Separation synthesis using Column Profile Maps

The task of separating a mixture of components, specifically via distillation, represents a significant and often costly part of almost any chemical process plant. Distillation is by far the most prevalent industrial separation technique, albeit an extremely energy intensive one, consuming an estimated 6% of the entire energy produced in the USA1. In lieu of the current energy crisis, engineers have therefore been forced to critically relook the way distillative separations are performed and identify cost and energy saving opportunities. Column Profile Maps (CPMs) have recently been developed within our group as a graphical method to synthesize distillation columns. The maps generated through this technique are essentially a family of composition profiles derived from a first order differential equation for a single, generalised column section. Because the CPM method is generalised it is not specific to any one configuration (a major downfall in several other design methods), the design engineer has the tools to come up with new and creative designs. Thus, the designer is not limited by current equipment to design new structures. The CPM principle has been applied and extended to a wide range of separation methods, such as Reactive Distillation, Membrane Separations and complex columns like Petlyuk and Kaibel columns. Moreover, the technique offers valuable insights in the selection of an appropriate thermodynamic model for a particular system. 1. Lucia A, McCallum BR. Energy targeting and minimum energy distillation column sequences. Computers & Chemical Engineering. 2010;34(6):931-942

Energy efficient distillation columns analysis for aromatic separation process

Distillation operations became a major concern within energy savings challenge, which it becomes a primary target of energy saving efforts in industrially developed countries. However, there is still one problem, which is how do we improve the energy efficiency of the existing distillation columns systems by without having major modifications. Recently, a new energy efficient distillation columns methodology that will able to improve energy efficiency of the existing separation systems without having major modifications has been developed. Therefore, the objective of this paper is to present new improvement of existing methodology by designing an optimal sequence of energy efficient distillation columns using driving force method. Accordingly, the methodology is divided into four hierarchical sequential stages: i) existing sequence energy analysis, ii) optimal sequence determination, iii) optimal sequence energy analysis, and iv) energy comparison and economic analysis. In the first stage, a simple and reliable short-cut method is used to simulate a base (existing) sequence. The energy consumption of the base sequence is calculated and taken as a reference for the next stage. In the second stage, an optimal sequence is determined by using driving force method. All individual driving force curves is plotted and the optimal sequence is determined based on the plotted driving force curves. Then, by using a short-cut method, the new optimal sequence is simulated and the new energy consumption is calculated in the third stage. Lastly, in the fourth stage, the energy consumption for both sequences (base and optimal) is compared. The capability of this methodology is tested in designing an optimal synthesis of energy efficient distillation columns sequence of aromatics separation unit. The existing aromatics separation unit consists of six compounds (Methylcyclopentane (MCP), Benzene, Methylcyclohexane (MCH), Toluene, m-Xylene and o-Xylene) with five direct sequence distillation columns is simulated using a simple and reliable short-cut method and rigorous within Aspen HYSYS® simulation environment. The energy and economic analysis is performed and shows that the optimal sequence determined by the driving force method has better energy reduction with total of 6.78% energy savings and return of investment of 3.10 with payback period of 4 months. It can be concluded that, the sequence determined by the driving force method is not only capable in reducing energy consumption, but also has better economic cost for aromatic separation unit

Sustainable energy efficient distillation columns sequence design of aromatic separation unit

Distillation operations became a major concern within sustainability challenge, which it becomes a primary target of energy saving efforts in industrially developed countries. However, there is still one problem, which is how do we improve the energy efficiency of the existing distillation columns systems by considering the sustainability criteria without having major modifications. Recently, a new energy efficient distillation columns methodology that will able to improve energy efficiency of the existing separation systems without having major modifications has been developed. However, this developed methodology was only considered the energy savings without taking into consideration the sustainability criteria. Therefore, the objective of this paper is to present new improvement of existing methodology by including a sustainability analysis to design an optimal sequence of energy efficient distillation columns. Accordingly, the methodology is divided into four hierarchical sequential stages: i) existing sequence sustainability analysis, ii) optimal sequence determination, iii) optimal sequence sustainability analysis, and iv) sustainability comparison. In the first stage, a simple and reliable short-cut method is used to simulate a base (existing) sequence. The sustainability index of the base sequence is calculated and taken as a reference for the next stage. In the second stage, an optimal sequence is determined by using driving force method. All individual driving force curves is plotted and the optimal sequence is determined based on the plotted driving force curves. Then, by using a short-cut method, the new optimal sequence is simulated and the new sustainability index is calculated in the third stage. Lastly, in the fourth stage, the sustainability index for both sequences (base and optimal) is compared. The capability of this methodology is tested in designing an optimal sustainable energy efficient distillation columns sequence of aromatics separation unit. The existing aromatics separation unit consists of six compounds (Methylcyclopentane (MCP), Benzene, Methylcyclohexane (MCH), Toluene, m-Xylene and o-Xylene) with five direct sequence distillation columns is simulated using a simple and reliable short-cut method and rigorous within Aspen HYSYS simulation environment. The energy and sustainability analysis is performed and shows that the optimal sequence determined by the driving force method has better energy reduction with total of 6.78 % energy savings and 0.16 % sustainability reduction compared to existing sequence with. In addition, the economic analysis shows that the return of investment of 3.10 with payback period of 4 months. It can be concluded that, the sequence determined by the driving force method is not only capable in reducing energy consumption, but also has better sustainability index for aromatic separation unit

