Glossary of Terms

Natural gas (NG)
NG is a gaseous fossil fuel consisting primarily of methane. It is found in oil fields and natural gas fields, as well as - in smaller quantities - in coal beds.

When methane-rich gasses are produced by the anaerobic decay of non-fossil organic material, these are referred to as biogas. Sources of biogas include swamps (swamp gas), marshes (marsh gas), landfills (landfill gas), sewage sludge and manure (by way of anaerobic digesters) and flatulence (most notably in cows.)

Methane is an extremely efficient greenhouse gas which may contribute to enhanced global warming when free in the atmosphere, and such free methane, would then be considered a pollutant rather than a useful energy resource. However, methane in the atmosphere reacts with ozone, producing carbon dioxide and water, so that the greenhouse effect of released methane is relatively short-lived. As a pollutant, significant biological sources of methane are termites, cows (ruminants) and cultivation (estimated emissions 15, 75 and 100 million tons per year respectively.

Compressed Natural Gas (CNG)
CNG is a substitute for gasoline or diesel fuel. It is considered to be an environmentally "clean" alternative to those fuels. It is made by compressing purified natural gas, and is typically stored and distributed in hard containers.

In response to high fuel prices and environmental concerns, compressed natural gas is starting to be used in light-duty passenger vehicles and pickup trucks, medium-duty delivery trucks and buses.

Liquefied Natural Gas (LNG)
Liquefied natural gas or LNG is natural gas that has been processed to remove impurities and heavy hydrocarbons and then condensed into a liquid at atmospheric pressure and stored in specially designed tanks. LNG has about 1/600th the volume of natural gas in standard atmospheric conditions, making it much more cost-efficient to transport over very long distances.

LNG offers an energy density comparable to petrol and diesel fuels, but its relative high cost of production and the need to store it in expensive cryogenic tanks have prevented its widespread use in commercial applications.

Conditions required to condense natural gas depend on its precise composition, the market that will be sold to and the process being used, but typically involve temperatures between - 120 and -170 degrees Celsius (pure methane liquefies at -161.6) and pressures of between 101 and 1000 kPa (14.7 and 150 PSI). The natural gas fed into the LNG plant will be treated to remove water, carbon dioxide and other components that will freeze under the low temperatures needed for storage.

The infrastructure needed for LNG transportation consists of a liquefaction facility, where the gas is cooled, a load-out terminal for loading the LNG onto ships, LNG-ships for transportation, and a regasification terminal at the destination, where the LNG is reheated and turned into gas. Regasification terminals are usually connected with a pipeline distribution network.