(573a) Flowability Performance of Pine Chips As a Function of Particle Size and Moisture Content

Authors: 
Westover, T. L., Idaho National Laboratory
Hernandez, S., Idaho National Laboratory

Pine wood is being considered as a feedstock to create liquid biofuels via thermochemical conversion processes; however, feeding and handling of the pine chips and powders can represent a significant challenge. Different preprocessing equipment results in feedstocks that have different particle size, shape and moisture content distributions, and consequently have different feeding and handling behaviors. In this work, the feeding performance of several lodge pole pine samples prepared with different particle size and shape distribution and also different moisture contents is assessed using a combination of feeding and handling tests and measurements of rheological properties. Materials were prepared by hammer milling using 1.6, 3.0, 16 and 25 mm screens and knife milling with a 6.0 mm screen. Then samples were wetted to moisture contents ranging from 10% to 40% to form a set of 17 unique samples. Flowability tests include feeding the materials with a bin weight screw feeder measuring power usage and feed rate consistency as a function of auger size and velocity, bridging tests using a custom hopper with an adjustable opening, measurements of unconfined yield strength and internal angle of friction using an automated Schulze ring shear tester, and measurements of bulk density, compressibility, and elastic recovery using an automated load frame. The highest time variation in the feed rate during the screw feeding tests approached 40% of the average value of the feed rate using a 40 mm auger to feed large particles, whether the materials were wet or dry. For the remainder of the feeding tests, time variation in the feed rate was below approximately 10% of the average feed rate. Hopper tests indicate that all of the materials gain strength under applied pressure, except for the 25 mm pine chips prepared with 20% MC, indicating that the materials are cohesive and can become lodged inside equipment if pressure is applied to move them through tight spaces. Shear tests indicate that, in general, the materials become stronger as the particle size decreases, and bulk density tests indicate that the materials significantly compressed when subjected to 10 kPa pressure but only expand 5-10% after the pressure is released.