The effect of process variables on drum granulation behavior and granules of wet distillers grains with solubles

• DDGS was successfully granulated using a lab-scale drum granulation apparatus.
• Desired granule properties were defined by binder, binder solids content, and feed size.
• Growth rates and granule properties depended on process conditions and formulation.
• Defined optimum process variables that achieved about 80% DDGS granule yield.

A laboratory scale batch drum granulation process was used to manufacture granules of DDGS by adding condensed distillers solubles (CDS) as a binder to wet distillers grains (WDG), coproducts from corn dry-grind ethanol process, under varying formulation and process conditions. A full factorial experimental design was used to test all combinations of factor levels, which included the amount of CDS binder (30%, 35%, and 40% (w/w)), CDS binder solids content (22% and 38%, wet basis), screen size opening (3.175 and 6.35 mm), and residence time (1, 2.5, 5, and 10 min). Measured response variables included granule size (geometric mean diameter), granule yield (1.68–3.35 mm), bulk density, true density, and porosity. Results show that as the amount of binder added increased from 30% to 40% the granule size significantly increased from 2.08 to 4.45 mm, respectively. Increasing the binder solids content resulted in granules with greater bulk density. Granules produced from the low solids CDS had lower porosity as a result of intraparticle voids in them. Screen sizing influenced nucleation and produced significant differences in the final granule size distribution. The greatest growth was observed for granules prepared with 40% amount of binder and low solids content CDS. Compression testing of wet granule compacts corresponded to observed growth behavior; wet pellets made from higher solids CDS had greater resistance to deformation and enhanced plasticity while the opposite was observed for the low solids CDS. The best yields of granules between 1.68 and 3.35 mm were achieved at ∼80% using 35% amount of binder with the high solids content CDS, the small screen size opening and residence times between 2.5 and 10 min.

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