Correlation between gas molecular weight, heating value and sonic speed under variable compositions of natural gas

A simulation study of likely uncertainties in molecular weight and heating value of the gas mixture as predicted from measured or calculated sonic spe ed. The sonic speed, molecular weight and heating value of natural gas were studied as a function of random fluctuation of the gas fractions. A method of sonic speed prediction was developed and used for over 50,000 computer- simulated variants of component concentrations in four- and five-component mixtures. Comparison of the obtained and the reference data on binary (meth ane-ethane) and multicomponent (Gulf Coast) gas mixtures under standard pre ssure and moderate temperatures indicates predictability of sonic speed on the basis of the binary virial coefficients, sonic speeds and heat capaciti es of the pure components. The results for two natural gas mixtures - with and without nonflammable components - are reported. Bivariate distribution and covariance elliptic zone plots are presented for three pairs of depende nces of practical interest: molecular weight-sonic speed, heating value-son ic speed and heating value-molecular weight. The correlation coefficients, covariance, and regression equations are given for each pair of variance an d mixture. (C) 1999 Elsevier Science Ltd. All rights reserved.