Overview of Process Control
Ref. 9.01.00 Bioethanol Process (pdf)
After the corn is ground to the correct size, water and the first enzyme (alpha-amylase) are added to breakdown the starch. During the first step, called gelatinization, hot water (85°C or 185°F) is mixed with the flour for 20-60 min, followed by the addition of superheated water at 105°C (221°F). During this step the starch absorbs water, swells up and loses its compact crystalline structure. This enables the first enzyme, Alpha-amylase, to break the long starch chains into smaller variable length chains called dextrins via hydrolysis. This process usually takes between 2-4 hours to complete and is referred to as liquefaction. The second enzyme, glycoamylase, is added during the passage to the fermentation tank. This enzyme breaks the dextrins into individual glucose molecules. It usually takes 40+ hours to to complete this stage of the process. This step is called Simultaneous Saccharification Fermentation (SSF). During fermentation the yeasts convert the simple sugar into ethanol. This step takes between 40-70 hours.
Ref. 9.01.01 Bioethanol Cooking and Fermentation (pdf)
Following fermentation, further ethanol concentration is required. This is achieved through distillation and by using molecular sieve columns. Once the ethanol is 100% pure, a denaturant, usually 2-5% gasoline, is added to render the alcohol unfit for human consumption. It is then ready to be placed in storage tanks to wait for transportation and distribution.
Ref. 9.01.02 Bioethanol Purification (pdf)
The remaining stillage or residues left from the distillation process contains nutrients, minerals and unfermented sugars. These are valuable by-products, providing an additional source of revenue as animal feed. The average stillage amount produced in the bioethanol process is approximately 13 h/L per h/L of bioethanol. Decanting centrifuges mechanically dewater the spent grains carried in the stillage. Thin stillage, containing both dissolved and suspended solids, is produced as the centrate. Some of the thin stillage is recycled as backset to the fermentation process, while the remaining thin stillage, normally with a concentration ranging between 5 and 10% bw, is concentrated in an evaporator to produce the condensed soluble ingredient of distiller’s dried grains (DDGS). The decanting centrifuges simultaneously produce a wet cake of spent grains, or WDG (wet distiller’s grains), which can be marketed as cattle feed or processed further in a dryer creating DDGS, a higher revenue product.
Ref. 9.01.03 Bioethanol Stillage Processing (pdf)
Overview of Process Control
Ref. 9.02.00 Biodiesel Process (pdf)
Glycerol is a by-product of the petrochemical, animal fat and vegetable oil based biodiesel industries. However, crude glycerol derived from biodiesel production is of low value because of impurities. Further refining of crude glycerol is dependent on the economics and the availability of facilities. Larger scale biodiesel producers refine their crude glycerol and market it to other industries. For every 9 kg (19.8 lbs) of biodiesel produced, about 1 kg (2.2 lbs) of a crude glycerol by-product is formed. Effective usage, or conversion, of crude glycerol with specific products will offset biodiesel production costs. Glycerol is generally treated and refined through filtration, chemical additions and fractional vacuum distillation, yielding a variety of commercial grades. When destined to be used in food, cosmetics, and drugs, further purification such as bleaching, de-odoring, and ion-exchange will be required to remove trace properties.
Ref. 9.02.01 Biodiesel Glycerol Refining (pdf)