Grayson -Streed equation

Case 3 T > Tci In this case, the liquid phase does not exist at any pressure. Lewis and Kay40 suggested the extrapolation of a plot of log f tPi or log P( vs. /Tr while Souders et al.61 used experimental K values and heats of solution data in their extrapolation procedure. Adler et al.2 suggested the use of the Chao-Seader (or Grayson-Streed) equations or back-calculation from experimental vapor-liquid equilibrium data. 

The first three methods use one set of equations for the vapor phase and another for the liquid, in a similar technique. These methods are identified as Chao-Seader (2), Grayson-Streed (3), and Lee-Erbar-Edmister (4). The other three methods employ the same equations for both vapor and liquid phases. They are identified as Soave-Redlich-Kwong (5), Peng-Robinson (6), and Lee-Kesler-Ploecker (7, 12). At this writing, the present... 

The Chao-Seader and the Grayson-Streed methods are very similar in that they both use the same mathematical models for each phase. For the vapor, the Redlich-Kwong equation of state is used. This two-parameter generalized pressure-volume-temperature (P-V-T) expression is very convenient because only the critical constants of the mixture components are required for applications. For the liquid phase, both methods used the regular solution theory of Scatchard and Hildebrand (26) for the activity coefficient plus an empirical relationship for the reference liquid fugacity coefficient. Chao-Seader and Grayson-Streed derived different constants for these two liquid equations, however. 

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. 

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 ... 

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. 

Grayson and Streed (1963) extended the C-S equation for use with hydrogen-rich mixtures and for high-pressure and high-temperature systems. It can be used up to 200 bar and 4700 K. 

These coefficients obtained by Grayson and Streed are presented in Table 14-11. When Eq. (14-112) is applied to methane and hydrogen, co is set equal to zero. The quantity 0(1) is calculated by use of Eq. (14-114). In this case, however, the limits of this equation were altered in order to fit the high-temperature data. In particular, for values of Tr > 1.0, the values of [Pg.539]

Equation (4-28) has been ignored but, since 1960, (4-29) has received considerable attention. Applications of (4-29) to important industrial systems are presented by Chao and Sender Grayson and Streed Prausnitz et al. Lee, Erbar, and Edmister and Robinson and Chao. An important modification of (4-29) not presented here is developed by Prausnitz and Chueh. ... 

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