Mass Exchange Network Synthesis Research Articles

A Novel Chessboard Model for Optimization of Mass Exchange Network Synthesis

A Novel Chessboard Model for Optimization of Mass Exchange Network Synthesis

An efficient and random synthesis method for mass exchange networks with multi-component using a node-based vertical non-structural model

Mass exchange network (MEN) synthesis is an important technique to ensure efficient purification of industrial waste gas sources and water streams. However, most existing models for MEN synthesis are not capable of dealing with multi-component problems and achieving optimal designs. In this study, an innovative process integration strategy based on a node-based vertical non-structural model (NV-NSM) is proposed. The developed strategy allows for a more random representation of process configuration and aids in handling both single- and multi-component problems. The NV-NSM arranges several groups of main nodes in the process streams and the sub-nodes in their branches and results in design configurations by connecting any two sub-nodes on the rich and lean streams at the same main node number. When dealing with multi-component synthesis, the number of tray column is directly optimized to balance the mass transfer needs of different components. As part of the current investigation, the random walk algorithm with compulsive evolution (RWCE) is established to realize the simultaneous optimization of multiple variables, including the mass transfer loads, the number of trays, the stream split ratios, and the flowrates of lean streams. Furthermore, the fine-search strategy based on the RWCE is applied to improve global and local optimization performance. Finally, the proposed method is applied to four MEN cases featuring different exchanger specifications and considering both single and multiple components. The implementation and analysis result in more optimal solutions compared to those published in the literature, demonstrating the feasibility and effectiveness of the proposed method in analyzing and evaluating different MEN problems, including multi-component ones.

An efficient two-step optimization method for mass exchanger network synthesis

Mass exchanger networks have been considered a promising solution for reducing impurity in streams and maximizing energy recovery in the chemical industry. This paper adjusts two non-structural models with distinct optimization variables and a heuristic algorithm according to the MEN synthesis characteristics. Considering the requirement of the objective function, a two-step optimization method that combines these two models is proposed. In the first step, a feasible solution is determined by the model using the transferred mass as an optimization variable. In the second step, the aforementioned model is employed to maximize tray utilization by adopting the tray number as an optimization variable. The results of the two cases obtained by the proposed method are 406,330 $/yr and 329,326 $/yr, which are lower than the published results, and is verified on two cases regarding quality and efficiency.

Towards cost-effective osmotic power harnessing: Mass exchanger network synthesis for multi-stream pressure-retarded osmosis systems

Pressure-retarded osmosis (PRO) is a promising technique for osmotic power generation by recovering salinity gradient from high concentration effluents. Prior research has shown that the PRO systems integrating multiple draw/feed streams can achieve a 20+% increase in energy recovery compared with standalone design. However, to date few approaches have been developed to fully utilize this potential. Herein, we propose a novel method for the multi-stream PRO system that optimizes its modules (mass exchangers) layout as a mass exchanger network in three steps. In the first step, the maximum energy conversion is determined and used as an energy target for subsequent mass exchanger network synthesis. In accordance with the energy target, the second step establishes the optimal match of streams by introducing three criteria of “number of streams”, “KP coefficient”, and “maximum mass exchange”. The third step balances the system complexity and energy recovery by relaxing the energy target. An economic model is formulated to evaluate the performance of PRO systems. Several multi-stream PRO system design examples are presented to illustrate the proposed method. Results indicate that the integrated designs generally outperforms the standalone designs by 11.75–21.65 % for energy recovery, and achieves better economic performance and higher power density for large osmotic pressure difference cases with minimum net osmotic pressure difference greater than 0.8 MPa. A minimum levelized cost of energy of 0.1364 $/kWh can be achieved by the proposed design method, constituting a 6.95 % reduction compared with the standalone design.

