Optimisation of the higher pressure of pressure-swing distillation of a maximum azeotropic mixture

The pressure-swing distillation separation of a maximum azeotropic mixture, water-ethylenediamine, is simulated and optimised. In contrast to our previous works, the top pressure of the high-pressure column (HPC) is considered as an optimisation variable. The total annual cost (TAC) is minimised first without heat integration (NHI), then different energy demand reduction options are applied and optimised: partial (PHI) and full (FHI) heat integration and vapour recompression (VRC) heat pumps. For heat pumps, working fluid flow rate is optimised to minimise the work and thus the compressor costs. Environmental impacts are also considered by calculating CO2 emissions and Eco-indicator 99 (EI99) values. The application of HI does not significantly change the pressure optimum. The lowest TAC is obtained by the optimal PHI, which decreases TAC by 16% compared to the optimal NHI process. Applying VRC is uneconomical, but very favourable environmentally: CO2 emissions and EI99 are reduced by 44 and 95%, respectively

Thermodynamic Insight for the Design and Optimization of Extractive Distillation of 1.0-1a Class Separation

Nous étudions la distillation extractive continue de mélanges azéotropiques à temperature de bulle minimale avec un entraineur lourd (classe 1.0-1a) avec comme exemples les mélanges acétone-méthanol avec l’eau et DIPE-IPA avec le 2-méthoxyethanol. Le procédé inclut les colonnes de distillation extractive et de régénération de l’entraineur en boucle ouverte et en boucle fermée. Une première stratégie d’optimisation consiste à minimiser la fonction objectif OF en cherchant les valeurs optimales du débit d’entraineur FE, les positions des alimentations en entraineur et en mélange NFE, NFAB, NFReg, les taux de reflux R1, R2 et les débits de distillat de chaque colonne D1, D2. OF décrit la demande en énergie par quantité de distillat et tient compte des différences de prix entre les utilités chaudes et froides et entre les deux produits. La deuxième stratégie est une optimisation multiobjectif qui minimise OF, le coût total annualisé (TAC) et maximise deux nouveaux indicateurs thermodynamiques d’efficacité de séparation extractive totale Eext et par plateau eext. Ils décrivent la capacité de la section extractive à séparer le produit entre le haut et le bas de la section extractive. L’analyse thermodynamique des réseaux de courbes de résidu ternaires RCM et des courbes d’isovolatilité montre l’intérêt de réduire la pression opératoire dans la colonne extractive pour les séparations de mélanges 1.0-1a. Une pression réduite diminue la quantité minimale d’entraineur et accroît la volatilité relative du mélange binaire azéotropique dans la région d’opération de la colonne extractive. Cela permet d’utiliser un taux de reflux plus faible et diminue la demande énergétique. La première stratégie d’optimisation est conduite avec des contraintes sur la pureté des produits avec les algorithmes SQP dans les simulateurs Aspen Plus ou Prosim Plus en boucle ouverte. Les variables continues optimisées sont : R1, R2 et FE (étape 1). Une étude de sensibilité permet de trouver les valeurs de D1, D2 (étape 2) et NFE, NFAB, NFReg (étape 3), tandis l’étape 1 est faite pour chaque jeu de variables discrètes. Enfin le procédé est resimulé en boucle fermée et TAC, Eext et eext sont calculés (étape 4). Les bilans matières expliquent l’interdépendance des débits de distillats et des puretés des produits. Cette optimisation permet de concevoir des procédés avec des gains proches de 20% en énergie et en coût. Les nouveaux procédés montrent une amélioration des indicateurs Eext et eext. Afin d’évaluer l’influence de Eext et eext sur la solution optimale, la seconde optimisation multiobjectif est conduite. L’algorithme génétique est peu sensible à l’initialisation, permet d’optimiser les variables discrètes N1, N2 et utilise directement le shéma de procédé en boucle fermée. L’analyse du front de Pareto des solutions met en évidence l’effet de FE/F et R1 sur TAC et Eext. Il existe un Eext maximum (resp. R1 minimum) pour un R1 donné (resp. Eext). Il existe aussi un indicateur optimal Eext,opt pour le procédé optimal avec le plus faible TAC. Eext,opt ne peut pas être utilisé comme seule fonction objectif d’optimisation mais en complément des autres fonctions OF et TAC. L’analyse des réseaux de profils de composition extractive explique la frontière du front