*2.4. Pellet Properties Measurement*

Pellet moisture content before and after drying, bulk density, and durability were measured using the American Society of Agricultural and Biological Engineers (ASABE) 2007 Standard S269.4 [46]. A complete description of these methods was given by Tumuluru [21–23] and Tumuluru et al. [40]. In the case of moisture content, the biomass is dried in a mechanical oven at 105 ◦C for 24 hours. In the case of bulk density, the dried pellets were poured in a cylindrical container, and the excess material was removed by striking a straight edge across the top of the container. The weight of the pellets in the container divided by the volume of the container gives the bulk density. Pellet durability was measured using the pellet durability tester, which has four compartments. Pellet samples were placed in each compartment and then rotated at 50 rpm for 10 min. The ratio of the mass of the pellets after tumbling to the mass of the pellets before tumbling is defined as pellet durability. All pellet properties are measured in triplicates. Power-consumption data during pelleting were logged using LabVIEW software (2010 Professional Service Pack 1, National Instruments, 11500 N Mopac Expwy, Austin, TX, USA) [21]. An APT power-monitor meter (NK Technologies, San Jose, CA, USA) connected to the pellet mill records the power in kilowatts. The no-load power at 60 Hz rotational speed was recorded by running the pellet mill empty. Specific energy consumption was calculated by subtracting the no-load kW from the full-load power using Equation (1).

$$Specific\ energy\ consumption = \frac{(\text{Full load power (kW)} - \text{No load power (kW)}) \* time\ (h)}{weight\ of\ biomass\ processed\ (ton)} = \frac{kW \cdot h}{ton} \quad (1)$$
