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Item type:Publication, Access status: with files , Rapid multi-criteria screening of energy-integrated distillation processes for nonideal mixturesSeveral thousand distillation columns are industrially employed for various separations, accounting for a substantial share of the industrial energy demand. In order to reduce their energy requirements various means for energy integration, such as direct heat integration, multi-effect distillation, thermal coupling, or vapor recompression can be applied. Considering these options and combinations of these, several hundred possible process configurations can be designed even for separations into three product streams, while the choice for a best option depends strongly on the specific separation task and system properties. In order to enable a reliable case-specific evaluation, which avoids simplified heuristics or simplified thermodynamics, this article presents a computationally efficient, algorithmic framework for a multi-criteria evaluation of more than 750 energy-integrated distillation sequences for multicomponent separations in three product streams. The framework employs thermodynamically sound pinch-based shortcut models that do not rely on constant relative volatility and constant molar overflow assumptions, making it applicable to nonideal and azeotropic mixtures. Based on the minimum energy duties and the respective flowsheet information, classical estimation methods for equipment sizes, operating costs, and capital investment, are employed. Several case studies demonstrate the framework's applicability to azeotropic systems, its computational efficiency benefits that enable performing sensitivity analyses for varied process, thermodynamic, and economic scenarios.Publicationtype: Journal Article72 44 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Beyond dividing wall columns: Improved process intensification through liquid-only transfer and heat integrationMany chemical companies aim to achieve climate neutrality by 2050, requiring raw material changes and significant reductions in process energy. Since distillation accounts for a large share of energy use, it is a key target for process improvements. One promising approach is thermal coupling between columns, which is already industrially implemented, especially in dividing wall columns. However, such configurations often suffer from limited operational flexibility due to the fixed vapor split between parallel sections, which is largely fixed during design and difficult to adjust during operation. This limitation can be overcome by replacing each bidirectional vapor-and-liquid connection with a liquid-only transfer side stream. This concept allows each column to operate at an individual pressure and enables new options for heat integration. The present study introduces a structured approach for assessing and optimizing such systems with one or two liquid-only transfer side streams, particularly when combined with direct heat integration. Promising configurations are first identified through an efficient shortcut screening and can further be optimized using superstructure optimization. A case study on separating benzene, toluene, and para-xylene demonstrates that liquid-only transfer configurations with direct heat integration can significantly reduce energy and costs, and in many cases outperform conventional thermally coupled systems.Publicationtype: Journal Article51 60 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Electrified distillation – optimized design of closed cycle heat pumps with refrigerant selection and flash-enhanced mechanical vapor recompressionImproving 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.Publicationtype: Journal Article66 61 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Electrifying distillation − Optimization-based evaluation of internally heat-integrated distillation columnsImproving the energy efficiency of distillation processes is essential for reducing the chemical industry's substantial energy demand and environmental footprint. The use of mechanical heat pumps with compressors is an important asset in this transformation process, as it not only enables the recovery of heat rejected at low temperature, reducing external energy requirements, but also facilitates the electrification of chemical processes and distillation in specific. The necessary temperature lift dictates the required compression rate for the compressor and is therefore of considerable importance for the applicability of mechanical heat pumps. By operating the rectifying and stripping sections of a column at different pressures and enabling heat exchange between the respective sections, temperature lift and compression ratio can be reduced for the so-called Internally Heat-Integrated Distillation Columns compared to mechanical vapor recompression. In order to enable a quick problem specific evaluation of the possible benefits of this concept we propose two novel superstructure models for optimal design, that allow for heat exchange between stages at the same height or arbitrary stages in the rectifying and stripping section, provided a minimum temperature difference is maintained. The respective optimization problems are solved as a series of successively relaxed mixed-integer nonlinear programming problems in GAMS. An automatic stepwise initialization and optimization strategy provides a computationally efficient approach for the determination of optimized designs.Publicationtype: Journal Article38 47