A simultaneous method for phase identification and equilibrium calculations in reactive mixtures

Phase identification is an important aspect of flash calculations which can affect the phase and chemical equilibria. A new simultaneous approach for reactive mixtures, based on τ-method which relies on modification equation for mole fraction summation, is introduced in this paper. In the proposed methodology, phase identification and solution of governing equations can be performed simultaneously and effectively. In addition, prior knowledge of the number of phases in advance is not required. Present methodology has been verified with the help of case studies and results are discussed in the present paper. The results indicate that the present method gives us information about presence of reactive phases at equilibrium, their quantities and compositions simultaneously. The method is easy to implement and it may be used by several thermodynamic models.     

Solution theory model for thermophysical properties of refrigerant/lubricant mixtures

A general model for predicting the thermophysical properties of refrigerant/lubricant mixtures has been developed based on applicable theory for the excess Gibbs energy of nonideal solutions. In our approach, flexible thermodynamic forms are chosen to describe the properties of both the gas and liquid phases of refrigerant/lubricant mixtures. After an extensive study of models for describing nonideal liquid effects, the Wohl [3]‐suffix equations, which have been extensively used in the analysis of hydrocarbon mixtures, have been developed into a general form applicable to mixtures where one component is a polyolester or alkylbenzene lubricant. We have developed a nonideal solution computer code, based on the Wohl model that predicts dew point or bubble point conditions over a wide range of composition and temperature and includes the calculation of the enthalpy and entropy of refrigerant/lubricant mixtures. Our present analysis includes the thermodynamic properties of an ideal solution mixture and the corrections due to nonideal solution behavior. These nonideal solution corrections are based on analysis of the excess Gibbs energy of the mixture. We find that these nonideal solution corrections are small (<4%) for most refrigerant/lubricant mixtures, except at very low temperatures. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Combined monte carlo/thermodynamic model of formation of microporous aggregate structure like silica from quaternary ammonium silicate solutions

Quaternary ammonium silicate is a surfactant with very high content of silica that allows its use for preparation of protective coatings. The problem of silica aggregation from quaternary ammonium solution in limited volume is the focus of this paper. The system is described by a model based on a Monte Carbo approach with thermodynamic limitations. Thermodynamic characteristics are estimated by statistical polymer method. The model is employed for estimation of such properties as monomer concentration and tortuosity. The results of computer simulation are used for forecasting properties of coatings and for practical preparation of samples coated with quaternary ammonium silicate-based composition.     

The effects of the size of nanocrystalline materials on their thermodynamic and mechanical properties

This work has considered the intrinsic influence of bond energy on the macroscopic, thermodynamic, and mechanical properties of crystalline materials. A general criterion is proposed to evaluate the properties of nanocrystalline materials. The interrelation between the thermodynamic and mechanical properties of nanomaterials is presented and the relationship between the variation of these properties and the size of the nanomaterials is explained. The results of our work agree well with thermodynamics, molecular dynamics simulations, and experimental results. This method is of significance in investigating the size effects of nanomaterials and provides a new approach for studying their thermodynamic and mechanical properties.     

A speciation solver for cement paste modeling and the semismooth Newton method

The mineral assemblage of a cement paste may vary considerably with its environment. In addition, the water content of a cement paste is relatively low and the ionic strength of the interstitial solution is often high. These conditions are extreme conditions with respect to the common assumptions made in speciation problem. Furthermore the common trial and error algorithm to find the phase assemblage does not provide any guarantee of convergence. We propose a speciation solver based on a semismooth Newton method adapted to the thermodynamic modeling of cement paste. The strong theoretical properties associated with these methods offer practical advantages. Results of numerical experiments indicate that the algorithm is reliable, robust, and efficient.     

Fault detection of non-Gaussian processes based on modified independent component analysis

In this paper, some drawbacks of both the original independent component analysis (ICA) algorithm and the FastICA algorithm are analyzed as follows: the order of the independent components is difficult to be determined; because of using the Newtonian iteration, FastICA method often leads to local minimum solution, and the suitable source signals are not isolated. To solve these problems, a modified ICA algorithm based on particle swarm optimization (PSO) called PSO-ICA is proposed for the purpose of multivariate statistical process monitoring (MSPM). The basic idea of the approach is to use the PSO-ICA algorithm to extract some dominant independent components from normal operating process data. The order of independent components is determined according to the role of resumption of the original signal. The proposed monitoring method is applied to fault detection and diagnosis in the Tennessee Eastman process. Applications indicate that PSO-ICA effectively captures the independent components.     

基于极值动力学机制和信息融合搜索的混合算法及其应用

提出了一种新的基于自适应lévy变异的极值动力学和信息融合搜索的混合算法.新算法将全局搜索和局部搜索机制有机地结合起来,在全局搜索过程中,信息融合搜索算法(IFA)作为一种群智能进化算法,能够快速地逼近近似最优解;在局部搜索过程中,通过选择近似解的最差组元进行自适应lévy变异,利用极值动力学算法(EO)强大的局部搜索...     

