Effects of nitrogenous substances on heat transfer fouling using model thin stillage fluids
Fouling is unwanted deposition of materials on surfaces of processing equipment, which leads to additional investment, lower processing efficiency and potential 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 (17 to 33% db). Protein contributions to fouling have been investigated in the dairy industry. Whey proteins and calcium phosphate 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, their hydrolyzed products of amino acids and residual sugars in thin stillage 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 effects of nitrogenous substances and protease on fouling using model and commercial thin stillage fluids. Nitrogenous substances urea and yeasts, as model protein sources in thin stillage, were mixed with glucose. Thermocouples in an annular probe were used to monitor surface temperature; fouling resistance was obtained by using overall heat transfer coefficients of fouled and unfouled surfaces. Fouling was characterized by maximum fouling resistance (Rmax), induction period and fouling rate during 5 hr test periods. Urea addition did not lead to fouling while glucose-yeast model fluids displayed fouling tendency that had a positive correlation with yeast protein concentration. Protease from pineapple stem (bromelain) incubation increased fouling in both model and commercial fluids, which were indicative that hydrolyzed molecules such as peptides, amino acids or protease itself can be involved in deposit formation. Adjustment of pH in model fluids during incubation reduced Rmax and fouling rate and extended induction periods longer than 300 min. Fouling resistance profiles varied as the amount of bromelain changed from 1 to 3 g, showing a reduction in induction periods. Total suspended solids (TSS) of commercial thin stillage were measured during 14 days of storage; TSS was affected more by sample batch than storage time.
Heat transfer fouling, Corn ethanol, Evaporator
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign