Two-Phase LNG expanders increase the production of LNG by replacing the Joule-Thomson valve in natural gas liquefaction plants. The expansion of the condensed LNG across the expander converts the available pressure energy into electrical energy and reduces the enthalpy of the LNG. Any reduction in enthalpy increases the production of LNG.

Across the expansion process vaporization and condensation occur affecting the energy conversion of the expander. This thermodynamic expansion process can be modeled by a non-linear differential equation for the enthalpy and pressure.

The paper presents practical methods to determine the thermodynamic expansion process in two-phase LNG expanders.