An enhanced heuristic algorithm with coordination evolution strategy for waste-mass minimization and heat integration network design

The issue of clean production and energy efficiency has become a major concern, especially in the chemical and processing industries. In this paper, an enhanced optimization algorithm satisfying heat-waste minimization and waste-mass minimization is proposed. First, a nodes-based non-structural model and random walk algorithm with compulsive evolution for mass exchanger network synthesis are constructed. The optimization mode of continuous variables is analyzed after analyzing the characteristics of the mass exchange process. To enhance the optimization ability of the heuristic algorithm, a novel coordinated evolution strategy combining the dynamic operations of the walk length optimization and participating evolution probability adjustment is proposed. The proposed strategy can adjust the walk length via an instant objective function change and simultaneously controls the participating evolution of the number of units for effective coupled evolution. The quantified data show that the proposed strategy assists the algorithm in enhancing the local and global optimization abilities, with the final TACs of a benchmark aromatic plant case and phenol absorption process achieved being 125,457 $/yr and 334,696.6 $/yr, respectively. To evaluate the effectiveness of the proposed strategy, it was successfully applied in two industrial-scale cases of heat exchanger network synthesis, where the TAC of the aromatics plant case achieved was 2,892,800 $/yr while the TAC of a gasoline distillation case was 5,089,402.7 $/yr.

A novel node-based non-structural model for mass exchanger network synthesis using a stochastic algorithm

The use of mass exchange networks is an effective means of reducing both pollutant emissions and investment costs in chemical industrial processes. Here, a new simultaneous model based on a mixed integer non-linear program called the node-based non-structural model is proposed for the synthesis of mass exchange networks. This model uses the concept of nodes in both rich and lean streams to represent the possible generation positions of mass exchange units, with no fixed matching pattern. The presented model is more random and flexible in forming structures compared to other structural models with fixed matching relationships. These characteristics, in addition to the adoption of non-iso-compositional mixing, resulted in the search region of the proposed model being significantly enlarged. The established model was also modified to incorporate networks with regeneration. However, the high nonlinearity and nonconvexity of studied problems make it difficult to obtain a global optimal network design. To overcome this, a random walk algorithm with compulsive evolution, a kind of stochastic algorithm first used in solving heat exchange network problems, was applied for the solution. The algorithm's strength is its feature of independent evolutionary strategy among individuals, which can optimize both the integer and continuous variables simultaneously. The effectiveness of the proposed method was demonstrated by solving four different examples from the literature. For each of the four examples, a lower total annual cost result which satisfied all kinds of constraints was obtained compared to previous studies.

Integral Function to Optimize Mass Exchange Network Synthesis Model

Integral Function to Optimize Mass Exchange Network Synthesis Model

Review of Mass Exchanger Network Synthesis Methodologies

In this paper, a review of the methodologies that have been applied to the synthesis of mass exchange networks is presented, including their chronology. The paper also discusses the differences between a heat exchanger network and a mass exchanger network, highlighting aspects where it is difficult to establish a direct analogy between the two networks. The paper reviews the different mass exchanger network synthesis problem types that have been synthesized using the existing methods, as well as discussions on the benefits of combining the synthesis of heat and mass exchange networks, and a critical analysis of the aspects of mass exchanger network problems that still need to be investigated to fully establish the utility of this process synthesis problem.

Synthesis of Renewable Energy Integrated Combined Heat and Mass Exchange Networks

In this paper, a methodology for systematically integrating the synthesis of combined heat, mass, and regeneration exchange networks with solar thermal is presented. The process considered involves the removal of ammonia from ammonia-rich gaseous streams using water-based solvents as the mass separating agent (MSA) and subsequent regeneration of the ammonia-rich MSA stream using steam stripping. A composite superstructure, which comprises the stage-wise superstructure for the synthesis of the heat exchanger network subsystem, primary mass exchanger network subsystem, regeneration subsystem and integrated solar thermal with periodic heat storage, is developed. In order to simplify the modelling of the unpredictable availability of solar thermal energy within the composite superstructure, a multi-periodic synthesis approach is adopted. Sensitivity analysis was performed to establish the price at which solar thermal is favoured over fossil-derived energy as the hot utility source. The economics of the resulting solution is evaluated using net present value, and it was found that, to obtain a positive NPV, the stripping cost in the retrofitted network will have to be as low as possible, or annual operating cost of the non-retrofitted primary mass exchange network will have to be high.

