Mass Exchange Network Synthesis Research Articles

Interval based MINLP superstructure synthesis of combined heat and mass exchanger networks

An interval based superstructure approach for combining the synthesis of heat and mass exchanger networks is presented in this paper. The technique involves combining the interval based MINLP superstructure (IBMS) for the synthesis of heat exchanger networks (HENs) with that of mass exchanger networks (MENs). The two networks are made to interact through the lean stream in the mass exchange network. The new approach involves the use of the lean substream concept to explore potential mass exchange temperatures. An example which involves a one-lean stream mass exchange problem alongside regeneration and hot and cold utilities is presented.

Minimização da emissão (de poluentes utilizando a análise pinch em conjunto com técnicas de programação matemática

Mass Exchanger Network Synthesis aims at the reduction of industrial pollutant emission. In mass integration the process is optimized from the point of view of consumption of the external mass transfer agents and of capital. A calculation system was developed for mass exchanger network synthesis by means of mathematical programming and concepts of Pinch Analysis. Algorithms are easy to use and do not require the designer’s profound knowledge on the process. An example from the literature has been chosen to test the applicability of the methodology. Results were consistent and achieved optimal mass exchanger network. In addition, a great number of new network possibilities were shown, guaranteed by the mathematical programming methods and Pinch Analysis. Due to its simplicity and applicability, the new systematic may be used for industrial and academic purposes

Interval based MINLP superstructure synthesis of mass exchange networks

A new simultaneous synthesis approach for mass exchange networks (MENs) is presented. The technique is adapted from the interval based mixed integer non-linear program (MINLP) superstructure (IBMS) synthesis of heat exchanger networks (HENs). The superstructure interval boundary compositions are defined by the supply and target compositions of either the rich or lean set of streams. Each rich and lean stream in the superstructure has the potential of exchanging mass with streams of opposite kind in each interval based on mass transfer feasibility. The model harnesses the strengths of the stagewise superstructure and the pinch technology methods for mass exchange network synthesis (MENS). The IBMS approach simultaneously trades-off the capital and operating costs for MENs. The superstructure composition interval defining approach introduced in this paper enforces the mixing of split streams at equal compositions, hence there is no need to include mixing equations in the model. Fixing the interval boundaries helps to eliminate the complexities involved in initialisations, thus the region of search for the optimum solution is reduced. The IBMS model is applied to MENS problems involving continuous contact and staged columns. It is also extended to problems involving multiple mass separating agents (MSAs) and regeneration. The results obtained compare well with those in the literature.

Optimization of combined heat and mass exchanger networks using pinch technology

AbstractThis article examines the benefits that may be obtained by combining the optimisation of heat and mass exchanger networks. This study uses a Pinch Technology approach to the targeting of Combined Heat and Mass Exchanger Networks (CHAMENs), and illustrates it with application to three examples. The first example has just one external mass separating agent (MSA), the second has both process and external MSAs, and the third is an extension of the second with a heat exchanger network integrated. The major benefits arise when it is possible to cool the process MSA with an excess capacity to remove mass. This reduces the flowrate of the external MSA (since this exists below the pinch) and can even do away entirely with the need for it. This also leads to a reduction in the capital cost requirements of both the process and the external MSAs, as well as a reduction in regeneration costs. The implication of this is that a limitation to the use of the available capacity of process MSAs is their mass exchange temperature. It was also found (in the example in which hot/cold utilities are used to enhance mass exchange) that the mass exchanger network synthesis (MENS) costs generally dominate over the heat exchanger network synthesis (HENS) costs. Other examples presented in this article support these conclusions. Copyright © 2007 Curtin University of Technology and John Wiley & Sons, Ltd.

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.

Superstructure-Based MINLP Formulation for Synthesis of Semicontinuous Mass Exchanger Networks

This paper deals with the synthesis of mass exchanger networks (MENs) for semicontinuous processes. The starts and endings of available process streams are time-dependent since they usually come from other batch plants. A periodically partitioned stagewise superstructure is presented for modeling the time-dependent mass exchange operations. The proposed stagewise superstructure can handle multiple transferable components and can also be extended to include storage tanks. Not using any heuristics that are based on the concepts of pinch point, the proposed superstructure-based representation for synthesis of semicontinuous MENs is formulated as a mixed-integer nonlinear program (MINLP) for targeting the consumption of external lean mass separating agents. The coke oven gases (COGs) problem from the literature is supplied to demonstrate the applicability of the proposed MEN synthesis method for semicontinuous processes.

