Rigorous Dynamic Simulation Research Articles

Design and evaluation of integrated energy system combining solar energy and compressed-air energy storage

A new integrated energy system (IES) has been proposed by combining the cooling, heating, and power generation (CCHP) system coupled with PV/T and compressed air energy storage (CAES). Based on the developed control operation strategy, rigorous system modeling and dynamic simulation are carried out by TRNSYS to determine the integrated operation effect of each subsystem. Energy utilization efficiency and annual value of costs were adopted to assess the benefits of the system. A building in Gansu Longnan area is selected as a study case. The study results show that the proposed system can meet the building load demand well. The PV efficiency and thermal efficiency are 0.17 and 0.19, respectively. The gas ratio of CAES storage tank is 0.94, which is safe and stable. In addition, the energy utilization is maximum when the internal combustion engine proportioning capacity is 30 % of the maximum heat load, which is 89.13 %. The annual value of the cost is 2.49 × 107 RMB during 40 years of operation.

Rigorous Dynamic Modeling and Simulation of an Industrial Liquid–Liquid Extraction Packed Column for Biodiesel Washing

Rigorous Dynamic Modeling and Simulation of an Industrial Liquid–Liquid Extraction Packed Column for Biodiesel Washing

Technical and economic analysis of multi-energy complementary systems for net-zero energy consumption combining wind, solar, hydrogen, geothermal, and storage energy

An integrated renewable energy supply system is designed and proposed to effectively address high building energy consumption in Zhengzhou, China. This system effectively provides cold, heat, and electricity by incorporating various clean energy sources such as wind, solar, hydrogen, and geothermal energy. Technical and economic analyses are conducted to optimize the integration of these renewable sources. Technical and economic analyses are conducted to optimize the integration of these renewable sources. Rigorous system modeling and dynamic simulation using TRNSYS software evaluate the seamless integration and optimal functioning of the PV/T subsystem within the CCHP system. The interaction between Photovoltaic/Thermal (PV/T) and borehole heat exchanger (BHE) coupling is investigated, analyzing their impact on individual system performance. Furthermore, key indicators, including overall electricity consumption (OEC), life cycle cost (LCC), heat pump coefficient of performance (COPHP), and system coefficient of performance (COPSYS) are analyzed. The robust response surface methodology (RSM) and Box-Behnken experimental design approach are employed to show remarkable agreement between predicted and simulated values, with a maximum deviation of only 1.45%. The optimal configuration consists of a PV/T area of 132 m2, 20 wind turbines, 12 alkaline fuel cells, and 17 borehole heat exchangers, resulting in highly favorable outcomes: an OEC of −35648.72 kW∙h/year, an LCC of $209113.85, a COPSYS of 2.91, and a COPHP of 3.82. Moreover, detailed assessments of each subsystem's performance enhances our understanding of the system's overall operation, affirming the feasibility of the proposed integrated energy supply system for buildings.

Rigorous dynamic simulation methodology for scenario-based safety analysis of pressure-swing distillation considering independent protections

Process engineers often assess process safety performance early in the design stage to reduce or eliminate potential hazards cost-effectively. Process simulation tools widely used in design can provide fast and precise hazard evaluation using limited design information. However, there is a knowledge gap on how to build rigorous dynamic process models and how model configurations can affect safety analysis results. This study applied commercial dynamic simulation software, Aspen Dynamics, to address these issues through rigorous dynamic simulations and safety analysis of a two-column pressure-swing distillation with top recycling. The study implements and simulates various layers of protection, including basic process controls, alarms, safety instrumented systems, and pressure relief systems, and evaluates their impact on accident prevention. The hazardous scenarios considered are overpressure and flooding in the distillation columns, and the dynamic responses to a set of deviations such as coolant and steam utility failures and undesired throughput and composition disturbances are investigated. A scenario-based safety analysis is performed to assess the dynamic safety performance and the effectiveness of protection layers. The results indicate that the presented scenario-based dynamic safety analysis methodology is essential for accurately determining dynamic column behaviors, thereby better assisting in determining process safety time and designing effective safety systems.

Compact process for cumene manufacture: Synthesis, design and control

A compact single-unit process is developed for continuous cumene manufacture via the alkylation of benzene with propylene. The design combines reactive distillation (RD) and dividing-wall separation in a single column. In terms of the TAC, it is significantly cheaper (42%) than the conventional “reaction followed by separation process” and only slightly more expensive than the RD process. The controllability of the developed compact design is confirmed via rigorous dynamic simulations that demonstrate effective process operation for large production rate and feed composition changes using a simple decentralized temperature inferential control system. The developed compact design is especially suitable for capacity expansion in space-constrained cumene manufacturing facilities.

