Chemical Engineering Research & Design, Vol.161, 130-145, 2020
Advanced imaging techniques to understand the impact of process variables on the particle morphology in a corn stover pellet
The objective of this study is to understand the impact of process variables on particle binding during corn stover pelleting. Initial particle attrition or percent fines <425 mu m in 1/4-in. (6.35 mm) and 7/16-in. (11.11-mm) hammermill screen size was measured at 34.36% and 20.24%, respectively. A single pellet press was used to do the pelleting tests by varying the hammermill screen size (1/4-in. [6.35 mm] and 7/16-in. [11.11 mm]), corn stover moisture (10, 15, and 20%, w.b.), and residence time (45, 90, 120 and 150 s). The pellet properties measured were the particle dimensions (e.g., geometric mean particle length, d10, d50, and d90 [mm]), percent fines (e.g., <425 mu m), and unit density (e.g., kg/m(3)). Results indicated that both hammermill grind sizes impacted the pellet properties. Residence time, corn stover moisture content, and hammermill screen size all influenced the percent fines in the corn stover pellets. At 10% (w.b.) corn stover moisture content and a 150-s residence time, the maximum percentage of fines observed was about 26% for a 6.35-mm and about 16-17% for a 11.11 mm hammermill screen size grind. The pelleting process conditions also influenced the particle dimensions (e.g., geometric mean particle length, d10, d50, and d90 [mm]). At lower residence times of 45 s for both 1/4- and 7/16-in. (6.35 and 11.11 mm) hammermill screen size grind pellets, the fines in the corn stover pellets were minimized. In the case of corn stover moisture content, about 10-15% (w.b.) minimized percent fines and unit density was maximized at 150-s residence time for both the grind sizes that were tested. X-ray CT-scan analysis indicated that the agglomerate size, shape, and surface area are influenced by both corn stover moisture content and residence time. Focused ion beam tomography showed a lamellar structure with voids, which might have formed due to weak adhesion between the particles. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.