A little bit of engineering (Несколько текстов для зачёта), страница 5

Landfills fill up quickly and acceptable sites for new ones are difficult to find because of objections by neighbors to noise and smells, and the hazard of leaks into underground water supplies. The two major ways to reduce the need for new landfills are to generate less initial waste and to recycle products that would normally be considered waste.

In 1994 about 6.8 million metric tons (7.5 million U.S. tons) of food and yard debris were composted in the United States, accounting for about one-sixth of the overall 23.6 percent recycling rate. The combined effort of reducing waste and recycling resulted in 41 million fewer metric tons (45 million U.S. tons) of material going to landfills.

Solid waste can also be burned instead of buried in the ground. Typically, waste-to-energy (WTE) facilities burn trash to heat water for steam-turbine electrical generators. This WTE recycling keeps another 16 percent of municipal solid waste out of the landfills.

E

Economic Savings

Recycling in the short term is not always economically profitable or a break-even financial operation. Most experts contend, however, that the economic consequences of recycling are positive in the long term. Recycling will save money if potential landfill sites are used for more productive purposes and by reducing the number of pollution-related illnesses.

IV

HISTORY

People have recycled materials throughout history. Metal tools and weapons have been melted, reformed, and reused since they came in use thousands of years ago. The iron, steel, and paper industries have almost always used recycled materials. Recycling rates were modest in the United States up through the 1960s, although rates increased during World War II (1939-1945). Since the 1960s, recycling has steadily increased. Recycling in the United States between 1960 and 1994 rose from 5.35 million metric tons (5.9 million U.S. tons) per year to 44.7 million metric tons (49.3 million U.S. tons). In 1930 about 7 percent of municipal solid waste was recycled. By 1994 that amount had climbed to 23.6 percent. Experts predict the MSW recycling rate will reach 30 percent by the year 2000.

European countries have a long history of recycling and, in some cases, stiff requirements. In 1991 the German parliament approved legislation setting recycling targets of 80 to 90 percent for packaging materials and banned the sale of products from companies that do not cooperate. France has set specific recycling goals. Other countries with significant overall recycling rates include Spain at 29 percent, Switzerland at 28 percent, and Japan at 23 percent.

Steam

Steam, water in vapor state, used in the generation of power and on a large scale in many industrial processes. The techniques of generating and using steam, therefore, are important components of engineering technology. The generation of electricity is largely accomplished by first generating steam, whether the heat is produced by burning coal or gas or by the nuclear fission of uranium (see Nuclear Energy; Steam Engine; Turbine). Steam also is still much in use for space heating purposes (see Heating, Ventilating, and Air Conditioning), and it propels most of the world's naval vessels and commercial ships (see Ships and Shipbuilding).

The boiling point of water at sea-level atmospheric pressure (760 torr or 14.7 lb/sq in) is about 100° C (212° F). At this critical temperature, the addition of 970.3 Btu of heat will convert 0.454 kg (1 lb) of water to 0.454 kg of steam at the same temperature. For water under pressure, the boiling point rises with the increase of pressure up to a pressure of 218 atmospheres of pressure (165,000 torr or 3200 lb/sq in). At this pressure, water boils at a temperature of 374° C (705° F), its critical point. Beyond critical pressure and temperature there is no distinction between liquid water and steam.

Pure steam is a dry and invisible vapor. In many cases, however, when water is boiling, a quantity of small droplets, or particles, of water are taken up with the steam, and the resulting mixture is visible as a white vapor. A similar effect occurs when dry steam is exhausted into the comparatively cool atmosphere. Some of the steam cools and condenses, forming the familiar white vapor seen when a kettle boils on a stove. Such steam is said to be wet.

Steam that is heated to the exact boiling point corresponding to the existing pressure is called saturated steam. Heating steam beyond this temperature produces so-called superheated steam. Superheating also occurs if saturated steam is compressed or if saturated steam is throttled by passing the steam through a valve from a high-pressure vessel to a low-pressure vessel. Throttling causes the temperature of the steam to drop somewhat, but the temperature of the throttled steam is still higher than that of saturated steam at the corresponding pressure. Steam in its superheated state is generally used in modern power generation systems.

Energy Supply, World

I

INTRODUCTION

Energy Supply, World, combined resources by which the nations of the world attempt to meet their energy needs. Energy is the basis of industrial civilization; without energy, modern life would cease to exist. During the 1970s the world began a painful adjustment to the vulnerability of energy supplies. In the long run, conserving energy resources may provide the time needed to develop new sources of energy, such as hydrogen fuel cells, or to further develop alternative energy sources, such as solar energy and wind energy. While this development occurs, however, the world will continue to be vulnerable to disruptions in the supply of oil, which, after World War II (1939-1945), became the most favored energy source.

