Energy, exergy, and environmental analyses of renewable hydrogen production through plasma gasification of microalgal biomass

In this study, an energy, exergy, and environmental (3E) analyses of a plasma-assisted hydrogen pro-duction process from microalgae is investigated. Four different microalgal biomass fuels, namely, raw microalgae (RM) and three torrefied microalgal fuels (TM200, TM250, and TM300), are used as the feedstock for steam plasma gasification to generate syngas and hydrogen. The effects of steam-to-biomass (S/B) ratio on the syngas and hydrogen yields, and energy and exergy efficiencies of plasma gasification (eta(En,PG), eta(Ex,PG)) and hydrogen production (eta(En,H2) , eta(Ex,H2)) are taken into account. Results show that the optimal S/B ratios of RM, TM200, TM250, and TM300 are 0.354, 0.443, 0.593, and 0.760 respectively, occurring at the carbon boundary points (CBPs), where the maximum values of eta(En,PG), eta(Ex,PG), eta(En,H2), and eta(Ex,H2) are also achieved. At CBPs, torrefied microalgae as feedstock lower the eta(En,PG), eta(Ex,PG), eta(En,H2), and eta(Ex,H2) because of their improved calorific value after undergoing torrefaction, and the increased plasma energy demand compared to the RM. However, beyond CBPs the torrefied feedstock displays better performance. A comparative life cycle analysis indicates that TM300 exhibits the highest greenhouse gases (GHG) emissions and the lowest net energy ratio (NER), due to the indirect emissions associated with electricity consumption. (c) 2021 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Automated summary

The study investigates the plasma-assisted hydrogen production process from microalgae through energy, exergy, and environmental analyses. Different microalgal biomass fuels are used for steam plasma gasification, with torrefied microalgae showing better performance at the carbon boundary points. The torrefied feedstock exhibits improved calorific value but increased plasma energy demand compared to raw microalgae, affecting the efficiencies of gasification and hydrogen production.