Efficient scheduling method of complex batch processes with general network structure via agent‐based modeling

A novel efficient agent‐based method for scheduling network batch processes in the process industry is proposed. The agent‐based model is based on the resource‐task network. To overcome the drawback of localized solutions found in conventional agent‐based methods, a new scheduling algorithm is proposed. The algorithm predicts the objective function value by simulating another cloned agent‐based model. Global information is obtained, and the solution quality is improved. The solution quality of this approach is validated by detailed comparisons with the mixed‐integer programming (MIP) methods. A solution close to the optimal one can be found by the agent‐based method with a much shorter computational time than the MIP methods. As a scheduling problem becomes increasingly complicated with increased scale, more specifications, and uncertainties, the advantages of the agent‐based method become more evident. The proposed method is applied to simulated industrial problems where the MIP methods require excessive computational resources. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2884–2906, 2013     

A hybrid algorithm based on extremal optimization with adaptive lévy mutation and information fashion algorithm and its applications

提出了一种新的基于自适应lévy变异的极值动力学和信息融合搜索的混合算法。新算法将全局搜索和局部搜索机制有机地结合起来,在全局搜索过程中,信息融合搜索算法(IFA)作为一种群智能进化算法,能够快速地逼近近似最优解;在局部搜索过程中,通过选择近似解的最差组元进行自适应lévy变异,利用极值动力学算法（EO)强大的局部搜索能力,协助IFA跳出局部极值点。将其运用于超临界水氧化去除率神经网络软测量建模,实验结果表明了方法的有效性和实用性。     

Calculation of solution-vapor thermodynamic equilibria by the method of minimizing the Gibbs energy

An algorithm of direct numerical minimization of the Gibbs energy for calculating the liquid-vapor thermodynamic equilibrium in multicomponent systems is proposed. The method makes it possible to simultaneously determine the distributions of concentrations in the vapor and solution and the vapor mole fractionwhen the temperature, pressure, and initial mixture composition are given. The developed algorithm is distinguished from the existing equilibrium calculation methods by a higher stability and the capability of obtaining solutions in the range of parameters in which the conventional algorithms are not able to produce a physically meaningful result. The Peng-Robinson equation of state is used to simulate the Gibbs energy. The accuracy of the proposed algorithm is illustrated by comparison with experimental data.     

Closed‐loop Fault Detection Using the Local Approach

Fault detection and isolation (FDI) has become a crucial issue for industrial process monitoring in order to increase availability, reliability and production safety. Model‐based FDI methods rely on a mathematical model and input‐output data of a process to perform detection. The local approach is a new model‐based FDI method that aims to detect slight changes of a system's parametric properties. Closed‐loop detection is an important issue for the local approach since all control systems work under closed‐loop conditions. A new algorithm was proposed to revise the original detection algorithm in order to make it work for closed‐loop data. Simulation results show that the proposed method can detect the changes of parameters of a system that can affect closed‐loop performance.     

On the Solution of Non-Isothermal Reaction-Diffusion Model Equations in a Spherical Catalyst by the Modified Adomian Method

We investigate the reactant diffusion within a porous catalytic pellet including the heat of reaction. The Lane–Emden boundary value problem with an Arrhenius reaction rate is used to model the reactant concentration. We combine the Volterra integral form with the Adomian decomposition method to solve the equivalent Fredholm–Volterra integral equation. We then estimate the reactant concentration at the center of the catalytic pellet and the iterated Shanks transform is used to improve the accuracy of the approximations. The objective error analysis formulas are used to demonstrate a high accuracy and rapid rate of convergence, which does not depend on a priori knowledge of the exact solution or comparison with an alternate approximation method. Thus low-stage approximations by the Adomian decomposition method are validated for parametric simulations of the reactant concentration profiles and the effectiveness factor profiles. Our approach demonstrates enhancements over previous investigations, and is readily extensible to more general diffusion reaction models in catalytic reactor engineering.     

Thermodynamics of wax formation in the fischer-tropsch synthesis products

A new method is suggested for calculating the thermodynamic equilibrium in a multicomponent multiphase system without chemical reactions. This method is based on ideas of statistical physics and non-equilibrium thermodynamics and includes numerical minimization of the Gibbs energy of the complex system. Component concentrations and the physically realizable roots of the equation of state are calculated as the steady state solutions of the set of ordinary differential equations that is implied by the procedure of seeking the probability maximum for the realization of the equilibrium distribution. The approach developed here is used to calculate the equilibrium distribution of the concentrations of vaporous, liquid, and solid substances in the Fischer-Tropsch synthesis products. A thermodynamic model of the formation of solid paraffins from the synthesis products is presented. The calculation of the properties of pure substances and liquid and gaseous products is based on the Lee-Kesler equation of state. The wax formation thermodynamics is considered in the regular solid solution approximation (Hildebrand-Scott model) and in the solid solution approximation taking into account the nonideality of the system (NRTL model). The calculated mass fractions of vaporous, liquid, and solid synthesis products are presented as a function of temperature for different values of the chain propagation constant.     

