of inorganic residues.
see also Chemistry and Energy; Coal; Energy Sources and Production; Gasoline; Industrial Chemistry, Organic; Petroleum.
Mary L. Sohn
Spiro, Thomas G., and Stigliani, William M. (1996). Chemistry of the Environment. Upper Saddle River, NJ: Prentice-Hall.
Yeh, The Fu (1999). Environmental Chemistry: Essentials of Chemistry for Engineering Practice, Vol. 4A. Upper Saddle River, NJ: Prentice-Hall.
Fossil fuel is a general term for any hydrocarbon or carbonaceous rock that may be used for fuel: chiefly petroleum, natural gas, and coal. These energy sources are considered to be the lifeblood of the world economy. Nearly all fossil fuels are derived from organic matter, commonly buried plant or animal fossil remains, although a small amount of natural gas is inorganic in origin. Organic matter that has long been deeply buried is converted by increasing heat and pressure from peat into coal or from kerogen to petroleum (oil) or natural gas or liquids associated with natural gas (called natural gas liquids). Considerable time, commonly millions of years, is required to generate fossil fuels, and although there continues to be generation of coal, oil and natural gas today, they are being consumed at much greater rates than they are being generated. Fossil fuels are thus considered nonrenewable resources.
This article provides a brief historical perspective on fossil energy, focusing on the past several decades, and discusses significant energy shifts in a complex world of constantly changing energy supply, demand, policies and regulations. United States and world energy supplies are closely intertwined (Figure 1). World supplies of oil, gas and coal, are less extensively developed than those of the United States and the extent of remaining resources is extensively debated. Fossil fuels such as coal, natural gas, crude oil and natural gas liquids currently account for 81 percent of the energy use of the United States, and in 1997 were worth about $108 billion. For equivalency discussions and to allow comparisons among energy commodities, values are given in quadrillion British thermal units (Btus). For an idea of the magnitude of this unit, it is worth knowing that 153 quadrillion Btus of energy contains about a cubic mile of oil. The world consumes the equivalent of about 2.5 cubic miles of oil energy per year, of which 1 cubic mile is oil, 0.6 cubic mile is coal, 0.4 cubic mile is gas, and 0.5 cubic mile is all other forms of energy. Total oil reserves are about 32 cubic miles of oil and total energy reserves are equivalent to about 90 cubic miles of oil. Quadrillion Btus can also be converted to billion barrel oil equivalents (BBOE) at the ratio of about 5:1 (i.e., 5 quadrillion Btu to 1 BBOE). Both energy consumption and production more than doubled between 1960 and 2000, reflecting the United States's increasing need for energy resources (Figure 1). In 2000 the United States was at its historically highest level of both fossil energy consumption and production. However, significant shifts in domestic energy consumption and production occurred between 1980 and 2000. Production of oil and natural gas in the United States did not meet consumption between 1970 and 2000.
Surprisingly, coal is the largest energy source in the United States and the world (Figure 1), despite perceptions that it has been replaced by other sources. In 1997 production of both coal (23.2 quadrillion Btus, or about 4.6 billion barrels of oil) and natural gas (19.5 quadrillion Btus, or about 3.9 billion barrels of oil) on an energy equivalent basis exceeded U.S. domestic oil production (13.6 quadrillion Btus, equivalent to about 2.7 billion barrels, or 3.1 billion barrels of oil if natural gas liquids are included). Coal production in the United States nearly doubled from 1970 to 2000 (from about 600 million tons to about 1 billion tons produced annually). Meanwhile, petroleum consumption at 18.6 million barrels of oil per day is near the all-time high of 18.8 million barrels of oil per day in 1978. Net U.S. petroleum imports (8.9 million barrels of oil per day) in 1997 were worth $67 billion and exceeded U.S. petroleum production (8.3 million barrels of oil per day). Concerns about petroleum supplies, specifically oil shortages, caused the United States to build a strategic petroleum reserve in 1977 that currently holds 563 million barrels of oil or about sixty-three days worth of net imported petroleum. This strategic supply is about half of the 1985 high when the reserve would have provided 115 days worth of net imported petroleum. Although U.S. oil and gas production generally declined from 1970 to 1993, natural gas production has been increasing since the mid-1980s and energy equivalent production from natural gas exceeded U.S. oil production in the late 1980s. Natural gas is expected to play an increasing role in the United States in response to both environmental concerns and anticipated major contributions from unconventional (or continuous) natural gas sources requiring reductions in carbon emissions, particularly if the Kyoto Protocol is passed by the United States.
