Reducing total annualized cost and CO2 emissions in batch distillation: Dynamics and control

In this contribution, the direct vapor recompression approach is introduced in a batch distillation operated at an unsteady state condition. This vapor recompressed batch distillation (VRBD) accompanies an isentropic compressor that runs at a fixed as well as variable speed. Aiming to ensure the optimal use of internal heat source, an open-loop control policy is proposed for the VRBD that adjusts either the overhead vapor splitting or the external heat supply to the reboiler. Again, the variable speed VRBD additionally involves the manipulation of compression ratio. Developing two alternative configurations of VRBD column, the best heat integrated scheme is attempted to identify in the aspects of energy efficiency and total annualized cost for further advancement. A closed-loop control algorithm for the best performing variable speed VRBD aiming to meet the end objective of relatively high-purity product discharged at a constant composition is developed. The separation of a reactive system is considered to illustrate these results and demonstrate the effectiveness of the novel VRBD scheme. Performing simulation tests, it is investigated that the closed-loop control operation substantially improves not only the distillate purity but also the total amount of product. Achieving significant improvement in thermodynamic efficiency and cost by the controlled heat integrated scheme over its conventional counterpart, finally the attractiveness of the VRBD column by investigating its potential to reduce the greenhouse gas (i.e., CO2) emissions is shown. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2821–2832, 2013

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