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Item type:Publication, Access status: without files , Optimization-based design of dividing wall columns with extended and multiple dividing walls for three- and four-product separations(2019-12); ; While dividing wall columns can be considered an established technology and success story of distillation process intensification, the application of the technology is still limited in relation to the vast number of existing distillation columns. This can at least to some extent be traced back to potential controllability issues and the complexity of the process design. While the first issue is especially related to internal vapor splits, which require an accurate design and consideration of column hydrodynamics, the latter issue becomes more severe with an increasing number of products and column sections, for which the number of degrees of freedom and design alternatives increase exponentially. While modified design concepts for dividing wall columns that allow for an external control of vapor splits have been proposed, similar to four-product dividing wall columns, there is still a lack of computationally efficient tools for the design and optimization of these energy-efficient thermally coupled distillation processes. The current article presents an optimization-based approach for the design of such complex and integrated distillation processes, enabling a case-specific economic assessment and benchmarking. The application is demonstrated for different case studies, including the separation of an azeotropic quaternary system in a multi-dividing wall column.Publicationtype: Journal Article67 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Efficient optimization-based design of energy-integrated distillation processes(2019-10-04); While providing only low thermodynamic efficiency, distillation is still the default option for the separation of liquid mixtures in the chemical industry. Fortunately, various concepts for energy integration have been proposed to improve the energy efficiency. Yet, the selection of the cost-optimal process among the potential alternatives is tedious, as the performance of the different options has to be evaluated for each specific separation. Thus, efficient means for rigorous design are required, that allow for a comparison of the competing alternatives. For this purpose, a computationally efficient method for a rigorous optimization-based design of various energy-integrated distillation sequences is proposed in the current article and demonstrated for 16 different process variants for the separation of a multicomponent mixture into three product streams. The application to three case studies, including the separation of ideal, non-ideal and azeotropic mixtures, demonstrates its computational efficiency and effectiveness in identifying economically attractive energy-integrated distillation processes.Publicationtype: Journal Article39 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Optimization of extractive distillation – integrated solvent selection and energy integrationThe separation of azeotropic mixtures is of particular importance for bio-based processes in the chemical industry. Extractive and heteroazeotropic distillation are oftentimes the favored solution for medium to large scale processes due to their proven robustness and the economics of scale. The feasibility as well as economic efficiency of these processes depends strongly on the selection of a suitable mass separating agent (MSA). Furthermore, energy integration can increase the energy and economic efficiency of these thermal processes. Since, MSA selection, process design and energy integration are usually performed as consecutive steps in process design, potential synergies are easily missed, resulting in sub-optimal choices. In order to determine an optimal process design, including solvent selection and energy integration, an efficient optimization-based approach for the design of extractive distillation processes is proposed. The application of the method is illustrated for the separation of the azeotropic mixture of acetone and methanol. The results highlight that the optimal MSA choice under consideration of energy integration differs from the selection without energy integration.Publicationtype: Conference Paper50 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Choosing the right model for distillation processes in packed columns: Theory and experimentsPacked distillation columns are usually designed on the basis of a sequential approach, in which first the Equilibrium Stage (EQ) model is used to quantify the separation effort before the required packing height is determined by HETP values. This approach is often sufficient for process design and proper sizing of the column. However, in certain cases the combination of the EQ model and HETP values results in an inappropriate column design. The design accuracy can be improved using a rate-based (RB) approach. Unfortunately, there is no reliable heuristic available to decide which modeling approach should be chosen. Therefore, the current study investigates the need for rate-based modeling in distillation processes by systematically evaluating the differences between EQ and RB composition trajectories. A criterion based on the Euclidean distance is proposed to evaluate the differences between the EQ and RB trajectories. Then, by means of a selectivity analysis basic criteria for model discrimination are derived and validated experimentally. Generally, for wide boiling mixtures the differences between the EQ and RB trajectories are the most distinct. The differences in the trajectories can be further increased or decreased by component specific mass transfer.Publicationtype: Journal Article211 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , A Systematic Approach towards Synthesis and Design of Pervaporation-Assisted Separation Processes(2017-11); ; While membrane processes like pervaporation are considered as key technology towards more sustainable separation processes, they are rarely considered in conceptual design. In order to enable an identification of promising applications, the current article proposes a systematic approach that covers the synthesis of pervaporation-assisted process variants and promotes the use of optimization-based methods for process analysis. It seeks to minimize and guide necessary experiments and includes competitive reference processes as well as further means for process intensification in the evaluation.Publicationtype: Journal Article32 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Efficient optimization-based design of energy-intensified azeotropic distillation processesThe separation of azeotropic mixtures is a difficult task in the downstream processing of many industrial processes. Although potentially less energy intensive separation techniques are available, the separation by extractive or heteroazeotropic distillation is often the method of choice, particularly for large scale processes. By application of different concepts for energy-intensification such as heat integration, the use of heat pumps or concepts of thermal coupling the separation efficiency of these thermal separation processes can be improved. However, the comparison of these different variants and the identification of the most energy or economicly beneficial option for a specific separation is an elaborate task. Therefore, an existing approach for the design of energy-intensified distillation processes has been extended to the design of extractive and heteroazeotropic distillation. The method utilizes a superstructure model based on the MESH equations including non-ideal thermodynamics. All considered process variants are evaluated by means of an automated procedure requiring nothing more than the definition of feed and product specifications as well as the thermodynamic model. The method is demonstrated for the dehydration of ethanol with the help of additional mass separating agents. While the investigated case study shows only small saving potential by the considered means of energy-intensification, it demonstrates the computational