Thermodynamic analysis of coconut shell biomass power generation system based on a combined supercritical CO2 Brayton and organic Rankine cycle

In the landscape of the global energy transition, the efficient thermal valorization of tropical waste biomass is paramount for enhancing regional energy self-sufficiency and fostering a sustainable circular economy. To address the suboptimal utilization of waste coconut shells and the substantial heat loss from supercritical carbon dioxide (sCO 2 ) cooling sources, this study proposes two novel biomass-driven combined power systems: the reheat main compression intermediate cooling cycle (RMIC) and the reheat recompression cycle (RRC), both integrated with a recuperative organic Rankine cycle (RORC). Thermodynamic models were developed using the Python platform. Employing energy and exergy analysis methodologies, the study investigated the impact of the split ratio ( SR ) and its synergistic interaction with the pressure ratio ( PR ) on system performance. Findings reveal that the SR governs the dynamic migration of heat exchanger pinch points by regulating the thermal capacity flow rate matching. Under multi-parameter coupling, the RMIC exhibits superior adaptability under high-pressure-ratio conditions (achieving 51.09% thermal efficiency at PR =4.5), whereas the RRC performs better in low-pressure-ratio scenarios (49.74% at PR =3). Exergy analysis confirms that irreversible heat transfer within the heater and reheater constitutes the predominant source of exergy destruction. This study systematically elucidates the performance evolution of sCO 2 -ORC systems under multivariable coupling, providing crucial optimization guidelines and engineering references for high-efficiency cascading thermal systems tailored to biomass energy utilization.