Upgrading proton exchange membrane fuel cell waste heat through isopropanol-acetone-hydrogen chemical heat pump for storage purposes

A new hybrid system integrating proton exchange membrane fuel cell with isopropanol-acetone-hydrogen chemical heat pump is proposed for simultaneous power generation and low-grade waste heat upgrading, where the upgraded waste heat can be stored for further usages. Based on the theories of thermodynamics and electrochemistry, a steady-state thermodynamic mathematical model is formulated by quantitatively considering the major within-system irreversible losses. Calculations predict that the achievable maximum output power density and its corresponding energy efficiency and exergy efficiency are, respectively, 14.72%, 6.56% and 6.57% higher than those of a proton exchange membrane fuel cell at 363 K, and the maximum output power density improvement rate is significantly higher than that of some available proton exchange membrane fuel cell-based hybrid systems. Optimal operating regions for key performance indicators are obtained. Effects of proton exchange membrane thickness, operating pressure, operating temperature, temperature of exothermic reaction, reflux ratio, molar ratio of hydrogen to acetone in the exothermic reactor before exothermic reaction, thermodynamic loss composite parameter and regenerator # 2 effectiveness on the thermodynamic performance and key current density indexes of hybrid system are discussed in detail. The results can provide some theoretical guidance for improving the performance of such a practical system through tuning some design and operation variables.