Liquefied Natural Gas By The Mixed Fluid Cascade Process

The increasing use of natural gas for power generation, the dwindling supplies of gas in developed regions, and the desire to monetize large reserves of stranded gas have revived interest in liquefied natural gas (LNG). As a liquid, LNG can be transported over long distances by tanker ship, providing access to remote natural gas that could not be economically delivered by pipeline. The liquefaction process, however, is very capital intensive and accounts for a significant part of the total investment to bring the gas to the end-user. Consequently, significant efforts have been made in recent years to improve the liquefaction technology and to achieve economies of scale.

Linde and Statoil have developed the new Mixed Fluid Cascade (MFC) process for baseload production of LNG. The concept uses three independent mixed-refrigerant circuits that are combined in a cascade system. In addition to achieving high thermal efficiency, the process can accommodate liquefaction capacities up to 8 million t/yr in a single train. MFC will be used in the first LNG baseload plant in Europe, located on Melkøya Island, off the northern coast of Norway. The Snøhvit project, named after the gas field there, will have an initial LNG capacity of 4.3 million t/yr in a single train. It is scheduled to begin operation in 2006.

This Review presents a technical and economic evaluation of the MFC process, based on the production of 6.47 million t/yr (915 million scfd) of LNG at a 0.912 stream factor (333 onstream days). Assuming a lean feed gas and a seawater temperature of 29°C (85°F), the estimated power consumption for refrigeration is 261 kWh per metric ton of LNG. Our analysis indicates that the low specific power consumption, combined with the large single-train capacity, results in very competitive economics for the MFC process