Due to factors such as extreme fluctuations in commodity prices, particularly oil prices, wasteful oil and gas field practices, and perceived national needs, U.S. government involvement in energy markets has been part of U.S. history from the turn of the century. The U.S. began importing oil in 1948. The 1973 oil embargo by the Organization of Petroleum Exporting Countries (OPEC) made a strong impact on U.S. policy makers who responded by developing regulations designed to encourage new domestic oil production. A two-tiered oil pricing system was introduced that changed less for old oil and more for new oil. The prospect of higher prices for new oil produced record high drilling levels, focusing on oil development, in the late 1970s and early 1980s. Domestic production fell dramatically in the early 1980s following oil price deregulation that permitted world market forces to control oil prices. Since that time, the United States has returned to a period of reliance on oil supplied by the OPEC comparable to early 1970s levels.
Regulations also have a strong impact on natural gas supply, demand and prices. Exploration for and development of natural gas historically have been secondary to oil because of the high costs of transportation, as well as a complex transportation and marketing system that allowed for U.S.-federally regulated interstate gas pipelines but essentially unregulated intrastate pipelines. The natural gas supply shortfalls in 1977 and 1978 resulted in The Natural Gas Policy Act of 1978, which was designed to deregulate natural gas on a 10-year schedule. The Act also extended U.S. federal regulation to all pipelines and gave incentives to explore for and develop certain classes of resources such as unconventional gas. Section 29 of the 1980 Windfall Profits Tax provided tax credits for coal-bed methane, deep-basin gas, and tight-gas reservoirs. These tax credits were graduated and substantial; for example, the tax credit on coal-bed methane was 90 cents per million Btus and 52 cents per million Btus for tight-gas reservoirs by the end of 1992 when the credit was terminated. The price of coal-bed methane during the years the credit was in effect ranged from $1 to $3 per million Btus. Drilling for Section 29 gas wells increased during the late 1980s and early 1990s, allowing drillers to establish production prior to 1993 and thus take advantage of the tax incentive, which remains in effect for gas produced from these wells through 2003.
By contrast, U.S. coal resources are not restricted by supply; however, the environmental consequences of coal use have had a major impact on coal development. The Power Plant and Industrial Fuel Use Act of 1978 was developed in response to perceived natural gas shortages; it prohibited not only the switching from oil to gas in power generation plants, but also the use of oil and gas as primary fuel in newly built large plants. However, coal remains the least expensive source of energy; consequently, coal has soared from 1980 to 2000. The most significant change in the use of coal reflects compliance with the Clean Air Act Amendments of 1990 (CAAA 90), which have stringent sulfur dioxide emission restrictions. Production of coal that complies with this Act has caused a shift from production east of the Mississippi to west of the Mississippi. Many western states have substantial coal resources, particularly low-sulfur coal resources, such as those in the Powder River Basin of Wyoming. In fact, Wyoming has been the largest coal-producing state since 1988. CAAA 90 allows utilities to bring coal-fired generating units into compliance, for example, by replacing coal-fired units with natural gas, or by using renewable or low-sulfur coals. Conversion to natural gas from coal in power plants, made feasible by the relatively low costs of natural gas generation in the late 1980s and early 1990s has eroded coal's 1990 share of 53 percent of domestic electricity generation. Clearly policy and regulations such as CAAA 90 impact U.S. coal quality issues and promote low-sulfur coal and natural gas usage.
Many of the resource additions to natural gas will come from unconventional accumulations, also called continuous deposits, such as tight-gas reservoirs and coal-bed methane. Since deregulation of the oil and gas industry in the 1980s, policy decisions have increasingly affected the energy industry (particularly of natural gas) by providing tax incentives to produce unconventional or continuous hydrocarbon accumulations. However, there are associated costs. For example, coal-bed methane is an important and growing natural gas resource, but the disposal cost of waste water generated by coal-bed methane production is thirty-eight times greater than the cost of disposing waste water generated by an onshore conventional gas well. Similarly, the electricity generated by alternative energy sources, such as windmills near San Francisco, is three times more expensive than electricity produced by conventional electric generators.