Determination of Mass Separating Agent Flows Using the Mass Exchange Grand Composite Curve

In this paper we set out the principles for using the grand composite curve (GCC) of mass exchange network synthesis (MENS) for selection of external mass separating agents (MSAs). These principles enable us to systematically choose between alternative external MSAs as well as the minimum flowrate for each MSA selected. This paper emphasizes that the cheapest MSA is not necessarily the one with the lowest cost per unit mass of MSA, but rather the one with the lowest overall cost of removal of the mass load, which depends on both the MSA cost and its permissible concentration change. It also demonstrates the importance of consideration of the composition levels of the MSAs in relation to the target compositions of the rich streams and to the capital cost implications of the resulting mass transfer driving forces. In this respect the use of the GCC is superior to procedures developed so far. We illustrate the principles presented by application to two example problems.

Fairly Linear Mixed Integer Nonlinear Programming Model for the Synthesis of Mass Exchange Networks

A fairly linear optimization model for the synthesis of mass exchange networks has been developed. Superstructure, detailed modeling equations, and solutions of example problems are presented. The predominantly linear character of the model can be kept as long as single-component mass exchange network synthesis problems and packed columns as mass exchangers are considered. At the cost of introducing nonlinear constraints, the optimization model can be extended to handle multicomponent problems and staged columns as well. The new model applies the key ideas of the simultaneous heat exchanger network synthesis model of Yee and Grossmann [Comput. Chem. Eng.1990, 14 (10), 1165-1184].

Simultaneous synthesis of mass exchange networks for waste minimization

The paper deals with the synthesis problem of mass exchange networks (MEN's) for waste minimization by adopting a mathematical programming approach based on the stage-wise superstructure representation of the MEN's, analogous to the one introduced by [Yee, T. F., & Grossmann, I. E. (1990a). Simultaneous optimization models for heat integration. I. Area and energy targeting and modeling of multi-stream exchangers. Computers and Chemical Engineering 14, 1151; Yee, T. F., & Grossmann, I. E. (1990b). Simultaneous optimization models for heat integration. II. Heat exchanger network synthesis. Computers and Chemical Engineering 14, 1165] for synthesis of heat exchange networks (HEN's). This stage-wise superstructure-based representation cannot only handle multiple transferable components and reactive separating agents directly, but also be extended to include regeneration networks straightforwardly. Not using any heuristics that are based on the concept of pinch points, the proposed superstructure-based representation for MEN's is formulated as a mixed-integer nonlinear programming (MINLP) optimization model, and therefore the operating cost for the external lean mass separating agents as well as the regenerating agents and the annualized equipment cost for exchange units can be minimized simultaneously. Four benchmark examples from literatures—including those with single recovery component, multiple waste components, reactive mass separating agent, and regenerating streams—are examined to illustrate the applicability of proposed approach for synthesis of various MEN's.

Synthesis of mass exchange network for batch processes—Part I: Utility targeting

Synthesis of optimal mass exchange network (MEN) for continuous processes based on Pinch Analysis has been rather well established. In contrast, very little work has been done on mass exchange network synthesis (MENS) for batch process systems. The batch process systems referred to in this work can be defined as processes which operate discontinuously and deliver the products in discrete amounts, with frequent starts and stops. There is a clear need to develop a MENS procedure for batch process systems which are industrially very common as well as important. Techniques developed in this paper for the batch MENS involved the first key steps in the synthesis task, i.e. setting the utility targets ahead of batch MEN design. The utility-targeting approach employs the vertical and horizontal cascading approaches in a newly developed tool, i.e. time-dependent composition interval table that has been adapted from heat exchange network synthesis for batch processes. Prior to MEN design, the targeting procedure establishes the minimum utility (solvent) and mass storage targets for a maximum mass recovery network. These targets are essential for network design and batch process rescheduling.

