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Natural Gas Liquids or NGLs are commonly removed from natural gas streams not because they are impurities, but because they have a higher value if they are sold as separate products. The separation processes take place in processing plants, using different techniques, one of which is a bit similar to that used in removing water from natural gas streams.
There are two processes that are used to extract NGLs from natural gas: absorption and cryogenic expansion.
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Similar to how the absorption process uses glycol to remove water from the natural gas stream, the NGL absorption process uses a substance that absorbs NGLs from the gas stream. This substance, called absorption oil, is now a mixture of substances like propane, butane, pentane, etc. It is then heated, which allows for the separation and recovery of the NGLs. The cryogenic expansion processes are used to extract the lighter hydrocarbons like ethane and involves freezing the gas stream to condense ethane and other hydrocarbons while leaving methane in gaseous form.
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However, for these extracted NGLs to be useful, they have to be broken down into their base components. This is called fractionation. It works by using the different boiling points of the hydrocarbons to separate them from each other, starting from the lightest hydrocarbons to the heaviest.
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