Green hydrogen production plants via biogas steam and autothermal reforming processes: energy and exergy analyses

The use of biogas to produce “green hydrogen” represents an interesting solution for assuring sustainability in the energy and mobility sectors with lower costs and a continuous production. In this study, two hydrogen production plants using biogas as primary source, are studied and compared by applying the energy and exergy analyses for both the overall plant and components. The plants are designed as polygeneration systems able to produce high-pressure hydrogen, heat, and electricity for self-sustaining the energy consumption for purification, compression, and storage of the produced hydrogen. In this sense, these plants are proposed as on-site hydrogen production plants for the development of novel refueling stations. The two proposed plants differ for the hydrogen production process: i) a biogas-to-hydrogen plant through steam reforming, ii) a biogas-to-hydrogen plant through autothermal reforming. The results of the study have highlighted that the steam reforming-based configuration allows for achieving the best performance in terms of hydrogen production energy-based efficiency (59.8%) and hydrogen production exergy-based efficiency (59.4%). Moreover, the steam reforming-based configuration represents the best solution also considering the co-production of heat and hydrogen (energy-based efficiency 73.5% and exergy-based efficiency 64.4%), while the ATR-based layout, globally more exothermic, can be adopted when a larger local heat demand exists (energy-based efficiency 73.9% and exergy-based efficiency 54.8%).