With sensor information on board LNG vessels and enrichment using the laws of physics and mathematics, companies have developed the technology to precisely ascertain the real time rate of boil-off on an LNG vessel at any instant and in any situation that the vessel finds itself. The LNG rate of boil-off is not an unknown entity as such, as it can be calculated in test conditions in a laboratory. This has however not until recently been attempted on board in a scientific manner due to its sheer complexity.
The instantaneous rate of boil-off when it is in a tank on a ship in routine operation, facing the fluctuations in ambient temperature, dynamic conditions at sea, with rolling, pitching and sloshing is a matter altogether different. When added with the complexity of cargo operations enroute, such as working of re-liquefaction plants with continuous outflow of natural gas vapour and inflow of liquid natural gas into tanks, running of gas combustion units, boil off processing for use in engines or boilers, etc., computing the boil-off in real-time becomes even more complex.
For a cargo that is carried at temperatures below -260°F, the implications of being able to calculate boil-off in real-time are enormous. To begin with monitoring the performance of the insulation system becomes possible. Measuring the impact of repairs to LNG tanks and insulation is key to knowing if the repair was effective or further repairs are to be undertaken. Selecting the right insulation for a new build LNG vessel means reducing the effective boil off and far better performance when it comes to boil off management and reduction in cargo out turn shortages at the discharge ports during the operational life of the vessel.
When this information can be mathematically modelled, it gives the capability of predictive simulation of boil-off in any expected sea state or weather condition. This will allow the crew and the operator a better estimation of voyage boil off losses in advance. Similarly knowing in advance that vessel is going to encounter conditions where there is going to be spike in the boil-off rate, allows the crew to take proactive action to reduce tank pressures well in time. Early insights and visibility allows better decision making on whether to run the re-liquefaction plants or use the boil-off LNG as a fuel.
The system is installed on over 10% of the worldwide LNG fleet. The technology to monitor boil-off being unique is a well-researched area.
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