Economically Recover and Reject Ethane with Novel Configuration for a Cryogenic NGL Gas Processing Plant

The Challenge

Recover or reject ethane? This is the question midstream gas processing plant operators face every day. Ethane can either go with the sales gas stream and be sold at the price of natural gas based on BTU value, or it can be liquefied and sold as a component of Natural Gas Liquid (NGL) based on gallons. When the market demands more ethane to feed ethylene crackers, it is worthwhile to recover ethane and sell it as liquid. On the other hand, when there is little or no ethane demand, it is more economical to blend ethane with sales gas. With a fluctuating and unpredictable market, what shall we do as plant operators?

The Solution

While the ethane market is not predicable, the available processing technology is. Therefore, it is necessary to design a flexible plant that can operate in either ethane recovery or ethane rejection mode. The Gas Subcooled Process (GSP) has been the natural gas industry’s workhorse for cryogenic NGL recovery over the past several decades. It is highly efficient for high ethane recovery, but when it comes to significant ethane rejection, GSP performance deteriorates very quickly. Alternatively, a different process called OverHead Recycle (OHR) is not suitable for substantial ethane recovery, but the performance is much more efficient when it comes to ethane rejection.

To maximize profits in this ever-changing ethane market, one solution is to combine these two technologies into a single, more efficient plant design. No matter how the market changes, operators have the flexibility to sell ethane either as gas in OHR mode or as liquid in GSP mode.