LNG production for either offshore or onshore
Pretreated and dehydrated natural gas (1) is cooled in cold box (2) and then expanded to low pressure via an expansion valve or liquid expander (3) and sent to storage as LNG. Refrigeration for liquefaction is obtained by continuous expansion of gases through two independent cycles, one using methane (4) [mostly the same gas being liquefied] and the second with nitrogen (5). The methane cycle works in the warmer end; while nitrogen provides refrigeration on the cold end.
When superimposed, these two cycles act like a binary system. This process is a unique candidate for offshore opportunities due to the refrigerants always being in a gas phase. A propane pre-cooling step can be added at the process’s front end (6), to achieve a high-efficiency process for onshore base load production. Operating conditions: Feed gas should be above 800 psig. For associated gases, LPG and condensate recovery is integrated with the same process. LNG is produced at –260°F.
Efficiency: Depending on gas composition, energy consumption varies between 11–16 kW/ton LNG/day.
Licensor: Randall Gas Technologies, ABB Lummus Global Inc., US Patent 6,412,302