(578e) New Thermophysical Properties Measurements of Complex Mixtures Relevant to Liquefied Natural Gas (LNG) Processing

Knowledge and understanding of the thermodynamic and thermophysical properties such as viscosity, surface tension, heat capacity and density have always been essential to LNG’s (Liquefied Natural Gas) evolution because of the tremendous technical challenges present at all stages in the supply chain from production to liquefaction to transport. Each stage is designed using predictions of the mixture’s thermophysical properties as a function of temperature, pressure and composition. Unfortunately, current available models lead to equipment over designs of 15% or more. To achieve better designs that work more effectively and/or over a wider range of conditions, new fundamental property data are essential, both to resolve discrepancies in our current predictive capabilities and to extend them to the higher-pressure conditions characteristic of many new gas fields. Due to the insufficient current available experimental data, new innovative techniques are required to measure different thermophysical properties at high pressures and wide range of temperatures including near the mixture’s critical points (where gas and liquid become indistinguishable and the existing predictive fluid property models used breakdown).

In this work, we present a wide range of experimental measurements on different binaries and ternaries mixtures relevant to LNG processing’s, with particular focus on viscosity, surface tension, heat capacity and density. For this purpose, customized and specialized high-pressure wide-temperature range apparatus were designed and constructed. The viscosity was measured using a vibrating wire viscometer apparatus consisting of centreless ground tungsten rod while mixtures densities were obtained by means of a single-Titanium sinker magnetic-suspension densimeter and an Isochoric cell apparatus. The surface tension was measured using a capillary rise method while the heat capacity was measured using a differential scanning calorimetry (DSC), that was also used to obtain the enthalpy of fusion and melting temperatures. Mixtures compositions were determined by knowing the mass of each component used to prepare the mixture. This was verified by means of sampling using a Gas Chromatography. Measurements were then made of (CH₄ + C₃H₈), (CH₄ + C₃H₈ + CO₂) and (CH₄ + C₃H₈ + C₇H₁₆) over the temperature range (203 to 423) K, pressures up to 35 MPa and different compositions, with a combined overall standard uncertainty of 0.5% for density, 3% for viscosity, 5% for heat capacity and 5% for surface tension. The extensive experimental data gathered in this work were compared with a variety of different advanced models frequently used for predicting thermophysical properties of LNG mixtures.

The current work presents a step forward towards accurate design of LNG processing’s by providing essential data on complex mixtures that wasn’t studied before. This work enabled new models, implemented in process simulation software, to predict reliably the fluid properties needed for equipment and process design. The current work also aided the community of scientists working to advance theoretical descriptions of fluid properties by allowing to identify deficiencies in theoretical descriptions and calculations.