In this study, the feasibility of using an organic Rankine cycle (ORC) in trigeneration plants is examined through thermodynamic modeling and thermoeconomic optimization. Three novel trigeneration systems are considered. Each one of these systems consists of an ORC, a heating-process heat exchanger, and a single-effect absorption chiller. The three systems are distinguished by the source of the heat input to the ORC. The systems considered are SOFC-trigeneration, biomass- trigeneration, and solar-trigeneration systems. For each system four cases are considered: electrical-power, cooling-cogeneration, heating-cogeneration, and trigeneration cases. Comprehensive thermodynamic analysis on each system is carried out. Furthermore, thermoeconomic optimization is conducted. The objective of the thermoeconomic optimization is to minimize the cost per exergy unit of the trigeneration product. The results of the thermoeconomic optimization are used to compare the three systems through thermodynamic and thermoeconomic analyses. This study illustrates key output parameters to assess the trigeneration systems considered. These parameters are energy efficiency, exergy efficiency, net electrical power, electrical to cooling ratio, and electrical to heating ratio. Moreover, exergy destruction modeling is conducted to identify and quantify the major sources of exergy destruction in the systems considered. In addition, an environmental impact assessment is conducted to quantify the amount of CO2 emissions in the systems considered. Furthermore, this study examines both the cost rate and cost per exergy unit of the electrical power and other trigeneration products. This study reveals that there is a considerable efficiency improvement when trigeneration is used, as compared to only electrical power production. In addition, the emissions of CO2 per MWh of trigeneration are significantly lower than that of electrical power. It was shown that the exergy destruction rates of the ORC evaporators for the three systems are quite high. Therefore, it is important to consider using more efficient ORC evaporators in trigeneration plants. In addition, this study reveals that the SOFC-trigeneration system has the highest electrical energy efficiency while the biomass-trigeneration system and the solar mode of the solar trigeneration system have the highest trigeneration energy efficiencies. In contrast, the SOFC-trigeneration system has the highest exergy efficiency for both electrical and trigeneration cases. Furthermore, the thermoeconomic optimization shows that the solar-trigeneration system has the lowest cost per exergy unit. Meanwhile the solar-trigeneration system has zero CO2 emissions and depends on a free renewable energy source. Therefore, it can be concluded that the solar-trigeneration system has the best thermoeconomic performance among the three systems considered.

In this study, the feasibility of using an organic Rankine cycle (ORC) in trigeneration plants is examined through thermodynamic modeling and thermoeconomic optimization. Three novel trigeneration systems are considered. Each one of these systems consists of an ORC, a heating-process heat exchanger, and a single-effect absorption chiller. The three systems are distinguished by the source of the heat input to the ORC. The systems considered are SOFC-trigeneration, biomass- trigeneration, and solar-trigeneration systems. For each system four cases are considered: electrical-power, cooling-cogeneration, heating-cogeneration, and trigeneration cases. Comprehensive thermodynamic analysis on each system is carried out. Furthermore, thermoeconomic optimization is conducted. The objective of the thermoeconomic optimization is to minimize the cost per exergy unit of the trigeneration product. The results of the thermoeconomic optimization are used to compare the three systems through thermodynamic and thermoeconomic analyses. This study illustrates key output parameters to assess the trigeneration systems considered. These parameters are energy efficiency, exergy efficiency, net electrical power, electrical to cooling ratio, and electrical to heating ratio. Moreover, exergy destruction modeling is conducted to identify and quantify the major sources of exergy destruction in the systems considered. In addition, an environmental impact assessment is conducted to quantify the amount of CO2 emissions in the systems considered. Furthermore, this study examines both the cost rate and cost per exergy unit of the electrical power and other trigeneration products. This study reveals that there is a considerable efficiency improvement when trigeneration is used, as compared to only electrical power production. In addition, the emissions of CO2 per MWh of trigeneration are significantly lower than that of electrical power. It was shown that the exergy destruction rates of the ORC evaporators for the three systems are quite high. Therefore, it is important to consider using more efficient ORC evaporators in trigeneration plants. In addition, this study reveals that the SOFC-trigeneration system has the highest electrical energy efficiency while the biomass-trigeneration system and the solar mode of the solar trigeneration system have the highest trigeneration energy efficiencies. In contrast, the SOFC-trigeneration system has the highest exergy efficiency for both electrical and trigeneration cases. Furthermore, the thermoeconomic optimization shows that the solar-trigeneration system has the lowest cost per exergy unit. Meanwhile the solar-trigeneration system has zero CO2 emissions and depends on a free renewable energy source. Therefore, it can be concluded that the solar-trigeneration system has the best thermoeconomic performance among the three systems considered.

Ce travail de thèse concerne l’étude de la faisabilité des cycles organiques sous-critiques et supercritiques de Rankine pour la valorisation de rejets thermiques industriels à basse température. Dans un premier temps, un état de l’art des cycles ORC (acronyme anglais pour Organic Rankine Cycle) et leurs fluides de travail a été réalisé. Nous avons réalisé une comparaison préliminaire de plusieurs configurations à partir de la littérature scientifique. Dans un second temps, les méthodes d’analyse énergétique et exergétique ont été appliquées pour évaluer et optimiser les performances des cycles ORC. En effet, la seule méthode d’analyse énergétique n’est pas suffisante pour juger de la bonne utilisation du potentiel énergétique de la source de chaleur disponible correspondant à un rejet industrielle de chaleur (chaleur fatale). L’analyse exergétique, intervient en complément de l’analyse énergétique du système, afin de permettre de localiser les pertes des ressources énergétiques dans les différentes composantes du système et de déterminer leurs importances relatives et leurs causes. Une optimisation thermo-économique des installations de valorisation de rejets thermiques utilisant un cycle sous-critique ou supercritique de Rankine a été effectuée. Nos résultats montrent que la valorisation de rejets thermiques industriels à basse température (ex. source thermique de 150 °C) en utilisant un cycle ORC sous-critique est plus intéressante sur le plan énergétique que celle opérée en utilisant un cycle supercritique de Rankine. / This thesis concerns the feasibility study of subcritical and supercritical organic Rankine cycles for industrial waste heat recovery at relatively low temperature. Initially, a state of the art of ORCs (Organic Rankine Cycles) and their working fluids has been achieved. We conducted a preliminary comparison of several configurations from the scientific literature. In a second step, methods of energy and exergy analysis were applied to evaluate and optimize the performance of the ORCs. Indeed, sole energy analysis is not enough to access the proper use of the energy potential of the available heat source that corresponds to an industrial waste heat. Exergy analysis, in a complementary way to the energy analysis, enables us to locate the energy resources losses in the various components of the system and to determine their true magnitude and their causes. A thermo-economic optimization of waste heat recovery systems using a subcritical or supercritical Rankine cycle has been performed. According to the results, the industrial waste heat recovery at low temperature (e.g. heat source 150 ° C) using a subcritical ORC is more interesting on economic point of view than the system using a supercritical Rankine cycle