Ethanol can be produced by fermentation of sugars and is used as a gasoline blending component. Because the sugars can be derived from biomass, ethanol is potentially a renewable fuel. In the fermentation of cane sugar to ethanol, sucrose (C11H12O11 ) is converted by yeast ( saccharomyces cerevisae ) to yield ethanol and CO2. Some sucrose is also consumed in maintaining the cell culture in the fermentation reactor. The fermentation reaction can the carried out in a continuous reactor as long as the ethanol concentration does not execeed about 8 wt%, at which point the productivity of the yeast declines significantly . the sucrose is fed as a 12.5 wt% solution in water, which must be sterilized before it can be fed to the reactor. The sterilization is usually accomplished by heating with steam. Carbom dioxide is vented from the fermentation reactor. The liquid product of the fermentation reactor is sent to a hydrocyclone to concentrate the yeast for recycle to the reactor.
The remaining liquid is sent to a distillation column known as a "beer column," which concentrates the alcohol to about 40 mol% ethanol and 60mol% water in the distillate. The recovery of ethanol in the beer column is 99,9%. The bottoms stream from the beer column contains the remaining components of the fermentation broth and can be processed for use as animal feed
1. Draw a flowsheet for this process
2. Estimate the steam flow rates and compositions for a production rate of 200,000 U.S. gal/d of dry (100%) ethanol.
3. Estimate the ethanol lost in the CO2 vent gas.as
4. Estimate the reboiler duty of the beer column Data
1. Yield per kg sucrose: ethanol 443.3 g, CO2 488 g, nonsugar solids 5.3 g, yeast 21 g, fermentation by products 43.7 g, higher alcohols ( fusel oil) 2.6g
2. Conversion of sucrose, 98.5%
3. Yeast concentration in fermentation reactor as steady state, 32 wt%.