Biodiesel Production from Microalgae: Exergy Analysis Using Specific Exergy Costing Approach

Current biodiesel production research has focused on improving its energy performance and identifying and decreasing inefficiencies. To this end, exergy analysis can help develop, assess, and enhance biodiesel production plants. This study presents the exergy assessment of microalgae biodiesel production, which includes mixers, a photobioreactor (PBR), centrifuges, pumps, dryers, an extractor, tanks, heat exchangers, reactor, a washer, a distillation column, flash valve, and hydro-cyclone. The first phase is algae cultivation, followed by oil extraction. The third phase is transesterification, where algal oil is separated by methane into biodiesel and glycerin. The fourth phase is biodiesel purification, followed by methanol recovery/glycerin separation. The model of the biodiesel production plant is based on mass, chemical species, energy, and exergy balances. It was verified that 93.4% of the inlet exergy originates from sunlight, with a low exergy efficiency (11.46%) obtained for the PBR. This component presented a very low energy efficiency (2.7%) and the highest destruction of exergy: 2287 GJ is destroyed, corresponding to 99.36%. The highest exergy efficiency was obtained for dryer #3 (99.99%), but other components also presented values over 99%. Finally, this study critically compares the results obtained herein with scientific literature data, highlighting data gaps and inconsistencies. The exergy assessment presented a detailed biodiesel production process from microalgae and can be used to support the improvement of production costs to motivate widespread adoption.