Optimal design and comprehensive performance analysis of a PEMFC waste heat-driven direct–flash hybrid steam-generating heat pump

Low-carbon industrial steam supply and efficient utilization of low-grade waste heat are essential for improving energy-system efficiency. To recover cooling-water waste heat from proton exchange membrane fuel cells (PEMFCs), this study proposes a direct–flash hybrid steam-generating heat pump system (DF-SGHP) driven by 80 °C waste heat for low-pressure steam supply. Using R1233zd(E), the system couples condenser-side direct steam generation, throttling-induced flashing, and steam reheating to produce 135 °C superheated steam without a water vapor compressor. Multi-objective optimization is implemented through Aspen Plus–MATLAB co-simulation using pre-flash water-side pressure, compressor inlet temperature, and compressor discharge pressure as decision variables to maximize steam production and minimize power consumption. Energy, exergy, economic, and environmental performances are evaluated. The Pareto front gives steam production of 309.62–357.62 kg/h and system power consumption of 50.01–62.96 kW. The TOPSIS optimum produces 331.88 kg/h of steam at 52.06 kW, with a COP of 4.67, SEC of 0.1569 kWh/kg, and exergy efficiency of 59.72%. Condenser-side direct steam generation dominates, with an average direct-generation ratio of 92.34%. The flash process mainly contributes to vapor–liquid separation and circulating-water reuse. The economic and environmental analyses show that the LCOS is 17.69–19.62 USD/t, and the payback period decreases to 0.96–1.12 years when environmental benefits are considered. Annual reductions in CO 2 , SO 2 , and NO x emissions are 409.58–449.29 t, 19.18–21.83 t, and 10.10–11.55 t, respectively. This study provides a feasible route for upgrading low-grade PEMFC waste heat into high-quality steam.