Gasification of wet microalgae to produce H₂-rich syngas and electricity: A thermodynamic study considering exergy analysis

In this work, a novel integrated gasification system was developed for wet microalgae to produce hydrogen-rich syngas and electricity. The proposed system consists of six major stages: (i) in-situ drying of wet microalgae, (ii) pyrolysis of dried microalgae, (iii) conversion of tar (produced in the pyrolysis stage), (iv) gasification of pyrolysis products, (v) combustion of biochar producing electricity, and (vi) post-treatment of syngas to remove CO₂. The proposed gasification was modeled by thermodynamic simulation using Aspen Plus®. The developed thermodynamic model was first validated against experimental data concerning product composition and yields of the pyrolysis stage under the same operating conditions. Then, performance of the developed system was evaluated for gasification of Porphyra under various operating parameters, including moisture contents, gasifying agent (O₂/steam) flow rates, and biochar distributions between gasification and combustion units. Syngas quality, cold gas efficiency (CGE), and overall energy and exergy efficiencies were considered as the performance metrics. Finally, it was found that under certain operating conditions, moisture content is beneficial to syngas composition, while adverse trends are found for CGE, and overall energy and exergy efficiencies. A proper adjustment of O₂ flow rate can improve both syngas composition and energy performance.