The dynamic behaviour of packed distillation columns
Thesis DisciplineChemical Engineering
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
The dynamic behaviour of packed distillation columns separating binary mixtures has been studied, both by means of a computer simulation, and by experimental testing of a column. The numerical solution of the partial differential equations of the mathematical model, obtained using a digital computer, was found to be fast, accurate and stable. The advantages obtained by using this approach, compared With previous analytical solutions, included: no restriction on the equilibrium relationship which could be used, variable coefficients could he used in the partial differential equations, and the method allowed any desired boundary conditions to be used, The model was first solved for an enriching column section, and was later extended to the cases of batch and continuous columns. A 150 mm diameter column packed with 10 mm Raschig rings was used to measure the transient response following step-change upsets in the liquid reflux rate. The shapes of: the measured transient responses of the distillate composition agreed well with those predicted by the model. However, the predicted time scale of the response was from 0.6 to 2.2 times faster than the measured time scale. Factors which hindered the ability of the model to predict the experimental transient responses included poor correlation of the mass transfer coefficients with flow rates and composition, and lack of knowledge of the rate of change of the liquid holdup with time.