Aspen Tech Research Articles

Exergy Load Distribution Analysis Applied to the Dehydration of Ethanol by Extractive Distillation

This study presents the analysis of the exergy load distribution in a separation process by extractive distillation for ethanol dehydration. The methodology carried out is divided into three parts: the calculation of the flow exergy considering the physical and chemical exergies of the distillation process; the calculation of the primary and transformed exergy contributions considering the consumed exergy; and finally, the overall process efficiency, which shows the real percentage of energy being used in the process. The simulation of an extractive distillation separation system is carried out using Aspen Plus®, from Aspen Tech Version 9. In general, heat transfer processes (heating or cooling) are the ones that generate the greatest exegetic destruction, which is why they must be the operations that must be optimized. As a result of our case study, the local exergy efficiency of the extractive distillation column is 13.80%, which is the operation with the greatest energy loss, and the overall exergy efficiency of the separation system is 30.67%. Then, in order to increase exergy efficiency, a sensitivity analysis is performed with the variation of the azeotrope feed, number of stages, reflux ratio, and solvent feed variation on ethanol purity to reach an overall efficiency of 33.53%. The purity of ethanol is classified as higher than that of the specified, 99.65%.

Modelling and simulating CO and CO2 methanation over Ru/γ-Al2O3 catalyst: An integrated approach from carbon capture to renewable energy generation

The looping of carbon capture with power-to-gas technology is getting tremendous focus for the efficient inception of the methanation process. This will not only meet the growing energy demand but also reduce fossil fuel dependency and the climate change effects associated with it. In this work, a simulation approach was developed to model the methanation of CO and CO2 on a ppm basis over a ruthenium catalyst. The fast equilibrium reaction of CO2 to CO and slow kinetically-controlled hydrogenation of CO to CH4 was modelled within the same reactor. The catalyst particles of 0.5% Ru on γ-Al2O3 pellet supports were simulated on the Aspen Tech program. The fixed bed reactor was split into segments, consisting of equilibrium and kinetic reactors to model the relevant reactions. The effect of the reaction temperature, feed composition, and reactor volume was investigated. These parameters affected the reactor’s conversion with the reaction rate and the number of reactor segments required for convergence. An approach was developed to size a reactor for specific CO and CO2 conversions. With a reactor size of 13.85 m3, a 99.0% and 97.55% conversion of CO and CO2, respectively was achieved with 96.50% CH4 yield. This proved to have a high level of accuracy, with a maximum difference between the graphical and simulated conversions of 1.96%. Furthermore, the reaction mechanism was also elucidated, showing associative adsorption based CO2 and CO methanation over Ru-catalyst, forming oxygenated intermediates that subsequently hydrogenated to CH4. Altogether, results suggest this combined carbon capture approach and its utilization with power-to-gas technology can effectively contribute to sustainable renewable energy.

Separation of nitrogen from methane by multi-stage membrane processes: Modeling, simulation, and cost estimation

This study focuses on the application of multi-stage membrane separation processes for the removal of nitrogen from natural gas. Reliable modeling and process simulation are essential for the analysis of the gas separation process. A mathematical model was developed using thermodynamic models, like lattice fluid (LF) and non-equilibrium lattice fluid (NELF), for gas sorption and transfer model for gas diffusion in the membrane. The proposed mass transfer model was validated with the experimental data for the gas solubility and permeability in various glassy and rubbery membranes. Then the proposed model was coupled with Aspen Plus software (Aspen Tech) for simulation of different proposed configurations of the multi-stage membrane processes. The performance of various gas separation configurations was investigated in terms of product purity, methane recovery, total capital investment, and total annual cost. The results indicated that the membranes with higher permeability had more suitable economic parameters. For example, the total annual cost for the AF1600 membrane was seven times the total annual cost value for the PTMSP membrane in the single-stage membrane separation process. It was observed that the methane purity of above 96 %mol and methane recovery of 90% could not be achieved by the single-stage process. However, the specified separation criteria can be achieved via the multi-stage membrane processes by two or three membranes. The best configuration was selected from various proposed configurations by evaluating the economic parameters.

