Session: 20-03 Gas turbine package and expanders

Paper Number: 101990

101990 - Two-Phase Cryogenic Expander for Nitrogen Rejection and Cooling Process in Natural Gas Applications 

A typical refinery process of natural gas requires cyclic cooling (liquefaction) and vaporization of the fluid in stages to separate and remove certain impurities, primarily nitrogen, from the ‘raw’ gas.

Natural gas from underground sources often has nitrogen contamination due either to its natural occurrence or from previous nitrogen injection to enhance recovery of the natural gas.

Nitrogen content must be limited or reduced by a nitrogen rejection process in order to meet the heating value requirement for the natural gas. This process is fundamentally a refrigeration cycle, within which the process pressure must be reduced; traditionally via a throttling process with a Joule-Thomson valve. Replacing the Joule-Thomson valve with a two-phase flashing expander can improve the overall efficiency of this refrigeration process with enhanced cooling, and electrical power co-generation.

This paper considers prior art, and reviews the current design considerations and technical challenges for a two-phase expander to be used in the Nitrogen Rejection process. Hydraulic and aerodynamic components of such two phase expanders are reviewed, and their operational characteristics are studied in this paper. Thermodynamic analysis of cooling and liquefaction processes are conducted to quantify the benefits of two phase expanders in terms of cooling, energy recovery and production rate. Site operational data and performance characteristics of an actual two-phase expander are reviewed to better understand two phase expansion within the expander.

Lastly, advantages of two-phase expanders are discussed and the process performance is compared to similar applications that involves pressure reduction and cooling where Joule-Thomson valves have typically been used.

Presenting Author: Enver S. Karakas Elliott Group, Ebara Corporation

Presenting Author Biography: Enver Karakas is a Senior Mechanical Engineer with over 20 years of experience in design and development of turbomachinery for oil and gas applications. Enver has been working for Elliott Group – Ebara Corporation since 2003. Enver specializes in cryogenic pump and turbine technology and is responsible for design, development, testing and troubleshooting cryogenic equipment. Enver has Master of Science and a Doctorate Degree in Mechanical Engineering from University of Nevada, Reno. He has been a research associate with University of Nevada, Reno and has lead Turbomachinery Laboratory at University of Nevada, Reno where he studied and investigated cavitation performance of pumps and multiphase flow in cryogenic turbines.

Authors:

Enver S. Karakas Elliott Group, Ebara Corporation
David Stasenko Elliott Group, Ebara Corporation