The COSTALD method (COSTALD) was developed to accurately predict the liquid densities of LNG fluids. It is a corresponding states model and is 98.8 % accurate in predicting the densities of light hydrocarbon mixtures. The method uses two correlating parameters for each component in the mixture, a characteristic volume and a "tuned" acentric factor chosen such that the SRK equation best matches the vapor pressure data.
See "COSTALD" under "Generalized Correlation Methods" in Chapter 2, Volume 1, of the PRO/II Reference Manual for more information.
Application Guidelines
The method is valid for aromatics and light hydrocarbons up to a reduced temperature of 0.95. The PRO/II Databank contains characteristic volumes for many components. If this parameter is not available for a component, the critical volume will be used. The characteristic volume is "back-calculated" for petroleum and assay components, to provide a correct specific gravity for the pseudocomponent.