Gas tanker loading in port, Japan
These specially designed ships are capable of carrying liquefied natural gas at temperatures of -160 degrees C. Photo: Thinkstock

Preventing LNG accidents

Eskil Aursand is working to make marine production and shipping of liquefied natural gas (LNG) safer. His efforts were recently recognized with the award of a Fulbright Scholarship.

Natural gas is very important for the Norwegian economy. In fact it recently surpassed oil, making it Norway’s largest export in terms of revenue.

While natural gas is a fossil fuel, it is the most environmentally friendly of them all, and will likely be a part of the world economy for decades. But shipping it to far-away markets requires it to be liquefied by cooling it to -160 C, so that it can be loaded in large carrier ships.

The mystery is the motivation

There is a risk of spilling LNG when it is loaded or offloaded, or during shipping. These spills have been shown to cause a special kind of explosive and dangerous accident called Rapid Phase Transition (RPT). However, spills don’t always lead to an explosion and nobody can clearly predict if and when an explosion will happen. This mystery is the core motivation for Aursand’s PhD project at the Department of Energy and Process Engineering.  His PhD project is part of the SINTEF project called Predict RPT.

The scientific literature has identified film boiling as a key concept in explaining the triggering of RPT explosions. Film boiling occurs when there is a big temperature difference between a substance (like extremely cold LNG) and its warmer surroundings. A thin film of vapour forms on the surface of the LNG, which initially stabilizes the LNG boiling process, but if the film boiling process suddenly breaks down, it can trigger an explosion.

Aursand says this is a complex and multidisciplinary physics problem that involves transient multi-phase fluid mechanics, thermodynamics, high-gradient heat transfer and strong vaporization effects.

“The main objective of my work is to reveal the conditions of film-boiling stability for a cryogenic droplet submerged in water. If this is achieved, one can more easily predict the explosions and one may be able to engineer for accident avoidance,” he said.

Aursand mainly works in fluid mechanics, but will also draw on thermodynamics and kinetic gas theory. His goal is to develop appropriate and consistent model simplifications to reduce the mathematical and computational complexity of the problem while preserving the important features of its physics.

You can see an example of what happens when film boiling goes wrong in this YouTube video.

You can also read more about his work on the NTNU TechZone blog.