Transportation and distribution

Transportation of gas. Gas fields are often located far from major consumption centres; consequently, the gas has to be transported, although chemical industry transformation plants are frequently installed in the vicinity of production fields. Transportation of natural gas depends upon its form – in a gaseous form it is transported by pipeline under high pressure, and in a liquid form it is transported by boat.

Large gas pipelines enable gas to be transported over thousands of kilometres. Examples are the North American pipelines, which extend from Texas and Louisiana to the northeast coast, and from the Alberta fields to the Atlantic Seaboard.

Transportation pressure is generally 70 bars (70 kilograms per square centimetre [1,000 pounds per square inch]) because economic studies, in keeping with technological advances, have shown that transportation costs are at a minimum for pressures of this magnitude. Pipeline diameters for such long-distance transportation have tended to increase from an average of about 60 to 70 centimetres (24 to 29 inches) in 1960 to a size of 1.20 metres (about four feet). Some Soviet projects involve diameters of more than two metres (6.5 feet) and pressures of about 40 bars (41 kilograms per square centimetre [580 pounds per square inch]).

Because of pressure losses, the pressure has to be boosted at regular intervals to keep a constant flow rate in the pipeline, and economic surveys indicate that a compression station should be located every 80 or 100 kilometres (50 or 60 miles) in order to obtain maximum flow under the most economically advantageous conditions. At greater intervals, the pipeline is doubled in size if the gas flow is to be increased.

Despite the high pressure and circulation rates of 10 to 15 metres (33 to 49 feet) per second for gas, the energy carried by a gas pipeline is still one-third or one-half as much as that carried by an oil pipeline because one cubic metre of oil contains as much energy as 1,000 cubic metres (35,000 cubic feet) of natural gas.

Petroleum prospecting has revealed the presence of large gas fields in Africa, the Middle East, Alaska, and elsewhere. Transportation from such areas is effected by boat. The gas is liquefied to -160 °C (-256 °F) and transported as oil in tankers designed especially for this purpose. One cubic metre of liquid natural gas is equivalent to 600 cubic metres (21,200 cubic feet) of gas at atmospheric pressure, with the specific gravity of the liquid being relatively low (about 0.55).

This technique has developed very quickly since the first industrial operations involving it began in 1965 from Africa to Great Britain and France. Two other lines opened up in 1970, the first from Libya to Spain and Italy, and the second from Alaska to Japan. Since then other large-scale projects, including lines from African, South American, and Indonesian fields to the United States, Europe, and Japan, have been undertaken.

After 1965, when methane tankers with a capacity of 20,000 cubic metres (706,300 cubic feet) began to be used, the size of these ships rose to 90,000 and even 120,000 cubic metres (3,178,000 and 4,237,000 cubic feet), an increase that enabled them to carry from 50,000,000 to 70,000,000 cubic metres (1,800,000,000 to 2,500,000,000 cubic feet) of gas per trip.

Distribution and consumption. Production and marketing arrangements vary in different parts of the world. In some nations, such as Mexico and the U.S.S.R., the industry is completely nationalized. In Britain, Japan, Italy, and France exploration and development are carried out by either private firms or the government, but transportation and distribution are a government monopoly. In the United States, exploration, production, and transportation are handled by private firms, regulated by federal, state, and local commissions.

Consumption patterns for natural gas also vary. In western Europe, natural gas was not available in most countries until after the mid-20^th century; therefore, it supplied only a relatively small percentage of gas demand, but production and consumption of natural gas increased in the late 20th century to account for about one-seventh of the total energy requirements of western Europe. Natural-gas demand in North America, on the other hand, remained fairly constant during the same period, contributing about one-quarter of the total energy requirements. Residential and commercial uses have consumed the largest proportion of natural gas in North America and western Europe, while industry consumes the next largest amount and electric-power generation is a distant third in natural-gas consumption. In western Europe, natural gas provides the same advantages to industrial users as it does in homes and thus is expected to continue making significant inroads into this market at the expense of coal and, to a lesser extent, oil.

By far the major use of natural gas is as fuel, though increasing amounts are being taken by the chemical industry for raw material. Among industries consuming large volumes are food, paper, chemicals, petroleum refining, and primary metals. In the United States, a large amount fuels household heating plants; in the U.S.S.R., a considerable volume goes for electric-power generation.

In the chemical industry, natural gas supplies an ideal feedstock (raw-material source) for the manufacture of such widely used industrial gases as methanol, acetylene, helium, and hydrogen.

Although helium, for example, can be separated from the air, all commercial production is from natural gas, containing helium in relatively high percentages. Helium is extracted by cooling natural gas to the point at which it condenses to a liquid, leaving behind an uncondensed mixture of helium and nitrogen. Known as crude helium, this mixture is separated from the liquid natural gas and then further cooled until the nitrogen condenses. The liquid nitrogen is removed, and the helium gas remaining is purified to a concentration of 99.995 percent by passing it through a bed of activated charcoal at liquid-nitrogen temperatures.

With the widespread introduction of natural gas into commercial markets, hydrogen manufacturers shifted from coke to natural gas, from which hydrogen can be made by two different methods. In the first, known as the steam-reforming process, natural gas is reacted with steam over a catalyst at high temperatures to produce a mixture of hydrogen and carbon oxides. In the second, called the partial-oxidation process, the natural gas is reacted with oxygen under pressure, forming a mixture of hydrogen and carbon monoxide along with small quantities of other impurities.