21 ISSN 0040-5795, Theoretical Foundations of Chemical Engineering, 2019, Vol. 53, No. 1, pp. 21–28. © Pleiades Publishing, Ltd., 2019. Russian Text © A.M. Toikka, A.A. Samarov, M. Farzaneh-Gord, I.A. Zvereva, 2019, published in Teoreticheskie Osnovy Khimicheskoi Tekhnologii, 2019, Vol. 53, No. 1, pp. 23–30. On Calculation of Some Properties of Natural Gas Using a Limited Number of Experimental Parameters A. M. Toikka a, *, A. A. Samarov a , M. Farzaneh-Gord b , and I. A. Zvereva a a Saint Petersburg State University, St. Petersburg, 199034 Russia b Shahrood University of Technology, Shahrood, 3619995161 Iran *e-mail: a.toikka@spbu.ru Received January 31, 2018; revised July 12, 2018; accepted September 27, 2018 Abstract—Some calculation aspects of natural gas properties based on limited numbers of initial experimental parameters, namely temperature, pressure, and speed of sound, were considered. The application possibilities for a wide range of compositions, temperatures, and gas mixtures pressure, simulating natural gases of various fields using the previously proposed Farzaneh-Gord method were discussed. It has been shown, that this method, in reality, yields fairly accurate results, calculating molecular weight of natural gas and its density. We note that good calculation results of mass flow rate make it possible to recommend this method for prac- tical express calculations. Keywords: thermodynamic properties, equation of state, natural gas, density DOI: 10.1134/S0040579519010159 INTRODUCTION Determination of the thermodynamic properties of natural gas is significant to studying properties in a wide range of temperatures, pressures, and the content of the main components and impurities. Nevertheless, these problems, from a formal point of view, are not new and, the values of basic thermodynamic proper- ties can be determined by traditional methods under laboratory conditions. More complex aspects of deter- mining the basic thermodynamic parameters are related to the actual conditions of gas transportation: first of all, in gas pipelines, when significant pressure drops, their values do not simply associate the values of volumetric flows with its quantity due to nonideal- ity of gas, temperature effects, and in the course of necessary instantaneous measurements. Practical solutions are reduced to the simultaneous determina- tion of the velocity and density at gas distribution sta- tions. Measurement of gas flow by means of, for exam- ple, turbine or ultrasonic meters, does not provide a sufficiently accurate amount of gas consumption due to changes in its composition (molecular weight), density, temperature dependence, or pressure. More- over, at gas distribution stations, with sufficiently intensive use of this equipment, we must continuously check the calibration of measuring instruments, not to mention their relative fragility in actual operating con- ditions. In this regard, works continue on the search for new approaches to measure the properties of natu- ral gas, which would, first of all, increase the accuracy of determining its density, preferably based on stable, easily determined parameters and minimum of mea- surements [1].Such traditional analytical methods as gas chromatography make it possible to determine the composition of gas and liquid mixtures with high accuracy, but their inclusion in the systems of gas dis- tribution stations seems to be an expensive and irratio- nal element under high flow conditions. The development of thermodynamic simulation methods has identified new opportunities to optimize the determination of gas flow rate in the stream. Nev- ertheless, in earlier works, for example, to calculate the true flow, they also resorted to a rather incorrect assumption about the ideality of the gas mixture. More productive was the search and application to describe the behavior of natural gas by more universal equa- tions of state, allowing to characterize the set of ther- modynamic (and thermophysical) properties. Along with the classical Peng–Robinson equations [2], equations were proposed directly for the description of gases and gas mixtures. First of all, we must note the equation of state AGA8-92DC [3], adopted as an American Gas Association standard. The same equa- tion of state (EOS) was recommended by the National Standard of the Russian Federation [4]. Despite the emergence in the future of other EOS, first GERG-2008 [5], also adopted by the State Standards of the Russian Federation [6], the AGA8 EOS remains a sufficiently reliable criterion for solving problems associated with