de Pareto et pourquoi Eext augmente lorsque FE diminue et R1 augmente, le tout en lien avec le nombre d’étage. Visant à réduire encore TAC et la demande énergétique nous étudions des procédés avec intégration énergétique double effet (TEHI) ou avec des pompes à chaleur (MHP). En TEHI, un nouveau schéma avec une intégration énergétique partielle PHI réduit le plus la demande énergétique. En MHP, la recompression partielle des vapeurs VRC et bottom flash partiel BF améliorent les performances de 60% et 40% respectivement. Au final, le procédé PHI est le moins coûteux tandis que la recompression totale des vapeurs est la moins énergivore. ABSTRACT : We study the continuous extractive distillation of minimum boiling azeotropic mixtures with a heavy entrainer (class 1.0-1a) for the acetone-methanol with water and DIPE-IPA with 2-methoxyethanol systems. The process includes both the extractive and the regeneration columns in open loop flowsheet and closed loop flowsheet where the solvent is recycled to the first column. The first optimization strategy minimizes OF and seeks suitable values of the entrainer flowrate FE, entrainer and azeotrope feed locations NFE, NFAB, NFReg, reflux ratios R1, R2 and both distillates D1, D2. OF describes the energy demand at the reboiler and condenser in both columns per product flow rate. It accounts for the price differences in heating and cooling energy and in product sales. The second strategy relies upon the use of a multi-objective genetic algorithm that minimizes OF, total annualized cost (TAC) and maximizes two novel extractive thermodynamic efficiency indicators: total Eext and per tray eext. They describe the ability of the extractive section to discriminate the product between the top and to bottom of the extractive section. Thermodynamic insight from the analysis of the ternary RCM and isovolatility curves shows the benefit of lowering the operating pressure of the extractive column for 1.0-1a class separations. A lower pressure reduces the minimal amount of entrainer and increases the relative volatility of original azeotropic mixture for the composition in the distillation region where the extractive column operates, leading to the decrease of the minimal reflux ratio and energy consumption. The first optimization strategy is conducted in four steps under distillation purity specifications: Aspen Plus or Prosim Plus simulator built-in SQP method is used for the optimization of the continuous variables: R1, R2 and FE by minimizing OF in open loop flowsheet (step 1). Then, a sensitivity analysis is performed to find optimal values of D1, D2 (step 2) and NFE, NFAB, NFReg (step 3), while step 1 is done for each set of discrete variables. Finally the design is simulated in closed loop flowsheet, and we calculate TAC and Eext and eext (step 4). We also derive from mass balance the non-linear relationships between the two distillates and how they relate product purities and recoveries. The results show that double digit savings can be achieved over designs published in the literature thanks to the improving of Eext and eext. Then, we study the influence of the Eext and eext on the optimal solution, and we run the second multiobjective optimization strategy. The genetic algorithm is usually not sensitive to initialization. It allows finding optimal total tray numbers N1, N2 values and is directly used with the closed loop flow sheet. Within Pareto front, the effects of main variables FE/F and R1 on TAC and Eext are shown. There is a maximum Eext (resp. minimum R1) for a given R1 (resp. Eext). There exists an optimal efficiency indicator Eext,opt which corresponds to the optimal design with the lowest TAC. Eext,opt can be used as a complementary criterion for the evaluation of different designs. Through the analysis of extractive profile map, we explain why Eext increases following the decrease of FE and the increase of R1 and we relate them to the tray numbers. With the sake of further savings of TAC and increase of the environmental performance, double-effect heat integration (TEHI) and mechanical heat pump (MHP) techniques are studied. In TEHI, we propose a novel optimal partial HI process aiming at the most energy saving. In MHP, we propose the partial VRC and partial BF heat pump processes for which the coefficients of performance increase by 60% and 40%. Overall, optimal partial HI process is preferred from the economical view while full VRC is the choice from the environmental perspective

