A NEW COMBINING RULE FOR MIXTURE EQUATIONS OF STATE - HIGHER-ORDER COMPOSITION DEPENDENCIES REDUCE TO QUADRATIC COMPOSITION DEPENDENCE - APPLICATION TO NATURAL-GAS MIXTURES

A combining rule that reduces third and higher order virial coefficien t type mixing rules to quadratic is used to simplify the form of a ver y accurate equation of state and is applied to various natural gas com ponent binary mixtures. The accuracy obtained is comparable to that re ported for the original equation of state and yet it reduces significa ntly the number of parameters necessary to describe the mixture. The s ystems tested are binary mixtures of the following gases: CH4, N-2, CO 2, C2H6, H-2, C3H8 and CO. This study proves that the representation o f the third virial coefficient as quadratic in the mole fractions is h ighly accurate for these binary systems. This representation, therefor e should be accurate for systems which are non-associating and non-hig hly polar fluids. Published by Elsevier Science Ltd.