K-chart

Step 6. Using the convergence pressure determined in Step 5, together with the system temperature and system pressure, obtain K-values for the components from the appropriate convergence-pressure K-charts. 

Test to determine if a is varying significantly by = 2 (yi/cq). Evaluate temperature of heavy component at the column bottoms pressure (estimated) using K charts or the equivalent. If necessary, calculate new Oj values for each component at the new temperature. Recheck every two or three trays if indicated. 

From K charts, determine values for each component at the column temperature and pressure. 

Kj = 14.7 (Hj)/176, where Hj is Henry s constant expressed as atm/mol fraction for each component. Note that conventional K charts are only applicable to hydrocarbon oil systems, and do not apply for any special solvents. 

For hydrocarbons, these equilibrium relations are often represented by y, = K,x, where K, = Ps,/P = K-factor for component i. K-factors are functions of both pressure and temperature but assumed to be independent of composition. Also, for a multi-component mixture, a relative volatility (a,) can be defined for each component with one of the components, say 3, as a basis such that a, = K/K . Charts for K-factors for various components are available in Handbooks. 

The same vapor-liquid equilibrium ratio (K) charts were used for the rigorous solution as for the shortcut. For the rigorous, however, values of K, were combined with total pressure P, and die product was treated as effective vapor pressure in die Antoine equation. The rigorous program was run in a trial-and. rror fashion, with constant redux ratio of 1.722 (from the shortcut) and with iterations of DIF ratio, total plates, and feed plate location. 

We proceed then to demonstrate how Bubble Point, Dew Point, and Flash calculations are carried out - in principle - at these conditions, and then apply such procedures using the simplest of the methods, the K-Charts. Use of EoS in carrying out bubble point temperature calculations is made through the computer programs presented in Appendix E. 

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