Inherently Safer Design and Optimization of Intensified Separation Processes for Furfural Production

Currently furfural production has been the subject of increased interest because it is a biobased chemical able to compete with fossil-based chemicals. Furfural is characterized by flammability, explosion, and toxicity properties. Improper handling and process design can lead to catastrophic accidents. Hence it is of most importance to use inherent safety concepts during the design stage. This work is the first to present several new downstream separation processes for furfural purification, which are designed using an optimization approach that simultaneously considers safety criteria in addition to the total annual cost and the eco-indicator 99. The proposed schemes include thermally coupled configuration, thermodynamic equivalent configuration, dividing-wall column, and a heat integrated configuration. These are compared with the traditional separation process of furfural known as the Quaker Oats Process. The results show that because of a large amount of water present in the feed, similar values are obtained for total annual cost and eco-indicator 99 in all cases. Moreover, the topology of the processes has an important role in the safety criteria. The thermodynamic equivalent configuration resulted as the safest alternative with a 40% reduction of the inherent risk with respect to the Quaker Oats Process, and thus it is the safest option to purify furfural

Extension of a multi-criterion performance indicator model for post combustion Co2 capture using amine solvents.

Masters Degree, University of KwaZulu-Natal, Durban.Energy generation by carbonaceous fuel combustion has been identified as one of the predominant sources of CO2 emissions. Many scientists and researchers believe that rising CO2 levels have an adverse effect on the environment, therefore research on the capture and storage of CO2 is ongoing. Post-combustion capture with amine-scrubbing has been identified as a practical short-term solution to the problem. The alkanolamine, monoethanolamine (MEA) is the current solvent of choice for this application. However, due to disadvantages connected to its use, there is a need to identify alternative superior solvents or solvent blends. A quick and inexpensive method to identify alternative solvents is via process simulation and modelling. These tools enable the assessment of solvent viability on a large scale and the elimination of unsuitable candidates without the expense of extensive laboratory testing. The main units considered in a post-combustion CO2 capture simulation are the absorber, where the amine solvent is used to remove CO2 from a flue gas stream, and the stripper, which enables the separation of the CO2 from the solvent to facilitate recycle of the solvent for re-use in the absorber. User inputs into these simulations include the flow rate and composition of the flue gas to be treated, the solvent composition, and the desired CO2 capture rate. A multi-criterion performance model for the evaluation of solvents used for CO2 capture from a coal-fired power plant, was previously developed by Daya (2017) within the Thermodynamics Research Unit at the University of KwaZulu-Natal. The inputs to this performance indicator model are primarily solvent flow rates and equipment heat duties, which were obtained from ASPEN Plus® simulations. Among the other inputs required are price data for the various factors considered in the model, which include energy requirements, make-up flows and carbon taxes. The solvents investigated to test the performance model’s viability consisted of primary, secondary, tertiary and sterically-hindered alkanolamine solvents and their blends. MEA was used as the basis of comparison. In this study, the performance indicator model is used to evaluate the performance of the previously studied amines, n-methyldiethanolamine (MDEA) and 2-amino-2-methyl-1-propanol (AMP), in different blends as along with an additional component, piperazine (PZ). Different concentrations of the binary blends MDEA+PZ and AMP+PZ as well as the ternary blend, MDEA+AMP+PZ, were investigated. The solvent selected as the basis for the ratings was also changed from 30 wt.% MEA to 30 wt.% AMP, as AMP was previously proven to outperform MEA. The rating for the benchmark case calculated by the performance model formulae, is one. When the same calculations are applied to the other amine blends investigated, ratings below one show a performance inferior ABSTRACT v than the benchmark, whilst a rating above one show better performance compared to the benchmark. Of the blends studied, the solvent with composition 25 wt.% AMP + 5 wt.% PZ + 70 wt.% H2O was the best performing with an overall performance increase of approximately 35% (which corresponds to a rating of 1.359). This solvent was further studied using alternative process configurations: the absorber intercooling (ICA) and rich solvent splitting (RSS) configurations. These configurations have been reported to noticeably reduce the energy requirements for solvent regeneration, with minimum additional equipment. A rating of 1.483 was obtained for the ICA configuration, which is a 9% improvement on the rating of the conventional configuration with the same solvent. The results for the RSS configuration, however, shows no improvement on the performance of the conventional configuration.Only available in English

