Ethanol is a clean burning, high octane, renewable fuel produced from abundant agricultural and cellulosic feed-stocks. Ethanol can be used as an effective octane-boosting fuel additive or as a stand-alone fuel. E10 is a blend of 10% ethanol and 90% gasoline. It is approved for use by every major automaker in the world, and currently comprises about 10% of the US fuel supply (14.3 billion gallons in 2014). E15 is a blend of 15% ethanol and 85% gasoline, and has been approved by the US EPA for use in light-duty motor vehicles (cars) model year 2001 and newer. E85 is a blend of 85% ethanol and 15% gasoline, and is designed for use in Flex-Fuel Vehicles (FFVs) only. Aemetis owns and operates a 60 million gallon per year dry milling ethanol Biorefinery in Keyes, California.
Ethanol is the only low carbon alternative to gasoline available in adequate and growing supplies today. All credible comparisons to gasoline demonstrate a clear reduction in greenhouse gas (GHG) emissions with the use of ethanol. A study published by Yale University’s Journal of Industrial Ecology show current ethanol production provides greenhouse gas reductions between 48-59% compared to gasoline.
Ethanol Biorefineries also produce valuable co-products, such as wet or dry distiller’s grains (WDG/DDG), which are sold as a high-protein animal feed to dairies and cattle feedlots. In addition, many US ethanol producers extract corn oil during the production process, which is then sold as animal feed or used in the production of low carbon fuels such as biodiesel or jet fuel. On an annual basis, the Aemetis Keyes ethanol Biorefinery produces over 420,000 tons of wet distiller’s grains and over 5,200 tons of corn oil.
How Ethanol is Made
Today, roughly 91% of the nation’s ethanol is produced using the dry mill process. Also, slightly more than 90% of the energy needed to run the nation’s 200+ ethanol biorefineries comes from natural gas—a plentiful domestic energy resource. Finally, nearly a quarter of these facilities are using Combined Heat and Power (CHP) technologies, also known as co-generation.
In dry milling, the entire corn kernel or other starchy grain is first ground into flour, which is referred to in the industry as “meal” and processed without separating out the various component parts of the grain. The meal is slurried with water to form a “mash.” Enzymes are added to the mash to convert the starch to dextrose, a simple sugar. The mash is processed in a high-temperature cooker to reduce bacteria levels ahead of fermentation. The mash is cooled and transferred to fermenters where yeast is added and the conversion of sugar to ethanol and carbon dioxide (CO2) begins. The fermentation process generally takes about 40 to 50 hours. During this part of the process, the mash is agitated and kept cool to facilitate the activity of the yeast. After fermentation, the resulting “beer” is transferred to distillation columns where the ethanol is separated from the remaining “stillage.” The ethanol is concentrated to 190 proof using conventional distillation and then is dehydrated to approximately 200 proof in a molecular sieve system.
The anhydrous ethanol is then blended with about 2% denaturant (such as natural gasoline) to render it undrinkable and thus not subject to beverage alcohol tax. It is then ready for shipment to gasoline terminals or retailers. The stillage is sent through a centrifuge that separates the coarse grain from the solubles. The solubles are then concentrated to about 35% solids by evaporation, resulting in Condensed Distillers Solubles (CDS) or “syrup.” The coarse grain and the syrup are then dried together to produce dried distillers grains with solubles (DDGS), a high quality, nutritious livestock feed. The CO2 released during fermentation is either processed through a scrubber and released, or it is captured and liquefied for use in carbonating soft drinks and beverages and the manufacture of dry ice.
According to the latest research, the average dry mill ethanol plant today uses 28% less thermal energy per gallon than it in 2001. Electricity demand per gallon of production fell 32% since 2001 and water use fell by 47%. All the while, ethanol producers are increasing the amount of ethanol they can produce from the same bushel of corn. At 2.8 gallons of ethanol per bushel of corn, ethanol yields per bushel have increased by 6% over the past decade. In addition to corn, Aemetis has processed over 60,000 tons of grain sorghum (also known as Milo) into fuel ethanol. Grain sorghum is considered a lower carbon feedstock than corn. In 2013, Aemetis was the first US ethanol producer approved by the EPA to qualify for a higher value D5 Renewable Identification Number (RIN) to produce lower carbon ethanol by using a process combination of grain sorghum, biogas/landfill gas/and our CHP unit.
Source Note: Renewable Fuel Association (RFA)