On efficient solution of complex systems of interlinked multistage separators

Solution procedures are described for reducing the computational resources required for the simultaneous solution of complex arrangements of interlinked fractionators. These methods use a block structure in the manner of the Naphtali-Sandholm approach to single column problems, but employ bordered matrix forms to maintain sparsity during the solution. The procedures are particularly useful in conjunction with quasi-Newton solution methods.     

Multicomponent distillation calculations using computer simulation principles

Computer simulation of a chemical process (e.g., distillation) usually reduces to solving a system of nonlinear equations with many unknowns using a database of physicochemical properties of gases and liquids. Here, Broyden’s method is applied to systems of nonlinear equations involved in multicomponent distillation calculations, with the convergence of the algorithm ensured.     

旋风分离器的计算机模拟与设计

在对不同效率和压降模型进行分析的基础上 ,建立了旋风分离器的模拟和设计模型。基于该模型开发了用于旋风分离器校核、模拟和设计的计算机程序 ,该程序包含了效率模型、压降模型和分离器结构数据 ,可用来进行串并联组合旋风分离系统的模拟和设计计算。通过实例表明 ,该程序具有较高的准确性     

Analysis of global approaches to the simulation of counter-current separators

The status of research and development of simulation of counter-current separation processes via global approach is discussed. A general numerical method for calculation of separation equipment should be able to handle easily various modifications in configuration. Global solution of all governing equation results in a procedure which is flexible enough to perform all types of calculations. Classification of difficult separation problems indicates which one should be solved by a global approach. A general strategy of calculation of multicomponent counter-current separation processes via a global approach is presented.     

Assessing the quality of the sampling of fuel peat using computer simulation

A simulation scheme to assess and improve the performance of the sampling of fuel peat is considered. The scheme provides a practical possibility to inspect all possible sources of variation and error. Test results from a district heating plant are reported.     

Monitoring of the commercial operation of reforming catalysts using a computer simulation system

A methodology of constructing nonstationary kinetic models of multicomponent catalytic processes of hydrocarbon conversion on platinum-containing catalysts was developed. Their kinetic and technological parameters in industrial catalytic reforming were estimated. The simulation system in gasoline production allows for the testing and choosing of an optimum catalyst depending on the composition of the processed hydrocarbon raw materials. The developed testing technique is based on the processing of the results of the commercial operation of platinum-containing reforming catalysts using the computer simulation system. It allows the estimation of kinetic parameters, the prediction of selectivity, and raw cycle duration after catalyst regeneration under conditions of commercial operation, taking into account the reactivity of hydrocarbons.     

Modeling and simulation of a multistage absorption hydration hybrid process using equation oriented modeling environment

Separation of light hydrocarbon mixtures is one of the most important topics in chemical engineering research. With development of theories on hydrate equilibriums and kinetics, researchers are trying to apply hydration based separation technology to industrial applications. It is increasingly important to develop the corresponding simulation strategies for process design purposes. In this work we use an equation oriented modeling environment, named Aspen Custom Modeler^® (ACM^®), which enables rapid model development and provides powerful simulation solvers. With the help of ACM^®, a multistage absorption hydration hybrid process (AHHP) for refinery dry gas separation is modeled and simulated. Sensitivities of key parameters such as water content and absorbent flow rate, are analyzed. Features of the multistage AHHP are discussed. For comparison, based on an industrial data, a butane absorption process is established and simulated. Economic evaluation shows that the multistage AHHP is competitive compared to current absorption process.     

A simulation package for the plato educational computer system

A simulation package has been developed for the PLATO educational computer system which allows the user to apply numerical and graphical solution techniques to small-scale problems. Current state-of-the-art numerical algorithms are used with the interactive graphic capabilities of a PLATO terminal to provide efficient problem solution in less than a minute of terminal time. Convenient entry, execution, modification, and output options are combined with on-line input error detection and extensive error messages. Although primarily intended for educational purposes, industrial users will also find this package very efficient for solving small-scale problems.     

A method for steady-state simulation of multistage separation columns involving nonideal systems

A new algorithm is developed for steady-state simulation of multistage separation columns. The algorithm decouples the model equations into two groups. The component-material balance and summation equations are solved simultaneously by the Newton-Raphson method for temperatures and component flow rates in the inner loop. The energy-balance equations are solved in the outer loop to obtain total flow rates. The K-factor is separated into three parts, each representing separately the effect of temperature, composition and apparent volatility. This makes the analytical calculation of the partial derivatives of the K-factors in the Jacobian matrix a simple task. The stability and efficiency of the algorithm is illustrated by solving a variety of problems for distillation, absorber and reboiled absorber columns. The algorithm does not require large storage space.     

