Liquefied Natural Gas (LNG)

Exponent has broad experience with the LNG industry and assists with engineering design reviews, third-party technology evaluation, research and development, and process hazards assessments associated with LNG facilities. Our capabilities include conducting inspections and safety audits, environmental impact studies, and consequence modeling, which involves computer modeling of fire radiation and vapor dispersion hazard zones. This work has included numerous site-specific LNG vapor dispersion analyses using computational fluid dynamics (CFD) modeling. Exponent engineers have project experience with material selection and material performance issues (metals and concrete) that are unique to LNG and cryogenic applications. We also provide services in process safety management, construction management, and wetland restoration planning. Using this experience, we routinely assist our clients in solving performance-based design challenges and in providing technical support for regulatory applications.

Natural gas is converted to its liquid state (LNG) at export facilities called liquefaction plants. LNG is natural gas that has been cooled to the liquid state at –260°F and atmospheric pressure. Liquefying natural gas reduces its volume by more than 600 times, making it more practical to store and transport. The LNG imported to the United States comes via ocean tanker, primarily from Asia, Africa, and the Caribbean. The ships can carry LNG over long distances; they are constructed of specialized materials and equipped with sophisticated systems designed to store LNG safely. The LNG industry continues to maintain one of the safest records in all maritime transportation industry.

After a period of approximately 30 years during which only five LNG receiving terminals were operating in the United States and Puerto Rico, there are now over 60 LNG receiving terminals that have either already been approved, have entered the permitting process, or are being proposed throughout North America; a sixth LNG receiving terminal has begun operations in the Gulf of Mexico. Both onshore and offshore terminals are being pursued, and the strong demand for gas has led to numerous technological developments in all segments of this industry (liquefaction, marine transportation, and regasification). An example of this is the use of large arrays of ambient air vaporizers to regasify LNG without burning fuel or pumping large quantities of sea water.

If LNG is spilled, it vaporizes. The natural gas vapors are initially heavier than air and they form a cloud close to the ground, which is pushed downwind and eventually dissipates. If a viable ignition source is present where a vapor cloud exists at a 5%–15% concentration in air, the vapor cloud can ignite and burn. Therefore, the permitting of LNG terminals requires thermal radiation and vapor dispersion hazard distances to be quantified and demonstrated to pose no threat to people or property outside the plant.

The possibility of large releases from LNG tankers has raised the need to analyze larger spills than have been investigated previously. Models have been developed to address these scenarios; however, these models are based on the extrapolation of small-scale experimental data and/or the adaptation of light hydrocarbon spill models. The lack of experience with large LNG spills continues to challenge the engineering community to develop better fire and atmospheric dispersion models.



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