Optimal retrofit and process design of distillation plants for energy saving and process intensification

This work is divided in two principal sections. The first concerns the application of more convenient structures to intensive energy consuming plants built before the energy crisis. Two case studies are considered. The first regards the implementation of a preflash device (drum or column) on a crude distillation unit. The limitations of both apparatuses are considered together with the energy saving realized. Particular emphasis is given to the evaluation of the best structure that matches the scope in the energy plant reduction and the respect of the production specifications. The second case considered regards a light ends distillation plant. Different separation sequences derived from the plant configuration are considered. The possibility to reach a reduction of the energy consumption is considered together with the maximum reusage of the plant apparatus, that allows to minimize the capital cost investment. The total annual cost is associated to the required heat exchanger area for the condensers and the reboilers and to the column section diameter. The best solution, that satisfy the scope of the retrofit work minimizing at the same time the employing of new equipment and the energy consumption, is then identified. In the second section of the work the column sequence design is considered. The starting point was the separation of a four components mixture considered with five different feed compositions. All the possible simple column sequences were first analyzed using different sets of heuristic rules and after with more rigorous evaluation. The different solutions are compared to put in evidence the limitations of the heuristic rules, which anyway remain a good tool for a first screening of the most promising structures. The best distillation sequence for each feed composition case is also considered for the implementation of a divided wall column to perform a three component separation. The resulting “hybrid” sequences are made by a simple column that follows or precedes a divided wall column. This type of column was modeled using the modified Underwood-Fenske-Gilliland method to obtain the first design parameters to be utilized as the input to a more rigorous simulation performed with the Aspen Plus simulation package. The different hybrid configurations are then compared with respect to the best simple column structures from which are derived. In the last part of the work a new method to map the space of distillation columns with less than n-1 columns is proposed. Up to now this configuration space was never predicted in a systematic way and only heuristic rules are available to predict only a few of all the possible configurations. Including more distillation column configurations in the research space increases the possibility to identify the sequence that satisfies the research scope. The generation method is presented for a four components mixture but is absolutely general and can be applied for any number of components

Optimal retrofit and process design of distillation plants for energy saving and process intensification

This work is divided in two principal sections. The first concerns the application of more convenient structures to intensive energy consuming plants built before the energy crisis. Two case studies are considered. The first regards the implementation of a preflash device (drum or column) on a crude distillation unit. The limitations of both apparatuses are considered together with the energy saving realized. Particular emphasis is given to the evaluation of the best structure that matches the scope in the energy plant reduction and the respect of the production specifications. The second case considered regards a light ends distillation plant. Different separation sequences derived from the plant configuration are considered. The possibility to reach a reduction of the energy consumption is considered together with the maximum reusage of the plant apparatus, that allows to minimize the capital cost investment. The total annual cost is associated to the required heat exchanger area for the condensers and the reboilers and to the column section diameter. The best solution, that satisfy the scope of the retrofit work minimizing at the same time the employing of new equipment and the energy consumption, is then identified. In the second section of the work the column sequence design is considered. The starting point was the separation of a four components mixture considered with five different feed compositions. All the possible simple column sequences were first analyzed using different sets of heuristic rules and after with more rigorous evaluation. The different solutions are compared to put in evidence the limitations of the heuristic rules, which anyway remain a good tool for a first screening of the most promising structures. The best distillation sequence for each feed composition case is also considered for the implementation of a divided wall column to perform a three component separation. The resulting “hybrid” sequences are made by a simple column that follows or precedes a divided wall column. This type of column was modeled using the modified Underwood-Fenske-Gilliland method to obtain the first design parameters to be utilized as the input to a more rigorous simulation performed with the Aspen Plus simulation package. The different hybrid configurations are then compared with respect to the best simple column structures from which are derived. In the last part of the work a new method to map the space of distillation columns with less than n-1 columns is proposed. Up to now this configuration space was never predicted in a systematic way and only heuristic rules are available to predict only a few of all the possible configurations. Including more distillation column configurations in the research space increases the possibility to identify the sequence that satisfies the research scope. The generation method is presented for a four components mixture but is absolutely general and can be applied for any number of components

