A System to Store Waste Heat as Liquid Hydrogen Assisted by Organic Rankine Cycle, Proton Exchange Membrane Electrolyzer, and Mixed Refrigerant Hydrogen Liquefaction Cycle

Abstract

This study proposes a system to store waste heat as liquid hydrogen using a proton exchange membrane electrolyzer (PEME) and a mixed refrigerant hydrogen liquefaction cycle. The novelty of this study lies in proposing a waste heat recovery system that stores electricity as liquid hydrogen, consuming less power due to the improved exergy efficiency of the components. The proposed system is analyzed to achieve better efficiency in terms of thermal and exergy efficiencies. Waste heat is used to generate power by an organic Rankin cycle (ORC), produced electricity is utilized in the PEME unit and compressors of liquefaction cycle to produce and liquefy hydrogen, respectively. Codes are written in EES software to simulate the system. Thermodynamic analysis is done in order to achieve better thermal efficiency for the proposed model. Membrane potential at different values of current density is calculated and compared with validate the simulated model. The exergy efficiency of the liquid hydrogen production process is 57%. The exergy efficiency, rate of power produced in ORC, and rate of hydrogen production by the electrolyzer increase significantly by increasing the isentropic efficiency of the turbine. At a temperature of 340 K for the evaporator, the thermal efficiency of ORC is obtained at 8.5%, which is approximately 3% higher compared with that of the previous similar process.