Modeling of industrial-scale anaerobic solid-state fermentation for Chinese liquor production
Jin, Guangyuan ; Uhl, Philipp ; Zhu, Yang ; Wijffels, René H. ; Xu, Yan ; Rinzema, Arjen - \ 2020
Chemical Engineering Journal 394 (2020). - ISSN 1385-8947
Chinese liquor - Heat transfer - Mathematical modeling - Product inhibition - Solid-state fermentation - Temperature modeling
Traditional solid-state fermentation processes can give fluctuating product quality and quantity due to difficulties in control and scale up. This paper describes an engineering study of an industrial-scale anaerobic solid-state fermentation process for Chinese liquor (Baijiu) production, aimed at better understanding of the traditional process, as an initial step for future optimization. This mixed-culture fermentation is done in 0.44-m3 vessels embedded in the soil. At this scale, the fermentation is limited by product inhibition. We developed mathematical models based on the Han-Levenspiel equation for product inhibition, with parameters derived from measured data. The models accurately predicted the concentrations of starch and dry matter. A model with radial conduction into a small soil volume around the fermenter and consecutive vertical conduction into the underlying soil accurately predicted the pit temperature in the heating and cooling phases. This model is very sensitive to the values used for the enthalpies of combustion, meaning that direct measurement of the heat production rate would be preferable. In the industry practice, the fermenter volume can be from around 0.20 to 15.00 m3. The model predicts that overheating will occur not only in larger fermenters, but also in the 0.44-m3 fermenters when the soil temperature is high in summer. Our model predictions are consistent with observed behavior in the industry. Our findings can be used to improve this traditional process, as well as similar systems.
Model development for conductive thin film drying processes
Qiu, Jun ; Boom, Remko M. ; Schutyser, Maarten A.I. - \ 2020
Journal of Food Engineering 268 (2020). - ISSN 0260-8774
Conductive drying - Drum drying - Heat transfer - Process modelling - Thin film
A heat-transfer governed model is proposed to describe drying in a lab-scale conductive thin film dryer, which was designed to investigate the drying kinetics relevant to drum drying. The model calculations were compared to experimental data from drying experiments with maltodextrin DE12 and potato starch, considering the three distinct periods (heating, boiling and conductive drying) of the lab-scale process. The model uses measured temperatures and evaporation rate during the boiling period as input to calculate the decrease in moisture content during the drying process. Model calculations were evaluated by determining the root-mean-square-error (RMSE) values. The RMSE were very small (<0.24) indicating that the model was successful in describing the film drying process. During the last drying period, the starch films exhibited a higher initial heat transfer resistance (~0.0004 (m2∙K)/W) compared to maltodextrin (~0.0002 (m2∙K)/W). This reflects the formation of larger vapour bubbles in the boiling period impeding the heat transfer for starch films. Subsequently, the model was modified to describe a pilot-scale drum drying process for maltodextrin suspensions. The initial heat transfer coefficient for drum drying of maltodextrin was obtained from the lab-scale experiments. The simulations indicated residual moisture contents and optimal drying times for different drying conditions.