20.1 Natural Gas

  • The principal component of most natural gases is methane. Higher molecular weight paraffinic hydrocarbons (\(\ce{C2-C7}\)) are usually present in smaller amounts with the natural gas mixture.

  • Non-associated natural gas is found in reservoirs containing no oil (dry wells). They have a higher percentage of methane. Associated natural gas, on the other hand, is present in contact with and/or dissolved in crude oil and is coproduced with it. Heavier hydrocarbons constitute a major proportion of associated natural gas.

  • Moisture removal from natural gas:

    • Moisture must be removed from natural gas to reduce corrosion problems and to prevent hydrate formation.

    • Ethylene glycol, diethylene glycol, and triethylene glycol are typical solvents for water removal.

  • Liquefied Natural Gas (LNG)

    • Natural gas is liquefied by cooling it to -162\(^\circ\)C to reduce the cost of transportation.

    • Two methods are generally used to liquefy natural gas: the expander cycle and mechanical refrigeration.

    • In the expander cycle, part of the gas is expanded from a high transmission pressure to a lower pressure, thus producing necessary cooling to liquefy the natural gas.

    • In mechanical refrigeration, a multicomponent refrigerant consisting of nitrogen, methane, ethane, and propane is used through a cascade cycle.

  • Regasified Liquefied Natural Gas( RLNG)

    • As the name suggests, LNG is converted to gaseous form during distribution via regasification process.

    • RLNG is the feed in hydrogen generation units in petroleum refineries.

  • Shale Gas: Shale gas is natural gas that is found trapped within shale formations. Shale gas has become an increasingly important source of natural gas in the United States since 2000. Horizontal drilling is often used with shale gas wells.