Torrefaction of wood and garden wastes from municipal solid waste to enhanced solid fuel using helical screw rotation-induced fluidised bed reactor: Effect of particle size, helical screw speed and temperature

Using wood (WW) and garden (GW) wastes from municipal solid waste as renewable biofuel is hindered by their high moisture content, volatile matter (VM), and low calorific value (CV). This study aimed to evaluate the fuel properties of torrefied WW and GW in a helical screw rotation-induced fluidised bed reactor. The torrefaction process was conducted at 250–300 °C with sample particle size of 0.5, 1–2, and >2 mm, and helical screw speed of 0–100 rpm. The torrefied WW and GW grindability, thermal, and structural properties were analysed at different temperatures and compared with raw samples. The results showed that the mass and energy yields decreased by 32.71% and 22.04% for WW and 16.07% and 12.21% for GW as the temperature and speed increased, while particle size had no significant effect. Temperature had the most significant influence, followed by speed and particle size. The VM, oxygen, and hydrogen content decreased with increasing temperature, while fixed carbon, CV, and carbon content increased. These properties remained relatively constant with increasing particle size and speed, except at 50 rpm. Furthermore, the grindability, thermal, and structural properties improved with increased temperature.