SYNTHESIS OF FLEXIBLE MASS-EXCHANGE NETWORKS

In this work, a new algorithm for the synthesis of cost effective flexible mass-exchange networks that can accommodate a given range of potential variations in the waste streams is presented. In order to automatically synthesize the network, a structural-representation scheme is developed to embed all potential configurations of the network. With this representation, both economic and flexibility aspects in the design can be simultaneously handled. The synthesis task is formulated as a mixed-integer nonlinear programming (M1NLP) problem which seeks to minimize the total annualized cost, while incorporating thermodynamic, technical and flexibility constraints. An iterative procedure is devised to solve this optimization program by decomposing the problem into two subproblems: synthesis and flexibility analysis. The synthesis subproblem attempts to generate a minimum-cost solution by identifying the most appropriate mass-exchange technologies along with their types, sizes, operating conditions, and stream distribution. The flexibility analysis subproblem is aimed at insuring that the synthesized system can be feasibly operated over the entire range of potential variations. A case study is tackled to outline the merits of the proposed strategy.     

Synthesis of Multi-component Mass-exchange Networks

This paper presents a superstructure-based formulation for the synthesis of mass-exchange networks （MENs） considering multiple components. The superstructure is simplified by directly using the mass separation agents （MSA） from their sources, and therefore the automatic synthesis of the multi-component system involved in the MENs can be achieved without choosing a ＇key-component＇ either for the whole process or the mass exchangers A mathematical model is proposed to carry out the optimization process. The concentrations, flow rates, matches and unit operation displayed in the obtained network constitute the exact representation of the mass exchange process in terms of all species in the system. An example is used to illustrate and demonstrate the application of the proposed method.     

Global optimization of reactive distillation networks using IDEAS

In this work, we present a methodology for the global optimization of reactive distillation (RD) networks, through the Infinite DimEnsionAl State-space (IDEAS) approach. Within the IDEAS framework, network synthesis is formulated as an infinite dimensional linear optimization problem. The IDEAS conceptual framework is realized through solution of a series of finite dimensional linear programs whose optimum values converge to the infinite program’s infimum. The proposed optimal design methodology is demonstrated on a case study involving reactive distillation-based synthesis of methyl tert-butyl ether (MTBE) from isobutene and methanol.     

An ignition model for heterogeneous systems under nonstationary heat- and mass-exchange and its application to the composition PMMA+AP

The mathematical modeling of ignition processes for heterogeneous systems under nonstationary heat- and mass-exchange is performed with regard for the two-stage thermal degradation of oxidizer and fuel binder the heterogeneous oxidation of fuel around AP grains, the integral heat release in gas-phase reactions through the effective heights of individual flames, as well as the effect of the products of thermal decomposition on radiative and convective heat- and mass-exchange with the environment. The model is applied to a model composite system PMMA+AP. Scientific-Research Institute of Applied Mathematics and Mechanics, Tomsk 634005. Translated from Fizika Goreniya i Vzryva, Vol. 30, No. 5, pp. 18–29, September–October, 1994.     

IDEAS approach to process network synthesis: minimum utility cost for complex distillation networks

This work aims at quantifying the minimum utility cost necessary to complete a given separation task using vapor-liquid equilibrium (distillation) operations. The Infinite DimEnsionAl State-space (IDEAS) process is introduced as a new paradigm for this process synthesis activity. The IDEAS conceptual framework includes all possible process configurations, and yields mathematical programs that are convex (linear), thereby guaranteeing the global optimality of the obtained solution.A case study, on nitrogen/oxygen mixture separation, is employed to illustrate the power of the proposed approach. The obtained IDEAS designs are compared with the corresponding McCabe-Thiele (conventional) minimum utility designs, and are shown to be as much as 50% more thermodynamically and economically efficient.     

质量交换网络集成的状态空间法

State space approach is an effective method to mass-exchange network (MEN) synthesis. By decomposing the network into two interactive parts, a distribution network and a process operator, the synthesis problem can be formulated into a mixed integer nonlinear programming (MINLP) model. In this article, a generalized state space model based on typical MEN is established and verified in two cases. A new asymmetrical operator and cost index are also adopted to speed up the solution process. The results demonstrate the efficiency of the proposed approach.     

A shortcut method for the preliminary synthesis of process-technology pathways: An optimization approach and application for the conceptual design of integrated biorefineries

Synthesis and screening of technology alternatives is a key process-development activity in the process industries. Recently, this has become particularly important for the conceptual design of biorefineries. This work introduces a shortcut method for the synthesis and screening of integrated biorefineries. A structural representation (referred to as the chemical species/conversion operator) is introduced. It is used to track individual chemicals while allowing for the processing of multiple chemicals in processing technologies. The representation is used to embed potential configurations of interest. An optimization approach is developed to screen and determine optimum network configurations for various technology pathways using simple data. The solution to the optimization formulation provides a quick and effective method for screening and interconnecting the technological pathways and to distributing the flows over the network. Case studies are solved to illustrate the applicability of the proposed approach.     

