Evaluation of prediction models for the physical parameters in natural gas liquefaction processes

Abstract

The natural gas liquefaction process is a complicated and dynamic thermal system. Operation conditions change during the process of compression, throttling and heat transfer, which inevitably leads to changes of the thermodynamic property parameters and the phase state of the natural gas and refrigerants. Performing a simulation of the liquefaction process is one of the main methods to improve the economic efficiency of the process and to reduce the production cost; such a simulation can be conducted using a process simulation software package, such as Aspen HYSYS, Aspen Plus, SIMSCI PRO-II and Honeywell UniSim Design. Accurate prediction of the thermodynamic properties of natural gas and refrigerants with the change of working conditions, such as density, specific heat capacity, enthalpy, and entropy, is of significant importance for the simulation of natural gas liquefaction processes. There are many types of property methods embedded in simulation software. Because each property method achieves good performance in a certain range of working conditions, it is crucial to choose the proper method to conduct the simulation. The Soave–Redlich–Kwong equation, the Peng–Robinson equation and the Lee–Kesler–Plocker equation are the main calculation models for physical parameters in natural gas liquefaction processes. According to a literature review, the GERG-2008 equation shows high precision in calculating the thermodynamic properties and phase equilibrium of natural gas and similar mixtures in a wide range of temperature and pressure. Based on accurate experimental data, a comprehensive comparison and analysis among these equations is conducted in this paper. The GERG-2008 equation is recommended as the basis for the calculation of the physical parameters in natural gas liquefaction processes.