Ethanol: Production Overview
Ethanol production is one of the earliest chemical technologies known to man. While Process Plus is involved in cellulosic ethanol production, corn is the primary source for ethanol production. Production of ethanol from grain is a simple process that involves several different processing areas. Over the years the technology has evolved to incorporate improved methods to maximize yield, lower costs, and provide for recovery of valuable by-products. It involves the following steps:
Grain Receiving / Handling
Grain is unloaded via rail car or bulk truck for storage as required maintaining continuous operations.
There are a variety of milling options including dry, wet or modified, with dry milling being the most commonly used method and therefore is the method described.
The grain feedstock passes through hammer mills, which grind it into a fine meal.
The meal is mixed with water to form a mash that passes through a high temperature (~200-300°F) cooker for a brief period of time, followed by a lower temperature (~140°F) holding period with an alpha-amylase enzyme, where the starch is liquefied. Heat is applied to release bundled starch molecules so that they can be broken down by the enzyme in the liquefaction process. The high temperatures also reduce bacteria levels in the mash.
After liquefaction, the mash is further cooled and the secondary enzyme (gluco-amylase) is added to convert the liquefied starch to fermentable sugars (dextrose).
Yeast is added to the mash to ferment the sugars to Ethanol and carbon dioxide (CO2). If continuous fermentation is used, the mash flows, or cascades, through several fermenters in series until the mash is fully fermented and then leaves the final tank. In a batch fermentation process, the mash is held in one fermenter for about 48 hours to complete the fermentation. Fermentation heat must be removed to maintain optimum temperature for yeast activity.
The fermented mash, now called “beer”, contains about 12-15% alcohol by volume, along with all the nonfermentable solids from the grain and the yeast cells. The mash is pumped to a continuous flow distillation tower where the alcohol is removed from the solids and the water. The alcohol leaves the top of the tower at about 95% strength (190 Proof), and the residue mash, called stillage, is transferred from the base of the tower to the co-product processing area.
The 95% alcohol from the top of the column must be dehydrated in order to be suitable for blended ethanol fuel. There are a few different ways to dehydrate ethanol; including molecular sieves, grits and azeotropic (entrainers). However, molecular sieves are the most popular method in North America.
Dehydration captures the last bit of water in the ethanol. The alcohol product at this stage is called anhydrous (without water) ethanol and is 99.5%+ ethanol.
To make it unfit for human consumption and suitable for fuel use, ethanol is denatured with a small amount (2%-5%) of some product such as gasoline.
Ethanol production is a no-waste process that adds value to the feedstock by converting it into more valuable products. Two main co-products — Carbon Dioxide (CO2) and distillers grains — are created during Ethanol production. CO2 is released during fermentation. Many Ethanol plants collect the CO2, clean it of any residual Ethanol, compress it, and sell it for use in carbonated beverages or to flash freeze meat (“Dry Ice”). By-product DDGS (Dried Distillers Grains with Solubles) is high in protein and other nutrients and is used extensively in animal feed. Production of DDGS utilizes centrifuges to separate the liquid and solid fractions. The liquid is evaporated to syrup that is added back to the solids in the final drying step. Some Ethanol plants may sell the syrup separate from the distiller’s grain.
Wet Milling Facilities
Wet milling of corn is used in the manufacture of high-fructose corn sweetener. Dextrose, which is produced as an intermediate product, may be diverted to ethanol production during the seasonal downturn in the sweetener market. This provides the flexibility to produce the more value-added product as the market changes.
Cellulosic process technologies are currently being researched and developed by a variety of interests around the nation. Process Plus is working with industry leaders to help bring cellulosic ethanol to market. As the technologies become established and marketable, Process Plus will continue to provide support to ethanol producers.