Biological wastewater treatment system design Part I. Optimal synthesis

Common practice for design of biological wastewater treatment systems involves evaluation of certain fixed structure systems at several alternative conditions. This study considered optimization of both the structure and the design of the system using the structural parameter system synthesis technique. The system was composed of a trickling filter, an activated sludge aeration vessel, and a secondary clarifier. Results of optimal synthesis indicated that the activated sludge system was the most cost effective system for the specific set of process parameters employed. The same conclusion was reached by optimizing several systems with different structures.     

Synthesis of industrial systems based on value analysis

In this contribution, we present a novel methodology for flexible design of industrial systems based on their detailed differential value analysis. Evolving from graph theory, this methodology devises a mechanism for systematic structural decomposition of large-scale industrial systems into basic processing elements (paths and trees), combination of elements into subsystems and evaluation of individual elements/subsystems to correlate with the overall system margin. This helps to reduce the size of the large combinatorial problems and comprehensively analyse the multiple objectives and the sets of optimal operating states, capital investments and marginal contributions at elemental/subsystems levels that are critical for flexible designs. The approach generates the whole set of optimal solutions compared to the one point solution of the deterministic approaches (MINLP) while allowing additional complexity of process level models in the site-wide integration due to the systematic structural decomposition of a system into its basic elements/subsystems. A recent industrial application on oil upgrading system design is used to illustrate the methodology.     

Optimal synthesis of multiproduct resource-conserving reactor systems

The procedure for synthesizing optimal multiproduct reactor systems is proposed. At the first stage, the theoretically possible values of selectivities with respect to products are determined for the specified market demand for the products. The capacity of processing the initial reagent is specified. At the second stage, the engineering, operating, and structural parameters of the unit that provides the values of selectivities, which are closest to the theoretical parameters, are determined.     

精细搜索策略应用于质量交换网络综合

质量交换网络是化工过程系统的重要组成部分,其优化设计对降低污染排放具有重要意义。采用启发式算法优化质量交换网络时,存在难以兼顾全局搜索和局部搜索的问题。通过分析不同精度优化参数下的优化结果,揭示了该问题的成因,并提出一种精细搜索策略用于基础算法所得结构的深度优化。该策略包含两种方法,方法1采用具有个体回代与分化的高精度强制进化随机游走算法,可保留个体结构变异能力;方法2采用确定性方法依次对多维目标函数中的每个变量进行一维搜索,具有精度高收敛快的优点。将该策略应用于焦炉气脱硫和空气除氨算例,得到的结果分别为407308 USD·a^-1和127807 USD·a^-1,经济性优于现有文献中的结果,验证了本策略的有效性。     

精细搜索策略应用于质量交换网络综合

质量交换网络是化工过程系统的重要组成部分,其优化设计对降低污染排放具有重要意义。采用启发式算法优化质量交换网络时,存在难以兼顾全局搜索和局部搜索的问题。通过分析不同精度优化参数下的优化结果,揭示了该问题的成因,并提出一种精细搜索策略用于基础算法所得结构的深度优化。该策略包含两种方法,方法1采用具有个体回代与分化的高精度强制进化随机游走算法,可保留个体结构变异能力;方法2采用确定性方法依次对多维目标函数中的每个变量进行一维搜索,具有精度高收敛快的优点。将该策略应用于焦炉气脱硫和空气除氨算例,得到的结果分别为407308 USD·a^-1和127807 USD·a^-1,经济性优于现有文献中的结果,验证了本策略的有效性。     

Decomposed algorithmic synthesis of reactor-separation-recycle systems

A two-level algorithmic approach to synthesis of reaction-separation-recycle systems is presented. On the upper level, reactor conversion and purge fraction are optimized using a simple direct search method, and the flows among subsystems such as the reactor system and separation system are calculated. On the lower level, individual subsystems are optimized in every iteration of the upper level loop. On this level, the structure and operating conditions of the subsystems are determined, and the cost is returned to the upper level. This decomposed approach makes the synthesis of the overall system less complex and more robust than approaches addressing the entire problem simultaneously. The proposed approach is demonstrated on the well-known HDA process. The results are comparable to previously published results using the Hierarchical Decomposition Procedure, and the optimal results are demonstrated to be insensitive to initial estimates.     

