Gas Processors Association Europe

Simon Cathery, Costain Oil, Gas & Process Ltd, UK & Dr Hans Kimmel, Ebara International, USA

Modern process plants for the liquefaction of natural gas operate at high pressure to improve the overall efficiency of the cryogenic process. Following the condensation of the refrigerated gas the pressurized Liquefied Natural Gas (LNG) is expanded across a liquid-vapour two-phase expander to a lower pressure suitable for storage and transportation. The near-isentropic expansion process generates some vapour and the remaining liquid is cooled down.

The aim of using an expander rather than a Joule-Thomson valve is to increase the amount of liquid and to decrease the amount of vapour at the outlet of the two-phase expander. By employing a two-phase draft tube at the exit of the two-phase expander, an increased amount of liquid is produced. The fluid dynamic operation and the thermodynamic performance of two-phase LNG expanders is presented and analyzed