II

BACKGROUND OF TODAY’S SITUATION

Wood was the first and, for most of human history, the major source of energy. It was readily available, because extensive forests grew in many parts of the world and the amount of wood needed for heating and cooking was relatively modest. Certain other energy sources, found only in localized areas, were also used in ancient times: asphalt, coal, and peat from surface deposits and oil from seepages of underground deposits.

This situation changed when wood began to be used during the Middle Ages to make charcoal. The charcoal was heated with metal ore to break up chemical compounds and free the metal. As forests were cut and wood supplies dwindled at the onset of the Industrial Revolution in the mid-18th century, charcoal was replaced by coke (produced from coal) in the reduction of ores. Coal, which also began to be used to drive steam engines, became the dominant energy source as the Industrial Revolution proceeded.

A

Growth of Petroleum Use

Although for centuries petroleum (also known as crude oil) had been used in small quantities for purposes as diverse as medicine and ship caulking, the modern petroleum era began when a commercial well was brought into production in Pennsylvania in 1859. The oil industry in the United States expanded rapidly as refineries sprang up to make oil products from crude oil. The oil companies soon began exporting their principal product, kerosene—used for lighting—to all areas of the world. The development of the internal-combustion engine and the automobile at the end of the 19th century created a vast new market for another major product, gasoline. A third major product, heavy oil, began to replace coal in some energy markets after World War II.

The major oil companies, which are based principally in the United States, initially found large oil supplies in the United States. As a result, oil companies from other countries—especially Britain, the Netherlands, and France—began to search for oil in many parts of the world, especially the Middle East. The British brought the first field there (in Iran) into production just before World War I (1914-1918). During World War I, the U.S. oil industry produced two-thirds of the world’s oil supply from domestic sources and imported another one-sixth from Mexico. At the end of the war and before the discovery of the productive East Texas fields in 1930, however, the United States, with its reserves strained by the war, became a net oil importer for a few years.

During the next three decades, with occasional federal support, the U.S. oil companies were enormously successful in expanding in the rest of the world. By 1955 the five major U.S. oil companies produced two-thirds of the oil for the world oil market(not including North America and the Soviet bloc). Two British-based companies produced almost one-third of the world’s oil supply, and the French produced a mere one-fiftieth. The next 15 years were a period of serenity for energy supplies. The seven major U.S. and British oil companies provided the world with increasing quantities of cheap oil. The world price was about a dollar a barrel, and during this time the United States was largely self-sufficient, with its imports limited by a quota.

B

Formation of OPEC

Two series of events coincided to change this secure supply of cheap oil into an insecure supply of expensive oil. In 1960, enraged by unilateral cuts in oil prices by the seven big oil companies, the governments of the major oil-exporting countries formed the Organization of Petroleum Exporting Countries, or OPEC. OPEC’s goal was to try to prevent further cuts in the price that the member countries—Venezuela and four countries around the Persian Gulf—received for oil. They succeeded, but for a decade they were unable to raise prices. In the meantime, increasing oil consumption throughout the world, especially in Europe and Japan, where oil displaced coal as a primary source of energy, caused an enormous expansion in the demand for oil products.

C

The Energy Crisis

The year 1973 brought an end to the era of secure, cheap oil. In October, as a result of the Arab-Israeli War, the Arab oil-producing countries cut back oil production and embargoed oil shipments to the United States and the Netherlands. Although the Arab cutbacks represented a loss of less than 7 percent in world supply, they created panic on the part of oil companies, consumers, oil traders, and some governments. Wild bidding for crude oil ensued when a few producing nations began to auction off some of their oil. This bidding encouraged the OPEC nations, which now numbered 13, to raise the price of all their crude oil to a level as high as eight times that of a few years earlier. The world oil scene gradually calmed, as a worldwide recession brought on in part by the higher oil prices trimmed the demand for oil. In the meantime, most OPEC governments took over ownership of the oil fields in their countries.

In 1978 a second oil crisis began when, as a result of the revolution that eventually drove the Shah of Iran from his throne, Iranian oil production and exports dropped precipitously. Because Iran had been a major exporter, consumers again panicked. A replay of 1973 events, complete with wild bidding, again forced up oil prices during 1979. The outbreak of war between Iran and Iraq in 1980 gave a further boost to oil prices. By the end of 1980 the price of crude oil stood at 19 times what it had been just ten years earlier.

