(123e) Flashing Two-Phase LNG Expanders

Conventional liquefaction processes for natural gas operate at high pressure through the condensation phase, after which the pressure of the liquefied natural gas, the LNG is reduced by expansion across a Joule-Thomson valve or a liquid expander before rundown to storage at near atmospheric pressure.

When the condensed fluid is flashed across a J-T valve with constant enthalpy an undesirable amount of LNG is vaporized. The aim of using an LNG expander rather than a J-T valve is to increase the amount of liquid and to decrease the amount of vapor at the expander outlet. By employing a flashing two-phase LNG expander an increased amount of liquid is produced in a near isentropic expansion process.

Flashing two-phase LNG expanders were developed and installed in 2001 and 2002. Since then they are successfully operating in the field for ten years without failures or interruptions except for routine maintenance shut downs. Flashing two-phase LNG expanders increase the LNG production output continuously by 3 - 5 %.