Efficient evaluation of intensified distillation processes in the scope of plant-wide energy integration

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Distillation is the C used fluid separation technology and accounts for approximately 95% of industrial fluid separations, but it is also responsible for a significant fraction of the chemical industry's energy consumption. With rising energy prices and the need to reduce greenhouse gas emissions, it is essential to increase the efficiency of distillation processes.

Depending on the specific separation task, different improvement measures such as thermal coupling, heat integration or the use of heat pumps can be considered in addition to various column configurations for separation into multiple fractions. Accordingly, the most efficient process alternative must be evaluated from a wide variety of options.

 

To achieve this, a shortcut screening tool for automated and computationally efficient simulation of process alternatives is applied and extended in this research project. A wide range of distillation processes is modelled including individual columns and ternary sequences as well as variants of these processes with different forms of heat integration, thermal coupling, and use of heat pumps. Energy requirements are calculated using the pinch-based Rectification Body Method which uses rigorous thermodynamics without the need to assume constant molar overflow or constant relative volatility. The process performance can be evaluated regarding the energy demand, operating and investment costs and exegetic efficiency. The most promising concepts for energy integration are identified and rigorously optimized for detailed evaluation.

The concept of Liquid Only Transfer has been identified as one of the most promising energy integration methods. Thermally coupled configurations can be transformed to column sequences with liquid side streams by adding column segments and heat exchangers. These configurations retain the energy saving potential of the thermally coupled configuration, while hydrodynamically decoupling the individual columns. Such modified configurations with a single side stream can closely approach the energy requirements of a dividing wall column or even match it exactly when two sides streams are used. In addition, Liquid Only Transfer allows additional heat integration by operating the individual columns at different pressures.

Another possibility with great saving potential is the use of heat pumps by means of compressors, such as vapor recompression. In addition to the drastic reduction in energy demand, this also offers the possibility of operating the process with electricity produced from renewable sources. Vapor recompression is the most commonly used concept, but external heat pumps with freely selectable refrigerants and internally integrated distillation columns (HIDiC) with the individual sections operated at different pressure are attractive alternatives.