Conventional Ethanol Distillation System
The solid particulate matter such as yeast cells and non-fermented residual solids in the fermented solution are first removed by centrifugation or filtration. Then distillation of the fermented solution, or "beer," is the next step in the separation of ethanol from this ethanol-water mixture. A conventional ethanol distillation system is a combination of three columns as shown in Figure 14.2. The
first column is known as beer column or stripping column and the second column is known as rectifying or refining column, and the third column is called side stripper. In the conventional separation process, fermented mixture, or beer, is first passed through a beer column. This column essentially behaves as a steam stripping column and produces a vapor stream having an ethanol composition between 40% and 60% by mass. The bottoms stream leaving the beer column is composed mainly of water, with some residual solids. The vapor stream leaving the beer column then enters the second column known as the rectifying column. The bottoms product leaving the rectifying column can go to a separate stripping column known as the side stripper column. The distillate leaving the rectifying column is normally near the azeotropic composition (89.4 mol% ethanol and 10.6 mol% water). This distillate stream then undergoes dehydration to produce fuel grade ethanol product [1, 2].