Attainable region of reactive distillation—Part IV: Inclusion of multistage units for complex reaction schemes

Reactive distillation (RD) can be advantageously used to improve selectivity of the desired product in a multi-reaction system. Because of the complexity in vapor liquid equilibrium and reaction kinetics, the design methodology is not straightforward and one has to adopt conceptual design and synthesis methods to arrive at the appropriate RD configuration. This paper is continuation of our earlier work (Amte et al., 2011), aimed at extending the concept of attainable region to a larger family of reactors that includes different reactive distillation units. In this work, we incorporate multistage reactive rectification and reactive stripping models with total reflux and total reboil, respectively. We further define the respective vectors, which justify the need of the corresponding units in the RD network. The van de Vusse schemes with both non-azeotropic and azeotropic vapor?liquid equilibria are considered and the attainable regions are constructed. Explanation is provided based on the visualization of selectivity lines in the composition space. In all the cases studied here, the feasible region is significantly broader than the one realized for the network of only conventional reactors.     

基于神经网络混合整数线性规划的精馏分离序列优化综合

针对精馏分离序列综合问题,运用图论方法研究网状超级结构。结合相对费用函数建立了混合整数线性规划模型。开发了面向大规模精馏分离序列综合问题的自动求解程序,实现了10组分精馏分离序列综合问题的成功解算,探索了神经网络混合整数线性规划的思想框架。     

A novel stochastic optimization method to efficiently synthesize large-scale nonsharp distillation systems

This study presents a novel stochastic optimization method for the efficient synthesis of large-scale nonsharp distillation systems, where heat integration and thermal coupling can be involved simultaneously. A new binary tree encoding method was developed to represent distillation sequences with no limits on the number of middle components in nonsharp splits to ensure a complete solution space. Thermally coupled structures were defined by 0–1 binary variables. Evolutionary rules were developed to generate neighboring distillation configurations randomly. Finally, an optimization framework was proposed, where simulated annealing (SA) algorithm was used to optimize distillation configurations; for a certain distillation configuration randomly generated by SA, its continuous variables were optimized using particle swarm optimization algorithm. Four cases—including the synthesis of six- and seven-component nonsharp heat integrated and thermally coupled distillation sequences—were studied to demonstrate that the proposed method was efficient and could obtain optimal and valuable suboptimal solutions with high probabilities.     

用于热集成精馏序列综合的改进模拟退火算法

提出一个用于多组分热集成精馏系统综合问题的改进模拟退火算法.将优化问题表示为混合整数非线性规划（MINLP）问题,将算法设计同研究问题的特征相结合,运用本文方法可在同一退火策略下实现流程结构和操作参数的同步优化,并能达到计算精度和计算速度的更好均衡.通过对大规模算例（产品数≥10）的计算表明,该方法对求解此类问题非常有效.     

Design and synthesis of multicomponent thermally coupled distillation flowsheets

The design and synthesis of thermally coupled distillation flowsheets for separations of five-component mixtures are studied. Four types of possible configurations are identified when simple and complex columns are both considered in a flowsheet. A universal design procedure is developed for design of any types of the identified configurations based on the abstraction of the three basic units in the flowsheets. Two examples demonstrated that this shortcut design method can be used in design of any types of the identified multicomponent thermally coupled distillation flowsheets, as well as give very good initializations for rigorous simulation of such configurations. Moreover, with a proposed computer representation of all the types of the feasible configurations, a synthesis algorithm is developed for synthesizing of multicomponent complex distillation flowsheets with both simple and complex columns. It is practical by the proposed methods for optimal design of multicomponent distillation systems in an extended search space to include the complex distillation flowsheets for industrial problems.     

基于随机优化的热耦合复杂精馏系统的综合(Ⅰ)模型化方法

基于随机型最优化策略,针对包含简单塔、带有侧线蒸出及侧线汽提塔的复杂塔、全热耦合（或Petlyuk）塔的热耦合复杂精馏塔系统的综合问题,提出一种模型化方法.针对热耦合复杂精馏流程系统所需塔段数目以及冷凝器和再沸器数目的不确定性,提出了一种分解求解策略,将原问题分解成一系列具有不同塔段数的子问题分别求解;针对流程结构的优化提出一种流程结构的编码表达法,该方法将问题的分离序列结构和热耦合方式分别用两组编码表示,对分离序列的编码采用了数据结构理论中的二叉树排序方法,使流程结构的描述变得更加简便;最后以预分馏塔组分回收率及回流比为连续变量,建立了热耦合复杂精馏系统优化的[JP+1]混合整数非线性规划（MINLP）模型,该模型用改进的模拟退火算法求解,可同时得到优化的流程结构和操作参数.     

模拟退火方法用于带有中间换热器精馏塔的优化综合

This article presents a simulated annealing-based approach to the optimal synthesis of distillation column considering intermediate heat exchangers arrangements. T-he number of intermediate condensers and/or intermediate reboilers, the placement locations, the.operating pressure of column, and the heat duties of intermediate heat exchangers are treated as optimization variables. A novel coding procedure making use of an integer number series is proposed to represent and manipulate the structure of system and a stage-to-stage method is used for column design and cost calculation. With the representation procedure, the synthesis problem is formulated as a mixed integer nonlinear programming （MINLP） problem, which can then be solved with an improved simulated annealing algorithm. Two examples are illustrated to show the effectiveness of the suggested approach.     

