Simulation Of Chemical Processes Research Articles

Enhancing low-grade thermal energy recovery in a thermally regenerative ammonia battery using elevated temperatures.

A thermally regenerative ammonia battery (TRAB) is a new approach for converting low-grade thermal energy into electricity by using an ammonia electrolyte and copper electrodes. TRAB operation at 72 °C produced a power density of 236 ± 8 Wm(-2), with a linear decrease in power to 95 ± 5 Wm(-2) at 23 °C. The improved power at higher temperatures was due to reduced electrode overpotentials and more favorable thermodynamics for the anode reaction (copper oxidation). The energy density varied with temperature and discharge rates, with a maximum of 650 Wh m(-3) at a discharge energy efficiency of 54% and a temperature of 37 °C. The energy efficiency calculated with chemical process simulation software indicated a Carnot-based efficiency of up to 13% and an overall thermal energy recovery of 0.5%. It should be possible to substantially improve these energy recoveries through optimization of electrolyte concentrations and by using improved ion-selective membranes and energy recovery systems such as heat exchangers.

Reaction kinetics of the electrochemical oxidation of CO and syngas fuels on a Sr2Fe1.5Mo0.5O6−δperovskite anode

Concurrent simulation of chemical and electro-chemical processes on Sr2Fe1.5Mo0.5O6−δpredicted a higher activity for CO/syngas fuels for a surface with higher Mo content.

Establishment of Three Components of Biomass Pyrolysis Yield Model

Abstract Based on the chemical process simulation software Aspen Plus, the biomass pyrolysis model was established by Ryield reactor. In the Ryield reactor, a compiled fortran subroutine was embedded to calculate the yield of reaction product. With rice straw as the sample, the model calculated the product yield and component contents of pyrolysis gas under different temperatures. The results indicate that with the temperature increases from 350 o C to 600 o C, the yield of coke and bio-oil gradually decrease, while the yield of non-condensable gas gradually increases. Meanwhile, among the non-condensable gas components, the volume fraction of CO rapidly increases, the volume fraction of CO 2 rapidly decreases, and the volume fraction of CH 4 increases slowly. Compared the calculated values with the experimental values, the results show that biomass pyrolysis model can simulate the variation of biomass pyrolysis effectively and it can provide some reference for the development and optimization of biomass pyrolysis technology.

A comparison of conventional and reduction approaches for phase equilibrium calculations

A major part of the computational effort in chemical process simulation and compositional reservoir simulation is spent by phase equilibrium calculations: phase split and phase stability analysis. The calculation algorithms must be efficient and highly robust. The reduction methods offer an attractive alternative to conventional methods. Several recent papers have questioned on the efficiency of the reduction methods as compared to conventional methods, concluding that reduction methods become faster than conventional ones starting from a certain number of components. In this work, besides evaluating the computational effort required by various conventional and reduction formulations, the efficiency (per iteration and global) of stability testing and flash calculations is evaluated separately, the condition of the linear system of equations is analyzed, as well as the influence of symmetry properties and of the linear solver. Some important links are formally established between conventional and reduced methods and between different reduction methods. Numerical experiments carried out with several mixtures confirm that flash calculations using the reduction methods are more efficient than conventional methods only for mixtures with many components (more than 20) and few non-zero binary interaction parameters; this means that reduction methods for phase split are suitable for process simulation (mixtures may contain hundreds of components), but there are not suitable for compositional simulation, where the number of components is limited, typically to a dozen. On the contrary, for phase stability testing, it is shown that reduction methods are more efficient than conventional ones even for mixtures with few components, thus they are suitable for compositional simulation. This observation is very important since, in most compositional reservoir simulators, no explicit phase split is required, flash calculations being part of a larger problem (coupled with flow equations), while phase stability testing must be performed in most grid blocks.

