Assessment of thermodynamic models for the design, analysis and optimisation of gas liquefaction systems

Abstract

Natural gas liquefaction systems are based on refrigeration cycles -they consist of the same operations such as heat exchange, compression and expansion, but they have different layouts, components and working fluids. The design of these systems requires a preliminary simulation and evaluation of their performance. However, the thermodynamic models used for this purpose are characterized by different mathematical formulations, ranges of application and levels of accuracy. This may lead to inconsistent results when estimating hydrocarbon properties and assessing the efficiency of a given process. This paper presents a thorough comparison of six equations of state widely used in the academia and industry, including the GERG-2008 model, which has recently been adopted as an ISO standard for natural gases. These models are used to (i) estimate the thermophysical properties of a Danish natural gas, (ii) simulate, and (iii) optimize liquefaction systems. Three case studies are considered: a cascade layout with three pure refrigerants, a single mixed-refrigerant unit, and a turbine-based configuration. Significant deviations are found between all property models, and in all case studies. The main discrepancies are related to the prediction of the energy flows (up to 7 %) and to the heat exchanger conductances (up to 11 %), and they are not systematic errors. The results illustrate the superiority of using the GERG-2008 model for designing gas processes in real applications, with the aim of reducing their energy use. They demonstrate as well that particular caution should be exercised when extrapolating the results of the conventional thermodynamic models to the actual conception of the gas liquefaction chain.

Physicochemical Properties for the Reaction Systems: Levulinic Acid, Its Esters, and γ-Valerolactone

“…Hysys Redlich−Kwong−Soave (HYSSRK) implements the Soave−Redlich−Kwong (SRK) cubic equation-of-state property package from Aspen HYSYS. 42 It is used for hydrocarbon and high-hydrogen pressure systems. The form of the equation of state is…”

“…BWRS is a virial equation of state based on the Benedict− Webb−Rubin−Starling equation of state with optional purecomponent and binary interaction parameters. 42 It was advocated for the prediction of properties of hydrocarbon mixtures. The form of the equation of state is:…”

Liquefaction of Natural Gas in Offshore Installations: Effects of Irreversibilities and Composition of Natural Gas

“…There is also the possibility to use both effects, like in the Claude cycle. For land systems, weight, size and complexity are not great concerns, and various researchers presented comparison among different system [4], or optimization of systems [5,6]. A comprehensive review for cryogenic cycles can be found in [7].…”