Natural Gas:
Natural gas is a mixture of hydrocarbon (lower) that occurs in nature and exits in a gaseous state at ordinary pressure and temperature. It mainly contains methane (CH4 ), a small amount of ethane (C2H6), Propane (C3H8), and higher hydrocarbons like butane (C4H10), Pentane, etc.
The Common impurities of natural gas include-
- Nitrogen (N2)
- Carbondioxide (CO2)
- Hydrogen sulfide (H2S)
The presence of hydrogen sulfide in natural gas is very harmful. So it can not be used without proper purification.
Origin of Natural Gas:
- Bacterial gas
- Thermogenic gas
- Gas from coal
- Gas from oil cracking
Composition of Natural Gas:
The predominant component is methane, with an additional amount of ethane, propane, butane, and other higher hydrocarbons. They are all members of the paraffin group or alkane. Natural gas also contains some inorganic gases such as carbon dioxide, hydrogen, sulfide, argon, helium, and nitrogen.
Classification of natural gas:
Depending on various aspects, natural gas has been divided in many ways-
Depending on hydrogen sulfide content:
Secret gas:
If the natural gas contains very little or no sulfur compounds, it is called secret gas.
Sour gas:
If natural gas contains a significant amount of sulfur compounds, then it is called sour gas. Most natural gas contains water vapour, and this is removed by refrigeration, glycol absorption, or dry desiccant at the surface gas plant.
Depending on Condensate:
Condensate refers to that portion which condensates and separates out from natural gas as liquid when the gas is produced at the surface. Most Condensate are composed of saturated hydrocarbons in the light gasoline range butane, pentane and hexane.
Dry gas:
Natural gas that contains less than 0.1 gallon / 1000 ft3 of condensate, chemically dry gas is largely methane and it can be used as high quality petroleum.
Wet gas:
Natural gas that contains more than 0.3 gallon/1000 ft3 of condensate, chemically these gases contain ethane, propane, butane etc.
Lean gas:
Natural gas that contains 0.1 to 0.3 gallon / 1000 ft3 of condensate.
Depending on occurrence:
Associated gas:
When natural gas occurs in association with oil as gas cap ore dissolved gas in oil, it is called associated gas.
Non-associated gas:
When natural gas occurs singly and is not associated with oil, it is called non-associated
Dissolved gas:
It is in the solution in the crude oil in the reservoir.
Processed natural gas:
CNG – Compressed natural gas:
Refers to natural gas made available in compressed form for use as fuel in vehicles. Usually, natural gas is compressed to 3000 pounds per square inch gauge in refueling stations and put in a cylinder for CNG run vehicles.
LNG – Liquified natural gas:
Refers to the liquid form of natural gas that is produced in a special liquefaction process in a plant at the surface. Production of LNG is a costly process and involves cooling the gas to minus 161 degrees centigrade. When produced, one ton of LNG is approximately equivalent to 50,000 cubic feet of natural gas. LNG is transported and reclassified before pipeline use
NGL- Natural gas liquid. (Condensate):
This refers to a mixture of all hydrocarbon except methane, which can be extracted by compression and cooling in a separator. After separation, NGL is distilled to be separated into ethane, Propane, butane, and natural gasoline.
LPG – Liquefied petroleum gas:
Refers to a mixture of essentially propane and butane, which are extracted from wet natural gas. LPG is also available during the refining of crude oil. It is liquified under pressure at room temperature and is commonly stored in the cylinder as a convenient and portable fuel for domestic uses where supplies of pipeline gas are not possible.LPG can also be used in industrial and commercial establishments and to run automobiles.
