Gas to LNG
How it’s Done in Trinidad and Tobago
Raw natural gas is brought to the surface from gas fields deep beneath the seas off the southeast or north coast of Trinidad. It is transported onto the shore by pipelines 40 inches in diameter. The gas is then carried overland to the plant at Point Fortin, Trinidad, for some 50 miles by 36-inch pipelines. At the plant, the natural gas is processed to remove impurities, water, gas liquids and carbon dioxide.
Raw natural gas is brought to the surface from gas fields deep beneath the seas off the southeast or north coast of Trinidad. It is transported onto the shore by pipelines 40 inches in diameter. The gas is then carried overland to the plant at Point Fortin, Trinidad, for some 50 miles by 36-inch pipelines. At the plant, the natural gas is processed to remove impurities, water, gas liquids and carbon dioxide.
The ConocoPhillips Optimized Cascade Process was developed by ConocoPhillips Corporation, and is utilized by the Atlantic facility to liquefy natural gas. This is done by cooling the gas: running it through successive levels of propane, ethylene and methane refrigeration. Each chilling cycle reduces the temperature of the gas until it eventually liquefies. The liquefaction plant is somewhat like a huge refrigerator with giant compressors, condensers, pressure expansion valves and evaporators. A single liquefaction unit, or ‘train’ as it is called, may contain hundreds of meters of cold-resistant piping. As a liquid, the LNG is processed to atmospheric pressure. Heavy hydrocarbon liquids removed during liquefaction are passed on for further processing.The process is complex and somewhat expensive yet to date it is the most efficient way to reduce natural gas so that it can be transported. Pure LNG produced is then piped to heavily insulated storage tanks, which are not unlike huge thermos flasks except that insulation, rather than vacuum is used to retain cold temperatures. LNG containers need to be made of materials strong enough to withstand the sub-zero temperature at which LNG is maintained. The LNG tank lining is therefore constructed of ‘cryogenic material’, which includes nickel-steel, stainless steel, aluminum alloys, with external protective walls of compounded, pre-stressed concrete.The Atlantic facility has four tanks, each some 45 meters tall, about the height of a 17-storey building, and are designed to withstand earth movements and high winds. They each have two walls: an outer wall of reinforced concrete lined with carbon steel and inner walls of nickel-steel. Between both walls is a layer of insulation. From these tanks, LNG is loaded onto specially equipped carriers. On board, the LNG is maintained at a -161 degrees Celsius. Even though the carrier is heavily insulated to maintain the -161 degree temperature, some of the LNG which evaporates is compressed and used as fuel to propel the carrier.