Increased energy use both for coal and natural gas likely will have the greatest impact on western U.S. federal lands because major unconventional or continuous natural gas deposits are known to exist in Wyoming, Utah, Montana, and New Mexico. The U.S. Geological Survey, in cooperation with the Department of Energy, estimates that an in-place natural gas resource in the Green River Basin in Wyoming is more than ten times larger than a recent estimate of the entire recoverable conventional natural gas resources of the United States. However, recoverable resources make up only a small percentage of this large in-place resource. These continuous deposits are distributed over a wide area as opposed to conventional resources that are localized in fields. The majority of conventional undiscovered oil and natural gas resources will likely be found on U.S. federally-managed lands, and thus the federal government and policies will continue to play an increasing role in energy development.
Implementation of the 1998 Kyoto Protocol, which is designed to reduce global carbon emissions, will have dramatic effects on fossil fuel usage worldwide. The Kyoto Protocol mostly affects delivered prices for coal and conversion of plants to natural gas, nuclear and/or renewable resources. However, as pointed out by the International Energy Agency, increased natural gas consumption in the United States may likely have the effect of increased reliance on imported oil in the short-term to fulfill transportation sector needs. New technologies, such as gas to liquid conversion, have the potential to create revolutionary industrywide change. This change is contingent upon sufficient commodity prices to support the necessary infrastructure to develop underutilized gas resources worldwide.
Some economists argue that civilization moves toward increasingly efficient energy resources, moving from sources such as wood to coal to oil to natural gas and ultimately to non-carbon based energy sources in 100 to 200 year cycles. Others argue for a far more complicated process involving demand, supply and regulations. Fossil fuels will remain critical resources well into the next century. In the meantime, their abundance and potential shortages are debated.
Thomas S. Ahlbrandt
Ahlbrandt, T. S. (1997). "The World Energy Program." U.S. Geological Survey Fact Sheet.FS 007–97.
Ahlbrandt, T. S., and Taylor, D.J. (1993). "Domestic Conventional Natural Gas Reserves—Can They Be Increased by the Year 2010?" In The Future of Energy Gases, ed. David B. Howell. U.S. Geological Survey Professional Paper 1570, 527–546.
Campbell, C. J. (1997). The Coming Oil Crisis. Brentwood, United.Kingdom: Multi-Science Publishing Company.
Edwards, J. D. (1997). "Crude Oil and Alternate Energy Production Forecasts for the Twenty-first Century: The End of the Hydrocarbon Era." American Association of Petroleum Geologists Bulletin 81:1292–1305.
Gautier, D. L.; Dolton, G. L.; Attanasi, E. D. (1998). 1995 National Oil and Gas Assessment of Onshore Federal Lands. U.S. Geological Survey Open-File Report 95–75.
International Energy Agency. (1998). World Energy Outlook. Paris, France: International Energy Agency/OECD.
Jackson, J., ed. (1997). Glossary of Geology, 4th ed. Alexandria, Virginia: American Geological Institute.
Klett, T. R.; Ahlbrandt, T. S.; Schmoker, J. W.; and Dolton, G. L. (1997). Ranking of the World's Oil and Gas Provinces by Known Petroleum Volumes. U.S. Geological Survey Open File Report 97–463, CD-ROM.
Law, B. E., and Spencer, C. W. (1993). "Gas in Tight Reservoirs—An Emerging Major Source of Energy." In The Future of Energy Gases, ed. David B. Howell. U.S. Geological Survey Professional Paper 1570, 233–252.
Masters, C. D.; Attanasi, E. D; and Root, D. H. (1994). "World Petroleum Assessment and Analysis." Proceedings of the 14th World Petroleum Congress. London: John Wiley and Sons.
Munk, N. (1994). "Mandate Power." Forbes, August, 41–42.
Nakicenovic, N. (1993). "The Methane Age and Beyond." In The Future of Energy Gases, ed. David B. Howell. U.S. Geological Survey Professional Paper 1570, 661–676.
National Petroleum Council. (1992). The Potential for Natural Gas in the United States. Washington, DC, National Petroleum Council.
U.S. Department of Energy. (1998). Comprehensive National Energy Strategy. Washington, DC: Author.
U.S. Energy Information Administration. (1998). Annual Energy Review 1997. Washington, DC: Department of Energy/Energy Information Administration.
U.S. Energy Information Administration. (1998). International Energy Outlook 1998. Washington, DC: Department of Energy/Energy Information Administration.
U.S. Energy Information Administration. (1998). What Does the Kyoto Protocal Mean to U.S. Energy Markets and the U.S. Economy?. Washington, DC: Department of Energy/Energy Information Administration.
U.S. Geological Survey. (1993). The Future of Energy Gases. U.S. Geological Survey Circular 1115.
