Application of exergy balances for evaluation of process configurations for biological hydrogen production

Exergy analysis was applied to a novel process for biological production of hydrogen from biomass employing thermophilic and photo-heterotrophic bacteria. The exergy content of the process streams is calculated using a MS-Excel spreadsheet. The scrutinized process incurs an exergy loss of 7–9% of the total exergy input. The efficiency based on chemical exergy of biomass feed and produced pure hydrogen refers to 36–45% depending on the configuration of the overall process. The results presented in the paper underline the strong dependence of obtained exergetic efficiency from definition of products and shows options for process improvement and optimization.