Thermo-economic analysis and optimization of a novel cascade ORC-transcritical CO2 cycle to recover energy from PEM fuel cells

Abstract

This study introduces a novel cascade flash organic Rankine cycle − transcritical CO₂ cycle for recovering waste energy from a PEM fuel cell, aiming to improve its efficiency. The recovered energy serves two purposes: partially fueling the liquid hydrogen gasification process to supply hydrogen to the fuel cell and converting the remaining energy into electricity. A combination of thermodynamic and economic evaluations is conducted to assess the proposed system’s feasibility, complemented by a sensitivity analysis to explore the influence of key parameters. Subsequently, based on these insights, a genetic algorithm is employed to optimize system performance. The findings indicate that the proposed configuration performs better than other waste heat recovery systems in the literature. It is shown that, compared to a standalone PEM fuel cell, the proposed system has the potential to increase net output power by up to 60% and efficiency by up to 33 %. However, due to the conflicting nature of these two objective functions, achieving both maximum power and maximum efficiency simultaneously is not possible. This necessitates performing a multi-objective optimization to determine the best trade-off between these competing objectives. Applying NSGA-II combined with a minimum distance method identified balanced operating conditions that offer a practical compromise between objective functions. These trade-off solutions deviate from the extreme settings favored in single-objective optimization and instead point to moderate current densities and temperatures that enhance overall system viability.