Process intensification of multi-stage heat pump assisted distillation with liquid injection

Abstract

Multi-stage mechanical vapor recompression (MVR) is a promising route to electrify and intensify distillation for wide-boiling separations, yet its deployment is often constrained by the requirements for effective inter-stage cooling and utilization of the associated sensible heat. This work proposes and evaluates liquid injection as a compact intensification alternative to conventional exchanger-based intercooling in a two-stage MVR system. Unlike prior work on the discretely heat integrated distillation column (D-HIDiC), this study introduces liquid injection directly into MVR systems, eliminating intercooler hardware while maintaining energy performance. Four configurations are examined: a two-stage MVR without intercooling (MVR #1), an intercooled MVR with internal heat recovery to an additional bottom reboiler (MVR #2), a liquid injection MVR without an intercooler (MVR #3), and a liquid injection MVR combined with pre-compressor splitting (MVR #4) to mitigate the increased second-stage compressor load caused by injection. Compared with conventional distillation (CDiC, 10,073 kW reboiler duty), all MVR cases reduce the final energy input to 1759–1850 kW (81.6–82.5% savings) with COP values of 5.445–5.727; MVR #4 achieves the lowest compressor power (1759 kW) and the highest COP (5.727). On a primary-energy basis (36.6% electricity conversion efficiency), the MVR schemes deliver 49.8–52.3% savings versus CDiC. Overall, liquid injection enables equipment simplification with competitive efficiency, while pre-compressor splitting provides a practical tuning degree of freedom to recover or improve performance without sacrificing compactness.