Separation of isobutanol/water mixtures by hybrid distillation-pervaporation process: Modeling, simulation and economic comparison

Hybrid separation processes based on the membrane processes are becoming more important in practice to overcome the thermodynamic limitations of the conventional separation processes as well as to develop more sustainable and economic processes. This study focuses on the use of the hybrid distillation-pervaporation process for the separation of isobutanol/water mixtures. For engineering design of the hybrid processes, reliable modeling and simulation of the process is indispensable. For the simulation of different configurations of the hybrid processes with Aspen Plus software (Aspen Tech), a mathematical model was developed for the pervaporation process based on the solution-diffusion mechanism using the Flory-Huggins and UNIFAC thermodynamic models and Lee’s equation. The simulation was performed for the separation of isobutanol/water mixtures with various isobutanol feed concentrations (5, 7, and 15 %wt.). It was found that for both single-phase and two-phase feed solutions, the hybrid hydrophobic-hydrophilic pervaporation process was the most economical configuration to reach the desired product purity. For the hybrid hydrophobic-hydrophilic pervaporation process with feed concentrations of 5, 7 and 15 %wt., the total annual cost was 62.9 %, 58.7 %, and 58.4 %, respectively, lower than the distillation process. Furthermore, by increasing the feed concentration, the membrane area required for the pervaporation-based hybrid process enhanced.

Thermo-economic analysis of PEM fuel cell fuelled with biomethane obtained from human waste by computer simulation

Fuel cells, especially Proton Exchange Membrane (PEMFC) is considered as perfect alternative energy source that can either replace or complement existing energy source which is fossil fuel. However, the technology is still at developmental stage due to the lack of availability of fuel sources that is safe and economical. This study, therefore focused on thermo-economic analysis of PEMFC fuelled with biogas from human waste. To achieve the purpose of this study, thermo-economic analysis was used to analyse PEMFC designed to generate 1.45 MW of electricity from domestic human waste. The stages involved are biogas generation, hydrogen production and fuel cell application. The processes were modelled using Aspen HYSYS V8.8, a software developed by Aspen Tech®. The Hydrogen was produced at a rate of 358 kgmole/h, temperature of 330 K, pressure of 4.8 bar and 99% purity from the Preferential oxidation (PrOx) exit stream. Data generated from the simulation model were subsequently used for the thermodynamic and economic analysis and a fuel processor efficiency of 83.5% was obtained. Energy analysis of the process showed that the principle of energy conservation was satisfied, requiring and producing energy simultaneously and a net electrical efficiency of 42.32% was realized, while the result of exergy analysis showed that the unit associated with high irreversibilities and maximum exergy destruction is the steam generator. From the economic analysis, a rate of return of 20% was realized which is an indication that the investment is safe and profitable. The general overview of the processes based on economic and thermodynamics performance shows that the investment is worthwhile and indeed waste can be turned to wealth.

Property Data Estimation for Hemiformals, Methylene Glycols and Polyoxymethylene Dimethyl Ethers and Process Optimization in Formaldehyde Synthesis

Polyoxymethylene dimethyl ethers (OMEn) are frequently discussed as alternative diesel fuels, with various synthesis routes considered. OME3–5 syntheses demand significant amounts of thermal energy due to the complex separation processes that they entail. Therefore, innovative process designs are needed. An important tool for the development of new processes is process simulation software. To ensure sound process simulations, reliable physico-chemical models and component property data are necessary. Herein we present the implementation of a state-of-the-art thermodynamic model to describe the component systems of formaldehyde-water and formaldehyde-methanol using Microsoft® Excel (2010, Microsoft Corp, Redmond, WA, USA) and Aspen Plus®, (V8.8, Aspen Tech, Bedford, MA, USA) determine the deviation between the calculated results and experimental literature data, and minimize the deviation by means of parameter fitting. To improve the accuracy of the estimation of the missing property data of hemiformals and methylene glycols formed from formaldehyde using group contribution methods, the normal boiling points were estimated based on molecular analogies. The boiling points of OME6-10 are determined through parameter regression in accordance with the vapor pressure equation. As an application example, an optimization of the product separation of the state-of-the-art formaldehyde synthesis is presented that helps decrease the losses of methanol and formaldehyde in flue gas and wastewater.

Post-pyrolysis treatments of biochars from sewage sludge and A. mearnsii for ammonia (NH4-n) recovery

NH4-N-loaded biochars are suitable candidates for soil amendment and fertilization. Sewage sludge-based biochar and biochar from the invasive species black wattle were used as sorbents for the adsorption of ammonia from a concentrated solution to mimic the wastewater treatment plant reject water stream. To increase ammonium recovery efficiency, two post-pyrolysis activation techniques were compared: steam activation and hydrogen peroxide treatment. It was found that the success of the treatment options was material dependent; therefore, post-pyrolysis treatments will require optimization for different applications based on feedstock. A simplified version of an adsorption process simulated in Aspen Tech predicts that NH4-N may be recovered at an energy cost lower than that of the Haber-Bosch process for black wattle biochar yields of below 19.5%. The biooil and syngas produced during pyrolysis can be used to lessen the energy requirements of the process, so that the solid portion may be utilized as an adsorbent and soil fertilizer. The energy-based sustainability of this technology warrants a more in-depth investigation for evaluation of the techno-economic feasibility for this class of loaded sorbents, and whether this method of nitrogen capture from wastewater is a suitable replacement of the costly Haber-Bosch process.

