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Evaporator Fouling Tendencies of Thin Stillage and Concentrates From the Dry Grind Process

Ravi K. Challa, Yizhe B. Zhang, David B. Johnston, Vijay Singh, Nicki J. Engeseth, Mike Tumbleson, Kent D. Rausch
Heat Transfer Engineering 2016 v.38 no.7-8 pp. 743-752
cleaning, corn, corn oil, evaporators, fermentation, fouling, glycerol, grinding, proteins, total solids
In theUnited States, more than 200 maize processing plants use multiple-effect evaporators to remove water from thin stillage and steepwater during dry grind and wetmilling processes, respectively. During the dry grind process, unfermentables are centrifuged and the liquid fraction, thin stillage, is concentrated in multiple effect evaporators. Evaporator fouling occurs during thin stillage concentration andmay be from deposition of proteins, fat, fiber, and/or carbohydrates on evaporator surfaces. Studies on evaporator fouling from maize processing streams are limited and fundamental causes are not well understood. Therefore, the overall objective was to investigate effects of compositional variation on evaporator fouling during thin stillage concentration. Effects of total solids during evaporator concentration, removal of post fermentation oil, corn oil and glycerol addition, and overall plant operation were studied. Thin stillage had lower fouling rates compared to evaporator concentrates. Addition of postfermentation corn oil (0.5 to 1.0% added) increased thin stillage fouling rates, but at higher oil concentration (1.5% added), rates decreased. At 10% solids content in evaporator concentrates, oil recovery had no influence on fouling rates. Glycerol addition (1%) to thin stillage increased fouling rates. Simultaneous plant shutdown and evaporator cleaning decreased subsequent fouling rates.