Approaching virtual process engineering with exploring mesoscience

Different disciplines deal with mesoscale problems between the scales of element (micro) and system (macro) in different ways. Usually, coarse-graining or statistical approaches, which are averaging approaches, are used. However, averaging approaches tend to lack or ignore the governing principles ruling phenomena at mesoscales between elements and systems. Mesoscience will enable us to explore the principles common to all mesoscales to correlate parameters between micro- and macroscales.In chemical engineering, understanding dynamic multiscale structures, which are critical to reaction and transport processes, remain a challenge because they are all complicated at mesoscales of three levels: material, reactor and system, making it difficult to solve problems at each level and to correlate these levels. This paper reviews three decades of work on mesoscale phenomena in chemical engineering from principles, modeling, and simulation, through to application and generalization. It is revealed that all mesoscale phenomena in these systems follow a common principle of compromise in competition between dominant mechanisms, and can be generally formulated as a multiobjective variational problem. This leads to recognition of the possibility of an interdisciplinary science, mesoscience, to encompass all mesoscale problems existing between elemental particles and the observable universe.The possibility of realtime simulation of chemical processes based on mesoscale modeling is discussed, focusing on the structural and logical similarity between problem, model, software and hardware. Finally, this review is concluded with the prospects of the emerging mesoscience, the development of multiscale computation, and the possible realization of virtual reality. It is believed these advances will mark a new age of chemical engineering if materialized, subject to the resolution of three mesoscales and bridging of the two gaps between levels.

Homotopy with Second-Order Correction Based Backtracking Method for Chemical Process Simulation

The design and management of chemical manufacturing processes, including performance assessment and product quality evaluation, always involve frequent simulation. The equation-oriented approach is one of the most competitive strategies in process simulation, but this approach is difficult to implement because of the complexity and nonlinearity of chemical processes. In this study, a homotopy-based backtracking method (HBM) for simulation is improved with a second-order correction, which can be calculated with low computational cost. The theoretical foundation for the proposed homotopy with second-order correction based backtracking method (SOC-HBM) is also established. Simulation runs of production of secreted protein in a fed-batch reactor, a penicillin fermentation process, and a binary distillation column system are demonstrated using SOC-HBM.

A parallel finite element method for two-phase flow processes in porous media: OpenGeoSys with PETSc

In past decades, high performance computing has became a valuable tool in many fields of environmental science and technology to utilize computational power for better characterization of the complexity of environmental systems as well as predicting their evolution in time. In this work, a parallel computing technique is presented for the numerical simulation of two-phase flow processes in porous media. The Galerkin finite element method (FEM) is used to solve the initial boundary value problem arising from the underlying mathematical model. The PETSc package is utilized for parallelization of the computational task in both the global assembly of the system of linear equations and the linear solver. In order to parallelize the global assembly of the linear equation system, the overlapping domain decomposition method is used. The preset parallel FEM approach is realized within the framework of OpenGeoSys, an open source C++ finite element code for numerical simulation of thermal, hydraulic, mechanical and chemical processes in fractured porous media. The computational efficiency of the approach has been tested with three examples of increasing complexity, the five spot benchmark, dense non-aquaeous phase liquid infiltration into a inhomogeneous porous medium and a real-world application to the $$\mathrm {CO}_2$$ storage research site: Ketzin, in Germany.

Efficiency Analysis of Advanced G Class Gas Turbine Feed with Synthetic Natural Gas (SNG) and Mixture Gas of Syngas and SNG

