New mid-scale standard loop to accelerate traceability in LNG custody transfer
Liquefied natural gas (LNG) is considered to be the only alternative for diesel fuel for heavy duty transport, with a better CO2 footprint and less engine noise than diesel. The transportation of LNG by ship is expected to continue to grow in volume and to become as important as pipeline transport of natural gas.
However, LNG being a liquefied mixture of hydrocarbons, stored and used at a temperature of approximately -162oC, changes in composition during transport. Thereby, the quality and all related physical and chemical properties change as well. This makes LNG metrologically much more challenging than natural gas.
To enable the broad scale use of LNG in the complete custody transfer chain, reliable measurements are needed from source to engine. The project “Metrology for custody transfer and transport fuel applications” is to develop a mid-scale loop with traceability to a primary standard loop, developed in a project prior to the current, thereby building the next step towards full traceability of large scale LNG flow metering.
Challenges in measuring LNG today
Custody transfer of LNG is based on energy measurements of the transferred LNG. The energy is determined by volume, density and the gross calorific value of the LNG. The volume of ship tanks is measured using tank level gauging. This method is currently the only established procedure to measure the LNG volume transferred.
The alternative is use of flow meters, used often as secondary standards at LNG terminals. These flow meters are commercially available, but hardly used for custody transfer purposes, due to lack of direct traceability to a LNG flow standard at this scale and the lack of an ISO standard.
The development of novel and traceable calibration standards for in-line LNG mass and volume flow, is thus an important part to support the use of flow metering technology throughout the LNG production and distribution chain.
New mid-scale standard LNG loop for commercial and research purposes
An essential component of the new mid-scale LNG flow calibration standard, is the existing LNG flow calibration primary standard for flow rates up to 25 m3/h (11250 kg/h) and measurement uncertainties (k=2) of 0.10 – 0.13%. The primary standard was developed and validated within a previous joint research project (2009 – 2013) and is placed at VSL in Rotterdam.
The new mid-scale standard loop takes the next step towards full traceability of large scale flow metering. This concerns the design, construction and validation of a mid-scale mass and volume flow calibration standard operating for flow rates up to 400 m3/h (180000 kg/h) and a target measurement uncertainty of 0.15% on mass and 0.20% on volume.
The new LNG facility will be used to validate models for extrapolating flow meter calibrations from low to high flow rates and from water to LNG, also since until today LNG flow metering is relying on calibrations with water.
Besides determining energy content and calculating the transferred LNG, lower uncertainties and improved reliability are important for field measurement results and thereby for custody transfer measurements.
A new three-year project period within the framework of the European Metrology Program for Innovation and Research (EMPIR) will demonstrate the effects of flow disturbances, the presence of multi-phase flow and the effects of insulation and inclination on the flow measurements.
Furthermore, the LNG facility will be finalized, thereby building the next step towards full traceability of large scale LNG flow metering.