A New Apparatus for the Accurate Measurement of LNG Densities

For the accurate measurement of the densities of liquefied natural gas (LNG) a special densimeter has been designed in detail. The new densimeter will cover the range from 10 kg x m-3 to 1000 kg x m-3, thus enabling density measurements in the homogeneous liquid region, along the saturated liquid line (incl. vapour pressures) and in the homogenous gas region. The apparatus is designed for measurements in a temperature range from 90 K to 293 K at pressures up to 12 MPa. The achievable experimental uncertainty is estimated to be 0.02 %. The densimeter is based on the Archimedes (buoyancy) principle and is a single-sinker system incorporating a magnetic suspension coupling. The density is obtained directly, without the need for calibration fluids. The setup of the new densimeter will be carried out as part of the European Metrology Research Programme (EMRP) in combination with a project of the European Gas Research Group (GERG).