Pinch analysis for aggregate production planning in supply chains

Global competition has made it imperative for the process industries to manage their supply chains optimally. The complexity of the supply chain processes coupled with large computational times often makes effective supply chain management (SCM) difficult. Production system is an important component of a supply chain. This paper introduces a novel approach for aggregate planning of production in supply chains. The approach derives inspiration from pinch analysis, which has been extensively used in heat and mass exchanger network synthesis. By representing demand and supply data as composites, it gives planners greater insight into the SCM process and thus facilitates re-planning and quick decision-making. Two case studies are solved, one involving a single product and another involving multiple products on a single processor. For the first case study, optimal production plans are obtained and matched with the results obtained by solving equivalent optimization problems in GAMS ®. For the second case study, an algorithm is proposed to determine the sequence of production of the multiple products. The initial guess obtained by following the algorithm reduces the computational time to one-sixth of the time otherwise taken by the solver. It may be concluded that plans obtained by pinch analysis provide either the best aggregate plans or excellent starting points to reduce the computational time for solutions by mixed integer programming formulations.

Handling of removable discontinuities in MINLP models for process synthesis problems, formulations of the Kremser equation

This paper presents a new method for handling removable discontinuities in non-convex mixed integer non-linear programming (MINLP) models for chemical process synthesis and design. First, the occurrences of different kinds of discontinuities in design equations are discussed. Then methods so far developed for handling discontinuities in an MINLP design environment are summarized. In the main part of the paper, a new method is presented for handling removable discontinuities. Our new method is compared to five conventional literature methods applied to three mass exchange network synthesis problems of different size, where the Kremser equation is used for calculating the number of equilibrium stages. In addition, a heat exchange network synthesis problem is considered where the logarithmic mean temperature difference is calculated rigorously. Our method proved to be much faster than the other methods examined and shows less sensitivity to the change of initial values in terms of optimal objective function value and solution time.

An integrated approach to the retrofitting of mass exchange networks

The synthesis of optimal mass exchange networks (MENs) deals with the identification of a cost-effective network of mass exchangers that preferentially transfer certain species from rich streams to lean streams. To date, MEN synthesis has dealt with grass-root design where the emphasis is on the maximization of process lean streams usage and the minimization of operating cost. Another important class of problems is the retrofit of MENs in which mass-exchange units already exist in the plant and the focus is to maximize the usage of the process units so as to minimize capital cost of newly added units and trade it off with operating cost. In this paper, we develop a systematic procedure for the retrofitting of MENs. First, we identify alternative structural configurations of interest through heuristics. Series and parallel structures are addressed. Next, we focus on two primary retrofitting strategies: those restricted by no capital constraints and those involving capital expenditure. The no-capital alternatives include enhancing performance of a current system as well as solvent substitution. The capital-based alternatives include the addition of new equipment. A new type of mass-pinch analysis is developed to maximize the utilization of existing capital while reconciling added capital with operating cost. The main concept in this novel pinch diagram is identifying maximum performance as dictated not only by thermodynamic limitations but also by physical size limitations. Different process alternatives are considered and screened to attain the optimum design. A case study is presented to demonstrate the broad applicability and potential benefits of the novel approach.

Mass exchange network synthesis using genetic algorithms

Mass Exchange Networks (MENs) are used in the chemical industry to reduce the waste generated by a plant to an acceptable level at the cheapest cost. Finding the optimal network, however, is often difficult due to the non-convexity of the mathematical representation of the problem. This paper describes a novel approach for the synthesis of MENs and MENs with regeneration using Genetic Algorithms (GA), a stochastic optimisation technique based on the concepts of natural evolution. We present an encoding for a genetic algorithm which describes a rich search space, considering both stream splitting and in-series exchangers. For a certain class of problems, all encoded solutions are feasible and require a simple evaluation to yield a cost, resulting in an efficient genetic algorithm. For other problems, the number of infeasible solutions is small, having little effect on the convergence of the genetic algorithm. In comparison with other methods, the GA presented herein is able to find better networks than have been reported elsewhere.

