Chao-Seader method

Calculations were made with the Grayson-Streed modification of the Chao-Seader method for K values and the Lee-Kesler method for enthalpy departures. Initial estimates for stage temperatures and flow rates were as follows, where numbers in parentheses are consistent with specifications ... 

The module FLASH simulates the reformer flash separator by using a modified Chao-Seader method. The necessary constants for the Chao-Seader correlation have been developed for the lumped components. The output from this module determines the liquid yield and the composition of recycle gas. 

Figure 2.40 (a) Selection physical property method (b) Chao-Seader method chosen. 

The Grayson-Streed method was developed for hydrogen-petroleum systems at high temperatures and pressures, i.e., hydrofining conditions. Thus the constants, including some critical temperatures and pressures, differ slightly from those recommended in the Chao-Seader method. 

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 number of other equations of state have been proposed. Some of these are presented in Table 14-9. Lee et al.38 proposed an equation of state in which a procedure similar to the Chao-Seader method (described below) was used for the calculation of K values. Lee et al. state that the K values obtained by this method are more accurate than those given by the Chao-Seader method,12 particularly at low temperatures. 

A number of methods are presented for the prediction of K values. First, methods are presented for the calculation of K values for mixtures which form ideal solutions in both the vapor and liquid phases. Then the convergence-pressure method, the Chao-Seader, and the Grayson-Streed modification of the Chao-Seader method are presented. 

The Chao-Seader method uses the Redlich-Kwong equation of state for the calculation of Hildebrand s equation for the calculation of the liquid activity coefficient yf, and an extension of Pitzer s modified form of the principle of corresponding states for the calculation of the liquid fugacity ratio [. 

The Grayson-Streed Modification of the Chao-Seader Method for Calculation of K Values25... 

Note that the RKJZ method not only predicts qualitatively the approach to mixture critical conditions it is also quantitatively superior to the Teja and Rawlinson procedure in this instance. The ability of the RKJZ method to sense the approach to mixture critical conditions has been a great advantage in its application, by comparison with the Chao-Seader method, which has a stated limitation of pressure less than 0.8 times the true critical pressure. 

Scatchard-Hildebrand Equation, Chao-Seader method Solubility parameters and partial molar volumes are referred to 25 °C, suitable for hydrocarbon systems Chao, K.C., and Seader, J.D., AIChE. J. 7 (1961) 4, 598. 

For companies using the Chao-Seader method, where 5 is already available in computer storage, transition to Soave is certainly advantageous. 

Separate treatment of the two phases, mainly the Chao-Seader method 3.Simultaneous description of both phases with an equation of state. 

Within the limits of the Chao-Seader method, especially the restriction to pressures below about 0.8 of the critical value of the mixture, good results are obtained. 

Cubic equations of state have become the main tool for high pressure VLE calculations. They combine simplicity with accuracy comparable to -or better than - that of other methods, including non-cubic EoS. For a comparison of the EoS approach with the Chao-Seader method, see Maddox and Erbar (1981). 

Prepare a flow diagram for a bubble point pressure calculation with the Chao-Seader method. 

Calculate the total pressure and vapor phase composition for the system Ci(l) - C02(2) at 230 K, jcj = 0.170 and = 0.543, using the Chao-Seader method. Compare your findings with the experimental values given in Table 14.P.1. 

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