Synthesis of mass exchange networks: A novel mathematical programming approach

Mass integration is an efficient tool to prevent pollution derived from chemical processes. In recent years, several advances have been reported in methodologies for the design of mass exchange networks (MENs), using approaches as the pinch point and mathematical programming. Recently, simultaneous design and optimization methodologies have been proposed. The design methods based on simultaneous optimization offer the possibility of synthetizing MENs in a single step, formulating the synthesis problem as a mixed-integer nonlinear programming problem (MINLP). In this work, a MINLP model for the synthesis of mass exchange networks is presented. The model is based on a superstructure represented with disjunctions. The proposed superstructure is obtained from a state-task-network representation and is applied to a process for copper removal from an etching process. The obtained mass exchange network showed a lower total annual cost than the networks previously reported for the same process.

Synthesis of mass exchanger networks in a two-step hybrid optimization strategy

We present a new method for the synthesis of mass exchanger networks (MENs) involving packed columns. Simultaneous synthesis of MENs is typically done through the use of mixed-integer nonlinear program (MINLP) optimization, with simplifications made in the mathematical representations of the exchangers due to computational difficulty in solving large non-convex mixed-integer problems. The methodology proposed in this study makes use of the stage-wise based superstructure MINLP formulation for the network synthesis. This stage-wise superstructure model incorporates fixed mass transfer coefficients, fixed column diameters, no pressure drops, and unequal compositional mixing for models. In this paper, the simplified MINLP model is further improved by including a detailed individual packed column design in a non-linear programming (NLP) sub-optimization step, where orthogonal collocation is utilized for the partial differential equations, and optimal packing size, column diameter, column height, pressure drops, and fluid velocities. Detailed designs are then used to determine correction factors that update the simplified stage-wise superstructure models to more accurately portray the chosen design. Once the MINLP is updated with these correction factors, the model is re-run, with new correction factors obtained. This iterative procedure is repeated until convergence between the objective function of the MINLP and that of the NLP sub-optimization is achieved, or until a maximum number of iterations is reached. The methodology is applied to two examples and is shown to be robust and effective in generating new topologies, and in finding superior networks that are physically realizable.

Application of Composition Interval Diagram for Cost Minimization in Mass Exchanger Networks

This article presents a technique of reducing the Total Annual Cost (TAC) in mass exchange network synthesis (MENS). The method can minimize the pollutants getting into the environment through selective transfer of such wastes from rich process stream to lean process stream. It also enables the product to be obtained in their pure form. The method was applied to two problems with the aim of reducing the total annual cost (TAC) of production. The results obtained in this study demonstrate that the approach adopted in this paper is capable of giving costs that are comparable with other techniques in literature.

Synthesis of mass exchange networks for single and multiple periods of operations considering detailed cost functions and column performance

Mass exchange network synthesis (MENS) can be used to reduce pollutant emissions into the environment as well as reduce the need for mass separating agents (MSAs). Designing an efficient network using mathematical programming is not a trivial task, due to the fact that the design equations involved are highly non-linear. Chemical plant process parameters also change from time to time due to issues such as changes in environmental conditions, plant start-up/shut-downs, changes in process feed quality, change in product quality demand, and some other disturbance in the system. Such changes in process parameters result in what is known as multi-period operations; hence the synthesised network has to be flexible to handle these changes. In order to circumvent the issues associated with solving non-linear equations in mathematical programming environment, most methods have simplified the cost functions for MENS. Solutions obtained from these methods may not be realistic because the simplified cost functions are based on the assumption that the diameter of a column is 1m or 2m and that the capital cost of packed columns are dependent only on the height of the column. The simplified models do not make provision to check whether the resulting designs are prone to flooding, operate at optimal pressure drops or even whether the ratio of column diameter to size of packing materials would enhance efficient operations. Furthermore the models assumed single period operations for mass exchange network systems. This paper presents a new synthesis method for single and multi-period MENS using detailed cost functions and correlations which check whether selected columns are prone to flooding or not and whether they have optimal pressure drops that ensure efficient separations as well as optimal use of MSAs. The solutions obtained are compared with an existing method that used pinch technology.

