Fouling Rates of Synthetic Thin Stillage

Proteins, carbohydrates, fats, ash and fiber in corn thin stillage are involved in evaporator fouling. It is not understood which components increase fouling rates. Costs associated with fouling include labor and equipment needed to clean fouled heat transfer surfaces, increased capital, antifoulant chemicals and production losses. Effects of starch (STA) and glucose (GLU) composition in a synthetic thin stillage fluid on fouling resistance (R_f) were studied. Effects of total solids (TS) content (1 to 10% db) on R_f (m²K/kW) was investigated. Synthetic thin stillage viscosity was measured using a Rapid Visco Analyzer to determine the synthetic thin stillage Reynolds Number (N_Re). Fluid flow was turbulent (N_Re > 4000) for synthetic thin stillage with 1% TS and was constant, irrespective of STA:GLU ratio. N_Re for synthetic thin stillage with 5 and 10% TS and having various starch:glucose (STA:GLU) ratios was laminar (N_Re < 2100) and ranged from 500 to 1100. An annular probe was used to measure fouling tendencies of synthetic thin stillage and R_f was found at the end of 10 hr or until the probe temperature reached 170°C. Treatments with 1% TS, 10 hr long and STA:GLU composition varying from 1:9 to 9:1 ratio had R_f range of 0.254 to 0.303 m²K/kW. Synthetic thin stillage with STA only had R_f range of 0.287 to 0.365 m²K/kW. Synthetic thin stillage with 5% TS and GLU only did not foul after 10 hr while 5% TS and STA only reached the maximum probe temperature, 170°C in 4.2 hr and had R_f = 0.264 m²K/kW. Synthetic thin stillage with 10% TS and STA:GLU of 1:9 had R_f = 0.163 m²K/kW at the end of 10 hr but did not reach the maximum probe temperature, 170°C. As STA:GLU increased to 3:7, maximum probe temperature was reached in 4.2 hr with final R_f = 0.264 m²K/kW. Therefore, for 1, 5 and 10% TS, R_f increased mainly because of the starch present in synthetic thin stillage, while glucose had a smaller effect on R_f.  Higher concentrations of starch in synthetic thin stillage had shortened the time to reach the maximum probe temperature.