A generalized methodology for optimal configurations of hybrid distillation-pervaporation processes

The aim of this work is to illustrate the structural and parametric optimization of continuous hybrid distillation-pervaporation process with different configurations such as series, parallel, and series-parallel arrangement of pervaporation modules in the pervaporation network, and to propose a generalized methodology for difficult separations. A superstructure representation of hybrid process is considered and the process is modeled and optimized using an MINLP approach. The optimization strategy is to obtain the desired degree of either the retentate or the distillate purity without violating the composition constraints of products and heat exchange policy which minimizes the required membrane area by increasing the flux through the membrane. The structural and operating parameters such as number of trays required, feed tray location, reflux ratio, retentate recycle location, permeate recycle location, membrane feed location, number of pervaporation modules required, target composition (which is directly related to membrane area), and membrane selectivity are optimized for each configuration by minimizing the total annual cost (TAC) for the separation system. The optimization studies have been carried out with General Algebraic Modeling System software (GAMS/SBB/CONOPT) and the results of different configurations have been compared on the basis of TAC required for the separation. A total of three industrial case studies have been dealt with. The separation of isopropanol-water as an azeotropic mixture, propylene-propane as a close boiling mixture (system with a low relative volatility) and acetone-water as a tangent pinch mixture have been studied as representative examples.     

Synthesis of non-isothermal heat integrated water networks in chemical processes

This paper presents a new approach for the simultaneous synthesis and optimization of heat integrated water networks. A new superstructure for heat exchanger network (HEN) synthesis is proposed. The procedure is based on mixed integer non-linear mathematical programming (MINLP). Four relevant examples are presented to illustrate various aspects of the proposed approach.     

Synthesis of flexible heat exchange networks and mass exchange networks

A simple strategy is proposed for the synthesis of flexible heat exchange networks (HEN's) or mass exchange networks (MEN's) that involves expected disturbance range in the flow rates and temperatures (for HEN's) or compositions (for MEN's) of the inlet process streams. The network synthesis problem is decomposed into three main iterative steps: (1) synthesizing a network candidate with a minimum total annual cost (TAC) according to a finite number of operating conditions; (2) performing flexibility test without considering the size restrictions to verify whether the current network candidate is operable for a large number of uncertain parameters that are generated randomly within the expected operating ranges; appending test point(s) that mostly violates the constraints of the candidate network when the network configuration is proved infeasible through simulations, then returning to step (1) again to synthesize a new candidate structure; (3) considering the size restraints that have been ignored previously, executing flexibility test to the network qualified in step (2), and increasing the size of exchange units if necessary. A few iterations of these design steps may be required to secure the desirable results. Also in this paper are several numerical examples supplied to demonstrate the applicability of the proposed strategy for the synthesis of flexible heat exchange networks or mass exchange networks.     

MINLP synthesis of optimal cooling networks

A mixed-integer nonlinear programming (MINLP) algorithm for the synthesis of cooling networks is presented. As opposed to previous models in which the minimization of utility consumption has been formulated, the algorithm considers simultaneously the capital cost for the coolers and the utility costs. The strategy is based on a superstructure that allows bypass and splitting of utility streams. Also, the superstructure considers a combination of arrangements in series and in parallel that allows for an efficient use of cooling streams. The typical arrangement of cooling networks in parallel usually conducts to higher total costs. Also, it is shown that the use of minimum amounts of cold utilities does not necessarily conduct to the minimum total cost. Three case studies are used to show the application of the proposed method.     

Combined mass and heat exchange network synthesis based on stage-wise superstructure model☆

Integrating multiple systems into one has become an important trend in Process Systems Engineering research field since there is strong demand from the modern industries. In this study, a stage-wise superstructure-based method is proposed to synthesize a combined mass and heat exchange network (CM&HEN) which has two parts as the mass exchange network (MEN) and heat exchange network (HEN) involved. To express the pos-sible heat exchange requirements resulted from mass exchange operations, a so cal ed“indistinct HEN super-structure (IHS)”, which can contain the all potential matches between streams, is constructed at first. Then, a non-linear programming (NLP) mathematical model is established for the simultaneous synthesis and optimiza-tion of networks. Therein, the interaction between mass exchange and heat exchange is modeling formulated. The NLP model has later been examined using an example from literature, and the effectiveness of the proposed method has been demonstrated with the results.     

A computerized and integrated approach for heat exchanger network design in multipurpose batch plants

Significant savings in the utility cost of batch plants can be obtained by heat integration. In this study, an integrated mathematical programming approach is developed for the determination of the cost optimal heat exchanger network for multipurpose batch chemical plants. A single step, interactive computer program (BatcHEN) which is developed for the determination of the campaigns (i.e. the set of products which can be produced simultaneously), the heat exchange areas of all possible heat exchangers in the campaigns and finally the heat exchanger network are all discussed. A matrix search algorithm is used for the determination of the campaigns. Heat exchange areas for the possible heat exchangers are found by solving a nonlinear optimization model with a grid search algorithm. Finally the heat exchanger network optimization is modeled as a mixed integer linear programming problem and then solved by the modeling and optimization software GAMS/XA.     