The system-level simulation model for Natural Gas Combined-Cycle (NGCC) plant combines advanced G class turbine with various fuels was performed in the study. The commercial chemical process simulator, Pro/II® V8.1.1, is used in the study to build the analysis model. There are three major sections which are gas turbine (GT), heat recovery steam generator (HRSG) and steam turbine (ST).The study envisages two analyses as the basic and feasibility cases. The former is the benchmark case which is verified with the reference data of exist NGCC power plant located in Dah-Tarn, Taiwan. The Dah-Tarn NGCC power plant introduces the advanced M501G gas turbine from Mitsubishi Heavy Industries, Ltd. (MHI) and the system efficiency of the combined-cycle is 58.75 % (LHV). The latter introduces a feasibility study with advanced gas turbine and actual parameters in Taiwan. The SNG from carbonate fuel feed to M501G based combined-cycle is evaluated in the feasibility study cases first, and the mixture gas of SNG and syngas is also evaluated to compare the different of overall performance with the pure SNG case.The results show that the system efficiency of pure SNG case is around 57 % (LHV). For the mixture gas case, the maximum ratio of syngas to SNG is 1:19, due to keep the same composition of methane is 85.9 % with the Dah-Tarn NGCC power plant. The efficiency of mixture gas case is 55.75 % (LHV).The study shows the possibility way to use coal and reduce the CO2 emission. The another advantage is the using of SNG could increases the usage of combined-cycle in Taiwan, due to the prices of natural gas is higher than coal in Taiwan and results in the higher idle capacity.

Predictive displays for a process-control schematic interface.

Our objective was to examine the extent to which increasing precision of predictive (rate of change) information in process control will improve performance on a simulated process-control task. Predictive displays have been found to be useful in process control (as well as aviation and maritime industries). However, authors of prior research have not examined the extent to which predictive value is increased by increasing predictor resolution, nor has such research tied potential improvements to changes in process control strategy. Fifty nonprofessional participants each controlled a simulated chemical mixture process (honey mixer simulation) that simulated the operations found in process control. Participants in each of five groups controlled with either no predictor or a predictor ranging in the resolution of prediction of the process. Increasing detail resolution generally increased the benefit of prediction over the control condition although not monotonically so. The best overall performance, combining quality and predictive ability, was obtained by the display of intermediate resolution. The two displays with the lowest resolution were clearly inferior. Predictors with higher resolution are of value but may trade off enhanced sensitivity to variable change (lower-resolution discrete state predictor) with smoother control action (higher-resolution continuous predictors). The research provides guidelines to the process-control industry regarding displays that can most improve operator performance.

Transient analysis of shell-and-tube heat exchangers using an educational software

Computer-aided design has become extremely popular and its use in classroom can be very helpful, adding more analysis capabilities to all engineering areas. A free piece of educational software to teach transient analyses of shell-and-tube heat exchanger equipment to undergraduate students is presented. The software was developed to provide unit operation courses with realistic exercises involving dynamic simulation of chemical processes. The use of the program improves the efficiency of the course since it let students practice heat exchanger analysis while relieving them of tedious repetitive calculations.

Recent developments in QM/MM methods towards open-boundary multi-scale simulations

Combined quantum mechanics/molecular mechanics (QM/MM) methods have been widely used in multi-scale modelling and simulations of physical, chemical and biological processes in complex environments. In this review, we provide an overview of the recently developed QM/MM algorithms, with emphasis on our works, towards the ultimate goal of establishing an open boundary between the QM and MM subsystems. The open boundary is characterised by on-the-fly exchanges of partial charges and atoms between the QM and MM subsystems, allowing us to focus on the small QM subsystem of primary interest in dynamics simulations. An open-boundary scheme has the promise to the utilisations of small QM subsystems, high-levels of QM theory and long simulation times, which can potentially lead to new insights.

Integration of different models in the design of chemical processes: Application to the design of a power plant

With advances in the synthesis and design of chemical processes there is an increasing need for more complex mathematical models with which to screen the alternatives that constitute accurate and reliable process models. Despite the wide availability of sophisticated tools for simulation, optimization and synthesis of chemical processes, the user is frequently interested in using the ‘best available model’. However, in practice, these models are usually little more than a black box with a rigid input–output structure. In this paper we propose to tackle all these models using generalized disjunctive programming to capture the numerical characteristics of each model (in equation form, modular, noisy, etc.) and to deal with each of them according to their individual characteristics. The result is a hybrid modular–equation based approach that allows synthesizing complex processes using different models in a robust and reliable way. The capabilities of the proposed approach are discussed with a case study: the design of a utility system power plant that has been decomposed into its constitutive elements, each treated differently numerically. And finally, numerical results and conclusions are presented.

