Wood Pellet Production with the Inclusion of Rice Hull Derived Bio-oil

Highlights Inclusion of heavy bio-oil (0.5%) improved pellet PDI by 0.4 percentage points when compared to the control. Inclusion of heavy bio-oil (0.5%) improved the HHV by 0.4 MJ kg-1 when compared to the control. Inclusion of heavy bio-oil (at 0.3% and 0.5% levels) improved the NPV over the control by $279K and $959K, respectively. 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. Keywords: Biomass, Bio-oil, Hull, Husk, Pelletization, Pellets, Rice, Wood.