Once natural gas liquids (NGLs) have been separated from a natural gas stream, they are broken down into their component parts, or fractions, using a fractional distillation process, also known as fractionation.

NGLs contain the following hydrocarbon fractions: ethane, propane, butane and natural gasoline (pentanes and heavier hydrocarbons). Fractionation works by heating the NGL stream and boiling off the various fractions in sequence from the lighter to the heavier hydrocarbons. Each fractionating column, or fractionator, is named for the hydrocarbon that is boiled off.

The process starts with the deethanizer, which separates ethane from the NGL stream. Next, the depropanizer separates the propane, then the debutanizer boils off the butane, leaving natural gasoline. In some plants, a butane splitter then further separates normal and isobutane. Sometimes the order of the Depropanizer and debutanizer are reversed.

Extensive experience
CB&I has designed and built NGL fractionation plants with capacities ranging from 10,000 to 75,000 barrels per day in locations around the world. Depending on the size of the plant, we can perform some or all of the work utilizing modular construction methods. Modular units are fabricated and pre-assembled at our fully equipped shops and shipped to the installation site.

Modular construction allows us to fabricate and assemble the units under controlled conditions, ensuring the work is performed according to our quality and safety standards and also reducing weather delays. Installing a modular unit usually requires less highly skilled labor onsite, which can lower the customer's labor costs. In addition, modular construction techniques allow many of the taller vertical structures to be built horizontally at ground level and then transported to site for assembly. This translates into less above-grade construction activity on site, which in turn lowers risk for the customer.