Grayson-Streed correlation

Coefficients for use in the Grayson-Streed correlation of the liquid fugacity coefficient ... 

Data for a 4% H2 in hexane system are given in Figure 8. The phase envelope represented by the solid lines is predicted from the Grayson-Streed correlation. The dashed line represents the experimental phase envelope. Again notice the minimum in the bubble-point curve, and that as many as three bubble-points. A,... 

We can now use the Redlich-Kwong equation of state [6] and a liquid-phase correlation (or an equation of state) to obtain expressions for and as functions of temperature, pressure and component critical properties. This is the approach taken by the very popular Chao-Seader [6] and Grayson-Streed [6] methods. The only factor that remains undefined is the liquid activity coefficient. The Chao-Seader and Grayson-Streed methods use the regular solution theory to obtain an expression for as follows ... 

We also select a thermodynamic system to model vapor-hquid equilibrium for these pseudocomponents. For crude fractionation columns, an euqation-of-state (EOS) approach yields good results. However, an EOS approach does not predict liquid densities accurately and tends to give poor equilibrium predictions of heavy pseudocomponents. We can improve the EOS density predictions with more accurate density correlations such as COSTALD. If the feed and products contain significant amounts of heavy products, it may be better to rely on empirical thermodynamic models such as Grayson-Streed or BK-10. 

The FCC system is mostly hypothetical and light hydrocarbons. Consequently, the Peng-Robinson equation of state is sufficient. We discuss the implications of the process thermodynamics in Chapter 1. In the case of the FCC model, equation of state or hydrocarbon correlation methods (Grayson-Streed, etc.) can sufficiently model the processs. 

The last step before building the reformer flowsheet is to verify the interaction parameters (Figure 5.45). If we had chosen a correlation-based approach (Grayson-Streed, etc.), we do not have to examine the interaction parameters. Since we choose an equation of state approach, we must make sure that the binary interaction parameters for the equation-of state are meaningful. In Aspen HYSYS, the interaction parameters for defined components (such as methane. 

Because of its simplicity and generality, the original correlation and its modifications by Cavett (17) and Grayson and Streed (18) have found wide applications in petroleum and gas processing industries. However, articles, too many to enumerate, have pointed out the weaknesses in the correlation. Some of our observations are listed below ... 

---