Logic hybrid simulation-optimization algorithm for distillation design

In this paper, we propose a novel algorithm for the rigorous design of distillation columns that integrates a process simulator in a generalized disjunctive programming formulation. The optimal distillation column, or column sequence, is obtained by selecting, for each column section, among a set of column sections with different number of theoretical trays. The selection of thermodynamic models, properties estimation etc., are all in the simulation environment. All the numerical issues related to the convergence of distillation columns (or column sections) are also maintained in the simulation environment. The model is formulated as a Generalized Disjunctive Programming (GDP) problem and solved using the logic based outer approximation algorithm without MINLP reformulation. Some examples involving from a single column to thermally coupled sequence or extractive distillation shows the performance of the new algorithm.Spanish Ministry of Science and Innovation (CTQ2012-37039-C02-02)

The preliminary design of heat-integrated multicomponent distillation sequences through generation of flowsheet superstructures

Given that in 2012 distillation was estimated to consume roughly 3% of energy globally, managing the heating and cooling duties of these processes is essential. Currently, many process design strategies involve designing the separation system before energy integration is considered, leading to suboptimal solutions. In this thesis, a model for the preliminary design of a distillation sequence is presented as a MILP, using only basic thermodynamic data from feed components. The model has been developed based on a reduced superstructure with temperatures calculated via a discrete grid. Process streams from elsewhere in the plant are also considered concurrently, and consideration of these often changes the optimal sequence. The examples suggest cost reductions of over 30% when ancillary streams are not considered when compared to a basic heuristical approach, and up to 50% when a small number of additional process streams are included. The model was then further developed to include multieffect distillation, where separators are considered as a system of two parallel columns. Including the opportunity for multieffect distillation led to changes in the optimal sequence, with associated costs reduced by up to a further 30% compared to the previous iteration of the model. The model has been demonstrated on two industrial case studies; crude oil refining and platformate separation. Both examples demonstrate the flexibility of the model to deal with complex industrial problems, with the crude example showing optimise under an uncertain feedstock, while the platformate demonstrates the importance of including as much information about the process as possible to find the optimal result. As a preliminary design tool, the model should be used as initialisation for detailed process design. This has been investigated, with the distribution between multieffect columns made continuous. This led to further cost reductions with a short solution time, due to the initialisation offered by the linear models.Open Acces

