Above: Shell's LNG animation as published on YouTube.
What is LNG?
LNG stands for liquefied natural gas. LNG is primarily methane, nature’s simplest and most abundant hydrocarbon fuel. Methane is composed of one carbon and four hydrogen atoms (CH4). When natural gas is cooled to a temperature of approximately –160°C (-260°F), at atmospheric pressure, it condenses to LNG. When natural gas is cooled down to LNG, it is reduced to approximately one six-hundredth of the volume of natural gas from which it is made, making shipping of LNG possible.
The liquefaction of natural gas dates back to the early 1900's. Natural gas is processed at a gas processing plant where most of the impurities and water are removed. The gas is then sent to a liquefaction plant, where additional processing removes the remaining water vapour and carbon dioxide from the gas. A refrigeration process turns it into a liquid and further purifies the stream so that LNG is predominantly methane. LNG is the liquid form of the same gas you use to cook and heat. Natural gas and its components are used as fuel for generating electricity and as raw material to manufacture a wide variety of products, from fibres for clothing, to plastics for healthcare, computing, and furnishings. LNG is transported and stored at atmospheric pressure and is a colourless, odourless, clear fluid which is less than half the density of water. Natural gas vapour rises under normal atmospheric conditions.
LNG Carriers are designed and constructed to international rules (IMO IGC Codes) and subject to the approval by a “classification society” such as Bureau Veritas (BV), Det Norske Veritas (DNV), Lloyd’s Register of Shipping, Nippon Kaiji Kyokai (NKK/ClassNK), RINA and the American Bureau of Shipping (ABS). The ships' safety systems can be divided into ship handling and cargo handling systems. The ship handling safety features include sophisticated radar and positioning systems that alert the crew to other traffic and hazards around the ship. There are also distress systems and beacons that automatically send out signals if the ship is in difficulty. Exclusion zones keep other ship traffic distant from tankers, and tankers are assisted to their moorings by tugboats. Some major ports around the world have VTS (Vessel Traffic Services), which is best described as “air traffic control” for ships.
The cargo system safety features include an extensive instrumentation package that monitors pressures, levels and temperatures and safely shuts down the system if it starts to operate outside predetermined parameters. Ships are double hulled and heavily insulated, and there are systems that constantly monitor the condition of the cargo and check for leaks. Equipment in the insulation spaces can detect leakage through a hole the size of a pin head. Ships are also equipped with gas and fire detection systems. The LNG industry prides itself of an impressive safety record and is through Society of International Gas Tanker and Terminal Operators (SIGTTO) taking all possible steps to maintain such record. LNG officers and crew undergo extensive training to meet internationally recognised standards. Ships have anti-piracy and boarding measures, and must comply with the requirements of the International Ship and Port Security (ISPS) code. At sea the bridge is manned 24 hrs a day and the cargo control room is manned continuously during periods of cargo transfer to/from the ship.
Export and import terminals are sited, designed and constructed according to stringent national codes and international standards. Safety studies such as those complying with European Directive Seveso II 96/82/EC for European countries are carried out prior to construction. The design process incorporates identification and assessment of potential hazards including evaluation of “worst-case” spill scenarios. Risk analysis and relevant measures for mitigation of consequences result in a risk level, which shall be acceptable to the authorities.
Extensive safety systems and monitoring equipment are in place. Safety features include methane detectors, Ultraviolet or Infrared (UV/IR) fire detectors, closed circuit TV, offsite monitoring, training requirements for personnel, emergency shut down buttons and emergency release couplings. An Emergency Shut Down (ESD) shuts off all pumps and closes off all piping in a predetermined and safe way, so that the LNG stays either on the ship or in the storage tank. In addition, the stringent design parameters for LNG terminals require that proper measures are in place in the unlikely event of a spill or equipment failure. LNG is stored at –160°C (-260°F) in special, low temperature, double walled, heavily insulated tanks that are made of materials such as nickel steel and concrete, suitable for these low temperatures. Tanks are designed and built to withstand very severe hazard scenarios such as earthquakes and high winds. LNG is pumped from the storage tanks to heaters where it vaporises to its natural gas state. Seawater is often used as a source of heat to vaporise LNG into gas. After being converted back into gas, it leaves the LNG facility through a pipeline, the gas is the same as you use at home.
Terminal security measures include restricted access to terminal property, manning 24 hours a day 365 days a year, fencing of the perimeter of the facility, motion detection on the fencing, closed circuit TV, and lighting. Terminals must comply with the requirements of the newly developed International Ship and Port Facility Security code (ISPS).