Modeling scaleup effects on a small pilot-scale fluidized-bed reactor for fuel ethanol production

摘要

Domestic ethanol use and production are presently undergoing significant increases along with planning and construction of new production facilities. Significant efforts are ongoing to reduce ethanol production costs by investigating new inexpensive feedstocks (woody biomass) and by reducing capital and energy costs through process improvements. A key element in the development of advanced bioreactor systems capable of very high conversion rates is the retention of high biocatalyst concentrations within the bioreactor and a reaction environment that ensures intimate contact between substrate and biocatalyst. One very effective method is to use an immobilized biocatalyst that can be placed into a reaction environment that provides effective mass transport, such as a fluidized bed. Mathematical descriptions are needed based on fundamental principles and accepted correlations that describe important physical phenomena. We describe refinements and semi-quantitatively extend the predictive model of Petersen and Davison to a multiphase fluidized-bed reactor (FBR) that was scaled-up for ethanol production. Axial concentration profiles were evaluated by solving coupled differential equations for glucose and carbon dioxide. The pilot-scale FBR (2 to 5 m tall, 10.2-cm ID, and 23,000 L month(sup -1) capacity) was scaled up from bench-scale reactors (91 to 224 cm long, 2.54 to 3.81 cm ID, and 400 to 2,300 L month(sup -1) capacity). Significant improvements in volumetric productivites (50 to 200 g EtOH h(sup -1) L(sup -1) compared with 40 to 110 for bench-scale experiments and 2 to 10 for reported industrial benchmarks) and good operability were demonstrated.