Beer Column or Stripping Column
The beer or stripping column is used in the initial separation of ethanol from fermented sugar solution or beer. The distillation system is fed with the fermentation process product that contains 10% to 12% alcohol in water. Most of the non-fermentable solids from the biomass hydrolyzate and yeast cells can be removed from the fermentation broth by centrifugation. However, some small solid particulate matter may remain in beer, which is introduced from the top of the column, and the steam is introduced from the bottom of the column as shown in the Figure 14.2. A stack of sieve trays inside the column help to enhance the vapor-liquid contact and separation. A top and side view of a sieve tray used in ethanol distillation columns is shown in Figure 14.3. One side of the sieve tray is open and allows downward draft, and the other catches the down coming liquid from the sieve tray just above this tray. Typically 19-20 sieve trays are used in the beer column. As vapor rises and the beer falls through trays, heat from the vapor causes alcohol to evaporate. The tray-by-tray vaporization/condensa — tion continues, moving the ethanol concentration lower at each descending tray. At the bottom of the column, the remaining beer (minus alcohol) is called whole stillage and is sent to the whole stillage tank for centrifugation. The countercurrent flow removes nearly all the ethanol from the feed to the beer column. Ethanol — water vapor exiting from the top of the column contain 40-60%
alcohol by volume. Typical temperature at the top of the beer column is about 70-74°C, whereas the bottom is about 85-88°C.