In early societies, wood or other biological fuels were the main energy source. Today in many non-industrial societies, they continue to be used widely. Biological fuels may be seen as part of a solar economy where energy is extracted from the sun in a way that makes them renewable. However industrialization requires energy sources at much higher density and these have generally been met through the use of fossil fuels such as coal , gas, or oil. In the twentieth century a number of other options such as nuclear or higher density renewable energy sources (wind power, hydro-electric power, etc.) have also been available. Nevertheless fossil fuels represent the principal source of energy for most of the industrialized world.
Fossil fuels are types of sedimentary organic materials, often loosely called bitumens, with asphalt, a solid, and petroleum , the liquid form. More correctly bitumens are sedimentary organic materials that are soluble in carbon disulfide. It is this that distinguishes asphalt from coal, which is an organic material largely insoluble in carbon disulfide.
Petroleum can probably be produced from any kind of organism, but the fact that these sedimentary deposits are more frequent in marine sediments has suggested that oils arise from the fats and proteins in material deposited on the sea floor. These fats would be stable enough to survive the initial decay and burial but sufficiently reactive to undergo conversion to petroleum hydrocarbons at low temperature. Petroleum consists largely of paraffins or simple alkanes, with smaller amounts of napthenes. There are traces of aromatic compounds such as benzene present at the percent level in most crude oils. Natural gas is an abundant fossil fuel that consists largely of methane and ethane, although traces of higher alkanes are present. In the past, natural gas was regarded very much as a waste product of the petroleum industry and was simply burnt or flared off. Increasingly it is being seen as the favored fuel.
Coal, unlike petroleum, contains only a little hydrogen . Fossil evidence shows that coal is mostly derived from the burial of terrestrial vegetation with its high proportion of lignin and cellulose.
Most sediments contain some organic matter, and this can rise to many percent in shales. Here the organic matter can consist of both coals and bitumens. This organic material, often called sapropel, can be distilled to yield petroleum. Oil shales containing the sapropel kerogen are very good sources of petroleum. Shales are considered to have formed where organic matter was deposited along with fine grain sediments, perhaps in fjords, where restricted circulation keeps the oxygen concentrations low enough to prevent decay of the organic material.
Fossil fuels are mined or pumped from geological reservoirs where they have been stored for long periods of time. The more viscous fuels, such as heavy oils, can be quite difficult to extract and refine, which has meant that the latter half of the twentieth century has seen lighter oils being favored. However, in recent decades natural gas has been popular because it is easy to pipe and has a somewhat less damaging impact on the environment . These fossil fuel reserves, although large, are limited and non-renewable. The total recoverable light to medium oil reserves are estimated at about 1.6 trillion barrels, of which about a third has already been used. Natural gas reserves are estimated at the equivalent of 1.9 trillion barrels of oil and about a sixth has already been used. Heavy oil and bitumen amount to about 0.6 and 0.34 trillion barrels, most of which has remained unutilized. The gas and lighter oil reserves lie predominantly in the eastern hemisphere, which accounts for the enormous petroleum industries of the Middle East. The heavier oil and bitumen reserves lie mostly in the western hemisphere. These are more costly to use and have been for the most part untapped. Of the 7.6-trillion ton coal reserve, only 2.5% has been used. Almost two thirds of the available coal is shared between China, the former Soviet Union, and the United States.
Petroleum is not burnt in its crude form but must be refined, which is essentially a distillation process that splits the fuel into batches of different volatility. The lighter fuels are used in automobiles, with heavier fuels used as diesel and fuel oils. Modern refining can use chemical techniques in addition to distillation to help make up for changing demands in terms of fuel type and volatility.
The combustion of fuels represents an important source of air pollutants. Although the combustion process itself can lead to the production of pollutants such as carbon or nitrogen oxides , it has often been the trace impurities in fossil fuels that have been the greatest source of air pollution . Natural gas is a much favored fuel because it has only traces of impurities such as hydrogen sulfide. Many of these impurities are removed from the gas by relatively simple scrubbing techniques, before it is distributed. Oil is refined, so although it contains more impurities than natural gas, these become redistributed in the refining process. Sulfur compounds tend to be found only in trace amounts in the light automotive fuels. Thus automobiles are only a minor source of sulfur dioxide in the atmosphere . Diesel oil can have as much as a percent of sulfur, and heavier fuel oils can have even more, so in some situations these can represent important sources of sulfur dioxide in the atmosphere. Oils also dissolve metals from the rocks in which they are present. Some of the organic compounds in oil have a high affinity for metals, most notably nickel and vanadium. Such metals can reach high concentration in oils, and refining will mean that most become concentrated in the heavier fuel oils. Combustion of fuel oil will yield ashes that contain substantial fractions of the trace metals present in the original oil. This means that an element like vanadium is a useful marker of fuel oil combustion.
