Co-processing of oil palm waste and waste oil via microwave co-torrefaction: A waste reduction approach for producing solid fuel product with improved properties

Microwave co-torrefaction (MCT)was performed on empty fruit bunch (the most abundant waste from oil palm industry)mixed with waste oil (used engine oil, used cooking oil)to simultaneously utilize these waste materials to produce better quality solid fuel product. The effect of temperature and types of waste oil on the product yield and fuel properties (high heating value (HHV), energy yield, and fuel ratio)were investigated. MCT provided a rapid heating (50–65 °C/min)and a shorter process time of 5–8 min than that shown by conventional torrefaction performed using furnace (> 30 min). The rapid heating could be attributed to the use of a cubical microwave cavity with helical lift for 2-dimensional movement (rotational and translational motion)that allows uniform distribution of microwave radiation for heating and torrefaction. The empty fruit bunch torrefied with used engine oil at 250 °C showed maximum energy yield of 100 wt% and produced solid fuel product with high mass yield (85.5 wt%), fuel ratio (1.8), carbon content (68.3 wt%)and fixed carbon content (62 wt%). Solid fuel product of high higher heating value (28.0 MJ/kg)was produced from microwave co-torrefaction of empty fruit bunch with used engine oil at 300 °C. Our results demonstrate that microwave-co-torrefaction represents a promising waste reduction approach to convert empty fruit bunch mixed with waste oil to produce solid fuel with improved properties.