Optimal design of cryogenic distillation columns with side heat pumps for the propylene/propane separation

Propylene is one of the most important products in the petrochemical industry, which is used as raw material for a wide variety of products. The propylene/propane separation is a very energy-intensive process because their boiling points are quite similar. In addition, at atmospheric conditions, their boiling points are −47.6 °C and −42.1 °C, respectively. To separate this mixture conventional columns which operate at high pressure and cryogenic distillation columns which operate at low pressure have been used, however, this approaches are still energy-intensive. This work presents energy-efficient and intensified distillation columns which are adiabatic such as the vapor recompression column (VRC) or diabatic such as columns with heat-integrated stages. A design and optimization procedure, which minimizes the energy consumption in the propylene/propane separation is presented. Conceptual design, superstructure representation, rigorous simulations and mathematical programming techniques are effectively combined to assess all the candidate distillation structures, refrigeration cycles, and heat integration possibilities simultaneously. Results showed that VRC and diabatic distillation columns with heat-integrated stages can reduce the energy consumption between 58 and 75% when compared with conventional distillation at high pressure. Furthermore, the proposed synthesis procedure derived simplified optimal distillation structures with few heat-integrated stages and still attained important energy savings.     

Conceptual design of single-feed kinetically controlled reactive distillation columns

Reactive distillation, simultaneous reaction and separation within a single unit, represents an exciting alternative to conventional processes, leading to significantly reduced in capital and operating costs. Process design for reactive distillation is facilitated by fast and effective methods for synthesis and conceptual design that take into account reactions that do not instantaneously reach equilibrium. This work presents a new methodology for synthesis and design of single-feed kinetically controlled reactive distillation columns. The design method allows rapid and relatively simple screening of different reactive distillation column configurations. Feasibility is assessed and operating conditions are determined using an extension of boundary-value methods. The approach is limited to systems with four or fewer chemical species. Both fully reactive and hybrid columns are considered. The methodology is illustrated for a metathesis reaction and for MTBE production.     

Systematic optimisation technology for high-level screening and scoping of complex distillation systems

Established procedures for complex distillation synthesis employ detailed models that are unable to function for high-level screening. In this article, a new approach is presented in the form of Conceptual Programming for the preliminary screening of complex distillation systems. Conceptual Programming employs a generic supertask representation that replaces the need of superstructures. Tasks stand for simple distillation columns and hybrids represent complex distillation arrangements. A supertask accounts for all possible configurations without introducing representation and modelling difficulties. The basic tasks are then modelled using appropriate shortcut or semi-rigorous methods. A mixed integer linear programming (MILP) problem is formulated to obtain the optimum structure and performance targets. The strengths of the approach are highlighted with a light alcohol separation problem.     

A systematic procedure for synthesis of intensified nonsharp distillation systems with fewer columns

Nonsharp separation sequences can intrinsically improve thermodynamic efficiency than that of sharp sequences for a multicomponent distillation. There are much more nonsharp sequences than that of sharp sequences. In this paper, the synthesis of new intensified distillation systems from nonsharp separation sequences is presented. Such intensified distillation systems have fewer columns and have the potential to reduce both energy and capital costs than conventional configurations. First, the representation of any nonsharp sequence with the simple column configuration is found to be the necessary starting point. Then, five strategies are introduced which present different mechanisms to change the structures of the distillation configurations. Third, a systematic procedure is formulated which can achieve the intensified distillation systems with fewer columns systematically. Finally, the systematic method has been applied to different examples of nonsharp separation sequences. It is demonstrated that the method can be used to generate the new intensified distillation systems from any nonsharp separation sequences. The method is easy to use and can explicitly derive all of the intensified distillation systems for the nonsharp separation sequences for a multicomponent distillation.     

过程系统能量集成同步最优综合法

将换热网络超结构混合整数非线性规划多目标同步最优综合方法进一步扩展到与过程系统的联合优化,提出了改进的过程热集成同步综合方法,并以反应分离过程与换热网络能量集成为例,建立了同步优化超结构模型,采用混合整数非线性规划的遗传算法求解,可同时得到热集成系统最优的流程结构和操作条件。     

Simultaneous synthesis of distillation trains and heat exchanger networks

A new mathematical formulation for the optimal synthesis of heat-integrated distillation systems that accounts for constrained heat matches between columns and the rest of the process is presented. The definition of temperature intervals commonly used by heat exchanger network synthesis procedures is embedded in the proposed formulation that can be regarded as a generalization of the network flow model of Cerdá and Westerberg (1983, Chem. Engng Sci.38, 1723) under conditions of variable stream temperatures. The minimization of the total flow-sheet utility cost has been chosen as the design target.The problem has been represented through a mixed-integer linear program. By performing the search with a standard branch-and-bound technique the global optimality of the solution found is guaranteed. Three case studies involving the separation of a ternary mixture by distillation have been solved. The consideration of the rest of the process produces in two of them new distillation train designs costing less overall.