Coal is often seen as the most polluting fuel because low grade coals can contain large quantities of ash, sulfur, and chlorine . However, it should be emphasized that the quantity of impurities in coal can vary widely, depending on where it is mined. The sulfur present in coal is found both as iron pyrites (inorganic) and bound up with organic matter. The nitrogen in coal is almost all organic nitrogen. Coal users are often careful to choose a fuel that meets their requirements in terms of the amount of ash, smoke or pollution risk it imposes. High rank coals such as anthracite have a high carbon content. They are mined in locations such as Pennsylvania and South Wales and contain little volatile matter and burn almost smokelessly. Much of the world's coal reserve is bituminous, which means that it contains about 20–25% volatile matter.
The fuel industry is often seen as responsible for pollutants and environmental risks that go beyond those produced by the combustion of its products. Mining and extraction processes result in spoil heaps, huge holes in open cast mining, and the potential for slumping of land (conventional mining). Petroleum refineries are large sources of hydrocarbons, although not usually the largest anthropogenic source of volatile organic compounds in the atmosphere. Refineries also release sulfur, carbon, and nitrogen oxides from the fuel that they burn. Liquid natural gas and oil spills are experienced both in the refining and transport of petroleum.
Being a solid, coal presents somewhat less risk when being transported, although wind-blown coal dust can cause localized problems. Coal is sometimes converted to coke or other refined products such as Coalite, a smokeless coal. These derivatives are less polluting, although much concern has been expressed about the pollution damage that occurs near the factories that manufacture them. Despite this, the conversion of coal to less polluting synthetic solid, and liquid and gaseous fuels would appear to offer much opportunity for the future.
One of the principal concerns about the current reliance on fossil fuels relates not so much to their limited supply, but more to the fact that combustion releases such large amounts of carbon dioxide . Our use of fossil fuels over the last century has increased the concentration of carbon dioxide in the atmosphere. Already there is mounting evidence that this has increased the temperature of the earth through an enhanced greenhouse effect .
[Peter Brimblecombe ]
Campbell, I. M. Energy and the Atmosphere. New York: Wiley, 1986.
Fossil fuels are buried deposits of petroleum, coal, peat, natural gas, and other carbon-rich organic compounds derived from the dead bodies of plants and animals that lived many millions of years ago. Over long periods of time, pressure generated by overlying sediments and heat from within the Earth have concentrated and modified these materials into valuable energy sources for human purposes. Fossil fuels currently provide about 90% of all technological energy used in the world. They provide the power to move vehicles, heat living spaces, provide light, cook our food, transmit and process information, and carry out a wide variety of industrial processes. Modern agriculture is also deeply dependent on fossil fuels, since most of the nitrogen in fertilizers is derived from natural gas. It is no exaggeration to say that modern industrial society is nearly completely dependent on (some would say addicted to) a continual supply of fossil fuels. How we will adapt as supplies become too limited, too remote, too expensive, or too environmentally destructive to continue to use is a paramount question for society.
The amount of fossil fuels deposited over history is large. Total coal reserves, for example, are estimated to be in the vicinity of ten trillion metric tons. If all this resource could be dug up, shipped to market, and burned in an economically and environmentally acceptable manner—which, at this point, it cannot— it would fuel all our current commercial energy uses for several thousand years. Petroleum (oil) deposits are thought to have originally amounted to some four trillion barrels (600 billion metric tons), about half of which has already been extracted and used to fuel industrial society. At current rates of use the proven oil reserves will be used up in about 40 years. World natural gas supplies are thought to be at least 10 quadrillion cubic feet or about as much as energy as the original oil supply. At current rates of use, known gas reserves should last at least 60 years. If we substitute gas for oil or coal, as some planners advocate, supplies will be used up much faster than at current rates. Some unconventional hydrocarbon sources such as oil shales and tar sands might represent an energy supply equal to or even surpassing the coal deposits on which we now depend.
