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A new approach of retrofit design methodology in cogeneration heat and power systems based on constructal theory is presented in this paper. A cogeneration system may consist of different turbines, steam levels and steam generators. The steam demand of each level is determined and should be supplied. The purpose of this paper is to retrofit the existing total site heat and power cogeneration system utilizing the concepts of constructal theory. Developing constructal theory to total site cogeneration systems may lead to divide the total site into different constructs. In this paper the total site cogeneration system will be divided into three constructs: turbines, turbine array between each two levels and steam generators array. Using constructal theory simplifies the total site complex system to a simpler system that can be solved easily by a simple search and sort method. The best configuration of the total site would have the minimum operating cost. Using constructal theory would simplify the optimization procedure of cogeneration systems in addition to reach better conceptual design especially in more sophisticated systems. The methodology is applied to a sophisticated total site heat and power cogeneration system as case study from literatures. The constructal retrofit results 14.1% and 14.3% reduction in operating cost and fuel consumption respectively.

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In this study, the integration of multi-effect desalination (MED) system with cogeneration of heat and power system has been considered. Low-pressure steam in two case studies has been utilized as the motive steam of MED system. R-curve is a powerful tool that can be used to identify fuel utilization amount in different operation points of the cogeneration system. R-curve explains utility system operation improvement procedure without capital cost. By deploying and development of the R-curve concept, the freshwater demand of the total site and total annual cost of the site have been evaluated. These curves can be used as a tool to improve the operation and economic parameters in every operating point of cogeneration system and present comprehensive view about the improvement of utility system operation condition at each operating point. For the first time, R-curve has been used to identify the impact of cogeneration system integration with a thermal desalination system on the cogeneration system operating point. The performance of the cogeneration system can be either enhanced or impaired by integration of desalination system. As demonstrated in a case study, integration of 2.2 MW MED system can either provide 52.765 MW energy saving or deprive 30.257 MW fuel energy based on the operating state of the cogeneration system before and after integration.