Table 2. Percent Terminal Velocity Difference between Node and Internode.

Sieves and Image Analysis

Of switchgrass prepared by larger knife mill screen, from 25 to 30 % of switchgrass had  node sections presented on the 19.0 mm sieve compared with 17.5 % nodal particle population average. This difference suggests that larger screen installed in the knife mill would be used to produce particles with optimum sizes for the nodes separation from the internodes.
Switchgrass nodes particles could be separated after size reduction. Our test suggested that potential separation of biomass material, such as nodes, could be achieved based on slight differences in the physical properties. Switchgrass nodes could be separated from the particles during sieving by using knife mill equipped with larger screens, e.g. 50.8 mm or 25.4 mm screen used in knife mill. The results show that there are about 25 to 30 % mass with nodes presented on the 19.0 mm sieve as apposed to 17.5 % of average nodes population in the sample. On the contrary, switchgrass prepared by 12.7 mm knife mill yields less than 5 % of the mass with nodes on the same sieve.
IA shows great potential in the analysis of biomass particle. The size and size distribution of switchgrass, wheat straw, and corn stover can be analyzed by IA. This method is fast, easy, and low cost. Analysis by IA takes about 10 minutes per 50 samples compared with 1 to 2 hours by manual measuring individual particle dimensions depending on the condition of the samples. The results show that the standard deviation of GMD calculated from IA ranges from 0.04 to 0.31 mm for switchgrass particles with GMD length from 24.93 to 95.64 mm. This IA method yields much better accuracy than the traditional sieving analysis. The IA provides far more detailed information about individual particle physical dimensions than traditional sieving test, which only yields the cumulative mass curve and an overall GMD. From the IA data, particle projected area, length, width, and perimeter could be obtained. Such detailed information could be used to calculate the volume, surface area, length/width ratio, etc. This would greatly facilitate the design of biomass particle handling equipments, fermentation units, and biofuel production units.