Integrated design and control of semicontinuous distillation systems utilizing mixed integer dynamic optimization

Semicontinuous distillation systems are notoriously difficult to design and optimize because the structural parameters, operational parameters, and control system must all be determined simultaneously. In the past 15 years of research into semicontinuous systems, studies of the optimal design of these systems have all been limited in scope to small subsets of the parameters, which yields suboptimal and often unsatisfactory results. In this work, for the first time, the problem of integrated design and control of semicontinuous distillation processes is studied by using a mixed integer dynamic optimization (MIDO) problem formulation to optimize both the structural and control tuning parameters of the system. The public model library (PML) of gPROMS is used to simulate the process and the built-in optimization package of gPROMS is used to solve the MIDO via the deterministic outer approximation method. The optimization results are then compared to the heuristic particle swarm optimization (PSO) method.     

RWCE算法中采用单元重构策略激励换热网络结构优化

应用强制进化随机游走算法优化换热网络的过程中,通过监测最优结构中换热单元优化进程,探究总体结构进化特点,发现存在换热单元先入为主的现象,主体结构稳固难以被突破,导致换热网络优化进入“停滞”状态。基于此,提出了换热单元重构策略,该策略旨在增强结构变异能力,经过一定阶段概率性消除结构中既有换热单元,腾出结构进化空间,再依据约束条件重新构建换热单元,既丰富了结构多样性又扩大了搜索域。此外建立优化状态监测指标,维持结构较高的变异活性,增强算法全局寻优能力。最后将该策略加入算法流程优化多个换热网络实例,总结分析其作用机理,所得结果均优于现有文献结果,证实了该策略的有效性。     

Optimal synthesis of heat exchange systems Necessary conditions for minimum heat transfer area and their application to systems synthesis

Necessary conditions for the optimal structure of a heat exchange system are discussed with the minimum heat transfer area employed as acriterionto express efficiency of the system. On the basis of the necessary conditions obtained, an algorithm to synthesize heat exchange systems with auxiliary heating and cooling equipment is proposed. an application to a practical heat exchange system show that the algorithm provides far more efficient than that which has been conventionally used.     

采用结构融合策略优化换热网络

利用强制进化随机游走算法优化换热网络至后期时,个体网络结构基本定型,很难再被破坏或改变,潜在进化能力难以发挥作用,无法求解出更优结构。基于此,探究个体进化过程中的结构变化特性,分析后期结构优化的重心所在,提出结构融合策略,将两个个体结构融合到一起,形成新个体,放大原个体结构进化潜力。对新个体进行优化,其结构中所有换热单元互相竞争,引导结构进化潜力发挥作用,保留有益于结构进化的换热单元,淘汰阻碍结构进化的换热单元,生成部分新换热单元,促进个体进化形成更优换热网络结构。最后应用两个算例验证该策略的有效性,取得了可观的优化效果。     

An algorithmic procedure for the synthesis of distillation sequences with bypass

When a separation system is to produce multicomponent products, it is frequently not necessary to separate a feed mixture completely into pure components. Instead, column bypasses can reduce both capital and operating costs by reducing mass load on the columns.

This paper presents an algorithmic procedure for the synthesis of a sequence of simple, sharp split distillation columns with both bypasses and mixers that minimizes annualized costs. This procedure can solve problems in which a single feed is to be separated into two or more multicomponent products. We use models that are linear except for stream splitters. We present an analysis of the problem structure that suggest a decomposition which allows significant reductions both in the problem search space and nonlinearities caused by the splitters. The decomposition permits one to solve any three component problem for its global optimum as two linear programs. Four and five component problems require six and twenty-four nonlinear programs, respectively, each of which models a structurally different flowsheet for the process. For each flowsheet, one can establish a lower bound for the corresponding nonlinear program by using a relaxation that allows the splitters to be treated linearly: giving a linear program which is readily solved.

