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The solution to date

Up to now, the only feasible way of measuring LNG was shore tank level measurement. On-ship tank measurement has the disadvantage that it is difficult to compensate for lilting of the ship. The low dielectric of the LNG meant the best way was to use a TDR contact measurement, since a radar cone becomes too cold and switches will not vibrate at -163°C. Flow measurement with moving turbine blades does not work, nor do pressure transmitters and mechanical meters.


The better solution

Ultrasonic flow meters didn’t work until KROHNE developed the ALTOSONIC V LNG. This difference lies in the way we have isolated the transducers to eliminate cross-talk and related noise, and in the way the measuring tube is formed, including the transducer windows. A new algorithm was elaborated and incorporated into the converter.


Limitations of tank level measurements

Tank level measurement is dependent of the quality of the strapping tables and the ability to measure the temperature adequately throughout the tank. The measurement is a combination of the accuracy of the measurement before filling, after filling and the difference in filling level. The overall inaccuracy of a level measurement can drop by 0.31% and 1 % even for a quoted ± 1 - 2 mm laboratory accuracy.


Continuous measurement with instantaneous temperature compensation

The ALTOSONIC V LNG will give on-site custody-transfer accuracy of 0.2%. And being an ultrasonic measurement, it stays accurate and is not subject to period drift. It can also be used for on-ship measurements directly on the LNG FPSO. Moreover, in the rare event of flashing, it is impossible to become damaged by the occurrence of gas.