Electrified distillation – optimized design of closed cycle heat pumps with refrigerant selection and flash-enhanced mechanical vapor recompression

Improving the energy efficiency of distillation processes is crucial for reducing the high energy demand and environmental impact of the chemical industry. Compression heat pumps play a significant role in this transformation as they are able to upgrade and recover heat rejected at low temperatures, reducing the need for external heat sources and simultaneously enable process electrification. Mechanical vapor recompression is the most prominent heat pump concept in distillation but limited by its reliance on process streams, which can lead to high external heat demand, or even inapplicability of the concept due to thermal instability or mechanical compressor limitations. Closed cycle heat pumps are less explored, since they require an extra heat exchanger and increased temperature lift compared to mechanical vapor recompression. However, they can overcome some of the limitations by allowing for unrestricted selection of the most attractive refrigerant, which may outplay the structural disadvantages. The current study presents a novel design approach for rapid heat pump evaluation, applicable to any subcritical refrigerant solely based on temperature levels and duties. A two-step approach enables the identification of the best-performing refrigerant from a set of suitable candidates for a given distillation process, considering practical constraints such as the need for superheating to avoid condensation, as well as limits for the compressor discharge temperature and compression ratios. The most promising refrigerant and heat pump configuration is further evaluated by a techno-economical optimization based on a superstructure model for which the performance is compared with a novel mechanical vapor recompression design utilizing a vapor recycle and internal preheating. The optimization results not only showcase fully electrified distillation for all heat pump-assisted processes but also highlight that closed cycle heat pumps with proper refrigerant selection can provide significant energy and cost savings while clarifying the respective advantages and limitations of competing concepts.

Subjects

DDC Class

621: Applied Physics

660.2: Chemical Engineering

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publishedVersion

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https://creativecommons.org/licenses/by/4.0/

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1-s2.0-S1359431125011512-main.pdf

Type

Main Article

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4.97 MB

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Adobe PDF

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Electrified distillation – optimized design of closed cycle heat pumps with refrigerant selection and flash-enhanced mechanical vapor recompression