Mechanism of molasses-water mixing behavior in bioethanol fermenter : experiments and CFD modeling

Molasses is a first-generation bioethanol feedstock that is a byproduct of sugar production. Molasses is a viscous fluid; consequently, when it serves as a substrate, it needs to be dissolved in water to obtain the appropriate conditions for the yeast. Therefore, the mixing process of molasses and water is an essential factor that significantly affects the efficiency of the fermentation process. This work aims to study the molasses-water mixing behavior in a cylindrical cone-shaped stirred-tank system reviewed by the effect of the molasses-water rheological characteristics. The molasses-water mixing behavior was investigated through a simple visualization method by using a camera and a 650 nm red laser as an observation plane of molasses-water interface height changes. Based on the results of the rheological characterization, it is known that molasses are a non-Newtonian fluid that exhibits shear thinning behavior. A rheological model molasses-water mixture has been developed. The behavior of molasses-water mixture comprises three zone mechanisms. The Eulerian multiphase model is the closest to the experimental results, and the combination of the Eulerian multiphase model and Large Eddy Simulation can be applied to predict the mixing behavior in an industrial scale stirred-tank.