Numerical analysis of a serial connection of two staged SOFC stacks in a CHP system fed by methane using Aspen TECH

Abstract The objective of the study was to develop a steady-state system model in Aspen TECH using user-defined subroutines to predict the SOFC electrochemical performance. In order to achieve high overall fuel utilization and thus high electrical efficiency, a concept of Combined Heat and Power system with two-stage SOFC stacks of different number of cells was analyzed. The concept of two-stage SOFC stacks based system was developed in the framework of the FP7 EU-funded project STAGE-SOFC. The model was validated against data gathered during the operation of the proof-of-concept showing good agreement with the comparative simulation data. Following model validation, further simulations were performed for different values of fuel utilization to analyze its influence on system electrical performance. Simulation results showed that the concept of two-stage SOFC stacks configuration was viable and reliable. The model can be useful for development the optimal control strategy for system under safe conditions.

Response Surface Methodology and Aspen Plus Integration for the Simulation of the Catalytic Steam Reforming of Ethanol

The steam reforming of ethanol (SRE) on a bimetallic RhPt/CeO2 catalyst was evaluated by the integration of Response Surface Methodology (RSM) and Aspen Plus (version 9.0, Aspen Tech, Burlington, MA, USA, 2016). First, the effect of the Rh–Pt weight ratio (1:0, 3:1, 1:1, 1:3, and 0:1) on the performance of SRE on RhPt/CeO2 was assessed between 400 to 700 °C with a stoichiometric steam/ethanol molar ratio of 3. RSM enabled modeling of the system and identification of a maximum of 4.2 mol H2/mol EtOH (700 °C) with the Rh0.4Pt0.4/CeO2 catalyst. The mathematical models were integrated into Aspen Plus through Excel in order to simulate a process involving SRE, H2 purification, and electricity production in a fuel cell (FC). An energy sensitivity analysis of the process was performed in Aspen Plus, and the information obtained was used to generate new response surfaces. The response surfaces demonstrated that an increase in H2 production requires more energy consumption in the steam reforming of ethanol. However, increasing H2 production rebounds in more energy production in the fuel cell, which increases the overall efficiency of the system. The minimum H2 yield needed to make the system energetically sustainable was identified as 1.2 mol H2/mol EtOH. According to the results of the integration of RSM models into Aspen Plus, the system using Rh0.4Pt0.4/CeO2 can produce a maximum net energy of 742 kJ/mol H2, of which 40% could be converted into electricity in the FC (297 kJ/mol H2 produced). The remaining energy can be recovered as heat.

Dynamic simulation of modified claude cycle

The dynamic simulation of a modified Claude cycle has been carried out to liquefy Nitrogen. The cycle consists of two heat exchangers, one turboexpander and one J-T Valve. A phase separator is present to separate the liquid and vapor. The simulation model has been built using commercially available software Aspen Hysys® of Aspen Tech company. The paper aims to study the dynamic behavior to estimate the cool down time to get the liquid. To get the accurate results the sizing data of the heat exchangers and phase separator are given as input to the model. A level controller also used to maintain the liquid level of the phase separator. The transient behavior of streams inside the heat exchangers, the J-T valve, turboexpander and liquid volume percentage in the phase separator are discussed. This knowledge of simulation can be utilized for optimized operation of the plant.

DME 생산공정에서 메탄올을 이용한 이산화탄소 제거 공정 연구

본 연구에서는 Dimethyl ether (DME) 생산 공정 중에 포함되어 있는 이산화탄소 제거를 위한 용매로써 메탄올 수용액을 사용하는 공정에 대한 전산모사를 수행하였다. 공정모사를 위하여 Aspen tech 사의 Aspen Plus release 7.3을 사용하였으며, 열역학 모델식으로는 PC-SAFT 모델식을 사용하였다. PC-SAFT 모델식에서 필요한 이성분계 상호작용 매개변수를 결정하기 위하여 실험 데이터를 수집하고 회귀분석을 통해 새롭게 결정하였으며, 결정한 매개변수의 정확성은 실험 데이타와의 비교를 통해 검증하였다. 한편, 이러한 모델식과 검증한 매개변수를 사용하여 공정을 모델링 하였으며 최적 순환유량과 운전압력 그리고 원료 주입단 등을 결정하여 공정 최적화를 수행하였다. In this study, simulation works have been performed for the modeling of <TEX>$CO_2$</TEX> removal process contained in the DME production process through an absorber-stripper system using methanol aqueous solution. Aspen Plus release 7.3 in AspenTech company was utilized as a simulation tool and PC-SAFT modeling equation of state was used as a thermodynamic model. Fitting parameters built-in PC-SAFT model was determined by regressing experimental data, predicted results using PC-SAFT model were compared with experimental data in order to verify the exactness of the thermodynamic model. Optimization works have been performed to reduce the utility consumptions using solvent circulation rate, column operating pressure and feed stage location as manipulated variables.