三元体系汽液平衡数据的热力学一致性逐点检验

用曲面样条函数表达三元ＶＬＥ体系过量自由焓Ｑ函数，非线性方程组用Ｂｒｏｙｄｅｎ改进的ＮｅｗｔｏｎＲａｐｈｓｏｎ法求解，对１６个不同类型三元ＶＬＥ体系的检验表明，本方法具有计算结果可靠，算法稳定，对初值要求不高及收敛速度快等特点，为三元ＶＬＥ数据的热力学一致性逐点检验提供了一种有价值的方法。     

Measurement and Modeling of Refractive Indices for Multicomponent Chromium Compound Solutions

The aim of this work is to solve the key problems of the green production process for chromium trioxide and to study the thermodynamic properties of corresponding solutions. The refractive indices of quaternary mixtures (chromium trioxide + potassium chromate + potassium dichromate + water) have been measured from 298.15–333.15 K. A molecular thermodynamic model of refractive indices for aqueous solutions of chromium compounds is proposed, based on the author's molecular model for solution structure and an equation for the excess enthalpy of a binary solution obtained from the experimental measurements. The model parameters are confirmed and quantitative equations for the variation of the model parameters with temperature and the molality of potassium dichromate in the mixed solvent are established. The data predicted by the model are in good agreement with the experimental results.     

Generation of operating procedures for a mixing tank with a micro genetic algorithm

This paper explores the use of a micro genetic algorithm that uses variable-length chromosomes and a seeding scheme based on tabu search. The problem is to find the sequence of actions that have to be executed in the shortest time possible, but also in a way that minimizes the possibility of situations that may endanger the plant personnel and plant facilities. The proposed approach was tested on the generation of the optimum sequences for startup and shutdown of a mixing vessel similar to the equipment used in the synthesis of acrylic acid. The results show that the proposed method outperforms the traditional GA algorithm both in terms of the quality of the solution and computational effort.     

Optimization of short-time gasoline blending scheduling problem with a DNA based hybrid genetic algorithm

Gasoline blending is a key process in the petroleum refinery industry posed as a nonlinear optimization problem with heavily nonlinear constraints. This paper presents a DNA based hybrid genetic algorithm (DNA-HGA) to optimize such nonlinear optimization problems. In the proposed algorithm, potential solutions are represented with nucleotide bases. Based on the complementary properties of nucleotide bases, operators inspired by DNA are applied to improve the global searching ability of GA for efficiently locating the feasible domains. After the feasible region is obtained, the sequential quadratic programming (SQP) is implemented to improve the solution. The hybrid approach is tested on a set of constrained nonlinear optimization problems taken from the literature and compared with other approaches. The computation results validate the effectiveness of the proposed algorithm. The recipes of a short-time gasoline blending problem are optimized by the hybrid algorithm, and the comparison results show that the profit of the products is largely improved while achieving more satisfactory quality indicators in both certainty and uncertainty environment.     

大范围工况变化下联塔的严格机理模拟研究

建立基于严格机理的乙烯生产过程联塔系统开放式模型,采用大规模系统优化方法和自动微分方法,对此联塔系统进行大范围工况变化下的模拟.求解结果和收敛效率与Aspen Plus进行了对比.在初值相同、标度相同、建模和求解方式一致的情况下,本文联立求解方法的结果与Aspen Plus的EO模式的求解结果一致;对于进料工况大范围变化的情形,本文的联立求解方法收敛性明显优于Aspen Plus.采用大规模优化计算方法和稀疏自动微分方法对于提高求解效率、降低初值依赖性具有明显的效果.     

Estimates of energy consumption and selection of optimal distillation sequence for multicomponent distillation

An estimate has been obtained of the energy consumption on 1 mol of separated mixture based on thermodynamic balances for processes that use mechanical and heat energy. Only irreversible losses depend on the order of separation for mixtures in mechanical systems, while for the systems using the heat, the order of separation also affects the reversible energy consumption. In the latter case, in order to obtain a reversible estimate of the heat consumption, one should solve the problem of selecting the order of separation. An algorithm has been obtained for its solution that enables one to approximately choose the order of separation at the stage of preliminary calculations knowing only the properties of the feed.     

Computing multiple steady states in homogeneous azeotropic and ideal two‐product distillation

Multiple steady states are typically discovered by tracing a solution path, including turning points. A new technique is presented here that does not follow this approach. The original problem is solved directly, without tracing a solution path. The proposed branch‐and‐prune algorithm is guaranteed to find all solutions automatically. Core components of the framework are affine arithmetic, constraint propagation, and linear programming. The C++ implementation is available as an open‐source solver and has an interface to the AMPL® modeling environment. In certain difficult cases, only continuation methods have been reported to find the unstable solution automatically. The proposed method seems to be the first published alternative method in those cases. Although this article focuses mainly on distillation, the presented framework is fairly general and applicable to a wide variety of problems. Further, computational results are given to demonstrate this. © 2010 American Institute of Chemical Engineers AIChE J, 2011