Sergio Mussati

Optimal MSF plant design

The aim of this paper is to present a rigorous model for Multi-Stage Flash Evaporation System (MSF). The MSF system is represented as a No Linear Programming (NLP) model. The model incorporates a high number of non-linear restrictions; so the achievement of the global optimum is difficult. Here, the study of an algorithm for the system optimisation is presented.

Global Optimal Design of Mechanical Vapor Compression (MVC) Desalination Process

Abstract This paper deals with the optimal design of Mechanical Vapor Compression (MVC) desalination process. Precisely, a detailed mathematical model of the process and a deterministic global optimization algorithm are applied to determine the optimal design and operating conditions for the system. The resulting model involves the real-physical constraints for the evaporation process. Nonlinear equations in terms of chemical-physical properties and design equations (efficiencies, Non-Allowance Equilibrium, Boiling Point Elevation, heat transfer coefficients, momentum balances, among others) are used to model the process. The model has been solved by using a deterministic global optimization algorithm previously developed by the authors [7] and implemented in a General Algebraic Modeling System GAMS [1]. The generalized reduced gradient algorithm CONOPT 2.041 [2] is used as NLP local solver. The model was successfully solved for different seawater conditions (salinity and temperature) and fresh water production levels. The influence of the production requirements on the process efficiency as well as the algorithms performance is presented.

Dual-purpose desalination plants. Part II. Optimal configuration

Abstract Large dual-purpose power desalination plants are used to reduce the production cost of both electricity and water. Various combinations of power-desalination systems are conceivable in order to satisfy both power and water demands. The preference of one scheme over another would depend mainly on many factors, such as the required power to water ratio, cost of fuel energy charged to the desalting process, electricity sales, capital costs, and local requirements. The allocation of the total annual cost of a dual-purpose plant to desalted water and electricity can be made by various methods. In this paper, credit method is adopted to calculate the total annual cost. Credit methods allocate a predetermined value to one of the products and determine the cost of the other product by subtraction from the total cost of the dual-purpose plant. In this way, according with the power credit method, the toal cost is calculated in the following way: Cwater=Ctotal − W; where W is the benefit of the net electrical generated. Non-linear equations are extensively used for the cost equipment and for the plant performance. The aim of this paper is to design a dual-purpose plant system at minimum cost determining the equipment configuration and its corresponding operating conditions given the water production. The optimal solution is selected from a superstructure containing different possible configurations. One case study illustrating the methodology, robustness and computational performance is presented.

Global optimal synthesis of integrated hybrid desalination plants

Abstract Seawater desalination is one of the main alternatives to overcome the problem of fresh water supply. Thermal and membrane processes are the conventional technologies widely used to obtain potable water from the sea. Hybrid desalination plants integrating reverse osmosis (RO) and multi stage flash (MSF) systems result interesting alternatives. The hybrid systems combine the advantages of the high separation efficiency of thermal processes with the low energy consumption of reverse osmosis. These systems reduce dramatically the final fresh water cost; meanwhile the recovery ratio is increased. In the present work, a mathematical model for MSF and RO hybrid systems is derived on energy, mass and momentum balances meanwhile the most important aspect of the processes are introduced. Precisely, a superstructure is proposed embedding alternative and feasible arrangements for hybrid plants that will be simultaneously optimized. The resulting mathematical model is solved in order to determinate the global optimal plant layout, optimal equipment sizes and operating conditions, minimizing the fresh water cost. The cost equations evaluate accurately the presence or absence of equipments, streams or systems. The model was successfully solved for different seawater conditions (salinity and temperature). The optimal solutions depend strongly on the salt concentration and temperature of the feed water. Due to space limitations only one case study is presented here.

Hybrid Desalination Systems: Alternative Designs of Thermal and Membrane Processes.

