(60c) Processes for High C2 Recovry from LNG – Part II: Schemes Based on Expander Technology

Extracting ethane plus (C2+) components from LNG may serve different purposes. The most basic one is to meet pipeline gas interchangeability, for which a C2 recovery level below 50% would typically suffice. A higher recovery level may become desirable depending on the marketability of the products. With the dwindling domestic production of natural gas, the associated natural gas liquid (NGL) production also decreases. To make-up the deficiency, the demand for improved C2 recovery from LNG may become a common trend.

The methods for high C2 recovery can be classified into two approaches: refluxed demethanizer and expander-based technology. The former utilizes the refrigeration in the incoming LNG to support the operation of the reflux condenser. The second approach borrows the extensive experiences of the gas processing industry, where many innovative processes have been patented in the past decades.

This work will focus on the expander-based technology. The performances of the aforementioned two approaches will be compared so that rational choices can be made during process selections. Furthermore, the LNG application represents an extreme scenario that the feed stream contains plentiful refrigeration. Studying the extreme scenario will shed light on the intrinsic limitations of expander-based processes. The conclusions can be translated to conventional gas processing designs.