Development of an integrated production and liquefaction system of hydrogen and green natural gas: energy, exergy, economic and sensitivity assessments

Hydrogen (H 2 ) and green natural gas (GNG), which are low-carbon energy carriers, have relatively low volumetric energy densities compared with conventional liquid fossil fuels. As a result, storing these substances requires either compression or liquefaction. However, liquefaction of them remains highly energy-intensive and costly, potentially reducing their expected environmental benefits. In this study, a new integrated process is developed where liquid hydrogen (LH 2 ) and green methane are co-produced by a cascade of four Joule-Brayton (J-B) refrigeration cycles at low temperatures, a mixed-refrigerant (MR) cycle, an organic Rankine cycle (ORC), and a proton exchange membrane (PEM) electrolyzer. The proposed system achieves an energy efficiency of 52.08%, an exergy efficiency of 56.23%, and a refrigeration cycle coefficient of performance (COP) of 0.1630. The exergy analysis results indicate that the highest exergy destruction occurs at the electrolyzer (85.83%), followed by heat exchangers (4.47%), compressors (4.19%), turbines (3.09%), and reactors (2.36%). Composite curves, as presented by pinch analysis, are used to optimize the configuration of multi-stream heat exchangers and reduce overall energy demand. Economic evaluation reveals a rate of return of 16.22%, a period of return of 6.16 years, a prime cost of LH 2 of 5.596 US$/kgLH 2 , and a net annual benefit of 27.03 million US$/yr. According to the sensitivity analysis results, reducing the electricity price from 0.095 to 0.030 US$/kWh results in the LH 2 production cost decreasing to 2.163 US$/kg.