Retrofitting industrial, conventional column systems to petyluk/divided wall columns

Master'sMASTER OF ENGINEERIN

Conceptual design, simulation and experimental validation of divided wall column: application for non-reactive and reactive mixture

Les colonnes à cloison et la distillation réactive présentent de nombreux avantages. Si ces deux concepts sont couplés, cela conduit à un procédé intensifié appelé : colonne à cloison réactive. Ce nouveau procédé intensifié constitue le principal objet d’étude de cette thèse. Dans une première partie, une procédure de design d’une colonne à cloison basée sur le modèle FUGK a été proposée. Dans cette procédure les aspects technologiques et hydrodynamiques sont abordés. Ces paramètres de design obtenus sont ensuite utilisés pour réaliser une simulation rigoureuse et une optimisation de cette colonne en utilisant le logiciel ProSim. Afin de tester cette procédure, des mélanges idéaux et non idéaux ont été utilisés. Il a été montré que cette procédure de design aboutit rapidement aux paramètres de pré design qui permettent d’initialiser de manière satisfaisante la simulation rigoureuse. Dans un second temps, un pilote d’une hauteur de 4m a été conçu, monté et testé au laboratoire. Des résultats expérimentaux ont été obtenus qui valident la procédure sur des mélanges non réactifs en termes de profils de composition et de température ainsi que sur les compositions et les débits de sortie du procédé. Enfin, dans une dernière partie, cette procédure a été adaptée à des mélanges réactifs en combinant les approches de R. Thery et al (2005) et celle de Triantafyllou et al (1992). Ces ultimes développements ont été testés sur la production d’acétate de méthyl par estérification du méthanol par l’acide acétique à la fois d’un de vue expérimental et théorique. ABSTRACT : Divided wall column and reactive distillation have many advantages. If a divided wall column and a reactive distillation are integrated, they leads to a higher integrated process is a reactive divided wall column. However reactive divided wall column has still a new research area. First of all, the thesis proposed a procedure for design of divided wall column, which based on the FUGK model. Both technological and hydrodynamic aspects in the divided wall column are considered in the procedure. Design parameters are then provided to the rigorous simulation and optimization in the ProSimplus software. In order to test this procedure, both ideal and non-ideal ternary mixtures are chosen to be separated in a divided wall column. The results show that the procedure can determine parameters quickly in the case studies and can give a good initialization for rigorous simulation. Secondly, a pilot plant has been design, built and operated in our laboratory (LGC, Toulouse, France, 2013). The pilot plant will provide necessary experimental evidence to validate the previous procedure. Ternary mixture and four-component mixture of alcohols have been used in our pilot plant in steady state conditions. The results show that the composition of products, composition and temperature profile along the column are in very good agreement with simulation results. Finally, a conceptual design method for reactive divided wall column is presented. The pre-design method of R. Thery et al., (2005) and a modified shortcut method for reactive divided wall column that is based on the classical shortcut adapted to a non-reactive divided wall column by C. Triantafyllou and R. Smith (1992) are applied. To verify, simulation and experiment are considered. The methodology has been illustrated for the synthesis of Methyl Acetate from Methanol and Acetic Acid

