Industrial-scale Pelletization of Southern Pine Energy Pellets with Various Additives

The energy pellet industry desires to improve processing techniques and the characteristics of fuel pellets by including additives with the feedstock. In this study, the industrial-scale pelletization of southern yellow pine (SYP) planer shavings was performed along with experiments involving the effect of production rate and moisture on the energy required for production (measured in kWh Mg-1). Multiple additives were investigated to determine their effects on southern yellow pine pelletization performance and pellet characteristics. These additives included southern-yellow-pine-derived biochar (BC), southern-yellow-pine-derived bio-oil (BO), corn starch (CS), vegetable oil (VO), sweet potatoes (SwP), microcrystalline cellulose (MCC), micronized rubber powder (MRP), and mixed hardwood planer shavings (HW). A control was compared to 20 different treatments at various additive concentrations, and the effect on pellet durability, bulk density, and higher heating value was determined. The production rate of the pellets with additives varied but were able to be compared with the baseline regression line (production rate vs. energy required for production per Mg) control trials so that the appropriate amount of energy required to produce one Mg of biomass could be compared to the control. The data for the additives, which outperformed the control using the economic study, are listed below. The control, HW10%, HW 25%, HW 50%, BC 0.5%, BC 1%, BC 2%, BC 4%, MRP 1%, and BO 0.5% had a mean pellet durability index (PDI) of 97.9%, 98.1%, 98.1%, 97.7%, 98.2%, 98.6%, 98.4%, 98.7%, 98.0%, and 98.0%, respectively. The control, HW10%, HW 25%, HW 50%, BC 0.5%, BC 1%, BC 2%, BC 4%, MRP 1%, and BO 0.5% had mean bulk density values of 703.0, 700.8, 704.8, 692.2, 693.9, 695.6, 695.6, 683.2, 658.8, and 684.6 kg m-3, respectively. The mean higher heating values (HHV) for the control, HW10%, HW 25%, HW 50%, BC 0.5%, BC 1%, BC 2%, BC 4%, MRP 1%, and BO 0.5% were 19.0, 18.9, 18.6, 18.2, 19.4, 19.5, 19.6, 19.6, 19.6, and 19.2, MJ kg-1, respectively. The normalized energy requirements for production for the control, HW10%, HW 25%, HW 50%, BC 0.5%, BC 1%, BC 2%, BC 4%, MRP 1%, and BO 0.5% were 112.0, 110.5, 112.1, 115.3, 110.7, 111.7, 112.1, 118.1, 108.5, and 111.1 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 certain pellet additives in the feedstock. The following additives could increase the profit of the mill over just using the control: hardwood planer shavings at 10%, 25%, and 50%, biochar at 0.5%, 1%, 2%, and 4%, MRP at 1% and bio-oil (with volatiles removed) at 0.5% (all on a dry basis).