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Highlights

Inclusion of heavy bio-oil (0.5%) improved pellet PDI by 0.4 percentage points when compared to the control.

Abstract.Rice hulls or husks have the potential to aid in wood pelletization as they possess high calorific values. However, this material also has a high ash content and is therefore not viable to be of use in the pelletization process without modification. This study focuses on using rice hull-derived bio-oil from pyrolysis, which decreases the overall ash content when compared to the original rice hulls and was postulated as a means to improve wood pellet characteristics (e.g., pellet durability index and the calorific value). Two groups of rice hull-derived bio-oil were used as an additive in wood fiber pelletization: Group 1 consisted of heavy bio-oil (products with a distillation vapor temperature only above 100°C) at a 0.2% (H2) and 0.5% (H5) additive inclusion rate (dry basis) with a matched control group (C1), and Group 2 consisted of bio-oil with light keys (products with a distillation vapor temperature of 20°C to 95°C and above 100°C) added from distillation process at a 0.2% (L2) and 0.5% (L5) concentration (dry basis) with a matched control group (C2). The C1, H2, H5, C2, L2 and L5 treatments had a mean pellet durability index (PDI) of 97.6%, 97.7%, 98.0%, 98.2%, 98.2%, and 98.3%, respectively. The C1, H2, H5, C2, L2, and L5 treatments had average bulk density values of 683.2, 678.4, 678.4, 673.6, 687.2, and 681.6 kg m^-3, respectively. The mean higher heating values (HHV) for the C1, H2, H5, C2, L2, and L5 treatments were 24.6, 24.8, 25.0, 24.0, 24.0, and 24.0, MJ kg^-1, respectively. The normalized energy requirements for production for the C1, H2, H5, C2, L2, and L5 treatments were 105.7, 96.3, 96.7, 97.9, 97.4, and 93.2 kWh Mg^-1, respectively. An economic feasibility analysis showed that the discounted net present value (NPV) at a rate of 12% could be improved when using the H2 and H5 additives when compared to the control.