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

Green hydrogen (H2) and green natural gas (GNG), which are recognized as potential fuels and 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 (LH2) and green methane are co-produced by a cascade of 4 J-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%). The composite curves, as presented by pinch analysis, are used to optimize the configuration of multi-stream heat exchangers and reduce overall energy demand. An economic evaluation reveals a rate of return of 16.22%, a period of return of 6.16 years, a prime cost of LH2 of 5.596 US$/kgLH2, and a net annual benefit of 27.03 million US$/yr. According to the sensitivity analysis results, reducing the electricity price from 0.095 to 0.030 US$/kWh results in the LH2 production cost decreasing to 2.163 US$/kg, respectively.