Maximazing LNG Ship Efficiency through Integrated Optimization

Today’s LNG carriers are amazing engineering feats. Not only is their cargo extremely dangerous because of its highly flammable properties but their dual/tri-fuel engines and reliquification plants (in some cases) make them among the most complex pieces of floating engineering marvels in the world.

Pierre Guillemin, Chief Systems Architect at Eniram, gives us a taste in the following text of an experience onboard a modern LNG tanker, from a couple of months ago, while explaining how these complex sea giants actually work.

Liquefied gas is no joke. Imagine for a moment, that you’re running or cycling with a can of soda in a backpack. When you shake the soda can, some of its content will vaporize as CO2 which increases the can’s internal pressure. A similar process occurs in a tank filled with LNG though the somewhat inert gas is replaced with a variety of different natural gases. This is called boil-off. The increasing pressure must be relieved by releasing gas from tank.

 

LNG tanks are extremely well insulated to limit the boil-off that naturally occurs after the cargo is loaded; typically the cargo is loaded at circa -170C. Yet despite the insulated tanks a small percentage of cargo is converted to gas each day during a sea voyage. That percentage will depend on how efficient the insulation is and how the weather plays out enroute.

 

However, improvements in insulation and clever engineering have increased storage effectiveness. A small number of LNG vessels are now equipped with reliquification plants that are able to take the excess boil-off gas, reliquify it, and return it to the tanks, making these ships more environmentally efficient. For the majority of vessels not equipped with reliquification plants, the excess gas can be used for running the vessels engines or boilers. Of course, in practice things get a little bit more complicated.

 

Rough seas are part of the game. These type of sea states can act like that can of soda in your backpack, jostling the cargo about, increasing the pressure in the tanks. As luck would have it on our trip, we encountered not one but two typhoons. Typhoon Francisco and Lekima kept the officers and crew on their toes but the ship was able to ride out the storms without any problems. Some of the excess gas was used in the engines. The rest got reliquified. Older LNG ships would have had a harder time in this type of situation, and would possibly just burn the fuel without utilizing it.

 

Complex vessels need to be matched with sophisticated, yet easily-understood data-gathering solutions. The first step of the process is data integration. We collect data from all the various automated systems already installed onboard as well as from our own attitude sensors. In addition, we receive readings from other equipment located on the bridge or in the cargo control room.

 

This deep integration is necessary in order to obtain the highest level of accuracy regarding the ship’s physical behavior. For example, we can typically see how offset a speed log is, or the reading errors of an anemometer. This is essential in order to truly understand the actual performance of a ship.

 

This also helps model its energy usage and the breakdown of where the energy is consumed. On an LNG vessel, there are countless systems, source of several hundreds of variables being use.

 

Once all the sensors and variables are integrated, both the onboard and onshore systems are automatically synchronized. This is the second step of the process.

 

Modeling takes into account a wide variety of variables, such as fuel flow meters, navigation equipment, engines and reliquification plant usage. The speed profile, for example, needs automatic updates based on the latest current and wind data available onshore. No additional work is required from the navigation officer to import the data, and yet it is achievable in real-time.

 

The third step of the process is the actual data-crunching in order to provide the optimum guidelines you would typically see on the display.

 

We use onboard and onshore dedicated calculation servers to improve the accuracy of the optimums we provide. For example, during our installation, the weather certainly didn’t help us get to the next port any sooner.

 

However, the integrated system enabled us to quickly and easily devise a very good approximation of our ETA, taking into account all the effects of the rough weather and its energy cost.

 

Engineers could then very well use our prediction regarding the required energy necessary to reach port as close as possible to the original schedule.

 

Officers and engineers aboard a LNG ship are already extremely busy people. They need to get their hands on real-time, user-friendly data derived from the vessel’s systems as well as accurate individual metrics. Maximizing fuel efficiency shouldn’t take over other tactical in-the-moment decisions, in order to keep sailing as safely as possible with their strategic cargo.

[mappress]
Eniram, June 19, 2014