Computer-Aided Sustainable Process Synthesis-Design and Analysis

Processyntese involverer undersøgelse af kemiske reaktioner, der er nødvendige for at producere det ønskede produkt, udvælgelse af separationsteknikker nødvendige for downstream forarbejdning, samt beslutninger om sekvensering af de involverede separationsprocesser. For en effektiv og fleksibel designtilgang, er der behov for en systematisk måde at identificere de typer af opgaver og operationer, der skal udføres, den tilsvarende design af operation-udstyr, deres konfiguration, masse-energistrømme m.v., hvilket giver et optimalt processkema. På grund af det faktum, at processynteseproblemer er af natur kombinatoriske og med flere mulige løsninger, er der blevet foreslået en forskellige metoder til at overkomme dette. Men løsningen til ethvert syntese-design problem er afhængig af søgningsområdet af alternativer og kriterierne for procesydeevne, som i de fleste tilfælde er påvirket af økonomiske faktorer. Dette arbejde fokuserer på udvikling og anvendelse af et computerstøttet platform for bæredygtig syntese-design og analyse af processkemaer ved at generere mulige alternativer, der dækker hele søgningsområdet og omfatter analyseværktøjer for bæredygtighed, LCA og økonomi. Syntesemetoden er baseret på en gruppebidragsbaseret hybridmetode, hvor kemisk processkemaer syntetiseres på samme måde som atomer eller grupper af atomer syntetiseres til dannelse af molekyler i computerstøttet molekylært design (eng: CAMD) teknikker. Byggestenene i et processkemasyntese problem er betegnet som procesgrupper, som repræsenterer en enkelt eller et sæt af enhedsoperationer, der er udvalgt på metoder baseret på termodynamiske grundlag. Disse byggesten kombineres derefter under anvendelse af regler for tilslutningsmuligheder for at generere alle de mulige processkemaalternativer. Den største fordel ved at repræsentere processkemaer med procesgrupper er, at udførelsen af hele processen kan vurderes fra bidragene fra de enkelte procestrinsgrupper mod processkemaegenskaberne (f.eks forbrugt energi). De udviklede processkemaegenskabsmodeller omfatter energiforbrug, carbon footprint, produktudvinding, produktrenhed osv. På denne måde er hele listen over mulige kemiske processkemaer hurtigt genereret, screenet og udvalgt til yderligere analyse. I det næste trin, er udformningen af de mest lovende processkemakandidater udført gennem en omvendt simulationsmetode, hvor designparametre for enhedsoperationer i processkemaet er beregnet ud fra udvalgte definitioner af procesgrupper. I næste fase analyseres det valgte design, til at identificere begrænsninger eller flaskehalse (hot-spots) ved hjælp af en omfattende analysemetode bestående af økonomiske, livscyklus og bæredygtigheds faktorer, der omsættes til procesdesignmål. I den afsluttende fase identificeres hot-spotsne, som er målrettet til den samlede procesforbedring og til at skabe innovative designs. I dette arbejde er den udviklede platform testet sammen med de tilhørende metoder og værktøjer gennem tre casestudier med relation til både kemiske og biokemiske industri med henblik på at fastslå anvendelsesmulighederne af platformen. I hvert af tilfældene er de mange alternativer og litteraturdesignene hurtigt genereret og evalueret. I alle de testede casestudier var de endelige designs, der genereres af platformen, nye og mere bæredygtige.Process synthesis involves the investigation of chemical reactions needed to produce the desired product, selection of the separation techniques needed for downstream processing, as well as taking decisions on sequencing the involved separation operations. For an effective, efficient and flexible design approach, what is needed is a systematic way to identify the types of tasks-operations that need to be performed, the corresponding design of the operation-equipment, their configuration, mass-energy flows, etc., giving an optimal flowsheet. Due to the fact that process synthesis problems are by nature combinatorial and open ended, a number of different solution approaches have been proposed. However the solution for any synthesis-design problem is dependent on the search space of alternatives and the process performance criteria which in most cases are influenced by economic factors. This work focuses on the development and application of a computer-aided framework for sustainable synthesis-design and analysis of process flowsheets by generating feasible alternatives covering the entire search space and includes analysis tools for sustainability, LCA and economics. The synthesis method is based on group contribution and a hybrid approach, where chemical process flowsheets are synthesized in the same way as atoms or groups of atoms are synthesized to form molecules in computer aided molecular design (CAMD) techniques. The building blocks in flowsheet synthesis problem are called as process-groups, which represent a single or set of unit operations that are selected by employing a thermodynamic insights based method. These building blocks are then combined using connectivity rules to generate all the feasible flowsheet alternatives. The main advantage of representing the flowsheet with process-groups is that, the performance of the entire process can be evaluated from the contributions of the individual process-groups towards the selected flowsheet property (for example, energy consumed). The developed flowsheet property models include energy consumption, carbon footprint, product recovery, product purity etc. In this way, the entire list of feasible chemical process flowsheets are quickly generated, screened and selected for further analysis. In the next stage, the design of the most promising process flowsheet candidates is performed through a reverse simulation approach, where the design parameters of the unit operations in the process flowsheet are calculated from selected process-groups definition. In the next stage the selected design is analyzed, for identifying process limitations or bottlenecks (hot-spots) using a comprehensive analysis method consisting of economic, life cycle and sustainability factors that are translated into design targets. In the final stage the identified hot-spots are targeted for overall process improvement and to generate innovative designs. In this work the developed framework along with the associated methods and tools is tested through three case studies related to both chemical and biochemical industry in order to ascertain the applicability of the framework. In each of the cases numerous alternatives of novel and designs reported by others are quickly generated and evaluated. In all the case studies tested, the final design generated by the framework was novel and more sustainable

An alternative disjunctive optimization model for heat integration with variable temperatures

This paper presents an alternative model to deal with the problem of optimal energy consumption minimization of non-isothermal systems with variable inlet and outlet temperatures. The model is based on an implicit temperature ordering and the “transshipment model” proposed by Papoulias and Grossmann (1983). It is supplemented with a set of logical relationships related to the relative position of the inlet temperatures of process streams and the dynamic temperature intervals. In the extreme situation of fixed inlet and outlet temperatures, the model reduces to the “transshipment model”. Several examples with fixed and variable temperatures are presented to illustrate the model's performance.The authors gratefully acknowledge financial support from the Spanish “Ministerio de Ciencia e Innovación” under project CTQ2012-37039-C02-02

Achievements and perspectives of process integration in cis countries

Due to the rapid growth in the world population, there has been an increase in energy consumption globally. The problem of efficient energy use becomes more relevant and stimulates research and development of new energy and resource-saving technologies. This task is becoming more complicated when the other factors are accounted for, resulting in multiple-factor trade-offs, such as the water-energy-food nexus. This paper highlights the main points for the development of Process Integration in the Commonwealth of Independent States (CIS) countries. It shows the main achievements in the field to date and demonstrates the scientific schools that are working on these problems. A comprehensive review of modern approaches and methods, which are now being developed or have been recently developed, was done. It shows a research gap in Process Integration in CIS and other leading countries. It demonstrates the significant research potential as well as practical applications. The main challenges in process systems engineering and for the sustainable development of industrial energy systems are also discussed. Industry digital transformation, energy transition, circular economy, and stronger energy and water integration are pointed out as priorities in analysis, design, and retrofit of society in the future. A state-of-the-art review in the area of integration of continuous and batch processes, mass integration technologies, and process intensification is presented to show the variety of existing approaches. The necessity of Process Integration development in the CIS is shown to be a necessary condition for building a more sustainable society and a resource-efficient economy