Hybrid simulation-equation based synthesis of chemical processes

A challenging problem in the synthesis and design of chemical processes consists of dealing with hybrid models involving process simulators and explicit constraints. Some unit operations in modular process simulators are slightly noisy or require large CPU times to converge. In this work, this problem is addressed by combining process simulators and surrogate models. We have replaced some unit operations, which cannot be used directly with a gradient-based optimization, by surrogate models based on Kriging interpolation. To increase the robustness of the resulting optimization model, we perform a degree of freedom analysis and aggregate (or disaggregate) parts of the model to reduce the number of independent variables of the Kriging surrogate models (KSMs). Thus, the final model is composed of KSMs, unit operations (maintained in the process simulator) and also explicit equations. The optimization of the well-known vinyl chloride monomer (VCM) production process is performed to test the proposed approach. The effect of the heat integration is also studied. In addition, the economic feasibility of the optimized process is calculated assuming uncertainty in raw material and product prices.The authors gratefully acknowledge the financial support by the Ministry of Economy and Competitiveness from Spain, under the project CTQ2016-77968-C3-02-P (AEI/FEDER, UE), and Call 2013 National Sub-Program for Training, Grants for pre-doctoral contracts for doctoral training (BES-2013-064791)

Comparative evaluation of two nonconventional distillation technologies for separation of ethanol water mixtures by extractive distillation

In this document, extractive distillation for the separation of Ethanol-Water-ethylene glycol is studied from the conceptual point of view. A methodology for the design of conventional extractive sequences is detailed based on non-linear analysis and the state of the art of extractive distillation. The used methodology can be systematically applied to the design of alternative homogeneous minimum boiling point azeotrope systems. A graphical analysis of extractive distillation sequences is presented by means of the solution of the pinch equations. Obtained pinch branches and column profile maps are analyzed to develop a conceptual based design of an Extractive Dividing Wall Column. This analysis led to reduce the computational effort of designs based on simulation. In order to improve the efficiency of the separation, the obtained designs are studied as a partially diabatic column or a column with Sequential Heat Exchangers (SHE). Finally, an approximation to the application of the results in a pilot scale is made.Maestrí

Tools for efficient design of multicomponent separation processes

Separations account for as much as 85% of plant operating costs in chemical production; it is therefore important that they be designed with energy efficiency in mind. This can only be achieved if two things are achieved: the complete space of design options is known, and an accurate way is developed to compare all possible design options. For both membrane separation cascades and multicomponent distillation configurations, this dissertation explores methods for designing energy efficient separations.^ The operating cost of membranes used in production of nitrogen gas from air is largely driven by the compressors required to maintain a pressure differential. Optimization of the total compressor duty can reveal an ideal cascade arrangement and set of operating conditions for a given feed and recovery. With this optimization technique in hand, it is then possible to examine the effect of introducing extra stages to form intermediate stage cascades. Furthermore, the effect of varying the recovery of the nitrogen stream can be examined to discover a U-shaped relationship between recovery and energy requirement.^ Conventional distillation configurations use n – 1 distillation columns to separate a multicomponent feed mixture into pure products. Past research has identified a way to quickly and algorithmically generate the complete ranklist of regular-column configurations using an integer programming formulation called the matrix method. Using this method, a formulation is here presented for the complete nonlinear programming problem which, for a given configuration, can ensure the globally minimum vapor duty of the configuration. Furthermore, a set of nonlinear equations designed to represent the capital and operating costs of the system are described. The need for a global optimization algorithm in the formulation of the cost product is demonstrated by comparison with a two-stage search algorithm; in addition, the cost formulation is compared to that of the vapor duty formulation and the relative effect of capital and operating cost is weighed for an example feed.^ Previous methods based on Underwood\u27s equations have no accounting for the temperature at which utilities are required. To account for this, a thermodynamic efficiency function is developed which allows the complete search space to be ranklisted in order of the exergy loss occurring within the configuration. Examining these results shows that this objective function favors configurations which move their reboiler and condenser duties to milder temperature exchangers. ^ A graphical interface is presented which allows interpretation of any of the above results in a quick and intuitive fashion, complete with system flow and composition data and the ability to filter the complete search space based on numerical and structural criteria. This provides a unique way to compare and contrast configurations as well as allowing considerations like column retrofit and maximum controllability to be considered.^ Using all five of these screening techniques, the traditional intuition-based methods of separations process design can be augmented with analytical and algorithmic tools which enable selection of a process design with low cost and high efficiency