Internal heat integrated distillation columns (iHIDiCs)-New systematic design methodology

Distillation of close-boiling mixtures, such as propylene-propane and ethyl benzene-styrene systems, is an energy intensive process. Vapor recompression techniques and heat pumping-assisted columns have been adopted for such applications for their high potential of energy savings. In direct vapor recompression columns, the vapors leaving the top of the column are compressed, and in the reboiler of the same column, these vapors are condensed to provide heat for vapor generation. Internal heat integrated distillation columns or iHIDiCs are new developments employing the same concept of vapor recompression. These new column configurations can have significantly lower energy demands than common vapor recompression units. In iHIDiCs, rectifying section is operated at a higher pressure (i.e. higher temperature) than in stripping, and therefore its heat can be used to generate vapor in stripping section. So far, design of these column configurations is performed based on engineering experience, simulation or experimental studies on given cases, including dynamic control simulations. Within previous and most recent research efforts on iHIDiCs, there exist no generalized design methods or systematic approaches for design of these internal integrated distillation columns. The present paper presents a systematic design procedure for iHIDiCs. A design hierarchy for iHIDiCs is developed, which includes two phases of design, thermodynamic and hydraulics. This design procedure is applied using commercial simulation-based design methods. In thermodynamic design, temperature profiles for column sections are used as a design tool to guide designers. On the other hand, hydraulic capacities of stages for heat exchange are analyzed to determine the maximum physical space area available for heat exchange. Hence, feasibility regions for both heat integration and hydraulic design are identified. (C) 2009 The Institution of Chemical Engineers. Published by Elsevier B.V All rights reserved.