共查询到19条相似文献,搜索用时 265 毫秒
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提出了一种多相平衡计算的改进τ因子法,该方法基于一种修正各相摩尔分数和的概念,研究模型的建立和用遗传算法计算多组分复杂体系的相平衡问题。首先通过建立数学模型,将相平衡计算问题转化为带线性约束的非线性规划(NLP)问题;其次用遗传算法对模型进行求解,并通过对优化变量采取动态边界的可行域编码方法保证了算法的有效实施;最后对2个体系的计算表明,结果与文献值相吻合,且此方法不仅可以求解不含化学反应体系的相平衡问题,也同样适用于含化学反应体系的相平衡计算,是一种比较可靠和通用的方法。 相似文献
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在101.325 kPa下用沸点仪测定了二甲基硫醚-吡啶、二甲基硫醚-N,N-二甲基乙酰胺、吡啶-N,N-二甲基乙酰胺3个二元体系以及二甲基硫醚-吡啶-N,N-二甲基乙酰胺三元体系不同液相组成时的汽液平衡数据,3个二元体系活度因子分别用Wilson、NRTL、Margules、van Laar和UNIQUAC模型进行关联,用最小二乘法求出了它们的液相活度因子模型参数,用这些模型参数计算它们的汽相组成.根据过量Gibbs自由能函数,采用间接法由Tpx预测了3个二元系的汽相平衡组成.用所得的液相活度因子计算3个二元体系的过量Gibbs自由能.3个二元体系的Wilson、NRTL、Margules、van Laar和UNIQUAC模型参数分别对所测的三元体系数据进行关联,建立该系统汽液平衡的热力学模型并计算平衡时的汽相组成和泡点温度.分别由Herington法和McDermott-Ellis法对3个二元体系和三元体系进行热力学一致性检验,结果表明这些相平衡数据满足热力学一致性. 相似文献
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从热力学原理出发,建立了一种固液相平衡级计算的通用方法,通过自动判别平衡时的相数及析出固相的种类,经过较少的迭代次数就可获得固液相平衡时各相分率和组成,从而满足化工过程模拟计算与实际生产的需要。由于该解法为虚拟的等温蒸发过程,在判别平衡相数的同时给出了过程中晶体的析出顺序与各晶体刚析出时溶液组成,这些中间结果为分离过程的模拟计算提供了理论指导。此算法不仅完全不依赖于相图,而且还可通过对不同进料配比的计算,绘制出全范围内的固液相图。通过实例计算证明该方法可适用于目前文献中尚难以处理的复盐、含结晶水盐以及多离子体系。 相似文献
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对于给定温度和压力的系统,平衡状态时其吉布斯自由能最小。根据热力学基本关系式,在多组分体系中元素和电荷守恒的限制条件下,最小化吉布斯函数,通过SQP方法来求解此有约束的优化问题,通过迭代法求解反应后的温度。该方法可用于复杂的非理想、多相流体、电解液或非电解液混合物的相平衡计算,平衡计算结果包括温度、密度、组分浓度等。对于某新型热动力系统中使用的一种含铝火药,应用本文方法,获得了化学平衡计算结果。 相似文献
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本文对有固相碳的碳-氢-氧-硫-惰气(CHOSI)非均相系统,提出了一种计算气相平衡组成的迭代算法。将化学平衡方程和物料衡算方程进行数学变换,用牛顿迭代法求解二元三次方程,从而达到快速、准确地计算CHOSI非均相系统的平衡组成。该算法能计算200~1800℃,0.1~10.0MPa和不同原子比下,有固相碳的化学平衡组成。 相似文献
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Jacques F. Gouws Thokozani Majozi Mamdouh Gadalla 《Chemical Engineering and Processing: Process Intensification》2008,47(12):2323-2335
This paper presents the least constrained mass transfer mathematical formulation for freshwater minimization in multipurpose batch chemical processes with central reusable water storage. The mathematical formulation is an extension of the model developed by Majozi [T. Majozi, Wastewater minimization using central reusable water storage in batch processes, Computers and Chemical Engineering Journal 29 (7) (2005) 1631–1646]. In the latter model four scenarios were considered with various limitations or constraints. In the scenario presented in this paper only the mass load is fixed, whilst both the quantity of water used in a particular operation and outlet concentration are allowed to vary. In essence, fixing the mass load is more representative of the practical case. A solution procedure for the resultant nonconvex mixed integer nonlinear programming (MINLP) model is also presented. The solution procedure first involves reformulating the MINLP into a relaxed linear model (MILP). The MILP is first solved, the solution of which forms a feasible starting solution for the MINLP. Presented are two illustrative examples. 相似文献
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Gonzalo Guillén‐Gosálbez Ignacio E. Grossmann 《American Institute of Chemical Engineers》2009,55(1):99-121
This article addresses the design of sustainable chemical supply chains in the presence of uncertainty in the life cycle inventory associated with the network operation. The design task is mathematically formulated as a bi‐criterion stochastic mixed‐integer nonlinear program (MINLP) that simultaneously accounts for the maximization of the net present value and the minimization of the environmental impact for a given probability level. The environmental performance is measured through the Eco‐indicator 99, which incorporates the recent advances made in Life Cycle Assessment. The stochastic model is converted into its deterministic equivalent by reformulating the probabilistic constraint required to calculate the environmental impact in the space of uncertain parameters. The resulting deterministic bi‐criterion MINLP problem is further reformulated as a parametric MINLP, which is solved by decomposing it into two sub‐problems and iterating between them. The capabilities of the proposed model and solution procedure are illustrated through two case studies for which the set of Pareto optimal, or efficient solutions that trade‐off environmental impact and profit, are calculated. These solutions provide valuable insights into the design problem and are intended to guide the decision maker towards the adoption of more sustainable design alternatives. © 2008 American Institute of Chemical Engineers AIChE J, 2009 相似文献
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《Chemical engineering science》1987,42(12):2847-2863