The very high oil prices again contributed to a worldwide recession and gave energy conservation a big push. As oil demand slackened and supplies increased, the world oil market slumped. Significant increases in non-OPEC oil supplies, such as those in the North Sea, Mexico, Brazil, Egypt, China, and India, pushed oil prices even lower. Production in the Soviet Union reached 11.42 million barrels per day by 1989, accounting for 19.2 percent of world production in that year.

Despite the low world oil prices that have prevailed since 1986, concern over disruption has continued to be a major focus of energy policy in the industrialized countries. The short-term increases in prices following Iraq’s invasion of Kuwait in 1990 reinforced this concern. Owing to its vast reserves, the Middle East will continue to be the major source of oil for the foreseeable future. However, new discoveries in the Caspian Sea region suggest that countries such as Kazakhstan may become major sources of petroleum in the 21st century.

D

Current Status

In the 1990s, oil production by non-OPEC countries remained strong and production by OPEC countries rebounded. The result at the end of the 20th century was a world oil surplus and prices (when adjusted for inflation) that were lower than in 1972.

Experts are uncertain about future oil supplies and prices. Low prices have spurred greater oil consumption, and experts question how long world petroleum reserves can keep pace with increased demand. Many of the world’s leading petroleum geologists believe the world oil supply will peak around 80 million barrels per day between 2010 and 2020. (In 1998 world consumption was approximately 70 million barrels per day.) On the other hand, many economists believe that even modestly higher oil prices might lead to greater supply, since the oil companies would then have the economic incentive to exploit less accessible oil deposits.

Natural gas may be increasingly used in place of oil for applications such as power generation and transportation. One reason is that world reserves of natural gas have doubled since 1976, in part because of the discovery of major deposits of natural gas in Russia and in the Middle East. New facilities and pipelines are being constructed to help process and transport this natural gas from production wells to consumers.

III

PETROLEUM AND NATURAL GAS

Petroleum (crude oil) and natural gas are found in commercial quantities in sedimentary basins in more than 50 countries in all parts of the world. The largest deposits are in the Middle East, which contains more than half the known oil reserves and almost one-third of the known natural-gas reserves. The United States contains only about 2 percent of the known oil reserves and 3 percent of the known natural-gas reserves.

A

Drilling

Geologists and other scientists have developed techniques that indicate the possibility of oil or gas being found deep in the ground. These techniques include taking aerial photographs of special surface features, sending shock waves through the earth and reflecting them back into instruments, and measuring the earth’s gravity and magnetic field with sensitive meters. Nevertheless, the only method by which oil or gas can be found is by drilling a hole into the reservoir. In some cases oil companies spend many millions of dollars drilling in promising areas, only to find dry holes. For a long time, most wells were drilled on land, but after World War II drilling commenced in shallow water from platforms supported by legs that rested on the sea bottom. Later, floating platforms were developed that could drill at water depths of 1,000 m (3,300 ft) or more. Large oil and gas fields have been found offshore: in the United States, mainly off the Gulf Coast; in Europe, primarily in the North Sea; in Russia, in the Barents Sea and the Kara Sea; and off Newfoundland and Brazil. Most major finds in the future may be offshore.

B

Production

As crude oil or natural gas is produced from an oil or gas field, the pressure in the reservoir that forces the material to the surface gradually declines. Eventually, the pressure will decline so much that the remaining oil or gas will not migrate through the porous rock to the well. When this point is reached, most of the gas in a gas field will have been produced, but less than one-third of the oil will have been extracted. Part of the remaining oil can be recovered by using water or carbon dioxide gas to push the oil to the well, but even then, one-fourth to one-half of the oil is usually left in the reservoir. In an effort to extract this remaining oil, oil companies have begun to use chemicals to push the oil to the well, or to use fire or steam in the reservoir to make the oil flow more easily. New techniques that allow operators to drill horizontally, as well as vertically, into very deep structures have dramatically reduced the cost of finding natural gas and oil supplies.

Crude oil is transported to refineries by pipelines, barges, or giant oceangoing tankers. Refineries contain a series of processing units that separate the different constituents of the crude oil by heating them to different temperatures, chemically modifying them, and then blending them to make final products. These final products are principally gasoline, kerosene, diesel oil, jet fuel, home heating oil, heavy fuel oil, lubricants, and feedstocks, or starting materials, for petrochemicals.