Abstract
The water consumption of fermentation-based bio-ethanol production has recently begun to attract public attention. We calculate a minimum consumption of 2.85 gal water/gal of ethanol produced assuming zero liquid discharge and otherwise current industrial practice data. Including cooling tower blowdown and drift this value may increase to on the order of 4 gal water/gal of ethanol produced. Reduction of the thermal energy input to the process is vital to reduce this irretrievable water consumption.
Highlights
It appears that ethanol production from biomass via yeast-based fermentation ("bio-ethanol") will play an increasingly important role world wide (4.2 billion gallons produced in Brazil from May 2005 to April 2006, 6% increase projected for 2006/2007 [1], projected 12 billion gallons ethanol per year in 2012 in the U.S [2])
We assume that the above thermal energy input of 34,800 BTU per gallon of ethanol is via a boiler where natural gas is combusted and 77% of the liberated heat is transferred to process steam. 26,796 BTU per gallon of ethanol produced will thereby enter the process
This cooling water is evaporated in a cooling tower and released as vapor as a heat sink for the energy input of the process and can not be recycled
Summary
It appears that ethanol production from biomass via yeast-based fermentation ("bio-ethanol") will play an increasingly important role world wide (4.2 billion gallons produced in Brazil from May 2005 to April 2006, 6% increase projected for 2006/2007 [1], projected 12 billion gallons ethanol per year in 2012 in the U.S [2]). The minimum water consumption of a state-of-the-art ethanol facility is calculated here under the very stringent assumption of complete process water recycling. The calculated minimum water consumption of 2.85 gal water/gal of ethanol produced is essentially due to the significant cooling needs with the water irretrievably lost as vapor to the atmosphere. The cooling needs result to a large extent from the energy input for ethanol/water separation among other process steps. There is still a lively discussion in regard to the merits and demerits of bio-ethanol [6,7]. It appears to be an undeniable fact that there will be very significant and increasing world-wide bio-ethanol production for years to come
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
