The accurate and traceable determination of LNG compositions is crucial for the custody transfer as it allows for the accurate calculation of the physical properties as well as the methane number – both used in transport and trade. For natural gas, the most widely used method for measuring the composition is using a calibrated gas chromatograph (GC), but in the case of LNG sampling from the liquid and transferring it into a homogenous gaseous sample is a demanding and challenging extra step in the analysis. An alternative approach envisaged for on-line measuring the composition of the LNG pipeline stream is Raman spectroscopy, but this approach is comparably new and still in the testing phase.
In this work, the emphasis is on the development and validation of an LNG sampling and composition reference standard, consisting of a sampler, a vaporizer and a GC. It has been demonstrated and validated by comparing results obtained by GC (from the reference standard) and by a Raman system. The Raman system was calibrated by an independent party (using a liquefier and gas compositions in the same range as used by VSL) prior and after using it measuring real LNG sample (from Maasvlakte LNG flow meter calibration facility or from industry). The reference standard will be further tested in near future by comparing the measurement results obtained by gas chromatography following two different methods. One of the methods using the familiar approach of feeding each composition from the set of certified gas mixtures into a GC, whereas, using the other method, each composition from the set was first liquefied and then using the reference standard sampled & vaporised and fed into the same GC.
The novel LNG sampling and composition reference standard will become available to industry, as a new VSL service to test and validate their LNG sampling and composition measurement systems using industrial samples of LNG as well as LNG from the Maasvlakte LNG calibration facility. Details on the development and validation results will be shown.
Dr. Jianrong Li is working at the Van Swinden Laboratory (VSL), the Dutch Metrology Institute, as scientist in the R&D Department. Her work focuses on metrology and gas analysis in the fields of Energy and Environment. Jianrong is project coordinator of “16ENG05 – Metrology for biomethane” (under EMPIR programme) and work package and/or task leader of several other research projects under the European Metrology Research Programme (EMRP), such as Biogas, LNG and KEY-VOCs. Currently she has been working on the project ENG60 LNG II “Metrological support for LNG custody transfer and transport fuel applications”. Within this project, she is leading the task “design, build and validate LNG composition reference standard”.