Characteristics of torrefied fuel pellets obtained from co-pelletization of agriculture residues with pyrolysis oil

Abstract

Agricultural wastes have the potential to contribute to global energy by converting low value by-products to high value products e.g. fuel pellets, which can be used for heat and power generation. In this study, co-pelletizing characteristics of canola hull, oat hull and barley straw with water were investigated while pyrolysis bio-oil was used as binder. Co-pelletization has been conducted using bench-scale extruder. Canola hull was used as base feedstock due to having a small portion of oil (8 wt%) which provides lubricating effects during pelletization. Increase in biomass to water mass ratio, increased the mechanical strength and durability of pellets but pellets yield decreased. The optimum biomass to water mass ratio was found 2.5. Pyrolysis bio-oil worked as effective additives, enhanced the flow properties, made extrusion smooth, advanced the internal structure of pellet by facilitating strong interlocking of particles, and thus boosted the physical firmness of fuel pellet. Results showed that co-pelletization of oat hull and barley straw with canola hull was optimum for 30 wt% of oat hull or barley straw, but pelletization was successful for up to 45 wt% of those feedstocks. Microwave torrefaction was conducted to boost up the hydrophobicity and higher heating value of pellet. Torrefied pellet showed higher heating value, higher energy density, higher carbon content, lower atomic ratio, lower moisture uptake rate compared to untreated pellet. Synchrotron-based computed tomography shows that porosity increased by up to 39% after torrefaction. Additionally, to assess the mechanical, physical and chemical properties of pellet, various characterization methods were employed.