LNG for Petroleum Engineers

Abstract

Abstract 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 can't 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 -260°F (-162°C), 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 $1.5 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 will 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.