精对苯二甲酸连续多级蒸发结晶的模拟

利用研究得到的精对苯二甲酸结晶动力学,建立了精对苯二甲酸连续多级降压蒸发结晶过程的数学模型,并采用工业数据进行验证。结果表明研究得到的模型能够较好地用于模拟精对苯二甲酸连续多级降压蒸发结晶过程,并进一步研究了主要工艺变量对精对苯二甲酸结晶过程的影响。     

Experimental investigation on mechanisms of fine particles generation for the Borealis Borstar multistage olefin polymerization process

Simultaneous production of large amount of undesired fine particles is a big trouble in the Borstar multistage olefin polymerization process. Aiming at reducing the fine particles, the formation mechanism and formation location of the fine particles were thus studied. First, the influence of catalyst nature was considered. Second, the ash content, bulk density, morphology, and molecular weight distribution of polyethylene with different particle sizes from the small‐scale loop prepolymerization reactor, supercritical loop reactor, and gas phase fluidized bed reactor were studied, respectively. In combination with particle growth model, scanning electron microscope, gel permeation chromatography, and laser particle size analyzer, the particle morphology and growth kinetics were investigated. The results showed that fine particles were mostly generated in the supercritical loop reactor, and were significantly affected by the particle size distribution, residence time distribution, and particle fragmentation of the catalyst. Furthermore, scanning electron microscope images showed the catalysts with low activity tended to generate more fine particles. Based on these results, several strategies for reducing the amount of fine particles were proposed, which could be applied in the industrial process. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46589.     

Automatic generation of the symptom tree model for process fault diagnosis

The Symptom Tree Model (STM) has been studied extensively as a model for fault diagnosis in chemical processes and has been applied to real processes. In this study, a program to build a model, AUSST (Automatic Synthesis of the Symptom Tree model), which generates the STM automatically is developed. The input information supplied to AUSST includes the process topology and the unit model library. The unit model library is represented in the form of mini-fault trees which can be constructed systematically through qualitative abstraction from the mathematical model or the operation data and experienced operators. AUSST has worked well, the generated symptom trees describe the paths of fault propagation sufficiently and contain all the possible primal faults. AUSST helps to assure the accuracy of the STM as well as managing the STM consistently. It is expected that AUSST reduces the engineering efforts required to develop a fault diagnostic system for a new process.     

A modified “inside-out” algorithm for simulation of multistage multicomponent separation processes using the UNIFAC group-contribution method

A computational procedure using a modification of Boston and Sullivan's “inside-out” multistage multicomponent separation algorithm (1974) is developed. In order to improve convergence behavior for problems involving mixtures with highly nonideal liquid phases, a two-parameter model is used to describe liquid-phase compositional effects upon the K-factor. The quasi-Newton methods of Mehra et al. (1983) and Nghiem (1983) are applied to solving various sets of solution variables in the proposed algorithm. Activity coefficients are calculated using the UNIQUAC activity-coefficient model (1975) with parameters obtained from the UNIFAC group-contribution method (1975). The computational procedure is applicable to distillation, absorption and reboiled-absorption configurations. The proposed algorithm was implemented in a FORTRAN 77 program and tested on the Honeywell DPS 8/70M computer at the University of Calgary. Inclusion of the liquid-phase model resulted in improved convergence behavior for nonideal systems in which the original “inside-out” method failed to converge.     

Studies of iron corrosion inhibition using chemical, electrochemical and computer simulation techniques

The inhibitive action of some benzimidazole derivatives namely 2-(2-furanyl)-1H-benzimidazole (FB), 2-(2-pyridyl) benzimidazole (PB) and 2-(4-thiazolyl) benzimidazole (TB), against the corrosion of iron in solutions of nitric acid has been studied using density function theory calculations (DFT), weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The calculated electronic parameters involved in the activity of the benzimidazole derivatives confirmed that the position of the side chain in the benzimidazole moiety affects the pattern of activity. The effectiveness of the benzimidazole derivatives is following the order TB > PB > FB. The same order is supported by the experimental chemical and electrochemical measurements. The relationships between inhibition efficiency of iron in 1.0 M HNO₃ and the molecular orbitals of the studied molecules as well as number of electrons transferred ΔN from the inhibitor molecules to the iron surface were calculated by DFT method. The inhibition efficiency increased with the increase in E_HOMO and decrease in E_LUMO-E_HOMO. TB had the highest inhibition efficiency because it had the highest HOMO energy and ΔN values, and it was most capable of offering electrons. Molecular modeling was used to evaluate the structural, electronic and reactivity parameters of the selected benzimidazole derivatives in relation to their effectiveness as corrosion inhibitors. Results obtained from weight loss, dc polarization and ac impedance measurements are in reasonably good agreement and show increased inhibitor efficiency with increasing inhibitor concentration.Data obtained from EIS were analyzed to model the corrosion inhibition process through equivalent circuit.     

