Selection of a Thermodynamic System

The choice of thermodynamic system can have significant impact on the results. The primary source of this error is the poor representation of K-values, especially for heavier crudes. The following options are typically available for hydrocarbon-rich streams (like crude)  

Equations of state generally rely on pure component properties such as critical temperature, critical pressure and acentric factor. In addition, an interaction parameter is required to account for mixtures of components. Correlation-based approaches rely on measured vapor pressures and observed data to provide empirical correlations for various hypothetical or pseudocomponents. 

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The previous sections in this chapter address the creation of pseudocomponents by cutting an assay curve into a set of discrete components based on boiling-point ranges. We also briefly alluded to physical properties and process thermodynamics selection in the earlier workshops of this chapter. In this section, we consider, in detail, the problem of how to represent these components in the process modeling software. There are two major concerns in this area physical properties of pseudocomponents and selection of a thermodynamic system that can deal with these hydrocarbon pseudocomponents in the context of refinery modeling. 

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