Milling, Oil Extraction, and Fermentation
Dry-milled feedstock is conveyed to the Mash Preparation Tank where it is combined with enzymes, recycled water (Process Condensate), and backset. Backset is a non-food grade oily emulsion and is recovered from Thin Stillage and clarified by the Backset Clarification System described later. Backset must be processed further to meet Corn Distillers’ Oil (CDO) specifications. Mash slurry is heated and pumped to the 1st Pass Dewatering/Milling paddle screens where the slurry is dewatered. There, two (2) paddles screens operate in parallel. Mash slurry is divided between the screens. The paddle screens discharge two streams. First is a centrate stream containing approximately 30% DS (dissolved solids). The centrate DS contains much of the water and soluble solids and smaller insoluble particles. The second stream from the paddle screens is a cake stream with 38% DS. The cake stream contains larger insoluble particles. The paddle screens are equipped with wedge wire screens. The size of the screen selected determines the split between the centrate and cake stream. The cake stream is gravity fed to rotary grind mill which uses interlocking teeth to shear the solid particles, thus reducing particle size and releasing starch. The centrate bypasses the rotary grind mill and is recombined with ground cake in the 1stPass Collection Tank (not shown on diagram).Slurry from 1st Pass Collection Tank is pumped to 2nd Pass Dewatering/Milling operation similar to the 1st Pass operation consisting of paddle screens, rotary grind mill and collection tank. Centrate and ground cake are recombined in 2nd Pass Collection Tank. Slurry from 2nd PassCollection Tank is sent to the Liquefaction Tank.
The Liquefaction Tank operates at approximately 195oF and provides additional residence time for the enzymes to continue breakdown of starches and reduce the viscosity of the slurry. Liquefied material, having gone through 2 prior stages of grinding and washing, is sent to 3rd Pass Dewatering/Milling similar to 1st and 2nd Pass Dewatering/Milling.Centrate from the 3rd pass is sent to the Triton Centrifuge, a three-phase disc-nozzle centrifuge capable of separating the centrate into three streams based on density. The lightest density stream, light phase, is comprised mostly of oil and water emulsion. The light phase containsNFG oil from backend Thin-Stillage comingled with some free oil released during milling. The next lightest phase is called the overflow and the heaviest phase is called the underflow. Both overflow and underflow are collected in a Mash Collection Tank and mixed with the 3rd Pass cake stream.
The light phase is gravity fed to oil polisher feed tank (not shown) and then sent to the Oil Polisher Centrifuge. The polisher is a decanting centrifuge, and is used to remove impurities in the oil. The polisher is a three-phase centrifuge. The light phase is non-food grade corn oil (CDO) which is sent to storage for sale. The other two phases are the solids discharge and the liquids discharge. Both are gravity fed to Mash Collection Tank to be mixed with the 3rd Pass solids, the overflow and underflow from the Crude Oil Separation Centrifuge.
The Mash Collection Tank collects the streams mentioned above and homogenizes them before charging mash containing starch, fiber, protein and unrecovered oil to Fermentation. Mash in the Mash Collection Tank is cooled to approximately 90 oF and transferred to one of four (4) Fermentation tanks. Yeast, additional enzymes, and nutrients are added. These enzymes convert starch to simple sugars and the yeast then converts those sugars into ethanol and CO2. The product from the fermentation tanks, called “beer”, is approximately 13% alcohol and the balance is water and solids. The CO2 is emitted from Fermentation to atmosphere after being treated in vent and CO2 scrubbers. Distillation, Dehydration, and Evaporation
From the Fermentation process, fermented mash (Beer) then separated in three distillation columns, beginning with the Beer Column. The overhead from the final column (the Rectifier) is 95% ethanol (190 proof) and water. The bottoms from the Beer Column containing solids, water, and other high-boilers is further processed to make Dried Distillers Grains with Solubles (DDGS) as described below. The other column is known as the Stripper Column. The Stripper column works in tandem with the Rectifier to purify the ethanol-water mixture. The bottoms from the Stripper Column are a water stream that is recycled in the process as “Process Condensate.”
An azeotrope exists at 5% water in ethanol. Therefore, the 190 proof overhead stream from the Rectifier is routed to the Sieve Vaporizer and then to one of two molecular sieves to remove the final 5% water. The product stream from the molecular sieves is 100% ethanol (200 proof) and is routed to day tanks. Extracted water is routed back into the process as reflux for the rectifier column or to the Process Condensate Tank (not shown).
Ethanol from the day tanks is denatured with approximately 2.1% gasoline to produce fuel grade ethanol which is stored in two 60,000 barrel tanks on site. This product is then loaded out onto barges or trucks for customers.