Optimization of the properties of cathode materials based on lithium manganese silicate compounds using computer simulation

Using the method of crystallochemical analysis (the TOPOS program package), the 14 most promising and stable structures of lithium manganese (iron) silicate compounds have been selected based on the data on 132 experimentally received and predicted compounds (Materials Project resource).     

The use of a computer algebra system in the analysis of chemical engineering problems

Computer algebra systems are powerful processors designed to treat formal mathematical expressions. Routine features include many operations that occur frequently in the analysis of engineering problems, and provide the analyst with a powerful and reliable tool for manipulating algebraic, differential and integral equations. The power and general utility of one particular computer algebra system is first demonstrated on two elementary examples—the first involving the solution of an ordinary differential equation by weighted residual techniques, and the second, a perturbation solution of Duffing's equation. Ideas stemming from these examples are then applied to a current research problem involving the determination of the amplitude and frequency of self-sustained density wave oscillations in a once-through evaporator. All examples show the power of this system in handling large amounts of tedious algebra with relative ease, thus eliminating the potential for manual error.     

A personal computer software program for coathanger die simulation

A good extrusion die must distribute the polymer melt in the flow channel such that the material exits from the die with a uniform velocity and temperature. Coathanger dies are commonly used for the extrusion of plastic sheets and films. The die is usually provided with a straining bar allowing a regulation of the flowrate in the case of a poor design. But this, in turn, can affect temperature uniformity. Therefore, the design of coathanger die is a complex task which is mainly accomplished by trial and error in industry. Analyses of the flow in coathanger dies have been reported in the literature. Analytical and numerical approaches are used to solve this problem. The first one involves many simplifying assumptions: the most important ones being the unidirectional and isothermal flow of the polymer. Most numerical methods deal with a 2-D geometry, but only a few of them have considered the non-isothermal flow. A new model has been developed using a modified FAN method (Flow Analysis Network introduced by Tadmor) for the calculation of the 2-D flow, coupled with a finite-difference scheme for the calculation of temperature. The overall model can run on a PC with only a few minutes of calculation. Good agreement was obtained between experimental data and simulations.     

闭路浮选流程计算机模拟程序包GFSTESIM

建立了按粒度、矿物组成和可浮性划分的多组分物料的分批磨矿模型、解离模型和分批浮选模型,开发了实验室闭路浮选试验模拟程序包GFSTESIM。该程序包已用于云浮硫铁矿贫矿石含再磨作业的闭路浮选流程的模拟。根据简单的开路分批浮选试验估计出模型参数,模拟了13种结构的浮选流程,从中推选出较优的浮选流程。对建议的工艺流程进行了磨矿细度模拟研究,模拟结果令人满意,与传统试验方法相比,有明显的优点。     

Crystallization kinetics of PPS composites and quantification of fiber nucleation density using a computer simulation

Differential scanning calorimetry and hot-stage optical microscopy were used to study the isothermal crystallization kinetics of unreinforced poly(phenylene sulfide) (PPS) and PPS reinforced with aramid, carbon, and glass fibers. The influence that fibers have on the crystallization kinetics of PPS was found to depend on the characteristics of the fiber as well as the type of PPS used. For one kind of PPS, fibers enhanced the crystallization rate, while for another type of PPS, reinforcing fibers had a moderate depressing effect on the polymer crystallization rate. To clarify these effects, we used a new method of quantifying the nucleation process in fiber-reinforced composites that employs a 3-D computer simulation of spherulitic crystallization. Using this method, the nucleation density in the bulk polymer, N_b, and the nucleation density on fiber surfaces, N_f, were calculated for PPS composites as a function of crystallization temperature. The calculated values of N_b and N_f were used to explain differences in the effectiveness of the fibers as well as differences in the nucleating characteristics of the two polymers. © 1995 John Wiley & Sons, Inc.     

石墨烯生物毒性的计算机模拟研究进展

石墨烯是一种由平整的单层碳原子密集堆积成二维蜂窝晶格的碳纳米材料,具有优异的光学、电学、力学等特性,在生物医药、材料学等领域具有重要的应用前景。随着石墨烯在以上研究领域的广泛应用,其生物安全性问题也备受关注。尽管有大量研究表明石墨烯的生物相容性较好,但是部分研究却发现石墨烯具有一定的生物毒性。石墨烯粒径小,容易通过皮肤进入体内,可能与蛋白质、脂质或核酸等生物大分子相互作用。近年来,由于计算机模拟技术具有成本低、安全性高、易获得实验无法获取的动态结构等优势而被广泛用于生物、化学、制药等领域。本文综述了石墨烯与细胞膜、蛋白质和DNA等生物大分子相互作用的计算机模拟研究进展,从而评估石墨烯可能存在的生物毒性,为石墨烯的生物安全性评价和生物医学应用提供了参考。