Geddes—Hengstebeck equation

Chang (1980) gives a computer program, based on the Geddes-Hengstebeck equation, for the estimation of component distributions. 

The distribution of components for the distillate and the bottoms is given by the Hengstebeck-Geddes equation [124,125, 126] ... 

Hengstebeck and Geddes (1958) have shown that the Fenske equation can be written in the form ... 

A, B, = correlation constants in Hengstebeck-Geddes equation b = number of moles of a component in the bottoms B = bottoms flow rate moles/hr d = number of moles of a component in the distillate D = distillate flow rate moles/hr F = feed flow rate moles/hr f = number of moles of a component in the feed... 

This simplified procedure is based on the assumption that the concentrations of all the components in the distillate are constant if the reference component concentration in the distillate is constant. If the concentrations of the nonreference components change, the authors (Diwekar and Madhavan, 1991) recalculate the concentrations based on the Hengstebeck-Geddes equation (Hengstebeck, 1946 Geddes, 1958). The authors also describe a procedure for the constant reflux case, where all the component compositions in the distillate change as the distillation progresses. 

The constant Ci in the Hengstebeck-Geddes equation is equivalent to the minimum number of plates, Nmin, in the Fenske equation. At this stage, the variable reflux operating mode has Gi and R, the constant reflux has and Ci, and the optimal reflux has, Ci, and R as unknowns. Summation of distillate compositions can be used to obtain Gi for variable reflux and for both constant reflux and optimal reflux operation, and the FUG equations to obtain R for variable reflux and Gi for both constant reflux and optimal reflux operations. The optimal reflux mode of operation has an additional unknown, R, which is calculated using the concept of optimizing the Hamiltonian, formulated using the different optimal control methods. 

---