Second law analysis of a fossil-geothermal hybrid power plant with thermodynamic optimization of geothermal preheater

There is an urgent and compelling need to develop innovative and more effective ways to integrate sustainable renewable energy solutions into the already existing systems or, better yet, create new systems that all together make use of renewable energy. This study aims to establish the optimum working conditions of a geothermal preheater in a power plant that makes use of both renewable and nonrenewable energy resources, where renewable (geothermal) energy is used to boost the power output in an environmentally sustainable way. Hence, two models, one, a simplified model of a Rankine cycle with single reheat and regeneration, and another, with a geothermal preheater substituting the low-pressure feedwater heater (LPFWH), were compared. The Engineering Equations Solver software was used to perform an analysis of the thermodynamic performance of the two models designed. An analysis was done to evaluate the energetic and exergetic effects of replacing a LPFWH with a geothermal preheater sourcing heat from a low temperature geothermal resource (100°C-160°C). Results from the thermodynamic analysis reveal that the hybridization boosts the power output by approximately 4% and it is superior in terms of the second law. Entropy generation minimization analysis was then employed to establish optimal working conditions of the hybrid system (ie, the geothermal preheater modeled as a downhole coaxial heat exchanger).