COMPUTER SIMULATION AND CONTROL OF SMALL-SCALE ETHANOL DISTILLATION SYSTEMS (AUTOMATED, ALCOHOL, MICROPROCESSOR, MODELING)

The production of ethanol as a substitute for liquid petroleum fuel sources has been considered since internal combustion engines were developed. Alcohol fuel can be produced in small-scale systems using locally grown and lower quality fermentation products, such as damaged corn. The traditional high investment costs for controlling the alcohol distillation system to improve efficiency and reduce labor cannot be justified in small scale systems. However, other approaches to controlling the small scale distillation system using a control/benefit analysis may be implemented at far lower costs. A steady-state computer simulation model was developed to characterize the performance of a small-scale, sieve tray ethanol distillation system using direct steam injection. The model was used to characterize the potential benefits of controlling specific distillation system parameters with the objective of reducing operating costs. The model predictions were compared to the actual performance of the 68 kg (25 gallon) per hour distillation system under various control strategies. The agreement between model predictions and actual data was accurate to (+OR-)6.0 percent. Results from both the model predictions and field tests indicated that as much as 20 percent of the energy required for distillation could be saved by reducing the reflux ratio as much as possible and by increasing the beer feed concentration and the beer pre-heat temperature. The specific strategies included were for control of: steam line pressure, condenser water temperature, and reflux rate. Energy savings with steam pressure control were as high as 23 percent while reflux control was ineffective and caused unstable system performance. Control of condenser water temperature reduced operator adjustment time considerably but was not important in terms of energy savings. The computer simulation model developed may be used interactively for a variety of alcohol distillation systems using direct steam injection to predict the performance of different operating and control strategies