For two example problems, we first produced lower bounds for each structural alternative (a linear program for each). Solving the nonlinear program for the most promising structure eliminated the need for solving the nonlinear program for all remaining alternatives. Upper and lower bounds within 1% of each other strongly imply the solutions were globally optimal.     

Optimal design of renewable energy systems with flexible inputs and outputs using the P‐graph framework

The P‐graph framework introduced by Friedler et al. (Chem Eng Sci. 1992;47:1973–1988) is a general mathematical methodology based on Graph Theory which is applicable to many process design problems. We propose an extension of the P‐graph framework and the associated MILP model to account for operating units and systems where the inputs and outputs are variable. This is important because the P‐graph framework in its current form would otherwise apply only to systems where the ratios of inputs to outputs are fixed. Consequently, it is difficult to apply the method to many emerging systems without the new mathematical model presented here. We discuss and develop the model in detail, and we then illustrate its application with the case study of an energy system. We establish a structure with optimal cost for a baseline heat demand, and we further explore how the energy system structure and the feedstocks change as the heat demand increases. © 2015 American Institute of Chemical Engineers AIChE J, 62: 1143–1153, 2016     

液化天然气深冷-膜蒸馏海水淡化系统集成与分析

提出了一种PRICO天然气液化-膜蒸馏（MD）海水淡化系统集成方法,利用PRICO过程压缩机出口的余热驱动MD海水淡化。采用Aspen Plus和GAMS建立了集成系统的数学模型,综合考虑系统的结构、物流物性、设备规模、操作参数等系统设计问题,分析不同设计下系统的投资、能耗、运行费用以及MD单位产水成本。模型应用于一个处理量为1 kmol/s的PRICO天然气液化系统与MD集成的案例研究。计算结果表明,单位产水成本最小时,系统产水成本为1.98 USD/m³,淡水产量为5.78 m³/h,与反渗透等海水淡化技术相比,MD在经济性方面具有较强的竞争力。     

Design of reverse osmosis networks for multiple freshwater production

Reverse osmosis (RO) desalination, which produces multiple freshwater from seawater, has been studied in this work. An optimization method based on process synthesis has been applied to design the RO system. First, a simplified superstructure that contains all the feasible design for this desalination problem has been presented. In this structural representation, the stream split ratios and the logical expressions of stream mixing were employed, which can make the mathematical model easy to handle. Then, the membrane separation units employing the spiral wound reverse osmosis elements were described by using a pressure vessel model, which takes into account the pressure drop and the concentration changes in the membrane channel. The optimum design problem can be formulated as a mixedinteger non-linear programming (MINLP) problem, which minimizes the total annualized cost of the RO system. The cost equation relating the capital and operating cost to the design variables, as well as the structural variables, has been introduced in the objective function. The problem solution includes the optimal streams distribution, the optimal system structure and the operating conditions. The design method could also be used for the optimal selection of membrane element type in each stage and the optimal number of membrane elements in each pressure vessel. The effectiveness of this design methodology has been demonstrated by solving a desalination case. The comparisons with common industrial approach indicated that the integrative RO system proposed in this work is more economical, which can lead to significant capital cost and energy saving and provide an economically attractive desalination scheme.     

Industrial application of an extended fully thermally coupled distillation column to BTX separation in a naphtha reforming plant

Aromatic compounds are yielded from naphtha reforming in a petrochemical plant, and the products are separated with binary distillation columns for benzene, toluene, xylene and heavy components in sequence. In this study, the first three columns of the fractionation process in the naphtha reforming unit are replaced with an extended fully thermally coupled distillation column (EFTCDC) also known as the extended Petlyuk column. An industrial-sized application of the EFTCDC is examined to compare the performance of the column with a conventional system. From a structural design giving the optimum structure of the column, a practical column structure is derived and used in the HYSYS simulation to find the optimal operation condition for a given set of product specifications. The EFTCDC gives an energy saving of 9.7% over a conventional three-column process. In addition, it is proved that the design procedure is good for an industrial process of 18 components.     

