The natural gas that is used to meet power, commercial, and domestic needs throughout the world is over 90% pure methane, the lightest occurring hydrocarbon with a low carbon footprint.
Although predominantly methane, the “Feed Gas” from the interior of Oman also contains “sour gases” (in Oman mainly carbon dioxide, CO2), water (H2O), some mercury, and heavier hydrocarbons. These are removed before the methane is cooled to liquefied Natural Gas (LNG).
The process of producing LNG is in three steps.
Treatment (Remove CO2, water (H2O) and mercury from the Feed Gas)
Acid gas (mainly CO2), water and mercury are removed from the gas delivered to Oman LNG. This “clean-up” is a necessary step to enable liquefaction of the natural gas and a safe product for our customers.
Removal of “Condensates” (Remove heavier hydrocarbons (NGLs) by Fractional Distillation)
Condensates (natural gas liquids made up mainly of pentane and hexane) are removed by Fractional Distillation of the feed gas after treatment.
Liquefaction of Natural Gas (Cool remaining light hydrocarbons to -162°C to liquefy)
The gas (now mainly methane) is sent to the Main Cryogenic Heat Exchanger (MCHE), where it condenses to a liquid at -162°C. The liquid is sent to special storage tanks awaiting shipment by LNG vessels to customers in Asia and Europe.
Liquefaction of LNG takes place in “LNG Processing Trains”. Each “Train” consists of the “Treatment Step”, removal of the condensates by fractional distillation, followed by liquefaction of the natural gas. In some LNG trains, where the volumes allow and markets exist, an intermediate cooling and distillation step to remove LPGs (propane and butane) is undertaken. This is not currently done at Oman LNG.
The liquefaction step is driven by two large turbine driven compressors, which through a series of compression and adiabatic and non-adiabatic cooling steps cools the gas to -162°C to turns the gas into liquid.
Each LNG Train has a nominal capacity that is determined primarily by the size of the compressors. In the early days of LNG, trains were less than 1 million tons per annum (MTPA). At Oman LNG, each of the three trains can produce over 3 MTPA.