Ethanol is commercially produced using either a wet mill or dry mill process. Wet milling involves separating the grain kernel into its component parts (germ, fiber, protein, and starch) prior to fermentation. ICM-designed plants utilize the dry mill process, where the entire grain kernel is ground into flour. The starch in the flour is converted to ethanol during the fermentation process, creating carbon dioxide and distillers grain.
Learn more about the Dry Mill Process when you mouse over the steps.
Grain is delivered by truck or rail to the ethanol plant where it’s loaded in storage bins designed to hold enough grain to supply the plant for 7–10 days.
The grain is screened to remove debris, then milled into ground material to allow water and enzymes to contact and to react with starch in the ground material.
In slurry tanks, the ground material is mixed with recycled water and enzymes. The contact and reaction of these components cause starch gelatinization.
Selective Milling Technology™ (SMT™) (Bolt-On Option)
The slurry flows through a separation device, where solids are selectively separated and ground further in a mechanical milling device, and then returned to the process stream.
In liquefaction tanks, the process hydrolyzes the gelatinized starch into glucose to produce mash.
Simultaneous Saccharification Fermentation
The glucoamylase enzyme breaks down the dextrins to form simple sugars. Yeast is added to convert the sugar to ethanol and carbon dioxide. The mash is then allowed to ferment for 50–60 hours, resulting in a mixture that contains about 15% ethanol as well as the solids from the grain and added yeast.
The fermented mash is pumped into a multi-column distillation system where additional heat is added. The columns utilize the differences in the boiling points of ethanol and water to boil off and separate the ethanol. By the time the product stream is ready to leave the distillation columns, it contains about 95% ethanol by volume (190-proof). The residue from this process, called stillage, contains non-fermentable solids and water and is pumped out from the bottom of the columns into the centrifuges.
The 190-proof product stream is pumped into the molecular sieve system. These specialized tanks contain molecular sieve beads that adsorb water molecules from the process stream while ethanol molecules pass through unaffected. When the product stream leaves the molecular sieves, it contains approximately 99% ethanol by volume (200 proof).
Before the ethanol is sent to the storage tanks, a small amount of denaturant is added, making it unfit for human consumption.
Most ethanol plants' storage tanks are sized to allow storage of 7-10 days of production capacity.
The stillage from the bottom of the distillation columns contain solids from the grain and added yeast, as well as liquid from the water added during the process. It's then sent and separated through the centrifuges into thin stillage (a liquid with 5-10% solids) and wet distillers grain.
The liquid that is not routed back to the cook/slurry tanks is sent through a multiple-effect evaporation system where it is concentrated into syrup containing 25-50% solids.
The syrup, which is high in protein and fat content, is then mixed back in with the wet distillers grain.
The wet cake is conveyed to dryers where it is converted into a low-moisture (10-12%) product called dried distillers grains with solubles.
Bio-Oil Recovery (Bolt-On Options)
Base Tricanter System™: Separates oil from the post-fermentation syrup stream as it leaves the evaporators. The oil is routed to settling tanks, and the remaining concentrated syrup is routed to your plant's existing syrup tank.
Advanced Oil Recovery™ Skid: Breaks the emulsion concentrate (a mixture of water, oil, soluble proteins, sugars, and starches), dramatically increasing the volume of oil recovered from the plant's process stream.
The bio-oil is then pumped to settling tanks where majority of residual solids and wax-bound oil have settled out and pumped to another tank. Then, high quality bio-oil in the settling tanks is transported via tanker trucker or rail.