Effects of pH, Slurry Composition, and Operating Conditions on Heat Transfer Fouling during Evaporation of a Lignocellulosic Biomass Process Stream

Fouling of stainless steel heat transfer surfaces by soluble and suspended solids within lignocellulosic biomass process streams during evaporation elevates energy consumption and cleaning costs associated with this unit operation. Efficient evaporation is important for long-term economic stability of the biorefinery industry. In this study we evaluated the effect of hydrolysate pH, pretreatment variety (dilute acid versus hot water), and shear forces at the evaporator surface on fouling, as measured by the performance parameters such as induction period, fouling rate, and final total heat transfer resistance. Using an annular fouling probe, fouling tests were conducted at pH 1.5, 3.0, and 5.0 at 120, 130, and 140 °C with 0, 10, and 20% (w/v%) total suspended solids. Effects of Reynolds number and Ca2+ ion concentration on fouling rate and induction periods were also determined. Fouling deposits were characterized using scanning electron microscopy (SEM), inductively coupled plasma (ICP), and ash analysis...