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Improving LNG measurement and quality control through inline composition analysis 

The challenge with sampling systems  

Sampling is the most critical point of the LNG measurement chain. During the sampling process, each measurement must be taken without a change in composition. This is by far the most complicated phase of LNG’s measurement process and most issues related to the determination of energy unloaded are a result of the sampling system. Since LNG exists in a state close to its boiling point ( ≈ -164 ºC) and there is a large variation among boiling points of its components, any small heat input or pressure variation in the LNG sample probe or transfer line may produce LNG partial evaporation. If this happens, the collected LNG sample that goes to the vaporizer may not be a true representation of LNG unloaded. For this reason, extreme precautions should be taken to ensure the collected LNG sample is representative of the transferred LNG. 

Benefits of using Raman Spectroscopy for inline analysis 

Retrieving readings directly from the LNG stream without any type of vaporizers, sampling lines, valves, heaters or regulators results in a more stable, reliable and accurate measurement of the LNG composition and calorific value. 

Raman spectroscopy uses a laser to produce light of visible or near-infrared wavelengths. When various molecules pass through this light, the light’s energy causes molecular bonds, such as the bond between two hydrogen atoms, to vibrate. This vibration creates a scattering effect, casting the laser light into different wavelengths. 

What started as a single laser-generated color now becomes its own rainbow spectrum because each molecule in the sample produces a signal at a unique wavelength. A Raman analyzer looks for these specific wavelengths and intensities to create a chemical profile of the sample. When this concept is applied to LNG analysis, a probe is inserted into the pipe to analyze the flowing liquid or gas. 

The probe is inserted into the flowing LNG stream. Laser light is emitted from the end of the probe into the LNG sample, and the scattered Raman light is collected back through the same probe tip. The collected Raman light travels through a second fiber optic cable, then enters a detector in the analyzer. From here, the resulting individual wavelengths are identified and quantified, giving an outcome and accurate measurement of the composition and calorific value of LNG.

Learn more about the difference between Raman Spectroscopy vs Gas Chromatography (GC) in LNG transport 

Improve accuracy and reliability with LNG composition analyzers  

Whether you are working in LNG liquefaction and export terminals, satellite plants, LNG bunkering barges or LNG import terminals, your processes can benefit from an inline LNG composition analyzer.  This technology can improve your measurement accuracy and reliability, in addition to lower lifetime costs and maintenance for LNG process control and custody transfer applications. 

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