Fifteen Years of Field Experience in LNG Expander Technology

From the earliest days of gas liquefaction, the thermodynamic process advantage of employing cryogenic liquefied gas expanders in place of throttling valves was very well recognized. The available technology was unable to offer reliable cryogenic liquefied gas expanders until the aerospace industry developed materials and designs suitable for the cryogenic environment. LNG expanders reduce the high pressure of the condensed LNG by converting the static pressure energy of the fluid into electricity and sub-cooling the refrigerated LNG. The Carnot efficiency of the liquefaction process is significantly increased by using LNG expanders, resulting in a very short amortization time of less than six months for the financial investment in LNG expanders. During the past fifteen years cryogenic LNG expanders have experienced an accelerated development in design and performance. Every newly built LNG liquefaction plant since 1996 has included two or more LNG expanders operating in each train. The evolutionary design and performance of LNG expanders is presented, discussed, and fifteen years of practical field experience is demonstrated. Particular linear and non-linear phenomena in rotor-dynamics and fluid dynamics that are specific to the design and operation of single phase and twophase LNG expanders are described. An outlook for upcoming and future requirements of the LNG Expander Technology indicates trends towards both much higher and much smaller flow rates, together with much higher pressures. New design concepts to meet these future requirements are also disclosed.