LNG densities for custody transfer
摘要
Work has been carried out over the past ten years at the National Bureau of Standards to provide alternate methods for the accurate determination of the density of liquefied natural gas (LNG) that would serve as a basis for equitable custody transfer. A magnetic suspension densimeter was used to obtain density data for LNG components and their mixtures with a total uncertainty in density of less than 0.1%. These data were used to optimize and test mathematical models for LNG density calculations. Four mathematical models for the calculation of LNG densities have been optimized, tested, and compared. These models are an extended corresponding states model, a cell model, a hard sphere model, and an empirical model due to Klosek and McKinley. A density reference system (DRS) was constructed to determine the uncertainty of measurements made by several different types of densimeters proposed for use in the commercial trade of LNG. Several commercial densimeters have been tested and a transfer standard program implemented as a means of producing a calibration service for commercially built densimeters. The total uncertainty of the DRS is estimated to be + or - 0.076%. A portable reference densimeter (PRD) has been developed specifically for calibrating LNGmore » densimeters ''in place.'' The measurements of density using the two systems, DRS and PRD, are statistically indistinguishable.« less