A Thiele-Geddes equilibrium stage calculation
Akers, W. W.
Master of Science
The Thiele-Geddes method as developed by Holland uses dew and bubble point calculations to determine new stage temperatures for each succeeding iteration. The method to be considered here involves the use of enthalpy balances to determent these temperatures. This way of determining stage temperatures is more applicable for wide boiling range mixtures, while that used by Holland is more applicable for a narrow boiling range mixture. The proposed method was utilized for a distillation column (employing a relatively narrow boiling range feed) and for both absorbers and strippers (employing relatively wide boiling range feeds). The absorber and stripper problems yielded good results; however, in. a problem with wide boiling mixtures, the round-off error which arises in the solution of the mate¬ rial balance equations becomes significant. This error was effectively eliminated by performing a top-down calculation for the light components, and a bottom-up calculation for the heavy components. The decision as to when a component is heavy enough to warrant a bottom-up calculation is to be based on the magnitude of the absorption factor (Aij = Lj/VjKij). For an Aij (averaged over all the equilibrium stages) less than or equal to unity, the top-down calculation is to be used; and for an Aij avg greater than or equal to unity the bottom-up calculation is to be used. Convergence could not be attained for the distillation calculation though several modifications were tried. The use of a wide boiling range feed for the distillation calculation was not used since a' major change in the basic procedure would be required to eliminate the round-off error.