Mathematical Model for Determination of Liquefied Natural Gas Density by Its Parameters and Composition

Abstract

Liquefied natural gas (LNG) production and export are becoming one of the most strategically important segments in the Russian gas industry, and therefore the maintenance of LNG production and transporting infrastructure is deemed a critical problem. The commercial accounting of LNG is carried out in the tankers of LNG marine vessels using the static method. The shifting to the indirect dynamic method used in commercial accounting for other liquid hydrocarbons is hindered by the lack of a change measurement chain for flow and density transmitters. The regulatory documents recommend defining the density through calculations using the modified Klosek-McKinley method applied to the LNG composition, which leads to certain difficulties. This article offers a mathematical model for the calculation of density using the compositional analysis and the state parameters of LNG. The adequacy of the model was tested on five LNG mixtures with different compositions (from 72% up to 90% methane), temperatures (from 110 K up to 130 ), and pressure (from 0.08 MPa up to 0.4 MPa). In all cases, the calculation error did not exceed 0.15%. Using this model will help to shift to the dynamic method of LNG commercial accounting. It can also be used for forecasting density values based on changing LNG parameters, which can be useful during overseas transporting and reservoir filling in order to increase the safety of these processes.