Grayson thermodynamics

Six alternate methods for predicting the thermodynamic properties are included. These are known by the names of the authors of the methods, which are Chao-Seader (2), Grayson-Streed (3), Lee-Erbar-Edmister (4), Soave-Redlich-Kwong (5), Peng-Robinson (6) and Lee-Kesler-Ploecker (7, 12). 

Example 6 ReboUed Stripper Compute stage temperatures and interstage vapor and liquid flow rates and compositions and reboiler heat duty for the reboiled stripper shown in Fig. 13-48. Thermodynamic properties may be estimated by using the Grayson-Streed modification of the Chao-Seader method. 

A first issue is the thermodynamic modelling. For the high-pressure part including the stabiliser, an equation-of-state model is appropriate, as for example Peng-Robinson or Soave-Redlich-Kwong. A specific model for hydrocarbons, as Chao-Seader or Grayson-Streed, may be used equally for the low-pressure part. 

Thermodynamic properties (Chapters 4, 5) Soave-Redlich-Kwong Chao-Seader/Grayson-Streed van Laar Wilson UNIQUAC UNIFAC... 

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. 

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