Optimization and analysis of a novel hydrogen liquefaction process based on liquefied natural gas cold energy utilization integrating with steam methane reforming

The widespread application of hydrogen liquefaction is constrained by two major challenges: high energy consumption and significant carbon emissions. To address these issues, this study proposes a novel integrated process that combines steam methane reforming (SMR) with the utilization of cold energy from liquefied natural gas (LNG). Unlike the conventional method of sequestering the carbon dioxide produced by SMR as a waste stream, this study innovatively utilizes the captured carbon dioxide as a working fluid in a Brayton cycle for hydrogen precooling. This strategy not only reduces direct carbon dioxide emissions but also lowers overall energy consumption. Furthermore, using carbon dioxide as a refrigerant reduces the demand for LNG cold energy, thereby enhancing heat exchange efficiency. The proposed process was simulated in Aspen HYSYS and optimized using a genetic algorithm to minimize specific energy consumption (SEC). To evaluate its performance, a comprehensive 4E analysis (energy, exergy, economy, and environment) were conducted and compared with two reference processes: one using LNG for carbon sequestration, and the other directly emitting carbon dioxide. For a plant producing 300 tons of liquid hydrogen per day, the proposed process exhibits a competitive specific energy consumption (SEC) of 5.52 kWh/kgLH 2 and an exergy efficiency of 54.8%. Compared to the LNG-based carbon sequestration process, due to enhanced temperature compatibility, the SEC of this process is reduced by 7.5%, and the exergy destruction in the precooling stage is reduced by 67.4%. The results indicate that integrating a carbon dioxide Brayton cycle can effectively convert environmental burdens into thermodynamic advantages, providing an economical and sustainable approach for hydrogen liquefaction.