efficiency of the proposed design approach. Moreover, the method can easily be adapted for other separation tasks, requiring only minor changes.Publicationtype: Conference Paper30 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Conceptual Design of Highly Integrated Processes – Optimization of Dividing Wall Columns(2017-05); Process intensification provides a whole toolbox of innovative solutions for improved energy efficiency of chemical processes. However, evaluation of this potential is hampered by the unavailability of suitable models and design tools. Integrated processes like dividing wall columns either have to be mapped by available unit operation models or tailored equation-based models have to be developed. The current article reviews available methods for conceptual design and optimization of dividing wall columns and provides a detailed comparison of two representative optimization approaches.Publicationtype: Review Article22 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Computationally efficient evaluation of energetically improved distillation processes for the separation of nonideal mixtures(2016-11); The majority of fluid separations in the chemical industry are still performed by means of distillation columns, accounting for about half of the total energy consumption in this industry and 10-15% of the US industrial energy use [1]. Besides the pure quantity of these processes, with approximately 40,000 distillation columns in the US [2], another reason for this high energy consumption is to be found in the low thermodynamic efficiency of 10-15% for conventional distillation processes [3]. Consequently, energetically improving these processes provides a huge potential for energy savings [4]. While a variety of different options for heat integration, thermal coupling and heat pump configurations have been proposed in order to improve the energy efficiency of distillation processes, even academic investigations are almost always restricted to specific options, such as dividing wall columns (DWC) [5], or the implementation of heat-pump designs up to a fully heat-integrated distillation column (HIDiC) [6]. The same holds true for the investigation of hybrid separation processes, such as membrane-assisted distillation or the combination of crystallization and distillation [7], for which the achieved improvements are almost always related to conventional distillation processes as benchmark. One of the reasons for this non-compliance of energetically improved distillation processes is the limited availability of efficient means for their evaluation. For the separation of zeotropic mixtures, powerful synthesis methods to derive all simple and thermally coupled configurations have been developed (see e.g. [8]) and superstructure-based optimization approaches have been proposed to determine the optimal design of these configurations [9]. However, in the way these approaches have been described the application of the methods was limited to the separation of ideal mixtures. Similar statements can be given for the design of heat-integrated distillation processes, for which elegant superstructure optimization approaches have been presented [10-11], but the applicability was limited to the separation of ideal mixtures as well. Despite this limitation, these methods are also not available in commercial process modeling and simulation software, such that complex configurations like DWCs have to be assembled from the connection of a thermodynamically equivalent combination of conventional distillation column models [12]. Current approaches for screening thermally coupled configurations rely on shortcut methods like the Fenske-Underwood-Gilliland method (FUGM) for the determination of the most suitable options. These are further verified by means of rigorous simulation [13]. However, the FUGM is limited in applicability and accuracy by the underlying assumptions of constant molar overflow and constant relative volatilities. The rigorous simulation of the thermally coupled configurations is complicated by the absence of readily available models, while the complex configurations, which are required in order to depict the thermally coupled configurations by means of conventional column models, have to be initialized manually [14]. In order to efficiently address the problem of evaluating a large set of process configurations, including heat-integration, thermal coupling, heat pumps and multi-effect distillation, a systematic screening procedure is proposed, which operates in two steps. In a first step a full enumeration of all process variants based on reliable shortcut methods is proposed. In order to account for non-ideal thermodynamic models, the rectification body method (RBM) [15] is integrated in an automated evaluation procedure which automatically investigates various ways of heat-integration between single columns by means of variating the operating pressures in the different columns. Thermally coupled configurations and the thermodynamically equivalent DWC configurations are evaluated based on the decomposition method proposed by Carlberg and Westerberg [16], while the distribution of the intermediate boiling component is optimized by means of a simple bisection algorithm. The application of vapor recompression is performed based on isentropic compression computation. For the separation of a mixture into three products more than 30 different configurations are evaluated, including the non-improved direct, indirect and intermediate split. Due to the computationally efficiency of the shortcut-based approach even uncertainty associated to the feed composition, utility costs and the thermodynamic model can be addressed, based on a screening of these configurations for several hundred different scenarios. Based on the full enumeration of all the configurations and potentially all resulting scenarios the most efficient configurations as well as the most relevant scenarios can be identified, and can further be investigated by means of a rigorous optimization approach based on equilibrium-tray models. In order to evaluate the cost optimal process design from the various configurations, an efficient optimization-based method is proposed. The method relies on a superstructure approach including rigorous thermodynamic models for equilibrium and enthalpy computations [17], making it applicable to ideal as well as non-ideal mixtures. Optimal designs are determined on the basis of the total annualized costs (TAC), considering investment and operating costs. All configurations associated to one sequence of splits are initialized by means of the common column sequence, while subsequently the optimization of each energetically improved configuration is performed by means of an automated adaption of the superstructure. The different process options are optimized for minimum energy demand and TAC. The application of the overall method is demonstrated for the separation of ternary non-ideal mixtures.Publicationtype: Conference Paper37 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Efficient optimization-based design of energetically intensified distillation processes(2016-06); Although suffering from low energy efficiency, distillation is still the most widespread separation technique in industry. Different means for the improvement of energy efficiency, such as heat-pump assisted and thermally coupled distillation columns, have been developed. However, the comparison of these different configurations and the identification of the most energy or economicly beneficial option for a specific separation is an elaborate task. Therefore, an efficient optimization-based method for the evaluation of the different options is proposed. In contrast to most previous approaches, the method is based on a superstructure equilibrium tray model including rigorous thermodynamics. It is therefore directly applicable to the separation of non-ideal mixtures and considers a broad range of different options for energetically intensified distillation processes. For illustration purposes the design method is applied to the separation of a ternary non-ideal mixture.Publicationtype: Conference Paper24