Abstract
•Waste heat recovery of proton exchange membrane fuel cells for poly-generation purpose.•Energy and exergy-economic analyses are done through a parametric study.•Fuel cell stack is the major contributor to exergy destruction and cost rates.•Two-objective optimization results in the exergy efficiency and net present value of 22.67 % and 56.61 M$, correspondingly.
In the present study, a novel poly-generation system is introduced and studied from energy, exergy, economic and exergy-economic standpoints. In the proposed configuration, the waste heat of proton exchange membrane (PEM) fuel cells is recuperated by an organic Rankine cycle (ORC). Also, an LNG subsystem is chosen as a heat sink medium for the ORC. In this study, the impact of system irreversibilities on the environment is considered as part of the exergoenvironmental analysis, which is a relatively new type of study. In the considered system, PEM fuel cells are responsible for output power while the output power of the ORC and LNG subsystem is transmitted to a trans-critical CO2 compression refrigeration subsystem and a reverse osmosis desalination unit for cooling and freshwater production. A sensitivity analysis is done to assess the effect of changes in PEM fuel cells temperature, PEM fuel cells pressure, current density, and condensation temperature of ORC on the output parameters. Considering the just-mentioned parameters as design variables, the results of two-objective optimization reveals that the exergy efficiency and net present value are calculated to be 22.67 % and 56.61 M$, correspondingly. At the optimum point, the proposed system can produce 1214 kW power, 1116 kW cooling, 161.1 kW heating, and 6 kg/s freshwater. Also, exergoenvironmental index and sustainability index were obtained as 0.5472 and 2.256 at the optimum point.