Ternary Distillation Simple Model

The reflux ratio is discretised into two control intervals for each operation task. Three cases were considered with different sales values for the two main-cuts. For all cases, the optimal recovery of component 1 in task 1 and that of component 2 in task 2, the optimal amounts of main-cut 1, off-cut 1 and main-cut 2, the optimal 

Case 2, where both main distillate products have the same unit value, is taken as the base case and used as a reference. Case 2 is similar to case 1 except that the composition of the off-cut was also optimised. The results are similar to case 1 in terms of recoveries and profit although the reflux ratio profiles are slightly different. Case 2 operation is slightly shorter and more profitable. The losses of component 2 in the off-cut for the two cases are close. 

8 Reprinted from Computers Chemical Engineering, 17, Mujtaba, I.M. and Macchietto, S., Optimal operation of multicomponent batch distillation- multiperiod formulation and solution, 1191-1207, Copyright (1993), with permission from Elsevier Science.  

In case 3, the sales value of the second main-cut is much higher compared to that of the first main-cut. Therefore, a larger recovery of component 2 is now obtained to maximise the profit. Relative to the base case, less of main-cut 1 is produced in a shorter time but with very little loss of valuable component 2 and with 

Mujtaba and Macchietto (1993) reported that the outer loop solution typically required 4-6 function and 3-4 gradient evaluations with 7-10 function and 5-6 gradient evaluations in each inner loop problem. One complete function and gradient evaluation of the outer loop required about 8-10 minutes CPU and 15-18 minutes, respectively, on a SPARC-1 Workstation. 

---

Table 6.3. Input Data for Ternary Distillation (Simple Model/...

Table 6.4. Results For Ternary Distillation (Simple Model)8...

Figure 6.6. Ternary Distillation (Simple Model) with Off-cut Production (Case 2) a) Accumulated Distillate Composition and Reflux Ratio Profile b) Instant Distillate Composition and Reflux Ratio Profile1.

---