While remote parts of the world are awash with hundreds of trillions of cubic feet (Tcf) of natural gas, the industrialized West and emerging economies of the East cannot get enough of the clean-burning, environmentally friendly fuel. The problem is transporting this compressible fluid long distances, across major bodies of water. For markets greater than 1,500 miles, liquefied natural gas (LNG) has proved to be the most economic option. By refrigerating natural gas (primarily methane) to -260ºF (-162ºC), thereby shrinking its volume by 600:1, LNG can be transported in large insulated cryogenic tankers at reasonable cost.
Natural gas liquefaction is a series of refrigeration systems similar to the air conditioning system in our homes consisting of a compressor, condenser and evaporator to chill and condense the gas. The difference is in the scale and magnitude of the refrigeration. A typical single-train LNG plant may cost $5 billion and consume 6-8% of the inlet gas as fuel. Since many of the impurities (water vapor, carbon dioxide, hydrogen sulfide, etc.) and heavier hydrocarbon compounds in natural gas would freeze at LNG temperatures, they must first be removed, and disposed or marketed as separate products.
This paper will provide an overview of LNG liquefaction facilities, from inlet gas receiving to LNG storage and loading. However, the focus is on the liquefaction process and equipment. Differences among the commercially available liquefaction processes (cascade, single mixed refrigerant, propane-pre-cooled mixed refrigerant, double mixed refrigerant, nitrogen, etc.) will be discussed. The aim is to provide SPE members with a clear understanding of the technologies, equipment and process choices required for a successful LNG project.
Michael Choi is a Process Engineering Fellow in ConocoPhillips’ Global Production Department located in Houston, Texas. His specialties are production facilities, sour gas treating and LNG. He was the lead process engineer for CoP’s Qatargas3 LNG project. Prior to joining Conoco in 1985, Michael worked in various engineering capacities with El Paso Natural Gas, Aminoil and Getty Oil/Texaco.
His work has led to a number of SPE publications and six US patents for separator design, emissions control system for glycol dehydrators and subsea processing and storage systems. Michael has been active in SPE as member of the PF&C Committee, program chairman and member of the ATCE and other international conferences and forums. He graduated from the University of Southern California in 1974 with a BS degree in chemical engineering.
Michael was an SPE Distinguished Lecturer during the 2012-13 lecture season.