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Maximize LNG carrier efficiency through integrated optimization

07.01.2014  |  Guillemin, P.,  Eniram, Helsinki, Finland

Officers and engineers aboard an LNG carrier are busy. They require real-time, user-friendly data derived from the vessel’s systems, as well as accurate individual metrics.

Keywords: [LNG] [marine] [data monitoring]

When installing a data collection platform onboard new liquefied natural gas (LNG) carriers, the first step is to gather as much knowledge as possible about onboard operations. The results of this data collection help determine vessel efficiency, which, in turn, assists owners in maximizing ship efficiency and operations.

Today’s LNG carriers are amazing feats of engineering (Fig. 1). The ship cargo is extremely dangerous because of its highly flammable properties. Furthermore, the dual-fuel/tri-fuel engines used, as well as the occasional presence of reliquefication plants, make these vessels among the most complex floating engineering projects in the world.

 
  Fig. 1.  Today’s LNG carriers represent considerable feats
  of engineering. Photo courtesy of Eniram.



The transport of LNG can be compared to running with a full soft drink can in a backpack. When the can is shaken, some of its contents will vaporize as CO2, which increases the can’s internal pressure. A similar process occurs in a tank filled with LNG, although the somewhat inert gas is replaced with a variety of different natural gases [i.e., boiloff gas (BOG)]. The increasing pressure must be relieved by releasing gas from the tank.

LNG tank design

LNG tanks are extremely well insulated to limit the BOG that naturally occurs after a cargo is loaded. Typically, the cargo is loaded at an approximate temperature of −170°C. However, despite the insulation, a small percentage of the LNG cargo is converted to gas during each day of a sea voyage. The size of the percentage will depend on the efficiency of the insulation and the weather patterns en route.

Improvements in insulation and clever engineering have increased storage effectiveness. A small number of LNG vessels are now equipped with reliquefication plants that are able to reliquefy the excess BOG and return it to the tanks, making these ships more environmentally efficient. For the majority of vessels not equipped with reliquefication plants, the excess gas can be used for running vessel engines or boilers. In practice, however, LNG carrier operations are more complicated than this description suggests.

Transport challenges

Rough seas are part of the scenario. These types of sea states can behave exactly like the example of a soft drink can in a backpack, jostling the cargo about and increasing the pressure in the tanks. On one of the author’s recent LNG carrier trips, the ship encountered not one but two typhoons. Typhoons Francisco and Lekima kept the officers and crew on alert, but the ship was able to sail through the storms without any problems. Some of the excess gas was used in the engines; the rest was reliquefied. In this type of situation, older LNG ships may have been forced to burn the fuel without using it.

Complex vessels should be matched with sophisticated, yet easily understood, data-gathering solutions. The first step of the process is data integration. Data is collected from the various automated systems already installed onboard, as well as from proprietary sensors. Readings are also received from other equipment located on the bridge or in the cargo control room.

Monitoring carrier operation

This deep integration is necessary to obtain the highest level of accuracy regarding the ship’s physical behavior. Essentially, all of the information being gathered must be validated. Sensors are attempting to analyze real phenomena, and trusting such devices should be done with caution before a proper calibration is performed.

This data can be used to observe how offset a speed log is (Fig. 2), or to monitor the reading errors of an anemometer, for example. These actions are essential to understanding the actual performance of a carrier. They also aid in the modeling of ship energy usage and in mapping the breakdown of where energy is consumed. On an LNG vessel, numerous systems are the source of hundreds of variables. The initial target of a data collection platform is to make sense of this information, and to present it in a normalized way.

 
  Fig. 2.  Speed log device errors can be assessed quickly.
  A clear offset is seen on the vertical axis, which represents
  the difference between speed through water and speed
  over ground.

After the integration of all sensors and variables, 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 flowmeters, navigation equipment, engines and reliquefication plant usage. The speed profile, for example, requires automatic updates based on the latest sea 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.

Measurements performed onboard will also be taken into account to better reflect the forecast measurements provided from onshore. Forecast and data share one simple fact: taken alone, the flow coming out of a device or data source is only as reliable as the device or the forecast itself. Ship-wide integration of a platform can help put into context all of that information, as in the speed log example.

The third step of the process is the actual data crunching to provide the optimum guidelines typically seen on the display. Onboard and onshore dedicated calculation servers are provided to improve the accuracy of the optimums.

Successful integration

During the installation of the system described earlier, the weather threatened to delay the carrier’s arrival to the next port. However, the integrated system enabled the rapid approximation of an estimated time of arrival, taking into account all of the effects of the rough weather and its energy cost. Engineers could then use the prediction regarding the required energy necessary to reach the next port as close to the original schedule as possible.

Officers and engineers aboard an LNG carrier are extremely busy. They require real-time, user-friendly data derived from the vessel’s systems, as well as accurate individual metrics. Maximizing fuel efficiency should not trump other tactical, on-the-spot decisions needed to ensure that the ship continues to sail as safely as possible with its strategic cargo. HP

The author
 
  Pierre Guillemin leads the development team for Eniram’s onshore and onboard platforms. As an enthusiast builder, he has a broad experience in converting ideas into usable, concrete technologies. Prior to Eniram, Mr. Guillemin spent most of his career in startup companies in the data crunching field, from search engine development to crowdsourcing services. He holds an MEng degree in computer science from ESIEA Paris in France. 


 



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