Optimal synthesis of an emulsion pertraction process for the removal of pollutant anions in industrial wastewater systems

This work reports a synthesis model for the optimal design of an emulsion pertraction process for the removal and recovery of pollutant anions from industrial wastewaters. The goal is to define the minimum membrane area needed in order to obtain an environmentally acceptable stream with minimum concentration of the pollutant and at the same time a concentrated solution for further processing. A superstructure is proposed which consists of a prespecified number of modules that are interconnected in all possible ways in order to account for all potential configurations. The selection of the optimal design from this superstructure is formulated as a non-linear programming (NLP) problem that is solved with CONOPT2 from GAMS.In order to reduce the membrane area, alternative configurations that provide flexibility to the emulsion phase inlet and higher residence time values were analyzed obtaining 56% reduction of the membrane area.     

Stabilized gold clusters: from isolation toward controlled synthesis

Bare metal clusters with fewer than ～100 atoms exhibit intrinsically unique and size-specific properties, making them promising functional units or building blocks for novel materials. To utilize such clusters in functional materials, they need to be stabilized against coalescence by employing organic ligands, polymers, and solid materials. To realize rational development of cluster-based materials, it is essential to clarify how the stability and nature of clusters are modified by interactions with stabilizers by characterizing isolated clusters. The next stage is to design on-demand function by intentionally controlling the structural parameters of cluster-based materials; such parameters include the size, composition, and atomic arrangement of clusters and the interfacial structure between clusters and stabilizers. This review summarizes the current state of the art of isolation of gold clusters stabilized in various environments and surveys ongoing efforts to precisely control the structural parameters with atomic level accuracy.     

LSSVM过程建模中超参数选取的梯度优化算法

基于结构风险最小的最小二乘支持向量机（least squares support vector machine, LSSVM）为标准支持向量机（SVM）的约简;训练简易;性能良好。其模型精度受超参数影响;常规的网络搜索法很难搜得最佳超参数。在快速留一法的基础上;以全样本留一预测误差平方和最小化为目标;导出基于梯度的最优化算法;用以优选为LSSVM超参数;进而构建G-LSSVM模型。以柠檬酸发酵过程为算例对G-LSSVM进行检验;结果表明G-LSSVM的超参数选取耗时少;模型稳定性良好;且拟合和预报性能都优于标准SVM和神经网络。有望适用于机理不明、高度非线性、小样本的化工过程建模。     

Worst-case identification in structured process systems

An improved method for identifying the worst-case set of parameter combinations in controllable systems is presented that is based on branch and bound search in the space of the uncertain parameters. A characteristic of controllable structured systems frequently appears wherein the limiting condition is localized in a part of the system that has only limited coupling to the other parts. While there may be many uncertain parameters varying in parts upstream of the limiting constraints, often there will remain sufficient control degrees of freedom in those other parts to compensate.

The branch and bound method in its simplest form cannot recognize this situation, and will usually engage in searching among combinations of such parameters, when in the end they have no effect on the limiting condition. Modifications to the basic method are presented that allow these parameters to be recognized a priori. The complexity of the branch and bound search is reduced accordingly, while the rigor of the original method is maintained. As shown in three heat exchanger network examples, a substantial reduction in effort is often achieved.     

Integrated design of flexible chemical processes,devices, and control systems

Methodology of designing flexible chemical engineering processes, apparatuses, and systems, which form prerequisites of efficient process control and automation was proposed, and the multistage iteration procedure of solving the problems of the integrated design of flexible automated chemical engineering systems (CESs) was formalized. A method of calculating the structural parameters and regime variables (optimal tasks for the controllers of a system of automatic stabilization (SAS)) that provide the optimal (from the viewpoint of energy- and resource saving and product quality) and safe operation of chemical engineering processes, apparatuses, and systems for the technological equipment implementation of chemical engineering systems has been developed.