Protein effects on heat transfer fouling using model thin stillage fluids
J. YOU (1), D. Johnston (2), V. Singh (3), M. Tumbleson (3), K. Rausch (3) (1) University of Illinois Urbana Champaign, Urbana, IL, U.S.A.; (2) Eastern Regional Research Center, ARS, USDA, , U.S.A.; (3) University of Illinois Urbana Champaign, , U.S.A..
Fouling is unwanted deposition of materials on surfaces of processing equipment, which leads to additional investment, lower processing efficiency and fluid contamination. In the corn ethanol industry, fouling occurs when thin stillage is concentrated into condensed distillers solubles. Several researchers have investigated operating conditions and constituents’ influence on fouling characteristics. However, understanding protein effects on fouling is limited despite its high concentration in thin stillage (approximately 33% db). Protein contributions to fouling were investigated in the dairy industry. Whey proteins, together with phosphate-calcium, interact with each other or other proteins to form aggregates on heated surfaces. Maillard browning is another potential factor influencing fouling since amino acids in thin stillage are able to react with reducing sugars and form brown pigments. Proteins, as well as their hydrolyzed products amino acids, with accompanying sugars in thin stillage have been shown to contribute to fouling. Due to complex components in commercial thin stillage, it is difficult to study a single effect on fouling without interference from other factors. The objective was to investigate protein effects on fouling using various thin stillage models. Nitrogenous substances (urea, yeasts, glutamic acid, leucine and cysteine) were mixed with glucose. An annular probe was used to detect surface temperature and fouling resistance was obtained by using overall heat transfer coefficients of fouled and unfouled surfaces. Fouling was characterized by fouling resistance, induction period and fouling rate. Compared with a 1% starch model, no fouling occurred during test using glucose-urea fluids. Addition of urea reduced maximum fouling resistance by 29%. Molecular weight, structure of proteins as well as their properties may affect evaporator fouling.
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