Water leaching for improving fuel properties of pongamia Pod: Informing process design

Abstract

Pongamia seedpods are recognized as a potential feedstock for sustainable aviation fuel production due to the relatively high oil content of the seeds. Pongamia pods are byproduct residues available after seed separation. Pods have high chlorine and potassium content that may be problematic in thermochemical energy conversion systems. Leaching experiments were performed to remove inorganic constituents of pods and thereby reduce the potential for fouling, slagging, and agglomeration. A 23 factorial design determined the impacts of process operating parameters (i.e. rinse water temperature (25 °C vs. 75 °C), rinse duration (10 min vs. 2 h), and particle size (<2 mm vs. whole pod)) on the composition and physicochemical properties of the pods and the water. The higher heating value of the pods was found to increase from 16 to 18–19 MJ/kg after leaching, while the ash content was reduced from 6.5% to as low as 2.8%wt, with significant removal of sulfur (S), chlorine (Cl), and potassium (K). The chemical oxygen demand, non-purgeable organic carbon, and total nitrogen of the post-experiment leachates were all found to increase with the rinse water temperature and rinse duration but decrease with the increase of particle size. Leached pods were further processed via torrefaction and the targeted mass and energy yields, ~70% and 85%, respectively, were reached at a process temperature of 270 °C. The S, Cl, and K contents of the leached, torrefied pods were found to be lower than that of the raw pods. The reuse of leachate on successive batches of fresh pods showed that ash removal efficiency was reduced after three cycles, although some removal was possible through 15 cycles.