Estudo energético da configuração em série de colunas de destilação por filme descendente

Tese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Química, Florianópolis, 2017.Processos de destilação são largamente empregados na indústria de petróleo e petroquímica. Unidades intensificadas energeticamente tem sido propostas, visando a minimização dos requerimentos energéticos que intrinsicamente são altos neste tipo de processo. Colunas de múltiplo efeito, cuja separação é realizada em uma série de unidades, são um exemplo da possibilidade de otimizar a energia necessária para a separação. Neste sentido, este trabalho teve como objetivo avaliar a eficiência energética de uma configuração em série de destilação por filme descendente com aquecimento por termossifão na separação de uma mistura etanol-água. Experimentos foram realizados com três unidades em série, obtendo-se fração mássica de etanol na terceira coluna igual a 82,7%. Este resultado demonstra a possibilidade da utilização de uma série de colunas de filme descendente para incrementar a fração do componente mais volátil. Em paralelo, um modelo matemático para simulação desta unidade foi proposto, a partir do qual foram calculados os requerimentos energéticos da configuração proposta. Este modelo foi desenvolvido utilizando o software Wolfram Mathematica®. O modelo e as simulações correspondentes permitiram avaliar os perfis de temperatura ao longo do comprimento da unidade, cujos valores não podem ser determinados experimentalmente. Em relação a análise energética, observou-se que unidade de filme descendente é mais vantajosa do ponto de vista energético, representando economia de cerca de 29,5% quando comparada com a separação em uma unidade convencional.Abstract : Distillation processes are widely used in petroleum and petrochemical industry. Energetically intensified units have been proposed aiming at minimizing the energy requirements that are intrinsically high in this type of process. Multi-effect columns, whose separation is performed by a series unit, are an example of the possibility of optimizing energy needed for the separation. For this sense, this work had as objective to evaluate the energy efficiency of a series configuration of falling film distillation columns with thermosyphon heating in the separation of an ethanol-water mixture. Experiments were performed with a three units series, obtaining a mass fraction of ethanol in the third column equal to 82,7 %. The result demonstrated the possibility of using a series of falling film distillation columns to increase the concentration of more volatile component. In addition, a mathematical model of this unit was proposed and simulated, where the energy requirements of the proposed configuration were calculated. This model was developed using Wolfram Mathematica® software. The model and its simulations allowed to evaluate the temperature profiles along the unit length, whose values cannot be determined experimentally. With regard to energy analysis, it has been observed that falling film distillation unit was more energy-efficient conventional unit, representing savings of about 29,5 % as compared to separation in a conventional unit

Dynamic Behavior and Performance of Different Types of Multi-Effect Desalination Plants