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 possible heat exchange requirements resulted from mass exchange operations, a so called “indistinct HEN superstructure (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 optimization 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.

Systematic Synthesis of Mass Exchange Networks for Multicomponent Systems

The synthesis of mass exchange networks (MENs) is an important systematic tool for screening mass-separating agents (MSAs) and satisfying the mass transfer demands while considering process, enviro...

Supply-based superstructure synthesis of heat and mass exchange networks

A new simultaneous mixed integer non-linear programing (MINLP) approach to heat exchange network synthesis (HENS) and mass exchange network synthesis (MENS) is presented. This supply-based superstructure (SBS) approach uses the supply temperatures/compositions of all the streams (including utilities) present in the synthesis problem to define heat/mass exchange superstructure intervals. The intermediate temperatures/compositions are variables used in the optimization of the network total annual cost (TAC). The ability of each stream to exchange heat/mass in any interval in the SBS is subject to thermodynamic/mass transfer feasibility. The paper presents the mathematical formulations for optimizing the TAC for HENS and MENS. The SBS synthesis technique has been applied to nine literature problems involving both HENS and MENS. The solutions obtained are in the same range as those in the literature, with one solution being the lowest of all.

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.

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.

Extended Interval-Based Mixed Integer Nonlinear Programming Superstructure Synthesis of Heat and Mass Exchanger Networks

In this paper we present a method for extending the interval-based mixed integer nonlinear programming superstructure (IBMS) model of Isafiade and Fraser [Chem. Eng. Res. Des. 2008, 86, 245−257; 909−924] for heat and mass exchanger networks synthesis to handle split streams going through two or more exchangers in series. A major shortcoming of the IBMS generation approach is that only parallel heat/mass exchange can take place for split streams. Individual split stream branches cannot exchange heat/mass in more than one exchanger since split streams must be mixed immediately after exchanging heat/mass in order to define the next interval boundary temperature/composition. A major deficiency of this is the tendency for the search space to be reduced thereby limiting the number of possible network configurations which can be generated. A method for overcoming this shortcoming is presented in this paper. The approach involves splitting every stream into subsuperstructures just before it enters into the parent...

Interval Based MINLP Superstructure Synthesis of Multi-Period Mass Exchanger Networks

A new method for the synthesis of mass exchanger networks for multi-period operations is presented in this paper. The new technique which is called multi-period interval based MINLP superstructure (MIBMS) for mass exchange network synthesis (MENS) is adapted from the interval based MINLP superstructure for MENs presented by Isafiade and Fraser (2008). Process parameters such as supply and target compositions and flowrates of streams can vary over a specified range due to environmental or economic reasons. In this paper, the IBMS model for MENS is modified to handle variations in the aforementioned set of parameters by including the index ‘p' in the IBMS model and using the maximum area approach in the objective function as presented by Verheyen and Zhang (2006) for multi-period heat exchanger networks synthesis (HENS). The index ‘p' represents each period of operation which in this paper can be unequal. The maximum area approach ensures that each mass exchanger connecting the same pair of streams in more than one period is able to transfer mass in such streams for all the periods. It should be known that this technique applies to multi-period problems where the process parameters for each period of operation as well as the duration are specified. The method does not handle scenarios where the process parameters are uncertain. The new technique is applied to three examples.