Alternative Design 1 for a Two-Column System

TABLE 8.1 NRTL Parameters for IPA-Water-Cyclohexane System. 

Aspen Plus extended Antoine vapor pressure model is 

The economic optimal process flowsheet was obtained by minimization of the total annual cost (TAG) with five design variables IPA distillate composition (XD2) in the recovery column, total number of stages for the heterogeneous azeotropic column and the recovery column (Ni and N2), and the two feed stages (Api and Apa). The product specification of IPA is set to be ultrapure (99.9999 mol%) to be used in the semi-conductor industry. The product specification of water is set to be 99.9 mol%. In each simulation run, the IPA product specification is achieved by varying the reboiler duty of the heterogeneous azeotropic column, and the water product specification is achieved by varying the reboiler duty of the recovery column. The entrainer makeup flowrate will be very small to balance the entrainer loss from the two bottom streams. 

The TAG of the overall system includes the annualized capital costs and the operating costs. The annualized capital costs include the column shells of the two columns, internal trays of the two columns, and also the reboilers and condensers of the two columns. The payback period was assumed to be 3 years in the calculation. The operating costs include the steam and cooling water required for operating these two columns and also a very small entrainer makeup cost. 

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