Technique to measure surface-fouling tendencies of steepwater from corn wet milling

Surface-fouling tendencies of raw light steepwater (LSW) and membrane-filtered light steepwater (FSW) from corn wet-milling were studied using an annular fouling probe. The probe contained a heated surface to simulate the surface temperature of an evaporator. The heated region caused a fraction of solids in the steepwater to adhere to the surface, thus fouling the probe over time. FSW samples were prepared by filtering LSW using a microfiltration membrane with a nominal pore size of 0.1 μm. Fouling tendencies of both samples were established at an initial probe wall temperature of 99°C. Batches (30 L) were circulated through the fouling probe until the inner surface temperature of the probe reached 200°C. Temperature and power supplied to the probe were measured over time and used to calculate fouling resistance and rate of fouling. Measurement of maximum fouling resistance and fouling rate had a coefficient of variation (COV) of 5.1 and 7.4%, respectively. Maximum fouling resistances attained over a 12-hr period were 0.36 and 0.049 m² °C/kW for LSW and FSW, respectively. Average rates of fouling were 4.53 × 10^-4 and 0.82 × 10^-4 m² °C/kW/min for LSW and FSW, respectively, showing an 80% decrease in fouling rate using microfiltration to remove 19% of solids.