Rigorous Dynamic Simulation of a Dehydration and Desalting Crude Oil Unit Using Aspen HYSYS®

Rigorous Dynamic Simulation of a Dehydration and Desalting Crude Oil Unit Using Aspen HYSYS®

Evaluation of Process Control Schemes for Sour Water Strippers in Petroleum Refining

For the sour water strippers in petroleum refinery plants, three prediction models were developed first, including the estimators of sour water feed concentrations using convenient online measurements, the minimum reboiler duty and the corresponding internal temperature at a specific location (Tstage,29). Feedforward control schemes were developed based on these prediction models. Four categories of control schemes, including feedforward, feedback, feedback with external reset, and feedforward-feedback, were proposed and evaluated by the rigorous dynamic simulation model of the sour water stripper for their dynamic responses to the sour water feed stream disturbances. The comparison of control performance, in terms of the settling time, integrated absolute error (IAE) of the NH3 concentration of the stripped sour water and IAE of the specific reboiler duty, reveals that FFT (feedforward control of Tstage,29) and FBA-DT3 (feedback control with 3 min concentration measurement delay) are the best control schemes. The second-best control scheme is FBAT (cascade feedback control of concentration with temperature).

Arterial pulsations drive oscillatory flow of CSF but not directional pumping

The brain lacks a traditional lymphatic system for metabolite clearance. The existence of a “glymphatic system” where metabolites are removed from the brain’s extracellular space by convective exchange between interstitial fluid (ISF) and cerebrospinal fluid (CSF) along the paravascular spaces (PVS) around cerebral blood vessels has been controversial. While recent work has shown clear evidence of directional flow of CSF in the PVS in anesthetized mice, the driving force for the observed fluid flow remains elusive. The heartbeat-driven peristaltic pulsation of arteries has been proposed as a probable driver of directed CSF flow. In this study, we use rigorous fluid dynamic simulations to provide a physical interpretation for peristaltic pumping of fluids. Our simulations match the experimental results and show that arterial pulsations only drive oscillatory motion of CSF in the PVS. The observed directional CSF flow can be explained by naturally occurring and/or experimenter-generated pressure differences.

Enhanced separation of mixing diols by distillation in dividing wall column

Dividing wall column (DWC) was used to separate the system (1,2-propylene glycol + 1,3-butanediol + 1,4-butanediol). No research in a DWC has focused on such systems which were difficult to be separated for their great similarity in both molecular structures and properties. The rigorous steady-state and dynamic simulations, as well as the optimization of DWC alternative were performed with Aspen Plus and Aspen dynamics. Sequential quadratic programming (SQP) optimization method and the efficient sensitivity analysis tool were used to minimize the total reboiler and condenser duties. Moreover, a flow rate-composition cascade control structure was first developed to maintain targeted product purity under various external disturbances as feed flow rate and side product composition changed. DWC was compared with both a side rectifier configuration and conventional two-column distillation sequence in energy requirements and total annual costs (TACs) with the same number of stages. It showed that the energy requirements and TAC by DWC were reduced 47.60 % and 35.40 % respectively, compared with conventional distillation sequence, energy savings of 48.00 % and 34.11 % lower TAC compared with side rectifier configuration. This study provided a potential solution for the distillation of the systems with similar molecular structures and properties in a DWC.

Use of Modern Digital Software to Model the Motion Dynamics of Spacecraft during Landing

Landing systems for future space missions in Earth and Mars require trustable technologies capable of achieving their aim in the most accurate way possible. For this purpose, systems should go through rigorous dynamic simulations run by precise and efficient software. This study aims to approximately determine the dynamic motion of a landing vehicle using the modern digital software of Universal Mechanism and MATLAB. Universal Mechanism applies the classic mechanics theory on a model based on the geometry of the spacecraft, taking into account the environmental conditions that affect its motion and the properties of the ground to resist its impact [1]. The forces implied in the vehicle phase of descent are also included in MATLAB code to calculate the landing area of the vehicle according to its re-entry velocity [2-4]. Studies were conducted for different initial conditions and approaches to the surface. As a result, the values of the arising overloads and forces acting on the descent vehicle were obtained [1]. The data provided by the simulations conclude the safest landing options that should be taken into account for the success of future missions.

Rigorous Dynamic Simulation of Cryogenic Distillation of Hydrogen Isotopologues in the Fuel Cycle of a Thermonuclear Reactor Based on UV Flash

Operation of the fuel cycle of a thermonuclear fusion reactor naturally leads to accumulation of surplus protium, but in some cases it can also lead to accumulation of surplus deuterium. Both surplus protium and deuterium have to be separated, detritiated, and discharged to the environment, normally passing a final detritiation stage based on either the liquid phase catalytic exchange or water distillation process. The concept of a multicolumn cryogenic distillation (CD) system capable of discharging a time-varying surplus of deuterium is presented in this paper. A model of a CD column based on a UV (internal energy U – volume V) flash formulation and equation of state (EOS) thermodynamic model for hydrogen isotopologue mixtures is also presented at the principal step to a comprehensive model of the isotope separation system. Although fundamental for constant volume systems, the UV formulation of the thermodynamic state has not been widely used in transient simulations; in particular, for distillation dynamics modeling, other approaches are much more common. At the same time, in helium cryogenics the UV formulation has gained wide usage in large-scale dynamic simulations. It is known from the literature that a UV formulation of the distillation problem is very challenging for a numerically stable implementation. To cope with this situation, we present our findings on the sources of numerical instabilities and approaches.

High-purity liquefied gases: Aspen Dynamics simulation of a purification process in a middle-vessel batch distillation column

The paper explores the use of Aspen Plus and Aspen Dynamics for simulating and optimising a high-precision process of liquefied gases high purification in a middle-vessel packed distillation column. The example studied involves the removal of lower- and higher- boiling impurities from the upper- and lower rectifying sections and maintaining the purified product in the middle vessel. Total reflux operation is studied in the pressure range between the normal boiling point of the purified product and the critical point. Among the considered aspects are the column design and sizing, hydrodynamics study (flooding calculations), the effect of operating pressure and temperature on the thermodynamics of vapour-liquid equilibrium and mass-transfer kinetics in a wide range of operating conditions. The paper demonstrates that the effects and dependencies observed previously through the experiments and by using user-developed custom models are adequately reproduced in the commercial simulator (Aspen Plus) by setting up a fictitious steady-state continuous process with rigorous built-in models. The optimised flowsheet can be converted to Aspen Dynamics as a pressure-driven process where a rigorous dynamic simulation gives a realistic dynamic response, and alternative control structures can be explored.

Evaluating isotherm models for the prediction of flue gas adsorption equilibrium and dynamics

We evaluated isotherm models for the precise prediction of adsorption equilibrium and breakthrough dynamics. Adsorption experiments were performed using pure N2, CO2 and their binary mixture with an activated carbon (AC) material as an adsorbent. Both BET and breakthrough measurements were conducted at various conditions of temperature and pressure. The corresponding uptake amount of pure component adsorption was experimentally determined, and parameters of the four different isotherm models, Langmuir, Langmuir-Freundlich, Sips, and Toth, were calculated from the experimental data. The predictive capability of each isotherm model was also evaluated with the binary experimental results of binary N2/CO2 mixtures, by means of sum of square errors (SSE). As a result, the Toth model was the most precise isotherm model in describing CO2 adsorption equilibrium on the AC. Based on the breakthrough experimental result from the binary mixture adsorption, non-isothermal modeling for the adsorption bed was performed. The breakthrough results with all of the isotherm models were examined by rigorous dynamic simulations, and the Toth model was also the most accurate model for describing the dynamics.

One-layer gradient-based MPC + RTO of a propylene/propane splitter

Here, the implementation of the gradient-based Economic MPC (Model Predictive Control) in an industrial distillation system is studied. The approach is an alternative to overcome the conflict between the MPC and RTO (Real Time Optimization) layers in the conventional control structure. The study is based on the rigorous dynamic simulation software (SimSciDynsim®) that reproduces the real system very closely and is able to communicate with Matlab. The gradient of the economic function, is obtained through the sensitivity tool of the real-time optimization package (SimSciROMeo®). In order to study the pros and cons of the new strategy, a propylene distillation system is simulated with both, the proposed approach (one-layer MPC+RTO) and the conventional two-layer hierarchical structure of control and optimization. The results show that, for this particular system, from the performance, stability and disturbance rejection viewpoint, the proposed gradient-based extended control method is equivalent or better than the conventional approach.

Continuous diisobutylene manufacturing: Conceptual process design and plantwide control

The complete process design cycle encompassing flowsheet synthesis, design and controllability evaluation is studied for continuous DIB manufacturing. The residue curve map tool is applied to synthesize two new flowsheets, FS1 and FS2, exploiting pressure swing distillation. A unique feature of these is the use of a decanter for recovery and recycle of water, which allows maintaining the reactor tert-butyl alcohol content at the desired level for suppressing the side reaction. Unlike the literature flowsheet (FS0), this innovation makes it possible to achieve both high conversion and high yield for an economically superior design. Between FS1 and FS2, FS1 is found to be superior with significantly lower capital and energy costs as well as lower fresh water consumption. A “smart” control strategy for holding the single-pass reactor conversion and the overall process yield towards economic process operation is also developed. Rigorous dynamic simulations demonstrate the controllability of FS1 and FS2.