In the United States, oil currently supplies about 40% of all commercial energy use, while coal contributes about 22%, and natural gas provide about 24%. Oil and its conversion products, such as gasoline, kerosene, diesel fuel, and jet fuel are the primary fuel for internal combustion engines because of the ease with which they can be stored, transported, and burned. Coal is burned primarily in electric power plants and other large, stationary industrial boilers. Methane (natural gas) is used primarily for space heating, cooking, water heating, and industrial processes. It is cleaner burning than either oil or coal, but is difficult to store or to ship to places not served by gas pipelines.
The use of fossil fuels as our major energy source has many adverse environmental effects. Coal mining often leaves a devastated landscape of deep holes, decapitated mountain tops, toxic spoil piles, and rocky rubble. Acid drainage and toxic seepage from abandoned mines poisons thousands of miles of streams in the United States. Every year the 900 million tons of coal burned in the United States (mainly for electric power generation) releases 18 million tons of sulfur dioxide, five million tons of nitrogen oxides (the main components of acid rain), four million tons of carbon monoxide and unburned hydrocarbons, close to a trillion tons of carbon dioxide, and a substantial fraction of the toxic metals such as mercury, cadmium, thallium, and zinc into our air. Coal often contains uranium and thorium, and that most coal-fired power plants emit significant amounts of radioactivity—more, in fact, than a typical nuclear power plant under normal conditions. Oil wells generally are not as destructive as coalmines, but exploration, drilling, infrastructure construction, waste disposal, and transport of oil to markets can be very disruptive to wild landscapes and wildlife. Massive oil spills, such as the grounding of the Exxon Valdez on Prince William Sound, Alaska, in 1989, illustrate the risks of shipping large amounts of oil over great distances. Nitrogen oxides, unburned hydrocarbons, and other combustion byproducts produced by gasoline and diesel engines are the largest source of air pollution in many American cities.
One of the greatest concerns about our continued dependence on fossil fuels is the waste carbon dioxide produced by combustion. While carbon dioxide is a natural atmospheric component and is naturally absorbed and recycled by photosynthesis in green plants, we now burn so much coal, oil, and natural gas each year that the amount of carbon dioxide in the atmosphere is rapidly increasing. Because carbon dioxide is a greenhouse gas (that is, it is transparent to visible light but absorbs long wavelength infrared radiation), it tends to trap heat in the lower atmosphere and increase average global temperatures. Climatic changes brought about by higher temperatures can result in heat waves, changes in rainfall patterns and growing seasons, rising ocean levels, and could increase the frequency and severity of storms. These potentially catastrophic effects of global climate change may limit our ability to continue to use fossil fuels as our major energy source. All of these considerations suggest that we urgently need to reduce our dependency on fossil fuels and turn to environmentally benign, renewable energy sources such as solar power, wind, biomass, and small-scale hydropower.
Fossil fuels are buried deposits of plants and animals that have been converted to coal, petroleum, natural gas, or tar by exposure to heat and pressure in the Earth's crust over hundreds of millions of years. The energy in fossil fuels comes from sunlight, either directly or indirectly.
Coal comes primarily from the remains of plants that were buried in anaerobic conditions (without oxygen). Coal ranges from 55 percent to 90 percent carbon mixed with water and other substances including compounds of nitrogen and oxygen. Coal is graded according to hardness and carbon content. The lowest grade, lignite, is soft and brown in color. The hardest, anthracite, is nearly pure carbon. It is so hard it can be polished like a gemstone.
Petroleum (crude oil) is a liquid containing primarily hydrocarbon compounds along with small amounts of compounds containing oxygen, sulfur, and nitrogen. Crude oil originates with the buried remains of various types of plankton, primarily diatoms. It varies in consistency from a thin liquid the color of port wine to a thick, black, tarlike substance that must be heated before it will flow. Crude oil is the source of gasoline, jet fuel, diesel, heating oil, bunker oil, plastics, and other compounds.
Natural gas is usually found in varying amounts along with crude oil and with coal. It is also found by itself. Natural gas consists of a mixture of methane (CH4) and other hydrocarbons such as ethane (C2H6), propane (C3H8), and butane (C4H10). Methane is a natural byproduct of the anaerobic decomposition of organic remains.
Oil and Natural Gas
Petroleum ranges in quality from a relatively thin, free-flowing liquid called light or sweet crude to a thick, gooey black liquid with high sulfur content called heavy or sour crude. Because sweet crude is cleaner to burn and easier to transport, it is more valuable. Some oil flows naturally to the surface but most must be pumped. After primary recovery, hot water, steam, or high-pressure carbon dioxide can be injected into adjacent wells to force out some additional wells. Only about one-third of the oil can be extracted in primary and secondary recovery.
