stripping factors, KiJVj/Lj, for components i, which make use of volatility and energy parameters. erwise, the inner-loop calculations utilize computational features of the BP, SR, and SC methods, to compute stage temperatures, compositions, and flow rates. The inside-out method takes advantage of the following observations: (1) relative volatilities vary from iteration to iteration much less than the K values, (2) enthalpy of vaporization varies from iteration to iteration much less than phase enthalpies, and (3) component stripping factors combine effects of temperature and liquid and vapor flows at each stage.
As an example of how the approximate thermodynamic-property equations are handled in the inner loop, consider the calculation of K values. The approximate models for nearly ideal liquid solutions are the following empirical Clausius-Clapeyron form of the K value in terms of a base or reference component, b, and the definition of the relative volatility, a.
KiJ =aiJKiJ (13-107)
Values of A and B for the base component are back-calculated for each stage in the outer loop from a suitable K-value correlation (e.g. the SRK equation, which is also used to compute the K values of the other components on each of the other stages so that values of aij can be computed). The values of A, B, and a are passed from the outer loop to the inner loop, where they are used to formulate the phase equilibria equation:
The initial version of the inside-out method was developed for rapid calculations of simple and complex distillation, absorption, and s i—
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