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Analysis of Heat Transfer Fouling by Dry-Grind Maize Thin Stillage Using an Annular Fouling Apparatus

¹Department of Biosystems and Agricultural Engineering, Oklahoma State University, Stillwater, OK 74078. ²Department of Animal Sciences, University of Missouri, Columbia, MO 65211. ³Department of Agricultural and Biological Engineering, University of Illinois, Urbana, IL 61801. ⁴Department of Veterinary Pathobiology, University of Illinois, Urbana, IL 61801. ⁵Department of Veterinary Biosciences, University of Illinois, Urbana, IL 61801. ⁶Corresponding author. Phone: 217-265-0697. Fax: 217-244-0323. E-mail: krausch@uiuc.edu

In dry-grind processing to produce ethanol from corn, unfermented solids are removed from ethanol by distillation and dried to produce distillers dried grains with solubles (DDGS), an animal food. Fouling of thin stillage evaporators has been identified as an important energy consumption issue in dry-grind facilities. Using an annular fouling apparatus, four batches of thin stillage were analyzed to determine repeatability of fouling rate and induction period measurements. Dry solids, protein and ash concentrations, and pH were correlated to fouling rate and induction period to determine how variation in thin stillage from the same dry-grind facility affects these fouling parameters. Effects of increasing Reynolds number (Re) in the laminar region on fouling rate, induction period, and fouling deposit protein and ash concentrations were also determined. Repeatability of fouling rate measurements was similar to other studies (CV < 7.0%) but repeatability of induction period measurements was high relative to other studies (CV < 88.7%). Fouling rate increased with increasing dry solids concentration. Thin stillage at Re = 440 had shorter induction periods and greater fouling rates than at Re = 880. Fouling deposits collected from Re = 440 tests had similar protein concentrations and lower ash concentrations compared with deposits from Re = 880 tests.