On the state space approach to mass/heat exchanger network design

In this paper, the conceptual framework and applications of the State Space Approach to Process Synthesis are presented. It is shown that the State Space Approach contains the concept of a Network Superstructure as a special case. Additionally, through various operators, it is shown to provide increased flexibility in formulating process network synthesis problems. As an example, it is demonstrated that an Assignment Operator can be used to facilitate the solution of large-scale problems. Pinch Operators are also employed in solving combined heat and mass exchange network synthesis problems. To demonstrate the usefulness of this new approach, two important problems are discussed. First, a one-step procedure is developed that minimizes the total annualized cost (TAC) of heat/mass exchange networks. Next, a novel problem, namely the pinch-based calculation of Minimum Utility Cost for a separable heat and mass exchange network, is solved.

Pollution prevention through process integration: systematic design tools

Overview of Pollution Prevention and Process Integration. Modeling of Individual Mass Exchange Units for Environmental Applications. Synthesis of Mass Exchange Networks. Graphical Techniques for Mass Integration: Segregation,Recycle, Interception, and Unit Manipulation. Optimization Techniques for Mass Integration. Synthesis of Reactive Mass Exchange Networks. Combined Heat and Mass Integration. Design of Heat-Induced Separation Networks. Recovery of VOCs. Modeling and Design of Membrane Systems. Environmentally-Benign Chemistry and Species. Subject Index.

Capital cost targets for mass exchange networks A special case: Water minimisation

Pinch analysis has been applied to mass exchange network synthesis. Until now, minimum utility targets have existed, but not capital cost targets. Previous work minimised the number of units in a network, but this paper shows that this does not necessarily minimise the capital cost. This paper focuses on the special case of water minimisation. It considers a simple example involving a network of absorption columns which use water to remove sulphur dioxide from a set of gas streams. The paper describes the first known method for targeting the minimum number of trays in the network, based on a specified ‘minimum composition difference’. This is then translated into a capital cost target. An interactive design method is presented which allows the targets to be approached to within 5%. The example is then extended to demonstrate how the targets can be used to trade off capital and operating costs in order to optimise the network before design. A further extension deals with multiple water sources. This work may be extended to other absorbents and generalised to other mass exchange networks.

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 d...

A multiperiod MINLP model for the synthesis of flexible heat and mass exchange networks

This paper addresses the problem of how to synthesize mass and heat exchange processes, in which stream flowrates and their inlet compositions and temperatures may vary according to a set of discrete values. A unified hyperstructure representation of mass and heat exchange alternatives is introduced to account for all mass and heat integration possibilities. A multiperiod mixed integer nonlinear programming (MINLP) model is then developed, where a total annualized cost is minimized by balancing capital investment cost (of the heat and mass exchange equipment and their interconnections) to operating cost (of the hot-cold utilities, mass separating agents, etc.). As illustrated with the example problems, the proposed model can be effectively employed for the synthesis of flexible heat exchanger networks (HENs) and mass exchanger networks (MENs) separately or, for the synthesis of separation processes involving both heat and mass transfer.

Synthesis of combined heat and reactive mass-exchange networks

In this work we introduce the problem of synthesizing combined heat and reactive mass exchange networks “CHARMENs”. The synthesis task involves the preferential transfer of a certain species from a set of rich streams to a set of lean streams and at the same time accomplish a specified heat transfer task in a cost effective manner. The economic objectives of mass exchange and heat recovery are in general incompatible and need to be addressed simultaneously. The proposed work introduces a systematic and generally applicable procedure to trade-off the two objectives and synthesize a CHARMEN. First, we derive a number of important properties of the problem. Based on these characteristics, a two-stage targeting procedure is developed. In the first stage, the minimum operating cost “MOC” of the network is identified via a mixed-integer nonlinear program “MINLP”. A shortcut linear formulation is also devised to identify a near-optimum MOC solution which may be used as an initial guess for the MINLP. The optimum solution to the MOC problem results in a natural decomposition of the original CHARMEN problem into two independent subproblems that may be solved to identify the minimum number of heat and reactive mass exchangers. The applicability of the synthesis procedure is demonstrated by tackling a case study on the desulfurization of gaseous wastes with simultaneous heat recovery.