Analysis of a solar driven ORC-absorption based CCHP system from a novel exergy approach

Abstract

The present study comprehensively analyses the thermodynamic performance of a zero-emissions solar driven trigeneration system using a numerical approach. The analysis is conducted from both the First and Second law of Thermodynamics viewpoints, employing a novel and coherent exergy approach. Solar parabolic trough collectors (SPTCs) provide the heat input to an organic Rankine cycle (ORC) system, while a single-effect H2O/LiBr absorption heat pump is coupled in cascade to the ORC. The proposed ORC layout is based on a single-pressure regenerated, recuperated and superheated cycle. There is divergence of opinion among researchers regarding key aspects of the exergy analysis of trigeneration systems. Therefore, this study proposes the definition of the dead state conditions for each subsystem individually, taking into account their specific constraints. Unlike temperature, specific dead state conditions for pressure and composition are defined separately. An energy-exergy parametric approach is conducted to evaluate the effects of different system parameters on the system performance. The system is also optimized following single and multi-objective approaches with different criteria. The optimum system achieve an energy efficiency of 152.4%, an exergy efficiency of 21.1%, and an electrical-exergy efficiency of 17.5%. The electricity, cooling and heating productions are 82.1 kW, 200.4 kW and 471.7 kW, respectively. The SPTCs are identified as the main source of exergy destruction, responsible for 73% of inlet exergy is destructed. In addition, the systeḿs performance is shown to be sensitive to the variations in the solar field outlet temperature and in the ORC condensation temperature. Consequently, controlling these parameters could be effectively utilized for regulating power generation as well as cooling and heating production.