Supply and target based superstructure synthesis of heat and mass exchanger networks

This paper presents new methods for the optimisation of superstructures involving heat exchanger networks (HENs) and mass exchanger networks (MENs). The techniques developed in this study explore the use of key variables (namely supply temperatures/compositions and target temperatures/compositions) in HENs and MENs to define the intervals of superstructures. Such superstructures are modeled as mixed integer non linear programmes (MINLP) with the objective of minimisation of the total annual cost (TAC) for each network. The superstructures presented in this paper are derivatives of the interval and supply based superstructures (IBMS and SBS) developed previously. Two different superstructures are developed in this paper: the first uses the supply temperature/composition of hot/rich streams and the target temperature/composition of cold/lean streams (denoted supply and target based superstructure, S&TBS), while the second superstructure uses the target temperature/composition of hot/rich streams and the supply temperature of cold/lean streams (denoted target and supply based superstructure, T&SBS). Five HEN examples and three MEN examples are presented. The results obtained compare well with those in the literature.     

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.     

热集成复杂精馏系统综合的研究

将夹点分析法应用于热集成复杂精馏系统综合的换热网络设计中,避免了以换热网络结构作为独立变量,建立了一个以预分馏塔组分回收率、回流比及操作压力为连续变量,以分离序列和热耦合方式为离散变量的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。对多个五组分混合物分离问题进行了求解,并对不同优化方案的优化结果及其经济性作了比较和分析,结果表明采用热集成复杂精馏塔流程可以显著地降低系统的总费用,还表明该方法是求解热集成复杂精馏系统综合问题的有效方法。     

A grid-based facilities allocation approach with safety and optimal heat exchanger networks synthesis

A new approach is presented to determine optimal layout of facilities where toxic releases may occur in an existing or new facility. The land area is divided in equally sized rectangular grids, where each grid contains up to one facility surrounded by streets. Some facilities may produce hot and/or cold streams and the associated heat exchangers network (HEN) is simultaneously optimized with the layout problem. The three dimensions of geographical allocation points for each generated stream are included in the model. No additional cost for geographical allocation of heating and cooling services is considered since every facility is expected to contain these services regardless of their use in the HEN. The toxic effect is estimated via probit functions and its associated risk reduction results in providing safety to the combined HEN-facility layout problem. The grid-based allocation eliminates numerical difficulties appearing with conventional non-overlapping and Euclidian distance equations.     

Separation network design with mass and energy separating agents

The mathematical model developed in this paper deals with simultaneous synthesis of the integrated separation network, where both mass separating agents (MSAs) and energy separating agents (ESAs) are taken into account. The proposed model formulation is believed to be superior to the available ones. Traditionally, the tasks of optimizing ESA-based and MSA-based processes were either performed individually or studied on a heuristic basis. In this work, both kinds of processes are incorporated into a single comprehensive flowsheet and a novel state-space superstructure with multi-stream mixings is adopted to capture all possible network configurations. By properly addressing the issue of interactions between the MSA and ESA subsystems, lower total annualized cost (TAC) can be obtained by solving the corresponding mixed-integer nonlinear programming (MINLP) model. A benchmark problem already published in the literature has been investigated to demonstrate how better conceptual designs can be generated by our proposed approach.     

Synthesis of Rice Processing Plants. II. MINLP Optimization

Abstract

A systematic design approach was applied to develop the optimal process flowsheet for a rice processing plant. The optimization problem was formulated as a Mixed-Integer NonLinear Programme, MINLP, consisting of vectors of binary and continuous variables. A superstructure flowsheet comprising all serial structures of drying, cooling, and tempering units in the process was postulated. The set of optimum decision variables including the number of drying, cooling, and tempering units, temperature and relative humidity of drying air, drying time, cooling time, and tempering time were determine as the solution of the corresponding MINLP. Six objective functions were investigated as possible performance criteria: production time, number of the operating units, energy consumption, total operating cost, head rice yield, and the profit. The choice of objective function was found to have a significant effect on the optimal solution. Comparison with typical design and operating conditions, the MINLP results showed that a 22% reduction in energy consumption was possible along with a 2.4% increase in head rice yield. These savings, if applied to the world-wide rice industry, translate into more than $3 billion dollars/year increase in profit.     

Synthesis of Rice Processing Plants. II. MINLP Optimization

A systematic design approach was applied to develop the optimal process flowsheet for a rice processing plant. The optimization problem was formulated as a Mixed-Integer NonLinear Programme, MINLP, consisting of vectors of binary and continuous variables. A superstructure flowsheet comprising all serial structures of drying, cooling, and tempering units in the process was postulated. The set of optimum decision variables including the number of drying, cooling, and tempering units, temperature and relative humidity of drying air, drying time, cooling time, and tempering time were determine as the solution of the corresponding MINLP. Six objective functions were investigated as possible performance criteria: production time, number of the operating units, energy consumption, total operating cost, head rice yield, and the profit. The choice of objective function was found to have a significant effect on the optimal solution. Comparison with typical design and operating conditions, the MINLP results showed that a 22% reduction in energy consumption was possible along with a 2.4% increase in head rice yield. These savings, if applied to the world-wide rice industry, translate into more than $3 billion dollars/year increase in profit.