Application of Vapor Recompression to Heterogeneous Azeotropic Dividing-Wall Distillation Columns

Although heterogeneous azeotropic dividing-wall distillation columns (HADWDCs) can achieve considerable reductions in capital investment and operating cost as compared to conventional heterogeneous azeotropic distillation systems, their steady-state performance is likely to be greatly enhanced by the application of vapor recompression heat pump (VRHP) technology owing to their unique process configuration of one top condenser and two bottom reboilers and favorable steady-state behavior of relatively small top-to-bottom temperature elevations. In the current work, the feasibility and effectiveness of reinforcing the HADWDC with the VRHP (HADWDC-VRHP) are examined. A systematic procedure is developed to effectively determine the optimum combination of the VRHP and the HADWDC in order to minimize the total annual cost. Two example systems for the separation of isopropyl alcohol and water and pyridine and water with cyclohexane and toluene as entrainers, respectively, are studied to evaluate the steady-state economics of the HADWDC-VRHP. It is shown that the proposed procedure can yield the most effective connection between the VRHP and the HADWDC (in terms of the number, locations, and heat duties of intermediate heat exchangers employed between them), and the resultant HADWDC-VRHP requires a considerably lower operating cost than the corresponding HADWDC. Although additional capital investment is needed, the reduction in operating cost generally leads to a reasonable payback time. These outcomes reflect the potential economic advantages of employing the VRHP in the synthesis and design of the HADWDC.