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SUMMARY The optimal design for heat recovery steam generator (HRSG) should be chosen based on technical and economic considerations. Therefore, parameters that are related to thermodynamic and economic aspects should be considered in optimization approaches. It is worth mentioning that one of the significant issues in the HRSG design is the diversity of arrangements between various components (economizer, evaporator, and superheater), which absolutely affect the HRSG performance. According to these facts, in the present article, different arrangements of a dual pressure HRSG are analyzed, and the economizer at the high‐pressure level is divided into two parts; these arrangements are optimized by applying different optimization approaches to achieve the optimal configuration. These approaches include the reduction of gas pressure drop, the reduction of generated steam cost and the consideration of both approaches as the third approach. These three approaches are also considered to perform economic and thermodynamic optimization. With regard to the limitations of optimization such as the pinch and approach point, seven different configurations are considered. First, a comprehensive model is developed for calculating thermodynamic, heat transfer, and pressure loss. To perform a thorough optimization, both thermodynamic and geometric variables as well as diversity of various arrangements is considered using genetic algorithm. The results of the optimization study show that the best arrangement is not unique, and each arrangement has different characteristics. Hence, the best arrangement for the HRSG is chosen according to the importance of the objective functions. Copyright © 2012 John Wiley & Sons, Ltd.

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A B S T R AC TMaking potable water through desalination plants is a very important process in areas where clean water is highly required. One of the most common and acceptable desalination processes is multiple effect evaporation desalination (MED) process. The main objective of this paper is optimization of MED desalination with thermal vapor compression (METVC) from economical and thermodynamic point of view. Hence, fi rst, a comprehensive thermodynamic model for METVC is developed and then the effect of operating parameters on thermal performance of the system is analyzed. Since the values of operating parameters have a great effect on both thermal performance and cost of the plant, the optimization of these parameters is very important. In this regard, some researchers have focused on improving the economical or thermodynamic aspect of the system. However, in practice it is reasonable to optimize both these criteria simultaneously. Based on this, in order to optimize the process of METVC and show infl uence of objective function on optimization results, four objective functions are chosen as four cases for optimization. These cases include 1) minimizing specifi c heat transfer area, 2) maximizing exergy effi ciency, 3) maximizing performance ratio (PR) and 4) minimizing specifi c heat transfer area and maximizing PR. In fact, cases 1 to 3 are single objective problem while case 4 is a multi objective problem. All of the optimization problems are solved by a heuristic optimization problem, namely, Genetic Algorithm (GA). From optimization study, it can be seen that the results of multi objective problem are perfect and more reasonable than other cases. In other words, the results of cases 1 to 3 demonstrate some improvement in either thermodynamic or economical aspects of the system although multi objective optimization satisfy both thermodynamic and economical aspects of METVC and exhibit a rational system that could be applied for a real design approach.