THE USE OF COMPACT HEAT EXCHANGERS IN HEAT-INTEGRATED DISTILLATION COLUMNS

摘要

The Heat-Integrated Distillation Column (HIDiC), in which heat is transferred directly from the rectification section to the stripping section of the column, has a much higher energy efficiency than either a normal distillation column or a vapour-recompression column. Although the HIDiC concept has been researched for a number of years, it has not yet been commercialised. Recent literature describes an embodiment of the concept, which resembles a shell-and-tube heat exchanger. However an alternative embodiment based on a compact (plate) heat exchanger has several potential advantages over the shell-and-tube design. These advantages include compactness, a closer temperature approach, modular structure, and flexibility in design.rnIn order to investigate the feasibility of a HIDiC design based on a plate-fin heat exchanger, a computer program has been developed. This approach is based on an existing model for conventional distillation, coupled to a spreadsheet program that incorporates correlations for such factors as flooding, wetting, and fin efficiency, and that takes account of geometric constraints in the plate-fin design. The software was applied in a preliminary case study for a propane-propene splitter. This confirmed the scope for energy savings, with energy savings of about 37% compared to a vapour-recompression column. First indications suggest that the economics may also be favourable. It was concluded that the plate-fin design is feasible in principle. However the required hydraulic diameter was larger than currently available in commercial plate-fin heat exchangers.