Design of a High Gravity Distillation Unit for On-farm Ethanol Dewatering

Abstract

High gravity (Higee) distillation refers to separation of components in a rotating packed bed type contacting device. Rotating packed beds utilize centrifugal force to create artificial gravity up to 200 times greater in magnitude than earth's gravity. The increased acceleration results in smaller liquid films and smaller bubble sizes. Consequently, higher mass transfer fluxes and throughputs can be obtained in a small size, low weight unit. Height Equivalent to Theoretical Plate (HETP) reduction from 1.5-3 feet for conventional columns to 1-3 inches in Hi-Gee units has been reported. The reduced weight and size, low residence time and possibility of setting up mobile units, makes Hi-Gee attractive for on-site distillation of heat sensitive and fouling fermented juice. Previous study by the Department of Bio-Systems and Agriculture Engineering at Oklahoma State University (OSU) has established the need to distill 250 GPH of fermented juice with 6-10 vol % ethanol to produce 15 GPH of 190 proof ethanol, on farm. The aim of this study is to size the Higee rotors for processing 250 gallons per hour of fermented juice. Concepts employed in design of packed columns can be utilized with appropriate modifications. The designed rotor configurations are; 30.47 in x 11.01 in x 11.01in for the Rectification Higee and 56.01 in x 27.19 in x 27.19 in for the Stripping Higee. A trade- off between the increase in overall mass transfer coefficient and the power consumed was utilized for selecting the above mentioned configurations of Higee, respectively. The footprint of both the designed rotors is relatively small. A small 3 HP (brake) motor is adequate to drive the two rotors. An indirect material balance control strategy has been established for Higee. This study presents the first documented design of a Higee unit to meet pre-specified production rate and purity targets.