Simulation of Two-Stage Fuel Reactor Chemical Looping Hydrogen Process Using Solid Fuel

Chemical looping hydrogen (CLH) has become a promising technology for hydrogen production with inherent separation of carbon dioxide. Aspen Plus was used to simulate a two-stage fuel reactor CLH process of coal as solid fuel. Simulation results show that the two-stage reactor can fully convert the fuel and generate the maximum Fe0.947O component to react with the steam in steam reactor. The optimum OC/coal molar ratio in the two-stage fuel reactor was 2.8. The CO2 fraction of the flue gas in the fuel reactor reached 99% when the vapor was condensed at the temperature of 950 °C. The fraction of dry-based H2 in the steam reactor was nearly 100% when the steam reactor temperature was 700 °C and the steam/oxygen carrier molar ratio was 0.48.

A novel high level canonical piecewise linear model based on the simplicial partition and its application

The piecewise linear (PWL) model has attracted more and more attention in recent research because it can handle complex nonlinearity while maintaining linearity in local regions. A large number of compact representations for PWL modeling have been introduced, such as hinging hyperplanes and its generalized version. However, the existing methods usually give rise to many and complex subregions, which is an issue known as “curse of partitions”, and hampered practical applications of PWL models. In this paper, a novel high level canonical PWL model is presented to tackle the curse of partitions. In more detail, an improved simplicial partition strategy with alterable intervals is proposed to improve the model representation capability. The proposed PWL model guarantees an unchangeable topology during training and thus a limited number of subregions after training. Several numerical experiments, and a simulated chemical process, are used to demonstrate the effectiveness of the proposed model.

Comparative Assessment of Gasification Based Coal Power Plants with Various CO2 Capture Technologies Producing Electricity and Hydrogen

Seven different types of gasification-based coal conversion processes for producing mainly electricity and in some cases hydrogen (H2), with and without carbon dioxide (CO2) capture, were compared on a consistent basis through simulation studies. The flowsheet for each process was developed in a chemical process simulation tool “Aspen Plus”. The pressure swing adsorption (PSA), physical absorption (Selexol), and chemical looping combustion (CLC) technologies were separately analyzed for processes with CO2 capture. The performances of the above three capture technologies were compared with respect to energetic and exergetic efficiencies, and the level of CO2 emission. The effect of air separation unit (ASU) and gas turbine (GT) integration on the power output of all the CO2 capture cases is assessed. Sensitivity analysis was carried out for the CLC process (electricity-only case) to examine the effect of temperature and water-cooling of the air reactor on the overall efficiency of the process. The results show that, when only electricity production in considered, the case using CLC technology has an electrical efficiency 1.3% and 2.3% higher than the PSA and Selexol based cases, respectively. The CLC based process achieves an overall CO2 capture efficiency of 99.9% in contrast to 89.9% for PSA and 93.5% for Selexol based processes. The overall efficiency of the CLC case for combined electricity and H2 production is marginally higher (by 0.3%) than Selexol and lower (by 0.6%) than PSA cases. The integration between the ASU and GT units benefits all three technologies in terms of electrical efficiency. Furthermore, our results suggest that it is favorable to operate the air reactor of the CLC process at higher temperatures with excess air supply in order to achieve higher power efficiency.

A software environment for economic NMPC and dynamic real-time optimization of chemical processes

Abstract This paper presents the OptoEcon-Toolbox, a modular software environment for the simulation of chemical and energy processes, and their control using optimizing sampled-data controllers. Key features of this toolbox are modularity, which allows the realization of general multi-layer control architectures, and interfaces to powerful numerical software, which allows the usage of controller and plant surrogate models formulated in different modeling languages such as Modelica or gPROMS. The capability of this toolbox is illustrated in a case study of an industrial copolymerization process.

