THE USE OF MATLAB IN THE DETERMINATION OF THERMODYNAMIC PROPERTIES OF NATURAL GAS

Abstract

During the preliminary phases of typical operations in the petroleum industry, particularly those involving distribution networks and/or natural gas transmission projects, when complete information is not available, it is sometimes necessary to estimate some thermodynamic properties of natural gas. The behavior of natural gas is affected directly by its chemical composition. It comprises a mixture of volatile hydrocarbons, nitrogen, oxygen, carbon dioxide, and traces of other components. This knowledge is crucial to engineers involved in the areas of equipment design, processing and transportation of such fluids. The design of these systems uses conventional flow equations for both stationary and transient systems, which also include various natural gas fluid properties such as density, gas constant, specific heat, critical temperature and pressure, compressibility factor, and dynamic viscosity, among others. In view of this, a proposition is given to determine the main properties of natural gas from its average chemical composition and related operational conditions (pressure and temperature). This proposal, developed in Matlab, allows the determination of some of the key properties of natural gas, giving users the option to choose the most representative equation of state among the available models, namely, Peng-Robinson, Patel-Teja-Valderrama, Shell Oil Company, Soave-Redlich-Kwong, and van-der-Waals, to determine the compressibility factor of the samples. The results of a particular simulation were compared with actual data from the distribution network COMPAGAS, which is the company responsible for the distribution of piped natural gas in the state of Paraná (Brazil), demonstrating a good convergence between the values obtained and encouraging their use in future.