W Cd

Figure 3.1 Conventional process.

*D1j

XB1,j

3. The bottoms product stream B2 contains some amount of component B as an impurity, Bioss = 0.63mol/s (xB2,B = 0.05 mole fraction). There is no A or C going out the bottoms (xB2A = xB2C = 0.).

4. The impurity of product C in the recycle stream D2 is xD2C = 0.05.

5. The impurity of component D in D2 is xD2D = 0.05.

6. As a result of the previous two assumptions and the fact that C and D have identical stoichiometric coefficients, the concentrations of components C and D in the reactor (zC and zD) are equal for all cases (zC = zD) but vary in value from case to case.

7. The column pressures are set using the vapor pressures PS of pure components and liquid compositions in the reflux drum xDj at 320 K (so that cooling water can be used in the condenser).

8. In each column, the reflux ratio RR is 1.2 times the minimum reflux ratio RRmin calculated via the Underwood equations.

9. In each column, the number of stages NT is twice the minimum number of stages NTmin calculated via the Fenske equation.

10. Kirkbride's method is used to find the optimal feed tray location NF.

Several different specifications in items 2-5 will be used to investigate the effects of product quality, conversion, and recycle impurities on the economically optimal steady-state design. However, these do not affect the general structure of the design procedure.

A grid-search optimization strategy is used in this work to find the optimum values of the three design optimization variables. Other methods could be used, such as gradient nonlinear programming techniques. However, the grid method is more robust because a numerical programming method can easily drive the process into an infeasible region in which the specified purities and production rates cannot be achieved.

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