Lowering the Energy Cost of Carbon Dioxide Capture using Ejectors for Waste Heat Upgrading

Abstract The largest technical challenge to full-scale post-combustion carbon capture in power plants is the enormous energy consumption for solvent regeneration. If legislative requirements impose CO 2 capture, chemical absorption/desorption using amine solvent solutions is the most mature commercial technology available. The use of ejectors to upgrade external waste heat has recently been shown to significantly reduce the amount of valuable turbine steam required to regenerate the solvent. Using the Aspen Plus chemical process simulator, this study considers three different liquid sources for producing the ejector secondary steam in a waste heat supplied flash tank. In each case the goal is to minimize the sum of the heat duty of the ejector primary steam generator and the stripping tower reboiler. A base case 20 wt% MEA absorption/desorption CO 2 capture process was modeled, with flue gas data from a 400 MW net power coal-fired electric plant. Using stripping column condensate or lean solution to create the ejector secondary steam were found to be viable options for reducing valuable turbine steam consumption, with respective reductions of 14% and 23% shown for the completed simulations. With ejectors, lower temperature waste heat can be used to partially replace valuable turbine steam normally required in the reboiler for solvent regeneration in CO 2 capture.

Research on Simulation of Complex Distillation System for Biomass Fuel Ethanol Based on Virtual Assembly

Virtual assembly was introduced in the chemical process simulation, and the method of virtual assembly for common chemical process was studied. The process of biomass fuel ethanol was analyzed which is combined by the first-grade distillation system in industrial ethanol production and the salt-added extractive distillation system in fuel ethanol production, and the scene graph structure was established. According to the assembly characteristics of the chemical process, the assembly equipment model was designed and constructed. The assembly points were added, and the assembly, simulation and transitive properties of the assembly points were defined. The 1+1and 1+n universality assembly method was proposed. By choosing unit equipment freely to assembly, the complex distillation system was realized. Results have shown that the assembly effect was good and accuracy, the method was proved correct and feasible. It is of great significance in the visual design of chemical process, digital construction of chemical plant and development of three-dimensional (3D) chemical process simulation technology.

Numerical Simulation of Chemical Stripping Process in Resid Fluid Catalytic Cracking Stripper

Abstract The chemical stripping process in a commercial scale V-baffled resid fluid catalytic cracking stripper was simulated using computational fluid dynamics method. At the outset, it was assumed that the stripping steam initially desorbs hydrocarbons from the catalysts, and the hydrocarbons are then cracked through thermal and catalytic cracking reactions before entering the disengager. The Eulerian–Eulerian two-fluid model coupled with a modified drag model was applied to simulate the gas–solid flow behavior. A desorption model and five-lump kinetic model for thermal and catalytic cracking were utilized to represent the desorption and cracking processes during stripping. The flow modeling results indicated that three different flow regions exist in the stripper: bubbling flow, intermediate flow and turbulent flow. Increasing gas velocity improves the flow conditions of the gas, but adversely affects the particle flow. The degree of mixing of the gas and solid increases along the flowing direction. The results of reaction modeling showed that about 80% of hydrocarbons desorbed from the catalysts. The amount of desorbed oil increases with bed height leading to an increase of heavy oil in the disengager which induces coking problem. By increasing the catalyst temperature, the partial pressure of heavy oil can be lowered down which helps to decrease the disengager coking.

Modeling of Uranium Oxides Hydrofluorination Process with AREVA Firm Technology (Malvési, France)

The analysis of hydrofluorination process at AREVA plant in Malvési was carried out as part of the development algorithm aimed at building self-consistent models for chemical technology processes. This algorithm was developed within the framework of the contract for creating a computer-assisted system of simulation and optimization of chemical technology processes on behalf of State Atomic Energy Corporation “Rosatom”. The hydrofluorination process was selected due to uranium tetrafluopride (UTF) being the main precursor in the process of uranium hexafluoride (UHF) production.