Abstract In this paper, desalination systems integrating thermal and membrane processes are investigated. Specifically, a hybrid desalination plant integrating reverse osmosis (RO) and multi stage flash (MSF) systems is mathematically modeled. The non linear programming problem is developed in order to optimize the configuration and operating conditions in order to satisfy fresh water demands at minimum costs. Both implementations, with one and two reverse osmosis stages are considered at the particular framework RO-MSF adopted. The system is modeled in such a way that the RO unit receives brine feed from the MSF. In addition, partial extractions of flashing brine stream from flash chambers of MSF can be performed in order to feed the RO system. In fact, the flow-patterns and flow-rates of the brine streams of MSF are optimization variables. Heat transfer areas of pre-heaters and the geometric design of stages are design variables to be optimized. The optimization procedure will also decide between one and two RO stages and the number of modules operating in parallel at each stage. Moreover, all the operative conditions will be optimized. Different case studies considering various seawater conditions were successfully solved without convergence difficulties. It can be concluded that the optimal arrangement of hybrid system depends strongly on the seawater conditions (salinity and temperature) and the fresh water demand as well.

Dual-purpose desalination plants. Part I. Optimal design

In this paper, a methodology for optimization of a given system configuration for dual-purpose desalination plants will be presented. The whole system is represented as a non-lineal programming (NLP) model solved using general algebraic modeling system (GAMS) [1]. The rigorous model incorporates a high number of non-linear restrictions; so the achievement of the optimal solution is difficult. It is important to point out that the initialization of variables are very important, especially to guarantee the convergence and the determination of the optimal solution. The proposed methodology in this work consists on the resolution of simplified model in order to provide the initial values and critical bounds to solve the rigorous model. In this way, a procedure for the optimization of a given configuration involving the total annual cost (TAC) minimization is presented. The results obtained from one study case applying the methodology are analyzed.

Optimal synthesis and design of the number of cycles in the leaching process for surimi production

Water consumption required during the leaching stage in the surimi manufacturing process strongly depends on the design and the number and size of stages connected in series for the soluble protein extraction target, and it is considered as the main contributor to the operating costs. Therefore, the optimal synthesis and design of the leaching stage is essential to minimize the total annual cost. In this study, a mathematical optimization model for the optimal design of the leaching operation is presented. Precisely, a detailed Mixed Integer Nonlinear Programming (MINLP) model including operating and geometric constraints was developed based on our previous optimization model (NLP model). Aspects about quality, water consumption and main operating parameters were considered. The minimization of total annual costs, which considered a trade-off between investment and operating costs, led to an optimal solution with lesser number of stages (2 instead of 3 stages) and higher volumes of the leaching tanks comparing with previous results. An analysis was performed in order to investigate how the optimal solution was influenced by the variations of the unitary cost of fresh water, waste treatment and capital investment.

Seawater Desalination Processes: Optimal Design of Multi Effect Evaporation Systems

Abstract This is the first paper of a series of articles that deals with the modeling and optimization of dual-purpose desalination plants which combine thermal desalination processes and combined heat and power systems, specifically solid oxide fuel cell SOFC electricity generators. This paper presents preliminary results obtained for the multi effect evaporation (MEE) process (stand alone process). The steady state performance of the MEE system is described by a simplified and no linear programming (NLP) model. Optimal operating conditions including profiles of temperature, flow-rate and heat transfer area along the evaporator are analyzed. In addition, the influence of the effect number on the evaporation efficiency is also investigated.

Mathematical Model of Carbon Dioxide Absorption into Mixed Aqueous Solutions

Abstract In this paper, a mathematical model of CO2 chemical absorption system using MDEA (MethylDiEthanolAmine) and PZ (Piperazine) aqueous solutions is investigated. Precisely, the complex reactive absorption behavior is modeled by an NLP mathematical model. The resulting mathematical model is implemented in GAMS and CONOPT is used as NLP solver. The proposed model will allow to optimize the operating conditions to maximize the CO2 capture. The model is successfully validated using data from the literature.