Oil, a useful fuel that can power automobiles, trucks, and airplanes, is a relatively inexpensive energy source. It has a high energy content and is easily transported. However, most experts expect little of the world's original oil reserves to remain by the middle of the twenty-first century. If world oil consumption increases at a rate of 2 percent per year, 80 percent of the world's supply will be used up by 2037.
When natural gas deposits are tapped, the gas is pressurized, which causes the propane and heavier hydrocarbons to liquefy. This liquefied petroleum gas (LPG) is stored in pressurized tanks and used in rural areas where natural gas supplies are not available. The remaining gas, mostly methane, is dried, cleaned of hydrogen sulfide, and distributed through pressurized pipelines.
Natural gas is a very clean-burning substance. If the gas is properly treated to remove sulfur and other contaminants, combustion products consist of water and carbon dioxide. Natural gas burns hotter and produces less pollution than any other fossil fuel.
The U.S. Department of Energy has estimated that all known and unknown reserves of natural gas will last until 2045 at present levels of consumption. If consumption rises by 2 percent per year, natural gas reserves will be depleted by 2022.
Coal is the world's most abundant fossil fuel. The United States, China, and Russia contain about two-thirds of known and estimated undiscovered coal reserves. Much of that coal contains large amounts of sulfur. When coal containing sulfur is burned, sulfur dioxide is created. Sulfur dioxide is one of the primary components of acid rain, so it is a pollutant. It is very difficult to remove the sulfur before the coal is burned, so the sulfur must be removed from the stack gases. Removing the sulfur is costly, although part of the cost can be recovered by selling the byproduct, sulfuric acid. World reserves of coal will last 220 years at current consumption rates and 65 years if consumption rates increase by 2 percent per year. Identified coal reserves in the United States will last about 300 years at current consumption rates.
Coal must be extracted by mining, the most environmentally destructive and expensive form of extraction. The least expensive form of mining is strip mining. The layer of rock and soil over the coal is removed by heavy machines, the coal is extracted by other heavy machines, and the rock and soil are replaced. Existing laws require that strip-mined land be returned to its original contour and replanted in suitable ground cover. When properly done, this restoration leaves the land in good condition.
Unfortunately, much of the land that was strip-mined before the laws were passed has not been restored. This results in erosion and pollution. Much of the coal that can be strip-mined in the United States is in the arid west, where restoration is more difficult and expensive. These requirements have made coal more expensive. Since natural gas is cheaper and burns cleaner, most new electric power plants being built are gas-fired.
All fossil fuels represent millions of years of stored solar energy. Plants remove carbon dioxide from the air and use the energy of sunlight to separate the carbon from the oxygen. The oxygen is released and the carbon is used to build carbohydrates, fats, and proteins. The carbon stored in fossil fuels is the result of this process. When fossil fuels are burned, this process is reversed. Oxygen from the air combines with carbon in the fossil fuels to form carbon dioxide, which is released into the atmosphere. Carbon dioxide levels in the atmosphere have been increasing steadily since the beginning of the industrial revolution. Most scientists now think that these increasing levels of carbon dioxide in the atmosphere are contributing to global warming through a process known as the greenhouse effect.
see also Global Warming.
Miller G. Tyler, Jr. Living in the Environment. 6th ed. Belmont, CA: Wadsworth, 1990.
Fossil fuels are buried deposits of petroleum , coal , peat, natural gas , and other carbon-rich organic compounds derived from the dead bodies of plants and animals that lived many millions of years ago. Over long periods of time , pressure and heat generated by overlying sediments concentrate and modified these materials into valuable energy sources for human purposes. Fossil fuels currently provide about 90% of all commercial energy used in the world. They provide the power to move vehicles, heat living spaces, provide light , cook our food, transmit and process information, and carry out a wide variety of industrial processes. It is no exaggeration to say that modern industrial society is nearly completely dependent on (some would say addicted to) a continual supply of fossil fuels. How we will adapt as supplies become too limited, too remote, too expensive, or too environmentally destructive to continue to use is a paramount question for society.
