Design of heat integrated distillation column by using H-xy and T-xy diagrams

An interactive design methodology of HIDiC with finite internal heat exchange stages is proposed. When the number of heat integrated stages is limited, the number of possible combinations of heat integration increases. Thus, the optimal design problem usually becomes a complex mixed integer nonlinear programming problem. In this research, a novel design methodology using modified Ponchon-Savarit diagram is proposed. The first modification of the diagram is the introduction of the reversible distillation curve, which shows the enthalpy profile at reversible condition. By using this curve, the target enthalpy profile in the column can be determined and the plausible stages for heat exchange can be determined by taking the predetermined theoretical stages into account. The second modification is the integration of the T-xy diagram with H-xy diagram. By doing so, the temperature difference of side exchangers can easily be identified, and it becomes possible to determine the pairing of heat integration stages between the rectifying section and the stripping section in consideration of the heat transfer area of side exchangers. The conditions obtained by the diagram methodology can be directly used in rigorous process simulation. Case studies demonstrated that the results obtained from the proposed methodology have good agreement with the conditions obtained through numerical optimization. The designer can modify the design condition interactively by checking the obtained diagram. Thus, the proposed methodology is especially beneficial at the preliminary design stage of HIDiC.