LNG: Efficient technology needs effective safety

LNG is produced by cryogenically cooling natural gas to a temperature below -162 °C in a gas liquefaction plant (LNG train). Before this can occur, however, detrimental or toxic components in the raw natural gas need to be separated out via a process of absorption, washing out or pre-cooling to -35 °C. The actual process of liquefaction of almost pure methane consists of a sequence of compression, cooling (heat extraction) and pressure relief stages, which is repeated until the natural gas has reached liquid state. The requirements regarding explosion protection are extremely strict. Natural gas and LNG are extremely flammable; according to ATEX and IECEx, they belong to explosion group IIA. For North America it is Group D.

There is an explosion hazard not only during the actual liquefaction process, but through out the entire process, including purification and transport to individual plants or plant parts. So precautions to avoid explosions must be taken at all stages of gas pre-treatment and separation.

There are many different LNG liquefaction technologies (small, mid and large scale) in use around the globe currently. Owners select a technology based on their business plan and schedule. The more-established “large scale” technologies require lots of capital, time and equipment to get up and running. The newer small & mid-scale technologies have shorter schedules and are less-capital intensive allowing for quicker ROI but require more units to produce the same amount of LNG. Each of these types process hazardous gases so in that respect, they are all similar.

The typical design for any LNG liquefaction facility is long and involved plus includes many, many stages of safety checks throughout the entire design process. The EPC and consulting companies designing these facilities are experienced and use licensed Professional Engineers for final approval of drawings, designs, etc. In the USA for example, these facilities require many permits from government agencies such as the Federal Energy Regulatory Commission (FERC) to help insure safe operation at each plant. Decisions about economic considerations while meeting environmental constraints are made by each owner early in the cycle to insure they can produce an asset that meets their needs and is safe.

Many of the same hazards exist in both types of installations but there are some differences between on and offshore applications. The same gases are processed so explosion protection techniques are still required.