The bottoms from the Beer Column, whole stillage, which is laden with solids, is further processed to remove water and volatile impurities to create animal feed. This slurry stream is sent to the Whole Stillage Tank where it is held prior to centrifugation.
EBF utilizes three horizontal Decanter Centrifuges operating in parallel to decant much of the water from the whole stillage. Centrate (Thin Stillage) from the Decanter Centrifuges is sent to the Backset Clarification System. Solids from the centrifuge are either yielded as Wet Distillers Grains with Solubles (WDGS) or processed through a natural-gas fired dryer to be sold as Dried Distillers Grains with Solubles (DDGS). The dryer combines centrifugal force and heat to separate the solids from the liquid. The exhaust from the DDGS drying process is controlled by an 18 MMBTU/hr thermal oxidizer. DDGS from the dryer are cooled and stored onsite in the DDGS storage building.
The purpose of the Backset Clarification System is to recover non-food grade (NFG) oil from Thin Stillage for DCO sales. Thin Stillage from the Decanter Centrifuges is charged to the Thin Stillage Centrifuge, a two-phase disc-stack centrifuge. The light phase contains recovered oil and some water. This phase is an emulsion and must be further processed as described above to meet CDO specifications. It is recirculated to the Mash Preparation Tank as backset. The underflow from the centrifuge is a clarified Thin Stillage and contains mostly water and fine insoluble and soluble fiber and protein. This stream is sent to the Thin Stillage Tank.
Thin Stillage is dewatered in triple-effect evaporators to produce concentrated syrup. Energy for the evaporation is supplied by condensing overhead vapor from the Rectifier. The water from the evaporators is either recycled to the Process Condensate Tank. The concentrated syrup from the evaporators is stored in the CDS Storage Tank prior to being either combined with the solids from the Decanter Centrifuge to produce WDGS and DDGS or sold as Condensed Distillers Solubles (CDS).
Plant uses the following general utilities: 80 psig steam, process condensate, city water, wet air, and dry air.
To minimize water consumption, process water is recovered as Process Condensate throughout the separating and distillation processes. This Process Condensate is recycled to front of the process into the Mash Preparation Tank.
Process heat is supplied by two (2) onsite 95 MMBTU/hr natural gas fired boilers. These boilers produce steam for heat required in the fermentation, separation, and other processes. The Dryer and Regenerative Thermal Oxidizer also utilize natural gas. EBF’s air permit also allows for a temporary boiler to be operated on site in instances when one of the permanent boilers is down for maintenance or repair. At this time, there is no temporary boiler on site.
The facility also has an 18,000 gpm cooling tower for process cooling and a refrigeration system to provide additional cooling for the Fermentation when the water temperature rises above 89oF.
Plant (dry) air is supplied by two 410.2 cfm (100 hp) air compressors and is dried by a two air dryers in series. Aside from the general plant “dry air,” is that is not dried, “wet air” is supplied to the Yeast Propagation tank via a 158 hp air compressor and is supplied to the hammermills via a 118.7 cfm (30 hp) air compressor.
Feedstock and Products
Plant receives #2 yellow corn and grain sorghum (milo) as feedstock. These raw materials arrive on barge or by truck though the facility can also receive raw materials via railcar.
The facility may also receive non-cellulosic separated food waste (SFW) as feedstock. SFW is received in discrete shipments via barge, truck, or railcar, and is not comingled with other feedstocks. SFW may be rice or other starches and is “considered to be ‘wastes’ since they would otherwise normally be discarded or used for another secondary purpose because they are no longer suitable for their original intended use. They may be unsuitable for their original intended use either because they are themselves waste from that original use (e.g., table scraps) or because of contamination, spoilage or other unintentional acts.”
The facility produces fuel-grade ethanol from #2 Yellow corn, corn products, grain sorghum and non-cellulosic separated feed waste (SFW) utilizing a dry milling process. Grain sourcing and handling are outsourced. The plant restarted June 1st, 2015. The process is designed to operate approximately 350 days a year, with the balance of days down for maintenance and turnarounds.
The facility receives corn by barge or truck and conveys it to grain storage houses or a storage pile. The facility has certified weigh station capabilities to verify the weights of corn received and has laboratory facilities to verify quality of the corn received. The facility also receives grain sorghum by barge or truck and stores it in segregated storage tanks. The facility receives SFW by barge, truck, or railcar and stores it in tanks segregated from the other feedstocks.
From these storage locations, unmilled feedstock (corn, SFW, and grain sorghum) is conveyed to a hammer-mill where it is dry milled and where large impurities, such as cobs, are screened and removed. If the feedstock is purchased in milled form, (e.g. waste starch) it bypasses the hammer-mill and is charged directly to the Mash Preparation Tank where it comingles with the dry-milled feedstock. Each of these feedstock volumes may vary depending on market conditions and availability.
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