Raw natural gas consists primarily of methane ( CH4 ) , hydrocarbon molecules shortest and lightest also a number of:
  • Heavier hydrocarbon gases : ethane ( C2H6 ) , propane ( C3H8 ) , normal butane ( n – C4H10 ) , isobutane ( i – C4H10 ) , pentane and even hydrocarbons with a higher molecular weight . When processed and refined into finished products , all these are collectively referred to as NGL ( Natural Gas Liquids ).
  • Acid gases : carbon dioxide ( CO2 ) , hydrogen sulfide ( H2S ) , methanethiol ( CH3SH ) and Ethanethiol ( C2H5SH ).
  • Other gases : nitrogen ( N2 ) and helium ( He).
  • Water vapor. Also as a solution of salt and dissolved gas ( acid ).
Raw natural gas must be purified to meet the quality standards set by the company the main transmission and distribution pipelines . Quality standards vary from pipe to pipe and usually depends on the design of the pipeline system and market it serves. In general , standard-setting natural gas between alain is :
  • Rated heating value ( calorific value ) must be within a certain range . For example , in the United States , should be about 1,035 +/- 5 % BTU per cubic foot of gas at 1 atmosphere and 60 degrees Fahrenheit ( 41 MJ +/- 5 % per cubic meter of gas at 1 atmosphere and 15.6 degrees Celsius ) .
  • Dew -point adjustment for the reduction of water and heavy hydrocarbons in natural gas so that condensation does not occur during the transportation process in the pipeline.
  • The content of hydrogen sulfide H2S 0:25 grain per 100 cubic feet of gas , or about 4 ppm . Specifications for CO2 are usually no more than two or three percent per 100 cubic feet of gas.