A technical analysis of solid recovered fuel from torrefied jatropha seed residue via a two-stage mechanical screw press and solvent extraction process

This study investigated the torrefaction of de-oiled Jatropha seed residue after a two-stage sequential process consisting of mechanical screw pressing and solvent extraction using n-hexane (denoted as JMS). The optimal torrefaction temperature (T_r) and torrefaction time (t_r) were determined in the ranges of 260–300 ^◦C and 10–60 min, respectively, so to achieve a better heating value and satisfactory energy densification (E_D) with acceptable mass loss. Thermogravimetric analysis was employed to elucidate the thermal decomposition behaviors of JMS. By comparison with the torrefaction of Jatropha seed residue after mechanical oil extraction by screw pressing only (namely, JME_T), the results indicated that the E_D of the torrefaction of JMS yielding the torrefied product JMS_T (two-stage product) was higher than that of the torrefaction of JME giving the torrefied product JME_T (single-stage product). Further, it was found that JME_T contained some tar, which was attributed to a thermal reaction in the residual oil in JME during torrefaction. The tar/oil content of JME_T was about 1.0–1.8 wt.% in the determined optimal conditions. Thus, the enhanced recovery of the residual oil is advantageous not only because it allows obtaining more oil from Jatropha seed residue with a positive net energy gain but also because it prevents the formation of tar in torrefied biomass products.