Exergy analyses of green hydrogen production methods from biogas-based electricity and sewage sludge

In this study, five models are considered for the use of biogas-based electricity and sewage sludge obtained from a municipal wastewater treatment plant for green hydrogen production. These models include alkaline, PEM, high temperature water electrolysis, alkaline hydrogen sulfide electrolysis and dark fermentation biohydrogen production processes. Energy and exergy analyses are performed on these models by applying thermodynamic procedures and the results are compared. The daily hydrogen production rates of the models are found as 594, 625.4, 868.6, 10.8 and 56.74 kg and the exergetic efficiencies of the models are calculated as 19.81, 20.66, 25.83, 24.86 and 60.54%, respectively. In terms of the exergetic efficiency, the dark fermentation biohydrogen production process is found to be superior to the other models, followed by the high temperature steam electrolysis process. This paper aims to determine the most appropriate model for a wastewater treatment plant among the considered models in terms of exergy efficiency.