Introducing process simulation in ionic liquids design/selection for separation processes based on operational and economic criteria through the example of their regeneration

The integration of COSMO-RS methodology to Aspen Tech’s process simulators is used in this work to elaborate new criteria for the design/selection of ionic liquids to specific applications. These criteria are related to the operating conditions and energetic consumptions being the procedure capabilities demonstrated through the example of the IL regeneration in separation processes. Previously, the predictive capacity of the COSMO-RS method respect to VLE of mixtures (organic solvent+IL) is assessed and the correct transferability of the COSMO-RS results to Aspen Plus/Aspen HYSYS process simulators demonstrated.

Simulation for Polymerization Process of Styrene Butadiene Rubber (SBR)

In this paper, Polymer Plus of Aspen Tech Inc. is used to establish a styrene-butadiene rubber (SBR) polymerization process model; the sensitivity analysis method is used to analyze concentration of the initiator, reaction temperature and other factors which influence production and molecular weight of product. It is concluded that increasing amount of initiator can improve production, while the molecular weight would increase at first and then decline; and along with the increasing temperature, weight-average molecular weight would lower and production of polymer PBS would increase; molecular weight of polymer and production of polymer would magnify along with increase of amount of emulsifier and volume of the reactor.

Performance evaluation of the conservation element and solution element method in SMB process simulation

The computational performance of the space–time conservation element and solution element method (CESE) is evaluated in solving simulated moving bed (SMB) chromatographic models, compared with a 2nd-order upwind discretization method (UDS2) and 4th-order orthogonal collocation finite element method (OCFE4) of ASPEN chromatography (ASPEN Tech, USA). A novel finite volume discretization is proposed for the CE/SE method to treat the exit boundary condition in the adsorption column close to plug-flow operation. A single column model and a linear/equilibrium SMB model which have the analytic solutions are used for the computational performance assessment of the numerical methods. For the two examples, CESE shows the superiority over UDS2 and OCFE4 in terms of computational efficiency and accuracy. Other five practical SMB examples which have no analytic solution are used to examine computational features of the three numerical methods. Using UDS2, it shows a fast calculation but the sufficient number of mesh points is required to enhance accuracy. The accuracy of CESE is comparable with OCFE4. Since CESE enforces both local and global flux conservation in space and time and is combined with the finite volume discretization of the exit boundary condition, its numerical solution of SMB adsorption models is accurate and computationally efficient.

Simulation of a hybrid pervaporation–distillation process

This study explores the possibility of simulating a hybrid pervaporation membrane process with the help of Aspen Plus™ (Aspen Tech) flowsheeting. Because Aspen Plus does not contain membrane modules in its Model Library, the pervaporation membrane is simulated within Excel Visual Basic for Applications (VBA). Excel VBA is then linked with Aspen Plus to perform the hybrid simulation. In this way, the user can control the simulation even during the calculations. Case studies, in which industrially relevant hybrid distillation–pervaporation processes are simulated, are used to test the program. First, the dehydration and recycling of ethanol in an industrial plant is looked at, to explore whether an economic improvement can be established with a hybrid process. Secondly, the same is done for the purification of acetic acid in an industrial plant. The results presented here indicate the value of this software as a design tool.

Producing fuel alcohol by extractive distillation: Simulating the process with glycerol

Downstream separation processes in biotechnology form part of the stages having most impact on a product's final cost. The tendency throughout the world today is to replace fossil fuels with those having a renewable origin such as ethanol; this, in turn, produces a demand for the same and the need for optimising fermentation, treating vinazas and dehydration processes. The present work approaches the problem of dehydration through simulating azeotropic ethanol extractive distillation using glycerol as separation agent. Simulations were done on an Aspen Plus process simulator (Aspen Tech version 11.1). The simulated process involves two distillation columns, a dehydrator and a glycerol recuperation column. Simulation restrictions were ethanol's molar composition in dehydrator column distillate and the process's energy consumption. The effect of molar reflux ratio, solvent-feed ratio, solvent entry and feed stage and solvent entry temperature were evaluated on the chosen restrictions. The results showed that the ethanol-water mixture dehydration with glycerol as separation agent is efficient from the energy point of view.

