Rick Hill, age 14, of Prescott, Ariz., for his question:
HOW IS NATURAL GAS TRANSMITTED?
Natural gas is found in the holes of limestone, sandstone and other rocks that are porous. A dome of nonporous rock forms a cap over the gas bearing rock, trapping the gas. Drilling for gas involves the same methods as those used in drilling for oil. Then the raw natural gas that flows from a well must be cleaned, treated and transmitted to distant cities.
A pipe called a gathering line carries the gas from the well to an extraction unit, which removes such impurities as dust, sulfur and water. The gas may then flow to nearby processing plants which remove butane, propane natural gasoline and other substances not needed in the fuel.
The processed natural gas is then fed into underground long distance transmission pipelines which carry it to cities and towns along their routes.
Gas is sent through transmission pipelines under tremendous pressures. Usually this pressure is 1,000 pounds per square inch. The pressure drops along the route because of the friction of the gas against the pipe walls
The pressure in the transmission pipelines also falls when communities remove gas. Compressor stations along the line restore high pressure and push the gas on to its farthest destination.
Many lines have automatically operated stations that increase or decrease the pressure to meet the demands of various communities. Gas usually travels through pipelines at about 15 miles per hour. If gas produced in Texas starts its journey on a Friday morning, it will reach New York City on Tuesday afternoon, taking a bit longer than four days.
Inspectors on foot and in airplanes check continually for conditions that might damage the pipelines. In addition, instruments along the lines automatically report leaks and other faulty conditions.
In cities and towns, distribution lines carry the gas to customers. There are two kinds of distribution lines: mains and individual service lines.
Mains are large pipes connected to the transmission pipelines. Service lines are smaller pipes that branch out from the mains. They carry the fuel sold by gas utility companies to homes, stores and other buildings
The utility companies add to the gas a chemical that can be smelled. They do this because pure natural gas is odorless and would not be noticed if it leaked out.
The United States has more than 1 million miles of gas pipeline, not counting individual service lines. This is enough pipe to circle the earth at the equator about 50 times. Canada has almost 100,000 miles of line.
Because more natural gas is used in winter than in summer, the gas must be stored when the demand is low for use when it is high. Many gas companies pump great quantities of natural gas back into the ground. Most underground storage areas are old gas or oil fields that are no longer productive.
Ideal storage areas lie near pipelines, compressor stations and large market areas. The United States has more than 300 underground storage reservoirs in over 25 states. These reservoirs can hold about 25 percent of all gas products yearly in the country.