Here are the basic steps in the dry mill process of ethanol:

1. Grain Milling Operation.  Cleaned corn is transferred to a surge tank where the corn is fed into grinders and the resulting “flour” is stored in a day tank. 

2. Slurry Preparation and Liquefaction.  Flour is transferred to mixer from the grain milling operation and mixed with water to form a slurry. The slurry from mixer is transferred to slurry mixing tank where the desired temperature is maintained for a specified retention time (cooked). A part of the liquefying enzyme is added to initiate the liquefaction of the starch.

The slurry from the slurry mixing tank is transferred to an initial liquefaction tank where remaining part of liquefying enzyme is added to complete liquefaction. The liquefied slurry is then transferred to the final liquefaction tank where the resulting mash is cooled and transferred to fermentation section.  Heat integration is achieved by using the heat of the liquefied slurry to pre-heat the recycle streams and also to heat the fermented mash to be fed to distillation section. 

3. Fermentation.   Yeast is added to the mash to ferment the sugars to ethanol and carbon dioxide.  In a batch process, the mash stays in one fermenter for about 48 hours before the distillation process is started.

4. Distillation. The fermented mash, now called beer, contains about 10% alcohol plus all the non-fermentable solids from the corn and yeast cells. The mash is pumped to the continuous flow, multi-column distillation system where the alcohol is removed from the solids and the water. The alcohol leaves the top of the final column at about 95% strength, and the residue mash, called stillage, is transferred from the base of the column to the co-product processing area.

5. Molecular Sieve Dehydration. Hydrous ethanol is pumped from the distillation plant or hydrous ethanol storage to the molecular sieve dehydration section. Hydrous ethanol is preheated in the feed preheater and regeneration preheater with the help of dehydrated ethanol product vapors and then fed to top tray of evaporator column. The objective of the evaporator column is to evaporate hydrous alcohol.  Most ethanol plants use a molecular sieve to capture the last bit of water in the ethanol. The alcohol product at this stage is called anhydrous ethanol (pure, without water) and is approximately 200 proof.

6. Denaturing. Ethanol that will be used for fuel must be denatured, or made unfit for human consumption, with a small amount of gasoline (2-5%). This is done at the ethanol plant.
 Two main co-products created in the production of ethanol are wet distillers grain (WDG) and syrup. WDG is an economic, high protein dairy and cattle feed;and the syrup is a high-protein dietary supplement in dairy and cattle feed.

Additional information:

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