The aim with this study was to combine a simulation study with an experimental in the investigation of intermediate heat exchange as a method to change the distribution of the driving forces in the column. It was applied to a pilot plant sieve tray distillation column for a binary separation of ethanol from n-propanol. Intermediate heat exchange has been accomplished experimentally both in the stripping section and in the rectifying section. Optimal sidestream return in intermediate heat exchange is the focus of attention here. The experimental studies were performed on a pilot plant column with twelve sieve trays. When comparing experimental results from the pilot plant column, to simulation results the inclusion of tray efficiency is of interest. For this purpose a calculation routine was developed in MATHCAD based on a correlation by Chan and Fair. The resulting data was than transferred to the PROII simulation program. The results show that intermediate heat exchange can be used to improve the recovery, the separation capacity and to decrease the entropy production if the points of sidestream withdrawal and sidestream return are chosen properly. It is important that the heat exchanged liquid stream returned as vapour enters at a position in the column where the vapour phase has the same composition. Even if the composition coincides, the actual position for an added vapour stream is important for the flow profiles in the column.
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