This paper discusses a minimization algorithm for the solution of the Gibbs free energy minimization problem involving at most two phases. There are three major aspects to this paper. The first is the selection of descent directions and step lengths in order to handle the poorly scaled phase equilibrium problems associated with mixtures near bubble points and critical points. The second is the prevention of convergence to trivial solutions in both the Gibbs free energy minimization problem for two-phase mixtures and the associated phase stability test for single-phase mixtures. The third is the use of effective convergence criteria to obtain either the desired level of accuracy in the solution or the maximum accuracy allowed by the problem and the computer. 相似文献
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The multiperiod blending problem involves binary variables and bilinear terms, yielding a nonconvex MINLP. In this work we present two major contributions for the global solution of the problem. The first one is an alternative formulation of the problem. This formulation makes use of redundant constraints that improve the MILP relaxation of the MINLP. The second contribution is an algorithm that decomposes the MINLP model into two levels. The first level, or master problem, is an MILP relaxation of the original MINLP. The second level, or subproblem, is a smaller MINLP in which some of the binary variables of the original problem are fixed. The results show that the new formulation can be solved faster than alternative models, and that the decomposition method can solve the problems faster than state of the art general purpose solvers. 相似文献
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随着炼油厂对氢气的需求量不断扩大,氢气系统已成为炼油厂的重要组成部分。炼油厂氢气网络的优化设计既要实现总成本最小的经济性目标,还要保证各种工况下氢气系统的安全稳定运行。针对炼油厂氢气系统不断变化的工况和氢气需求,提出了炼油厂氢气网络柔性优化策略,建立了多工况下的氢气网络柔性优化混合整数非线性规划(MINLP)模型,并对优化模型进行了线性化处理,采用优化建模工具Lingo建模求解。采用本文提出的柔性优化策略对某炼油厂氢气网络进行了柔性优化设计,与炼油厂的原始氢气网络对比表明,柔性优化后的网络可操作性强且具有较好的柔性调节能力,既节省了大量的运行成本,又为各种工况下氢气系统的安全稳定运行提供了保障,对实际炼油厂氢气网络的优化管理起了指导作用。 相似文献
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Demetrios Chaconas Patricia Pichardo Ioannis V. Manousiouthakis Vasilios I. Manousiouthakis 《American Institute of Chemical Engineers》2021,67(1):e17052
Gibbs free energy minimization is employed to carry out thermodynamic equilibrium analysis studies of mixtures containing methane, carbon monoxide, carbon dioxide, water, and hydrogen ideal gases, and possibly solid carbon. The employed global minimization approach represents a general, unifying, conceptual framework that allows reaction and phase equilibrium analysis to be simultaneously carried out in the atom-mol fraction space (aH, aO) , thus capturing in a comprehensive manner the equilibrium behavior of a number of industrially important processes, such as methane reforming (steam, dry, energetically enhanced), and methanation. Two theorems are presented, establishing necessary and sufficient (necessary) feasibility and regularity (optimality) conditions for the aforementioned minimization problem. The equilibrium results obtained through application of these theorems are guaranteed to be globally optimal. They quantify in (aH, aO) space, the feasible region, the carbon formation region, and all species mole over total atom-mol normalized ratios, for a range of temperatures and pressures. 相似文献
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Ramkumar Karuppiah Kevin C. Furman Ignacio E. Grossmann 《Computers & Chemical Engineering》2008,32(11):2745-2766
In this work we present an outer-approximation algorithm to obtain the global optimum of a nonconvex mixed-integer nonlinear programming (MINLP) model that is used to represent the scheduling of crude oil movement at the front-end of a petroleum refinery. The model relies on a continuous time representation making use of transfer events. The proposed algorithm focuses on effectively solving a mixed-integer linear programming (MILP) relaxation of the nonconvex MINLP to obtain a rigorous lower bound (LB) on the global optimum. Cutting planes derived by spatially decomposing the network are added to the MILP relaxation of the original nonconvex MINLP in order to reduce the solution time for the MILP relaxation. The solution of this relaxation is used as a heuristic to obtain a feasible solution to the MINLP which serves as an upper bound (UB). The lower and upper bounds are made to converge to within a specified tolerance in the proposed outer-approximation algorithm. On applying the proposed technique to test examples, significant savings are realized in the computational effort required to obtain provably global optimal solutions. 相似文献