Water and energy are two of the most vital resources for the socio-economic development and sustenance of humanity on earth. Desalination of seawater has been practiced for some decades and is a well-established means of water supply. However, this process consumes large amounts of energy and the global energy supply is also faced with some challenges. In this research, multi-effect desalination (MED) has been selected due to lower cost, lower operating temperature and efficient in terms of primary energy and electricity consumption compared to other thermal desalination systems. The motivation for this research is to address thermo-economics and dynamic behavior of different MED feed configurations with/without vapor compression (VC). A new formulation for the steady-state models was developed to simulate different MED systems. Adding a thermal vapor compressor (TVC) or mechanical vapor compression (MVC) unit to the MED system is also studied to show the advantage of this type of integration. For MED-TVC systems, results indicate that the parallel cross feed (PCF) configuration has better performance characteristics than other configurations. A similar study of MED-MVC systems indicates that the PCF and forward feed (FF) configurations require less work to achieve equal distillate production. Reducing the steam temperature supplied by the MVC unit leads to an increase in second law efficiency and a decrease in specific power consumption (SPC) and total water price. Following the fact that the MED may be exposed to fluctuations (disturbances) in input parameters during operation. Therefore, there is a requirement to analyze their transient behavior. In the current study, the dynamic model is developed based on solving the basic conservation equations of mass, energy, and salt. In the case of heat source disturbance, MED plants operating in the backward feed (BF) may be exposed to shut down due to flooding in the first effect. For all applied disturbances, the change in the brine level is the slowest compared to the changes in vapor temperature, and brine and vapor flow rates. For MED-TVC, it is recommended to limit the seawater cooling flow rate reduction to under 12% of the steady-state value to avoid dryout in the evaporators. A reduction in the motive steam flow rate and cooling seawater temperature of more than 20% and 35% of steady-state values, respectively, may lead to flooding in evaporators and plant shutdown. Simultaneous combinations of two different disturbances with opposing effects have only a modest effect on plant operation and they can be used to control and mitigate the flooding/drying effects caused by the disturbances. For the MED-MVC, the compressor work reduction could lead to plant shutdown, while a reduction in the seawater temperature will lead to a reduction in plant production and an increase in SPC

Evaluation of efficiency improvements and performance of coal-fired power plants with post-combustion CO2 capture

The power sector needs to be decarbonised by 2050 to meet the global target for greenhouse gas emission reduction and prevent climate change. With fossil fuels expected to play a vital role in the future energy portfolio and high efficiency penalties related to mature CO2 capture technologies, this research aimed at evaluating the efficiency improvements and alternate operating modes of the coal-fired power plants (CFPP) retrofitted with post-combustion CO2 capture. To meet this aim, process models of the CFPPs, chilled ammonia process (CAP) and calcium looping (CaL) were developed in Aspen Plus® and benchmarked against data available in the literature. Also, the process model of chemical solvent scrubbing using monoethanolamine (MEA) was adapted from previous studies. Base-load analysis of the 580 MWel CFPP retrofits revealed that if novel CAP retrofit configurations were employed, in which a new auxiliary steam turbine was coupled with the boiler feedwater pump for extracted steam pressure control, the net efficiency penalty was 8.7–8.8% points. This was close to the 9.5% points in the MEA retrofit scenario. Conversely, CaL retrofit resulted in a net efficiency penalty of 6.7–7.9% points, depending on the fuel used in the calciner. Importantly, when the optimised supercritical CO2 cycle was used instead of the steam cycle for heat recovery, this figure was reduced to 5.8% points. Considering part-load operation of the 660 MWel CFPP and uncertainty in the process model inputs, the most probable net efficiency penalties of the CaL and MEA retrofits were 9.5% and 11.5% points, respectively. Importantly, in the CaL retrofit scenarios, the net power output was found to be around 40% higher than that of the CFPP without CO2 capture and double than that for the MEA retrofit scenario. Such performance of the CaL retrofit scenario led to higher profit than that of the 660 MWel CFPP without CO2 capture, especially if its inherent energy storage capability was utilised. Hence, this study revealed that CaL has the potential to significantly reduce the efficiency and economic penalties associated with mature CO2 capture technologies

Zeolitic Imidazolate Frameworks / Polybenzimidazole Nanocomposite Membranes for Hydrogen Purification.

Ph.DDOCTOR OF PHILOSOPH