Evaporator fouling tendencies of thin stillage and concentrates from the dry grind process

Authors: CHALLI, RAVI - University Of Illinois; ZHANG, YIZHE - University Of Illinois; Johnston, David; SINGH, VIJAY - University Of Illinois; ENGESETH, NICKI - University Of Illinois; TUMBLESON, MIKE - University Of Illinois; RAUSCH, KENT - University Of Illinois

Submitted to: Heat Transfer Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/26/2016
Publication Date: 4/1/2017
Publication URL: http://handle.nal.usda.gov/10113/5678129
Citation: Challi, R.K., Zhang, Y.B., Johnston, D., Singh, V., Engeseth, N.J., Tumbleson, M., Rausch, K.D. 2017. Evaporator fouling tendencies of thin stillage and concentrates from the dry grind process. Heat Transfer Engineering. 38(7-8):743-752.

Interpretive Summary: In the corn to ethanol production process, the removal of water from the processing streams is done using evaporators. These evaporators have a heated surface that the liquid stream is passed over to vaporize the water into stream resulting in a concentration of the remaining material. The heated surface in the evaporators frequently develops fouling deposits on the hot surface that reduce flow and the overall energy efficiency. The reasons for fouling deposit formation are not well understood. To better understand the formation of the fouling deposits, the effects of variations on the composition of the liquid stream were studied in a laboratory evaporator system. The results show that the oil content in the liquid stream increased fouling deposits to a point and then decreased. Glycerol (a common component of yeast metabolism) was also found to increase fouling deposits when added at levels above 1%. These results will be useful to ethanol producers who can use this information to potentially decrease or prevent fouling deposits and improve overall energy efficiency.

Technical Abstract: In the US, more than 200 maize processing plants use multiple effect evaporators to remove water from thin stillage and steepwater during dry grind and wet milling 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 and may 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 post fermentation 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.