Environmental/Economic assessment and multi-aspect optimization of a poly-generation system based on waste heat recovery of PEM fuel cells

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 tem-perature, PEM fuel cells pressure, current density, and condensation temperature of ORC on the output pa-rameters. 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 ob-tained as 0.5472 and 2.256 at the optimum point.

Automated summary

In this study, a novel poly-generation system is introduced and analyzed from various perspectives such as energy, exergy, economy, and exergy-economy. The system recovers waste heat from proton exchange membrane fuel cells through an organic Rankine cycle and utilizes an LNG subsystem as a heat sink. The impact of system irreversibilities on the environment is also considered.