Control of Quaternary Ideal Endothermic Reactive Distillation with and without Internal Heat Integration

AbstractDecentralized control system design is evaluated for a basic and an internally heat‐integrated generic, ideal, double‐feed, two‐product reactive distillation system. The internally heat‐integrated reactive distillation column (HiRDC) is obtained via catalyst redistribution into the rectifying zone and feed tray relocation. For basic regulatory control, three two‐point control structures with a fixed reflux rate or a fixed reflux ratio operation policy are synthesized and evaluated for their closed‐loop disturbance rejection characteristics using rigorous dynamic simulations. To eliminate the purity offsets for on‐target product purities, product purity composition controllers manipulating the reflux ratio and stripping tray temperature set point are implemented. Reactive tray section composition control is necessary for on‐target product purity operation of HiRDC.

Numerical analysis of thermal decomposition for RDX, TNT, and Composition B

Demilitarization of waste explosives on a commercial scale has become an important issue in many countries, and this has created a need for research in this area. TNT, RDX and Composition B have been used as military explosives, and they are very sensitive to thermal shock. For the safe waste treatment of these high-energy and highly sensitive explosives, the most plausible candidate suggested has been thermal decomposition in a rotary kiln. This research examines the safe treatment of waste TNT, RDX and Composition B in a rotary kiln type incinerator with regard to suitable operating conditions. Thermal decomposition in this study includes melting, 3 condensed phase reactions in the liquid phase and 263 gas phase reactions. Rigorous mathematical modeling and dynamic simulation for thermal decomposition were carried out for analysis of dynamic behavior in the reactor. The results showed time transient changes of the temperature, components and mass of the explosives and comparisons were made for the 3 explosives. It was concluded that waste explosives subject to heat supplied by hot air at 523.15K were incinerated safely without any thermal detonation.

Off-cut Recycle for Batch and Batch Extractive Distillation Separation of a Multicomponent Azeotropic Mixture

The influence of recycling off-cuts for the batch and batch extractive distillation separation of a four component (methanol- THF- water- toluene) waste solvent mixture of a pharmaceutical plant is studied by rigorous dynamic simulation. The evolution of the charge composition, of the amount of fresh feed and that of methanol product are determined for six consecutive productions of batch rectification. As an alternative of the traditional batch distillation, batch extractive distillation by using water as entrainer is also studied. Water feeding is applied during the heating-up phase, in order to decrease the methanol concentration in the column top, in this way reducing methanol loss with the fore-cuts. The profit of the productions is calculated on the basis of the operational and incineration costs and the price of the methanol. The influence of the volume of the first fore-cut, which is later incinerated, on the profit of the whole production process is also investigated and its optimal amount is determined for both separation methods. For the extractive process the profit of the regeneration is higher, the optimal volume of the first fore-cut is lower, which means a reduction in the air pollution caused by the incineration.

A new batch extractive distillation operational policy for methanol recovery

The recovery of methanol from a multicomponent aqueous waste solvent mixture was studied. The components form several minimum azeotropes, of which the methanol-THF and methanol-toluene azeotropes limit the recovery of methanol by traditional batch distillation (BD). THF and toluene are removed in the fore-cut, causing a significant loss of methanol. The addition of water decreases both methanol-THF and methanol-toluene relative volatility, and therefore by feeding water as entrainer, methanol loss can be decreased. A new BED operational policy is suggested, where water feeding is applied only during the heating-up of the column (BED1). Compared to BD, at the end of the heating-up, the concentration of organic pollutants is increased, and that of methanol is significantly decreased in the top of the column. Water feeding can continue during the fore-cut (BED2), but this increases the amount of fore-cut and dilutes the mixture from which methanol is recovered. Laboratory experiments were performed in a packed column to compare the BD and the two BED operational policies. The highest recovery was obtained by BED1, the lowest one by BD. The preliminary and posterior rigorous dynamic simulation of the experiments was made with a professional dynamic flowsheet simulator. Industrial-size pilot productions of BD and BED1 in a 50 bubble cap tray column also showed a 5% increase in methanol recovery.

Heat-Integrated Pressure-Swing Distillation Process for Separation of a Maximum-Boiling Azeotrope Ethylenediamine/Water

A partially heat-integrated pressure-swing distillation process is designed for the separation of a maximum-boiling azeotrope of ethylenediamine/water. Aspen Plus and Aspen Dynamics are used to study rigorous steady state and dynamic simulations for this neat operation. An optimized configuration of this process is developed based on the proposed partial optimization and global economical optimization. From the results, it is found that the process with partial heat integration is more competitive than the non-heat-integrated one from the economic point view. The partially heat-integrated process helps save energy consumption of 19.79% and TAC of 15.30%, respectively. Basic and improved control structures are explored in this system, so that the better control solutions are discussed from the comparison. Purity fluctuations of products can be decreased by adding a ratio control block in the process. And the dynamic control is kept within acceptable limits.