The amount of fossil fuels deposited over history is astounding. Total coal reserves are estimated to be in the vicinity of ten trillion metric tons. If all this resource could be dug up, shipped to market, and burned in an economically and environmentally acceptable manner, it would fuel all our current commercial energy uses for several thousand years. Petroleum (oil) deposits are thought to have originally amounted to some four trillion barrels (600 billion metric tons), about half of which has already been extracted and used to fuel industrial society. At current rates of use the proven oil reserves will be used up in about 40 years. World natural gas supplies are thought to be at least 10 quadrillion cubic feet or about as much as energy as the original oil supply. At current rates of use, known gas reserves should last at least 60 years. If we substitute gas for oil or coal, as some planners advocate, supplies will be used up much faster than at current rates. Some unconventional hydrocarbon sources such as oil shales and tar sands might represent an energy supply equal to or even surpassing the coal deposits on which we now depend.
In the United States, oil currently supplies about 40% of all commercial energy use, while coal contributes about 22%, and natural gas provide about 24%. Oil and its conversion products, such as gasoline, kerosene, diesel fuel, and jet fuel are the primary fuel for internal combustion engines because of the ease with which they can be stored, transported, and burned. Coal is burned primarily in power plants and other large, stationary industrial boilers. Methane (natural gas) is used primarily for space heating, cooking, water heating, and industrial processes. It is cleaner burning than either oil or coal, but is difficult to store or to ship to places not served by gas pipelines.
The use of fossil fuels as our major energy source has many adverse environmental effects. Coal mining often leaves a devastated landscape of deep holes, decapitated mountain tops, toxic spoil piles, and rocky rubble. Acid drainage and toxic seepage from abandoned mines poisons thousands of miles of streams in the United States. Every year the 900 million tons of coal burned in the U.S. (mainly for electric power generation) releases 18 million tons of sulfur dioxide , five million tons of nitrogen oxides (the main components of acid rain ), four million tons of carbon monoxide and unburned hydrocarbons, close to a trillion tons of carbon dioxide , and a substantial fraction of the toxic metals such as mercury, cadmium, thallium, and zinc into our air. Coal often contains uranium and thorium, and that most coal-fired power plants emit significant amounts of radioactivity—more, in fact, than a typical nuclear power plant under normal conditions. Oil wells generally are not as destructive as coal mines, but exploration, drilling, infrastructure construction, waste disposal, and transport of oil to markets can be very disruptive to wild landscapes and wildlife . Massive oil spills , such as the grounding of the Exxon Valdez on Prince William Sound, Alaska, in 1989, illustrate the risks of shipping large amounts of oil over great distances. Nitrogen oxides, unburned hydrocarbons, and other combustion byproducts produced by gasonine and diesel engines are the largest source of air pollution in many American cities.
One of the greatest concerns about our continued dependence on fossil fuels is the waste carbon dioxide produced by combustion. While carbon dioxide is a natural atmospheric component and is naturally absorbed and recycled by photosynthesis in green plants, we now burn so much coal, oil, and natural gas each year that the amount of carbon dioxide in the atmosphere is rapidly increasing. Because carbon dioxide is a greenhouse gas (it is transparent to visible light but absorbs long wavelength infrared radiation ), it tends to trap heat in the lower atmosphere and increase average global temperatures. Climatic changes brought about by higher temperatures can result in heat waves, changes in rainfall patterns and growing seasons , rising ocean levels, and could increase the frequency and severity of storms. These potentially catastrophic effects of global climate change may limit our ability to continue to use fossil fuels as our major energy source. All of these considerations suggest that we urgently need to reduce our dependency on fossil fuels and turn to environmentally benign, renewable energy sources such as solar power, wind , biomass , and small-scale hydropower.
Coal, petroleum, and natural gas are referred to as fossil fuels. Their common origin is as living matter, plants, and, in particular, microorganisms that have accumulated in large quantities under favorable conditions during the earth's long history. They have been preserved (fossilized) through burial under younger sediments, to great depths and over many millions of years. The "organic" elements hydrogen (H) and carbon (C) are the primary source of their heat content (hence the derivation of the word hydrocarbons ). Coal has a relatively high carbon content; petroleum and natural gas have much higher hydrogen contents. The burning of fossil fuels releases large quantities of the powerful greenhouse gas carbon dioxide (CO2) into the atmosphere, where it remains for a long time and contributes to global warming.
Fossil fuels have powered the industrialization of the world for several centuries. During the nineteenth and early twentieth centuries, coal was the primary source of energy. Then, after World War I, petroleum and later natural gas became increasingly important and together they contribute approximately 62 percent of the primary energy sources in the United States. Coal nevertheless still provides about 23 percent, mostly by conversion into electricity at large power plants.
see also Coal; Electric Power; Energy; Petroleum.
energy information administration. "monthly energy review." available from http://www.eia.doe.gov/emeu/mer.
Heinz H. Damberger