Natural gas processors frequently use a cryogenic expansion process to recover valuable condensates, or natural gas liquids (NGLs), which can be sold as feedstocks for refining and petrochemical applications. NGLs include ethane, propane, butanes and heavier natural gasoline. Ethane is the most efficient feedstock for production of ethylene, which in turn is used to produce polyethylene for use in the manufacture of plastic films for packaging, carrier bags and trash can liners.

The ethane recovery process involves chilling the natural gas stream sometimes using external refrigerants, then expanding the gas through a turbo-expander, which causes the temperature to drop to approximately -120 to -160 degrees Fahrenheit. This rapid temperature drop condenses ethane in the gas stream, while maintaining most of the methane in gaseous form. The chilled gas stream then enters the demethanizer column, where excess methane is removed.

Optimum process design
CB&I designs and builds high ethane recovery plants using the refluxed demethanizer gas subcooled process (GSP), which typically achieves 85-90% ethane recovery. Other proprietary plant designs are also offered for higher ethane recoveries. For every installation, we optimize the process design, plant configuration and installed compressor horsepower, while carefully addressing personnel safety, environmental protection, customer preferences, space limitations, service access, available utilities and other design factors. We work to minimize capital, labor and material costs to yield low life cycle costs, while improving operating flexibility and reliability. Our process optimization typically evaluates the fraction of liquids recovered, inlet refrigeration options, side reboiler configurations, turbo-expander compressor configurations and other process options.

Efficient erection methods
Ethane recovery plants can be built utilizing modular construction methods, which can result in shorter schedules and sometimes lower costs for our customers. Modular plants are prefabricated and pre-assembled at our fabrication shops and can be shipped anywhere for installation. By fabricating most of the unit in our own shops, we can implement rigorous quality and safety controls and reduce project delays due to inclement weather. Minimizing fieldwork also reduces the project's impact on other operations at the installation site and allows some procedures, such as permitting and transportation arrangements, to be handled concurrently. Modular construction also requires less on-site skilled labor, which can translate into lower costs for the customer.