Exan™ Pro: Process visualization tool: Increasing your insight into energy conversion and large chemical processes

Exan Pro is a powerful tool for the visualization of process modeling results, which can be obtained using Aspen Plus™ or other flowsheeting packages. Clear Exergy, Energy, Molar, Mass, Volume, Process and Block flow diagrams can be created in an automatic way. In a flow diagram, the width of a stream schematically represents its contents. Exan Pro especially allows you to perform and visualize a complete exergy or energy analysis, which has been calculated using Aspen Plus, by Aspen Tech. Inc., and ExerCom, by Stork Engineers & Contractors b.v. In addition to the visualization using flow diagrams, the results can also be presented using total exergy or energy balance graphs and pies, showing the relative exergy losses. After loading the simulation results, the flowsheet is automatically laid out using specially developed algorithms. The main process flow path is shown in a straight line. Next, the other process paths branch from this main process path. This way the backbone of the flowsheet, is visualized in the form of a Tree. If the process is too complex for complete visualization in one step, the process can be partitioned into sub processes using the partitioning tools. Next, the utilities, which are used by the unit operations, can be assigned to the units, allowing separate modeling of the main process and the utility generation processes. After selecting the desired type of flow diagram, the flow diagram of the (partitioned) flowsheet is automatically send to Visio, a powerful technical drawing package. The flow diagrams can easily be sized, printed, edited and published in high quality, using this package. It can be concluded that clear visualization of process information through flow diagrams can be used as an efficient communication tool during process design. It increases the insight of process engineers into the processes. Weak spots in the simulated processwe quickly recognized and consequently the optimization of the process structure is accelerated. Therefore, process visualization contributes to a more rigorous design of efficient processes.

Split: A separation process designer

The development of chemical processes is a complex design problem, commonly performed as an evolution among synthesis, analysis and evaluation steps. Experience and skilled use of existing tools for process analysis and optimization allow designers to focus on the development of relatively few promising flowsheets. However, there is still a need for software systems supporting this activity. The blackboard-based integrated software environment SPLIT (“Separation Process Layout by Invention and Testing”) is conceived to automate the design of separation systems, while allowing the user the option to guide the solution process. The system can handle problem specifications at various levels of detail, using any available knowledge to restrict the number of alternative designs investigated. Resembling the control architecture AKORN-D proposed by Lien (Ph.D. Thesis, Univ. of Trondheim, Norway, 1988), SPLIT combines data-driven and goal-oriented strategies to provide a framework for opportunistic reasoning. Representations of the problem and the current state of the solution are embedded in the blackboard as several semantic hierarchies, some of which are dynamically created. Knowledge sources (KS) of two types screen the common memory blackboard for data patterns indicating their ability to be executed. Domain KS implement procedural knowledge about physical properties, the technologies available to perform required tasks, etc. Control KS are used to guide the problem solving behavior of the system; they are integrated in the same recognition/bidding cycle, but when selected by the scheduling function, only change foci of attention on tasks, partial solutions, or in general any object on the blackboard. Using a distributed problem solving framework (Cardozo, Ph.D. Thesis, Carnegie Mellon University, Pittsburgh, U.S.A., 1987), the blackboard system is being integrated with existing analysis/optimization tools. This framework is used within several domain knowledge sources to invoke such external programs as the flowsheeting program Aspen Plus (Aspen Tech, Aspen User Guide to Release 8.2 and 8.3, Cambridge, MA, 1988) or the optimization package DICOPT + + (Viswanathan and Grossmann, Computers chem. Engng, 14, 769–782, 1990) (a mixed-integer nonlinear programming package) for the analysis and optimization of partial and complete flowsheets. The focus of this paper is the way SPLIT addresses the presynthesis problem, i.e. the generation of a reasonable set of alternative separation processes, which may be incorporated in a superstructure in order to determine the best solution. The system first decomposes separation problems initially described through specifications of feed and product streams into explicitly represented binary split tasks. A classification of the components according to a criterion such as molecular structure is used to identify abstract tasks. This abstraction aids in the selection of technologies that can accomplish the necessary separations. Combined with novel representations of separation and mixing functionality, this approach enables the current prototype version of SPLIT to systematically develop promising flowsheet alternatives, including complex processes with recycles.