Binary Distillation Simple Model

The reflux ratio is discretised into two time intervals for task 1 and one time interval for task 2. Thus a total of 3 reflux ratio levels and 3 switching times are optimised for the whole multiperiod operation. Three cases are considered, corresponding to different values of the main-cut 1 product. For each case the 

Mujtaba and Macchietto (1993) reported that, in general, the outer loop requires 4-5 function evaluations and 3-4 gradient evaluations to converge. Each inner loop problem requires 6-8 function and 4-6 gradient evaluations. One complete function evaluation of the outer loop requires about 5-6 minutes (CPU) using a SPARC-1 Workstation. The outer loop gradient evaluation time is approximately 20-25% smaller than that of a function evaluation. 

of Ideal Separation Stages (including a reboiler and a total condenser) = 6 

Costs Cbo = 1-0 /kmol, Crj — Cg2= 0.0, Cfc — 5.0 S/kniol Cdi = 20, 30, 40 /kmol Initial Outer Loop Decision Variables Re D1 = 0.75 Initial Inner Loop Decision Variables Reflux Ratio Levels 0.80 0.90 0.65  

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The added separation power of a two-stage distillation column (Figure 3.3) over a single stage results from the fact that the two stages can be maintained at two different temperatures. For a binary system, the compositions are given by Equations 3.3 and 3.4 or 3.5 and 3.6. These equations indicate that separation, expressed in terms of mole fractions of the products, is a function of F-values. In this simple model, the F-values are a function of temperature only. Hence, the temperature effect is the only active one in binary distillation. 

The variation of efficiencies is due to interaction phenomena caused by the simultaneous diffusional transport of several components. From a fundamental point of view one should therefore take these interaction phenomena explicitly into account in the description of the elementary processes (i.e. mass and heat transfer with chemical reaction). In literature this approach has been used within the non-equilibrium stage model (Sivasubramanian and Boston, 1990). Sawistowski (1983) and Sawistowski and Pilavakis (1979) have developed a model describing reactive distillation in a packed column. Their model incorporates a simple representation of the prevailing mass and heat transfer processes supplemented with a rate equation for chemical reaction, allowing chemical enhancement of mass transfer. They assumed elementary reaction kinetics, equal binary diffusion coefficients and equal molar latent heat of evaporation for each component. 

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