Thin stillage fouling in multiple effect evaporators

Evaporator fouling decreases heat transfer rates, causes pressure losses and an overall loss of product quality from inefficient solvent separation. Fouled evaporators decrease plant operating efficiency and require frequent cleaning which results in production downtime. Maintenance costs increase from evaporator cleaning, chemical detergents and sanitizers. In a corn dry grind plant, thin stillage is concentrated in multiple effect evaporators and mixed with wet grains to produce distillers dried grains with solubles. During thin stillage concentration, fouling occurs on evaporator surfaces due to deposit formation from thin stillage components. Thin stillage is composed of carbohydrates, proteins, fat and fiber. Research on evaporator fouling in corn processing has been limited. Early work on thin stillage fouling has not determined the components of thin stillage that accelerate fouling. Unpublished work from our group showed that shorter chain carbohydrates such as corn syrup solids and glucose did not cause fouling but a longer chain glucose polymer, starch, had higher fouling rates. To study the effects of solids content, thin stillage fouling rates were determined and compared to concentrates collected from individual effects of a multiple effect evaporator. Unrefined corn oil was added to original thin stillage and mixture fouling rates were determined. Effect of oil skimming on concentrated thin stillage also was determined. Thin stillage samples were collected before and after evaporator cleaning and effects of cleaning on fouling rates was determined.