Energetic, exergetic and ecological evaluations of a hybrid system based on a phosphoric acid fuel cell and an organic Rankine cycle

The waste heat from phosphoric acid fuel cells is available and suitable for additional power generation by means of organic Rankine cycles. A new hybrid system model is proposed by integrating a phosphoric acid fuel cell with an organic Rankine cycle, where the organic Rankine cycle model is modified in absence of complex working fluid properties. The energetic, exergetic and ecological performances for the phosphoric acid fuel cell-organic Rankine cycle hybrid system are evaluated based on thermodynamic laws and steady-state mathematical models. Numerical results show that maximum power output density and maximum ecological objective function density of the hybrid system are 6036.7 W m⁻² (at 9470.8 A m⁻²) and 2913.1 W m⁻² (at 7050.8 A m⁻²), which are increased about 25.2% and 57.5% by comparing to that of the single phosphoric acid fuel cell system, respectively. Optimum working regions of various performance parameters are determined considering the trade-offs between multiple optimization criteria. Furthermore, the impacts of the operating temperature, exchange current density, electrolyte thickness and pinch temperature ratio on the hybrid system performance are analyzed. The derived results may offer some help for understanding the energetic, exergetic and ecological performances of such an actual cogeneration system.