Investigation of torrefaction conditions for oil palm empty fruit bunches: A step towards scale-up

This work presents results from the EFB torrefaction process, performed in a pilot-scale continuous processing reactor, the Vibrating Electrical Elevator and Reactor (REVE), and a laboratory tubular furnace as a complementary analysis procedure. Raw EFB was processed in the pilot-scale reactor at three temperatures (220 °C, 250 °C, and 300 °C) for 30 min. Meanwhile, in a tubular furnace (TF), EFB briquettes were processed at six temperatures (210 °C, 220 °C, 230 °C, 240 °C, 250 °C, and 300 °C) and two processing times (15 min and 30 min). The biocoal resulting from both processes was characterized using proximate, ultimate, thermogravimetric analysis (TGA) and higher heating value (HHV) determination. TF results show that temperature has the most decisive influence on energy yields than processing time, suggesting the feasibility of processing EFB with shorter retention times, such as 15 min, particularly at low to moderate temperatures (e.g., 210–250 °C), where greater values of energy yield and HHV are obtained (95.7–79.4 % and 19.5–22.9 MJ). The type of reactor also influenced the observed data. While the atmosphere inside the REVE reactor during the torrefaction process is not inert, this was not a significant issue, as its performance, measured by the properties of its biocoal, can be compared to that found in the literature (HHV of 27.5 MJ for 300 °C processing). The samples processed in the REVE reactor achieved O/C and H/C ratios approaching the thresholds required for efficient gasification, 0.26 and 0.57, respectively. Finally, biomass-bound oxygen loss follows the same behavior in both processes evaluated, regardless of the environment.