Natural gas is more than just clean-burning methane; when extracted from the ground it also contains other components that can removed and processed as natural gas liquids (NGLs). We know these final products as ethane, propane, and butane among others. But how are they removed for use? We separate the individual NGL molecules using fractionation.

NGLs are first removed from natural gas using processes like absorption or controlled expansion through a distillation column. Once the NGLs drop out from the column, they then must be processed for separation at a fractionation plant. Fractionators separate components based on boiling points and vary in many ways depending on product specification, connections, timings, storage requirements, and method of delivery. The biggest determiner, though, is what NGL molecule is to be isolated and removed. Most plants will have multiple fractionation towers connected together, customized to the intended NGL molecule for removal. Those towers are organized such that as the NGL is introduced at a certain temperature, molecules will fractionate based upon their boiling point condition under a specific pressure.

The first fractionation column reduces pressure to 425 psia, where ethane is boiled off, condensed, and transported for industrial use. The NGLs then flow into a second column designed to handle the removal of propane molecules at 250 psia, following a similar process of boiling off, condensation, transportation, and/or storage. The remaining NGL finally makes its way to a third column that splits butane into its variants. Anything left is referred to as natural gasoline, typically used for fuel blending.

Fractionation is also a big midstream business. Energy consultancy RBN Energy estimated U.S. fractionation capacity alone in 2014 at about four and a half million barrels per day. And as long as “wet” natural gas is being extracted, NGLs will also be collected: in September 2013 NGLs made up 5.5 percent of marketed production volume of U.S. gas processing plants.